Study On Face Stability And Control Technology Of EBP Shield-Driving Tunnel In Composite Ground With Consideration Of Seepage Condition

In recent years, as the unceasing development of urban economic and the enlargement of construction scale, the transport resources become scarce and the transport problems become prominent. Environment problems from urban non-point source pollution have greatly confined the urban economic and sustainable development of our society. In order to alleviate the urban traffic congestion and improve the urban transportation and environment, at the same time to promote the sustainable development of cities and the coordinated development between urban and rural areas, the development of urban underground Space is an important content of modern urban construction and management. Shield tunnel is an attractive excavation method in the construction of municipal underground engineering. Along with the rapid development of shield tunneling, the geologic and hydrologic conditions are usually very complex, the stability of excavation face is very difficult to forecast and control during construction stage. It is easily causing disasters, such as surface subsidence, water inrush accidents. According to incomplete statistics, in the construction of subway shield tunnel the instability of shield-tunneling faces have sometimes taken place for recent years to make heavy losses of economy and calamities of injuries and deaths in Beijing, Shanghai, guangzhou, nanjing, shenzhen and other major cities of China. For the complicated environmental conditions, formation sensitivity and the strict control standards, the stability of excavation face is a key problem to shield tunnel construction technology.In this paper, earth pressure balanced (EPB) shield tunneling projects as the main object of study. Studied the instability mechanism of shield-tunneling faces, disaster evolution characteristics of instability of shield-tunneling faces under seepage action and its control technology system of instability in depth by laboratory experiment, theoretical analysis, numerical calculation, model test and field test. The result has theoretical significance and practical value in engineering project, mainly includes:(1) Summarized and proposed the construction method and equipment selecting. The equipment selecting suitability obtains from the permeability coefficient of formation, grain composition, characteristics of geotechnical and groundwater state. Developed the software system which had a good man-machine interface with shield construction method. The rules to select the shield method under complex geological environment especially the water-rich sand stratum is conducted in-depth study.(2) By sorting and analyzing the cases of surface subsidence and water inrush, caused by excavation surface instability, the disaster environment and evoked factor are analyzed. The basic characteristics of disaster sources were introduced in the paper. And set up a system of evaluation indexes of excavation surface instability. The attribute recognition model is established. It provided a dynamic assessment of the high risk period of tunnel based on the software system. Put forward the prevention and control measures of excavation surface instability by earth pressure balance shield construction.(3) Based on the limit analysis upper limit theorem, the 3D revolving body damage model is built. The formula of ultimate supporting force of excavation face is derived by the critical failure power of doing work by external forces is equal to the internal dissipation of soil. The critical failure supporting force of excavation face in homogeneous formation and complex strata is solved by the computer program. The computer program is compiled by MATLAB. For complex strata, this paper respectively analyzed the influence factors such as tunnel depth, characteristics of soil, groundwater level under two working cases. They are the casing soil and crossing layer. Compared with the calculated results with the predecessor’s results, it verify that the validity of the theoretical model.(4) Based on the 3D revolving body damage model, introduced the groundwater seepage action to the limit analysis of excavation face stability. Then the seepage force formula deductions of collapse of the soil and excavation face are demonstrated. The relationship between seepage force and groundwater level was obtained. The upper limit solution of supporting force of excavation face under complex strata was finally solved.(5) The construction mechanics process of earth pressure balance shield under complex strata is calculated by numerical method considering the effect of groundwater seepage. The relationship between the damage forms of excavation face, deformation of excavation face, surface deformation, limit supporting force and tunnel buried depth, mechanical properties of rock and soil, groundwater state are studied in the paper respectively earth pressure balance shield construction under homogeneous formation and complex strata.(6) In order to study the change rule of excavation face supporting force and failure mode of shield tunnel excavation face under seepage force, then shield tunneling construction model test system was developed. It includes visual test platform, waterproof automated monitoring system. Take shield tunnel that cross limestone and sand layer of Jinan Metro line R1 as engineering backgrounds, and carry out model test about the excavation face stability in complex ground, to study the problem for stability of excavation face of shield construction in complex ground under different buried depth and water head height, analyze influence law that buried depth and water head height affect ground settlement, limit supporting force and soil deformation of excavation face, reveal the evolutionary mechanism about excavation face unstable failure.