| With the acceleration of urbanization,the construction of underground tunnels is developing rapidly.Shield tunneling has become the main method of urban tunnel because of safety,efficiency and environmental protection.However,due to the dense population and housing in the city,the construction of shield tunnel can cause the displacement of surrounding strata and the deformation of adjacent buildings,which affects its normal use and even endangers the personal safety.Therefore,it is particularly important to predict and control the ground deformation caused by shield construction.Considering the complexity of this problem,the current prediction theory and calculation method of ground deformation are still to be improved.Meantime,the stability of shield construction has close connections with strata properties,and it tendes to be different in different regions and different strata.It is of great engineering significance to discuss and analyze shield construction in combination with stratum properties.This paper was based on mai-xiao shield tunnel of the north extension project of Nanjing metro line 1,for the special strata conditions of the upper soil and lower rock,a series of research methods including theoretical analysis,field test and finite element simulation were conducted to analyze surface subsidence and building deformation caused by shield tunneling.The main research contents and results of this paper are as follows:(1)The influencing factors of surface subsidence caused by shield tunneling were clarified,and the surface subsidence mechanism and development law in the course of shield tunneling were introduced in detail.The formula for calculating the lateral surface settlement in the case of uneven radial displacement of the strata around the tunnel was derived by using image theory,and the influence of different engineering parameters on the surface displacement was analyzed.(2)The field test of shield tunneling in soil-rock composite strata was carried out and the horizontal and vertical settlement of the ground surface and the deformation characteristics of shallow foundation buildings were analyzed from two aspects of time effect and space effect.The application of Peck formula in soil-rock composite strata was modified by regression analysis,and the value ranges of correction coefficients were put forward.In addition,the safety risk assessment of Adjacent building was conducted,and the weight of each risk index was calculated by AHP,which could guide to take targeted risk measures.(3)The three-dimensional model of shield tunneling in soil-rock composite strata was established to simulate the dynamic process of shield tunneling side-crossing on existing shallow foundation buildings.A systematic analysis was conducted on the indicators of surface subsidence,horizontal displacement of strata and uneven settlement of buildings.Besides,the rationality of the model was verified by comparison with the numerical results,analytical results and measured data,and the reasons for the differences between three research methods were analyzed.(4)The influence law and degree of each construction parameter were analyzed one by one,and the optimization proposal was proposed by changing the parameter value including shield construction parameters,the rock layer proportion of excavation face,the excavation method of double-line tunnel,upper soil parameters and the position between the tunnel and the building.Finally,the control measures to reduce the disturbance of shield tunneling to the surrounding environment were summarized,which can provide reference for similar projects. |
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