International Journal of Advances in Mechanical and Civil Engineering, ISSN: 2394-2827
Volume-3, Issue-2, Apr.-2016
PETROGRAPHIC AND PHYSICO-MECHANICAL STUDIES ON
GRANITIC ROCKS AROUND BIDADI, RAMANAGARAM TALUK,
KARNATAKA STATE
1
A.V.GANESHA, 2K.N. PRAKASH NARASIMHA, 3C. KRISHNAIAH
1
Dept. of Civil Engineering, Ghousia College of Engg.,
(Under Viswesvaraya Technological University), Ramanagaram – 562 159, Karnataka.
2
Dept. of Studies in Earth Science, Manasagangotri, University of Mysore, Mysore-570 006, Karnataka.
3
Dept.of Marine Geology, Mangalore university, Mangalagangotri, Konaje, Mangalore- -574199, Karnataka.
E-mail: [email protected]
Abstract- The quality of dimension stones not only depends on aesthetic look and elegance, but also its petrographic
characteristics and mechanical properties. The systematic studies in the laboratory on unconfined compressive strength
(UCS) and unconfined tensile strength (UTS) are the key properties for characterization of rock materials in engineering
practices. The present study is on the determination of the quality of granite for its exploitation for dimension / ornamental
purposes by petrographic and strength studies.
The study area of the present investigation is a quarry site near Bidadi, Ramanagaram district. The petrography, index
properties, and mechanical properties were studied as per standard methods. Thin section studies reveal that granite has 3040% quartz, 45-65% feldspar and 5-8% accessories. Quartz is anhedral showing wavy extinction. Microcline are tabular and
exhibits typical cross hatched twinning. Biotite occurs as minute flakes and shows preferred orientation. Optically pleochoric
from yellowish brown to green. The results of UCS for all selected samples vary from 201- 218 MPa and were classified as
very high compressive strength material. Similarly TCS varies from 7.00-10.17 MPa.
Based on petrography and strength studies, the granite can be used not only as regular foundation stones, coarse aggregate,
and railway ballast but also as dimension stones and for civil engineering projects.
Keywords- Granite, petrography, index properties, UCS, TS, dimension stone.
laboratory as per the standard methods do not
normally reflect in-situ properties because of the
geological structures like joints, faults and plane of
weakness in the field. However, systematic studies in
the laboratory on compressive strength and tensile
strength are the key properties for characterization of
rock materials in engineering practices.
I. INTRODUCTION
The physico-mechanical rock properties are one of
the most important parameters used in the analysis
and design of any major engineering structures. The
physical properties of the rocks are influenced by the
presence of cracks and fractures but, the mechanical
properties strongly depend on its mineralogy, texture,
structure and degree of weathering. Further, the rock
strength also depends on the behaviour of
discontinuities such as fissures, bedding planes, faults
and joints. Most of the igneous and metamorphic
rocks are proved to be stronger when compared to
sedimentary rocks and hence they are quarried for
aggregates and dimension stones. The essential
properties of building stones are strength, durability,
colour, workability and availability. Rock aggregates
are used as building material and for road and
railroad construction and for the manufacture of
asphalt and concrete. In fact, now a days, dimension
stones have been extensively used as slabs and tiles
for flooring because of its fascinating colours,
textures, patterns and surface finish apart from its
durability and strength.
The uniaxial compressive strength (UCS) is one of
the important index properties to determine the
strength of the rock. It is determined by axially
loading a cylindrical specimen with a diameter of
approximate 54 mm and a length to diameter (L/D)
ratio equal to 2.5:1 (NX size) until the specimen fails.
Similarly the tensile strength of rock is usually
obtained through Brazilian test, consists of loading a
circular disc with a diameter of approximate 54 mm
and a thickness to diameter ratio of 1:2 of the
specimen using two curved jaws until failure occurs
(ISRM, 2007).
Granite has become one of the most popular building
materials. Generally any crystalline, hard, pleasing
coloured rocks are widely recognised as ‘Granite’ by
dimension-stone trade people. Further, any igneous
rock closely related to granodiorite, porphyry, gabbro
and dolerite and metamorphic rocks such as gneiss
are considered as ‘granite’ (Walle and Heldal, 2001).
However, granite is defined by the American Society
for Testing and Materials (ASTM) as a "visibly
granular, igneous rock generally ranging in color
from pink to light or dark grey, and consisting
The quality of dimension stones not only depends on
aesthetic look and elegance, but also its petrographic
characteristics and mechanical properties. Further,
determination of physical index properties such as
specific gravity, dry density, porosity and water
absorption are also important. The strength and
deformation properties of rock measured in the
Petrographic And Physico-Mechanical Studies On Granitic Rocks Around Bidadi, Ramanagaram Taluk, Karnataka State
36
International Journal of Advances in Mechanical and Civil Engineering, ISSN: 2394-2827
mostly of quartz and feldspars, accompanied by one
or more dark minerals". Granite usually has medium
to coarse grained texture. The BIS specification of
granite are as per IS : 14223 (Part 1) -1994
(Reaffirmed, 2001, 2002) is as follows: The
compressive strength for coarse grained grey granite
should be between 130-220 N/mm2, tensile strength
ranges from 9-12 N/mm2and shear strength ranges
from 30-55 N/mm2. The physical properties like
moisture content (~0.15%), specific gravity (~2.75),
porosity (1-2%) and water absorption (~0.50%) are
characteristic feature of granite. Further, granite
should be free from all imperfections and deleterious
minerals.
