World Journal of Engineering 10(4) (2013) 359-365
1. Introduction
In open pit mining, drilling, at the initial stage of the exploitation operations, has a significant role in the other stages of exploitation. Considering high operation costs as well as the expen of the machinery, full recognition of the parameters involved in drilling, and an attempt to optimize exploitation methods, would be desirable. More efficient drilling would result in suitable blasting,desired fragmentation, as well as a decline in operation cost (Hoinie et al ., 2007).
The drillability of a rock mass is determined by various geological and mechanical parameters.
Evaluation of physical and mechanical properties of rock for drilling condition
classification
B. Adebayo *and B.O. Adetula
Department of Mining Engineering, Federal University of Technology, Akure
*E-mail:
(Received 28 July 2012; accepted 20 April 2013)
Abstract
This work deals with the investigation of physical and mechanical properties of lected rocks for condition of drilling categorization. Rock samples collected from five drilling locations were tested in the laboratory for uniaxial compressive strength, tensile strength, and Drilling Rate Index (DRI) using 1,100 kN compression machine, point load tester and miniature drill. Similarly,hardness, brittleness, Rock Abrasivity Index (RAI), penetration rate and bit wear rate were determined. The results showed that uniaxial compressive strength, tensile strength and Drilling Rate Index varied from 47.78 – 111.11 MPa, 8.09 – 19.44 MPa, and 20 - 52 respectively. The Nast point system chart was ud to classify the rocks into drilling conditions. The drilling classification shows that the drilling condition of the rocks varied from slow to fast. The drillability characteristics of the rocks vary from extremely low to medium as specified by the Drilling rate Index (DRI). It was concluded that uniaxial compressive strength, texture and grain size, drilling rate index and Equivalent Quartz Content (EQC) are importa
nt parameters affecting drilling condition of the rocks.
Key words: Mechanical, Drilling, Condition, P enetration rate, Classification, Rocks Abrasivity
World Journal of
Engineering
Drilling velocity is dependent on a lot of geological parameters: Tho principal parameters include jointing of rock mass, orientation of schistosity (rock anisotropy), degree of interlocking of microstructures, porosity and quality of cementation in clastic rock, degree of hydrothermal decomposition and weathering of a rock mass (Thuro, 1997). It had been obrved that to study drillability, two key parameters have proved to be most valuable: the net drilling rate in meters per minute (i.e. the drilling performance, derived from the time of drilling one single borehole); and the bit life span in meters per drilling bit that can be drilled
ISSN:1708-5284
360 B. Adebayo et al./World Journal of Engineering 10(4) (2013) 359-365
in a homogeneous tunnel ction (Thuro, 1997;Adebayo et al., 2010) examined the drillability and strength characteristics of lected rocks in Nigeria by studying various parameters such as uniaxial compressive strength (UCS), tensile strength and drilling rate index (DRI).
(Hoinie et al., 2007) noticed among the past studies, that Wilbur’s classification system was the best known one. Wilbur classified rock mass for drilling purpos by the u of the above-mentioned factors. Considering the past studies, especially Wilbur’s classification system, and adding the joint properties to the classification system, (Hoinie et al.,2007) developed a new quantitative method for evaluating rock drillabiltiy, the Rockmass Drillability Index (R Di). When the characteristics of a rock fall into different conditions, which are usually the ca, it is necessary to compute final drilling conditions. This was done by (Singh and Goel, 1999) by using a point system chart and the chart of (Nast, 1995) is shown in Table 1.
Rock samples were classified for drilling purpos using Drilling Rate Index (DRI) and Nast Point System Chart. The interest for embarking on this rearch work primarily lies in the area of improving drilling efficiency. The objectives of this therefore are to determine the physical and mechanical properties of lected rock samples affecting penetration rates of blast hole drills and classify the formations for drilling purpos using different classification schemes.
2. Materials and method
Ewekoro quarry lies within Ogun State, between longitude 3˚ 05'E to 3˚ 15'E and latitudes 6˚ 40'N to 6˚ 55'N. Ebenezer quarry is located along Owo road,Akure, Ondo State. It lies within longitude E5˚14'55.8'' and Latitude N7˚ 17'004'' Raycon and Madonna Quarry are located at Otu-costain, along Ore road, Ondo State. The study areas are designated on the map as shown in Figure 1.
Nature of
Rock
Fast Fast Average Average Slow Average Slow
Hardness 8 4 3 2 1 Texture 8 4 3 2 1 Fracture 8 4 3 2 1 Formation 8 4 3 2 1 Total 32 16 12 8 4
Table 1.
