Expansive soil is featured with expansibility

multi-crack and over consolidation. When exposed to natural conditions

it vulnerable to the drying-wetting cycle effect of rain and evaporation

thus the shear strength of expansive soil will decreases with time

resulting in expansive soil slope instability. A series of ring shear tests is conducted on weak expansive soil sampled from Jinmen

Hubei province under the condition of drying-wetting cycles to investigate the variation of peak strength and residual strength. Results show that the shear strength of the sample is related to the normal stress

both its peak strength and residual strength increase with the increase of normal stress. Meanwhile

the greater the normal stress is

the smaller the shear displacement is when the sample reaches the residual strength. As the drying-wetting cycle increases

the peak strength of the expansive soil obviously attenuates

while the residual strength of expansive soils varies slightly

but it is not obvious

which can be approximately considered stable as stable. The peak cohesion and residual cohesion of expansive soils after three dry-wet cycles are almost the same. The difference between the peak internal friction angle and residual internal friction angle is always 2°

which is largely unaffected by the number of drying-wetting cycles.