Geotechnical Investigations for AECOM | Stellenbosch, Western Cape, SA

Retrieving core samples

In June 2020 AECOM commissioned Geomech Africa (Pty) Ltd. to assist with the drilling of four geotechnical boreholes, a total of 70 meters, at the abutments of the existing Distillery Road Bridge crossing the Plankenberg River near Bosman’s Crossing in Stellenbosch, Western Cape. The existing bridge is the only access to Bosman’s Crossing. Due to its narrow dimensions, the bridge width needs to be widened to accommodate the increase of traffic.

Given the Heritage around this site, the newly installed sewer system and all of the various purposes this crossing serves, it was critical that the locations of the boreholes were surveyed and placed in safe locations and as close to the bridge in order to provide AECOM with the most accurate information possible. The locations of the boreholes were in confined areas which made access to the borehole locations rather tricky. With the use of a small rubber tracked undercarriage and our YWE D90 drilling rig mounted on top of it, it made it easier for us to move between drilling locations.

Drilling alongside a river and on riverbanks would pose great challenges to any drilling team. These areas are well known for their soft sands, weathered formations, cobblestones, and boulders. All of which makes it extremely difficult to produce quality core samples. Drilling in these conditions required patience, extensive knowledge of soil types, and most of all experience. With a good team at his side, our Drill Operator Patrick Sibiya, was able to deliver top-quality core to the client.

At some drill sites, we had to slow down drilling to a minimum, with runs of 400mm at a time at the correct speed and pressure. In most cases, we needed to advance the casing in broken formations to stop the boreholes from collapsing. Besides having to deal with tricky formations, it was also required that we conduct in-situ testing such as SPT’s (Standard Penetration Tests), produce undisturbed Shelby tube samples of the appropriate soils and to install Piezometers.

Patrick Sibiya and the team from Geomech Africa managed to conquer the adverse conditions. Our team was able to produce outstanding results and quality core samples. As a result, we were able to successfully meet the requirements of our client, AECOM.