RMR and SMR as Slope Stability Preliminary Studies of Rajamandala Limestone Mine Area

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1 1th Asian Regional Conference of IAEG () RMR and SMR as Slope Stability Preliminary Studies of Rajamandala Limestone Mine Area Ilham PRASETYA (1), Rizqi NARENDRA (1), Agus WIRAMSYA (), Irvan SOPHIAN (), and Dicky MUSLIM () (1) Undergraduate of Geological Engineering Faculty, Padjadjaran University, Indonesia () Postgraduate of Geological Engineering Faculty, Padjadjaran University, Indonesia () Geological Engineering Faculty, Padjadjaran University, Indonesia Abstract Rajamandala Limestone in Padalarang area in Indonesia has a long history of mining and exploitation. Most Rajamandala Limestone mining is performed in open-pit. Slope stability is often a major issue in an open-pit mine. The stability of the open-pit mine slope must be maintained so as not to disrupt the mining process. Rock Mass Rating (RMR) has been widely used as a method of classifying the strength of the rock mass. RMR values in this study derived from observations of the rock mass characteristics directly in Padalarang area at three different mine sites and testing of the materials of intact samples in the laboratory. RMR values are then correlated into Slope Mass Rating (SMR) which is a system of classification of a rock slope. The study showed that the Rajamandala Limestone Mine area has RMR values of -71 and included in the class or and SMR ranged between 61-7 and belong to Good Slope class. Keyword: Rajamandala Limestone, Open Pit Mining, RMR, SMR 1. Introduction Rajamandala Limestone in Padalarang area in Indonesia has a long history of mining and exploitation. Most Rajamandala Limestone mining is performed in open-pit. Slope stability is often a major issue in an open-pit mine. The stability of the open-pit mine slope must be maintained so as not to disrupt the mining process. This paper aimed to perform how to correlate rock mass observations data from field to RMR and SMR and use it as mining slope stability preliminary studies.. RMR and SMR The RMR (Rock Mass Classification) was developed By Bieniawski during (Bieniawski, 197). It was modified over the years as more case histories became available and to conform with international standards and procedures (Bieniawski, 1979). Due to the RMR system having been modified several times, and since the method is interchangeably known as the Geomechanics Classification or the Rock Mass Rating system, it is important to state that the system has remained essentially the same in principle 1

2 1th Asian Regional Conference of IAEG () despite the changes (Bieniawski, 1989). The following suggest the SMR value as follows : discussion is based upon the 1989 version of the SMR = ln RMR-71 () classification (Bieniawski, 1989). The following six. Laubscherr (197, in Djakamihardja & Soebowo, parameters are used to classify a rock mass using the 1996) discusses the relationship of RMR and SMR as RMR system : follows : Table 1. Laubscherr relationship of RMR and SMR 1. Uniaxial compressive strength of rock material. RMR Total Value SMR, recommended slope angle. Conditions of discontinuities Groundwater conditions Orientation of discontinuities Rock Quality Designation (RQD).. Spacing of discontinuities. Methodology RMR values in this study derived from observations of the rock mass characteristics directly in Padalarang area at three different mine sites (X1, X, X) and testing of the materials of intact samples in the laboratory. Fig 1. Sample of a rock mass with discontinuities (Hoek and Bray, 1981, in Wyllie ) The RMR system is presented in Table. Each of six parameters is assigned a rating corresponding to the characteristic of the rock. These ratings are summed to give a value of RMR which lies between - 1. The Slope Mass Rating (SMR) is the application of the RMR to estimate the angle of slope stripping. Some methods of mathematical calculation of the SMR from RMR value has been developed by several authors, here are some theme : 1. Hall (198, in Djakamihardja & Soebowo, 1996), providing the SMR value as follows : SMR =.6 RMR + Fig. Study area (Courtesy of Google Maps, ) Figure 1 shows the spacing, conditions, and orientation of discontinuities in a jointed rock mass. (1). Orr (199, in Djakamihardja & Soebowo, 1996)

