Nanoindentation-based characterization of micromechanical properties of greenish mudstone from deep Fushun West open-pit mine (Fushun city, China)

The greenish mudstone in the Fushun West open-pit mine (Fushun city, China), the largest open-pit mine in Asia, is weak due to the presence of clay minerals and may induce the failure and collapse of rock slopes. It is therefore of great importance to accurately assess the mechanical properties of the mudstone. However, due to the properties of mudstone, is it challenging to perform traditional experiments, which require numerous large specimens. In the present paper, nanoindentation experiments were performed to measure the mechanical parameters, such as elastic modulus and indentation hardness, of the greenish mudstone from the Fushun West open-pit mine at the microscale. These microscale properties were upscaled to the centimeter scale using the K-means and Mori-Tanaka methods. A numerical model was then built to perform nanoindentation simulations, the results of which are in good agreement with the nanoindentation experiments. A dual-indentation technique was then used to obtain the cohesion and the angle of internal friction of the mudstone from the experiments and simulations. Finally, our mechanical data were compared with data from a uniaxial compressive strength experiment. Although the upscaled values from the nanoscale experiments and models by Berkovich indenter are slightly higher than the values determined from the uniaxial experiment, and can be explained by the increase in void space at longer length-scales, we conclude that the methods employed here can be used to determine the upscaled mechanical properties important for slope stability analyses and safety assessments of the Fushun West open-pit mine.