Indonesian Journal on Geoscience Vol. 5 No. 1 April 2018: 23-31 INDONESIAN JOURNAL ON GEOSCIENCE Geological Agency Ministry of Energy and Mineral Resources Journal homepage: hp://ijog.geologi.esdm.go.id ISSN 2355-9314, e-ISSN 2355-9306 The Stability of Metasedimentary Rock in Ranau, Sabah, Malaysia Ismail Abd. Rahim and Baba Musta Natural Disasters Research Centre, Faculty of Science & Natural Resources, Universiti Malaysia Sabah, Jalan UMS, 88400 Kota Kinabalu, Sabah, Malaysia Corresponding author: [email protected] Manuscript received: January 4, 2016; revised: April 2, 2016; approved: December 27, 2017; available online: January 29, 2018 Abstract - The aim of this paper is to determine the stability of slopes and to propose preliminary rock cut slope protection and stabilization measures for Paleocene to Middle Eocene Trusmadi Formation along Marakau-Kigiok in Ranau, Sabah, Malaysia. The rock of Trusmadi Formation is slightly metamorphosed and dominated by interbeds of sandstone with quartz vein (metagreywacke), metamudstone, shale, slate, sheared sandstone, and mudstone. The rock unit can be divided into four geotechnical units namely arenaceous unit, argillaceous unit, interbedded unit, and sheared unit. Twelve slopes were selected for this study. Geological mapping, discontinuity survey, kinematic analysis, and prescriptive measure were used in this study. Results of this study conclude that the potential modes of failures are planar and wedge. Terrace, surface drainage, weep holes, horizontal drain, vegetation cover, wire mesh, slope reprofiling, and retaining structure were proposed protection and stabilization measures for the slopes in the studied area. Keywords: Trusmadi Formation, Ranau, metasedimentary rock, slope stability, mode of failure © IJOG - 2018. All right reserved How to cite this article: Rahim, I.A. and Musta, B., 2018. The Stability of Metasedimentary Rock in Ranau, Sabah, Malaysia. Indonesian Journal on Geoscience, 5 (1), p.23-31. DOI: 10.17014/ijog.5.1.23-31 Introduction concentrated at the western part of the studied area. This lowland area is usually used for agriculture The studied area is located in the southeast of activity such as paddy cultivation. Ranau Town which covers Marakau-Kinapulidan- The studied area is underlain by the Trus- Kigiok road alignment (Figure 1). Generally, the madi Formation and Quaternary alluvial deposit topography of the studied area can be divided (Figure 1). The age of the Trusmadi Formation is into hilly and lowland areas with the elevation Palaeocene to Middle Eocene (Jacobson, 1970; of above 500 m and below 500 m, respectively. Sanudin and Baba, 2007). This formation consists The hilly topography is situated at the western, of interbedded mudstone and sandstone units of eastern, and southernIJOG parts of the studied area. sedimentary rock with various thicknesses from The topography also represents the northeastern- thin to very thick. The mudstone is more domi- southwestern ranges in Ranau area. The highest nant than the sandstone. elevation is about 900 - 1,000 m. The lowland area The Trusmadi Formation also experienced a is situated at the middle part of the studied area low grade metamorphism into green schist fa- and mainly controlled by Liwagu River. This river cies. The metamorphism caused the Trusmadi provides alluvial plain during flooding event and Formation has altered into metasedimentary and/ AccreditedIJOG/JGI by:(Jurnal - LIPI, Geologi valid AugustIndonesia) 2016 - -Acredited August 2021 by LIPI No. 547/AU2/P2MI-LIPI/06/2013.Indexed valid by: 21 Scopus, June 2013 since -October 21 June 30, 2016 2017 - RISTEKDIKTI, valid May 2016 - May 2021 23 Indonesian Journal on Geoscience, Vol. 5 No. 1 April 2018: 23-31 116o39" E 116o40" E 116o41" E 116o42" E o o o Kg. Marakau 116 00" E 117 10" E 118 20" E Liwagu River N Geographical Symbol: 00" N 00" N o o 7 South Chinea Sea 7 Paved Road Sulu Sea 500 Unpaved Road 10" N 10" N o o 6 6 Studied S1 65 Sandakan 600 Kinabalu area River City S2 60 56" N 700 o 26 900 S3 800 100 Contour 20" N 20" N o o 5 5 Kg. 24 (20m interval) MALAYSIA Lahad Datu Kituntul Baru S4 Kg. Village 30" N 30" N o o 20 4 4 S5 Slope Section 116o00" E 117o10" E 118o20" E No.3 Kg. Lipoi S6 35 Geological Symbol: S7 Ranau - 45 Strike S8 63 o Road Tambunan 500 40 and Dip 63 800 600 Rock boundary 500 500 700 Kg. Kinapulidan Rock Unit: 55" N 5 o Kg. Kigiok 800 5 Alluvium S9 S11 S10 (Holocene) 55 Pinosuk Gravel (Pleistocene) 600 Trusmadi Formation (Paleocene - Middle Eocene) Scale 700 500 500 0 0.5 1.0 800 kilometres 116o39" E 116o40" E 116o41" E 116o42" E Figure 1. Geological map (from Yin, 1985) and sampling station of the studied area. or metamorphic rock unit. The typical character- Slope failure is the main factor in causing istic of Trusmadi Formation is the appearances of traffic interference, maintance coast to increase, foliation (slaty cleavage) and quartz veins. property damage as well as lost of lives, espe- The fieldwork