The successful use is described of shotcrete in conjunction with 10-ft and 15-ft rock bolts as primary tunnel support. The diversion tunnel was 3,800 feet long with a horseshoe cross-section nominally 30 ft wide by 18 ft to 24 ft below spring line. During the top heading operation in the diversion tunnel, two inches of shotcrete were placed from spring line to spring line immediately after mucking. In fault zones, steel sets were placed after shotcreting and prior to advancing the heading another round. Behind the jumbo, an additional 2 inches of shotcrete were placed over the top 90 deg of the back except in areas of steel sets. In massive rock no other support was used while in foliated rock, rock bolts were installed on a 5-ft. by 7-ft. pattern lifts of shotcrete. Shotcrete and rock bolts were extended to the tunnel invert in rock with foliation parallel to the tunnel center line and in serpentine. In the power tunnels and the irrigation and flood control tunnel, two inches of shotcrete were placed over the top 90 deg of the back and no other support was used. Details are given of the specifications which required the use of the dry mix process of application. The pre-job investigation is described and the quality control (mix design and development and monitoring procedures) is reviewed. Beginning 90 days prior to tunnel excavation, several shotcrete mixes with increasing cement content, various accelerator percentages and various percentages of aggregate free moisture were tested. Shotcrete material delivered at the jobsite were certified for compliance prior to their use. Shotcrete from each application was tested for compressive strength. Details of the sampling are outlined. Compressive strengths of cored specimens were corrected to a L/D ratio of 2 according to A.C.I. recommendations. Gloetzel cells and photo elastic stress meters were installed at a few locations in an attempt to determine rock and shotcrete load characteristics.

Media Info

  • Pagination: p. 235-245

Subject/Index Terms

Filing Info

  • Accession Number: 00263692
  • Record Type: Publication
  • Report/Paper Numbers: SP-45 Conf. Proc
  • Contract Numbers: H0111881
  • Files: TRIS
  • Created Date: Dec 19 1974 12:00AM