| Taking Yanghe Road station to jianhuzhen station of Shaoxing Rail Transit Line1 as the main research object,First of all,based on the summary and analysis of the geological conditions of the subway tunnel passing through the karst collapse prone area,the basic conditions,control factors,distribution and development pattern of karst development are studied by means of drilling and elastic wave CT.Then,according to the development of karst,MIDAS / GTS software is used to discuss the influence of the underlying karst cave on the stability of shield tunnel construction,and the influence law of karst on the stability of shield tunnel is analyzed when the distance between the karst cave and the bedrock surface h,the diameter D of the karst cave and the filling degree W are different.Then,the mechanism of karst collapse is studied under the stratum condition of geological structure "limestone karst and clay contact directly".On this basis,based on the fuzzy AHP comprehensive analysis method,the karst collapse grade of special geological structure is rated as high risk,medium risk and low risk,and the corresponding disposal scheme is proposed for different risk grades.The main conclusions of this paper are as follows:(1)Based on the existing engineering investigation data in the study area,the topography,geological structure and formation lithology of the area are identified.According to the engineering geological characteristics of the study area,the comprehensive exploration method of drilling and elastic wave CT is adopted to find out the distribution and law of karst scale,distribution scope,spatial position,vertical and horizontal direction in the underlying bedrock,as well as the filling situation in the karst tunnel Condition and physical and mechanical properties of fillings;(2)Based on the MIDAS / GTS finite element software,a three-dimensional numerical model is established,and various conditions such as the distance h between karst and bedrock surface,the size D of karst cave and the filling degree w of karst cave are analyzed.The influence rules of different karst cave occurrence conditions on the displacement field of tunnel and soil and the stress field of lining are obtained;(3)Based on the analysis of karst geology and overburden structure in Shaoxing City,the mechanism of overburden karst collapse is studied.The risk degree of karst collapse is quantified by fuzzy AHP,and then accurately evaluated.According to the specific quantitative grade of actual karst collapse risk,the influence scope and risk degree of the risk in the study area are judged and formulated Perfect corresponding measures to prevent risks during construction. |
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