SEEPAGE CONTROL IN CONCRETE-LINED

IRRIGATION DITCHES *

G. E. LaliberteMember C.S.A.E.

by

E. RappMember C.S.A.E.

Research Station, Canada Department of Agriculture,Lethbridge, Alberta

N. Paziuk

INTRODUCTION

Approximately 7.5 percent of theirrigable land in southern Alberta, or50,000 acres, has been salinized because of seepage from canals andditches. This seepage can be effectivelycontrolled by lining the canals andditches with relatively impermeablematerials. Polyethylene and compactedclay have been the most popular liningmaterials in southern Alberta. Exceptfor a few isolated cases, concrete hasnot been used, probably because of itshigh initial cost and a lack of knowledge of its performance under thewidely fluctuating temperatures of thechinook climate in the area.

In 1914 a half-mile of concretelining was manually placed in a canalnear Strathmore, Alberta, by the Canadian Pacific Railway (5). In 1966the lining appeared to be still in goodcondition but no quantitative information on its effectiveness in seepagecontrol is available.

In 1950 a 964-foot section of canalnear Swift Current, Saskatchewan, waslined with shotcrete (pneumaticallyapplied mortar) as part of a studyundertaken by the Prairie Farm Rehabilitation Administration (PFRA)ott canal and dugout linings. In 1953,both precast concrete slabs and 'cast-in-place' concrete linings were installedin a 450-foot section of canal nearOutlook, Saskatchewan, under thePFRA program. Periodic reports (1,2, 3, 4) indicate that shotcrete liningcontrolled seepage and was particularlyeffective when reinforced with wiremesh. The unreinforced sections werebeginning to deteriorate, and the use ofsteel reinforcement was strongly recommended for concrete lining incanals and ditches. Shotcrete, precastconcrete slabs, and 'cast-in-place' concrete, although effective in lining canalsand ditches, all had high initial costs.

Since 1946 the United States Bureauof Reclamation has conducted a research program aimed at reducing thecost of seepage control (7). The result

ing relaxation of specification standards and elimination of reinforcingsteel to permit greater mechanizationof placing equipment have made iteconomically feasible to line smallcanals and ditches in the United States.

In the opinion of the authors the 50-foot expansion joint intervals in theshotcrete lining of the Swift Currentcanal were responsible for much of theuncontrolled cracking between joints.With the use of shorter intervals andthe elimination of reinforcing steel animproved concrete lining could be constructed at reduced cost. Consequentlya study was undertaken in 1963 todetermine the performance, under theclimatic extremes of southern Alberta,of unreinforced concrete ditch liningnlaced with a subgrade-guided slip-form.

MATERIALS AND METHODS

A farm ditch in a recently developedirrigated pasture near Hays, Alberta,was selected. The loam soil there isrepresentative of much of the irrigatedarea in southern Alberta. In October1963, 1550 feet of unreinforced concrete lining were placed directly on thissoil without gravel underlay, using asubgrade-guided slip-form. The designspecifications for the completed ditchwere: bottom width 18 inches, sideslopes 1.14 to 1, depth 18 inches,slope 0.001, capacity 6 cfs, and liningthickness 3.6 inches.

Before the concrete was placed theditch was shaped to the desired crosssection with a specially constructedbucket on a truck-mounted hydraulicexcavator. The slip-form used in placing the concrete lining was towed bya crawler tractor (figure 1). Concretewas hauled to the slip-form by transitmix trucks from a mixing plant temporarily set up at the site (figures 2 and3). Expansion joints were made at10-foot intervals using a template anda grooving tool (figure 4). After placement the concrete was moist-curedunder a polyethylene film. The expan

CANADIAN AGRICULTURAL ENGINEERING, JAN. 1967

sion joints were later filled with asealing compound.

The coarse aggregate used in theconcrete mix was well graded but onthe fine side of the limits for a 1 Vi -inch

Figure 1. Subgrade-guided slip-form being towed inshaped ditch by crawler tractor.

Figure 2. Front view of slip-form showing fillingoperation.

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Figure 3. Rear view of slip-form showing freshlyplaced concrete lining.

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Figure 4. Construction of expansion joints using template and grooving tool.

maximum size aggregate as specifiedby the Canadian Standards Association(CSA). The fine aggregate was aslightly coarse sand having a minordeficiency in sizes between the No. 50and No. 200 sieves. The weight ratioof sand to total aggregate in the mixwas 0.43.

The weight ratio of water to cementwas 0.47, about the maximum recommended by CSA for thin concrete sections in a severe or moderate climateand within the influence of fluctuatingwater tables. A 2-inch slump providedthe most suitable compromise betweenworkability and bank stability at the4 to 5 percent air content maintained

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in the mix. The unit water requirementwas 245 pounds per cubic yard andso, with a water to cement ratio of0.47, the cement factor was 6 sacksper cubic yard.

