The stress-path of the soilmass surrounding the periphery of a foundation pit project during excavation is simulated using a true triaxial unit; and two kinds of unloading tests are conducted under drainage and undrainage conditions respectively. It can be known from the comparison between the testing results that there is a remarkable difference in the stress-strain relationship of the soilmass provided the drainage conditions are different

which shows that the drainage

condition has an effect to a certain degree on the soilmass’s deformability. Further studies are conducted on the relationship between generalized shear stress and generalized shear strain under drainage conditions during unloading

the results showing the nonlinear relationship of those strain and stress. Finally

the equation to calculated the soil’s unloading shear modulus is deduced when the intermediate principal stress coefficient is defined in the real stress-strain path of the soils.