Analysis Method On Excavation And Lining Structure For Large-span Tailrace Bifurcation Tunnel

Due to non-regular geometric shape, complicated geological conditions and high stress concentration of large-span tailrace bifurcation tunnel, it is of important engineering and scientific significance to study the analysis method systematically for excavation stability and lining reinforcement.Based on previous study results, an evaluation system to analyze excavation and lining structure stability is put forward, and the main contents and results are as follows:(1)An evaluation system to analyze excavation and lining structure stability is suggested.(2)Based on nonlinear analysis with FLAC3D, a mechanic method is proposed to calculate the circumferential stress of arbitrary section of non-regular bifurcation tunnel, by adopting coordination transformation, Cauchy stress formula and Lagrange interpolation. In order to test the accuracy of the mechanical method, a simple model, a thick-wall cylinder in an infinite elastic body, was adopted to coMPare the difference between theoretical and numerical solutions of circumferential stress of lining, and it indicates that they are in well agreement.(3)A FISH program is written for exhibition of specific stress value in arbitrary section of tunnel, which helps to derive the moment, shaft force and reinforcement parameters of arbitrary section, and they are converted into CAD script files to put out automatically and vividly.(4)By employing this evaluation system, the tailrace bifurcation tunnel of Xiluodu and Guandi project are analyzed, including the deformation, stress distribution and yield zone in the surrounding excavated rock mass and the reinforcing effect under different stress releasing conditions; the deformation and stress state in surrounding rock mass and lining structure under operation and maintenance loading conditions. Based on study results on practical projects, it shows that the approached evaluation system and 3D nonlinear mechanical reinforcement method can be applied to the design of related tailrace bifurcation tunnels and are also beneficial to the design and construction of the similar projects.