3 1th Asian Regional Conference of IAEG () Table. Classification parameters for RMR The strength value of rock material in this study is calculation is : RQD = 1 (.1 λ + 1) e-.1λ obtained from point load test to each samples of intact () rock from field observation in laboratory. The RQD Where λ is ratio between the amount of value in this study is also obtained by direct discontinuities passed by scan-line and the length of measurement in field using scan-line method which is scan-line introduced by Hudson, 1979 (Wyllie, ), the The obtained RMR values then correlated into Table. Summary of RMR Value Lithology Description SLOPE X1 Limestone, medium size grained, dark grey, very hard, low permeability, low slacking potential SLOPE X Limestone, fine grained, pale brown, very hard, low permeability, low SLOPE X Limestone, fine grained, pale brown, very hard, low permeability, low slacking potential % 7.% 98% Strenght of Intact Rock Material (Point Load Strenght Index (Mpa)) RQD (Hudson, 1979, in Djakamihardja & Soebowo, 1996)) Spacing of Discontinuities (m) Conditions of Discontinuities Discontinuity Length (m) Separation (cm) Slightly Rough Smooth Slightly Rough 1 Soft (<mm) None Soft (<mm) 6 Flow General Conditions TOTAL 71 Roughness Infilling (gouge) Weathering Ground Water.16

4 1th Asian Regional Conference of IAEG () SMR using Hall, Orr, and Laubscherr method. So, in angle, it proved by the fact in the field on sites X and each slope we have three values from three different X that their overall slope ranges between - method that can be used to estimate the slope stripping (Photo 1) As the RMR and SMR value in this study is angle for each slope. obtained from preliminary study based on surface data, further investigation is required to obtain more. Result From the observations of the Rajamandala conclusive results. Limestone characteristics directly at three different mine sites (X1, X, X), we obtain that the study area based on RMR classification system is consist of same rock class, which is Class or, and Table. RMR and SMR value in study area RMR Ratings Class Description SMR Laubscherr Hall Orr X1 71 X X X X X based from three method (Laubsherr, Hall, Orr) the Photo 1. Local failure at Site X with slope angle SMR value range between (Table ). The descriptions and weighting for each RMR parameters in each sites can be seen in Table. From those three sites (X1, X, X), the obtained RMR and SMR values are similar. This can be explained if we think geologically. We already know that these sites are consist of Limestone Members of Rajamandala Formation, which geologically they were deposited together and had experienced the same tectonic periods, this made this three sites has similar physical characteristic from their strength into their discontinuities properties. Photo. Field documentation. (A) Site X, (B) Fault gauge at Site X, (C) Joint sets in Site X1, (D) Calcite vein in site X.. Conclusion Based on RMR clasiffication system, in three Reference different sites, The Rajamandala Limestone mining area has classified into Class or and has the SMR value range between The SMR value Bieniawski, Z. T. (1989). Engineering Rock Mass can not be the main criterion in determining a safe slope Classification : A Complete Manual For Engineers and Geologist in Mining, Civil, and Petroleum

5 1th Asian Regional Conference of IAEG () Engineering. Wiley_Interscience. ISBN Bieniawski, Z.T. (1976). "Rock Mass Engineering" Exploration for Rock Engineering, ed. Z. T Bieniawski, A. A. Balkema, Johannesburg. Djakamiharja, A.S., & Soebowo, E. (1996). Studi Kemantapan Lereng Batuan Pada Jalur jalan Raya Liwa - Krui, Lampung Barat, Prosiding Seminar Sehari Kemantapan Lereng Pertambangan ITB. Direktorat Teknik Pertambagan, Departemen Pertambangan dan Energi. Wyllie, Duncan. (). Rock Slope Engineering Civil and Mining th Edition. Spon Press Taylor & Francis Group. London.