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BY
Dr. L. AJAY KUMAR, PROFESSOR & HEAD
Dr. S. RAJARATHNAM, PROFESSOR & DIRECTOR
REPORT ON
IMPACT OF ROUGH STONE QUARRY BLASTING
OPERATION IN THE VICINITY OF S.F.No.118/7
ERACHA KULAM VILLAGE, THOVALAI TALUK
KANYAKUMARI DISTRICT
COLLEGE OF ENGINEERING, GUINDY
ANNA UNIVERSITY, CHENNAI 600025
JULY 2013
S.F.No.118/7
REPORT ON
IMPACT OF ROUGH STONE QUARRY BLASTING
OPERATIONS IN THE VICINITY OF S.F.No.118/7
ERACHAKULAM VILLAGE,
THOVALAI TALUK, KANYAKUMARI DISTRICT
Name of the Lease Holder : Mr. S.M.Lucose
Survey No. : 118/7 Part
Village : Erachakulam
Taluk : Thovalai
District : Nagercoil
BY
Dr. L. AJAY KUMAR, Professor & Head
Dr. S. RAJARATHNAM, Professor & Director
COLLEGE OF ENGINEERING, GUINDY
ANNA UNIVERSITY, CHENNAI 600025
JULY 2013
CONTENTS
S. NO DETAILS PAGE NO.
1.0 INTRODUCTION 1
2.0 OBJECTIVES 1
3.0 LOCATION 1
4.0 GEOLOGY 3
5.0 EFFECTS OF BLASTING 4
5.1 Blast Induced Ground Vibrations Background 4
5.2 Factors Influencing Blast Induced Ground Vibrations 5
5.3 Permissible Limits of Blast Induced Ground Vibrations (PPV) for
Surface Structures 5
5.4 Ground Vibration Predictor Equations 7
5.5 Blast Induced Fly Rock 7
5.6 Control of Fly Rock 9
5.7 Blast Induced Air Blast / Noise 9
5.8 Human Perception 10
6.0 CONTROLLED BLASTING TECHNIQUES 10
7.0 BLAST VIBRATION MONITORING INSTRUMENTATION
(INSTANTEL DSS-077) 11
7.1 Instrument Description 11
8.0 INITIATION SYSTEMS 11
8.1 Electrical Initiation 12
8.1.1 Advantages of Electric Initiation System 12
8.1.2 Disadvantages of Electric Initiation System 12
8.2 Electric Delay Detonators 12
8.2.1 Advantages of Electric Delay Detonators 12
8.2.2 Disadvantages of Electric Delay Detonators 14
9.0 METHOD OF QUARRYING 14
10.0 SITE INVESTIGATIONS 14
11.0 OBSERVATIONS AND DISCUSSIONS 14
12.0 DATA ANALYSIS 16
13.0 CONCLUSION AND RECOMMENDATIONS 18
LIST OF TABLES
Table No Details Page No.
1. Natural frequency of surface civil structures after Central Mining and
Fuel Research Institute (CMFRI), (Report 1991). 5
2. Directorate General of Mines Safety (DGMS) (Tech) (S&T) Circular
No.7 of 1997} 6
3. USA Standard (after Siskind, et al, 1980) 6
4. Australian Standard 2008 (AS 2187.2) 6
5. German Standard (after German DIN 4150, 1986) 6
6. Current air blast limits is USA Office of Surface Mining Reclamation &
Enforcement 9
7. Details of blast hole parameters and explosives used during investigation
at S.F.No.118/7 16
8. Blasting details and blast induced vibration observation details at
S.F. No. 118/7 16
9. Scaled distance for maximum safe charge and peak particle velocity of
2.5 mm/sec 17
LIST OF FIGURES
Figure No. Details Page No.
1. Map showing the location of Rough stone quarry at S.F.No.118/7 and
surroundings 2
2. Fly-rock Generation 8
3. Electric Delay Detonators 13
4. Electric Delay Detonators Constructional features 13
5. Satellite imagery showing the Blast and Monitoring station locations in
the vicinity of Rough stone quarry at S.F.No.118/7 15
6. Regression line for the blast induced vibrations surrounding the rough
stone quarry 17
LIST OF ANNEXURES
S. No DETAILS PAGE No.
1. Event Report at Monitoring Station 1A 19
2. Event Report at Monitoring Station 1B 20
3. Event Report at Monitoring Station 2A 21
4. Event Report at Monitoring Station 2B 22
5. Event Report at Monitoring Station 3A 23
6. Event Report at Monitoring Station 3B 24
LIST OF PHOTOS
No. DESCRIPTION PAGE No.
