Soil Cement Lininng Channels
Content
Irrigation and Drainage Systems 5: 151-163, 1991 © 1991 Kluwer Academic Publishers. Printed in the Netherlands
Soil-cement tiles for lining irrigation canals
A . K H A I R 1, C. N A L L U R I 2 a n d W . M . K I L K E N N Y 3 l Department of Irrigation Water Management, Bangladesh Agricultural University, Mymensingh, Bangladesh; 2,3 Department of Civil Engineering, University of Newcastle upon Tyne, UK Received 12 September 1990; accepted 25 February 1991
Key words: irrigation canal, soil-cement tile, compressive strength, durability, erosion due to flowing water, seepage losses Abstract. Laboratory flume test was conducted to investigate the effect of flowing water an soilcement canal tiles. For this purpose, soil-cement tiles were constructed from different soils at various cement contents. A flume, 3 metre long and 100 mm wide, was lined with the tiles and the lined bed was subjected to flow velocities of around 2 m/s for a period of 7 days. The tiles made from coarse-textured soil (sandy loam and silt loam) aggregates of 5 mm and from fine textured soil (clay loam) aggregates of 2 mm size were found to be intact and smooth even when constructed at a cement contents lower than that needed to meet the durability requirements. Attempts were also made to measure seepage losses of soil-cement tile linings. A channel section of approximately 1 metre length with a side slope of 1:1 was constructed in the laboratory with the tiles and seepage losses measured by the ponding method were found to be in the range of 0.00123-0.00343 m3/mZ/day. The results clearly suggest that soil-cement tiles (irrespective of type of soil) made with 2 mm or less size of soil aggregates are erosion resistant and due to very little or negligible rates of seepage losses, the soil-cement tile lining of irrigation canals is expected to be very promising especially in the areas where irrigation water is costly.
Introduction G a r g & C h a w l a (1970) r e p o r t e d t h a t in u n l i n e d i r r i g a t i o n c a n a l s y s t e m s s e e p a g e losses a r e so h i g h t h a t , in s e v e r a l s y s t e m s , t h e q u a n t i t y o f w a t e r d e l i v e r e d to t h e fields m a y be less t h a n 5 0 % o f t h a t d r a w n in t h e h e a d . A c c o r d i n g t o t h e F A O (1971) t h e s e e p a g e losses p e r 1.6 k m l e n g t h o f an i r r i g a t i o n c a n a l c a n be as h i g h as 20O7o o f its c o n v e y a n c e c a p a c i t y . A h u j a & M e h n d i r a t t a (1967) r e p o r t ed 18 to 50070 o f w a t e r losses in i r r i g a t i o n c a n a l s in I n d i a . S a r a n et al. (1967) s t a t e d losses o f a r o u n d 4 7 % in i r r i g a t i o n c a n a l s in I n d i a , 33 to 6 0 % in U S A a n d 25 to 6 0 % in M e x i c o . A c c o r d i n g to J e n k i n s (1981) t h e c a n a l w a t e r losses in B a n g l a d e s h w e r e a b o u t 5 0 % in a 300 m l o n g , 57 l i t r e s / s size e a r t h c h a n n e l . Besides s u c h a h e a v y loss o f v a l u a b l e i r r i g a t i o n w a t e r , excess s e e p a g e c o n t r i b utes to w a t e r l o g g i n g o f f a r m l a n d s , salt a n d alkali c o n c e n t r a t i o n s in soils
152 resulting in costly maintenance roads and drainage systems and reduction in total agricultural output. USBR (1963) and Sarker (1967) stated that in many irrigation projects this led to very uneconomical irrigated agriculture and at times to abandoning of the entire project. Canal lining is considered to be most effective in reducing water losses and practical linings should be near impervious, inexpensive, strong and durable. Hard surface linings of reinforced and plain concrete, sand-cement blocks, stone and brick masonry and asphalt concrete meet many of these requirements but are the most expensive. Although brick and stone masonry linings are commonly used in many developing countries as low cost materials for lining main canals, branches and distributories, the cost are prohibitive for small channels. In many countries low cost materials such as impermeable earth, bentonite, vegetative covering, polythene sheets, asphalt mats, etc. are being used as low cost linings to minimise water losses in irrigation canals at varying degrees of success. Although these linings have been characterized as low cost techniques, their durability is very uncertain. While initial costs may be low, maintenance costs could be high. These linings may be highly susceptible to damages by burrowing animals, weed puncture, rain and flowing water. Besides many substances also have been used to stabilize or seal canal and lateral subgrade materials. These include specially treated resins, chemicals such as sodium silicate in combination with sodium and clacium chloride, a commercial resin cement, lime, portland cement, asphalts, petrochemicals, and others including combinations of the above. Corps of Engineers (1956) described several promising chemical soil stabilizers, but attached certain limitations in their use as well as their unfavourable economics and concluded that the best way forward was re-evaluation of stabilization with conventional materials, i.e. cement or asphalt. USBR (1963) reported that soil-resins linings often deteriorate badly shortly after construction and chemicals are not adaptable to canal use because of the high cost as well as their poor resistance to wetting-drying or freezing-thawing cycles. Kinori (1970) stated that asphalt concrete lining is very costly and can be used only for large channels. Asphaltic oil linings deteriorate rapidly when exposed to rain and sunshine. There is a tendency for asphalt to separate from the aggregate when exposed to water over a long period causing rapid disintegration. Asphalt mats are usually damaged by weed puncture. Plastic film and synthetic rubber membrane linings are usually damaged by weed growth. Soil is the oldest, cheapest and probably the most use of construction materials. However, there are limitations to the use of natural soils due to its lack of strength and its valnerability to moisture content changes and the erosive effects of external agencies. Soil stabilization is a technique aimed at increasing or maintaining the stability of the soil mass. Lambe & Moh (1957) describe that portland cement is one of the most
153 common and successful stabilizer for soils. When cement is used as a soil stabilizing agent to improve its strength and its resistance to change, it is termed soil-cement. Portland Cement Association (1984) has described that engineers and contractors have been using soil-cement to pave roads, streets, airports and parking areas and its performance has been outstanding. The Portland Cement Association also stated that soil-cements' low-cost, ease of construction utilization of local or inplace soil make such application economical practical and environmentally attractive. The extensive use of soil-cement for road pavements and runways has led to the experimental use of this material for canal and ditch lining. There are two types of soil-cement lining: compacted (standard) and plastic. Standard soilcement lining has proved to be unsuccessful mainly due to lack of optimum compaction. The portland cement Association (1956) reported that a higher percentage of cement is always needed to make durable plastic soil-cement lining and also is susceptible to damages due shrinkage cracks. However, the outstanding service record of soil-cement in other fields indicates that soilcement could be a promising low cost lining if it can be properly placed and compacted to obtain maximum density without difficulty. In the circumstances, Khair (1988) showed that soil-cement tiles of 20 to 25 mm thickness if constructed with a cement contents to satisfy the criteria as mentioned below is durable in the irrigation field to withstand the stresses induced by the sun and rain: - Soil-cement specimens should not suffer a loss in strength more than 10% after 7-day immersion test (British durability test). - Soil-cement specimens should give a minimum wet unconfined compressive strength of 1.724 M N / m 2 after 7-day curing in the humidity cabinet. Khair also showed that such type of lining with a life expectancy of 8 years is economically superior to all other linings (plastic soil-cement, asphalt mat, precast concrete section, brick lining, clay plastering and unlined section) currently being used in Bangladesh. The merit of a satisfactory lining not only lies in its ability to resist destructive forces of weathering (sun and rain) but it must be resistant to erosion caused by flowing water as well as impermeable engough to reduce seepage losses. Hence, a detailed experimental programme was undertaken at the University of Newcastle upon Tyne, UK to investigate the resistant of soilcement tile to flowing water and as well as to assess its merit in reducing seepage losses.
