wyznaczanie bloczności skał węglanowych w złozach

PUBLS. INST. GEOPHYS. POL. ACAD. SC., M-29 (395), 2006
Calculation of Block Divisibility Using Structural
and Refraction Seismic Methods
in Dębnik and Imielin Raw Material Deposits
Zbigniew MIRKOWSKI, Radosława TOMASZEWSKA and Adam IDZIAK
University of Silesia, Faculty of Earth Sciences, Department of Applied Geology
ul. Będzińska 60, 41-200 Sosnowiec, Poland
Abstract
The structural research was done in the Silesian-Kraków Upland in two
open-cuts of building stone: Dębnik (limestone) and Imielin (dolomite). As a result of the investigations, the directions of fracture systems were delineated and
block divisibility was calculated, as principal parameters in the documentation of
building stone.
Simultaneously, geophysical methods were applied using shallow seismic
refraction. According to the azimuthal velocity of wave propagation, the orientation of fracture was estimated. In Dębnik a strong anisotropy of seismic waves
occured and there was an excellent correlation between structural and seismic
measurements, whereas in Imielin this correlation was rather weak, which was
probably caused by using explosives for mining in the open-cut. The calculation
of block divisibility using a seismic method was not possible in this case.
1. Description of Research Area
Dębnik and Imielin raw material deposits are situated in the southern part of the
Silesian-Kraków Upland. They belong to different structural formations: the Dębnik
anticline which is built of Paleozoic deposits of the Kraków-Lubliniec zone, and the
Imielin monocline, which includes the Mesosoic formation of the KrakówCzęstochowa Monocline (Fig. 1). The Dębnik deposit is composed of dark grey to
black Devonian limestone, mostly granulated as well as crumbly and pelitic limestones with wavy beds (Bednarczyk and Hoffman 1989). Dębnik limestones (Dębnik
“marble”) were used as famous and prized decorative building stones for a few centuries. At present, the quarry in Dębnik village is idle, though some blocks of stone are
sometimes manually excavated. The Imielin deposit is composed of yellow and grey
Triassic dolomite which is a massive and fine-grained structure (Smulikowski 1946).
The open-cut in Imielin works and it is a significant producer of crushed stone. In the
past, blocks of stone were occasionally excavated at this site.
0
5 km
Trzebinia
Dębnik
Chrzan ów
Imi eli n
Krzeszowice
Devonian
Carbonifer ous
Permian
Me sozo ic
main faul ts
Neogene
Fig. 1. The geological map of the Silesian-Kraków region with measurement site locations
(after Gradziński 1972).
2. Block Divisibility and Structural Measurements
The definition of block divisibility has two meanings – in a geological and a
mining sense (PN-88/B-04120). Geological block divisibility is characterized by rock
materials in an outcrop or a bore-hole profiles. Mining block divisibility is the output
of stone blocks in all materials excavated in an open-cut. Mining block divisibility is a
principal parameter for using rocks as a building stone and is applied in geological
documentation of the deposits. Block divisibility is calculated according to structural
measurements using the formula (Bromowicz and Karwacki 1982):
b = Px i Py i Pz i100%
where Px, Py, and Pz are the probabilities that x-, y- and z-dimensions are higher than
or equal to the limit. The dimension probabilities are shown in the diagram of cumulated frequency. When the three main fracture sets are not perpendicular to each other
(blocks are non-orthogonal) the correction coefficient must be used:
k = f (d , β )
where d is the form index and β is the angle deviation.
The structural measurements were done by using a compass along a perpendicular line on the wells of the open-cut. In the Dębnik deposit two main fracture sets were
observed: A – in azimuth range of 130-160o (average 144o) and B – 30-80o (Fig. 2).
The fracture of the B-set is composed of two secondary sets of fractures: B1 – 30-40o
(average 32o) and B2 – 50-80o (average 63o). This is a typical case for anticlinal forms.
Dimensions of the average block from this deposit were 121 cm × 127 cm × 57 cm
and the volume of this block was 0.88 m3. In the Dębnik deposit, blocks of stone have
a non-orthogonal shape, so in this case a correction coefficient must be used and thus
the block volume is 0.6 m3. The marginal volume of the block for this type of limestone established by Polish standard PN-B-11200 is 0.25 m3. The block divisibility in
Dębnik is equal to 41%.
N
1212
%
0
1010
B
88
66
44
n = 73
22
90
0
A
180
S
Fig. 2. Rose-diagram of fractures in the Dębnik deposit.
In the Imielin deposit two distinct directions of fracture occurred: 120-160o (average 144o) – system A and 40-80o (average 53o) – system B (Fig. 3). The block from
this deposit has average dimensions of 134 cm × 132 cm × 124 cm and its volume is
2.2 m3. The marginal volume of the block for dolomite is 0.3 m3 (PN-B-11200). In the
Imielin deposit, block divisibility is equal to 84%.
