dam construction and facing with soil-cement · dam construction and facing with soil-cement by p....

RESEARCH AND DEVELOPMENT BULLETIN

Dam Construction and Facing

with Soil-Cement

By P. J. Nussbaum and B. E. Colley

t PORTLAND CEMENT 1 ’ ASSOCIATION m

Dam Construction and

Facing with Soil-Cement

By P. J. Nussbaum and B. E. Coney*

SYNOPSIS

This paper reports on laboratory tests to obtain design factors for the application ofsoil-cement in earth dams as slope protection, impermeable barriers, and as an erosion-resistant surface in areas of rapid flow. The stability of embankments constructed withcement-stabilized soils is also considered.

Severity of climatic exposure governs the amount of cement required to stabilizesoil used for slope protection. Current practice of increasing the cement content 2percentage points above that required by standard tests is desirable when the facing inthe splash zone is exposed to freezing. In milder exposures, stabilization with theminimum amount of cement required to make soil-cement may be considered. Whenslope protection is exposed to rapid flow carrying stones or debris, the higher cementcontent and at least 20 percent gravel should be used in the soil-cement.

Soil-cement slope protection constructed in stepped layers will lessen wave run-upas compared to run-up on smooth embankment slopes. Methods to compute waveheight and run-up are presented. Increases in slope steepness result in higher run-up.

Seepage through dams can be reduced by construction of soil-cement upstreamblankets, core walls, or cutoff trenches. Seepage flow in the direction perpendicular tolayering due to construction is considerably less than flow parallel to layering, al-though the use of a thin layer of cement grout at the interface of the compactionplanes will reduce seepage significantly.

Key Words: cement content, cutoff walls, earth dams, erosion control, permeability,seepage, slope protection, soil-cement, triaxial shear, wave run-up.

INTRODUCTION

Cement has been mixed with soil to im-prove the engineering properties of pave-ment bases and subbases for many years.When the cement, soil, and water are pro-portioned to produce a hardened materialmeeting freeze-thaw and brush-loss crite-ria, the product is called soil-cement. It isused in the construction of base coursesand subbases for streets, roads, highways,shoulders, airfield pavements, and parkingareas to provide a firm, durable pavementlayer with considerable bearing strength.Catton( 1)“’* has described the use of soil-cement in road construction over theyears, and Felt(2) has developed test

*Senior Research Engineer and Manager,respectively, Paving Research Section, Researchand Development Division, Portland CementAssociation, Skokie, Illinois.

* *Superscript nlrmbera in parentheses desk-nate references on page 11.

methods and determined property param-eters for a range of soil-cement mixtures.

The superior stability of soil-cementover natural soils with respect to erosion,permeability, and shear strength is desir-able for earth dams. Therefore, it waslogical that soil-cement would be con-sidered for dam construction.

The first use of soil-cement as slopeprotection for earth dams was a test sec-tion on the south bank of Bonny Reser-voir near Hale, Colo., in 1951, At thissite, the material was subjected to severeexposure conditions and tfie adaptabilityof cement-stabilized slope protection forearth dams was established. A view of thesteppe d soil-cement slope protection atBonny Reservoir is shown in Fig. 1. De-tails of construction procedures for soil-cement slope protection are provided in aPCA publication~ 3,

Due in part to this successful applica-tion, the U.S. Bureau of Reclamation

authorized use of soil-cement in 1961 forthe Merritt and Cheney Dams.(4) Grow-ing acceptance of this material is indi-cated by the fact that, to date, soil-cement slope protection has been used inmore than 30 earth dams by both publicand private agencies. It is being used alsoto provide erosion-resistant surfacings fora variety of earth slopes such as canal lin-ings and shore protection, and it has beenfound effective in other parts of dams toprovide impervious cutoff trenches andcores to reduce seepage flow,

Objectives of Test Program

The purpose of this investigation was tosupplement existing data on the field per-formance of soil-cement in dam construc-tion with laboratory data. The specificobjectives were:

1. To determine the effect of variouscement contents on the performance ofcement-stabilized soils under exposureconditions similar to those encounteredby a dam or canal.

2. To obtain wave run-up factors forsoil-cement slope protection.

3, To investigate seepage flow fordams incorporating soil-cement as slopeprotection or as a core wall.

4. To obtain triaxial shear data for usein considering the construction of anearth dam in which all the soils are stabi-lized with cement.

SOILS AND CEMENT REQUIREMENTS

Properties of the soils used in the investi-gation are described. In addition, test pro-cedures and data are presented to indicatemethods used to evaluate cement require-ments for the various types of exposurethat might be encountered in dams orcanals.

Soil Materials

A wide range of ~anular soils has beenused for slope protection. Amounts pass-ing a No. 40 mesh sieve have varied from22 to 95 ‘percent, and amounts passing a200-mesh sieve from 5 to 35 percent.

Three soils were used in this investiga-tion. The A-1-b and A-2-4 soils(s) arerepresentative of the types most fre-quently used for past construction andare considered ideal for stabilization withcement. In addition, an A-4 soil was usedto determine if a fine-grained soil couldbe used for slope protection in locationswhere more suitable materials are not

@ Portland Cement Association 1971

2 Dam Construction and Facing with Soil-Cement

Fig. 1. Soil-cement slope protection.

