Pf-

HIGHWAY RESEARCH BOARD

Special Report 19

Stabilized Turf Shoulders

RECEIVED 4uU 1 3 1954

M4t I'LS LAB.

HIGHWAY RESEARCH BOARD Officers and Members of the Executive Committee

1954

OFFICERS

W. H. RooT, Chairman G. DONALD KENNEDY, Vice Chairman FRED BURGGRAF, Director

Executive Committee

FINcIs V. DU PONT, Commissioner, Bureau of Public Roads

HAL H. HALE, Executive Secretary, American Association of State High-way Officials

LouIs JORDAN, Executive Secretary, Division of Engineering and Industrial Research, National Research Council

R. H. BALDOCIC, State Highway Engineer, Oregon State Highway Com- mission -

PYKE JOHNSON, Consultant, Automotive Safety Foundation

G. DONALD KENNEDY, Executive Vice President, Portland Cement Association

0. L. Kn', Assistant Commissioner and Chief Engineer, Minnesota De-partment of Highways

BURTON W. MARSH, Director, Safety and Traffic Engineering Department, American Automobile Association

W. H. ROOT, Maintenance Engineer, Iowa State Highway Commission

C. H. SCHOLER, Head, Applied Mechanics Department, Kansas State Col-lege

K. B. WOODS, Associate Director, Joint Highway Research Project, Purdue University

Editorial Staff

FRED BTJRCCRAF W. J. MILLER

2101 Constitution Avenue, Washington 25, D. C.

HIGHWAY RESEARCH BOARD

Special Report 19

Concluding Report of •

Special Task Committee on

Stabilized Turt.. Shoulders'

PRESENTED AT THE

Thirty-Third Annual Meeting January 12-15, 1954

1954

Washington, D. C.

DEPARThENT OF DESIGN.

T. E. Shelburne, Chairman Director of Research

Virginia Department of Highways

CMITTEE ON R&DS IDE DEVELOPMENT

Frank H. Brant, Chairman; Landscape Engineer, North Carolina State HighwayS and Public Works Commission, Raleigh, North Carolina

Astrup, Mark H., Landscape Engineer, Oregon State Highway Commission, State Highway Building, Salem; Oregon ..

Betts, Clifford A., 6216 Winston Drive, Bethesda, Maryland Bowers,'. H. Dana, Supervising Landscape Architect, California Division of

Highways, 1120 N. Street, Sacramento 7, California Deakin, Oliver A., Engineer of Parkway Design, 'New Jersey Highway Authority,

1035 Parkway Avenue, Trenton, New Jersey '. Disque, Earl A., Landscape Architect, National Park Service, U. S. Depart-

ment of the Interior, Washington 25, D. C. Eckert, E. C., Chief Forester, Michigan State Highway Department, Lansing 13,

'Michigan Garmhausen, Wilbur J., Chief Landscape Architect, Ohio Department of Highways,

State Office Building, Columbus '15,' Ohio . ' " Gordon, George B., Supervising Landscape Architect, Bureau of Public Roads,

U. S. Department of Commerce, Washington 25, D. C. Gries, Albin, Chief Landscape Engineer, Illinois Division of Highways, Cen-

tennial Building, Springfield, Illinois Holmes, A. B., Landscape Engineer, Mississippi State Highway Department,

Jackson 114, Mississippi Hottenstein, Wesley L., Supervisor of .Roadside'Development, Pennsylvania

Department of Highways, Capitol North Office Building, Harrisburg, Pennsylvania

lurka, Harry H., Senior Landscape Arôhitect, New York Department of Public Works, Babylon, New York

Levin, David R., Chief, Land Studies Section, Financial and Administrative Research Branch, Bureau of Public Roads, U. S. Department of Commerce, Washington 25, D.C.

NcNanmon, John V. ,, Landscape Engineer, Massachusetts Department of Public Works, 100 Nashua' Street, Boston 14, Massachusetts

Marshall, Dr. Rush P., Director, Bartlett Tree Research Laboratories, Stamford, Connecticut

Monteith, Dr. John, Jr., Consultant, .3346 North Randolph Street, Arlington, Virginia

Neale, Harold J., Landscape Engineer, Virginia Department of Highways, Central Highway Office Building, Richmond 19, Virginia

Olson, H. B., Engineer of Roadside Development, Minnesota Department of Highways, 1246 University Avenue, St. Paul 4, Minnesota

Potter, Miss Olive E., Drushy Hill Road 4 R. F. D. #2, Danbury, Connecticut Rose, Franklin T., Landscape Architect, State Highway Commission of Kansas,

Masonic Temple, Topeka, Kansas Sears, Bradford G., Associate ProfessorofLahdscape Engineering, College

of Forestry, New York State University, Syracuse 101. New York

1].

