lab manual rock & aggregate

7/28/2019 lab manual rock & aggregate

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ROCK

And

AGGREGATE

Test procedures


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Rock and aggregate laboratory manual

INTRODUCTION

The test procedures collected in this manual are based on ISRM Suggested Methods, on ASTM, French

and British Standards. However, in various cases the test procedures were adapted to the type of

equipment generally used in a rock mechanics laboratory and in some cases to the equipment present at

de laboratory of Engineering Geology, Delft University of Technology. This means that often a realistic

compromise had to be found between strict requirements and practical possibilities.

Test procedures are continuously updated as a result of further development of rock mechanics. This

manual reflects the situation at the time that the manual was prepared.

Warning: Whenever tests have to be performed following a prescribed standard, always

consult that standard before testing.

This laboratory manual is an extended and improved version of the manual made by Dr Niek Rengers

from the International Institute for Aerospace Survey and Earth Sciences (ITC ) Enschede.

W. Verwaal and A. Mulder

Laboratory of Engineering Geology,

Faculty of Civil Engineering and Geosciences,

Department of Applied Earth Sciences,Delft University of Technology

September 2000

References: ISRM: "Rock Characterization, Testing and Monitoring", ISRM Suggested Methods,

Editor E.T. Brown. Pergamon press 1981

ASTM: "1985 Annual Book of ASTM Standards", Volume 04.08: Soil and Rock;

Building Stones. Published by ASTM in 1986.

BS: 812: Published by British Standards Institution.

Geotechnical Laboratory DGM, Thimphu Bhutan

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Geotechnical laboratory DGM, Thimphu Bhutan

CONTENTS

1.1: Standard test procedure for the determination of rock material dry density............................. ...................... 4

1.2: Standard test procedure for the determination of the (natural) water content of rock material. ..................... 6

1.3: Standard test procedure for the determination of porosity of rock material. .................................................. 8

2.1: Standard procedure for the determination of Schmidt Hammer Rebound Hardness. ................................... 10

2.2: Equotip hardness number ............................................................. ................................................................ 13

2.3: Standard laboratory test procedure to determine the ultrasonic velocity in rock........ .................................. 15

2.4: Standard test procedure for the determination of rock material toughness in the laboratory........................18

2.5: Standard test procedure for the determination of rock swelling properties. ................................................. 19

2.6: Standard test procedure for the determination of the slake durability. ......................................................... 21

2.7: Standard test procedure for the determination of the point load strength of rock material........................... 23

3.1: Standard procedure for the determination of rock material indirect tensile strength by the Brazilian test ... 30

3.2: Standard test procedure for the determination of unconfined compressive strength of rock material. ......... 32

3.3: Standard test procedure for the determination of the strength of rockmaterial in triaxial compression ....... 35

3.4: Standard test procedure for the determination of the shear strength of rock material in direct shear........... 38

3.5: Shear strength of rock discontinuities with Golder Shear Box....................................... .............................. 41

4.1: Standard test procedure for the determination of the modulus of elasticity.................................................. 43

4.2: Standard test procedure for the determination of the Poisson Ratio............................................................. 46

5.1: .Standard test procedure for the determination of the resistance to abrasion of aggregate by use of the Los

Angeles machine. .......................................................... ............................................................ ................ 49

5.2: Aggregate impact value BS 812:part 112 1990 ....................................................... .................................... 54

5.3: Aggregate crushing value BS 812:part 110:1990 ............................................................. ........................... 58

5.4: Ten per cent fines value BS 812:part 111 1990........................................................ .................................... 62

5.5: Micro-Deval abrasion test NF P 18-572 (AFNOR 1978) ............................................................. ................ 65

6.1: The methylene blue adsorption spot test............................................................... ........................................ 67

Appendix I: Rock core preparation............................................................... ....................................................... 72

Appendix II: Table with indications of strength properties of rock......................................................................69


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1.1: Standard test procedure for the determination of rock material dry density.

Scope of the test

The objective of the test is to measure the dry density of samples of cylindrical or other regular form.(For samples of irregular form see Remarks). The dry density is expressed in units of mass (kg or g) per

unit of volume (m or cm or mm). All individual steps for this test are also contained in the porosity

determination test.

Apparatus used

- Oven (24 hours at 105 C +/- 5 C)- Desiccator

- Calliper with accuracy of 0.1mm

- Balance with accuracy of 0.01 g and range of 100 g

- Sample container (not-corrodible) with airtight lid.

Procedure

- Prepare three specimens of regular form from a representative sample of rock. The size of the

specimens should be such that both following conditions are fulfilled:

- the specimen mass should be at least 50 g (cube of 3x3x3cm, or cylinder with diameter of 2.5 cm

and length 5 cm.)

- the minimum specimen dimension should be at least ten times the maximum grain size of the rock.

- The specimen volume (V) is calculated from the average value of several calliper readings (3 at least,

with an accuracy of 0.1 mm) for each dimension of the specimens.

- The specimen is located in a container (to avoid loss of mass during subsequent specimen handling),

but without the lid, and dried in an oven to constant mass (generally 24 hours is enough) at atemperature of 105 C. After replacing the lid, the specimen is cooled in a desiccator for 30 minutes.The mass (C) of the container (and lid) with the specimen is determined with an accuracy of 0.1 g.(d)

The container with the lid is cleaned and dried and its mass (A) is determined.

Calculation

Dry density:

)mmg/orcmg/ormkg/(inV

A-C=

volume

massdry=d 333

(dry unit weight = d x 9.8 (in kN/m))

Reporting

The report shall include the following information:

(a) Data on the sampling:

- Project name, location, date of sampling, sample number, depth below terrain (in case of

borehole)

- Type of sample (core, block, disturbed, or other), sample dimensions

- Lithology, weathering grade, grain size, natural water content

- Sample transport and storage conditions.

(b) Data on the specimens:

- Form, dimensions and weight of all specimens.


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(c) Data on the testing procedure:

- The individual results for the three specimens (or more) per rock sample should be reported,

together with the average result for the sample. Density values should be given to the nearest 10

kg/m. The report should specify that bulk volume was obtained by calliper measurement.

Remarks

If irregular samples are used the volume can be determined by measurement of the saturated-submerged

mass (Msub) and the saturated mass (Msat)of the samples. The volume is then calculated as follows

water

Msub-Msat=V

It should be specified in the report that the volume was determined by measurement of the saturated

submerged mass.

Reference

International Society for Rock Mechanics Suggested Methods "Rock Characterisation, Testing and

Monitoring" Editor E.T. Brown, Pergamon Press 1981, pages 81 - 85

ASTM Standard Test Method C97-83


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1.2: Standard test procedure for the determination of the (natural) water content of rock

material.

Scope of the test

The objective of the test is to determine the water content of the rock material as it was retrieved in the

field. For the accurate determination of the in-situ water content, the sampling, storage, transport and

handling precautions should be such that the water content remains within 1% of the in situ value.

Apparatus used

- Oven (24 hours at 105 C +/- 5C)- Desiccator

- Calliper with accuracy of 0.1 mm

- Balance with accuracy of 0.1 g and range of 1000 g

- Sample container (non corrodible) with airtight lid.

Procedure

- A representative sample must consist of at least 10 lumps, fulfilling the following conditions:

- the mass of each lump should be at least 50 g

- the minimum lump dimension should be at least ten times the maximum grain size of the rock.

