Weakening behavior of waterproof performance in joints of shield tunnels under adjacent constructions

Groundwater leakage in shield tunnels poses a threat to the safety and durability of tunnel structures. Disturbance of adjacent constructions during the operation of shield tunnels frequently occurs in China, leading to deformation of tunnel lining and leakage in joints. Understanding the impact of adjacent constructions on the waterproofing performance of the lining is critical for the protection of shield tunnels. In this study, the weakening behavior of waterproof performance was investigated in the joints of shield tunnels under transverse deformation induced by adjacent construction. First, the relationship between the joint opening and transverse deformation under three typical adjacent constructions (upper loading, upper excavation, and side excavation) was investigated via elaborate numerical simulations. Subsequently, the evolution of the waterproof performance of a common gasket with a joint opening was examined by establishing a coupled Eulerian-Lagrangian model of joint seepage, and a formula describing the relationship between waterproof performance and joint opening was proposed. Finally, the weakening law of waterproofing performance was investigated based on the results of the aforementioned studies. It was determined that the joints with the greatest decline in waterproof performance were located at the tunnel shoulder in the upper loading case, tunnel crown in the upper excavation case, and tunnel shoulder in the side excavation case. When the waterproof performance of these joints decreased to 50% and 30%, the transverse deformations were 60 and 90 mm under upper loading, 90 and 140 mm under upper excavation, and 45 and 70 mm under side excavation, respectively. The results provide a straightforward reference for setting a controlled deformation standard considering the waterproof performance.

Effect of seepage on soil arching effect in deep shield tunnel

Shield tunneling and post-tunneling steady seepage are accompanied by stress and displacement variations,which could induce and influence the soil arching effect.Although there are many studies on the tunneling-induced soil arching effect,the research about the effect of seepage on soil arching effect is extremely lacking.In this study,a numerical model is firstly established and verified by field data.Then,a series of numerical models,whose simulation method of steady seepage is verified by adopting the conformal mapping technique,are established to study the soil arching evolution of deep-buried tunneling and post-construction steady seepage.The results indicate that seepage leads to an increase in effective vertical stress,which is consistent with the existing theory.The seepage weakens the soil arching effect resulting in the height of the arch zone reducing from 2.38D(D is the tunnel diameter)to 1.25D.The seepage leads to the further development of ground consolidation settlement,but the differential displacement in the soil mass decreases.The ground reaction curve in the steady seepage condition shows a bigger value than that after excavation.It is reasonable to control the ground loss ratio in the range of 0.5–1.0%,which can minimize overburden pressure with moderate ground deformation.