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Expansive soil is one of the problematic soil which it changes in volume by moisture. This soil tends to increase in volume due to water absorption And if It does not allow to increase in volume due to water absorption the pressure create which is said swelling pressure. Swelling pressure can cause more displacement and damage to structures which are adjacent to this soil or buried in this soil. There are different solutions to dealing with the swelling pressure which Geofoam (EPS) is one of the most innovative of them. In this paper, the results of tests which were conducted on a flexible pipe that it is buried in the expansive soil are presented. In this experimental research two boxes were used. The smaller box were putted in larger box. The flexible pipe and geofoam (EPS) were located in the center of small box and then the space around the geofoam (EPS) and flexible pipe was filled by expansive soil. The expansive soil which was used in this research was bentonite. The space between two box was filled by water. On wall of the smaller box The holes were embedded to transmit the water. A dial gage was used to measure the displacement of flexible pipe which was caused by swelling pressure. The measurements of displacement were performed in two parts, one above the pipe and the other in the middle of the pipe. In each part, the displacement was measured in two side, one in the wall side of the box and other in diameter side of the box. Therefore in each test the displacement were measured for 4 points. Subsequent with the measured displacement and the Modulus of elasticity of flexible pipe the swelling pressure was calculated. The purpose of this experimental research is to determine the influence of geofoam (EPS) in reducing the pressure and displacement caused by swelling. In this research, four tests are done on flexible pipe which is buried in expansive soil. In the first experiment, only the flexible pipe was buried in expansive soil. In subsequent tests geofoam (EPS) was used, for protection of buried flexible pipe in expansive soil, in a thickness of 4 mm, 20 mm and 40 mm respectively and the influence of geofoam (EPS) in reducing swelling pressure and displacement was measured. The time of each test was 32 days because after 32 days the dial gage did not show any changes. A comparison conducted on the values of swelling pressure and displacement determined that using a geofoam (EPS) with thickness of 4 mm and 20 mm causes that swelling pressure and displacement decrease up to 50 and 80 percent, respectively. But, no significant reduction of swelling pressure and displacement are saw where geofoam (EPS) with thickness of 40 mm was used. Therefore it can be concluded that increasing in geofoam (EPS) thickness can partially reduce swelling pressure and displacement of expansive soil but The process of decreasing swelling pressure and displacement soil with increasing in geofoam (EPS) thickness not continue.

Keywords: Geosynthetic, Geofoam(EPS), Expansive soil, reduction of swelling pressure

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