Study of pore size distribution of expansive soil during wetting-drying cycle and its application

Mercury intrusion porosimetry (MIP) test is used to study the change of pore size distribution of expansive soil during wetting-drying cycle. It is found that the microstructural parameters of expansive soil are increasing with the increasing number of cycles, such as the total volume of the pores, the porosity and the average pore diameter. After theoretical analysis and contrast experiments, the cause of test result deviation mainly stemms from two respects: one is the volume shrinkage of expansive soil samples during the wetting-drying cycle; the second is the influence of pore shapes and limited test pressures. And a reasonable amendment is given to the test data. Furthermore, the soil-water characteristic curves (SWCC) of expansive soil during wetting-drying cycle are calculated through the modified pore size distribution curves which are obtained from MIP test. Finally, the change rule of matrix suction of expansive soil during wetting-drying cycle is studied to deduce the relationship between the matrix suction and number of cycles. The results show that the moisture content 28% is the critical point; when the moisture content is larger than the critical value, the matrix suction increases linearly with the increase of cycle number; when the moisture content is smaller than the critical value, those are on the contrary. The paper gives a new approach to explain the wetting-drying effect of expansive soil mechanical behaviors.