The discusser is presently involved in the construction of two diversion tunnels for the Magat River Multipurpose Project which have top headings almost identical to that discussed in the paper. The rock is agglomerate with some tuff and generally of good quality (Class I or II,) although occasional shear zones of altered rock are encountered (Class III and IVA). The general method of tunnel support is prestressed rock bolts in the better rock and steel ribs in the poorer rock. In contrast to that discussed in the paper where ribs were used in the better rock even though rock bolts would usually be considered cheaper and quicker. At Magot spiling has been used only in areas where steel ribs are required and was found to be of most value when fully grouted. The best results are obtained with longer (They are more likely to extend into rock unaffected by the blasting), steeper (If prestressed, they give a thicker stable arch; and, if not, the load tends to be applied in tension rather than in shear) and prestressed (They form a stable arch over the area to be excavated before it is excavated) bolts.

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Filing Info

  • Accession Number: 00196155
  • Record Type: Publication
  • Source Agency: Urban Mass Transportation Administration
  • Report/Paper Numbers: ASCE 14599 Proceeding
  • Files: TRIS, USDOT
  • Created Date: Oct 17 1979 12:00AM