Analysis of uplift deflection of subway tunnel due to adjacent pit excavation

To predict the uplift deflection of subway tunnel due to adjacent excavation more reasonably, the soft soil foundation is considered to be a viscoelastic body with the constitutive relation of three-parameter H-K model at the first stage, and the Mindlin's time-domain solution of a semi-infinite viscoelastic body under internal concentrated load is derived. Furthermore, a calculation method is presented by integration and superposition to study the additional stress of a tunnel due to adjacent pit-excavation and dewatering, and the tunnel is assumed to be a long Euler-Bernoulli beam on a Pasternak-type viscoelastic foundation. The governing differential equation for the tunnel is formulated, and the analytical expressions for the deflection and internal force of the tunnel are deduced. Finally, the proposed method is used in a practical foundation pit which is adjacent to the exiting subway tunnels, and the analytical solution is compared with the results from 3-D rheological numerical simulation and in-situ measurement. It is found that the proposed method can reflect the development trend of tunnel deflection with time better. The longitudinal deflection, curvature and bending moment obtained by the analytical method are basically consistent with those from numerical simulation and in-situ measurement. The research results may provide a theoretical basis to study and protect the existing tunnels influenced by adjacent excavation.