Study on longitudinal nonlinear deformation of adjacent existing tunnels induced by deep foundation excavation.

The simplified calculation methods for predicting the longitudinal deformation of neighboring existing tunnels caused by deep foundation excavation in engineering practice all use linear foundation model to interact with tunnel structure, and less use of nonlinear foundation model of soil body. The nonlinear Pasternak foundation model is combined with Mindlin solution to obtain the differential equations of longitudinal deformation of the tunnel, and the improved Hermite difference method and Newton iterative method are used to solve the numerical solution of the longitudinal nonlinear deformation of the neighboring tunnels induced by the excavation of the deep foundation pit. The rationality and applicability of the improved Hermite difference method for solving the nonlinear foundation model are verified by analyzing and comparing with the measured data. The calculation results of the engineering case show that the computational comparative analysis was carried out using the nonlinear Pasternak foundation model, the traditional Pasternak foundation model, the finite element model and the measured deformation data. The longitudinal deformation trends of the tunnels solved by several methods are consistent with the measured values, but the nonlinear Pasternak foundation model is closer to the measured values. The maximum bending moments of the left and right lane of the shield tunnel obtained by the nonlinear Pasternak foundation model are directly below the foundation pit; the maximum shear force values all appear at the corresponding shield tunnel position below the sidewall of the foundation pit. The research results can provide a simplified and convenient calculation method for the prediction of longitudinal deformation of the neighboring existing tunnels during the excavation and construction of the foundation pit, and guide the construction of similar projects.