Scholarly article on topic 'Variation of vertical and horizontal drilling rates depending on some rock properties in the marble quarries'

Variation of vertical and horizontal drilling rates depending on some rock properties in the marble quarries Academic research paper on "Earth and related environmental sciences"

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Abstract of research paper on Earth and related environmental sciences, author of scientific article — Demirdag Servet, Sengun Nazmi, Ugur Ibrahim, Efe Tamer, Akbay Deniz, et al.

Abstract The main objective of this study is to determine the rates of vertically and horizontally oriented drilling processes in marble quarries and to observe the factors affecting the drilling rates in terms of physical and mechanical properties of the rocks. In situ drilling tests were performed in different marble quarries with different marble types and drilling times and penetration rates for a series of successive depth-increments were trying to be determined under vertically and horizontally oriented conditions. In order to understand the relation between the parameters that are investigated within the scope of this research, uniaxial compressive strength, Brazilian tensile strength, impact strength, Bohme abrasion strength, P-wave velocity, porosity, unit volume weight, Schmidt hardness index and brittleness index values were correlated with the drilling rates. It was noticed that the porosity and unit volume weight could be taken as the key parameters among them for obtaining meaningful correlation with drilling performance. It was also observed that the physical and mechanical rock properties are more relevant in vertical drilling than horizontal drilling.

Academic research paper on topic "Variation of vertical and horizontal drilling rates depending on some rock properties in the marble quarries"

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International Journal of Mining Science and Technology

journal homepage: www.elsevier.com/locate/ijmst

Variation of vertical and horizontal drilling rates depending on some rock properties in the marble quarries

Servet Demirdag *, Nazmi Sengun, Ibrahim Ugur, Tamer Efe, Deniz Akbay, Rasit Altindag

Mining Engineering Department, Suleyman Demirel University, Isparta 32850, Turkey

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ARTICLE INFO

ABSTRACT

Article history:

Received 20 September 2013 Received in revised form 20 October 2013 Accepted 22 November 2013 Available online 12 February 2014

Keywords:

Mechanical properties Drilling Drilling rate Marble quarry

The main objective of this study is to determine the rates of vertically and horizontally oriented drilling processes in marble quarries and to observe the factors affecting the drilling rates in terms of physical and mechanical properties of the rocks. In situ drilling tests were performed in different marble quarries with different marble types and drilling times and penetration rates for a series of successive depth-increments were trying to be determined under vertically and horizontally oriented conditions. In order to understand the relation between the parameters that are investigated within the scope of this research, uniaxial compressive strength, Brazilian tensile strength, impact strength, Bohme abrasion strength, P-wave velocity, porosity, unit volume weight, Schmidt hardness index and brittleness index values were correlated with the drilling rates. It was noticed that the porosity and unit volume weight could be taken as the key parameters among them for obtaining meaningful correlation with drilling performance. It was also observed that the physical and mechanical rock properties are more relevant in vertical drilling than horizontal drilling.

© 2014 Published by Elsevier B.V. on behalf of China University of Mining & Technology.

1. Introduction

A variety of techniques are used to extract minerals around the world, including drilling, blasting, excavating, crushing and cutting operations. These operations are often encountered in civil and mining engineering applications [1].

In the past years, given the importance of rock drilling in mining and petroleum engineering applications, several studies were performed on the drilling properties of materials like rock. Controllable parameters (rotational speed, thrust, blow frequency and flushing) and uncontrollable parameters (rock properties and geological conditions) are effective on rock drillability. The prediction of the penetration rate of drilling machine represents the most important step in the cost estimation during the planning of the project [2]. For planning an efficient drilling operation, we must learn how these parameters influence penetration rate in the drilling process. Several scientists investigated theoretically and experimentally about drillability of rocks by correlating the penetration rate with the various rock properties to prediction of penetration rate [3].

Drilling has a significant role in open pit mining. Considering high operation costs it would be desirable to optimize exploitation methods. Operation costs decline when drilling becomes more

* Corresponding author. Tel.: +90 246 2111308. E-mail address: servetdemirdag@sdu.edu.tr (D. Servet).

efficient [4]. Drilling takes too much time before the cutting operation, so to perform optimum drilling speed is very important in quarries because of other operations start after drilling. Rotary drills, diamond drills and percussive drills are most common drilling techniques used in open pits, quarries and construction sites. Total drilling costs could be estimated by using prediction equations. Also, one could use a prediction equation to select the drilling rig type, which is best suited for given conditions [5]. Kahraman suggested penetration rate models for rotary, down the hole and hydraulic top hammer drills using multiple curvilinear regression analysis [5]. Furthermore, the prediction of physical and mechanical properties of rock formations from drilling rates may help the mining engineers to control the changing characteristics of the formations [6]. Kahraman suggested a new drillability index from force-penetration curves of indentation tests and also a mathematical model for rotary drills using this new drillability index [6]. The main parameters of rocks that affect drillability are given in Table 1 [7].

