Type of Earthcache: Engineering with a geology theme (Engineering Geology)
Site Geology
The entire Bukit Permai is underlain by Kuala Lumpur Granite (Yin, 1976) that extent from Batang Kali and Rawang in the north, passes through Gombak, Ampang, Cheras, Hulu Langat and Kajang to Seremban in the south. The Kuala Lumpur Granite is part of the western flank of the Main Range Granite. Geochronological studies (Bignell & Snelling, 1977; Darbyshire, 1988) suggested that the age of the granite is around 215-199 million years or Late Triassic.
The granite of Taman Bukit Permai is generally medium- to coarse-grained, sparsely to moderately porphyritic and grey to bluish-grey. Petrographically the granite can be classified as muscovite granite. Coarse-grained biotite granites are also present (Ng, 1992). The slopes in this area are entirely cut in the granites (Tajul Anuar Jamaluddin, 2011).
Stability of a Rock Slope
There are a number of factors that affect the stability of a rock slope (Tajul Anuar Jamaluddin, 2011b). They are; Geology, Weathering profile, Discontinuities, and Slope geometry.
Different rock types (igneous, sedimentary, metamorphic) exhibit different characteristics, structures and resistance to weathering. Igneous rocks show relatively little post-formation deformation; as a consequence, they form relatively uniform material over large areas. On the other hand, sedimentary rocks exhibit bedding planes that are primary sedimentary structures reflecting changes in the depositional environment. Therefore adjacent beds may comprise materials of significantly different composition, grain size and cementing properties, which in turn leads to heterogeneity in the engineering geological properties. In the case of metamorphic rocks, the key engineering geological effect of dynamic metamorphism is the development of foliation. When foliation coincides with an unfavourable slope aspect and angle, instability can result. Metamorphic rocks, notably slate, phyllite and schists are vulnerable to rapid deterioration due to wet tropical weathering, after they are exposed subaerially.
The weathering profile of a rock slope also determines the stability of the slope. The higher the degree of weathering the weaker would be the rock material resulting in increase unstability of the rock slope.
Discontinuities such as faults, shears, tectonic joints and stress-relief joints weaken the rock mass and promote irregular weathering where groundwater penetration has occurred.
High vertical or subvertical rock slopes without properly engineered beams or benches are more unstable than gentler angled slopes.
How to claim this EarthCache?
From the listed coordinates, look at the rock slope and the pile of rock fall at the foot of the slope. Walk to the foot of the slope and examine the cause of the rock fall.
Email me the following;
1. The text "Bukit Permai - Granite I" on the first line.
2. The answers to the following questions;
- Besides the factors that affect the stability of a rock slope discussed above, what other factor do you think determine the stability of a rock slope?
- What would you recommend if you were to stabilised the rock slope that you have examined?
3. Optional task: Share your experiences and photos taken during your visit.*
References
1 Bignell, J.D. & Snelling, N.J., 1977. Geochronology of Malayan Granites. Overseas Geological Mineral Resources, London, 47, 73p. 2 Darbyshire, D.P.F., 1988. Geochronology of Malaysian granites. NERC Isotope Geological Centre Report, no. 88/3. 3 Ng, T.F., 1992. Petrography, structure and geotechnical studies of the Kuala Lumpur Granite, Eastern Part of Kuala Lumpur, Peninsular Malaysia. Unpubl. Mphil. Thesis, University Malaya. 4 Tajul Anuar Jamaluddin, 2011a. Engineering geology and rock slope stability for developments in former granite quarry sites (Field trip guide). IGM Professional Short Course Series – Engineering Geology of Rock Slopes, UKM, Bangi, Selangor. 5 Tajul Anuar Jamaluddin, 2011b. Geological features and their significance in rock (cut) slope engineering. Lecture 1, p. 1-35. IGM Professional Short Course Series – Engineering Geology of Rock Slopes, UKM, Bangi, Selangor. 6 Yin, E.H., 1976. The geology and mineral resources of the Kuala Lumpur Area. Geological Survey Malaysia Manuscript.
* It is understood that finding the answers to an EarthCache can be challenging, and many people tend to shy away from these caches because of this. However, it is my opinion that geocaching is also meant to be a fun family experience that simply aims to introduce interesting and unique locations such as this one. Flexibility on logging requirements, however, can only be applied if it can be established that you have actually taken the time to visit the site. For this reason, a proper log describing your adventure accompanied by a good number of photos would be much appreciated.
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