Abstract: To study the effect of precipitation and drought weather on soil shear strength, a series of quick shear tests is performed on karst red clay samples sampled from Yanshan area of Guilin city, which have been subjected to several wetting/drying cycles. The experimental results show that after several drying and wetting cycles, the red clay samples under fully saturated conditions have no significant peak value in their shear strain-shear stress relationship, showing strain hardening behavior, whereas the oven-dried samples have significant strength peak values, showing strain softening behavior, and their strength tend to be stable as the development of strain. With the increase of the drying/wetting cycle number, both cohesion and frictional angle gradually decrease for both fully saturated and oven-dried samples. Both the cohesion and internal friction angle of oven-dried samples are larger than those of the fully saturated samples, showing more significant variations. In order to study the effects on shear strength and strength parameters of soil samples, the volume changes of the soil samples are also measured after different cycles of wetting and drying. It is found that with the increase of the number of cycles, the volume of the sample decreases first and then remains unchanged.

Key words: red clay, wetting and drying cycles, shear strength