CHAPTER 01 INTRODUCTION 1.1 OVERVIEW In geological exploration, mechanical rock properties are one of the most important parameters that will be later used in the analysis and design of any engineering structures in rock mass. To obtain these properties, the rock from the site is extracted normally by means of core drilling, and then transported the cores to the laboratory where the mechanical testing can be conducted. Laboratory test machine is normally huge and cannot be transported to the site. Onsite testing of the rocks may be carried out by other technique, but only on a very limited scale. This method is called point load strength testing. This test however provides unreliable results, and lacks theoretical supports. Its results may imply to other important properties (e.g. Compressive and tensile strengths), but only based on an empirical formula, which usually poses high degree of uncertainty. To save cost and energy that are consumed by drilling processes, rock core transportation, and laboratory testing, a new method for on-site testing is needed. The researcher proposes to modify the currently used point load testing machine to be able to yield the compressive and tensile strengths of the rock specimens with
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Co Relation of Pont Load With Uni Axial Compressive Strength
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CHAPTER 01
INTRODUCTION
1.1 OVERVIEW
In geological exploration, mechanical rock properties are one of the most important parameters
that will be later used in the analysis and design of any engineering structures in rock mass. To
obtain these properties, the rock from the site is extracted normally by means of core drilling,
and then transported the cores to the laboratory where the mechanical testing can be conducted.
Laboratory test machine is normally huge and cannot be transported to the site. Onsite testing of
the rocks may be carried out by other technique, but only on a very limited scale.
This method is called point load strength testing. This test however provides unreliable results,
and lacks theoretical supports. Its results may imply to other important properties (e.g.
Compressive and tensile strengths), but only based on an empirical formula, which usually poses
high degree of uncertainty.
To save cost and energy that are consumed by drilling processes, rock core transportation, and
laboratory testing, a new method for on-site testing is needed. The researcher proposes to modify
the currently used point load testing machine to be able to yield the compressive and tensile
strengths of the rock specimens with irregular shapes. The new technique which is thereafter
called “modified point load (MPL) testing,” will be backed by solid theoretical ground.
The testing machine will also remain small and will be easy to operate on-site. If the new
Technique can be invented successfully; it may significantly reduce the cost, time and energy
that have been consumed by the convention methods.
1.2 DESCRIPTION
The PLT is an attractive alternative to the UCS because it can provide similar data at a lower
cost. The PLT has been used in geotechnical analysis for over thirty years. The PLT involves the
compressing of a rock sample between conical steel platens until failure occurs. The apparatus
for this test consists of a rigid frame, two point load platens, a hydraulically activated ram with
pressure gauge and a device for measuring the distance between the loading points. The pressure
gauge should be of the type in which the failure pressure can be recorded. A state of the art point
load testing device with sophisticated pressure reading instrumentation is shown in Figure 1.
Figure 1.1: Point Load Index Test
Indirect tensile strength is more useful than direct tensile strength in rock mechanics application,
partly because tensile stress field in rock mass is usually induced indirectly by compressive
deviatoric stresses and partly because direct tension is difficult to apply to rock specimens
without inducing any eccentric moments. The point load strength test (PLST) is one of the most
popular indirect tensile strength tests used in rock engineering.
The strength index measured in this test is called the point load strength index (PLSI), which is a
measure of the indirect tensile strength and has been correlated empirically to both the tensile
strength and compressive strength of rock. The PLST has been applied most commonly to
cylindrical specimens, either axially or diametric.
Figure 1.2: A Cylindrical Rock Specimen Subjected To The Diametrical Plst. The Origin Is
At The Centre Of Cylinder And The Indentors Act Along A Diameter Passing Through
The Origin.
1.3 PROPOSED CONCEPT
In the rock mechanics and engineering geology, the point load test is regarded as valuable field
test to give an estimate of the unconfined compressive strength. Well known in the is the scale
effect concerning the point load strength since the first compressive paper by Broch and Franklin
(1972) after carried out a large high number of point load tests in different rock types with
different devices.
Several other researchers have correlated the point load index with the uniaxial compressive
Strength of the rocks (e.g. Miller, 1965; Reichmuth, 1968; Bieniawski, 1975; Pells, 1975; Jaeger
and Cook, 1979; Turk and Dearman, 1986; Kaczynski, 1986 and Chau and Wong, 1996). Brook
(1977, 1985, and 1993) has also established a relation between the point load strength with the
uniaxial compressive strength of intact rocks. It is however recognized here that the tensile
failure is the dominant mode of failure for the point load specimen. As a result, the point load
strength should be related to the tensile strength of the rock rather than the compressive strength.
