The Numerical Simulation Of Earth Pressure Balance Shield Cutter Head Design Based On CFD

With economic development and population growth, tunneling plays a moreand more important role in underground space exploration and utilization. The earthpressure balance (EPB) shield tunneling machine has obtained the most extensiveapplication in various tunneling engineering because of its safety, rapidity, economyand adaptability to complicated geological conditions. The three important tasks ofthe cutter head are the cutting of soils, supporting the soil face and mixing theexcavated soil. Therefore, the EPB shield cutter head structure is one of the keytechnologies in EPB shield design. In fact, the reason why the EPB shield cutterhead can tunnel effectively and safely is that the influence of the change in openingratio or opening distribution on the EPB shield tunneling efficiency and the usageefficiency of the cutter head are taken into account during the cutter head structuredesign. However the cutter head structure design is a challenging area of researchdue to the complexity of geological conditions, operating conditions, constructionrequirements and many other factors, there are complex interactions betweenmechanical and physical factors. The paper developed the following work andresearch:(1) The computational fluid dynamics (CFD) method is applied to study thedesign of EPB shield cutter head structure. By using visco-plastic fluid theory, a newmodel for soil is introduced, and then the CFD model for comprehensively analyzingthe cutter head structure is established, which consists of the soil, the cutter head, theworking chamber, and the screw conveyor. Then the feasibility and accuracy of theCFD model and its analysis method is verified by comparison between the pressuresimulation results and the site record data. The model provides the basis for furtheranalysis the influence of changing the opening ratio and opening distribution on thestability situation and tunneling performance of the cutter head.(2) The formation mechanism of shield cutter head opening design is proposed.By using the formation mechanism, the different opening ratio and openingdistribution of cutter head are established for a given geological condition. Then thepressure distribution rules and velocity distribution rules of excavated soil on shieldcutter head excavation face under different opening ratio of cutter head and buried depths are researched. The mathematical model of pressure and velocity distributionof excavated soil are also established. The influence of opening distribution on thefore-and-back pressure distribution rules of shield cutter head excavated soil areanalyzed, and the mapping relationship of the fore-and-back pressure transfer of cutterhead excavated soil in same opening ratio and different opening distribution areproposed. At last the relationship between the opening distribution and thefore-and-back pressure transfer of cutter head excavated soil are observed.(3) The accuracy of the shield cutter head opening design theory above isinvestigated with the example of Tianjin Metro number three line and nine line andothers. The research content lay a theoretical foundation for the EPB shield cutterhead opening design and the pressure balance control of cutter head excavation face.(4) A new method for design and analysis of the EPB shield cutter head structureis proposed that fits changes in geologic conditions. The conclusions will definitelyprovide guidelines for the structure design of EPB shield cutter head, and make agreat contribution to its safety, rapidity, economy, wide applicability and reducedpollution.