{'fraction_non_alphanumeric': 0.018691588785046728, 'fraction_numerical': 0.002156721782890007, 'mean_word_length': 5.660287081339713, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Fracture Characteristics and Anisotropic Strength Criterion of Bedded Sandstone

Bedded sandstone is classified as sedimentary rock, which is a typical bedded rock with obvious layered structure characteristics. Bedded rocks formed different bedding orientations in the long and complicated geological tectonic evolution and thus have anisotropic mechanical characteristics. Therefore, the strength anisotropy of bedded sandstone depends on the bedding dip angles. In this study, the fracture characteristics and strength criterion of bedded sandstone were studied by triaxial compression tests on rock specimens with different bedding dip angles under different confining pressure. The test results show that the failure mode and strength of the bedded sandstone are related to the bedding dip angles, showing obvious anisotropy. The experimental data are broadly in line with the Jaeger’s surface of weakness (JPW) model. However, considering the difference in the strength of sandstone specimens with horizontal bedding dip (β = 0°) and vertical bedding dip (β = 90°), an improved JPW model is proposed to distinguish the strength criteria for the aforementioned differences. On the basis of considering the nonlinear relationship between confining pressure and rock strength, the JPW model is improved accordingly to make it suitable for predicting the strength behavior of bedded rocks.