Rock slopes stability is important for personnel and equipment safety in the open-pit mine. Instability and failure of slope occur due to many factors such as unsuited slope geometry, geological discontinuities, weak slope material due to weather influences. External loads such as high rainfall and seismicity could play an essential role in slope failure. Consequently, a precise classification of rock mass is needed for the basis of determining technical policy. Rock slopes in open pit coal mining areas, especially in Indonesia, are characterized by applying various rock mass classification systems, such as Rock Mass Rating (RMR) and Geological Strength Index (GSI), because the study area comprises well-exposed rock formations. In the RMR system, there are five main parameters i.e. Rock Quality Designation (RQD), Uniaxial Compressive Strength (UCS) of rocks, discontinuity spacing, discontinuity and groundwater conditions were considered. Several rock mass classification systems developed for the assessment of rock slope stability were evaluated with the condition of rock slopes in the tropics, especially Indonesian region, particularly in sedimentary rocks in the open pit coal mining area in order to get the corrected GSI equation used to characterize rock slopes based on rock mass structure quantitative analysis and discontinuities surface conditions. This paper provides correlation between the GSI and RMR for sediment rock in coal mines.

Publisher Summary Coal is an organic sedimentary rock whose chemical composition changes with coalification. As metamorphic development of coal (coalification) is synonymous in chemical terms with progressive enrichment of the coal substance in organically bound carbon, all coals, regardless of their origin or type, can be arranged in an ascending order of carbon content. Coal chemists distinguish coals into three structures: (1) first-order structure that gives the size distribution of the macromolecules and molecules in coal and the degree of cross-linking, (2) second-order structure that details the cross-links and the structure of the carbon skeleton, (3) third-order structure that is the nature and distribution of the functional groups. In all coal classification systems by rank, volatile matter content and calorific value (heating value) are the most important indices. Lower-rank coals are classed according to their calorific values calculated on a moist basis. Coal, an organic sedimentary rock, is very heterogeneous; it contains organic matter that consists of various components with distinct chemical and physical properties referred to as “macerals” and inorganic matter mostly in the form of minerals. The definition of the macerals is based on microscopic examination. The macerals are classified into three groups—vitrinite, exinite (liptinite) and inertinite—either because of similar origin (exinite group) or because of differences in preservation (macerals of vitrini

List of rock types List Sorted by name; initial letter means Igneous, Sedimentary or Metamorphic rocks. A - I Andesite – an intermediate volcanic rock - M Anthracite – a form of hard coal B - S Banded iron formation – a fine grained chemical sedimentary rock composed of iron oxide minerals - S Bauxite – the main ore of aluminium. It is mostly aluminium oxide. - I Basalt – grey/black fine-grained rock from lava which cooled on the surface of the Earth. - S Blue Lias – a formation of rocks, part of the Jurassic Coast World Heritage Site. - S Breccia – a sedimentary or tectonic rock composed of fragments of other, broken rocks C - S Chalk – a fine grained carbonate rock composed mainly of coccoliths - S Chert – a fine grained chemical sedimentary rock composed of silica - S Clastic rock – composed of fragments, or clasts, of pre-existing rock. - S Claystone – a sedimentary rock formed from clay - S Coal – a sedimentary rock formed from peat - S Concretion – a concretion is a rock in which a mineral cement fills the spaces between the sediment grains.