Experimental Investigation on the Anisotropic Behaviors Induced by Bedding Planes in Mechanical Properties of Ma′quan Oil Shale

The anisotropic behavior induced by the bedding planes is a key point for the underground exploitation in oil shale, which is becoming a significant energy source worldwide. To elucidate the physical and mechanical properties of Ma′quan oil shale and the anisotropic behavior of the elastic, strength, and fracture properties, several experiments were conducted to investigate the mineral composition, pore structure, and mechanical properties. According to the results, the mineral composition of Ma′quan oil shale mainly comprises clays, quartz, silicate minerals, and pyrite. Additionally, 42.10% of apatite was measured in the randomly distributed darker blocks, which intensified the anisotropic behavior. The experimental results obtained for the elastic, strength, and fracture properties also reveal an enormous difference between the rock matrix and the bedding planes, which is much larger than that of other sedimentary rocks. The measured mechanical properties varied with the loading angle with respect to the bedding planes, because the existence of the bedding planes changed the failure modes. Moreover, the maximum compressive strength with better interlocking of Ma′quan oil shale occurred when the loading angle with respect to the bedding planes was equal to 75°, whereas previous studies considered 0° or 90°. The empirical correlations were established based on the correlation analysis for the measured mechanical properties of Ma′quan oil shale. This study provides beneficial insights into the anisotropic behaviors of Ma′quan oil shale, which is of great value to its underground exploitation because it can assist in solving the subsurface problems.