Abstract: The size of the north anchor deep pit of Runyang Bridge is about 69×50×50m. The excavation support structure in this pit is concrete diaphragm wall with internal support structure, and the diaphragm wall is embedded into rocks. In order to know the safety margin and the failure process of this pit, 3-D nonlinear finite element analysis with excavation simulation is carried out with the finite element analysis software of ANSYS. The excavation process is simulated with the “Element Die/Active” function of ANSYS. The self-weight of soil in the finite element model is increased hypothetically until the support structure is destroyed, so that the failure process of support structures can be simulated. Comparing the assumed self-weight of soil to the real one, the safety margin of the pit can be obtained. The numerical results show that all the failures of the pit begin with the collapse of the internal support and the failure models are different in various excavation depths. This method also can be applied to other pits if their support structure is relatively stiff.
Keywords: deep pit, spatial finite element analysis, failure model.
Abstract: The size of a very deep pit is about 69×50×50m and it is difficult to analyze with traditional approximate method. In order to know the details of the deformation and internal force of the excavation support structure, spatial non-linear finite element analysis is carried out in which the excavation process is considered. The interaction between the excavation support and the soil, the difference between various excavation plans, the influence of ground water lowering and sensitive analysis of critical parameters are discussed in detail. The numerical results show that the deformation of the continuous concrete wall with interaction effect will be 10 times of that without interaction effect, while the difference of support axial force will be 1.5 times in the two cases. At the same time, the excavation plan and ground water lowering are also important for the deformation and internal force in the support. The analysis results show that the interaction between soil and structure and simulation of excavation process are necessary in such complex problems.
Keywords: interaction, deep pit, spatial finite element analysis