Influence of inclination angle on the failure behavior and mechanism of cement-coal composites

Grouting reinforcement is a key technology to maintain the stability of deep coal mines, and cement is the most commonly used grouting material. To study the failure behavior and mechanism of cement-coal composites, uniaxial compression tests were carried out on composites with different inclination angles by combining acoustic emission (AE) and digital image correlation (DIC) techniques, and scanning electron microscope (SEM) tests. Results show that as α increases, the uniaxial compressive strength and AE b -value show a decreasing and then increasing trend (the minimum value corresponds to α =45°). Conversely, the cumulative AE counts and energy show an increasing and then decreasing characteristic. With the increase of α , the failure mode transitions from tensile-dominated to tensile-shear mixed mode, and the type of microcracks transitions from tensile-dominated to tensile-shear composite type. Moreover, Numerical simulations show that the stress concentration zone migrates from the coal matrix to the cement-coal interface with the increase of α , which is consistent with the main strain characteristics of DIC . SEM results show that as α increases (0°∼30°), the microporosity at the cement-coal composite interface is increasing. At high angles ( α ≥45°), continuous shear friction zones develop, and hydration products undergo localized fragmentation. Finally, the inclination angle control mechanism for cement-coal composites' mechanical properties were discussed. • Failure behaviors of cement-coal composites were studied by AE, DIC, and SEM. • Demonstrates stress and strain concentration migration via DIC analysis. • Failure mode evolves from tensile to tensile-shear mixed failure as α increases. • PFC model was adopted to discuss angle control mechanism on composite sample.