Earth Pressure Balanced Shield’s Stable Control Method Based On Pressure Field’s Normal Vector

Earth Pressure Balanced shield is a type of large engineering machinery, used in underground space development and shield tunneling. EPB shield is widely employed in underground engineering construction, such as subway tunnel, municipal construction, resource mining, water conservancy project etc. In shield excavating process, tunnel face instability, the main reason leading to the collapse or upheaval accident, has a serious damage to the security of tunneling construction.In order to control surface subsidence and ensure construction security, EPB shield keeps the internal pressure of work chamber balanced with the soil pressure and water pressure in front of tunnel face by regulating the rotating speed of screw conveyor and the advance speed. Because of complicated excavation process and unpredictable working conditions, the evaluation of tunnel face stability and the control of earth pressure balance situation are frequently accomplished by manual operation of experienced operators. It probably leads to tunnel face instability and has a bad impact on the security and efficiency of tunneling construction. So it is necessary to develop an effective evaluation method for tunnel face stability and an advanced control strategy for the automatic control of EPB shield. In traditional evaluation method, pressure sensors in work chamber are mainly considered as the evaluating index for tunnel face stability. However, this method depends on the actual experience of operator and ignores the pressure distribution on the excavation face. Considering these disadvantages, the main work of this paper is shown in the following:The internal pressure field of work chamber for EPB shield is analyzed firstly. Then an evaluation method for tunnel face stability, based on pressure field surface’s geometric features, is presented. In this method, the discrete pressure values are used to estimate the normal vector of the pressure field surface online. Meanwhile, the active and passive earth pressures in front of tunnel face are analyzed to evaluate the tunnel face stability. Then an optimization model, taking into account of screw conveyor’s rotating speed, is established to keep tunnel face stable and solved by particle swarm optimization algorithm. Finally, a simulation analysis is given to illustrate effectiveness of the proposed method.