154
Experimental investigations
Selection o f soils
Three different types of soil (clay loam, sandy loam and silt loam) were collected for this investigation whose physical and chemical properties are shown in Table 1. The results in Table 1 show that soils collected for the present investigation are almost suitable for cement stabilization. The soils for this investigation were not selected merely on the basis of the suitability according to the criteria set by previous investigators for the construction of road pavements and rural houses, rather the soils were selected randomly with a view to establishing criteria for the construction of soil-cement tiles for lining small irrigation canals.
Preparation o f soil-cement tiles
The Brepak (Developed by the Building Research Establishment, UK) block making machine was used for the manufacture of soil-cement tiles. The press consists of a moulding area of fixed size which, together with the structural frame, forms an integral unit of an all steel construction. Access to the mould area is via a top cover plate, pivoting about a corner mounted located pin. The press is fittted with a lever arm extension and mechanical linkage which provides a means of locking the top cover plate onto the mould and also allows for initial compaction of the block material within the mould area. Once the lever arm and cover plate are secured the compaction pressure is then applied using a hand operated hydraulic pump. This manually operated machine is especially suitable for rural areas where there is no power supply. The standard size of building block as produced by the Brepak press is 290 x 140 x 100 mm. The press is a constant volume type and ram moves a fixed distance so that always a standard block size with a thickness of 100 mm is produced. Therefore,
Table 1. Physical and chemical properties of soil samples.
Soil type Liquid limit (%) 33 27 35 Plastic limit (%) 20 non-plastic non-plastic Plasticity index (070) 13 Organic content (%) 1.07 2.27 1.69 Sulphate content (%) 0.056 0.047 0.052
Clay loam Sandy loam Silt loam
155 to produce tiles of varying thickness, steel separator plates were introduced into the moulding cavity of the press. In order to construct tiles of 25 m m thickness, two separator steel plates measuring 289 × 138 × 12.5 m m were used. The mass of cement treated soil mixture required to make a tile of the size 290 × 140 × 25 m m was calculated f r o m the following relationships: m = (1015 + 10.15 w) P~ where, m w (1)
= mass of cement-treated soil mixture, g = o p t i m u m moisture content of the mix in per cent obtained at a compaction pressure of 10 M N / m 2 Pd = m a x i m u m density of dry soil plus cement in M g / m 3 achieved at a compaction pressure o f 10 M N / m 2 As the maximum density of soil-cement mixture varies only slightly (Portland Cement Association 1956) with cement content the result of the moisture density (Table 2) relationship obtained at 6% cement content at a compaction pressure of 10 M N / m 2 were used for moulding the tile specimens at different cement (ordinary Portland Cement) contents. The measured amount of stabilized soil needed to produce a tile of 25 m m thickness as calculated using Eq. 1 was put into the mould, then a separator plate, a further amount of mix for another tile followed by the second plate and finally another amount of mix for the third tile. Then the top cover plate of the press was moved to its closed position and the main hand lever was removed through an arc to initially compact the soil. Next, the flow control valve on the hand hydraulic p u m p was closed and the handle was operated until a pressure of 8,000 psi, approximately 10 M N / m 2 effective pressure on the tile, was indicated. Then the flow control valve was released and the lever arm was lifted from its horizontal position and reversed to its original start position. By applying downward force on the lever arm, the newly pressed tiles were demoulded f r o m the mould box. In one operation of the machine, 3 tiles of size 290 × 140 × 25 m m are produced and a man is capable of producing 150 tiles per day. Cost incurred to produce such type of 1,000 tiles is approximately US $ 5.0 only. After construction, the tiles were wrapped in polythene bags and
Table 2. O p t i m u m moisture contents and m a x i m u m densities of soil-cement mixture.
Soil type
Aggregates
M a x i m u m dry density ( M g / m 3) 1.984 1.886 1.630
O p t i m u m moisture content (%) 12.45 12.40 15.00
Clay loam Sandy loam Silt loam
Soil + 6% cement Soil + 6°70 cement Soil + 6% cement
156
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CEMENT
CONTENT (%),C
Fig. 1.
Effect of
cement content on strength of soil-cement specimens after 7 days curing and 24
hour immersion.
the bags were sealed to prevent any loss of moisture and to reduce carbonation effect. The sealed bags were then stored in a humidity cabinet for 28 days curing.
Durability and compressive strength tests
Tests were conducted on soil-cement cylindrical specimens in accordance with Britsh Standard (BS1924. 1975) to establish the durability requirements with various cement contents in the mix. Figure 1 shows the relationship between the cement content and 7-day wet unconfined compressive strengths (1.724 M N / m 2 and 1.4 M N / m 2 are the c o m m o n minima for soil-cement used for road pavements and for building blocks, respectively) of the specimens whereas Fig. 2 shows their resistance to 7-day immersion. Figures 1 and 2 suggest that the criteria of minimum unconfined compressive strength of 1.724 M N / m 2 and 7-day immersion test (not to suffer a loss in strength by more than 10%) are met with the cement contents of 8%, 11 °70 and 10% for clayey, sandy and silty loams, respectively.