- The lumps are located in a container, the lid placed, and the mass (B) is determined with an accuracy

of 0.1 g.

- The lumps are kept in the container, but with the lid removed, and dried in an oven to constant mass

(generally 24 hours is enough) at a temperature of 105C. After replacing the lid the lumps are cooledin a desiccator for 30 minutes. The mass (C) of the container with the lumps is determined with an

accuracy of 0.1 g.

- The container with the lid is cleaned and dried, and its mass (A) is determined.

Calculation

Water Content:

%100%100

==AC

CB

grainmass

assporewatermw

Reporting

The report includes the following information:



borehole).

- Type of sample (core, block, disturbed, or other), sample dimensions.

- Lithology, weathering grade, grain size, natural water content.




- Density and water content during testing.

(c)Data on the testing procedure.


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The water content should be reported to the nearest 0.1 %. It should be stated whether this

corresponds to "in-situ" water content. If this is the case then the precautions which were taken to

preserve the natural water content during sampling and storage should be specified.

Reference


Monitoring" Editor E.T. Brown, Pergamon Press 1981, pages 83

ASTM Standard Test Method D2216-80.


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1.3: Standard test procedure for the determination of porosity of rock material.

Scope of the test

The objective of the test is to measure the porosity of rock specimens of cylindrical or other regular

form.(For samples of irregular form see Remarks). The porosity is the volume of the pores in the rock

expressed as a percentage of the total volume of the rock.

Apparatus used

- Oven (24 hours at 105C +/-5C)- Desiccator

- Calliper with an accuracy of 0.1 mm

- Balance with an accuracy of 0.01 g and a range up to 200 g

- Sample container (non-corrodible) with airtight lid

- Vacuum chamber with pressure less than 800 Pa (6 Torr)

Procedures

- Prepare three specimens of regular form from a representative sample of rock. The size of the

specimens should be such that both following conditions are fulfilled:

- the specimen mass should be at least 50 g (a cube of 3x3x3 cm, or a cylinder with a diameter of 2.5

cm and a length of 5 cm).

- the minimum specimen dimension should be at least ten times the maximum grain size of the rock.

- The specimen bulk volume (V) is calculated from the average value of several calliper readings (3 at

least, with an accuracy of 0.1 mm) for each dimension of the specimen.

- The specimen is saturated by water immersion in a vacuum of less than 800 Pa (6 torr) for a period of

at least 1 hour, with periodic agitation to remove trapped air.

- The specimen is removed from the water and surface dried using a moisten cloth, care being taken toremove only surface water and to ensure that no fragments are lost. The specimen is located in a

container to avoid loss of mass during subsequent sample handling. The mass of specimen plus

container (B) is determined with an accuracy of 0.01 g.

- The specimen (in the open container) is dried in an oven to constant mass (generally 24 hours is

enough) at a temperature of 105C. After closure of the container and cooling in a desiccator for 30minutes, the mass (C) of the dry sample with the container (and lid) is determined with an accuracy of

0.01 g.

- The container with the lid is cleaned and dried and its mass (A) is determined with an accuracy of

0.01 g.

Calculation

Saturated surface dry mass ABMsat =

Dry specimen mass ACMs =

Pore volumewaterDensity

MsMsatVv

=

Porosity %100=V

Vvn


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Reporting




borehole).







- The individual results for the three specimens (or more) per rock sample should be reported,

together with the average result for the sample. Porosity values should be given to the nearest 0.1

%.

- The report should specify that bulk volume was obtained by calliper measurement, and thatporosity was obtained by water saturation.

Remarks

If irregular samples are used the volume can be determined by measurement of the saturated-submerged

mass (Msub) and the saturated mass (Msat) of the samples. The volume in this case is:

It shall be specified in the report if the volume has been determined with the saturated-submerged mass.

Reference


Monitoring" Editor E.T. Brown, Pergamon press 1981, pages 81 to 85.

ASTM Standard Test method C97-83


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2.1: Standard procedure for the determination of Schmidt Hammer Rebound Hardness.

Scope of the test

The rebound value of the Schmidt Hammer is used as an index value for the intact strength of rock

material, but it is also used to give an indication of the compressive strength of rock material. The

Schmidt Hammer is essentially a field instrument but it may be used as well in the laboratory. When

used in the laboratory special attention has to be given to the connection of the sample with the V-block

and the base, and to the connection with the supporting table, as these factors have a great influence on

the testing results.

The method is of limited use on very soft and on very hard rocks.

Apparatus used

- A standard Schmidt Hammer of the L-type having an impact energy of 0.74 Nm.

- A calibration test anvil for the calibration of the test hammer rebound numbers.

- A steel base of minimum weight of 20 kg with a steel V block for cylindrical samples and with aclamping device. Such a base can also be used if irregularly formed samples (lumps) should be tested

in the laboratory.

- A vertically oriented cradle to guide the Schmidt Hammer in a vertical downward direction during

the testing.

Test Procedure

- Prior to the testing sequence, the Schmidt Hammer should be calibrated using the calibration anvil

supplied by the manufacturer of the Schmidt Hammer for that purpose. The average value of 10

readings on the test anvil should be obtained.

- The specimens obtained for the laboratory testing should be representative and characteristic for the

rock material to be studied. The type-L hammer should be used on NX (54 mm) or larger diametercore samples or on block samples having an edge length of at least 60 mm. The specimens must be

securely clamped to a rigid base to adequately secure the specimen against vibration and movement

during the test. The base must be placed on a flat surface that provides firm support.

- The test surface of all specimens in the laboratory and testing locations in the field, should be smooth

and flat over the area of contact with the plunger. This area and the rock material beneath the surface

to a depth of 60 mm shall be free from cracks, or any discontinuity in the rock.

- The hardness values obtained will be affected by the orientation of the hammer. In the laboratory the

vertical cradle will hold the Schmidt Hammer in vertical downwards position during the testing.

During in-situ testing in the field the testing direction must always be perpendicular to the surface

tested. The orientation of the Schmidt Hammer in that case should be recorded and reported in the

results. With the Schmidt Hammer a chart is provided to make corrections for non vertical

measurements.- At least 20 individual tests must be conducted on any rock sample. The test locations shall be

separated by at least the diameter of the plunger. Any test that causes cracking or any other visible

failure of the rock should be rejected. Errors in specimen preparation and testing tend to produce low

hardness values.


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Fig.2.1.1: Relation between the Schmidt Hammer Hardness, type L hammer and the Uniaxial

Compressive Strength of Rock (ISRM).


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Calculation

- The correction value is calculated as follows

- For tests in the laboratory on rock material of uniform strength the measured test values for the

sample must be ranked in descending value. The lower 50% of the values should be discarded and the

average calculated of the upper 50% values. This average shall be multiplied by the correction factor

to obtain the Schmidt Rebound Hardness.

- When a number (15 to 20) readings is taken in the field to characterise a unit with some variation of

hardness and strength, the same procedure for reporting as used with point load strength testing can

be applied, which involves ranking, discarding of the upper and lower 2 or 3 values and averaging of

the remaining values. The maximum and minimum of the remaining values are recorded as the range

of the Schmidt Hammer Rebound Value. (For the influence of rough surface conditions in situ see

remarks)

Reporting




borehole)

- Type of sample (core, block, broken, in situ or other), sample dimensions


- Sample transport and storage conditions


- Form, dimensions and weight of all specimens

- Density and water content during testing

(c) Data on the testing procedure:- Orientation of the Schmidt Hammer during every test in the field

- Method of clamping used in the laboratory

- The Schmidt Hammer Rebound Hardness value as obtained from the calculations explained

above.