Extraction of the quarry stone happens in several ways depending on the technology owned by the quarrymen. The most critical operations are drilling vertical holes, using a twin-headed rig, and the use of a wire-saw cable for cutting the marble blocks [8].

In marble quarries through the production process before diamond wire cutting, the first step is drilling three holes, one vertical and two horizontal. Then the process goes on threaded of diamond wire through these holes. The speed of the drilling operation is the most effective and important parameter of the process [9].

http://dx.doi.org/10.1016/j.ijmst.2014.01.020

2095-2686/© 2014 Published by Elsevier B.V. on behalf of China University of Mining & Technology.

Table 1

Main factors affecting the drillability of rock [7].

Geological parameters Machine parameters Operating parameters

Rock type Drilling machine Drilling methods

Physical-mechanical properties Thrust force Operation

Orientation of foliation Rotation Maintenance of machine

Discontinuities Bit type Experience of operator

Mineral composition Flushing Logistic support

Rock drilling is a complex process. It is obvious that a single rock property does not completely define rock drillability for different rock types. Also, many researchers have proposed many penetration rate models and factors affecting penetration rate in the literature, but these studies are related to the rock properties and kind of hammers rather than direction of drilling.

Hartman determined the behavior of the rock under the action of a drill bit by performing drop-test studies and proposed a drilling-rate model [10,11]. Paone and Madson carried out the relationship between penetration rates and rock properties for diamond and rotary drilling with impregnated diamond bits on a variety of rock types both in the laboratory and in the field [12]. Early studies on drilling were examined in detail by Maurer [13]. He noted that drill bits were loaded both tensile and shear strength which were produced in the rock near the bit. Howarth et al. correlated rock properties such as bulk density, saturated compressive strength, apparent porosity and saturated P-wave velocity with penetration rate [14]. They stated that porosity has an effect on drillability, since high porosity was likely to assist the formation of fracture paths and networking of such paths. Wijk studied drop hammer experiments and stated that the stamp strength index could be used for the rock drilling efficiency and demonstrated the validity of this index [15]. Kahraman investigated the experimental works of different researchers and noticed relations between the penetration rate of rotary and diamond drills and he showed that there was no correlation between the penetration rate of diamond drills and brittleness values [16]. Altindag suggested a new brittleness index and correlated this new brittleness index with the drillability index for rotary blast hole drills [17]. Bilgin and Kahraman observed rotary blast hole drills in several rock types at open pit mines and correlated the penetration rates with rock properties [18]. Kahraman et al. correlated penetration rates with the rock properties such as uniaxial compressive strength, Brazilian tensile strength, point load strength and Schmidt hammer value exhibit strong correlations with the penetration rate [19,20]. They investigated the effect of porosity on the correlations between the modulus ratio and penetration rate.

If it is examined in an obvious manner, it would be seen that there is a lack of studies in the literature providing sufficient relationships between the drilling rates depend on the direction and rock properties.

Since the drilling operation is one of the most important stages for marble block production in quarries, the effect of the mechanical and physical properties such as uniaxial compressive strength (UCS), Brazilian tensile strength (BTS), impact strength (IS), Bohme abrasion strength (BAS), P-wave velocity (Vp), Porosity (P), unit volume weight (UVW), Schmidt hardness index (SHI) and brittleness index (BI) of four different rock types on drilling rates of five meters both vertically and horizontally oriented holes were investigated in this study.

2. Experimental method

In this study, four marble quarry visits were performed in Turkey (Table 2), and in situ drilling rates were measured from

Table 2

Details on rocks studied.

Rock name Rock type Rock class Location

Travertine Travertine Sedimentary Bucak-Burdur

Beige Limestone Sedimentary Isparta

White marble Marble Metamorphic Usak

Lymra Limestone Sedimentary Finike-Antalya

horizontally and vertically oriented drill holes to determine drilling rates for a series of successive depth-increments.

Travertine is a form of limestone having some distinctive characteristics as building and facing stone with varying color and porosity. It is primarily composed of calcium carbonate (CaCO3), and therefore the dominant mineral is calcite. White marble is a re-crystallized white limestone containing tiny white and yellow veins and the palest of large size grey crystals on the white background are cemented with micro-crystalline structure. Beige marble is a micritic limestone type composed primarily of calcium carbonate (CaCO3) in the form of the mineral calcite. It is known as chemical or organic sedimentary rock formed by the precipitation of calcium carbonate, shells and fossils from lake, ocean or clear, warm and shallow marine waters. It has a homogeneous color distribution, rich in calcite (capillary cracks filled with calcite), does not contain silica minerals or containing trace amounts of silica minerals. Lymra is a calcareous sedimentary rock, occurred as a result of the millions of years of sediments being buried, compressed and cemented by precipitation from mineral rich waters. It is generally used as an ornamental stone in varying architectural applications such as old-build construction and exterior claddings for buildings. It is remarkable due to its suitable mechanical properties for high workability as well as its high level of color homogeneity.

