The Water Gushing Mechanism And Treatment Measures For The Soft Rock Tunnel

With the continuous development of the economy,the continuous improvement of comprehensive national strength and the continuous application of high and new technology,China’s tunnels and underground projects have experienced unprecedented rapid development,and the number of tunnels built in soft rock areas is also increasing.When the soft rock tunnel passes through or is close to the fault fracture zone,due to the excavation disturbance and the instability of the fractured rock mass itself,phenomena such as large deformation,instability,and water inrush of the surrounding rock are prone to occur during the construction process,which make a big security risk for project.The reason why the water gushing in the soft rock tunnel is difficult to predict and contain is that its catastrophic evolution and related mechanical mechanisms are more complicated.At present,there is no clear understanding of the water gushing mechanism of soft rock tunnels,and the research on the technology of water gushing treatment is not systematic.Therefore,research on the mechanism of water gushing and treatment of soft rock tunnels is conducive to solving the above-mentioned engineering problems when constructing tunnels in soft rock areas.This paper takes a soft rock tunnel as the engineering background,aiming at the occurrence of the water gushing and collapse accident in the tunnel,and on the basis of summarizing a large number of literatures,the method of the theoretical analysis,numerical simulation and on-site measurement are used to study the water gushing mechanism and treatment technology of soft rock tunnel.Firstly,on the basis of in-depth investigation and theoretical analysis,the causes of the disasters are analyzed.Based on the theory of sediment kinematics,the evolution mechanism of the gushing mechanics of soft rock tunnels is deduced.Secondly,based on the previous conclusions,the numerical analysis of the influencing factors of soft rock tunnel is carried out,and a numerical model of the disaster factors and the sensitivity analysis of the influencing factors of the tunnel water-fault fault zone were established.Then,the current technology of tunnel water inrush and reinforcement is summarized.For the water blocking method of grouting,the application research of double-shell grouting reinforcement in the water treatment of soft rock tunnel is carried out.At the same time,combined with orthogonal experiment principle,analytic hierarchy process and linear comprehensive evaluation model,a comprehensive optimization analysis of reasonable double-shell grouting parameters was carried out.Finally,based on the actual situation of the Fotouling Tunnel and the previous engineering experience,the targeted engineering treatment measures were put forward and verified by the field measured data,including:（1）After theoretical and numerical analysis,natural factors such as weak surrounding rock mass,groundwater,rainfall and fault fracture zone,in-situ stress were the internal causes of this water gushing with collapse.Support and construction plan factors such as support is not timely and too much excavation is the main cause of this accident.Surrounding rock level difference is the key reason for the amount of water inflow.（2）Under the premise of excavation disturbance and groundwater softening,the soft rock tunnel has reduced shear strength and activation strength in the fault fracture zone.Under the continuous action of seepage,the large amount of lost fluid in the broken rock mass is further widened.Under the premise that the tunnel construction has no protection,enhanced drainage and support parameters,the supporting force of the face is insufficient.The macro performance is that there is a large amount of water in the construction face and entrainment of broken rock blocks until the collapse of the collapse.（3）Establish a numerical model for the sensitivity of influencing factors of tunnel gushing fault fracture zone.After analysis,the fault fracture zone of dip angle,which the range of the water gushing is 90.53m³?d^-1and the range of surrounding rock deformation is15.06%,the corresponding value of the net distance to tunnel and the filler mechanical properties is 67.23m³?d^-1,15.11%and 54.32m³?d^-1,7.79%.These three factors are important factors affecting the water gushing and the stability of surrounding rocks.The width of fault fracture zone is general factors,which value is 29.93m³?d^-1and 5.81%respectively.（4）Summarizing the previous literature and previous research results,at present,mainly blocking and limiting emissions are the main principles in the treatment of tunnel groundwater.In the process of gushing water treatment,it is often the use of water blocking method and drainage method.According to the actual situation of the water in the Fotouling tunnel,a targeted engineering countermeasure was proposed.Through on-site inspection and monitoring of the measured data,the water treatment measures of the Fotouling tunnel are reasonable and effective.（5）The numerical model of double-shell grouting was established and combined with orthogonal test analysis,analytic hierarchy process and linear comprehensive evaluation model to determine the reasonable value of relevant key factors.The orthogonal test results indicated that the values of various types of indicators are small,indicating that the double-shell grouting has a good reinforcement effect on the whole.The optimum value of shallow grouting shell thickness,ratio of permeability coefficient between shallow grouting shell and surrounding rock,central buffer layer thickness,and surrounding rock are respectively 4 meters,0.01,6 meters and 0.1.The weight coefficients of tunnel section water inflow,vault settlement,vault deformation rate ratio and maximum principal stress of vault support are respectively 0.0953,0.1603,0.4668 and 0.2776.The best value of the final grouting shell thickness is 5 meters by linear comprehensive evaluation model analysis.