TABLE 1. Soil Date

I I I I IStandard dry Optimum Percant

AASHO densityjs) moisture L L, Pl, passingpcf content, YO % % 0.074 mm

A-2-4 124.5 10.5 19 4 22

A-1 -b 138.5 7.8 NP NP 10

A-4 114.5 13,2 NP NP 74

NP (nonplastic)

00~~

ASTM Standard Sieve Sizes %k *$~g : g $

‘*I* :

[ I I I I I I I I I I I t I I I

A-4

0

PARTICLE SIZE, m.m,

Fig. 2. Grain-size accumulation curve.

available and economics would permit thesomewhat greater amounts of cementrequired for freeze-thaw durability anderosion resistance. Some of the character-istics of the soils included in this studyare shown in Table 1 and grain-size curvesare shown in Fig. 2.

Cement Requirements for Zones ofExposure

Cement requirements for slope protectionhave varied with the type of soil beingstabilized. For some projects, the require-ment has been established as 2 percentagepoints greater than the percentage neces-sary to meet ASTM(6J wet-dry, freeze-thaw tests plus the Portland CementAssociation(T) brush-loss criteria as usedfor highway applications. On other proj-ects, cement content has been based onthe amount of cement required to givethe soil being considered the same dura-bility as the soils used at the Bonny TestSection. Neither approach considers theseverity of exposure for a given dam loca-tion nor the variations of exposures fordifferent portions of a dam facing.

A more economical design maybe ob-tained if the face is constructed in zones,with materials treated with cement asneeded for each exposure condition. Forthis procedure, the face of the dam isdivided into three exposure zones: (1) thelower portion below the minimum poolelevation that is constantly exposed towater and only very rarely to freeze-thawcycles, (2) the zone between minimumpool elevation and the normal splash zonethat is exposed to severe changes of freez-ing and thawing in the presence of water,and (3) the topmost portion that is gener-ally in a dry state but is exposed to theclimatic environment. It is evident thatzone 2 exposure is most severe, zone 3intermediate, and zone 1 least affected.

To determine the required amount ofcement, laboratory tests were made simu-lating the severity of exposure for eachzone. Specimens were compacted in twolifts at standard density(8) and optimummoisture content. The top lift was placed2 hours after compaction of the bottomlift. This procedure was followed to ob-tain a separation plane with a partialbond similar to the type encountered infield construction. Treatments at theinterface included scarification of thebottom lift prior to placement of the top,spreading a cement grout on the bottomlift, and a wet or dry condition at the

PCA Research and Development Bulletin 3

surface of the bottom lift. In addition, astudy was made of the effects of delaytimes of 24 to 60 hours between place-ment of the top and bottom lifts.

After fabrication, specimens werecured for 7 days in a fog room and thensubjected to exposure conditions. Itshould be noted that the 7-day curingperiod is considerably less than the timethat might be expected in practice be-tween construction and severe exposureconditions. For accelerated exposure, thecyclic treatment for zone 1 consisted of17 hours of drying at 72 F and a relativehumidity of 50 percent followed by 7hours of exposure to a water jet from anl/8-in. -diameter orifice at a pressure of27 psi. This was computed to be a verysevere condition, equivalent to a head of62 ft of water or to the impact of a16-ft-high wave. The water-jet erosiontest was used to simulate the erosionforces of waves on the upstream dam fac-ing. The high water pressure was selectedto accelerate the laboratory testing. Zone2 exposure consisted of 17 hours of freez-ing at minus 20 F and 7 hours of water-jet exposure. Zone 3 exposure was simu-lated by the standard freeze-thaw andbrush-loss tests for soil-cement. All testswere repeated for 12 cycles. The weightloss in percent determined at the end oftest is shown in Fig. 3 for the A-2-4 soil.

For an allowable weight loss of 14 per-cent and a dry interface, the requiredamounts of cement as determined frombest fit lines through the data for zones 1,2, and 3, respectively, were about 0.7,6,and 4 percent by weight. As the zone 2requirement was 2 percent above that forzone 3 and because of the impracticalityof effective stabilization with less than 2percent cement, a practical guide forcement content for zone 3 is the amountof cement determined from standardfreeze-thaw and brush-loss tests; for zone2, this amount plus 2 percentage pointsand for zone 1, 2 percent less than thatrequired from standard tests, but not lessthan 2 percent. Similar tests were madeusing the A-1-b and A-4 soils. Resultsfrom the A-1-b confirmed the findingthat for granular soils a cement content 2percent above that determined by stand-ard tests will meet requirements for thesevere exposure of zone 2. In addition,the results for tests simulating zones 1and 3 confirmed the conclusions shownfor the A-2-4 soil.

The cement requirements for the three

5C

4C

3C

2C

*. [calo-l58

56(9Z34

2

I I I I [

;pl#’f!!

I I I I IZone 2

“\

oZone 3 . 0AboveSplash

7

0

0

c❑ Zone I

\

BelowWater

❑\

●

a

,~.6 .8 I 2 4 68

CEMENT CONTENT BY WEIGHT, “/.

d

Fig. 3. Cement requirements for various exposures.

zones, when using the three soils used inthis investigation, are tabulated in Table2. Based on these data, the current prac-tice of increasing the amount of cement 2percentage points above that required bystandard tests appears warranted; how-ever, it may be possible to achieve econ-omy by reducing cement requirementscurrently used in zones 1 and 3.