Samples collected for each rock type to determine mechanical and physical properties such as UCS, BTS, IS, BAS, Vp, P, UVW, SHI and BI. The physical and mechanical properties of rocks are given in Table 3.

The procedure for measuring UCS has been standardized by International Society for Rock Mechanics (ISRM). The samples for UCS test are 54 mm in diameter and have a minimum length to diameter ratio of 2 and met the strict tolerance limits as specified in the suggested test procedure and the test applied on 8 dried samples for every rock type.

BTS of rock samples were determined according to ISRM. The BTS tests were conducted on core samples having a diameter of 54 mm. Platens loaded the specimen diametrally with the axes of rotation for specimen and apparatus coincident. The specified loading rate was set as 200 N/s until the failure occurs in 15-30 s.

To determine the impact resistance of the stone types, a standard 50 kg steel hammer was free fallen on the 40 mm x 40 mm x 40 mm marble test pieces from the several heights on the anvil center of the sand bed as defined in TS 699 standard. Number of impacts which causes breakage (n) is recorded and the impact strength of the stone was calculated as follows:

Is = n(n + 1) (1)

Table 3

Physical and mechanical properties of rocks.

Rock type UCS (MPa) BTS (MPa) IS (kgf-cm/cm2) BAS (cm3/S0cm2) Vp (m/s) P (%) SHI UVW (kN/m3) BI

Travertine 62.4S 3.3S S.90 29.00 442S 11.69 43.77 23.3S 104.6S

Beige 147.39 S.67 20.00 14.17 64S1 0.S1 SS.00 26.S7 417.85

White S2.44 4.0S 13.30 21.6S 4S10 1.42 40.27 26.61 166.94

Lymra 66.43 2.S6 1S.40 40.S0 4179 11.23 42.77 23.S1 SS.03

Table 4

Technical properties of drilling machine.

Parameter Travertine Beige White Lymra

Energy (kW) 3S0 220 380 220

Air pressure (Bar) s 8 8 8

Oil pressure (Bar) 0-200 80 0-200 80

where Is is the impact strength value of the stone in kgf.cm/cm3; n the number of impacts causing breakage.

The experimental procedure conducted for abrasion test was TS EN 14157 standard. For the abrasion resistance evaluation, Bohme abrasion test was applied on 71 mm x 71 mm x 71 mm cube-shaped samples prepared for each rock by sawing. The abrasion loss was calculated from the differences in weight of the samples measured before and after the each 22 revolutions and converted into volume loss from the known bulk density of rock by the following equation:

M0 - M1

where DV is the volume loss of rock in cm3 for the 50 cm2 abraded sample surface area; M0 the initial weight of the sample in g; M1 the weight of the sample after abrasion in g; A the abraded surface area of the sample in cm2, and q the bulk density of rock in g/cm3. The open porosity and UVW of rock samples were determined using saturation and buoyancy techniques, as recommended by ISRM and TS. After drying the all samples to constant mass (M1), all samples were saturated by water immersion for a period of 48 h with periodic agitation to remove trapped air. Later, the samples were transferred underwater to a basket in an immersion bath and their saturated-submerged weights were measured with a scale having 0.01 g accuracy (M2). Then, the surface of the samples was dried with a moist cloth and their saturated-surface-dry weights were measured outside water (M3). The UVW was determined as the ratio of the dry mass to the bulk volume of the sample (Eq. (3)). The open porosity (P) is expressed as the ratio of the volume of the pores accessible to water to the bulk volume of the sample (Eq. (4)).

M3 - M2

(kg/m3)

p = M-M * 100 (%)

M3 - M2

SHI testing method and sample preparation were carried out in accordance with the specifications of the ISRM. Tests were performed with L-type hammer having impact energy of 0.74 Nm. All tests were made with the hammer held vertically downwards (±5°) on the cubic block samples having an edge dimension of 110 mm.

Drilling times or drilling rates of the horizontal and vertical holes were in situ measured with chronometer and recorded for every 1-m rig length. The holes having 5 m length for each direction were consecutively drilled by individual rigs without the assembly time is not taken into consideration. The properties of drilling machines are given in Table 4.

3. Results and discussion

Drilling rates of vertical and horizontal holes of rock types are given in Table 5. According to the table, average drilling rates of travertine are about 28.9 cm/min in vertically and 24.0 cm/min in horizontally oriented holes. However, lower drilling rates were obtained for Lymra, beige and white marbles for both vertically and horizontally drilled holes. All measurements have revealed that bits can penetrate through vertical direction faster than horizontal direction (Fig. 1).

