Acuus2012 Paper 103 (Tls)

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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.

[email protected]

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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Paper ID‐ 103 Paper ID‐ 103

INTERACTION BETWEEN MINERAL CONSTITUENTS,

WEATHERING, FRACTURING AND STRENGTH AND THE

HYDRAULIC

PROPERTIES

OF

THE

BUKIT

TIMAH

GRANITE

TINT LWIN

SWE

[email protected]

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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