The severity of the water-jet exposurewas confirmed by the fact that with theA-4 soil, the water jet bored a holethrough the specimen. Thus, this soilwould not be recommended for use invery severe exposure conditions withoutmodification. One type of modificationof an A-4 soil by the addition of coarsematerial is described in the discussion oferosion resulting from streams carryingdebris.

When the water jet was directed per-pendicular to the compaction plane, noimportant differences in losses due toerosion were observed on any of thematerials for various delay times betweenplacing successive lifts of soil-cement.However, when the jet was directed onthe interface and parallel to it, a signifi-cant reduction of erosion was achievedwhen a cement grout was placed on thebottom lift immediately prior to con-

TABLE 2. Cement Requirements

Cement, % by weightAASHO

Zone 1 Zone 2 Zone 3*

A-2-4 2.0 6.0 4.0

A-1 -b 2.0 5.0 3.0

A-4 5.5 9.5 7.5

*Standard freeze-thaw testing with F’CAbrush-loss criteria.

struction of the top lift even when delaytime between successive layers of con-struction was 60 hours. For example, agrout layer placed at the interface of theA-2-4 soil reduced erosion loss from 14 toabout 4 percent.

Resistance to Abrasion by Water-BorneParticles

Cement-stabilized embankments aresometimes used in locations where swift-flowing, debris-laden streams abrade theslope-protecting materials. The cementand gradation requirements necessary toresist this erosion were investigated byexposing test specimens to flows of watercarrying 1/8- to 1/4-in .-size gravel. Speci-


237 t Fl(

i

PMo 2 4 6 8 10 1’ 14

CEMENT CONTENT BY WEIGHT, “A

I I I1

I b“’$“n, Flow 4.2 Tons

Gravel per Day1=+ ,

0GRAVEL CONTENT BY WEIGHT, ‘%

Fig. 4. Erosion resistance of stabilized soils.

mens were subjected to the abrasion testafter 7 days of fog-curing. Approximately8,000 gal of water per day carrying 4.2tons of gravel flowed at 3.8 ft per secondin a 1-in.-wide by %-in.-deep streamacross a specimen. To achieve maximumabrasive action, the flow rate was low andthe stream of water was directed so thatthe gravel was carried in the lower por-tion of the flow.

Results from tests simulating streambank erosion are shown in Fig. 4 as plotsof time for 1-in. depth of erosion, Theupper curves show the effect of cementcontent on abrasion resistance of theA-1-b and A-4 soils. The lower curvesshow the effect of the gravel component(plus %-in.-size component of the soil-cement materials). It is seen from Fig. 4that the erosion resistance of the A-1-bmaterial was excellent and superior to theA-4 soil for all cement contents tested.The time required to wear away a depthof 1 in. of A-4 material was less than twodays even when the cement content was13.5 percent. In contrast, the A-1-b soilexhibited good erosion resistance. Whenthis soil was stabilized with 5 percent

cement, it took 15 days to erode a depthof 1 in.

Because of the better performance ofthe granular soil, additional tests weremade by scalping various amounts ofgravel from the A-1-b soil and by addingmaterial greater than ?4 in. to the A-4material. Results from these tests showthat the percentage of gravel affects abra-sion resistance significantly. For example,the time necessary to erode 1 in. of themodified A-4 soil-cement was signifi-cantly increased when the gravel com-ponent was more than 20 percent byweight. In fact, at 30 percent gravel and9.5 percent cement, the modified A-4 soilwas almost as resistant to erosion as theoriginal A-1-b soil.

Gravel erosion tests were also made ona special low-strength gravel concrete toobtain a rough concept of the severity ofthe test. The water-cement ratio was 0.6for this 2,000-psi, 28-day-strength con-crete. After 7 days of moist-curing, thisspecimen was exposed to the water-borne-gravel test. Thirty-three days wererequired to erode away 1 in. of material,Thus, the abrasion resistance of this con-

crete was about double that of the A-1-bsoil-cement at 7 percent cement, and itwas concluded that the water-bornegravel test greatly accelerated abrasion.

The influence of strength gain by agingwas evaluated by increasing curing timefrom 7 to 28 days. The abrasion resist-ance of the soil-cement made with theA-4 and A-1-b soil stabilized with 7.5 and3 percent cement by weight, respectively,increased by 50 percent. When exposedfor 6 days to a stream of water only (thatis, a flow not carrying gravel) at a rate of16,000 gal per day, no erosion was ob-served for the A-4 and A-1-b soil stabi-lized with 1.5 and 0.75 percent cement,respectively. This indicates that flows notcarrying debris will of themselves havelittle or no erosive effect on soils stabi-lized with even minimal amounts ofcement. Soil-cement canal linings aregenerally only exposed to flows not car-rying sand and gravel loads or debris andthus may be constructed with the mini-mum amount of cement as determinedfrom standard tests.

WAVE RUN-UP

Besides providing erosion protection, adam facing may function as a buffer bybreaking wave action and reducing waverun-up. Embankment slope and theroughness of the slope facing material areboth important factors in establishingheight of the dam above maximum poolelevation. Run-up factors for soil-cementslope facings were determined experimen-tally in a wave tank.

Wave-Tank Tests

Reduced scale soil-cement test slopeswere constructed at one end of a30-ft.-long wave tank. The tank was 12in. wide and 36 in. deep, with the depthof water maintained at 21 in. Waveswereformed with a piston-type wave genera-tor. The height of wave and the waveperiod were varied by changing the traveldistance and velocity of the piston bulk-head, The water depth to wave heightratio (D/H) was equal to or greater than 3at the toe of the structure for all tests.Test variables were slope of the embank-ment and roughness of the slope facing.