Shurnate, Charles .E., Administrative Engineer, Colorado State Highway De- partment, Denver 2, Colorado

Simonzon, Wilbur H., Chief, Roadside Section, Bureau of Public Roads, U. S. Department of Commerce, Washington 25, D. C.

Slack, Torbert, Roadside Development Engineer, Louisiana Department of Highways, Box 4245 Capitol Station, Baton Rouge 4, Louisiana

Sutton, John G.,Drainage Engineer, Soil Conservation Service, U. S. De- partment of Agriculture, Washington 25,D. C.

Wells, Nelson M., Director, Landscape Bureau, New York Department of Public Works, Albany 1, New-York

Wright, John L., Engineer of Roadside. Development, Connecticut State Highway Department, P. 0. Box 2188, State Office Building, Hartford 15, Connecticut

SPECIAL COMMITTEE ON STABILIZED TURF SHOULDERS

Harry H. lurka, Chairman; Senior Landscape Architect, New. York State Depart-ment of Public Works, Babylon, Long Island, New York

Astrup, Mark H., Landscape Engineer, Oregon State Highway Comm:Lssion, Salem, Oregon

Blomquist, Professor Gail C., Civil Engineering Department, Michigan State College, East Lansing, Michigan

Daniel, Dr. W. H., Department of Agronony, Purdue University, Lafayette, Indiana

Chastain, W. E., Sr., Engineer of Physical Research, Illinois Division of Highways, 126 E. Ash Street, Springfield, Illinois

Garmhausen, W. J., Chief Landscape Architect, Ohio Department of High- ways, Department of State Building, Columbus 15, OhiQ

Harvey, Richard, Chief, Grounds Section, Headquarters, U.S.A.F., Wash- ington 25, D. Co •

Madigan, G. F., Airport Agronomist, CAA, Office of Airports, U. S. Depart- ment of Commerce, Washington 25, D. Co

Monteith, Dr. John, Jr., Consultant Agronomist, 3346 N. Randolph St.,

Arlington, Virginia Nikola, H. C., Soils Department, Rutgers University, New ,Brunswick,

New Jersey Rabbitt, A. E., Head Agronomist, Bureau of Aeronautics, Department of

the Navy, Washington 25, D. •C. Skrdla, Dr. W. H., Agronomist, Tactical Air Conunand, Langley Field,

Virginia Spelman, H. J., Division Engineer, Bureau of Public Roads, 1440 Columbia

Pike, Arlington, Virginia

iii

CONTENTS

•. : - - Page

INTRODUCTION •. 1

CONSTRUCTION .. . •. • 2

Stability ........................... .......... ............ • 2

Turf ...... •................. .................. ...... i Comparative Costs . . . 5

MA.INTEIIANCE .......... ................................• ....... -6

Build-up................................................ ... 6

Turf....... .................................................... 6

Comparative. Costs ............................... 6

CONCLUSIONS............................................ 6

TABI:JE 1: Comparative Costs of Establishment and Maintenance.. 7

TABLE 2 Comparative Shoulder-Construction Costs • 8

TABLE 3:: Cost, Maintaining Shoulders - Indiana S. R.135 •.. 8

DISCUSSION • . 9

.•.. . . •• ....... io ..•• .•. .•..• ........................• •

RffERENCES ..................................... .................• - io

iv

CONCLUDING REPORT OF COMMITTEE ON STABILIZED TURF SHOULDERS

The earliest known studies of development of turf on mechanically stabil-ized soils were reported in 1944; At the time, very little was known of the possibility of and requirements for turf on compacted soil materials. Study of the design, construction, and maintenance of stable turf shoulders was initiated in 1945 by the Committee on Roadside Development of the Highway Research Board, and a Committee was appointed for this study. This Committee, in an early ana],y-sis of the problems, recognized the necessity of cooperation of construction, maintenance, soils, traffic, and landscape engineers and agronomists, and has subsequently obtained the aid of representatives from these fields. A consider-able literature has been developed in the past decade which reflects not only interest in stabilized turf but also recognition of the importance of the shoulder as a part of the highway. There have been investigational projects reported from 23 locations in the United States (see Fig. 1). The Committee on Stabilized Turf Shoulders presents in this report a suimnary of its study of the literature and the projects reported, together with conclusions and recoimnendatiOns drawn there-

from.

