Study On The Safety Of Diversion Tunnel Structure During Closure Period Based On Hydro-mechanical Coupling Model

With the development of dam building technology, construction of high dam hasentered a stage of rapid development, the scale of construction become larger andlarger，but also a series of technical problems are brought. Hydro-mechanicalcoupling theorys of fractured rock are the domestic hot issue recently, the research ofsecurity of tunnel under water with hydro-mechanical coupling model is beneficial forsolving practical engineerings, and which has important significance. The designdiversion tunnel structural is usually met the requirements of large flow, high waterpressure head internal in operating period and high water pressure head outside inClosure perio, the safety of diversion tunnel closure structural would be moreconcerned.Relying on the actual project, building three-dimensional finite element modelsbased on the equivalent pore medium model in this paper which can reflect the actualengineering properties, and study the seepage field of the whole mountain in thediversion tunnel closure period, how to simulate the drainage holes and the drainageeffect;Surrounding rock stability and structural safety of diversion tunnel in closuringperiod are analysed based on hydro-mechanical coupled analysis method;based on thenonlinear finite element method, the force characteristics and the overall stability ofthe permanent closure body was studied in this paper.The main findings are:（1）The main seepage direction of mountain in closure period of diversiontunnel is from upstream to downstream along the axis of tunnel, setting anti-seepagecurtain can reduce the total head of groundwater effectively in mountain downstreamthe dam; groundwater’s recharge takes greater impact on seepage field of mountain;permeability of lining and drainage facilities in tunnel take greater impact on seepagefield of local area around the tunnel and take less impact on seepage field of totalmountain.（2）Using hydro-mechanical coupling model agrees with reality because of itcan consider the interaction between groundwater and the rock; considering the effectof groundwater, rock tensile stress and plastic zone occurs mainly in the middle of theside walls and the floor in closure period of diversion tunnel, tensile stress of thelining occurs mainly in the inner surface of in the middle of the side walls and thefloor also. These results accord with general rules; for diversion tunnel suffers high external water pressure in closure period, drainage holes are added in the top archrock can strengthen the outer lining of the drainage,and which can effectivelyimprove the lining of the force conditions.（3）Under the action of high-head, the displacement of the diversion tunnelclosure is mainly along the hole axis. There is widespread area of tensile stress aroundcontact surface where sealing in the water body and basement meet, but the wholebody stress level is not high. The general instability failure mode for the block isforming plastic breakthrough area through the circumferential direction along thepotential sliding surface in the junction of the sealing body and bedrock near theupstream. To ensure sealing body meets the requirements under the condition ofstability in each calculation, limit equilibrium method, over-loading method andstrength reduction coefficient method can be used in the comprehensive evaluation ofthe overall stability of the sealing body.