A Study of the Weathering of the
Seremban Granite
Vahed Ghiasi
Mountainous Terrain Development Research Center Department of Civil
Engineering, and Faculty of Engineering, University Putra Malaysia 43400
Serdang, Selangor, Malaysia
Email: Ghiasi_upm@yahoo.com
Husaini Omar
Mountainous Terrain Development Research Center Department of Civil
Engineering, and Faculty of Engineering, University Putra Malaysia 43400
Serdang, Selangor, Malaysia
Email: Husaini@eng.upm.edu.my
Bujang K Huat
School of Graduate Studies, University Putra Malaysia 43400 Serdang, Selangor,
Malaysia Email: bujang@eng.upm.edu.my
ABSTRACT
This paper presented the weathering profile, modulus of elasticity and compressive
strength of weathered granite in Seremban, Malaysia. The granite of Seremban is found
to exhibit a full range of weathering grades. With increased weathering, the modulus of
elasticity and uniaxial compressive strength of the granite is found to decrease.
KEYWORDS: Weathered Granite, Engineering Parameters, Modulus of Elasticity,
Compressive Strength.
INTRODUCTION
Weathering in rock is caused by physical disintegration, chemical decomposition
affects and biological effects. Physical disintegration involves the mechanical breakdown
of the rock mass (usually controlled by discontinuities in the mass) and of the rock
material (controlled by micro-discontinuities such as grain boundaries and mineral
cleavages). Chemical decomposition affects almost all minerals except only a few,
especially quartz, are more or less unaffected. The processes involved in decomposition
are oxidation, reduction, hydration, hydrolysis, carbonation and solution.
Under temperature humid climatic conditions, decomposition and disintegration take
place simultaneously and it is difficult to separate the direct effects of the two processes.
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Their relative importance is very much a function of the climate (Peliter, 1950: Thomas,
1974; Fookes, 1991). In humid tropical Malaysia, decomposition is far more effective
than disintegration. A third group of processes is recognized as the biological weathering.
The organic material from animals and plants react with the rock mass and cause further
decomposition of the rock. The rate at which the various weathering processes occur
depends mainly on the following three factors:
•
•
•
Environmental, dominated by the climate and temperature, but also involved
are topography, the hydrological conditions and the biological systems are
important;
The properties of rock mass, especially the homogeneity, and the nature,
spacing and pattern of the discontinuities, i.e., the macro fabric;
The properties of the rock material, including composition, fabric, texture
and permeability.
At present, the weathering classification system initially proposed by Fookes et al.
(1971) and modified by Dearman (1974, 1978) is commonly used. The main factors
which rule the weathering of rocks are the climatic and the geographic conditions during
the weathering, the composition of the source material, the groundwater condition, and
the period of time over which weathering have been active. The weathering processes as
affected by the climate has been studied in the past by Iliev (1967), Sanders and Fookes
(1970), Farjallat et al. (1974), Onodera et al. (1974), Wilson (1975), Baynes and
Dearman (1978a, 1978b, 1978c), Baynes et al. (1978), Irfan and Dearman (1978a,
1978b), Saito (1982), Oilier (1984), Beavis (1985), Martin (1986), Dearman et al. (1987),
Fookes (1991), Malone et al. (1992), Zhao and Broms (1993). The climate affects the
weathering both directly and indirectly (Peliter, 1950; Oilier, 1984; Saito, 1981).
Temperature governs the rate of the chemical reactions, but frost action, heating and
cooling are important which can cause physical disintegration of the mass rock. Chemical
decomposition is important in a warm and humid climate, and of particular importance is
the solution of silica.
The chemical weathering depends both on the rainfall (frequency and duration) and
on the temperature (frequency and duration). The reaction rate doubles or triples for
every 20°C increase of the temperature (Saito 198l). Rainforest in the tropics are
subjected to heavy rainfall, so that cracks and other voids in the rocks and in the soils are
filled with water even close to the ground surface. The pH value is typically low between
3.5 and 5.5, due to the rapid weathering of the soil areas with a hot and humid climate
(Zhao 1994).
The sodium, potassium, magnesium and calcium content of the residual soil are low
(Oilier 1984). The relative importance of the various weathering processes for different
temperature and rainfall conditions is shown in Figure 1. It can be seen that the main
weathering mechanism in humid tropical Malaysia is chemical decomposition. The
chemical reactions involve such aggressive atmospheric agencies as water, oxygen and
carbon dioxide which affect the quartz and alkali feldspars. Table 1 summarizes terms
used in describing stages of weathering.
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Figure 1: Relationship between climate and type of weathering (after Fookes et al., 1971).
