Mechanical properties and fracture evolution of sandstone specimens containing different inclusions under uniaxial compression

To investigate the effects of inclusions filled in holes, including inclusion strength, stiffness and shape, on the mechanical properties and fracture evolution of rock, a series of uniaxial compression tests were conducted on prismatic sandstone containing a prefabricated hole filled with different types of inclusions using a servo-hydraulic machine. Digital image correlation (DIC) and acoustic emission (AE) techniques were applied jointly to record and analyze the deformation and crack process of sandstone. The results indicate that both the inclusion type and shape are important factors affecting the strength and deformation properties of sandstone. The relatively rigid inclusion not only significantly improves the mechanical properties of pre-holed specimens, but also can provide a better support for structural integrity of rock after failure. Observations show that both DIC and AE techniques are capable of revealing the fracture evolution of specimens, and there is a good consistency between the mechanical behavior and surface strain fields and internal AE signals. Based on the strain localization characteristics, the crack sequences and relative stress levels for each group of specimens are summarized, especially the crack development inside the inclusion is first observed. The crack behavior and crack type around inclusions are greatly influenced by the inclusion type and shape due to dramatic changes in stress distribution around inclusions. After rock failure, the crack extent around inclusions can be characterized by the cumulative AE counts, and the final failure modes of specimens under different filling conditions can be categorized as tensile failure, shear failure and mixed tensile/shear failure.