157
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Fig. 2. Resistance to i m m e r s i o n of soil-cement specimen at different c e m e n t contents.
Erosion and seepage tests in f l u m e s Tiles of 25 m m thick made (using Brepak machine) from various soils at different cement contents with o p t i m u m moisture contents and densities were used for erosion tests. Curing period has significant effect on strength of soilcement specimens. Khair (1988) showed that the strength at 7-day are approximately 60 to 70°7o of those at 28 days. Hence 28 days curing period was considered to be appropriate to obtain a quality of soil-cement tile. Therefore, after 28 days curing in the humidity cabinet, the tiles were cut to size to be accommodated within a laboratory flume of 3 m long and 100 m m wide. The tiles were fixed on to the bed of the flume using water-proof glue and the joints between the tiles were filled with cement treated soil-mixtures. The flow rates supplied to the flume were measured by an on-line orifice-meter introduced in the supply pipe line. Knowing the water depth (hence the area of flow) the flow velocities were computed. The lined bed of the flume was immersed under water for a period of 7-day to allow the expansive clays, organic matter, sulphate and other detrimental constituents to be fully active. The bed was subjected to flow velocities of around 2 m/Is for a period of further 7 days at a rate of 6 hours per day.
158
Table 3. Erosion (due to flowing water) tests results.
Soil type
Soil aggregate passing sieve size (mm) 5.00
Cement content % 6.00
Bed load gm/hr Negligible
Suspended load gm/hr Negligible
Visual observations
Clay loam
Clay loam Clay loam Clay loam
5.00 3.35 2.80
8.00 8.00 8.00
Negligible Negligible Negligible
Negligible Negligible Negligible
Clay loam Clay loam Sandy loam Silt loam
2.00 2.00 5.00 5.00
8.00 6.00 8.00 8.00
0 0 0 0
0 0 0 0
Surface roughening all unpulverised clay particles washed away -do-doSurface almost smooth, little roughening Smooth surface, no roughening -do-do-do-
D u r i n g this test p e r i o d the tile surface was visually o b s e r v e d for any erosion a n d a t t e m p t s were m a d e to m e a s u r e the e r o d e d m a t e r i a l s q u a n t i t a t i v e l y b y installing a b e d l o a d t r a p at the d o w n s t r e a m end o f flume. A l s o water samples were t a k e n by a specially a d o p t e d pipette at regular intervals a n d a n a l y s e d for the traces o f s u s p e n d e d load, if any, caused by erosion. The e r o s i o n test results are s u m m a r i s e d in T a b l e 3. Seepage tests were c o n d u c t e d in a l a b o r a t o r y channel specially c o n s t r u c t e d a n d lined with soil-cement tiles (after 28 days curing in t h e h u m i d i t y cabinet a n d the j o i n t s being filled with b o t h the plastic soil-cement a n d cement mortars). The tiles were o f 25 m m thick a n d m a d e o f clayey, s a n d y an silty l o a m s with
350
.¢v
IN FILL - -
IN CuT tic ORIGINAL GROUND SURFACE
":"
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~/"~':~
190T mm
/
Fig. 3.0.056 cumec canal to be lined with soil-cement tiles.
159
350
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IN CUT
----=
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o Rqrcq N'a-C"G ~ 0 " ~ 7 7
i suRfAcE
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~ORIGINAL GROUND SURFACE / I ~ 2 2 1 2 2 ~ o G ~ M~A N ~ M [ N T
Fig. 4. 0.028 cumec canal to be lined with soil-cement tiles.
8, 11 and 10% cement contents (as needed to satisfy durability requirements see Figs. 1 and 2), respectively. Figures 3 and 4 show such test channels representing small channels of 0.056 and 0.028 m3/s conveyance capacities, respectively with 0.1% bed slopes and an average Manning's n around 0.012. After curing the joints the channel was filled with water and the total loss of water (due to seepage and evaporation) measured to an accuracy of 0.1 of a mm of water depth. The reduction in depth was then converted to a volume to estimate the loss by the ponding method using the following relationship: 24 W (d 1- d2) Pt
S = where S W d1 d2 P = = = = =
(2)
seepage rate in m3/m2/day average width of water surface in m depth of water at the beginning of measurement in m depth of water in m after t hours average wetted perimeter in m
Figure 5 shows the rates of water loss in 0.028 m3/s channel section plotted against time in days lapsed after the beginning of the tests. It can be seen that a steady rate of water loss establishes after a period of about 8 - 1 0 days in all cases. The water losses when nearly constant were considered as the water losses due to seepage and evaporation for tile linings. In order to quantify the evaporation losses, if any, the channel was covered by spreading an impervious polythene sheet around its perimeter and water depths measured at 24 hours intervals over a period o f 8 days. The losses of depth due to evaporation were then expressed as the equivalent rate of seepage losses. The seepage losses for the soil-cement linings were computed deducting the average evaporation loss from the total losses as obtained from the Fig. 5.
160
I00
:>-
A O H
A O
SILT-LOAM
SOIL SOIL SOIL
< cl 9.0 ~ 8.0
SANDY- LOAM CLAY-LOAM
E
im 7.0
6.0
bJ
~D <
5.0
A A ^
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-3 klJ p-
cr <
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I I I I i I i
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0
4
6 TIME
8
I0
12
14
16
IN DAYS
Fig. 5, Rate of water losses in a smaller canal section lined with soil-cement tiles made from different type of soils.
Results and discussion Tile surface, made from clay loam soil aggregate of above 2 mm size, were roughnened due to the washing away of unpulverised clay particles when subjected to flow (bed shear stress) velocities of around 2 m / s . The soil loss due to erosion in these cases was so small that the usual methods failed to detect it. The tiles made from sandy loam soil aggregates of 5 m m and above and from clayey soil aggregates o f 2 m m and less in size were found to be intact and smooth even after 7 days flume operation at velocities around 2 m / s . Tiles made from clay loam soil need, 8°70 cement content to meet the standard durability criteria (Figs 1 and 2) but were found undurable to flowing water when constructed with soil aggregates larger than 2 m m size. On the otherhand, tiles made from silt and sandy loam soils were found unaffected to flowing water even when constructed at a cement contents lower than those needed to meet the standard durability criteria.
