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.

4

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.

6

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

7

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

8

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

9

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)

10

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

11

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

13

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

14

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

16

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

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