Method of Average Vertical Earth Pressure for HFCCTs Based on Differential Settlement

This paper presents a modified and simplified calculation method, taking into account the differential settlement between the soil columns surrounding the cut-and-cover. High-filled cut-and-cover tunnels (HFCCT) are usually subjected to high earth pressures above the top of the CCT due to an ultra-high backfill. However, the estimation methods for earth pressure above the top of CCT are ambiguous. Through the theoretical analysis of the average vertical earth pressure (AEP) at the top of the CCT, it is found that an additional earth pressure above the top of the overburden pressure is induced, and the magnitude is related to the differential settlement between interior and exterior soil columns. Thus, through a combined theoretical derivation and numerical analysis, a modified formula is proposed. The results show that the vertical earth pressure increment above the top of CCT can be linearly correlated to the differential settlement. In addition, the correlation needs to be calibrated by considering several effects on sites, such as slope angle, groove-width ratios, cross-sectional shape, and the type of backfill. The change in influencing factors has no effect on the function type of the p−δ fitting curve, but it will affect the coefficient k.