For the purpose of this report, definitions of the terms involved are

given as follows:

Shoulder - The portion of the roadway contiguous with the traveled way for accommodation of stopped vehicles, for emergency use, and for lateral support of base and surface courses.

Stable - The ability to carry, at all seasons of the year, the maximum load permitted, without damage to the structure which would require repair.

Turf - A vegetative growth which serves as a wearing surface. This may include any kind of vegetation considered acceptable in the locality.

A "turf" shoulder may or may not be stable, depending on the structure, whereas a "stabilized turf shoulder" is designed and constructed to be stable. In a technical periodical',s forum there appeared some years ago the statement by a contributor that turf shoulders were not considered satisfactory in his state, partly because of their instability when wet. He then stated that the soil-aggregate type of shoulder where grass came up and was kept mowed was most sat-isfactory. Although this case affords an amusing illustration for one of the im-portant findings of this study, it is also an example of the general bias result-ing from sad experience with turf on unstable materials. Turf has been associ-ated with instability to such an extent that motorists, particularly truck drivers, are prone to avoid a shoulder with a turf cover even though it may be stable. The many projects reported show, that the fault is in the structure rather than the turf, that turf can be grown on a stable soil-aggregate material.

2.

There is a tendency to blame turf for decrease in density of compacted ma- terials • In one of the Indiana studies, densities of compacted materials decreased more in 41 years where there was no turf cover than they did under a turf cover. Projects with sandy soils reported in New York State showed no decrease in density (and no "build-up") over a period of two years. • Compacted fine-textured soils may

be expected to decrease in density due to normal weathering of the soil, i.e., freezing and thawing, wetting and drying, and the movement of air, but the soil-aggregate materials recommended below do not include such materials. Furthermore, it is known that a turf cover reduces frost penetration. --

Increase of the organic content of the soil under turf takes place slowly, and its increase in a shoulder surface course is not likely to be of an order to cause concern.

There are maintenance problems asso-ciated with every type of shoulder. "Build-up" of stabilized turf is to be expected from accumulation of wind-and water-borne materials, and of debris from snow and ice bladed off the pave-ment, and frojn weathering of compacted fine-textured soils. Shoulders not cov-ered with a surface material are subject to erosion which may require more expen-sive maintenance than that required to correct build-up.

Figure 1. Locations of Projects Inves-tigated.

CONS1UCTIQN

Stability

In the design and construction of a 'stabilized turf shoulder, stability is of primary importance and should be the foremost consideration. Drainage of soil and surface water must be adequate. The coarser surface texture of a turf requires a steeper slope than that for paved or even soil-aggregate surfaces to drain off the water from the pavement and shoulder area. A slope of 1 inch per foot is - recommended.

To support the maximum loads permitted on highways, the surface, base, and subgrade of the shoulder must be considered as an entity. If the base of the pave-ment is not carried through under the shoulder, particular consideration must be given to drainage and to the load-carrying characteristics of the materials under the surface course. For the surface course, this Committee recommends use of the.

3. current standard specification of AASHO for "Materials for Soil-Aggregate Sur-face Courses" without superimposed impervious surfacing. These materials should be compacted to at least 95 percent of the maximum density determined by the cur-rent standard tests of. AASHO.

Satisfactory performance with materials outside these limits has been re-ported even under conditions of high moisture content of the structure on several projects. Materials well beyond the Hmits specified may give satisfactory per-forinance even under maximum loads permitted except during the most critical periods of the year in respect to moisture. With the advice of soils engineers, it is possible that such revision of the recommended specifications may be made for a specific project when materials meeting the specifications are not avail-able. Climate, type of highway, and character and volume of traffic will, of course, influence such design considerations. There have been reports recently of establishing stability of a shoulder of fine-grain soil by the addition of coarse granular material. This practice may defeat its purpose under certain conditions, and it is recommended that soils engineers, be consulted before making such a specification.

One of the most important contributions this Committee has to make as a result of its studies is the confirmation, based on data from virtually all the projects reported, that topsoil is not essential for turf and might be the cause of instability. The term "topsoil" is not synonymous with fertility; in fact, some subsoils and "made" soils are better growing. media

I than some topsoils. Fer-tility can be provided by the use of fertilizers. Where precipitation is ade-quate, sufficient moisture to supply' plant growth will be retained by the ma-terials specified for stability. Reference to Figure 1 will show that the range of this prerequisite is quite broad. Organic material for the benefit of plants is not essential, and in appreciable quantities it is certainly undesirable for stability. There is nothing in "topsoil" essential for plant growth which can-not be provided with a soil-aggregate material which is satisfactory for stabil-ity; furthermore, the projects reported show that the specifications for stabil-ity provide a material which is satisfactory for plant growth. A concomitant advantage of the omission of topsoil is that there is less lilçelihood of the in-troduction of weed seeds and, therefore, less competition for the establishment of the desired plants.

