Numerical study on the impact of local failure on adjacent structures in a shield tunnel

Many previous accidents have indicated that a small local failure in a shield tunnel might induce progressive failure of the tunnel structure, and the underlying mechanisms are still unclear. Before the study of the progressive failure of shield tunnels, the response of the tunnel structure adjacent to the local failure zone should be first clarified because it could help explain how progressive failure is triggered by a small local failure. In this article, physical model tests were reviewed briefly and reproduced by numerical modelling based on the coupled Eulerian-Lagrangian (CEL) method. Good agreement was achieved between the results of the numerical models and physical model tests, which showed the reliability of the numerical models. Then, a full-scale simulation was conducted to quantitatively investigate the impact of local failure on adjacent structures (segments and bolts) in practical engineering. It was shown that the torsions and shear forces of the adjacent segments would increase and exceed the bearing capacities. Parametric analyses were also performed to investigate the effect of the assembly method, cover depth and number of initial dismantled segments (IDSs) on the safety of adjacent tunnel structures. The results indicated that 1) the impact of the local failure in a straight-jointed tunnel was smaller than that in a stagger-jointed tunnel; 2) when the cover depth of the tunnel was greater, the number of unsafe structures and the maximum of state evaluation factor (SEF) were also greater; and 3) when the number of IDSs was greater, the impact of the local failure was much larger.