Blasting

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Blasting

Back 1

Blasting is the use of explosive energy to destroy the media around the explosive medium.

In the construction of hydraulicengineering, blasting methods are widely used to

* excavate foundation pits and underground buildings,

* to complete other specific construction tasks.

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Advantages & Disadvantages of blasting

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Drilling & blasting is an very economical and practical method for the excavation of earth rock.】

Disadvantages

Meanwhile, blasting produces negative effects like flying stone, dust,vibration which cause the loss of humanproperty and life

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How to improve blasting efficiency and reduce blasting damage?

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* Basic blasting principle,

* blasting equipment,

* blasting design and itsoptimization method …

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Process of Blasting

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Blasting equipment

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Explosive

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Any substance that can produce a chemical explosion

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Performance Indicators of explosive

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*Strength and brisance: characterize the ability of the explosiveto crush the medium.

*Sensitivity: reference for safe production, transportation, storage and use of explosive.

*Oxygen balance: considering the combustion oxygen demand, explosives are usually configured for trace amounts of positive oxygen balance.

*Stability: the ability to remain stable in long-term storage.

* Gap distance : The maximum safe distance between detonation explosive and adjacent explosive cartridge.

* Optimum density

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Examples of industrial explosives

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* Emulsion explosive widely used

* Slurry explosive is also called water-gel explosive

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Emulsion explosive

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* Strong water resistance,

* Good explosive performance,

* wide source of raw materials,

* Simple processing technology,

* Small environmentalpollution,

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Priming materials

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* Detonator ; (according to different ignition device, divided into firedetonators and electric detonators)Blasting fuse ; (low cost, but low precision, application gradually reduced)

* Detonating cord ; (divided into safety detonating cord and outdoor detonating cord, and the latter is often used in hydropower projects)

* Detonation tube ; (use to transmit the shock waves in a detonation network , need the detonator to detonate)

* Nonel Detonator

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Detonating methods

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* Spark detonating ; (Non-electrical detonation)

- (the earliest method,only for the large stone dissolving, the small-scale slope blasting)

* Electric detonating ; (The power is transmitted by electric wire togenerate electric detonator and detonate explosive, which is suitablefor the project with large charge blasting, and detonation on time at afar distance can be achieved.It is easily affected by highpiezoelectric, thunder and electrostatic)

* Nonel tube detonating ; (New non-electrical detonation, quasi-explosive can not be checked)

* Detonating cord detonating ; (Non - electric detonation)

the highest security, good explosive network, but network cost is high; widely used in smooth surface blasting and pre - crack blasting

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Drilling machine

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* Rotary drilling rig

* Impact drilling rig

* Down-the-hole drilling rig

* Hydraulic drilling rig

* Multi-arm drilling machine

* Hand drill

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Blasting mechanism

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Rock fragmentation by blasting

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Shock energy

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* The explosive energy expanded by Explosion gases until it reaches an equilibrium with the stress

* Energy during this phase is used to develop the fracture network

NB:

Shock stress > Compressive strength – leads to crushing

Tangential stress > tensile strength – leads to radial cracking

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Blasting crater

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It is formed when rock near the free surface in a semi-infinite medium are thrown or ejected from the ground surface by explosive event above or below the ground.

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Blasting method

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Drilling blasting

* Short-hole blasting - hole diameter less than 75mm and hole depth less than 5m-

* Deep-hole blasting-

hole diameter larger than 75mm and hole depth deeper than 5m.

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Blasting method(Short-hole blasting)

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Front 18

Blasting method(Deep-hole blasting)

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Chassis resistance line, Wd

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The horizontal distance from the center line of the borehole to the foot of the bench.

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Measures to improve the effect of deep-hole blasting

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1) Make use of or create the free face.

2) Improve the charge structure; (The bottom hole is installed with high-power explosive, the upper part is installed with ordinary explosive)

3) Optimize the blasting network; (Select a reasonable blasting sequence and the difference between the time interval)

4) Using differential extrusion blasting; (Millisecond blasting that residue pile existed in front of blasting work)

5) Ensure stemming length and stemming quality.

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Chamber blasting

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Also called the bulk blasting,its chamber is specially excavated.

The chamber is connected withadit or shaft.

After charging, the adit or shaftrequires to be clogged.

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Characteristics of Chamber blasting

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1. chamber blasting has a large amount of blasting at one time, which is beneficial to speed up the construction progress；；

2) the drilling equipment needed is simple;

3) labour saving and high blasting efficiency;

4) the excavation of pilot or chamber is less affected by the climate, but the excavation condition is bad;

5) the fragmentation is uneven and the lump rate is high;

6) blasting vibration, air shock wave and other pollution hazards are serious;

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Application conditions of Chamber blasting

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1) projects with a large and concentrated amount of excavation, projects and needs to create benefits in the short term;

2) steep hillside which is not suitable to the drilling and blasting safely;

3) directional blasting to dam construction;

4) when the geological and topographical conditions meet the requirements, chamber blasting can be used for directional blasting to dam construction, sub-stacking area material field excavation of concrete facing rockfill dam and directional blasting closure.

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Cartridge bag layout

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In order to achieve a good blasting effect, it is necessary to arrange group charges according to the geological conditions and engineering requirements.

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Blasting parameters of chamber blasting

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In chamber blasting, the line of the least resistance W and the blasting action index n determine the blasting massand the throwing rate, the throwing distance and the blasting piledistribution.W and n are two basic parameters that determine the scale ofblasting.

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Calculating

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Front 27

Detonating Network

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When using group packs for blasting, in order to achieve the purposeof enhancing the blasting effect and controlling the blasting vibration, it isnecessary to use the method of detonating together, delay or detonatingtogether within the group, delay within the group.

This requires the explosive materials to connect each drug bag to a network that can beused for both explosive and explosive delay.