| Shallow burried&unsymmetrical pressure tunnel under complex geological conditions is prone to surrounding rock instability and other safety accidents in the construction process.It is particularly important to adopt scientific and reasonable methods for risk identification and evaluation in the construction stage.This paper is based on the horizontal project commissioned by the China Construction Fourth Engineering Division(Guangzhou): the key construction technology research topic of shallow burried&unsymmetrical pressure tunnel of Guizhou Zhengxi Expressway.Taking the Tianexue Tunnel of Zhengxi Expressway as the background,the systematic theory and safety evaluation of tunnel construction risk are carried out.The main research contents and results are as follows :Combined with the relevant reports of highway tunnel construction accidents in recent years and the research status of related issues at home and abroad,the tunnel risk theory is comprehensively expounded.Based on the catastrophe theory of risk accidents,the cusp catastrophe model of tunnel construction risk events is established to systematically study the mechanism of risk accidents.Application of statistical theory and tunnel mechanics analysis of shallow burried&unsymmetrical pressure tunnel construction risk sources,the establishment of shallow burried&unsymmetrical pressure tunnel construction safety evaluation index system;In order to consider the objectivity of the evaluation results,based on the grey clustering evaluation model,this paper introduces the group decision entropy model and the variable weight theory to modify the original evaluation model,and establishes the tunnel construction safety risk evaluation model based on the grey variable weight theory.The risk assessment model of tunnel construction based on grey-variable weight theory is applied to the risk assessment of shallow burried&unsymmetrical pressure tunnel relying on engineering,and the calculation effect is analyzed.The applicability and effectiveness of variable weight theory for the actual situation of this project are discussed.The evaluation results show that the calculation process of variable weight will improve the weight of the more dangerous index,and enlarge the influence of the more dangerous index in the comprehensive evaluation,so as to objectively reflect the risk represented by the index.For shallow burried&unsymmetrical pressure tunnel under complex geological conditions,the risk assessment of variable weight calculation is more important.FLAC3D,a large-scale geotechnical engineering numerical analysis software based on finite difference,was used to establish the numerical model of the outlet section of the right line of the unsymmetrical pressure tunnel relying on the project.The stress and displacement of the surrounding rock after excavation were analyzed by finite difference simulation,and the construction risk sources of the tunnel in this project were discussed quantitatively and compared with the evaluation results of the risk evaluation model constructed in this paper.The analysis shows that the surrounding rock of Tianexue tunnel in this project is weak,and the hole is located in the shallow buried section.The tunnel is prone to instability of surrounding rock during construction due to the influence of bias.The numerical simulation results are in good agreement with the risk assessment results,that is,terrain and geological factors are the most approximate risk factors for the construction risk of this tunnel project. |
