HIGHWAY BRIDGE SURVEYS

TECHNICAL BULLETIN NO. 55 FEBRUARY, 1928

UNITED STATES DEPARTMENT OF AGRICULTURE

WASHINGTON, D. C.

HIGHWAY BRIDGE SURVEYS By C. B. McCuLLouGH

Engineer f Oregon State Highway Commission y in Cooperation with Bureau of Public Roads

CONTENTS

Page Introduction -- 1 Method of reporting survey data 2 Scope of bridge survey 3 Materials survey 4 Waterway survey 14

Determination of current velocity 22 Stream gradients and erosion 26

General factors controlling erosion 26 Local conditions affecting erosion

Foundation data - Sounding-rod exploration.-- Soil-auger exploration Wash borings Dry-churn drilling.

Page Foundation data—Continued.

Core samples 47 Special light drilling outfits 52 Test pits 53 Interpretation of results 53 General instructions for test holes 56 Bearing-power tests 58 Test piles 64

Traffic surveys 66 General data and recommendations for new

work 67 Vicinity maps and profiles 73 Hydrographie surveys— 74

INTRODUCTION

An attempt has been made to discuss and evaluate the principal factors which control the location of highway bridges in Department Bulletin 1486, Highway Bridge Location. The purpose of this bulletin is to enumerate each of the various kinds of data needed for the design of a bridge as a guide to the engineering party in the field.

The importance of accurate and adequate preliminary data as a basis for bridge design warrants a detailed discussion of the subject. Too much stress can not be laid upon the value of a comprehensive and accurate bridge survey. Incorrect or inadequate information renders useless any nicety of design or detail. Lack of adequate information often makes it impossible to properly select the type of structure affording the greatest economy for the conditions at hand, and a design predicated upon information which later proves incorrect or incomplete is quite apt to involve changes or modifications subsequent to the letting of the contract. Modification of plans generally involves expensive work, is quite often a source of conten- tion between the engineer and contractor, and is bound to cause delay to the work. Modification often involves the abandonment of work already done, which obviously entails a direct financial loss. It frequently involves the use of special equipment which would not

73813°—28 X 1

2 TECHNICAL BULLETIN 55, U. S. DEPT. OF AGRICULTURE

otherwise have been needed. In many cases it renders necessary the organization of night shifts or double-time work to complete portions of the project while favorable weather conditions exist, and it increases the cost of the work in other ways. Any time limit or penalty in the contract is automatically invalidated by modifications in the design and in some cases (those involving extensive changes in plan) there might be a question as to whether or not the bondsmen or surety company could be held in case the contractor desired to abandon the work. Notwithstanding these facts, a disposition to slight preliminary engineering work seems universal, especially in the case of highway bridges and culverts.

The detailed bridge survey embracing all the points discussed in this bulletin may be made either before or after the location of the structure is definitely established. If the various control features discussed in Department Bulletin 1486 can be determined without the aid of a detailed survey or by means of a partial survey, the location may be established as soon as these preliminary studies are completed and the balance of the detailed survey made later. If such control features can be evaluated only by a careful comparison of alternate routes, then surveys in complete detail for each of the possible locations are needed as a prerequisite for the final location.

METHOD OF REPORTING SURVEY DATA

All data secured by the field party should be compiled and reported on blank forms, supplementary sheets (for explanatory matter and sketches), and on maps and profiles. The use of printed forms is recommended for as much of this material as possible. Blank forms sent from the ofiice to the field engineer indicate, first of all, an arrangement of data such as has proven desirable for office use. Such forms plainly call attention to each of the various points on which information is desired, thus insuring that no detail is omitted or forgotten.

If printed forms are used alone, however, it frequently happens that certain conditions peculiar to the particular site in question are not covered in sufficient detail due to lack of requisite space on the forms. For this reason, it is desirable to have supplementary data sheets of the same size as other forms upon which to record any information which can not be fully given on the first form sheets and upon which to include all sketches necessary to properly supplement or explain the written matter.

The maps and profiles which supplement the form sheets should be of standard size or of such size as to fold conveniently to standard size. The arrangement and character of information to be shown on 'these maps and profiles will be discussed later.

It is important that an orderly and systematic scheme be adopted for the recording and filing of all data secured in the preliminary survey. Every structure built may be considered as constituting a practical experiment in bridge building, and it is through careful study of the service records of such bridges that further data relative to the art of bridge building may be secured. To secure service records which will be of value, all conditions pertaining to the construction of a bridge must be kept as a matter of permanent record. A logical way to do this is to create for each new bridge a permanent and

HIGHWAY BRIDGE SURVEYS 3

separate file, and the first material to go into the record is the complete detailed report of the preliminary survey. This is the first chapter in the history of the structure and all further service and maintenance records are of greatest value when studied in the light of such information.

For example, suppose that in later years data may be secured as to the behavior of a structure during flood periods such as eroding action around piers and pedestals, of flood currents, cross currents, eddies, the action of ice or drift in the channel, the formation of bars, the erosion of banks or stream bed due to channel construction, or any other data of like nature. These data are clearly of greatest value when studied in connection with the waterway investigations which formed a part of the preliminary work, and may prove of considerable value in throwing more light upon the correctness of the formulas or assumptions used as a basis for the original design.

As another illustration, the service record of a structure in throwing light upon the quality of structural materials employed, such as concrete aggregates, will be of maximum value only in case all information concerning the aggregates actually employed is available. All of these points are features covered, to a certain extent, in the preliminary survey.

All preliminary-survey data should be made a permanent record constituting the first chapter in the history of the bridge structure and the method of recording and filing such survey data described in this bulletin has been adopted with this end in view.

At the top of every blank form including the supplementary data sheets there should be listed data which will quickly and completely identify the structure. This is a precaution the necessity for which has been demonstrated many times by experience. Where organiza- tions are handling a large volume of bridge work, dozens and hundreds of sketches and sheets of supplementary data concerning certain structures are passed through the office at one time, many times piled upon a single desk, and it is easy to misplace certain data or to fail to identify it. For this reason information completely identifying the project is required at the top of each of the sheets, as shown in Figure 1. To save space in this bulletin other sample supplementary data sheets will show only the sketch without the form heading.

SCOPE OF BRIDGE SURVEY

The points to be covered in a bridge survey and the methods to be used in collecting information can best be treated by presenting a set of typical blank forms, designed for this purpose, with the following general instructions for collecting, compiling, and recording all material pertaining to bridge surveys.

All data should be collected and arranged in the following manner: (1) On form 1 to form 7, inclusive. (2) On standard supplementary data sheets attached to forms 1 to 7. (3) On maps and profiles of standard size arranged in accordance with the

standard practice outlined.

The scope and completeness of the data required will vary to some extent with the size and importance of the structure, but field engineers should be impressed with the necessity, particularly on all large structures, of a complete and accurate survey embracing all of the


points covered in the blank forms which may in any degree apply to the structure under consideration. In addition to the material called for on the forms, the supplementary sheets should be freely used for sketches wherever they are necessary to supplement or illustrate subject matter given on the forms, and also whenever it is necessary to furnish additional information not fully covered on the printed forms.

The location data at the top of each form should be completely filled out for each sheet used in order to identify any single sheet should it become lost or misplaced. If the bridge structure is located on a section line, it should be identified as *^between sections — and —.^' If located in the interior of any section, it should be noted as ^în section —.'' In giving the range number care should be taken to state to which meridian the range is referred.

Forms 1 to 7 have been prepared by the writer from records and data covering about 12 years' experience and the construction of highway bridges aggregating in cost over $25,000,000. These forms are a complete list of every item of data which has been found necessary during the design of the above work, segregated and classified for ready reference. They are much more elaborate than those used in many cases of bridge practice, but for a structure of any size they are amply warranted, and it is the lack of such information that has in many instances caused waste and inferior construction. For the smaller structures they are too elaborate and a condensed form, shown on pages 6 and 7 has been prepared. This form should be used only for small structures.

MATERIALS SURVEY

Accurate and complete data concerning construction materials are of value both in the selection of type of structure and in the detailed design. For example, for locations where concrete aggregates are unusually expensive, light concrete sections heavily reinforced will often prove economical, while for locations where concrete aggregates are very cheap and readily obtainable, mass concrete construction may be desirable. For long hauls, through mountainous country, and for locations remote from railway facilities in combination with a plentiful local supply of concrete aggregates, a reinforced concrete structure may prove considerably cheaper in first cost than one of structural steel or of timber (provided, of course, that the timber must be shipped in). For mountainous roads and long hauls structural steel work should be detailed in rather small sections and with more field splices than would otherwise be necessary. The above and many other points must be decided from information furnished by the preliminary-materials survey.

The data needed for a complete materials survey is indicated on form 1 which is self-explanatory. There are a few points, however, concerning which additional discussion may be of value.

HIGHWAY BRIDGE SURVEYS

BRIDGE CONSTRUCTION WATERWAY SURVEY

SUPPLEMENTARY DATA

FOR BRIDGE NO OVER NAME OF WATERWAY

LOCATED- MILES FROM DISTANCE DIRECTION NEAREST R.R.STATION

IN SECTION OR BETWEEN SECTIONS , TWP. RANOE.

COUNTY OF STATE OF.

NAME(OR°) NO. OF HIGHWAY

LOCAL NAME OF BRIDGE

DATE OF SURVEY DATE OF REPORT REPORT BY_. ENGINEER

^VEGETATION-BRUSH,WILLOWS

CROSS-SECTIONAL STREAM AREAS (AREAS BY PLANIMETER)

LOW WATER (EL. 101.8) 194 SQ.FT.

WATER STAGE 10-3-20 (EL. lOA.O) .476 SQ.FT.

ORDINARY H.W. (EL. 110.8) 2100 SQ.FT.

EXTREME H.W. (EL. 113.2) 3280 SQ.FT,

riG. 1.—Sample supplementary data sheet showing sketch to illustrate the width, depth, and cross- sectional area of a stream at various water stages, ignoring channel deepening at high-water stages. The sketch should be to a scale sufficiently large to permit the determination of areas by planimeter or trapezoidal areas


(Condensed form used for small structures)

STATE HIGHWAY COMMISSION

BRIDGE CONSTRUCTION—SURVEY DATA

(Page 1)

For bridge over Bridge No Located miles from _

^Distance.) (Direction.) (Nearest E. R. Station.) in section (or between sections , ),twp »range

County of Name and number of road Local name of bridge Date of report Report by

(Engineer) (A) MATERIALS SURVEY

Material Source of supply Haul to site

(Distance and character of road)

Estimated cost (f. 0. b. site)

(1) Cement (2) Fine aggregate (3) Gravel for coarse aggregate (4) Crushed stone for coarse aggregate (5) Structural timber (6) Falsework timber (7) Piling..

1

(8) Other materials data .

(B) WATERWAY SURVEY

(1) Location and elevation of bench mark and datum used (2) Drainage area in acres Character of watershed (3) Width, depth and cross section of stream: (1) at flood stage

(Show by sketches if necessary) (2) at low water stage (3) at ordinary stage

(4) Elevations (a) Lowest point in stream bed at bridge site (&) Highest water. (c) Lowest water- (d) Highest ice _ (e) Highest drift.

(5) Frequency and duration of floods Season of year (6) Extent of damage to be feared.from ice or drift _

(7) Will all flood water pass through new structure or will relief be afforded through high water channels or over approach fills? (Illustrate by sketch)

(8) Is stream in general cutting or silting up and at what rate?

(9) Is there any tendency for stream to shift laterally or to change its channel?

(10) Is there need of any of the following work in connection with construction of new bridge? (a) Channel changes _ (&) E nlargement or clearing of channel to afford more waterway (c) Bank protection, revetments, wing dams, etc

(Illustrate by sketches)


(Condensed form used for small structures) (Page 2)

(11) Location of nearest existing structure over same waterway __ Give following data for this structure:

(o) Number and length of spans and approaches __ (&) Waterway area produced by old structure _._ (c) Is this area too small? _ -.. Is it too large? _._ (d) Is there any indication of erosion around piers or abutments, of damage from ice or drift or of

damage due to inadequa te clearances or inadequate span lengths? _

(e) What is the elevation of the clearance line on this structure referred to same datum as used above _ .__

(C) FOUNDATION SURVEY

(1) C haracter of material composing stream bed and banks (2) Character of foundation material (give all data from soundings or borings) -

(3) Distance from stream bed to solid foundation material __ _ ___ ___ _ (4) If piling have been driven into these strata at any point near at hand, furnish following data: (a) Char-

acter of driving _. (Ö) Depth of penetration. _ (¡S) What type of foundations have been used on structures near by _.

(D) GENERAL DATA AND RECOMMENDATIONS FOR NEW WORK

(1) Total recommended length for structure and approaches, from sta tosta or feet.

(2) Number and length cf spans recommended _ _ (3) Can any of the approach structure recommended above be filled should the same prove economical?. If so, between what stations _.- _ ___ _

(4) Type of structure recommended . ._. (5) Width of roadway and number and width of sidewalks (6) Recommended grade lie (show by sketch) (7) What is approximate cost of approach filling material per c. y. at this site? (8) Will temporary bridge be needed or can traffic be detoured? (9) Recommended clearance for superstructure to permit passage of logs or drifts, etc

Elevation _._ (10) Are there any special conditions controlling the following:

(o) The location of any one or more piers or abutments .-- (&) The length or vertical clearance ofany one or more spans (c) The length or angles recommended for any special wingwall construction ? (d) The depth of any one or more footings.-

ill) Are there any other special features to provide for?

If the structure contemplated involves a grade separation with an existing railway or a crossing of a navigable waterway, special information must be furnished to cover same. Blank forms covering the specific data needed in this connection will be mailed upon request. Accompanying the above report should be submitted a map of the site on a sheet 22 by 34 inches, giving the data mentioned on p. 2 with reference to vicinity of maps.


[Form 1]

BRIDGE CONSTRUCTION MATERIALS SURVEY Pagel

For bridge No , over

Located miles from (Distance.) (Direction.)

in section (or between sections ), Twp. . _ Name and/or No. of highway, Local name of bridge, Date of report __ ._ ._ Report by .

(Name of waterway.)

(Nearest R. R. station.) _, Range , county of

(Engineer.)

Cement 1 2 3

1. Brands available.._ _ 2. Source of supply (give location and state whether same is mill or

warehouse) 3. Cost at source... 4. Quantity available, barrels 6. Railhaul to nearest station, miles... 6. Water haul to nearest port, miles 7. Cost at nearest shipping point . . 8. Highway haul to site, miles... _

Character of roads _ _ Estimated ton-mile hauling cost-

9. Estimated total cost per barrel at site 10. Has this cement been tested recently? (If so, give laboratory test

numbers). r 11. Has it recently failed to pass specifications?

12. Additional data regarding cement available .

Fine aggregate 1 2 3

1. Source of supply (state whether from bank or stream) 2. Quantity available . ._ _ 3. Cost at source.. 4. Rail haul to nearest station, miles 5. Water haul to nearest port, miles 6. Cost at nearest shipping point . .. .. 7. Highway haul to site, miles

Character of road . . . . Estimated yard-mile hauling cost...

8. Estimated total cost at site per cubic yard 9. Has this material been tested recently?

If so, give laboratory test number for identification or attach copy oftest.

If not, send herewith 50-pound sample marked for identification as follows

10. Additional data regarding fine aggregate available i

1 Include at this point, for each aggregate supply, any data as to color, workability, etc., which may be of value in determing its suitability for the use intended.

Gravel for coarse aggregate 1 2 3

1. Source of supply (state whether from bank or stream) 2 Quantity available 3. Cost at source _._ ._.... _ 4 Rail haul to nearest station, miles 5. Water haul to nearest port, miles — ..... 6. Cost at nearest shipping point 7. Highway haul to site, miles . . «

Character of roads .. Estimated yard-mile hauling cost • -.- ----- --.---.--.. -


[Form 1]

BRIDGE CONSTRUCTION MATERIALS SURVEY Page 2

For bridge No over (Name of waterway)

Located miles from (Distance) (Direction) (Nearest R. R. station)

in section (or between sections ), Twp. , Range , county of - Name and/or No. of highway, Local name of bridge, _ Date of report, Report by

(Engineer.)


If so, give laboratory test numbers for identification or attach copy of test -

If not, send herewith 100-pounds sample, marked for identification as follows

10. Additional data regarding gravel aggregates available .

Crushed stone for coarse aggregate 1 2 3

1. Source of supply (state whether stock pile or crusher) . 2. Quantity available 3 Cost at source . 4. Rail haul to nearest station, miles 5 Water haul to nearest port, rniles 6. Cost at nearest shipping point _ 7. Highway haul to site, miles

Character of roads _ Estimated yard-mile hauling cost


If so, give laboratory test number for identification or attach copy of test .-

If not, send herewith 100-pound sample marked for identification as follows

10. Additional data regarding crushed stone aggregates available .

11. If stone is to be crushed locally at or near site furnish, following information: (o) Are there any crusher plants in operation near site?

1. Amount of material which may be purchased from plant 2. Cost at plant per cubic yard.. 3. Distance from plant to site of work 4. Cost at site per cubic yard 5. Months during which plant will be in operation 6. Data as to recent tests. If any (see above). If not, send 100-pound sample of material

marked for identification as follows: _ (&) Are there any available quarry sites which may be opened up for this work, (Give complete

data as to location, character of rock, etc.)

(c) Is there any crusher equipment available near by for purchase or rental? (Give complete data.)


LForm 1]

BRIDGE CONSTRUCTION MATERIALS SURVEY Pages

For bridge No over .

Located miles from (Distance) (Direction)

in section (or between sections Name and/or No. of highway, Local name of bridge, _. Date of report, Report by

(Name of waterway)

(Nearest R. R. station) ), Twp. , Range , county of .

(Engineer)

Stone for masonry construction

Source of supply.- Quantity available Cost at source Rail haul to nearest station, miles Waterhaulto nearest port, miles Cost at nearest shipping point Highway haul to site—distance, miles .

Character of roads Estimated ton-mile hauling cost

Estimated cost at site Will this material be worked at site? . _

10, General character of stone for purpose intended.

