Investigating the softening of weak interlayers during landslides using nanoindentation experiments and simulations

Probing Nanomechanical Properties of a Shale with Nanoindentation: Heterogeneity and the Effect of Water–Shale Interactions

“…Previous studies revealed that the petrophysical model of shale can be transformed into a micromechanical parameter model that consists of three dominate mineral groups: high-, medium-, and low-strength minerals. 27,39 For different mineral groups, the mechanical responses to the indentation load were different, which manifest themselves as the different clusters in the mixture distribution. According to the statistical analysis, three clusters were recognized, with mean values of 35.3, 40.2, and 74 GPa, corresponding to the mean estimations of the three mineralogical phases of the shale sample.…”

“…In our experiment, a slight increase of the elastic modulus at the beginning of the water treatment was observed, which agreed with the results of previous experiments. 27 This may be caused by capillary suction. At low saturation, water filled the small pores and narrow spaces between grains, generating high capillary suction inside the shale that acted as a confining pressure and led to the closure of pre-existing microcracks possibly increasing the strength after water vapor sorption.…”

“…Organic matter, as the relatively soft part in shale, exhibits compliant mechanical behaviors to loads. Previous studies reported an overall negative correlation between Young’s modulus and the clay content, total organic carbon (TOC), and porosity, whereas a positive correlation has been noted between the contents of carbonate/quartz and Young’s modulus based on experimental data from different shales. , The distinct elastic–plastic responses of the minerals result in a diverse set of mechanical properties. − The micrometer-sized clay minerals play a vital role in the mechanical behaviors of shale due to their orientation-preferred stacking arrangements and hydration characteristics, which depend on the structure units that form the clay minerals. Nonclay minerals in shale, such as quartz and feldspar, are formed by different dense crystal structures that may be attributed to the distinct elastic–plastic behaviors among these mineral grains .…”

“…23−25 Previous investigations found that the mechanical responses of the rockforming minerals are significantly different. 26,27 These minerals demonstrate clear elasticity-or plastic-preferred characteristics to the load and show various degrees of irrecoverable deformation. 27−30 The mechanical differences among the minerals, either relatively hard granular particles or soft kerogens, have been shown to have a crucial impact on the bulk mechanical properties of shale.…”

“…In view of the inherent heterogeneity and anisotropy of the geomaterials, the characterization of its mechanical properties at the nanoscale is necessary for the multiscale modeling of shale. Former studies reported that mechanical properties of rocks at the submicron scale can be determined by nanoindentation techniques, such as Young’s modulus, hardness, fracture toughness, and creep behavior. − Previous investigations found that the mechanical responses of the rock-forming minerals are significantly different. , These minerals demonstrate clear elasticity- or plastic-preferred characteristics to the load and show various degrees of irrecoverable deformation. − The mechanical differences among the minerals, either relatively hard granular particles or soft kerogens, have been shown to have a crucial impact on the bulk mechanical properties of shale. , In addition, it is found that the mechanical properties such as its strength, stiffness, and fracture roughness are orientation-dependent, and the multiscale anisotropy of shale is attributed to mechanisms corresponding to the observed scale. ,,− For the purpose of ultimate application in the industry, upscaling the nano- or micromechanical properties to the engineering scale is a key step. Although still in infancy, some studies have tried to upscale the nanoscale strength of shale rock to bulk strength by homogenizing the multiphase elastic composites using the Mori–Tanaka model. ,− …”