observation shows that the out- cially in a weak and deformed rock formation crops of metasedimentary rocks consist of mud- such as metasedimentary Trusmadi Formation. stone, metamudstone, shale, and metasandstone Therefore, the main objectives of this study are with quartz vein. The metamudstone of the rock to assess the stability and to propose protection is represented by slate. The Trusmadi Formation and stabilization measures of rock cut slope along was faulted and folded by moderate to high degree the road in the studied area. of deformations. These moderate and high degree of deformations are responsible for the formation of metasedimentary and metamorphic rock units, Methods respectively. The high degree of deformation in the soft rock unit also contributed to the formation Geological mapping, discontinuity survey, and of fault zone and shear zones. a stereographic analysis have been used in this Quaternary deposits of Pleistocene and Ho- study. Geological mapping includes lithological locene ages are distributed in the lowlandarea and structural identification, measurement, and along the main rivers and flood plain in the stud- interpretation. A discontinuity survey has been ied areas. The field observation shows that the conducted using a random method. Pleistocene alluvial depositIJOG is characterized by In a stereographic analysis, Dips V5.013 com- unconsolidated and poorly sorted sediment. The puter programme (Rocscience, 2003) of lower material comprises eroded and transported ma- hemisphere spherical projection was used to per- terials such as clays, sands, organics, pebbles, form the pole plot of discontinuity. The results gravels, boulders, etc. The maximum thickness obtained were used for the clustering of the discon- of this alluvial deposit is approximately 50 m tinuity and identification of the discontinuity set (Hutchison, 2005). or the average orientations of the discontinuity set. 24 The Stability of Metasedimentary Rock in Ranau, Sabah, Malaysia (I.A. Rahim and B. Musta) To assess the relative stability and potential for performing the Markland test. Data of the strike future rock failures in the studied area, a graphi- and dip values of slope have been obtained from cal stereonet kinematic analysis by Markland the discontinuity survey and discontinuity sets (1972) has been carried out. The Markland test from a pole plot. The slope face is shown as a allows the orientation of joints, bedding planes, great circle and friction angle is represented by and fractures to be analyzed at numerous sta- an interior circle. A representative value of 30 tions to discriminate which discontinuities are degrees was selected for the internal friction likely to provide failure surfaces for future rock angle along discontinuities in the meta- sedimen- failures. This method compares the orientation of tary Trusmadi Formation following Hoek and the slope with orientations of rock discontinuities Bray (1981). Selections of slope protection and and internal friction angle (frictional component stabilization measures were conducted by using of shear strength) of the rock mass to see which prescriptive measures (Yu et al., 2005) as well as fractures, joints, or bedding planes render the the kinematic analysis result. rock mass theoretically unstable. Slope orientation, discontinuity set orienta- Slope Stability Assessments tion, and friction angle of the Trusmadi For- The slope stability assessment was conducted mation are the main parameters required in on twelve slopes along the road (Figure 2). In this a b c d e f g h i j IJOGk l Figure 2. Slope sections. (a) slope 1; (b) slope 2; (c) slope 3; (d) slope 4; (e) slope 5; (f) slope 6; (g) slope 7; (h) slope 8; (i) slope 9; (j) slope 10; (k) slope 11 left; (l) slope 11 right. 25 Indonesian Journal on Geoscience, Vol. 5 No. 1 April 2018: 23-31 slope stability assessment, the rock units (Trus- Slope geometry and geotechnical unit madi Formation and alluvial deposit) are also di- The summary of slope geometry and geo- vided into five geotechnical units, i.e. arenaceous technical unit are shown in Table 1. Slope S2 unit, argillaceous unit, interbedded unit, sheared (55.6 m) and slope S11 left (3 m) are the highest unit, and alluvial unit (Figure 3). The first four and the lowest cut slopes in the studied area, units are collected from the Trusmadi Forma- respectively. The thickest arenaceous unit, ar- tion. The arenaceous unit consists of sandstone gillaceous unit, interbedded unit, sheared unit, with quartz vein (metagreywacke) (Figures 4a and alluvial unit were found in slopes S1 (70 and 4b), argillaceous unit of metamudstone and m), S4 (55.8 m), S4 (111.6 m), S3 (81.3 m), shale (Figures 4c and 4d), interbedded unit of and S9 (20 m), respectively. metagreywacke and slate (Figure 4e), sheared unit of sheared sandstone and mudstone (Figures Kinematic analysis 4f, 4g, and 4h), and alluvial unit of alluvial deposit Discontinuities sets and mode of failures (Figure 4i).