Introduction
The stability of existing metro stations under nearby construction is a critical concern for urban infrastructure. When unilateral large-scale excavation occurs adjacent to underground transit facilities, the surrounding soil-structure system experiences complex stress changes that can elevate the risk of station or tunnel failure. This article synthesizes findings from experimental studies and finite element analyses to outline how such excavation activities can influence metro safety and performance, and what monitoring and design strategies can mitigate risk.
Scope of the problem
Unilateral (one-sided) excavation imposes asymmetric ground movements, vertical and horizontal ground strains, and altered pore pressures. For deep excavations, the influence zone can extend toward nearby underground stations and tunnels, potentially inducing ground settlement, heave, or crack opening in structural linings. The key challenge is to quantify the interaction between excavation-induced soil deformations and the seismic or static loading conditions that metro structures experience during service life.
Methodological approach
Research in this domain typically combines experimental work with numerical modeling. A representative approach includes controlled laboratory tests and field observations of excavation-induced failure precursors, along with finite element analysis (FEA) to simulate soil-structure interaction. Finite element studies often leverage soil models capable of capturing nonlinear stiffness, soil strength degradation, and the effects of time-dependent settlements to predict load paths on tunnel linings and station vaults.
Experimental insights
Experimental investigations assess material properties, excavation sequences, and boundary conditions that replicate unilateral excavation near a metro asset. Tests may measure settlement profiles, lateral earth pressures, and displacement vectors at critical interfaces. These data help identify thresholds of excessive deformation or crack initiation that could compromise essential components such as tunnel crowns, invert regions, and station platforms.
Numerical modeling and case studies
Finite element analyses provide a versatile platform to examine various scenarios: different soil stratifications, excavation depths, support systems, and backfill conditions. A notable case study from Bangkok MRT demonstrates how deep excavations adjacent to metro lines produce stress redistributions in surrounding soils and linings. Such work highlights the importance of calibrated material models and accurate geometrical representation to forecast potential failure modes and to design appropriate ground improvement or shielding measures.
Key findings and implications
Across studies, common themes emerge: (1) asymmetric excavation induces localized zones of high shear and tensile stresses, (2) the proximity and scale of excavation relative to the tunnel crown largely govern the severity of risk, and (3) timely monitoring and adaptive design—such as bracing, ground improvement, or excavation sequencing—are critical to maintaining serviceability. Importantly, models emphasize that small differences in soil properties or loading history can produce significant changes in predicted outcomes, underscoring the need for conservative design paired with real-time surveillance.
Design and monitoring recommendations
To mitigate failure risk in existing metro infrastructure subject to unilateral large-scale excavation, practitioners should consider:
- Detailed geotechnical characterization of soil layers and groundwater conditions in the excavation corridor.
- Calibration of constitutive soil models with site-specific data, including stiffness, strength, and degradation patterns under monotonic and cyclic loads.
- Construction sequences that minimize peak ground movements near critical tunnels, with staged support and backfilling strategies.
- Installation of continuous monitoring networks for settlement, ground movement, and lining strains, enabling early warning and adaptive response.
- Incorporation of ground improvement techniques or protective barriers when risk thresholds are approached.
Conclusion
Unilateral large-scale excavation near metro stations can pose substantial failure risks if ground-structure interactions are not properly accounted for in design and construction planning. By integrating experimental observations with robust finite element simulations and adopting proactive monitoring, engineers can better anticipate potential failure modes and safeguard underground transit operations.