11. Additional data regarding stone

Structural timber

1. Source of supply, state whether from mill or yard. 2. Variety of timber 3. Cost at source 4. Reliability of mills or yards as regards dehvery 5. Quantity available 6. Rate of delivery ._ 7. Rail haul to nearest station, miles __. 8. Water haul to nearest port, miles 9. Highway haul to site, miles

Character of roads. Estimated hauling cost per M per mile

10. Total estimated cost per M at site

11. Additional data:

Timber for false work

1. Source of supply, state whether from mill or yard. 2. Cost at source 3. Reliability of mills or yards as regards delivery— 4. Quantity available 5. Rate of delivery 6. Rail haul to nearest station, miles 7. Water haul to nearest port, miles --. 8. Highway haul to site, miles

Character of roads Estimated hauling cost per M per mile

9. Total estimated cost per M at site

10. Additional data .

HIGHWAY BRIDGE SURVEYS 11 [Form 1]

BRIDGE CONSTRUCTION MATERIALS SURVEY Page 4

For bridge No over .

Located miles from _ (Distance.) (Direction.)

in section (or between sections Name and/or No. of highway, Local name of bridge, Date of report, Report by

(Name of waterway.)

(Nearest R. R. station.) ), Twp Range »countyof

(Engineer.)

Piling 1 2 3

1. Source of supply 2. Variety of timber 3. Cost at source _ 4. Quantity available 6. Rate of delivery _ 6. Rail haul to nearest station, miles 7. Water haul to nearest port, miles 8. Highway haul to site, miles

Character of roads No. of piling which can be hauled at one load Estimated cost per load per mile

9. Is the above material suitable for— a. Trestle work? _ b. Foundation work? _ _ c. Falsework? _ .

10. Are piling cut or standing? _ .. .. _ . 11. Can winter cut piling be obtained?

12. Additional data (include data as to maximum lengths obtainable and general quality, density, etc., if different from specification requirements) __

WATER SUPPLY

1. Availability of water supply for mixing concrete— a. Source b. Amount "-"'"-.7....I"I c. Is there any question as to the suitability of the water for mixing concrete? .SSSSIllVîy d. If so, give complete detailed information and send herewith one five-gallon sample of water for

test _ _

e. Is there any other possible source of water for this purpose? .

2. Availability of water for jetting piles _.

LABOR SUPPLY

1. Common labor, prevailing rate per hour Quantity available 2. Teams ___ __ prevailing rate per hour Quantity available .

3. Can board and room be obtained for crew near site or will camp be necessary? (Give fuÜ'añd"complete data, including estimated cost of subsistence, etc.)

4. General condition as regards labor supply.

HAULING DATA

1. General character of road between site and nearest shipping point.

2. What months per year may hauling be done? "ll"lll""llllll[l["[liy 3. Are there any steep grades which limit the loads? If so, to what tonnage?" Give "complete

data .

4. Are there any narrow points or sharp hair-pin curves which limit length of piling or timber or lenigth of structural steel members which may be hauled over same? If so give complete data

OTHER MATERIALS

If any additional constructional materials such, for example, as treated timber, brick, paving blocks, bituminous surfacing, etc., are to be used in the proposed construction, complete data should be supplied on form la supplementary data sheets.


For each material space is left on the forms for data covering different supply sources. Complete data should be given for every material supply which is available, and if more space is desired additional form sheets should be used, pasting these sheets to the original form sheet and marking the first form sheet with the following notation: ^^See additional sheet attached hereto for other brands of cement (or deposits of gravel, etc., as the case may be)/'

Space is provided on the form for the cost of each material at the source of supply, at the nearest shipping point, and at the site. In general, all of these cost values should be given in order to enable the office to check the figures by which the final cost has been determined. If, however, the cost at the nearest shipping point can be given direct, the cost at source, water haul, rail haul, etc. need not be given.

The data concerning the quantity of any one brand of cement available should be supplied in order to avoid the possibility of having to change brands of cement for any one project. Several instances have occurred where one brand of cement was exhausted and it became necessary to change brands during the progress of the work. Changes of this character involve a change in the color of the concrete and also in its texture and workability. This is a condition to be avoided if possible.

The data on recent cement tests is important. It sometimes happens that some particular brand of cement shows poor in quality on repeated tests owing to certain conditions at the plant or to other reasons. If this has ever happened to any of the brands of cement available for the job such information should be noted on the forms.

If possible, all data from laboratory reports should be furnished, either by attaching a copy of the test report or by giving reference to laboratory test number or other identification.

Under the heading, ^^ Additional data regarding cement available,'' information should be given as to its color, workability, or any other information of value in this connection. Even the standard brands of cement differ greatly in color, texture, and workability, and it may be necessary where certain architectural treatments are desired or where a certain color scheme is to be preserved to select carefully and specify the brand to be used.

In investigating any natural deposit of aggregate care should be taken that the sample sent in is representative. If different portions of the deposit appear to vary in any degree each section should be sampled and reported upon separately. It should be remembered that many deposits vary greatly in quality even for contiguous sections. In reporting upon the quantity available it should be remembered that this implies the quantity available of the same quality as the sample submitted and estimates of quantities should therefore be conservative. Aggregate samples must be shipped in strong cloth sacks or other suitable containers and a special tag should be placed inside of the sack with complete identifications as follows:


Sample of taken in connection with bridge Fine aggregate, coarse aggregate, etc.

survey for bridge No. over located Name of waterway Distance

miles from in section Direction . Nearest R. R. station (or between sections ) Twp. Range Name and/or No. of highway Local name of bridge Sample herein contained is marked for identification and is from the deposit marked No. on form No. Page of the bridge survey data.

The data for crusher set-ups are obviously applicable only to large jobs or to jobs in extremely remote localities where natural aggregates are not available, as it would clearly not be economical otherwise to set up a plant for this purpose.

It may happen sometimes that natural sand is so diíñcult to obtain as to warrant the manufacture of a substitute by crushing local rock and passing it through sand rolls. If there is a possibility that this method of securing fine aggregate may be worth considering, complete data should be included under the heading. Additional data regarding fine aggregates available.

When structural timber, false-work timber, or piling are to be obtained from local sources the reliability of all mills or other supply sources as regards delivery and data as to quantity production are very important. Many times an entire project is held up on account of the slow delivery rate of mills or yards, and in preparing designs these facts should be known beforehand so that, if necessary, shipped- in material may be specified or bidders be advised of conditions.

In certain cases the quality of the local lumber or piling is not such as will quite come up to the specification requirements. If this is the case, full and complete information should be given under the heading, Additional data, for it may be possible to effect considerable saving in cost by utilizing the local material even though the specifications have to be modified to fit the product.

The data as to water supply is self-explanatory. In sending in water samples care should be taken to fully and completely mark the container for identification as in the case of aggregate samples.

The labor-supply data should include full and complete information regarding amount of labor available, its general attitude, boarding and housing facilities, etc.

The information given under the head, ''Hauling data,'' is important as it affects not only the cost of the proposed work but also in many cases the detailed design; for example, the location of field splices in steel truss bridges.

Form la is for the purpose of submitting any further information or data not fully covered on the printed form. All data as to the cost of treated lumber, wherever there is a possibility that it may be used, or any data as to other materials such as brick, paving blocks, etc., should be given on this form.

If there are any bituminous paving plants set up in the vicinity, full and complete cost data should be supplied in case it is desired to place a bituminous wearing surface upon the bridge floor. This should be given in the form of cost per square yard in place for various thicknesses, and also the cost per thousand pounds delivered


at the site in case it should be desired to include the labor of placement upon the bridge floor in the bridge contract proper.

[Form la]

BRIDGE CONSTRUCTION MATERIALS SURVEY

SUPPLEMENTARY DATA SHEET

For bridge No. over (Name of waterway.)

Located miles from (Distance.) (Miles.) (Nearest R. R. station.)

in section (or between sections ), twp. , range , county of , State of

Name and/or No. of highway Local name of bridge Date of report Report by

(Engineer.) Include in the space below any data necessary to supplement that given for any construction material

on Form 1, and also data pertaining to any construction material (such as treated timber, creosoted block, paving brick, asphaltic surfacing materials, etc., etc.) not fully covered on Form 1.

WATERWAY SURVEY

Form 2 contains the outline of data pertaining to the behavior of the waterway and is to a certain extent self-explanatory.

Bench marks should be established conveniently near the proposed work but far enough away to preclude the possibility of disturbance during construction. These should be permanent monuments clearly marked and readily accessible. For important work two or more bench marks, well referenced in, should be established. If possible, bench marks should be tied into an established datum, such as mean sea level at a certain point or the United States Geological Survey or United States Coast and Geodetic Survey levels.

Drainage or watershed areas may be determined from existing maps such as the United States Geological Survey quadrangles, if available. For small areas a rough stadia traverse may be run for this purpose or the area estimated by walking around it and pacing or estimating the distance from points on the divide to certain known points such as railway lines, section corners, etc. Drainage areas need not be exact as the formulas involving them are by no means exact; they should, however, be approximately correct.

Engineers having a definite territory such as a county, district, or other subdivision, should start the preparation of a drainage map of the entire district showing all the watercourses and divide lines. Such a map will prove of considerable value in quickly determining watershed areas. If a comparatively large scale map is used, these areas may be obtained by means of a planimeter.

The character of a watershed is to be reported in terms of the general slope or gradient for which purpose the classifications flat, gently rolling, rolling, hilly, and mountainous may be used. If different parts of the watershed vary greatly as to general gradient, each portion should be listed separately, giving roughly the percentage in each classification, as for example '^flat 25 per cent, rolling 50 per cent, mountainous 25 per cent.'' These data are for the purpose of determining the waterway opening required by the use of waterway formulas and the general gradient of the watershed, together with other considerations, determine the value of corstants employed in these formulas.


[Form 2] Page 1


For bridge No over (Name of waterway.)

Located miles from (Distance.) (Direction.) (Nearest R. R. station.)

in section (or between sections ), Twp. , Range , county of Name and/or No. of highway, Local name of bridge, Date of survey Date of report, Report by -

(Engineer.)

STREAM FLOW DATA

1. Location and elevation of bench mark

2. Datum used 3. Drainage area to be served by structure, acres. 4. Character of watershed:

(a) General gradient (flat, gently rolling, rolling, hilly, or mountainous). (&) Average slope of watershed in feet per thousand (c) Percentage of watershed under timber (d) Percentage of watershed under cultivation (e) Average rainfall per annum, inches (f) General shape of watershed

5. Width, depth, and cross-sectional area of stream (show by sketch) : (a) At low water stage (b) At ordinary water stage (c) At ordinary high water stage.. (d) At extreme flood stage

6. Elevation of water surface at lowest water stage , at date of survey (give date) . at ordinary high water stage , at extreme flood stage

7. Highest ice mark 8. Highest mark left by drift and debris 9. Frequency and duration of floods

10. Profile of flood line (show by sketch) 11. Cause of flood conditions and season of year when apt to occur

12. Velocity of current (miles per hour) and measured cross-sectional flow: (a) At ordinary stage - (Ö) At ordinary flood stage

. (f) At extreme flood stage 13. Is stream subject to sudden rises with swift currents at flood stage and does it carry large drift on first

flood crest? ^

14. Will ail flood water pass through structure or will relief be provided: (a) Through high-water channels (b) Over rolling approach grades .

(Discuss in full and illustrate by complete sketches.)

15. Are frequent ice jams to be feared?

STREAM BEHAVIOR DATA

1. Character and direction of currents at normal water stage

At flood stage. (Include complete statement of direction and strength of currents, points of impinge ment against banks, etc. Illustrate by complete sketches.)

2. General character of material composing (a) stream bed_

(&) Banks of stream

Gradient of stream at bridge site and for 1,000 feet above and below. (Furnish this information in profile form marked ___ for identification.)

Is stream in general cutting or silting up and at what rate - ---

(a) Do any of foflowing local influences affect erosion? 1. Stream alignment 2. Channel movement 3. Islands, necks, points of natural drift and ice lodgement, etc - - -

(Give complete data, including sketches.)


[Form 2J Page 2


For bridge No over _ _ (Name of waterway.)


in section (or between sections ), twp. , range , county of Name and/or No. of highway, __ Local name of bridge, Date of survey, Date of report, Report by

(Engineer.)

5. Is there any tendency for channel to shift laterally? (If so, indicate direction and probable extent by complete sketches.)

6. Is there need of any channel work in connection with the new bridge structure? (List under following heads:)

(a) Channel change __ (6) Bank protection:

(1) Stream banks (2) Highway embankment slopes

(c) Enlargement of present channel section

(d) Current retards, wing dams, dikes, etc _ (e) Other type of protection.

(If any work as above listed is necessary, describe fully on supplementary data sheet with complete sketches and recommendations.) ^

WATERWAY DATA FROM EXISTING STRUCTURES IN VICINITY

1. Location of existing structures over waterway in question, immediately above and below proposed site (show by means of small sketch on supplementary data sheet, giving distances).

2. Data on old structure marked "No. 1" on above map: (a) Type ._ (b) No. and length of—

(1) Main spans

(2) Approaches _

(c) Cross sectional area of waterway provided (d) Has this waterway proven inadequate during flood yi^riods? (State how frequently.)

(e) Is the above waterway larger than necessary? (/) Are there indications of erosion around piers and footings? .

(g) What is the character of natural foundation material at this site? .

(h) What indications of ice and drift effects

(i) Has channel ever been obstructed by drift or ice? Ifso, to what extent?

(i) Distance from underclearance of this structure to water surface on date of survey (give date)

(k) Are span lengths on this structure adequate for passage of drift or ice?

(I) Is vertical clearance adequate for passage of drift or ice?

3. Sketches of old structure. (A complete sketch of the existing structure in side elevation, showing all pier spacing, vertical and horizontal clearances and all footing depths, if available should be furnished on supplementary data sheets.)

If there are other structures near by which furnish data of value in this connection, furnish full information on additional sheets of this same form or on supplementary data sheets.


The average slope in feet per thousand for the watershed can, of course, be determined only very roughly. These data are needed for solving formulas for stream discharge, and, as in the case of the general gradient classification, the slope for different portions of the watershed must be reported separately if these vary greatly in value.

The shape of the watershed (whether compact or long and narrow) determines to a certain extent the rapidity with which the run-off from the remote portions of the drainage basins will reach the structure and this in turn determines the critical storm duration necessary for the entire watershed to discharge storm water through the bridge opening. There is a relationship between storm duration and intensity of rainfall, the shorter storms having in general a greater intensity. Compact drainage areas, therefore, will discharge more quickly and hence will come to a full discharge for a shorter and therefore heavier storm period. Long, narrow drainage basins on the other hand require (for equal areas) considerably more time for discharge from the remote portions of the basin to reach the structure so that the stream will not come to full discharge except for very long pro- tracted storms which are generally of low intensity. In other words, for drainage basins of the latter class a great deal of run-off will pass through the structure under ordinary storm conditions long before the run-off from the remote portions of the basin has had time to arrive. The shape of the watershed is, therefore, very important in connection with the proportioning of the waterway opening.

Rivers or streams are in general fed from run-off or surface discharge and bank seepage. A part of the water which falls upon any watershed is disposed of by evaporation, and, hence, does not con- stitute a portion of the stream supply (high temperature and wind action have an important effect upon the percentage of evaporation loss). The remainder of the water is disposed of as run-off (as above stated) and by percolation. The run-off constitutes the first or rapid discharge in the waterway, while the percolation water is disposed of much more slowly, gradually finding its way to the stream through bank seepage, thus constituting the slow or seasonal stream feed. The percentage of run-off depends upon many factors and may vary from 5 to 95 per cent of the total precipitation. Vegetation, forestation, or cultivation of the land tend to increase percolation, and therefore decrease the run-off, thus tending to remove ''peak loads" from the stream and making it possible to provide smaller openings. In view of the above facts, data as to percentage of watershed under forestation, vegetation, or cultivation are very important.

The cross-sectional outline of the stream at the various water stages may be shown on the vicinity map or upon a separate sketch as shown in Figure 1. In order to compute the cross-sectional area of flow at various water stages from this sketch (called for under item 12) it is necessary in some cases to allow for channel deepening at flood stage. The elevation of stream beds of rock, cemented sand and gravel, or other resistant material remains practically fixed for varying water stages. When the bottom is of alluvium or silt, however, the channel is deepened by erosion as the water stage rises, silting up again as the flood crest passes and the water lowers so that the elevation of channel bottom is more or less a function of the water stage. This phenomena is observed in streams like the Colorado

73813°—28 2


River, the Missouri River, and others which flow over a channel bed of silt or fine material of considerable depth. This action is not to be confused with the permanent erosion of the channel, being rather an elastic yielding or enlargement and contraction of the channel to accommodate itself to varying flood currents.

When the stream bed is fairly resistant, this correction may be ignored and the stream-bed sketch submitted as shown in Figure 1. Where the bottom is soft material of limited depth overlying a resistant strata, the probable elevation of stream bed at flood stage

15.0

ÂNNEL WILL PROBABLY' NOT ERODE GRAVEL

PROBABLE UNE OF MAXIMUM CHAN- NEL DEEPENING

CROSS-SECTIONAL AREAS NOT INCLUDING CHANNEL DEEPENING

LOW WATER EL.100.3 _72.0 SQ.FT.

WATER STAGE ( lO-2-ao) EL.IO4.O 482.0 SQ. FT

ORDINARY HIGH WATER EL. 108.£ 1,442-0 SQ. FT.

EXTREME HIGH WATER _EL.114.0 3,600.0 SQ.FT

VOLUME OF CHANNEL DEEPENING AT EXTREME HIGH WATER ( ESTIMATED)-. 580. 0 SQ.FT

FIG. 2.—Sketch showing width, depth, and cross-sectional area of a stream taking into account channel deepening during flood stages. This sketch and others such as are illustrated in Figures 4 to 12 should be made on supplementary data sheets

may be determined from the sounding data (see form 3) and the stream-bed sketch submitted as shown in Figure 2.

For important crossings of streams having soft alluvial or silty beds, it is necessary to determine this elastic channel movement with a greater degree of accuracy than that given by the above method.