- Indication of the value of uniaxial compressive strength in Mpa +/- the average dispersion as read

from the graph in figure 2.1.1, with reference to the fact that the graph has been used for this

purpose. The rock density (test nr.1.1) must be known when this graph is used.

Remarks

When measurements are taken in situ, the testing location is usually not as flat as is required. By

repetition of the test several times at exactly the same location the rebound value usually is observed toincrease until a constant value is reached. This is due to cracking of points of the surface asperities and

the subsequent increase of the contact area between the plunger and the rock surface. The reading must

be taken after it has reached a stable value.

References


Monitoring" Editor E.T. Brown, Pergamon Press 1981, pages 101 and 102.


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2.2: Equotip hardness number

Scope of the test

The equotip is de developed by Proceq SA, the company with manufacturers the Schmidt Hammer, to

measure the hardness of metallic material. According to research at the section of Engineering Geology

of Delft University the equotip can also used as a index test to estimate the rock strength. An article

about Equotip is added to this manual as appendix 2.

Apparatus used

figure 2.2.1.

1 loading tube

2 guide tube

3 coil with coil holder

4 release button5 connection cable leading to the indicating device with coil plug

6 large support ring, 6a small supportring

7 impact body

8 spherical test tip

9 impact spring

10 loading spring

11 catch chuck

12 material to be tested

figure 2.2.2.: Using the Equotip impact device

Fig 2.2.1


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Test Procedure

- Prior to the testing the equotip should be calibrated using the anvil supplied with the equotip

apparatus. The correct reading on the anvil is located on the anvil.

- The test sample should be representative and characteristic for the rock material to be studied.

- Although smaller sample can be used, it is recommended to use rock sample with a minimum volume

of 200 cm3.

- The test surface of all specimens in the laboratory and testing locations in the field should be smooth

and flat over the test area, minimum about 10 cm2.

- At least 10 individual test must be conducted on any rock sample. the test locations shall be separated

by at least 5mm. On a core sample we can take 5 reading on each side.

Calculation

From the ten readings the highest en the lowest reading must be discard, from the remaining values the

average is calculated and expressed as the L value.

We can estimate the Unconfined compressive strength with the following formula:

valueL*E4.906=.C.S.e

stimatedU 2.974-7

Reporting



- Project name, location, date of sampling, sample number, depth below terrain (in case of borehole)

- Type of sample (core, block, broken, in situ or other), sample dimensions


- Sample transport and storage conditions(b) Data on the specimens:




- The type of equotip device

- The equotip L value as obtained from the calculations explained above.

- Indication of the value of uniaxial compressive strength in MPa with reference to the fact that the

graph has been used for this purpose.

Remarks

When measurements are taken in situ, the testing location is usually not as flat as is required. The use ofa battery operated hand-held drilling machine with a small grinding stone is advisable.

References

Verwaal W. and Mulder A. Estimating Rock Strength with the Equotip Hardness Tester Int. J. Rock.

Mech. Min. Sci. & Geomech. Abstr. Vol. 30, No. 6. pp. 659-662, 1993.


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2.3: Standard laboratory test procedure to determine the ultrasonic velocity in rock.

Scope of the test

This test is used to determine the velocity of propagation of elastic compression- and shear waves in

rock samples in the laboratory. The ultrasonic (dynamic) elastic constants of a rock can be determined

from the compression and shear wave velocities and the rock density for isotropic or slightly anisotropic

rock.

Apparatus used

- A pulse generator unit. Three different types of pulse generators are used for three different types of

test procedures:

- high frequency ultrasonic pulse technique

- low frequency ultrasonic pulse technique

- sine wave resonant technique

- The transducers consist of a transmitter which converts electrical pulses into mechanical pulses and areceiver, which converts mechanical pulses into electrical pulses. environmental conditions such as

average temperature, air moisture and impact should be considered in selecting the transducer

element. Piezoelectric elements are usually recommended, but magnetostrictive elements may de

suitable.

- Display and timing unit. An oscilloscope is needed for the display of the transmitted and received

pulse, which is necessary to separate arrivals of compression and shear waves. The timing unit must

be capable of measuring time intervals between 2 micro seconds and 5 milliseconds to an accuracy of

1% .

- Measuring calliper with an accuracy of 0.1 mm

- Acoustical bench which can keep the sample and the transducers properly aligned along one axis with

the required contact pressure between transducers and sample.

- Contact fluid to ensure a good contact between the transducers and the flat and polished rock surface.

Test procedure

- Sample preparation. Care should be taken that core drilling, handling, storage, sawing, grinding and

lapping does not cause mechanical damage of the test sample. As sample form a cylinder with

perpendicular and flat end faces is usually applied.

- Three different types of test procedure are possible:

- The high frequency technique, in which pulses with a frequency of 100 kHz to 2 MHz are used.

Rectangular blocks, cylindrical cores or even spheres can be used. The lateral minimum

dimension (perpendicular to the direction of wave propagation) is recommended to be not smaller

than 10 times the wave-length. The travel distance of the pulse through the rock must be at least

10 times the average grain size. The positioning of the transducers on the sample is illustrated infigure 2.2.1.

In case the velocities of compression and shear waves are calculated from the measured travel

time and the distance between transmitter and receiver. In case b the distance between transmitter

and receiver is varied. The velocities of compression and shear waves are calculated from the

curves of travel time vs. distance.

- The low frequency technique, in which pulses with a frequency of 2 to 30 kHz are used. This

method is suitable for samples which are long compared to the diameter (length to diameter ratio

> 3). The wave length of the pulse must be long compared with the diameter (ratio > 5). The

positioning of the transducers is in principle the same as in figure 2.3.1., when measuring

compression wave velocity, but figure 2.3.2 shows the preferred arrangement for positioning

when measuring the shear wave velocity.


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The velocities of compression and shear waves are determined as in the high frequency technique.

- The sine wave resonant technique. Samples of cylindrical form with a length to diameter ratio > 3and a wavelength to diameter ratio > 6 can be used in this method. Positioning of transducers is

as shown in fig 2.2.1. for the determination of compression wave velocity, and as shown in

figure 2.2.2. for shear wave velocity.

Figure 2.3.1.: Positioning of transmitter and receiver on the test sample used in the high frequency

technique.

Figure 2.3.2.; Positioning of transducers when measuring shear wave velocity with the low frequency

technique.

Calculation

For the high frequency and low frequency techniques the velocities are calculated from the travel time

(tp and ts) and the distance between transmitter and receiver (d), by using the following equations:

sec)/( Mints

dVpwavencompressiovelosity =

and

sec)/( mints

dVswaveshearvelosity =

If the seismic profiling technique was used (positioning of transducers as in figure 2.2.1.b) the velocities

are given by the slope of the curve travel time versus distance d.

For the resonant technique the following calculation is used

sec)/(02 minfLVd =

where Vd is the wave velocity, L is the length of the sample , and f0 is the resonant frequency of zero

mode of either longitudinal (compressional) or shear (torsional) vibrations.