1. 25
2. 25
1
1.0 INTRODUCTION
Ground vibrations are integral part of rock blasting. Trial blasts were carried out to study the effect of
blasting in the vicinity of rough stone quarry to have an in-depth understanding of the level of vibrations.
The rough stone quarry operated in S. F. No. 118/7 of Erachakulam Village, Thovalai Taluk,
Kanyakumari District is carrying out blasting operations. In this regard, Mr. S.M. Lucas had requested
Department of Mining Engineering, Anna University, Chennai to conduct a detailed study in the above
area and furnish the report on the impact of blasting operations in the vicinity of the quarry.
2.0 OBJECTIVES
To conduct Site visit and collection of field data to assess the existing situation.
Carry out a minimum 3 trial blasts and monitor blast induced ground vibrations as per the
Director General of Mine Safety Circular No. 9/97 of 1997.
Study the influence of the existing blast design on the residential and other structures of the
surrounding villages of Erachakulam village of Thovalai Taluk, Kanyakumari District of
Tamil Nadu.
Develop a scaled distance equation for the site to determine the maximum permissible
explosive charge per delay, distance of the blasting site and Peak Particle velocities (blast
induced ground vibrations).
Submit a report suggesting suitable blasting technique to be adopted in future for safety of
the residential settlements in the neighbouring villages can tolerate vibrations without
damage.
As proposed above, the field visit was undertaken on 02-06-2013. During the field visit, 3 Nos. of trial
blasts were carried out. Blast induced ground vibrations were recorded at 6 locations using two vibration
monitoring seismographs which are capable of recording vibrations in all the three directions. Based on
the analyses of the above trial blasts, the following report is prepared and submitted.
3.0 LOCATION
The Erachakulam Rough Stone Quarry in S. F. No. 118/7 of Mr. S. M. Lucas is located to the north of
Nagercoil town, the district head quarters of Kanyakumari district. The mining leases is situated close to
Sun College of Engineering and Technology and few residential buildings surrounding the lease area. The
details of the quarry, its location from the neighbouring buildings are shown in Figure 1. The mine is
producing 75 rubble units per day and is at a distance of 370 m from the college building and more than
240 m from the neighbouring residential buildings.
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4.0 GEOLOGY
Geology of the Kanyakumari district area based on the work done by Geological Survey of India in
consonance with the occurrence and observations of different litho- units.
Recent and Sub-recent
Tertiary formations
--------------Non-Conformity---------------
Pegmatite and quartz veins
Granite veins
Charnockite(II)
Granite Gneiss
Garnetiferous granitoid biotite gneisses
Granulite (leptynite)
Basic Charnockite
Granitoid gneiss with extensive intercalations of leptynite occurs in the south western part of the district.
In the study area, Granitoid gneiss with extensive intercalations of charnockite. The nature of occurrence
of charnockite is ubiquitous, often in two modes. One type of occurrence is in the form of profuse
enclaves as large islands, lensoid bodies etc; within granitoid gneiss. Basic nature of the charnockite has
been preserved only at few places where in it contains occasionally noritic/pyroxene granulite patches and
calc granulite pockets. Retrogression of mafics pyroxenes to hornblende and biotite aggregates and
granitisation with intercalations of quartzofeldspathic veinations are the common features that
characterise these enclaves. Having attained intermediate or acidic compositions, the charnockite shows
mostly gradational contacts with the host rocks granitoid gneiss.
Charnockite is medium green in colour, very coarse grained consisting mainly of blue quartz, green relic
pyroxenes, pale green feldspars and dark coloured hornblende and biotite. Weak to strong foliation exists,
not at the core but on the peripherals in the gradational contact with granitoid gneiss /leptynite.
Charnockite II is dark green in colour, uniformly medium grained consisting mainly of blue quartz, green
pyroxenes and feldspars. The body is generally massive but occasionally exhibits weak foliation. Minor
intrusions of quartz veins are common.
The general gneissosity and foliation in the gneisses and linearity of the bands are in the trend NW-SE
dipping around 50o south westerly. Though regional folding of the litho units is quite possible, yet the
evidences for the same have not been reflected as minor structures in the quartz and pegmatite veins are
along trends NW-SE, N-S and E-W.
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Four sets of joints are common in the litho units.
i) Longitudinal (with respect to the trend of the rock bodies) NW-SE dipping 70 south westerly;
ii) Transverse, N44-50E-S40-50W, dipping 80 south easterly;
iii) Oblique joint N65-70E-S65-70W, dipping 70 north northeasterly and
iv) N- S with vertical dip.
