Limit Analysis Theory and Numerical Simulation Study on the Cover Thickness of Tunnel Crown in Soil–Rock Strata

Fang Ji, Qinshan Wang, Hongtao Wang (), Yaotao Yuan, Zhenxiang Hao, Ping Liu and Rongli Liu
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Fang Ji: School of Traffic and Transportation, Beijing Jiaotong University, Beijing 100044, China
Qinshan Wang: Jinan Rail Transit Group Construction Investment Co., Ltd., Jinan 250101, China
Hongtao Wang: School of Civil Engineering, Shandong Jianzhu University, Jinan 250101, China
Yaotao Yuan: School of Civil Engineering, Shandong Jianzhu University, Jinan 250101, China
Zhenxiang Hao: School of Civil Engineering, Shandong Jianzhu University, Jinan 250101, China
Ping Liu: School of Civil Engineering, Shandong Jianzhu University, Jinan 250101, China
Rongli Liu: School of Civil Engineering, Shandong Jianzhu University, Jinan 250101, China

Mathematics, 2025, vol. 13, issue 20, 1-20

Abstract: When constructing subway tunnels in composite strata consisting of overlying soil and underlying rock, placing the tunnel within the overburden rock strata and setting a certain thickness of safety cover rock on top is an effective way to ensure the safety of tunnel construction and the stability of the surrounding rock. However, there is currently no unified understanding or standard regarding the safe overburden thickness of the tunnel and its general rules. To investigate the effect of changes in the roof overlying rock thickness on the surrounding rock stability of subway tunnels, this study is based on the typical soil–rock strata of an underground tunnel section of Jinan Metro Line 4 in China. A total of 4 different conditions for the thickness of the overlying soil layer were considered, and 48 comparison schemes were designed. A systematic study of numerical simulation comparisons of tunnel excavation under different cover rock thicknesses was conducted. The deformation and plastic zone evolution characteristics of the surrounding rock were revealed under different cover rock thicknesses, and the existence of an optimal cover rock thickness range for tunnel crowns in soil–rock strata was identified. Based on this, a theoretical analysis model for the failure of the tunnel roof overlying rock was constructed. Using the upper-bound approach limit analysis method, the theoretical formula for the critical overburden thickness of the tunnel crown was derived. The influence of different rock mechanical parameters and tunnel design parameters on the critical overburden thickness was analyzed. The results were compared with numerical simulation results to verify the effectiveness of the proposed method. The research findings provide theoretical references for selecting reasonable buried depths and support designs for mining-bored tunnels in soil–rock composite strata.

Keywords: soil–rock composite strata; conventional tunneling; overburden thickness; numerical simulation; limit analysis (search for similar items in EconPapers)
JEL-codes: C (search for similar items in EconPapers)
Date: 2025
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