Meso-scale mechanical properties of mudstone investigated by nanoindentation

Abstract

The widespread occurrence of heterogeneous mudstone poses several challenges for the stability of engineering structures. To understand the failure mechanism of argillaceous projects, and reveal the heterogeneity of mudstone, the mechanical properties of mineralogical compositions in mudstone were investigated, by using the nanoindentation technique at the meso-scale. Through “X-ray diffraction (XRD), scanning electron microscope (SEM)- energy dispersive spectrometer (EDS), and mercury intrusion porosimeter (MIP)” observations, the mineralogical compositions in mudstone can be divided into two constituents: clay matrix and silt inclusions, further, the multiscale structure model of mudstone includes three scales: macro-, meso- and micro-scale. Nanoindentation technique was adopted to investigate the meso-scale mechanical properties of mudstone by setting four peak loads ranging from 1 mN to 30 mN on different positions to avoid measuring errors. A superposition of 2 Gaussian probability densities was used to represent the distributions of the mechanical parameters of the mudstone by applying a coupled mineral-mechanical approach proposed in this study. The results showed that the mean hardness and elastic modulus of clay matrix are 398.22 MPa and 11.89 GPa, which are much smaller than that of silt inclusions (1529.43 MPa and 22.08 GPa) in mudstone, inducing the soft properties of mudstone and argillaceous projects. Due to the influence of macro- and meso-scale pores and cracks in mudstone, the elastic modulus of both the clay matrix and silt inclusions in it, is larger than that of mudstone.