Strictly speaking, the dominant mode of failure for the point load specimens is governed by the
size or the distance the loading points. For small specimens, the failure should be in biaxial or
poly axial compression modes. For a large specimen, the biaxial tension will be predominant
mode of failure. Recognizing this phenomenon, an attempt is made here to distinguish between
the compressive and tensile failures under a wide range of specimen sizes. Theoretical derivation
and numerical simulation may be used to assist in describing the stress and strain distribution
between the loading points for various specimen sizes. Relationships between the point load
index and the compressive and tensile strength may therefore be established. The final goal is
that one can conduct point load testing on various specimen sizes, and use the results as an
indicator of compressive and tensile strengths of the intact rocks.
1.4 REASONS FOR DEVELOPING INDEX TESTS
The index tests are devised to overcome some of the difficulties encountered in the laboratory
test as follows.
1. Laboratory testing of rock material is elaborate, time consuming and therefore expensive.
2. Delay in assessment.
3. Index test are essentially field tests devised to obtain test results
Without much specimen preparation
With portable equipment
Correlated to strength and deformation properties for design calculations
Some test give representative of properties for design calculation
Sometimes open boreholes test for litho logical classification and structural
mapping can also be correlated to the index properties.
1.5 CLASSIFICATION AND TYPES OF INDEX TESTS
1.5.1 BRAZILIAN TEST
The tensile strength of a material is a measure of its ability to resist uniaxial tensile loads without
yielding or fracture. A direct-pull uniaxial test is difficult to apply to rock and in many cases
some type of indirect test is employed to determine tensile strength.
The Brazilian test, where a disc of the test material is loaded across a diameter, is often
employed.
Brazilian test can be correlated to tensile strength used for classification of rocks by strength for
drill ability, rock breakage and crushing classification.
t = 2P/λDt
Where;
t = uniaxial tensile strength
P = Load at failure on a portable machine
D = diameter of the core (m)
T = thickness of core (m)
1.5.2 POINT LOAD INDEX TEST
Point load index tester, a rock testing instrument for determining the Diametrical Point Load
Strength Index of rock cores and Irregular lumps which may be tested without any treatment.
The Point Load Test is primarily as index test for strength classified of rock materials.
This instrument is mainly intended for field measurements on rocks specimen, but it can be used
in the laboratory. The results of the test may also be used to predict the uniaxial compressive
strength of rock from correlations
Point load index for strength classification of rocks which can be used by geotechnical engineers
for predicting the strength and deformation properties of rock to the design of mining
excavations.
1.5.3 DYNAMIC IMPACT STRENGTH TEST
Dynamic impact strength test (Pomeroy, 1955; Ghose et al, 1964) to estimate resistance of coal
to degradation and applicable to rock workability studies in order to assess the degradability of
coal that control subsequent breakage
This may occur in the loading coal in face conveyor, during transfer from one conveyor to
another or into storage bunkers.
1.5.4 CONE INDENTER HARDNESS TEST
Cone indenter hardness test developed the British coal; Mining Research and Development
Establishment for assess strength of coal in underground coal mines.
The NCB Cone Indenter which was developed by the British National Coal Board to evaluate the
compressive strength of rock by measuring the force required to cause a specific indentation in a
small chip of rock.
It measures the penetration of tungsten carbide cone on a prepared core specimen in 38mm in
diameter and 10mm thick under the normal force.
1.5.5 SLAKE DURABILITY TEST
Sake durability is a simulated weathering test to determine abrasion resistance during wetting
and drying cycles of shale and similar soft rocks as used in embankments and other construction-
related applications. Samples are alternately tumbled in mesh drums through water medium and
oven-dried for two cycles. The percent loss of mass is referred to as the slake durability index.
Slake durability test, therefore applicable to assess the durability of rock for near surface
excavations or swelling of roof and floor strata in underground excavations.
1.5.6 SCHMIDT HAMMER TEST
A Schmidt hammer, also known as a Swiss hammer or a rebound hammer, is a device to measure
the elastic properties or strength of concrete or rock, mainly surface hardness and penetration
resistance.
The hammer measures the rebound of a spring-loaded mass impacting against the surface of the
sample. The test hammer will hit the concrete at a defined energy. Its rebound is dependent on
the hardness of the concrete and is measured by the test equipment. Schmidt hammer test, a
rebound test devised for field condition and can be used for estimating strength and deformation
characteristics of rock.
1.5.7 SHORE SCLEROSCOPE TEST
The Scleroscope test consists of dropping a diamond tipped hammer, which falls inside a glass
tube under the force of its own weight from a fixed height, onto the test specimen. The height of
the rebound travel of the hammer is measured on a graduated scale. The scale of the rebound is
arbitrarily chosen and consists on Shore units, divided into 100 parts, which represent the
average rebound from pure hardened high-carbon steel. The scale is continued higher than 100 to
include metals having greater hardness. The Shore Scleroscope measures hardness in terms of
the elasticity of the material and the hardness number depends on the height to which the
hammer rebounds, the harder the material, the higher the rebound.