The placing of a thin layer of soil considered fertile as a growing medium for turf on top of a stabilized course of soils-aggregate material is not necessary for turf and is undesirable for stability. For the same reason, the surface of the compacted surface course should not be cultivated deeper than about 1/2 inch, if at all, to produce a good seedbed. Good results have been secured by seeding just prior to final compaction and with no other surface treat- ment.

The Committee récomnends that landscape engineers use terms ' such as clay, silt, and sand, definitions for which are accepted by soils engineers in describ-ing a soil material, and not use such general terms as "topsoil," and "loam" which, undefined, have been used as a panacea for turf growth with the consequent hazard to stability.

4. Turf

Turf serves as a wearing surface which has shear value, but it has little bearing value for the maximum loads permitted on highways and the heavy loads apt to be imposed on turf shoulders of large airfield runways. For light vehicles, some turfs.have been shown to have some bearing value, but this should not be a factor in the- design of the shoulder. The turf further serves to protect the sur-face of soilaggregate materials from erosion by wind and water and, therefore, from loss of material and the resultant -lowering of the -shoulder surface and -the development of hazardous drop-off s at the edge of pavement. -.

The projects.reported demonstrate that turf can be- grown on any of the soil-aggregate - materials recommended for stability, where moisture is adequate, and can be maintained under occasional traffic. Adequacy of moisture is indicated by the existence of turf in - similar situations • --Turf has been grown on soil ma-- terials compacted to a density asgreat as 153.9 lb. per cu. ft. in- greenhouse tests, 147.2. lb. per Cu. ft. infield tests,. and with-aslittle.as 5 percent-of- - silt and clay and virtually no organic material. - - - - - -

Because use of shoulders increases withdecrease in pavement width below 22 feet persistence of turf on the- shoulder adjacent to the pavement -of. such roads cannot be expected. Turf on stabilized soil-aggregate has, -been observed to fail in the track- used, in delivering to a mailbox once a day., but turf will - recover from damage - by a considerable amount of traffic • Good - turf has - been main-tained on stone-block paved shoulders- (see -Figs. 2 and 3) with seeded- joints - - where traffic is more- than-occasional. - - -- - --. - - - '- - -

Establishment of turf on stabilized material is not more (and no less) difficult than establishment on other areas • The specific materials and methods, within reasonable limits, areof less importance, than that uncontrollable--factor of the weather immediately following construction and that. controllable factor of maintenance- after construction.

It is recommended that lime be used as indicated by-analysis of the soil pH and as further indicated by experience. It has been found, for example, that Kentuc1i- bluegrass grew exceedingly well on one sandy soil haveing a pH of 4.0 - to 4.5. Relatively large amounts of fertilizer as repired by the soil should be used. The -term "large" cannot be defined specifically but for the soil-aggregate mixtures recommended 80 to 100 lb. -of nitrogen per- acre proved effective. Nitro-gen is the critical element and the most economical kind of high-nitrogen ferti-lizer available should be used. Minor- element- deficiency for - turf - growth has not. been a-prob1em - - - -- - --- -

Although one of the studies reported better results from incorporating - the-fertilizer within the full stabilized depth, others have shown that surface application of fertilizer is just-as effective. For simplicity of construction and, therelore, economy, surface application may be desired. - - -- -

- - Fertilizing and liming may be done - immediately before seeding and after stabilizing compaction. There need not be any appreciable intervalbetween these operations. -

-

4..

-. .,- •::' .. . •.••.1.i ,

5.

Figure 2. Construction of stone-block Figure 3. Turf stone-block shoulders shoulders. (1953).

The kinds of plants found to be existing under similar ecological condi-tions should be used. So-called "nurse-crop" plants are really competitive plants and interfere with the rapid establishment of desirable perennial plants. 1 heir use should be limited to those conditions where a quick-germinating temporary cover must be established to prevent erosion. The percentage of seeds of these plants in the seed mixture should be kept low (5 to 10 percent).

Turf has been successfully established on stabilized materials by the con-ventional methods of seeding and sprigging. The least-expensive effective method suitable to a locality and the conditions is recommended. The development of vol-unteer growth on stable shoulders has been reported from many states. It is an indication of the adaptability of turf as herein defined.

