GEOTECHNICAL EVALUATION WELBY ROAD REALIGNMENT …

GEOTECHNICAL EVALUATION

WELBY ROAD REALIGNMENT

NORTH OF 88TH

AVENUE

THORNTON, COLORADO

CITY OF THORNTON PROJECT NO. 12-703-A

PREPARED FOR:

ICON Engineering, Inc.

8100 Akron Street, Suite 300

Englewood, Colorado 80112

PREPARED BY:

Ninyo & Moore

Geotechnical and Environmental Sciences Consultants

6001 S. Willow Drive, Suite 195

Greenwood Village, Colorado 80111

January 26, 2015

Project No. 500907001

January 26, 2015

Project No. 500907001

Mr. Matthew J. Ursetta, P.E.

ICON Engineering

8100 Akron Street, Suite 300

Englewood, Colorado 80112

Subject: Geotechnical Evaluation

Welby Road Realignment North of 88th

Avenue

Thornton, Colorado

City of Thornton Project No. 12-703-A

Dear Mr. Ursetta:

In accordance with our proposal dated November 13, 2014 and your authorization, Ninyo &

Moore has performed a geotechnical evaluation for the proposed realignment of Welby Road

north of 88th

Avenue in Thornton, Colorado. The attached report presents our methodology,

findings, and recommendations regarding the geotechnical aspects of the project.

We appreciate the opportunity to be of service to you during this phase of the project.

Sincerely,

NINYO & MOORE

JMJ/SS/ceb

Distribution: (1) Addressee (via e-mail)

Jeffrey M. Jones, PE

Senior Project Engineer

Serkan Sengul, PE

Principal Engineer

1.26.151.26.15

Welby Road Realignment – North of 88th

Avenue January 26, 2015

Thornton, Colorado Project No. 500889001

500907001 R.doc i

TABLE OF CONTENTS

Page

1. INTRODUCTION ....................................................................................................................1

2. SCOPE OF SERVICES ............................................................................................................1

3. ALIGNMENT DESCRIPTION AND PROPOSED CONSTRUCTION .................................2

4. FIELD EXPLORATION AND LABORATORY TESTING ....................................................3

5. GEOLOGY AND SUBSURFACE CONDITIONS .................................................................3

5.1. Geologic Setting ...........................................................................................................4 5.2. Subsurface Conditions ..................................................................................................4

5.2.1. Fill .......................................................................................................................4

5.2.2. Alluvium .............................................................................................................5 5.3. Groundwater .................................................................................................................5

6. GEOLOGIC HAZARDS ..........................................................................................................5

6.1. Expansive Soils .............................................................................................................6 6.2. Collapsible Soils/Consolidation Settlement .................................................................6

7. CONCLUSIONS ......................................................................................................................7

8. RECOMMENDATIONS ..........................................................................................................8 8.1. Earthwork .....................................................................................................................8

8.1.1. Clearing and Grubbing ........................................................................................8

8.1.2. Excavations .........................................................................................................9

8.1.3. Treatment of Alignment Subgrade Soils .............................................................9 8.1.4. Alignment Grading............................................................................................11

8.1.5. Imported Alignment Grade Raise Fill Material ................................................12 8.1.6. Fill Placement and Compaction ........................................................................12 8.1.7. Utility Installation .............................................................................................13

8.1.8. Temporary Cut Slopes.......................................................................................13 8.2. Pavements ...................................................................................................................16

8.2.1. Pavement Section Design ..................................................................................16 8.2.2. Pavement Materials ...........................................................................................17 8.2.3. Roadway Subgrade Preparation ........................................................................17

8.3. Corrosivity ..................................................................................................................19

8.4. Concrete ......................................................................................................................20 8.5. Scaling ........................................................................................................................20 8.6. Construction in Cold or Wet Weather ........................................................................21

8.7. Construction Plan Review and Pre-Construction Conference ....................................22 8.8. Construction Observation ...........................................................................................22

9. LIMITATIONS .......................................................................................................................23

10. REFERENCES .......................................................................................................................25




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Figures

Figure 1 – Site Location Map

Figure 2 – Boring Location Map

Appendices

Appendix A – Boring Logs

Appendix B – Laboratory Testing

Appendix C - Flexible Pavement Calculations




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1. INTRODUCTION

In accordance with our proposal dated November 13, 2014 and your authorization, we have

performed a geotechnical evaluation for the proposed realignment of Welby Road north of 88th

Avenue, in Thornton, Colorado. The approximate location of the site is depicted on Figure 1.

The purpose of our study was to evaluate the subsurface conditions and to provide design and

construction recommendations regarding geotechnical aspects of the proposed project. This

report presents the findings of our subsurface exploration, results of our laboratory testing,

conclusions regarding the subsurface conditions at the site, and geotechnical recommendations

for design and construction of this project.

2. SCOPE OF SERVICES

The scope of our services for the project generally included:

Reviewing readily available aerial photographs and published geologic literature, including

maps and reports pertaining to the project site and vicinity.

Notifying Utility Notification Center of Colorado (UNCC) of the boring locations prior to

drilling.

Drilling, logging, and sampling four small-diameter exploratory borings along the proposed

roadway realignment. The borings were drilled to depths of approximately 8.5 feet below the

ground surface (bgs). The boring logs are presented in Appendix A.

Performing laboratory tests of selected samples obtained from the borings to evaluate in-situ

moisture content and dry density, No. 200 sieve analyses, gradation analyses, Atterberg

limits, swell/consolidation potential, R-value, and corrosivity characteristics (including pH,

minimum electrical resistivity, water-soluble sulfates and chlorides). The results of the in-situ

moisture content and dry density testing are presented on the boring logs in Appendix A. The

remainder of the laboratory test results is presented in Appendix B.

Compiling and analyzing of the data obtained. Pavement section thickness calculations are

presented in Appendix C.

Preparing this report presenting our findings, conclusions, and geotechnical

recommendations regarding design and construction of the project.




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3. ALIGNMENT DESCRIPTION AND PROPOSED CONSTRUCTION

The proposed Welby Road realignment is planned to diverge from the existing alignment

immediately south of Beachwood Drive in a general north-south direction and cross an area that

has been previously graded before entering agricultural land to its termination at 88th

Avenue.

The realignment topography is relatively flat with grades of less than 1 percent.

The proposed roadway alignment, extending northerly from 88th Avenue to the proposed RTD

Access intersection, will be located across a farmed land. Based on our preliminary review of the

available historic aerial photographs, it that the portion of the alignment located north of the RTD

Access intersection and south of Welby Road will cross a property that used to be occupied by

single-family residences. The aerial photography depicts the placement of a significant amount

of fill material across portion of the alignment north of the RTD Access intersection. The fill was

light brown in color and was placed as a series of end dump piles during the spring to summer

months of 2007. By June of 2010, the fill was spread across the property and the single-family

residences that occupied the land were demolished. The area was re-graded and re-seeded

between 2013 and 2014. At this time, we have not been provided documentation that suggests

the fill was placed in a controlled manner.

The realignment project consists of the design and construction of a new 1,440 lineal-foot road.

In addition, the project will include a new traffic signal at the intersection of the realigned Welby

Road and 88th

Avenue. Preliminary design information indicates the realignment segment

between 88th

and 89th

Avenue will consist of a four lane divided roadway with a center median.

The realignment segment north of 89th

Avenue will consist of three lanes. Both segments will

include bike lanes. Curb and gutter will be installed along the east side of the realignment while

the west side will include a gravel shoulder. A culvert is planned for the Lower Creek Creek

Ditch crossing at the north end of the alignment. We understand the culvert may include cast-in-

place concrete headwalls and wing walls. The proposed roadway realignment is depicted on

Figure 2.




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We understand that the realignment will be designed and constructed in general accordance with

the City of Thornton Standards and Specifications and that Welby Road will be designed as a

Major Collector.

