| In view of the development of the rail transit and the distribution of karst geology in China,the construction of urban rail transit in karst areas is inevitable,in addition,Kunming is an underground karst area,all kinds of underground karst have different depth,size and shape,which will bring harm to engineering construction,which not only increases the investment of construction,but also seriously affects the normal operation of engineering construction and the safe use of buildings.Therefore,it is necessary to study the safety and stability of shield tunnel in karst section.In the paper,taking the karst section of Kunming Rail Transit Line 4 as the engineering background,the stability of surrounding rock of shield tunnel and the safety distance between tunnel and tunnel are studied for different types of caverns,and the main contents are as follows:(1)Based on the research on existing karst tunnels,in this paper,the factors affecting the stability of surrounding rock and the safety distance between dissolved tunnels are selected(location of cavern,size of cavern,filling degree of cavern,surrounding rock level,buried depth of tunnel).In accordance with a large number of actual exploration data,relevant codes and existing theoretical basis of karst area,it’s to determine the reasonable range of each influencing factor.(2)The numerical simulation scheme is obtained by using the control variable method to arrange the influence factors in combination.With regards to three different forms of cave size,location,filling degree,and two different geological factors of buried depth and surrounding rock level,Midas GTS NX is used to simulate the construction process of shield tunnel under different working conditions.The influence of various factors on the stability of tunnel surrounding rock during shield construction is analyzed by the use of displacement field and plastic zone.(3)The factors affecting the safe distance between dissolved tunnels(cave size,cave filling,tunnel depth,surrounding rock level)were arranged by orthogonal test.A numerical simulation scheme was designed and the result of range and varianceanalysis was carried out,which obtained the influence law of the influence factors on the safety distance of dissolved tunnel under the existence of upper,side and lower cavern.(4)Based on the prediction model of safe distance between cave and tunnel in different directions,it’s summarized the scope of treatment for karst,in addition,in combination with the influence of different cave forms on the stability of tunnel surrounding rock,this paper puts forward some measures of karst treatment in shield tunnel in order to provide reference for engineering practice. |
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