Modification of Vertical Earth Pressure Formulas for High Fill Cut-and-Cover Tunnels Using Experimental and Numerical Methods

Abstract

The high-filled cut-and-cover tunnel (HFCCT) is a solution to reclaim more useable lands due to the unique landforms of Loess Plateau in northwestern China. Because of the ultrahigh backfill, the estimation of vertical earth pressure will significantly affect the design and safety of the cut-and-cover tunnel (CCT). The current methods for estimating the vertical earth pressure are either to overestimate or underestimate the vertical earth pressure on the top of HFCCT. To more precisely estimate the vertical earth pressure distribution, the vertical earth pressure based on the soil column pressure, γh (h: the height of backfill above the CCT), needs to be properly modified. Considering different influential factors, four corresponding coefficients are proposed: k0: cross-sectional shape of CCT effect, k1: stiffness of backfill effect, k2: width of CCT effect, and k3: coupling effect of slope angle, θ, and the ratio of B/D. It is found that k0 has little influence; the k3 and k1 reduce and k2 amplifies the γh. The corresponding general forms for these coefficients are determined based on finite element analysis results. A general equation for estimating vertical earth pressure for the HFCCT including these four coefficients is proposed. Meanwhile, this general form is verified by the numerical analysis results and experimental results for different cases. Therefore, this proposed equation is applicable to estimate the vertical earth pressure for existing or newly designed HFCCT. Furthermore, this proposed method can significantly reduce the computational work in engineering analysis.