Soil Stabilizers for Seepage Control in Reservoirs Irrigation Canals C. W. LAURITZEN U . S. DEPARTMENT OF AGRICULTURE. AGRICULTURAL RESEARCH SERVICE. A N D THE UTAH AGRICULTURAL EXPERIMENT STATION, LOGAN. UTAH
Seepage losses f r o m canals a n d reservoirs i n irrigated lands are t h e source of m u c h economic waste. These losses can be controlled b y lining. M a n y types of linings have been used w i t h varying degrees of effectiveness. T h e results of t r e a t i n g soil m a t e r i a l w i t h stabilizer A M 955 are presented. T h e possibility of employing t h i s stabilizer t o control seepage losses in irrigation canals a n d reservoirs is discussed.
W
A T E R for irrigation must be conveyed from a stream or reservoir source t o the land where it is to be applied. Open ditches or canals are employed largely for this purpose. Most of these canals consist of earth channels; and as the water is conveyed, a portion of i t percolates through the canal bed. The loss by this process is commonly referred t o as seepage. It is estimated that about one third of all the water diverted for irrigation purposes is lost in this manner. A large portion of this loss can be prevented by lining canals. This is generally recognized and yet only about 5% of the irrigation canals are lined. The cost and effectiveness vary with the type lining employed. Many types of material are used for canal lining, but in the United States these are limited primarily t o earth, asphalt, and concrete. Linings constructed of a n y of these materials, when adapted t o site conditions and properly constructed, control seepage. A lining t o be effective must be relatively watertight and in order t o be serviceable must be resistant t o stream erosion and mechanical damage. There are fine-textured earth materials from which low permeability linings can be constructed, and by using a coarse-textured topping, such as gravel, the lining can be made resistant to stream erosion. The properties of earth material are readily modified by treatment, and it is common practice to compact and blend earth materials during construction t o impart the properties essential t o linings. Concrete results from the addition of portland cement t o sand and gravel aggregates, and soil cement results where fine-textured materials such as sands and sandy loams are substituted for the sand and gravel aggregate. Asphalts and oils likewise have been used t o reduce the permeability and increase stability of earth material, employed as lining to control seepage losses. The use of chemicals suggests itself as another means of obtaining the desired characteristics in earth lining. While this subject has been investigated rather extensively, success has been relatively limited. T o the author’s knowledge there have been no effective linings constructed from chemically stabilized earth nor have successful methods been devised for treating canal bed material t o control seepage and impart a high degree of resistance t o stream erosion. T h e results reported in this paper deal exclusively with the use of a soil stabilizer developed by the American Cyanamid Co. under the name stabilizer AM-955. This material is water soluble and its solutions can be copolymerized by the addition of a catalyst, ammonium persulfate, and an activator, sodium thiosulfate. Polymerization results in the formation of a gel, the stiffness of which depends on the concentration of the monomer mixture. When a catalyzed solution of the stabilizer is added t o soil under appropriate conditions, a n impermeable stable mass results following polymerization. The stabilized November 1955
soil mass is flexible when wet and hard when dry. When rewet, the soil regains its flexibility. Purpose a n d Scope of Investigation
A study of the factors influencing gel formation and treatment methods was made to determine something of the value of the stabilizer for lining irrigation canals and reservoirs. I n addition, some test linings were installed in the Agricultural Research Service Outdoor Laboratory. The work reported in this paper is restricted t o the influence of selected extraneous materials on gel formation, the efiect of liquid content and the amount of catalyst and activator on soil stabilization, and a description of some test lining installations. Factors Affecting Gel Formation
Polymerization occurred so rapidly t h a t the equipment became clogged when a n attempt was made t o spray a solution of the stabilizer on a prepared soil surface although beaker tests with a n identical solution had indicated there would be sufficient time before polymerization t o utilize all the liquid in the sprayer tank. This accelerated polymerization prompted a study to determine some of the factors t h a t affect the rate of polymerization. Metal strips, when immersed in a solution of the stabilizer, became encrusted with the polymer; it is this action which caused t h e sprayer to clog. Absorptive materials such as dry filter paper, cloth, and asbestos accelerate the reaction when immersed in t,he solution. When these absorptive materials are soaked in water before being added t o the stabilizer solution, the setting time is not aftected. T h e accelerating effect of absorptive materials is probably due t o the removal of water from the system with a resultant increased concentration of the stabilizer. Unreactive materials such as glass, nonmetallic substances, and poly(viny1 chloride) and polyethylene film have no effect on the setting time. Polymerization is also accelerated by passing a n electric current through a solution of the stabilizer. The application of an electric field from a 110-volt a.c. source, however, did not affect the rate of polymerization. I n using electric current t o accelerate the reaction, it did not appear t h a t polymerization was caused by the heating effect of the current since the temperature rise did not occur until polymerization began. Conditions Influencing Soil Stabilization