4. FIELD EXPLORATION AND LABORATORY TESTING

On December 29, 2014, Ninyo & Moore conducted a subsurface exploration along the

realignment limits in order to evaluate the existing subsurface conditions and to collect soil

samples for visual observation and laboratory testing.

Our evaluation consisted of drilling, logging, and sampling four exploratory borings along the

subject roadway alignment. The borings were advanced using a CME-55 truck-mounted drill rig

equipped with solid-stem continuous-flight augers. The borings were drilled to depths of

approximately 8.5 feet bgs. Bulk and relatively undisturbed soil samples were collected at

selected intervals. Detailed descriptions of the soils and groundwater encountered in our borings

are presented on the boring logs in Appendix A. The approximate locations of the borings are

depicted on Figure 2.

Soil samples collected during our subsurface exploration were transported to the Ninyo & Moore

laboratory for geotechnical laboratory analyses. Selected samples were analyzed to evaluate

engineering properties including in-situ moisture content and dry density, Atterberg limits, No.

200 sieve analyses, gradation analyses, swell/consolidation potential, R-Value, and corrosivity

characteristics (including pH, minimum electrical resistivity, soluble sulfates, and chlorides). The

results of the in-situ moisture content and dry density testing are presented on the boring logs in

Appendix A. A description of each laboratory test method and the remainder of the test results

are presented in Appendix B.

5. GEOLOGY AND SUBSURFACE CONDITIONS

The geology and subsurface conditions at the site are described in the following sections.




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5.1. Geologic Setting

The alignment is located approximately 17 miles east of the Rocky Mountain Front Range,

within the Colorado Piedmont section of the Great Plains Physiographic Province. The

Laramide Orogeny uplifted the Rocky Mountains during the late Cretaceous and early

Tertiary Periods. Subsequent erosion deposited sediments east of the Rocky Mountains,

including the Denver Formation in the area. As a result of regional uplift approximately 5 to

10 million years ago, streams such as the South Platte River downcut and excavated into the

Great Plains forming the Colorado Piedmont section (Trimble, 1980). The surficial geology

of the site vicinity is mapped by Trimble and Machette (1979) as loess soil (wind-blown or

eolian silt generally derived from upwind glacial deposits). Based on the sandy clay

composition of the material encountered during our subsurface exploration and the

proximity to the South Platte River, we are referring to the material as alluvium. The Denver

Formation is mapped underlying the proposed roadway alignments at depth.

5.2. Subsurface Conditions

Our understanding of the subsurface conditions at the project site is based on our field

exploration and laboratory testing, review of published geologic maps, historic topographic

maps, historic aerial photographs, and our experience with the general geology of the area.

The following sections provide a generalized description of the subsurface materials

encountered. Descriptions that are more detailed are presented on the boring logs in

Appendix A.

5.2.1. Fill

Undocumented fill was encountered in Boring B-4 and extended to a depth of

approximately 4 feet bgs. The undocumented fill generally consisted of brown, moist,

loose to medium dense, silty sand with varying amounts of gravel and construction

debris including concrete.

The thickness and composition of the undocumented fill material encountered in our

boring does not represent the amount of undocumented fill present along the alignment.




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The design and construction team should assume additional uncontrolled fill materials

are present along the northern end of the alignment. The fill material encountered is

considered undocumented and is not suitable to support the loads generated during the

placement of grade-raise fill or roadway and associated improvements.

5.2.2. Alluvium

Alluvium was generally encountered at the surface or underlying fill material and

extended to the boring termination depths of approximately 8.5 feet bgs.

Alluvium encountered generally consisted of brown to light brown, moist, stiff to very

stiff, lean to fat clay with varying amounts of sand. In Borings B-1 and B-4 granular

alluvium was encountered at a depth of approximately 7 feet bgs consisting of light

brown to brown, moist, medium dense, clayey sand.

Based on the results of our subsurface exploration and laboratory testing, the alluvium

exhibited low to high plasticity. Selected samples had in-place moisture contents

between 16.3 and 27.1 percent and dry densities between 96.1 and 106.9 pcf.

5.3. Groundwater

Groundwater was not encountered during drilling to the total depth explored of

approximately 8.5 feet bgs. Groundwater levels will fluctuate due to seasonal variations,

irrigation, groundwater withdrawal or injection, and other factors. In general, groundwater is

not expected to be a constraint to construction of the project.

6. GEOLOGIC HAZARDS

The following sections describe potential geologic hazards at the site, including expansive soils,

and collapsible soils.




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6.1. Expansive Soils

One of the more significant geologic hazards in the Front Range area is the presence of

swelling clays in bedrock or surficial deposits. Moisture changes to bedrock or surficial

deposits containing swelling clays can result in volumetric expansion and collapse of those

units. Changes in soil moisture can result from precipitation, irrigation, pipeline leakage,

surface drainage, perched groundwater, drought, or other factors. Volumetric change of

expansive soil may cause excessive cracking and heaving of pavements supported on these

materials.

A review of a Colorado Geological Survey map delineating areas based on their relative

potential for swelling in the City of Thornton area by Hart (1974) indicates that the soil and

bedrock materials in the alignment vicinity typically exhibit low to moderate swell potential.

Selected samples tested exhibited percent swell values of 1.7 percent to 6.5 percent when

wetted against a surcharge pressure of 200 pounds per square foot (psf). The plasticity index

of the shallow subgrade soils generally varied between 28 and 33. Based on the plasticity

index, percent swell, and swell pressure results, the probable swell damage risk of the

subgrade soils are considered low to high on a scale of none, low, medium, high, and very

high.

6.2. Collapsible Soils/Consolidation Settlement

Compressible soils are generally comprised of soils that undergo consolidation when

exposed to new loadings, such as fill or foundation loads. Soil collapse (or hydro-collapse)

is a phenomenon where soils undergo a significant decrease in volume upon and increase in

moisture content, with or without an increase in external loads. Buildings, structures, and

other improvements may be subject to excessive settlement-related distress when

compressible soils or collapsible soils are present. Based on the subsurface exploration and

information obtained from our background review, the site is underlain by fill material and

alluvium that extends to depths ranging between approximately 8.5 feet bgs or more.




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Considering the relatively minor (less than 4 feet of material cuts and fills) alignment

grading that will be needed to achieve the finished roadway grades, combined with the

relatively light loads that the roadway will impose onto the subgrade, consolidation of the

site soils is not a design concern for the proposed roadway. Select samples tested did not

exhibit significant consolidation when wetted against a surcharge pressure of 200 psf.

7. CONCLUSIONS

Based on the results of our background review, subsurface evaluation, laboratory testing, and

data analysis, it is our opinion that proposed public roadway realignment is feasible from a

geotechnical standpoint provided the recommendations presented herein are implemented and

appropriate construction practices are followed. Geotechnical design and construction

considerations for the proposed project include the following:

The proposed Welby Road realignment is underlain by 4 or more feet of fill at the northern

end of the alignment. The fill material encountered consisted of brown, moist, loose to

medium dense, silty sandy with varying amounts of gravel as well as construction debris

including concrete chunks. The fill material encountered is considered undocumented and is

not suitable to support the loads generated during the placement of grade-raise fill or

roadway and associated improvements. Undocumented fill will need to be removed, moisture

conditioned, and recompacted prior to roadway construction to reduce probable settlement

risk. As the fill material encountered in Boring B-4 contained various amounts of

construction debris, some of the excavated fill material may not be suitable for re-use. The

geotechnical engineer should be retained to conduct additional observations during grading

to further evaluate fill material re-use suitability.

