The Malaysian Journal of Analytical Sciences Vol 15 No 2 (2011): 138 – 149

 

KEGAGALAN CERUN DI BUKIT ANTARABANGSA, AMPANG, SELANGOR DAN HUBUNGANNYA DENGAN SIFAT FIZIK TANAH

(Slope Failure at Bukit Antarabangsa, Ampang, Selangor, and Its Relationship to Physical Soil Properties)

Muhammad Barzani Gasim¹*, Sahibin Abd. Rahim¹, Mohd. Ekhwan Toriman², dan Diyana Ishnin¹

¹Pusat Pengajian Sains Sekitaran dan Sumber Alam,
Fakulti Sains dan Teknologi
Pusat Pengajian Sosial, Pembangunan & Sekitaran,
Fakulti Sains Sosial dan Kemasyarakatan
Universiti Kebangsaan Malaysia
43600 UKM Bangi, Selangor, Malaysia

*Alamat email pengarang: dr.zani@ukm.my

Abstrak

Kegagalan cerun yang berlaku pada 6 Disember 2008 di Bukit Antarabangsa, Ampang, Selangor telah menyebabkan kematian dan kerosakan harta benda yang melibatkan lebih daripada 20 rumah penduduk telah ranap. Hujan lebat yang berlaku beberapa jam sebelum kegagalan cerun, telah meningkatkan ketepuan dan keplastikan tanah. Sebanyak 10 sampel  tanah telah diambil secara rawak di cerun-cerun stabil dan gagal untuk menentukan sifat fizikal tanah, kadar penyusupan serta hubungannya dengan corak hujan. Tanah dianalisis berdasarkan sifat fiziknya, lima tahun (2005-2009) data hujan harian dianalisis untuk mendapatkan hubungannya dengan penyusupan air disetiap stesen persampelan. Kadar penyusupan diukur menggunakan infiltrometer “double rings”. Hasil analisis sifat fizik tanah menunjukkan bahawa tekstur tanah didominasi oleh tanah berpasir yang mencatatkan peratusan kandungan pasir yang relatif tinggi. Nilai kadar serakan lempung adalah sederhana stabil sehingga sangat stabil atau berjulat daripada 0.013% sehingga 11.85%, kandungan organik antara 1.38 sehingga 2.74 %. Julat ruang rongga diantara 50.12% sehingga 62.31% dan purata tahap kekonduksian hidraulik diantara tahap 2 sehingga 5 atau agak perlahan sehingga pantas. Peratusan kestabilan agregat tanah berjulat dari 5.12 % sehingga 48.42%, nilai ini menunjukkan kekuatan relatif tekanan mekanik tanah adalah bernilai songsang terhadap peratusan kandungan air. Nilai keplastikan tanah berjulat tinggi sehingga sangat tinggi yang dicirikan dengan koloid yang tidak aktif. Taburan hujan bulanan berjulat daripada 38 mm hingga 427 mm. Kadar penyusupan semasa persampelan bernilai diantara 3.0 cm/jam hingga 7.0 cm/jam tetapi semasa kegagalan cerun dijangkakan berjulat diantara 10.94cm/jam sehingga 915.05cm/jam. Secara keseluruhan ditafsirkan bahawa sifat fizik tanah mempengaruhi kestabilan cerun, struktur tanah berpasir akan meningkatkan tahap keporosan tanah dan selanjutnya meningkatkan kadar penyusupan semasa hujan lebat dan akhirnya mencetuskan berlakunya kegagalan cerun.

Kata kunci: Bukit Antarabangsa, kadar penyusupan air, tanah berpasir, kegagalan cerun

Abstract

Slope failure which occurred on 6 December 2008 at Bukit Antarabangsa, Ampang Selangor has caused mortalities and loss of properties whereas more than 20 houses were flattened. Prior to slope failure, it was heavily downpoured for a few hours that increased the soil saturation and plasticity properties. A total of 10 soil samples were randomly taken from stable and unstable slopes to determine physical soil properties, infiltration rate and their relationship to rainfall pattern. Soils were analyzed in terms of their physical properties; five years (2005-2009) of daily rainfalls were analyzed to determine their relationship to infiltration rate at each sampling station. Infiltration rate is determined by using infiltrometer double ring. Analysis of physical soils properties shows that soil texture was dominated by sandy soil with relatively high percentage of sand. Values of clay dispersion coefficient were relatively stable to very stable  from 0.013% to 11.85% and organic content from 1.38 % to 2.74 %. Range of porosity was from 50.12% to 62.31%, while the average levels of hydraulic conductivity was from level 2 to 5 or relatively slow to fast. Percentage of soil aggregate stability was from 5.12 % to 48.42 % and this value indicates that relative strength of soil mechanical pressure is inversely proportional to the percentage of water content. Soil plasticity value was high to very high but characterized by inactive colloids. Distribution of monthly rainfall was from 38 mm to 427mm. The infiltration rate during sampling time was from 3.0 cm/hr to 7.0 cm/hr; but it was expected from 10.94cm/hr to 915.05 cm/hr during slope failures. Overall, it was interpreted that physical soil properties was closely interrelated with slope stability, structure of sandy soil will enhanced soil porosity stage and enhance the infiltration process during heavy rainfall, and finally  triggering of slope failure.

Keywords:  Bukit Antarabangsa, infiltration rate, sandy soil, slope failure

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