Geomech Africa was recently contracted by Michael Pavlakis & Associates Consulting Geotechnical Engineers to assist at the Petroleum Plant in Sasolburg to perform a Geotechnical Investigation for the foundation design for a new chimney as part of the plant upgrade.
Geomech Africa was commissioned to perform a Geotechnical Investigation that consisted of drilling 3 boreholes including Standard Penetration Testing (SPT’s) and Undisturbed sampling, retrieve water samples for analysis, and install Piezometers at these drill sites. The aim of the project was to retrieve the highest possible quality core samples with the greatest possible sample recoveries on a small congested site. This intricate and demanding task fell upon Geomech Africa and specifically Espee van Huyssteen, the site supervisor, and the skilled drilling crew to see if they could produce the sought-after quality core samples the client required. The challenge faced by the Geomech Africa team, and many others who have attempted this task previously, was that they were drilling into closely jointed and fractured dolerite.
Operators had to drill very carefully while adjusting their drill methods to retrieve quality core. In these conditions, one can easily lose core as the fractured formation can get wedged in the drill bit causing it to become blocked. Drill operators must also be very careful not to add too much pressure while using the hydraulic feed cylinders as this can cause the core to grind away at the tip of the drill bit which in turn will stop the core from entering the core barrel. Nevertheless, with careful execution and an experienced team, they were able to retrieve high-quality core.
As one could expect, sites of this nature are intricately designed with many pipes and walkways in the surrounds. Operators must constantly be aware of these potential obstacles. Thus, mobility was quite limiting to the team. That is why the team decided to use a YWE D45 drill rig. The YWE D45 is smaller and more mobile than the YWE D90 which they intended to use at first. With the bigger drill rigs (YWE D90) you have more stability of the drill and the drill direction. They are equipped with a drill mast (attached to the frame of the drill rig) for pulling and lowering of the rod string with the rig’s hoisting winch. However, with the smaller YWE D45 rig, they do not have a permanent drill mast but a tripod and snatch block system that is separate from the rig. To compound matters, one of the drill positions was on top of a solid concrete slab/floor. The legs of the tripod are subjected to easy slipping on such a surface. To overcome the risk of slipping, the team had to think out-of-the-box and decided to anchor the tripod legs to the concrete floor by drilling holes in the concrete and anchoring the tripod footplates to the floor surface with 16mm steel pegs. This secured the tripod in place and ensured that it would not slip on the smoother cement surface. In this way, a stable and safe structure was created for rod string-pulling and lowering as well as to conduct the SPT’s with the SPT hammer.
The Geomech Africa team faced many challenges to retrieve the quality core that the client needed. They overcame them one-by-one and completed the 10-day project on time. The core samples provided were of higher quality than what the client expected which allowed the client to gain a far greater appreciation for the ground conditions with the analytical data they received. The experience and dedicated workmanship of the Geomech Africa team left a lasting impression on the client.