Stability And Safty Analysis Of Yellow River Water Conveyance Tunnel Base On Coupled Seepage-stress-damage Theory

In the surrounding rock mass of a water-conveyance tunnel below ground water table, besides fissures and pores, micro-cracks form due to redistribution of the initial stress during the excavation process and seepage force. The seepage body force is dependent on the rock mass permeability. On the other hand, the permeability and porosity depends upon the state of stress, the magnitude of pore pressure and the rock deformation. Plasticity occurs during rock deformation. Development of micro-cracks in the rock mass results in progressive deterioration of the strength and stiffness properties, and possible loss of stability of the surfaces of excavation. The coupling of seepage-elastoplasticity-damage must be considered in the mechanical and hydraulic analyses of tunnels below groundwater table, and a relational model of evolution between the plasticity-damage growth, permeability and porosity changes should be established.In this thesis, the stability analysis is carried out for the water conveyance tunnel project under the Yellow River, which is part of the South-North Water Diversion Project in China. The theories of plasticity, damage and seepage are jointed in a single model to account for the coupling of seepage-elastoplasticity-damage mechanisms of saturated rock surrounding the tunnel.First, an extensive literature review is carried out on the thoey of coupled seepage and stress in saturated porous medium and stability of tunnel. Based on the geological reports and design drawing of the Yellow River Tunnel, the research objectives are proposed.Second, the coupling mechanism between groundwater and the rock medium is analysised. Two volumetric strain dependent parameters, the porosity and permeability, are also adopted corresponding to the evolution of plasticity and damage, and the coupled stress-seepage constitutive equations are derived..Then, the proposed constitutive model is implemented in the Finite Element commercial program Abaqus, and a2D model for leveled shaft and a3D model for inclined shaft are established for the transient coupled pore pressure/effective stress analysis and stability analysis of the water conveyance tunnel project. An extended Drucker-Prager model is used to describe the yielding criterion and deteriorated cohesive strength and friction angel of the grain skeleton, and a non-associated flow rule is defined to control inelastic dilatancy. The transient stress, strain, displacement, seepage field of the surrounding rock and concrete linning, the plastic zone and damage zone distribution of rock, and the stress of the anchorages and reinforcement during the stage of excavation, anchoring and grouting, secondary RC lining, water conveyance and water drainage. In addition, according to the condition of the Yellow River Tunnel, this response of the tunnel structure due to grouting area failure and secondary lining cracking are also analyzed.And then, based on the FE analysis results and different stability criteria such as stress intensity, plastic deformation zone, limit strain and the allowable relativity displacement, the stability analysis of the surrounding rock is performed, and some valuable conclusions are obtained.Finally, a conclusion about the performance of the tunnel structure is given, and the issues for further development are discussed.