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

Huayong Lv,Zhanbo Cheng,Tao Zhou,Yaning Zhang,Defeng Wang

doi:10.3390/math10020177

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.

Highlights

Many cracks can normally be observed in the coal seam and rock under the impact of the geological structure or mining activities
Yang et al [21] explored the influence of confining pressure to the crack propagation and fracture mode of rock samples and established a mechanical model of crack propagation based on fracture mechanics theory
Through uniaxial and triaxial compression tests of pre-cracked specimens, cracks initiated in the form of tensile cracks and ultimate failure modes were dominantly caused by tensile cracks combined with shear cracks

Summary

Introduction

Many cracks can normally be observed in the coal seam and rock under the impact of the geological structure or mining activities. Wang and Tian [35] used numerical simulations to explore the mechanical properties, crack evolution characteristics and propagation forms of the initial and final crack distribution of coal–rock specimens with different fracture holes They concluded that the crack angle significantly influenced the mechanical behaviors of the coal–rock combined body. With the selection of mudstone as the typical composite of the immediate roof layer, an unconfined compression test was performed to explore the mechanical properties and failure modes of a coal–mudstone combined body with different angles of a single prefabricated crack. RFPA2D was adopted to simulate the whole process of an unconfined compression test to verify the results of the unconfined compressive strength and failure modes in experim3eonf t1a8l tests It can further explore the stress evolution, crack propagation and acoustic emission evolution of the coal–mudstone combined body.

Homogeneity Coefficient

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