Table 1: Terms used in the description of stages of weathering of rock material
Term
Fresh
Discolored
Decomposed
Disintegrated
Description
No visible sign of weathering of rock material.
The color of the original fresh rock material is changed and is evidence of
weathering. The degree of change from the original color should be
indicated. If the color change is confined to particular mineral constituents
this should be mentioned.
The rock is weathered to the condition of a soil in which the original
material fabric is still intact, but some or all of the mineral grains are
decomposed.
The rock is weathered to the condition of a soil in which the original
material fabric is still intact. The rock is friable, but the mineral grains are
not decomposed.
The weathering profile in the rock mass may be described on the basis of the
distribution of the variously weathered materials within it. Dearman ( 1978) proposed a
scale of weathering grades of rock mass, indicating that for particular situations
modifications might be needed, for example by subdivision of grade II. Table 2
summarizes the weathering classification system for granite and volcanic rocks.
This paper presents the weathering profile, modulus of elasticity and compressive
strength of weathered granite of Seremban, Malaysia. The fracturing accompanies
weathering and the replacement of brittle minerals by soft clays, to result in a significant
reduction of the modulus of elasticity (Beavis, 1985: Baynes et al., 1978). It has been
noted that with increased weathering, the modulus of elasticity decreases linearly with
decreasing uniaxial compressive strength (Irfan and Dearman, 1978a).
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Table 2: Weathering classification system for granite and volcanic rocks
(Hencher and Martin, 1982)
GRADE
DESCRIPTION
TYPICAL DISTINCTIVE CHARACTERISTIC
VI
Residual Soil
A soil formed by weathering in place but with original texture
of rock completely destroyed.
V
Completely
weathered rock
Rock wholly weathered but rock texture preserved
No rebound from N Schmidt hammer
Slake readily in water
Geological pick easily indents surface when pushed
IV
Highly weathered
rock
Rock weakened so that large pieces can be broken by hand
Positive N Schmidt rebound value up to 25
Does not slake readily in water
Geological pick cannot be pushed into surface
Hand penetrometer strength index greater than 250 kPa
Individual grain may be plucked from surface
III
Moderately
weathered rock
Completely discolored
Considerably weathered but possessing strength such that
pieces 55mm diameter cannot be broken by hand
N Schmidt rebound value of 25 to 45
Rock material not friable
II
Slightly weathered
rock
I
Fresh rock
Discolored along discontinuities
Strength approaches that of fresh rock
N Schmidt rebound value greater than 45
More than one blow of geological hammer to break specimen
No visible signs of weathering or discolored
SAMPLE COLLECTION & TEST PROCEDURES
Granite rock was selected as type of rock to study because of its availability and
could be found in abundance in Peninsular Malaysia. It is the most prominent lithology of
Peninsular Malaysia and outcrop over some 40% of the land surface. They form the
bedrock of the main mountain ranges called Titiwangsa range and have been
differentiated into four broad groups on the basis of differences in mineralogy,
geochemistry and radiometric ages, i.e. epizonal late Cretaceous granite, epizonal
Triassic granites, epizonal Permo-Triassic granites, and mesozonal Permo-Triassic
granites (Hutchison, 1977). Figure 2 shows general geological map of Peninsular
Malaysia and location of the sampling site.
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Figure 2: Geologiccal map of Penninsular Malaaysia, which shows
s
the loccation of
igneo
ous rocks (Maalaysia Minerral and Geoscciences Deparrtment, 1983)).
From field
d observationss, the Serembban granite waas found to shhow distinctivve changes
frrom fresh rocck in terms of
o discoloratiion, chemical decomposittion and disinntegration.
Seven stages of
o weathering were recogniized as follow
ws:
Fresh granite: The rocck shows no changes
c
attributable to weaathering.
mely strong with highlyy interlockinng texture.
Light bluiish-grey in color, extrem
Schmidt hamm
mers value. SHV:
S
h4)
(S
Partially sttained granitee: The rock iss partially disscolored and can
c be sub-diivided into
thhree divisionss in terms of the amount off discolorationn.
Slightly stained
s
graniite: The rockk is stained brrownish-yelloow on the joinnt surfaces
onnly; there is no
n penetrationn of weatherinng agents: exttremely strong (SHV: 64).
Moderately stained granite:
g
Disscoloration has
h penetrateed inwards from
f
joint
suurfaces, and is less than 5 (1 per ceent by volum
me: the discoolored rock material
m
is
yeellowish-brow
wn and there is a slight grrittiness to the plagioclasee feldspars (i.ee. they are
paartially altered): very stronng (SHV: 58-665).
ained granitee: Discoloration by volum
me is more thhan 50 per cennt but less
Highly sta
thhan 100 per cent; the outerr rim is yellow
wish- brown and the innerr core is pale yellowishgrrey in color; some plagiocclase feldsparrs are gritty inn the outer zoone: fracturess are tight;
veery strong (SH
HV: 56).