Shore Scleroscope test, a non-destructive test for classifying hardness and, therefore, selecting
excavation machinery or blasting.
1.5.8 NEUTRON-NEUTRON LOGS TEST
The neutron log is sensitive mainly to the amount of hydrogen atoms in a formation. Its main use
is in the determination of the porosity of a formation.
The tool operates by bombarding the formation with high energy neutrons. These neutrons
undergo scattering in the formation, losing energy and producing high energy gamma rays. The
scattering reactions occur most efficiently with hydrogen atoms. The resulting low energy
neutrons or gamma rays can be detected, and their count rate is related to the amount of
hydrogen.
Neutron-neutron logs are carried out in open bore hole which can be correlated to rock density
and point load index test table 5.1 summarizes the index properties of rocks.
1.6 POINT LOAD INDEX TEST:
A cylindrical core obtained from the bore is approximately cut to the length to diameter ratio 1.5
to 1 and diametrically loaded against conical platens on a portable loading machine the load of
failure can be related to the point load index rock shown in equation 1.1.
Is=P/d2 (1.1)
Uniaxial compressive strength is correlated with point load index as shown in equation 1.2.
c =24 Is (1.2)
Where;
P = Load at failure
D = Diametrical distance between conical platens at failure (m)
Is = Point load index of rock
c = Uniaxial compressive strength of rock (MPa)
Is50 = Point load index for 50 mm diameter core (fig 1-size correction)
Idealized condition for this test is as follows.
Portable loading machine
Use of calibration chart for size correction (figure 1)
Minimum core diameter 50mm
Length-to-diameter ratio 1.5 to 1
Number of samples- 10 to 15
No slandered rate of loading
Loading platens 600 conical platen with 5 mm curvature tip.
CHAPTER 02
POINT LOAD INDEX TESTING
2.1 SCOPE
This test is intended as a method for measuring the strength of rock specimens in the field, and
uses portable equipment. Specimens in the form of either rock core (the ‘diametric’ and ‘axial’
tests) or of irregular lumps (the ‘irregular lump’ test) are broken by application of a concentrated
loud using a pair of conical platens.
A Point-Load Strength index I (50) is obtained and may be used for rock strength classification.
2.2 SUMMARY OF TEST METHOD
This index test is performed by subjecting a rock specimen to an increasingly concentrated load
until failure occurs by splitting the specimen. The concentrated load is applied through coaxial,
truncated conical platens. The failure load is used to calculate the point load strength index and
to estimate the uniaxial compressive strength.
2.3 SIGNIFICANCE AND USE
The uniaxial compression test is used to determine compressive strength of rock
specimens, but it is a time-consuming and expensive test that requires specimen
preparation. When extensive testing is required for preliminary and reconnaissance
information, alternative tests such as the point load test can be used in the field to reduce
the time and cost of compressive strength tests.
The point load strength test is used as an index test for strength classification of rock
materials. The test results should not be used for design or analytical purposes.
This test method is performed to determine the point load strength index (Is50) of rock
specimens, and the point load strength anisotropy index (Ia50) that is the ratio of point
load strengths on different axes that result in the greatest and least values.
Rock specimens in the form of either core (the diametrical and axial tests), cut blocks (the
block test), or irregular lumps (the irregular lump test) are tested by application of
concentrated load through a pair of truncated, conical platens. Little or no specimen
preparation is required.
However, the results can be highly influenced by how the specimen is treated from the
time it is obtained until the time it is tested. Therefore, it may be necessary to handle
specimens in accordance with Practice.
2.4 TEST SPECIMENS
SAMPLING: Rock samples are grouped on the basis of both rock type and estimated
strength. When testing core or block specimens at least ten specimens are selected. When
testing irregular-shaped specimens obtained by other means at least 20 specimens are
selected. Specimens in the form of core are preferred for a more precise classification.
DIMENSIONS: The specimen’s external dimensions shall not be less than 30 mm and
not more than 85 mm with the preferred dimensioning about 50 mm..
SIZE AND SHAPE: The size and shape requirements for diametric, axial, block or
irregular lump testing shall conform to the recommendations. The sides of the specimens
shall be free from abrupt irregularities that can generate stress concentrations. No
specimen preparation is required.
WATER CONTENTS: Determines the water content of each specimen after testing
since it can affect the value of the point load strength..
MARKING AND MEASURING SPECIMENS: The specimens shall be properly
marked and measured..
