Key Takeaways & Executive Findings
- •• A novel analytical framework integrates modified pseudo-dynamic seismic loading and steady unsaturated seepage to evaluate tunnel face stability in inclined layered soils. • The derived suction stress distribution formula captures spatial variability under inclined stratification and hydraulic hysteresis, enhancing prediction accuracy. • The three-dimensional discretized failure model with integrated optimization yields critical face support pressures, validated against previous studies. • The study provides practical insights for shield tunneling design in seismic and unsaturated conditions, emphasizing the coupled effects of stratification and dynamic loading.
Abstract
The tunnel face stability is investigated in inclined layered soils under steady unsaturated seepage and seismic loading. The rigorous estimate of the maximum face pressure is provided during tunnel excavation. The modified pseudo-dynamic method is applied to capture the spatial and temporal characteristics of seismic forces. A spatial distribution formula for suction stress under steady seepage conditions is derived for inclined layered soils. The study examines how inclined stratification influences the shape of failure mechanisms, the suction head profile, and variations in seismic acceleration. The spatial and temporal changes in suction stress and seismic loading are integrated into the energy equilibrium formulation based on a three-dimensional discretized failure model, and the critical face support pressure can be calculated via an integrated optimization strategy. The distributions of seismic acceleration ratios are obtained under various dynamic parameter conditions and the spatial variation of suction stress in the soil ahead of the tunnel face under different hydraulic hysteresis scenarios. The proposed analytical approach is compared with previous research, and the differences in results under different representations of seismic waves are also discussed. The research results can provide a valid framework to evaluate the influence of seismic excitation, steady-unsaturated infiltration, hydraulic hysteresis, and inclined stratification on tunnel face stability.
1. Introduction
With the advancement of urbanization, the utilization of underground space has become a critical issue of modern urban development. Shield tunneling ensures excavation stability by applying supporting pressure on the tunnel face during the advancement of the shield machine. The interaction between the shield machine and the surrounding soil is within the scope of elasto-plastic mechanics in geotechnical engineering. Insufficient support pressure or the presence of seepage may lead to tunnel face instability, posing risks to both property and human safety. Therefore, tunnel face stability during excavation is a critical concern in underground space development.
The methods for investigating tunnel face instability can be categorized into experimental, analytical and numerical methods. In experimental methods, centrifuge experiments are commonly conducted to simulate the stress environment during tunnel excavation, utilizing the high acceleration produced by a centrifuge. CHAMBON and CORTÉ [1] studied the tunnel face stability in sandy soils using small-scale models in a centrifuge. STERPI et al [2] constructed a semi-symmetric tunnel model, revealing a horseshoe-shaped passive failure mechanism at the tunnel face. KAMATA and MASHIMO [3] experimentally investigated the reinforcing effect of fore-poling bolts on tunnel face stability. The numerical methods derive and solve differential equations based on constitutive models to research the responses of the tunnel face during excavation. JING et al [4] developed a three-dimensional numerical model for the stability analysis of earth pressure balance shield tunnel faces using the discrete element method. PATERNESI et al [5] analyzed the excavation stability of tunnel faces in clay using finite element software under both reinforced and unreinforced conditions. CHENG et al [6] employed software to study face instability during shield tunnel excavation along a longitudinally inclined axis. YANG and WANG [7] proposed a procedure for predicting the ground movement of the tunnel.
The limit equilibrium method primarily considers sliding force as the main adverse factor contributing to soil failure. By constructing a static stress field, the method evaluates the balance between resisting and sliding forces to determine the needed support pressure. HORN [8] proposed a classical failure mechanism within the framework of the limit equilibrium method based on earth pressure theory. ANAGNOSTOU and KOVÁRI [9] analyzed the face stability of EPB shield tunnels using limit equilibrium approach. ORESTE and DIAS [10] proposed an improved failure mechanism within the limit equilibrium framework to address the stability of tunnel faces in fragile surrounding formations.
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WU Huan-jiang, ZHOU De, LIAO Hong, ZHU Jian-qun (2026). Seismic stability analysis of tunnel face in inclined layered soils with unsaturated flow. Journal of Central South University. https://doi.org/10.1007/s11771-026-6203-8
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Frequently Asked Questions
What is the main objective of this study?
The study aims to analyze the seismic stability of tunnel faces in inclined layered soils under steady unsaturated seepage, providing a rigorous estimate of the maximum face pressure during excavation.
How is seismic loading incorporated in the analysis?
A modified pseudo-dynamic method is used to capture the spatial and temporal characteristics of seismic forces, allowing for a more realistic representation of dynamic loading.
What is the significance of considering unsaturated flow?
Unsaturated flow affects the suction stress distribution in the soil, which influences the stability of the tunnel face. The study derives a spatial distribution formula for suction stress under steady seepage conditions.
How does inclined stratification affect tunnel face stability?
Inclined stratification influences the shape of failure mechanisms, the suction head profile, and variations in seismic acceleration, which are all integrated into the stability analysis.
What are the practical applications of this research?
The proposed analytical framework provides a valid tool to evaluate the combined effects of seismic excitation, steady-unsaturated infiltration, hydraulic hysteresis, and inclined stratification on tunnel face stability, aiding in the design of shield tunneling projects.
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