Soil-cement slope facing configura-tions representing different degrees ofsurface roughness were tested for em-bankment slopes of 1 on 3 and 1 on 2.The 1 on 3 slope was constructed in in-

PCA Research and Devekprnent Bulletin 5

‘-’ crements of 1-in. -thick layers, with a 3-in.setback for each successive layer. In addi-tion, tests were made using 2-in. layerswith 6-in. setbacks. Surfa=e roughnessvaried as a function of the type of edgeon the slope; both a sharp-edge and arounded-edge condition were tested. Afacing made of concrete finished with awood float was considered representativeof a smooth surface, and data from thistest are used as a basis for comparisonwith data obtained from the soil-cementfacings.

A photograph of a test in progress isshown in Fig. 5; the type of measure-ments obtained is illustrated in Fig. 6. Inthis figure, wave height, H, is the verticaldistance between peak and trough of thewave train; the run-up, R, is the verticalprojection of the distance the water flowsup the slope measured from the stillwater elevation; and the wave period, T,is a measure of the time between succes-sive wave peaks,

The ex~erimental data are reported inFigs. 7 and 8 and nondimensional plots ofthe run-up factors R/H versus wave steep-ness H/~ where L, the wave length, is

“-’-’ equal to 5.12P. About 110 individualwave run-up tests were used as the basisfor drawing the best-fit curves. The stand-ard error of estimate was 0.13. In termsof wave run-up, this represents about 0.6ft for a 5-ft -high wave.

Recalling that freeboard height re-quirements decrease as the run-up factordecreases, it is apparent that all of thesoil-cement facin-gs inhibit run-up. Asexpected, both the 2 on 6 and 1 on 3sharp-edged configurations were moreeffective in reducing run-up than the 1 on3 rounded edge. Also, the 1 on 3 configu-ration was more effective than the 2 on 6.

In practice, the rounded edge resultsfrom erosion of inadequately compactedmaterial at the upstream face of the lift.The inadequate compaction is due to lackof confinement at the edge during rollingoperations. Because of the considerablybetter performance of the sharp edge,full-scale compaction tests were madeusing a pan vibrator to determine if it wasfeasible to construct an edge that wouldbe more resistant to erosion. It was deter-mined that soit-cement made from theA-2-4 and A-1 -b soils used in this study

‘-- was readily compacted to 100 percent ofstandard density with a pan vibrator. Inaddition, vibratory compaction of thesesoils contained within a movable wooden

Fig. 5. Wave run-up on soil-cement.

H = Wave Height L = Wove Length

R = Wave Run. iJp T ❑ Wave PeriodS= Slope

Fig. 6. Wave run-up measurements.

2.5 , [ I I I I I 1 I I I I n

‘~’10n2Rounded

)

Ionzlon3

Rounded> Sharp

\

‘1\

\ \

\

>

\10n3

Shorp\

\

\

\ ‘~-

~J.03 .04 .06 .08 .1 .2 .3 .4 .6

WAVE STEEPNESS FACTOR, H/T*

Fig. 7. Wave run-upon soil-cement slope facing.


2.0

.7

I I I I I I

lon3Rounded

2on6Shorp

lon3Sharp

t 1I I I I I I I I I I I I

.03 .04 .06 .08 ,1 .2 .4 .6WAVE STEEPNESS FACTOR, HIT 2

Fig. 8. Effect of slope steepness on wave run-up.

form produced a sharp edge with anequally high degree of compaction. Vibra-tion of a second lift on top of a newlyplaced bottom lift did not crack the bot-tom layer. It would appear that a trialfield installation should be considered.

In addition to the significance of sharpversus rounded edges, the data showedthat the larger steps of the 2 on 6 slopewere not as effective in reducing run-upas the smaller but more frequent steps ofthe 1 on 3 slope. Also, as shown in Fig. 8,the 1 on 3 slope was considerably moreeffective than the steeper 1 on 2 slope.

Analysis of Run-Up Data

To illustrate the use of the data in Fig. 7,the following sample computation is pre-sented for determination of freeboardheight.

A 1 on 3 rounded slope is assumed fora reservoir with:

Fe = effective unobstructed fetchlength, 19,000 ft

F. = total fetch, 8 milesV= wind velocity over water, 93

ft/sec or 63.5 mphD = average depth of reservoir, 50 ftg = 32.2 ft/sec2

Wave height H is computed from theBretschneider revision of the Sverdrup-Munk equation, weighted for data frominland reservoirs as presented bySaville19J

H=;[0.0026@)0”47] =,ft

Wave period T is also computed from

the Bretschneider equation, weighted fordata from inland reservoirs as presentedby Saville.t9)

‘=:E’46(%)””21=44S’CThe wave height and period are used

to calculate a value of 0.26 for wavesteepness, H/T’. Entering Fig. 7 with awave steepness of 0.26, a value for R/Hof 1.25 is obtained; therefore the waverun-up for a 5.1-ft-high wave is 6.4 ft.

Freeboard height to prevent overtop-ping is measured from the maximumoperating pool elevation and consists of arequirement for wave run-up, R, plus aheight for wind-tide effects, S, that iscomputed from the equation:f9J

V’F8— = 0.45 ft; use 0.5 ft

s = 1,400D

Adding wave run-up and wind-tidevalues gives a freeboard requirement of6.9 ft. In the same manner, freeboardrequirement is computed to be 5 ft forthe sharp-edged soil-cement and 7.6 ft forthe smooth concrete.