There are three methods which may be employed by the field engineer :

1. By actual measurements during flood periods. 2. By means of a relationship curve. 3. From existing records.


For soundings at extreme flood stages it will be necessary to secure a large, heavy power boat or for very strong currents to construct an aerial cableway and traveling bucket unless it happens that an old existing bridge structure near the proposed site may be used as a platform from which to drop a sounding line. In taking soundings in swift current, it is necessary either to eliminate or to measure and correct the error introduced by the current sweeping the sounding line out of plumb and also introducing considerable sag in it. There are several methods which may be employed for this purpose. Probably one of the simplest is the use of a heavy lead weight suspended by fine piano wire and raised and lowered by means of a reel fastened to the railing of the platform, bridge deck, or boat deck. The piano wire offers very little resistance to the current, so that the depth d (fig. 3) may be closely determined from the equation d = L cos 0 ignoring the effect of sag. Table 1 gives sizes and strengths of ordinary piano wire and will be of value to the field engineer in determining the maximum size of sounding weight which may be used for different sizes of wire.

TABLE 1.—Strength of ordinary 'piano wire

Size Safe value Size Safe value (music wire Diameter of sound- (music wire Diameter of sound-

gauge) ing weight gauge) ing weight

Indies Pounds Indies Pounds 12 0.029 78 17 0.039 126 13 0.031 88 18 0.041 139 14 0.033 100 19 0.043 148 15 0.035 107 20 0.045 175 16 0.037 119

The theoretical current pressure against the weight TFis given very closely by the equation

2g

Where P = total pressure in pounds against the weight W X = the weight of a cubic foot of water ?; = current velocity in feet per second A = the projection of area presented to the current in square

feet K=ei constant depending upon the shape of the weight W

For rounded surfaces such as spheres or cylinders K may be taken as from 0.60 to 0.75, whence

P = ^ Av^ (very closely)

The theoretical angle 0 (fig. 3) is given by the expression

tan ^--^-3-^

20 TECHNICAL BULLETIN 55, XJ. S. DEPT. OF AGRICULTURE

WIRE SLIDES THROUGH GROOVE CUT IN BEAM FLANS

GRADUATED ARC

REEL FOR SOUNDING WIRE

I BEAM SUPPORT

OBSE^ÊD AN5LE'

RAILtNe

ERROR IN ANGLE DUE TO CURREW SAG

SAGGED WIRE (MEASURED LENGTH FROM POINTU^^ZJ

THEORETiCAL PCSJTION GFWmECLENGTH«¿

^-^TRUE DISTANCEVf6SA6C0RR.)C0Sö 'L COS 0 (VERY CLOSELY)

FLOOD PR0FUJ5

FIG, 3.—Apparatus and derivation of approximate formula for determination of channel depth


For a spherical weight

0.75 radius Xwt. per cu. ft.

and

tan 6 = 2 X radius X wt. per cu. ft.

This last equation shows that the angle 6 is reduced by the use of a heavy material like lead and that if a solid spherical weight is used, the larger the diameter the less will be the value of the angle 6.

If the stream is not at flood stage during the survey or at a time when it can be observed, it may be possible to predict the depth to which the channel will be lowered from soundings taken at various intermediate stages simply by extending a curve through the known values as shown in Figure 4. If this is done, the field engineer should clearly indicate on the sketches submitted just how the maximum values were obtained, showing each point determined from actual measurement.

-20

•

^""^^v^ô O

o^^^ —

LOW WATER

o ÊXTREME F LOOO STAGE

15

WATER STAGE-FEET FIG. 4.—Diagram showing method of estimating the maximum channel deepening when the ^¿

amount of deepening at flood stages less than the maximum is known

Field measurements of channel movement at flood stage should be secured if possible, but whether or not actual field measurements are taken, all data from existing records and published reports should be included in the report.

High-water marks may be determined from existing records, from interviews with old residents, or from inspection. Actual gauging records, if available, are the best evidence, but unless the gauging station happens to be located right at the site, such records may fail to give an exact indication of local conditions. Interviews with adjacent property owners or residents are apt to yield exaggerated information. Such matters as high-water elevation and current velocity for floods of times gone by appear to grow with repeated telling.

A visual inspection is of value in determining recent evidence of high water, but has the disadvantage that all but recent traces have been obliterated. In making a reconnaissance to determine high-


water elevations, examinations of the banks and flood plains should be made both above and below the site. The character of the vegetation on the flood plains or overflow flats will indicate roughly the frequency with which such flats are under water and the strength of flood currents at these points. Heavy vegetation, willow trees, etc., indicate edther very infrequent floods or else flood currents which are rather sluggish. Where gullies or washes occur over the flood plain, the character of the deposit will roughly indicate the velocity of flood currents. Heavy coarse gravel indicates a swift current, while fine silt points to the existence of a more sluggish current. Where there are high, steep banks on one or both sides of the river, considerable information as to high-water elevations in recent years may be gathered from the visual evidence of erosion or wash. The presence of drift hanging on fences, trees, or portions of old structures is valuable as an indication of recent flood elevations.

In many localities high-water elevation may be determined from a minute examination of the moss growing on the trunks of trees. The moss below flood line will be found full of very fine silt deposited by flood currents, while above flood line the moss will be comparatively clean. V(3ry old flood elevations may be determined in this way as this fine deposit of silt will be preserved for many years.

The elevation of lowest water is important in determining the elevation below which it is not necessary to attempt to hide construction joints and also in determining the depth to which cofferdams or cribwork must be removed.

The frequency and duration of floods affects the extent to which it is advisable to make provision for them. For very rare floods, occurring once or twice in a century, it is permissible, if considerable cost can be avoided, to dip the lower chords of steel truss bridges below water, provided, of course, that the chords are designed to resist the impact of maximum drift or ice occurring at this water stage. For floods as rare as this it is also permissible to lay a grade line which will place portions of approach trestles or embankments slightly under water. Unless floods, however, are very rare, such a practice should not be allowed. For this reason accurate data as to the probable frequency and duration of floods should be obtained.

The profile of the flood line is of value in applying certain formulas for stream discharge, and should be reported in sketch form, as shown in Figure 5.

The cause of floods and season of the year when they are apt to occur will affect the sequence of construction operations and also indicate the most advantageous time for the letting of the contract. Such data will also help to fix the maximum elevation at which an ice jam may be feared.

DETERMINATION OF CURRENT VELOCITY

Current velocities may be determined in several ways. The following methods are commonly used:

SURFACE FLOAT

A small ball or piece of wood is allowed to float in the current and the velocity of the current is determined by timing the float between two points a known distance apart.


DOUBLE FLOAT

A double float is constructed by fastening a wooden float to a heavier-than-water ball by means of a chain or wire and letting the two together be carried with the current. The size of the upper float must, of course, be sufficiently large to prevent its being submerged by the weight of the lower ball. The observed velocity v is assumed

9-KlLE CURRENT

AT FLOOD STAGE BED WILL PROBABLY CUT HERE-CUTTING WILL BE

' SLOW AS BANK AND BED ARE OF GRAVEL

EL. MID

^^^ ,^0^MAL_FL0^^g^JjIi^5PR0rH.

EL.HOO STREAM SPREADS OUT-CURRENTS> NOT SO RAPID-FLOOD STAGE ONLY 3 FT. HIGHER THAN 10-30-18 STAGE

AVERAGE SLOPE OR SCOUR

EL.I09O EL 1090

SLIGHT SILTING UP HERE

FIG. 5.—A typical sketch showing stream gradient and flood profile

to be the average of the true surface velocity and the velocity at the depth of the lower submerged weight. That is

where v' and v'^ represent respectively the velocities at the surface and at the depth of the lower weight. By varying the length of chain or wire, the current velocities v" at different depths may be obtained.

THE CURRENT METER

This is the most commonly used device for obtaining current velocities. One type in common use consists of a screw propeller direct connected to a worm and worm wheel. The current passing through the propeller gives it a rotary motion proportional to the current velocity, which is transmitted to the worm and thence to the worm wheel which actuates an automatic indicating device. There is also a device to throw the worm wheel in and out of gear and the speed is obtained by counting the revolutions indicated by the worm


wheel for a definite length of time. Current meters must first be calibrated by determining the number of revolutions per minute made by the indicator wheel for different currents of known velocity.

Relief openings should be reported either on the vicinity map or on separate sketches. The data should include all flood-relief waterways, whether through high-water channels or over rolling approach grades, and if, as in the case shown in Figure 6 there is a question as to closing any natural relief opening, full data should be furnished whereby

REUCF AREA OVER PAVEMENT AT EXTREME $ FLOOD STAGE 276 SQ.FT. 5!

PAVEMENT 6RA0E

END OF PAVEMENT

AREA OF FLOOD WATERWAY OBSTRUCTED ÔY FILL 126 SQ.FT.

40 FT. RELIEF OPENING RECOMMENDED UNLESS MAIN CHANNEL IS CLEARED AS SHOWN BELOW

RECOMMENDED LIMIT DESTRUCTURE

MAIN CHANNEL MAY BE ENLARGED 480 SQ.FTAT THIS POINT IF DESIRED

eßAY£L BOTTOM

o 2 o w U. ui

a. a.

NOTE=-REVETMENT OR ^N DAM AT THIS POINT TO \ ELIMINATE RELIEF OPEN-

iy'^\ IN6 MAY BE FEASIBLE \ IF MAIN CHANNEL IS

\ CLEARED AS SHOWN

FIG. 6.—Method of reporting on relief openings

trestle work, channel enlargement, or other expedients may be compared in cost.

Sketches indicating the direction and character of currents should be submitted as illustrated in Figure 7. Complete data should be given for all structures near the proposed site which may in any way influence the flood flow, such as spoil banks, dikes, intersecting streams, old piers or abutments, trees, buildings or retaining walls, etc. These sketches also should clearly show all points of impingement of the current against banks. Impingement against banks may be caused


by the presence of islands, submerged rock reefs, drift piles, gravel bars, and other causes. All of these conditions should be noted in complete detail upon the above sketch.

The general character of the material composing the stream bed and bank will be determined by the foundation soundings and by a visual inspection of the banks. This information is important in fixing the limits to which it may be possible to restrict the waterway. For any given material there is, within rough limits, a certain critical velocity beyond which scouring takes place. The more resistant this material the higher the velocity. It may be desired to use filled approaches restricting the free waterway, which will increase flood- current velocities. The degree to which this restriction can be

ONLY CURRENTS ABOVE EL.106.0 AND BELOW ELIIO.O DO ANY DAMAGE;AS WATER RISES ABOV/E EL.IlO.O '^CURRENT SHOOTS OVER ISLAND AND STRAIGHTENS OUT.

CURRENTS AT WATER STAGES BETWEEN EL.106.0 AND EL.IlO.O

^CURRENTS AT WATER STAGES ABOVE EL.IlO.O

HARD SHALE BANK.NO CUTTING TO BE FEARED

.->^^^^ e «^: ,F^_HANN£LÂT^,OR^,, V%

'^ ^ WHEN WATER REACHES EL.I06 ROW STARTS OVER

^^Ô^ 07 NECK AT"a"lNDUCING CROSS CURRENTS AS SHOWN.

m <j,,/ tff ^::2s5<cr NORMAL "L^ NORMAL

MASONRY WALL BUILT TO PROTECT THIS PROPERTY, DEFLECTS CURRENTS ABOVE EL.106.0 AS INDICATED.

^ AT NORMAL WATER STAGES ISLAND HAS PENINSULAR CONNECTION WITH MAINLAND AND THIS IS BACKWATER.

■â AVERAGE EL. 105.8

BANK CUTTINGAND CAVING BETWEEN THESE POINTS. AS WATER RISES FROM EL.106.0 TO EL.IlO.O POINT OF GREATEST IMPINGE- MENT MOVES DOWNSTREAM. NEED REVETMENT OR WING DAM

OLD BRIDGE PIER DEFLECTS CURREN-j; AGAINST BANK AT THIS POINT. SHOULD BE REMOVED.

FIG. 7.—A typical report on direction of stream currents

carried is determined by the limiting current velocity for the materials composing the bank and bed of the stream.

Stream banks sometimes contain strata of erodible material overlain by a much more resistant material, so that bank erosion takes place at certain definite flood stages. Figure 8 shows a bank of this kind, the upper strata being a hard, cemented gravel overlying a layer of sand. As the river rises, flood crests between elevations of 143 feet and 147 feet cut into this sand strata and cause the overlying strata to become undermined and to cave in large pieces. As the flood crest passes above elevation 147 the erosion of the sand strata is materially decreased and the banks are more stable. Obviously a condition of this kind may be remedied by revetment work, which need be only high enough to protect the sand strata, as the upper cemented gravel strata is amply resistant to the maximum erosive flood current.

26' TECHNICAL BULLETIN 55, V. S. DEPT. OF AGRICULTURE

STREAM GRADIENTS AND EROSION

Stream gradients may be reported in profile form as shown in Figure 5. All marked breaks in grade, rapids, etc., should be clearly indicated.

Whether a stream is permanently eroding its channel or silting up depends not only upon local conditions but upon the geology and topography of the entire watershed as well. In reporting on this question, therefore, the following should be borne in mind.

ra.r53.o

'^'^f'^CEMENTED GRAVEL"'v'^X ^^^^^ UNDERMINED BY EROSION OF SAND BELOW

SHALE

FIG. 8.—Sketch of stream bank containing alternate strata of erodible and resistant material

GENERAL FACTORS CONTROLLING EROSION

Streams in the early stages of development are generally a function of the topography, although later the topography may be a function of the waterway. In the earlier stages the stream erodes a uniform grade or base level for its channel, while in the latter stages of development the channel is approximately cut to grade and its energy diverted to the formation of a broad flood plain. For these reasons, streams flowing through the later geologic formations (late glacial) are more often found to be eroding throughout a major portion of their length than the older streams.

Streams flowing in broad valleys with well-developed flood plains, but fed by a large number of tributaries having steeper gradients, may erode locally due to the formation of bars and spits. During flood periods the steeper tributaries deliver to the main stream more load than it can carry except at its maximum velocity. The ability of a stream to carry sediment in suspension varies as the sixth power of the velocity so that any local factor which in any degree checks the stream velocity may cause the formation of a bar or spit as a flood


crest lowers. These bars deflecting the stream current from its normal or balanced course cause local erosion both in the channel bed and against the stream banks.

Streams in general will erode in inverse ratio to the resistance of the natural material coniposing the banks and bed and also in inverse ratio to the depth.

LOCAL CONDITIONS EFFECTING EROSION

Every stream tends to establish a uniform gradient unless other conditions interpose. Humps or high spots in the channel erode first and rapids tend to move up the stream and to finally disappear altogether unless the stream bed is very resistant to scour. Points of natural lodgment of drift are quite apt to cause local erosion.

SRiOGE SITE NO.»

.d=PROBABLE LOWERING OF STREAM BED AT BRIDGE SITE NO.I

HUMP IN STREAM GRADE

INTRODUCED BY CHANNEL CHANGE

\

C

POTHOLE MAY SCOUR HERE DUE TO CHANGE IN DIRECTION OF GRADE OF STREAM INTRODUCED

BY CHANNEL CHANGE ABOVE. ÖC^SHQf?T£NED DISTANCE bC

FIG. 9.—Showing how channel changes above or below a bridge site may cause erosion

A channel change below the bridge site, as shown in Figure 9, which increases the general stream gradient below the structure, will likely result in a tendency to move the grade vertex, 6, upstream, thus lowering the channel bed at the bridge site. A channel change above the bridge site on the other hand may cause the impingement of currents against the bottom and result in pothole scour at the bridge site. A very careful study of all conditions, both local and general, should be made before answering the question with regard to silting and scouring.

The probable scour line should be reported by means of a sketch, giving cause of scour if possible. Any local condition affecting erosion such as islands, necks, points of drift lodgment, sudden bends, or sharp turns in the channel, should be reported upon the vicinity map, or, if more space is required, on a separate sketch.


^ Lateral movement of a stream is generally the result of the conditions outlined above, namely, an old stream flowing in a broad flood plain and fed by steeper tributaries delivering an overload to the main stream during flood periods. Probable channel movements can be determined only by a very careful study of the stream for a considerable distance above the bridge site. Figure 10 is a typical report on such conditions.

If any channel work or bank protection is necessary in connection with the new work, sketches should be submitted as shown in Figure 11. ^ These, of course, should be accompanied by complete cross- section notes, contour maps and all other data necessary to com-

FLaoo PLAIN LiMrrs

BANK CUTTING STREAM WILL CUT THROUGH UNLESS REVETTED

ROBERTS CREEK DRY EXCEPT IN CLOUD-BURSTS OR WATERSPOUTS WHEN RIVER CARRIES HEAVY DEBRIS AND BUILDS LARGE DAMS OR DELTAS AT MOUTH

ISLAND OF BOWLDERS AND DEBRIS IN ROBERTS CREEK BROUSHTDOWM BY CLOUD-BURSTS OR WATERSPOUT

FLOOD PLAIN LI-MITS

FIG. 10.—A typical report on tendency toward lateral stream movement

pletely design and estimate the stream-protection work. " Figure 11 indicates only the general layout.

The waterway data for existing structures in the vicinity is of considerable importance in determining the size and type of structure needed for the proposed construction. The information listed on the form should be amplified by complete sketches such as Figure 12. The data called for upon the forms is for one structure only. If there are other structures over the same waterway in the immediate vicinity which will yield data of value in this connection, such data should be reported, using an additional sheet for each structure and pasting them all together.

The data as to the natural foundation materials at the site of the existing structure are to supplement the data as to scour. Obviously


if natural foundation conditions at the old site are radically different from those at the proposed site, the scour data at the old site may have no direct value as a basis of prediction as to scour at the proposed site. If scour at the old site is caused by obstructions, the nature of the obstructions and their relationship to the proposed structure should be fully stated.

The sketches submitted with the bridge-survey notes, such as Figures 1 to 12, do not take the place of the vicinity maps and profiles, but are for the purpose of amplifying the notes and clarifying them. In general, sketches of this character need not be to scale and may be submitted in pencil. The vicinity map on the other hand is a finished scale drawing of the site with accurate contours and profile lines.

WIN6 DAM HERE WOULD COST ABOUT $3^500.00

DIKE CLEAR ACROSS CHANNEL WOULD COST ABOUT $7,000.00

CHANNEL CHANGE HERE WOULD INVOLVE ipOO CU.VDS.AT 65 CENTS.

