Processing model and application of sand and gravel of earth pressure balance shield

Compared with the soft soil layer, sand and gravel layer contains large diameter and high strength gravel, has the character of poor fluidity, high friction coefficient and low cohesion. Therefore shield machine allways encounters with the problems of excreting of large-diameter gravel, over-torquing, serious tool wearing and low tunneling efficiency. While excretion of large-diameter gravel and tool wearing would be especially obvious. These issues may be directly related to the selection of shield, of which the arrangement of cutter head and the selection of screw conveyor may be the most important. Thus in order to find out the specific measures for the solution. Two models are prososed of which the first is aimed at broking gravel, while the second focused on guiding, exhausting then transiting the grave. At the same time, the sheild machine's tunnlling characters and both models' features and scope are also compared. Taking a construction project as an example, the earth pressure balance shield is selected for sand and gravel layer tunnelling and researched existing problems during shield selection and construction. The conclusions is that the sheild selection should be abides by the second model of guiding, exhausting then transiting the grave and requirements for key facilities of earth pressure balance shield is put forward.