Model for the simulation of swelling-pressure measurements on expansive soils

Abstract

Numerous laboratory swelling tests have been reported for the measurement of swelling pressure and the amount of swell of an expansive soil. These test methods generally involve the use of a conventional one-dimensional oedometer apparatus. Few attempts, however, have been made to formulate a theoretical framework to simulate the testing procedures or to visualize the different stress paths followed when using the various methods. The simulation of the oedometer tests on expansive soils is required to fully understand the prediction of heave. The correct measurement of swelling pressure is required for an accurate prediction of heave. It is further anticipated that some information on unsaturated soils property functions may be approximated from the back-analysis of the data. A theoretical model is proposed to describe the pore-water pressures with time and depth in a specimen as well as the volume changes during various oedometer swell tests. The model is formulated based on equilibrium considerations, constitutive equations for an unsaturated soil, and the continuity requirement for the pore fluid phases. The transient water flow process is coupled with the soil volume change process. The model can be used to describe the volume-change behaviour, pore-water pressure, and vertical total stress development in an unsaturated soil during an oedometer test performed by any one of several test procedures. The model has been put into a finite element formulation using the Galerkin technique. All the parameters required to run the model can be obtained by performing independent, common laboratory tests. The proposed model was used to simulate the results from free-swell, constant-volume, constant water content, and loaded-swell oedometer tests. Computed values of volume change, vertical total stress, and pore-water pressure are in good agreement with measured values.Key words: unsaturated soil, expansive soil, swelling pressure, theoretical simulation, constant-volume oedometer test, free-swell oedometer test, loaded-swell oedometer test.