The Unloading Mechanical Effects Of Retaining Structure Of Super Large And Deep Excavation Pit

For the safety of the neighboringbuilding, it is of great significance to research on the unloading mechanical effects of the large-scale soft soil deep foundation excavation, because high-level, ultra-high-rise buildings and underground transportation projects are boomed nowdays, more and more deep foundation pits are located in the urban built-up areas. Among the various effecting factors for the calculations of stability and deformation, the soil shear strength parameters and the constitutive model are very important, and the accuracy of shear strength parameters and the constitutive model are closed related to soil stress path. In addition, the deformation and stability calculations are not only related to the stress path but also the groundwater seepage.Based on the large foundation pit at haiba road which is representative among the Pearl River Delta region, conventional triaxial apparatus is respectively used to test the soil samples through the conventional triaxial compression test and active unloading test, the true triaxial apparatus is used to test the soil of the passive zone through unloading tests, and the stress-strain relationship, the initial elastic modulus and shear strength of soft soil under different stress paths are comparative analyzed. Based on the unloading stress-strain relationship of the soil at active area, the unloading nonlinear elastic constitutive model of soil is derivated by simulating the building method of Duncan-Chang model; Based on the unloading stress-strain relationship of the soil at passive zone, tangent modulus is derivated.Based on the theory coupling seepage and stress, a new idea was expounded that the unloading stress of field method was introducted to the coupled stress and fluid analysis, then the finite element analysis model coupling seepage and unloading stress of field for the foundation pit is established.By monitoring the construction of the large foundation pit at haiba road, the horizontal displacement of retaining wall at the top, the deflection curve of retaining structure, the settlement curve of soil outside, the axial force of the supportings are provided as a reliable source of data for the research. Based on the FEM analysis software of Midas GTS, the large foundation pit at haiba road is researched, the conventional loading test parameters of the soil and unloading the test parameters were used to make numerical simulation for the deep foundation excavation, the retaining structure internal force and deformation in different excavation conditions were analyzed, the conclusion was given that calculation results with unloading mechanical parameters was greater than the results with conventional loading test parameters and closer to the monitoring.Based on the finite element model coupling seepage and unloading stress, the Midas GTS finite element analysis software was used to make numerical simulation for the deep foundation excavation and the deformation and stability of the deep foundation project considering groundwater seepage was explored, the numerical simulation results and the monitoring value was analyzed, the conclusion was given that the calculation results of the internal force and deformation coupling seepage and unloading stress was greater than the calculation results only considering the unloading effects and closer to the monitoring value.