Several authors have worked on determining the
engineering properties of granites (Tugrul and Zarif,
1999; Akesson et al., 2003; Sousa et al., 2005;
Dwivedi et al., 2008; Shivapragasam et a., 2012
Anurag and Yadav, 2014). The percentage of quartz
in rock also influence the mechanical properties of
rocks (Tugrul and Zarif,1999).
The present study is on the determination of the
quality of granite for its exploitation for dimension /
ornamental purposes by petrographic and strength
studies.
Volume-3, Issue-2, Apr.-2016
Granite’. Closepet is the old name for Ramnagaram,
which is the type area. This belt with an average
width of 20 km extends from Bilgi in the north,
forming the basement to Kaladgi Supergroup upto
Sivasamudram in the south. Closepet Granite is
constituted of a cluster of individual plutons or plugs
of different sizes, emplaced along the suture zone
welding the eastern and western blocks of Dharwar
Craton (Swami Nath and Ramakrishnan, 1981). By
and large, Closepet Granite is composed of pink and
grey coarse grained and porphyritic granite and the
age is determined to be around 2500 million years
old. Figure 2 shows the simplified geological map of
the area.
II. THE STUDY AREA:
The study area of the present investigation is a quarry
site near Bidadi, Ramanagaram district, belongs to
root zone of Closepet granite, which is 12 kms from
Ramanagaram towards Bangalore, beside BangaloreMysore high way. The active quarry is just beside
Kenchanakuppe
village
(77o22’30”N
and
o
12 48’10”E) belongs to SOI toposheet no. 57H/5.
Figure 1 shows the location map along with quarry
site of the study area.
Figure-2: Simplified geological map of the Closepet granite
(after Jayananda et al., 1995).
IV. EXPERIMENTAL METHODOLOGY
Granite rock in the form of blocks and hand
specimens were collected from the quarry site. The
rock is fresh, homogenous, compact, hard and
nonfoliated. Ten blocks (12" x 12" x 7") were
collected from different parts of the same quarry.
III. GEOLOGY OF THE AREA:
Petrography of rock is very important tool to
determine the physical and chemical features. It is
the first and foremost requirement as it unravels the
geological processes of formation of rock. This
includes the study on mineralogy, grain size and
texture which reflects the suitability of the rocks for
different engineering purpose. Mineralogical, textural
and modal studies were carried using petrological
microscope at Dept. of Studies in Earth Science,
University of Mysore, Mysore. Several polished thin
sections were prepared and examined for each rock
type using optical microscopy techniques.
The dominant litho unit of the study area is granite,
which is 500 km long North-South trending linear
belt rich in potash feldspar and is popularly
called ‘Closepet
The physical index properties such as specific
gravity, dry density, porosity and water absorption
were determined as per ISRM standard procedure
(ISRM, 2007).
All the index properties and unconfined compression
and tensile strength of the core samples were
determined at National Institute of Rock Mechanics
(NIRM), KGF, Karnataka. The samples were cored
Figure-1: Location map of the study area
Petrographic And Physico-Mechanical Studies On Granitic Rocks Around Bidadi, Ramanagaram Taluk, Karnataka State
37
International Journal of Advances in Mechanical and Civil Engineering, ISSN: 2394-2827
in the laboratory and were cut to standard size
according to suggested method ISRM (Brown, 1981).
The mechanical properties were determined using the
MTS 815 Rock Mechanics Testing System (MTS
815), a computer controlled, servo hydraulic
compression machine and Brazilian Tensile strength
machine.
Uniaxial compressive strength tests were conducted
on the eight rock specimens. The trimmed core
specimens have a diameter of 54-mm (NX size) and a
length-to-diameter (L/D) ratio of 2.5. All specimens
were loaded to failure under a constant loading rate of
0.5 - 1.0 MPa/s. Post-failure characteristics are
observed.
It is very difficult to carryout uniaxial tensile test for
rock materials, hence an indirect method have been
used since several decades which is nothing but
diametrical compression test of thin discs, referred as
Brazilian test. This is a standard method approved by
ISRM (Bieniawski, 1979). Brazilian tensile strength
test were conducted on eight samples which have
L/D ratio = 0.5. The loading rate is controlled at
approximately 200 N/s. Post failure characteristics
are observed.
