SOIL SUCTION AND ANALYSIS OF RAFT FOUNDATION RESTING ON EXPANSIVE SOILS

Abstract

This study introduces a practical and simple solution for two major problems: (1) predicting moisture movement and estimating the associated volume changes in expansive soils, and (2) analysis of the interaction between a raft foundation and the movements in .the supporting expansive soils. The solution of these problems are accomplished through the development of two computer models.

A three-dimensional moisture diffusion and volume change model named SUCH has been developed. The model SUCH is able to predict the distribution of soil suction and the resulting volume changes in expansive soils with respect to time under a covered area (i.e., raft foundation or pavements) when the supporting soil mass is subjected to different edge conditions that commonly cause moisture changes (i.e., climate, trees, or ponded water). The model SUCH has been validated against field data at four test sites in different countries (i.e., United States, Saudi Arabia, and Australia) with widely varying climatic and soil conditions. In each of these widely divergent sites, the moisture diffusion and volume change model SUCH was shown to be valid. Using the new model SUCH, a method for calculating the edge moisture variation distance is developed. The results of the model analysis showed that different moisture barrier systems and the sand cushion technique can be used to minimize the moisture and volume changes in the supporting expansive soils. The model can also show the effect of either trees or ponded water located adjacent to the foundation, either of which can cause excessive moisture and volume changes in the supporting expansive soils.