Study on Movement Law of High-Position Thick and Hard Roof and Mine Earthquake Control by Ground Fracturing Technology

Abstract

The field monitoring data showed that the fracture of high-position thick and hard roof (THR) was the main reason for the frequent occurrence of high-energy mine earthquake events ( magnitude > 2.0 ) in the no. 6 mining district of Dongtan coal mine. In order to study the fracture characteristics of high-level THR and seek a reasonable and effective control method, taking the 63up06 working face as the engineering background, the FLAC model was built to simulate the strata movement law before and after fracturing. The simulation results showed that the THR first breaking span was 340 m, the tensile failure runs through the whole THR, and the subsidence increased rapidly when THR reached the first breaking span. The THR breakage is related to the continuous upward transfer of horizontal compressive stress, which results in the concentration of horizontal compressive stress in THR. After ground fracturing, the first breaking span of THR decreased, and different fracturing positions have a great impact on the THR fracture form. When the fracturing position is close to the center of the first breaking span, there is no large cantilever breaking form in the THR, the THR breaks on both sides of the top and sinks along the hydraulic fracture in the middle, and the collapse degree is relatively uniform. Then, the fracturing test was carried out in the 63up06 working face, the results showed that during the first 400 m of the 63up06 working face mining after fracturing, 702 microseismic events occurred in total, including 12 high-energy vibration events which include 4 mine earthquakes of magnitude 2.0 and 8 mine earthquakes of magnitude 1.0-2.0. Compared with the adjacent working face, the quantity of high-energy mine earthquake events in the 63up06 working face has been significantly controlled.

Seismic Mitigation Effect of Overlying Weakening Strata in Underground Coal Mines

“…Gao et al [14] established the mechanical model of the strong-soft-strong structure, and they concluded that the weak rock layer can provide good energy absorption to protect the roadway. Horizontal well fracturing, which is applied to the hard rock layer above the coal seam, can effectively reduce the occurrence of high-energy mining-induced seismic events by facilitating the fracture of the hard rock layer, decreasing the integrity of the rock mass, and increasing the quantity and distribution range of internal fractures within the rock mass [15][16][17][18][19]. After ground hydraulic fracturing was performed, the fractured strata experienced stress relief, resulting in reduced rock strength.…”

Propagation and impacts on roadway of mining-induced far-field strong tremors: insights from numerical simulations

“…These tremors, given their proximity to the surface, frequently result in significant vibration on the ground, instigating widespread concern. Currently, coal mines with a high frequency of such far-field strong mine tremors include Hongqinghe (Zhang et al, 2021), Jinjitan, Shilawusu (Yang et al, 2023), Dongtan, Nantun (Guo et al, 2022;Liang et al, 2022), Baodian (Cao et al, 2015;He et al, 2022). Notably, Dongtan, Nantun, and Baodian all fall within the Yanzhou coalfield, positioned near one another, and share similar mining conditions characterized by the presence of substantial, maroon thick sandstone layers above the coal seam, often referred to as the "red layer".…”