The effect of lithology on slake durability of 51 mudrock samples was investigated with the objective of developing a comprehensive durability classification. Grain size distribution, clay mineralogy, void ratio, micro-fracture frequency, Atterberg limits and scanning electron microscopy were used to characterize lithology, whereas second cycle slake durability index was used to measure durability. The mudrock samples were classified into five distinct lithologies that included 10 claystones, 18 mudstones, 12 shales, 5 siltstones and 6 argillites. In addition to clay content and presence of laminations, Atterberg limits were used to differentiate between these lithological classes.
The second cycle slake durability index was correlated with the lithological characteristics of each mudrock lithotype. The results indicate an exceptionally strong relation (r = -0.98) between the percentage of expanding clay minerals and slake durability index for claystones. Mudstones exhibit a strong relation (r = -0.94) between the ‘micro-fracture frequency index’ and slake durability index. A strong relation (r = -0.98) between void ratio and slake durability index is indicated for shales. These results underscore the importance of distinguishing mudrock lithology in durability investigations.