Failure of concrete irrigation canal linings in the forms of cracking, rupture , uplifting and opening of joints , causes loss of water and money in many countries. Foliwing appearance of extensive cracking of concrete linings in Shoeybieh Sugar Cane Industries Unit in khoozestan province ,Iran, extensive research programs were conducted to find the main reasons . In this paper the final results of the researches are presented.
The testing program consisted of laboratory as well as field tests, including identification chemical and mechanical tests of soil samples taken from the borrow pits and canal embankments . Dispersivity tests were performed using pin- hole and chemical methods and swelling tests were conducted using ASTM standard and ISSMFE method. The field test includes the measurement of deformations of the concrete lining and embankment of an actual lined canal with a length of 60 m , due to filling by water. The deformations were recorded by surveying of the elevations of steel bars driven to different depths under canal lining and at different points of canal and its embankment sections.
The results of laboratory tests showed that the soil is low to medium plastic with a classification of CL-ML, having less than one percent soluble content, and being nondisperssive. Swelling tests conducted by ASTM and ISSMFE methods showed completely different results. ISSMFE method resulted in high free swell potential ,while ASTM method indicated a low to medium potential,The results of full scale field tests were all in favor of ISSMFE method. The great difference between. the results of two methods was found due to the different compaction methods as well as the moisture content of the soil sample being prepared for swell tests. While in ASTM method, the sample is compacted by dynamic effort , at optimum water content , in ISSMFE method compaction is done using static effort and a low water content near the shrinkage limit. Therefore, two main factors causing discrepancy between the results of the two methods, i.e. the type of compaction and moisture content are responsible for difference in the structures of the samples being tested and finally different behaviour upon water absorption. The fiocculent structure and lower compaction water content of soil sample in ISSMFE method would result to much higher free swell. Similarity between compaction methods used in the field and static effort used in ISSMFE method, as well as very low soil water content of the canal embankments during lining operation, are the main reasons for swelling of the soil and finally cracking of the concrete linings.
The overall results of the field and laboratory experiments showed that even soils of low to medium plasticity have a high swelling potential when dessication and shrinkage occur due to high temprature and aridity , as it is the case for Khoozestan province . Experiments proved that lower relative density (less than 95%) and compaction in the wet side of optimum water content (about 2 to 3 percent) can effectively control the swelling potential . The research has also proved the superiority of ISSMFE method for evalaution of swelling potential in hot - arid zones like Southern parts of Iran.
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