Study On The Lower Bound Analysis Method To Obtain Bearing Capacity Of Subway Tunnel In Karst Areas

Abstract:The traffic problem is increasingly prominent for rapid population growth and urbanization.As a result, subway construction has been spreading successively in major cities throughout the country.As carbonate rocks are widely distributed in our country, which are the main material basis of karst,the existence of the karst geology become a problem that cannot be ignored in the construction of the subway.Therefore it is significant to seek an effective method to calculate the foundation bearing capacity for the subway construction safety and normal working.This paper is based on the item of National Science Foundation of China’study on the limit analysis method of the karst foundation stability in the subway construcion’(No.51108462). And the research content is as follows:(1)The general principle of limit analysis method is discussed, and bearing capacity is calculated on the basis of a simplified hinged truss model.(2)The general principle of the lower bound analysis using finite element method is expounded. Taking advantage of the MATLAB language and MATLAB toolbox, a program is designed to realize the finite element method. The program is applied to get the bearing capacity of a strip foundation.And by comparing with the exact solution, the effectiveness of the approach is tested and verified.And then it is applied to the subway tunnel problems.(3)By using ANSYS software and adopting appropriate yield criterion, bearing capacity of subway tunnel in karst areas is studied with the method of step-loading.(4) Using the two methods above, the relationship between the lower bound solution under the condition that there is only one cave below the tunnel and factors such as the cave diameter, the thickness of the rock cover is studied.(5) Through the analysis of the lower bound solution under the condition that there is a serie of caves below the tunnel,the conclusion that the top-down first cave has much more influence on the bearing capacity is deduced.(6)Based on the the karst geological reports of GuangZhou metro, tunnel foundation bearing capacity is calculated as there are different soil layers.This paper contains80figures,18tables and93references are cited.