Development and application of an instrument for simulating wetting-drying cycles of expansive soils under loads

Alternating rainfall and evaporation in nature severely impact the shear strength of expansive soils. This study presents an instrument for simulating the effect of wetting-drying cycles on the strength of expansive soils under different loads, and its testing error is verified. With this instrument, direct shear tests were performed on samples experiencing 0–6 cycles under vertical loads of 0 kPa, 5 kPa, 15 kPa, and 30 kPa. The results found that this instrument provides a new method for evaluating the effects of wetting-drying cycles on soils, and this method represents actual engineering conditions more accurately than do preexisting methods. It accurately controls the water content within 1% while simulating the specified loads at different soil depths. Cohesion is significantly affected by wetting-drying cycles, while the friction angle is not as sensitive to these cycles. Decrease in shear strength can be attributed to the fissures in soils caused by wetting-drying cycles. The existence of vertical loads effectively restricts shrinkage fissuring and cohesion attenuation, consequently inhibiting the attenuation of shear strength.