Alluvium was encountered at the surface or below the fill material in each of our borings and

extended to the boring termination depths of approximately 8.5 feet bgs. Alluvium

encountered generally consisted of brown to light brown, moist, stiff to very stiff, lean to fat

clay with varying amounts of sand. In Borings B-1 and B-4 granular alluvium was

encountered at a depth of approximately 7 feet bgs consisting of light brown to brown, moist,

medium dense, clayey sand. The alluvium has low to high swell potential and low

consolidation potential. A portion of the alluvium will need to be moisture conditioned and

recompacted prior to roadway construction to reduce probable swell damage risk.

Groundwater was not encountered to the total depth explored of approximately 8.5 feet bgs.

Groundwater levels will fluctuate due to seasonal variations, irrigation, groundwater

withdrawal or injection, and other factors. In general, groundwater is not expected to be a

constraint to construction of the project.




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The on-site soils should generally be excavatable to the anticipated removal depths with

heavy-duty earthmoving or excavating equipment in good operating condition.

Site soils generated from on-site excavation activities consisting of alluvium that are free of

deleterious materials, and do not contain particles larger than 3 inches in diameter, can

generally be used as engineered fill during utility installation and alignment grading. The

undocumented fill material may contain deleterious material and should be further evaluated

prior to use as engineered fill. Based on our understanding of the subsurface conditions,

addition of moisture, drying, blending with drier material, may be needed to raise or lower

the moisture contents of the excavated site soils prior to placement.

Corrosivity test results indicate that subgrade soils at the site are generally considered severly

corrosive to ferrous metals.

The sulfate content of the tested soils presents a negligible risk of sulfate attack to concrete.

Notwithstanding the sulfate test results, we recommend the use of Type II cement for

construction of concrete structures at this site.

8. RECOMMENDATIONS

Based on our understanding of the project, the following sections present our geotechnical

recommendations for design and construction of the proposed commercial development. These

recommendations were prepared based on the assumption that minor cuts and fills of 5 feet or

less will be needed to achieve finish grades.

8.1. Earthwork

Public roadway and utility improvements should be constructed in accordance with the City

of Thornton Standards and Specifications for the Design and Construction of Public and

Private Improvements, latest edition (City of Thornton Specifications). The following

sections provide our earthwork recommendations for this project. In case of conflict, City of

Thornton Specifications will govern.

8.1.1. Clearing and Grubbing

Prior to grading, the ground surface along the proposed roadway alignments should be

cleared of any surface obstructions, debris, topsoil, organics (including vegetation), and

other deleterious material. Abandoned utilities, septic fields, and relic foundations may




500907001 R.doc 9

be present along the northern portion of the alignment that was previously occupied by

single-family residences.

Materials generated from clearing operations should be removed from the site and

disposed of at a legal dumpsite. Obstructions that extend below finish grade, if present,

should be removed and the resulting holes filled with compacted soil or cement slurry,

in accordance with the recommendations of the geotechnical consultant.

8.1.2. Excavations

Our evaluation of the excavation characteristics of the on-site materials is based on the

results of the subsurface exploration, our site observations, and our experience with

similar materials. The on-site surface and near surface soils (fill and alluvium) may

generally be excavated with heavy-duty earthmoving or excavation equipment in good

operating condition.

Equipment and procedures that do not cause significant disturbance to the excavation

bottoms should be used. Excavators and backhoes with buckets having large claws to

loosen the soil should be avoided when excavating the bottom 6 to 12 inches of

excavations as such equipment may disturb the excavation bases.

The contractor should provide safely sloped excavations or an adequately constructed

and braced shoring system, in compliance with Occupational Safety and Health

Administration (OSHA) guidelines, for employees working in an excavation that may

expose employees to the danger of moving ground. If material is stored or equipment is

operated near an excavation, stronger shoring should be used to resist the extra pressure

due to superimposed loads.

8.1.3. Treatment of Alignment Subgrade Soils

Undocumented fill was encountered in Boring B-4 and should be anticipated along the

northern portion of the alignment. As the behavior of uncontrolled fill material is

difficult to predict, the undocumented fill materials should be removed and replaced




500907001 R.doc 10

prior to roadway construction to reduce the post-construction settlement related damage

risk.

Select samples of the alluvial deposits tested exhibited percent swell values of

approximately 1.7 percent to 6.5 percent when wetted against a surcharge pressure of

200 psf. The plasticity index of the shallow subgrade soils generally varied between 28

and 33. Based on the plasticity index, percent swell, and swell pressure results recorded,

the probable swell damage risk of the subgrade soils are considered low to high on a

scale of none, low, medium, high, and very high.

The probable swell damage risk for roadways was evaluated based on the driver’s

perception of a bump on the roadway that is caused by the potentially swelling soils. In

accordance with the 1998 Metropolitan Government of Pavement Engineer’s Council

(MGPEC, 1998) publication referenced within the 2015 Colorado Department of

Transportation (CDOT) Pavement Design Manual, a driver’s perception of pavement

bump is directly related to the slope of the bump, and the driver’s perception of

pavement roughness is related to the speed of the vehicle. According to this study, the

streets with speeds less than 35 mph and more than 35 mph have a discomfort level of a

2 percent change of slope and 1 percent change of slope, respectively.

In order to reduce the potential for post-construction settlement related damage risk

associated with the undocumented fill material and to reduce the probable swell damage

risk related to the subgrade soils, we recommend three (3) or more feet of moisture

treatment of the subgrade soils below the bottom of the pavement section. Additional

removal and replacement will be needed in areas of uncontrolled fill. Removal and

replacement should extend under the proposed curb and gutter and bike lanes.

The recommended moisture treatment consists of excavation of the site soils, and

replacement of the site soils as moisture treated and compacted engineered fill.




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8.1.4. Alignment Grading

Based on the laboratory test results and our experience with similar projects, it is our

opinion that the alluvium generated from on-site excavation activities is suitable for use

as engineered fill provided it is processed and moisture conditioned in accordance with

the recommendations set forth in Section 8.1.6.

Suitable engineered fill should not include organic material, clay lumps, bedrock

fragments (claystone, sandstone, siltstone, etc.), construction debris, rock particles, and

other non-soil fill materials larger than 3 inches in dimension. This material should be

disposed of off-site or in non-structural areas.

Excavated fill may be incorporated into engineered fill, provided it does not contain

deleterious material. Laboratory testing of the alluvium indicate varying in-place

moisture contents. It may be difficult to compact these soils at their in-place moisture

contents. The addition of moisture, drying, or blending with drier material may be

needed to raise or lower the moisture content prior to placement.

Prior to placement and compaction of engineered fill, the project’s geotechnical

consultant should be retained to observe excavation bottoms to evaluate the exposed

soils and evaluate if removals to more competent soils are needed. The subgrade

stability should be evaluated by means of a proof roll performed in accordance with

CDOT standards and visual observations.

The contractor should be prepared to either dry the subgrade materials or moisten them,

as needed, prior to placement of engineered fill. Some site soils may pump or deflect

during compaction if moisture levels are not carefully monitored. The contractor should

be prepared to process and compact such soils to establish a stable platform for paving,

including use of chemical stabilization or geotextiles, where needed.

Based on our understanding of the conceptual alignment grading, portions of the

proposed roadway alignment may receive sufficient amount of fill material above the

existing grades to meet the above recommended engineered fill section. In those areas,




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the exposed alluvial deposits should be scarified to a depth of 8 or more inches,

moisture-conditioned, and compacted prior to placement of engineered fill.

8.1.5. Imported Alignment Grade Raise Fill Material

We understand the proposed alignment grades will be achieved using the on-site soils. If

importation of additional off-site material is needed to achieve the alignment grades, the

imported materials should be free of organic material, claystone bedrock fragments, and

deleterious materials. Imported fill should have low expansion potential (less than 2

percent swell potential under 200 psf surcharge), 20 to 50 percent passing the No. 200

Sieve and should not contain particles larger than 3 inches in dimension.

Representative samples of the materials proposed for import should be tested by the

Geotechnical Engineer prior to transport to the site.

