Study On Bearing Characteristics Of Tunnel Invert Under Different Basement Conditions

With the rapid development of China’s railway and highway industry,the construction of mountain tunnels has increased significantly,when the tunnel passes through different strata,the surrounding rock conditions of the tunnel basement are generally different,and the stress and failure characteristics of the tunnel invert structure caused by different types of basement surrounding rock are also different.By combining theoretical analysis,numerical simulation and laboratory model test,this paper explored the stress failure mode of tunnel invert under various basement surrounding rocks,and summarized the stress failure characteristics of invert under various conditions.Based on the investigation of literature and building code,the mechanical calculation method of tunnel surrounding rock and invert structure are summarized.A numerical model was established to analyze the effect of invert on the overall structure of the tunnel.The typical failure modes of invert and the influencing factors of invert diseases are also summarized.The laboratory model test was designed to study the expansion condition of surrounding rock at the bottom of the tunnel invert.By deducing the similarity ratio and selecting reasonable similarity materials,a simple and effective loading method was explored to simulate the expansion effect of surrounding rock at the bottom of the tunnel.Strain gauge is used to monitor the strain value of each point on the tunnel model,then the strain result is converted into other mechanical parameters by mechanical formula,it is concluded that when the tunnel is subjected to the vertical upward expansion pressure at the bottom,the corresponding stress,axial force and bending moment of each measuring point on the tunnel increase with the increase of the loading pressure,and the corresponding safety coefficient decreases accordingly.According to the data collation results and the model phenomena after the test,the location of the failure is located at the joints of the ribs on both sides of the invert and the side wall invert.It was found that the failure position of the inverted arch predicted by numerical calculation was basically corresponding to that of the model test,and the distribution of internal forces at various points on the lining was basically consistent.In this paper,the simulation method of the expansion pressure of surrounding rock,the softening effect of surrounding rock and the over-excavation and under-excavation phenomenon in engineering in the Midas-GTS-NX finite element software is explored.In view of the surrounding rock factors and construction factors that might cause the bottom heave cracking in tunnel engineering,the numerical model was established and calculated respectively.Under the condition of surrounding rock expansion,it can be divided into different conditions of bottom surrounding rock expansion,side surrounding rock expansion and side biased expansion.The softening condition of surrounding rock can be divided into whole softening and part softening.The construction factors mainly focus on the over-excavation and under-excavation of the inverted arch,which is one of the reasons for the uneven surrounding rock of the tunnel basement.By sorting out and analyzing the results of various calculation models,the stress and deformation rules of invert under corresponding working conditions are obtained,and the possible failure location is speculated.This paper summarizes the stress modes of invert under various conditions of tunnel basement surrounding rocks,and the research results can provide a reference for similar tunnel engineering conditions in practical engineering.