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[Music]
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let me introduce all of you to the
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drilling and lecture number 21 of
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drilling and blasting technology NPTEL
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online certification course in this
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lecture we'll study about the explosive
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properties and but prior to that like
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every class what we do with respect the
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previous lecture and in last few classes
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we are being introduced with the
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explosives and explosive accessories and
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we are trying to understand the need of
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evolving this different explosive
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accessories and at this point we are in
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a position to understand the different
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important properties of explosive and
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its accessories and we should know how
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these properties are influencing the
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performance of those explosives and
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their accessories so this is very very
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important so our learning objective for
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today's class is to understand different
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influential physical explosive
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properties to understand the testing and
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measurement procedure of these
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properties to understand different
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influential chemical explosive
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properties and to understand the testing
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and measuring procedure of this
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properties basically we have classified
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these properties into two groups
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physical properties and chemical
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properties most of the time we rely
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mostly on the physical properties and we
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measure those things chemical properties
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are not within the purview of the mining
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engineers generally chemical chemists
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and chemical engineers are take care of
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those properties basically we are more
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accustomed with the physical explosive
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properties and we will discuss more on
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the physical explosive properties only
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but like every class let us observe this
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video this video is basically giving you
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the idea about the use of a explosive
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for the demolition of the building this
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video is available in the YouTube there
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are
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number of other similar videos are
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available in the YouTube but by
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observing these videos it is easier for
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a for you to understand how this
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explosive can be used for demolish the
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buildings so buildings may be placed in
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the close proximity of the other nearby
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buildings and the challenges are that
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you should not damage those existing
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buildings neither you will allow the fly
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of the building broken a pieces to a
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longer distance so that it can hit
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someone and some accident may occur so
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that is why the demolition of the
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building is very very important and it's
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a very very artistic job in the last
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video you have seen the demolition was
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not in a proper manner that is why the
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toppling of the building block occurred
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but the last video this video was
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showing you a very good example of the
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blasting of the demolitions building
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so let us understand what are the
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important properties are there which we
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should know for the explosive and its
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accessories the first important property
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is density next the velocity of
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detonation next the strength of the
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explosive then the sensitivity of the
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explosive thermal stability of the
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explosive waterproofness gallery test
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and incendiary test etc n number of
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other tests are possible with the
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explosive and its accessories so in this
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class we will mainly concentrate on the
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density and velocity of detonation will
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understand how they are influencing the
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performance of an explosive you know
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density or specific gravity is basically
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dictates the mass in unit volume so
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density of explosive is important
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because mainly of three reason first the
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explosive with specific gravity less
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than one is not allowed to use in watery
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holes because it will float on the water
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so if we try to place the explosive
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below the hole that means in the bottom
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of the hole
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that is not possible if the hole is
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filled with the water it may be rain
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water it may be ground water so in those
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cases we should use some explosive whose
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specific gravity is more than one second
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is drained density of explosive
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basically directly dictates the charge
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concentration inside the hole that means
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if the density of explosive is more then
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per meter of drill length if we are
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placing the explosive with the increase
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in the density the charge quantity is
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becoming more second is the third is
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that the direct energy transfer from the
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explosive to the rock depends on on the
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density of the explosive will come all
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these points gradually but let us see
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this picture
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you can see in this picture this is a
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common method of measuring the explosive
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specific gravity or density so this is
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the container in this container we fill
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the container with the full of explosive
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then I find out the weight of the
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container nina oma seen in from the very
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beginning we know the empty weight of
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the container now with the measuring the
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weight we can understand what is the net
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weight of the explosive placed inside
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the container and we know the container
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volume so from that we can easily find
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out we can easily find out what is the
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density or specific gravity of the
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explosive now
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a density that is the basically dictates
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the quantity of the charge per kg of
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explosive column can be expressed in
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this equation which basically LC gives
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us the linear charge concentration
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linear charge concentration which is
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basically a measure of our blast design
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so the moment we are increasing the