SEEPAGE THROUGH DAMS

Seepage is an important consideration inthe stability of earth dams. Seepage canbe controlled by proper selection of em-bankment soils, by drainage methods, orby construction of impervious barriers.Flow of water through the dam can beinhibited by construction of relatively im-

permeable zones such as cores, cutoffs, orupstream blankets. The materials for theimpermeable zones are generally selectedfrom the least permeable soils near thedamsite. However, in areas where lower-permeability soils are not available, it ispossible to reduce permeability by stabili-zation with cement.

Test data are reported to show the ef-fects of cement content and delayed com-paction time on permeability. Becauseshrinkage cracks develop in soil-cementslopes, data from model tests are used toillustrate the influence of cracking onseepage.

Permeability

To facilitate testing with the flow ofwater directed both normal and parallelto the compaction plane, constant headpermeability tests were made in speciallycons tructed square molds. Specimenswere compacted dynamically in two liftsto standard density( 8, at optimum mois-ture content, then cured in a fog roomfor 7 days prior to testing, The effects ofcement content and direction of flow onpermeability of the A-1-b, A-2-4, and A-4soils for conditions of no time delay be-tween compacting the lifts are shown inTable 3.

For these soils and test conditions per-meability decreased as cement contentincreased, For example, when the cementcontent met standard soil-cement require-ments, tests normal to the compactionplane gave permeabilities that were only1,2 to 12 percent of the values for thesoils without cement. When the flow wasparallel to the compaction plane, perme-abilities were reduced also as cement con-tent was increased. However, permeabili-ties for flow parallel to the compactionplane were 2 to 20 times larger thanvahres for flow normal to the compactionplane.

To simulate field construction prac-tice, tests were made also on specimensprepared with a time delay between com-paction of the two layers. For time delaysof O to 6 hours and flow normal to thecompaction plane, permeabilities wererelatively unchanged from the valuesreported in Table 3. However, as shownin Table 4, when the flow was parallel tothe compaction plane permeability in-creased with increased time delay. Forexample, permeabilityy for the A-2-4 soilstabilized with 3 percent cement byweight increased from 0.4 to 1.2 ft per


year when the time delay was varied from TABLE 3. Permeability, Ft/Yr, No Time Delay Between LiftsO to 6 hours. Similarly, for the A-1-b soilstabilized with 3 percent cement, perme-ability increased from 0.6 to 12 ft peryear. In the last example, the applicationof a neat cement paste to the bottom liftjust prior to placement of the second liftreduced permeabilityy to a value compar-able to that obtained for flows normal tothe compaction plane. Although not aseffective as the cement paste layer, seep-age was also reduced by a mechanicalprocess. In this method, the surface ofthe bottom lift was scarified to a mini-mum depth of about 0.5 in. with a spike-tooth instrument. The second lift wasthen compacted on top of the first lift toobtain an interlocking of the two layers.

Cement content,% by weight

o

1

3

5

7.5

9.5

11.5

A-l-b

7Normal

3.0

0.7

0.07

0.01

Perallel

2.3

1.1

0.6

0.1

—

—

A-2-4

Normal

0.5

0.06

0.02

0.02

—

—

Parallel

1.0

0.2

0.4

0.2

—

—

40.5

0.3

0.2

0.1

0.06

0.05

0.03

I

Parallel

1.2

—

0.4

—

0.1

0.08

SeepegeTABLE 4. Permeability, Ft/Yr, Time Delay Between Lifts

Seepage tests were made in a model flumeto determine the effect of cracks in animpervious upstream blanket on theamount of flow through the retainingstructure. In addition, the effectiveness ofcutoff trenches was evaluated. The modelflume was 7 ft long, 1 ft wide, 2 ft deep.Permeability coefficients of materialsused in the model flume tests were 3 X106 ft per year for the embankment, k,,and 3 X 104 and 3 X 103 ft per year fortwo facing or cutoff materials, kc.

Seepage rate measurements to deter-mine the effect of cracks were made for2.5 to 1 embankment slopes with thewidth of crack opening varied from 0.03to 0.25 in. by a metal frame and gageblock system. Results of the seepage testsare expressed in Fig. 9 in terms of per-centage of crack area to solid upstreamfacing and in percentages of increasedflow when compared to seepage quanti-ties in the absence of a formed crack.Tests were made for two conditions: (1)for a dam on impervious foundation, and(2) for a dam with cutoff trench extend-ing from base of dam to a lower imper-vious boundary. It is noted that flow in-creased exponentially from 3 percent to150 percent as crack area was increasedfrom 0.2 to 2.5 percent.

