| In karst region of Guizhou province,karst groundwater is so rich that caused many problems to the tunnel construction,mainly is tunnel gushing water bursting. Because of the limitation of terrain conditions,the highway from Dejiang to Wuchuan of Guizhou province must cross the geological structure with groundwater is very rich in Shichao syncline. And planned to cross it with Dejiang tunnel which is 5.4km,which is the longest tunnel in the planning and construction of Guizhou province. Shichao syncline forms huge underground river system that the head is up to 210 m,the flow rate is reach 3.8m3/s above Dejiang tunnel as the tectonic action and waterproof function of the mudstone at the bottom. Tunnel gushing water inrush is the key issue to affect the extra-long tunnel hydrogeological problems. The aquifer above Dejiang tunnel is permian Maokou group limestone with concealed high-pressure water caves is very rich,the lithology of the Dejiang tunnel hole body and roof are Permian qixia group limestone with mudstone which has relative waterproof ability. But the expect the thickness is only 45 m or less than 45 m m. Tunnel excavation and high head groundwater seepage have certain disturbance for surrounding rock even split it,it may lead to water inrush when roof thickness too thin. As a result,the Dejiang tunnel safe distance of weak tunnel waterproof roof water inrush distance prevention is the key to the Dejiang tunnel plan succeed or not,which has important research significance and value. This paper made a roof properties qualitative analysis for De Jiang tunnel which is based on Dejaing tunnel engineering and hydrogeological conditons evaluation. In order to determine the safe distance of roof water inrush disaster prevention of De Jiang tunnel,using two-dimensional discrete element UDEC numerical simulation to simulate fracture network of fluid-solid coupling reference with the thinking that lead water fracture zones take shape under "three " mining,Mainly have the following conclusion:1.Through standard geological profile measurement,rilling,lithology and exposed karst calculate that the dejiang tunnel roof lithology is limestone clipped calcareous mudstone. Through hole water pressure test,the roof stratum under 2.3MPa bibulous rate is 3.14 Lu for the weak permeable layer. So,the threaten is come from that the rock mass permeability change caused by tunnel excavation unloading and the further evolution of the crack under the action of high water,it may lead to water inrush when roof thickness too thin.2.The strength of surrounding rock,the strength of structural plane,rock occurrence and buried depth have different affect to tunnel excavation unloading causing rock mass crack expansion for tunnels with shallow buried and the surrounding rock occurrence nearly horizontal through the discrete element numerical simulation,at the same time,the influence range greater than 45 m by tunnel excavation unloading stress of Dejiang tunnel,the water transmitting fissure is greater than 45 m,Dejiang tunnel excavation will be affected by overlying high pressure karst groundwater,the results that 45 m tunnel roof thickness are obtained by engineering analogy methods as the same.3.The tunnel roof will collapsed with pour water bursting pressure under the action of fluid-structure interaction if the roof thickness of Dejiang is 10m?15m and 20 m,water inrush is happen,the water pressure are greater than 1MPa,the biggest is 1.6MPa,the maximum instantaneous flowrates were greater than 0.1m3/s,the largest is 0.665m3/s,the roof waterproof ability were lost,so,water inrush happened. the action of fluid-structure interaction can only lead to produce large deformation of surrounding rock when the roof thickness is greater than or equal to the thickness of 25 m,and the water pressure and the flowrate with the increase of the thickness of top plate are decrease,so,the water inrush disaster prevention and safety distance of Dejiang tunnel is about 25 m.4.The roof thickness is expected to 45 m,The maximum deformation is 0.137 m under the action of fluid-structure interaction and the condition of not supporting, the maximum deformation is 0.072 m under the action of fluid-structure interaction and the condition of supporting,surrounding rock deformation is under controlling,the maximum water pressure is 0.413 MPa under the action of fluid-structure interaction and the condition of not supporting,the maximum water pressure is 0.25 MPa under the action of fluid-structure interaction and the condition of supporting,the maximum water pressure is 0.0268 MPa that not considering crack expansion and based on groundwater dynamics method,that is less about 10 times to the results of fluid-structure coupling calculation. But both above results is far less than 2.1MPa head,so,the tunnel water inrush risk is controllable if the roof roof thickness is large than 45 m,surrounding rock still have certain waterproof ability,tunnel can only hit part of the groundwater. But its still can not meet the design requirements,so,grouting reinforcement must be done before tunnel excavating,grouting reinforcement ring parameters reach ng=1/50 and tg?6m can reduce the influence of the groundwater of the tunnel by theoretical calculations. |
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