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What to Consider in Pre-Split Design

  • Can the pre-split be drilled in advance of the main production blast?

  - A minimum of two rows of holes in front of the pre-split should be left

  - It is advised that the production blast should be fired parallel to the pre-split and not at right angles, especially if the pre-split holes are angled, to   avoid damage to the final pre-split line

  - How many pre-split holes are being fired at the same time, does it   exceed the site MIC, will overall blast timings be effected

  - Can the whole line of pre-split holes be fired instantaneously, check the   site Maximum Instantaneous Charge (MIC) and Air Overpressure (AoP)   limits

  - Bag off or cover all drilled holes in order to avoid blockages, cones are   also a good alternative with the hole number written on them

  - If the line cannot be fired instantaneously a minimum of 10 holes per. panel is advised be fired per. delay, firing less number of holes goes  against the   principle of firing a pre-split instantaneously

  • What angle is the pre-split to be drilled at?

  - Too shallow an angle i.e. > 20’ will make drilling and charging the hole   difficult, especially if the ground is broken or fractured and/or water is   present

  - Ensure the correct azimuth can be achieved

  • What type of explosive to use, i.e. detonator cord or a bespoke pre-split explosive product
  • Initiation Sequence and Timings of Pre-split holes, even more critical   when fired in conjunction with production holes in front of the Pre-split
  • If a panel has been drilled and there are more holes to drill at a later date, leave a couple of holes uncharged to avoid damaging the ground on the start of the next set of holes
  • If holes are fired in advance ensure they are surveyed and physically marked for future reference, for example use marker posts
  • If detonating cord is to be used consider the following

      - Charge Weight g/m2

      - What type of product is used to take the cord to the bottom of the hole,   i.e. cast primer, slurry cartridge and how is this coupled to the cord line?

      - Is the coupling strong enough and waterproof

      - What about the coupling of the main cord line to the trunk cord line, is   it strong enough and waterproof, especially when a gas or stemming bag   is pushed in and stemming placed in the hole 

      - Is the main surface trunk line out of water

  • Whether using Detonator Cord or a Bespoke Pre-split product 

      - Consider using a separate continuous 10gm Detonating Cord line besides the main product in order to avoid separation and water ingress on joints and avoid misfires and keep MIC limits favorable.

      - Use waterproof tape and cable ties for a more secure connection

      - Use suitable and safe tools

      - Consult the manufacturer or supplier for best use of the product

    Cover the main trunk line, especially with site AoP limits

      - With dust (damp) at least 0.5m and not chippings or crusher run type material

 

Pre-Split Drilled and Blasted in Advance

 

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Pre-Split Blasted with Bulk Blast

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