Although the conventional methods of seeding may be used following con-struction of the stabilized shoulder, it is possible to effect certain economies and yet obtain satisfactory results. Seeding directly on the compacted surface resulting from the stabilization operation, without tillage, raking, and rolling, provided an adequate mulch is used, has been successful. Seeding may also be done without tilage, raking, and rolling over an existing light vegetation, this vegetation serving as a mulch.

Mulching of seeded areas is desirable. If hay, straw, or similar mater-ials are used, anchorage is essential because of wind and the air movement created by traffic. The mulch material should not contain seeds of undesirable plants. Inorganic materials such as sand, gravel, stone chips, and cinders have been re-ported as giving as good results as the organic materials.

Comparative Costs

The cost of construction of a stable turf shoulder is much less than that of most other stable shoulders (see Table 1 and 2). The cost of seeding a sta-bilized soil-agfregate shoulder is relatively small.

6. MAINTENANCE

Build-up

This Committee has not determined the specific order of importance of the causes of build-up. It is generally accepted that build-up is due to the natural weathering processes and to the accumulation of debris. It is obvious that turf will cause more deposition of wind- and water-borne material than will surface materials such as bitumens, for example.

Rolling shoulders when the soil is moist to recompact them and sweeping turf shoulders to remove accumulated debris have been reported. The rolling op-eration may be of limited application since it must be done when there is enough roisture to permit satisfactory compaction. The most usual method, of course, is blading off the surface material. The Committee recommends that, when this is done, the cut should be sufficiently deep to result in an adequate slope of 1 inch per foot where possible, recognizing that the economy of fewer such operations of blading is far more important than the possible saving of plant roots in order to preserve the existing vegetation. The cost of seeding or sprigging the newly graded shoulder is relatively small in comparison, and adequate turf can be ex-pected to develop in a very short time.

Turf

Maintenance of the, turf is the most important controllable factor of sat-isfactory vegetative growth. The height of mowing should never be less than 3 to 4 inches primarily for the benefit resulting therefrom to the turf, but also for the greater economy of the operation itself. There is no need for removal of cut-tings. This organic matter decomposes rapidly and in itself adds essentially nothing to the accumulation of debris. Fertilizing should be done as required by, the appearance of the turf. Turf should not be permitted to retrogress so far that considerable bare areas result. The color, density, and height of the growth may be used as an index of the need of fertilizing, with the understanding that density of cover is desirable but rankness of growth is not for this only creates additional maintenance. It is recommended that for average use, 40 lb. of nitro-gen in the most economical form be applied per acre. This may be necessary as often as once a year for some materials containing small amounts of silt and clay, but on materials containing larger amounts ofthese fractions, fertilizing may not be necessary at all.

Comparative Costs

In Tables 1 and 3 cost data on maintenance of shoulders reported are re-. produced. These figures represent the thinking of many authorities that a soil-aggregate material with a satisfactory turf wearing surface is much more econom-ical to maintain than one without such a protective surface.

CONCLUSIONS

1. Turf can be growm on stabilized soil-aggregate materials where mois-ture is adequate and, under occasional traffic, will serve as an economical wear-ing surface having shear value and preventing wind and water erosion.

7. Turf can be established and maintained on soil-aggregate materials com-

pacted to the densities.required for stability for highway purposes.

"Topsoil" is not essential for turf and, if used without further defi-nition as a soil material, might adversely affect stability.

Stability of the shoulder is of primary importance. Stabilized turf should be constructed with consideration for stability of surface, base, and sub-grade. For the surface course, materials within the limits of the specification of AASHO for "Materials for Soil-Aggregate Surface Courses" should be compaôted to at least 95 percent maximum density. Turf should be established directly on the stabilized course by the appropriate procedures for turfing.

The slope of the shoulder should be adequate to permit surface water to drain properly and to aid in delaying as long as possible the necessity of blading. One inch per foot is recommended.

Appropriate maintenance procedures are essential to maintain ,a vege-tative cover under the imposed conditions of growth. Mowing height should be no lower than 3 to 4 inches. Fertilizing should be dictated by the condition of the turf and econony of maintenance.

With proper design, construction, and maintenance, the cost of con-struction and maintenance of stabilized turf shoulders is less than that of other stable shoulders. "Build-up". is not a characteristic of all shoulders of this type; when it' does occur, it is less costly to correct than the constant erosion of an unsurfaced soil-aggregate material.

