A case study on deformation characteristics of a large cross-section tunnel passing through a soft-plastic layer with different spatial locations

This paper presents a case study of large cross-section high-speed railway tunnel passing through the soft-plastic loess layer. The distribution of the soft-plastic loess in different parts of the tunnels inevitably affects the deformation characteristics of the surrounding rock mass due to its poor engineering properties of low shear strength and high water content. Construction distresses including falling block and collapse of surrounding rock indicate there is great difficulty and risk during tunneling. In this paper, deformation characteristics are studied by carrying out a series of in situ measurements and numerical simulations. The results show that the different spatial locations between the soft-plastic loess layer and the tunnel result in different mechanical behaviors. When the tunnel is totally embedded in the soft-plastic loess, the radial displacement values above the wall waists undergo dominant deformation, while the radial displacement of wall feet is smaller. The settlement and horizontal convergence decrease obviously when the arch crown is constructed in the soft-plastic loess layer. When the soft-plastic loess is mainly distributed in the arch crown, the radial displacement above wall waists presents a great deformation.