To interpret these data, it is necessaryto consider field observations from in-service facings that show shrinkage crackopenings of 1/8 to 1/4 in. at spacings of 9to 18 ft. Assuming the larger opening atthe shorter spacing gives an open area ofonly 0.23 percent of the slope. EnteringFig. 9 with 0.23 percent open area yieldsan increased seepage quantity of about 5

A-l-bCement content,

A-2-4 A-4Delay

YO by weight hours Normal Parallel Normal Parallel Normal Paral Iel

o 0.7 1.1 0.061

0.2 – –

6 0.8 13 0.08 0.9 – –

o 0.07 0.6 0.02 0.4 0.2 0.43

6 0.06 12 0.03 1.2 0.2 0.5

0 – – 0.02 0.2 – –5

6 – – 0.01 2.1 – –

o – – – – 0.06 0.17.5

6 – — — — 0.05 2.0

[ I I I I I I II I I I

200 -o*

I

~-1 40ILz

w(na 20wa,vz

10:1 /’Ao

A

1 0 kc/kc E 100

6

H

● kc/kc = 10000

A ke/kC s 1000 PIUS CutOff4 m 1

I,-

3J 1 I I I I Ill I I I I.1 .2 4 .6 .8 I 2 4

OPEN AR EA, %

Fig, 9, Effect of crack opening on seepage.


I 00

s 80 –>-1- Cedergren

1= . ●

~060 –

w0g 0

u ●

% 40 —w>~

g 20 — o Below Core

● Below Upstreom Blonket

o

20

w“

40 ~ww07

o~o 20 40 60 so 100

PENETRATION OF PERVIOUS STRATUM “lo

Fig. 10. Effectiveness of cutoff trench.

‘L;1~’00L!!2.uv’

E kc/kc

2 50 2

w 20E! 100 +1s

10000

0 50 100 150 200 250 300LENGTH, ft.

Fig. 11. Effectiveness of core wall in lowering saturation line.

percent. This indicates that increases inflow due to shrinkage cracking of the soil-cement are probably not significant.Therefore, when the permeability of thefacing is less than the permeability of theinterior, the facing contributes to damstability.

Results from seepage flow tests toevaluate the applicability of soil-cementas a cutoff trench are plotted in Fig. 10.These data are forapermeability ratio ofpervious foundation to cutoff trench of50 and for designs where the cutoffs ex-tend downward below a core or belowthe toe of an upstream blanket. The datapoints agree well with the work of Ceder-grenf 1‘) and demonstrate that seepagethrough pervious dam foundations can bereduced significantly by construction ofsoil-cement cutoff trenches.

Core walls can be constructed fromsoil-cement concurrently with placing andcompacting the earth embankment. Theresulting lowering of the saturation line

depends on the permeability ratio of theembankment soil to the cement-stabilizedcore and has been computed on the basisof equations presented by Pavlovskyt11Jfor an example of a 100-ft-high dam withan average core width of 20 ft. As shownin Fig. 11, the saturation line is loweredsignificantly for embankment to core per-meability ratios greater than 20, Lower-ing the saturation line enhances the stabil-ity of the dam and increases the econom-ic benefits by reducing seepage losses.

Rapid Drawdown

Provisions for drainage in back of rela-tively impermeable upstream slope pro-tection blankets need only be made forunusual operating conditions where rapiddrawdown could lead to piping failure.One method of designing an upstreamdrainage layer requires calculation of thetime, t,required to lower the saturationline within the embankment:( 1z)

whereC’= correction factor, 1.0

n== effective soil porosity, 0.20k = coefficient of permeability,

35 ft per yearL = length from upstream toe to

downstream drainage struc-ture, 500 ft

H = height of saturation lineabove base of dam, variable/increment

Hi= drawdown, 120 ft

()F # = function of saturation linei elevation to magnitude of

drawdown (obtained fromgraphs in Reference 12)

This equation applies to homogeneousearth dam embankments constructed onan impervious foundation. The valuesassigned to the various factors were usedfor the following example of applicationof the drawdown expression. A solutionfor the time required to incrementallylower the saturation line and a plotting ofits loci for four stages of drawdown, asindicated by the H/H~ ratio in percent, isshown in Fig. 12. For an embankment ofa very fine sand and silt with a k value of35 ft per year, the time to lower the satu-ration line by 40 percent of total draw-down was 300 days; it was about 8 hoursfor a sand with a k value of 3.5 X 104 ftper year. The coefficients of perme-ability, k, used in this example are usedsolely to illustrate the nature of the cal-culations and are not intended to berepresentative of the types of materials tobe used in a 150-ft high dam. For a damwith the dimensions shown in Fig. 12 andan embankment with a k value of 3,5 X103 ft per year, the amount of water, Q,drained toward the upstream slope fromthe center of the dam is about 340 cu ftper day when the line of saturation islowered 20 percent. The greatest flowrate, 360 cu ft per day, was noted for theincremental lowering of the saturationline from 20 to 40 percent. This greatestrate of flow is used for the design of thedrainage layer in accordance with theequation:

The head, h, for this example is 10 ft,


which is conservative. A sand and gravelwith a k value of 3.5 X 10Gft per year isselected for the filter blanket, The lengthof the drain, L, is about 350 ft and thevalue of Q/t is 360 cu ft per day. Thethickness of the drainage layer at the up-stream slope is thus about 1.3 ft. How-ever, from construction considerations aminimum thickness of 2 to 3 ft may berequired.

The integrity of soil-cement slope pro-tection without a drainage layer is assuredfor earth dams when the reservoir operat-ing conditions preclude sudden draw.downs that would create pressures greaterthan those that can be counterbalancedby the weight of the soil-cement. Whensudden drawdowns are expected, a drain-age layer is required for all types of slopeprotection. The soil-cement slope protec-tion placed over the drainage layer pro-tects it from becoming clogged by debrisand suspended fines carried in the waterand also protects it from displacement bywave forces.

