In this study, the effect of calcium carbonate on triaxial compression strength, uni-axial compression strength (UCS), indirect tensile strength (σt) and slake durability index (Id) were investigated. Additionally, according to triaxial compression strength tests results were investigated on the effect of calcium carbonate for Mohr-Coulomb (c, φ) and Hoek-Brown (σci, mi) failure criterion parameters. For this purpose, experimental studies have been carried out on core samples taken from blocks of marl formation in two different lignite basins which is a major open pit mine in Turkey. The results of experimental studies were analyzed statistically. Clay and carbonate content of marl is one of the main factors controlling the engineering properties of marl. Finally, the high compression strength and high slake durability index value especially for Soma district samples have been develop to its clay and carbonate minerals compositions.
Marlstones are the most challenging soft rocks in geotechnical projects, mainly composed of clay minerals and carbonates. Their engineering properties, mineral compositions, and geotechnical specifications vary widely at different regions. There are numerous descriptions for marls based on their clay and calcium carbonate percentage contents (Ghazvinian et al. 2008, Lamas et al. 2002, Lokin et al. 1993). The amount of calcium carbonate (CaCO3) of marls varies from 35% to 65%, and the amount of clay minerals is the same. Marlstones are classified based on the contents of calcium carbonate as given in Figure 1 (Atalla 1993; Ghazvinian et al. 2008).
In this study, the cores taken from the two lignite coal districts were examined. The research fields are GLE (Garp Lignite Enterprise); BY-H, 48C and 48 panels and ELE (Ege Lignite Enterprise) I¸sıklar, Kısrakdere and Eynez panels (Fig 2).