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diameter this is the diameter of the
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hole and this is the density of
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explosive so the moment we increase the
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diameter of the hole or we increase the
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density of the explosive the linear
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charge concentration will increase so
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suppose we are having we are having some
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explosive placed at this position to
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blast this portion of rock mass then if
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we are increasing the density of the
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explosive the charge quantity placed at
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this will be increased then the charge
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per unit volume of rock mass unit volume
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of rock mass will be increased so if we
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are using more dense explosive material
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then our charge concentration is more
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and our unit volume per charge
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requirement is also becoming more so
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basically the charge concentration
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requirement depends on the strength of
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this rock mass strength of this rock
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mass
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if the strength is more in those case we
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should use high density explosive so
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that our charge concentration will be
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more for the x4 that stronger rock mass
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so let us have one example calculation
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here if the explosive available to use
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in a blast hole of 125 mm diameter and
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we are having the option to use blasting
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gelatinous specific gravity of 1.6 and
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ammonium nitrate fuel oil mixture with a
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specific gravity of 0.85 in those case
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if we calculate using this formula we
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will find out the charge concentration
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per meter in case of blasting gelatine
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will become 19 point 6 3 kg per meter
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for in case of ANFO it is 10 point 4 3
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kg per meter so you can find out it like
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this pi into 125 divided by 4000 sorry
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let me clear this pie into 0.125 by 2
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whole square into 1 point 6 into
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thousand to convert it into the kg per
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meter cube so we can find out this is
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the 19 point 6 3 kg per meter similarly
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in that case it is coming 10 point 4 3
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kg per meter so this source the blasting
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guillotine is a showing almost double
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charged concentration over and for so in
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case of a very strong rock mass if the
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rock mass strength is high and it
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demands it demands more charge
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concentration increased charge
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concentration in that case we should go
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for blasting gelatin not for the
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and for but for the week rock mass we
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should go for an pho instead of choosing
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the blasting gelatin
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the third point which we are discussing
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that that is the transfer of energy from
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the explosive to the rock you know in a
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blast hole if we are considering this is
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a blast hole and we are placing our
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explosive column on this the moment we
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provide some initiation in this
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explosive column the first the shock is
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exerted from the explosive so this sock
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basically propagates in a form of wave
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propagates in a form of wave in a
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similar manner if you drop a stone on
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the in the water of a pond the waves are
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propagating in all direction similarly
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the moment you detonate the explosive
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the shock waves are generated and the
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shock waves propagate in all direction
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similar manner and this propagation is
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similar to the propagation of sound and
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that propagation you know it's in
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compression dilation manner so this is
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in compression then again in dilation
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again in compression again in dilation
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so it is moving in compression and
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dilation manner and by that way the
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shock waves travel from the explosive to
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the all direction so what will happen in
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the interface in this interface the
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shock waves are generated from the
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explosive the next adjacent medium is
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rock and how the shock will propagate
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from the explosive to the rock that
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depends on the simple wave propagation
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law that means any interface any
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interface if some wave is coming and in
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interface what will happen the some
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portion of the wave will be reflected
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and some will be reflect reflect back so
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the wave propagation follows the Snell's
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rule of
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Furguson and similar way here the wave
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generated from the explosive some
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portion of that will be transferred to
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the rock some portion will be reflected
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back now how much portion of the shock
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energy in terms of the wave will
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transfer to the rock that will depend on
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the impedance of the shock and impedance
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of the energy impedance of the energy
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and impedance of the rock
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what is impedance impedance is basically
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the multi value multi which can be
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obtained by multiplying the density and
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the wave velocity of that medium so wave
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velocity of that medium in case of
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explosive is called VOD velocity of
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detonation in case of rock it is called
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seismic wave velocity or P wave velocity
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which can be considered as the CP so
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explosive impedance is the density is
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the value obtained from the multiplying
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the density of explosive and multiplying
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the VOD of explosive and the rock
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impedance will will be the value you can
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obtain multiplying the density of the
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rock mass and the velocity of the rock
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mass now the maximum energy will be
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transferred from the explosive to the
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rock the maximum energy will be
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transferred from the explosive to the
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rock if this impedance of the explosive
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and the impedance of the rock is coming
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closer to each other that means if these
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are equal then the one hundred percent
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energy will be transferred from the
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explosive to the rock but rarely you can
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have the equal impedance you may have a
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have an impedance closer to one
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basically our requirement is that as the
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rock part we do not have any control on