CEMENT-STABILIZED DAMS

Stabilization with cement of the entiredam embankment can result in significantsavings in materials. The considerable in-creases in compressive and shear strengthof soils stabilized with even smallamounts of cement can be exploitedthrough the use of steeper slopes, result-ing in a reduction of the total volume ofmaterial handling and placing as well as inconstruction time. Additional advantagescan be gained by a reduction in the lengthof diversion structures and spillways.Also, overtopping due to unexpectedflooding during construction or duringthe life of the structure would not be dis-astrous, as it might be for an embank-ment compacted with unstabilized soils.

Triaxial Strangth

Triaxial strength tests were made on2.8x5 .6-in. cylindrical specimens com-pacted to standard density(’) at optimummoisture content. Specimens were curedin a fog room at 72 F until testing. Thetriaxial tests were undrained with a rateof loading such that the test was com-pleted in about 10 minutes. Even at thelowest cement contents, the total strainat failure was less than 2 percent. Datafrom the triaxial tests on the untreatedand cement-stabilized A-1-b, A-2-4, andA-4 soils are presented in Tables 5 and 6.

H XlooR

?!*- —● 20 % 100 days~ 40 % 300 1’a 50 “10 900 S*6 80 % 3000 ‘*

* For Homogeneous Embonkmeniwith k = O. I ft./cloy

I L= 500’I

Fig. 12. Nonstaady stata of flow for rapid drawdown.

TABLE 5. Triaxial Strangth and Cament ContentAfter 28 Days Curing

3 58 44A-2-4

4 70 44

6 90 48

8 100 49

0 10 38

‘-l-b~4 72 52

5 95 55

0 5 37

2,5 30 46

A-4 5.5 65 45

7.5 85 45

9.5 125 45

The stabilized soils showed substantialincreases in the coefficient of internalfriction and cohesion when compared tothe untreated soils. It was noted that co-hesion increased with either cement con-tent or curing time. Also, considerable in-creases in the angle of internal frictionvalues were observed when the stabilizedsoils were compared with the untreatedsoils; however, only small changes werenoted when the amount of cement used

to stabilize the soil was varied. The in-creases in cohesion with increasedamounts of cement is significant in con-siderations of slope steepness and stabil-ity.

The data from triaxial tests after 28days of curing were used to compute theslope angle, i, permissible for cement-stabilized embankment construction. Theslope angle was computed based on a sub-merged case and analyzed as a simple


TABLE 6. Triaxial Strength and Curing Time

Soil Percent cement Cohesion, Slope an Ie,

8

Age,by wt. psi deg, days

2 10 43 7

2 50 41 28

2 40 40 90A-2-4

6 75 48 7

6 90 48 28

6 95 53 90

1 12 47.5 7

1 27 45.5 28

1 35 45,5 90A-1 -b

3 33 49 7

3 50 51 28

3 85 46 90

I I Io

80 -A-l-b

6

:60 -0

i

z

w

: 40 --1(n

20 Height of Dom = 150 ft.

Submerged Cose

o F. S.:+= 3; Cd=6

2.5 25 43 7 01 I I I Io 2 4 6

2.5 30 46 28 CEMENT CONTENT BY WEIGHT, %

lEE+== ‘nkments”Fig. 13. Allowable slopes for cement-stabilized

slope with circular failure, having a safetyfactor of 3 for friction angle and 6 forcohesion. The relationships between slopeangle and percent cement are shown inFig. 13. It is seen that by stabilizing thesoils with only 2 percent cement byweight, the allowable slope angle is about54 deg for the A-l-b and A-2-4 soils andabout 38 deg for the A-4 soil. These rela-tionships were used to compute the vol-ume of material required to build a150-ft-hig,b dam for comparison with thevolume of material required for the sameheight dam made of unstabilized materialon a 3 to 1 slope. In Fig. 14, it is seenthat the volume of material placed andcompacted in a dam section may be re-duced by 60 to 70 percent when 2 per-cent cement by weight is used to stabilizesoil materials of the type used in thisinvestigation.

CONCLUSIONS

1. A wide range of granular soils hasbeen used successfully for soil-cementslope protection in earth dams. Data fromthis investigation show also that fine-grained, nonplastic soils can be usedwhere more suitable soils are unavailable

8

em-

,ooo~3

CEMENT CONTENT BY WE IGHT, Ofo

Fig. 14. Embankment volume for cement-stabilized soils.

and economics permit use of the greateramounts of cement required for dura-bility and erosion resistance.

2. Cement requirements for variousportions of a dam facing may be variedwith exposure. Requirements for surfacesexposed to freezing in the splash zone areabout 2 percentage points greater thanthose determined from standardtestsl 6J7J Areas exposed to freezing, butabove the splash zone can be stabilizedwith the amount of cement required by

standard tests. Those areas not exposedto freezing can be stabilized with about 2percentage points less than that requiredby standard tests, but not less than a totalof 2 percent.

3. When soil-cement is used in areasexposed to rapid stream flow carryingsand or gravel or other debris, the cementcontent should be 2 percentage pointsgyeater than the minimum required bystandard tests. In addition, the soil se-lected should have a gravel component


exceeding 20 percent. When exposed toflows without debris, such as canal lin-ings, the amount of cement may be theminimum required by standard tests andthe material need not have a gravel com-ponent.

