Study On The Cracking Characteristics Of Tunnel Structure And The Safety Under The Impact Of The Void Behind Lining

During the construction and operation of tunnel engineering,tunnel diseases often occur due to the void behind the lining,which affects the durability of the tunnel structure and threatens the operation safety of the tunnel.Therefore,this paper takes the tunnel structure with void behind the lining as the research object,through numerical simulation and indoor model test methods,deeply studied the cracking performance of tunnel structure under the influence of void behind the lining and the influence of void induced lining cracks on the safety of tunnel structure.The main work and research results are as follows:(1)The cracking mode of tunnel structure under the influence of void behind lining is proposed.Considering the three-dimensional space effect of voids,the cracking process of tunnel structure under the influence of different sizes of voids is compared and analyzed.The cracking modes of vault lining caused by voids are divided into three main types.The direction,distribution and order of cracks are closely related to the size of voids.(2)The research reveals the cracking reason of tunnel structure under the influence of void behind lining.Due to the loss of surrounding rock pressure at the voids,the lining structure near the voids produces relative radial deformation,and both the annular and longitudinal internal forces of the arch lining change.At the longitudinal boundary of the tunnel,the toroidal positive bending moment(inward bending)of the lining structure is significant,which is prone to longitudinal cracks.Within the scope of the void and at the annular boundary of the void,when the longitudinal dimension of the void is small,the influence of longitudinal bending moment on the arch lining is significant,resulting in high longitudinal tensile stress of the arch lining and easy to generate annular cracks.When the longitudinal dimension of the void is large,the arch lining is affected by both the circumferential and longitudinal bending moments.At this time,both the circumferential and longitudinal tensile stresses at the arch are high and the circumferential and longitudinal cracks are easy to occur.(3)The failure mode of tunnel structure under the influence of lining crack induced by vault void is defined.The failure mode of lining structure is closely related to the position of cracks.The failure of lining is mainly concentrated on the inside of the vault of lining structure and the section of induced cracks.When the cracks are located on the outside of the vault or far away from the void inside the lining,the failure of lining structure is dominated by the collapse of the vault.When the inner cracks of lining are close to the boundary of the void,the failure of lining structure changes into crack shear failure.(4)The failure cause of tunnel structure under the influence of lining crack induced by vault void is studied and analyzed.The existence of cracks reduces the bearing area of the lining structure,decreases the overall rigidity of the structure,and weakens the continuity of the lining structure,resulting in a significantly reduced bending moment at the cracks of the lining,but has a little influence on the bending moment at other locations of the lining.The deformation of lining structure near the crack increases,and the deformation of lining structure far away from the crack increases slightly,but it is relatively small.Induced cracks at different locations reduce the bearing capacity of lining structure to varying degrees.