Quantitative And Qualitative Comprehensive Risk Assessment For Construction Safety Of Shield Tunnel In Soft Soil

There exist many uncertainties in the construction of shield tunnels in soft soil.Despite of various research method of risk assessment of metro projects,but many risk assessment methods appear to be influenced by human factors.This theis analyzes the quantitative and qualitative indicators of shield tunnel in soft soil respectively and proposes corresponding risk assessment methods.The main research contents are as follows:(1)The data of subway tunnel accidents are collected and analyzed statistically to reveal the risk of soft soil shield tunnel construction.Based on the cause analysis of accident cases,risk indicators are selected and classified.For quantitative indicators,including cohesion,internal friction angle,compartment pressure,earth chamber pressure and gap between shield and soil and distribution pattern,their statistical features are summarized from the literature review and field monitoring.For qualitative indicators,a two-stage risk assessment system is established from five aspects: human,material,machinery,method and environment.(2)A numerical model considering earth chamber pressure and gap between shield and soil is established based on the 3D finite difference software FLAC3 D.The influence of quantitative indicators on surface vertical and horizontal displacement during shield advancing is studied by quantitative analysis.The results showed that the influence of gravity on surface deformation is negligible.Among these quantitative factors,tunneling parameters have greater influence on surface deformation than soil parameters.(3)Based on random finite element simulation method,the random field models of soil parameters and shield tunneling parameters are generated.Compare deterministic calculation results with uncertainty calculation results,the influence of soil parameter variable coefficient and tunneling parameters variable coefficient on ground settlement is analyzed.A quantitative risk assessment method for correcting the results of deterministic calculations is proposed.The results showed that the influence of shield tunneling on ground settlement is significantly underestimated without considering the variability of soil parameter and tunneling parameters.These uncertainty factors are in the descending order of degree of influence are internal friction angle,earth chamber pressure,modulus,cohesion and unfilled gap.(4)A two-stage fuzzy qualitative risk assessment method based on numerical analysis results,entropy weight extension theory and the statistical results of accident cases is proposed.