Good stabilization can be obtained with a 10% solution of the stabilizer and 5% catalyst and 5% activator, if enough solution is used t o saturate the soil completely and the soil worked t o expel the air from the soil. Permeability measurements made
INDUSTRIAL AND ENGINEERING CHEMISTRY
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ENGINEERING, DESIGN, AND EQUIPMENT
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was poor. Apparently polyrnerization took place with the increased catalyst content before the air was completely displaced, Table I, B. The appearance of the cylinders after soaking is shown a t right of B. It was possible t o obtain good stabilization in all tests with 20% activator if the soil was completely saturated. I n the majority of rases with complete soil saturation, 10% activator has been sufficient t o give satisfactory stabilization while 5% catalyst was sufficient. When the soil was worked or mixed with the solution instead of adding it t o the top of the soil column, 20% water compared to 34% was sufficient to saturate the soil
FINE
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on samples prepared with varying liquid contents and varying monomer-water ratios seem t o confirm the fact t h a t saturation is needed for complete sealing. Initial tests in which the treated soil was compacted a t optimum moisture failed to produce an impermeable or a permanently stable structure. The high liquid content in wet mixes and uncompacted saturated soil columns is undesirable because of the shrinkage which accompanies drying. Where shrinkage takes place, it is doubtful if complete sealing will occur on rewetting when stabilized soil is employed as a lining for irrigation canals and reservoirs. Even if this did occur, zones of greater porosity may develop as a result of the deposition of coarse-textured material in the cracks during periods when the cracks are open. Later tests indicated the degree of stabilization obtained by treating soil with the stabilizer varied widely with conditions. I n an attempt to isolate some of the factors responsible for the ineffectiveness of the stabilizer, a n investigation was undertaken to determine the factors influencing stabilization. Since preliminary work indicated t h a t complete saturation was necessary to produce stabilization, columns of a loamy sand were treated by applying the solution from the bottom under a head sufficient to cause the solution t o move through the soil t o the top of the column. The results indicate satisfactory stabilization may be obtained by this method of saturating the soil with stabilizer AM 955 solution using 5% catalyst and 5 t o 10% activator based on the percentage of stabilizer. The soil column treated was dry packed and required approximately 34% water to saturate it completely. The soil specimens, saturated with solutions containing 15 and 20y0 activator, exhibited areas on their sides where there was no stabilization, and the soil quickly eroded away when immersed in water, specimens 1-34-3 and 1-34-4, Table I. The cores of these specimens comprising approximately 80% of the soil column were well stabilized and did not erode, Table 1, A . No immediate explanation can be offered for these unstabilized areas. When the catalyst content was 10% or above, stabilization did not occur. Solutions of stabilizer added t o the surface of coil columns, using a solution of 5y0 catalyst and from 5 t o 20y0 activator, likewise effectively st,abilized the soil. When the catalyst was 2246
amount of catalyst and activator used varied. When the amount of activator used was four times the normal amount of catalyst-the normal amount of catalyst and activator is 5% each, based on the weight of the monomer -variable results were obtained as shown in Table I, D, specimens 1-12-4 to 1-24-4. As was previously observed, it was necessary to have a condition of complete saturation to produce stability, and only those specimens in which the moisture content was above 20% were well stabilized. Using twice the normal amount of both catalyst and activator, essentially the same results were obtained. Again it was necessary to have sufficient moisture t o produce saturation t o get stability, Table I, specimens 2-14-1 to 2-23-1. Specimens 2-12-1 t o 2-12-5, Table I, E, were treated with a solution of the stabilizer t o provide a moisture content of 12y0, or the optimum for maximum compaction. The amount of catalyst used was double the normal amount, and the amount of activator varied from twice to 5 times the amount of catalyst used. Good stabilization resulted, when the amount of activator ranged from 20 to 40y0, Table I, E, specimens 2-32-2, 2-12-3, and 2-12-4. At moisture contents of 14 and 16% and the same amount of catalyst and activator, little stability resulted, Table I, specimens 2-14-1 to 2-14-5 and 2-16-1 t o 2-16-5. These results were thoroughly confusing, since, if stabilization was obtained a t 12% moisture, previous results indicated it could be expected a t the higher moisture levels. It developed t h a t while the same soil source was used for the specimens compacted at 14 and l6Y0 moisture as a t 129/, it came from a different batch and was somewhat coarser in texture, Figure 1. The same was true for specimen 2-12-5. Where fines were added t o the coarsertextured soil t o make the texture of the two soils similar, stabilization resulted when the treated material was compacted a t 12% moisture; and stabilization would probably have resulted a t 14 and 16% moisture levels. Test Linings
Four test installations were made at the Irrigation Research Laboratory. A description is given of the methods employed and the results obtained.