5.0 EFFECTS OF BLASTING
Globally, blasting is the principal method of rock breaking in mining and construction industry because of
its distinct advantages like economy, efficiency, convenience, ability to achieve large production, high
productivity and ability to break the hardest of the rocks. When an explosive or a blasting agent is
initiated, the chemical energy of it is converted into mechanical energy, which is used for breaking the
rock. Even in a properly designed blast, only a portion of the total energy of the explosive is used for
fragmenting and displacing the rock and the rest utilized in producing undesirable environmental and
other adverse effects like ground vibrations, fly rock, air overpressure (noise), air pollution, over-break
and production over size boulders making them an integral part of blasting. These undesirable effects
cause damage to the civil structures and other properties in the vicinity.
With increasing mining and construction activities in areas close to human settlements, ground vibration
has become a critical environmental issue as it can cause human annoyance and structural damage. The
adverse environmental effects produced by blasting cannot be totally eliminated, but effectively
controlled by proper design of appropriate controlled blasting techniques. Further, optimum design of
blast, based on scientific investigations relating to the explosives used, rock properties and other
geological aspects, which are site specific, can also address the issues.
5.1 Blast Induced Ground Vibrations - Background
Generally most of the explosive energy (left over after rock breaking), of blasting, is transmitted to the
surrounding rocks as elastic waves. As these waves travel, they displace particles in their path causing the
particles to oscillate before returning to their original positions. These oscillations constitute ground
vibrations. Special three dimensional seismographs are used to measure these vibrations in terms of
displacement, velocity, acceleration and frequency.
The ground vibrations generated from the blast are compressive in nature and spread away from the
blasting site in all directions like ripples spreading outwards when a stone is dropped in still water in a
pond or tank. When these waves reach a free face, they get reflected back and get converted into tensile
waves and cause breaking of rock (as rock is weak in tension). When no free face is available, they travel
to a longer distance and finally get attenuated. These waves, which are not doing any useful work of
breaking the rock, generate ground vibrations and cause damage to the surface structures like dams, canal,
residential buildings, etc. The ground vibrations have three mutually perpendicular components namely
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radial or longitudinal (R), transverse (T) and vertical (V). The R and T directions are oriented in
horizontal plane with R directed along the line between the blast and recording transducer.
5.2 Factors Influencing Blast Induced Ground Vibrations
Reviewing all the research and available literature, it can be seen that peak particle velocity (PPV) and the
frequency of the vibrations are the most important parameters over which the stability of the structures
depend. Peak particle velocity is defined as the greatest velocity with which the ground vibrates during
the vibration history and the same is measured in millimetres per second. Frequency is the number of
cycles of the to-and-fro movement of ground particles per second. The units for measurement of
frequency are Hz. The frequency of vibrations depends on the geology of the area, the rock type, etc.
When the frequency of the vibrations is equal to the natural frequency of the structures, maximum
damage occurs to the structure. The range of natural frequency of surface civil structures is given in
Table 1.
Type of Structure Natural Frequency, Hz
Single storey brick structures 12-14
Double storey brick structures 8 - 10
Concrete Structures 9 - 16
Table 1. Natural frequency of surface civil structures after Central Mining and Fuel Research
Institute (CMFRI), (Report 1991).
In addition, blast induced ground vibrations are dependent on many more factors like type of rock and its
properties, geological parameters, maximum charge per delay, strength of the explosive, distance of the
structure from the blasting site, time delay between holes and rows, priming sequence, sequence of blast
hole detonation, spacing between holes and burden, angle of drill holes, stemming depth and type, charge
length and diameter, confinement, blast geometry, total charge, etc. Amongst them, type of rock and its
properties, the charge per delay and the distance of the blasting site from the structures are the most
important ones. To keep the ground vibrations within desired levels, a clear understanding of the causes
or factors, which influence generation, and propagation of ground vibration is essential.
5.3. Permissible Limits of Blast Induced Ground Vibrations (PPV) For Surface Structures
The permissible levels of vibrations of various surface civil structures and other details specified by
Directorate General of Mines Safety (DGMS), Dhanbad and others are given in Tables 2 to 5.
