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Pre-ripping
Pre-ripping occurs after mined pits have been landscaped but before soil return. The objective of pre-ripping is to relieve mining-related soil compaction and fracture the ground. This is important because pit floor hardness is far greater than the surrounding non-mined areas due to heavy vehicle compaction and the removal of the naturally friable bauxite ore during the mining process. Research has shown that deeper ripping helps the vegetation grow into a sustainable forest by allowing roots and water to penetrate through the soil profile.
Alcoa has made commitments to government to deep rip all pits and rip the majority of the pit to a minimum of 1.2 m. More stringent internal Alcoa standards were developed to ensure these commitments are met - rip 80% of the pit (excluding batters and waste islands) to 1.5 m or greater. A real-time monitoring system located in the cab of the dozer is used to monitor the area that has been ripped and the depth of ripping. This monitoring system enables the dozer operator to meet target for the pit and identifies areas where rework is required prior to shifting to another location. Following pre-ripping a grader is used to smooth the surface ready for the return of topsoil and overburden.
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