Finite element modeling of lateral swelling pressure distribution behind earth retaining structures
Expansive soils swell laterally as well as vertically. Lateral volume changes will be accommodated by the cracks and fissures if there are cracks and fissures in the soil mass. However, when there are no cracks or the cracks are very small and close up without accommodating all of the volume increase that is required by the expansive soil, the swelling soil becomes restrained in the lateral directions. The result of this restrained case is the development of a lateral swelling pressure. In well compacted high plasticity clay fills, the process of swelling is likely to continue for many years. Thus, classical methods cannot be used to estimate the lateral pressure of expansive soils behind a retaining structure.
In this study, a new finite element modeling of swelling behavior of expansive soil is made by using an analogy between the thermal expansion of the solid material and swelling of the expansive soil. Soil suction profiles for the driest and the wettest steady-state conditions are produced by using static soil suction theory. Thus, a suction envelope can be produced. The validity and applications of the study are investigated by considering several experimental works. Then, some hypothetical considerations that depend upon moisture changes in expansive soil, and in cohesive nonswelling soil (CNS) with different thicknesses and geometries as the backfill behind a retaining structure have been analyzed. The parameters that affect the transmitted lateral pressure on retaining structures are investigated. The results from the numerical modeling compare closely with the results of large-scale laboratory tests. The results also show that the swelling behavior of expansive soils is dependent upon soil suction change of the soil media.
Since the numerical model considers backfill materials with different properties, for example, each finite element in the system can have its own modulus of elasticity,
Poisson's ratio, soil unit weight, and soil suction all can change from point to point in a soil mass; thus, soils with different properties can be simulated as backfill material behind the retaining structure in this model. In the hypothetical cases, effect of size, shape, material, density, and moisture conditions of a backfill on the transmitted lateral pressure are investigated. A comparison of the cases that are simulated in the numerical model are made with results from full-scale tests done by others in order to evaluate the best size, shape, material, or soil moisture condition for transmitting the least lateral pressure to, say, a basement wall.