Numerical modelling of microseismicity associated with longwall coal mining

Abstract

A B S T R A C TMicroseismicity has long been a precursor for underground mining hazards such as rockbursts and coal and gas outbursts. In this research, a methodology combining deterministic stress and failure analysis and stochastic fracture slip evaluation, based upon the widely accepted fracture slip seismicity-generation mechanism, has been developed to simulate microseismic events induced by longwall mining. Using the built-in DFN facility in FLAC 3D, discrete fractures following a power law size distribution are distributed throughout a 3D continuum model in a probabilistic way to account for the stochastic nature of microseismicity. The DFN-based modelling approach developed was adopted to simulate the evolution of microseismicity induced by the progressive face advance in a longwall top coal caving (LTCC) panel at Coal Mine Velenje, Slovenia. At each excavation step, global stress and failure analysis with reference to the strain-softening post-failure behaviour characteristic of coal, and fracture slip evaluation for microseismicity are conducted sequentially. The model findings are compared to the microseismic event data recorded during a long-term field monitoring campaign conducted at the same LTCC panel. It was found that the released energy and frequency-magnitude distribution of microseismicity are associated with the slipped fracture sizes and fracture size distribution. These features for recorded microseismic events were fairly constant until a xylite rich heterogeneous zone ahead of the working face was approached, which indicates that fractures within the extracted coal seam follow the same size distribution. The features obtained from modelled microseismic events were consistent over the production period, and matched well the field observations. Furthermore, the model results indicate that the power law fracture size distribution can be used to model longwall-mining-induced microseismicity. This model provides a unique prospective to understand longwall coal mining-induced microseismicity and lays a foundation to predict microseismicity, or even rockburst potential in specific geological realisations.

The Role of Mining Intensity and Pre-existing Fracture Attributes on Spatial, Temporal and Magnitude Characteristics of Microseismicity in Longwall Coal Mining

“…(1) microseismicity occurred up to 800 m away from the extracted panel, which may be explained by the reactivation of fractures at critical stress states subjected to minute stress perturbations; (2) the source-scaling property of microseismicity is dominated by that of natural fractures (Cao et al 2018); and (3) both spatial and energy distribution of mining-induced microseismicity is panel specific, which is believed to be governed by the attributes of underlying natural fractures.…”

“…Previous research by the authors (Cao et al 2018(Cao et al , 2019) developed a microseismicity modelling methodology based upon the premise that microseismicity is triggered due to the interplay of mining-induced stress and the pre-existing fracture field throughout the coal seam and surrounding rock masses during longwall mining. The modelling methodology combines deterministic stress and failure analysis of the coal seam with slip evaluation of stochastically distributed pre-existing fractures.…”

Method for Assessing the Development of Underground Hard Coal Mines on a Regional Basis: The Concept of Measurement and Research Results

“…The most important factors influencing the establishment and functioning from a long-term perspective are mainly operational resources adequacy, their quality, and the possibility of extraction [18][19][20][21]. Important and frequently analyzed development determinants in underground hard coal mining are also the scale and the level of natural hazards that significantly influence the efficiency and effectives of mining production [22], [23,24]. Due to the above, the analysis and assessment of the development of hard coal mines takes place in the context of conditions of natural and technical character.…”

Scale Effect on the Anisotropy of Acoustic Emission in Coal

“…ey are primary parameters on the AE activities in both laboratory and filed work. e variation of AE counts and energy dissipation provides the precursor information of various failures during the loading process in coal and rock [41,42], and the microseismic event and energy dissipation are still the primary parameters in the dynamic disaster preventing (coal bump and rock burst) [43][44][45] and the analysis of earthquake and various microseismic activities [46,47]. e fractal features are naturally existing in the laboratory AE experiments and the field microseismic activities [12,34,35].…”