# Structural Stress Characteristics and Joint Deformation of Shield Tunnels Crossing Active Faults
## 5 Conclusions  
Considering the nonlinear characteristics of the segment joints and the plastic damage theory of concrete, a three-dimensional numerical model of the cross-fault segmental tunnel was established by ABAQUS. The mechanical response characteristics of the existing shield tunnel subjected to fault dislocation were investigated, and the relevant factors affecting the mechanical properties of cross-fault segmental tunnels were analyzed. The following main conclusions can be drawn from this study.  
(1) When normal fault dislocation occurs, the shield tunnel structure is mainly subjected to longitudinal force, and the tunnel structure close to the annular joint is primarily damaged. Under reverse faulting, the shield tunnel structure is mainly subjected to lateral force, and the tunnel structure located at the arch haunch of the segments is initially damaged. The bearing capacity of the shield tunnel structure is more significant than that of the normal fault displacement.  
(2) When normal fault dislocation of 15 cm is imposed, both the deformation of the circumferential joints and the longitudinal joints are large, and the tensile deformation of the circumferential joints is much larger than that of the circumferential joints. When the reverse faulting occurs by the same displacement, the deformation of the circumferential and longitudinal joints is relatively slight.  
(3) Subjected to fault displacement, the larger the elastic modulus of the soil around the tunnel, the greater the forced displacement of the tunnel structure, and consequently, more severe structural damage and larger joint deformation of the segmental tunnel.  
(4) In the buried faulting cases, the soil layer between the shield tunnel and the top of the fault plane weakens the forced displacement caused by fault displacement to some degree. As the vertical distance \(h\) between the top of the fault and the tunnel increases, the structural damage of the segmental tunnel, the stress of the longitudinal bolts, and the deformation of the longitudinal joints decrease significantly.  
(5) In normal faulting cases, the stress characteristics of the segments are not significantly affected by the fault dip angle. Under the same fault displacement, the smaller the fault dip angle, the easier the tunnel linings suffer a tensile failure. When reverse fault displacement occurs, the fault dip angle significantly affects the stress characteristics of the segments near the projection of the fault. According to the results in the current study, when reverse faulting of 15 cm is imposed, the tunnel structure subjected to an 85\({}^{\circ}\) dip angle causes obvious shear deformation in the longitudinal direction. In contrast, the tunnel segments under a 55\({}^{\circ}\) dip angle are still mainly subjected to lateral force, and their longitudinal shear deformation is not obvious.  
H.L. and X.L.: conceptualization, methodology, project administration, and writing the original draft; Y.Y., Y.L. and M.M.: validation, plotting curves and analysis, and review. All authors have read and agreed to the published version of the manuscript.  
This article was supported financially from the National Basic Research Development Program of China (No. 2015 CB057800).  
Figure 26: Effect of the fault dip angle on the maximum stress of joint bolts: (**a**) normal faulting condition and (**b**) reverse faulting condition.