Effects of in situ wetting–drying cycles on the mechanical behaviour of an intact loess

In situ wetting–drying cycles significantly and repeatedly influence the soil water content in the active zone but not in the steady zone. To investigate effects of in situ wetting–drying cycles on the mechanical behaviour of intact loess, a series of pressure plate tests was carried out with an intact loess sampled from the active and steady zones. Results show that the specimens from the steady zone have higher yield stresses at given suctions and a larger inclination of normalized loading collapse (LC) curve than the specimens from the active zone. As evidenced by the scanning electron microscopy results, the clay particles accumulating around the contacts between silt particles are widely observed in the former specimens but not in the latter specimens. The distribution of clay particles in the former specimens results in a stabilized skeleton with mechanical properties sensitive to suction variations. On the other hand, the maximum collapse potential of the specimen from the steady zone is 37% larger than that of the specimen from the active zone, mainly because of the larger inclination of normalized LC curve owned by the former specimen.