Computational Analysis on Longitudinal Equivalent Bending Stiffness under the Influence of Shield-tunnel Transverse Deformation

Abstract

In order to study the lining longitudinal deformation rule under the influence of the lining transverse deformation in the process of long-term settlement of operating metro shield tunnel with straight joint, based on the field test monitoring data of Tibet Road-Zhongxing Road shield tunnel in the M8 of shanghai, and considering the tunnel convergence, this problem is studied by amending equivalent continuous model. Then there is a comparison between the existing theoretical methods and this calculation method. The results showed that, in the ring joints, no considering shearing, the maximum of ring joint open, the tension and compression stress of segment, and bolt stress slightly decrease with the increase of deformation of tunnel convergence under the bending. The smaller the curvature radius of the shield-tunnel longitudinal deformation is, the larger the ring joint open under the influence of tunnel convergence is. Introduction Due to the joint, the stiffness of the lining is reduced in the shield tunnel with straight joint. When the longitudinal differential settlement occurs, there is joint staggering and joint opening between the rings. These will cause the joint leakage, the segment crack and track irregularity, etc. endangering the safety of operational tunnel. Therefore, to ensure the safety of operational tunnel, it is very important of the deformation and force characteristics of the ring joint longitudinally along tunnel. But so far, this research is still at a preliminary stage. In the process of long-term settlement of operational tunnel, the transverse deformation and the longitudinal deformation often occur simultaneously with the longitudinal differential settlement increasing. For the reason, the influence of tunnel convergence should be considered when analyzing the longitudinal deformation and stress of the ring with straight joint. The longitudinal equivalent bending stiffness model was studied in the references[1, 2, 3, 4], but without having considered the relationship between the transverse deformation and the longitudinal deformation. To sum up, with considering the relationship between the transverse deformation and the longitudinal deformation, a new longitudinal equivalent bending stiffness model is put forward for interpreting the longitudinal deformation and force of shield tunnel with straight joint more accurately, and providing more valuable theoretical reference for the operational safety jugement of metro tunnel. Field Measurement Test Summary The Tibet road ~ Zhongxing Road Tunnel of Shanghai metro line No.8 is 1226m. It is mainly through Gray muddy clay and Gray clay. The joint segment is used in the shield tunnel. Each lining ring contains a key block, two adjacent blocks, two standard blocks, and an arch bottom block. The design strength grade of segment concrete is C55. The joint bolt is M30. The elastic gasket used for joint waterproofing is composed of water swelling rubber and EPDM. The main design parameters are shown in table 1. International Conference on Mechanics and Civil Engineering (ICMCE 2014) © 2014. The authors Published by Atlantis Press 458 Tab.1 The Main Design Parameters The segment Value The bolt Value Thickness(m) 0.35 diameter(m) 0.03 Width(m) 1 The number of Ring-joint bolts 17 Outer diameter (m) 6.2 The number of Longitudinal-joint bolts 12 Inner diameter (m) 5.5 The tensile yield strength (MPa) 640 Ring-joint initial deformation (m) 0 The elastic modulus of bolt (GPa) 206 The design value of the concrete compressive strength (MPa) 26 length(m) 0.4 The design value of the concrete tensile strength (MPa) 21 The elastic modulus of concrete (MPa) 35500 The field measurement test section is near the work well, standard section, and the connected aisle respectively, as shown in figure 1. Monitoring projects includ the tunnel convergence and the joint opening. Monitoring period is one year. The monitoring frequency is 3 months. 1 Miscellaneous fill 22 Yellow clayey soil 23-1 Grey clayey silt 51-1 Gray clay 51-2 Grey silty clay 3 Muddy silt clay 4 Gray muddy clay Tibet Road station Standard section Near the connected aisle Uplink tunnel ring (1~5) Downlink tunnel ring (859~863) Uplink tunnel ring (152~156) Downlink tunnel ring (781~785) Uplink tunnel ring (464~471) Downlink tunnel Ring (401~407) -6.85 -12.12 -14.8 Near the work well Fig. 1 Schematic Diagram of Monitoring Tab. 2 Number of Points (tunnel convergence)