Experimental study on the deformation behavior of soils under one-dimensional unloading

Soils are usually subjected to one-dimensional unloading due to the excavation, groundwater recharge, and other activities. This paper investigates the deformation behavior of soils under one-dimensional unloading. A series of oedometer tests with loading–unloading cycles were conducted on silty sand, silt, silty clay, and muddy silty clay samples extracted from southern Jiangsu, China. The influence of effective vertical stress before unloading on rebound deformation of soils was investigated. Test results show that the unloading deformation of soils increases nonlinearly with the increasing unloading ratio. When the unloading ratio reaches 0.8, only 30% of the total rebound deformation occurs. The rebound ratio increases with the increasing effective vertical stress before unloading. A power function was proposed to describe the relationship between one-dimensional unloading modulus and unloading ratio with two parameters named initial one-dimensional unloading modulus and decrease rate of the one-dimensional unloading modulus. The initial unloading modulus increased linearly with the increase of effective vertical stress before unloading, and a power function could be used to describe the relationship between the decrease rate and effective vertical stress. Formulas were also proposed to predict the initial unloading modulus and decrease rate of the one-dimensional unloading modulus based on piezocone test measurements.