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5/28/2018 Opencast Quarries

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Vibration Assessing MethodsGuido Alfaro Degan, Dario Lippiello, and Mario PinzariDepartment of EngineeringUniversity ROMA TRE, Roma, Italy

Abstract. The proposed work is a prediction of the propagation of seismic waves

induced by the cultivation of quarries through the use of explosives. The paper is

divided in two different stages: first of all it is necessary to choose, among the

various explosives for industrial use and all possible blasting designs, the one with

which it would be possible to get an embraceable result from the industrial point

of view and with the minimal possible forecasted disturbance for the buildings

present in the surrounding areas (receptors); as a second step it was found, with

the simulations, the indicative values (for different distances) for the peak particle

velocity (PPV - peak particle velocity). In order to work with the values as real as

possible, we used the data contained in a draft E.I.A. (Environmental Impact

Assessment) of the Lazio Region, regarding the project of a quarry. The optimal

blasting design choice was made considering that a substantial amount of the work

has to be spent at thefoot of each blastholes; therefore, we considered two

different types of plughole, one obtained with two different diameters of drilling

(the larger for the lower portion of the blasthole) containing only one type ofexplosive, and another one having the same diameter along its entire length, but

containing two different types of explosives.

Obtained the mine parameters (blasting design), the peak particle velocity

(PPV) and its trend was determined, assuming an exponential decaying of the

mathematical functionf = PPV(t). At the conclusion of the paper "iso-PPV"

maps were created regarding the quarry adjacent area.

Keywords: Vibration assessment, blasting design, PPV forecasting methods.

1 ForewordQuarrys Drill and Blast planning consists first of all, in creating the right blast

pattern in order to obtain a prefixed value of productivity. According to data

contained in a Lazio Region E.I.A. draft, it was possible to arrange the optimal

design choice, purposed to minimize the forecasted PPV values in an adjacent

amenable area (figure 1 below shows a particular of the Technical Regional Chartn. 364040, Lazio, Italy).254Fig. 1 The quarry location an

Once obtained the bla

assumed to achieve the e

working with parallel pa

choice, it was calculated t

trend as a mathematical ti

2 The Quarry PrThe present work refers a

(Viterbo, Italy), where th

stone. As for its lithology

alternation of pyroclasticWhinstone quarries gen

1) Hill-side quarries

excavated material fr

(lower down the slope

2) Open-pit quarries

of the processing plan

Hill-side quarries ma

excavation has reached, a

The choice of whethe


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usually dictated by the

structure and environmen

features and have a high v

It is assumed that, for t

identified and is consider

technological, environmeG. Alfaro Degan, D. Lippiello, and M. Pinza

nd the adjacent protected area (right side)

asting parameters with specific computer codes, it wa

nforced productivity value (817 m3 of ore per day) bot

anels and with serial ones; according with the differen

the provisional peak particle velocity (PPV) value and i

ime depending function.

rojectabout a whinstone quarry project, located near Setteven

hey will extract whinstone for the production of crushe

y the area is made up of major volcanic complexes wit

products and lava flows.

nerally take one of two forms:

characterized by a general downward haulage o

rom the quarry area (up slope) to the processing plane);

where quarrying workings are generally below the lev

t and excavated material is hauled up and out of the pit.

ay often become open-pit quarries once the level o

nd subsequently extends below, the quarry plant area.

er a hill-side or open-pit operation is contemplated

e site topography, ownership boundaries, geologic

ntal considerations (hill-side quarries can be very obviou

visual impact).

the purposes of this paper, a hard-rock resource has bee

red suitable for quarrying subject to the usual economi

ental and legislative matters being satisfied. From th

arias

th

nt

its

ne

ed

th

of

nt

el

of

is

alus

en

ic,

hisOpencast Quarries: Vi bration Assessing Methods 255

point of view, quarry management planning will be assumed, according with a

simple scheme in which the whinstone is extracted using explosives. Loose

materials are captured with diggers and sent to a crushing and sifting plant. In this

phase materials are processed and then loaded into trucks for road transportation.


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3 Ore Description: The WhinstoneWhinstone is a term used in the quarrying industry to describe any hard darkcoloured

rock. Examples include the igneous rocks basalt and dolerite as well as

the sedimentary rock chert. The name 'whin' derives from the sound it makes when

struck with a hammer. It is used for road chippings and dry stone walls, but its

natural angular shapes do not fit together well and are not easy to build with, and

its hardness makes it a difficult material to work.Whinstone is an igneous rock, which formed as the volcanic molten magma

cooled. Being such hard, resistant rock, dolerite stands out as prominent cliffs or

crags.

