Law of monitoring parameters of water injection coal based on the combined analysis of CT and ultrasonic technology

In order to reveal the relationship between the structural parameters of the dominant low-pressure water injection and the water movement distance and ultrasonic monitoring parameters obtained in the process of coal and rock water injection in the laboratory, a research method based on CT reconstruction combined with acoustic emission transducer array monitoring was proposed. The spatial distribution and parameters of pores and fractures structure of coal were determined through the CT scan, while the acoustic emission transducer array was used to monitor the water movement and extract the ultrasonic parameters of the monitoring path. The relationship equations between coal and rock structure parameters, water movement distance, and ultrasonic parameters, which dominate low-pressure water injection, were constructed. And itlays the foundation for detecting the range of coal seam water injection by the mine acoustic method. The results show that: the coal void ratio as well as the mineral ratio, which dominate the movement of water are all negatively correlated with the P-wave velocity. The ultrasonic energy consumed owing to the acoustic coupling mismatch caused by the fractures is greater than the increased ultrasonic energy consumed by the change of the propagation medium from air to water in the fractures, and the void ratio before and after water injection plays a more significant role on ultrasonic parameters than the mineral ratio. The change of ultrasonic parameters before and after water injection is mainly affected by the change of medium in the hole and fissure and the change of acoustic impedance matching degree. It is not that the higher the content of connected pores, the greater the interference to the monitoring results, but the greater the interference to the monitoring results when the connected fracture surface in the monitoring path cuts off the monitoring path.And when the content of connected pores on the monitoring path is low, the only connected fracture surface contained in the medium cuts off the propagation path of ultrasonic wave, resulting in outliers of monitoring data. The porosity ratio and mineral ratio have a great influence on the calculation accuracy of this method. When the void ratio and mineral ratio are small, the difference between the calculated results and the experimental results increases and the maximum error is 0.94 cm. © 2022, Editorial Board of Journal of Mining & Safety Engineering. All right reserved.