Mechanical Analysis And Application Of Several Types Of Water Inrush Mechanism In Highway Tunnel

In recent years,with the continuous development of China’s social economy,highway traffic construction has also been greatly improved.Due to the constraints of terrain conditions,which resulting the highway construction is more complex and more difficult in the southwest of China,Sichuan Province and other places as a representative.Tunnels are often selected in certain sections of the highway design route.The tunnel construction is often faced with a variety of complex geological disasters.At present,the tunnel water inrush problem is still one of the three major geological hazards in tunnel construction,so it is still a problem to be solved urgently.Based on the analysis of different types of water inrush mechanism,the characteristics and differences of different type’s water inrush mechanism are presented.Based on the classification of water inrush mechanisms of highway tunnel,this paper focuses on: Static-Dynamic Disturbanceof the Discontinuities of Rockmasses Mechanism,and Hydraulic Splitting of Fissures Mechanism.Finally,based on the water inrush cases,the parameters are substituted into the formula that used to judge whether the tunnel water inrush occurs or not.In addition,the numerical simulation method is used to simulate the actual cases.The results of numerical simulation are compared with the results of mechanical analysis to verify the accuracy of the mechanical analysis.Through the research,this paper obtains the following results:1)Taking the key water-blocking as the research object.This type of mechanism belongs to Static-Dynamic Disturbanceof the Discontinuities of Rockmasses Mechanism.The characteristics of structural plane that influences the stability of the rock mass is divided into: flat and smooth without filling structural surface;rough undulation without filling structure plane and non-penetrating structural plane,etc.Based on the limit equilibrium theory,the formula for calculating the critical groundwater pressure of the key block is derived,which is considering the effect of the underground water pressure,the horizontal and vertical pressure of the surrounding rock and the weight of the block.2)Based on the parameters of surrounding rock getting from the Qinling Ⅲ tunnel at mileage K0+347,the formula is verified and the results are consistent with the actual situation.In addition,the above results are verified by numerical simulation.Based on the Qinling III tunnel water inrush,the influence of roughness coefficient(at 3、6、9、12、15)on the critical groundwater pressure is studied.It is found that the mechanical analysis results are similar to the numerical simulation results.That is,with the increase of the roughness coefficient of the structure,the bearing capacity of the key water-blocking is also increased.3)On the basis of the water inrush at mileage K42+192 of the Shizizhai tunnel,the two fixed ends beam is used as the geomechanical model to analyze the water inrush which happened at the first lining and aquifuge.The formula for calculating the critical thickness of the aquifuge which is under underground water pressure,surrounding rock pressure,tunnel lining and self-weight of the water layer is obtained.The rectangular thin plate with fixed end is used as a geomechanical model.And the formula for calculating the critical thickness of the aquifuge which is under underground water pressure,surrounding rock pressure and self-weight of the water layer is obtained.4)Through collecting the relevant parameters of the water inrush at the Shizizhai tunnel and brought them into the two formulas above,and it is found that the results were consistent with the actual situation.It is found that the main factors that affecting the thickness of the critical thickness of the aquifuge are the groundwater pressure and confining pressure.When the underground water pressure and the surrounding rock pressure are large,adequate thickness of the aquifuge should be provided to ensure the stability of the rock.In addition,the numerical simulation results show that the results derived from the model of beam and thin plate are relatively reasonable.Through the analysis of beam,the plate and numerical simulation results,it is found that the calculated results of the thin plate are more close to the numerical simulation results.By comparing the calculation results of the beam and thin plate model,it is found that the beam model is simpler.5)Based on the water inrush at Mingyueshan Tunnel K5+398 and the fixed end circular thin plate as a geomechanical model are introduced,the formula for calculating the critical thickness of aquifuge that is under water pressure is derived.Through collecting the parameters of the water inrush at the Mingyueshan Tunnel and brought them into the formulas above,and it is found that the results were consistent with the actual situation.In addition,the numerical simulation results show that the critical thickness of the aquifuge is similar to that of the mechanical analysis.The numerical simulation results also show that the most easily water inrush position for the bottom end face,which coincides with the actual.6)A case study on the water inrush from the K23+708 of the Feixianguan tunnel,Based on the discriminant formula for the occurrence of water inrush,the water inrush in this area is determined and the calculated results are in good agreement with the actual results.The effective verification of the related formulas deduced above is achieved...