RGS was recently contracted to work on the Grwyne Fawr Dam in the Brecon Beacons, Wales, a now disused reservoir, where construction was completed in 1928. Safety concerns were mounting due to the age and therefore the integrity of the structure.
The aim for the investigation was to characterise the fracture orientations present within the underlying sandstone formations and to log the interface between the concrete structure and the natural bedrock. Our suite of televiewers are the quintessential tools for performing such a high priority task. The High Resolution Optical Televiewer (Hi-OPTV)®, High Resolution Acoustic Televiewer (HRAT)® and RGeo-eye® downhole camera were deployed, each offering an advantage in specific circumstances.
The Optical Televiewer utilises its fisheye lens to generate an ‘unwrapped’ image of the borehole wall orientated to magnetic north. The Acoustic Televiewer utilises ultrasound rather than visible light giving it the distinct advantage of being able to work in opaque borehole fluids. The RGeo-eye® probe allows for rapid recording with its downhole facing camera.
The logging was successfully conducted by two experienced RGS engineers. Access to the site was difficult, requiring the use of a 4×4 vehicle customized for logging by RGS. For the most difficult to reach areas a portable setup was used, using the Robertson Geo Mini Winch.
