Study On Effects Of Shield Tunnelling Underneath Pile Foundation Of Existing Building On Bearing Capacity In Zhengzhou

With the further development of urbanization, a lot of high-rise buildings and viaducts come together in crowds densely in the urban environment. However, a majority of these buildings and structures are supported by pile foundations. So the excavation of shield tunneling adjacent to the pile foundations of existing buildings is inevitable, while the ground movements caused by excavation will inevitably lead to additional internal forces and displacements on the adjacent pile foundations, which will affect the bearing capacity of pile foundations and the stability of the upper structure in a way. So it appears especially important to study on the influence on the adjacent pile foundations caused by excavation of shield tunneling.This paper mainly takes advantage of ABAQUS, a finite element analysis software, to simulate the bearing performance of the pile foundations just above the shield tunnel when the shield is in the dynamic construction process, considering several specific construction parameters, such as the construction disturbance of soil caused by shield machine cutter, soil warehouses pressure and grouting effect, The principal research contents are as follows:(1)The features, mechanisms and effect factors of movements of surrounding strata caused by shield tunnelling are summarized, the operating mechanisms of shield, some basic theories of pile foundations and the impact principle of adjacent pile foundations caused by shield tunneling are introducted briefly.(2)Based on previous reseachers’ experience, this paper utilizes ABAQUS to simulate the shield tunneling under several simplified assumptions, and the general movement law of surrounding strata in the X, Y, Z three directions is got from the result of numerical simulating.(3)The two working conditions that single pile and single pile with cap are just above the tunnel are simulated when the shield is working, aimed at finding out the varying laws of deformation and internal force of pile body respectively, and then make a comparison with each other.(4)The single factor method is utilized, which changes the length and stiffness of pile body and the load on the top of pile cap, to study on the impact mechanisms of pile foundation just above the tunnel when the shield is working and search for a safe construction distance, which is about 3m.(5)The single factor method is utilized, which changes the magnitude of front soil warehouses pressure, surrounding grouting pressure and the degree of construction disturbance of front soil caused by shield machine cutter, to study on the response of deformation and internal force of pile foundations caused by changing construction parameters.(6)With the artful assistance of the principle of mathematics, the differential settlement between piles is analyzed theoretically, and the theoretical approaches to control differential settlement are proposed. Based on the above research results, several technology measures of monitoring and reinforcing for protecting adjacent existing building in the process of shield tunneling are introducted briefly, which can provide useful experiences for future similar projects.