Experimental study on lining response of metro shield tunnel under the influence of ground cavity

In order to explore the influence of the cavity behind the shield tunnel segment on the tunnel structure, the model test is used to study the response rules of the deformation, stress and contact pressure with the stratum of the lining structure under the four working conditions of no cavity, arch crown, arch waist and cavity behind the arch bottom. The results show that when there is no cavity, the lining is subjected to uniform stratum pressure, and the stratum also provides sufficient stratum reaction force for the lining, and the internal force of the segment is symmetrical. When there is a cavity, the existence of the cavity changes the contact state between the lining and the surrounding strata, the formation resistance of the lining near the cavity disappears, the lining section tends to deform at the cavity under the action of bias pressure, the overall stress state of the lining structure deteriorates, the internal force distribution is complex, and the stress concentration effect appears at the edge of the cavity. The influence of different cavity positions on the safety of tunnel structure is as follows: arch waist > arch crown ≥ arch bottom. When there is a cavity behind the arch waist, the bending moment of this section increases by about 2.78 times compared with that without cavity, and the outer side of the segment is subjected to large tensile stress. When there is a cavity behind the arch crown and arch bottom, the deformation and stress trend of the lining structure are relatively similar, which shows that the segment bending moment value at the section where the cavity is located is significantly lower than that without cavity, while the bending moment value at the adjacent sections on both sides increases, and the bending moment value of the original section is shared by the adjacent sections on both sides; The difference is that when there is a cavity behind the arch crown, when the size of the cavity increases to a certain value, reverse bending points appear on both sides of the arch crown, the bending moment value of the arch crown reverses, and the arch crown changes from the original positive bending to negative bending (it is specified that the positive bending moment is when the inner side of the lining is in tension and the outer side is in compression). The bending moment of the section where the void is located varies greatly and the segment is susceptible to concentrated load. © 2022, Central South University Press. All rights reserved.