8.1.6. Fill Placement and Compaction

The excavated site soils used as engineered fill should be moisture-conditioned to

within 1 percent below and 3 percent above optimum moisture content and compacted

to 95 percent, or more, as evaluated by ASTM D 698 (or AASHTO T-99).

Fill should be placed in horizontal, uniform lifts and compacted by appropriate

mechanical methods. The optimal lift thickness of fill will be dependent upon the type

of compaction equipment used, but should generally not exceed 8 inches in loose

thickness. Fill materials should not be placed, worked, rolled while they are frozen,

thawing, or during poor/inclement weather conditions.

According to our laboratory test results, the on-site soils range between low plasticity

clayey sands to high plasticity sandy clays, and have variable in-place moisture

contents. Consequently, it may be difficult to compact these soils at their in-place

moisture contents. The addition of water or drying may be needed to adjust the

moisture contents prior to compaction.




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Earthwork operations should be observed and compaction of engineered fill and backfill

materials should be tested by the project’s geotechnical consultant in accordance with

the City of Thornton Specifications.

Compaction areas should be kept separate, and no lift should be covered by another

until relative compaction and moisture content within the recommended ranges are

obtained.

8.1.7. Utility Installation

The contractor should provide adequate mechanical compaction in utility trench

backfills. The contractor should take particular care to achieve and maintain adequate

compaction of the backfill soils around manholes, valve risers and other vertical

pipeline elements where settlements are commonly observed. Use of “flowable fill,”

(e.g. a controlled low strength mix (CLSM), or a similar material) should be considered

in lieu of compacted soil backfill for areas with low tolerances for surface settlements in

deep excavations and areas with difficult access.

Pipe bedding materials, placement and compaction should meet the specifications of the

pipe manufacturer and applicable municipal standards. Materials proposed for use as

pipe bedding should be tested for suitability prior to use.

Special care should be exercised to avoid damaging the pipe or other structures during

the compaction of the backfill. In addition, the underside (or haunches) of the buried

pipe should be supported on bedding material that is compacted as described above.

This may need to be performed with placement by hand or small-scale compaction

equipment.

8.1.8. Temporary Cut Slopes

Temporary excavations will be needed for this project during utility installation. Based

on the subsurface information obtained from our exploratory excavations and our

experience with similar projects, we anticipate that the soil conditions and stability of




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the excavation sidewalls may vary with depth. Soils with higher fines content may stand

vertically for a short time (less than 12 hours) with little sloughing. However, as the soil

dries after excavation or as the excavations are exposed to rainfall, sloughing may

occur. Soils with low cohesion (such as the alluvium that was encountered near or

below the groundwater table), will likely slough, cave, or flow during site excavations,

especially if wet or saturated.

In our opinion, the on-site fill and alluvium site soils above the groundwater table

should generally be considered a Type B soil when applying the OSHA guidelines. For

these soil conditions, OSHA recommends a temporary slope inclination of 1H: 1V

(horizontal: vertical) or flatter for excavations 20 feet or less in depth. Appropriate slope

inclinations should be evaluated in the field by an OSHA-qualified “Competent Person”

based on the conditions encountered.

The contractor should provide safely sloped excavations or an adequately constructed

and braced shoring system, in compliance with Occupational Safety and Health

Administration (OSHA) guidelines, for employees working in excavations that may

expose them to the danger of moving ground. Reducing the inclination of the sidewalls

of the excavations, where feasible, may increase the stability of the excavations. If

construction or earth material is stored, or equipment is operated near an excavation,

flatter slope geometry or shoring should be used during construction.

8.2. Culvert Crossing Recommendations

We understand a culvert will be constructed at the location where the proposed realignment

will cross the Lower Clear Creek Ditch. Foundations for culvert headwalls and wing-walls

may be placed on undisturbed alluvium and should extend to 36 inches or more below

adjacent finished grade (for frost protection). Footings should be reinforced in accordance

with the project structural engineer’s recommendations.

An allowable bearing pressure of 1,500 pounds per square foot (psf) may be used for

conventional spread footings bearing on undisturbed alluvial soils or on compacted




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engineered fill. The allowable bearing capacity was developed considering a factor of safety

of 2.5.

The average footing bearing pressure should not exceed the allowable equivalent uniform

bearing pressure presented above; however, peak edge stresses may exceed this value as

long as the resultant passes through the middle third of the footing base. The allowable soil

bearing pressure may be increased by one-third when considering total loads including

transient loads such as wind or seismic forces.

Walls that are not restrained from movement at the top and have a level backfill behind the

wall may be designed using an “active” equivalent fluid unit weight of 60 pcf/ft. This lateral

earth pressure value assumes compaction within about 5 feet of the wall will be

accomplished with relatively light compaction equipment.

For “passive” resistance to lateral loads, we recommend that an equivalent fluid weight of

250 pcf be used up to value of 2,500 psf. This value assumes that the ground is horizontal

for a distance of 10 feet or more behind the wall or three times the height generating the

passive pressure, whichever is more. We recommend that the upper 12 inches of soil not

protected by pavement or a concrete slab be neglected when calculating passive resistance.

A coefficient of friction of 0.30 may be used between soil and concrete contacts. If passive

and frictional resistances are to be used in combination, we recommend that the passive

resistance be limited to one-half of the ultimate lateral resistance. The passive resistance

values may be increased by one-third when considering loads of short duration such as wind

or seismic forces.

Measures should be taken so that moisture does not build up behind wing-walls. Wing-walls

should be backfilled and provided with drains that outlet away from the wall. Weepholes

may be used in lieu of drainage pipes. Drainage details should be developed by the structural

engineer.




500907001 R.doc 16

8.3. Pavements

Pavement sections for the proposed public roadways were developed in general accordance

with the guidelines and procedures of the American Association of State Highway and

Transportation Officials (AASHTO), the Colorado Department of Transportation (CDOT),

and the City of Thornton. We understand that Portland cement concrete (PCC) pavement

will not be utilized on this project. Therefore, recommendations for PCC pavements were

not provided.

8.3.1. Pavement Section Design

The design of the flexible pavement sections was based on our conversations with the

City of Thornton that the subject roadway will be designed as a major collector. Based

on Table 500-4 of the City of Thornton – Standards and Specifications the EDLA value

for a major collector is 75 which correlates to an ESAL value of 547,500 for a 20-year

service life.

We also assumed full depth flexible hot mix asphalt (HMA) pavements or composite

HMA pavements placed over Aggregate Base Course (ABC) will be utilized for this

project. The design of flexible pavements was based on the input parameters provided

on Table 3.

Table 1 – Flexible Pavement Design Input Parameters

Terminal Serviceability Index 2.5

Reliability (%) 85

Overall Standard Deviation 0.44

Resilient Modulus (psi) 3,026

Stage Construction 1

Overall Drainage Coefficient 1

Hot Mix Asphalt Strength Coefficient 0.44

Aggregate Base Course Strength Coefficient 0.14

The result of the laboratory testing performed on composite samples collected from the

pavement borings advanced along the alignment soils exhibited R-Values that range

between 5 and 6 (see Appendix B). Therefore, an R-Value of 5, corresponding to an




500907001 R.doc 17

approximately resilient modulus value of 3,026 psi was used for the design of the

pavement sections recommended below.

Based on the above-mentioned design traffic and input parameters, and following the

City of Thornton Specifications (2012), the following structural pavement sections

were calculated for the alignment.

Full Depth Asphalt – 10 inches of asphalt.

Composite Section – 7 inches of asphalt over 10 inches of aggregate base

course.