MARKING: The desired test orientation of the specimen shall be indicated by marking
lines on the specimen. These lines are used for centering the specimen in the testing
machine, and to ensure proper orientation during testing. These lines may also be used as
reference lines for measuring thickness and diameter.
MEASURING: Measure each dimension of a specimen at three different places, and
calculate the averages.
Figure 2.1: Different Size And Shape Of Cylindrical\Irregular Specimens With Contact Of
Axial And Diametric Force Of Point Load Test.
2.5 DIGITAL POINT LOAD APPARATUS:
The testing machine incorporates a loading system (comprising for example, a loading Frame:
pump: ram and platens).
A system for measuring the load P required breaking the specimen and a system for measuring
the distance D between the two platen contact points. It’s essential features are the following:
1. The loading system should be adjustable to accept and test available rock specimens for
example in the size range 25-100 mm for which a loading capacity up to 50 KN is
commonly required.
2. A quick-retracting ram helps to minimize delay between tests. Ram friction should be
low so as not to impair the accuracy of load measurement.
3. Spherically truncated conical platens (Fig. 4) are used to transmit loud to the specimen.
The 60” curie and 5 mm radius spherical truncation should meet tangentially, and the
platens should be hardened so that they remain undamaged during testing.
4. The platens should be accurately aligned so that each is coaxial with the other, and the
machine should be rigid to ensure that the platens remain aligned during testing. No
spherical scat or other non-rigid component is permitted in the loading system.
5. The load-measuring system should indicate the failure load P to an accuracy of 2 %
irrespective of the strength of specimen tested. It should incorporate a maximum
indicating device so that the reading is retained and can be recorded after specimen
failure.
6. It should be resistant to hydraulic shock and vibration so that the accuracy of readings is
maintained during testing.
7. The distance-measuring system should indicate the distance D between platen-contact
points to accuracy of 0.5 mm. It should be designed to allow zero check and adjustment
and should be robust so that its accuracy is maintained during testing.
The function of this apparatus is given below
This is a portable instrument which can be used in either the laboratory or in-situ to ascertain the
rock strength index of samples of rock or core with diameters up to 102 mm.
The values required for the calculation of the rock strength index are failure load and distance
between the conical points.
Hydraulic loading ram with manual pump
Capacity: 60 KN
Scale: 0-6000 daN (resolution 1 daN -6000 divisions)
Measurement: microprocessor based digital gauge (linearity-hysteresis ≤ ± 0.20 F.S)
battery run using lithium battery 3.6V -2/3 AA type.
Peak value memorized
Pair of conical points
Poly carbonate safety guard
Instrument dimensions: 240 × 280 × 660 (h) mm
Pump dimension: 500 × 150 × 230 (h) mm
Overall weight: 37 kg
Accessories and spares parts:
Ts 70 6/7 two testing plates, 40 mm diameter for compression test on cylindrical specimen
AD 010 microprocessor based digital gauge (battery run)
TS 706/6 set of two conical points.
Figure no 2.2 Point Load Portable Testing Device
Figure 2.3: Point Load Testing Machine
Figure 2.4: Loading Platens Of Point Load Tester
2.6 GENERAL INSTRUCTION FOR USING POINT LOAD EQUIPMENT
The instrument is basically a hydraulic compression machine with a dynamometer. The jack "A"
is moved upwards by the hand pump "B"; its descent is made by pushing directly on the piston
"C" after having opened the discharge valve "D". Naturally the discharge valve "D" must be
closed when the hydraulic jack "A" is to be activated to perform a test. The precision digital
gauge E measures load in daN.
The dial gauge has 3 keys indicating SET, ZERO and PEAK..
SET: when pressed this key turns on dial gauge -when pressed for 5 seconds this key
turns off dial gauge. If pressed, held for 3 seconds and then released this key enables the
user to enter the configuration (setting) menu of the instrument.
ZERO: when pressed for 3 seconds, this key enables display to be zeroed (tare). When
pressed for 6 seconds, this key disenables ZERO function of digital gauge and displays
digital gauge offset.
PEAK: when pressed for 2 seconds, this key activates PEAK function which enables
maximum pressure measured to be displayed after activation of the function. When
pressed for 5 seconds, the temperature in °C is shown. To revert to pressure readout press
key again.
The user now positions a rock fragment in the test chamber, closes valve "D" and activates the
hand pump. The piston stem is thus raised so as to block the rock sample between the two
loading points.
While piston is rising, before contact is made, the gauge should indicate zero.
By continual pumping, the lower display will show an increasing value which corresponds to the
force applied to the sample, expressed in daN. In the test the data of interest is the force
necessary to break the sample; it is therefore useful to preset the device so it only shows
increasing values and maintains the peak value on the display.
Peak value is obtained by pressing F key (PEAK).
