Experimental and simulation study on rock-breaking efficiency of disc cutters on composite rocks

There are many studies on rock-breaking efficiency of TBM's disc cutters on homogeneous rocks; however, there are few studies on the cutter's rock-breaking efficiency on composite rocks. Specifically, research on the breaking efficiency of cutters on composite rocks with substantial differences in strength and composite ratios has not yet been systematically reported. The aim of this study was to numerically simulate the rock-breaking process of the TBM disc cutters to investigate the performance of the cutters on composite rocks. The underlying numerical simulation was validated by our full-scale laboratory tests. A series of numerical simulations were shown to lead to an accurate determination of the disc cutters performance on composite rocks of sandstone and granite in terms of the normal force, torque and specific energy. This indicates that there are some similarities between homogeneous and composite rocks, e.g., both show an optimal ratio of cutter spacing, s, to penetration depth, p, i.e., optimal s/p. Nevertheless, there are many more significant differences demonstrated in our study, including the composite ratio-dependent different ranges of the cutter force, torque and specific energy, changes of the optimum s/p, and the characteristic that s/p decreases linearly with the increase of the composite ratio. Although the optimal s/p is different for different composite ratios, it is possible to obtain a representative optimal s/p, e.g., 14, in our case, i.e. composite rocks of sandstone and granite, which may approximately optimise the composite rock-breaking, irrespective of different composite ratios. The paper also suggests that it is possible to study the rock-breaking efficiency of the disc cutters on composite rocks with appropriate consideration of composite UCS.