Tests for slump and air content weremade as the concrete was produced.Compressive strength and freeze-thawtests were carried out on cylinders andbeams which were molded during mixing.

Inspections and ponding tests werecarried out annually or oftener to determine the performance of the concrete lining in controlling seepage. Ateach inspection the location and orientation of new cracks between the expansion joints were recorded. In eachponding test, seepage losses were determined from the drop in the level ofwater ponded between checks in theditch. Seepage losses (corrected forevaporation during tests) were compared with those measured in a ponding test prior to lining. For comparisonthe ditch was divided into seven approximately equal sections.

RESULTS AND DISCUSSION

Slump tests during the mixing operation gave slump values from \Va to3Vfi inches. This moderate variabilityin slump was attributed to non-uniformity of the moisture content ofthe fine aggregate and to difficulties in

accurately measuring the water. Goodcontrol of air content was obtained;measured values were between 4.5 and5.0 percent for all tests.

The 28-day compressive strength ofsix out of seven test cylinders exceeded4800 psi. In the seventh cylinder failureoccurred at 3440 psi and was probablyrelated to the unusually high 3V2-inchslump of that batch. However, all sevenvalues are considered adequate for concrete ditch lining.

Tests on three beams indicated thatthe concrete would perform very wellunder freeze-thaw conditions. According to a system used by PFRA (6)for evaluating freeze-thaw resistance,this concrete was classified as fair togood on the basis of weight loss duringthe test and excellent on the basis ofdurability factor.

The results of inspections and ponding tests are presented in tables I andII. Only data on cracks appearing between the expansion joints are includedin table I. The November 1963 inspection was conducted about six weeksafter construction. The cracks observedthen were probably the result of shrinkage. The total length of cracks betweenexpansion joints increased each year. Aspectacular increase in cracking in the

TABLE I. CUMULATIVE LINEAL FOOTAGE OF CRACKS IN CONCRETE

(EXCLUDING CRACKS IN EXPANSION JOINT GROOVES)

Date of Ditch section

inspection 1 2 3 4 5 6 7 1-7

Nov. 27, 1963 24 6 — _ 3P

Apr. 27, 1964 39 6 6 2 2 .— 5 60

Sept. 28, 1964 44 12 12 9 2 — 9 88

Apr. 28, 1965 83 14 16 9 3 — 12 137

May 4. 1966 132 65 70 9 4 12 292

TABLE II. SEEPAGE LOSSES IN CUBIC FEET PER SQUARE FOOT OF WETTEDPERIMETER PER DAY

Date of Ditch section

ponding tesl 1 2 3 4 5 6 7 1-7

Sept. 17-19, 19631 0.25 0.30 0.34 0.52 0.23 0.34 0.40 0.34

Sept. 15-21, 19642 0.07 0.07 0.07 0.04 0.02 0.02 0.10 0.06

Oct. 8-13, 1964 0.04 0.04 0.05 0.01 0.00 0.00 0.04 0.03

Oct. 26-29, 1965 0.12 0.08 0.12 0.04 0.04 0.01 0.15 0.08

Oct. 4-7, 1966 0.15 0.10 0.22 0.02 0.07 0.02 0.13 0.10

Trior to lining October 16-18, 1963.

"Prior to joint sealing September 30, 1964.

CANADIAN AGRICULTURAL ENGINEERING, JAN. 1967

first three sections was noted in theMay 1966 inspection. This increasewas due primarily to the formation oflongitudinal cracks, which were notpresent in the remaining four sections.

The water table at this site has beenrising each year as a result of seepagefrom an adjacent unlined canal anddeep percolation during the irrigationseason. The average depth of the watertable during the winter preceding theMay 1966 inspection was 8 feet. Thewater table had risen more rapidlyunder the first three sections becauseof the proximity of the unlined canal.Probably the rising water table hasincreased frost heave and acceleratedcrack formation.

The expansion joint grooves in thefirst three sections were smaller than isusually considered adequate. Thegrooves in these sections were about XAinch wide and % inch deep; in the remaining four sections they were aboutVi inch wide and % inch deep. Presumably the smallness of the groovesin the first three sections was partlyresponsible for the formation of cracksbetween expansion joints, particularlyin the presence of a high water table.

The seepage loss from this ditch wasreduced by more than 80 percent fromthe pre-lining value of 0.34 cubic footper square foot of wetted perimeter perday (table II). There was a further 10percent reduction after the expansionjoint grooves had been filled with asealing compound. During the twoyears after the joints were sealed therewas a slight increase in seepage loss.However, the seepage loss reductionwas still greater than 70 percent.

