Investigation Of Tunnel Lining Design Method Considering The Uncertainty Of Geotechnical Parameters

The uncertainty of geotechnical parameters poses a severe challenge to the design of support structure in tunnel engineering.This kind of uncertainty comes from the natural variability(random uncertainty)of geological materials in the process of its complex formation and continuous evolution,as well as the cognitive uncertainty(cognitive uncertainty)caused by the lack of site-specific information and errors introduced in the test and design stages.Although the uncertainty can be treated subjectively by using conservative design parameters,due to the lack of in-depth understanding of the response of variable ground,this approach may lead to an overly conservative support design that has a negative impact on the project cost and schedule.The design method based on reliability provides a way to consider the uncertainty of geotechnical parameters.The key point is to quantify the uncertainty of geotechnical parameters and directly reflect it to the whole design process.The design method based on reliability can calculate the failure probability of the support structure according to the specified limit state,thus providing a measure of the performance of the support structure.In addition,when considering multiple design schemes,reliability method can be combined with quantitative risk analysis to determine the optimal support design based on safety and minimum cost,rather than the traditional subjective conservative design.Although reliability-based design method has significant advantages,due to some technical and conceptual challenges,its application in geotechnical engineering,especially in tunnel engineering has been relatively small,and the promotion speed is relatively slow.The purpose of this study is to consider the uncertainty of tunnel geotechnical parameters,and try to introduce the reliability-based design method into the tunnel support design,and provide a reliability-based tunnel support design method.This study can be divided into the following five parts:(1)Research on the uncertainty in tunnel engineeringThe sources of uncertainty in tunnel engineering are classified,and the uncertainty is quantified by probability theory and mathematical statistics.Understand and reduce the uncertainty in rock test and geotechnical test.(2)Research on the reliability-based design methodFirstly,from the concept of acceptable risk,this paper explores the acceptable risk level in geotechnical engineering.Then,according to the uncertainty variables,such as the geotechnical property parameters,different treatment methods,the reliability-based design method is classified.Finally,according to the difference of the limit state function solution method and(or)calculation accuracy,the failure probability calculation methods under different levels are divided.(3)Study on tunnel lining design considering the inherent randomness of geotechnical parametersFirstly,the mean value,covariance and probability distribution type of geotechnical parameters are considered by using the level Ⅱ reliability design method;secondly,the influence of the inherent randomness of geotechnical parameters on the stability reliability of the tunnel and its supporting structure is explored by using the convergence confinement model.Finally,the failure probability of the support structure is related to the support design,such as the design of shotcrete thickness,so as to form the tunnel support design based on the randomness of geotechnical parameters and reliability.(4)Design of shield tunnel lining considering the spatial variability of geotechnical parametersFirstly,a two-dimensional random field model of geotechnical parameters is established by using the random field theory of level Ⅲ reliability design.Then,the random field of geotechnical parameters is mapped to the two-dimensional finitedifference model of the tunnel,and the finite-difference simulation is carried out under the Monte Carlo simulation framework,so as to obtain a set of response variables about the tunnel support structure.Finally,the probability analysis of the calculated response variables and the reliability-based design of the support structure are carried out.(5)Design of shield tunnel lining considering conditional random fieldFirst of all,make full use of the existing geological exploration data,such as drilling data,and establish conditional random field based on the obtained geotechnical properties.Then,the random field of the geotechnical property conditions is mapped to the twodimensional finite-difference model of the tunnel,and the finite-difference simulation is carried out to explore the influence of the geotechnical property parameters,such as variation coefficient,correlation length and correlation number,on the failure probability of the tunnel support structure.Finally,the reliability design of the tunnel support structure is based on the support strength and thickness.The results show that the uncertainty of geotechnical parameters has an important influence on the stability of tunnel and its lining structure.In general,the higher the uncertainty of geotechnical parameters,the lower the reliability of the tunnel and its lining structure,and the more complex the reliability-based design of the lining.In addition,this study provides a quantitative risk analysis method of tunnel lining based on random field of geotechnical parameters,which can be used to evaluate the performance of lining structure and optimize its design based on reliability.Meanwhile,the traditional safety factor is linked with the target reliability(or target failure probability)of the lining structure,so as to form a more intuitive and objective understanding of the risk of the lining structure.