Roller compacted concrete expert speaks in Bundy dam inquiry
BUNDABERG hearings for the Paradise Dam Commission of Inquiry started yesterday at the Bundaberg Courthouse with Daryl Brigden as the first witness on the stand.
The inquiry is set to examine the root cause of structural and stability issues identified with the dam, which the Queensland Government intends to lower by five metres for safety.
The first hearing was held in Brisbane last month and will continue in Bundaberg until Friday.
Currently "trying to retire", Mr Brigden started working with the Irrigation Water Supply Commission, now known as SunWater, in 1965.
Between 1984 and 2000, he worked as a principal material officer and has experience working with high-paste, roller compacted concrete.
Mr Brigden said his experience with roller compacted concrete began with the construction of Bucca Weir in about 1986.
Where Bucca Weir is a medium-paste mix, Paradise Dam is a low-paste roller-compacted concrete RCC dam made with 63-65kg of cement per cubic metre.
Mr Brigden worked on a preliminary design and was one of the members undertaking a due diligence workshop in August 2005, but had no involvement in the delivery of Paradise Dam or proceedings after the workshop.
Speaking to the due diligence report, Mr Brigden confirmed at the time he could not find any shear strength testing, which could have been because of costs.
He said this assumption was based on past experience and speculation.
While coring existing concrete and testing existing joints is a means to quantify the shear strength of a structure, Mr Brigden said was possible but quite expensive and could not be performed on lean-RCC, until the concrete had sufficiently hardened to support the forces of the drilling by specialist drillers and methodology.
While his expertise were in high-paste RCC, Mr Brigden agreed that there were dam engineers who work with low-cementitious mixes, and Dr Ernest Schrader was one of them.
When asked, "whether a rigorous and careful application of the lift joint quality index to the construction of the RCC at Paradise Dam might appropriately inform any conclusion as to whether strength parameters were achieved in fact, is a question more appropriately answered by a person with more extensive experience" than Mr Brigden with lean-RCC, he agreed.
Mr Brigden also concurred, that questions surrounding the reliability of the lift joint quality index without the need to perform shear strength testing, was also better answered by someone with expertise in lean-RCC.
Nonetheless, Mr Brigden said shear strength was an inherently important parameter in the design of the dam.
The Paradise Dam Commission of Inquiry continues today at the Bundaberg Courthouse from 10am.
For more information about the dam inquiry head to https://paradisedaminquiry.qld.gov.au/