control blasting

8/3/2019 CONTROL BLASTING

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TECHNIQUES OF CONTROLLEDBLASTING

By,

J4U


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Adverse Impacts of Blasting

Controlled blasting methods are used to control

adverse impacts such as:

Over-break

Reduce ground vibrations

Reduce fractures within remaining rock walls Reduce noise

Reduce dilution / waste of ore etc.


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Techniques of Controlled

BlastingFollowing are the techniques of controlled blasting:

Line drilling, Trim (Cushion) blasting,

Smooth (contour or perimeter) blasting,

Pre-splitting, Selecting and employing various parameters of

blast design, using modern technology, etc.


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Trim (Cushion) Blasting

Like line drilling trim or cushion blasting involves a singlerow of holes along the specified final excavation line.

This technique generally uses 2 to 4 inch diameter holes.

Holes are loaded with light charge, well-distributed,completely stemmed and fired after the main excavation isremoved.

By firing the trim holes with minimum or no delay betweenholes, the detonation tend to shear the rock web betweenholes and give a smooth wall with minimum over-break.

It is better to put trim holes just before removing the finalberm.

As compare to line drilling technique trim or cushionblasting is simpler and economical as increased holespacing are used.


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Blast damage and over-break in

Tunneling


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Signature-Hole Blast Analysis

Structural response to blast-induced ground vibration is a phenomenonthat has been analyzed for many years.

Residential structures level of response to blast induced groundvibration is dependent on both the peak particle velocity and thefrequency of the waveform.

Researchers have shown that, above ground structures resonatewhenever they are excited by a vibration containing adequate energymatching the fundamental frequency of the structure.

The value of this frequency is mainly dependent upon the mass, heightand stiffness of the structure.

The maximum response of a house to blast induced ground vibrationoccurs whenever the frequency of the ground vibration matches thenatural resonant frequency of the house.

When little or no energy at the resonant frequency of the structure, thestructural response to the vibration will be negligible.


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cont. The crucial point of the methodology is the use of a pilot-blast

signal which takes account of the seismic properties of allcomplex geology between the blast and the target locations.

The delay interval between blast-holes can be chosen to control

and minimize the vibration energy within the structural responseband of most houses.

Studies had indicated that blast vibration could be simulated bydetonating a Signature Hole with the vibration monitored atcritical locations, and then using a computer to superpose thewaveforms with varying delays.

By choosing delay times (t) that create destructiveinterference at frequencies that are favored by the local geology,the ringing vibration that excites structural elements instructures, houses and annoys neighbors could be reduced.


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cont. In other words, Signature Hole Analysis is a modeling

technique, to help control adverse effects of blast inducedvibrations.

The process involves controlling the frequency content by

adjusting delay times within a blast containing several explosivecharges.

The risk to adjacent structures is thereby mitigated.

Thus, with the growing adoption rate of electronic initiationsystems as a tool to control nuisance of vibrations, the modelingtechniques are becoming more popular.

M/s Instantel has recently developed and launched a SignatureHole Analysis software tool, which allows users to simulate alarge number of charge delay times very quickly.


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Electronic Detonators

Technology that is developed to improve techno-economics and reduction of most ofadverse effects in usage of explosive and blasting is Precise and Accurate DelayTiming Electronic Detonators system.

Advantages

a) Better ground vibration control

b) Better fragmentation

c) Better control of rock movement and muck profile

d) Enhancement in productivity by optimizing utilization of explosive energy.

All Electronic Detonators has a system to store electrical energy (capacitor) inside thedetonator as a means of providing delay timing and initiation energy.

In electronic detonator the Igniter is located below the delay (timing) module.


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Working Electronic

Detonators The electronic detonator utilizes standard lead as the input signal, which

is transformed into electrical pulse through the use of principalcomponent.

A small explosive charge (booster) coupled to a highly efficient electricalenergy storage cell (capacitor).

Upon receipt of an electric signal causes current to flow through thesteering diode to charge storage capacitor. A voltage regulator providesa substantially constant voltage source to oscillator to control thefrequency.

A power on reset circuit preloads the counter upon the initialapplication of the input voltage.

Once the voltage on the storage capacitor has increased beyond athreshold setting the counter begin decrementing upon each input pulsefrom oscillator. As the counter digitally decrement past zero, the outputto the firing switch activate and all remaining energy in the storagecapacitor flows to the igniter. The end result is an electronic delaydetonator.


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Effects of Control Blasting

The ground vibration is restricted to ease the publicrelation problem,

The mines / constructions techno-economics are

improved, Preservation of host rock strength and safety

standard are improved to a considerable level,

As far as possible modern techniques andequipments are also to be used in order to mitigate

the adverse blast effects Regular monitoring is needed

Training to the blasting supervisors on controlledblasting techniques is very much essential.


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Thank You!

control blasting

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