INDUSTRIAL ANC ENGINEERING CHEMISTRY
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SOIL STABILIZATION Table 1.
Conditions Influencing Soil Stabilization (Stabilizer content 2% by weight of dry soil) Test d a t a given with photos of test sections: Column 1. Specimen No. Column 2. Activator % stabilizer b y wt. Column 3. Catalyst % stabilizer by wt. Column 4. Water content Column 5 . Stabilization
a
A.
1-34-1 5 1-34-2 10 1-34-3 15 1-34-4 20 1-34-5 10 1-34-8 10 Photos not shown.
5 5 5 5
10
10
34 34 34 34 34 34
Very good Very good Good Good Very poora Nonea
1-12-4 1-14-4 1-16-4 1-18-4 1-20-4 1-22-4 1-24-4
20 20 20 20 20 20 20
5
5 5 5
5 ?
12 14 16 18 20 22 24
Fair Fair Fair Good Verygood Verygood Verygood
D.
Stabilizer solution mixed w i t h soil and compacted
E.
Stabilizer solution mixed w i t h soil and compacted
Dry packed soil column saturated w i t h stabilizer applied from bottom
1-34-1 1-34-2 1-34-3 1-34-4 2-34-1 2-34-2 2-34-3 2-34-4 2-34-5
5 10
15 20
5 5 5 5
10
10
20 30 40 50
10 10
10 10
B. Stabilizer solution added t o surface
34 34 34 34 34 34 34 34 34
Good Good Very good Very good Poor Poor Fair Fair Fair
% Stabilizer
of dry packed soil column
Speoimen
No.
1-20-1 1-20-2 1-20-3 1-20-4 C.
5
10
15 20
5 5
20 20 20 20
Verygood Verygood Verygood Verygood
Stabilizer solution mixed w i t h soil t o produce paste
Section 1-D. A loamy sand was treated with a catalyst: monomer: water ratio of 2:lO:lOO. Various concentrations of catalyst, monomer, and water have been indicated by a 3-number ratio. The first number indicates t h e proportionate weight of catalyst eystem, the second the proportionate weight of monomer, and the last the proportionate weight of water. For example, a 1:10:200 solution would indicate 1 part total catalyst, 10 parts monomer, and 200 parts water. This gave a plastic mix with 18% moisture and 1.9% monomer based on the d r y weight of the soil. T h e soil and stabilizer solution were mixed in a concrete mixer and placed in the test sections by hand t o a depth of approximately 3 inches, Figure 2. On stabilization or setting of the November 1955
Activator
2-14-1 2-17-1 2-20-1 2-23-1
10 10
2-16-1 2-16-2 2-16-3 2-16-4 2-16-6
10 20 30 40 50
10 10
b y Wt.
Catalyst 10 10 10 10
10 10 10 10 10
Hz 0 Content 14 17 20 23
16 16 16 16 16
Stabilization Poor Fair Good Verygood
Verypoor" Poor" Poora Poora Faira
a Soil used i n preparation of these specimens was the coarser textured soil shown in Figure 1. Poorer stabilization is due t o Soil used rather than treatment.
mix, cracks developed between each successive pour. An attempt was made t o seal these cracks by filling them with a solution of the stabilizer. T h e seepage through the lining, however, was not reduced by this treatment. Except for a few short periods, water was in the channel continuously from June 30 t o September 25, 1954. Between September 25 and December 1, 1954, water was in the channel only intermittently. During the summer the seepage through the lining was 0.145 cubic feet per square foot per day or 1.09 gallons per square foot per day. However, most of the seepage was through the cracks and a t the ends of t8heliner rather than through the stabilized soil.
INDUSTRIAL AND ENGINEERING CHEMISTRY
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ENGINEERING, DESIGN, AND EQUIPMENT the rest of the lining material and left a n unstable permeable material. Section 5-D. This lining, like the lining in section 4-D, was installed late in the season. Mixing of the soil with the stabilizer solution was accomplished on the berm of the channel by means of a rotary garden tiller similar t o the manner employed in section 7-A. A solution having a catalyst: monomer: water ratio of 3.8:10:49 was used. The treated soil was shoveled into t.he channel, screeded, and immediately compacted with a Jackson Soil Vibrator. The stabilizer apparently did not gel completely and the soil was not stabilized as a result. When water was turned into the section, the lining eroded at the upper end. Immediately following the lining installation, water was placed in the channel for a period of 2 days. During this time considerable seepage was observed, b u t no measurements were made. Discussi on
Figure 2.
