Classification criteria for coal bursting liability based on scratch testing

The bursting liability is an inherent property of coal-rock masses prone to impact failure, serving as an intrinsic factor for coal mines to induce rockburst accidents and a critical indicator for assessing the risk of rockburst. However, the traditional testing procedures for coal bursting liability are relatively cumbersome. To address this, a novel indirect evaluation method based on scratch testing has been proposed to determine the coal bursting liability. Coal samples from five different mines were subjected to both scratch test and uniaxial compression test. A fitting model was established to correlate the scratch specific energy of the coal samples with their physical and mechanical parameters (uniaxial compressive strength and elastic modulus). Additionally, the energy evolution patterns of coal samples with different the scratch specific energy during uniaxial compression were investigated. The post-peak energy release rate index K_PE was used to quantitatively characterize the bursting liability of coal,and the correlation expression between the scratch specific energy and K_PE was established through fitting and regression analysis. Then, the classification criterion of coal bursting tendency based on the srathch specific energy was established, and the criterion is verified by using the national standard comprehensive evaluation method and the ejected mass ration (F) of coal fragments. The results demonstrated that the the scratch specific energy of coal samples exhibited a positive correlation with uniaxial compressive strength (R²=0.96577) and a negative linear correlation with elastic modulus (R²=0.88196).With increasing scratch specific energy, both the pre-peak accumulated elastic strain energy and the post-peak capability for rapid energy release were progressively enhanced The scratch specific energy of coal samples shows a positive correlation power function relationship with the elastic strain energy index, impact energy index and K_PE, and a negative correlation power function relationship with the dynamic failure time. Taking the national standard comprehensive evaluation method and the discrimination result of the ejected mass ratio (F) of coal fragments as the standard respectively, the evaluation of goodness of fit based on scratch specific energy classification criteria is 100%, so so the scratch method can be used as an indirect test method for coal bursting liability.