4. Wave run-up factors were obtainedfor soil-cement slope facing materials.Slope profiles that inhibited wave run-upto the greatest extent were those withsharp-edged steps. Run-up factors for aconcrete slope were about 1.5 timesgreater than those for sharp-edgedstepped surfaces. Run-up factors for steepslopes are greater than those for flatterslopes. Sharp-edged steps can be con-structed with granular soils using a panvibrator and a sliding form on the up-stream face.

5. The permeability of soils generallyused for dam facing is reduced consider-ably when stabilized with cement. Whensoil-cement is to be used for imperviousbarriers, scarification of the bottom liftwith a spike-tooth instrument to a mini-mum depth of 0.5 in. and removal of theexcess material prior to compacting thenext lift will decrease seepage at the inter-face. A thin neat cement grout placedbetween the horizontal lifts reduced seep-age to an amount equal to that deter-mined from permeability tests made withthe flow perpendicular to the compactionplane.

6. Shrinkage cracks in upstream soil-cement facings do not increase seepagethrough the dam by appreciable quanti-ties when compared to a condition with-out cracks. Cutoff trench excavations andplacement of the impervious cutofftrench materials should be carriedthrough pervious foundation layers.

7. Triaxial strength factors and there-fore the stability of slopes of embank-ments built with cement-stabilized soilsincrease with cement content and age.When compared with untreated soils,both the angle of internal friction and co-hesion increased considerably even whensmall amounts of cement were used.

8. Volume of dam embankments canbe reduced when the entire embankmentis constructed with soils stabilized withsmall amounts of cement.

REFERENCES

1. Catton, Miles D., “Early Soil-Cement Research and Develop-

ment,” Proceedings of the Ameri- 12. Browzin, B. S., “Nonsteady-Statecan Society of Civil Engineers, Flow in Homogeneous Earth DamJournal of the Highway Division, After Rapid Drawdown~’ Proceed-Vol. 85, 1959, pages 1-16. ings, Fifth International Confer-

2. Felt, E. J., and Abrams, M. S., ence on Soil Mechanics and Foun-“Strength and Elastic Properties of dation Engineering, Vol. 2, 1961,Soil-Cement Mixtures,” ASTM pages 551-554.Special Technical Publication No.206, American Society for Testingand Materials, 1957, pages152-178.

3. Soil-Cement Slope Protection forEarth Dams: Construction, Port-land Cement Association, 1967.

4, Holtz, W. G., and Walker, F. C.,“Soil-Cement as Slope Protectionfor Earth Dams,” Proceedings ofthe American Society of CivilEng”neers,Journal of Soil Mechan-ics and Foundations Division, Vol.88, 1962, pages 107-134; and“Discussion” by Sellner, E. P.,Vol. 89, 1963, page 220.

5. American Assoctition of StateHighway Officials Publication No.M 145.

6. Book of ASTM Standards: (a)

ASTM D 559-57, 1965, “Wetting-and-Drying Test of CompactedSoil-Cement Mixtures”; (b) ASTMD 560-57, 1965, “Freezing-and-Thawing Tests of Compacted Soil-Cement Mixtures”; (c) ASTM D1632-63, “Making Soil-CementSpecimens in the Laboratory”;American Society for Testing andMaterials, Philadelphia.

7. Soil-Cement Laboratory Hand-book, Portland Cement Associa-tion, 1959, pages 28-31.

8. Book of ASTM Standards: ASTMD 558-57, 1965, “Moisture-Den-sity Relations of Soil-Cement Mix-tures.”

9. Saville, Thorndike, Jr., McClen-don, E. W., and Cochran, A. L.,“Freeboard Allowances for Wavesin Inland Reservoirs,” Proceedingsof the American Society of CivilEn@”neers,Journal of the Water-ways and Harbors Division, 1962,pages 93-124.

10. Cedergren, H. C., Seepage, Drain-age, and Flow Nets, John Wiley &Sons, New York, 1967, page 213.

11. Pavlovsky, N. N., and Davidenkov,R. N., “The Percolation of WaterThrough Earthen Dams,” 1‘RCongres des Grands Barranges,1931, pages 193-208.

This publication is based on the facts, tests, and authorities statedherein. It is intended for the use of professional personnel com-petent to evaluate the significance and limitations of the reportedfindings and who will accept responsibility for the application of thematerial it contains. Obviously, the Portland Cement Associationdisclaims any and all responsibility for application of the statedprinciples or for the accuracy of any of the sources other than workperformed or information developed by the Association.

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I KEYWORDS: cement content, cutoff walls, earth dams, erosion control, per- ~II meability, seepage, slope protection, soil-cement, triaxial shear, wave run-up. ~iI ABSTRACT: Discusses laboratory tests to obtain design factors for applica- !II tion of soil-cement in earth dams as slope protection, impermeable barriers, ~II and erosion-resistant surfaces in areas of rapid flow. Also discussesstability of ~II embankments constructed with cement-stabilized soils. Methods to compute ~II

wave height and run-up are included. II

II REFERENCE: Nussbaum, P, J., and Coney, B. E., Dam Construction and ~II Facing with Soil-Cement (RDO1O.OIW),Portland Cement Association, 1971. ~II

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PCA RID Ser. 1441

mlPORTLAND CEMENT I I ASSOCIATIONAn organization of cement manufacturers to improve and extend the uses of port land cement and concrete through scientific research, engineering Iiild work, and market denlopment,

Old Orchard Road, Skokie, Illinois 60076

Printed in U.S.A. RDOIO.01 W

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