Effect of soil arching evolution on tunnel face stability considering spatially variable sandy soils

Tunnelling, an essential tool of underground space exploration, often encounters the challenge of face instability, especially in spatially variable soils, which poses significant risks to infrastructures. Tunnel face instability frequently manifests through the collapse of soil arching effect. This study explores how the cutterhead framework and soil spatial non-uniformity affect arching evolution and tunnel face stability, by conducting threedimensional numerical analyses incorporated with random field modelling. The results reveal a strong correlation between face instability and soil arching collapse process. A novel formula was introduced to evaluate the impact of arching effect on face stability, with the maximum arching effect occurring at the limit equilibrium state of tunnel face. Our findings show that the load factor in spatially variable soils is averagely greater than that in uniform soils, indicating potential underestimation of failure risk in uniform soils. Finally, a practical framework is established to estimate the probability of failure for a tunnel face in spatially non-uniform sandy soils based on the factor of safety. This approach provides a significant advancement over traditional deterministic methods for designing face pressure, offering a more nuanced and probabilistic tool for assessing the likelihood of face failure.