DIRECTION OF ERODING FLOOD CURRENTS

BRUSH MATTRESS WORK OR REVETMENT NECESSARY TO PREVENT CHANNEL CHANGING AS SHOWN

NOTE: MUST EITHER MAKE CHANNEL CHANGE AND DIKE 0RW1N6 0AM

^ AT a OR ELSE PROTECT \ BANKS AT b AND C

SECTION OF BANK PROTECTION NEEDED AT POINT C. QUANTITIES APPROXIMATE 30 FOOT PILE SPACED 5FT. C.TO C.(PLUS NECESSARY BRACIN6 AND BULKHEAD PLANK). 3.2 SQ.YDS. PER LINEAL FOOT OF HAND PLACED RIPRAP. 0.5 CU.YD. PER LINEAL FOOT OF MASSIVE ROCK. 0.7 CORD PER LINEAL FOOT OF BRUSH OR FASCINES.

FIG. 11.—A general sketch showing necessary channel work and bank protection

FOUNDATION DATA

There is no portion of the preliminary survey wherein external indications may be more deceptive than in the examination of foundations. The occurrence of solid rock on the banks of a stream does not by any means indicate the existence of bedrock foundation. The appearance of bed rock in the bed of the stream may be taken by the inexperienced as indicative of the presence of suitable foundation material. This, however, is, in many cases, far from the truth. The existence of buried or submerged river channels may result in mistaking an overhanging cliff or projecting edge of a fissure or former river gorge for solid bed rock. This condition may result in the placement of footings upon insecure foundations. Even if this is

30 TECHNICAL BULLETIN Ô5, tJ. S. t>EPT. O^ AGRICULTURE

not the case, foundation exploration during construction operations may disclose the presence of this thin ledge, with the result that the footings must be carried through and into softer material, and therefore must be widened to accommodate themselves to the decreased bearing resistance of the softer understrata.

In the sections of the country whose geology has a volcanic origin deep fissure gorges are frequently encountered. Many times these are bridged at the surface with a layer of cemented gravel, which is comparatively thin. While a casual investigation might indicate a

1891 WATER COVERED LOWER CHORD OF THESE 2 SPANS.RESIDENT NEAR SITE SAYS BIG DRIFT HUNG UP ON CHORDS. LOGS 18 INCHES DIAM- ETER AND 20 FEET LONG AND QUITEAJAM OCCURED. NO EVIDENCE OF DAMAGE TO CHORD.

' U SAND AND 'y^ ^ GRAVEL -^> SHOWS NO

F( IRn/ SIGN OF ^•-'^^-^ EROSION

TUBE SET ON GRAVEL AT EL.180.5,HAS ERODED ABOUT 2-0"SINCE BUILT, AS SHOWN.

HIGH WATER HAS NOT BEEN ABOVE EL.192.4 EXCEPT AS FOLLOWS: 1891 EL. 197. 2; 1900 EL.195.0; 1914 EL. I96.I

AREA OF WATERWAY BELOW EL.192.4: GROSS AREA, 3,000 SQ.FT. RESTRICTION OF PIERS AND TRESTLE BENTS 108 SQ FT. RESTRICTION OF OLD FILL, 206 SÇ.FT. NET AREA 2,686 SQ.FT.

ANO ^

W\LLO>NS

COUNTY BRIDGE FOREMAN SAYS PILING 8 FEET INTO GRAVEL.DRIFT HANGS UP ON FIRST 3 BENTS EVERY YEAR.SOME EVIDENCE OF LOCAL SCOUR AT a AND b. APPROACH FILL HAS NEVER BEEN RIP- RAPPED OR PROTECTED IN ANY WAY AND HAS NEVER SHOWN ANY SIGNS OF EROSION. BUILT IN 1887.

BOTH BRIDGE AND APPROACH FILL BUIL.T

IN 1887. FILL NOT SURFACED. COUNTY RECORDS

AREA OF WATERWAY BELOW EL. 197.2: GROSS AREA 7,000 SQ.FT. RESTRICTION FROM TRUSS MEMBERS AND DECK ESTIMATED 280 SQ.FT. RESTRICTION FROM PIERS AND TRESTLE BENTS 200 SQ.FT. RESTRICTION FROM OLD FILLED APPROACH yOO SQ.FT. NET AREA, 5,420 SQ.FT.

FIG. 12.—A typical report giving waterway data for an existing bridge near a proposed bridge site

natural foundation of heavy cemented gravel, further exploration discloses an entirely different foundation condition—a condition requiring wider footings or perhaps piling through volcanic ash or sand. In limestone formations large channels or cavities are often encountered. These range in size from the smallest channels or cavities up to great cave formations of extensive magnitude. In regions with lava beds it is observed that some of the lava flows have been extremely thin and are interbedded with layers of volcanic ash or tufa. It happens frequently that what is apparently solid bed rock proves to be simply a thin sheet of igneous rock overlaying a strata of soft and unsuitable foundation material.

Sandstone is frequently found interbedded with shale and limestone interbedded with layers of clay. When the shale or clay strata


become wet there is danger of sliding, especially where the strata dips sharply. This condition is particularly objectionable for foundations for approach structures because the degree of ground-water saturation is less uniform than in the case of river foundations.

These are but a few of the many reasons why a thorough and comprehensive investigation of the natural foundation is absolutely essential in order that any bridge structure may be economically and safely designed. Form 3 has been prepared for reporting on foundation conditions and is largely self explanatory.

Foundations may be explored by several methods. The five most commonly used are (1) sounding rod, (2) soil auger or boring machine, (3) wash boring or churn drilling, (4) core drilling, and (5) test pits.

The method to be used in any particular investigation will depend upon the conditions encountered, the size and importance of the project, its accessibility, available equipment, and other factors. In general detailed instructions regarding each individual project will be issued from the central office and equipment for the particular job will be assembled and shipped from headquarters. The field engineer, however, should be familiar with the general principles involved in the various methods of foundation exploration. When equipment is to be shipped to the job from headquarters, the recommendations from the field engineer will, to a certain extent, determine the type of equipment selected. The field engineer should be qualified to proceed on his own initiative in the absence of detailed instructions. He should be sufficiently familiar with general equipment requirements to enable him to look over any drilling or boring equipment available locally and to pass upon its adequacy. Many times he will be called upon to visit well-drilling outfits, going over their equipment and advising the office as to the desirability of contracting the drilling work. He should be able to judge as to the relative merits of different outfits and also as to the advisability of contracting at a price per lineal foot or renting the outfit on a per diem basis.

Many times, especially for small jobs, it is not feasible to rent or contract a well-drilling outfit and the cost of shipment for an assembled plant is prohibitive. The field engineer may be forced to assemble an outfit with the material and equipment which he can pick up locally.

The paragraphs which follow present a brief description of the five methods of exploration. The treatment is by no means complete as even a brief description of the various types of drills and drilling apparatus in common use would fill a volume in itself. For more complete description of the various types of drills and the various methods employed for drilling, their limitations and scope, the engineer should consult available published reports, records, and text books on the subject. The manufacturers of core and churn drills put out very complete and comprehensive literature in which may be found complete descriptions of the various drilling processes and types of apparatus commonly used.^

1 For a more complete treatment of this subject, reference may be made to SMITH, R. C, HOOL, KINNE and BAKER'S FOUNDATIONS, ABUTMENTS AND FOOTINGS, Section 1,1923, 414 pp., New York, and WADDELL, J. A. L., BRIDGE ENGINEERING, 1916, 2 v., New York.

32 TECHNICAL BULLETIN 55, U. S. DEPT. OF AGRICULTUKE

[Form 3]

BRIDGE CONSTRUCTION FOUNDATION SURVEY

For bridge No: over (Name of waterway.)


in section (or between sections ), Twp , Range , county of , Name and/or No. of highway, Local name of bridge, _ Date of survey, Date of report, Report by

(Engineer.)

1. Method used for soundings: (a) Sounding rod; (&) soil auger; (c) wash borings or churn drillings; (d) core drilling; (e) test pits. (Indicate which one.)

2. Location and log of borings or soundings. (Show by means of sketches and profiles on supplementary data sheets, including a full description of each material encountered and estimated bearing value of same.)

3. Log of material encountered in drilling wells near by or from other foundation pits in the vicinity. (Give complete data as to location of well or foundation pit with reference to proposed work, description of material encountered, referring all elevations to datum used for waterway survey.)

(Amplify by sketches on supplementary data sheet if necessary.) 4. Have piling been driven into these strata at any point near at hand? If so, furnish complete data as to—

(a) General character of driving

(&) Elevation (referred to bridge datum) of bottom of piles (average) (c) Weight and type of hammer used and any other available data of value in this connection—

5. Recommendations as to type of cofferdam required: 1. Timber sheet piling 2. Steel sheet piling 3. Timber crib ___ 4. Puddle dam ._ 5. Other types ___

(Indicate recommendations for first and second choice.) 6. Will foundation seal be necessary or can base be deposited in dry by pumping from sump or catch basin?

7. What is probable lowest elevation of permanent ground water? 8. What type of foundations are used on adjacent structures? (Describe in full with sketches where

needed.)

9. Is there any evidence of slides or slips on either bank or of any movement of strata? (Discuss in full with sketches if necessary)

10. Is there any indication of wind erosion on banks or flood plains? (Discuss in full.) _

11. Is there any indication of weathering, air slaking or frost action on either bank or in the near vicinity?


SOUNDING-ROD EXPLORATION

PROCESS

The process consists simply in driving, churning, or otherwise forcing a sounding rod through penetrable strata to determine the elevation of any solid strata below. The bar is worked or churned down as far as it will go, using water to lubricate the hole if necessary, and then driven dow^n the balance of the way, using either a hand maul or rammer. If possible, the driving is continued until the bar strikes solid material.

EQUIPMENT

The equipment needed may generally be purchased locally and consists essentially of the following items :

Solid round bar (or heavy pipe), three-fourths to seven-eighths inch in diameter, threaded for standard coupling at upper end and pointed for driving at the lower end. This bar is for the lower section and should be from 6 to 12 feet long.

Additional sections of pipe or rod from 4 to 6 feet long. These sections should be threaded for standard coupling at both ends.

The upper section of rod should be fitted with a drive cap. This drive cap may be fitted with a suitable wooden cushion if desired. If advisable, a short drive section (2 to 4 feet long) may be used either with or without a drive cap. This section is taken off as additional sections are added and placed on top of the last added section.

Heavy maul or rammer with vertical handle to be used for driving rod. An ordinary pipe wrench to turn rod. A lever and chain or other suitable device to pull rod or pipe.

If the strata is such that the rod must be driven from the start, the first section should not be over 6 feet long in order to avoid the necessity of building an elevated driving platform.

PRECAUTIONS REGARDING OPERATION

All rods should enter couplings for the full length, so that adjacent rod sections abut to make close contact and severe driving will not strip the threads. Where driving is exceptionally difficult, extra heavy or hydraulic couplings should be used. These can generally be purchased locally. Hydraulic couplings are longer and stronger than standard couplings and are cut with a perfect taper and longer threads. Couplings known as recessed couplings may generally be obtained. This coupling projects beyond the limits of the pipe thread, thus protecting the pipe at its weakest point.

All soundings should continue until the rod ^^brings up.'^ If the rod ^^brings up'^ with a sharp ring, it probably rests on rock or a large bowlder. If the rod ^^ brings up ^' with a dull ring or if repeated driving causes it to break through for a short additional penetration, the material is probably stiff gravel. Indications of solid rock should be checked by several other tests a few feet distant to guard against mistaking a heavy bowlder for solid bed rock.

All rod sections should be cut to even lengths and each section numbered and recorded in a note book prepared for that purpose, so that at any time the exact position of the point of the rod may be determined without the necessity of withdrawing the rod and measuring.

73813°—28 3

34 TECHNICAL BULLETIN 6S, V. S. DEPT. OP AGRICULTURE

SOIL-AUGEK EXPLORATION

PROCESS

Boring with a soil auger is usually done by hand, but horse-power and gas-power outfits (for well-boring operations on a large scale) are on the market. The hand auger is made to bore into the soil by turning levers or wrenches fastened to the stem. This method may be employed for any material which wiU adhere to the bit such as loam, clay or clayey sand, or gravel. For shallow borings through material not too wet an ordinary post auger may be employed. For deeper holes, when hand power is used, the auger bit is generally from 13^ to 2 J^ inches in diameter. Where the material penetrated will'not stand without support, a pipe or well casing is placed.

The auger is first used to penetrate the soil as far as possible and is then withdrawn and the casing is driven or churned down as described later under wash boring.

Several kinds of casing are used for this class of work. The cheapest is a light sheet-iron pipe riveted together very much like stovepipe. It can not be used where it is necessary to force or drive the casing. It is easily injured in handling and is not to be

recommended except for temporary case- ment of comparatively large and shallow holes. Other types are known as well casing (which is considerably lighter than ordinary standard pipe), ordinary black pipe, and "drive pipe" or extra heavy pipe employed for churn or wash borings where the driving is exceptionally difficult or the holes are very deep.

Several types of joints are used for the different types of casing. For well casing,

Fio. i3.-Types of couplings used for the socket Coupling, the inserted joint and ÄSTofntt'ÄhS'"'' ^' th? flush joint are most commonly^ used.

(Fig. 13.) The socket couplmg is the only one suitable to withstand heavy driving. The socket coupling is generally employed with ordinary black or steam pipe (flush- loint drive pipe is sometimes used) while for drive pipe, extra heavy or hydraulic couplings are generally used. Drive pipe ends should be cut square to furnish an effective bearing against each other within couplings. Other types of joints or couplings are on the market but the above types are the most commonly used.

A shoe or cutting edge must be provided where casing is to be driven and there must also be a drive head at the top, as will be described in more detail under wash borings. The size of the casing should be sufficient to afford clearance for the auger bit.

The type of casings or couplings selected will depend upon the resistance of the strata. In general, time will be saved by adopting a heavier type of casing than perhaps is necessary, even at a slightly increased cost rather than run the risk of delays owing to failure of light casing to withstand driving.

As soon as a casing has been worked and driven down as far as it will go, the auger is reinserted and the hole cleaned out to the bottom of the casing and as much further as it is possible to go without caving. The process of driving and cleaning is then repeated until the desired depth is obtained or a solid strata is encountered.

aïOHWAY BEIDGÈ SURVEYS 35 EQUIPMENT

The following equipment is needed: Soil auger. Pipe casing where needed. A tripod or stiff-leg derrick with suitable block and tackle for pvilling auger

bit and casing, A ram or drop hammer for driving casing (see wash borings). Necessary pipe fittings and small tools (see wash borings). A bailer or sand pump when needed (see wash borings). A water jet outfit when needed (see next paragraph).

PRECAUTIONS HEGABDING OPERATIONS

The auger stem should be of èubstantial construction as it maj^ twist off, particularly when the boring is through clayey gravel containing large pebbles. Each section of auger extension and each

Ordinary bailer with dart- valve

Bailer with flat valva

Vacuum sand pump with dart valve

y^m Vacuum Sand pump with flaf valve

FIG. 14.—Types of bailers and sand pumps

section of casing should be cut to an even length and numbered. The numbers and lengths should be recorded in a notebook in order to determine readily the depth penetrated. If the material is such that it will not come up on the auger bit, the hole may be cleaned by means of a bailer or sand pump. The bailer device is a piece of pipe with a valve inserted in its lower end. This bailer is lowered through the casing and churned up and down until full. Typical bailers and sand pumps are illustrated in Figtu"e 14. If in bailing out the hole the material is not fluid enough to pass through the valve of the bailer, or sand pump, water is added to facihtate the operation. If the sand pump or bailer will not work, a water jet may be employed to clean out the hole. If a water-pressure line is not available, a suitable force pump must be secured to supply the water jet.

When bowlders are encoimtered, they may be drilled through with a hard rock chum drill or drilled and shot as described vinder wash borings.


Soil-auger explorations are sometimes made with a horsepower rotary well-boring machine. These machines are in more or less common use in some sections of the country and may be obtained at reasonable cost to do foundation-exploration work. In one of the commonly used machines, a horse is hitched to the platform lever and operates the auger bit directly. When the auger is jBlled, the operator engages the hoisting clutch and the continued motion of the horse raises the auger stem. When the bit has been raised to the platform, a small crane is used for swinging the auger out upon the bank for emptying.

a

JIG. 16.—Types of auger bits used with rotary boring machines. Type A is the one most commonly used, type B Is adapted to boring through stiff gravel, type O is a spiral bit for use in loose soils, and type D is a half pod auger for use in hard earth formations.

This type of machine will bore holes from 6 to 24 inches in diameter an^ usually to a sufficient depth. Figvire 15 illustrates some of the most commonly used types of bits employed with this machine. Fur- ther details of operation and equipment, such as underreamers for enlargement of the hole for casing, may be obtained from the manu- factiu-ers' catalogues.

The companies manufacturing this type of eqmpment also make A complete boring and drilling machine operating a churn drill with jars and sand pumps. These machines are also arranged for gasoline power.


WASH BORINGS

PROCESS

The term ''wash boring'' is used to describe the operation of churn drilling with a hollow drill pipe having on the lower end a cutting bit through which a stream of water is forced to wash the cuttings to the surface.

The type of bit used depends upon the nature of the material. For cutting through clay and light gravel, a chisel-faced bit is used, while a chopping bit or fluted rock bit is generally used through bowlders, sandstone, or other solid material. The drill bits are pierced with small openings cut so as to direct the water jet against the sides of the hole. Water under pressure (either from city supply or a force pump) is forced down the hollow drill rod and through the bit openings. The hole is drilled by churning the drill up and down turning it at each stroke. The hole is started or ''spudded in'' either by hand or by means of a mechanical device described on page 46.

When a hole has been churned down as far as it will go without danger of caving, the drill is withdrawn and casing is driven as described under soil-auger operation. From this point on, the operation is one of alternately drilling and driving casing and the equipment should be so arranged as to make it possible to change from ODC operation to the other with a minimum of time loss.

EQUIPMENT

Drilling outfits of this kind are generally to be assembled and shipped from the headquarters office if available and the shipping cost is not prohibitive. Sometimes it is possible to secure equipment on a rental basis. If neither of these can be done, it is necessary to purchase and assemble equipment on the ground.