TABLE 1

CONPARATIVE CCTS (1944-1945) OF ESTABLISIOMT AND MAINTENANCE

Initial Cost Annual Main- Types of Grounds Treatments per Acre tenance per

Acre 1. Grassing with natural rainfall 15 to 4 50 10 to $'15

2. Grassing with portable irrigation / systems:

Water supply and distribution 50 to 200 20 to 30 Grassing 15 to 50 10 to 15

3. Anchored straw or hay mulch 50 to 100 25 to 50 for replacement

a. If seeded to perennial grasses at time of after 2 yrs. mulching ' 10 to 15

4. Gravel and cinder blankers 2 inches thick 600 to 750 Variable

5. Asphaltic treatments (oil palliatives) $300 to $500. $150 to $225

8.

TABLE 2

C(PARATIVE SHOULflER-CONSTRUCTION COSTS (1951-1953)

Cost per bpe of Shoulder Sq. Yd,

2k-in. asphaltic concrete on 5-in, stone base ' $ 3.40 Soil, cement-stabilized 2.50 Bituminous-stabilized gravel mix (plant nüx - 5-in, depth) , 3.00 Bituminous mulch' gravel (3-in, plant mix on 6-in, gravel foundation) 2.00 Bituminous concrete (4-in. base course - 3-in, intermediate -

1-in, top) 2.50 Stabilized turf - 6-in, depth - imported granular materials ' 1.40 Stabilized turf - 6-in, depth - imported granular materials 1.25 Bituminous stabilized earth - 4-in, depth ' 1.35 Improved stone - 8-in, depth ' ' 1.25 Run-of-bank gravel (not stabilized, not turfed) 0.60 Oiled (surface) ' ' ' 0.40 Transition strip (3-ft. width, modified penetration

macadam - 7 in. depth) - 2.05 Stabilized turf shoulder (selected native soil materials compacted

with moisture control and paid for as unclassified excavation. Average bids received on three contracts in New York in 1952 0.153 to and 1953). ' ' 0.323 -

TABLE 3*

COST, MAINTAINING SHOULDERS - INDIANA S.R. 135

Type of Sec. 11 011-8.16 ml. , Sec. 11p11-6.61 ml. Total Year i1aint. ' 14.77 ni.

1939 720,56 936.45 , ' 19657.01

1941 ' 900.88 742.00 ' 19642.88 1942 19089.82 19054.97 2,144.79 1943 Drag , 949.59 ' 595.05 1,544,64 1944 3,273.87 763.88 4,037.75 194 . 1.238,62 1.206.61 2.445.23 1946 269.70 244.61 514.31 1947 567.05 384.44 ' 951.49 1948 Turf 478.04 588.20 1,066.24 1949 374,74 249.22 623.96 ' 1950 277.54 616.13 893.67 Total Cost 7,452.78 ' 4,362.51 ' 119815,29 1941 to Drag Maint. 1945 mci. Total Cost Turf Naint. ' 1,967.07

2,082.60

4,049.671946 to 1950 md.

Difference 7765.62 1he index value of the doflar during the 10 years should be a factor for considera-tion, as well as the increased traffic count during the post-war years. Under drag maintenance, the shoulder, approximately 8 feet wide was bare to the ditch, i.dth the ditch and valance of R/V1 in turf,. Today, it is turf from the pavement edge to the R/\1 line.

9. DISCUSSION

George McAlpin. Directors Bureau'of Soil Mechanics New York State Depart-ment of Public Works. The final report of your committee fairly and adequately describes the knowledge available at this time on the characteristics of soils as related to shoulder stability. We suggest that a clearer definition of accepta-. bility, as far as shoulder rutting is concerned, may be in order. It is possible that the permissible degree of rutting may be such that shoulders constructed with a high percent of material passing the 200-mesh sieve but with a low.plastic in-dex may be acceptable. If such is the case, it would be avery significant find-ing.

Mark H. Astrup. Landscape Engineer.'Oregon State Highway Department. Turf is generally considered to mean grass. Does the Committee's definition of turf mean any variety of grass considered acceptable in the locality?

Mr. lurka. No. The Committee's definition of turf is "A vegetative growth which serves as a wearing surface. This may include any kind of vegeta-tion considered acceptable, in the locality." The grasses generally are more wear-resistant than other plants, but if other plants grow more successfully, pro-viding the desired' wearing Surface 'with no more maintenance effort, they might well be used.

Edgar J. Hunter, Agronomist, Brookhaven National Laboratory, Upton. L. I., New York It has been ny experience that, to most people, the word "turf" means a lawn or a product in the luxury class found on well-kept golf courses. 'Among these people are engineers and administrators who have to be convinced that turf for stable' 'shoulders is a functional and utilitariah material.

