Study On Effect Of Loosening Contact Between Support With Surrounding Rock On Safety Of Tunnel Structures

During the tunnel construction and operation,the loose contact between the lining support and the surrounding rock is an important inducement for the cracking and failure of the tunnel structure,and even directly affects the stability of the tunnel structure.In this paper,the tunnel lining structure with different loose contact ranges between the support and the surrounding rock is taken as the research object,and the research method combining theoretical analysis,model test and numerical simulation is used to investigate the cracking situation of the tunnel lining structure with different loose contact ranges.In-depth study of its structural safety impact.The main work and research results are as follows:(1)The cracking characteristics of the single-arch tunnel lining structure under the condition of loose contact between the lining support and the surrounding rock are revealed.In the loose contact state,tensile failure first appeared on the outside of the lining structure vault,and with the increase of the loose contact range,the cracks generated by the lining model increased.The existence of loose contact aggravates the local cracking situation near the loose contact.The cracking position inside the spandrel varies with the loose contact range,and the cracking and distribution sequence near the loose area are closely related to the loose contact range.(2)The disaster mechanism of loose contact between lining support and surrounding rock on lining is analyzed.The existence of the loose contact leads to the redistribution of the pressure of the supporting surrounding rock,which causes the axial force of the lining structure to increase in tension,and the structure at the loose area is bent outwards by the negative bending moment.The outside of the lining structure in the loose contact area changes from compression to tension,and is under the action of negative bending moment.The influence of contact on the internal force of the lining structure increases with the increase of the loose contact area.(3)The mechanical properties of the lining structure in the loose contact area are analyzed,and the correction method of the lining load structure model under the loose contact state between the support and the surrounding rock is proposed.Considering that the contact pressure between the supporting surrounding rocks includes the surrounding rock pressure and elastic resistance acting on the lining structure in the load structure model analysis,the results of the three-dimensional numerical simulation calculation results of the loose contact state between the supporting-surrounding rock are analyzed.The distribution law of contact pressure,and the existing load structure model is revised.(4)The cracking law of the lining of the multi-arch tunnel and the deformation law and cracking situation under the action of loose contact between the supporting and surrounding rocks in different ranges are revealed.Differences in the mechanical response of a single-cavity tunnel.Under normal dense contact conditions,the cracks at the bottom of the partition wall are the most serious.The inner side of the vault,the outer side of the arch foot,the inner side of the inverted arch,and both sides of the partition wall are the areas where the cracks are concentrated.The cracking of the lining structure on the loose contact side of the multi-arch tunnel is more serious,and the uneven distribution of surrounding rock pressure near the loose contact is the root cause of local cracks in the structure.