Experimental Study on Calibration of Amplitude-Frequency Measurement Deviation for Microseismic Sensors in Coal Mines.

Microseismic monitoring systems (MMS) have become increasingly crucial in detecting tremors in coal mining. Microseismic sensors (MS), integral components of MMS, profoundly influence positioning accuracy and energy calculations. Hence, calibrating these sensors holds immense importance. To bridge the research gap in MS calibration, this study conducted a systematic investigation. The main conclusions are as follows: based on calibration tests on 102 old MS using the CS18VLF vibration table, it became evident that certain long-used MS in coal mines exhibited significant deviations in frequency and amplitude measurements, indicating sensor failure. Three important calibration indexes, frequency deviation, amplitude deviation, and amplitude linearity are proposed to assess the performance of MS. By comparing the index of old and new MS, critical threshold values were established to evaluate sensor effectiveness. A well-functioning MS exhibits an absolute frequency deviation below 5%, an absolute amplitude deviation within 55%, and amplitude linearity surpassing 0.95. In normal operations, the frequency deviation of MS is significantly smaller than the amplitude deviation. Simplified waveform analysis has unveiled a linear connection between amplitude deviation and localization results. An analysis of the Gutenberg-Richter microseismic energy calculation formula found that the microseismic energy calculation is influenced by both the localization result and amplitude deviation, making it challenging to pinpoint the exact impact of amplitude deviation on microseismic energy. Reliable MS, as well as a robust MS, serve as the fundamental cornerstone for acquiring dependable microseismic data and are essential prerequisites for subsequent microseismic data mining. The insights and findings presented here provide valuable guidance for future MS calibration endeavors and ultimately can guarantee the dependability of microseismic data.

Slip instability behavior of block rock masses on dynamic-static combined loads.

A rock mass is a system of various scale blocks embodied into one another. Inter-block layers are usually composed of weaker and fissured rocks. On the action of dynamic-static loads, it can induce slip instability between blocks. In this paper, the slip instability laws of block rock masses are studied. Based on theory and calculation analysis finding that the friction force between rock blocks varies with block vibration and the friction between rock blocks can drop sharply, resulting in slip instability. The critical thrust and occurrence time of block rock masses slip instability are proposed. The factors affecting block slipping instability are analyzed. This study has significance to the rock burst mechanism induced by slip instability of rock masses.

Evaluation of Anti-Burst Performance in Mining Roadway Support System.

The hazardous effect of a mine earthquake on a roadway is not only related to its energy scale but also to its distance from the roadway. In this study, a signal attenuation model and a disaster-causing model were established to evaluate the mine earthquake effects based on peak particle velocity (PPV) data recorded for 37221-1 upper roadway of the Dongxia Coal Mine, China. The characteristic of dynamic loads due to mine earthquake propagation to roadway surfaces was researched, and critical PPV values were identified using FLAC3D numerical simulation, which can be used to evaluate the roadway anti-burst performance under the existing support system. The results show that the support system is able to resist a mine earthquake with energy below 2.33 × 103 J; however, considering the energy accumulation volume of surrounding rocks and the range of source fracture, the maximum resistible mine earthquake energy can be up to 7.09 × 106 J when the roadway is 50 m away from the source. The validity and applicability of the disaster-causing models was verified by two rockburst cases that occurred during the excavation of the working face.

Experimental Study on the Mechanical Behavior of Coal Samples during Water Saturation.

When mining-induced fractures reach overlying aquifers, water enters the mining area and the coal is under different natural water saturation conditions, which significantly affect the mechanical behavior of the coal. In this study, uniaxial compression tests were conducted on dry, partially saturated, quasi-saturated, and fully saturated coal samples. The mechanical parameters, acoustic emission (AE) activities, and failure patterns of differently saturated coal samples were analyzed. The effect of water content on the behavior of coal and suggestions to ensure safe underground coal mining were discussed. The results indicate that the water content in coal increases nonlinearly with intrusion time and can be regarded as a logarithmic function. With increasing water saturation, the mechanical strength of the coal decreases on the whole and the AE activities, crack development, and burst severity are weakened significantly. The failure pattern of the coal samples changes from a dynamic type to a quasi-static one and from a compressive-shear type to a tensile one. Water content has four main effects on the mechanical behavior of the coal samples. These are a liquid bridge force, a water softening effect, a wedge effect, and a lubrication effect. With increasing water saturation, the effect of water gradually increases and predominates the coal failure, leading to a continuous decline in the strength of the coal samples. When the coal around the mining space is subjected to water, the high degree of water saturation in the coal decreases the risks of coal bursts significantly; however, it causes a large deformation and instability of the roadways. To ensure safe mining, more measures should be taken to decrease the amount of inrushing water, reduce the stress, and reinforce the anchor bolting support.

Investigation of coal and gas outburst risk by microseismic monitoring.

In order to improve the monitoring and prediction of coal and gas outburst, this paper proposes a new method for dynamic regional prediction of coal and gas outburst using microseismic (MS) monitoring. The theoretical basis of this method is presented. An index evaluation system was established and applied, based on which field tests were carried out in a coal mine. The results show that seismic monitoring with frequency and energy indexes can obtain good results for mining disturbance intensity monitoring and geological structure detection; the regional stress distribution detected by seismic wave tomography is consistent with the theoretical stress field, making its use of great significance for optimizing coal and gas outburst drilling parameters and improving overall tunneling efficiency. This approach overcomes the limitations of traditional methods in the temporal and spatial dimensions and realizes dynamic and continuous monitoring of coal and gas outburst-prone areas.