Research On The Cause And Treatment Measures Of Water Burst In The Lufanggou Fault Fracture Zone Of Binghui Tunnel

Geological disasters have always been a hot issue in tunnel engineering construction.Water inrush caused by unfavorable geology such as fault fracture zone is one of the most common disasters in tunnel engineering,which causes harm to construction personnel and mechanical equipment.If the treatment of the water inrush section is not in place,it will also cause harm to the subsequent operation.Therefore,it is necessary to study the causes and treatment measures of tunnel water inrush.In this paper,Lufanggou water-rich fault fracture zone of Binghui Tunnel is taken as the research object.By combining engineering data,theoretical analysis,numerical simulation and field monitoring are used to verify the causes and treatment measures of tunnel water inrush.The research results can provide an important basis for the construction of subsequent projects.The specific contents and results are as follows:（1）According to the data,it is concluded that the surrounding rock of the tunnel in the Lufanggou fault fracture zone is basalt with tuff,the overall stability of the surrounding rock is poor,and there are many joint combinations that endanger the stability of the structure.The primary joints and weathering structural fissures are well developed and have good connectivity.During the investigation,the boreholes revealed that the Lufanggou fault fracture zone was rich in water,and there was a large risk of water inrush during tunnel excavation.（2）Through the analysis of surrounding rock lithology and surface weathering,the Lufanggou fault is a tensile normal fault.Then,through the rose diagram,histogram and isodensity diagram,the joint statistical analysis is carried out,and the direction of tectonic stress field is solved by the stereographic projection method.It is judged that the Lufanggou fault fracture zone is an uncemented water-rich extensional fault fracture zone,and the causes of water inrush are analyzed on this type of disaster-causing structure.Through the comparison of different water inflow calculation methods,the groundwater dynamics method is selected for prediction.The calculated water inflow in the Lufanggou fault fracture zone is large,indicating that there is a risk of water inrush during tunnel excavation.（3）Fuzzy comprehensive evaluation method is used to evaluate the risk level of water inrush in Lufanggou fault fracture zone of Binghui tunnel.According to the analysis of reference materials,the evaluation factor set is established,and the membership function is established by fuzzy mathematics to link the risk factors to the risk probability and risk scale.The improved product scale method using analytic hierarchy process increases the comparability of each evaluation factor.The practical application is carried out in the affected section of Lufanggou fault in Binghui tunnel,and the process and method of risk assessment are described in detail.Finally,the risk level of water inrush in the affected section of Lufanggou fault of Binghui tunnel is grade III（early warning level）.The research results are consistent with the actual water inrush accidents,which points out the goal for the next construction and treatment.（4）A three-dimensional numerical model was established using FLAC 3D finite difference software.The situation of considering gravity stress field and tectonic stress field in dry season is compared with the situation of considering gravity stress field,tectonic stress field and seepage field in rainy season.Based on the principle of fluid-solid coupling theory,the deformation characteristics of surrounding rock,the stress characteristics of supporting structure and the distribution law of plastic zone in Lufanggou fault fracture zone under two working conditions are simulated and analyzed.（5）Based on the causes of tunnel water inrush,grouting prevention measures are proposed.Numerical simulation was used to study different grouting methods,different grouting ring thicknesses and different grouting permeability coefficients.The influence of various working conditions on tunnel displacement,plastic zone and initial pore water pressure is analyzed.The monitoring measurement and numerical simulation are compared and analyzed.Combined with the dangerous and complex geological conditions of Lufanggou water-rich fault fracture zone,it is concluded that the construction method of full curtain advance grouting,grouting thickness of 5 m and grouting permeability coefficient of 1×10^-5cm/s can not only control the deformation of tunnel surrounding rock,improve the stress of supporting structure and strengthen the stability of tunnel,but also save cost and be scientific and reasonable.