The equipment needed will vary to a certain extent with the particular job, and where it is assembled on the ground it is necessary to utilize such material as is readily at hand. With this in mind, the equipment list which follows has been made rather general, being simply a brief statement of the essential requirements, leaving the details to be worked out by the field engineer.,

1. A truck, barge or platform upon which to mount the plant. Figure 16 shows a truck-mounted outfit of a type satisfactory for land operation (in the figure it is shown working in about 18 inches of water). For land operation, the outfit can be mounted upon a timber platform or skid frame or it can be used without mounting of any kind. For water operation, the outfit should be mounted upon a barge or upon pile platforms. Figure 17 shows a plan for a barge of a type which has proven satisfactory. Two small barges fastened together by a plank platform with the drill operating through the opening between them, have been used with good results. These small barges should be at least 6 to 8 feet wide and 20 to 25 feet long. All barges should be provided with suitable anchors and anchor lines. Concrete blocks may be used for anchors.

2. A derrick, frame, or tripod for supporting the drill rod and water line (figs. 17 and 18).

3. A suitable force pump for supplying water under pressure if a city or other supply is not available. The pump should be fitted

38 TECHNICAL BULLETIN 55, Ü. S. DEPT. OP AGRICULTURE

with a discharge connection for three-quarters or 1 inch hose and with 15 to 20 feet of suction hose with foot valve and strainer.

4. Device for spudding or churning drul. This may be done by hand, lifting the drill rod several inches and churnLng it down again, or mechanically. The mechanical devices most frequently employed are either the walking beam, horizontal drum and "niggerhead" line,

-^-t/' '4'.:u^. •

Fia. 16.—Wash-boring outfit mounted upon truck with light steel leads for drop hammer used tor driving casing

horizontal drum to which drill-rod line is fastened and which is thrown in and out of gear by means of a lever clutch, or a cam or eccentric.

The walking-beam device shown in Figure 24, is probably the most frequently used, especially with commercially assembled drilling outfits. This device is described on page 46.

When a horizontal drum is used the drul rod and bit are hoisted a few feet and released for a free drop by slacking off on thç niggerhead line or releasing the lever clutch. The cam or eccentric device

HIGHWAY BKIDGE SURVEYS 39

imparts a churning motion to the drill in somewhat the same manner as the walking beam. There are a number of other devices which have been used and others which may suggest themselves to the field engineer who is assembling equipment in the field. Any device which will impart a churning motion to the drill without an excessive consumption of power and without restricting its free fall and which is not too expensive or complicated for practical use will be satis-

2-6> 8 CAPS FASTENED TO

e'xS'POSTS WITH LAG BOLTS

WITH NUTS ON UPPER END SO

AS TO BE READILY KNOCKED -

DOWN FOR SHIPMENT.

G^'G POSTS —

3"PLANK—

NOTE - ALL BRACING. ETC. BOLTED WITH |"<t

BOLTS AND 0 6 WASH- "

ERS. IFRIG IS TO BE USED

BUT ONCE, BOAT SPIKES

MAY BE USED INSTEAD

OF BOLTS.

1 SHIP CHANNEL 6-15.3 LBS.

2 STIFF [? Zi^l^'k (6R0UND TO BEAR)

2-| BOLTS

k FLAT BAR

CLAMPS AND TIMBER BLOCKS

RING FOR GUY CABLE

4^4 5TRAKES

J BOTTOM WITH CAULKING SEAMS

4«4 5TRAKES

OPENING IN DECK FOR FASTENING SPLICES/ PLAN 3 " 14 SOLID BRIDGING SPACED AT 2-6 CIO CFflOM END TO END.

FIG. 17.—Plan for a derrick frame for wash-boring outfit mounted on a scow. This outfit is designed for knocking down for shipment

factory. The height of drop necessary will depend upon the character of the material and varies from 6 to 36 inches.

5. Suitable power equipment for the spudding device, water pump, lifting the drill rods, and to operate the hammer line in case a drop hammer is used for driving the casing. For the small drilling outfits commonly assembled in the field, a two to five horse-power engine will probably be sufficient.

6. Device for driving casing. The casing may be driven by means of a ram or weight operated by hand, as shown in Figure 18, with an


ordinary hand maul, or by the use of a drop hammer. Figure 16 shows a set of light steel leads for use with a gravity hammer. The hammer line is wound on the horizontal drum shown in the rear of the truck and released for a free fall of the hammer by disengaging a clutch. Figure 19 illustrates two methods of driving casing with a cylindrical drop hammer having a central guide. This figure also shows typical construction for the driving shoe and driving head.

WHEN CASING HAS BEEN DRIVENAS FAR AS POSSIBLE REMOVE RAM AND COUPLE ON

SECTION SHOWN ABOVE, REMOVE CLAMP AND PROCEED WITH DRILLING.

SHEAVE 8L0CK

RAM MAYBE WORKED

UPAND DOWN BY MAN POWER DIRECTWITH-

OUT USING SHEAVE AND LINE IF DESIRED

-TO HAND POWER OR WINCH

WHEN DRIVING CASING RAISE DRILL PIPE AT LEAST 3-0" FROM BOTTOM OF HOLE AND HOLD IN PLACE BY MEANS OF CLAMP

FIG. 18. —Tripod for a hand-operated wash drill

The walking beam illustrated in Figure 24 may be rigged up to drive casings.

With some drilling outfits the ram is cored out to fit over the drill rod which acts as a guide for the ram. With this arrangement casing may be driven without pulling the drill pipe clear up. This arrangement saves much time where there must be frequent alter- nation between drilling and driving casing, to prevent the casing from ^^freezing'^ in the hole,

HIGHWAY BRIDGE SUKVEYS 41

7. Suitable drill rods and bits. The drill rods should be made up in sections of even lengths of from 5 to 10 feet, each section of rod being numbered and its exact length recorded. For ordinary work, 1-inch standard black pipe may be "used for drill rods. For difficult boring or where the depth exceeds 75_ to 100 feet, extra heavy pipe should be used. Standard outside pipe couplings may be used in ordinary cases, but extra heavy or hydraulic couplings are better, if available. Recessed couplings, if available, are to be preferred for reasons already discussed.

In drilling to a considerable depth it often happens that conditions are encomitered which make it necessary to use smaller size casing in the lower part of the hole. If the outside couplLags on the drill rod wül not clear the smaller casing it is necessary to change to smaller (irill rods or use flush couplings. The ordinary flush-joint coupling shown in Figure 13 ia not as strong as the outside coupling and will not stand heavy usage. Extra heavy flush couplings are generally obtainable and should be used if a flush-type joint is employed.

Drül bits should be of special alloy or of hardened steel. In general a chisel-edge bit is used for clay, loam, and gravel, chopping bit (two right angles) or a is employed for bowlders, or rock, borings should be

while a cross chisel edges at fluted rock bit heavy gravel. Drills for wash perforated by

FIG. 19.—Two methods of driving casing pipe: A, Driving witli drive weight; B, driving with water j^t and drive weight

apertures for the water jet, the per forations being so bored that the iet is thrown against the sides of the hole. ChiseTbits may be made locally, if necessary, by inserting a solid stub into the lower end of the drill pipe, then forging out to correct shape and hardening.

8. Casing pipe. A description of the various types of casing ordinarily employed has been given under the discussion of auger borings.

Well casing is generally rather light for wash-boring work. The threads on this type of casing are finer and the shell üiickness considerably less so that it wiU not stand driving to the same extent as standard black pipe or steam pipe. The cost of well casing is about two-thirds of that for standard black pipe and about one-half that of extra heavy pipe, so that for material through which casing can be "tmned down" or seatjed with very light driving, this type of casing wül show distinct economy. For ordinary conditions, how-

42 TECHNICAL BULLETIN 55, U. S. DEPT. OF AÖEICULTURE

ever, standard black pipe with ordinary standard outside couplingg should be used. _ Extra heavy pipe or "drive" pipe should be used for all heavy driving and for all holes exceeding 75 to 100 feet in depth. The drive pipe should be cut square and should butt squarely at the center of the coupling. Hydraulic couplings (preferably recessed couplings) should be used for heavj casing. These can generally be obtained in sizes up to 4 inches which covers all couplings ordinarily used. Casings should be fitted with a drive section having a cutting edge around its entire perimeter and also with a specid

1 1

PIG. 20.—TWO typical arrangements of drilling apparatus showing drive head, drive shoe, spudding bit, casing ram, water swivel, etc.

FIG. 21.—One type of water swivel

drive head. Figure 20 shows the details of a typical drive head and drive shoe. For very heavy driving it may be necessary to use a timber shock block over the drive head. For ordinary work 2j^-iach casing is used. For deep or difficult work it is generally advisable to start with 3-itich casing as it may be necessary to use a smaller casing telescoped inside the first. Where the ground to be penetrated is soft and casings may be worked or churned through, rather than driven, ñush-type couplings (fig. 13) Avill reduce side friction.

In purchasing casing material the engineer should keep in mind the salvage value. For example, standard galvanized-iron pipe is


used for well casings, and if only one set of borings is to be made' it may be economical to purchase this type of casing, as it will have a much more ready resale and a higher value than black pipe.

9. Suitable hose connection. For connecting the water hose to the drill rod, a suitable water swivel should be obtained, if possible. Figure 21 illustrates a standard type of water swivel now on the market. If a water swivel is not obtainable the hose may be connected direct to the drill pipe with an ordinary hose connection, a standard coupling, and a return bend.

10. Fifty to 100 feet of rubber hose. 11. Chain block and set of screw jacks.

FIG. 22.—Typical nnderreamer used when it is necessary to enlarge the hole lor easing

12. Supply of pipe fittings for casing and drill pipe, including- standard couplings, flush-type couplings (if available), elbows, tees, bends, bushings, etc.

13. Small tools—pipe cutters, wrenches, pipe tongs, stacks and dies, a pipe vise, rope and tackle, pipe clamp and set of wedges, hammers, saws, shovels, etc.

PRECAUTIONS RBOABDINO OPERATION

The hole should be started without casing if possible, washing down until caving starts or until the bit starts to stick or j am. Work or chum the casmg down as far as possible before starting to drive.

If it is possible to keep the bit ahead of the casing pipe, the pipe will follow down plumb, the bit tending to "lead" the pipe down,


but if driving is necessary the casing may easily become deflected from a vertical position by a bowlder or rock and may cause difíiculty later. Driving should not be resorted to until absolutely necessary, but the casing churned or worked down, following the bit at as great distance as possible. When it becomes necessary to start driving the casing, the drill rod must be pulled up from the bottom of the casing for a distance of at least 3 or 4 feet; otherwise material will work up from the bottom around the drill point and cause it to jam.

Casing should be driven comparatively short distances at a time and driven frequently in order to avoid ^^freezing'^ in the hole.

Every joint on the drill pipe and on the casing should have sufficient thread to fully enter the couplings. For heavy driving the end of the pipe should be cut square to furnish a butt joint in close contact around the entire perimeter of the pipe; otherwise, the driving is quite apt to strip the threads.

The size of casing used must be such as to give free clearance for drill rods, and prevent binding. If, on the other hand, too much clearance is left between the drill rod and casing, the volume of water necessary to wash cuttings to the surface will be so great as to require larger pumping equipment than would otherwise be necessary. For ordinary work drill rods of 1-inch pipe, using ordinary outside couplings, either standard or hydraulic, may be used with 23^-inch standard pipe casings. Inside and outside diameters for various standard and extra heavy pipe sizes are given in Table 2. The clearance C (fig. 23) should never be less than one-fourth inch.

TABLE 2.—Inside and outside diameter for stated sizes of standard and extra heavy pipe and hydraulic couplings

Hydrau- Standard Extra heavy lic

coupling Size pipe (nominal)

Inside Outside Inside Outside D diameter diameter diameter diameter

Inches Inches Inches Inches Inches Inches M 0.824 1.050 0.742 1.050 1.44

1 1.049 1.315 .957 1.315 1.63 IM 1.380 1.660 1.278 1.660 2.07 . m 1.610 1.900 .1.500 1.900 2.31 2 2.067 2.375 1.939 2.375 2.81 2K 2.469 2.875 2.323 2.875 3.31 3 3.068 3.500 2.900 3.500 4.00

Care must be taken not to drill too far ahead of the casing or the bit is likely to become jammed in the hole and broken off in pulling.

When the casing will not penetrate further and the desired depth has not been obtained, it becomes necessary to underream or to drive a small casing inside the first one. Figure 22 shows one type of underreamer manufactured for this purpose. If smaller sized casing is used, the original size drill rod should be worked down as far as possible ahead of the casing. This drill rod is then withdrawn and the small casing driven as far as possible. From this point on, a drill rod having a smaller over-all dimension, must be used on account of the decreased size of the second casing. This clearance may be obtained by shifting to a smaller size drill pipe or using a flush-type coupling.

HIGHWAY BKIDGE SURVEYS 45

The hammer or ram employed for driving the casing should preferably be arranged to work over the drill rod to eliminate the necessity for withdrawing the drill rod while driving casing.

Where driving is exceptionally difficult and for holes deeper than 75 feet, extra heavy pipe, with hydraulic recessed couplings, should be used for a casing.

If the casing becomes jammed in the hole and will not penetrate further, it may be pulled for 3 or 4 feet and the uncased hole ^'sprung^' with a charge of a half or three-fourths of a stick of 40 per cent dynamite.

When the drill is stopped, the pump should be kept running until the overflow water is clear of washings, and the bit raised a few feet or the drill may stick in the bottom.

When solid rock is reached, drilling should be continued for several feet to make certain that the strata is sufficiently thick to distribute the load of the structure. Solid rock should be penetrated 3 or 4 feet and shale 6 to 12 feet.

As soon as hole is down and all data are secured, the casing should be pulled. This may be done with either a chain block and pipe clamps, block and tackle and pipe clamps (using a multi- part line), lever and chain, or screw jacks and pipe clamps. If it is impossible to pull the casing, break it below the lowest coupling with a stick of 40 per cent dynamite. This will allow sal- vaging all but the lower section of casing.

Be sure that all barges or platforms in navigable streams, and all work adjacent to highways or railways, are suitably protected at night by red lanterns.

FIG. 23. -Diagram illustrating pipe dimensions in Table 2

DRY-CHURN DRILLING

"this type of drill sometimes known as the cable drill, and used in the oil fields, consists of a heavy bit, drill stem and a set of jars fastened to a cable by means of a rope socket. An up and down or churning motion is imparted to the cable by means of a cam or walking beam. The bottom of the hole is kept filled with water. The material in the hole is chopped and ground up by the drill bit and removed by means of a sand pump or bailer. Figure 24 shows a well drilling outfit of this type. Three types of bits are used with this particular outfit as illustrated in Figure 25. The spudding bit is

46 TECHNICAL BULLETIN 65, V. 8. DEFT. OF AGRICULTURE

used for cutting through clay or loose stone. The paddle bit is used for seamy and fissured rock and the fluted rock bit is used for other rock formations. The paddle bit is of special construction and is not

Pia. 34.—A cable-drilling outQt mounted on a tractor.

used as much as the other two. Figures 24 shows that the drill cable passes over an idler pulley at the top of the derrick leads and down over another idler fastened to the walking beam and thence over the cable drum. The jars shown in Figure 25 are used as a safeguard against the drill becoming jammed m the mud or in crevices in the

The Spudding bit

The paddle bit

í^^-,;ü¿;^»T^jj!»gî,j.llHliU i5Sia9^fii.«11rf

The fluted rock bif

The jars used toprevent the bit from jamming or sticking in hole. The two I inks Interlock in the same

manner as the I inks ofa chain FiQ. 25.—Types of bits and jars used in cable drilling.

rock, or to prevent a newly dressed bit from wedging. The slack motion in the links is about 6 inches with this type of equipment and the weight of the jars for a 55^-inch hole is about 200 pounds.


During the first process of drilling, or what is known as "spudding in/' the drill is fed into the hole by means of the cable drum on the rear of the machine. For greater depths, the cable is removed and fastened to what is known as a temper screw, suspended from the yoke of the walking beam, which allows a more closely regulated feed. The cable is generally of hawser laid manilla rope.

With this type of drill, the casing can be driven by using the string of drill tools as a hammer or ram. Driving clamps are clamped on the drill stem and engage a drive cap screwed on the casing. The walking beam can be made to deliver up to 60 strokes per minute, causing the string of tools to deliver a series of rapid blows to the casing. These rapid blows from a comparatively heavy weight fall, ing through a short distance are very effective in tapping down the casing pipe.

In drilling with this type of equipment, a method known as drilling on the spring of the cable is employed. At a depth of 50 feet when the drill tools are at the lowest point of their stroke, the point of the bit should be adjusted to hang about 2 or 3 inches from the bottom of the hole. At 100 feet this distance is adjusted to 4 or 5 inches, with greater distances for increased depth. The downward stroke of the drill will spring the cable an amount sufficient to let the bit strike a practically uncushioned blow. The advantage is that at the upper limit of the up stroke the drill tools lag behind the walking beam, so that on the down stroke the entire weight has a free gravity fall.

After the material is chopped and ground the hole is cleaned out by means of bailers or sand pumps, as shown in Figure 14. The principal difference between this type of drilling and wash boring is the method of transporting the cuttings to the surface. This type of drill may be used for any foundation-exploration work to which the churn drill is adapted. The general principles regarding the selection and driving of casing pipe apply in,work of this kind as well as in the case of wash borings.

CORE SAMPLES

PERCUSSION CORE DRILLS AND CYLINDRICAL CUTTERS

Core samples are necessary if an examination of the material in its natural and undisturbed condition is desired. A device which will cut core samples at various depths is therefore an essential part of churn-drilling and wash-boring equipment.

One device known as a percussion core drill is designed for use with apparatus such as shown in Figure 24 and is adapted to coring any reasonably soft material such as soft sandstone, coal, or fire clay. This device extracts the core without the use of wash water. When a core is desired the cable tools are withdrawn and the drill bit and stem removed, leaving the jars and rope socket in place. The percussion core drill is joined to the jars, the tools lowered into the hole, and the drilling resumed at a moderate speed. Two core barrels are provided so that when the first core has been cut the tools can be raised and the core barrels exchanged. A core extractor is used to remove the core.