Completelly stained granite: The rock is com
mpletely staineed yellowish brown to
yeellowish-oran
nge: plagioclaase feldspars are partiallyy decomposedd throughoutt: fractures
arre tight to sliightly open: there
t
is a tenndency, for grain
g
boundarries to be opeen (i.e. the
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rock is moderately micro fractured); strong to very strong (SHV: 50-52). The corners of
blocks arc very slightly rounded.
Weakened Granite: The rock is completely discolored and slightly to moderately
bleached thus assuming a pale yellowish-grey color.
Plagioclases are partially to completely decompose; potash feldspars are hard to
gritty (as a result of partial alteration). This is a transitional stage between the completely
stained rock and granitic soil. The fabric is weakened, particularly on the outside of the
block, due to opening up of grain boundaries and intense micro fracturing, and hence
shows granular disintegration and slaking on the outside of the block. Strong to
moderately strong (SHV: 39-48). The corners of blocks taken to the laboratory were
rounded, indicating that there had been some soil formation around the blocks in situ.
Granitic soil: completely discolored and highly bleached, assuming a pale
yellowish-orange to pale grayish-yellow color. Plagioclases are completely decomposed,
and potash feldspars are gritty (as a result of partial alteration). The structure is very
much weakened due to opening up of grain boundaries and intense micro fracturing, but
the fabric is still intact, Slakes readily in water. It ranges from weakly cemented cohesive
granitic soil (weak to moderately weak; SHV: 15-24) to friable soil (very weak. SHV: no
instrument response).
Residual Soil: Pale yellowish-orange, discolored; plagioclases are completely
decomposed, and potash feldspars are gritty. The structure is disturbed and the original
granitic fabric is lost. Slakes is readily in water Very weak.
Samples of the Seremban granite were collected at site and tested in the laboratory of
their modulus of elasticity and uniaxial compressive strengths. Figure 3 shows core logs
of the Seremban granite and their uniaxial compressive strength tests.
Figure 3: Core logs of the Seremban granite and their compressive test
TEST RESULTS
Figure 4 shows results of modulus of elasticity and compressive strength with depth
of the Seremban granite. As shown the modulus of elasticity the Seremban granite was
26.57 kN/mm^2 in depth 16.8m; increased to 60.73 kN/mm^2 at depth 18.35m (Figure
4a). Modulus elasticity and compressive of strength would generally increased with
depth. There was a change in degree of weathering of the granite from grade IV (closer to
surface) to grade III-II (deeper down) as shown in Figure 4 (b). The degree of weathering
generally decreases with depth, from grade VI to I.
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Yo
oung Mo
odulus and
a
De
epth
100
80
60
40
20
0
Compresssive
C
Stren
ngth and
d Degree
e
off Weathering
100
80
60
40
20
0
Comp
pressi
ve
ngth
Stren
(N/m
mm2
or MPa)
M
Dep
pth
E Young
(m) Modu
ulus (kN/mm
Series2
18.35
1
60
0.73
Series1
16.8
1
26
6.57
III - II
IV
79
81.7
26.33
(b)
(a)
(c)
F
Figure
4: The relationshipp of modulus of elasticity, compressive strength, deggree of weatheering
with depth of Seremban granite
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CONCLUSION
The process of weathering may be defined as that process of alteration of mass rocks
caused by the direct effect of the hydrosphere and the atmosphere. The rate at which the
various weathering processes occur is a function of environmental conditions, the
properties of the rock mass and of the rock material. In a humid and hot or warm climate,
decomposition is far more effective than disintegration. In humid tropical Malaysia, the
main mechanism of the weathering is chemical decomposition. The high annual
precipitation has caused secondary weathering of the residual soils. The weathering
profiles and field observations suggest that the weathering of the Seremban granite is
stratified and with a sharp boundary between the residual soil and the slightly to
moderately weathered granite. It was noted that with increased weathering, the modulus
of elasticity and uniaxial compressive strength of the granite decreased.
ACKNOWLEDGMENT
The authors wish to acknowledge University Putra Malaysia and MTD-RC for their
support of the research project.
REFERENCES
1. Baynes F.J. & Dearman W.R., 1978a: The micro fabric of chemically weathered granite, Bulletin
of International Association of Engineering Geologists. Vol, lB, pp. 91-100
2. Baynes F.J, & Dearman W.R., 1978a: The relationship between micro fabric and the engineering
properties of weathered granite. Bulletin of International Association of Engineering Geologists.
