Stability analysis of shield tunnel face in sandy pebble strata considering the route slope angle

Abstract

Unique physical characteristics of sandy pebble strata amplify disadvantages of the route slope angle for tunnel-face stability. This study uses Lanzhou Metro Line 1 as support project to investigate tunnel-face stability in sandy pebble strata. Using PFC 3D to simulate the tunnel-face failure mechanism of the horizontal tunnel and the longitudinal inclined tunnel. The results show that the slip line ahead of the tunnel face is like a logarithmic spiral, likewise, an ellipsoid failure region forms above the tunnel vault. Based on the above, the theoretical analysis model of tunnel-face stability considering the route slope angle is established. The logarithmic spiral-elliptical model comprises an upper elliptical loose region I and a logarithmic spiral slip region II. Moreover, the limit support pressure is derived by combining the upper bound theorem and associated flow rule. Finally, existing theoretical analysis models are compared with the proposed model, showing that the proposed model fits well with the tunnel-face failure mechanism in sandy pebble strata.

Keywords:

• Shield tunnel
• face stability
• sandy pebble strata
• soil arch
• numerical simulation
• limit analysis method

Data availability statement

All the data used in our research are included in the paper.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This research work was supported by National Natural Science Foundation of China (No. 51878060, No. 52108360), the Fundamental Research Funds for the Central Universities, CHD (No. 300102213206), and the research project of China Railway First Survey and Design Institute Group Ltd. (No. 20-21-1). The financial support is highly appreciated.