This situation can be explained by two ways; the first one is the vertical stress (rv) is more effective for horizontal drilling resulting from additional loads due to the unit volume weight of the rock and height of bench (Table 6 and Fig. 2).

The second one is the physical and mechanical properties of rocks are closely related to vertical drilling rates than horizontal ones (Fig. 3). In drilling operations, the impacts produced by repeated blows of the piston generate shock waves that are transmitted to the rock by the bit. The shock waves generate new discontinuities and fractures in rocks, so that higher penetration rates could be obtained in vertical drilling. However, the whole mass behavior of the rocks resulting from the vertical stress and Poisson's ratio cause low penetration rates in horizontal drilling.

In vertical drilling, it was observed that the drilling rate values were considerably increased through the whole length, unlike for horizontal drilling. Fig. 4 shows that there is a meaningful correlation between vertical and horizontal drilling rates with 0.94 and vertical drilling rate is higher than horizontal drilling rate.

Table 5

In situ measurements of drilling rate.

Length (m) Drilling rate (cm/min)

Travertine Beige White Lymra

Horizontal Vertical Horizontal Vertical Horizontal Vertical Horizontal Vertical

1 26.1 31.3 12.8 17.1 14.4 17.4 17.1 22.1

2 23.7 26.1 14.2 15.7 12.6 16.8 19.2 23.6

3 24.5 28.3 14.0 15.0 14.6 15.7 21.1 25.4

4 25.0 29.0 14.7 17.2 13.6 19.4 20.7 26.7

s 20.9 29.9 12.7 17.9 13.0 18.5 19.8 26.1

Average 24.0 28.9 13.7 16.6 13.6 17.6 19.6 24.8

Fig. 1. Horizontal and vertical drilling rate vs. drilling length.

Table 6

Vertical stress values depend on depth.

Rock type UVW (kN/m3) Depth (m) av (MPa)

Travertine 26.61 5 0.117

Beige 26.57 5 0.133

White 23.38 5 0.133

Limra 23.81 5 0.119

0 5 10 15 20 25 30

Horizontal drilling rate (cm/min)

Fig. 4. Vertical drilling rate vs. horizontal drilling rate.

It can be seen from the Fig. 3 that, similar relationships were obtained for drilling rates vs. rock properties in vertical drilling than horizontal. UCS, BTS, BAS, Vp and BI have a close relation with drilling rate (Figs. 3 and 5a).

According to the Fig. 3f, there is a weak relation between SHI and the drilling rates. However, the most significant relations in drilling rates with P and UVW of rock were observed since the pores in rock structure facilitate drilling operation (Fig. 3g and Fig. 5b).

in) 30

cm/m 25

rat 15

llin 10

y=197.65xJJ-

r=0.77 ♦ Horizontal

■ Vertical

100 150 UCS (MPa) (a) UCS

35 30 25 20 15 10 5 0

in) 30

1 25 üe 20

rat 15

3 10 a 5

y=201938*10' r=0.78

y=92802ï10 r=0.70

I y=40.008e r=0.79

y=31.109e r=0.72

4000 5000 6000

Vp (ms) (e) Vp

in) 30

rat 15 illin 10 a 5

y=-8.904lnx+44.442 r=0.80

y=-7.774lnx+37.341 r=0.81

BTS (MPa) (b) BTS 35

in) 30

1 25 ^ 20 rat 15 llin 10 Q 5 0

y=48.62e"a" r=0.44

y=33.371e r=0.34

IS (kgf-cm/cm2) (c) IS

in) 30

1 25 ^ 20

rat 15

llin 10 Q 5

in) 30

1 25 ^ 20

rat 15

llin 10 Q 5

y=16.365e ' r=0.98

y=13.066e r=0.96

y=3.9767x r=0.73

(d) BAS

30 35 40 45 50 55 SHI

(f) SHI

2 4 6 8 10 12 14

BAS (cm3/50 cm2)

Fig. 3. UCS, BTS, IS, BAS, Vp, SHI and P vs. drilling rate.

Fig. 5. BI and UVW vs. drilling rate.

4. Conclusions

In marble quarries, although the heights of the benches may be up to 6-7 m in safety limits, 5 m hole lengths were considered in this study. The drilling rates and their effects on 5 m vertically and horizontally oriented hole lengths of four different rock types were investigated. It was seen that, although physical and mechanical rock properties are more effective in vertical than horizontal drilling, vertical stress (rv) and Poisson's ratio are more effective in horizontal than vertical drilling. So it could be mentioned that, higher penetration rates were acquired for vertical drilling. In addition, the most meaningful correlations were obtained between the drilling rate and porosity/unit volume weight in comparison to other rock properties. UCS, BI, IS, BAS, BTS, Vp and SHI are the most relevant rock properties respectively on drilling rates.

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