Physical Modelling On The Behavior Of Unsaturated Compacted Clay Slope Under Wetting-drying Cycles

Wetting-drying cycle is a natural phenomenon which has effects on the clay slope project. Generally, the slope will go through wetting process under rainfall conditions or long-time humidity seasons, while in the long-time dry seasons the slope will experience drying process. The wetting-drying cycles exert their effects through changing the slope volumetric water content periodically. In wetting process the volumetric water content rises and the suction decreases while the volumetric water content decreases with the suction rises in the drying process. The slope properties will be changed in some extent in every cycle, and these changes will accumulate as the wetting-drying cycles go on. The change in slope properties will affect the slope stability state, which means it is needed to take the effect of wetting-drying cycles into consideration when analyzing the slope stability. The soil properties under wetting- drying cycles have already been widely studied while the slope behavior under wetting-drying cycles is still not fully investigated. The characteristic of wetting-drying cycles can be expressed as the number of cycles and the amplitude of each cycle. The response of slope to wetting-drying cycles with different times and amplitude is of great importance when studying the effects of wetting-drying cycles on slope.In this thesis, a model slope experiment system is established to study the effects of amplitude and times of wetting-drying cycles on the model slope. In the experiment the model slope is established in the model slope box, the wetting-drying cycles are simulated by artificial rainfall and desiccation system. The volumetric water content of the slope is logged by TDR-3 soil water content monitoring system and the suction is logged by FTC-100 thermal conductivity suction sensors. The deformation of the slope is monitored by PIV (particle image velocimetry) technique. The experiment results show that the slope peak volumetric water content decreases as the number of cycles increases, and the peak volumetric water content will reach a steady value after four cycles. The model slope undergoes swell deformation in the first two cycles but swell deformation begins to vanish in the following cycles. Instead, the deformation in the down slope direction increases as the number of cycle increases. We conclude that the times of cycles change the deformation mode. In addition, wetting-drying cycles can only affect the surface layer of the slope. The deformation amount does not increase remarkably as the cycles go on. The wetting-drying amplitude determines the minimum volumetric water content and the maximum suction, but the deformation amount decrease remarkably under high wetting-drying amplitude cycle than that of low amplitude cycle. The higher wetting-drying cycle amplitude results in a deeper deformation region of the slope than that of the lower amplitude cycle. These results explain the effects of wetting-drying cycles on the behavior of unsaturated compacted clay slope.