Volumetric Behavior of Compacted Stiff Clay Subjected to Wetting and Drying Cycles

Expansive stiff clays are inevitably exposed to wetting and drying cycles in the earthwork. During which, the distinct volumetric responses of the soils can have significant influences on engineering safety. For this reason, one-dimensional swelling-shrinking tests under cyclic controlled-suction between 0 and 38 MPa were conducted on compacted Nanning stiff clay samples subjected to different vertical stresses (σv = 100, 200, and 400 kPa). Results showed that under vertical stress of 400 kPa, the drying induced shrinkage was always larger than wetting induced swelling, thus the irreversible contraction was accumulated. Whereas, at vertical stresses lower than 200 kPa, the swelling upon wetting gradually decreased with no obvious changes in shrinkage upon drying, therefore the accumulated irreversible deformation changed from dilation to contraction from the third cycle. In addition, the samples were found to reach an equilibrium stage after five to six cycles, thereafter only elastic volumetric deformation occurred in further wetting–drying cycles. Such phenomena were interpreted from the perspective of microstructural adjustment in samples during wetting–drying cycles based on swelling kinetics analysis.