The development is described of the mine (which will produce molybdenum ore from 3,000 feet below the surface) through two large concrete shafts over a mile deep and in which shotcreting supplemented by rock bolting is the routine method of rock support. Monthly placement of shotcrete is 600 cubic yards per month with two truck-mounted shotcrete placers and three underground transported trucks. Shotcrete is batched from the surface (1,000 pounds of 0.375 inch pea gravel; 2,000 pounds sand 650 pounds of Type I cement) and trucked to the shaft. The mix is dropped on call, down an 8-inch slick line with a decelerator at the bottom which directs the material to the transporter truck which carries it to the placer. At the placer, water is added as well as calcium chloride solution (less than 2 percent by weight of cement). The calcium chloride is the only admixture used. Placement is by a boom-mounted nozzle on the front of the truck. Shotcrete is applied to the arch section of the drift; in shot and office areas it is first applied to a footing for support and from there on the upper parts of the chamber. On the average 0.5 to 0.7 cubic yard of shotcrete is applied to each lineal foot of drift. Each shift places about 40 feet. Costs are about $46 per cubic yard for material. Details of the process are discussed. The most serious problem encountered involved the dumping of the dry mix down the slickline and the air drawn into the line by the faolling material. The unique factors that have contributed to the success of this particular operation include a very good ventilation system, warm rock temperatures (84 deg F) and water temperatures (80 def F). A flexible mining system that allows an area to be available for the time needed to properly complete the job is also an advantage, although in several high priority drifts drilling and blasting cycles have been continued immediately following shotcreting up to the face of the drift.

Media Info

  • Pagination: p. 50-57

Subject/Index Terms

Filing Info

  • Accession Number: 00263677
  • Record Type: Publication
  • Report/Paper Numbers: SP-45 Conf. Proc
  • Contract Numbers: H0111881
  • Files: TRIS
  • Created Date: Dec 19 1974 12:00AM