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Tanzania CPTu Testing & Sonic Drilling

Geomechanics (Pty) Ltd. successfully completed a combined CPTu and Sonic drilling investigation in Tanzania.  This project required a multifaceted approach, including targeted soil sampling using both MOSTAP and Shelby techniques.

The team encountered unforeseen hard layers during drilling, creating some challenges in conducting the CPTu tests. However, Geomechanics' innovative approach proved successful. Utilizing the GEO601 sonic rig's dual-head system, they were able to rotary core through these hard layers. The H-size wireline system was instrumental as it allowed drilling up to 5 meters into the bedrock.

A significant advantage of sonic drilling for this project was the minimal water usage required. Without the introduction to mass amounts of water meant that any of the in-situ tests could record accurate data. 

For the CPTu tests, it was established early on that the team would use the Titan CPT-150 rig. This made quick work at some of the CPTu test locations. This customised CPTu rig allowed the truck to act as a counterweight that prevents the rig from lifting mid-test and provides the reaction force needed to offset the 190kN of thrust applied while advancing the CPTu probe and rods.

The availability of multiple drilling methods played a crucial role in the project's success. The team retrieved 35mm MOSTAP samples using both the CPT truck and the sonic rig, demonstrating the complementary nature of these techniques. Sonic drilling provided a way to circumvent limitations encountered during CPTu testing without resorting to excessive water injection. Conversely, CPTu data provided valuable insights for selecting locations for undisturbed soil sample collection using the sonic rig.

Heavy rainfall created access difficulties in specific areas, necessitating a shift to sonic rig-based MOSTAP sampling. The crew's quick thinking and the client's collaboration ensured the on-site creation of appropriate adapters and testing methodologies.

By combining CPTu and sonic drilling techniques, Geomechanics (Pty) Ltd. ensured they obtained the most accurate data possible, even in the face of unforeseen challenges. This project exemplifies the importance of having a versatile drilling toolbox and a commitment to finding solutions.