The following so called ultrasonic (dynamic) elastic constants can be calculated if the density of the

material is determined and if the sample is isotropic or very slightly anisotropic:


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)Mpa(inVs-Vp

)Vs4-Vs3(*Vs*D=EelasticityofModulus

22

222

Mpa)(inVsxD=GrigidityofModulus2

)Vs-Vp2(

Vs2-Vp=ratiooissonsP

22

22

(inMpa))Vs2-Vp(D=constantamesL22

(inMpa)3

)Vs4-Vp(3D=KmodulusBulk

22

In these formulas D is the rock material density in kg/m.

Reporting

The report should include the following information:



borehole).








- Description of experimental technique and of electronic equipment used.

- Tables with the values of the velocities measured and the calculated ultrasonic elastic constants.

Remarks

More detailed information on the electronic equipment can be found in the ISRM and ASTM standard

procedure (see references).

References


Monitoring" Editor E.T. Brown, Pergamon Press 1981, pages 107 to 110.

ASTM standard D2845-83


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2.4: Standard test procedure for the determination of rock material toughness in the

laboratory.

Scope of the test

The objective of the test is to determine the resistance of rock material against impact by a falling

hammer.

Apparatus used

- ASTM standard testing machine for the drop impact toughness test.

Test procedure

- Samples needed for this test are cylindrical in form, with flat end faces, which are perpendicular to

the axis of the cylinder. The length of the sample is 25 mm, the diameter must be 24 to 25 mm. The

test samples should be free of cracks or weakness zones.- The sample is placed with one of its end planes on an iron anvil. A weight of 2 kg is permitted to fall

vertically between parallel guides upon a spherical-ended plunger weighing 1 kg, which rests on top

of the specimen. The height of the first blow is 1 cm and each successive blow thereafter is increased

in height by 1 cm, until the sample fails.

- The height in cm of the fall which caused failure of the sample is recorded as the toughness of the

material.

- At least six specimens of the same rock material, three being prepared so that the direction of impact

is perpendicular, and three parallel to the plane of structural weakness if such a plane is apparent.

Reporting

The report shall include the following information:(a) Data on the sampling:


borehole).








- The individual and the average toughness of the three specimens in each set are separately

reported.

References

ASTM Standard Testing Technique ASTM D-3-18

Deere, D.U. and R.P Miller : "Engineering Classification and Index Properties for Intact Rocks" Air

Force Weapon Lab. New Mexico, USA 1966.


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2.5: Standard test procedure for the determination of rock swelling properties.

Scope of the test

This test is intended to determine the rock swelling properties when an undisturbed specimen of that

rock is immersed in water.

Two swelling properties are distinguished:

- the swelling pressure index under conditions of zero volume change.

- the swelling strain index for a radially confined specimen with axial surcharge.

Apparatus used

Adaptation of soil consolidation testing equipment, as described in the ISRM suggested methods on

pages 89 and 90, consisting of the following:

- A metal ring for rigid radial restraint of the specimen, polished and lubricated to reduce side friction

and of depth sufficient to accommodate the fully swollen specimen.

- Porous plates to allow water access at top and bottom of the specimen, the top plate of such adiameter to slide freely in the ring. Filter paper may be inserted between specimen and porous plates.

- A cell to contain the ring with the specimen, capable of being filled with water to a level above the

top porous plate (the principal features of the cell and specimen assembly are illustrated in the ISRM

publication).

- A micrometer dial gauge (0.0025 mm) mounted to measure the swelling displacement at the central

axis of the specimen.

for the swelling pressure index :

- A load measuring device capable of measuring to an accuracy of 1% the force required to resist

swelling.

- A loading device such as a screw jack, capable of continuous adjustment to maintain the specimen at

constant volume as swelling pressure develops. The force should be applied through rigid members toensure that the porous plates remain flat, a spherical seat allowing rotation of the top porous plate.

for the swelling strain index :

- A loading device capable of applying a constant pressure of 5kPa to the specimen, this pressure to be

maintained within 1% throughout the swelling of the specimen. The force should be applied through

rigid members to assure that the porous plates remain flat, a spherical seat allowing rotation of the top

porous plate.

Test procedure

- For testing at natural initial water content, preparation of the specimen should be such as to retain

water content within 1% of its in situ value. Per sample three test specimens must be prepared.- The specimen should be a cylinder fitting closely in the ring. It should have a diameter not less than

four times its thickness. The thickness should be more than 15 mm or ten times the maximum grain

size, whichever is greater.

- The initial thickness and the diameter of the specimen are recorded with an accuracy of 0.1%.

for swelling pressure index :

- The apparatus is assembled and a small axial stress of about 10 kPa is applied to the specimen.

- The cell is flooded with water to cover the top porous plate.

- The applied force is regularly adjusted to maintain zero specimen swelling (less than 0.01 mm)

throughout the test.


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- The swelling force is recorded as a function of time until it reaches a constant level or passes a peak.

for swelling strain index :

- The apparatus is assembled and the specimen is loaded axially to a pressure of 3 kPa.

- The cell is flooded with water to cover the top porous plate.

- The swelling displacement is recorded as a function of time until it reaches a constant level or passes

a peak.

Calculation

MPa)(inA

FindexpressureSwelling

In this formula F = maximum axial swelling force recorded during the test and A = cross sectional area

of the specimen

(ratio)100%xL

d=indexstrainSwelling

In this formula d = maximum swelling displacement recorded during the test and L = initial thickness of

the specimen.

Reporting




borehole).

- Type of sample (core, block, disturbed, or other), sample dimensions.- Lithology, weathering grade, grain size, natural water content.



- Dimensions and weight of all specimens.

(c) Data on the testing:

- The report must clearly indicate that the specimen was radially confined during the swelling test.

- For each specimen the value of the swelling pressure index or swelling strain index respectively.

- The initial water content of the specimen. It must be indicated if this equals the natural water

content (see also section 5a).

Remarks

The ISRM suggested method describes a third possible type of swelling testing for unconfined rock

specimen. This type of test is to be used for rock material which does not change appreciably its

geometry when swelling. It needs a specially built cell which is described in the ISRM book.

References

International Society for Rock Mechanics Suggested Methods "Rock Characterization, Testing and



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2.6: Standard test procedure for the determination of the slake durability.

Scope of the test

This test is intended to assess the resistance offered by a rock sample to weakening and disintegration

when subjected to cycles of drying and wetting. The ISRM standard is based on two cycles of drying

and wetting. Four or five cycles of drying and wetting are recommended when evaluating rocks of

higher durability.

The slake durability index is expressed as the percentage ratio of the final dry sample mass to the initial

dry sample mass.

Apparatus used

- Standard slake durability testing equipment as specified by ISRM (page 92+93)

- Oven capable to maintain a temperature of 105 C (+/-5C) for a period of at least 12 hours- Balance capable to determine the mass of the drum plus sample to an accuracy of 0.5g

Procedure

- A representative sample is selected, consisting of ten lumps of rock, each with a mass of 40 to 60

grams, to give a total sample of 450 to 550 grams. The maximum grain size of the rock should not be

larger than 3 mm. Lumps should be as good as possible rounded in form and corners should be

rounded during preparation of the sample.

- The sample is placed in a clean drum and is dried to constant mass at a temperature of 105C, usuallyrequiring 2 to 6 hours in the oven. The mass (A) of the drum plus the sample is recorded with an

accuracy of 0.1 g. The sample is then tested after cooling.

