Research On Lining Stability Of Xiamen Xiang'an Subsea Tunnel In Weathered Trough

Combining with design and construction of xiang'an subsea tunnel in Xiamen, focusing on the key technology of mechanical properties of surrounding rock in the strongly weathered strata, tunnel construction consequences, its long-term stability and reliability, a series of laboratory tests including hydro-mechanical coupled triaxial tests and hydro-mechanical coupled creep tests have been carried out. On the basis of above coupled tests, nonlinear mechanical properties and rheology mechanism has been studied and coupled constitutive model for strongly weathered rock mass has been developed correspondingly. In addition, the suitable construction method and different water-proofing and discharge methods aiming to the tunnel in weathered trough are conducted as well as field-monitoring and inversion analysis. Finally, the large-scale three-dimensional calculation model is established to analyze the long-term stability and reliability of tunnel lining in weathered trough. The main achievements includes:1. Laboratory tests to study hydro-mechanical coupling characteristics of the weathered strata.With the help of hydro-mechanical coupling triaxial test machine, tests on the mechanical characteristic of host rock in the weathered strata in Xiamen has been carried out, including conventional triaxial compression test and creep test for a long time. Basing on the tests results, a strain hardening mechanical model and a creep damage model which considered creep stress and time for host rock in weathered strata has been established. It is indicated that the creep model can reflect changing trend of creep rate very well under different stress levels.2. Study on the reasonable construction methods of tunnel and stress characteristics of lining in the weathered strataWith the new developed mechanical model of weathered granite, numerical simulations have been done to simulate stability of tunnel by full-face curtain grouting, advanced tune shed, small pipe supporting and bench method, CRD method or two side-wall pilot tunnel excavation method respectively. By comparison, the numerical results show that CRD method is the best for Xiamen subsea tunnel in weathered strata. The characteristics of external water pressure of tunnel in weathered strata with different water-proofing and discharge methods are studied, Considering the hydro-mechanical coupling, the effect of tidal cyclic loading on stability of tunnel lining and surrounding rock is studied. With the load structure method, the axial force, bending moment and eccentricity of subsea tunnel under unfavorable combined loading are calculated. The optimized lining depth is evaluated by a comparative study of the safety of lining structure with different lining depths.3. Back analysis of field measurements and its long-term stability prediction on Xiamen xiang'an subsea tunnelBased on field measurements of displacements in weathered strata, a methodology of back analysis combing the Nelder-Mead algorithm and finite element method is proposed, mechanical parameters of surrounding rock in weathered strata is studied. Based on mechanical model of weathered strata and results of back analysis, the long-term stability of surrounding rock and supporting structure in tunnel construction is predicted4. Reliability theory of underground structure and its application at Xiamen xiang'an subsea tunnelBased on the improved Monte Carlo method, using the latin hypercube sampling method which has the advantage of reducing sample size obviously and produce arbitrary dimensions, a finite element reliability program based on Improved Monte Carlo method using Matlab and Abaqus combinablenably is developed, then reliability of Xiamen Under sea tunnel lining and supporting is analyzed. The results demonstrate that the supporting design is safe and reliable.