DRILLING AND BLASTING OF ROCKS - IRJMETS

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DRILLING AND BLASTING OF ROCKS

Deepak Parkash Gupta*1 *1Segmental Consulting and Infrastructure Advisory Pvt Ltd. Jammu and Kashmir, India.

ABSTRACT

Drilling and blasting is the most common practice involved in mining and Structural engineering activities such

as construction of Dams, Tunnels or Highways. This method can be used in all types of rocks. It involves use of

explosives. Drilling and Blasting was only the economical way earlier for excavation of rocks. Tunnel Boring

Machine (TBM), now made it more convenient to excavate hard rocks. Even today drilling and blasting method

is widely used for construction of tunnels. Chemical blasting is another method of blasting but is very

expensive. Though it is still used where drilling and blasting is not feasible like blasting of boulders on the

slopes of roads.

Keywords: Explosive, Drilling, Blasting, Tunnel, Rock, Detonator.

I. INTRODUCTION

Need of blasting, why blasting is preferred?

1. Blasting

2. Mechanical methods

Blasting is preferred over the mechanical method for its economy and productivity. It is the controlled use of

explosives to excavate, break down or remove rock. It is widely used in structural engineering works.

Explosives: It is the mixture of chemical compound which can be heat, shock, impact or friction or combination

of these forces, when ignited, it decomposes very rapidly in form of detonation. When the mixture is detonated,

it rapidly releases high temperature which rapidly expands and causes sufficient force to overcome the

confining pressure.

Explosive energy

Terminology of Blasting terms:

Over Break - Rock broken beyond the limits of the rear row of holes in a blast pattern.





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Blast – The disintegration of rocks by the use of explosives.

Blast Site - The area of a particular location where the execution of blasting is supposed to be done.

Blaster – A certified person who is taking care of the blasting activities on a particular site. He should have a

minimum experience of at least three years.

Blasting Galvanometer - An electrical device specifically designed for testing electric detonators and

circuits containing them along with blasting ohmmeters and blaster's multi meters. It is used to measure

resistance or to check electrical continuity.

Blast Hole - A hole drilled in rock or other material for the placement of explosive.

Blaster Log – A written record about a specific blasting material which is mandatory required by law or

regulation.

Blasting Machine/ Exploder - An electrical machine that provides electrical energy for energizing

detonators in an electric blasting circuit.

Cartridge - An individual closed shell, bag, or tube of circular cross section containing explosive material.

Circuit - A completed path for conveying electrical current.

Hookup Wire – The wire which is used to extend the firing line in electric blasting circuit.

Decibel - It is a unit which is used to measure air over pressure in an air blast.

Detonating Cord - A flexible cord which is used to initiate other explosives.

Emulsion – Emulsion is the mixture of water in oil and is used to enhance the water gel performance.

Initiator – It is a device that is used to explode an explosive device. There are four general classifications of

initiators currently being used in coal mine blasting which are: Non electric system, Electric system,

Electronic system and blasting cap and safety fuse system.

Detonators – It is device which is used to activate an explosive device. Detonators are either instantaneous

(no time delay element), millisecond (ms) delay or long period delay. Ms Delay are commonly used for

surface mine blasting and are manufactured with delay times upto 50 Ms. Long period delays are available

for periods upto several seconds.

Detonating cord – Detonating cord is round, flexible cord the exterior of which is water proof material. The

purpose of the detonating cord is to detonate other high explosives.





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Blasting in Tunnels:

Steps In Designing of Tunnel Blast

Step.1: Generate the geometry of the rock mass to be blasted and decide the location of the blast holes.

Step.2: Establish the regular pattern of blast holes to be adopted in the blast, after determining the burden

and spacing considering the nature and behaviour of rock.

Step.3: Determine the blast geometry parameters - Charge length, Energy, Powder factor, etc, based on the

known site parameters and operational parameters.

Step.4: Development of Initiation sequence system, which involves the placement of detonators/delays and

connectors

Step.5: After preparing the explosive charging configuration, the selected explosive is loaded into the holes

and proper stemming is done.

Step.7: In the post-blasting situation, the design can be given some amount of refinement through proper

analysis, for obtaining further improvement in blast results.

Types of cuts and design of blast rounds:

Cuts can be classified in two large groups:

Parallel hole cuts (for long pulls most widely used with mechanized drilling)

Angled hole cuts (applied for small pull length)

In tunnel blasting, blast holes can be classified into three categories:

Pattern Holes

Easer, Lifters, Contour holes

Burn Cuts:

Blast holes drilled parallel.

All the holes charged are of same diameter.

Some of the holes kept uncharged.

Uncharged holes may be of same/different diameter

Angled cuts or V- cuts:

◦ This is used for short pull length

◦ The advantage is a lower consumption of explosives.

◦ The bottom angle should not be less than 60o.

◦ It needs a very high accuracy in drilling.





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Blasting material used in tunnels

Emulsion explosive cartilage

Shock tube like detonation





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Detonating cord

Electric detonator

Hook up wire

Exploder





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Ohm meter

Measures taken to control overbreak:

Increasing Decoupling Ratio in Contour holes The Contour holes are drilled of Dia 45 mm; the charge placed is

25mm only. Because of this the compressive shock wave is reduced as the medium is less dense and thereby

cracked zone is limited.

Line drilling:

◦ Line drilling is the drilling a row of closely spaced holes along the final excavation limits and not loading the

holes with explosive.

◦ These holes are left as dummy holes so that these can act as the barrier line for perimeter charged holes.

◦ The line drilling is adopted at selective locations where heavy over break is expected because this technique

incurs high cost and is very time consuming.

Safety and Precautions:

Blasting caps or electric blasting caps stored in a same box is dangerous

Do not Store in wet place for storing

Keep Away from sparking metals and Smoke

Keep Away from dry grass and bush

Don’t use deteriorated explosives

Don’t stack surplus explosives near working areas during loading

The Codex Wire Should be locked with each other at upper end so that it does not get entangled in drill rod

while drilling below.

No loading of Bottom holes should be done when drilling or loading is done in upper face reach.

No loading near power supply.

MSDS Material safety Data Sheet to be displayed near the Explosive storage area so as to get the information

regarding Explosive.





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II. CONCLUSION

It is concluded that Drilling and Blasting is the economical methodology of excavation for Tunnels. Drilling and

Blasting is the controlled use of explosives to disintegrate the rocks for structural engineering activities. The

success of these techniques in surface and sub surface structures depends on the geology of the rock formation

being blasted. In hard massive rocks, controlled blasting techniques are usually successful, but in the loose

unconsolidated formations that will not support themselves, consistently good results may not be possible.

III. REFERENCES [1] Vassie, B. And Bonneau, M. 1992. Practical of Blasting, Optimisation and Performance assessment.

Quarry Management, pp 21-27.

[2] Rathore, S.S. 1989. Flyrock due to Blasting, Mining Engineering Department Report, University of

Jodhpur, 103 pp.

DRILLING AND BLASTING OF ROCKS - IRJMETS

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