Study On The Influence Of The Karst Cave To The Foundation’s Stability And Bearing Capacity In Shield Tunnelling

The stability of foundation engineering in karst area is a focus subject all the time. Along with the booming of the subway construction, the probability to encounter complicated karst geology in shield tunnelling is growing. Considering the karst environment combined with the construction factors, the analysis of the karst foundations’ ultimate bearing capacity has profound guiding significance for the subway construction and the underground space development in karst area.This paper is based on the item of National Natural Science Foundation of China’study on the limit analysis method of the karst foundation stability in the subway construction’(NO.51108462).From the point of the ultimate bearing capacity to evaluate the karst foundation stability in the subway construction, we put forward the research model at fist, and then use model test method and finite element limit analysis method to solve the problem. The main research contents are summarized as follows:(1)The physical and mechanics parameters of the rock and soil are presented by the engineering geological data, and these parameters are transformed to the similar materials according to similitude theorem. A series of ratio tests about the chosen mixed materials are taken to find the best similar materials which meet the maximum requirements of the similitude criterion.(2)Design the plain strain model test according to the similitude theorem, and research the difference of the ultimate bearing capacity caused by different arrangements of karst caves.By applying the loads step by step, watch the progressive failure characteristics and analyze the change of the soil’s stress and displacement.(3)Analyze the computation process of the step-loading finite element method and pay more attention to the relations among different yield criterions.(4)Use the step-loading finite element method to solve the ultimate bearing capacity and compare the results with the model test’s. Analyze the influence to the results’ accuracy by using different yield criterions. Furthermore, discuss the relationships between ultimate bearing capacity and five corresponding influencing factors which include roof thickness, roof width, multiple caves,rock joints and the form of loads.