Study On Epb Shield Tunnelling Technology In Upper Soft And Lower Hard Ground

With the rapid development of subway construction,complex strata is often encountered in subway construction.When the earth pressure balance shield is used in the upper-soft lower-hard ground,due to the difference of physical and mechanical properties between the upper and lower soils,the shield cutter head needs a large torque to excavate,and the excavation process will cause more disturbance,then causes large ground surface settlement and even instability of the face.This paper relies on the Jinkeng-ZhenLongnan shield section of Guangzhou Metro Line 21 to study the key construction problems such as cutterhead and cutter configuration,muck conditioning technology,and replacing cutters in the shield tunneling process in the upper-soft lower-hard ground.The research can provide reference for the construction of similar projects in China.The main research work is as follows:(1)By analyzing the selection and wear of the cutterhead and the cutter in the construction section,the selection and configuration principles of the cutterhead and cutter in complex stratum are summarized.The optimization of the cutterhead and cutter for this kind of complex stratum is proposed.(2)By studying different kinds of additives to improve the physical properties of the muck to ensure that the muck has a good soil plasticity flow,good viscosity-soft consistency,low internal friction and low water permeability,thereby we can effectively reduc the torque and thrust of the shield and then improve efficiency.(3)The Ansys finite element model is used to carry out the optimization analysis of the propulsion of the shield in the upper-soft lower-hard ground.By applying different jacking force at different positions on the face,the surface settlement caused by shield tunneling under different working conditions and the mutual influence of the left and right lines are analyzed.Finally the influence of the propulsion of the shield to the stress and deformation of the segment are analyzed.(4)Through the research on replacing cutters in the upper-soft lower-hard ground,the determination conditions of replacing the cutters are determined.According to the interval stratum conditions,the position of replacing the cutters and the measures of keeping the stability of the face during replacing are selected.And the factors that affect the stability of the face during the process of opening the soil warehouse are analyzed by numerical calculations.