To show that peak value is entered the display flashes.
To deactivate PEAK function, simply press F key (PEAK) again.
CHAPTER NO 3
POINT LOAD TESTING OF ROCK SAMPLES
3.1 PREPARATION OF ROCK SAMPLES
The Preparation procedure comprises of following steps.
1. A core specimen of various samples is cut to produce appropriate rock specimen for each test by a cutting machine.
Figure no 3.1 Core Sample Cutting Machine
2. After cutting of different rock specimens prepared for testing with various sizes and shapes.
Figure No 3.1.2 Various Cutting Sample For Testing
3. Select sample: Rock lumps, small size (less than 30 mm), standard size (30 to 85mm) and
large size (more than 85mm) are suitable for the irregular lump tests. D is the distance
between the loading points. Lump samples are selected with dimensions such that
l>0.5D, 0.3 W<D<W; i.e. the ratio, D/W, should be between 1/3 and 1, preferable close
to 1. The distance L should be at least 0.5W. Length 2L is the largest dimension, width W
the smallest. The specimen is installed to ensure that the platens of the testing machine
make contact along a minimal cross section, and not along a plane of weakness;
4. Measure and record the dimension of the lumps , smallest width W , distance between
loading points D and maximum width, length L. if the sides are not parallel then take the
mean width;
5. The dimension and desired test orientation of the lumps selected or indicated by marking
color lines on the specimen. These lines are used for centering the specimen in the testing
machine, and to ensure proper orientation during testing. These lines also are used as
reference line for measuring thickness and diameter;
6. Take picture of the lump. Photographs of all the specimens collected have been made
(For example, No S2 of samples ID)
Figure 3.1.3: Specimen Geometry.
3.2 LOADING CONDITION OF POINT LOAD INDEX
There are two types of loading condition which are applied in the point load index
which are defined as below:
Axial type of loading condition.
Diametric type of loading condition.
3.2.1 AXIAL TYPE OF LOADING CONDITION
When load or thrust are applied on the cylindrical body by thickness wise or vertically, this type
of loading condition are known as the axial type of loading condition. In fig: 3.1.1 clearly
mentions that the axial type of loading condition is applied on cylindrical shape of core specimen
rock with the help of point load index test.
Figure 3.2.1: Core Specimen dimensions for an axial point load test.
3.2.2 DIAMETRIC TYPE OF LOADING CONDITION
Diametric type of loading condition is that the load or thrust applied on the body by diametrically
shape. In fig: 3.2.2 the loading condition is the diametrically on the cylindrical core specimen
with the help of the point load index test.
Figure 3.2.2: Core specimen’s dimensions for a diametric point load test.
3.3 DIFFERENT TEST TYPES AFTER BROOK (1985), ISRM (1985) AND
ASTM
Known from the onset of testing, the point load strength is highly dependent on the size of the
specimen as well as the shape.
Using thick instead of tall specimens for the block and the irregular lump test and standardizing
the general shape of the specimens were steps forward Broch and Franklin (1972), Brook 1985.
Specimen shape requirements are to obtain more reliable testing results with a smaller standard
deviation. However, analysis and evaluation were limited by size variation and the lack of a
reliable and easy-to-comprehend method for size correction.
Broch and Franklin (1972) offered a Size Correction Chart with a set of curves to standardize
every value of the point load strength Is to a point load strength index (I(50)) at a diameter of D
= 50 mm. The purpose of the function was to describe the correlation between I and D and to
answer the question, whether this function is uniform for all rock types or if it depends on the
rock type together with grain size, composition of mineral bonds, grain cleavage etc.
Figure 3.3: Specimen Shape Requirements For Different Test Rock Types.
Brook (1985) and the ISRM (1985) suggest three options to evaluate the results of a test set:
1. Testing at D=50 mm only (most reliable after ISRM (1985).
2. Size correction over a range of D or De using a log-log plot. The most reliable method of size
correction is to test the specimen over a range of D or De values and to plot graphically the
relation between P and De. If a log-log plot is used, the relation is a straight line.
Points that deviate substantially from the straight line may be disregarded (although they should
not be deleted). The value of Is(50) corresponding to De =50 mm can be obtained by
interpolation and use of size corrected point load strength index ASTM.
3. When testing single-sized core at a diameter other than 50 mm or if only a few small pieces
are available, size correction may be accomplished using the formula containing the“Size
Correction Factor” f:
3.4 TEST PROCEDURE
Step # 01: Name/mark the samples.
Step # 02: Measure the Diameter of the each specimen along any reference axis, then rotates the
sample at 90o from reference axis and notes another Diameter by means of vernier calliper.
Step # 03: Take an average of the both diameter reading.
