Bulletin of the Geological Society of Malaysia, Volume 69, May 2020, pp. 79 – 88
Pengecaman mekanisme utama tanah runtuh cetek di Bukit Fraser, Pahang
Mohd Hariri Arifin, Nor Shahidah Mohd Nazer*, Abdul Qayyum Jalal
Program Geologi, Pusat Sains Bumi dan Alam Sekitar, Fakulti Sains & Teknologi, Universiti Kebangsaan Malaysia, 43600, UKM Bangi, Selangor, Malaysia
* Corresponding author email address: shahidahnazer@ukm.edu.my
Abstrak: Masalah kestabilan cerun di sekitar Bukit Fraser semakin membimbangkan apabila 22 tanah runtuh cetek dikesan setakat 6 Ogos 2017. Pengecaman mekanisme utama kegagalan cerun cetek dilakukan berdasarkan analisis geologi struktur, kejuruteraan tanah dan geofizik ke atas 6 buah cerun terpilih di sepanjang laluan mendaki dan menuruni Bukit Fraser. Berdasarkan maklumat lineamen rantau, Bukit Fraser mempunyai tiga set lineamen utama berorientasikan Utara- Selatan, Timur Laut-Barat Daya dan Barat Laut-Tenggara. Satu set lineamen yang minor pula berkedudukan Timur-Barat. Sistem saliran bercorak selari ke sub-reranting dan kebanyakkan mengalir ke arah Barat Laut, Timur Laut dan Selatan. Berdasarkan penilaian terhadap aspek kejuruteraan tanah, kesemua cerun bersudut curam melebihi 70º dengan material pembentuk cerun terdiri daripada tanah pasir berlodak (SM) berkeplastikan rendah. Kandungan lodak berkeplastikan rendah (ML) adalah tinggi berbanding lempung bagi kebanyakkan cerun menandakan kehadiran bahan organik yang tinggi. Berdasarkan survei keberintangan geoelektrik dan kaedah pengkutuban teraruh, kewujudan bahan tinggi kandungan air terdiri daripada lodak dan pasir bernilai kurang 100 Ωm dapat dicerap pada hampir semua kawasan sub-permukaan cerun. Kehadiran bahan berlodak memperlihatkan nilai kebolehcasan yang tinggi iaitu melebihi 10 milisaat dan sebaliknya bagi bahan berpasir. Mekanisme utama kegagalan cerun cetek keseluruhannya disebabkan oleh ketidakseimbangan dinamik cerun meliputi potongan cerun yang amat curam, jasad cerun yang telah sepenuhnya terluluhawa kepada tanah baki bergred VI, kehadiran air yang tinggi di dalam jasad cerun berlodak dan berpasir serta material cerun berkeplastikan rendah dengan indeks kebolehmampatan yang tinggi.
Kata kunci: Mekanisme, tanah runtuh cetek
Abstract: Slope stability problems in Bukit Fraser are raising concern where 22 shallow landslides were recorded as of 6 August 2017. Identification of main shallow slope failure mechanisms were done on the basis of structural geology analysis, soil engineering and geophysics from 6 selected slopes along ascending and descending route of Bukit Fraser. Based on the information of the regional lineament, Bukit Fraser consists of 3 lineament sets with North-South, North East-South West and North West-South East orientation. One minor lineament set was oriented to East-West. Fluvial system patterns are parallel to sub-dendritic and flowing mostly to the North West, North East and South direction. According to the engineering geology evaluation of the slope, all slopes angled at about 70º with slope materials consist of sandy soils (SM). The existence of silt of low plasticity (ML) is high as compared to clay for most slopes indicating existence of high organic content. According to the electrical resistivity survey and induced polarization method, the existence of materials with high water content consists of silt and sand with value lower than 100 Ωm can be seen at almost all sub-surface area. The existence of clayey materials is showing higher chargeability values of about 10 milisecond and vice versa for sandy materials. The main mechanisms for shallow slope landslides as a whole are caused by dynamic imbalance of the slopes including steep cut-slope angle, slope materials completely weathered to residual soils of grade VI, high water content existence inside sandy and silty slope materials and also low plasticity slope material with high compressibility indices.
Keywords: mechanisms, shallow landslides
DOI: https://doi.org/10.7186/bgsm69202007
