Photogrammetric Mapping of As-Constructed Geotechnical Works – Obi Obi Rock Slide, Queensland

摘要

On 29 April 2010, a major rockslide occurred within a 55 m high, geologically complex road cuttingrnadjacent to Obi Obi Road at Kidaman Creek, QLD (Lat. -26.6171°, Long. 152.7605°). Following thernrockslide, the Department of Transport and Main Roads (DTMR) commissionedrnGolder Associates Pty Ltd (Golder) to undertake geotechnical remedial options assessment andrndesign, and Designer’s site inspections to confirm design intent during construction. The remedialrndesign involved re-cutting the batter slope behind the unstable slipped material to a height of morernthan 75 m, at an overall angle of approximately 34°. Ground stabilization elements constructedrnincluded passive dowels, soil nails, drain holes, reinforced shotcrete, erosion control matting and revegetation.rnFollowing construction, Golder undertook an aerial photogrammetric survey of the asconstructedrnworks using the 3DM Analyst digital photogrammetry system. Conventional laser surveyrntechniques were utilised during construction by DTMR and the photogrammetric mapping was seen asrnproviding several additional benefits. These included a very detailed topographic profile of the slope,rna georeferenced 3D photographic record, an ortho-rectified photo mosaic, and the ability to undertakernretrospective mapping in the future without the need to re-visit the site. The aerial photography wasrnundertaken using a portable Unmanned Aerial Vehicle (UAV), which provided benefits in cost, safetyrnand logistics as compared with using a conventional helicopter. Digital photogrammetry is a versatilerntool, with applications including geological and geotechnical mapping, landslide mapping andrnmovement monitoring, as-constructed survey, and layer thickness/volume measurement.