Step # 04: Measure two lengths readings of the specimens, in the same the diameter by using
varnier calliper and takes an average.
Step # 05: Note down all the diameters and length of respective sample accordingly.
Step # 06: Load the sample in the point load tester, carefully between the pair of conical loading
platens
Step # 07: Set the equipment to “0” adjustments.
Step # 08: Set the equipment for “Peak” measurements.
Step # 09: Start loading and observe the developments of cracks (If any).
Step # 10: Note the Peak load reading after the failure of specimen has occurred.
Step # 11: The load “P” is used to calculate the point load strength of samples using:
Figure 3.4: Experimental
Apparatus For Point Load Testing.
Is = P/d2
Where;
P = Load at failure (daN).
d = Diametrical distance between conical platens at failure (m).
Is = Point Load index of rocks (MPa).
Is50 = Point load index for 50 mm diameter core (MPa).
3.5 LABORATORY EXPERIMENTS
Sample no. 01
Rock type: “Lime stone”
Loading type: Axial type loading condition.
Diameter: (d)
d1 = 99.53 mm
d2 = 99.70 mm
d = d1+d2/2
d = 99.53+99.70/2
d = 199.23/2
d = 99.615 mm
d = 0.09961 m
Length: (L)
L1 = 23.65 mm
L2 = 24.95 mm
L = L1+L2/2
L = 23.65+24.95/2
L = 48.6/2
L = 24.3 mm
L = 0.0243 m
Load: (P) = 423 daN = 4230 N
1 daN = 10 N
1 pascal = N/m2
Is = P/d2
Is = 4230/(0.09961)2
Is = 4230/0.00992
Is = 426411.29 N/m2
Is = 426411.29 pascals
Is = 426.411 Kpa
Is = 0.426 Mpa
c = 24*Is
c = 24*0.426
c = 10.224 MPa
Sample no. 02
Rock type: Lime stone
Loading type: Diametric type loading condition.
Diameter: d
d1 = 99.59 mm
d2 = 99.90 mm
d = d1+d2/2
d = 99.59+99.90/2
d = 199.49/2
d = 99.745 mm
d = 0.09974 m
Load: (P) = 1590 daN = 15900 N
Is = P/d2
Is = 15900/(0.09974)2
Is = 15900/0.00994
Is = 1599597.58 N/m2
Is = 1599597.58 pascals
Is = 1599.597 Kpa
Is = 1.599 Mpa
c = 24*Is
c = 24*1.599
c = 38.376 MPa
Sample no:03:-
Rock type:-“Clay Stone”
Loading type:- Diametric type loading condition.
Diameter: (d)
d1 = 61.83 mm
d2 = 61.91 mm
d = d1+d2/2
d = 61.83+61.91/2
d = 123.74/2
d = 61.87 mm
d = 0.0618 m
Load: (P) = 25 daN = 250 N
Is = P/d2
Is = 250/(0.0618)2
Is = 250/0.00381
Is = 65616.79 N/m2
Is = 65616.79 pascals
Is = 65.616 Kpa
Is = 0.0656 Mpa
c = 24*Is
c = 24*0.0656
c = 1.574 MPa
Sample no:04:-
Rock type:-“Silt Stone”
Loading type:- Diametric type loading condition.
Diameter: (d)
d1 = 62.26 mm
d2 = 60.94 mm
d = d1+d2/2
d = 62.26+60.94/2
d = 123.2/2
d = 61.6 mm
d = 0.0616 m
Load: (P) = 44 daN = 440 N
Is = P/d2
Is = 440/(0.0616)2
Is = 440/0.003794
Is = 115972.58 N/m2
Is = 115972.58 pascals
Is = 115.972 Kpa
Is = 0.115 Mpa
c = 24*Is
c = 24*0.115
c = 2.76 MPa
Sample no:05:-
Rock type:-“Silt Stone”
Loading type:- Diametric type loading condition.
Diameter: (d)
d1 = 61.32 mm
d2 = 62.80 mm
d = d1+d2/2
d = 61.32+62.80/2
d = 124.12/2
d = 62.06 mm
d = 0.0620 m
Load: (P) = 56 daN = 560 N
Is = P/d2
Is = 560/(0.0620)2
Is = 560/0.00384
Is = 145833.33 N/m2
Is = 145833.33 pascals
Is = 145.833 Kpa
Is = 0.145 Mpa
c = 24*Is
c = 24*0.145
c = 3.48 MPa
Sample no:06:-
Rock type:-“Clay Stone”
Loading type:- Axial type loading condition.