Wilbur J. Garmhausen. Chief Landscape Architect. State of Ohio Department of Highways. The committee report states that "Kentucky bluegrass grew exceeding-ly well ... (at) a pH of 4.0 to'4.5." To me this gives the wrong impression, as it is an'exception rather than a rule that' this grass thrives on so 'acid a 'soil.

Mr. lurka. The example, which is recognized as an exception, was given by Dr. James Tyson of Michigan State College to show' that lime should be applied for turf only- when soil tests and experience with the soils indicate it is nec-essary.

Frank Brant, Landscape Engineer. North Carolina State Highway and Public Works Commission. What thickness of sand, gravel, stone chips, or cinders is recommended as mulch

Mr. lurka. These mulches were placed just thick enough to cover the soil from view.

E. B. Cale, Consulting Agronomists Jacksonville, Florida. The Corps of Engineers had considerable success in stopping wind erosion by planting fast-growing nurse crops in rows spaced to 24 inches apart. This spacing seemed to limit adequately the competition to permanent grasses while at the same time pro-viding"'wirosio control. This method also'has some limited application to water-erosion control.

10.

ACKNGI1LEDGENT

The Special Committee on Stabilized: Turf Shoulders wishes to express its appreciation to the many cooperators who have aided in this study.

REFENCES

1. Blomquist, G. C., "The Infliienceof Soil Mixtures on Turf Growth and Soil Stability for Highway Shoulders and Airports," Report of Conuiittee .onRoad-side Development, Highway Research Board 32nd Annual Meeting, 1953.

2, Cale, E. B., "Development of Turf on Stabilized Soils," Report of Committee on Roadside Development, Highway Research Board 27th Annual Meeting, 1948.

Cale, E. B., "Turf on Stabilized Soils," Report of Committee on Roadside Development, Highway Research Board 28th Annual Meeting, 1949.

Cale, E. B., "Recommended Practices for Establishment and Maintenance of Turf," Office of the Chief of Engineers, Airfields Branch, Engineering Di-vision, Military Construction, April, 1953.

David, Joan, and J. R. Yarrow, "Let Your Airport Go to Grass," Flying, Feb-ruary 1945.

Deakin, Oliver A., "Preliminary Report - Experimental Stabilized Turf Shoulders for New Jersey Parkways," Report of Committee on Roadside. Development, High-way Research Board 27th Annual Meeting, 1948.

Deakin, Oliver A., "Progress Report - Experimental Stabilized Turf Shoulders for New Jersey Parkways," Report. of. Committee on Roadside Development, High-way Research Board 28th Annual Meeting, 1949.

Downey, Burleigh R., "Highway Shoulder Practice in Michigan," Report of Committee on Roadside Development, Highway Research Board 30th Annual Meeting. 1951.

Dupre, Dallas D. Jr., "Establishment and Maintenance of Stabilized Shoulders," Roads and Streets, May, 1948.

Finney, E. A., "Shoulder Construction Practice inNichigan," Report of Com-mittee on Roadside Development, Highway Research Board 28th Annual Meeting, 1949.

lurka, Harry H., "Stabilized Shoulders Which Will Support Vegetation - Progress Report," Proceedings, Highway Research Board 26th Annual Meeting, Vol. 26 (1946).

lurka, Harry H., "Progress Report on Stabilized Turf Shoulders Constructed on Long Island," Report of Committee on Roadside Development, Highway Research Board 27th Annual Meeting, 1948.

II.

Jones, Gordon H., and R • C. Dunning, "Turfing the Unpaved AU-Weather Air-port Southern Flight, January, 1946.

Monteith, John Jr., "Turf for Protection of Gutters and Slopes," Report of Committee on Roadside Development, Highway Research Board 21st Annual Meeting, 1941.

Monteith, John, Jr., "Turf for Airfields and Other Defense Projects," -Turf Cu1ture, Vol. 2, No. 4 (March, 1942).

Morrish, R. H., and .C. M..Harrison, "The Establishment and Comparative Wear Resistance of Various Grasses and Grass Legume Mixtures toVehicular Traffic," Abstract in Report of Committee on Roadside Development, Highway Research Board 28th Annual Meeting, 1948. Journal of American Society of Agrononr, Vol. 40, No. 2 (1949).

Mott, G. 0., "Turf on Stabilized Granular Materials," Group Meeting Book American Association of State Highway Officials, 1944.

18, Mott, G. 0., "Growing Grasses Under EcLsting and 'Made' Roadside Conditions," Fifth Short Course on Highway Development, Ohio Department of Highways and Department of Landscape Architecture, Ohio State University, 1946.

