Last Tuesday I assisted Stuart Read (on left of image) and Fred Baynes who were leading a two day course on Principles and Practice of Engineering Geology for 26 members of the New Zealand Geotechnical Society. We spent the morning inspecting, and logging part of the lower slopes of the abandoned quarry at Owhiro Bay, Wellington.
Ahead of the course, we flew a UAV (unmanned aerial vehicle, or drone) over the outcrop to record high resolution photographs that could be used as base maps for the course.
Above the area of the field mapping exercise we noted a well defined slope failure affecting one of the intermediate benches of the old quarry. We took the opportunity of using the UAV data to build a slope model to analyse with TSLOPE in 3D.
One of the objectives of the field logging course was to determine the applicable Geological Strength Index (GSI) for the indurated sandstone rock mass. Using our TSLOPE model we have been able to investigate, through back analysis, how GSI might vary at the bench failure.
How would you think the back analysis estimates of GSI compared with those made by the participants on the course?