Diameter: (d)
d1 = 62.89 mm
d2 = 61.64 mm
d = d1+d2/2
d = 62.89+61.64/2
d = 124.5/2
d = 62.26 mm
d = 0.0622 m
Length: (L)
L1 = 22.22 mm
L2 = 20.74 mm
L = L1+L2/2
L = 22.22+20.74/2
L = 42.96/2
L = 21.48 mm
L = 0.0214 m
Load: (P) = 39 daN = 390 N
Is = P/d2
Is = 390/(0.0622)2
Is = 390/0.00386
Is = 101036.26 N/m2
Is = 101036.26 pascals
Is = 101.036 Kpa
Is = 0.101 Mpa
c = 24*Is
c = 24*0.101
c = 2.424 MPa
Sample no:07:-
Rock type:-“Clay Stone”
Loading type:- Axial type loading condition.
Diameter: (d)
d1 = 62.49 mm
d2 = 62.23 mm
d = d1+d2/2
d = 62.49+62.23/2
d = 124.72/2
d = 62.36 mm
d = 0.0623 m
Length: (L)
L1 = 28.19 mm
L2 = 29.54 mm
L = L1+L2/2
L = 28.19+29.54/2
L = 57.73/2
L = 28.86 mm
L = 0.0288 m
Load: (P) = 32 daN = 320 N
Is = P/d2
Is = 320/(0.0623)2
Is = 320/0.00388
Is = 82474.22 N/m2
Is = 82474.22 pascals
Is = 82.474 Kpa
Is = 0.0824 Mpa
c = 24*Is
c = 24*0.0824
c = 1.977 MPa
Sample no:08:-
Rock type:-“Lime Stone”
Loading type:- Diametric type loading condition.
Diameter: (d)
d1 = 48.52 mm
d2 = 48.74 mm
d = d1+d2/2
d = 48.52+48.74/2
d = 97.26/2
d = 48.63 mm
d = 0.0486 m
Load: (P) = 1791 daN = 17910 N
Is50 = P/d2
Is50 = 17910/(0.0486)2
Is50 = 17910/0.00236
Is50 = 7588983.05 N/m2
Is50 = 7588983.05 pascals
Is50 = 7588.983 Kpa
Is50 = 7.588 Mpa
c = 29*Is50
c = 29*7.588
c = 220.05 MPa
Sample no:09:-
Rock type:-“Lime Stone”
Loading type:- Diametric type loading condition.
Diameter: (d)
d1 = 48.64 mm
d2 = 49.05 mm
d = d1+d2/2
d = 48.64+49.05/2
d = 97.69/2
d = 48.84 mm
d = 0.0488 m
Load: (P) = 542 daN = 5420 N
Is50 = P/d2
Is50 = 5420/(0.0488)2
Is50 = 5420/0.00238
Is50 = 2277310.92 N/m2
Is50 = 2277310.92 pascals
Is50 = 2277.310 Kpa
Is50 = 2.277 Mpa
c = 29*Is50
c = 29*2.277
c = 66.03 MPa
Sample no:10:-
Rock type:-“China Clay”
Loaidng type:- Axial type loading condition.
Diameter: (d)
d1 = 62.23 mm
d2 = 61.59 mm
d = d1+d2/2
d = 62.23+61.59/2
d = 123.82/2
d = 61.91 mm
d = 0.0619 m
Length: (L)
L1 = 28.19 mm
L2 = 29.54 mm
L = L1+L2/2
L = 28.19+29.54/2
L = 57.73/2
L = 28.86 mm
L = 0.0288 m
Load: (P) = 25 daN = 250 N
Is = P/d2
Is = 250/(0.0619)2
Is = 250/0.00383
Is = 65274.15 N/m2
Is = 65274.15 pascals
Is = 65.274 Kpa
Is = 0.0652 Mpa
c = 24*Is
c = 24*0.0652
c = 1.564 MPa
Sample no:11:-
Rock type:-“Silt Stone”
Loading type:- Diametric type loading condition.
Diameter: (d)
d1 = 62.88 mm
d2 = 62.81 mm
d = d1+d2/2
d = 62.88+62.81/2
d = 125.69/2
d = 62.84 mm
d = 0.0628 m
Load: (P) = 47 daN = 470 N
Is = P/d2
Is = 470/(0.0628)2
Is = 470/0.00394
Is = 119289.34 N/m2
Is = 119289.34 pascals
Is = 119.289 Kpa
Is = 0.119 Mpa
c = 24*Is
c = 24*0.119
c = 2.856 MPa
Sample no:12:-
Rock type:-“Lime Stone”
Loading type:- Diametric type loading condition.