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Type of structure
Max. Permissible PPV, mm/s
Dominant excitation frequency, Hz
< 8 8-25 > 25
(A) Buildings / structures not belonging to the owner
(i) Domestic houses/structures (kutchha brick &
cement) 5 10 15
(ii) Industrial buildings (RCC & framed structures) 10 20 25
(iii) Objects of historical importance & sensitive
structures 2 5 10
(B) Buildings belonging to the owner with limited span of life
(i) Domestic houses/structures(kutchha brick &
cement) 10 15 25
(ii) Industrial buildings (RCC & framed structures) 15 25 50
Table 2. Directorate General of Mines Safety (DGMS) (Tech) (S&T) Circular No.7 of 1997
Type of structure Peak particle velocity, mm/s
Frequency (40 Hz)
Modern homes, dry wall interior 18.75 50
Older homes, plaster on wood lath
construction 12.5 50
Table 3. USA Standard (after Siskind, et al, 1980)
Type of Structure Maximum Values
Historical building and monuments and building of special value 0.2 mm displacement for
frequencies less than 15 Hz.
Houses and low rise residential buildings, commercial buildings not
included below.
19 mm/s resultant ppv for
frequency greater than 15 Hz
Commercial buildings and industrial buildings or structural of
reinforced concrete or steel construction
0.2 mm maximum displacement
corresponds to 12.5 mm/s ppv at
10 Hz and 6.25 mm/s at 5 Hz
Table 4. Australian Standard 2008 (AS 2187.2)
Type of structure Peak particle velocity at foundation, mm/s
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5.4. Ground Vibration Predictor Equations
For effective prediction and subsequent control of ground vibrations, rock constants which are site
specific are determined for every site (by trial blasts) where blasting is to be carried out. These rock
constants are used in the predictor equation (Equation 1) to calculate the maximum explosive charge
per delay for a given maximum PPV the structure in question can tolerate without damage and the
distance between blasting site and the structure.
The tolerable PPV a structure can withstand (without damage) depends on the frequency of the vibrations,
type of structure, material used for the construction of the structure and the type of rock (soft or hard) on
which it is fixed.
For predicting ground vibrations, when both blasting and measurements are made on the surface, square
root scaled distance formula (Equations 1&2) is used (as per the DGMS (Tech.) (S&T) Circular No.7 of
1997) as it gives very reliable predictions of PPV to protect surface structures by limiting the vibrations to
the tolerable levels when maximum charge per delay is restricted.
= ()........... (mm/s) ... (1)
where,
V = Peak particle velocity (PPV), mm/s
SD = Scaled distance, m/kg
k and = Rock constants, which are site specific.
Where, SD is calculated by equation (2).
=
(m/kg) ... (2)
where,
D = Distance between the blasting site and the vibration monitoring station, m
W = Maximum explosive charge per delay, kg
A linear regression analysis between PPV (on the y-axis) and scaled distance (on the x-axis) is to be
carried out for the monitored data as per the DGMS guidelines; the best fit curve on log-log scale is to be
drawn to determine the rock constants k and for square root scaled distance formula. Linear regression
analysis is a statistical tool to determine the line of best fit through a distribution of points in a graph.
5.5. Blast Induced Fly Rock
When blasting is carried out, the rock gets fragmented and the fragmented material is moved away from
the bench and gets piled up as fragmented mass to enable loading by an excavator. In addition to this
desirable displacement of broken fragments, some stone pieces travel to certain distance away from the
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face resulting in scatter of the blasted muck pile and a few of them also project to a greater distance as
shown in Figure 2. This undesirable projection of stones is termed as fly rock. Fly rock is a serious
environmental hazard and is often a cause of fatalities and /or serious injuries to the people, cattle,
damage to the equipment, buildings and other property. Damage due to fly rock from blasting is one of
the main causes of strained relations between the mine management and the people residing, working or
passing by in the vicinity of blasting operations. This assumes prominence in mines having small
leasehold area (when the danger zone falls beyond the leasehold area) and when the quarry is shallow
with reference to the surroundings. These hazards become serious as the blasting rounds become bigger
with larger diameter blast holes, where fly rock of large sizes travel long distances.
Fly rock is caused by improper blast design. The important parameters, which cause fly rock problem, are
inadequate confinement of the explosive charge, high charge factor, decreased spacing and burden,
overcharging, inaccurate drilling, inadequate stemming, faulty delay timing including not using delay
detonators in multi-row blasting, improper initiation sequence, overlapping of delays, blast hole diameter,
bench height, inclination of holes, charge distribution in holes, loose rock lumps lying on the top of bench
or along slope, geological conditions like highly fractured and weathered rock and of course, human
errors like - carelessness and improper supervision. In addition, secondary blasting is also a major source
of fly rock and hence is to be avoided, wherever possible, or at least minimised by proper primary blast
design (considering the above stated parameters) using delay detonators in conjunction with inverse
initiation.
