Although commonly ignored in classical earth pressure methods, precipitation-induced failures in retaining structures highlight a need for explicit consideration of negative pore pressures or matric suction. Changes in the degree of saturation in the backfill can significantly affect active earth pressures. This paper presents an analytical framework for calculating the thrust of active earth pressures under unsaturated steady flow conditions. The proposed method addresses limitations associated with the collapse mechanism and effective stress representation in alternative analytical methods. The formulation was derived by implementing an analytical solution for one-dimensional (1D) steady flow into a limit equilibrium–based effective stress analysis. A closed-form solution for the thrust was obtained by employing a log spiral surface, considering the effect of tension cracks, backslope inclination, and batter for c′-ϕ′ soils with variable backfill saturation. A unified effective stress representa...

Active Earth Pressures for Unsaturated Retaining Structures

Lightly loaded structures constructed on expansive soils are often subjected to severe distress subsequent to construction, as a result of changes in the pore-water pressures in the soil. The structures most commonly damaged are roadways, airport runways, small buildings, irrigation canals, spillway structures and all near ground surface structures associated with infrastructure development. Changes in the pore-water pressure can occur as a result of variations in climate, change in depth to the water table, water uptake by vegetation, removal ofvegetation or the excessive watering of a lawn. An analytical tool for the prediction of heave is extremely valuable to geotechnical engineers. There has been little advancement in the development of such a tool for solving engineering problems. There does not appear to be a computer program that has been written and widely accepted for solving this problem. It is important that such an analytical tool be developed and that it be developed for both oneand two-dimensional problems. The primary objective of this research study is to apply the general theory of consolidation/swelling for unsaturated soils to provide a reliable, practical technique for the prediction of one-, twoor three-dimensional volume change associated with unsaturated, expansive soils. The void ratio constitutive surface of an unsaturated, expansive soil was estimated from volume change indices obtained from conventional oedometer tests. Mathematical equations, which can be applied over a wide range of stress conditions, are proposed to describe the constitutive surfaces for both soil structure and water phase. The elastic parameter functions that are required for the volume change analysis are calculated from the constitutive surfaces with an assumed value ofPoisson's ratio. The solutions to the volume change problems associated with an unsaturated, expansive soil are obtained using both an uncoupled and a coupled approach. In the uncoupled approach, the continuity equation for the water phase and the equilibrium equations are solved independently. Uncoupled solutions are obtained using a partial differential equation solver, called FlexPDE. In the coupled approach, the continuity equation and the equilibrium equations are solved simultaneously. Coupled solutions are obtained using a finite element program, called COUPSO. The examples presented in this study represent typical volume change problems that are often encountered in engineering practice (i.e., influence of vegetation on light engineering structures, water leakage under floor slab,

Uncoupled and coupled solutions of volume change problems in expansive soils

Evaluation of the lateral earth pressure in unsaturated soils with finite element limit analysis using second-order cone programming

Earth pressure profiles in unsaturated soils under transient flow

The calculation of active earth pressure has commonly been performed under dry or saturated conditions. However, in practice soils are usually unsaturated. With the aim of estimating active earth p...

Active earth pressure for soils with tension cracks under steady unsaturated flow conditions

Lateral earth pressures produced by saturated clays with negative pore-water pressures and unsaturated expansive clays with positive matric suctions are considered from a theoretical standpoint. Si...

D. E. Pufahl

Papers

Lateral earth pressures in expansive clay soils