- The lid of the drum is replaced, the drum is mounted in the trough and coupled to the motor.

- The trough is filled with slaking fluid (usually tap water at 20C) to a level 20 mm below the drumaxis, and the drum rotated for 200 revolution during a period of 10 minutes +/- 0.5 minutes.

- The drum is removed from the trough, the lid removed from the drum, and the drum plus retained

portion of the sample is dried to constant mass at 105C.. The mass B1 of the drum plus retainedportion of the sample is recorded after cooling with an accuracy of 0.1 g.

- Steps (c) to (e) are repeated and the mass B2 of the drum plus retained portion of the sample after

another 200 revolutions is recorded.

- The drum is brushed clean and its mass D is recorded with an accuracy of 0.1 g.

Calculation

100%xD-A

D-B

=Id(ISRM)indexdurabilitySlake

2

2

100%xD-A

D-B=Idcyclesnafter

nn

Reporting




borehole)


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- Form of the lumps


- The slake durability index after each cycle rounded to the nearest 0.1%

- The nature and temperature of the slaking fluid. This will usually be tap water at 20C, but forexample distilled water, natural ground water, sea water, a dilute acid, or a dispersing agent may

be specified.

- The appearance of the fragments retained in the drum.

- The appearance of the material passing through the drum.

Remarks

Samples which show a slake durability index after two cycles which is lower than 20% should be further

subjected to soil classification tests such as the determination of Atterberg limits and hydrometer grain

size distribution determination.

A classification combining slake durability index and plasticity index is suggested in cases where

detailed characterization (particularly of argillaceous rocks) is required.

References

International Society for Rock Mechanics Suggested Methods: "Rock Characterisation, Testing and


Goodman, R.E.: "Introduction to Rock Mechanics", John Wiley & Sons, 1980, pages 36 and 37.


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2.7: Standard test procedure for the determination of the point load strength of rock material

Scope of the test

The point load strength test is intended as an index test for the strength classification of rock material. It

may also be used to predict other strength parameters with which it is correlated, for example uniaxial

compressive and tensile strength. The test determines the Point Load Strength Index Is(50) of rock

specimens (expressed in units of stress, preferably in MPa) and their Strength Anisotrophy Is(50), which is

the ratio of Point Load Strength values in directions which give the highest and lowest values.

Rock specimens in the form of either core (the diametral and axial tests), cut blocks (the block test), or

irregular lumps (the irregular lump test) are broken by a pair of spherically truncated, conical platens

(see fig. 2.7.1).

figure 2.7.1 platen shape and

tip radius.

Apparatus used

- The standard testing machine for point load testing, according to the specifications listed in the

"suggested method for determining point load strength" issued by the International Society for rock

mechanics.

- A calliper to measure the width W of the specimens and the diameter D of core samples. Accuracy

0.1 mm.

Specimen selection and preparation

A test sample is defined as a number of rock specimens of similar strength for which a single Point Load

Strength value is to be determined (preferably 10 specimens at least are tested from 1 sample).

For diametrical tests the specimens should have a ratio of length to diameter which is greater than 1.0.

For axial tests the core specimens should have a ratio length/diameter between 0.3 and 1.0.

For block tests and for irregular lump tests the shape requirements are illustrated in figure 2.7.2.(c) and

2.7.2.(d). The ratio D/W should be between 0.3 and 1.0, preferably close to 1.0.

For all types of samples the size limits are 15mm


24/75


Test procedure for diametrical test

- The specimen is inserted in the testing machine and the platens are closed to make contact along a

core diameter, ensuring that the distance L between the contact points and the nearest free end is at

least 0.5 times the core diameter (fig. 2.7.2.a).

Figure 2.7.2.:Specimen shape requirements for (a) the diametrical test; (b) the axial

test; (c) the block test; (d) the irregular lump test

- The distance D is recorded +/- 2%.

- The load is steadily increased such that failure occurs within 10 to 60 seconds and the failure load P is

recorded. The test should be rejected if the failure surface passes through only one loading point (see

fig 2.7.3).

- The procedures above shall be repeated for the remaining specimens in the sample.


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figure 2.7.3.: Typical modes of failure for valid and invalid tests. (a) valid diametrical

test; (b) valid axial tests: (c) valid block tests; (d) invalid diametrical test; (e) invalid

axial test

Test procedure for the axial test- The specimen is inserted in the testing machine and the platens are closed to make contact along a

line which is perpendicular to the core end faces. In case of isotropic rock this is usually parallel to

the core axis, but for anisotropic rock see figure 2.7.3.

- The distance D between the platen contact points is recorded +/- 2%. The specimen width W,

perpendicular to the loading direction is recorded +/- 5%.

- The load is steadily increased in such a way, that failure occurs within 10 to 60 seconds, and thefailure load P is recorded. The test should be rejected as invalid if the fracture surface passes through

only one loading point see fig. 2.7.3.


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figure 2.7.4.: loading directions for test on

anisotropic rock. - The procedures above shall be repeated for the

remaining specimens of the sample.

Test procedure for the block and irregular lump test

- The specimen is inserted in the testing machine, assuring that the distance L (see fig. 2.7.2(c) and

2.7.2(d)) is at least 0.5 W. The specimen must be inserted in such a way that D is the smallest

dimension of the specimen and that the platens are in contact with the specimen away from edges and

corners.- The distance D between the platens is recorded +/- 2%. The smallest specimen width W

perpendicular to the loading direction is recorded +/- 5%. If the sides are not parallel, the W is

calculated as (W1 + W2)/2 as shown in fig. 2.7.2(d). This smallest width is used for further

calculation. It does not depend on the actual mode of failure.

- The load is steadily increased in such a way that failure occurs within 10 to 60 seconds and the failure

load P is recorded. The test should be rejected as invalid if the fracture surface passes through only

one loading point.

- The procedures above shall be repeated for the remaining specimens of the sample.

Testing of anisotropic rock

- When a rock is shale, bedded, schistose or otherwise anisotropic due to a clearly developed splittingdirection, it should be tested in directions which give the lowest and highest strength values, which

are in general parallel and perpendicular to the planes of anisotropy.

- If the sample consists of core drilled through the weakness planes, a set of diametrical test may be

completed first, spaced at intervals which will yield pieces which can then be tested axially.

- Best results are obtained when the core axis is perpendicular to the planes of weakness, so that when

possible the core should be drilled in this direction (this is possible when the cores are bored in the

laboratory from a large block of rock). The angle between the core axis and the line perpendicular to

the weakness planes should preferably not exceed 300.

- For measurement of the Is value in the directions of least strength, care should be taken to ensure that

load is applied along a single weakness plane. Similarly when testing for the Is value in the direction

of greatest strength, care should be taken to ensure that the load is applied perpendicularly to the

weakness planes (see fig. 2.7.4.).- If the sample consists of blocks or irregular lumps, it should be tested as two sub-samples, with load

applied firstly perpendicular to, then along the observable planes of weakness. Again, the required

minimum strength value is obtained when the platens make contact along a single plane of weakness.

Calculation

Uncorrected Point Load strength

The uncorrected point load strength Is is calculated as P/De2, where De (the equivalent core diameter) is

given by:


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De2

= D2

for diametrical tests

= 4A/, for axial, block and lump tests

and

A = W * D = minimum cross sectional area of a plane through the platen contact points

Size correction

- It varies as a function of D in the diametrical test, and as a function of De in axial, block and irregular

lump tests, so that a size correction must be applied.