3. Method and Analysis of Seismic Measurements
Seismic measurements were performed using a Terraloc MK6 (ABEM) seismograph. Measurement points were set up inside the quarry in Dębnik and outside the
open-cut in Imielin. The oriented profiles were 36 m long in Dębnik and 44 m long in
Imielin. The seismic waves were induced using a hammer. Shot-points were located at
the initial, central and final points of the measuring profile. After each measurement
cycle the profile was rotated by 20o.
N
0
1212
%
1010
B
88
66
44
22
n = 133
90
0
A
180
S
Fig. 3. Rose-diagram of fractures in the Imielin deposit.
As a result of seismic measurements the values of the seismic wave velocity (Vp
and Vs) were interpreted for each profile (Table 1). In the Dębnik deposit, wave velocity varied and the maximum of Vp (2626 m/s) was obtained for profile direction of 40o,
whereas the maximum of Vs (1726 m/s) was at 60o. The velocities of seismic waves in
Imielin are considerably less than in Dębnik, the maximum of Vp (1462 m/s) was at
60o and Vs (940 m/s) was at 40o.
T ab le 1
Velocities of seismic waves in the Dębnik and Imielin deposits
(Vp – velocity of longitudinal wave, Vs – velocity of distortional wave)
Azimuth
0o
Dębnik
Imielin
Vp [m/s]
Vs [m/s]
Vp [m/s]
Vs [m/s]
2372
1328
1218
744
o
1978
1018
1346
706
o
2626
1466
1424
940
o
2406
1726
1462
876
o
20
40
60
80
2520
1228
1390
888
o
1958
1130
1296
732
o
2170
1476
1184
782
o
2224
1252
1068
548
o
1412
992
1158
778
100
120
140
160
The velocity of wave propagation is strongly determined by direction of fractures in the rock mass and this phenomenon has been described in many papers (i.e.,
Crampin 1976; Oda 1984; Marcak and Mortimer 1986; Idziak 1988, 1992). The maximum velocities of seismic waves conform to the main directions of set fractures. Thus,
in Dębnik (Fig. 4) three strong maxima of velocity of seismic wave (of Vp in particular) occured, that conform to the three main directions of fractures: 40o, 80o and 140o.
A comparison of these directions with the orientation of fracture obtained as a result of
structural measurements indicates their good correlation. In Imielin the anisotropy of
seismic waves is much weaker and there is only one indistinct maximum at the point
of azimuth 60o (Fig. 5). This maximum can be correlated with only one fracture set
obtained from the structural measurements. Using explosives for mining in the quarry
is possibly the main reason for the poor result of seismic investigations in the Imielin
deposit because of the occurrence of additional, randomly oriented cracks.
max
max
max
Velocity [m/s]
3000
2500
2000
1500
Vp
1000
Vs
500
0
0
20
40
60
80
100
120
140
160
azimuth
Fig. 4. Azimuthal distribution of seismic wave velocity [m/s] in Dębnik deposit (Vp – velocity
of longitudinal wave, Vs – velocity of distortional wave).
3000
max
Velocity [m/s]
2500
2000
1500
Vp
1000
Vs
500
0
0
20
40
60
80
100
120
140
160
azimuth
Fig. 5. Azimuthal distribution of seismic wave velocity [m/s] in Imielin deposit (Vp – velocity
of longitudinal wave, Vs – velocity of distortional wave).
An application of the seismic refraction method to the calculation of block divisibility in these cases is not possible. The calculation of block divisibility is applica-
ble only when the fracture system is orthogonal and measurements of the linear density of fractures along the line for many different directions are made. The above conditions in Dębnik and Imielin were not suitable. As a result of a comparison of the
velocity of seismic waves and the linear density of fractures it is possible to create the
functions that allow us to approximately calculate the block divisibility index (Badera
et al. 2005).
4. Conclusions
In the investigated deposits, a good correlation of structural and seismic measurements was observed. In the Dębnik deposit the maximum of azimuthal distribution
of seismic wave velocity (particularly the velocity of the longitudinal wave) is consistent with the measurement of the bearing of the strike of the main fracture. Unfortunately, in the Imielin deposit the anisotropy of the seismic wave is not strong and its
correlation is less precise.
The analysis of block divisibility using the seismic method is not good for this
case. The calculation of block divisibility using this method may be possible but it
must be made on the ground of the linear density of the fracture. Unfortunately, the
result of this calculaton is approximate. The seismic refraction method is very suitable
for indicating the fracture systems before cutting a new portion of the deposit.
References
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Accepted October 16, 2006