Empirical models are developed to describe the influence on the cutting process of preweakening a rock, by cutting a series of parallel kerfs in the surface with high pressure waterjets, prior to excavating the rock with a polycrystalline diamond compact (PDC) drag bit. These models show that both the bit cutting force and the bit normal force are reduced substantially (by as much as a factor of four) when the spacing and the depth of the kerfs is appropriate to the depth of cut taken by the bit. The mechanical specific energy, or the mechanical energy applied to the bit to excavate a unit volume of rock, is also reduced dramatically when the rock is prekerfed.

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