A geotechnical assessment of the Oaklands Junction Quarry, Melbourne was undertaken to provide recommendations on pit wall design parameters for use in future quarry planning. Holcim (Australia) Pty Ltd plans to double the depth of the existing main pit over the remaining life of the quarry, and a robust geotechnical assessment of the existing pit walls was required to provide long term pit face stability during operation and subsequent quarry rehabilitation.Due to safety restrictions, access to the batters to undertake conventional (tape measure and compass) geotechnical mapping was very limited. The acquisition of geotechnical mapping data is described, using photogrammetric methods to undertake the mapping remotely. Measurements included the orientation, spacing, persistence and large scale waviness of the rock discontinuities that control the stability of the quarry pit walls.The use of photogrammetry provided far greater mapping coverage and a much larger set of high quality geotechnical data than could have been obtained by conventional mapping methods. The persistence and large scale waviness of the discontinuities are critical to the geotechnical design, due to the typically low shear strength of joint infill materials.The acquisition of high resolution digital terrain models (DTMs) of the quarry batter faces is described, generated using the 3DM Analyst Mine Mapping Suite (ADAM Technology, 2013) digital photogrammetry system from 'stereo pairs' of photographs taken of the pit walls. The same software was then used to carry out the remote geotechnical mapping. The results included more than 1,200 individual measurements of discontinuity orientation, as well as a smaller number of measurements of discontinuity spacing and persistence.The DTMs were used to quantitatively assess the large scale waviness of selected discontinuities, and provided justification to increase the large scale friction angle adopted for the subsequent stability analyses by up to 5°, as compared to the values that would otherwise have been adopted based on drill core alone. The assessment of safe pit slope angles is discussed, and observations of existing large scale failures in the pit walls were used to corroborate the use of increased friction angle in the design.
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