Study On The Reliability Of Tunnel Support Structure Constructed By Mining Method In Sandy Gravel Stratum

The Chengdu area is a typical sand-pebble formation,and it is difficult to describe the typical discrete characteristics of the sand-pebble formation by using certain stratum parameters to describe the sand-pebble formation.The method of probability reliability based on interval parameters is more suitable to be used in sand and gravel stratum mining tunnels.This paper relies on the hidden excavation wiring section of Jianshe North Road Station?Xinhong Road Station on the left line of Chengdu Chenghua District Metro Line 6 to carry out the physical and mechanical parameters of the sand and gravel stratum,the limit state equation of the subway tunnel structure and the probability reliability of the tunnel support structure.Research,the main research content and results are as follows:(1)Based on the Monte Carlo method,using Auto Cad secondary development and image recognition technology,the finite difference method software Flac2 D is used to establish a finite difference model of sand and gravel soil,and the mechanical parameters of sand and gravel soil are obtained by simulating triaxial tests.Numerical simulation shows that the elastic modulus of the sand and gravel formation increases as the proportion of pebbles increases,the flatness decreases,and the maximum particle size increases;the internal friction angle increases with the decrease of the proportion of pebbles,and the flatness increases And increase;(2)Analyze the correlation between the physical and mechanical parameters of the sand and gravel stratum,and obtain that the mechanical parameters of the sand and gravel have a greater influence on the mechanical parameters of the sand and gravel stratum than the mechanical parameters of the sand.A BP neural network model is established to determine the physical and mechanical parameters of the sand and gravel stratum.Value range.(3)Comparing the methods of checking and calculating the initial support structure of tunnel section steel in the "Road Tunnel Design Manual" and the "Technical Specification for Combined Structures",and refining the calculation formula,it is found that the former has greater correlation with the bending moment of the structure.The former has greater relevance to the axial force.For the results of the unfavorable position calculations,the former has a smaller safety factor,and the results are more conservative.It is applied to the safety check calculation of the initial supporting structure of the supporting engineering tunnel through two methods,and the most unfavorable position is at the vault and spandrel(Chapter 4);(4)Based on the stochastic finite element method,a stochastic finite element model based on the load structure method is established to analyze the mechanical behavior of each part of the tunnel structure and the sensitivity of the reliability to the input parameters.Only the initial supporting structure vault and spandrel have the possibility of failure in the supporting project.Combined with the reliability analysis results,the safety and reliability of the initial support structure can be improved by constructing the secondary lining as soon as possibleand adopting a steel arch with greater bending rigidity ?...