Study On Conveying Mechanism And Characteristics Of Shield Screw Conveyor Based On DEM

The screw conveyor is an important part of the EPB shield machine.It can transfer the soil under the cutter from the chamber out of the shield machine,and control the displacement by adjusting the rotational speed to maintain the dynamic balance of the pressure between the chamber and excavation face.To a certain extent,the performance of the shield screw conveyer is related to the stability of the excavation face.At present,the research usually regards the soil as a continuous medium fluid,which leads to the unclear understanding of the conveying state and law of the soil in the shield screw conveyer.It cannot reflect the discrete nature of the soil,and the result has deviations.Therefore,it needs to be used the study method which is more suitable for the soil properties.In this paper,based on the discrete element simulation as the main research means,combined with theoretical analysis,the conveying mechanism of the shield screw conveyor is discussed.The influence of the rotational speed and pitch is studied,as well as the wear of the screw conveyor.The main contents of the paper are as follows:1.The sand pebble stratum with rich water in Chengdu is poor in gradation and large permeability coefficient,which is not conducive to excavation and transportation.The cut soil should be improved first.In this paper,according to the characteristics and difficulties of the sand gravel stratum,the corresponding soil improvement scheme is put forward.The shield screw conveyor is the key mechanism of pressure control in the chamber.The control range of the chamber pressure is obtained by the calculation of the earth pressure.According to the conditions and requirements of a subway project in Chengdu,the parameters of the screw conveyor are analyzed,and the type selection and design of the screw conveyor is completed.2.The basic principle and solving process of the discrete element method are introduced.The Hertz-Mindlin with JKR model is selected as the discrete element model of the modified soil in various contact physical models.At the same time,in order to analyze the wear of the shield screw conveyor,the Archard Wear model is introduced.According to the special structure of screw conveyor,the force and movement of soil particles in the process of screw conveying are analyzed,which provides a theoretical basis for simulation analysis.3.Using EDEM to simulate the conveying of the shield screw conveyor,the movement distribution and law of the soil in the chamber and the screw conveyor,the influence of the rotational speed and pitch are studied.In addition,the wear distribution of the screw conveyor is analyzed.The results show that the discrete element method is suitable for the study of soil,and the obtained conclusions are more in line with the actual situation.It is helpful to analyze the movement mechanism of soil and the wear distribution of the structure in the shield screw conveyor.4.The anti-spewing ability of the large diameter screw conveyor is poor.It needs to transform its structure to form an anti-spewing soil plug.It introduces designs of the shield screw conveyor for the soil plug compression,and analyses the capacity of the spiral soil plug.Through using EDEM,the variable pitch screw conveyor is analyzed.The comparison of the results with the previous shows that the distribution of the soil movement is changed,and the wear of the soil plug segment increases,and the overall force and torque increase as well.