Analysis of Longitudinal Deformation of Existing Tunnel Caused by Overpassing of New Shield Tunneling Based on Timoshenko-Pasternak Model
It is easy to cause the uneven deformation of the existing tunnel during the overpassing construction of the new shield tunnel,which will affect the operation safety of the existing tunnel.In order to investigate the mechanical response,Timoshenko beam model and Pasternak two-parameter foundation model are introduced to establish a shield section-soil coupling model considering tunnel shear effect and the continuity of soil layer deformation.The governing differential equation between additional soil stress and longitudinal deformation of existing tunnel under overpassing of new shield tunneling is derived.Then a numerical method for solving the longitudinal deformation of existing tunnels is established by the finite difference scheme.Combined with the construction case of the shield crossing the existing metro Line 2 in the Xinsheng Road Station-Jiyuqiao Station section of Wuhan Rail transit Line 5,the theoretical calculation results,three-dimensional numerical simulation results and field measurement data are compared and analyzed to verify the rationality of the calculation method.The results show that:1)Pasternak two-parameter foundation model can improve the prediction accuracy of existing tunnel deformation by 2.5%compared with the traditional Winkler foundation model.2)The peak displacement of the longitudinal uplift of the existing tunnel is approximately proportional to the excavation radius of the new tunnel.As the net distance between the new tunnel and the existing tunnel decreases,the impact of the new tunnel on the existing tunnel becomes more obvious.3)When the angle of horizontal projection is greater than 60°,it can be approximately considered as orthogonal crossing.Compared with 90° orthogonal crossing,the increase rates of longitudinal uplift displacement peak of existing tunnels at 75° and 60° are only 1.60%and 6.59%.4)When the Angle of transverse projection is less than 60°,the longitudinal uplift curve of the existing tunnel changes obviously and the range expands.The uplift increase rates of the orthogonal traverse are 15.63%,29.71%,47.93%and 56.28%,respectively,for every 15° reduction.5)The Poisson's ratio has little effect on the additional stress and longitudinal deformation of the existing tunnel.The research results can provide a quick and simple calculation method for evaluating and reducing the adverse effects of new tunnel overpass construction on the existing shield tunnel.
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