Study On Retaining Structure Deformation Mechanism And Controlling Technology Of Shield Driving At Start And Arrival By Direct Cutting

With the accelerated development of municipal transportation and other infrastructure in China,the tunnel and underground engineering has a broad space for development.Shield tunneling method has been widely used in urban subway tunnels with complex environment due to its advantages of fast tunneling speed,little impact on surrounding environment,good construction safety and high degree of informatization and mechanization.As the key process of shield tunneling,shield tunneling starts and receives restrict the construction speed,it is easy to cause safety accident,which seriously affects the quality and progress of tunnel construction.In this thesis,basic characteristics of GFRP,component deformation mechanism and bearing performance are integrated,design parameter optimization,construction technology and structural deformation prediction and control based on starts and receives of GFRP,deformation mechanism and reinforcement measures of soil at the starting and receiving end of shield,the optimization of tunneling parameters of shield tunneling are studied systematically.The key technology system of rapid direct cutting starts and receives of EPB shield with control deformation as the core is established.The following results have been achieved in combination with the application practice in Beijing:1.By the 1:1 full-scale test of circular cross-section piles,the GFRP structure characteristics of low bearing capacity,large deformation,wide crack width and compression shear failure are discloured.A more scientific and reasonable acceptance method is proposed:under the condition that the allowable value of the test coefficient of bearing capacity of the member is set to 1.4,the maximum crack width at the main reinforcement or abdominal shear is up to 2.5mm as a sign of the ultimate bearing capacity,it provides a theoretical basis for the complement and perfection of the current design and inspection specifications of glass fiber reinforcement.2.Based on the comprehensive analysis of the stiffness and strength of glass fiber reinforced piles and the machinability of common shield machines,the bearing capacity calculation formula including the elastic modulus value of glass fiber reinforced piles and the maximum tensile strain value of glass fiber reinforced piles is proposed.The selection of main materials,the connection method between reinforcement and GFRP reinforcement,the setting of reinforcement,the thickness of protective layer and other suitable values of main design parameters are defined.3,Taking the deformation control of enclosure structure as the core,the "double balance" setting method of pile cutting parameters is proposed:the deformation balance between shield machine and surrounding environment and the power balance of shield machine itself.According to the whole process of cutting glass fiber reinforced piles by shield machine,the principle of setting and adjusting parameters of"small thrust,large torque,suitable rotation speed and slow pushing speed" is put forward.The total thrust value is set to be 12000-14000kN;In engineering application in Beijing subway line 16.Cutter head torque is 3700-4400kNm;The driving speed is 20-30mm/min,realizing the goal of fast and efficient pile cutting and starting.According to the whole process of cutting glass fiber reinforced piles received by shield machine,the principle of setting and adjusting parameters of "large thrust,suitable torque,suitable rotation speed and medium thrust speed" is put forward.The total thrust value is set at 14,000-20,000 kN in the engineering application in Beijing subway line 16.Cutter head torque is 2500-3100kNm;The driving speed is 30-40mm/min.It became the first case in Beijing to cut piles quickly and efficiently to complete the shield machine receiving project.