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Studies have shown that compressible materials between a rigid retaining wall and backfill reduced static and dynamic forces on the wall. Nowadays, panels with low density are used. Expanded polystyrene, which is one of the geo-synthetic products known as geofoam, is a compressible material. Geofoam is one of the geo-synthetic materials that are made of foam. Geofoam is very practical in geotechnical engineering due to its low bulk weight versus soil bulk weight and high compressibility, rapid and simple implementation, thermal insulation, and resistance against water absorption. It can be used in retaining walls, road construction projects as light fillers, and to reduce stress due to vertical loads in the base and sub base layers. Geofoam is one of the geosynthetic product which is made of lightweight expanded polystyrene (EPS) or extruded polystyrene (XPS). EPS geofoam is a block or planar rigid cellular foamed polymeric material that can be used in geotechnical applications. Studies have been shown that geofoam placed directly against a rigid retaining wall can reduce static loads on the wall. This study employed a finite difference method program, FLAC (Itasca, 2007), with considering yielding and non-yielding states for retaining walls to evaluate the effectiveness of geofoam panels in improving the statically behavior of retaining walls. To determine the effects of geofoam in soil displacement and earth force acting on the rigid wall, parameters such as the height of retaining wall, density and thickness of geofoam, cross-sectional shape of geofoam panel behind the wall, and also using of two geofoam panels with four panel spacing (50, 100, 150, 200 cm) have been studied via static analysis. In this numerical study three gravity –type retaining walls at heights of 3, 6 and 9 meters and geofoam panels with densities of 15, 20 and 25 (kg/m3) at three relative thicknesses of t/H=0.05, 0.2 and 0.4, were modeled. According to the results using of EPS15 with density equal to 15(kg/m3) which has the lowest density among other geofoam panels has a significant role in reducing of lateral stresses. Although the performance of geofoam in non-yielding retaining walls is better than yielding retaining walls. The results of the present research are as follows: 1- According to results, increasing the geofoam thickness increases soil lateral displacement and reduces forces on gravity retaining walls. The same effect can be achieved by reduction of geofoam density with equal thickness. In other words, Forces on gravity retaining walls are reduced and soil lateral displacement is increased by a reduction of geofoam density with equal thickness. 2- Using two geofoam panels with distance of 50 cm, unlike 3-meter high wall, is proper in the 6 and 9 meters yielding retaining walls. 3- Trapezoidal geofoam increases soil lateral displacement and reduces forces on retaining walls compared to a rectangular geofoam panel with the same cross-sectional area. 4- Effect of geofoam on the reduction of forces on non-yielding gravity retaining walls is more than that on yielding walls. 5- According to results, stiffness of geofoam panel (K=E/t) has significant role in reducing of lateral forces acting on retaining walls. In this study, it was observed that K≤5 MN/m3 provide the most effective range for the design of these system to reduce static forces acting on yielding retaining walls.

Keywords: Geofoam, Gravity retaining wall, Yielding and non-yielding wall, Numerical modeling, FLAC Software.

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