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When cutting rock hyperbaric, two cases may occur. The rock may encounter dilation or compaction due to shear. Dilation results in pore under pressures, while compaction results in pore overpressures. Dilation will increase the cutting forces considerably, while compaction may decrease the cutting forces. In both cases the cutting process is supposed to be cataclastic. To dimension cutting tools for deep sea mining, the worst case should be investigated, which is the dilatant case. To understand the cutting mechanism experiments are carried out in a pressure tank, simulating the hyperbaric conditions. Hyperbaric cutting appears to be very different from atmospheric cutting due to the pore water pressures. The experiments have revealed that the cutting mechanism changes from a chip type mechanism under atmospheric conditions to a cataclastic (crushed) type under hyperbaric conditions, resulting in higher cutting forces. An analytical model is presented to estimate the cutting forces under high hyperbaric conditions. The results obtained with the analytical model agree rather well with the experimental data. |
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