The tunnel crossing active fault is severely damaged under the action of fault dislocation. Considering the "economic and safety" principle in engineering design, the tunnel damage should be effectively reduced. In this work, a two-level design method for fault dislocation was proposed and the Urumqi subway tunnel in China was chosen as a typical model to deeply investigate its application feasibility. Based on the definition of the design events of different levels and corresponding design goals, threedimensional finite element soil-tunnel models were established to estimate the response of tunnel. Meanwhile, the rationality of soil-tunnel model was judged by tunnel deformation and internal forces distribution characteristics analysis, and the two-level design goals were evaluated by comparing tunnel damage degree and volumes. The results suggest that under the condition of fault dislocation, the tunnel without disaster mitigation method suffers severely shear, tensile-crack, and compressive damage, which may eventually induce the tunnel collapse. The tunnel damage is reduced significantly by adopting the method of flexible joint. For Urumqi subway tunnel with flexible joints, both of the two-level design goals are effectively realized.

Severe seismic damage occurs to tunnels across or adjacent to the active faults in a high-intensity earthquake area. Therefore, investigating the response and failure mechanism of the utility tunnel structure with flexible joints across the reverse fault is of significant importance. This paper conducts a model test of 1:30, modelling reverse fault rupture with a 45° dip angle and a utility tunnel with flexible joints embedded in the sand layer. The results show that the lining structure in the hanging wall area appears to have longitudinal cracks, concrete falls off, and there is continuous dislocation. Then, a nonlinear three-dimensional finite element model (FEM) is adapted to reveal the utility tunnel response under reverse faulting and to simulate the model test. The numerical results show that the tensile failure area of the lining caused by reverse faulting is larger than the compression failure area. The damage distribution has regional characteristics, and especially the joint area is seriously damaged. The settlement profile of the tunnel under reverse fault can be fitted reasonably by a complementary error function. Finally, an analytical solution of the longitudinal response of the tunnel under reverse fault based on the double-parameter Pasternak model is derived. The analytical solution results show good agreement with the numerical and experimental results. The longitudinal response of the tunnel under reverse fault can be divided into two parts: the influence zone and the non-influenced zone. The flexible joints significantly reduce the damage degree and the damaged area of the tunnel caused by reverse fault dislocation.

Through studying on the application principle of existing metal lenticular gasket, the structure design was finished, and design methods and calculating models of lenticular gasket larger than 6inch diameter were attained. Seal mechanism of the lenticular gasket and contact mechanics of the flange joint was analyzed by using finite element method. Stress state, contact width and contact deformation parameters of the lenticular gasket on working was obtained. Based on the analyzing results, leakage forecast model of metal lenticular gasket was presented. In the influencing factors of actual working state, such as inner pressure, outer pressure, medium viscosity, and surface roughness and so on, surface roughness is important, so surface machining precision of an in-use large-diameter lenticular gasket should be improved as far as possible. The conclusions will lay foundation for the future engineering application of large-diameter lenticular gasket.

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