Diameter: (d)
d1 = 48.52 mm
d2 = 48.74 mm
d = d1+d2/2
d = 48.52+48.74/2
d = 97.26/2
d = 48.63 mm
d = 0.0486 m
Load: (P) = 2014 daN = 20140 N
Is50 = P/d2
Is50 = 20140/(0.0486)2
Is50 = 20140/0.00236
Is50 = 8533898.30 N/m2
Is50 = 8533898.30 pascals
Is50 = 8533.898 Kpa
Is50 = 8.533 Mpa
c = 29*Is50
c = 29*8.533
c = 247.45 MPa
Sample
Number
Rock type Loading
condition
Diameter(d) Length(L) Load:
(daN) Is Is50
c
MPa
In meter In meter And (N) (MPa) (MPa)
Sample No:01 Lime
stone
Axial 99.615 mm
0.09961 m
24.3 mm
0.0243 m
423 daN
4230 N
0.426 MPa ___ 10.224
MPa
Sample No:02 Lime
stone
Diametric 99.745 mm
0.09974 m
___ 1590 daN
15900 N
1.599 MPa ___ 38.376
MPa
Sample No:03 Clay stone Diametric 61.87 mm
0.0618 m
___ 25 daN
250 N
0.0656
MPa
___ 1.574
MPa
Sample No:04 Silt stone Diametric 61.6 mm
0.0616 m
___ 44 daN
440 N
0.115 MPa ___ 2.76
MPa
Sample No:05 Silt stone Diametric 62.06 mm
0.0620 m
___ 56 daN
560 N
0.145 MPa ___ 3.48
MPa
Sample No:06 Clay stone Axial 62.26 mm
0.0622 m
21.48 mm
0.0214 m
39 daN
390 N
0.101 MPa ___ 2.424
MPa
Sample No:07 Clay stone Axial 62.36 mm
0.0623 m
28.86 mm
0.0288 m
32 daN
320 N
0.0824
MPa
___ 1.977
MPa
Sample No:08 Lime
stone
Diametric 48.63 mm
0.0486 m
___ 1791 daN
17910 N
___ 7.588
MPa
220.05
MPa
Sample No:09 Lime
stone
Diametric 48.84 mm
0.0488 m
___ 542 daN
5420 N
___ 2.277
MPa
66.03
MPa
Sample No:10 China clay Axial 61.91 mm
0.0619 m
28.86 mm
0.0288 m
25 daN
250 N
0.0652
MPa
___ 1.564
MPa
Sample No:11 Silt stone Diametric 62.84 mm
0.0628 m
___ 47 daN
470 N
0.119 MPa ___ 2.856
MPa
Sample No:12 Lime
stone
Diametric 48.63 mm
0.0486 m
___ 2014 daN
20140 N
___ 8.533
MPa
247.45
MPa
3.5.1 Laboratory Experiments Table:
Table 3.5.1 : Readings Of Different Samples On Point Load
Strength
CHAPTER 04
RELATIONSHIP BETWEEN POINT LOAD INDEX AND THE
STRENGTH PARAMETERS OF COAL MEASURE ROCKS
4.1 INTRODUCTION
The point load test (PLT) is an accepted rock mechanics testing procedure used for the
calculation of a rock strength index. This index can be used to estimate other rock strength
parameters. The focus of this thesis is to present the data analysis used to correlate the point load
test index (Is50) with the uniaxial compressive strength (UCS), and to propose appropriate Is50 to
UCS conversion factors for different coal measure rocks. The rock strength determined by the
point load test (PLT), like the load frame strengths that they estimate, is an indication of intact
rock strength and not necessarily the strength of the rock mass.
4.2 UNIAXIAL COMPRESSIVE STRENGTH (UCS)
The UCS is undoubtedly the geotechnical property that is most often quoted in rock engineering
practice. It is widely understood as a rough index which gives a first approximation of the range
of issues that are likely to be encountered in a variety of engineering problems including roof
support, pillar design, and excavation technique (Hoek, 1977). For most coal mine design
problems, a reasonable approximation of the UCS is sufficient. This is due in part to the high
variability of UCS measurements. Moreover, the tests are expensive, primarily because of the
need to carefully prepare the specimens to ensure that their ends are perfectly parallel.
In rock mechanics and engineering geology the boundary between rock and soil is defined in
terms of the uniaxial compressive strength and not in terms of structure, texture or weathering.
Several classifications of the compressive strength of rocks have been presented, In this work a
material with the strength ≤ 0.25 MPa is considered as soil, refer to ISRM (1978) and figure 4.1.
Figure 4.1: Various Strength Classifications For Intact Rock (From Bieniawski, 1984)
The uniaxial compressive strength can be determined directly by uniaxial compressive strength
tests in the laboratory, or indirectly from point-load strength test (see Section 1.4.2). The tests
should be carried out according to the methods recommended by the ISRM (1972)
.
The classification of the uniaxial compressive strength suggested by ISRM is shown in Table