9781439834220.ch10

5 m above the floor at the center of tunnel this cut

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Unformatted text preview: ce. 10.10.1 HAMMER’S WORKING CYCLE Excavation at the tunnel face is first made at the height of 1 to 1.5 m above the floor at the center of tunnel. This cut is made to a depth of 1 to 2 m. This small ditch, or slot is then extended towards the sides and floor of the tunnel. Once this big slot is created, then hammer works to break ground in slices, till the final shape and size of the tunnel are dug. The cycle is then repeated to advance further. The procedure has been illustrated in figure 10.8(a).5 If the rock mass is jointed, natural planes of weaknesses are used to achieve maximum gain, or yield of the hammer’s impacts. This has been illustrated in figure 10.8(b).5 AEC Alpine Company developed loading apron and chain conveyor attachments, which fit onto standard excavators permitting excavator-mounted hammers to work in narrow tunnels. 10.11 MERIT AND LIMITATIONS5,7,13 ● ● ● Comparing convention drilling and blasting method; low over-break, less vibrations (5–10% of blasting) and smooth tunnel profile can be achieved. Low vibrations favor their use in urban areas. Large siz...
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