161 The losses (seepage + evaporation) estimated from Fig. 5 are 0.0018, 0.003 and 0.004 m3/m2/day for soil-cement tiles made from clay loam, sandy loam and silt loam soils, respectively. In the field condition, evaporation losses are generally neglected but the measurement of evaporation may be necessary when evaporation losses are significant in comparison to seepage losses. In this study, the average computed evaporation loss was 0.000572 m3/m2/day and was considered to be significant in comparison to seepage losses and hence seepage losses for the linings were computed by deducting this evaporation loss. The seepage losses thus obtained were 0.00123, 0.00243 and 0.00343 m3/m2/day for the tiles made from clay loam, sandy loam and silt loam soils respectively. These losses are negligible in comparison to even sophisticated concrete lining for which the average seepage toss is about 0.084 m3/m2/day. In the laboratory, under controlled conditions the losses ranged from 0.00123-0.00343 m3/m2/day, but even considering the field conditions (where proper controlled criteria may not be applicable) the seepage losses through the soil-cement tile lining may not exceed about 0.005-0.01 m3/ mZ/day. Khair (1988) stated that soil-cement tiles are not structurally strong enough to resist external forces such as walking animals, earth or hydrostatic pressures. Therefore, the channel for lining with soil-cement tiles should be constructed in such a way so that the bottom and sides of the channel should neither be subjected to uplift or horizontal pressures of earth and water. Earth pressure can be avoided if the bank of the canal is made flatter than the angle of the repose of the bank material. When the bottom of a channel is above the groundwater surface, the channel will not be subjected to uplift pressure due to water. A compacted, stable subgrade is a pre-requisite for soil-cement tile lining to avoid damages due to walking animals. Construction of soil-cement canal tiles to resist damages due to walking animals would be highly uneconomical and therefore, it is justified to accept periodic maintenance than to have a foolproof, stong but costly lining. Soil-cement tile linings may also fail due to adverse subgrade conditions such as loss of support through piping action or heave of expansive clays. Therefore, either lining should be avoided on expansive clays or such clays should be replaced by non-expansive soils. Failure by cracking of the lining in many cases can be attributed to the poor preparation of subgrades. Before, placing tiles, the subgrade should be prepared, dressed and compacted to a level according to the required cross-section of the canal. After the preparation of the subgrade in the shape of the channel, it should be wetted before placing the tiles in order to prevent the withdrawal of moisture from freshly placed plastic soil-cement mixture between the joints. The tiles also should be fully saturated, at least 24 hours before laying. For soil-cement lining, there will be a natural safeguard against cracking due
162 to closely spaced joints as in brick linings. As the soil-cement tiles will be saturated before laying, there will be little or no probability o f d a m a g e o f the lining due to expansion o f the tiles after absorpation. However, during the drying period, contraction o f tiles m a y result in cracks in the joints. Therefore, it is suggested to fill the joints with b o n d preventing materials. It is suggested that approximately 7.5 m m joints between the tiles should be provided. According to Khair (1980), the joints m a y be filled with b o t h plastic soil-cement mixtures and cement m o r t a r (1:3). Plastic soil-cement should be applied with an allowance so that at least 5.0 m m cement m o r t a r could be applied over the plastic mixtures after its curing. Besides, any b o n d preventing materials such as asphaltic materials m a y be used as a joint filler if f o u n d resistant to weather, insects, chemical attack and weeds.
Conclusions
Soil-cement tiles are expected to be durable to flowing (at a r o u n d 2 m/sec.) water if they are constructed to meet the standard durability criteria (7-day strength and British durability test) except those made f r o m plastic soil; plastic or non-granular soils should be pulverized to pass t h o r o u g h 2 m m sieve to be resistant against erosion due to flowing water. The seepage losses in channels lined with soil-cement tiles is not expected to be more than 0.00123-0.00343 m 3 / m 2 / d a y ; this is very small even in comparison with concrete lining. The soil-cement lining thus seems to be attractive and very promising in areas where irrigation water is costly.
References
Ahuja P.R. & Mehndiratta K.R. 1967. Canal lining - a review. Central Board of Irrigation and Power, Symposium on-Canal Lining, Publication No. 82. New Delhi, India. BS1924. 1975. Methods of Testsfor Stabilised Soils. British Standards Institution, UDC 624 131.3: 631.4, Gr. 9 London. Corps of Engineers, U.S. Army. 1956. Summary Reviewsof Soil Stabilization Process. ReportNo. 3. Soil-Cement, Miscellaneous Paper No. 3-122 (pp 1-27). FAO. 1971. Irrigation canal lining. Irrigation and Drainage Paper No. 2, Land and Water Development Division. Food and Agricultural Organization, Rome. Jenkins D. 1981. Irrigation and water distribution systems for tubewells and low-lift pumps in Bangladesh. USAID, CARE-Bangladesh. Khair A. 1988. Soil-cement tiles for lining small irrigation canals in developing countries. Ph.D. thesis, University of Newcastle upon Tyne, UK. Kinori B.Z. 1970.Manual of Surface Drainage Engineering, Vol. I. Elsevier Publishing Company, Amsterdam-London-New York.
163 Lambe T.W. & Moh Z. 1957. Improvement of strength of soil-cement with additives. Highway Research Board Bull 183: 38-47. Portland Cement Association. 1956. Soil-Cement Laboratory Handbook. 33, West Grand Avenue, Chicago 10, Illinois, USA. Portland Cement Association. t984. Soil-Cement for Facing Slope and Lining Channels, Reservoirs, and Lagoons. Soil-Cement, 5420 Old Orchard Road, Skokie, Illinois 60077-5321, USA. Saran R., Dwivedi N.K. & Sangal S.P. 1967. Lining water Courses. Central Board of Irrigation and Power, Publication No. 82, New Delhi, India. Sarker S.N. 1967. The Problem of Canal Lining. Central Board of Irrigation and Power, Publication No. 82, New Delhi, India. USBR. 1963. Linings for Irrigation Canals. United States Department of Interior Bureau of Reclamation, USBR, Fort Collins.
