The prediction of one-, two-, and three-dimensional heave in expansive soils

Abstract

The prediction of heave in unsaturated, expansive soils has historically been studied primarily as a one-dimensional type analysis. This paper proposes a methodology that can be used for the prediction of one-, two-, or three-dimensional heave. It is suggested that negative pore-water pressures (i.e., soil suctions) can be estimated through a saturated–unsaturated seepage analysis. The results of the seepage analysis are then used as input for the prediction of displacements in a stress–deformation analysis. The formulation of the governing partial differential equations for both seepage and stress–deformation is based on the general theory of unsaturated soils using two independent stress state variables. The elasticity parameter functions required for a stress–deformation analysis can be calculated from various tests, including conventional one-dimensional oedometer tests. The proposed method is studied and tested against data collected on a case history involving a slab-on-ground floor on Regina clay. The predicted results from the two-dimensional analysis agree well with the measured data in terms of both total vertical displacements and final water contents in the soil. The results of a parametric study are also presented to show the effect of measured soil parameters (i.e., swelling index and initial void ratio) and assumed parameters (i.e., Poisson's ratio and coefficient of earth pressure at rest) on the predicted displacements.Key words: heave prediction, unsaturated soil, expansive soil, seepage analysis, stress analysis.