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that it is in the in situ of the art
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rock is in the in situ of the art and
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as it is obtained there we have to take
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care of that but we are having the
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option we can change our explosive or we
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can change the property of the explosive
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so that we can match the explosive with
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the rock and that can be obtained only
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by changing this tool so our objective
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is that we can choose the explosive in
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such a manner so that the explosive
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impedance should come closer to the rock
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impedance but practically there are some
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problems the first problem is that in
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general the rock density is very very
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high you have seen in the first lecture
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where we have described our mother earth
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how it it is constitute and you have
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found the density of the earth is
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increasing towards the core of the earth
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and it is less in the surface then also
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though we are escalating our rock close
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to the surface then also on an average
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the earth surface is having a density
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more than to our specific gravity more
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than two density more than two ton per
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meter cube or two gram per CC so that is
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why the density of the rock is in
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general higher than the density of
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explosive the density of explosive which
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we are using nowadays having a range
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between the 0.85 to point 1.6 or 1.7
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something like that so that is why the
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density of the explosive is more or less
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less than the density of the rock
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sometimes in sandstone or limestone in
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those cases we are having wrong density
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in and around 2.5 in case of chromite
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etcetera which are very strong rock very
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heavy rock in those cases the density
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may go up to 7 also 7 ton per meter cube
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so these are very very high density
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material in those cases we have found
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our impedance matching is becoming
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difficult let us see the next slide then
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we will understand then we will
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understand how
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the density is basically influencing the
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influencing the impedance so for example
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explosive available to use in a blushed
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hole of diameter 125 mm as we have got
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in the last problem R and we are using
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the same blasting guillotine of specific
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gravity 1.6 and ammonium nitrate fuel
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oil of specific gravity 0.85 now if the
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blasting is being carried out in a
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limestone minds of rock specific gravity
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of 2.4 and which is having a spearville
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ah city of 54,000 meter per second then
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we can understand the impedance ratio
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that means the explosive impedance and
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rock impedance ratio will become 0.72
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for the blasting gelatin and 0.2 if you
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express it in percentage 72 percent for
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blasting gelatin 20% for the ANFO
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because the blasting gelatin is having
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the higher density and also the higher
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velocity of detonation
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whereas ANFO is having low specific
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gravity as well as the low velocity of
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detonation so that is why the energy
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transferred from the and for to the rock
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mass will be around 20% much much lesser
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than the energy generated on detonation
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which in but on the other hand in case
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of blasting gelatine it is becoming 72
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percent so which is much much better
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utilization of the energy so basically
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this specific gravity dictates a lot on
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the energy transfer condition from the
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explosive to the rock mass so that is
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why the specific gravity or density
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of the explosive material is very very
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important if if you are considering
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about the energy utilization of the
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explosive or the transfer of the energy
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from the explosive to the rock so that
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is why this density often becoming a
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free domain has a predominant role on
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the property performance of the
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explosive while you are carrying out the
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blasting similarly the second parameter
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which is very very important is the
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velocity of detonation that means the
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propagation of wave propagation velocity
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seismic wave propagation velocity inside
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the explosive material so velocity of
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detonation is another important
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explosive properties it is the speed at
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which the shock wave travels through the
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explosive medium is called velocity of
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detonation so the shock wave velocity in
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the rock and Sacher velocity in the
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explosive both are moves more or less
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similar both pierre-pierre are passing
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through those mediums but when it is
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passing through the medium that time its
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speed is considered as the velocity of
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detonation so from the previous problem
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it is clear to us that the VOD is
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basically dictates the transfer of the
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shock wave from the explosive to the
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rock and thus we always want the
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explosive should have a higher VOD so
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that we can have a better energy
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utilization in case of blasting but
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pure-d
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may not be always available very high
00:22:01
because especially in Indian mining
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condition it has been found that most of
00:22:05
the nitrate with best explosive which
00:22:09
are generating more VOD are banned here
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so the commercial explosive available
00:22:14
and ammonium nitrate based and that is
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why the VOD are relatively less okay so
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that is our present problem that is why
00:22:21
the energy utilizations are also very
00:22:23
limited however explosives are
00:22:26
classified in two groups depending on
00:22:30
the pewdie where this is already told
00:22:34
you file you have discussed the
00:22:36
explosive that time the low explosive is
00:22:39
called those explosives which which are
00:22:42
being subsonic VOD and high explosives
00:22:45
are those explosives which are having
00:22:47
supersonic VOD so that is why the beauty
00:22:52
is one very very important parameters
00:22:55
for the explosive drop as the explosive
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property
00:23:11
how we can measure the velocity of the I
00:23:18
think there is some problem in the slide
00:23:22
please correct it this is the velocity
00:23:25
of detonation so this is the velocity of
00:23:35
detonation so velocity of detonation of
00:23:42
an explosive may be measured using
00:23:44
different method so in this class we
00:23:47
will discuss more most common two method
00:23:50
one is the dirt rich method which can be
00:23:52
applicable in the laboratory condition
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and let us see what is the Smith or dr.
