Study On Risk Evaluation Of Karst Tunnel Water Bursting Disaster In The Plateau Of Eastern Yunnan

The carbonate rock strata from Sinian system to Permian system are widelydistributed in plateau of eastern Yunnan, with pure lithology, large area outcropingand abundant karst water resources, etc. Under the combined impact of specialgeological structure, complex field stress field and seepage field, the tunnels oftenencounter large water bursting and mud inrush disaster in this area. With the graduallytransiting of transportation-construction and water conservancy construction from theintermontane basin to mountainous terrain in the plateau of eastern Yunnan, more andmore tunnel engineering are faced with such severe challenges. Therefore, it has greatimportance to ensure the security of tunnel construction and normal operation thataccumulating the practice experience of the existing construction projects, discussingthe formation mechanism and evolution laws of water inrush disaster, building therisk evaluation system of karst tunnel water bursting which is suitable for the plateauof Eastern Yunnan.This paper establishes an appropriate evaluation system, under the study ofoccurrence and migration regularity of karst water from Sinian system to Permiansystem in the plateau of eastern Yunnan, and combining with the feature of waterinrush disaster characteristics of the tunnels of Dagongshan and Dawushan in Niulanjiang to Dianchi diversion project. Then, reliability verification is done by thetunnels of Dagongshan and Tonghai. Finally, the main conclusions follow:（1） The plateau of eastern Yunnan is located in the watershed area of Jinsha River,Nanpan river and Yuanjiang river. The plateau is shallowly cutted and geographicalenvironment has a big difference. Soluble rock are widely distributed from Siniansystem to Permian system in the east of “Red basin”, which is in Chu xiong, Lu Feng, Yi meng etc. There are strong karst development and abundance water in the solublerock, while springs and underground river are widely distributed. The study area islocated in the west margin of Yangzi platform, where has very complex geologicalconditions, with north east and nearly east-west and north-south tectonic systems.（2） By analyzing the formation characteristic of water gushing points in tunnelsof Dagongshan and Dawushan, the paper summarized the formation controllingfactors of water bursting disaster in karst tunnel. The lithology, structure,geomorphology and the relationship between tunnel and underground water level arethe four types of controlling factors.（3） This paper selects the soluble rock（K1）, geological structure（K2）, thecharacteristics of surface environment（K3）, the depth of tunnel（K4） four indicators asthe first grade evaluation index, and rock component(K₁₁), texture of rocks(K₁₂),structure of rock mass(K₂₁), strata dips(K₂₂), rainfall infiltration coefficient (K₃₁),terrain slope(K₃₂) as the secondary evaluation index.（4） At first, this paper establishes the evaluation system by quantifying theselected indexes, and confirms the weight of each indicator by adopting the AHP.Then, the risk evaluation model of water bursting is built, whichisTHK_DG=5（0.45*K₁+0.08*K₂+0.15*K₃+0.32*K₄）. Finally, the riskevaluation system of karst tunnel water bursting in the plateau of eastern Yunnan isobtained, and the controlling measures are given.（5） Combined with the tunnels of Dagongshan and Tonghai, this paper used theTHK evaluation system, which is suitable for the southwest mountainous area, andTHK_DGevaluation system to do assessment separately. Then, the results are comparedwith the actual water gushing situation, which shows that the THK_DGevaluation ismore reliable.