An experimental study of surface and sub-surface damage in pulsed water-jet breakage of rocks

This paper investigates the relative contributions of the pulse length and pulsation frequency on the surface and sub-surface damage that is caused by a pulsed water-jet on rock targets. Studies demonstrate that the failure zone directly under the impacted surface, including cavity formation and tensile crack-initiation, is caused by the impact stress and by water flows from the individual water-pulses. The magnitude of this damage is thus related to the pulsation frequency. The sub-critical cracks, which result from these impacts and which propagate to cause major rock-failure, are found to depend on the pulse length. Longer pulses are required to propagate cracks as the depth of damage (cavity depth) increases.