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.