Effect of Wetting-Drying Cycles on Mechanical Behaviour and Electrical Resistivity of Unsaturated Subgrade Soil

Compacted soil is widely used in road and railway subgrade, while alternation of seasons can cause fluctuations in moisture content of soil (i.e., wetting-drying cycles) and influence the performance of soil. In order to research the effect of wetting-drying cycles on mechanical behaviour and electrical resistivity of compacted unsaturated subgrade soil, wetting-drying tests considering different number and cyclic amplitude were conducted on compacted unsaturated clay specimens, and the electrical resistivity and unconfined compressive strength of soil were measured in this study. The AC (alternative current) two-electrode method was applied in the resistivity measurement. The experimental results show that increasing number and cyclic amplitude of wetting-drying cycles can both reduce the strength and electrical resistivity of the compacted unsaturated specimens. After 3-4 wetting-drying cycles, the strength and electrical resistivity tend to be constant value. The change of pore structure can be the key factor leading to the reduction of electrical resistivity of soil subjected to wetting-drying cycles and consequently causing the decrease of soil strength in the present study. Thus, the electrical resistivity can be adopted to indirectly assess the mechanical behaviour of unsaturated compacted soil after wetting-drying cycles.