Study On Shield Tunneling Efficiency In Sandy Pebble Stratum

In recent years,the rapid development of tunnel and underground engineering in China has put forward higher requirements for shield tunneling technology.The surrounding environment and geological conditions faced by shield tunneling during tunnel construction have become more and more complex and diverse,and shield tunneling has exerted disturbance influence on strata.By analyzing the formation disturbance law,the matching of shield tunneling parameters can be explored to optimize tunneling efficiency.The construction of shield tunneling machine is adapted to the specific geological environment to meet the requirements of fine and personalized construction of shield tunneling machine.Sand and gravel stratum has complex mechanical properties,poor self-stability and sensitive formation response.The main reason of formation disturbance is caused by shield tunneling.The tunnel construction in this stratum is faced with various difficulties.The disturbed soil layer increases during the tunneling process of the shield tunneling machine,which is easy to cause accidents such as instability collapse.During the excavation process,the cutter head of the shield tunneling machine is prone to serious wear and the attitude control is difficult,which causes the tunneling speed delay of the shield tunneling machine.In this paper,large-scale laboratory model test and discrete element numerical simulation are used to explore the disturbance characteristics of shield tunneling in sand and pebble formation,and analyze the characteristics and correlation of key shield tunneling parameters in sand and pebble formation.The main research work is as follows:(1)Carry out specific,dynamic and continuous indoor shield tunneling tests based on the self-developed Ф800mm soil pressure balancing shield tunneling large test system.In the driving test,the settlement characteristics of sand-pebble stratum are explored by dynamically adjusting the driving parameters of shield tunneling.The dynamic response of stratum deformation during the driving under different conditions of shield tunneling machine is analyzed from the aspects of transverse,longitudinal and time history,etc.,and the disturbance characteristics of sand-pebble stratum caused by the change of shield tunneling machine parameters are explored.(2)During tunneling,the test system records and outputs key tunneling parameters of the shield model machine,including seven key tunneling parameters,such as tunneling speed,shield thrust,cutter speed,cutter torque,soil tank pressure,screw conveyor speed,screw conveyor torque,etc.Combined with three different tunneling states of the shield model machine during tunneling test,the distribution rules are statistically analyzed.The relationship between cutter head torque and cutter head speed,earth tank pressure and screw conveyor speed,shield thrust and cutter head torque,shield thrust and earth tank pressure,cutter head torque and earth tank pressure is discussed.(3)The numerical model of sand and pebble stratum and shield machine is established for shield tunneling test in sand and pebble stratum,and discrete element simulation is carried out.The simulation process and model material parameters,model contact parameters and simulation parameters are explained.The settlement characteristics of sand and gravel stratum,the pressure of soil tank and the particle velocity distribution of soil tank in the shield tunneling process under different buried depths are compared and analyzed,and the formation settlement is compared with the laboratory test results.