Hard rock drilling technique with abrasive water jet assistance

Abstract A dense “boss” in the hole bottom by the conventional rotating mechanical drilling in the hard rock requires a more efficient drilling technique with great stress concentration, easy heat dissipation and slow bit wear. A new kind of hard rock mechanical drilling technique with the abrasive water jet assistance is developed for this issue, and the abrasive water jet is introduced to erode the “boss” for a “pilot hole” because of the lower rock tensile and shear strength compared with compressive strength. The exposed hole wall of the “pilot hole” provides a large area of free surface which can guide the cracks to the subsequent rock breaking, and promote the cutting edges to overcome the rock tensile strength to complete the tensile and shear failure of the rock around the “pilot hole”, which can reduce the drilling force and achieve the efficient drilling with low bit wear in the hard rock. By designing and manufacturing a hard rock breaking bit and a set of hard rock drilling equipment system with abrasive water jet assistance, the experiments are conducted and compared with the conventional technique. The results show that with the assistance of abrasive water jet, the drilling depth has increased by about 63%, the thrust force and torque have reduced by about 15% and 20% respectively, and the bit wear has been reduced significantly.

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