Proposal for simplified indicator of excavation efficiency for drag picks: chip size index

Existing indicators of excavation efficiency often rely on sieve analysis of rock debris generated during excavation, which may make it challenging to respond promptly to efficiency changes during mechanical excavation. This study proposed the chip size index (CSI) as a simplified and immediate indicator of excavation efficiency for drag picks. Rock cutting tests were conducted on two limestone samples using conical picks at various cutting depths and line spacings. The generated rock debris was subjected to sieve analysis to obtain traditional excavation efficiency indicators. Results showed that these indicators increased as specific energy (SE) decreased and formed strong power-law relationships with the coarseness index (CI). Increasing the cutting depth and line spacing also led to higher values of the indicators, which reached their maximum at the optimal ratio of line spacing to cutting depth (s/d = 3–4.5), where SE was minimized (32.48–127.59 MJ/m3 Similarly, CSI increased as SE decreased and exhibited a strong power-law relationship with CI. Furthermore, as cutting depth and spacing increased, CSI rose, ranging from 11.87 to 62.33 and reaching its peak at the same optimal s/d ratio. Further validation was performed using published linear cutting test datasets for drag tools obtained under comparable cutting configurations. These independent datasets confirmed the power law relationship between SE and CSI, with average coefficients of determination of 0.786 for conical picks and 0.619 for chisel picks. The proposed CSI may be a practical tool for monitoring and optimizing mechanical excavation operations without the need for sieve analysis of rock debris.