The short answer
A drilling and blasting rate is three costs added together: metres drilled per cubic metre of rock, explosive and initiation per cubic metre, and the fixed cost of licences, magazine, crew and monitoring spread over the monthly volume. Rock hardness, hole diameter and the distance to the nearest building move the figure far more than any contractor's margin does.
Nobody can give an honest rupee figure for drilling and blasting without seeing the face, and anybody who does is quoting an average. What can be set out is how the figure is assembled, so that two quotations can be taken apart and compared line against line.
01The three parts of the rate
| Cost head | Physical quantity | What pushes it up |
|---|---|---|
| Drilling | 0.08 to 0.15 m drilled per m3 in production benches | Small holes, hard or abrasive rock, low benches, tight patterns |
| Explosive | 0.25 to 0.6 kg per m3 in most quarry rock | Hard massive rock, small fragment size, wet holes needing cartridged product |
| Initiation | One detonator and booster per hole, plus surface delays | More holes per cubic metre, delay-by-delay timing near structures |
| Fixed site cost | Magazine, van, licensed crew, monitoring, survey | Low monthly volume to spread it over |
Ranges are typical of quarry and highway rock cutting. A particular face can sit outside them.
The first two rows are set by the pattern. Burden, spacing and bench height decide how much rock each metre of hole breaks, as worked through in reading a drilling pattern. Explosive per cubic metre is the powder factor, which has its own article.
02Solid, loose or tonnes
Before comparing rates, check the unit. The same job can be paid three ways, and the numbers look nothing alike.
| Unit | How it is measured | Equivalent |
|---|---|---|
| Cubic metre in the solid (bank) | Survey levels before and after | 1.00 m3 |
| Cubic metre loose | Tipper body or stockpile survey | About 1.5 to 1.6 m3 |
| Tonne | Weighbridge | About 2.6 to 2.9 t, by rock type |
A rate per loose cubic metre should be roughly two-thirds of the rate per solid cubic metre for the same work. A contract that does not say which is meant will be argued over at the first bill. Tonnes over a weighbridge are the hardest to dispute, and that is how we prefer to be measured.
03Why controlled blasting costs more
Close to buildings, a road or a pipeline, the charge that may be fired on any one delay is capped by the vibration limit. The blaster responds with smaller holes on a tighter pattern, more delays, shorter rounds and sometimes covering over the shot. Each of those adds drill metres, detonators or shifts for the same volume. The rate per cubic metre goes up, sometimes steeply.
It is still the cheap option. The alternatives are breaking the rock mechanically at several times the cost, or being stopped by the district administration after a complaint. Our Western Bhopal Bypass package is drilling and blasting only, with housing close to the alignment, and on a job like that the charge per delay decides the programme.
04What usually sits outside the rate
- Secondary breaking of oversize, unless a fragment size has been guaranteed.
- Vibration monitoring and the pre-blast survey of nearby buildings, where a consultant asks for a third party.
- The explosives magazine and van, where the client's licence is being used instead of the contractor's.
- Royalty on the mineral and any transit pass, which follow whoever holds the lease.
- Dewatering of wet benches, and the waterproof explosive that wet holes need.
- Standing time when the shot is ready and the site cannot be cleared.
05Taking two quotations apart
Ask each bidder for the pattern their rate assumes: hole diameter, burden, spacing, bench height and powder factor. A low rate built on a wide pattern is a low rate for boulders. Ask what fragment size they will stand behind, expressed against the feed opening of the crusher. Ask who pays for the breaker when the shot does not deliver it.
Then ask whose licence the explosive moves under and who the shotfirer is employed by. The cheapest rate on the sheet is often the one that has left those two answers vague. What our own rate carries is set out under controlled blasting and drilling.