CONTENTS PAGE

PREFACE 1

0 GENERAL

0.1 Project Reports about Drillability

0.2 Background

3

3

5

1 DRILLABILITY

1.1 Rock Sampling

1.2 The Drilling Rate Index DRI

1.20 General

1.21 The Brittleness Test

1.22 The Sievers' Miniature Drill Test

1.23 Assessment of DRI

1.24 The Mini-DRI

1.3 The Bit Wear Index BWI

1.30 General

1.31 The Abrasion Value AV

1.32 Assessment of BWI

1.4 The Cutter Life Index CLI

1.5 The Wear Parameter VHNR

1.6 Classification of Indices

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6

7

7

7

8

9

10

13

13

13

14

15

16

18

APPENDIX

A. Previous Editions

B. Research Partners

C. Laboratory Testing

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21

22

PREFACE

1

DRILLABILITY Test Methods

Project Report 13A-98 The report is one of three reports about drillability of rocks: • = 13A-98 DRILLABILITY Test Methods • = 13B-98 DRILLABILITY Catalogue of Drillability Indices • = 13C-98 DRILLABILITY Statistics of Drillability Test Results (to be published) Combined with the other reports in the Project Report Series from the Department of Building and Construction Engineering at NTNU, the reports present an updated and systematised material on rock excavation and tunnelling to be used for: • = Economic dimensioning • = Choice of alternative • = Time planning • = Cost estimates, tender, budgeting and cost control • = Choice of excavation method and equipment. A list of available Project Reports may be requested from the Department of Building and Construction Engineering at NTNU. The Drillability Catalogue also exists as a digital database of test results (Excel file). The report is prepared by Amund Bruland and is part of his dr.ing thesis about hard rock tunnel boring. The report is included in the thesis as a necessary basis for use and understanding of the prognosis model for hard rock tunnel boring. The report describes the methods used at NTNU and SINTEF when testing rock drill-ability and abrasiveness. The report is published in the Project Report Series of the Department of Building and Construction Engineering because of the relation to the other reports in the series.

PREFACE

2

The report is a result of the co-operation between the Department of Geology and Mineral Resources Engineering at NTNU, SINTEF Rock and Mineral Engineering and the Department of Building and Construction Engineering at NTNU. The project has been granted financial support by our external research partners, see list in Appendix. For reference, registration and similar, we ask for the following:

NTNU-Anleggsdrift (1998): Project Report 13A-98 DRILLABILITY Test Methods.

When copying from the report, the source should be stated. Trondheim, September 1998 Odd Johannessen Professor

0. GENERAL 0.1 Project Reports about Drillability

3

0.1 PROJECT REPORTS ABOUT DRILLABILITY 13A-98 The Drilling Rate Index DRI, the Bit Wear Index BWI and the Cutter Life Index CLI are indirect measures for the drillability of rocks. The report describes the laboratory methods used to determine DRI, BWI and CLI. Test apparatus and procedures are not described in detail. Such information may be obtained from the Department of Geology and Mineral Resources Engineering or the Department of Building and Construction Engineering at NTNU. Project Report 13A-98 is a revised and updated version of Project Report 13A-94 DRILLABILITY Test Methods. Appendix A shows a list of previous editions of the report. Other Reports Project Report 13B-98 DRILLABILITY Catalogue of Drillability Indices con-tains detailed test results for approximately 2050 samples. The report is updated regu-larly, and is also available as a digital database. Project Report 13C-98 DRILLABILITY Statistics of Drillability Test Results shows relations and statistics of the test results, based on the digital database BORBAR. The relations between the laboratory indices and performance, capacity and costs for various drilling equipment and excavation methods are shown in other reports in the series published by the Department of Building and Construction Engineering at NTNU. The Drillability Catalogue as a digital database is at present available as an EXCEL file. The database is available for research purposes and similar by agreement. The digital database will be updated more frequently than the printed catalogue.

0. GENERAL 0.1 Project Reports about Drillability

4

Use of Drillability Indices from the Database The database is aimed at being used through several stages in a project: • = Preliminary and feasibility studies • = Project design and optimisation • = Tendering and contract • = Construction • = Possible claims. Indices from the database should not be used as the single source of drillability infor-mation for a project. Combined with other geological information such as geological maps and reports, and particularly, engineering geological mapping and rock sam-pling, the database may be used to: • = Estimate drillability indices • = Assess risk with regard to variation in drillability • = Estimate time consumption and excavation costs, included risk • = Establish and manage price regulation in contracts • = Verify machine performance. The laboratory results must be critically evaluated when the catalogue is used to estimate drillability indices. The catalogue must be supplemented with labora-tory testing of samples from the actual site.

