Bulletin of the Geological Society of Malaysia, Volume 45, May 2002, pp. 335 – 340

Taburan ketakselanjaran dalam profil luluhawa batuan metasedimen – Kajian kes cerun potongan CH 11540 – CH 11700 Lebuhraya Baru Pantai, Kuala Lumpur

(Distribution of disconinuities in the weathering profiles of metasedimentary rocks – Case study of a cut slope between CH 11540 – CH 11700 of the New Pantai Expressway, Kuala Lumpur)

Tajul Anuar Jamaluddin

Geology Department, University of Malaya, 50603 Kuala Lumpur. Malaysia

Abstrak: Cerun Potongan di CH 11540 – CH 11700 Lebuhraya Baru Pantai, Kuala Lumpur, terdiri daripada batuan metasedimen Formasi Kenny Hill, yang berusia Perm-Karbon. Formasi ini terdiri daripada selang lapis metabatu pasir, metabatu lumpur dan syal yang telah termetamorf menjadi seakan-akan filit. Cerun potongan setinggi 23 m ini mendedahkan batuan terluluhawa sederhana (gred III) hingga sepenuhnya (gred V) dan tanah baki (gred VI).

Survei ketakselanjaran telah dilakukan pada setiap cerun teres dengan kaedah garis pengimbasan yang direntangkan pada permukaan cerun. Setiap satah ketakselanjaran yang memintasi garis imbasan ini direkodkan orientasinya (jurus dan kemiringan). Data-data ketakselanjaran tersebut diasingkan mengikut gred luluhawa batuan dan diplotkan ke dalam unjuran stereografi hemisfera bawah untuk menilai taburan ruangnya di dalam profil luluhawa.

Hasil kajian jelas menunjukkan bahawa orientasi ketakselanjaran relikta yang terawet di dalam “tanih kejuruteraan” (batuan gred IV – V), didapati hampir sama dengan orientasi ketakselanjaran yang terdapat di dalam “batuan dasar” (gred III). Ini membuktikan bahawa pemetaan struktur ketakselanjaran relikta secara terperinci dan teliti boleh memberikan gambaran sebenar orientasi ketakselanjaran pada batuan dasar, dengan syarat zon “tanah kejuruteraan” dan “batuan dasar” tersebut berada di dalam domain struktur yang sama.

Abstract: The cut slope between CH 11540-CH 11700 of the New Pantai Expressway, Kuala Lumpur consists of metasedimentary rocks of probable Permo-Carboniferous Kenny Hill Formation. The rocks consist of interbedded metasandstone, metamudstone and phyllitic shales. The 23 m high slope cut moderately (grade Ill) to completely weathered (grade V) rocks and residual soils (grade VI).

A discontinuity survey was conducted on all berm slopes by adopting the scan-line method. A measuring tape was stretched along the slope faces and for each discontinuity intersecting the scan line, their orientation (strike and dip) was recorded. The discontinuity data were separated according to the weathering grade of the rock mass and then plotted onto lower hemisphere stereographic projection, in order to assess their spatial distribution within the weathering profile.

Results of the study clearly show that the orientation of relict discontinuties in the “engineering soil” (grade IV and V) is almost similar to those encountered in the “bedrock” (grade Ill). This implies that results from the mapping of relict discontinuities can be reliably adapted to predict the orientation of structural discontinuities of bedrock, provided that the overlying “engineering soil” and underlying “bedrock” lie within the same structural domain.

https://doi.org/10.7186/bgsm45200252