Experimental studies of mechanical parameters of soft soil under different stress paths in the Tianjin Binhai New Area

By studying the marine soft clay 9-18 m below the land surface,on which many underground projects are laid in the Tianjn Binhai New Area,the consolidated-undrained triaxial compression test(CU),unconsolidated-undrained triaxial compression test(UU) and simulated pressure path tests(DEP) of excavation are carried out on the stress and strain controlled triaxial shear penetration apparatus.According to the experimental results,behaviors of soft soil under different stress paths are related to initial consolidation states.The stress-strain curves of CU and UU tests have hardening characteristics,pore water pressure and the strain of CU test exhibit property of contracting first and then dilating.The stress-strain curve of DEP test has softening characteristics,under constant stress controlled conditions the pore water pressure and the strain of DEP test has property of dilatancy and the pore pressure is negative.DEP test affects the total shear strength properties but has little influence on effective shear strength parameters.It is safe to use the soil shear strength properties of CU test in the design of foundation pit bracing of the Binhai New Area.