Research On Key Technology Of Pressure Control Of Working Chamber Of Earth Pressure Balance Shield

The earth pressure balance shield (EPBS) is the important technical equipment for infrastructure projects, resource development and national defence. It has been widely applied in metro tunnel, crossing-river tunnel, railway tunnel and so on. The pressure balance control of working chamber is one of the core technologies. It directly influences on stability of tunnel face, safety and efficiency of tunneling construction, energy consumption and so on. However, due to lack of understanding on mapping relationship between observed values of pressure measurement points of working chamber and support pressure of tunnel face, it is difficult to supply reasonable and exact basis for pressure balance control of working chamber. This condition causes difficulties for design, construction and control of EPBS. Thus localization process of EPBS is hindered seriously. Aiming at this problem, in this work, by adopting the method of combining model experiment with geotechnical test and numerical simulation technique, pressure distribution law and pressure transfer characteristic of working chamber are studied, definition and calculation method of equivalent pressure of working chamber are presented, at the same time, optimal arrangement of pressure measurement points in working chamber is put forward. These works should provide theoretical basis for pressure balance control of working chamber.By adopting6.28m diameter EPBS as design prototype, The experiment table of pressure control of working chamber has been set up, and then feasibility test is carried through to simulate pressure distribution law of actual working chamber on this experiment table. Through experimentizing in different kinds of conditioned sand, we can find out that pressure distribution of vertical and horizontal direction of working chamber is consistent with pressure distribution law in engineering. This condition indicates that experiment table can simulate flowing process of conditioned sand and it also can provide exhaustive and real data for verifying validity of simulation method on pressure field of working chamber.Based on model experiment, validity of simulating pressure field of working chamber is verified through discrete element method (DEM). According to triaxial test data of conditioned sand, inversion method which is based upon back-propagation (BP) network and gentic algorithm is adopted to obtain equivalent parameters of discrete element model of conditioned sand. By back analyzing, contact model parameters are obtained. The triaxial test result which is predicted by these parameters is basically consistent with actual measured data. It indicates that contact model can simulate mechanical behaviour of particles of conditioned sand, and inversion method is feasible and correct. On this basis, by adopting experiment table of pressure control of working chamber as prototype, research of DEM on pressure field of working chamber is carried out. The results of the numerical simulation are better consistent with actual measured results. This shows that simulation model of DEM is impactful. It lays the foundation for farther reaserch on pressure transfer characteristic and optimal arrangement of measurement points of working chamber.The calculation formula of pressure difference between tunnel face and bulkhead of working chamber are presented. The pressure transfer characteristic of working chamber of6.28m diameter EPBS employed in a certain project of metro is studied by adopting numerical simulation method, and construction data verifies that the pressure transfer characteristic of working chamber can be used to guide construction. At the same time, through changing geometric model and boundary condition of working chamber, impact on pressure transfer characteristic of working chamber by length of working chamber, tunnel depth and cutter head open ratio is studied. The results show that length of working chamber and tunnel depth have little effect on pressure difference between tunnel face and bulkhead. However, with cutter head open ratio increases, instead, the pressure difference reduces. There is quadratic function curve relation between the both. This provides theoretics basis for pressure setting of working chamber.The definition and calculation method of equivalent pressure of working chamber are presented, and mathematic model of optimal arrangement of pressure measurement points is established, at the same time, optimal arrangement method of measurement points is presented. By selecting6.28m diameter EPBS as study object, according to data of pressure numerical simulation of working chamber, the study on optimal arrangement of pressure measurement points is carried through by using the method of combining fuzzy clustering analysis with discriminant analysis. Through contrasting equivalent pressure error of working chamber, we can find out that equivalent pressure obtained by weighted algorithm is more exact and optimal arrangement method of pressure measurement points is feasible. It should give a theoretical basis to design of EPBS and pressure balance control of working chamber.Finally, some suggestions for further research are given in this thesis.