Figure 2. Fly-rock Generation
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5.6. Control of Fly-Rock
Fly rock can be controlled by judicious selection of blast parameters mentioned above based on
experience and calculations using certain empirical formulae developed from the site investigations.
The fly rocks produced during the blasting can be controlled by adopting the following measures:
Proper blast design and its implementation.
Careful inspection of site before laying out blast holes and deciding the drilling pattern to
be adopted based on the bench geometry.
Drilling in accordance with the requisite blast design.
5.7. Blast Induced Air Blast / Noise
When blasting is done, a loud noise is heard which is known as air blast. Air blast, however, is not simply
the sound that is heard. Just as blast vibrations are transmitted along the ground from the explosive
charge, Air blast is a pressure wave transmitted through the atmosphere from the blast site. As mentioned
earlier, the part of the explosive energy escapes into the atmosphere. This air blast produced by the
explosion is transmitted away from the site of blasting in the form of a wave. This wave travels at the
speed of sound pressure wave. The higher frequency portion of the pressure wave (20 Hz to 20,000 Hz) is
audible sound. While the lower frequency (below 20 Hz) portion is not audible, it excites structure, which
in turn causes a secondary and audible rupture within the structure. Unlike ground motions, air blast can
be described completely only with one transducer, since at any one point air pressure is equal in all three
R,T,V directions.
Blasting vibration are normally accompanied by an air blast wave causing a primary noise itself and
also giving rise to secondary noise, due to rattling of window panes, etc. Human response to a blast is
often more intense inside than outside a structure. This difference may be caused by the sound produced
inside the structure bye structure itself. There probably is due to the fact that the standard for limiting the
air blast due to mining are not important, as the charge contributing damage due to air blast is much
higher than for limiting the ground vibration. Hence, in a normal blast when ground vibration are limited
to safe value the over-pressure created due to air blast is automatically restricted within the safe limits.
Table 6 gives the current air blast limits in USA.
Air blast shall not exceed the maximum limits listed in Table 6 at the location of any dwelling,
public building, or community or institutional building outside of permit area
Lower Frequency Limits(Hz) Response Peak Sound level(dB)
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Air blast is an increased pressure wave consisting of high frequency sound that is audible (from 20
Hz to 20 kHz) and low frequency sound or concussion (less than 20 Hz) that is sub-audible and cannot be
heard. Although air blast seldom causes structural damage but sudden loud noise causes psychological
fear in the nearby inhabitants and in some cases even breakage of window panes have been reported. Air
blast is influenced by type and amount of explosive, adequacy and type of material for stemming,
direction of blast and meteorological conditions. The main cause of noise is the energy released in open
air by the initiation system and inadequate stemming column, burden etc.
Air blasts are produced either by the direct action of the explosion products from the unconfined
explosive (like, detonating cord) in air or by over charging of explosive in a shot hole. The waves
produced by the effect of blasting increases the air pressure from ambient pressure to peak and drops to
negative (i.e., below ambient pressure) slowly. Its travel thereafter is governed by air temperature, wind
direction & speed, and the presence of obstructions in the form of buildings, vegetation, and ground
contour. Hence, blasting is to be avoided when the wind is blowing towards a critical structure, proper
orientation of the face with reference to the joint pattern of the rock mass.
5.8. Human Perception
Human beings are very sensitive and can detect even very low level of vibrations (as low as 0.5 mm/s)
which can not cause damage to the structures. Vibration levels lesser than the ones that cause damage to
the structures could cause rattling of doors or windows. Many a times, the slamming of a door or passing
of a loaded lorry by the side of the house generates more vibration than a quarry blast. However, residents
become alert and inquisitive by noise and rattling of objects in the immediate surroundings due to blasting
in the neighbourhood and start looking for the damages to the structures like cracks in the walls in their
residence. Finding a crack that existed even before blasting activity commenced in the neighbourhood,
but not noticed, people start worrying attributing the crack to blasting activity.
Human sensitivity gets triggered by vibrations and air blasts and becomes inquisitive and suspicious about
them from a blasting activity in the vicinity reaching the structure and resulting in some form of damage
to it. The tolerance and reactions of humans to vibrations vary from person to person, the nature of the
work he/she is doing, the environment in which they are present at the time of blast, etc. Blast induced
ground vibrations may result in annoyance and interference with work proficiency.