Soil-cement tiles for lining irrigation canals
A . K H A I R 1, C. N A L L U R I 2 a n d W . M . K I L K E N N Y 3 l Department of Irrigation Water Management, Bangladesh Agricultural University, Mymensingh, Bangladesh; 2,3 Department of Civil Engineering, University of Newcastle upon Tyne, UK Received 12 September 1990; accepted 25 February 1991
Key words: irrigation canal, soil-cement tile, compressive strength, durability, erosion due to flowing water, seepage losses Abstract. Laboratory flume test was conducted to investigate the effect of flowing water an soilcement canal tiles. For this purpose, soil-cement tiles were constructed from different soils at various cement contents. A flume, 3 metre long and 100 mm wide, was lined with the tiles and the lined bed was subjected to flow velocities of around 2 m/s for a period of 7 days. The tiles made from coarse-textured soil (sandy loam and silt loam) aggregates of 5 mm and from fine textured soil (clay loam) aggregates of 2 mm size were found to be intact and smooth even when constructed at a cement contents lower than that needed to meet the durability requirements. Attempts were also made to measure seepage losses of soil-cement tile linings. A channel section of approximately 1 metre length with a side slope of 1:1 was constructed in the laboratory with the tiles and seepage losses measured by the ponding method were found to be in the range of 0.00123-0.00343 m3/mZ/day. The results clearly suggest that soil-cement tiles (irrespective of type of soil) made with 2 mm or less size of soil aggregates are erosion resistant and due to very little or negligible rates of seepage losses, the soil-cement tile lining of irrigation canals is expected to be very promising especially in the areas where irrigation water is costly.
Introduction G a r g & C h a w l a (1970) r e p o r t e d t h a t in u n l i n e d i r r i g a t i o n c a n a l s y s t e m s s e e p a g e losses a r e so h i g h t h a t , in s e v e r a l s y s t e m s , t h e q u a n t i t y o f w a t e r d e l i v e r e d to t h e fields m a y be less t h a n 5 0 % o f t h a t d r a w n in t h e h e a d . A c c o r d i n g t o t h e F A O (1971) t h e s e e p a g e losses p e r 1.6 k m l e n g t h o f an i r r i g a t i o n c a n a l c a n be as h i g h as 20O7o o f its c o n v e y a n c e c a p a c i t y . A h u j a & M e h n d i r a t t a (1967) r e p o r t ed 18 to 50070 o f w a t e r losses in i r r i g a t i o n c a n a l s in I n d i a . S a r a n et al. (1967) s t a t e d losses o f a r o u n d 4 7 % in i r r i g a t i o n c a n a l s in I n d i a , 33 to 6 0 % in U S A a n d 25 to 6 0 % in M e x i c o . A c c o r d i n g to J e n k i n s (1981) t h e c a n a l w a t e r losses in B a n g l a d e s h w e r e a b o u t 5 0 % in a 300 m l o n g , 57 l i t r e s / s size e a r t h c h a n n e l . Besides s u c h a h e a v y loss o f v a l u a b l e i r r i g a t i o n w a t e r , excess s e e p a g e c o n t r i b utes to w a t e r l o g g i n g o f f a r m l a n d s , salt a n d alkali c o n c e n t r a t i o n s in soils
152 resulting in costly maintenance roads and drainage systems and reduction in total agricultural output. USBR (1963) and Sarker (1967) stated that in many irrigation projects this led to very uneconomical irrigated agriculture and at times to abandoning of the entire project. Canal lining is considered to be most effective in reducing water losses and practical linings should be near impervious, inexpensive, strong and durable. Hard surface linings of reinforced and plain concrete, sand-cement blocks, stone and brick masonry and asphalt concrete meet many of these requirements but are the most expensive. Although brick and stone masonry linings are commonly used in many developing countries as low cost materials for lining main canals, branches and distributories, the cost are prohibitive for small channels. In many countries low cost materials such as impermeable earth, bentonite, vegetative covering, polythene sheets, asphalt mats, etc. are being used as low cost linings to minimise water losses in irrigation canals at varying degrees of success. Although these linings have been characterized as low cost techniques, their durability is very uncertain. While initial costs may be low, maintenance costs could be high. These linings may be highly susceptible to damages by burrowing animals, weed puncture, rain and flowing water. Besides many substances also have been used to stabilize or seal canal and lateral subgrade materials. These include specially treated resins, chemicals such as sodium silicate in combination with sodium and clacium chloride, a commercial resin cement, lime, portland cement, asphalts, petrochemicals, and others including combinations of the above. Corps of Engineers (1956) described several promising chemical soil stabilizers, but attached certain limitations in their use as well as their unfavourable economics and concluded that the best way forward was re-evaluation of stabilization with conventional materials, i.e. cement or asphalt. USBR (1963) reported that soil-resins linings often deteriorate badly shortly after construction and chemicals are not adaptable to canal use because of the high cost as well as their poor resistance to wetting-drying or freezing-thawing cycles. Kinori (1970) stated that asphalt concrete lining is very costly and can be used only for large channels. Asphaltic oil linings deteriorate rapidly when exposed to rain and sunshine. There is a tendency for asphalt to separate from the aggregate when exposed to water over a long period causing rapid disintegration. Asphalt mats are usually damaged by weed puncture. Plastic film and synthetic rubber membrane linings are usually damaged by weed growth. Soil is the oldest, cheapest and probably the most use of construction materials. However, there are limitations to the use of natural soils due to its lack of strength and its valnerability to moisture content changes and the erosive effects of external agencies. Soil stabilization is a technique aimed at increasing or maintaining the stability of the soil mass. Lambe & Moh (1957) describe that portland cement is one of the most
153 common and successful stabilizer for soils. When cement is used as a soil stabilizing agent to improve its strength and its resistance to change, it is termed soil-cement. Portland Cement Association (1984) has described that engineers and contractors have been using soil-cement to pave roads, streets, airports and parking areas and its performance has been outstanding. The Portland Cement Association also stated that soil-cements' low-cost, ease of construction utilization of local or inplace soil make such application economical practical and environmentally attractive. The extensive use of soil-cement for road pavements and runways has led to the experimental use of this material for canal and ditch lining. There are two types of soil-cement lining: compacted (standard) and plastic. Standard soilcement lining has proved to be unsuccessful mainly due to lack of optimum compaction. The portland cement Association (1956) reported that a higher percentage of cement is always needed to make durable plastic soil-cement lining and also is susceptible to damages due shrinkage cracks. However, the outstanding service record of soil-cement in other fields indicates that soilcement could be a promising low cost lining if it can be properly placed and compacted to obtain maximum density without difficulty. In the circumstances, Khair (1988) showed that soil-cement tiles of 20 to 25 mm thickness if constructed with a cement contents to satisfy the criteria as mentioned below is durable in the irrigation field to withstand the stresses induced by the sun and rain: - Soil-cement specimens should not suffer a loss in strength more than 10% after 7-day immersion test (British durability test). - Soil-cement specimens should give a minimum wet unconfined compressive strength of 1.724 M N / m 2 after 7-day curing in the humidity cabinet. Khair also showed that such type of lining with a life expectancy of 8 years is economically superior to all other linings (plastic soil-cement, asphalt mat, precast concrete section, brick lining, clay plastering and unlined section) currently being used in Bangladesh. The merit of a satisfactory lining not only lies in its ability to resist destructive forces of weathering (sun and rain) but it must be resistant to erosion caused by flowing water as well as impermeable engough to reduce seepage losses. Hence, a detailed experimental programme was undertaken at the University of Newcastle upon Tyne, UK to investigate the resistant of soilcement tile to flowing water and as well as to assess its merit in reducing seepage losses.
