Comparison between experimental and semi-theoretical disc cutter cutting forces: implications for frame stiffness of the linear cutting machine

In this study, full-scale linear cutting test results on three rocks with different strengths using same linear cutting machine and on different rocks using different linear cutting machines were analyzed, and experimental disc cutter cutting forces and semi-theoretical cutting force estimation results (Rostami and Ozdemir 1993; Rostami et al. 1996) were compared. After quantifying or excluding the influences of other factors, the deviation between the experimental and semi-theoretical disc cutter cutting forces is attributed to the different frame stiffness of the linear cutting machines. Generally, when cutting low-strength rocks, machine frame stiffness is relatively high, experimental disc cutter cutting forces will be much higher than the semi-theoretical estimation results (i.e. they are underestimated with high degree); when cutting extremely hard rocks, machine frame stiffness is relatively low, experimental disc cutter cutting forces will be less higher or even lower than the semi-theoretical estimation results (i.e. they are underestimated with low degree or even overestimated). Generally, when rock strength is same, high machine frame stiffness will result in high disc cutter cutting forces. Different deviation degrees and scatter characteristics of the comparison results indicate that different linear cutting machines possess different general frame stiffnesses and also different frame stiffness proportions in normal and rolling directions. Two indices are then proposed to evaluate the predictive ability of the semi-theoretical disc cutter cutting force estimation approach on experimental disc cutter cutting forces obtained using different linear cutting machines, namely predictive accuracy and reliability. Modification factor K, defined as the linear fitting line slope of the force data points, can be used to represent the predictive accuracy and to modify the initial semi-theoretical estimation formulas to reduce the discrepancy between the semi-theoretical and experimental cutting forces. Scatter factor S can reflect the scatter degree of the force data points with regard to the fitting trend line, and it greatly affects the predictive potential to predict disc cutter cutting forces more close to practical ones. It is thus strongly suggested that the semi-theoretical cutting force estimation approach and more actual interpretation of the linear cutting tests using different linear cutting machines and tunnel boring machines should be improved in the future.