The raising of Hazelmere Dam by an unprecedented 7m required technology never before seen in the KwaZulu natal region of South Africa. Extensive feasibility studies established that the optimum solution to facilitate the raising was to install 83 high capacity rock anchors through the 47m high concrete superstructure into the underlying rock. The anchors, installed in 355mm diameter boreholes, ranged in size from 49 to 91 strands (15.7mm diameter) and were up to 90m long. With test loads up to 19042kN, these are the highest capacity cyclically loaded post-tensioned anchors ever installed. In addition, ten of the anchors will be instrumented with the world’s highest capacity annular hydraulic pressure transducer load cells. These bespoke instruments will allow full remote monitoring technology, permitting authorised personnel to interrogate the anchor load throughout the design service life.
Circumstances associated with the works resulted in a four-year delay to the project. This raised concern that the anchor tendons allocated for load cell installation may have suffered adverse corrosion.
On behalf of Ingerop South Africa (ISA), lead anchor consultant Dr Mothersille (Geoserve Global Ltd) engaged the services of corrosion specialists Intertek to assist with a forensic investigation that included physical inspection and assessment of the anchor tendons. The detailed investigation involved using an illuminated x60 magnifying glass and a digital endoscope to examine the surfaces of the steel tendons in situ. Back at Intertek’s laboratories in Manchester (UK), replica moulding samples of steel strand surfaces were coated with gold using a Polaron 500 Sputter Coating Unit and photographed with a Keyence VHX-2000 Digital Microscope. This allowed the creation of 3D surface reconstruction and detailed measurements of surface profiles. Additional testing included tendon metallography, chemical analysis, hardness testing and water analysis to establish a thorough assessment of the tendon condition. Enjoy the images from this visit to South Africa.