0. GENERAL 0.2 Background

5

0.2 BACKGROUND The Drilling Rate Index, the Bit Wear Index and the Cutter Life Index are based on laboratory test results. For rock blasting and tunnelling, the drillability has a major influence on • = Time consumption and costs • = Choice of method and equipment. The DRI and BWI were developed at the Department of Geology at NTH1 in the years 1958 – 61 (Reidar Lien, Rolf Selmer-Olsen). The method was tested in the field during the next ten years, resulting in minor adjustments. The CLI was developed at The Department of Construction Engineering at NTH2 in the years 1980 - 83. Systematic follow-up of drilling and boring in rock quarries and tunnels has been car-ried out since 1972. The data have been normalised and related to the drillability indi-ces of representative rock samples. The results are presented as drilling rate diagrams. The various reports in the Project Report Series show relevant drilling rate diagrams and how to estimate capacity and costs based on that information. Registrations show that DRI and CLI give a good and reproducible measure of the drillability and abrasiveness of rocks. The BWI has been found to have some weak-nesses, one being that the DRI value to a large extent influences the BWI of a rock sample (see Section 1.3 and Figure 1.5). We are currently working to replace the BWI with VHNR, see Section 1.5. It is only when the drillability indices are related to performance through drill-ing rate diagrams and to costs for varying rock conditions through estimation models of drilling capacity and excavation costs that the indices get their full user value.

1 The present Department of Geology and Mineral Resources Engineering at NTNU 2 The present Department of Building and Construction Engineering at NTNU

1. DRILLABILITY 1.1 Rock Sampling

6

1.1 ROCK SAMPLING It is important that the rock sampling for drillability testing is based on a careful engi-neering geological mapping. The necessary number of samples for a project is determined by the variation of the rock properties and the rock types at the site. Rock samples to be tested in the laboratory should be representative concerning pe-trography and mechanical properties. It is very important to avoid weathered rock samples. Blocks with fissures or cracks from blasting, or blocks that have been sub-ject to high (anisotropic) rock stress should be avoided. In order to get reliable results from the testing, each sample should have a total weight of 15 - 20 kg. One sample may consist of several blocks (minimum weight per block is 0.5 kg). Samples from core drilling must have core diameter of 32 mm or more, and preferably 10 kg of core material. Less sample weight may be used, which will result in fewer parallel brittleness tests and a larger uncertainty in the indices. When it is difficult or very expensive to provide sufficient test material for standard DRI testing, performing a Mini-DRI test is an option, see Section 1.24. In most cases, a few hundred grams of sample material is sufficient for this test. At present, only the Laboratory of Engineering Geology at NTNU/SINTEF in Trond-heim has the equipment and long experience to perform the DRI, BWI and CLI tests. Other laboratories are planning to install or have recently installed equipment to per-form the necessary tests. The Technical University of Helsinki has developed a modified DRI test that requires less sample material than a standard DRI test. Necessary test material is in the order of 25 cm of drill core with a diameter of 32 mm.

1. DRILLABILITY 1.2 The Drilling Rate Index DRI

7

1.2 THE DRILLING RATE INDEX DRI

1.20 General The Drilling Rate Index is assessed on the basis of two laboratory tests, the Brittleness Value S20 and Sievers' J-value SJ.

1.21 The Brittleness Test The Brittleness Test gives a good measure for the ability of the rock to resist crushing by repeated impacts. The test method was developed in Sweden by N. von Matern and A. Hjelmér in 1943. Several modified versions of the test have been developed for various purposes. An outline of the test is shown in Figure 1.1.

Figure 1.1 The Brittleness Test.

1. DRILLABILITY 1.2 The Drilling Rate Index DRI

8

The sample volume corresponds to 500 grams of density 2.65 g/cm3 from the fraction 16 - 11.2 mm. The Brittleness Value S20 equals the percentage of material that passes the 11.2 mm mesh after the aggregate has been crushed by 20 impacts in the mortar. The Brittleness Value is the mean value of 3 - 5 parallel tests.

1.22 The Sievers' Miniature Drill Test The Sievers' Miniature Drill Test gives a measure for the surface hardness (or the re-sistance to indentation) of the rock. The test method was developed by H. Sievers in the 1950s. The test is performed on a pre-cut rock sample as shown in Figure 1.2.

