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doi: 10.3850/978-981-07-3757-3_RP-015-P103
Interaction Between Mineral Constituents, Weathering,
Fracturing and Strength and Hydraulic Properties of
Bukit Timah Granite
Tint Lwin Swe
M. E. Geo, MMGSS, MGeoSS.
ABSTRACT
Bukit Timah Granite generally consists of quart, feldspar, mica and hornblende and
other minor accessories. Individual mineral grains alter due to weathering of rock
mass. The alteration of those minerals increases with increasing degree of
fracturing and brecciation which in turn affects the great variation of the strength of
the rock material.
The intact rock samples are not always be tested for representing typical strength
value of the Singapore Granite. Most of the samples are affected by various degrees
of weathering and some internal cracks appeared as resulted from the tectonics
activities in the past. The relationship between the strength values of Singapore
Granite and weathering grades with or without the cracks in the material are
described in this study.
The density and network of discontinuities in a rock mass also play major role in
determining the hydraulic properties of the Bukit Timah Granite. Generally, the
highly fractured rock mass with a considerable thickness of in situ rock mass have
the larger the transmissivity and the hydraulic conductivity values. The interaction
between those physical processes and properties of Bukit Timah Granite is disclosed
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INTERACTION BETWEEN MINERAL CONSTITUENTS,
WEATHERING, FRACTURING AND STRENGTH AND THE
HYDRAULIC
PROPERTIES
OF
THE
BUKIT
TIMAH
GRANITE
TINT LWIN
SWE
7 Nov 2012
Marina Bay
Sands
Singapore
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Geological Map of Singapore (DSTA, 2009)
Bukit Timah Granite
Widely distributed in the central part of Singapore
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INTERACTIONS
Mineral composition
Fractures
Groundwater Strength
Weathering
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ROCK WEATHERING
Mechanical
Chemical
Decomposition of rock
• Hydration‐
react with
water
• Oxidation‐ react with oxygen
• Temperature and climate
• Carbonation
Biological
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Rock weathering of Bukit Timah Granite
Fresh Granite
Slightly
weathered
when exposed
and oxidized
Moderately
weathered
rock
Highly/
Completely
weathered
granite
Completely
weathered granite/
transition to
residual soil
Courtesy of Kyaw Win Sein (2012)
Residual
soil
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INTERACTIONS
Mineral composition
Fractures Weathering
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Petrographic analysis
Quartz
Plagioclase
Feldspar
Biotite
Hornblende
Chlorite
2.5mm
• quartz > 30 % of
the mineral
present,
• Feldspar, 60 ‐ 65 %
• varying amounts of
alkali feldspar and
acid
plagioclase
• subordinate
amounts of biotite
and hornblende
Courtesy of C.M. Gray
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Classification of
Weathering
(BS5930)
Grade Classifier Typical characteristics Graphic Remarks
I Fresh Unchanged from original state Intact
Microcracks
II Slightly
weathered
Slight discoloration, slight
weakening
Intact
Fissures
III Moderatelyweathered
Considerably weakened, penetrative discoloration, Large pieces cannot be broken by hand
Microcracks
Joints
IV Highlyweathered
Large pieces cannot be broken byhand. Does not readilydisaggregate (slake) when dry
sample immersed in water.
Often associatedwith joints andfractures
V Completely
weathered
Considerably weakened, Slake,
Original texture apparent
VI Residual soil Soil derived by in situ weathering but retaining none of the original
texture or fabric
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Fault Rock
and
Weathering
Brecciated Bukit Timah Granite (Loc. Gambas Avenue)
Rock samples of Bukit Timah Granite
(Various places of Singapore)
Highly weathered Granite and Completely weathered Granite
(Loc. Upp. Bukit Timah Road)
Weathering of Brecciatedgranite and fractured granite
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STRENGTH
OF
GRANITE
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UCS and
PLS
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Granite Core Samples for Testing
(Sample locations
‐various
places
of
Singapore)
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Relationship between Uniaxial Compressive Strength and Point Load Strength of Bukit
Timah Granite
(This
Study)
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INTERACTIONS
Fractures
Strength Weathering
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Typical rock core samples of Bukit Timah Granite for strength tests
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Effect of weathering and fracturing on the strength of Bukit Timah Granite
Description FreshFresh with
micorcracksSlight
Slight
with
some
cracks
ModerateModerate
with
cracks
High
Mean 100.5 41.3 86.5 37.0 34.7 15.9 10.9
Standard Error 2.4 4.1 3.5 2.2 4.4 3.3 1.9
Median 100.0 38.2 79.5 34.3 28.0 11.5 9.9
Standard Deviation 23.7 17.2 19.8 17.6 17.5 11.3 3.8
Minimum 59.1 15.8 60.5 5.9 12.5 3.4 7.8
Maximum 161.1 78.3 127.3 77.7 72.3 48.0 15.9
Count 96 18 32 65 16 12 4
Confidence Level (95.0%) 4.8 8.6 7.1 4.4 9.3 7.2 6.0
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FRACTURES AND ROCK MASS
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Fractured Granite
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RQD and Fracture Frequency
Deere and Deere (1988)
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Relationship between RQD and Fracture Frequency
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Typical Bedrock Profile of Bukit Timah Granite and Fracture Zone
Zoning of
fractured
rock
based
on
RQD
Rock Head Topography
Fractured rock = RQD
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INTERACTIONS
Fractures
Groundwater
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Pumping out test
Drilling and installation of pumping wellat Upp. Bukit Timah Road (2012)
Well development after installation
Drilling and installation of pumping well
at Upp. Bukit Timah Road (2012)
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Pumping Test Results
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Summary
of
Pumping
Test
and
RQD
Monitoring
Well
Discharge,
Q (l/s)
Thickness,
B (m)
Drawdown,
s (m)
Transmissivity,
T (m/day)
Permeability,
K (m/day)
Storage
coefficient,
S RQD#
MW1 1.3 2.4 1.17 17.57 7.32 0.00025734 *
MW2 1.3 3.3 0.95 21.64 6.56 0.00131088 77
MW3 1.3 3 1.05 19.58 6.53 0.00110114 0
MW4 0.42 1.7 0.32 20.75 12.21 0.00081063 51
MW6 1.62 3.9 1.07 23.94 6.14 0.00014962 47
MW7 1.62 6 1.05 24.39 4.10 0.00051457 31
MW8 1.62 2.2 1.11 23.08 10.49 0.00015324 *
MW8A 1.62 8 1.35 18.97 2.37 0.0000732 *
MW11 0.17 1.5 0.16 16.80 11.20 0.00103044 13
MW1 1.44 4 0.64 35.58 8.89 0.00101755 27
MW1A 1.44 5 0.86 26.47 5.29 0.00102744 20
MW2 1.69 8.25 1.06 25.28 3.10 0.000709 14
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Prediction of Permeability of Fractured Granite from RQD Values
If RQD
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Conclusions
• It is obvious that the strength property of Bukit Timah Granite
is strongly influenced by weathering and alteration of
constituent minerals
as
well
as
the
presence
of
fissures
in
the
rock.
• The effect of weathering and fissures on the strength is
described in terms of UCS and PLS values
• RQD is used to correlate with fracture count and hydraulic
conductivity of fractured granite
• RQD less than 75% are described as the fractured rock which
is correlated
to
hydraulic
properties
of
the
rock.
• The lower the RQD value, the higher the coefficient of
hydraulic conductivity.
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