Often a core cutter is rigged up from materials at hand for use with wash-boring, churn-drilling, or auger-boring outfits. A piece of pipe with the edge at one end sharpened and the other end arranged so that it can be attached in place of the cutting bit will do for the purpose. The core cutter is worked into the material until it is filled

48 TECHNICAL BULLETIN 55, U. S. DEPT. OF AGRICTJLTTTRE

with a sample. Figure 26 shows soft sandstone and stiff clay cores obtained in this manner, at H.arrisburg, Oreg., at depths ranging from 40 to 63 feet below the water level of the Willamette River. For material whose resistance is so great as to preclude the use of driven cylindrical cutters or percussion drills, rotary core drills must be employed.

BOTABY COEE DRILLS

The process consists in the cutting out of a solid core of the material by means of a cylindrical cutter to which is imparted a rotary motion. There are three types of core drills commonly used, known as the diamond drill, the diamondless or shot drill, and the saw-tooth drill or core cutter.

^^m^-¿. 1 1 frJfà-f- I 1 S

PIE«. 1 El-tVATION t»l.*

Pica 1 CLCVATIOM

262.8

* PIEB 1

ELEVATION 269.1

MER 4 El-EVATIOH

Z4e.s

I • I PICR 4 I ELEVATION 1 285.8

* PIER «

CiXVATIPM 2 58.8

OICR 4 1 KLOMTION ■

169.9 ■

HÍ ■■ ̂■J FiQ. 26.—Cores of stifl clay, shale, and soft sandstone taken in wash-boring operations with a

chiselêdge core cutter

DIAMOND DRILLS

The diamond drill consists of a soft steel, hollow cylinder with black diamonds or carbons set in the edge and which act as the abrasive. The cylinder is fastened to a hollow vertical stem, which is rotated by means of suitable gearing to an engine or other power unit. As the drill is rotated a water jet is fed to the bit to cool it and to wash the cuttings to the surface. Diamond-drill outfits are generally fitted with an automatic device for feeding the bit into the rock, and a derrick or tripod for operating and raising the bit, and a pump for supplying the water pressure. Diamond drilling is rather expensive worii owing to the high cost of equipment and the loss of diamonds during operation. The cost of diamonds for one drill bit ranges from $800 to $1,200. Diííerent rock formations require reset- ting of diamonds in order to cut with maximum efficiency and to avoid as far as possible the loss of diamonds, and this requires the presence of an experienced diamond setter on the job at all times.

Diamond drills are especially adapted for boring into rock or other solid material. Where hard material is overlain by soft strata a hole is generally washed down or churned down and cased into the rock before core druling commences. It is necessary to drive the casing well into the rock and to wash it clean in order to avoid the possibility of sand or loam entering the bore hole and working around the drill.


Foundation exploration with diamond drills is generally either by contract at a price per foot or on a per diem rental basis under the supervision of an experienced operator, and the field engineer will rarely be called upon to supervise diamond-drill operations.

DIAMONDLESS CORE DRILLS

The diamondless core drill or shot drill consists of a circular steel core bit generally with a notch cut out in its lower edge, as shown in Figure 27. Chilled steel shot or a crushed steel abrasive are fed under the edge of this bit. These shot are fed through a pipe from the top of the hole. The shot drill can be used for the same purposes as the diamond drill, except the drilling of holes inclined at an angle greater than approximately 45^ with the vertical, which rarely occurs in foundation exploration. The use of shot as an abrasive is many times cheaper than diamonds, and this type of drill does not require the services of a high-priced diamond setter, and if a bit is lost no great financial outlay'is wasted. When diamond drilling is employed it is generally necessary to have two bits for each drill in order to keep the machine in operation should it be necessary to reset the diamonds.

It happens frequently with both types of drills that a bit and core are lost. With a shot drill this does not necessarily mean the loss of the hole, as a new drill may be inserted and the hole continued, cutting through the original bit. On account of the low first cost of the shot bit, as compared with the diamond bit, it is economically possible to secure a much larger core. Diamond bits are generally limited in size to 2 or 3 inches, whereas it is possible to cut cores up to 20 inches in. diameter or even larger with the shot bit. One of the advantages of the shot drill is that cores of different diameters may be drilled with the same machine without extra equipment, other than an extra core barrel and cutter; whereas the diamond drill generally requires an entirely different set of tools and drill rods.

The value of core records depends to a certain extent upon the successful extraction of the material without injury or change of character. Cores can be taken with a shot drill of a much larger diameter than is possible with the diamond bit on account of the prohibitive cost of the diamond drill. Larger cores, except in the most resistant material, remain intact to a much greater extent than small ones. With the shot drill, cores 4 or 5 inches in diameter may be extracted nearly as cheaply as cores 1 or 2 inches in diameter, so that cores entirely adequate for foundation exploration may be obtained with slight additional cost.

OPERATION OF SHOT DRILL

One commonly used type of shot drill operates as follows: Power applied to the drill rod at the surface rotates the latter with the receptacle for cuttings, core barrel, and bit or cutter. (Fig. 28.) Water is pumped through the hollow drill rods and into the core barrel. As the bit rotates it cuts a circular groove in the material under it. The water passes from the core barrel, under the bit, and up through the annular space left around the core barrel by theclear-

73813°—28 4


ance on the bit, the stream carrying with it the cuttings. This water rises at high velocity until the top of the receptacle is reached, where its velocity is greatly reduced because of the larger passage afforded around the drill rod. The heavier cuttings carried by the water, therefore, have a chance to settle at this point, falling into the receptacle on top of the core-barrel plug. With a little experience

FiQ. 27.—Two views of a typical shot bit

the flow of water can be adjusted to remove the cuttings without liftiQg the shot. As the bit penetrates, a cylinder or core of the material drilled rises through the hollow bit into the core barrel. When the core barrel has been filled for nearly its full length the core is broken off (see p. 51), and#s hoisted to the surface with the string of tools. With this type of apparatus there is always a clean surface

HIGHWAY BRIDGE 8UEVEY8 51

for the bit or cutter to work upon and the tools do not stick or jam due to cuttings settling around them.

Figure 28 show's two arrangements of tools of this type. The illustration at the left shows the tool with the receptacle for cuttings, whereas the one to the right shows the tools without the receptacle. The shot for the shot drill are fed into the drill through the water swivel at the top of the drill rod. One type of swivel has two con- nections, the larger one being for the wash water and the smaller one for feeding the shot.

For soft materials a saw-tooth or chisel-tooth rotary cutter is sometimes used. The cutter illustrated in Figure 29 is said to drul successfully though soft and even moderately hard material. The cutter consists of a steel cylinder with forged steel teeth of a special alloy. This type of cutt«r is generally used in clay, shale, slate, sandstone, etc. This tool makes rapid progress in spft materials, but the shot bit is more economical in moderately hard materials. The chisel-tooth bit requires a slow- er speed than the shot drul, and one company manufacturing an outfit with which the two types of cutters are interchangeable has arranged the rotary mechanism to give two speeds.

LIFTING CORES

The diamond drñl has a special device which clamps the cores, thus enabling them to be lifted, but with the shot drill the core is generally _ lifted by washing sand or grout into the hole to jam the core in the core barrel. When it is desired to lift a core, rotation is stopped and the flow of the water increased in order to wash out the hole around the bit. Small gravel or sand is then introduced and pumped to the bottom of the hole. This sand lodges inside the bit between the core and the inner walls of the bit, where it is wedged by the water pressure around the core. The core is then broken loose by a few sharp twists of the rod and lifted to the surface. In soft and friable formations likely to disintegrate imder drilling a

FIG. 28.—TWO arrangements for core drilling with a shot bit :

A, core barrel plug; B, receptacle barrel; C, receptacle barrel; D, core barrel; E, matching coupling; F, drill rod: G, drill rod; H, shot bit; I, receptacle holder and cap; J, receptacle rod; K, matching coupling; L, shot.


tool known as a double-core barrel is sometimes used. Such' a device is shown in Figure 30. I* can be see^ that the inner tube

carries a core ring or lifter at its lower end. Core druling is generally done by con-

jj 11 11 1^ tract or with rented equipment for which ■^jfl ■■ H Wk experienced operators are available. The

|HH| IIH ,Hfc : foUowingbrief suggestions, however, may be î|PI Brfl IK of value should the field engineer be called

JM HI I ¡j^* upon to directly supervise core drilling: ^'** ■íABF**' When mud seams or fissures are en-

countered these will result in the loss of water, and in shot drilling the loss of shot. If the condition is serious, the hole may have to be cased through the mud seam or fissure. Either the hole must be reamed for a casing which will be large enough to clear the drill bit or else a smaller drill must be used for the remainder of the hole.

When drilling through soft or caving rock care must be exercised to avoid sticking or jamming the bit, as this may result in the loss of the tools. With the shot drill, when the tools are lost, it may be possible to redrill with a new bit cutting through the original bit. In some cases it may be necessary to either abandon the hole entirely or else ream and case down to the jammed bit.

In shot drilling the stream of water must be carefully regulated. If the water pressure is too strong the shot are washed away from the cutting edge; if not strong enough the cuttings wül not be removed.

Before withdrawing a drill and core wash out the hole with a strong jet of water, or the bit is very apt to jam.

Where a core must be made fast to the bit by washing down sand or grout to jam the core in the barrel considerable care must be exercised to avoid dropping the core.

SPECIAL UGHT DRILLING OUTFITS

A light outfit is now on the market to meet the demand for a portable drilling rig, readily set up and moved from hole to hole and also comparatively cheap in first cost. This outfit is especially designed for rapid and cheap druling. It consists of a small gasoline engine driving a force pump to

ir.„ nn nv,i „1 t™,th „,„ ™,«„. furnish a water jet for washing down the FiQ, 29.—Chisel-tootn core cutter ,, . t •^t , i , , * t i hole, casmg, drill tubes, cuttmg shoes, and

small tools. The casing is 2^ inches in diameter and is of special high-carbon cold-drawn seamless tubing upset and thickened on each


end for a special square thread and flush-joint connection. It is heat treated after finishing. The drill tubing is 1J^ inches in diameter. Both casing and drill tubing come in 4-foot lengths.

The casing is fitted with a cutting shoe at its lower end and the drill bit and casing are washed and churned down by hand, as described under wash borings, the gasoline-driven force pump furnish- ing the water supply. When it becomes necessary to drive the casing a special drive cap is fitted and the driving is done with a heavy maul. When the hole is finished the casing is pulled by means of chain tongs and jacks.

The net weight of this outfit, including sufiicient casing and tubing for a 50-foot hole, is about 800 pounds. This type of rig may be used for work where the magnitude does not warrant a more extensive layout for test borings. The principal parts of this outfit are shown in Figure 31.

The outfit may also be equipped with a core-drill rig operated by means of a water motor which, in turn, is driven by the gasoline- operated force pump. The core-drilling tools weigh approximately 350 pounds.

- INNCH-CME SMfa SUPfWT - peEssuK ea/EFy^ve MO CKs ,- D/mS CUTTOi

FIG. 30.—Sectional views of double-core barrel used with different types of bits

TEST PITS

Excavation of a large pit or hole and examination of the material in place is the most reliable but by far the most costly method of foundation exploration. In stiff material and shallow pits no sheeting is necessary; in soft material and for all holes in excess of 10 or 12 feet in depth bracing, shoring, and perhaps solid sheeting are needed. The size of the pit must be sufiicient to permit access for inspection. In general 23^ by 23^ feet is about the minimum size.

Excavation may be done by means of shovel and platform, hoist bucket and tripod, or a small orange-peel or clamshell bucket.

Figure 32 illustrates two different methods of shoring or bracing test pits through soft material. Where semisolid material is penetrated horizontal or vertical plank braced between opposite sides of the pit by means of shores or trench jacks may be employed. The method employed and equipment needed will obviously vary with the individual case.

INTERPRETATION OF RESULTS

It must be remembered that no methods except core drilling or test pits afford an opportunity to actually observe the material in its natural undisturbed condition. If other methods are used every possible check should be made upon the results. Such checks or


additional evidence may be obtained from records of borings in the near vicinity, from records from near-by wells, or from published geological reports. All such data should be reported either on Form 3 or upon the supplementary data sheets.

Wash borings bring the material to the surface more or less in suspension and in general have a tendency to show the material coarser

PERFORATED

CHISEL HYDRAULIC 1 CUTTING BIT

ASSEMBLY

HYORAUUC JETTING DRILLING METHOD

DRIVING CAP

FIG. 31.—Principal parts of a light, portable, jet-drilling outfit

than it really is. Clay may appear as fine sand and sand as fine gravel. An experienced driller is able to determine a great deal regarding the solidity of any strata from what is known as the "feel of the bit,'^ an instinctive judgment that comes from observation.of the action of the drilling tools.

HIGHWAY BEIBGE SURVEYS 55

ELEVATION

ELEVATION

2x4'

SECTION X-X SHAFT TIMBERING -SCHEME A

SECTION Y-y . SHAFT TIMBERING - SCHEME B

FIG, 32.—TWO methods of timbering large test pits


GENERAL INSTRUCTIONS FOR TEST HOLES

The number of test holes necessary for any project will depend upon conditions. In general, at least one boring should be made at each pier or abutment site unless the result of three or four borings covering the entire distance from end to end of the project shows the stratification to be very uniform. It is better to sink cased test holes just outside the limits of the pier location, so that in case a portion of the casing has to be left in the hole it will not interfere with excavation during construction.

The method to be used for test borings will depend upon conditions. The sounding rod may be used for depths of 20 to 30 feet or perhaps deeper. It may be used to locate solid strata, but gives no data as to the character of material passed through. The hand-operated soil auger is good for depths as great as 50 feet and the wash-boring method for depths up to 150 feet.

Samples from wash borings or auger pits at the various elevations should be taken and preserved in wide-mouth glass jars or bottles (ordinary glass fruit jars will do), each sample clearly labeled as follows: Samples from elevation __ test hole No. __ located __ feet right (or left) of center line at station __.'' All elÄâtions should be referred to the datum plane established for the bridge survey and all stationing and offset distances located by direct measurement where possible. If it is impracticable to measure across the stream a base line and simple triangulation system should be employed.

All cores from core drillings should be labeled as indicated above by means of gummed labels placed on the core. Two labels should be placed upon each core to guard against loss in packing for shipment or in handling.

The results of borings should be reported on a condensed profile of the stream, as shown in Figure 33. All data obtained from records of well drillings in the near vicinity should be reported in a similar manner, being careful to indicate the approximate location of the well with reference to the proposed crossing.

The data called for on Form 3 as to feasibility of driving piling into the various strata is of particular importance. Full investigation should be made of all available records from near-by bridges and buildings and a report made as called for upon the form.

The field engineer should make a definite recommendation as to types of cofferdam which, in his judgment, are best suited to' the proposed work and also should indicate under the proper head his judgment as to the necessity for a full-depth foundation seal. Much valuable data may be obtained from cased test pits by pumping them dry and observing the amount of water seeping up through the bottom of the hole. If the hole fills rapidly then either the strata from a to 6 (fig. 34) is permeable or else there is water in stratum No. 4 under sufficient head to force the water in the casing to the observed elevation. In either case it is probable that pumping from a catch basin to keep the foundation dry during construction will be an expensive matter and a trémie seal will probably be necessary. If, on the other hand, the casing fills very slowly or not at all, it may be possible to deposit concrete in the dry. This is an important feature, and until the casing has passed well below the probable depth of foundations, frequent determination of the permeability of the strata should be made and the result reported in detail on the


sketch showing.the soundings (fig. 33). The report should be complete in detail and should follow the general outline shown in the figure.

The elevation of lowest ground-water level is of importance, especially if a long reinforced concrete approach upon pile foundations is

3iO

300

290

240

230

200

MED.HARD BLUE CLAY. BEARING VAL 3 TONS PER SO, FT^

HARD BLUE CLAY-SAFE BEARING VALUE ABOUT 5 TONS

_BLùr~cTry- —~- "^

BLUE SAND STONE

CASING PUMPED DRY AT -THIS ELEVATION-EVENING

0F7-17-I6.AT 8A.M.NEXT " MORNING ONLY 18 INCHES OF WATER IN HOLE WATER VEIN CAN NOT BE PUMPED DRY

ESTIMATED BEARING VALUE 8 TO 10 TONS

_CEV1ENTED GRAVEL

r^Z^^P--'^~-JA^K2ro^S PER IGíSI

CASING PUMPED DRY AT THIS ELEVATION-EVENING OF7-I9-I8.AT8A.M.NEXT MORNING ONLY 2 FEET OF WATE_R

Î-S^~- - LA_YiR_ 2L i'LOWNJj

Sp_FT.

CASIN6T00K 6 INCHES OF WAfER' ---OVERNIGHT

VERY SOFT BLUE SAND" STONE OR HARD SANDY CLAY. SAFE BEARINS VALjJEABOUT 5 TONS

SA ND, ''J ~J7 ~ ~:^X

BLUE SANDSTONE

VERY HARD BLUE SAÍJDSTONE U HARDER BLUE ESTIMATED BEARING VALUE 15 TONS PER SQ.FT. SANDSTONE

4|—CASING TOOK ONLY 12 INCHES OF WATER OVER NIGHT AT THIS POINT

VERY HARD BLUE SANDSTONE.

ESTIMATED BEARINS, VALUE 25 TONS

260 I z o

250 5

240

230

210

20O

FIG. 33.—Typical sketch showing method of reporting test-hole data on supplementary data sheet

contemplated, for this elevation fixes the point above which timber piling should not extend (no timber foundation piling should ever be used above lowest ground-water level). If the survey is made during the dry season or if a dry season intervenes between the date

, STRATUM I

STRATUM 2

^V/C^ <<; STRATUM 3

'^^'V ''/'^'/ STR ATU M 4

FIG. 34.—Sketch illustrating discussion of determination of water-bearing capacity of foundation strata

of the survey and the preparation of the design, this data should be obtained by actual observation of test pits. Test pits should be dug for this purpose either during the survey or during the first dry season which follows. It should be remembered that the ground- water tables slope upward away from the stream and pits should be


located at the outer limits of the structure as well as some intermediate point.