- The size corrected Point Load Strength Index Is(50) of a rock specimen or sample is defined as the

value which would have been measured by a diametrical test with D = 50 mm.

- The most reliable method of obtaining Is(50), is to conduct diametrical tests at or close to D = 50 mm.

Size correction is then either unnecessary (D=50mm) or introduces a minimum of error. This is the

case, for example, for diametrical tests on NX core (D=54mm). Most point load strength tests,

however, are executed using other sizes or shapes of specimen. In such cases the size correction asbelow must be applied.

- The most reliable method of size correction is to test the sample over a range of D or De values and to

plot graphically the relation between P and De2. If log-log plotting is used the relation is usually a

straight line (see fig. 2.7.5). Points that deviate substantially from the straight line may be disregarded

(although they should not be deleted). The value P50 corresponding to De2=2500mm

2can then be

obtained by interpolation, if necessary by extrapolation, and the size corrected Point Load Strength

Index calculated as P50/502.

- When this method is not practical, for example when testing single sized core at a diameter other than

50 mm or if only a few small specimens or lumps are available, size correction may be accomplished

by using the formula:

Is*)50

De(=(50)Is

0.45

- It has been found, that the size correction procedures specified above are not influenced by the degree

of anisotropy Ia and the direction of loading with respect to planes of weakness; a result that greatly

enhances the usefulness of this test.


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figure 2.7.5.: Procedure for graphical

determination of Is(50) from a set of results at De

values other than 50mm.

Mean value calculation

The mean value of Is(50) is to be calculated by deleting the two highest and lowest values from the 10 or

more valid tests, and calculating the mean of the remaining values. If significantly fewer specimens are

tested only the highest and the lowest value are deleted and the mean calculated from those remaining.

Point Load Strength Anisotropy Index

The point load strength anisotropy index Ia(50) is defined as the ratio of mean Is(50) values measuredperpendicular and parallel to planes of weakness, i.e. the ratio of the highest to lowest Point Load

Strength Indices. The strength anisotropy index assumes values close to 1.0 for quasi-isotropic rocks and

higher values when the rock is anisotropic.

Reporting




borehole)


- Lithology, weathering grade, grain size, natural water content- Sample transport and storage conditions


- Form and dimensions of all specimens



- Results for diametrical tests, axial tests, block tests and irregular lump tests, and for tests

perpendicular and parallel to planes of weakness should be tabulated separately.

- For every specimen tested, it must be indicated which direction with respect to planes of

weakness in the rock (if recognisable) was tested.

- A tabulation of the values of P, D, (W, De2

and De if required), Is, (F if required) and Is(50) for

each specimen in the sample.


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- For all isotropic samples a summary tabulation of mean Is(50) values.

- For all anisotropic samples a summary tabulation of mean Is(50) values for sub-samples tested

perpendicular and parallel to the planes of weakness, and of the corresponding Ia(50) values.

Remarks

For a through discussion about the principles of the test and about the practical application of its results

see the "notes" on the pages 57 to 60 of the publication about the Suggested Method by ISRM.

References

ISRM - Commission on testing Methods. Working Group on Revision of the Point Load Test Method.

"Suggested Method for Determining Point Load Strength", Int. Journal Rock Mech. Min. Sc.

Vol.22,No.2,pp.51-60 1985


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3.1: Standard procedure for the determination of rock material indirect tensile strength by the

Brazilian test

Scope of the test

The purpose of the test is to determine the splitting tensile strength of rock material by diametrical line

compression of a disk form specimen.

Apparatus used

- A suitable testing machine, capable to load to the rock specimen at the required speed (see test

procedure) and measure the applied load with the required accuracy.

- Loading platens of hardened steel between which the rock specimen is compressed.

- ASTM procedure is based on flat platens

- ISRM procedure uses specially designed loading jaws (see figure 1 of the ISRM suggested method)

to reduce premature cracking due to high stress concentrations. If such loading jaws are used, then the

spherical seat of the testing machine must be kept in a locked position.

The following test procedure is based on the use of flat platens. To reduce stress concentrations,

cardboard with a thickness of 0.5 mm can be used between the specimen and the loading platens.

- Double thickness (0.2 to 0.4 mm) adhesive paper strip (masking tape) with a width equal or slightly

greater than the specimen thickness.

Test procedure

- The test specimen must have the form of a cylinder, with end faces perpendicular to the axis. The

cylindrical surface must be free from obvious tool marks and any irregularities across the thickness of

the specimen should not exceed 0.25 mm. The end faces must be flat to within 0.25 mm and square

and parallel to within 0.250. At least ten specimens should be taken from one sample to obtain ameaningful average.

If the sample rock is anisotropic due to the presence of weakness planes or preferred orientation of

minerals, the specimens should be prepared in such a way that both directions parallel as well as

perpendicular to such planes can be tested (axis of the cylinder parallel to the plane).

- The specimen diameter shall preferably be not less than NX core size (54 mm), or at least 10 times

the average grain size. The thickness/diameter ratio should be 0.5 to 0.6.

- The specimen must be wrapped with the extra thick masking tape around it. If masking tape is not

available cardboard can be used to prevent stress concentrations.

- The load on the specimen must be applied continuously at a constant rate such that failure occurs

within a few minutes. The actual loading rate depends on the strength of the material and the size of

the specimen and may vary from 10 to 50 kN/minute

Calculation

The splitting tensile strength of the specimen can be determined with the following formula:

Mpa)(inD*L*

P2=strengthtensile(indirect)

In this formula P is the maximum load at failure (in MN);

L is the length of the specimen (in m) and D is the specimen diameter (in m).

Reporting


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- Project name, location, sample number, co-ordinates, depth below terrain (in case of borehole),

date of sampling.

- Type of sample (core, block, disturbed), sample dimensions.







- Type of the testing machine used, loading rate

- Sketch of then mode of failure

- The indirect tensile strength of each specimen, together with the average result for the sample. If

the sample is anisotropic separate figures should be given for the directions parallel and

perpendicular to planes of weakness.

References



ASTM Standard Test Method D3967-81


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3.2: Standard test procedure for the determination of unconfined compressive strength of rock

material.

Scope of the test

The aim of this test is to determine the unconfined (or uniaxial) compressive strength of rock specimens

of cylindrical form. The test is mainly intended for use in strength classification and characterisation of

intact rock.

Apparatus used

- A testing machine of sufficient capacity and capable of applying axial load at a rate conforming to the

requirements described in the test procedure. The steel platens with which the specimen is loaded

shall consist of hardened steel (specifications see ASTM and ISRM) and be at least as large, but

preferably not more than double the diameter of the specimen.

- The upper bearing plate shall be equipped with a spherical seat. The centre of curvature of the

spherical seat must coincide with the centre of the top face of the specimen.

Test procedure

- Test specimens shall be right circular cylinders having a height to diameter ratio of 2.5 and a diameter

preferable of not less than 54mm. The diameter of the specimen should be at least 10 times larger

than the average grain size.

The number of specimens from one sample to be tested shall preferably be at least five. If the sample

rock is anisotropic due to the presence of weakness planes and/or preferred orientation of minerals,

the specimens should be prepared in such a way that both directions parallel as well as perpendicular

to such planes can be tested. If enough testing specimens are available various intermediate angles

can also be tested.

