Experimental Study on the Influence of Overlying Soil on Existing Shield Tunnels

In response to the problem of shield tunneling prone to lateral elliptical deformation exceeding the limit under the action of overlying soil, a 1:10 scale model shield tunnel is designed, the influence of overburden soil on the deformation of the existing shield tunnel is studied by experiment. The results show that: (1) As the thickness of the overlying soil layer increases, the maximum increase and change in soil pressure at the top of the tunnel, followed by the bottom, and the minimum on both sides. (2) Significant vertical soil pressure concentration occurs after the thickness of the overlying soil layer on the tunnel is greater than 0.4 m. As a result, the increase in vertical soil pressure is greater than vertical soil pressure concentration does not occur. (3) Under the action of soil cover on the tunnel, due to the vertical soil pressure being greater than the horizontal soil pressure, the tunnel undergoes transverse elliptical deformation. (4) At the location of the tunnel, the lateral soil pressure coefficient of the stratum gradually increases with the increasing thickness of the overlying soil layer. And after reaching a certain degree of thickness, the growth rate of lateral soil pressure coefficient significantly decreases. The results provide reference for the control of existing shield tunnels and the distribution of additional soil pressure around them.