Negative Soil Arching Effect Caused by the Floating of Rectangular and Circular Tunnels and the Calculation of Overlying Earth Pressure Distribution

Determining the variation of earth pressure around a tunnel is crucial for its structural safety. This paper adopts the FEM to investigate the negative soil arching effect caused by the floating of a rectangular tunnel (RT) and a circular tunnel (CT). The results show that the major principal stress trajectory within 0.3C (C is the buried depth) of the RT top presents a convex arch shape due to the stress concentration on both corners of the tunnel roof. However, within the range of 0.7C below the ground surface for the RT or the whole stratum above the CT, the major principal stress converges toward the tunnel top, resulting in the convex arch of the minor principal stress trajectory in this area. Then, two models by considering principal stress deflection are proposed to calculate the vertical earth pressure distribution (VEPD) above the RT and CT. Under the assumption that the principal stress trajectory is a circular arc, the calculation formula and distribution factor m for estimating the VEPD on the RT and CT are obtained. Finally, the effectiveness and rationality of the theory in this paper are verified by comparing experimental and numerical results with theoretical predictions.