Evidence regarding slides or slips is of importance. Slippage is generally due to movement along an under stratum (generally inclined) which has become lubricated due to saturation. Sliding may also occur over a sand vein due to loss of cohesion between sand particles on drying out. The data called for on the form includes complete discussion of sKdes (if present) giving in detail the probable cause of movement.

SPREAD GUYS

PIG IRON, BRICK, CEMENT

ETC MAY BE USED FOR LOADING.

fRON SADDLE GUY LINES STAPLED TO POST

HOLE TO BE SHEETED IF NECESSARY

-SAND FILLING /;'" R'V^T ^ ^

\V^^^..\V'>^

II

IF NECESSARY

SIDE STAKES MAY BE ADDED

AND LOOSE MATERIAL USED FOR LOADING

•TOBE VARIED WITH NEEDS OP TEST MINIMUM AREA- I SQUARE FOOT.

FIG. 35.—Apparatus for making bearmg-power test, redrawn from a progress report of the specification committee to codify practice on the bearing value of soils for foundations of the American Society of Civil Engineers

Wind erosion may prove an important factor in influencing the design of approach fills and trestle construction on concrete pedestals or mud blocks. Along the Columbia Kiver between Oregon and Washington great dunes of blow sand have formed and are con- stantly in motion. Concrete pedestals and mud-sill construction on trestle approaches must be carried much deeper in this locality than the natural bearing value of the soil necessitates. Approach fills are also subject to a rather high maintenance charge through this locality owing to the difficulty in protecting shoulders and toes of slopes.

Weathering of bank material, due either to air slaking or to frost action, should be reported in detail, as this will effect the design of the ends of the structure and also indicate the suitability of the local material for riprap work. Data of this character should be reported on supplementary data sheets.

BEARING-POWER TESTS

Apparatus for making foundation-bearing tests usually consists of a compression post fitted at its lower end with a steel compression plate and loaded at its upper end by means of a lever beam, or a loading platform or tank, and a suitable device for measuring the dçflçctio^ for various load increments. Figures 35 and 36 are sketch

HIÖHWAY BEIDGÉ SURVEYS 59 plans of different forms of testing apparatus which are suitable for field use. Figures 37, 38, and 39 illustrate a more elaborate plan proposed by the special committee of the American Society of Civil Engineers to codify present practice on bearing value of soils for foundations.

The location of test pits should be indicated by a sketch upon the supplementary data sheet and the general data for each test pit listed as shown on Form 4. The column for target elevations is for use when a level and target rod is employed for determining the settlement of the compression post. If this movement is read direct from a scale, as shown in Figure 35, the last two columns are filled in direct and the target columns are left blank. Form 4 shows information for one test pit partly tabulated in order to illustrate the method of filling out the form.

[Form 4]

BRIDGE CONSTRUCTION DATA FROM FOUNDATION TESTS

For bridge No. over _ ___ (Name of waterway)

Located miles from in section .. (distance) (direction) (Nearest R. R. station)

Twp, , .Range county of _ Name and/or No. of highway, Local name of bridge, Date of tests, Engineer in charge,

(or between sections ),

Test pit No. 1

[Location, 10 feet right of center line at station 16-Í-14.2. See also sketch on additional data sheet]

(Area of bearing surface, 1 square foot)

Date Time

Loading Target elevations Settlement

Initial Incre- ment Total Initial

10 min- utes after load application

Incre- ment Total

Get 11, 1922 11.00 a. m 11.10 a. m 11.30 a. m

Pounds 0

500 1,500

Pounds 500

1,000 1,000

Pounds 500

1,500 2, 500

96. 780 96. 740 96.730

96.740 96.730 96. 725

Feet 0.040 .010 .005

Feet 0.040 .050 .055

Do Do

General character of soil-

Probable cause of settlement. ( Discuss in full).

Water content- of soil at time of test. What percentage of the maximum water content at any time during year?

The following general instructions are for guidance in assembling the apparatus and making the tests:

The capacity of the testing apparatus should be such as to load the material to at least two and one-half times the probable allowable pressure which will be used in the design. The following capacities are recommended:

Tons per square foot

Alluvial soils, clay, and sand 10 Gravel 12 Hardpan, cemented gravel, soft sandstone, and shale 25


Y LEVELT

FIG. 36.—Apparatus for making bearing-power test, redrawn from a progress report of the specification committee to codify practice on the bearing value of soils for foundations of the American Society of Civil Engineers

SADDLE BEAM 2-l2"xi2'"

ANCHORAGE BOX

COUNTERWEIGHT BOX

A-^

PLAN

ANCHORAGE BOX

M :bè

•^STAY 1 X 10

¡L/ANCHORAGE BOX

SADDLE BEAM 2-l2"Xi2"

ANCHORAGE BOX bUXn

COMPRESSION POST "7

•HINGED JOINT

LJJ^

:nr GROUND^^

SURFACE

SECTION A-A

COUNTERWEIGHT BOX-y

ANCHORAGE' h/

BOX ^tkZ..

BREAST BOARDS 4F REQUIRED^

SAND ^ FILLING

COMPRESSION POST

15" SEWER PIPE

COMPRESSION PLATE

SECTION B-B

■^ï^- 37—Apparatus for making bearing-power test, redrawn from a progress report of the specification committee to codify practice on the bearing value of soils for foundations of the American Society of Civil Engineers. Parts shown by dotted lines may be varied at will to suit local conditions and materials available


The apparatus should be sensitive enough to measure deflections to 0.001 foot at least. It should be easily assembled on the ground from materials which may be obtained locally.

The bearing plate should be at least 1 square foot in area and preferably 2 square feet. For important tests an apparatus which will load an area of 4 square feet should be used if possible.

The soil should be tested in place at the level proposed for the foundations. The load should be applied in increments of not more than 1,000 pounds (for light compressible soils a much smaller increment may be necessary) and a load-compression diagram plotted as shown in Figure 40.

RECORDING BOARD^ «^^

CAST-IRON SHORERS LAG SCREWS

SCREW JACK—S^'*""^'^'^^'' '^^^

I0"X 10" S

LENGTH VARIABLE^

■LAG SCREWS'

VOOT PLATE I0"xi0"xr'

COMPRESSION POST

IRIVETÎ

^^' COMPRESSION PLATE ((cpj) /f\ J*-!-If "PIAMETER

8"

ALL ROUND-IRON FITTINGS TDIAMETER

STRAIGHTEDGE

BOX SHEATHING -

HINGE FITTINGS RECORDING DEVICE

FIG. 38.—Details of apparatus shown in Figure 37

The portion A-B of the diagram (fig. 40) represents the initial compression caused by a recompression of the topsoil layer which has been loosened in excavating the pit, plus the elastic yielding for that load increment. The portion B-C represents the true elastic curve of the soil and the portion C-D the breaking down after the elastic limit is passed. The soil tests should be carried far enough to develop the full curve for each test, after which the load above point C should be removed and the remaining load left in place for at least four additional days during which time the settlement should be carefully observed. If the continued application of this load without increment, causes an increased deflection, the test should be repeated, using a lower position for the yield point. This should be repeated if necessary until there is no further yielding after four days continued application of load. The point thus found is the elastic limit of the soil in compression.

62 TECHNICAL BULLETIN 55, IJ. S. DEPT. OF AGRICULTURE

O III

3130 2 n 5 z P 3;QO 1 to

zizo UJ Q

1:30 O 7

(2:30 :^ 5

li:30 < 3 o

n:oo 2

18" Í

r-s

,'-'^'

-10" I*" ^ "*1

FIG. 39.—Method of making field record of soil compression with apparatus shown in Figure 37

7000

YIELD POINT OR ELASTIC LIMIT

TAN. e MODULUS OF ELASTICITY

.10 .40 .20 .30

DEFLCGTION-FEET FIG. 40.—Typical load-deflection curve for foundation bearing-power test

.50


The probable cause of settlement called for upon Form 4 refers to the breaking down of the soil and not the elastic yielding and should be discussed under the following heads:

BREAKING OF BOND BETWEEN PARTICLES

The breaking of bond between particles is observed in compacted sand and gravel. When the binding material breaks the volume is decreased and settlement results.

CRUSHING OF PARTICLES

The crushing of particles is observed where grains are of soft material and generally starts by a crushing of the edges of sharp grain particles.

BY LOSS OF WATER CONTENT

The loss of water content is observed in fine sands or coarse- grained clays where the water is gradually forced out from between the

FIG. 41.—Method of reporting location of test pits

particles and results in gradual settlement. Settlement of this kind may not occur until months after construction is completed, when, because of a lowering of the surrounding water table, the weight of the structure squeezes out a part of the water, causing a compaction of the material and consequent settlement. It is important to note if possible whether or not the movement of soil during the test is due to this cause.

FLOWING OF SOIL DUE TO SATURATION

In arid localities a clayey soil is often encountered that is fairly stable during the dry season but very plastic when wet. Such soil should be tested when it is carrying its maximum water content or the tests are of little value. Any tendency to flow due to moisture lubrica- tion should be carefully noted.

FLOWING OF SOIL DUE TO OTHER CAUSES

Soilmay flow because of breaking of bond underpressure ormayflow because of sliding or slipping upon natural cleavage planes especially


when such planes contain a layer of material which acts as a lubricant.

Supplementary data sheets should be attached to Form 4 showing any supplementary data or sketches.

TEST PILES

The following quoted from the standard specifications of the Ameri- can Association of State Highway Officials outlines the method of determining the bearing power of timber piles adopted as a standard by highway engineers in general:

LOADING TESTS

When required, the size and number of piles shall be determined by actual loading tests. In general, these tests shall consist of the application of a test load placed upon a suitable platform supported by the pile, together with suitable apparatus for accurately determining the superimposed weight and the settlement of the pile under each increment of load. The safe allowable load shall be considered as 50 per cent of that load which, after 48 hours' application, causes a permanent settlement, measured at the top of the pile, o:^ not more than one- fourth inch. At least one pile for each group of 100 piles shall be thus tested.

TIMBER PILES

In the absence of loading tests, the safe bearing values for timber piles shall be determined by the following formulas :

P=o I ^ Q for gravity hammers.

'^ for single-acting steam hammers. " .S + 0.1

P= ry I n 1 for double-acting steam hammers. o-f-U.i

Where P = Safe bearing power in pounds. f^z= Weight, in pounds, of striking parts of hammer. H = Height of fall in feet. A —Area of piston in square inches. p = Steam pressure in pounds per square inch. >S=The average penetration ir. inches per blow for the last 5 to 10 blows

for gravity hammers and the last 10 to 20 blows for steam hammers.

The above formulas are applicable only when— (a) The hammer has a free fall. (h) The head of the pile is free from broomed or crushed wood fiber. (c) The penetration is at a reasonably quick and uniform rate. (d) There is no sensible bounce after the blow. Twice the height of the

bounce should be deducted from H to determine its true valueah the formula.

Form 5 indicates the arrangement and scope of field data required where loading tests are not made. The size of piling used in the test must be such as to pass specifications and in general of a size and quality comparable to those which will probably be obtained for the actual construction.

HIGHWAY BRIDGE SURVEYS 65 IForm 5]

BRIDGE CONSTRUCTION TEST PILE DATA

For bridge No over


in section (or between sections ), Twp Name and/or No. of highway, . Local name of bridge, Date of test, Engineer in charge.

(Name of waterway)

(Nearest R. R. station) ., Range , county of _

Test pile No 1

[Located 8 feet right of center line at station 16+40. Type of hammer used, drop hammer. Constants in bearing power formula, W = 3,600 pounds A.., P..]

(Elevation of top of ground, 105 feet)

Test increment

No.

Total number of blows

Total penetration in

feet

27 79

120 140

6.75 16.05 19.75 20.75

(After 12 hours' freeze).

Eleva- tion

bottom of pile

98.25 88.95 85.25 84.25

Average for last five blows

Drop

Feet 10 10

Penetra- tion per

blow

Inches 2.1 L5 0.7 0.3 0.1

Com- puted

bearing value

Tons n.6 14.4 16.9 22.2 26.2

Remarks

Remarks .

The general nature of the driving and the degree to which brooming or sphtting of the wood occurs at each test increment should be indicated under ^^Remarks.^' If driving is very difficult, steel-pile bands should be used to prevent brooming, and it may be advisable to try one or more steel-shod piles.

If a gravity hammer is used for testing, the weight should be not less than 2,000 pounds and the fall limited to not over 15 feet if possible and in no case more than 20 feet. The ground surface should be excavated to approximately the depth which will be used for the proposed footings or the test is of little value owing to the frictional resistance of the overburden.

If the test pile fails to develop a bearing value of 20 tons when driven to its entire length, a new and longer test pile should be driven. All test piles, whether satisfactory as to bearing value or not, should be re tested after being allowed to ^^ freeze'' or stand undisturbed for a period of 12 to 24 hours.

Ctncrete piling and occasionally timber piles are tested by applying an actual test load. Piling may be loaded by means of an apparatus similar to that employed for soil tests and the data recorded in a similar manner.

The number of test piles to drive and test on preliminary-survey work will vary with the importance of the project. In general, this work is very costly, owing to the necessity for excavating to the proposed footing level. Instructions regarding the number of test piles and their location will generally be sent from the general office for each particular project.

73813°—28 5

66 TECHNICAL BULLETIN 55, U. S. DEPT. OF AGRICULTUEE

TRAFFIC SURVEYS

Form 6 is a summary of traffic data to be used as a rough basis for proportioning the width of the roadway and sidewalks. Often this material can be obtained by digesting existing traffic records. In fact, this is generally the only available source of information, as in only a few cases is it possible to secure data on maximum traffic flow at the time of making the survey.

If no prior records have been taken, a traffic census for three typical days should be taken at the time of making the survey. If these days are typical of average traffic, they may furnish a basis for an assumption as to the probable maximum traffic flow which, while far from reliable, is somewhat better than a guess. If the road upon which the bridge is to be constructed is closed to traffic or if for any reason the traffic flow is not normal, a census is of little value.

Maximum traffic on a road is generally the result of some local gathering, such as fairs, carnivals, conventions, or other public gatherings. Traffic to summer resorts at certain seasons of the year or hauling of certain products throughout a short marketing season may determine the maximum traffic flow. If these conditions are known in advance, traffic counts should be made on all roads over which bridge structures are contemplated for the coming season, thus collecting in advance the material necessary for this portion of the bridge survey.

[Form 6]

BRIDGE CONSTRUCTION TRAFFIC SURVEY

For bridge No over


in section (or between sections Name and/or No. of highway, Local name of bridge, _ Date of traffic count, Report by

(Name of waterway)

(Nearest R. R. station) ), Twp, , Range , county of .

(Engineer)

Traffic summary _. i traffic

Average daily flow - Extreme maximum daily flow _. Frequency (average number of times per year) of extreme daily

maximum.. Extreme maximum flow in any single hour Number of hours per day when concentration may be expected..

Pedes- trian

Horse- draWn

and mis- cellaneous

Light motor

vehicles

Heavy motor

vehicles

1 Indicate whether east-bound, west-bound, etc., or total traflic both ways.

If there is an old structure now carrying same traffic, give following data: 1 Width of present roadway 2 Has this proven inadequate? 3 Number and width of sidewalks - 4 Have these proven inadequate?

General character of traffic


Under the heading '^General character of traffic'^ should be noted data as to whether the structure carries the traîne of a primary or secondary road, whether or not it is in or adjacent to the corporate limits of any city or town, whether the bridge will carry the accumu- lated trafRc from several branch roads leading to the structure, whether or not the road is apt to become in the future a link in any primary county. State, or national system or any other condition which may influence a prediction as to the ultimate traffic over the structure.

GENERAL DATA AND RECOMMENDATIONS FOR NEW WORK

The report on Form 7 contains the complete recommendations of the field engineer and is of considerable importance because of the weight which these recommendations carry, coming as they do from the man on the ground. The office may modify certain of these recommendations and a special representative from the bridge division may visit the site, but an intimate knowledge ,of actual conditions will always be assumed to be possessed by the field engineer in charge of the survey. For this reason, great care should be taken that this form is accurately filled out and that all statements and recommendations are well considered.

Form 7 is to a large extent self-explanatory. There are, however, a few points concerning which further explanation and discussion may be necessary.

The span lengths used for the main structure are generally determined in the office by considerations of economy, but the designer should know how far he can go in cutting span lengths and increasing the number of piers. For streams carrying drift or débris, increasing the number of piers means an increased maintenance hazard and also increases the possibility of erosion around channel piers.

The type of structure will probably be determined in the office, but the recommendation of the field engineer is important, and if the whole or any portion of the structure is to be paid for out of local funds the wishes of the proper local authorities and also the popular desire in this regard should be noted.

In making a recommendation as to roadway and sidewalk widths thought should be given to the trend of future development and the fitting in of the bridge project with any adjacent municipal or other improvement contemplated. In general, it is better to construct two rather narrow sidewalks than one wide one, as this balances the structural load and keeps pedestrians from crossing and recrossing the roadway, provided, of course, that adjacent improvements lend themselves to the use of two sidewalks. When there will never be but one sidewalk outlet to and from the bridge it is obviously unnecessary to consider but one walk.


[Form 7] (Page 1)

BRIDGE CONSTRUCTION GENERAL DATA AND RECOMMENDATIONS FOR NEW WORK

For bridge No over _ __ (Name of waterway)

Located miles from _ _._ in section (or between sections ), Twp , (Distance) (Direction) (Nearest R. R. station)

Range , county of ._ Name and/or No. of highway, _ Local name of bridge, __ ' Date of report, Report by __

(Engineer)

1. Total recommended length of structure and approaches: a. Approach embankment from Sta. to Sta or feet or north (or east) end and

from Sta. to Sta. or feet on south (or west) end. &. Can either of the above approach embankments be extended toward the stream without seri-

ously restricting waterway or obstructing drift? If so, indicate between what stations this may be done?

c. Trestle or viaduct approaches from Sta to Sta ..or feet on the north (or east) end and from Sta to Sta. or feet on south (or west) end.

d. What is the minimum span between bents or towers which may be used in the above approaches without danger from ice or drift? _._ _ __

e. Main structure from Sta. to Sta. or feet. /. What is the minimum span length which can be used in the main structure? __.

