Study on the Discharge System of Excavated Soils in a Vertical Shield Machine

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PURPOSE : In order to construct the space or tunnel in the deep underground, a large diameter vertical shaft is necessary to carry the excavation machines. Usually, large iron boards are penetrated into the ground around the shaft and the inside surrounded by the boards is excavated by power shovels or other machines. However, this method requires a long construction term and much costs. On the other hand, horizontal shield machines have been used widely to construct the horizontal tunnel, and they are already operated automatically. Therefore, if the automation technology of horizontal shield machine is applicable to the construction of a vertical shaft, the construction term and cost will be much reduced. However, the significant difference between the horizontal shield machine and vertical shield machine is the discharge system of the excavated soils. Since the direction of excavation coincides with the one of gravity in the vertical shield machine, a new mechanism to collect the ex … More cavated soils is necessary.Therefore, the purposes of this study are to investigate the collecting method of excavated soils and to propose an automatic discharge system of excavated soils in a vertical shield machine.RESEARCH PLAN :1) Measurement of jet extension by use of a fixed cutter spoke2) Measurement of jet velocity profiles by using tracer particles3) Observation of excavated soil behavior4) Theoretical consideration of the jet and excavated soil velocity profile5) Theoretical consideration of similarity between actual machine and small scale model6) Measurement of jet and excavated soil behavior by use of the small scale modelRESULTS : 1) It was confirmed that the jet extension decreases with increasing the flow rate and cutter spoke inclination. The effect of bit shape and clearance was negligible small.2) It was found that the behavior of excavated soils is nearly linear and most of the soils are transported by the central flows of the dispersed water jets. Therefore, it was confirmed that the central flows of the dispersed water jet are the most significant factor to design the actual machine.3) The equation of motion of excavated soils was theoretically obtained based on the energy equation of open channel flows.4) The theoretical consideration on the similarity was carried out, and the scale of the vertical shield machine model was determined.5) It was found that the effect of rotation of cutter spoke on the behavior of excavated soils was very small because the RPM of the cutter spoke was not high. Less