8.3.2. Pavement Materials

Asphalt pavement shall consist of a bituminous plant mix composed of a mixture of

high quality aggregate and bituminous material, which meets the City of Thornton

Specifications unless otherwise approved in writing by the City of Thornton

Development Engineering Manager. Grading S should be used for the lower lift(s) and

grading SX should be used for the surface course. Pavement layer thickness should be 2

to 3.5 inches for the lower lift(s) and 2 to 3 inches for the surface course with tack coat

layer(s) in between. The geotechnical engineer should be retained to review the

proposed pavement mix designs, grading, and lift thicknesses prior to construction.

The aggregate base material placed beneath pavements should meet the criteria of

CDOT Class 6 aggregate base and should have an R-Value of 78 or higher.

Requirements for CDOT Class 6 aggregate base can be found in Section 703 of the

current CDOT Standards and Specifications for Road and Bridge Construction.

8.3.3. Roadway Subgrade Preparation

Select samples tested exhibited percent swell values of 1.7 percent to 6.5 percent when

wetted against a surcharge pressure of 1,800 to 6,000 psf. The plasticity index of the

shallow subgrade soils generally varied between 28 and 33. Based on the plasticity

index, percent swell, and swell pressure results recorded, the probable swell damage




500907001 R.doc 18

risk of the subgrade soils are considered low to medium on a scale of none, low,

medium, high, and very high. Preparation of the alignment subgrade soils should be

performed in accordance with the recommendations provided in Section 8.1, so that the

recommended pavement sections under the Welby Road Realignment are constructed

over 3 or more feet of moisture treated subgrade soils.

The prepared subgrade should be protected from the elements prior to pavement

placement. Subgrades that are exposed to the elements may need additional moisture

conditioning and compaction.

Immediately prior to paving, the pavement subgrade should be proof rolled with a

heavily loaded, pneumatic tired vehicle in accordance with City of Thornton

Specifications. Areas that exhibit excessive deflection during proof rolling should be

excavated and replaced and/or stabilized.

8.3.4. Pavement Maintenance

The collection and diversion of surface drainage away from paved areas is vital to

satisfactory performance of the pavements. The subsurface and surface drainage

systems should be carefully designed to facilitate removal of the water from paved areas

and subgrade soils. Allowing surface waters to pond on pavements will cause premature

pavement deterioration. Where topography, site constraints or other factors limit or

preclude adequate surface drainage, pavements should be provided with edge drains to

reduce loss of subgrade support. The long-term performance of the pavement also can

be improved by backfilling and compacting behind curbs, gutters, and sidewalks so that

ponding is not permitted and water infiltration is reduced.

Drip irrigation systems are recommended for “island” planters within paved areas to

reduce over-spray and water infiltration beyond the planters. Enclosing the soil in the

planters with plastic liners and providing them with positive drainage also will reduce

differential moisture increases in the surrounding subgrade soils. ‘Xeriscape’-type




500907001 R.doc 19

landscaping is highly recommended. If this is not possible, we recommend edge drains

where the profile/slopes are less than 1 percent.

The standard care of practice in pavement design describes the recommended flexible

pavement section as a “20-year” design pavement; however, many pavements will not

remain in satisfactory condition without routine, preventive maintenance and

rehabilitation procedures performed during the life of the pavement. Preventive

pavement treatments are surface rehabilitation and operations applied to improve or

extend the functional life of a pavement. These treatments preserve, rather than

improve, the structural capacity of the pavement structure. In the event the existing

pavement is not structurally sound, the preventive maintenance will have no long-

lasting effect. Therefore, a routine maintenance program to seal cracks, repair distressed

areas, and perform thin overlays during the life of the pavement is recommended.

The estimated traffic loadings do not include excess loading conditions imposed by

heavy construction vehicles. Consequently, heavily loaded concrete, lumber, and

building material trucks can have a detrimental effect on the pavement.

8.4. Corrosivity

The corrosion potential of the site soils was evaluated using the results of selected,

representative soil samples obtained from our exploratory borings. Laboratory testing was

performed to evaluate pH, minimum electrical resistivity and chloride content. Sulfate

content is addressed in the following section. The pH tests were performed in accordance

with ASTM D 4972. The electrical resistivity tests were performed in accordance with

AASHTO T288. The test for chloride content of the soils was performed using CDOT Test

Method CP-L 2103. The laboratory test results are presented in Appendix B.

The results of our minimum resistivity tests indicated that minimum electrical resistivity of

near-surface site soils ranged from about 571 to 1,785 ohm-centimeters, which represents a

severe corrosion potential to ferrous metals. The soil pH was measured to range between 7.9

and 8.0, which is representative of a mildly alkaline environment. The soil chloride content




500907001 R.doc 20

was measured to range from about 15 to 80 parts per million (ppm), which represents a low

corrosion potential to metals. Based on these test results, the on-site soils may be considered

highly corrosive to ferrous metals. If metal pipes or other metal structures are in contact

with on-site soils, we recommend that these items be designed by a corrosion engineer

utilizing the results from our laboratory tests.

8.5. Concrete

Laboratory chemical tests performed on an on-site soil sample indicated soluble sulfate

contents ranging between 0.008 and 0.074 percent. Based on the ACI specifications, the on-

site soils should be considered to have a low sulfate exposure to concrete. Notwithstanding

the sulfate test results and due to the limited number of chemical tests performed, as well as

our experience with similar soil conditions and local practice, we recommend the use of

“Type II” cement for construction of concrete structures at this site.

The concrete should have a water-cementitious materials ratio of no more than 0.45 by

weight for normal weight aggregate concrete. The structural engineer should ultimately

select the concrete design strength based on the project specific loading conditions.

However, higher strength concrete may be selected for increased durability, resistance to

slab curling and shrinkage cracking. We recommend the use of concrete with a design 28-

day compressive strength of 4,000 psi or more, for concrete grade slabs at this site. Concrete

exposed to the elements should be air-entrained. Additional recommendations for exterior

concrete are provided in Section 8.5.

8.6. Scaling

Climatic conditions in the project area including relatively low humidity, large temperature

changes and repeated freeze-thaw cycles, may cause surficial scaling and spalling of exterior

concrete. Occurrence of surficial scaling and spalling can be aggravated by poor

workmanship during construction, such as ‘over-finishing’ the surfaces and the use of de-

icing salts on exterior concrete flatwork, particularly during the first winter after




500907001 R.doc 21

construction. The use of de-icing salts on nearby roadways, from where they can be

transferred by vehicle traffic onto newly placed concrete, can be sufficient to induce scaling.

The measures below can be beneficial for reducing the concrete scaling. However, because

of the other factors involved, including workmanship, surface damage to concrete can

develop, where the measures provided below were followed. The mix design criteria should

be coordinated with other project requirements including the criteria for soluble sulfate

resistance presented in Section 8.4.

Curing concrete in accordance with applicable codes and guidelines.

Maintaining a water/cement ratio of 0.45 by weight for exterior concrete mixes.

Including Type F fly ash in exterior concrete mixes as 20 percent of the cementitious

material.

Specifying a 28-day, compressive strength of 4,500 or more psi for exterior concrete.

Including ‘fibermesh’ in the concrete mix.

Avoiding the use of de-icing salts through the first winter after construction.

8.7. Construction in Cold or Wet Weather

During construction, the site should be graded such that surface water can drain readily

away from construction areas. Given the soil conditions, it is important to avoid ponding of

water in or near excavations and surface improvements. Water that accumulates in or near

excavations and surface improvements should be promptly pumped out or otherwise

removed and these areas should be allowed to dry out before resuming construction. Berms,

ditches, and similar means should be used to decrease storm water entering the work area

and to efficiently convey it off site.

Earthwork activities undertaken during the cold weather season may be difficult and should

be done by an experienced contractor. Fill should not be placed on top of frozen soils. The

frozen soils should be removed prior to the placement of new engineered fill or other

construction material. Frozen soil should not be used as structural fill or backfill. The frozen




500907001 R.doc 22

soil may be reused (provided it meets the selection criteria) once it has thawed completely.