Drilling condition point system chart (Nast, 1995)
Fig. 1. Map of Nigeria showing the location of Ogun and Ondo State within the country.
B. Adebayo et al./World Journal of Engineering 10(4) (2013) 359-365361
2.1. Materials
Rock samples were collected from five quarries.The samples ud in this work were a typical limestone and granite. Samples taken from Ewekoro, Raycon and Madonna Quarry are reprented as EWE01 and EWE02, RAY03,MAD04 and EBE05 respectively.
2.2. Methods
2.2.1. Determination of uniaxial compressive strength
Uniaxial Compression Strength is the most widely ud in measuring strength with the method clearly standardized (ISRM, 1981). The uniaxial compressive strength of the rock is determined using Equation 1.
(1)
Where:
C 0= Uniaxal compressive strength (MPa); P = the applied peak load, (kN); W = Width of the sample (m); L = Length of the sample (m)
2.2.2. Determination of tensile strength
The procedure for determination tensile strength is in accordance with (ISRM, 1981) and Equation 2was ud to calculate tensile strength,
(2)
Where P max is the maximum load exerted in the sample; A is the area of the cross ction of the sample. The general relationship between tensile strength (T 0), the point load strength (I s ) and compressive strength (C 0) are expresd in Equations 3 and 4,
(3)(4)
Point load strength index (I s ) was estimated using Equation 4. The summary of the result is prented in Table 2.
2.2.
3. Determination of equivalent quartz content (EQC) and vickers hardness number of rock (VHNR)
Equivalent Quartz Contact (EQC) was obtained
=T 1.5.I s
==C 20 T 30 I , o o s =
T P A
0max =
⋅C P W L
0by multiplying percentage of minerals prent in rock by Rosiwal abrasiveness value as shown in Equation 5 (Thuro, 1997),
(5)
Where:
A = mineral amount (%), R - Rosiwal abrasiveness (%); and n = number of minerals.
In addition, Vickers Hardness Number of Rock (VHNR) of the samples were obtained by multiplying Vickers Hardness Number, VHN (kg/mm 2), by amount of minerals,
(6)
Where:
VHN = Vickers Hardness Number (kg/mm 2), A =amount of minerals; and n = number of minerals.Eq
uations 5 and 6 were ud to establish wear parameters as shown in Table 7.
2.2.4. Determination of rock abrasivity index (RAI)The Rock Abrasivity Index was calculated using Equation 7. Where RAI = Rock Abrasivity Index;UCS = Unconfined Compressive Strength [MPa]; A i = specific amount of mineral [%]; S i = Rosiwal grinding hardness referred to quartz = 100; n =number of all minerals.
(7)
2.2.5. Determination of drilling rate index (DRI)The Drilling Rate Index was by evaluating the Brittleness Value S 20and Sievers’ J value SJ. The brittleness test is basically an aggregate impact test and this was conducted in accordance with Norwegian soil and Rock Engineering Association.The Siever J-Value test is a miniature drill test and the penetration in 1/10 mm after 200 revolutions of the drill was measured. S 20is defined as the percentage of material that pass through 11.2-mm sieve after 20 drops of 14-kg weight. The summary of the result is shown in Table 6.
2.2.6. Determination of penetration rates and drill bit life
The penetration rates of rotary drill and rotary percussive drills were measured in drilling locations. The penetration rates were correlated with
∑=⋅=UCS
RAI A S i n
i i 1
∑==VHNR VHN A i n
i i
1
∑==EQC A R (%)
i i i 1
n
362 B. Adebayo et al./World Journal of Engineering 10(4) (2013) 359-365
the rock properties for the development of reliable
equations in order to allow engineers predict the penetration rate from rock characteristics.
3. Results and discussion
3.1. Strength parameters analysis
Table 2 prents the values of tensile strength (T 0), compressive strength (C 0) and point load strength (I s(50)), obtained for the lected rocks. It was obrved that sample EBE05 has the highest compressive strength, tensile strength and point load strength of 111.11 MPa, 19.44 MPa and 12.96 MPa,respectively. The result indicates that sample EBE05 is the most competent among the five rock samples investigated. Sample EBE05 is therefore classified according to (Deere and Miller, 1966) as high strength rock. In the same vein, Samples EWE01, EWE02, MAD03, RAY04 were classified as medium, low, medium and high strength rock respectively. slower rate of drilling will be experienced on sample EBE05 and faster rate of drilling will be experienced on EWE02 compared to the other samples.