Vol 18, pp. 191-198.
3. Beavis F.C., 1985: Engineering geology. Blackwell Scientific Publication, Melbourne.
4. Dearman W.R., 1974: Weathering classification in the characterization of rock for engineering
purposes in British practice. Bulletin of international Association of Engineering Geologists. Vol.
9. pp. 33-42.
5. Dearman W.R., 1978: Weathering classification in the characterization of rock : a revision.
Bulletin of International Association of Engineering Geologists, Vol. 18. pp. 123-128.
6. Dearman W.R., Turk N, Irfan T.Y. & Rowshanei H., 1987: Detection of rock material variation
by sonic velocity zoning. Bulletin of International Association of Engineering Geologists, Vot,
35, pp. 3-8. 105
7. Farjallat, I.E.S., Tatam, YA C.T. & Yodhida R.. 1974: An experimental evaluation of rock
weatherability. Proceedings of 2rid Congress of International Association of Engineering
Geologists. pp. IV-30.1-9.
8. Fookes P.G., 1991: Geomaterial, Quarterly Journal of Engineering Geology. Vol. 24, pp. 3-15.
9. Fookes P.G., Dearclan W.R. & Franklin, I.A., 1971: Some engineering aspects of rock
weathering. Quarterly Journal of Engineering Geology. Vol. 4, pp. 139-185.
10. Hencher S.R. & Martin R.P... 1982: The description and classification of weathered rocks in
Hong Kong for engineering purposes. Proceedings of 7th South-east Asian Geotechnical
Conference. Hong Kong, vol. 1, 125-142.
Vol. 14, Bund. D
9
11. Hutchison, C.S., 1977, Granite emplacement and tectonic subdivision of Peninsular Malaysia,
Bulletin Geological Society Malaysia, No. 9, p 187-207
12. IlieviI. G., 1967 : An attempt to estimate the degree of ;,weathering of intrusive rock from their
physico-mechanical properties. Proceedings of 1st Congress of International Society for Rock
Mechanics, Lisbon. pp. 109-114.
13. Irfan T.Y. & Dearman W.R., 1978a: Engineering classification and index properties to weathered
granite. Bulletin of International Association of Engineering Geologists, Vol. 17, pp. 79- 90.
14. Irfan T.Y. & Dearman W.R., 1978b: The engineering petrography of weathercd granite in
Cornwall. England. Quarterly Journal of Engineering Geology. Vol. II, pp. 233-244.
15. Malaysia Mineral and Geosciences Department, 1983
16. Malone A.W., Ho K.K.S. & I, AM T.S.K., 1992 : Piling in tropically weathered granite.
Proceedings of Geotropika - International Conference in Geotechnical Engineering, Jahor Baharu.
17. Martin R.P., 1986: Use of index tests for engineering assessment of weathered rocks. Proceedings
of 5th Congress of International Association of Engineering Geologists, Buenos Aires, pp. 433450.
18. Oilier C., 1984: Weathering, 2nd edition. Longman. London.
19. Onodera T.F, Yashinaka R. & Odam, 1974: Weathering and its relation to mechanical properties
of granite. Proceedings of 3rd Congress of International Society for Rock Mechanics, Denver,
Vol 1, pp. 7I-8.
20. Peliter L., 1950: The geographic cycle in per glacial regions as it is related to climate
geomorphology. Annals of Association of American Geologists, vol. 40, pp. 21.-t--236.
21. Saito T., 1981: Variation of physical properties of igneous rocks in weathering. Proceedings of
International Symposium on Weak Rock, Tokyo, pp. 191-196.
22. Sanders M.K. & Fookes R.G., 1970: A review of the relationship of rock weathering and climate
and its significance to foundation engineering. Engineering Geology, Vol. 4, pp. 289-325.
23. Thomas. M.F., 1974: Tropical geomorphology - a study of weathering and landform development
in warm climates. McMillan, London,
24. Wilson M.J., 1975: Chemical weathering of some primary rock forming minerals. Soil Sciences,
Vol. 119, pp. 349-355.
25. Zhao J. & Broms B.B., 1993: Mechanical and physical properties of the weathered Bukit Timah
granite of Singapore. Proceedings of International Symposium on tardy Soil - Soft Rock, Athens,
pp. 883-890.
26. Zhao, B.B. Broms, Y. Ziiou & V. Choa, 1994: A study of the weathered of Bukit Timah Granite
Part A: Review ,field observation and Geophysical survey, Bulletin of the International
Association of Engineering Geology Paris - No 49 - April 1994
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