Volume-3, Issue-2, Apr.-2016
(A-Polarized light, B-Crossed Nichols. C-Alteration
of biotite to sericite and D- Cross hatching twinning
in feldspar, Qtz-Quartz, Feld-Feldspar, Bio-Biotite,
Seri-Sericite, Micr-Microcline)
Table 1: Modal and chemical analysis of typical
granite
5.2 Physical properties:
In the present study specific gravity and water
absorption were determined for all the samples.
Specific gravity for the rock ranges from 2.64 to 2.75.
This rock is suitable for dimension stones. Water
absorption is an important property which tells about
the durability of the rock. It should be less than 1%
for dimension stones or for heavy constructions and
in the present study it is less than 0.35%.
V. RESULTS AND DISCUSSION
5.1 Petrography:
Granite of the study area exhibits equigranular
texture and is medium to coarse grained in nature. It
is composed of quartz and feldspar with minor
amount of mica and opaques constitute the
magnetite in accessory amounts. The rock composed
of 22-25% quartz, 60-65% feldspar and 8-10% mica
and 1-2% accessories. Quartz is anhedral showing
wavy extinction and Microcline are tabular and
exhibits typical cross hatched twinning. Biotite
occurs as minute flakes and shows preferred
orientation and optically Biotites are dichroic from
yellowish brown
to green. Figure 3 shows
microphotographs of a typical granite under crossed
nicols and table-1 shows average modal composition
of the present study along with chemical composition
of granite (Jayananda et al., 1995).
5.3 Mechanical properties:
Compressive and tensile strength of rocks in the
laboratory is an inexpensive method to determine the
strength and in the present investigation eight
samples were tested. All the samples were tested until
they crushed and the maximum peak compressive
strength was recorded. The conventional split tensile
strength test for all the samples were done as it was
very difficult to prepare briquette of standard size.
The compressive strength ranged between 201 MPa
to 225 MPa and tensile strength is between 7.00 and
10.21 MPa.
Figure 4 shows
core specimens before
experimentation and specimen after subjected to
strength test (post failure). All results (index
properties and mechanical properties) are tabulated in
Table 2
Figure-3: Photomicrographs of typical granite of the study
area.
Figure-4: Photos showing specimens before and after strength
test
Petrographic And Physico-Mechanical Studies On Granitic Rocks Around Bidadi, Ramanagaram Taluk, Karnataka State
38
International Journal of Advances in Mechanical and Civil Engineering, ISSN: 2394-2827
(A-Core specimens before UCS, B-Circular discs
before TS, C-Crushed core specimen after UCS, DCircular disc showing crack after Split TS.)
Volume-3, Issue-2, Apr.-2016
UCS is its capacity to withstand axially loaded
compressive forces and the mean UCS of the granite
is 212.5 MPa. Similarly the TS is the ultimate
strength in tension for which rock can withstand and
the mean TS of the granite is 8.09 MPa. Comparing
the results obtained by various workers on
mechanical properties of granite and as per ISRM
standard, with the present investigation, it is found
that the UCS and TS have very high values.
Table.2: Physical properties, UCS and TS of core
samples
Based on petrography and higher UCS and TS, the
granite of the present study is hard, free from flaws,
durable and takes good polish. This is supported by
lower percentage of water absorption and medium
specific gravity. Hence, the granite and similar rock
types having same characteristics in Ramanagaram
district are suitable to quarry for dimension stones
and for any civil engineering projects.
Several classifications of the compressive strength of
rocks have been presented, Compressive strength
classification for various rocks has been determined
by many workers and as per ISRM (2007), very high
strength and extremely high strength values are 100250 MPa and >250 MPa respectively. Also, Hoek
and Brown, (1980) gave a data set for almost all the
rocks and maximum UCS for granite is 230 MPa.
ACKNOWLEDGEMENTS
The authors are grateful to HOD/Chairman of their
respective departments for constant encouragement.
The authors thank the MoES, New Delhi, for
providing financial assistance to publish this article.
They also thank the staff of NIRM, KGF for
conducting experimental procedures.
Experimental studies on mechanical properties of
granite determined by Alehossein and Boland (2004),
shows that UCS and TS are ~238 and ~11 MPa
respectively and can be comparable to present study.
Also, the strength obtained from the present study is
comparable to the standard granites having same
composition, of different areas of India (Subramani et
al., 2012, Table 3). The strength of present study is
higher than that of granite reported by Subramani et
al., (2012).
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CONCLUSION
The present work pertains to granitic rocks of one of
the quarries in Ramanagaram district, Karnataka.
The petrography and physico-mechanical properties
reflects the quality and durability of the rock suitable
for dimension stone.
Granite of this area is medium to coarse grained and
exhibits equigranular texture and mineralogically
around 25% of quartz and 60-65% of feldspar. The
Petrographic And Physico-Mechanical Studies On Granitic Rocks Around Bidadi, Ramanagaram Taluk, Karnataka State
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International Journal of Advances in Mechanical and Civil Engineering, ISSN: 2394-2827
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