Analysis Of The Influence Of Pit-in-pit To Foundation Pit

With the continuous expansion of China’s urban scale, infrastructure is also growing, The number of foundation pit engineering is also increasing. In the actual process of engineering constructions, secondary excavation is needed in the existing foundation pit in order to accommodate the structure of the elevator shaft and bearing platform, which we call pit-in-pit of inner pit. It’s so complicated that Classical theory can not be fully applicable when pit-in-pit exists. And current specifications are also difficult to provide accurate design basis. Therefore the research on the pit-in-pit is of great practical value. Aiming at the current research situation and some problems, the content of the thesis covers the following aspects:1. Analyze and summarize the constitutive models of soil and between soil and structure. The applicable conditions of different constitutive models are obtained by studying the fundamental theories of Mohr-Coulomb model, D-P model and modified Cambridge model. Provide the basis for the selection of the interface constitutive model of soil and structure in the process of the common finite element analysis by studying the constitutive models of the interface in normal and tangential directions.2. The numerical simulation is made of to analyze excavating of two pit-in-pits, for sample, by establishing pit-in-pit models using finite element software ABAQUS. The deformation characteristics of the Retaining Structure are studied in the cases of different positions, sequences, depths and areas of two pit-in-pits by changing the four control parameters of proximal end pit distance ratio, distal end pit distance ratio, depth ratio and area ratio.3. Rankine’s and Conclom’s theories based on semi-infinite space assumption are not suitable for calculating the earth pressure of pit-in-pit. Based on the limited equilibrium theory and the hypothesis of planar sliding plane, four formulas for calculating passive earth pressure are deduced with the consideration of cohesion force and different shapes of slide wedges. And formulas are proposed to calculate the angle of shear failure. Analyze of the influence of various parameters on the passive earth pressure and the angle of shear failure. The mechanical results calculated by the method in this paper and that of Rankine’s.4. Taking the Suzhou Rural Finance Building project as example, design and calculation on excavation of foundation pit using the method of Rankine’s and the passive earth pressure theory under the condition of pit-in-pit in this thesis respectively. Discuss the influence of pit-in-pit excavation on the design of foundation pit through the comparison of the two methods of passive earth pressure, axial force and embedded depth.