Investigation of Strong Strata Behaviors in the Close‐Distance Multiseam Coal Pillar Mining

Abstract

According to the new stress distribution pattern and the strong strata behaviors as the characteristics of the coal pillars in the close-distance multiseam coal pillar mining, the common characteristics of different types of overlying coal pillars were summarized and analyzed. Moreover, a theoretical model for the mechanism of strong strata behaviors in the close-distance multiseam coal pillar mining was established, which was validated by the monitoring data of seismic computed tomography CT, microseism, and electromagnetic radiation (EMR). Furthermore, the results of the study indicated that the main factors affecting the strong strata behaviors were the static stress concentration caused by the overlying coal pillars and the dynamic disturbance caused by the fracturing and slipping of the overlying coal pillars and roof under the influence of mining. In the case of Xinzhouyao coal mine, the transmitted stress and lateral support pressure of the overlying coal pillars accounted for 78.3% and 16% of the vertical concentrated stress, respectively, and the areas closer to the overlying coal pillars were more susceptible to dynamic load disturbances. The monitoring results of seismic computed tomography CT and EMR demonstrated the static load stress concentration area was distributed near the overlying coal pillar, and the stress concentration degree was greater in the area of superimposed lateral support pressure and advanced support pressure. Moreover, microseismic spatial positioning revealed that the high-energy microseismic events were mainly concentrated near the overlying large coal pillars and roof. The on-site multiparameter detection results were highly consistent with the characteristics of actual strata behaviors and the conclusions of the theoretical model. This method could provide a reference for the quantitative calculation of stress distribution under similar conditions and the identification of the danger zone of strata behaviors.

Moisture Content on Methane Desorption Characteristics in Coal and Its Effect on Outburst Prediction

“…From a microscopic view, the adsorption of water and methane in coal is due to the interaction of water molecules and methane molecules with coal-based molecules [35,36].…”

“…e maximum adsorption potential of methane on the coal surface is −2.704 kJ/mol, and the maximum adsorption potential of water on the coal surface is −24.0 k/mol. e larger the adsorption potential is, the more adsorbable molecules are adsorbed [35][36][37][38]. erefore, the water in coal has a great influence on the adsorption capacity of methane.…”

“…e gas emission V-index is a measure of the volume of gas desorption in the interval between 35 and 70 s in the condition of atmospheric pressure [11][12][13].…”

Failure Mechanism of Gob‐Side Roadway under Overlying Coal Pillar Multiseam Mining

“…After the overlying coal seam is mined, the load on goaf and pillars tends to evenly distribute after a long rebalancing of coal and rock structures. e unit length load of the coal pillar can be estimated according to the load estimation model of the coal pillar, as shown in Figure 5 [36].…”

Analysis of Failure Mechanism of Roadway Surrounding Rock under Thick Coal Seam Strong Mining Disturbance

“…e single-layer thickness can be up to 10 m or even dozens of meters, and in China, the proportion of coal produced from these extrathick coal seams is increasing yearly [1][2][3]. During coal mining, the dynamic influence of the roadway depends on the lateral stress concentration, the height of the mining coal seam, the fracture strata structure, and the properties of the rock mass [4][5][6]. In traditional mechanized top-coal caving mining, the working face lateral roof caving is rather extensive, and the caved gangue provides support for the overlying strata, which reduces the occurrences of collapse and the lateral stress in the roof strata, thereby reducing the disturbance on the surrounding rock [7].…”