Research Of Field Testing Of Large-diameter Underwater Metro Shield Tunnel With Double Lining

With the technological improvement of shield machine making and tunnel construction,large-diameter shields have been widely used in tunnel construction.The double lining structure is gradually adopted because the segment lining may not meet the demand of some large-diameter shield tunnel projects.Field test is an effective method to solve the problem,which is urgent to be solved at present,of revealing the mechanical properties of double lining structure.This paper is based on the Crossing-river Tunnel Project of Wuhan Metro Line 8,which is the largest-diameter metro shield tunnel with two tracks in one cave in China at present.A field test of large-diameter underwater metro shield tunnel with double lining is carried out.The main research work and results are as follows :1、Five typical sections were selected in field test.By measuring the formation water pressure,earth pressure,the force of the circular rebar of segment,the concrete strain of segment lining and secondary lining,the radial pressure between segment lining and secondary lining of these sections,the stress and deformation of structure under different geological conditions and water levels in constructing term and operating term were collected.The dynamic change curves and spatial distribution characteristics of the pressures on segment lining in defferent constructing process and the Yangtze water levers under different geological cinditions are revealed,thus the deformation pattern and distribution characteristics of internal force of segment lining and secondary lining structure are revealed.2、By analysing the change pattern of the internal force of secondary lining and segment lining before and after the construction of secondary lining,the influence of the construction of secondary lining on segment lining is revealed.The significance of the construction of secondary lining in large-diameter shield tunnel is discussed.3、The shell-spring model was established corresponding to the assembling position of segment during the construction period of the tunnel.By analysing the pressure on segment lining structure with the method of water and earth pressure calculating separately,the accuracy of the measured loads in the field test is judged.With the method of water and earth pressure calculating separately,comprehensive test and surface fitting,the optimal solution of water and soil pressure of the selected sections which are in sandy stratum in the field test was obtained by load back analysis.The calculation method of load design of the section of large-diameter shield tunnel is discussed,of which the buried depth is at least twice times as external diameter of the shield segment lining in sandy stratum.