00:23:59
each method is applicable for a column
00:24:01
of short column of explosive or for the
00:24:03
detonating fuses and you can see the
00:24:08
experimental setup where a column of
00:24:12
explosive is kept initiation to the
00:24:16
column is given from this side and the
00:24:20
explosive column is tied with two with a
00:24:24
detonating fuse at this point and that
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this point so
00:24:40
so this explosive and this detonating
00:24:45
fuse are tied at this point and a middle
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portion of the detonating fuse is kept
00:24:53
or tiled on a lead plate and the middle
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point of the determining fuse is mark at
00:25:01
this position now the moment initiation
00:25:06
is given to the explosive the initiation
00:25:09
first reaches at this point the moment
00:25:12
initiation at this point that
00:25:15
time that detonating fuse of this point
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got the initiation now
00:25:20
the initiation is carrying through the
00:25:24
explosive column towards this side and
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also the initiation carries from the
00:25:30
detonating fuse whose VOD is known to us
00:25:32
from this side the moment initiation
00:25:37
reaches at this point that time the dis
00:25:42
detonating fuse received the initiation
00:25:44
and the initiation starts detonation of
00:25:48
the detonating fuse started from this
00:25:50
side towards this direction so in both
00:25:53
the cases that detonating fuses are
00:25:56
having the initiation and the initiation
00:25:59
propagation directions are
00:26:00
mouth to mouth to each other and this is
00:26:04
the point where both the initiations are
00:26:07
meeting each other and as both the
00:26:09
initiations are meeting each other it
00:26:12
gives an impression on the lead plate
00:26:15
now from this we are having a known
00:26:20
point this one which is the middle point
00:26:22
of the detonating fuse we are having a
00:26:25
known point marked point at this one on
00:26:28
the lead plate which is the meeting
00:26:30
point of the both the initiation on the
00:26:33
detonating fuse now from here we are
00:26:36
having one known length that is L
00:26:39
distance between the middle point and
00:26:42
the mark on the plate and one known
00:26:45
distance from that is the distance apart
00:26:49
of the tying of the detonating phase on
00:26:51
the explosive column by knowing
00:26:54
- we can determine the beauty of this
00:26:56
explosive or deterrent increase whose
00:26:59
beard is not known to us if we are
00:27:01
having the knowledge about that VOD of
00:27:05
the detonating fuse in those case this
00:27:08
formula can be used to find out the VOD
00:27:12
of the unknown explosive as the distance
00:27:18
of the tying part of the detonating fuse
00:27:22
in the explosive the VOD of the
00:27:27
detonating fuse and dividing the twice
00:27:31
of the length of the distance between
00:27:35
the mark on the plate and the midpoint
00:27:38
of the detonating fuse so from there we
00:27:41
can identify we can calculate the VOD of
00:27:45
the explosive column but there are some
00:27:49
problems but there are some problems of
00:27:57
the about the dirt ridge method the
00:28:01
first problem is that it is not
00:28:03
applicable for the measurement of the
00:28:05
beauty of the explosive inside the blast
00:28:07
hole neither it provides us the Beauty
00:28:13
continuously for a long cylindrical
00:28:14
charge so this beauty which is obtained
00:28:19
from the dot dot reach method is
00:28:22
basically the average purity of the
00:28:25
explosive placed between the two tying
00:28:28
of the detonating fuse the second
00:28:31
problem is that in the blast hole purity
00:28:35
can be measured by different other
00:28:37
methods which is not described in the
00:28:41
which is not possible in case of the dot
00:28:44
reach method so the brush tool beauty
00:28:48
can be measured using the different
00:28:50
methods beauty probe using fiber optical
00:28:55
cables using swiffer technique and these
00:28:59
three technique can give us continuous
00:29:01
VOD for in case we are having a beauty
