Case Study 03

Raisebore Examination 1km Below Surface

Client:

Western Australian Gold Mine

Overview:

The client had engaged MineGeoTech to undertake the geotechnical design assessment for a 4.5m diameter ventilation raisebore between 1045m and 1208m below surface to assist development of a new area of the mine. As a means of validating the assessment a LiDAR scan was recommended.

Location:

Western Australia

Challenge:

Understanding the performance of the raise through multiple lithological units would assess the requirements for a liner for long term stability.

Calibration of empirical stability forecasts against actual performance for stress state with a k-ratio of 3.

Service/Approach:

MINELiDAR deployed their Hovermap unit mounted to a winch. The unit was lowered down through the pilot hole to scan the entire length of the raisebore.

Solution/Result:

The detail of scan along the complete raise provided

  • Confirmation of 90deg rotation of the stress field in proximity to a regional fault

  • Assessment of numerical modelling criteria to compare forecast deformation against measured maximum overbreak

  • Part of the raise with stress spalling and parts of the raise with stress induced damage to structure

  • Validation against site seismic system

  • Assessment of drillers comments on face stability and empirical face stability

  • Comparison of empirical stable diameters with overbreak depth and overbreak areas

  • Observation of buckling on one side of the rise and minor fall out on the other

  • Assessment of the influence of penetration rate on seismicity and overbreak

  • Lithological controls on overbreak

CTA/Conclusion:

MINELiDAR provided a detailed scan along the rough profile scan overbreak depths from 0.02m to 2m without slippage of the Simultaneous Localising And Mapping algorithm.

Technical staff could assess that no liner was required with the detailed information provided.

The forecast empirical stability assessment although varying from significantly larger to just larger than the bored diameter showed that raise stability does not mean there is no overbreak.

Results provided to site as point cloud, wireframe, sections, and analysis of rock mass response.

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