19. Nikola, H. C., "Stable Shoulders," Report of Committee on Roadside Develop-ment, Highway Research Board 31st Annual Meeting, 1952.

20, Russell, John E., "Soil Conditions and Plant Growth," Longmans, Green and Co., London, pp. 329-332.

Taragin, A., "Effect of Roadway Width on Vehicle Operation," Public Roads, Vol. 24, No. 6.

Tyson, J., and E. A. Finney, "Progress Report on Study of Turf Growth on Soil Mixtures Available for Highway Shoulder Construction in Michigan," Re-port of. Committee on Roadside Development, Highway Research Board 27th Annual Meeting, 1948.

Whiteside, E. P., and R. S. Smith,. "Soil Changes Associated with Tillage and Cropping in Humid Areas of the United States," Journal of the American So-ciety of Agrononr, 33:765-777. (1941)

Woods, K. B., and Lowell E. Gregg, "Pavement Performance Related to Soil Texture and Compaction," Proceedings, Highway Research Board, Vol. 24 (1944).

Yarrow, J. R., "The Case. for Turf Fields," Airports, August, 1945.

"Stabilized Soil and Turfing. Report," U. S. Arnr Airfields, Jacksonville,Fla., District;U. S. Arixr Engineer Offiàe, Jacksonville, Fla., August 1944.

"The Design at Stabilized Earth Shoulders for Turf Cover," Report of Committee on Roadside Development, Proceedings, Highway Research Board 25th Annual Meeting, Vol. 25 (1945). .

U. "A Study of Turf Shoulders," Report of Subcommittee on Shoulders, Committee on Roadside Development Report to Highway Research Board, 1947.

"Report of Project Committee on Shoulders," Report of Committee on Roadside Development, Highway Res'arch' Board 28th Annual Meeting, 1949.

"Report of Special Committee on Shoulders," Report of Committee on Roadside Development, Highway Research Board 29th Annual Meeting, 1950.

"Turfing Stabilized Shoulders," Highway Research Board Highway Research Cor-relation Service, Circular No. 164, May, 1952.

"Report of Project COmmittee on Stabilized Turf Shoulders," Report of Com-mittee on Roadside Development, Highway Research Board 32nd Annual Meeting, 1953.

Report of Special Task Committee on Stabilized Turf Shoulders, Report of Committee on Roadside Development, Highway Research Board 33rd Annual Meet-ing, 1954.

"Turf for Airfields," War Department, Office of the Chief of Engineers, October, 1945. S

"Turf-Base Shoulder Investigation - Maxwefl Field, Montgomery, Alabama," War Department, Corps of Engineers, Office of the District Engineer, Mobile, Alabama, May, 1947.

"Data Report Turf-Base InvestigatIons," MacDill Field, Florida, Department of the Anny, Corps of Engineers, South Atlantic Division, Office of District Engineer, Savannah, Georgia, March, 1948.

•"The Establishment and Maintenance of Turf on Stabilized Granular Materials," Corps of Engineers, U. S. Arn (Thesis by Willis H. Skrdla, Purdue University). August, 1949.

38.. "Turf Runway Investigation - Fort Ruckman, Nahant, Mass." Descriptive Book-let of Test Program, American Society of Civil Engineers, Department of the Army, Boston, Mass.,.1948.

"Turf Evaluation - Turf Runway Investigations, Fort Ruckman, Nahant, Mass.," New England Division, Corps of Engineers, U. S. Anny, Boston, Mass., 1949.

"Grounds Construction and Maintenance," AFM 90-1, Department of the Air Force, February, 1949.

"Airport Turfing," U • S. Department of Commerce, Civil Aeronautics Adminis-tration, June, 1949.

"Ecperimental Shoulder Stabilization," Bureau of Materials, State of Illi-nois, Department of Public Works and Buildings, Division of Highways, Report of Committee on Roadside Development, Highway Research Board 30th Annual Meeting, 1951.

13.

Panel on Use of Turf in Soil Stabilization of Shoulders, Slopes and Ditches, Eleventh Short Course on Roadside Development, Department of Landscape Arch-itecture, The Ohio State University, and the Ohio Department of Highways, Columbus, Ohio, April, 1952.

"Performance of Concrete Pavement on Granular Subbase," Highway Research Board Bulletin 52, pp. 27-36 (January, 1952).

45• 'oac1.cIe Vegetative Cover Research Project," Landscape Bureau, New York State Department of Public Works, 1953.'

46. "Roadside Vegetative Cover Research Project,t' Landscape Bureau, New York State Department of Public Works,1954. (in print.)

HRB: M-234