Method to Estimate Lateral Earth Pressure on High-Filled Cut-and-Cover Tunnels

Abstract

High-filled cut-and-cover tunnels (HFCCTs) can be used in northwestern China to reclaim usable land. Because of the ultra-high backfill used in HFCCTs, the stress on the cut-and-cover tunnel (CCT) will change. However, The calculation method adopted at present for earth pressure usually result in either overestimation or underestimation. Different from vertical earth pressure, lateral earth pressure (LEP) can help stabilize the structure of HFCCTs. The current methods for estimating LEP rely mainly on Rankine's theory or empirical formulas. Using conventional methods has led to errors between actual values and estimated values, and such deviation increases with an increase in the backfill height over the CCT. Due to the complex soil-arching effect, the current methods used for calculating LEP for HFCCTs need to be modified. These modifications need to consider characteristics of the CCT, mechanical properties of the backfill soil, and the geometry of the landform. In this work, several influential factors were identified through numerical analysis using the finite element method and propose four corresponding coefficients of modification: k0, the cross-sectional shape of the CCT; k1, the mechanical properties of the backfill; k2, the width of the CCT; and k3, the coupled effect of the slope angle and ratio of the width of the valley floor to the width of the CCT. Because current methods and specifications may overestimate the LEP for HFCCTs in valleys, a general equation was formulated for modifying the LEP coefficient. Also, this general modification equation was verified that agrees well with the numerical analysis results for different cases.