Technical Reports

Heat-Assisted Tunnel Boring Machines

  • 01
  • Sep
  • 1970
AUTHOR: J. P. Carstens, W. R. Davison, C. A. Brown, A. R. Smith, F. J. McGarry
OFFICE: RPD
REPORT NUMBER: FRA-RT-71-63
SUBJECT: Facilities & Test Equipment, Tracks & Structures
KEYWORDS: Tunneling Machine Performance, Laser Technology, Excavation
ABSTRACT: A study was performed to determine: a) the increase in tunneling machine performance in hard rock resulting from heat weakening of the rock in advance of the tunneling machine, b) the increase in hourly cost incurred by the heating system, and c) the net effect of the increased performance and the increased hourly cost on the cost of the finished tunnel. Rock-cutting experiments were performed on Barre granite using a 1-kw C02-N2-He gas laser for rock heating and disc-type cutters of various diameters. Analytical work included the preparation of specific heat-assisted tunneler designs' and their expected performance and economics. An alternative form of using heat for tunneling was also investigated in which slots were melted in the rock instead of merely heating it. The study concludes that the operation of tunneling machines incorporating lasers to provide the heat weakening is technically feasible but economically unattractive. Radiant heaters have insufficient power density to effectively heat the rock, and high-temperature jets create serious environmental problems. However, the test program indicated that a more effective way to assist mechanical cutters would be to use concentrated thermal energy to melt shallow slots in the rock between cutter paths .
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