Deformation Analysis Of Tunnels Due To Adjacent Underground Excavation

More and more underground excavations are built adjacent to the tunnels. In such a close distance, it will induce the deformation of soft-clay, result in the longitudinal deformation of tunnels and threaten greatly on tunnel. How to predict and control the longitudinal deformation and how to protect tunnel is a very important problem.Naturally, soil is deposits layered. However elastic half-space foundation model of isotropic is still applied to calculate additional stress and settlement. To resolve the problems of layered soil, it could be regarded as elastic layered half-space foundation model of uniform homogenization in each layer.Based on the general solution of axisymmetric spatial problem, we use the basic equation of isotropic elastic mechanics to derive the initial parameter solution of one-layer subsoil—the transfer matrix. The transfer matrix method is directly deduced and applied in the solution of layered subsoil problems. The analytic solutions of isotropic elastic layered soil under axially symmetric loads were derived from by means of transfer-matrix method. By the result, the additional stress and displacement in layered soil can easily be calculated.A simple Two-stage method based on finite difference principle of elastic foundation beam for determining the longitudinal deformation of existing tunnels in soil caused by adjacent excavation was presented. The additional stress of soil or the free soil settlement induced by adjacent excavation was calculated in the first stage; in the second stage the existing tunnel was regarded as the beam with infinite length on elastic foundation based on elastic layered half-space foundation model, composing additional stress of soil or free soil settlement to tunnel, the difference equation in order to solve longitudinal deformation was built up, and the analytical calculation formula of longitudinal displacement were obtained.Finally the validity and accuracy of the proposed method was demonstrated with the typical example and document case, and the different factors which affected longitudinal deformation were studied, it may provide certain basis to draw up correctly protective measurements of existing tunnels influenced by adjacent excavation.