In addition, compaction of the soils may be more difficult due to the viscosity change in

water at lower temperatures.

If construction proceeds during cold weather, aggregate base course, asphalt, and concrete

elements should not be placed on frozen subgrade soil. Frozen soil should either be removed

from beneath these elements, or thawed and re-compacted. To limit the potential for soil

freezing, the time passing between excavation and construction should be minimized.

Blankets, straw, soil cover, or heating could be used to discourage the soil from freezing.

8.8. Construction Plan Review and Pre-Construction Conference

We recommend that the approved construction plans be submitted for review by Ninyo &

Moore to evaluate adherence to the recommendations provided in this report and to provide

supplemental recommendations, as appropriate. We also recommend that a pre-construction

conference be held with the owner or agency representative, geotechnical consultant, civil

engineer, and contractor in attendance.

8.9. Construction Observation

The conclusions and recommendations presented in this report are based on analysis of

observed conditions in widely spaced exploratory borings. If conditions are found to vary

from those described in this report, Ninyo & Moore should be notified and additional

recommendations will be provided upon request. We recommend that Ninyo & Moore

observe and test fill placement and compaction. Project plans should also be reviewed by

Ninyo & Moore prior to the start of construction.

The recommendations provided in this report are based on the assumption that Ninyo &

Moore will provide geotechnical observation and testing services during the construction

phase of the project. In the event that Ninyo & Moore’s services are not used during

construction, we request that the selected consultant provide a letter to the client (with a

copy to Ninyo & Moore) indicating that they fully understand Ninyo & Moore’s




500907001 R.doc 23

recommendations, and that they are in full agreement with the recommendations contained

in this report.

9. LIMITATIONS

The field evaluation, laboratory testing, and geotechnical analyses presented in this geotechnical

report have been conducted in general accordance with current practice and the standard of care

exercised by geotechnical consultants performing similar tasks in the project area. No warranty,

expressed or implied, is made regarding the conclusions, recommendations, and opinions

presented in this report. There is no evaluation detailed enough to reveal every subsurface

condition. Variations may exist and conditions not observed or described in this report may be

encountered during construction. Uncertainties relative to subsurface conditions can be reduced

through additional subsurface exploration. Additional subsurface evaluation will be performed

upon request. Please also note that our evaluation was limited to assessment of the geotechnical

aspects of the project, and did not include evaluation of structural issues, environmental

concerns, or the presence of hazardous materials.

This document is intended to be used only in its entirety. No portion of the document, by itself, is

designed to completely represent any aspect of the project described herein. Ninyo & Moore

should be contacted if the reader requires additional information or has questions regarding the

content, interpretations presented, or completeness of this document.

This report is intended for design purposes only. It does not provide sufficient data to prepare an

accurate bid by contractors. It is suggested that the bidders and their geotechnical consultant

perform an independent evaluation of the subsurface conditions in the project areas. The

independent evaluations may include, but not be limited to, review of other geotechnical reports

prepared for the adjacent areas, site reconnaissance, and additional exploration and laboratory

testing.

Our conclusions, recommendations, and opinions are based on an analysis of the observed site

conditions. If geotechnical conditions different from those described in this report are




500907001 R.doc 24

encountered, our office should be notified and additional recommendations, if warranted, will be

provided upon request. It should be understood that the conditions of a site could change with

time as a result of natural processes or the activities of man at the subject site or nearby sites. In

addition, changes to the applicable laws, regulations, codes, and standards of practice may occur

due to government action or the broadening of knowledge. The findings of this report may,

therefore, be invalidated over time, in part or in whole, by changes over which Ninyo & Moore

has no control.

This report is intended exclusively for use by the client. Any use or reuse of the findings,

conclusions, and/or recommendations of this report by parties other than the client is undertaken

at said parties’ sole risk.




500907001 R.doc 25

10. REFERENCES

American Society for Testing and Materials (ASTM), 2010 Annual Book of ASTM Standards.

City of Thornton, 2012, Standards and Specifications, dated October.

Colorado Department of Transportation (CDOT), 2015, Pavement Design Manual.

Colorado Department of Transportation (CDOT), 2012, M&S Standards, dated July 4.

Colorado Department of Transportation (CDOT), 2011, Standard Specifications for Road and

Bridge Construction.

Hart, Stephen S., 1973-4, Potentially Swelling Soil and Rock in the Front Range Urban Corridor,

Colorado: Colorado Geological Survey, Sheet 1 of 4.

Trimble, Donald E., 1980, The Geologic Story of the Great Plains, Geological Survey Bulletin

1493.

Trimble, Donald E. and Machette, Michael M., 1979, Geologic Map of the Greater Denver Area,

Front Range Urban Corridor, Colorado: United States Geological Survey.

Aerial Photograph References

Source Dates

Google Earth September, 1994; December 2002; November 2006,

July, 2007, June, 2014.

N

APPROXIMATESITE LOCATION

SITE LOCATIONFIGURE

1DATE:

1/15

file no: 0907vmap0115

PROJECT NO:

500907001

WELBY ROAD REALIGNMENTTHORNTON, COLORADO

Source: Macvan Map Company, Denver, Colorado, 2011.


N

N


APPROXIMATE LOCATIONOF STOCKPILES




0

Ap p ro x i ma te Sca l e :1 i n ch = 20 0 0 f e e t

2000

Note: Dimensions, directions and locations are approximate.


Source: US Geological Survey 7.5-minute topographic map, Fort Morgan, Colorado, 1982, rev. 1984.


N


Note: Dimensions, directions, and locations are approximate.

LEGEND

Boring LocationB-2

LEGEND

Boring LocationB-2 Source: SPOT IMAGE, 10/06/14.

file

no

: 0

90

7b

lm0

115

0

Ap p ro x i ma te Sca l e :1 i n ch = 25 0

N

FIGURE

2DATE:

1/15

PROJECT NO:

500907001 THORNTON, COLORADOWELBY ROAD REALIGNMENT

BORING LOCATIONS250

LEGEND

Boring LocationB-6

B-2

B-1B-4

B-5

B-3

B-6

WELBY R

OAD

88TH AVENUE

BEACHWOOD DRIVE

B-1

B-2

B-3

B-4




500907001 R.doc

APPENDIX A

BORING LOGS

Field Procedure for the Collection of Disturbed Samples

Disturbed soil samples were obtained in the field using the following methods.

Bulk Samples

Bulk samples of representative earth materials were obtained from the exploratory borings. The

samples were bagged and transported to the laboratory for testing.

Field Procedure for the Collection of Relatively Undisturbed Samples

Relatively undisturbed soil samples were obtained in the field using the following methods.

The Modified California Split-Barrel Drive Sampler

The sampler, with an external diameter of 3.0 inches, was lined with thin brass rings with inside

diameters of approximately 2.4 inches. The sample barrel was driven into the ground with the

weight of a hammer in general accordance with ASTM D 3550. The driving weight was

permitted to fall freely. The approximate length of the fall, the weight of the hammer or bar, and

the number of blows per foot of driving are presented on the boring logs as an index to the

relative resistance of the materials sampled. The samples were removed from the sample barrel

in the brass rings, sealed, and transported to the laboratory for testing.

The California Drive Sampler

The sampler, with an external diameter of 2.4 inches, was lined with four 4-inch long, thin brass

liners with inside diameters of approximately 1.9 inches. The sample barrel was driven into the

ground with the weight of a hammer in general accordance with ASTM D 3550. The driving

weight was permitted to fall freely. The approximate length of the fall, the weight of the

hammer, and the number of blows per foot of driving are presented on the boring logs as an

index to the relative resistance of the materials sampled. The samples were removed from the

sample barrel in the brass liners, sealed, and transported to the laboratory for testing.

