The
micromechanical properties are crucial factors influencing
coal fracturing and efficient gas extraction. This paper employs nanoindentation
techniques to investigate coal micromechanical properties across various
ranks, analyzing their impact on fracture compressibility. The results
indicate significant variations in the distribution of micromechanical
parameters of lignite, exhibiting the strongest heterogeneity. Average
contact depth and creep displacement follow the order lignite >
bituminous
coal > anthracite. In terms of average hardness, reduced modulus,
and fracture toughness, the ranking is anthracite > bituminous
coal
> lignite. Guhanshan Mine (GHS) anthracite demonstrates the highest
values, exceeding Simengou Mine (SMG) lignite by factors of 2.73,
1.82, and 1.83, respectively. Both hardness and fracture toughness
show a significant linear relationship with the elastic modulus. The
average fracture compressibility coefficients for Daliuta Mine (DLT),
Pingdingshan Mine (PDS), Jiaozishan Mine (JZS), and GHS are 0.144,
0.098, 0.09, and 0.08 MPa–1, respectively. Coal
with greater micromechanical strength demonstrates enhanced resistance
to compressive deformation fractures. This indicates that higher fracture
toughness not only resists fracture propagation but also effectively
withstands compressive deformation. Quantitative relationship models
between the fracture compressibility coefficient and contact depth,
hardness, reduced modulus, and fracture toughness are obtained through
fitting analysis. These models facilitate the calculation of coal
fracture compressibility coefficients under varying micromechanical
strengths. The research findings offer theoretical guidance for optimizing
coal seam fracturing and enhancing permeability schemes.