154
Experimental investigations
Selection o f soils
Three different types of soil (clay loam, sandy loam and silt loam) were collected for this investigation whose physical and chemical properties are shown in Table 1. The results in Table 1 show that soils collected for the present investigation are almost suitable for cement stabilization. The soils for this investigation were not selected merely on the basis of the suitability according to the criteria set by previous investigators for the construction of road pavements and rural houses, rather the soils were selected randomly with a view to establishing criteria for the construction of soil-cement tiles for lining small irrigation canals.
Preparation o f soil-cement tiles
The Brepak (Developed by the Building Research Establishment, UK) block making machine was used for the manufacture of soil-cement tiles. The press consists of a moulding area of fixed size which, together with the structural frame, forms an integral unit of an all steel construction. Access to the mould area is via a top cover plate, pivoting about a corner mounted located pin. The press is fittted with a lever arm extension and mechanical linkage which provides a means of locking the top cover plate onto the mould and also allows for initial compaction of the block material within the mould area. Once the lever arm and cover plate are secured the compaction pressure is then applied using a hand operated hydraulic pump. This manually operated machine is especially suitable for rural areas where there is no power supply. The standard size of building block as produced by the Brepak press is 290 x 140 x 100 mm. The press is a constant volume type and ram moves a fixed distance so that always a standard block size with a thickness of 100 mm is produced. Therefore,
Table 1. Physical and chemical properties of soil samples.
Soil type Liquid limit (%) 33 27 35 Plastic limit (%) 20 non-plastic non-plastic Plasticity index (070) 13 Organic content (%) 1.07 2.27 1.69 Sulphate content (%) 0.056 0.047 0.052
Clay loam Sandy loam Silt loam
155 to produce tiles of varying thickness, steel separator plates were introduced into the moulding cavity of the press. In order to construct tiles of 25 m m thickness, two separator steel plates measuring 289 × 138 × 12.5 m m were used. The mass of cement treated soil mixture required to make a tile of the size 290 × 140 × 25 m m was calculated f r o m the following relationships: m = (1015 + 10.15 w) P~ where, m w (1)
= mass of cement-treated soil mixture, g = o p t i m u m moisture content of the mix in per cent obtained at a compaction pressure of 10 M N / m 2 Pd = m a x i m u m density of dry soil plus cement in M g / m 3 achieved at a compaction pressure o f 10 M N / m 2 As the maximum density of soil-cement mixture varies only slightly (Portland Cement Association 1956) with cement content the result of the moisture density (Table 2) relationship obtained at 6% cement content at a compaction pressure of 10 M N / m 2 were used for moulding the tile specimens at different cement (ordinary Portland Cement) contents. The measured amount of stabilized soil needed to produce a tile of 25 m m thickness as calculated using Eq. 1 was put into the mould, then a separator plate, a further amount of mix for another tile followed by the second plate and finally another amount of mix for the third tile. Then the top cover plate of the press was moved to its closed position and the main hand lever was removed through an arc to initially compact the soil. Next, the flow control valve on the hand hydraulic p u m p was closed and the handle was operated until a pressure of 8,000 psi, approximately 10 M N / m 2 effective pressure on the tile, was indicated. Then the flow control valve was released and the lever arm was lifted from its horizontal position and reversed to its original start position. By applying downward force on the lever arm, the newly pressed tiles were demoulded f r o m the mould box. In one operation of the machine, 3 tiles of size 290 × 140 × 25 m m are produced and a man is capable of producing 150 tiles per day. Cost incurred to produce such type of 1,000 tiles is approximately US $ 5.0 only. After construction, the tiles were wrapped in polythene bags and
Table 2. O p t i m u m moisture contents and m a x i m u m densities of soil-cement mixture.
Soil type
Aggregates
M a x i m u m dry density ( M g / m 3) 1.984 1.886 1.630
O p t i m u m moisture content (%) 12.45 12.40 15.00
Clay loam Sandy loam Silt loam
Soil + 6% cement Soil + 6°70 cement Soil + 6% cement
156
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0 A
C L A Y - L O A M SOIL SANDY-LOAM
E
Z -3.0 "r I--. 0 Z L~
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Z
-4 -M -/Tn-2
1.0
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,
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CEMENT
CONTENT (%),C
Fig. 1.
Effect of
cement content on strength of soil-cement specimens after 7 days curing and 24
hour immersion.
the bags were sealed to prevent any loss of moisture and to reduce carbonation effect. The sealed bags were then stored in a humidity cabinet for 28 days curing.
Durability and compressive strength tests
Tests were conducted on soil-cement cylindrical specimens in accordance with Britsh Standard (BS1924. 1975) to establish the durability requirements with various cement contents in the mix. Figure 1 shows the relationship between the cement content and 7-day wet unconfined compressive strengths (1.724 M N / m 2 and 1.4 M N / m 2 are the c o m m o n minima for soil-cement used for road pavements and for building blocks, respectively) of the specimens whereas Fig. 2 shows their resistance to 7-day immersion. Figures 1 and 2 suggest that the criteria of minimum unconfined compressive strength of 1.724 M N / m 2 and 7-day immersion test (not to suffer a loss in strength by more than 10%) are met with the cement contents of 8%, 11 °70 and 10% for clayey, sandy and silty loams, respectively.
