| The need for mechanized excavation of tunnels in cities has continuously increased in recent years, especially as a result of the global expansion in the number of tunnels being constructed for subways.Duo to the shield tunnel’s unique characteristics, there are some difficulties in construction process, such as the load of shield is hard to determine, the geological characteristics of wall rock can’t be observed, and the excessive upward floating of tunneling lining happened frequently, so the research on the characteristics of shield tunnel during loads and the controlling of lining upward floating has been very necessary until the present day.To solve the problems, numerical modeling and analytical methods were carried out in this thesis. The main contents are as follows:1) Based on the analysis of the interaction of shield and soil in the process of shield driving, the modified formulae of calculating thrust and cutter head torque which taking the influence of geological parameters, driving parameters and the structure of cutter head into consideration were deduced, and through the analysis of the measured data of one section in Shenzhen No.2Metro Line,the adaptability of these modified formulae in complex strata were proved.2) Considering the stratums of one section in Shenzhen No.2Metro Line, the relationships of driving parameters and geological parameters are studied.Conceptions of specific thrust force which can be used to characterize the compressibility of wall rock and specific torque which can be used to characterize the frictional effect between the wall rock and cutter head were persented. On the basis, the method to distinguish the wall rock conditions for shield tunnel was studied.3) Based on the mechanical characteristics of lining in construction process,the upward floating analysis model which included lining and bolt, the effects of shield, pressure of grouting and soil was founded. In virtue of ABAQUS, the characters of lining upward floating, the deformation of lining ring joint and the influence of distance between initial hardening location of the grout and shield, the thrust, and the pre-tightening force of bolt were studied. It’s found that reducing the distance between initial hardening location of the grout and shield is the most effective method of decreasing the upward floating value of lining. when the thrust is small, increasing the thrust can be used to control the upward floating value of lining, but increasing the pre-tightening force of bolt has less effect on it.4) The developing law of lining upward floating and the deformation mode of spring joint was analyzed.The results show that the lining upward floating includes three stages:linearly developing stage, arc-shaped developing stage, and deformation stabilizing stage, the main deformation of joint which was dislocation in linearly developing stage and tensile in arc-shaped developing stage. Based on the developing law of lining upward floating and the deformation mode of spring joint,the allowable upward floating value for shield tunnel lining,which was affected not only by the allowable dislocation value of spring joint and allowable tensile value of bolt, by the position where deformation stabilize and the width of lining spring, was studied. The allowable upward floating value for shield tunnel lining of Ningbo and Shenzhen metro whose structure of lining is different was compared,and the results show that the structure of lining has great impact on the allowable upward floating value. |
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