Blast Vibrations

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Blast Induced Ground

Vibrations

- P. VIDYA KIRAN The Ramco Cements Limited Jayanthipuram AP.


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What is Vibration?

A periodic motion of the particles of an elasticbody or medium in alternately oppositedirections from the position of equilibrium

when that equilibrium has been disturbed Blast induced ground vibrations are themovement of the Earth strata in all the threeDirections (3D) ie ransverse ! "ongitudanal!

#ertical from its position of rest due to groundwaves$


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What is Frequency ?

he hertz(symbol% Hz) is a unit derived from time which measures frequency$&requency is how often something happens$ A frequency of ' hert means thatsomething happens once a second$
https://simple.wikipedia.org/wiki/Frequencyhttps://simple.wikipedia.org/wiki/Secondhttps://simple.wikipedia.org/wiki/Secondhttps://simple.wikipedia.org/wiki/Frequency


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atural &requency * +esonance

Bridges! aircraft wings! machine tools! and all otherphysical structures have natural frequencies$

A natural frequency is the frequency at which the structure

would oscillate if it were disturbed from its rest position andthen allowed to vibrate freely$ All structures have at leastone natural frequency$

+esonance occurs when the applied force or base

e,citation frequency coincides with a structural naturalfrequency$ During resonant vibration! the responsedisplacement may increase until the structure e,periencesbuc-ling! yielding! fatigue! or some other failuremechanism$


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Air .ver /ressure

Air overpressure is a transient impulse that travelsthrough the atmosphere$ 0uch of the air overpressureproduced by blasting has a frequency below the audiblelimit of 12 $ Air overpressure! both audible andinaudible! can cause a structure to vibrate in much the

same way as ground vibrations 4t is a frequent cause ofthe complaints as a person senses air overpressuremore than vibrations$

he causes of generation are the energy released fromunconfined e,plosives such as uncovered detonatingcord trun- lines or mud caps used for secondaryblasting! the release of e,plosive energy frominadequately confined borehole charges (inadequatestemming! inadequate burden! or mud seams) and themovement of the burden and the ground surface$


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"in- b5w +oc- mass * #ibration

Effect of 6eology on Blast #ibration$

7avities! 8ea- seams! .pen 9ointsprovides paths along which e,plosiongases can rapidly vent to the face orsurface at high pressure and accelaratefragments to high velocities resulting inlarge throw distances$


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4nvestigations reveal that the e,tent ofblast vibrations in three orthogonaldirections! i$e$! "ongitudinal! #ertical andransverse are influenced by the lithounits of the roc- mass through which they

are propagating$

# : 7 (D5;ec D : Distance between point of blasting and the measuring station in meters

< : 0a,imum 7harge weight per delay! -g

7 : 7ombined +oc- mass +ating

a : &ield 7onstant (?2$@1)


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/arameters define the +0+

nia,ial compressive strength of roc-material$

+oc-


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8hen an e,plosive charge is detonated

in a blast hole! the roc- surroundingthe charge is fractured! split apart anddisplaced$

At a certain distance from the blasthole! the e,plosive energy decreases to

a level that causes no furthershattering! but continues to travelthrough the roc- as an elastic groundvibration$

Blast 4nduced #ibrations


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Effect of Ground Vibrations on the

Structures

he ground vibrations cause the ground to vibrate intransverse! longitudinal and the vertical direction leadingto its damage$

Although the differences in the accelerations! amplitudes!particle velocities and the frequencies in three directionsresult into the damage to the structures but the pea-particle velocity and the frequency are normally ta-eninto consideration for evaluating the structural response$he damage criteria due to ground vibrations aretherefore often specified with the pea- particle velocityand the associated dominant frequencies$


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Permissible PPV in mm/s as per DGMS Standards

ype of >tructure Dominant E,citation &requency C C to 1 1

! "uildin#s / Structures $%& belon#in# to o'ner

a( Domestic Houses

b( )ndustrial "uildin#

c( Sensiti*e Structure

+

,-

.

,-

.-

+

,+

.+

,-

"! "uildin#s / Structures "elon#in# to the o'ner

i( Domestic Houses

ii( )ndustrial "uildin#

,- ,+ .+

,+ .+ +-


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Why lo' requency 'a*es are dan#erous0!?

1o' Frequency

Hi#h Frequency


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Variables ectin# Ground Vibrations


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Factors Efecting Vibration

Ma2! char#e/ delay

Distance o the structures rom the blastin# site

Size o the blast

Strata condition

Front burden/ 3rest "urden

)nitiatin# de*ices4 $onel/ 5lectronic Dets

Firin# pattern

Free ace a*ailability

3oninement

Delay time / 6elie


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Delay &imin# and Scatterin#?

"enchtop7--ms in4hole

.8 scatter 9 :/4 ; ms

- ,< =7

;7 ,-,

7. +> ,+.,=+

,.=

;+;+,

$om )n4Hole 7,< 7=7 7+, 7;

7;+ :.8 7.+ 77. 7+> 7 7. 77= 7-

7;econdary blast$

@$ he face should be maintained straight anddirection of throw should not be towards thevillage$

'2$ Blast should be carried out between '1?3p$mwhen temperature inversions are not li-ely andbac-ground noise would be high$

''$ o blasting should be carried when strongsurface winds are blowing towards the village$

'1$ 6ood public relation programme may reducemost of the complaints from the villagers andmay safeguard the interest of the company$


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Line drilling:

his system involves a single row of closely spaced uncharged holesalong the neat e,cavation line$ his provides a plane of wea-ness to whichthe primary blast can brea-$4t also causes some of the shoc- waves generated by the blast to bereflected! which reduces shattering and stressing in the finished wall of thehost roc-$


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Vibration Measurin#

)nstrument


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Ground Vibration Measuring Instrument

Seismo#raph/Vibro#raphis used to measure theBlast induced ground vibration and air over pressuredue to blasting$

>eismograph consists of three sensors formeasuring ground vibration and one for measuringair over pressure i$e$ microphone

i) "ongitudinal

ii) ransverseiii) #erticalhe //# of vibration is measured in mm/seche Air over pressure is measured in Decibels


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Event monitoring measuresboth ground vibrations and airpressure$ he monitormeasures transverse! vertical!and longitudinal groundvibrations$ransverse groundvibrations agitate particles in aside to side motion$#ertical ground vibrationsagitate particles in an up anddown motion$"ongitudinal ground

vibrations agitate particles in aforward and bac- motionprogressing outward from theevent site$Events also affect airpressure by creating what is

commonly referred to as JairblastK$

Event 0onitoring with 0inimate


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/eso latest 7ircular


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Blast Vibrations

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