6.0. CONTROLLED BLASTING TECHNIQUES
As on date, many blasting techniques are available to control the adverse effects of blasts. However, the
selection of suitable technique primarily depends on the adverse parameter(s) of the blasting to be
controlled. Some of the common techniques are limiting the maximum charge per delay, line drilling, pre-
splitting, cushion or smooth blasting, air decking, muffling, etc. Out of these, the first one i.e. restricting
the explosive quantity per delay is to be adopted for designing the controlled blasting technique in the
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present case to protect the dam, canals and the residential structures in the villages. Also, the techniques to
achieve this include
1. Reducing the quantity of explosive blasted at each moment of time by adopting delay blasting
technique.
2. Selecting optimum delay interval between two successive shots or groups of shots.
3. Optimising the blast design parameters, viz. spacing, burden, length of the hole, charge factor, etc.
4. Use of low strength explosives (explosives having less velocity of detonation).
5. Reduced charge concentration by using less density explosives in small diameter drillholes.
6. Use of small diameter explosive charges (cartridges) in a large diameter holes (de-coupled
charges).
7. Use of air bags in the shot holes.
8. Decking of explosives.
9. Select and use appropriate explosives and accessories suitable for the ground conditions
prevailing at the site.
10. Select the appropriate charge factor (specific charge).
11. Select the maximum charges per delay based on the distance of the structure to be protected from
the blasting site.
12. Select the appropriate delay interval between holes in the same row and rows of the holes.
7.0. BLAST VIBRATION MONITORING INSTRUMENTATION (INSTANTEL DSS-077)
7.1. Instrument Description
The instrument used for monitoring blast-induced vibrations was Instantel DSS-077 Minimate that
provides tri-axial transducers for recording the blast vibration in the three R, T, V direction as mentioned
above and also consists of microphone for recording the sound pressure levels. Minimate is an extremely
powerful PC compatible computer based system with an built memory and incorporates 4 lines by 20-
character liquid crystal display. The seismography is capable of recording particle velocity in the range of
0 to 127 mm/s and the microphone in the range 100-142 dB. The software with instrument combines the
ease-of-use with Windows Operating System. The software module provides for copying, viewing,
analysis and printing. The software also provides for determination of scaled distance, linear regression
analysis and allowable charge for specified distance. The instrument is simple, light, compact, easily
portable, battery operated and user friendly.
8.0 INITIATION SYSTEMS
There are a number of initiation techniques which can be used for supplying necessary energy to a
column of explosive and thereby initiate the detonation process. The following initiation system is
suggested for the present case.
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8.1 Electrical Initiation
8.1.1 Advantages of Electric Initiation System
Each detonator and the entire round can be checked for electrical connectivity with an Ohm meter
before the round is fired.
As opposed to fuse initiation, the time of detonation is always under control.
No damage is done to the stemming column.
Delay blasting can be effectively carried out.
No surface noise
Occurrence of misfires in the blasting can be minimised.
System is cheaper and safe.
8.1.2 Disadvantages of Electric Initiation System
Electric blasting should not be carried out in the presence of extraneous electrical hazards of 0.06
amps or more. The principal sources of extraneous electricity hazards are:
Lightning
Static electricity
Stray currents: possible sources include electrical equipment, power transmission lines
Galvanic electricity
Electromagnetic induction: e.g. power lines
High voltages such as static electricity caused by severe snow or dust storms can initiate even
non-electric detonators.
8.2 Electric Delay Detonators
Initiation by Short Delay Electric Detonators is simple and quick to hook up and allows row by row or
any other desired firing sequence providing adequate relief resulting in good fragmentation and
controlling the ground vibrations. Use of Electric Delay Detonators (Figures 3 & 4) have the following
advantages.
8.2.1 Advantages of Electric Delay Detonators
The system of connecting up the blast holes is simple, reliable and swift, in order to promote fast,
safe and reliable blasting.
It controls the application of explosive energy during the detonation of the blast resulting in better
fragmentation.
It also controls explosive energy release at any point of time by firing the total explosive charge
at different points of time (based on the delay timing selected by the user) which provides relief
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and controls displacement of rockmass resulting in reduced ground vibrations and air blast along
with minimising overbreak and flyrock.
It enables maximum explosive energy utilisation in breaking the rock effectively and hence
reduces explosive consumption.
It improves productivity and reduces cost.
The system can result in appreciable time-saving in the loading/connecting up procedure.
The initiation system with Electric Detonators offer a primer system with a simple and safe in-
hole delay technique and allows firing decked charges with each deck fired on a separate delay.