00:29:05
placed in the blast hole
00:29:08
so that the possibilities is that this
00:29:11
is a full pleasure blasting maybe
00:29:13
carried out then also the beauty can be
00:29:15
measured we need not to depend on the
00:29:19
samples to be taken in the laboratory to
00:29:22
carry out the tests so let us see the
00:29:24
first one first one is the Buda probe a
00:29:27
beauty probe is basically during the
00:29:31
blasting it measures the time gaps foil
00:29:34
the pulses are passing through the
00:29:38
consecutive points of the probes which
00:29:41
are in contact with the explosive that
00:29:45
means the probe is placed along the
00:29:48
explosive column having the different
00:29:52
consecutive points and the whenever the
00:29:57
points are receiving the pulse that
00:30:00
pulsar time of those pulse are memorized
00:30:04
or calculated in the oscilloscope then
00:30:08
the time gap between two consecutive
00:30:10
points in the probe whose distances how
00:30:15
much distances apart they are previously
00:30:17
known to us can be easily obtained and
00:30:21
from there the distance divided by the
00:30:23
tank time gap is giving us the pure D
00:30:27
and in those case if we are having n
00:30:29
number of probes placed at NMM m number
00:30:32
of distance on those cases we can have
00:30:35
different time gaps in between those
00:30:38
cups consecutive probes and we can have
00:30:41
the different distances of those
00:30:44
consecutive cloths from there we can
00:30:46
have a continuous beauty measurement
00:30:48
along the column explosive column but as
00:30:52
probe is having little bit problem the
00:30:54
main problem is to probe that we need to
00:30:57
place the oscilloscope close to the
00:30:59
probe and that is why we cannot have a
00:31:02
very full fledged blasting system if we
00:31:07
are measuring the beauty using the probe
00:31:09
so probe cannot be used for a very long
00:31:12
explosive column not for a very large
00:31:14
blast now but in whole beauty can be
00:31:17
measured using the probe however the
00:31:20
problem of the probe
00:31:21
can be overcome by using the fiber-optic
00:31:24
cabling fiber optic cable is basically
00:31:28
consisting of optic stands and fitted
00:31:30
with a photodiode sensor which converts
00:31:33
the light signal to an electrical to an
00:31:37
electrical signal in case of fiber optic
00:31:40
cable one end of the cable is inserted
00:31:43
into the sensor and the other end is
00:31:46
embedded along the Xplosive column and
00:31:48
as the explosive is detonated from the
00:31:52
farthest side the moment the optical
00:31:55
fiber probes comes in contact with the
00:31:57
explosive it emits signal and those
00:32:01
signals are recorded in the oscilloscope
00:32:03
so consecutive such signals are recorded
00:32:06
and computed the VOD using the same
00:32:10
technique as the probes are carrying out
00:32:12
so we are having continuous input
00:32:14
signals and from those input signals we
00:32:19
can calculate the VOD continuously so
00:32:22
basically this is a continuous
00:32:25
monitoring almost continual continuous
00:32:27
monitoring of the VOD along the blast
00:32:30
hole and this is very easy and the
00:32:34
problem in the probe that we cannot have
00:32:37
a long explosive column cannot have a
00:32:41
large blast round that can be overcome
00:32:43
in the fiber of a fiber optic cable
00:32:45
because we can have a longer cable
00:32:47
length and we can remotely monitor the
00:32:51
VOD away from the blast hole so it may
00:32:54
be a a huge long explosive column it may
00:32:58
be a full-fledged blast off then also
00:33:01
the blast beauty of the explosive in
00:33:03
that blast round can be monitored using
00:33:05
the fiber-optic cable but there is a
00:33:09
little bit problem in the fiber-optic
00:33:11
cable the problem in the fiber-optic
00:33:14
cable is that it is a little bit costly
00:33:16
as the fiber-optic cable is crossed
00:33:19
costly so the purity monitoring cost
00:33:22
becoming high and that is why the people
00:33:26
are not encouraged enough to measure the
00:33:29
VOD frequently in the mind so to
00:33:33
overcome that problem
00:33:35
Slipher method that is the sorted
00:33:37
location indication by frequency sorted
00:33:41
location indication by frequency of
