The investigation of grindability of Zonguldak basin coal environment rocks and their excavability according to the bond work index

In the context of underground mining activities, research has been ongoing to develop new methods for selecting and performance prediction analysis of mechanized excavation machines (such as boom-type roadheaders, electro-hydraulic drills, etc.) that can provide insights into machine energy consumption. One key parameter to focus on in such studies is the grinding process and the determination of energy consumed during grinding. Grinding processes hold a significant place in the mining industry due to their impact on energy consumption. Increasing the efficiency of grinding is expressed by the reduction in energy expenditure. In this study, the relationships between the grindability and excavability of rocks and other parameters were examined. In this context, experiments were conducted on 24 different coal-associated rocks (sandstone, siltstone). All rock samples are clastic and sedimentary in origin. To determine the grindability of the rocks, the Hardgrove Grindability Index (HGI) test was conducted, and the Bond Work Index (Bwi) test was used to determine their excavability. To investigate the relationships between HGI, Bwi, and other parameters, strength, hardness, drillability, and abrasiveness tests were also performed. Additionally, petrographic analyses of 14 rocks were carried out to examine the relationships between petrographic properties and grindability and excavability. For strength testing, uniaxial compressive strength (σc) and Brazilian tensile strength (σt) tests were conducted. The hardness of the rocks was determined using the Equotip hardness test (ESD). To assess drillability, the S20 brittleness test and Sievers miniature drilling (SJ) tests were conducted, and the drilling rate index (DRI) of the rocks was calculated using a chart proposed by Dahl (2003). The abrasiveness of the rocks was evaluated using the Cerchar Abrasivity Index (CAI) test. Using the results of uniaxial compressive strength (σc) and Brazilian tensile strength (σt) tests, the brittleness values (B1, B2, B3, B4) of the rocks were determined, and the relationships between HGI, Bwi, and brittleness were analyzed. Furthermore, the energy values calculated using the Bond Work Index were compared in terms of excavability with specific energy (SE) values obtained through empirical correlations and cutting theories. The results of the experimental studies revealed significant relationships between HGI, Bwi, and other parameters. Negative significant relationships were found between HGI and strength tests (σc, σt) when rocks were evaluated within their respective series (Westphalian, Namurian). Positive strong relationships were observed between Bwi and strength tests (σc, σt). Similar results were obtained between B3 and B4 brittleness values calculated using σc and σt tests and HGI and Bwi tests. Strong positive relationships were found between HGI and the drilling rate index (DRI), while negative significant relationships were observed between Bwi and drillability tests. A significant relationship was identified between the HGI and CAI tests. A similar result was observed between Bwi and CAI tests. However, no significant relationships were found between HGI, Bwi, and ESD. The relationships between petrographic properties and HGI and Bwi tests were examined, and high correlations were found with the mean grain size of abrasive minerals. Additionally, the energy value obtained from the Bond Work Index test was compared with specific energy values calculated using empirical formulas and cutting theories in terms of excavability, revealing positive strong correlations. Various classification system recommendations were made based on the relationships between HGI, Bwi and other parameters.