Study On Modeling Earth Pressure Field In Pressure Chamber And EPB Control Methods Of Shield Machine

Earth pressure balance (EPB) shield machine is an engineering machine specialized in underground construction engineer, and is widely applied in metro tunnel, municipal construction, resources exploitation, hydraulic engineering and so on. The ground surface settlement must be taken into account first, and the earth pressure imbalance in pressure chamber is the main cause of ground settlement or even disastrous accident. The random diversity of geology condition and the multi-field coupling make the physical and mechanical properties of excavation face very complex and difficult to predict. Nowadays, the EPB control is manually operated based on experiences, so that it is difficult to ensure the construction safety. Consequently, the earth pressure balance control in chamber is an important issue of the shield construction technology. In this dissertation, some problems related to the earth pressure balance control in chamber are studied based on the mechanism analysis of tunneling process, such as modeling the earth pressure field in pressure chamber, the earth pressure balance control method, the coordinated control method of multiple sub-systems and so on. The main works of this dissertation are as follows:(1) The earth pressure distribution discipline and the earth pressure imbalance characteristic in chamber are studied, and a stability judgment method of shield excavation face is proposed based on the earth pressure field gradient. A distribution model of the earth pressure field is established by using non-uniform B spline method. On this basis, the ranges of the vertical and horizontal gradient are analyzed, subsequently, the stable region of the excavation face and the judgment method are given based on the norm of the earth pressure field gradient. For the norm extremum of the earth pressure field gradient, it is obtained through solving the optimization function by means of the multi-stage dynamic penalty function combined with particle swarm optimization (PSO) algorithm. Finally, the simulation experiment is carried out based on the field data, and the earth pressure distribution in chamber are revealed when it is balance or not, further the excavation face stability is analyzed, and the effectiveness of the method is demonstrated.(2) The mechanism of tunneling process is very complicated and the working conditions are changeable, and there is no more accurate and perfect earth pressure control model at present. A modeling method combining mechanism analysis with least squares support vector machine (LS-SVM) theory is proposed. Firstly, a relation model between earth pressure and control parameters is established based on mechanics balance equation, continuity equation and a weighting coefficient which reflects that the total thrust of shield, advance speed and screw conveyor speed have quite different influence on chamber earth pressure. Secondly, an error model is established by means of LS-SVM for optimizing the weighting coefficient, and an integrated earth pressure control model is established which lays the foundation for automatic control of EPB shield machine.(3) When shield machine excavates in homogeneous and stable soil layer, the earth pressure balance in chamber is controlled through adjusting advance speed or screw conveyor speed based on the discharge control mode. In order to control the earth pressure balance more efficiently, a new earth pressure balance control method is proposed which takes equivalent earth pressure in chamber as control target. Based on the earth pressure field model, by analyzing the relationship between tunneling control parameters and the earth pressure in chamber and considering the influence on earth pressure of the state change of earth pressure on excavation face, an equivalent earth pressure control model is established. Then, an EPB control system is constructed, in the mean time the fuzzy adaptive PID controller is designed to adjust the screw conveyor speed. The simulations illustrate that the system could track the set earth pressure very well, so that this method provides a new idea for control earth pressure balance of shield tunneling.(4) The lithology changes frequently, its physical and mechanical properties differ widely. When shield machine works under this condition, especially in composite soil layer, the earth pressure balance in chamber of shield should be controlled more efficiently by adjusting advance speed and screw conveyor speed simultaneously. But the commonly used method now depends greatly on experiences of operators, so that some problems such as meandering routes, ground subsidence, and machine failure tend to occur. For this purpose, an optimal control strategy for earth pressure balance is proposed in this paper, where an prediction model of earth pressure in chamber is established by means of LS-SVM considering thrust speed and screw conveyor speed as the control parameters. Further, by minimizing the difference between the predicted earth pressure and the desired one, an optimization model of the control parameters is established, and solved by the particle swarm optimization (PSO) algorithm. The advance speed and screw conveyor speed are optimized simultaneously, therefore, the dynamic balance control of earth pressure in chamber is realized. The simulation results demonstrate that the method is very effective.(5) The earth pressure in chamber is mainly affected by thrust system, discharge system and cutter head system. However, because it is not clear that how the composition and the mechanical characters of the soil in chamber influence the earth pressure, it is difficult to carry out earth pressure balance control efficiently through coordinated control thrust system, discharge system and cutter head system at present. For this reason, on the basis of soil layer identification, a coordinated control method of multiple subsystems is proposed which combines the expert system control with predictive control. The soil layer system identifies the layer status which takes the TPI and FPI as input character parameters. The expert system analyses and inferences to the quantitative results of the identification and gives the control strategy of cutter head. Then the advance speed and screw conveyor speed are coordinated through nonlinear model predictive control which corresponds to the cutter speed, and rolling optimization is realized by means of ACS. The experiments show that the earth pressure in chamber can keep a good balance even though the working condition changes, which demonstrate the feasibility of this method to achieve the multiple subsystems coordinated control of shield machine for earth pressure balance in chamber.