HIGH PRESSURE JETS TO BLAST ROCK BANDS

Developments in the use of high pressure jets for rock removal in quarries and tunnels are reviewed. Mention is made of a laboratory technique used by researchers at the Safety in Mines Research Establishment at Buxton, in which short pulses of very high pressure water were shot from a stationary nozzle at brittle rock, and which proved to be a more effective rock removal process than jet cutting. The technique involves the pressurizing of a soluble oil/water mixture to up to 700mn/sq.m. which is discharged through a nozzle with a 1mm exit diameter. An intensifier driven by compressed air at up to 70mn/sq.m. is used to step up the water jet pressure through an intensification ratio of 11.4: 1. exposure times are variable between 10ms and 3s. Rocks successfully fractured include pennart sandstone, Darley Dale sandstone, coal, limestone and granite. From these laboratory experiments using a high speed cine camera to analyze the mechanism of failure in the rock, it is deduced that, as the jet of water penetrates into the rock, fluid pressure is exerted within the cavity initially formed; this pressure builds up to form stress concentrations and initiate cracking. The fluid pressure assists crack propagation and thus the total amount of damage is governed partially by the duration of the pulse. From experiments carried out so far, the efficiency of this fracturing process for use in tunnelling compares favorably with that of established methods. An experimental rig is to be used by SMRE on quarry and open cast material in the very near future. /TRRL/

Language

  • English

Media Info

  • Features: Figures; Photos;
  • Pagination: p. 32-34
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00083300
  • Record Type: Publication
  • Source Agency: Transport and Road Research Laboratory (TRRL)
  • Files: ITRD, TRIS
  • Created Date: May 29 1975 12:00AM