Study On Face Stability Of Tunnelling Shield In Urban Areas

The development of underground space has become a necessary method of modern city sustaining development with the advacing of the reforming and opening in our country, which is a new tendency of harmonious development of city space. Shield tunneling method has become a primary method in underground excavation with its predominance, earth pressure balanced shield tunneling (EPBS) is the most universal type in our country. Face stability is key point of tunnel shields excavation, Which influenced circumjacent environment. Shields pressure most depend on engineering experience at present, moreover, the study of face tunneling shields in native is relatively less, so the study of the article has determinate academic value and instruction of practical engineering.The paper developed the following work and research according to the related circs.1 .The work of earth pressure balanced shield tunneling (EPBS) has been put forward, and environment offect has been analyzed ,so face stability is one of important factors of influencing circumjacent environment.2. According to the principle of nonlinear simulation analysis and practical actualizion course, the author has expatiated three kinds of nonlinear problem, discussed the elasticity- plastic basal equation and intensity rule and put forward judgement gist offace collapse of tunnel shields.3. According to limit-equilibrium theory and limit-equilibrium model (silo model), the author has deduced the pressure calculation model formula .calculated the pressure according to the conditions of Nanjing Metro, applied MATALAB software to obtain extremum of pressure and has simulated and analysed the result, put forward a new notion of applying limit-equilibrium theory.4.Based on the analysis of face stability index, the author has deduced the formula of pressure from the formula of face stability index, and moreover, the pressures have beened calculated according to the work conditions of Nanjing Metro.The emphases of this paper lay on discussing influence factor face stabilitythrough analyzing face mechanism of face collapse, bring forward ratio of cover is the most important factor. The author has deducted the formula of pressure tunnel shields according to silo model and face stability index. Based on on the base of ANSYS, the author designs calculation programs, upbuilds three-dimensional DP elastic-plastic apply model to carry on nonlinear simulation analysis. In the course of analyse of FEM, the author has compared ground deformation and soil plastic deformation, which give a satisfactory conclusion.