Study On The Influence Of Cavity Behind The Lining To The Safety Of Tunnel Lining Structure

With the wide occurrence of cavity diseases in the tunnel construction and operation, cavities as tunnel diseases have drew more and more attention of tunnel engineers and researchers. Taking an expressway tunnel as example, based on the actual condition of the cavity condition found in detection, the finite element analysis method is adopted to study adverse effects of cavity disease. Main works done are as follows.(1) On the basis of discussion and summary of general causes of cavity and its harmfulness, combined with the specific circumstances of the actual engineering cavity, the factors of the cavity behind the tunnel lining are analyzed pointedly, and management measures are put forward according to the specific location and the size of the cavity.(2) Taking the V level rock as the research object, whose hollow phenomenon is more serious, for the phenomenon of cavity and cavity group behind the lining, numerical simulation analysis are done in use of the stratum structure method, simulating and analyzing several types of cavity groups behind the lining, including vault cavity, bilateral hance cavity, double side wall cavity, vault and bilateral hance cavity, vault and double side wall, bilateral haunch and double side wall cavity. Adverse effects on the lining caused by the cavity are analyzed from three aspects which are the distribution and change of bending moment in the cross section of the lining, changes of the total displacement of surrounding rock, and changes of lining deformation state. The rules of influence of cavity and cavity group on the force of lining are analyzed and summarized, which provides theoretical basis for the adverse effect of the cavity on the lining of the tunnel.(3) When using load structure method to analyze the cavity, the numerical simulation analysis is carried out on the back of the roof lining using the correlation theory of surrounding rock pressure and considering the phenomenon that the pressure increases in the surrounding rock mass. And the stress state of lining is briefly discussed when the phenomenon happens that the pressure increases in a certain range of rock mass around the lining. Then the method is briefly summarized and evaluated in this paper.The main conclusions are as follows through the above several aspects of work done.(1) The vault cavity causes the lining to be changed from lateral compression to medial compression, and corresponding change of the bending moment occurs, and the position between the arch waist and the side wall increases greatly.(2) When there exists cavity group, the bending moment value of lining is greatly changed from hance to arch foot, where the bending moment value shows a large increase, and at the same time, the pulling and pressing state of the arch foot changes. The larger change of the bending moment value increases the unsafe factor in the section from hance to arch foot.(3) The most serious influence which the appearance of cavity and cavity group exert on the deformation of the lining is the place of the arch waist and the side wall, where the lining presents large irregular deformation. At the same time, this is also a larger section of the moment. It can lead to lining crack and other diseases if the deformation is too large.(4) When using the load-structure method to analyze the cavity, although the phenomenon that the pressure increases in some regions is considered, there are still some shortcomings, which lies in that the pressure value of the surrounding rock is difficult to obtain after the cavity appears.