Durability characterisation of weathered sedimentary rocks using slake durability index and jar slake test


Author : Wong Jia Mang & Abdul Ghani Md RafekPublication : Bulletin of the Geological Society of MalaysiaNo. : 66Page : 81 - 88Year : 2018DOI : https://doi.org/10.7186/bgsm66201811


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Bulletin of the Geological Society of Malaysia, No. 66, December 2018, pp. 81 – 88

Durability characterisation of weathered sedimentary rocks using slake durability index and jar slake test

Wong Jia Mang* & Abdul Ghani Md Rafek

Department of Geoscience, Faculty of Science & Information Technology, Universiti Teknologi PETRONAS,
32610, Seri Iskandar, Perak, Malaysia
*Corresponding author email address: jia_16001961@utp.edu.my

Abstract: Weathering causes the rocks to loose their original strength and the increment in slakability can trigger slope instability. Furthermore, weathering of heterogeneous sedimentary rock mass produces a non-systematic weathering profile that is dependent on the characteristics of the unweathered, interbedded sedimentary sequence. However, the increase in slakability limits sampling of rocks for physical and mechanical rock tests. Thus, slake durability test and jar slake test have been applied to characterise a sedimentary rock mass weathering profile. The advantages of these methods are in the simple test procedures which only requires small size of rock block samples and relatively low cost testing equipments. The study was conducted at a roadcut that consists of Kati Formation which had undergone slight to complete weathering. Results show that the durability decreases with increases of weathering grades. However, presence of iron staining and iron recementation improve the rock durability. Completely weathered sandstone has the mean second cycle slake durability index, Id2 of 0.3 % to 15.0 %, highly weathered sandstone is from 22.0 % to 67.0 %, slightly weathered sandstone is 87.0 % to 98.0 % depending on the presence of iron recementation and fresh sandstone is 91.0 %. For mudstone, mean Id2 for completely weathered is 2.0 % while highly weathered mudstone is 12.0 %. Moderately weathered mudstone has an average value of 68.0 %. Mean Id2 for slightly weathered shale, is 83.0 % and slightly weathered chert has the average Id2 of 98.0 %. Jar slake test has the advantage to differentiate between highly weathered and completely weathered sandstone and mudstone. Completely weathered rocks have higher slaking properties where the rock samples breakdown completely. For highly weathered rocks, the breakdown is into chips and fractures. Jar slake test is suitable only for weathered rocks with slake durability value, Id2 below 25 %.

Keywords: Durability, weathered rocks, sedimentary rocks, slake durability index, jar slake test

Abstrak: Luluhawa menyebabkan batuan kehilangan kekuatan asalnya dan peningkatan keperoian boleh mengakibatkan ketidakstabilan cerun. Tambahan pula, luluhawa jasad batuan sedimen heterogen menghasilkan profil luluhawa yang tidak sistematik yang dipengaruhi ciri-ciri asal jujukan batuan berlapisan sebelum terluluhawa. Tambahan pula, peningkatan sifat pemeroian batuan membatasi kerja pensampelan batuan untuk menjalankan ujian fizikal dan mekanikal batuan. Justeru, ujian kebolehtahanan pemeroian dan ujian pemeroian dalam balang telah diaplikasikan untuk mencirikan profil luluhawa batuan sedimen. Kelebihan kaedah-kaedah ini ialah prosidur ujian yang ringkas dengan hanya memerlukan sampel batuan kecil dan kos peralatan ujian rendah. Kajian ini telah dilakukan di cerun jalan yang terdiri daripada Formasi Kati yang telah mengalami luluhawa sedikit hingga lengkap. Hasilnya, kebolehtahanan batuan menurun dengan peningkatan gred luluhawa. Walau bagaimanapun, kehadiran perwarnaan besi oksida dan penyimenan semula besi oksida meningkatkan kebolehtahanan batuan. Batu pasir terluluhawa lengkap mempunyai purata index ujian kebolehtahanan pemeroian kitaran kedua, Id2 dari 0.3 % hingga 15.0 %, batu pasir terluluhawa tinggi dari 22.0 % hingga 67.0 %, batu pasir terluluhawa sedikit ialah 87.0 % hingga 98.0 % bergantung kepada kehadiran penyimenan semula besi oksida dan batu pasir segar ialah 91.0 %. Untuk batu lumpur, purata Id2 untuk terluluhawa lengkap ialah 2.0 % manakala batu lumpur terluluhawa tinggi ialah 12.0 %. Batu lumpur terluluhawa sederhana mempunyai purata nilai 68.0 %. Untuk syal terluluhawa sedikit ialah 83.0 % dan rijang terluluhawa sedikit mempunyai nilai purata Id2 98.0 %. Ujian pemeroian dalam balang mempunyai kelebihan untuk membezakan batu pasir dan batu lumpur yang terluluhawa tinggi dan terluluhawa lengkap. Batuan terluluhawa lengkap mempunyai sifat pemeroian yang lebih tinggi di mana sampel batuan terurai sepenuhnya. Untuk batuan terluluhawa tinggi, penguraiannya adalah kepada serpihan dan rekahan. Ujian pemeroian dalam balang hanya sesuai untuk batuan terluluhawa dengan nilai ujian keboletahanan pemeroian, Id2 di bawah 25 %.

https://doi.org/10.7186/bgsm66201811