Cheaper than Non-Electric Initiation system (shock tubes).
Often electric initiation system components are combined to give a larger selection of delays and
specific delay times.
Figure 3. Electric Delay Detonators
Figure 4. Electric Delay Detonators Constructional features
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The circuit test capability allows positive checking for proper hook-up.
They are noiseless on the surface as it eliminates the usage of detonating fuse on the surface.
Noise and associated public relations problems are reduced by initiating the charge in the
borehole with a blasting cap instead of using trunk lines and down lines of detonating fuse.
It reduces the air blast, ground vibration and dust generation from the blasting.
8.2.2 Disadvantages of Electric Delay Detonators
No protection against stray currents from DC power sources.
No protection against stray currents from AC power sources.
No Protection against electrostatic energy.
No Protection against radio frequency energy.
No Protection against current leakage.
Mishandling of the electric detonator can cause accidental firing hazards.
Costlier than detonating fuse and cap initiation system
9.0. METHOD OF QUARRYING
The rough stone quarry in Thovalai village of Erachakulam Taluk, Kanyakumari District is carrying out
mining by drilling 35 mm diameter holes with pneumatic Jack hammer drills and blasting with 32 mm
diameter cartridge explosives. The blasted material is being transported by dumpers/ trucks/ tractors after
loading it by backhole type of excavators or manually. The mine management is presently adopting
blasting of multiple rows of holes and firing them by detonating with millisecond electric delay
detonators. The residents of the surrounding villages were complaining about the blast induced ground
vibrations and fear that these vibrations may cause damage to the surrounding residential buildings in the
vicinity. The present scientific study is in response to the request made by the Lease Owner Mr. S.M.
Lucas of Kanyakumari District to investigate into the impact of blasting with explosives in the vicinity of
quarry.
10.0. SITE INVESTIGATIONS
The vibration studies were carried out on 2nd
of June 2013. Totally 3 blasts were conducted and the
vibrations are monitored at 6 different locations simultaneously for every blast. The details of the
observation stations are shown in Figure 5. The burden to spacing was 1.5mx1.5m with rectangular
pattern for V type of initiation pattern. The explosives used are SUN 90.
11.0 OBSERVATIONS AND DISCUSSIONS
The Q.L. area is located at a distance of 370 m north of the Sun College of Engineering and Technology
and is 240 m away from the nearest residential building. The blast details and details of the vibrations
recordings observed during the monitoring given in the Tables 7&8 and in Annexures 1 - 6. The
maximum vibration recorded is 0.381 mm/sec with the corresponding air blast value of 106 dB at
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station 2A. The monitoring point set up at the location very nearest has received the peak vibration of
0.191 mm/sec, with air blast value of 115.6 dB at 1A.
Location - S.F. No. 118/7
No. of
Blast
No. of Drill
Hole Per blast
Depth of
each hole
(m)
Spacing (m) Diameter of
each hole
Max. Charge per
delay (Kg)
3 40 1.5 1.5 35 mm 2.5
Explosives used for each of the above three blasts
SUN 90 2 cartridge per hole Each 125 gm 40 x 2 x 125
Total weight of explosive per blast 10 Kg
Electric detonators = 1, 5, 7, 9
Table 7. Details of blast hole parameters and explosives used during investigation at S. F. No. 118/7
Blast
No. Instrument
No. Station Date/Time
Tran
Peak
(mm/s)
Vert
Peak
(mm/s)
Long
Peak
(mm/s)
Mic
Peak
(dB)
Total
explosive
(Kg)
Dist.
(m)
Location
1.
4687 1A 02.06.2013
16:29:45 0.127 0.191 0.0635 115.6 10 235
Pond (SW
direction)
4688 1B 02.06.2013
16:29:48 0.381 0.254 0.381 106.0 10 180
Mine
Office
2.
4687 2A 02.06.2013
16:35:48 0.0635 0.191 0.0635 114.0 10 244
Pond (SW
direction)
4688 2B 02.06.2013
16:36:14 0.191 0.0635 0.254 106.0 10 180
Mine
Office
3.
4687 3A 02.06.2013
16:40:13 0.127 0.127 0.0635 112.0 10 197
Pond (SW
direction)
4688 3B 02.06.2013
16:40:13 0.0318 0.127 0.191 109.5 10 180
Mine
Office
Table 8. Blasting details and blast induced vibration observation details at S.F. No. 118/7
12.0 DATA ANALYSIS
Three rounds of blast were conducted on the 2nd
June 2013 to study the effects of blast induced vibration
at rough stone quarry situated at S. F. No. 118/7 of Mr. S. M. Lucas in Erachakulam Village of Thovalai
Taluk, Kanyakumari District. Forty holes were used for each blast. The distances of measuring stations
varied from as low as 180 m to as high as 244 m from the blast site. The depth of holes varied from 1.4 m
to 1.5 m. Millisecond delay detonators were used with four different delays numbering between 1 to 9.
