Mechanical Properties of Soft Soil considering the Influence of Unloading Stress Paths

The mechanical properties of soft soil are crucial for the design and construction of underground space excavation; however, the current design and numerical analysis of underground spaces consider the loading mechanical parameters, ignoring the influence of the unloading stress path resulting in frequent construction accidents in practice. Here, soft soil in Shenzhen, China, is taken as the research subject, and a series of consolidated-undrained unloading tests are performed. First, K0 consolidation is conducted. Then, unloading tests are performed with different unloading ratios to simulate different unloading stress paths. The test results show that the soft soil deformation characteristics are closely related to the stress path and unloading ratio. Under different unloading ratios, soft soil will undergo compression deformation or rebound deformation. Under unloading conditions, the deviator stress-strain curve satisfies a hyperbolic function and can be normalized with the average consolidation confining pressure. With the increase in the unloading ratio, the initial tangent modulus first decreases and then increases, the cohesion decreases, and the internal friction angle does not change significantly. The loading mechanical parameters are not suitable for numerical calculation in unloading engineering. In this paper, more unloading paths are considered, such as UU1.0 and UU0.5. The results of the study provide a theoretical basis for the calculation of the numerical analysis of the soil body at different depths in rich soft soil pits.