The end faces of the specimen shall be flat to 0.02 mm and be perpendicular to the specimen axiswithin 0.250 (0.25mm in 50mm). During the test capping of the samples is not permitted (see

appendix 1).

The sides of the cylinder shall be smooth and free of abrupt irregularities and straight to within 0.5

mm over the full length of the specimen.

- The diameter of the specimen shall be recorded to the nearest 0.1mm by taking two perpendicular

measurements at three different heights of the cylinder. The height of the cylinder shall be determined

to the nearest 0.1mm.

- Preferably specimens should be tested at their natural water content. Precautions have to be taken that

this water content is preserved during storage and specimen preparation.

- The load on the specimen shall be applied continuously at a constant stress rate such that failure will

occur within 5 to 10 minutes of loading. This means for relatively strong rock a stress rate between

0.5 and 1Mpa/sec. The maximum load on the specimen shall be recorded in Newton with an accuracyof 1% .

Calculation

2

D*

P=(U.C.S)strengthecompressivUniaxial

2

max

In this formula Pmax is the maximum load on the specimen (in N) and D is the average specimen

diameter (in m). The uniaxial compressive strength is expressed in Mpa.


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33


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Reporting




borehole)

- Sketch of the mode of failure








- Description of the testing machine and the stress rate used.

- A table listing of all the specimens that the values of unconfined compressive strength determined

and the orientation of weakness planes (if present) with respect to the specimen axis.

- The average value of unconfined compressive strength for all specimen, when necessary groupedtogether for the same orientation of their plane of weakness.

Remarks

An important part of this testing procedure is essentially identical with parts of the tests for the

determination of the rock elastic modulus and the Poisson ratio. Often the test is executed for the three

purposes simultaneously.

References





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3.3: Standard test procedure for the determination of the strength of rockmaterial in triaxial

compression

Scope of the test

The objective of this test is to determine the strength of cylindrical rock specimens subjected to triaxial

compression. From the results of this test the values of internal friction and cohesion of the rock material

can be calculated.

Apparatus used

- A triaxial cell body in which the specimen may be placed in order to apply the confining pressure.

- Both bearing plates shall be equipped with a spherical seat. The centres of curvature of the spherical

seats must coincide with the centres of the end faces of the specimen.

- A flexible jacket to prevent the hydraulic fluid from entering the specimen. It shall be sufficiently

rigid, so as not to enter surface pores.

- A testing machine of sufficient capacity and capable of applying controlling and measuring the axialload at a rate conforming to the requirements described in the test procedure. The steel platens with

which the specimen is loaded shall consist of hardened steel (specifications see ASTM and ISRM)

and be at least as large, but preferably not more than two mm larger than the diameter of the

specimen. The spherical seating of the testing machine (if present) shall be removed or placed in a

locked position.

- A hydraulic pump and oil pressure gauge, able to maintain and measure the confining oil pressure

with an accuracy of 2%.

Test procedure

- Test specimens shall be right circular cylinders having a height to diameter ratio of 2.5 and a diameter

preferable of not less than NX core size (54mm). The diameter of the specimen should be at least 10times larger than the average grain size.

The number of specimens from one sample to be tested shall preferably be at least five, each one at a

different level of confining stress. For the determination of cohesion and friction also the results from

specimen(s) tested in unconfined compression can be used. If the sample rock is anisotropic due to

the presence of weakness planes and/or preferred orientation of minerals, the specimens should be

prepared in such a way that both directions parallel as well as perpendicular to such planes can be

tested. If enough testing specimens can be prepared from the available sample, various intermediate

angles could also be tested.

- The end faces of the specimen shall be flat to 0.025 mm and be perpendicular to the specimen axis

within 0.250 (0.25 mm in 50 mm). During the test, capping of the samples is not permitted. The sides

of the cylinder shall be smooth and free of abrupt irregularities and straight to within 0.5 mm over the

full length of the specimen. (Methods for the check of specimen from requirements are described inappendix 1.

- The diameter of the specimen shall be recorded to the nearest 0.1 mm by taking two perpendicular

measurements at three different heights of the cylinder. The height of the cylinder shall be determined

to the nearest 0.1 mm.

- Moisture can have a significant effect on the triaxial strength of the test specimen. When possible the

natural water content shall be preserved until the time of the test. The moisture condition shall be

reported in accordance with test nr. 2 in this handbook.

- The cell must be assembled with the specimen aligned between the steel platens and surrounded by

the jacket. The specimen, the platens and the spherical seats shall be accurately aligned so that each is

coaxial with the others.


35


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- The cell is placed into the testing machine. The confining stress and axial load are increased

simultaneously and in such a way, that axial stress and confining pressure are approximately equal,

until the predetermined level of confining pressure is reached. Subsequently, the confining pressure

shall be maintained to within 2% of the prescribed value.

- The axial load on the specimen shall then be increased continuously at a constant stress rate such that

failure will occur within 5 to 15 minutes of loading. This means for relatively strong rock a stress rate

between 0.5 and 1 Mpa/sec.

- The maximum axial load and the corresponding confining pressure of the specimen shall be recorded.

Calculation

- The maximum axial load is converted to axial stress in the following way:

Pa)(inA

P=stressAxial

o

In this formula P is the maximum axial load (in Newton), A 0 is the cross sectional area of the

specimen at the start of the test.

- Construct Mohr circles for the test results from the unconfined compressive strength test and the

triaxial compressive strength tests at the different values of confining pressure (see figure 3.3.1.).

figure 3.3.1: Mohr diagram with plotting of the Mohr circles resulting from unconfined and

triaxial test. From the failure envelope the values for cohesion and friction can be determined

(ASTM).

Reporting




borehole)







36


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- Testing equipment used (loading frame, triaxial cell equipment to create and measure confining

pressure)

- Loading rate during the test, sketch of failure

- Table with specimen number, specimen height, specimen diameter, confining pressure and the

corresponding axial strength

- Mohr diagram with the Mohr circles from unconfined and triaxial strength tests

- Angle of internal friction and cohesion as determined graphically from the Mohr diagram

Remarks

The levels of confining pressure at which the triaxial test is executed shall be determined on the basis of

the result of the unconfined compressive strength testing plotted in the Mohr diagram.

References

International Society for Rock Mechanics Suggested Methods "Rock Characterisation, Testing andMonitoring" Editor E.T. Brown, Pergamon Press 1981, pages 254 to 127)



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3.4: Standard test procedure for the determination of the shear strength of rock material in

direct shear

Scope of the test

The objective of this test is to determine the shear strength of discontinuity planes or weak horizons in

rock as a function of the stress perpendicular to the sheared plane. Peak and residual strength are

distinguished.

Apparatus used

- A mould to set the test specimen at the required orientation and position in the filling material (plaster

or cement), leaving the shear plane free. This mould must have exactly the same form as the shear

box, to ensure perfect fitting when sample plus filler material are placed in the shear box.

- Testing equipment (shear box) consisting of the following parts:

- System to apply the normal load perpendicular to the plane to be tested. The resultant load should

pass through the centre of the area tested. The loading system must be capable to maintain andmeasure the normal force to within 2% of the selected value during the whole duration of the test.

- System to apply and measure the shear force to the specimen. The force must be directed parallel to

the shear plane and act through its centre. The system should enable shear displacements of the

order of magnitude of 10% of the length of the shear plane in the direction of sliding. The shear

force must be capable of increase at constant rates and of measuring the shear force with an

accuracy of 2%.

