Study on Mechanical Characteristics and Failure Modes of Coal–Mudstone Combined Body with Prefabricated Crack

Abstract

There are normally pre-existing cracks that can be observed in the coal seam and immediate roof that influences the stability of the rib spalling and the movement law of overlying strata. In this study, comprehensive research methods (e.g., theory analysis, experimental tests and numerical simulations) were adopted to reveal the mechanical characteristics, acoustic emission behaviors and failure modes of a coal–mudstone combined body with a single prefabricated non-penetrating crack. The results show that the influence of the crack angle on the elastic modulus of the coal–mudstone combined body samples was limited. With the increase in the crack angle, the unconfined compressive strength of samples decreased first and then increased in a V-shaped trend. In addition, the minimum unconfined compressive strength could be observed at a crack angle of 45°. Moreover, the number of acoustic emissions significantly increased with the process of continuous loading. In addition, the stress reduction zone could be observed in both ends of the prefabricated cracks at the initial stage of loading. The high- and low-stress zones were transformed with the process of continuous loading. Under an unconfined compression test, the failure models of the coal body part in the samples were mainly caused by shear failure, and only a few cracks occurred in the upper tip of the prefabricated cracks of the mudstone part. Therefore, airfoil cracks could be observed in the samples due to the strength difference of the coal mass and mudstone.

Bearing capacity of driven pile and determination of inhomogeneous mudstone around the pile

“…During rock formation, initial damage occurs due to environmental and geological forces (Wu et al, 2022). Mudstone shows primary and secondary micro-voids, micro-cracks, and other defects in the interior (Zhang et al, 2020;Lv et al, 2022) and is itself not uniform in certain dimensions; thus, it is easy to produce greater damage or even failure, which greatly influences the engineering characteristics of mudstone (Lv et al, 2022). Initial defects in mudstones can be observed at the mesoscopic level.…”

Study on Failure Characteristics and Control Technology of Roadway Surrounding Rock under Repeated Mining in Close-Distance Coal Seam

“…In addition, the anchor cables of Ф22 × 4300 mm are arranged in the roof strata of the roadway with the spacing of 1400 × 2400 mm, and three anchor cables are installed in each row. Similarly, the anchor cables are arranged in the side of the coal pillar and working face with the row spacing of 1600 × 2400 mm, and 2 anchor cables are installed in each row [26][27][28].…”

Molecular Dynamics Study on Crack Angle Effect on Amorphous Silica Fracture Performance

“…Li et al [12] explored the effect of crack angle on the mechanical properties, energy evolution, and damage evolution of sandstone under uniaxial compression test. Lv et al [13] studied the mechanical properties, acoustic emission behavior, and failure modes of coal shale composites with different crack angles through theoretical analysis, uniaxial compression experiment, and RFPA numerical simulation method. Most of the break experiments on specimens with pre-cracks are macro experiments, and it is urgent to enrich the theory of fracture mechanics from a micro perspective.…”