157
rio
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0 CLAY-LOAM z,. S A N D Y - L O ~
ff 9o
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,
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/
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2.0
4.0 6-0 B.0 I0.0 CEMENT CONTENT ( ~ )
t2.0
14.0
16,0
Fig. 2. Resistance to i m m e r s i o n of soil-cement specimen at different c e m e n t contents.
Erosion and seepage tests in f l u m e s Tiles of 25 m m thick made (using Brepak machine) from various soils at different cement contents with o p t i m u m moisture contents and densities were used for erosion tests. Curing period has significant effect on strength of soilcement specimens. Khair (1988) showed that the strength at 7-day are approximately 60 to 70°7o of those at 28 days. Hence 28 days curing period was considered to be appropriate to obtain a quality of soil-cement tile. Therefore, after 28 days curing in the humidity cabinet, the tiles were cut to size to be accommodated within a laboratory flume of 3 m long and 100 m m wide. The tiles were fixed on to the bed of the flume using water-proof glue and the joints between the tiles were filled with cement treated soil-mixtures. The flow rates supplied to the flume were measured by an on-line orifice-meter introduced in the supply pipe line. Knowing the water depth (hence the area of flow) the flow velocities were computed. The lined bed of the flume was immersed under water for a period of 7-day to allow the expansive clays, organic matter, sulphate and other detrimental constituents to be fully active. The bed was subjected to flow velocities of around 2 m/Is for a period of further 7 days at a rate of 6 hours per day.
158
Table 3. Erosion (due to flowing water) tests results.
Soil type
Soil aggregate passing sieve size (mm) 5.00
Cement content % 6.00
Bed load gm/hr Negligible
Suspended load gm/hr Negligible
Visual observations
Clay loam
Clay loam Clay loam Clay loam
5.00 3.35 2.80
8.00 8.00 8.00
Negligible Negligible Negligible
Negligible Negligible Negligible
Clay loam Clay loam Sandy loam Silt loam
2.00 2.00 5.00 5.00
8.00 6.00 8.00 8.00
0 0 0 0
0 0 0 0
Surface roughening all unpulverised clay particles washed away -do-doSurface almost smooth, little roughening Smooth surface, no roughening -do-do-do-
D u r i n g this test p e r i o d the tile surface was visually o b s e r v e d for any erosion a n d a t t e m p t s were m a d e to m e a s u r e the e r o d e d m a t e r i a l s q u a n t i t a t i v e l y b y installing a b e d l o a d t r a p at the d o w n s t r e a m end o f flume. A l s o water samples were t a k e n by a specially a d o p t e d pipette at regular intervals a n d a n a l y s e d for the traces o f s u s p e n d e d load, if any, caused by erosion. The e r o s i o n test results are s u m m a r i s e d in T a b l e 3. Seepage tests were c o n d u c t e d in a l a b o r a t o r y channel specially c o n s t r u c t e d a n d lined with soil-cement tiles (after 28 days curing in t h e h u m i d i t y cabinet a n d the j o i n t s being filled with b o t h the plastic soil-cement a n d cement mortars). The tiles were o f 25 m m thick a n d m a d e o f clayey, s a n d y an silty l o a m s with
350
.¢v
IN FILL - -
IN CuT tic ORIGINAL GROUND SURFACE
":"
-<--=~
~/"~':~
190T mm
/
Fig. 3.0.056 cumec canal to be lined with soil-cement tiles.
159
350
J~f--IN F I L L +
.....
IN CUT
----=
kV
o Rqrcq N'a-C"G ~ 0 " ~ 7 7
i suRfAcE
T-- m m
~ORIGINAL GROUND SURFACE / I ~ 2 2 1 2 2 ~ o G ~ M~A N ~ M [ N T
Fig. 4. 0.028 cumec canal to be lined with soil-cement tiles.
8, 11 and 10% cement contents (as needed to satisfy durability requirements see Figs. 1 and 2), respectively. Figures 3 and 4 show such test channels representing small channels of 0.056 and 0.028 m3/s conveyance capacities, respectively with 0.1% bed slopes and an average Manning's n around 0.012. After curing the joints the channel was filled with water and the total loss of water (due to seepage and evaporation) measured to an accuracy of 0.1 of a mm of water depth. The reduction in depth was then converted to a volume to estimate the loss by the ponding method using the following relationship: 24 W (d 1- d2) Pt
S = where S W d1 d2 P = = = = =
(2)
seepage rate in m3/m2/day average width of water surface in m depth of water at the beginning of measurement in m depth of water in m after t hours average wetted perimeter in m
Figure 5 shows the rates of water loss in 0.028 m3/s channel section plotted against time in days lapsed after the beginning of the tests. It can be seen that a steady rate of water loss establishes after a period of about 8 - 1 0 days in all cases. The water losses when nearly constant were considered as the water losses due to seepage and evaporation for tile linings. In order to quantify the evaporation losses, if any, the channel was covered by spreading an impervious polythene sheet around its perimeter and water depths measured at 24 hours intervals over a period o f 8 days. The losses of depth due to evaporation were then expressed as the equivalent rate of seepage losses. The seepage losses for the soil-cement linings were computed deducting the average evaporation loss from the total losses as obtained from the Fig. 5.
160
I00
:>-
A O H
A O
SILT-LOAM
SOIL SOIL SOIL
< cl 9.0 ~ 8.0
SANDY- LOAM CLAY-LOAM
E
im 7.0
6.0
bJ
~D <
5.0
A A ^
}.._
O 4.0
~3,0
LO
m 2.0 O
-3 klJ p-
cr <
I.O [, 2.
I I I I i I i
~: o o
0
4
6 TIME
8
I0
12
14
16
IN DAYS
Fig. 5, Rate of water losses in a smaller canal section lined with soil-cement tiles made from different type of soils.
Results and discussion Tile surface, made from clay loam soil aggregate of above 2 mm size, were roughnened due to the washing away of unpulverised clay particles when subjected to flow (bed shear stress) velocities of around 2 m / s . The soil loss due to erosion in these cases was so small that the usual methods failed to detect it. The tiles made from sandy loam soil aggregates of 5 m m and above and from clayey soil aggregates o f 2 m m and less in size were found to be intact and smooth even after 7 days flume operation at velocities around 2 m / s . Tiles made from clay loam soil need, 8°70 cement content to meet the standard durability criteria (Figs 1 and 2) but were found undurable to flowing water when constructed with soil aggregates larger than 2 m m size. On the otherhand, tiles made from silt and sandy loam soils were found unaffected to flowing water even when constructed at a cement contents lower than those needed to meet the standard durability criteria.
