Stability Evaluation Of Jinping Ⅱ Water Diversion Tunnel And Seepage Characteristics

China is the world’s richest hydropower resource,but more than 80% of it is distributed in the southwestern region.Therefore,it has many water diversion and power generation projects.Among them,the Jinping II deep-lying diversion tunnel is due to its special topography and geological conditions.It will face complex geological environmental problems such as high ground stress,high external water pressure and sudden water inflow,which poses serious challenges to the design and construction of the tunnel.Although the project has been completed,its stability during construction under complex environmental conditions.The evaluation method and the study of seepage characteristics around the tunnel are still few and need further research,which provides certain theoretical research significance and practical application value for the design,construction and engineering disaster treatment of similar projects.In this paper,the Jinping Ⅱ deep-lying diversion tunnel is taken as the research object.Based on the seepage-stress coupling theory and the plastic damage constitutive model,the excavation stability of the tunnel through the intact rock mass is carried out by strength reduction method,over-deformation method and overload method.Based on the non-Darcy law,the seepage characteristics of tunnel passing through fault-bearing rock masses under different conditions are analyzed.The main work and research results of this paper are as follows:(1)Summarize the advantages and disadvantages of the three geostress balance methods and their implementation methods;the rock mass medium is equivalent to a continuous porous medium,combined with the elastoplastic damage constitutive model and coupling theory,the strength reduction method and the super deformation method are applied.The stability evaluation of the 2D tunnel model passing through the intact rock mass during construction is compared with the overload method.The calculation results of different stability criteria show that the displacement mutation criterion unique to the strength reduction method can be used as the lower limit of stability evaluation.The evaluation results of the two methods of overload method are basically the same,the safety factor can be used as the upper limit of stability evaluation,and the safety factor of stability of Jinping Ⅱ deep-lying diversion tunnel through intact rock mass is in the interval [1.14,2.2].(2)Considering the different fault locations(orthogonal fault(90°),oblique fault(45°)and full fault),and the variation of inertia coefficient β,the non-Darcy seepage theory is applied to study the 2D tunnel model passing through the fault rock mass.The seepage characteristics of the pore water pressure,seepage velocity and seepage flow after the excavation of the diversion tunnel indicate that the inertia coefficient is inversely proportional to the seepage velocity and the seepage flow.The larger the fault width,the larger the seepage velocity and the orthogonal fault flow velocity.The variation of the fault is faster than that of the oblique fault;the wider the fault width,the larger the seepage flow,the orthogonal fault fault seepage flow is larger than the oblique fault under the same conditions,and the difference is significant with the increase of the fault width;compared with the full fault,the fault Partial crossing of the tunnel will cause concentrated seepage effects,forming a local funnel zone,which will aggravate the variation of pore water pressure around the tunnel.(3)Considering the time effect,the non-Darcy flow theory is used to study the seepage characteristics during the excavation of the 3D tunnel through the fault-bearing rock mass.The results show that the flow velocity at the bottom of the tunnel is greater than the flow velocity at the top,non-Darcy inertia coefficient and seepage velocity.It is inversely proportional;the seepage flow increases rapidly when the section crosses the fault section,and the seepage flow tends to be stable for less than the intact rock section.The non-Darcy inertia coefficient is inversely proportional to the seepage flow;the pore water pressure dissipation velocity of the upper and lower parts of the fault is better.Fast on both sides.