SOIL CLASSIFICATION CHART PER ASTM D 2488

PRIMARY DIVISIONSSECONDARY DIVISIONS

GROUP SYMBOL GROUP NAME

COARSE- GRAINED

SOILS more than

50% retained on No. 200

sieve

GRAVEL more than

50% of coarse fraction

retained on No. 4 sieve

CLEAN GRAVELless than 5% fines

GW well-graded GRAVEL

GP poorly graded GRAVEL

GRAVEL with DUAL

CLASSIFICATIONS 5% to 12% fines

GW-GM well-graded GRAVEL with silt

GP-GM poorly graded GRAVEL with silt

GW-GC well-graded GRAVEL with clay

GP-GC poorly graded GRAVEL with clay

GRAVEL with FINES

more than 12% fines

GM silty GRAVEL

GC clayey GRAVEL

GC-GM silty, clayey GRAVEL

SAND 50% or more

of coarse fraction passes

No. 4 sieve

CLEAN SAND less than 5% fines

SW well-graded SAND

SP poorly graded SAND

SAND with DUAL

CLASSIFICATIONS 5% to 12% fines

SW-SM well-graded SAND with silt

SP-SM poorly graded SAND with silt

SW-SC well-graded SAND with clay

SP-SC poorly graded SAND with clay

SAND with FINES more than 12% fines

SM silty SAND

SC clayey SAND

SC-SM silty, clayey SAND

FINE- GRAINED

SOILS 50% or

more passes No. 200 sieve

SILT and CLAY

liquid limit less than 50%

INORGANIC

CL lean CLAY

ML SILT

CL-ML silty CLAY

ORGANICOL (PI > 4) organic CLAY

OL (PI < 4) organic SILT

SILT and CLAY

liquid limit 50% or more

INORGANICCH fat CLAY

MH elastic SILT

ORGANIC

OH (plots on or above “A”-line) organic CLAY

OH (plots below “A”-line) organic SILT

Highly Organic Soils PT Peat

USCS METHOD OF SOIL CLASSIFICATIONExplanation of USCS Method of Soil Classification

PROJECT NO. DATE FIGURE

APPARENT DENSITY - COARSE-GRAINED SOIL

APPARENT DENSITY

SPOOLING CABLE OR CATHEAD AUTOMATIC TRIP HAMMER

SPT (blows/foot)

MODIFIED SPLIT BARREL

(blows/foot)SPT

(blows/foot)MODIFIED

SPLIT BARREL (blows/foot)

Very Loose < 4 < 8 < 3 < 5

Loose 5 - 10 9 - 21 4 - 7 6 - 14

Medium Dense 11 - 30 22 - 63 8 - 20 15 - 42

Dense 31 - 50 64 - 105 21 - 33 43 - 70

Very Dense > 50 > 105 > 33 > 70

CONSISTENCY - FINE-GRAINED SOIL

CONSIS-TENCY

SPOOLING CABLE OR CATHEAD AUTOMATIC TRIP HAMMER

SPT (blows/foot)

MODIFIED SPLIT BARREL

(blows/foot)SPT

(blows/foot)MODIFIED

SPLIT BARREL (blows/foot)

Very Soft < 2 < 3 < 1 < 2

Soft 2 - 4 3 - 5 1 - 3 2 - 3

Firm 5 - 8 6 - 10 4 - 5 4 - 6

Stiff 9 - 15 11 - 20 6 - 10 7 - 13

Very Stiff 16 - 30 21 - 39 11 - 20 14 - 26

Hard > 30 > 39 > 20 > 26

LIQUID LIMIT (LL), %

PLA

STI

CIT

Y IN

DE

X (

PI)

, %

0 10

1074

20

30

40

50

60

70

020 30 40 50 60 70 80 90 100

MH or OH

ML or OLCL - ML

PLASTICITY CHART

GRAIN SIZE

DESCRIPTION SIEVE SIZE

GRAIN SIZE

APPROXIMATE SIZE

Boulders > 12” > 12” Larger than basketball-sized

Cobbles 3 - 12” 3 - 12” Fist-sized to basketball-sized

Gravel

Coarse 3/4 - 3” 3/4 - 3” Thumb-sized to fist-sized

Fine #4 - 3/4” 0.19 - 0.75” Pea-sized to thumb-sized

Sand

Coarse #10 - #4 0.079 - 0.19” Rock-salt-sized to pea-sized

Medium #40 - #10 0.017 - 0.079” Sugar-sized to rock-salt-sized

Fine #200 - #40 0.0029 - 0.017”

Flour-sized to sugar-sized

Fines Passing #200 < 0.0029” Flour-sized and smaller

CH or OH

CL or OL

BORING LOG EXPLANATION SHEET

0

5

XX/XX

10

15

Bulk sample.

Modified split-barrel drive sampler.

2-inch inner diameter split-barrel drive sampler.

No recovery with modified split-barrel drive sampler, or 2-inch inner diameter split-barrel drive sampler.

Sample retained by others.

Standard Penetration Test (SPT).

No recovery with a SPT.

Shelby tube sample. Distance pushed in inches/length of sample recovered in inches.

No recovery with Shelby tube sampler.

Continuous Push Sample.

Seepage. Groundwater encountered during drilling. Groundwater measured after drilling.

SM MAJOR MATERIAL TYPE (SOIL):Solid line denotes unit change.

CL Dashed line denotes material change.

Attitudes: Strike/Dip b: Bedding c: Contact j: Joint f: Fracture F: Fault cs: Clay Seam s: Shear bss: Basal Slide Surface sf: Shear Fracture sz: Shear Zone sbs: Shear Bedding Surface

The total depth line is a solid line that is drawn at the bottom of the boring.

20

BORING LOGExplanation of Boring Log Symbols

PROJECT NO. DATE FIGURE

DE

PTH

(feet

)

BLO

WS

/FO

OT

MO

ISTU

RE

(%)

DR

YD

EN

SIT

Y(P

CF)

CLA

SS

IFIC

ATI

ON

U

.S.C

.S.

0

10

20

30

40

18

14

25.0 96.4

CL

SC

ALLUVIUM:Brown, dry to moist, very stiff, lean CLAY with sand.

Light brown to brown, moist, medium dense, clayey SAND.

Total Depth = 8.5 feet.Groundwater not encountered during drilling.Backfilled on 12/29/14 shorthly after completion of drilling.Notes:Groundwater, though not encoutered at the time of drilling, may rise to a higher level dueto seasonal variations in precipitation and several other factors as discussed in the report.The ground elevation shown above is an estimation only. It is based on our interpretationsof published maps and other documents reviewed for the purposes of this evaluation. It isnot sufficiently accurate for preparing construction bids and design documents.

BORING LOGWELBY ROAD REALIGNMENT

THORNTON, COLORADO

PROJECT NO.

500907001

DATE

01/15

FIGURE

A-1

DE

PT

H (

fee

t)

Bu

lkS

AM

PL

ES

Dri

ve

n

BL

OW

S/F

OO

T

MO

IST

UR

E (

%)

DR

Y D

EN

SIT

Y (

PC

F)

SY

MB

OL

CL

AS

SIF

ICA

TIO

N

U.S

.C.S

.

DESCRIPTION/INTERPRETATION

DATE DRILLED December 29, 2014 BORING NO. B-1

GROUND ELEVATION 5,126± SHEET 1 OF

METHOD OF DRILLING CME-55, Truck Rig, 4" Solid Stem Augers (Elite Drilling)

DRIVE WEIGHT 140 lbs - Auto Hammer DROP 30"

SAMPLED BY JF LOGGED BY JF REVIEWED BY JMJ

1

0

10

20

30

40

16

17

27.1 96.9

CL ALLUVIUM:Brown, moist, very stiff, sandy CLAY, trace gravel.

Light brown to brown.



THORNTON, COLORADO

PROJECT NO.