161 The losses (seepage + evaporation) estimated from Fig. 5 are 0.0018, 0.003 and 0.004 m3/m2/day for soil-cement tiles made from clay loam, sandy loam and silt loam soils, respectively. In the field condition, evaporation losses are generally neglected but the measurement of evaporation may be necessary when evaporation losses are significant in comparison to seepage losses. In this study, the average computed evaporation loss was 0.000572 m3/m2/day and was considered to be significant in comparison to seepage losses and hence seepage losses for the linings were computed by deducting this evaporation loss. The seepage losses thus obtained were 0.00123, 0.00243 and 0.00343 m3/m2/day for the tiles made from clay loam, sandy loam and silt loam soils respectively. These losses are negligible in comparison to even sophisticated concrete lining for which the average seepage toss is about 0.084 m3/m2/day. In the laboratory, under controlled conditions the losses ranged from 0.00123-0.00343 m3/m2/day, but even considering the field conditions (where proper controlled criteria may not be applicable) the seepage losses through the soil-cement tile lining may not exceed about 0.005-0.01 m3/ mZ/day. Khair (1988) stated that soil-cement tiles are not structurally strong enough to resist external forces such as walking animals, earth or hydrostatic pressures. Therefore, the channel for lining with soil-cement tiles should be constructed in such a way so that the bottom and sides of the channel should neither be subjected to uplift or horizontal pressures of earth and water. Earth pressure can be avoided if the bank of the canal is made flatter than the angle of the repose of the bank material. When the bottom of a channel is above the groundwater surface, the channel will not be subjected to uplift pressure due to water. A compacted, stable subgrade is a pre-requisite for soil-cement tile lining to avoid damages due to walking animals. Construction of soil-cement canal tiles to resist damages due to walking animals would be highly uneconomical and therefore, it is justified to accept periodic maintenance than to have a foolproof, stong but costly lining. Soil-cement tile linings may also fail due to adverse subgrade conditions such as loss of support through piping action or heave of expansive clays. Therefore, either lining should be avoided on expansive clays or such clays should be replaced by non-expansive soils. Failure by cracking of the lining in many cases can be attributed to the poor preparation of subgrades. Before, placing tiles, the subgrade should be prepared, dressed and compacted to a level according to the required cross-section of the canal. After the preparation of the subgrade in the shape of the channel, it should be wetted before placing the tiles in order to prevent the withdrawal of moisture from freshly placed plastic soil-cement mixture between the joints. The tiles also should be fully saturated, at least 24 hours before laying. For soil-cement lining, there will be a natural safeguard against cracking due
162 to closely spaced joints as in brick linings. As the soil-cement tiles will be saturated before laying, there will be little or no probability o f d a m a g e o f the lining due to expansion o f the tiles after absorpation. However, during the drying period, contraction o f tiles m a y result in cracks in the joints. Therefore, it is suggested to fill the joints with b o n d preventing materials. It is suggested that approximately 7.5 m m joints between the tiles should be provided. According to Khair (1980), the joints m a y be filled with b o t h plastic soil-cement mixtures and cement m o r t a r (1:3). Plastic soil-cement should be applied with an allowance so that at least 5.0 m m cement m o r t a r could be applied over the plastic mixtures after its curing. Besides, any b o n d preventing materials such as asphaltic materials m a y be used as a joint filler if f o u n d resistant to weather, insects, chemical attack and weeds.
Conclusions
Soil-cement tiles are expected to be durable to flowing (at a r o u n d 2 m/sec.) water if they are constructed to meet the standard durability criteria (7-day strength and British durability test) except those made f r o m plastic soil; plastic or non-granular soils should be pulverized to pass t h o r o u g h 2 m m sieve to be resistant against erosion due to flowing water. The seepage losses in channels lined with soil-cement tiles is not expected to be more than 0.00123-0.00343 m 3 / m 2 / d a y ; this is very small even in comparison with concrete lining. The soil-cement lining thus seems to be attractive and very promising in areas where irrigation water is costly.
References
Ahuja P.R. & Mehndiratta K.R. 1967. Canal lining - a review. Central Board of Irrigation and Power, Symposium on-Canal Lining, Publication No. 82. New Delhi, India. BS1924. 1975. Methods of Testsfor Stabilised Soils. British Standards Institution, UDC 624 131.3: 631.4, Gr. 9 London. Corps of Engineers, U.S. Army. 1956. Summary Reviewsof Soil Stabilization Process. ReportNo. 3. Soil-Cement, Miscellaneous Paper No. 3-122 (pp 1-27). FAO. 1971. Irrigation canal lining. Irrigation and Drainage Paper No. 2, Land and Water Development Division. Food and Agricultural Organization, Rome. Jenkins D. 1981. Irrigation and water distribution systems for tubewells and low-lift pumps in Bangladesh. USAID, CARE-Bangladesh. Khair A. 1988. Soil-cement tiles for lining small irrigation canals in developing countries. Ph.D. thesis, University of Newcastle upon Tyne, UK. Kinori B.Z. 1970.Manual of Surface Drainage Engineering, Vol. I. Elsevier Publishing Company, Amsterdam-London-New York.
163 Lambe T.W. & Moh Z. 1957. Improvement of strength of soil-cement with additives. Highway Research Board Bull 183: 38-47. Portland Cement Association. 1956. Soil-Cement Laboratory Handbook. 33, West Grand Avenue, Chicago 10, Illinois, USA. Portland Cement Association. t984. Soil-Cement for Facing Slope and Lining Channels, Reservoirs, and Lagoons. Soil-Cement, 5420 Old Orchard Road, Skokie, Illinois 60077-5321, USA. Saran R., Dwivedi N.K. & Sangal S.P. 1967. Lining water Courses. Central Board of Irrigation and Power, Publication No. 82, New Delhi, India. Sarker S.N. 1967. The Problem of Canal Lining. Central Board of Irrigation and Power, Publication No. 82, New Delhi, India. USBR. 1963. Linings for Irrigation Canals. United States Department of Interior Bureau of Reclamation, USBR, Fort Collins.
