Quality Assurance (QA) assessment of earthworks remains dominated by the 1930s Proctor laboratory density compaction model coupled with the California Bearing Ratio (CBR) test. Over the past two decades, compaction and testing equipment have moved ahead of these commonly employed QA techniques routinely used in Australia. Density tests are lag indicators and contractors often continue placing additional layers to avoid significant equipment standby costs without the formal QA report.
Industry widely assumes if density is increasing then strength or modulus is also increasing. An incorrect assumption. Excessive compaction may result in material breakdown, and could result in a decrease of strength and modulus, although density may still be increasing.
Modern geotechnical and pavement designs are based on insitu modulus and strength values. It is therefore reasonable to investigate the feasibility to use alternative test methods for QA purposes, which measures these parameters directly. A state-of-the-industry study was completed on behalf of Queensland Main Roads and ARRB to identify test methods that have the potential to: (a) reliably provide a direct measure of the strength or insitu modulus value; and (b) offer significant time savings in turnaround time of QA test results.
The field trials bench marked various alterrnative equipment to compare with traditional density QA measurements in terms of reliability, benefits and limitations. Traditional density testing was found to be very precise – but is not very accurate. Other benchmarks included ease of use, capital cost of equipment, time to do test and time to report. A related webinar may be also of interest to attendees.
Dr Burt Look
Senior Principal Geotechnical Engineer, DGE, FIEAust
Dr Burt Look is a Senior Principal at the Foundations Specialists Group. He completed his Master’s degree in Soil Mechanics and Engineering Seismology at Imperial College, London, and his PhD at The University of Queensland while also working at Queensland Main Roads. Burt is widely recognised in the areas of earthworks, expansive clays, landslides, ground improvement, buried pipes, risk assessment and site characterisation, and has been called upon as an expert witness and technical advisor in some of these areas.
He was formerly the Practice Leader at SKM and a Principal and Geotechnical Group Leader at Aurecon. He was the past Chairman of the Queensland Chapter of the Australian Geomechanics Society and Chairman of the organising committee for the 10th Australia New Zealand Conference held in Brisbane in 2007. Burt is a strong advocate in learning and development and sharing of experiences. He has published over 75 technical papers and 3 geotechnical books.
He is the 2014 Queensland Professional Engineer of the year, and a Diplomate of Geotechnical Engineering (DGE) from the ASCE Academy of Geo Professionals.
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