Research On Key Technology Of Tunnel Entrance’without Slope Cutting’ Jacking Method

With the continuous investment of the state in infrastructure,tunnel engineering has developed rapidly.In the construction of tunnel entry,slope cutting entry is mostly used.It may take a long time to restore the ecology of the tunnel entrance in areas with fragile ecological environment.For example,in some western tunnels,the topography and geomorphology of the tunnel entrance are complex,and the ecological environment is very sensitive and fragile.The breaking force of the slope cutting on the entrance environment is great,so the hand-driven jacking method is proposed.The entrance and the horizontal plane are at a certain angle,that is,the ’without slope cutting ’ entrance,which can not only reduce the impact of the construction on the environment,but also can be better connected and transformed with the subsequent tunnel construction method.In view of the above problems,this thesis studies and analyzes the ’ without slope cutting ’ jacking method and demonstrates its feasibility.The main research contents and results are as follows :(1)Combined with the construction characteristics of the jacking method,from the perspective of environmental protection of the tunnel portal,based on the relevant specifications,the applicable conditions of the jacking method are discussed.The manual jacking method can be used for projects with good stratum stability.Combined with certain engineering auxiliary measures(advanced reinforcement measures,tunnel face stability measures,etc),it can also be applied to soil layers with poor geology.For the broken loose rock area,it can also be applied with rock breaking equipment such as crushing hammer;for the relatively complete area of rock,it can be combined with smooth blasting,pre-splitting blasting and static pressure crushing rock to realize the excavation of the face of the jacking method.Improve the application scope of jacking method.(2)The explicit dynamic method is used to simulate the mechanical response of the whole dynamic process of the jacking method.The simulation results of implicit statics and explicit dynamic methods are compared,which proves that the explicit dynamic results are reliable.The explicit dynamic method is further studied.In the calculation process,the element deletion algorithm based on time and space is adopted to solve the problem that ABAQUS explicit dynamics cannot simulate excavation.The simulation results show that the explicit dynamic method can effectively simulate the construction process of the jacking method.For the three-center pipe section,the stress area is mainly concentrated in the lower part of about 40 %.Based on the comprehensive jacking force,economy and construction efficiency,the jacking method can be used without mud injection to reduce wear.(3)Assuming that the angle between the oblique earth pressure and the vertical above the tunnel satisfies that =(π/2-)/(1 + ),using the soil column theory and Terzaghi theory,the theoretical calculation formula of jacking force with slope at the entrance of the tunnel is derived.The theoretical calculation formula of Yu Binquan ’s manual jacking method is improved to meet the condition of slope at the entrance of the tunnel,and compared with the simulation results.The results show that the theoretical calculation formula of jacking force is more accurate,which reflects the influence of slope at the entrance of the tunnel on jacking force.(4)The stress and deformation characteristics of three different back structure types of continuous wall + reinforced concrete wall,continuous wall + steel frame and friction pile + steel frame are simulated and analyzed.The results show that the effect of continuous wall + reinforced concrete wall is the best,the effect of continuous wall + steel frame is the second,and the effect of friction pile + steel frame is the worst.With the increase of the depth of the underground part of the back structure,the maximum principal stress(tensile stress)of each structural concrete and the Mises stress of the steel frame do not change much.The maximum principal stress of each structural concrete has multiple symmetrically distributed peak areas,and the reinforcement density in this area needs to be densified during construction.From bottom to top along the height direction,the displacement of the back structure gradually increases,and the horizontal displacement of the structure does not change much.When adopting the continuous wall + steel frame back structure,it is necessary to pay attention to the connection type between the steel frame and the continuous wall.It is suggested to adopt the method of covering and pouring concrete after welding the steel bar of the lower structure and the upper steel frame.