Figure 1.2 The Sievers' Miniature Drill Test. The Sievers' J-value is the drill hole depth after 200 revolutions of the miniature drill bit, measured in 1/10 mm. The SJ-value is the mean value of 4 - 8 drill holes.

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1. DRILLABILITY 1.2 The Drilling Rate Index DRI

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The pre-cut surface of the sample must be parallel or perpendicular to the foliation of the rock. The SJ-value measured parallel to the foliation is used to find the Drilling Rate Index. If the SJ-value for drilling perpendicular to the foliation differs from the value for drilling parallel to the foliation, the drilling rate will most likely vary with drilling direction to the foliation.

1.23 Assessment of DRI Figure 1.3 is used to assess the Drilling Rate Index from the Brittleness Value S20 and the Sievers' J-value. The Drilling Rate Index may be described as the Brittleness Value corrected for the rock surface hardness. For a Sievers' J-value of 10, which is common for e.g. granite or syenite, the DRI equals the S20 value.

Figure 1.3 Diagram for assessment of DRI.

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1. DRILLABILITY 1.2 The Drilling Rate Index DRI

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1.24 The Mini-DRI In many cases, it is difficult or very expensive to provide sufficient sample material for a standard drillability test. Currently, NTNU and SINTEF are modifying the stan-dard tests to be able to test the rock drillability even with very little sample material available. The modifications are based on downscaling the test apparatus to use less sample volume and a less grain size than the standard tests. Furthermore, a sufficient number of parallel tests must be carried out to find the rela-tion between the modified and standard tests. The Brittleness Test In the modified test, the grain size is reduced from the fraction 11.2 - 16 mm to the fraction 2 - 4 mm. The sample weight is reduced from 500 g to 15 g (for a rock type with density of 2.65 g/cm3). The weight of the mortar lid is reduced from 4025 g to 115 g and the impact weight is reduced from 12 kg to 390 g. The height to width ratio of the sample volume in the mortar is maintained. Other test parameters have not been changed. Sievers' Miniature Drill Test The test has been downscaled by reducing the diameter of the drill bit from 8.5 mm to 2.5 mm and the weight of the sample fixture from 20 kg to 5.9 kg. Other test parame-ters have not been changed. Several types of test samples have been used: A pre-cut rock sample (as in the stan-dard test), rock fragments in cement mortar, rock fragments in epoxy and rock frag-ments in gypsum plaster. The tests with rock fragments in a matrix have not been suc-cessful yet. Drilling in a pre-cut rock sample and in rock fragments with d >> 2.5 mm held in a cement mortar has given reliable results.

1. DRILLABILITY 1.2 The Drilling Rate Index DRI

11

The available rock sample is usually of a size that will allow a standard SJ test to be performed, which is preferred. The downscaled SJ test is particularly being developed with the aim to be able to test the rock surface hardness when the test material con-sists of chips or similar. Preliminary Results Based on a limited number of samples, the results are promising. A medium to good correlation between the standard test and the modified test has been found. For the brittleness value the correlation is R2 = 0.8 and for Sievers' J-value the correlation is R2 = 0.97. The downscaled tests seem to be more influenced by grain size and foliation than the standard tests. Hence, the "down-scaling relation" for the parameters will vary with rock type and grain size (and most likely other factors also). The Drilling Rate Index Mini-DRI The Mini-DRI consists of a calculated brittleness value and a standard SJ value. The calculated brittleness value is meant to represent the standard brittleness value, and is found by the normalised relation between the downscaled and the standard brittleness value. The diagram in Figure 1.3 for assessment of the DRI is also used to find the Mini-DRI. The preliminary results show that the index is quite able to classify the drillability of rocks. However, the Mini-DRI must still be considered as having larger uncertainty than the standard DRI since the number of parallel tests still is low.

1. DRILLABILITY 1.2 The Drilling Rate Index DRI

12

Down-scaling the Brittleness Test and the Sievers' Miniature Drill Test The index consists of a calculated brittleness value and a calculated SJ value. Hence, the diagram in Figure 1.3 for assessment of DRI is also used to find this index. The preliminary results show that the index is able to classify the drillability of rocks. The index must at present be regarded as having high uncertainty. Among other things, we are trying to find a well-suited matrix material to cement the rock frag-ments in. Furthermore, a sufficient number of tests to find the relation between the downscaled and the standard SJ test must be performed.

