Aiming at mitigating the high risks associated with conventional explosive blasting, this study developed a safe directional fracturing technique, i.e. instantaneous expansion with a single fracture (IESF), using a coal-based solid waste expanding agent. First, the mechanism of directional fracturing blasting by the IESF was analyzed, and the criterion of directional crack initiation was established. On this basis, laboratory experiments and numerical simulations were conducted to systematically evaluate the directional fracturing blasting performance of the IESF. The results indicate that the IESF presents an excellent directional fracturing effect, with average surface undulation differences ranging from 8.1 mm to 22.7 mm on the fracture surfaces. Moreover, during concrete fracturing tests, the stresses and strains in the fracturing direction are measured to be 2.16-3.71 times and 8 times larger than those in the non-fracturing direction, respectively. Finally, the IESF technique was implemented for no-pillar mining with gob-side entry retaining through roof cutting and pressure relief in an underground coal mine. The IESF technique effectively created directional cracks in the roof without causing severe roadway deformation, achieving an average cutting rate and maximum roadway deformation of 94% and 197 mm, respectively. These on-site test results verified its excellent directional rock fracturing performance. The IESF technique, which is safe, efficient, and green, has considerable application prospects in the field of rock mechanics and engineering. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

The loaded rock experiences multiple stages of deformation. It starts with the formation of microcracks at low stresses (crack initiation, CI) and then transitions into unstable crack propagation (crack damage, CD) near the ultimate strength. In this study, both the acoustic emission method (AEM) and the ultrasonic testing method (UTM) were used to examine the characteristics of AE parameters (b-value, peak frequency, frequency-band energy ratio, and fractal dimension) and ultrasonic (ULT) properties (velocity, amplitude, energy attenuation, and scattering attenuation) of bedded shale at CI, CD, and ultimate strength. The comparison involved analyzing the strain-based method (SBM), AEM, and UTM to determine the thresholds for damage stress. A fuzzy comprehensive evaluation model (FCEM) was created to describe the damage thresholds and hazard assessment. The results indicate that the optimal AE and ULT parameters for identifying CI and CD stress are ringing count, ultrasonic amplitude, energy attenuation, and scattering attenuation of the S-wave. Besides, damage thresholds were detected earlier by AE monitoring, ranging from 3 MPa to 10 MPa. CI and CD identified by UTM occurred later than SBM and AEM, and were in the range of 12 MPa. The b-value, peak frequency, energy ratio in the low-frequency band (0-62.5 kHz), correlation dimension, and sandbox dimension showed low values at the peak stress, while the energy ratio in a moderate-frequency band (187.5-281.25 kHz) and amplitude showed high values. The successful application of FCEM to laboratory testing of shales has demonstrated its ability to quantitatively identify AE/ULT precursors of seismic hazards associated with rock failure. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).