Abstract:

To accurately characterize freely accumulated rock blocks and pore space properties in fully mechanized top-coal caving goafs, a PNM was introduced. Slice tests of free rock block accumulation in fixed space and corresponding image processing were conducted. Pore network information was extracted using Open-source libraries like OpenPNM and PoreSpy, followed by 3D visual reconstruction and quantitative characterization of PNM to analyze topological geometric and statistical features of the reconstructed model. Results show that with increasing freely accumulated rock block size in fixed space, pore-throat size increases significantly: the average diameters of pores and throats rise from 2.46 mm and 1.41 mm to 3.85 mm and 2.73 mm, respectively, with weak correlation to throat length. The numbers of pores and throats decrease from 3 146 and 6 428 to 1 043 and 2 225, respectively, and the pore coordination numbers concentrate between 2 and 5 (peak at 2). The proportion of pore space increases, and the connectivity of porous media is enhanced. The topological property parameters are approximately positively skewed distribution as a whole, with the peak shewed to the left and the concentrated values in the dataset being relatively small. Two-point correlation function calculations reveal that the relative errors of porosity between the original image data and the reconstructed model are less than 2.5%.

Key words: fully mechanized top-coal caving goaf of coal mines, free accumulation of rock blocks, pore network model (PNM) reconstruction, slice test, image processing, sub-network of an over-segmented watershed (SNOW), pore network extraction (PNE)