1. DRILLABILITY 1.3 The Bit Wear Index BWI

13

1.3 THE BIT WEAR INDEX BWI

1.30 General The Bit Wear Index is assessed on the basis of DRI and the measured Abrasion Value AV.

1.31 The Abrasion Value AV The parameter is a measure for the time dependent abrasion on tungsten carbide from crushed rock powder. The test method was developed at the Department of Geology at NTH1 in the years 1958 – 61 (Reidar Lien, Rolf Selmer-Olsen). An outline of the abrasion test is shown in Figure 1.4.

Figure 1.4 Abrasion testing.

1 The present Department of Geology and Mineral Resources Engineering at NTNU

1. DRILLABILITY 1.3 The Bit Wear Index BWI

14

Crushed rock powder less than 1 mm passes under the loaded tungsten carbide bit. The Abrasion Value is the weight loss in milligrams of the test bit after 100 revolu-tions of the steel disc. 100 revolutions equal 5 minutes testing time.

1.32 Assessment of BWI Figure 1.5 is used to assess the Bit Wear Index from the DRI and the Abrasion Value AV. The Bit Wear Index is used to estimate life of drill bits. The BWI expresses life in drilled metres or drilled volume.

Figure 1.5 Diagram for assessment of BWI.

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1. DRILLABILITY 1.4 The Cutter Life Index CLI

15

1.4 THE CUTTER LIFE INDEX CLI The Cutter Life Index is assessed on the basis of Sievers' J-value and the Abrasion Value Steel, AVS. CLI expresses life in boring hours for cutter disc rings of steel for tunnel boring machines. The AVS is measured by the same test equipment as the AV. The AVS test uses a test bit of steel from a new cutter ring. The testing time is 1 minute, i.e. 20 revolutions. The Sivers' J-value and the Abrasion Value Steel expresses the CLI by the equation:

The CLI is based on normalising field data of actual cutter ring life versus tested rock parameters.

)AVSSJ( 13.84 = CLI

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1. DRILLABILITY 1.5 The Wear Parameter VHNR

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1.5 THE WEAR PARAMETER VHNR The mineral composition of a rock type is partly determining the effective time de-pendent abrasion from crushed rock powder on drilling equipment. This is the basis for the development of new parameters for service life of drill bits and cutter discs. The mineral content of the rock may be measured by several methods. Microscopy of thin-sections and X-ray diffraction of rock powder are common methods. Vickers Hardness Number (VHN) is used as a measure for the abrasiveness of each mineral. The mineral hardness numbers are combined to a hardness number for the rock (VHNR, Vickers Hardness Number Rock) according to mineral percentage of the actual rock. Calculation of VHNR for one sample of gneiss is shown below.

Mineral Percentage

%

Mineral Hardness

VHN

Portion of Total

Hardness

Quartz

Plagioclase

Amphibole

Biotite

30

63

2

5

1060

800

600

110

318

504

12

6

Total Hardness VHNR 840

Table 1.1 Example of calculation of VHNR. VHNR seems to be a better parameter for life of drill bits than the indices DRI and BWI. The Department of Building and Construction Engineering is developing new relations for the life of drill steel, but the amount of field data is currently not suffi-cient to be able to show reliable relations of life as a function of VHNR for all types of drill bits. For drill and blast tunnelling, expected life of drill bits as a function of VHNR is shown in Project Report 2B-95 TUNNELLING Prognosis for Drill and Blast.

1. DRILLABILITY 1.5 The Wear Parameter VHNR

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Mineral VHN [kg/mm2] Corundum 2300 Quartz 1060 Garnet 1060 Olivine 980 Hematite 925 Pyrite 800 Plagioclase 800 Diopsid (clinopyroxene) 800 Magnetite 730 Orthoclase (alkali feldspar) 730 Augite (clinopyroxene) 640 Ilmenite 625 Hypersthene (orthopyroxene) 600 Hornblende (amphibole) 600 Chromite 600 Apatite 550 Dolomite 365 Pyrrhotite 310 Fluorite 265 Pentlandite 220 Sphalerite (zinc blende) 200 Chalcopyrite (copper pyrite) 195 Serpentine 175 Anhydrite 160 Calcite 125 Biotite 110 Galena (lead glance) 85 Chalcosite 65 Chlorite 50 Gypsum 50 Talc 20 Halite (rock salt) 17 Sylvite 10

Table 1.2 Vickers hardness VHN for common rock minerals. After P. Salminen and R. Viitala 1985, A. Lislerud 1997.