Stabilized earth lining immediatelyfollowing construction
Lining when placed had consistency of brick mortar
Section 4-D. A lining similar to the one installed in section 1-D, installed May 29, was installed in 4-D on November 23. The soil was mixed with a solution having a cata1yst:monomer:water ratio of 4:10:96 to produce a mix with 19.8% moist’ure. The amount of catalyst and accelerator used was about twice t h a t used in the mix for the lining in section 1-D. The per cent AM 955 based on the weight of dry soil was 2.06. T h e soil and stabilizer were mixed in a concrete mixer and placed in the test section by hand similar t o the manner in which the mix was placed in section 1-D. Special precautions were taken t o mix one batch with the next t o form a continuous lining structure and eliminate junctions between batches where cracks might develop. The lateness of the season, November 23, prevented measuring the seepage on this lining. Water was in the section for a period of 2 days, however; and there was very little water draining from the section. One week later, water was again turned in the channel. During the night, ice formed in the channel and the next day there was considerable leakage through the liner. The action of the ice and the freezing of the lining may have ruptured it so t h a t it leaked. Inspection showed that some of the leakage was coming from the end of the lining where it joined the bulkhead. Section 7-A. The same soil was used in this installation as was used for the linings in section 1-D and 4-D. The soil was placed in a windrow parallel t o the test section and AM 955 added in solution equivalent t o 12% of the dry soil weight. Mixing was accomplished by using a rotary type traveling mixer. After the A M 955 was thoroughly mixed, the catalyst system was added in solution and mixed in a similar manner. The total amount of solution used in adding the stabilizer and catalyst system was the amount required t o provide optimum moisture for maximum compaction or 12%. The cata1yst:monomer:water ratio of the solution was 1.2:10:59. T h e treated soil was then shoveled into the section, screeded, and compacted with a heavy lawn roller and hand tampers. After 24 hours there was no evidence of stability. It was assumed t h a t polymerization had not taken place because of insufficient catalyst, and a second catalyst treatment was applied by sprinkling a catalyst solution on top of the compacted liner. This resulted in the formation of a thin wrinkled “skin” on top of the liner. This skin pulled away from 2248
Polymerization of stabilizer AM 955 was affected by several factors including contact with metals and presence of salts and electric currents. T h e effect of contact with metals complicates construction because of the corrosion which results and t h e difficult operation of equipment due t o coatings which adhere t o the metal surfaces. Accelerating polymerization by electric currents may supply a n effective means of fixing the position of gel, securing polymerization in dilute solutions, and counteracting the inhibiting efiect of the soil. Stabilizer AM 955 stabilized soil, if a concentration of 1:10:100 or greater was used and sufficient liquid added t o completely fill the soil pores. The amount of liquid required depends on the method of application and the degree of soil compaction. Where the stabilizer was added t o the surface of a confined dry-packed column of loamy sand, the solution required was 34% by weight of the soil treated. Where the solution was mixed with the soil, about 20% by weight was sufficient. There is evidence t h a t loamy sand may be stabilized with just sufficient solution, 12%, t o provide optimum moisture for maximum compaction, if the amount of catalyst is 20% and the activator ranges from 20 t o 40% by weight of the stabilizer. If stabilization can be obtained a t this lower moisture level, not only will there be a reduction in theamount of stabilizer required, but the stabilized soil also will be subject t o less shrinkage on drying and a more durable lining of greater density should result. The studies reported are based on measurements primarily with one soil, a loamy sand. Sufficient work has not been done to learn much about the influence of soil properties on treatment results. Preliminary work indicates, however, that soil texture, a t least, will influence the character of the structure. A much firmer and more durable structure results when the soil material contains considerable fines in the silt and clay range. There is evidence also t h a t a certain amount of fines is necessary for stabilization at moisture levels below saturation, irrespective of the degree of compaction and the amount of catalyst and activator used. Furthermore, stabilization can be effected in sandy aoils while sufficient porosity persists due either t o the texture of the soil or t o the degree of compaction t o leave the stabilized soil permeable. Four linings of stabilizer-treated loamy sand were installed at the River Laboratory. Two were constructed of the wet mix and two compacted at optimum moisture for maximum compaction. The wet mixes were fairly effective in controlling seepage b u t subject t o cracking. Soil stabilization was not attained with compacted linings and consequently they were ineffeztive in controlling seepage. T h e normal amount of catalyst and activator was used in the installations made early in the season and twice the normal amount in the linings installed late in the season. Laboratory studies indicate t h a t a fairly satisfactory lining might be constructed, b u t this has yet t o be demonstrated. RECEIVED for review April 5, 1955.
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
ACCEPTED September 6, 1955.
Vol. 47, No. 11
