Review of soil behaviors under excavation unloading of foundation pits

With the construction and development of some large important projects, such as high-rise buildings, subways, earth dams and so on, deep foundation pit has been a critical question in geotechnical engineering. In unloading condition, the mechanical properties for a specified soil are the basis of determining parameters required to simulating analysis and design of deep foundation pit. For long time, parameters of shear strength of soil used in the design of foundation pit are obtained by means of the normal triaxial loading tests. Unloading condition in the excavation process is usually ignored. The research advances in soil behaviors under excavation unloading reported in the literature are reviewed. The research findings are summarized from the conventional triaxial unloading tests,<> K₀ consolidated triaxial unloading tests and true triaxial tests. The existing problems and potential research topics in this field are put forward.