3.2. Analysis of hardness and equivalent quartz content characteristics of rocks
Table 3 prents Vickers hardness number for rock and equivalent quartz content which are 334.94kg/mm 2, 186.84 kg/mm 2, 708.88 kg/mm 2, 695.24kg/mm 2, 784.83 kg/mm 2and 48.78%, 19.87%,47.44%, 43.22%, 51.71% for samples EWE01,EWE02, MAD03, RAY04, EBE05 respectively.Sample EBE05 has the highest Vickers hardness number and equivalent quartz content with the value being 784.83 kg/mm 2and 51.71% respectively.3.3. Analysis of bit wear rate of lected rocks
The bit wear and life of the lected rocks were classified in accordance with (Thuro, 1997) and the
results are prented in Table 4. The results show that the bit wear rate varied from low to very high wear rate; and the drill bit life ranged from very low to high life span. It was also obrved that the for the quarry utilizing tri-cone bit and button bit, the drilling rate reduced considerably as the wear on the bit increas.
3.4. Analysis of abrasiveness of lected rocks
The Rock Abrasivity Index of the lected rocks was classified in accordance with (Plinninger, 2002)as shown in Table 5. The results indicated that the rock abrasivity varied from Not abrasive to Abrasive. All rocks samples tested are abrasive with the exception of the rock sample EWE02 obtain
ed from Ewekoro 2nd bench.
3.5. Analysis of drilling rate index of lected rocks Table 6 prents Drilling Rate Index of the tested rock samples. It was obrved that the drillability of the lected rocks varied from extremely low to medium drillability. From the view point of drilling,sample RAY04 will offer the greatest resistance to penetration. In other words, the low DRI value of sample RAY04 indicated that, the least penetration rate is expected in RAYCON Quarry. Sample EWE02 will offer the least resistance to penetration as specified by the DRI value.
3.6. Analysis of penetration rate
Figure 2 shows bit penetration in the lected rock types. It was obrved that the tri-cone bits display excellent performance in the limestone formation. 3.7. Nast classification for drilling
Table 7 prents drilling condition classification using point system chart. Bad on this classification system, the highest rate of penetration is expected in the Ewekoro 2nd Bench and the lowest rate of penetration should be expected in Ebenezer granite formation.
Rock Code
o
T (MPa) o C (MPa) s(50)I
Strength Classification
EWE01 12.04 68.61 8.02 Medium S trength EWE02 8.09 47.78 5.40 Low S trength MAD03 15.96 86.11 10.64 Medium S trength RAY04 16.65 101.39 11.1 High S trength EBE05 19.44 111.11 12.96 High S trength
Table 2.
Compressive strength (C 0), tensile Strength (T 0), and point load strength (I s(50)) of lected rocks
B. Adebayo et al./World Journal of Engineering 10(4) (2013) 359-365363
Table 3.
Vickers hardness number and equivalent quartz content
Sample Code
Name
Minerals Amount (%) VHN
(2kg/mm )
VHNR (2kg/mm )
Rosiwal Value EQC (%) EWE01 Quartz Corundum Calcite Haematite Σ
15.20 2.64 77.30 1.78 1,060 2,300
125 925
161.12 60.72 96.63 16.47 334.94 120 1,000 4.5 37 18.24 26.40 3.48 0.66 48.78 EWE02 Quartz Corundum Calcite Hematite Σ
2.99 1.16 92.20 1.43 1,060 2,300
125 925
31.69 26.68 115.25 13.22 186.84 120 1,000 4.5 37 3.59 11.60 4.15 0.53 19.87 MAD03 Amphibole Biotite Quartz Microcline Plagiocla Σ
8.20 17.30 23.00 22.90 28.71 600
110 1060 730 800
49.20 19.03 243.80 167.17 229.68 708.88 6.5 1.25 120 37 37 0.53 0.22 27.60 8.47 10.62 47.44 RAY04 Opaque mineral (Hematite, Magnetite, Pyrite) Biotite Orthocla Plagiocla Quartz Σ
11.80 22.20 9.00 38.40 19.00 818
110 730 800 1,060 96.52 24.42 65.70 307.20 201.40 695.24 22 1.25 37 37 120 2.60 0.28 3.33 14.21 22.80 43.22 EBE05 Opaque mineral Biotite Microcline Plagiocla Quartz Σ
7.14 12.20 46.40 10.22 24.20 818
110 730 800 1,060 58.41 13.42 338.72 81.76 256.52 748.83
22 1.25 37 37 120
1.57 0.15 17.17 3.78 29.04 51.71
Fig. 2. Rate of penetration in the formations.
