An analytical investigation of soil arching induced by tunneling in sandy ground

The soil mass above the tunnel generally yields due to the tunnel volume loss. Depending on the amount of the volume loss, soil unit weight, overburden height and internal friction angle, a stress arching zone and a loosened zone can be formed above the tunnel. In this study, a two-dimensional stress field resulting from the tunnel volume loss inside the soil mass above the tunnel is investigated analytically. By presenting an analytical solution in rectangular coordinates, new equations were developed to evaluate and estimate the magnitude of vertical, horizontal and shear stress components inside the soil mass. The vertical stress changes resulting from the tunnel volume loss were analyzed and the height of the arching zone and the loosened zone above the tunnel were determined. In addition, a parametric study was conducted to evaluate the effect of soil unit weight, soil internal friction angle, surcharge on the ground surface and overburden depth on the stress distribution in the soil above the tunnel. The results showed that depending on the depth of the tunnel and the strength of the surrounding soil, the arching and loosened zones may or may not be created. In order to validate the proposed solution, the vertical stress distribution along the tunnel crest has been compared with some experimental and numerical data. It can be stated that the proposed solution provides relatively good approximations for the vertical stress component. The results of this research show that a safe and economical support system for tunnels in sandy ground can be designed using the proposed solution.