1. DRILLABILITY 1.6 Classification of Indices

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1.6 CLASSIFICATION OF INDICES On the background of the original classification done by Lien and Selmer-Olsen in the 1960s, and the more than 2000 samples that later have been tested in the labora-tory, the following intervals are recommended for the categories: Category DRI BWI CLI Extremely low - 25 - 10 < 5 Very low 26 - 32 11 - 20 5.0 – 5.9

Low 33 - 42 21 - 30 6.0 – 7.9

Medium 43 - 57 31 - 44 8.0 – 14.9

High 58 - 69 45 - 55 15.0 - 34

Very high 70 - 82 56 - 69 35 - 74 Extremely high 82 - 70 - ≥ 75

Table 1.3 Category intervals for drillability indices. The intervals are related to the distribution of the test results in the database. The in-tervals are based on the following: Category Cumulative percentage of total number of samples Extremely low 0 – 5 Very low 5 – 15

Low 15 – 35

Medium 35 – 65

High 65 – 85

Very high 85 – 95 Extremely high 95 – 100

Table 1.4 Cumulative percentage for category intervals of drillability indices.

1. DRILLABILITY 1.6 Classification of Indices

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Furthermore, it has been taken into consideration that the database most likely is not representative for the total rock mass. When testing rock samples, it is more interest-ing to test samples of low drillability or high abrasivity than samples of good drillabil-ity or low abrasivity, since the latter seldom represents any risk regarding costs. The recommended intervals for the categories are therefore moved towards the original (and higher) intervals of classification made by Lien and Selmer-Olsen.

APPENDIX A. Previous Editions

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A. PREVIOUS EDITIONS Previous editions of the Drillability Report including project group members: 6-75 THE DRILLING RATE INDEX DRI (Norwegian edition) Bjørn Kielland Halvdan Ousdal O. Torgeir Blindheim Odd Johannessen 8-79 DRILLABILITY Catalogue of Drillability Indices (Norwegian and English editions) O. Torgeir Blindheim Erik Dahl Johansen Arne Lislerud Odd Johannessen 4-88 DRILLABILITY Catalogue of Drillability Indices (Norwegian edition) Amund Bruland Sigurd Eriksen Astrid M. Myran Rune Rake Odd Johannessen 13-90 DRILLABILITY Catalogue of Drillability Indices (Norwegian and English editions) Amund Bruland Sigurd Eriksen Astrid M. Myran Odd Johannessen 13A-94 DRILLABILITY Test Methods (Norwegian edition) Amund Bruland

APPENDIX B. Research Partners

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B. RESEARCH PARTNERS The following external research partners have supported the project:

• =Statkraft anlegg as • =Norwegian Public Roads Administration • =Statsbygg • =Scandinavian Rock Group AS • =NCC Eeg-Henriksen Anlegg AS • =Veidekke ASA • =Andersen Mek. Verksted AS • =DYNO Nobel • =Atlas Copco Rock Drills AB • =Tamrock OY • =The Research Council of Norway

APPENDIX C. Laboratory Testing

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C. LABORATORY TESTING Samples for testing should be marked and sent to: The Laboratory of Engineering Geology SINTEF Rock and Mineral Engineering N-7034 Trondheim NORWAY Some information about the sample should be given: • = Rock type • = Location of sample site, preferably also co-ordinates • = Project name • = Registered data related to the sample, e.g. drilling rate and drill steel wear • = Laboratory tests to be performed. The information may, if desired, be confidential. At present (1998), testing of one sample with regard to DRI, BWI, CLI and quartz content (DTA, differential thermal analysis) amounts to NOK 7600. For testing of a series of samples, a special price may be arranged. The same costs are currently applied for the Mini-DRI test. To get the best possible information on the rock abrasiveness on drill bits or cutters, an analysis of the rock mineral content should be performed as well. The Laboratory of Engineering Geology applies XRD (X-Ray Diffraction), a semi-quantitative method. The cost of one XRD test is at present NOK 2000. Contact Persons SINTEF Rock and Mineral Engineering Filip Dahl e-mail: Filip.E.Dahl@civil.sintef.no tel: +47 73 59 48 35 Torill Sørløkk e-mail: Torill.Sorlokk@civil.sintef.no fax: +47 73 59 47 78 The Department of Building and Construction Engineering at NTNU Amund Bruland e-mail: amund.bruland@bygg.ntnu.no tel: +47 73 59 47 37 fax: +47 73 59 70 21