- Micrometer dial gauges for the measuring of shear and normal displacements with an accuracy of

0.05 mm. Shear and normal displacement measurements must be possible up to 5mm with an

accuracy better than 0.05 mm

Test procedure

- Test specimens can be taken from borehole cores or from block samples which are cut or bored in the

laboratory. Extreme care must be taken that during sample taking in the field, transport and storage

and during the preparation of the specimen for the test, the weakness plane is not damaged or

disturbed. For this purpose the sample can be protected against failure by metal wiring and against

drying out by wax or special foam material. No specific requirements exist for the form of the sample

as long as it fits in the shear box, is deep enough enclosed in the filling material, and the shear plane

is parallel to the shear direction of the shear box. The number of specimens from one sample to be

tested shall preferably be at least five, each one at a different level of confining stress.

- After placing the hardened filler with the enclosed rock specimen in the shear box, the normal

displacement and shear displacement measurement gauges are installed. A zero reading is taken on

the dial gauges and then the normal force is applied by the vertical hydraulic jack. The normal load is

increased gradually but continuously in such a way that the selected normal stress on the plane to betested is reached in a few minutes. The normal deformation during this process of consolidation is

recorded at regular time intervals. The binding wire connecting both halve of the sample may now be

cut. The normal stress must now be kept at a constant level during the remaining part of the test.

- After the displacement gauges have reached a steady value (less than 0.05mm displacement in 10

minutes), indicating that the consolidation process has come to an end, the shear load can be applied

in steps as to allow the various readings to be made. Approximately 10 readings should be taken

before the peak strength is reached. The rate of shear movement should not reach values higher than

0.2 to 0.5 mm per minute. The shear load should be recorded continuously so as not to miss the peak

value. After reaching the peak strength readings of all displacement gauges should be taken every 0.5

to 1 mm of displacement.


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- If at least four consecutive readings give not more than 5% of variation in shear stress over a

displacement of more than 0.5mm, it can be concluded that the residual shear strength value has been

reached.

- After a shear displacement of not more than 10% of the length of the shear plane in shear direction,

the shear load can be reduced to zero. The shear direction can now be reversed (without decreasing

the normal load) if residual values of shear strength for large amounts of shear displacements are

requested. If not, or if residual strength has already been reached, the normal load can also be

released, the specimen removed from the shear box and the shear plane inspected and described.

- An important observation is if the shear plane has coincided with the shear direction of the shear box.

If this is not the case, a correction must be made for the inclination of the shear plane when normal

and shear stress are determined.

Calculation

- The displacement readings are averaged, when several normal and shear displacement gauges are

used. The normal and shear stresses are calculated as follows:

AP=stressShear

AP=stressNormal sn

In these formulas Pn is the total normal force, Ps is the total shear force and A is the area of contact of

both parts of the specimen, corrected for a decrease of this area due to shear displacement.

- For each test specimen graphs are plotted for shear stress against shear displacement and for normal

displacement against shear displacement. In these graphs the value of normal stress should be

annotated for each test. The values for peak and residual shear strength and the normal stresses, shear

displacements and normal displacements at which these occur can be read from the graphs.

- Graphs of peak and residual shear strength versus normal stress are plotted from the combined results

for all test specimens. The peak and residual shear strength parameters of cohesion and angle of

friction can so be determined.

Reporting




borehole)





- Form, dimensions and weight of all specimens- Water content of the shear plane during testing.


- Testing equipment used and loading rates during the test, sketch of specimen shear plane after the

test.

- For each specimen the graphs of shear stress and normal displacement versus shear displacement

and the graph of shear stress versus normal stress.

- Table with specimen number, normal stress and the corresponding values for peak and residual

shear strength with the corresponding values for shear displacement and normal displacement.

- Shear stress versus normal stress graph for the values obtained from all test specimens. Table with

the concluded values of cohesion and angle of friction for peak and residual shear strength.


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3.5: Shear strength of rock discontinuities with Golder Shear Box

Scope of the test

The objective of this test is to determine the shear strength of rock discontinuities as a function of the

stress perpendicular to the sheared plane. Peak and residual strength, friction angle and roughness angle

are distinguished.

An article about the Golder shear box is added to this manual as appendix 2

Apparatus used

The Golder shear box of Engineering geology in Delft consists of the following parts:

- Upper and lower shear box.

- System to apply the normal load perpendicular to the plane to be tested. The normal load is applied

by means of dead load system and it remains constant throughout one test.

- Shear stress is applied via a hydraulic ram and the whole apparatus is relative portable.

- Vertical displacement up to 5 mm/10 mm (depending on the roughness of the discontinuity plane) ismeasured at a single point on the lever arm and registered by the computer.

- Horizontal displacement measuring device, 0 - 20 mm. The horizontal displacement transducer is also

registered by the computer.

- Converter, computer, plotter.

procedures

Sample

Test specimens can be taken from the borehole cores or from block samples which are cut to size to fit

the shear box (lower and upper box) and set in dental plaster or some other suitable fixing medium.

Extreme care must be taken that during the preparation of the specimen for the test, the weakness planeis not damaged or disturbed. The shear plane must be parallel to the direction of the shear box. When

shearing the upper part is kept in place while the lower part is moving. The sample is described before

the test: rock type, discontinuity type, dimensions, roughness. (JRC classification, measurement by

roughness meter device).

After describing the sample and the discontinuity plane the sample is placed in the shear box. The

vertical and horizontal displacement measuring devices are installed and connected to the computer. To

be able to analyse the results properly, horizontal and vertical displacements must be recorded

throughout the test.

Shear test

Testing can be carried out by either single or multistage procedures. For single stage test the sample is

sheared at one constant normal load. In the multistage test, the normal load is increased after peakstrength has been measured at each stage. After each stage the sample may be reset to the original

position, but if this can be avoided it should not be done because of the risk of damaging the surface.

Normally there is sufficient shear displacement still available to allow the next stage of peak strength to

be mobilised and shearing can continue from the same point after changing the normal load. Shear stress

is applied via a hydraulic ram and it is important to keep the rate of shearing constant and rather slow,

very high rates of shearing (> 1 mm/s) may cause errors to the results.

While shearing the sample, the increasing values of shear stress and the horizontal and vertical

displacements can be followed on the monitor. The computer-based retrieval system in use at TU-Delft

allows data from all channels to be read at the same time and at very short time intervals. Also the

results of the test can be plotted immediately after testing the sample. In the computer program there is


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also the possibility to apply correction of test data for dilation. As dilation occurs, work is done in lifting

the upper sample and this results in an increasing of shear force being required to continue shearing.

After testing the surface of the discontinuity plane should examined, particularly with regard to the

conditions of the areas involved in shearing.

Calculation

The data presented by separate graphs showing:

- shear stress versus horizontal displacement (3 stages = 3 tests)

- vertical displacement versus horizontal displacement (1 stage)

- shear stress versus normal stress (3 stages together)

- basic friction angle versus horizontal displacement (1 stage).

Reporting

Good reporting starts with clear sample description.

From the graphs obtained, shear strength and residual strength of the discontinuity plane should be

derived. Residual strength may not always be found. The incremental roughness angle i can be

calculated from a graph showing vertical horizontal displacement. From the graph showing shear stress

versus normal stress

lab manual rock & aggregate

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