In modern times whinstone has been extensively quarried to be used in the

construction of roads.

Whinstone is an extrusive igneous volcanic formed from the rapid cooling of

basaltic lava. By definition, it is an aphanitic igneous rock with less than 20%

quartz and less than 10% feldspathoid by volume, and where at least 65% of the

feldspar is in the form of plagioclase. Whinstone is usually grey to black in colour,

but rapidly weathers to brown or rust-red due to oxidation of its mafic (iron-rich)

minerals into rust. It almost always has a fine-grained mineral texture due to the

molten rock cooling too quickly for large mineral crystals to grow, although it can

sometimes be porphyritic, containing the larger crystals formed prior to the

extrusion that brought the lava to the surface, embedded in a finer-grained matrix.

Whinstone with a vesicular or frothy texture is called scoria, and forms when

dissolved gases are forced out of solution and form vesicles as the lava

decompresses as it reaches the surface.

4 Drill and Blast Design and the Forecasting ModelThe purpose of blasting operations is rock fragmentation. It provides appropriate

rock material granulation or size that is suitable for loading and transportation.

The blasting process and usage of explosives, however, remain a potential source

of numerous human and environmental hazards. Several studies indicate that

fragmentation accounts for only 20-30% of the total amount of explosive energy

used. The remainder of the energy is wasted away in the form of ground

vibrations, air-overpressure and flyrock. All of them can, under some

circumstances, cause damage to structures nearby and, apart from this, be the

source of permanent conflict with inhabitants who live close to the operation.256 G. Alfaro Degan, D. Lippiello, and M. Pinzari

Ground vibrations can be considered as acoustic waves that propagate through

the rocks. They differ from the round vibrations caused by earthquakes in terms of

seismic source, amount of available energy and travelled distances. Usually,

parameters such as velocity, displacement and acceleration of particles are

recorded during the vibration measurements, but several studies achieved that the

most important parameter, that has to be studied, is the Particle velocity. Many

scientists and engineers investigated on PPV prediction considered to be the

maximum velocity in any of the components and also on the peak vector sum

(PVS) that is the true vector sum of the three components. The first significant

PPV predictor equation was proposed by the United States Bureau of Mines.

There are also modified predictors from other researchers or institutions such as

Langefors and Kihlstrom, Ambraseys, Indian Standard, Ghosh and Daemen, PalRoy of CMRI, etc. However, the PPV predictor established by USBM is still the

most widely used equation in the literature. To the knowledge of the author, no

work has been reported in the literature that addresses the application of

geostatistical approach for the estimation of ground vibration.

4.1 Frequency of Ground VibrationThe dominant frequency of ground vibration was determined through the

developed forecasting software. The range of observed frequencies for different

mines and blasting projects varies between 5 and 40 Hz.

The provisional adopted formula assumes frequency decreases with distance:


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f = (Kf logR)-1 (1)

Where f is the frequency, R is the distance from the blasting hole (m), Kf is a

constant that takes into account the ground characteristics (tab.1).Table 1 Values of Kf in function of the ground characteristics

Ground KfSands and waterlogged soils 0,110,13

Middle hardness 0,060,09

Hard rocks 0,010,03

Studies [1] refer that the frequency is confined within 5-60 Hz in spite of

differing blast geometries and used explosives. In spite of the differing blast

geometries and the explosives used, blasts in coal, lignite and iron ore mines

produced low frequency. Relatively higher frequencies were found in case of

limestone quarries and construction projects. It is therefore inferred that large

blasts using higher bench heights and larger diameter blastholes are more likely to

produce lower frequency of ground vibration.Opencast Quarries: Vi bration Assessing Methods 257

The lowest frequencies were associated with coal mine blasting, intermediate

with quarry blasting and high frequencies with construction blasting.

