Research And Application In Control Of Conveying Mechanism Of Screw Conveyor Under Pressure Of EPB Shield

During the tunneling of EPB shield, it is realized that the dynamic balance control of working chamber earth pressure of EPB shield according to construction requirements and variations of geological condition, which can effectively control the land deformation and reduce the probability of accident. There is important strategic meaning and important application value for improving control level of complex boring equipment to master the dynamic balance control technologies of working chamber earth pressure of EPB shield. It is also the inevitable trend for the development of the future shield technologies. The mathematical description between pressure and flow for screw conveyor of EPB shield under complex plastic extrusion process is absent, which leads to difficulty for the dynamic balance control of working chamber earth pressure of EPB shield. So the conveying mechanism of screw conveyor of EPB shield under pressure becomes as urgent topic to be resolved for the dynamic balance control of working chamber earth pressure.Based on the above engineering backgrounds, aiming at the conveying mechanism of screw conveyor of EPB shield under complex plastic extrusion process for the dynamic balance control of working chamber earth pressure, this paper firstly studies rheological behavior of conditioned soil, then this paper realizes the numerical simulation for the work process of the working chamber earth pressure system. The characteristics of controlled object such as the conveying properties of screw conveyor under certain pressure difference, the effect mechanism between control parameters and earth pressure are exposited. The mathematical model is established. The dynamic balance control method of geological adaptability based on the on-line identification of model parameters and the optimization control for the working chamber earth pressure is proposed.The main contents of this dissertation are as follows:(1) A new pressure-dependent improved Bingham viscoplastic non-newtonian fluid model is presented. Based on the developed decive which is used to study rheological behavior of conditioned soil of EPB shield, conditioned sands are reproduced and the rheological tests are implemented in the laboratory. When confining pressure constant, conditioned sands exhibit the non-newtonian fluid characteristics of shear thinning, and the relations between shear stress and shear rate correspond with Bingham viscoplastic non-newtonian fluid model. The ranges of viscosity coefficient and yield stress are obtained. Furthermore, the viscoplastic parameters increase with the increase of the confining pressure. A new pressure-dependent improved Bingham viscoplastic non-newtonian fluid model is defined for the CFD numerical simulations. The model provides the basis for the numerical simulation for the work process of the working chamber earth pressure system.(2) The pressure dependent viscosity model and density model of viscoplastic non-newtonian fluid is established by user-defined method in CFD simulation environment. The numerical simulation of soil flow characteristics such as viscosity, elasticity and plasticity for the work process of the working chamber earth pressure system is realized. The numerical simulation results of the observed earth pressure field and velocity field distribution in working chamber are compared with experimental results. It provides the basis for further researching on the conveying properties of screw conveyor under certain pressure difference, as well as the effect mechanism between control parameters and earth pressure by the numerical simulation method.(3) The discharge efficiency of EPB shield screw conveyor under complex plastic extrusion process is proposed. By theoretical analysis and numerical simulation for the work process of the working chamber earth pressure system, the effects of pressure difference and rheological behaviors of conditioned soils and geometric parameters on discharge efficiency of screw conveyor are studied. The conveying properties of screw conveyor under certain pressure difference are exposited. The problems during establishing mathematical model of the working chamber earth pressure system are solved. It provides the basis for further researching on the dynamic balance control of the working chamber earth pressure system.(4) A new dynamic balance control method based on the on-line identification of model parameters and the optimization control for the working chamber earth pressure is proposed. A new mathematical model of the working chamber earth pressure system is established. In the model, the effect of earth pressure in working chamber on equivalent tangent modulus of deformation Et and discharge efficiency of screw conveyor η are considered. The control equations of the working chamber earth pressure system under two kinds of control mode such as the separate control of screw conveyor speed, the combination control of advancing speed and screw conveyor speed are given respectively. Based on optimization method, the on-line identification according to the field construction data of the parameter vector in control equation is realized. By the on-line identification, the time-varying problem of the control equation parameter vector which is caused by the randomness of geological conditions and inhomogeneity of conditioned medium is solved. Based on the optimization control strategy, the optimal control law of the working chamber earth pressure control system is obtained. The influence of the scaling factor and values of the parameter vector on control effect is discussed. The switch basis between two kinds of control mode is given. The optimization of speed under the double control mode is existent.The ideal control effect is obtained on the working chamber earth pressure simulation experiment platform.