New coring technique success

Posted 26 July 2011

Drilling and coring equipment in action on the Breeza plains.

Clay cores were successfully drilled on the Breeza plains using a new technique developed as part of research funded by the Australian Research Council and National Water Commission.

A drilling team led by the University of New South Wales and National Centre for Groundwater Research and Training (NCGRT) worked through the Easter holidays. They drilled, cored and installed a number of piezometers and geophysics casings and foundations at a research farm operated by the NSW Department of Primary Industries.

While not suitable for pottery, the swelling clay there can form effective flow barriers known as aquitards below the cracking zone. The research aims to measure moisture storage in clay sediments on the plains and the rate of leakage and recharge. Recharge to deep gravel aquifers on the plains is critical for providing town water supplies, irrigation bores and base flow for the Namoi River.

The clay cores were drilled to a depth of 40 meters below groundwater at three sites, but did not reach deep alluvial aquifers, or underlying bedrock. Work at one of the key sites is a collaborative effort with agronomists and soil scientists at the NSW Department of Primary Industries research station.

The drilling technique was perfected for clay sediments by drillers from the NSW Office of Water working with the research team. Cores produced with this technique are especially valuable for many types of testing because the large diameter format (100 mm) is extracted in a minimally disturbed state using triple tube core barrels with clear PET liners.

The team was surprised to find the clay cores were relatively dry, even below saturated sand layers. They also found geological logs from these cores are much more accurate that standard mud rotary mud methods, which can miss important sand layers.

Data obtained from the cores will be combined with meteorological and groundwater monitoring data and geophysical information including micro-gravity. These research outcomes are already being applied by UNSW team to develop more realistic 3D geological models.

Back in the lab, the cores are dissected and subjected to a number of analyses including moisture content, pore water chemistry and isotope content, density, compressibility and permeability.

Some of the analyses are currently being conducted using the new centrifuge permeameter facility at UNSW Water Research Laboratory. Test results so far show the clay cores are very low permeability below the cracking soil and can form an effective barrier to water leakage if there are no discontinuities in layering or leaky bores.

Preliminary findings will be presented by the UNSW team at a field day in the local catchment, and at the NSW Groundwater Symposium run by the International Association of Hydrogeologists in September.

Project team: W. Timms, A. Greve, G. Regmi, I. Acworth, B. Kelly, S. McCulloch, H. Studholme, M. Groskops, B. Bambrook, C. Farley, A. Rogan, H. Walmsley

Collaborators: NSW Department of Primary Industries

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