Research On The Lateral Unloading Behavior Of Soils In Deep Excavation

With the continuously increasing of our country economic scale and the rapid development of urbanization, the urban land increasingly nervous, development and utilization of underground space has become the common understanding. Therefore, the city’s subway, high-rise building and the underground mall in further increased, all of the engineering construction need reliable deep excavation to ensure project safety and normal use. However, for a long time, parameters of shear strength of soils used in design of excavation are obtained by normal triaxial tests. There is something difference to the foundation pit excavation’s unloading stress path, if ignored this difference, often makes between the foundation pit supporting structure of the earth pressure, deformation measurement values and design calculation value have significant differences.This paper uses the SLB-1type stress and strain control type triaxial compression penetration tester, simulation deep excavation lateral soil unloading stress path, studies the pit excavation soils project characteristic to determine the soil parameter, and validates the constitutive model of the unloading stress path. This makes the design and calculation parameters of deep foundation pit more conform to the project actual condition; This has the extremely vital significance theory and practice meaning regarding to the pit excavation project numerical analysis and the optimize design, also to ensuring the security and stability of the foundation pit engineering.By research in this paper, get the following conclusion:(1)Use the Beijing area silty clay simulated lateral unloading and conventional add lotus of soils in deep excavation, and research their deformation behavior, draw a conclusion that the unloading soils’stress-strain relations are still available use Duncan-Chang model, and can use the soil triaxial drained test get the rigidity parameters in HS model.(2)The results of the study show that, for different stress path triaxial test, the soil has different stress path, the soil shear strength parameters are significantly different from the conventional triaxial test. After the soil in unloading process, strength index is less, if use the conventional loading test index design foundation pit, may cause large deformation and even cause engineering accident. (3)In the same consolidation pressure, after the soil experience unloading process, whether the level of soil pit weeks deformation, or pit weeks of surface subsidence, than conventional loading test of the deformed by more than40%, for the safety of the project is unfavorable.(4)Through the simulation results of the finite element software PLAXIS, found that the deformation law of the foundation pit’ lateral soils experience unloading stress are good agreement with the test results, and show that through the finite element software for pit simulation is appropriate.