2. Type of structure recommended: " a. Approaches __ _. 6. Main structure ^ c. Type of floor desired ..Ill""""""

3. Width of roadway recommended II 4. Number and width of sidewalks recommended 5. Recommended grade line (show by sketch). 6. Recommended superstructure clearance. (Indicate minimum clearance required for passage of logs

drift or ice at flood stage) feet above high water or elev referred to bridge datum. Is there any special consideration which controlls the clearance on any one or more spans. If so give complete data _'

7. Are there any special conditions controiiing the spacing of any'öne'örmöre'of the"piërë,"the length o^^ any individual span or the depth of any one or more of the footings? (Give complete data including sketches if necessary on " Supplementary data " sheets).

8. Is piling recommended? If so, under whichYo'oting's'?" I

9. Estimated approximate length of piling (below elevatiônVIIII"),'! " 10. Need any pier or abutment be skewed? If so, indicate "by sketch giving data as to skew

11. What will be the approximate cost of filling material'for approache's*per"cubic" ya'rd'in î^^^^

12. Will "temporary bridge be necessary to carry traffic "during" ~co"ns"t"rüct"fo"n'örcän"träffic"be"de^^^^

If traffic is to be'detoured, furnish hereunder complete'dätä"ärtö"r"o"üting""c"o"nd"iti'o"n "of r"o"a"d "at" "a'Ü seasons, condition of any old bridges.

13. Will any of the material in the old bridge be'a vaiïabïë"fc)'r"faisê'wor"k "or for buifdYng tempora'ry'cr'os'siñg?

14. Recommended lengths and angles for any""spe"clarw]ng"wäil"cönstm"c"t"iön ö^äny ¿^^^^^ or rip rapping. Show by sketch.

15. Location of borrow pits where necessary for approach embankment.

16. Available electric power for construction'purposes.IIIIIIIIIIIIIIIIIIIIIIIIIIIiri

17. Are there any special tidal conditions or'sto'rm ö'r"w"äve'äctiöns"wh"i^h"ne'ed"to'bê^

18. Action of teredo or other marine borers "in vicinity"!

A* Jïi^^^^l®^^^^*^^^^^^^^! construction season. From to 20. Character of traffic for which structure should be designed:

a. Heavy highway traffic. b. Light highway traffic. c. Single-track street railway. d. Double-track street railway.

(For last two give complete data as to loadings for which provision must be made.)


BRIDGE CONSTRUCTION GENERAL DATA AND RECOMMENDATIONS FOR NEW WORK

[Form 7] (Page 2)

3TI0N GENERA N:

For bridge No. over _ _ (Name of waterway)

Located miles from __ (Distance) (Direction) (Nearest R. R. Station)

in section (or between sections ), Twp. , Range , county of ^__ Name and/or No. of highway, _ ___ Local name of bridge, _ _ Data of report, Report by

(Engineer)

21. Are there any public utilities (water or gas mains, power or telephone lines, etc.) for which provision should be made in the new design? (Give complete data) __ ,_..

22. Are the above utilities occupying the present right of way at "the bridge crossing and if so under what franchise rights? _ _:_ _ _ __

23. Are there any special features to provide for such as— a. Light posts. b. Removable floor sections. c. Method of taking care of drainage water from side ditches of roadway.

(If so, give complete data.)

24. For culvert work "furnish following data: Elevation flow line at upper end _ Elevation flow line at lower end.. Will drop inlets be necessary _ __

(If so, indicate arrangement necessary by sketch.) 25. If the structure contemplated involves a grade separation with an existing railway, the following infor-

mation should be given: a. Name of railroad company owning and operating tracks in question

h. Is t'his a new crossing , or "does it eliminate one or more existing grade crossings?

c. Number of public road grade crossings eliminated by proposed improvement?

d. Number of public road grade crossings which may be changed to ''gated" or private crossings by proposed improvement . __

e. Number of ''gated" or private crossings which may be eliminated by proposed improvement

/. Are there any existing grade crossings over which traffic will be reduced or otherwise modified by the proposed improvement _

g. Will there be any new grade crossing or crossings (either open or "gated") necessitate'd by the proposed improvement? _

Ji. Number, location and ownership of any wires which must be moved in connection with proposed structure _

Í. Number of tracks in use at site _

;. Number of contemplated future tracks at site ._

k. Width of railway right of way at site and for distance of at least 800 feet each way. (Show by means of sketches on "supplementary data" sheet, if necessary

6 i If the stream is navigable and a movable span is necessary, the following information should be furnished:

a. What general type of craft now operates over the waterway?

b. What vertical clearance (referred to bridge datum) will clear: L The tallest craft 2. 75 per cent of the traffic 3. 50 per cent of the traffic

c. Will it be permissable or feasible to place a pivot pier in the channel? d. If pivot pier may be used, what is maximum limiting diameter?

€. Estimated number of openings at high and low grade limits: At elevation Openings per month At elevation Openings per inonth __

/. Are harbor lines definitely established? (If so, indicate exact position on map.) g. What type of electric power is available for operating purpose:

1. Distance from bridge to nearest point of delivery 2. Voltage at point of delivery 3. Alternating or direct current _ _. 4. If alternating current give phase and frequency 5. Cost of power _

h. Any restrictions concerning channel booms or guides? ._—__ _

i. Thread of channel at different boating stages. (Show by sketch.)


Under the designation ^'Special conditions controlling the spacing of piers, span lengths, depth of footings, etc.,'' should be listed all such features as adjacent railway facilities, docks and wharves, locks or canals, or any other condition which may require a definite spacing of piers. Where railway yards are crossed future development may make it necessary to carry foundations for approach viaducts deeper than would otherwise be necessary.

ROAD UNSURFACED, CAN NOT TRAVEL IN WET WEATHER WILL BE VERY DUSTY AND CUT UP BY TRUCKS IN SUMMER.

LIGHT TIMBER BRIDGE IN FAIR / SHAPE. ¥:

GRAVELLED 18 FT. WIDE

^ GRAVELLED 12 FT WIDE

GRAVELLED BUT VERY HILLY, 10 PER CENT GRADES BOTH WAYS.

-^GRAVELLED 18 FT WIDE

STEEL SPAN, FAIR SHAPE,DECK PLANKS ROTTEN.'5ir

^ COMPLETE MEASUREMENTS FOR OLD BRIDGES TO BE SENT IN UNDER SEPARATE COVER.

FIG. 42.—Method of reporting traffic detours

For locations over drainage or irrigation canals with paved banks or walls, or for locations involving grade separations, skew angles for piers and abutments must be very accurately determined in order to fit the proposed construction into the old.

Where traffic is to be detoured over an old existing road, a detour sketch (fig. 42) should be furnished. This sketch should show the condition of the road, width, any special grade condition, and all

EL.114.0 RECOMMENDED FOR OROP INLET

EL. 105.0

FIG. 43.—Method of reporting recommendations for a drop inlet

other data which may be of value in determining the necessary restrictions under which traffic may be routed over the detour.

If there are old bridges on the detour road, these should be completely measured in order that the safe carrying capacity may be computed and load-limit signs posted if necessary. In many cases of this kind heavy loads are routed over roads and bridges which are not designed for such traffic, and the utmost precaution is necessary.


If the bridge structure is to carry street railway or interurban traffic, the field engineer should obtain the standard loadings used by the company operating the lines if possible; if not, the general office address of such company should be given so that the information can be secured before the design of the structure is begun.

For culvert work it is often necessary to use a drop inlet at the upper end of the barrel to avoid the use of a steep flow line with its attendant danger of scour at the lower end. Where such construction is recommended, the data should be submitted in sketch form as shown in Figure 43.

Where the proposed construction involves a separation of railway and highway grades, there must be complete data as to the proper

GRADE CROSSING NO.I; THIS MAY BE ELIMINATED AND ABANDONED.

PROPOSED OVERHEAD CROSSING STRUCTURE GRADE CROSSING N0.4, THIS MAYBE CONVERTED INTO A GATED PRIVATE CROSSING rOR HAMPTON AND JOHNS

GRADE CROSSING N0.5., MAIN TRAVEL TO GREENVILLE FROM JOHNSTOWN WILL 60 AROUND BY STATE! HIGHWAY WHEN COMPLETED TO TAKE ADVANTAGE OF PAVEMENT. TRAFFIC OVER THIS GRADE CROSSING WILL THEREFORE BE REDUCED, AT LEAST 50 PER CENT-

SKETCH SHOWING ADDITIONAL DISTANCE TO GREENVILLE FROM POINT a ALONG PAVED HIGHWAY.

FIG. 44.—Method of reporting crossings over which traffic may be eliminated or modified

clearances and spacing of spans to accommodate present and future development on the railway system, and also as to the degree to which the grade separation eliminates or reduces the railway company's operating hazard and liability for accident. The various items called for on Form 7 should be amplified by sketches and maps showing the relationship of all crossings open or with gates over which the traffic will be affected in any way by the proposed improvement. (See fig. 44).

If the stream to be crossed is navigable, the data called for under item 26 of Form 7 is necessary. The use of a pivot pier depends upon the width of channel necessary for navigation, the condition of the


banks, and dock and harbor facilities, and both present and possible future development. In general, a pivot pier obstructs the central portion of the channel, tends to deflect the current against the banks, and tends to obstruct dock and wharfing space by an amount equal to the swinging clearance of the draw. On the other hand, a swing span has distinct advantages and should be considered among other types. The investigation should be thorough, and the field engineer should be certain that there is adequate reason for eliminating this type before reporting against it.

FIG. 45.—Typical report on current direction at various water stages

Harbor lines, if definitely established, should be shown upon the vicinity map as these indicate the fixed boundaries of navigation control.

The direction of the thread of channel or main current at various boating stages is important as this may have a bearing not only upon the position of the movable span, but also upon the horizontal clearance required. Figure 45 is a typical sketch showing direction of current at different water stages.^

2 For a discussion of current direction and effective width of opening see MCCULLOUGH, C.B. HIGHWAY BRIDGE LOCATION. U. S. Dept. Agr. Bul. 1486. 32 p. illus. 1927.


VICINITY MAPS AND PROFILES

Accompanying Forms 1 to 7 and the corresponding supplementary data sheets there should be a large map of a size such as will fold to the standard size adopted for the forms and can be filed for permanent record.

This map should show the river crossing, the adjacent topography, street and right-of-way lines, and all other features which may in any way affect the design. Among the specific features to be covered may be mentioned the following:

(1) An accurate profile of the river crossing along the center line of highway and at intervals of 15 feet above and below the center line for the entire width of the right of way. Also a profile of the highway proper, extending not less than 1,000 feet from the ends of the bridge. This profile should indicate all control-grade points and

* should show not only the natural ground surface but also the present highway grade (if one exists) and a note showing which portions of this grade, if any, are surfaced. The field engineers should indicate upon this profile their recommendation for the structure and the elevation of extreme low, average high, and extreme high water.

(2) The alignment of the road for at least 1,000 feet each way, showing all control points.

(3) Sketch showing recommended angles and lengths for wing walls and the skew angle for any skewed piers or abutments. If this skew is to meet an existing wall or city street or property line, the angle must be exact and map should carry a note stating ^Hhis angle must be exact to fit retaining walP' or some similar notation. If, on the other hand, there is room for certain latitude in design the degree of latitude should be stated.

(4) For any railroad crossing, either at grade or one involving a grade separation, the map should show the number of tracks (present and contemplated) with the stationing ' of their intersection, their angle of intersection with the proposed highway center line and also the width of the railroad right of way for a distance of 800 feet either side of the highway center line. If the railroad tracks are on a curve, the degree of curvature and elevation of both rails (top of rail) should be given.

(5) All street, alley, and building lines, curbs, section lines, all section, township, and range numbers, and the name and address of the owners of all adjacent property.

(6) Location and description of all reference points and ties to any other survey either State, county, municipal, or Federal.

(7) Top and bottom bank lines of stream, location of all old channels, dikes, spoil banks, etc.

(8) All present right-of-way lines should be clearly indicated together with the outline limits of all additional right of way to be secured. Where there is need for additional right of way all data needed for writing a complete description of the property for deed purposes should be noted upon the map. The map should also clearly show the character of the property, whether timbered or under cultivation and the approximate value of any buildings which must be destroyed or moved on account of the proposed construction.

(9) The alignment of the stream for a distance of not less than 1,000 feet above and 500 feet below the proposed structure, showing


all bends or angles, all dikes, dams, trees, buildings, sand pits, intersecting streams or any other condition which in any way affects the stream flow at any season of the year.

(10) Location and elevation of all bench marks. (11) All buildings, intersecting roads or streets, sidewalks, alleys,

light, telephone or telegraph lines (indicating ownership and use, of each) conduits, sewers, and any other artificial structures or conditions that may in any way affect the design.

(12) Complete data for any modification of grades at any road intersection.

(13) Accurate contours over the entire vicinity. At the pier and abutment sites these contours should be spaced with a vertical interval not greater than 2 feet and should be accurate enough to furnish a basis for the computation of excavation quantities and the determining of the height of concrete-trestle pedestals.

(14) Cross-section notes for the computation of earth-work quan- ' titles for approach fills.

(15) Where portions of an existing structure can be used in the new construction, accurate detailed measurements of the old work should be furnished either on this map or upon a supplementary data sheet.

(16) Where channel changes or revetment works are involved, the map should contain all information needed to completely detail and estimate such work.

Figure 46 is a typical map of the character above described, indicating a suggested method of arrangement for the necessary data. The degree to which such a map should cover the various points of detail will of course depend upon the size and importance of the project and upon individual conditions. It may be said, however, that in general, bridge-vicinity maps rarely contain sufficient detailed information for which reason a model map of this character should prove of distinct value to the field engineer.

HYDROGRAPHIC SURVEYS

On March 23, 1906, the President approved a bill known as the general bridge law or a bill to regulate the construction of bridges over navigable waters from which the following is quoted:

Be it enacted by the Senate and House of Representatives of the United States of America in Congress assembledj That when, hereafter, authority is granted by Congress to any persons to construct and maintain a bridge across or over any of the navigable waters of the United States, such bridge shall not be built or commenced until the plans and specifications for its construction, together with such drawings of the proposed construction and such map of the proposed location as may be required for a full understanding of the subject, have been submitted to the Secretary of War and Chief of Engineers for their approval, nor until they shall have approved such plans and specifications and the location of such bridge and accessory works; * * *^

Where the waterway to be crossed by the proposed structure is a '^navigable water'' under the meaning of the above act, therefore, it becomes necessary to submit certain maps and plans to the War Department of the United States for approval.


Application for approval of plans is made upon a blank form provided by the War Department for this purpose and this form must be accompanied by the following plans and maps:

(a) A map showing the proposed location, and the waterway for the distance of 1 mile above and below, with the data in regard to low and high water, direction and strength of currents, soundings, existing bridges in the vicinity, etc., necessary to enable the Chief of Engineers and the Secretary of War to determine whether the location is a proper one.

(b) Plan of the bridge showing the length and height of spans, width of draw openings, position of piers, abutments, fenders, etc. and those features which affect navigation, giving on both horizontal sections and elevations the outside structure lines separating the area left for navigation from the area occupied by the bridge, and, in figures, the least clear width of openings at right angles to the axis of the channel; and the least clear heights with reference to high water, ordinary boating water, and low wâter.

(c) The essential features of the draw in two positions, closed and fully open.

In order to furnish the information called for above, soundings, bank lines, etc., for a distance of 1 mile above and below the bridge site are necessary and while the field party is engaged in this work it may be well to go slightly further, establishing a permanent base line and triangulation net and completing the data necessary for a hydrographie survey of the stream within the above limits.

Permanent transit points should be established at each bend or angle in the bank-traverse lines, and cross shots taken in such manner as to develop a complete triangulation system. Levels should be run over each bank and soundings taken covering the entire area. Gen- erally the stadia will prove a better method of spotting sounding points than the use of two transits as is sometimes done.

If the stream is inclined to shift laterally or if bank erosion at any point is to be feared a permanent bank-line traverse will be well worth while from a maintenance standpoint. With such a base line, careful bank ordinates may be taken from time to time and plotted in the form of an erosion progress record thus keeping an accurate check on the movement of the channel.

The determination of what constitutes ''navigable waters'' under the meaning of the above act of Congress has been made at various times by decisions of the United States Supreme Court. The following extract from an opinion by Mr. Justice Field will prove enlightening:

Those rivers must be regarded as public navigable rivers in law which are navigable in fact. And they are navigable in fact when they are used, or suscep- tible of being used, in their ordinary condition, as highways for commerce, over which trade and travel are, or may be, conducted in the customary modes of trade or travel on water, * * *.

ORGANIZATION OF THE UNITED STATES DEPARTMENT OF AGRICULTURE

February 13, 1928

Secretary of Agriculture W. M. JARDINE.

Assistant Secretary R. W. DUNLAP.

Director of Scientific Work A. F. WOODS.

Director of Regulatory Work WALTER G. CAMPBELL.

Director of Extension C. W. WARBURTON.

Director of Personnel and Business Adminis- tration W. W. STOCKBERGER.

Director of Injormation NELSON ANTRIM CRAWFORD.

Solicitor R. W. WILLIAMS.

Weather Bureau CHARLES F. MARVIN, Chief. Bureau of Animal Industry JOHN R. MOHLER, Chief. Bureau of Dairy Industry L. A. ROGERS, Acting Chief.. Bureau of Plant Industry WILLIAM A. TAYLOR, Chief. Forest Service W. B. GREELEY, Chief. Bureau of Chemistry and Soils H. G. KNIGHT, Chief. Bureau of Entomology C. L. MARLATT, Chief. Bureau of Biological Survey PAUL G. REDIN GTON, Chief. Bureau of Public Roads THOMAS H. MACDONALD, Chief. Bureau of Agricultural Economics LLOYD S. TENNY, Chief. Bureau of Home Economics LOUISE STANLEY, Chief. Federal Horticultural Board C. L. M ARLATT, Chairman. Grain Futures Administration J. W. T. DUVEL, Chief. Food, Drug, and Insecticide Administration^. WALTER G. CAMPBELL, Director of

Regulatory Work, in charge. Office of Experiment Stations E. W. ALLEN, Chief. Office of Cooperative Extension Work C. B. SMITH, Chief. Library CLARIBEL R. BARNETT, Librarian,

This bulletin is a contribution from

b>êau of Public Roads THOMAS H. MACDONALD, Chief,

76

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