After three years of service most ofthe seepage loss was occurring from thefirst three and the last sections. Thereason for the high loss from the lastsection is not apparent. However, therelatively high losses from the firstthree sections were probably due to thegreater amount of interjoint cracking inthese sections. In general, crack formation between joints was reflected bygreater seepage loss. Evidently the restriction of cracking to the expansionjoints is a significant factor in seepagecontrol. The relatively low losses fromsections four, five, and six indicatethat cracking between joints can becontrolled by proper groove construction.

Experience gained during the construction of this concrete-lined ditchindicated that its cost on a commercialbasis would be about $1.50 to $2.00per lineal foot.

SUMMARY

Seepage loss from an irrigation ditchwas reduced by more than 90 percentby installing an unreinforced concretelining with a subgrade-guided slip-form. After three years of service theseepage reduction was still greater than70 percent. Most of the increase inseepage is attributed to crack formationbetween expansion joints. The importance of providing adequate expansion joints is emphasized.

ACKNOWLEDGMENTS

The authors wish to acknowledgethe assistance of personnel of the BowRiver Project and Soil Mechanics Division of PFRA and the Canada Cement Company Limited in the construction of the concrete-lined ditchfor this study.

REFERENCES

1. Canada Department of Agriculture, Soil Mechanics and Materials Division, PFRA. 1951. FirstProgress Report on ExperimentalCanal and Dugout Lining. Saskatoon, Sask.

2. Canada Department of Agriculture, Soil Mechanics and Materials Division, PFRA. 1952. Second Progress Report on Experimental Canal and Dugout Lining.Saskatoon, Sask.

3. Canada Department of Agriculture, Soil Mechanics and Materials Division, PFRA. 1957. ThirdProgress Report on ExperimentalCanal and Dugout Lining. Saskatoon, Sask.

4. Pohjakas, K., and E. Rapp. 1967.Performance of Some Canal andDugout Linings on the CanadianPrairies. Can. Agr. Eng. 9: (12-17).

5. Sauder, P. M., Retired Manager,Colonization Branch, Alberta Department of Agriculture, Leth-bridge, Alberta. Personal communication.

6. Speers, E. W. Engineer, CanadaDepartment of Agriculture, SoilMechanics and Materials Divi

sion, PFRA, Saskatoon, Sask.Personal communication.

7. United States Department of theInterior, Bureau of Reclamation.1963. Linings for IrrigationCanals. 1st ed. 149 pp.

CANADIAN AGRICULTURAL ENGINEERING, JAN. 1967

. .. DEEP TILE DRAINS

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expressed as ECe/SAR ratios over therange of ECe from 1 to 20 mmhos/cm.Ratios obtained throughout this studywere combined and grouped accordingto the ECe values (table II). Although

TABLE II. ECe/SAR RATIOS FOR SOILSAT DIFFERENT ECe VALUESEXPRESSED IN MMHOS/CM

EC„ ECVSAR S.D.

1- 2 0.530 0.298 14

2- 4 1.198 0.534 42

4- 6 1.029 0.354 56

6- 8 0.789 0.105 35

8-10 0.695 0.070 5310-12 0.706 0.075 25

12-14 0.790 0.178 24

14-16 0.813 0.100 616-18 0.755 0.070 5

18-20 0.883 0.089 5

the standard deviation was fairly largefor the lower ECe, ratios did notchange very much. No differences inrelation to the ECe during the reclamation period were observed for thevarious drainage practices. Thus theconcentration of Na+ relative to Ca++and Mg++ decreased continuously withdecreasing ECe, indicating that watermovement through these soils was probably not restricted. The gypsum present probably had a beneficial effect.

CONCLUSIONS

The study showed that reclamationof salt-affected glacial soils can be attained on sloping land with deep tiledrains. However, it is questionable ifdeep tile drains are more useful thanshallow tile drains for salt removal atdepths from 3 to 6 feet. Care shouldbe taken that the water table is notwithin 3 feet of the surface for longperiods during the growing season.

Although the areas with a combination of shallow and deep tile drainsreceived more water than the area withdeep tile drains only, no significant difference was found in the effectivenessof reclamation of both treatments. Theinitial salt content of the soil with deepdrains only was higher than that of theother treatment but at the end of thestudy ECe values were nearly the samefor both treatments.

The ECe of soil leached withoutartificial drainage did not drop below7.5 mmhos/cm, indicating that fallleaching of soils in seepage areas isnot effective in reclaiming land.

continued on page 76

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