The hoe is either tripod or swivel mounted and also

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Unformatted text preview: ). Pushing off the tunnel’s lining thrust the shield forwards. It operates like a single shield, alternately thrusting forward and setting lining rings. The hoe is either tripod or swivel mounted and also serves the function to move the material from the face to the conveyor pickup point. The excavators are generally limited to reasonably competent, but soft ground. When truly hydraulic ground conditions are encountered, however, the excavators become unsatisfactory. Despite the excavator’s limited range of use, it is a popular choice due to its relatively low cost, the ability to handle large boulders, and visibility at the face.1 It is a high advance rate machine for compact © 2005 by Taylor & Francis Group, LLC 250 SURFACE AND UNDERGROUND EXCAVATIONS 2 5 3 1 4 6 Figure 10.10 The shields with partial face excavation. 1. excavator. 2. shield. 3. steering cylinder. 4. conveyor belt. 5. machine pipe. 6. hydraulic power pack. (Courtesy: Herrenknecht, Germany). talus, alluvium, or ancient flood plains, the types of soil on which the majority of urban areas...
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