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Surcharge due to improper soil dumping and irregular backfilling often causes excessive deformation along the adjacent shallow tunnel in soft-soil areas. Tunnel structures are usually modelled with beam elements where the bending of the concrete segments is considered while the shearing dislocation between segmental rings is usually ignored. In this work, a Timoshenko beam was used to consider such dislocation of a shield tunnel under surcharge and a Pasternak foundation was used to account for the tunnel–soil shear effect. A numerical method was then developed to assess the effect of surcharge loading on the longitudinal responses of the underlying tunnel based on a two-stage method. The proposed solutions were verified using a case history from Shanghai and a three-dimensional numerical simulation from the literature. Results of a further parametric study showed that the deformation induced by surcharge loadings would be underestimated without the shearing-induced dislocation of tunnel segments, which could overpredict the serviceability of the underlying tunnel in surcharge accidents.

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Based on Complete Fluid-solid Coupling Theory, this paper takes permeability coefficient and void ratio as variables changing with volume strain, defines damage variables to reflect damage of surrounding rock, establishes an elastoplasticity damage constitutive model of seepage coupling of stress in surrounding rock, and then analyzes a large water conveyance tunnel in view of adverse situation of grouting circle failure. The results show that grouting circle failure has significant adverse effects on stability of surrounding rock and stress of the lining and the anchor rods.