500907001

DATE

01/15

FIGURE

A-2

DE

PT

H (

fee

t)

Bu

lkS

AM

PL

ES

Dri

ve

n

BL

OW

S/F

OO

T

MO

IST

UR

E (

%)

DR

Y D

EN

SIT

Y (

PC

F)

SY

MB

OL

CL

AS

SIF

ICA

TIO

N

U.S

.C.S

.







1

0

10

20

30

40

15

36

26.0 96.1

CH ALLUVIUM:Light brown to brown, moist, very stiff, fat CLAY.

Hard.



THORNTON, COLORADO

PROJECT NO.

500907001

DATE

01/15

FIGURE

A-3

DE

PT

H (

fee

t)

Bu

lkS

AM

PL

ES

Dri

ve

n

BL

OW

S/F

OO

T

MO

IST

UR

E (

%)

DR

Y D

EN

SIT

Y (

PC

F)

SY

MB

OL

CL

AS

SIF

ICA

TIO

N

U.S

.C.S

.







1

0

10

20

30

40

32

20

18.6

16.3

106.9

106.3

SM

CH

SC

FILL:Brown, moist, loose to medium dense, silty SAND, varying amounts of gravel andconstruction debris.At 2', concrete encountered, hole caved in 3 times, offset 4' South.At 3.5', concrete and caving in, offset 5' Northeast twice.

ALLUVIUM:Light brown to brown, moist, very stiff, fat CLAY.

Light brown to brown, moist, medium dense, clayey SAND.



THORNTON, COLORADO

PROJECT NO.

500907001

DATE

01/15

FIGURE

A-4

DE

PT

H (

fee

t)

Bu

lkS

AM

PL

ES

Dri

ve

n

BL

OW

S/F

OO

T

MO

IST

UR

E (

%)

DR

Y D

EN

SIT

Y (

PC

F)

SY

MB

OL

CL

AS

SIF

ICA

TIO

N

U.S

.C.S

.







1




500907001 R.doc

APPENDIX B

LABORATORY TESTING

Classification

Soils were visually and texturally classified in accordance with the Unified Soil Classifications

System (USCS) in general accordance with ASTM D 2488. Soil classifications are indicated on the

logs of the exploratory excavations in Appendix A.

In-Place Moisture and Density Tests

The moisture content and dry density of relatively undisturbed samples obtained from the exploratory

excavations were evaluated in general accordance with ASTM D 2937-00. The test results are

presented on the logs of the exploratory excavations in Appendix A.

Atterberg Limits

Tests were performed on selected representative fine-grained soil samples to evaluate the liquid limit,

plastic limit, and plasticity index in general accordance with ASTM D 4318. These test results were

utilized to evaluate the soil classification in accordance with the Unified Soil Classification System.

The test results and classifications are shown on Figure B-1.

No. 200 Sieve Analysis

An evaluation of the percentage of particles finer than the No. 200 sieve in selected soil samples was

performed in general accordance with ASTM D 1140. The results of the tests are presented on Figure

B-2.

Gradation Analysis

Gradation analysis tests were performed on selected representative soil samples in general

accordance with ASTM D 422. The test results were utilized in evaluating the soil classifications in

accordance with the Unified Soil Classification System. The grain-size distribution curves are shown

on Figures B-4 and B-5.

Swell Potential Tests

The swell potential of selected materials was evaluated in general accordance with ASTM D 4546.

Relatively undisturbed and remolded specimens were loaded with a specified surcharge before

inundation with water. Readings of volumetric swell were recorded until completion of primary

swell. After the completion of primary swell, surcharge loads were increased incrementally to

evaluate swell pressure. The results of the swell tests performed on relatively undisturbed samples

are presented on Figures B-6 and B-7.

Soil Corrosivity Tests

Soil pH tests were performed on representative samples in general accordance with ASTM Test

Method D 4972. Soil minimum resistivity tests were performed on representative samples in general

accordance with AASHTO T288. The sulfate content of selected sample was evaluated in general

accordance with CDOT Test Method CP-L 2103. The chloride content of selected samples was




500907001 R.doc

evaluated in general accordance with CDOT Test Method CP-L 2104. The test results are presented

on Figure B-8.

R-Value Tests

The resistance R-value and expansion pressure of selected representative compacted soil samples

were evaluated in general accordance with ASTM D 2844. The results of the tests are summarized on

Figure B-9.




500907001 R.doc

APPENDIX C

FLEXIBLE PAVEMENT CALCULATIONS

AASHTO FLEXIBLE PAVEMENT CALCULATIONS

Project Name: Welby Road Realignment

Project Number:

Date: 1/16/15

Calculations by: JMJ

Case:

Structural Number Calculation

Equations: log(W18) = ZRSo+9.36log(SN+1)-0.20+log{[(Po-Pt)/(4.3-1.5)]/[0.40+(1094/(SN+1)5.19

]}+2.32log(MR)-8.07

MR = 10(0.0142*Rvalue+3.4098)

Design ESAL, W18 = 547,500 Equivalent TI = 8.4

Reliability, R = 85

Std. Normal Deviation, ZR = -1.037

Standard Deviation, So = 0.44

Initial Serviceability, Po = 4.2

Terminal Serviceability, Pt = 2.5

Subgrade R-Value = 5

Resilient Modulus, MR = 3,026 psi

Structural Number, SN = 4.22

target = 1.000

Structural Number (Design), SND = 4.22

Pavement Section Calculations

Equations: SNP = (aa)(Da) + (ab)(Db) + (as)(Ds)

SNP > SND

Asphalt Layer Coefficient, aa = 0.44

Base Layer Coefficient, ab = 0.12

Subbase Layer Coefficient, as = 0.07

Asphalt Concrete Thickness, Da = 10 in.

Base Thickness, Db = in.

Subbase Thickness, Ds = in.

Structural Fill Thickness, Dsf = in. Asphalt Concrete Thickness, Da = 10 in.

Structural Number (Provided), SNP = 4.40 OKAY Base Thickness, Db = 0 in.

Structural Number (Design), SND = 4.22 Subbase Thickness, Ds = 0 in.

Structural Fill Thickness, Dsf = 0 in.

Heavy Duty Collector - Full Depth Section

500907001

AASHTO FLEXIBLE PAVEMENT CALCULATIONS

Project Name: Welby Road Realignment

Project Number:

Date: 1/16/15

Calculations by: JMJ

Case:

Structural Number Calculation

Equations: log(W18) = ZRSo+9.36log(SN+1)-0.20+log{[(Po-Pt)/(4.3-1.5)]/[0.40+(1094/(SN+1)5.19

]}+2.32log(MR)-8.07

MR = 10(0.0142*Rvalue+3.4098)

Design ESAL, W18 = 547,500 Equivalent TI = 8.4

Reliability, R = 85

Std. Normal Deviation, ZR = -1.037

Standard Deviation, So = 0.44

Initial Serviceability, Po = 4.2

Terminal Serviceability, Pt = 2.5

Subgrade R-Value = 5

Resilient Modulus, MR = 3,026 psi

Structural Number, SN = 4.22

target = 1.000

Structural Number (Design), SND = 4.22

Pavement Section Calculations

Equations: SNP = (aa)(Da) + (ab)(Db) + (as)(Ds)

SNP > SND

Asphalt Layer Coefficient, aa = 0.44

Base Layer Coefficient, ab = 0.12

Subbase Layer Coefficient, as = 0.07

Asphalt Concrete Thickness, Da = 7 in.

Base Thickness, Db = 10 in.

Subbase Thickness, Ds = in.

Structural Fill Thickness, Dsf = in. Asphalt Concrete Thickness, Da = 7 in.

Structural Number (Provided), SNP = 4.28 OKAY Base Thickness, Db = 10 in.

Structural Number (Design), SND = 4.22 Subbase Thickness, Ds = 0 in.

Structural Fill Thickness, Dsf = 0 in.

Heavy Duty Collector - Composite Section

500907001

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