Earth Pressure Prediction And Intelligent Optimal Control Strategy For Shield Chamber

The rapid development of world economy promotes the urbanization on a large scale, however, as the construction is becoming more and more intensive and more ground space is limited, people have to turn to underground space, so the development of underground space has entered an unprecedented stage nowadays. Earth pressure balance shield machine is a type of special and large engineering machinery, used in underground tunnel excavation. EPB shield is now widely employed in city subway tunnel, resource mining, municipal construction and subsea tunnel project etc. It has become an important means of large underground engineering construction because of its distinct advantages, such as safety, reliability, fast driving speed, low labor intensity and little influence on stratum.During the process of shield excavating, the pressure unbalance of excavation surface is easy to cause the collapse or blow-out of ground surface, which may lead to disastrous accidents. Since the change of chamber earth pressure is closely related to the pressure of excavation surface, accurate prediction and control of chamber earth pressure is one of the key technologies to avoid the pressure unbalance of the excavation surface effectively. Because shield construction is an extremely complex process, with the mutational working condition and abnormal geological condition, and there is a strong coupling between the driving parameters, so it is difficult to establish accurate mathematical model. The present construction of shield tunneling mainly relies on artificial experience operation to be completed, so the control precision of earth pressure is difficult to guarantee, and it is difficult to fundamentally prevent catastrophic accidents. Therefore using the intelligent modeling method to establish earth pressure prediction and optimization control model is of important theoretical and realistic significance for realizing the intelligent control of shield tunneling process and ensuring the safety of tunneling construction.In order to establish the prediction model of chamber earth pressure, the relationships between the earth pressure and the excavating parameters, especially the influence of cutter torque on the earth pressure, are analyzed on the mechanism in detail firstly. On this basis, the new input and output parameters of earth pressure model are determined. Then, we take the typical EPB with four earth pressure sensors on the clapboard of chamber as an example, and then the intelligent modeling method of prediction model of earth pressure in the chamber is proposed based on the least squares radial basis kernel function of support vector machine. Then the particle swarm optimization (PSO) is used to optimize the two parameters of the least squares radial basis kernel function of support vector machine. Finally, based on the proposed prediction model, by minimizing the overall absolute deviation between the predicted earth pressure and the setting value, the particle swarm optimization is adopted to optimize on line the two control parameters——screw conveyor speed and advancing speed, which influence the changes of earth pressure in the chamber, so the optimum control of earth pressure balance is realized. In order to verify the validity and accuracy of prediction model and optimization control strategy, simulation experiments and comparative analyses are carried out by using the on-site construction data. The proposed method provides the technical support for accurate prediction and automatic control of chamber earth pressure and ensuring the safety in the tunneling construction process.