4.2 PPV ForecastingTo assess the PPV it has been used the arrangement of an important Italian

theoretical model [2]. This model considers that the seismic energy transmitted tothe rock by the explosive can be evaluated with the two following equations:

Es = 2 2 f2 2 Ds2 r Vc Tv 10-6 (2)Es = nt n1 n2 ET Q (3)Where:

A = displacement (m), f = Frequency (Hz), D S = Distance from the blasting

point (m), r = Density of the rock(kg/m), VC = Seismic velocity (m/s), TV =Duration of the vibration (s), n= Breaking factor (charges laid on the ground

n0.4), ET =Energy per unit of mass, Q =

amount of explosive. nand nare respectively the impedance factor and coupling

factor, represented by the following formulas:

n1 = 1 - [(ZeZr (Ze + Zr ] (4)n2 = 1 / (ED/d (5)Where:

Ze = impedance of explosive (kgms), Zr = impedance of rock (kg ms),

D = blasthole diameter (mm), d = charge diameter (mm). From previous equations

the following is obtained:

A(m/s2) = [(nt n1 n2 ET Q 10-6 4 f2 Ds2 r Vc Tv] (6)As the significative duration of vibrations is considered to be five times the

period:

TV = 5 TS = 5 / f (7)

According to the equation (1),f = (Kf logR)-1, the equation (6) can be written

as follows:

A(m/s2) = [(nt n1 n2 ET Q Kf logDS 6 Ds2 r Vc Tv] (8)And integrating,

V(m/s) = (Q/DS) [(nt n1 n2 106 Kf logDS r Vc] (9)258 G. Alfaro Degan, D. Lippiello, and M. Pinzari

5 Blasting DesignIt has been found that the type of explosives has significant influence on ground

vibration [1]. Hossaini and Sen [3] have found that ANFO generates lesser

vibration than slurry explosives. Among the different blends tested, it was found


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that the explosive with lower density and lower detonation velocity produced

lower level of ground vibration.

As the shock energy component of an explosive gives rise to unwanted

vibrations [4], explosives having larger portion of gaseous energy should be

preferred.Table 2 Explosives technical characteristics

Explosive [Kg/m3]

Impedance

Ie

Energy per kg

[MJ/kg]

GOMMA A 1550 11,63 6,74

GELATINA 1 1450 9,50 4,52

GELATINA 2 1420 8,66 4,44

SISMIC 2 1550 10,23 4,00

IDROPENT D 1550 12,25 7,47

PROFIL X 1200 3,89 2,66

TUTAGEX 210 1150 4,83 3,52

TUTAGEX 110 1150 4,60 2,79

VULCAN 3 1050 4,73 3,90

CAVA EXTRA 2 1050 4,78 4,31CAVA 1 1000 3,80 4,16

ANFO 5 800 1,84 3,66

5.1 Bl asthole DesignAccording to results obtained, it was found that the best issue can be reached

using two different quantity of explosives. The first explosive should be used to

charge the upper part of the blasthole (column area) and the second one to charge

the lower portion of the hole (foot area).

The lower portion of the blasthole, indeed, will be charged with a greater

quantity (kg) of explosives according to the equations (8) and (9):

QFoot = ( / 2)2 V e (10)QColumn = (c/ 2)2 H - V - b) e (11)Opencast Quarries: Vi bration Assessing Methods 259

This design choice (two different quantity of explosives) is coerced, according

to the occurrence that it is necessary develop a different amount of energy in the

lower part of the blasthole (foot portion), especially in case of sub-drilling

perforation.

The same result, indeed, can be obtained even using two different explosives

with different specific characteristics (density, detonation velocity, energy per kg

etc.).

5.2 Inf luence of Delay In terval on PPVUsing a combination of single hole waveforms and computer simulation, the

influence of delay interval was investigated. It is found that the delay of 25-35 ms

produces the lowest vibration in term of PPV propagation. We can say that this

agrees with the mines practice [5].

6 ConclusionIn order to respect the daily imposed productivity (817 m3) it was calculated (even

on the base of the geological site characteristics) that it is necessary to drill at least

56 blastholes. Those holes can be subdivided in two different blasting (benchs) of

28 holes each (single panel case study) or in 5 different blasting of 11 holes (case

of parallel panels).

Figure 2 and 3 show the PPV forecasting for the two cases (single panel,

parallel panels).Fig. 2 PPV Forecastingsingle panel case


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260 G. Alfaro Degan, D. Lippiello, and M. Pinzari

Fig. 3 PPV Forecastingparallel panels case

7 Discussion: Most Significant Study Findings1) This study identifies the blast design parameters that can be suitably modified

to control peak particle velocity (PPV).

2) When predicted or monitored vibrations exceed the statutory limits, ground

vibrations are to be controlled by modifying the blast design parameters.

Digging trenchs between the blast and the structure can further reduce ground

vibration seems to be a feasible solution. Numerical simulations show that the

percentage of reduction obviously depends on the trench depth to blasthole

depth ratio (at a ratio of 1.2, PPV value was reduced by 53%).

3) The PPV forecasting method shows its always preferable the productivity

process with parallel panels.

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