00:33:44
electrical resonance so this slippery
00:33:47
method is used this is similar to the
00:33:50
fiber optic cable method but instead of
00:33:53
fiber optic cable which is very costly
00:33:55
that is replaced by a coaxial cable
00:33:57
which is very very cheaper the coaxial
00:34:01
cable is embedded with the explosive
00:34:02
column and the ends of the cables are
00:34:05
connected with the oscilloscope to
00:34:08
complete the circuit now as the ends of
00:34:14
the cables are connected with the
00:34:15
oscilloscope to complete the circuit the
00:34:19
explosive point it is detonated and the
00:34:22
length of the cable is getting shorter
00:34:24
with the explosion in explosive column
00:34:28
this results into the changes in the
00:34:32
frequency of the oscillator pick signal
00:34:34
so what is happened as the electrical
00:34:39
resistance with the shorting of the
00:34:41
cable length coaxial cable length
00:34:43
electrical resistances are changing and
00:34:46
the oscilloscope is getting the
00:34:50
different frequency signal because of
00:34:52
that from the coaxial cable and that is
00:34:55
why if plotting is carried out between
00:34:58
the frequency and the time or frequency
00:35:02
and with the distance basically time is
00:35:06
giving us the sorting of the length so
00:35:08
it is a frequency with the lengths
00:35:10
wattage length shortage which will give
00:35:15
us the distance distance of initiation
00:35:22
travel or detonation travel in the
00:35:25
explosive and on the other hand this
00:35:30
length is also given in a time frame so
00:35:34
that means we can get we can obtain the
00:35:37
time versus length considering the
00:35:40
frequency and from there we can easily
00:35:42
compute the VOD this coaxial cable is
00:35:46
not very costly it is very very cheaper
00:35:48
and that is why this allows us for the
00:35:52
continuous VOD monitoring and remotely
00:35:56
monitoring for a full full project blast
00:35:59
round
00:35:59
so this basically eliminates all the
00:36:03
problems of infield beauty measurements
00:36:05
and nowadays popularly VOD is being
00:36:08
monitored so it has been found that a
00:36:11
number of parameters significantly
00:36:12
influence the VOD charge diameter in
00:36:16
fact increasing the diameter of the
00:36:18
charge the VOD get increased decreasing
00:36:25
the charge pure-d get reduced and on
00:36:30
doing so it has been found there is a
00:36:32
diameter there is a diameter below which
00:36:37
below which the explosive loads lost his
00:36:42
explosive properties and that diameter
00:36:44
is called critical diameter so every
00:36:48
explosive has a critical diameter and
00:36:50
below that diameter explosive lost his
00:36:55
explosive parameters that is why this
00:36:58
diameter of the charge is very very
00:37:01
important second is that it has been
00:37:04
found that the with the confinement of
00:37:06
the explosive VOD get increased that
00:37:09
means when the beauty is measured using
00:37:11
the dot reach method in the surface that
00:37:14
time the beauty obtained is very very
00:37:18
less than the beauty obtained in case of
00:37:22
in the whole VOD measurement so if the
00:37:26
beauty is measured if the beauty is
00:37:29
measured in case of in the whole in that
00:37:32
case we can have a increased VOD for the
00:37:36
confined condition
00:37:37
similarly the age of explosive is
00:37:40
another important factor and CI MFR has
00:37:45
found that the significantly the beauty
00:37:49
get reduced in the if it is if it is
00:37:52
edged is more and it is it has been
00:37:56
proposed that it a more explosive can be
00:37:58
allowed to be used if it exceeds six
00:38:01
months
00:38:02
so that is why the age of explosive is
00:38:06
very very important the allowable age of
00:38:10
explosive is called the self-life that
00:38:13
means that that is the limit up to which
00:38:16
the explosive can be kept in the store
00:38:19
so these are the field these are the few
00:38:24
reference you can read those reference
00:38:28
for knowing more on those explosive and
00:38:30
explosive properties specially the books
00:38:33
written by GK proton explosive and
00:38:36
blasting techniques will be very very
00:38:37
useful for this chapter thank you
