Definitions of Stabilising Blast Techniques 

PRE-SPLITTING – Stress relief involving a single row of holes drilled along a neat excavation line, where detonation of explosives in the holes causes shearing of the web of rock between the holes.  Pre-split holes may be fired in advance of production holes. In this technique disturbance beyond the design slope is minimal. 

LINE or STITCH DRILLING – A line of holes drilled at close centres and left uncharged. This technique is best suited to homogeneous rock conditions. 

SMOOTH BLASTING – A method of controlled blasting in which closely spaced holes are drilled at the perimeter of the excavation, charged with low charges to reduce over-break. The perimeter holes are fired with a higher delay number than the rest of the round. This technique is used when there is insufficent burden to allow pre- splitting to be carried out and in poor rock conditions to minimise overbreak.

 

Blast Area Preparation

 

• Whichever method of engineered blasting is chosen certain aspects will be the same for each method 

• Consultation between all relevant parties, Quarry Manager, Geo-Tech specialist, Explosive Supervisor, Shotfirer, Driller is crucial

  - Is it in line with the requirements of the Quarry Regulations 1999     including the Quarry design and development plans and site Shotfiring Rules? (Quarries Regulations 1999, ACOP Paragraph 197 refers) 

• Has the blast area been cleaned off and made safe to mark out and drill?

  - Rock traps in place

  - Edge protection in place as per QNJAC guidance    http://qnjac.co.uk/media/1741/blastsiteedgeprotection.ppt

  - If required Risk Assessments for working under final faces completed

  - Pre-drill surveys carried out

• In the case of Pre-split and Line drilling can the Drill Rig, drill over the line of holes rather than drilling at right angles to the line, even more critical with angled holes