Swell pessures and retaining wall design in expansıve soils

Date of Award


Degree Name

M.S. in Civil Engineering


Department of Civil and Environmental Engineering and Engineering Mechanics


Advisor: Ömer Bilgin


Expansive soils cause damages to civil engineering structures in various parts of the world, because they swell when absorb water and shrink when they dry out. Additional stresses applied to the structures due to the swell pressures are important in explaining some of the damages to the structures in expansive soils. Therefore, the prediction of the swell pressures and taking them into consideration in the design of retaining structures is needed. In other words, if these pressures are not included in the design, the stability of the structure will be reduced, potentially to the point of failure. Retaining walls in expansive soils are subjected to uplift forces and friction forces due to the swelling of surrounding soil. More importantly, the walls are also subjected to swell pressures tending to cause additional deformations and bending. In this study, the relationship between the index properties and swelling characteristic of expansive soils is examined. The earlier studies showed that an increase in dry density and plasticity index of the soil cause an increase in swell pressure, while a decrease in natural moisture content cause an increase in swell pressure. The process of swelling and shrinking is a cyclic behavior and continues for many years. Thus, when the expansive soils are present behind retaining walls, traditional lateral earth pressures cannot be used to estimate total pressures acting on the retaining structure. In this study, a new proposed method developed to predict potential swell pressures and to use in the design of retaining walls. A parametric study performed to study the effect of swell pressures on the design of anchored sheet pile walls constructed in expansive soils. The parametric study results show that, based on the soil properties and wall geometry, the expansive soils can significantly affect the design of retaining structures. More importantly, ignoring the effect of expansive soils on retaining walls would result in under design and unsafe structures. In addition, it was comparing between the proposed swell pressure method and the constant swell pressure method, the different between those methods, the previous method (constant swell pressure method) did not consider the changing in plasticity index and the moisture content. On the other hand, the proposed method takes in the account the changing in each of plasticity index and the moisture content that play important roles in the swell pressure.


Retaining walls Design and construction Testing, Soil mechanics Research, Swelling soils Research, Vertisols Research

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