The maximum explosive used during a single blast did not exceed 10.00 kg for 40 holes at a time. Out of
the 6 recordings, the maximum peak particle velocity was 0.381 mm/sec and the highest peak sound
17
pressure level recorded was 115.6 dB. The details of the blasts are given in Annexures 1 6. The scaled
distances based on the 6 blasts and 6 observations are analysed and the results are shown in Table 9 and
Figure 6.
Figure 6. Regression line for the blast induced vibrations surrounding the rough stone quarry.
Distance (m) Weight (Kg)
(Charge/delay)
Distance (m)
Weight (Kg)
(Charge/delay)
25 0.0801 400 20.50
50 0.320 425 23.10
75 0.721 450 25.90
100 1.28 475 28.9
125 2.00 500 32.00
150 2.88 525 35.3
175 3.92 550 38.8
200 5.12 575 42.4
225 6.49 600 46.1
250 8.01 625 50.0
275 9.69 650 54.1
300 11.50 675 58.4
325 13.50 700 62.8
350 15.70 725 67.3
375 18.00 750 72.1
Table 9. Scaled distance for maximum safe charge and peak particle velocity of 2.5 mm/sec
18
13.0 CONCLUSION AND RECOMMENDATIONS
Ground vibrations are an integral part of rock blasting. The wave motion set up in the ground spread
concentrically from the blast and attenuate as it spreads. In the nearby region, the vibration can cause
damage to structures if the peak particle velocity exceeds the threshold limits as given in DGMS Circular
No. 7 of 1997 dated 29/08/97 (Table 2). Hence, it is necessary to determine whether the levels of
vibrations are within the permissible limits or not.
The quarry owner was instructed to blast as per their original practice with reference to number of holes,
quantity of explosives and blasting pattern. Three trial blasts were conducted at the rough stone quarry at
S.F.No.118/7 of Mr. S. M. Lucas in Erachakulam village, Thovalai Taluk, Kanyakumari District and 6
monitoring stations observed to assess the effect of blasting in the vicinity of quarries and on neighboring
buildings. The monitoring stations were in the vicinity of quarry, structures, canal. The details are given
in the Photos 1 to 2.
The scaled distance table can be used to calculate the amount explosive i.e., charge per delay to be used
based on distance at which the structure is to be protected. For example, for structure at 100 m the charge
per delay should not exceed 1.28 kg. The details of permissible limits for different structures
(RCC/brick/cement/historical) are given in the Table 2.
The following conclusions are drawn:
1. The maximum vibration level recorded as peak particle velocity was 0.381 mm/s at a distance of 180 m
away from the blast site with a peak sound pressure level was 106.0 dB.
2. The PPV values (Table 8) fall well below the threshold statutory limits (as stipulated by the DGMS
circular No. 07 of 1997 dated 29/08/1997) to cause any concern to the nearby structures or villages.
3. The blasts were observed indicating that there were not many flying fragments or fly rock, the smoke
emissions are minimal. It is recommended that any future blasting operations should be in line with the
test blasts conducted on 2nd
June 2013.
4. Since much of the blasting is on the top of the hillock, muffelled blasting is suggested.
5. There was no effect of blast vibrations in the vicinity within 244 m during present study. The
quantity of explosives used should be 10.00 kg per blast with four different delays.
6. Keeping this in view, it is suggested that all future blasting operations may be allowed to continue in a
similar manner, i.e., in terms of blast design, quantity and type of explosives used on 2nd
of June 2013.
Any increase in usage of explosives to enhance production requirement may require further studies to
ascertain the safety of use of explosives.
7. The District authority should ensure that no increase in quantity of explosives or change in pattern of
blasting by the quarry lessees.
19
Annexure 1. Event Report at the Monitoring Station 1A
20
Annexure 2. Event Report at the Monitoring Station 1B
21
Annexure 3. Event Report at the Monitoring Station 2A
22
Annexure 4. Event Report at the Monitoring Station 2B
23
Annexure 5. Event Report at the Monitoring Station 3A
24
Annexure 6. Event Report at the Monitoring Station 3B
COVER (2)COVER PAGEContentsVargees REPORT