Posted 21 April 2016
The geotechnical centrifuge is also known as the ‘environmental time machine’
By Rick Arena
Researchers at the UNSW Connected Waters Initiative (CWI) have developed new methods for measuring how the properties of groundwater systems can be affected by activities such as extraction and mining.
Groundwater in confined aquifers is contained by layers of substrate such as clay that have low permeability. Called aquitards, these layers limit the rate at which the aquifer can be recharged by water moving through them, and can act as a barrier to external contaminants entering the aquifer.
"Low permeability barriers can be naturally occurring clay or rock, or constructed of clay and engineered materials," said Dr Timms of the UNSW School of Mining Engineering, who led the research team.
However, human activities can change the way aquitards limit the flow of water through them. Extraction of groundwater can stress aquitard materials by causing subsidence and compaction.
"Where mining occurs near water bodies, wetlands or farming land, these barriers to groundwater flow can be very important," Dr Timms said. "There is increasing need to improve the engineering design of flow barriers, and computer modelling predictions of natural barriers to flow."
The CWI team developed a technique to simulate these changes experimentally and measure how the hydraulic properties of the aquitard materials can change in response to these stresses.
Compacted, or 'tight', clay collected from an aquitard near Gunnedah in the Namoi catchment in NSW, was analysed at the CWI Centrifuge Permeameter Facility and the mining geo-mechanics laboratories at UNSW.
Using the geotechnical centrifuge, Dr Steve Bouzalakos found that the hydraulic permeability of the tight clay could change depending on stress conditions. The variations in stress in the experiment simulated the stressing of aquitard materials affected by activities such as extraction of large volumes of groundwater or by mining and coal seam gas developments.
The geotechnical centrifuge is also known as the ‘environmental time machine’. Accelerated gravity is used to gradually speed up processes that usually occur over time periods measured in years or decades to help evaluate the long-term effects of changes in the subsurface environment.
In related research, Dr Richard Crane and Dr Wendy Timms pioneered a new technique to analyse tight clays at the CWI Centrifuge Permeameter Facility. In a world first, an interrupted-flow centrifuge method was developed to show how small flow channels could allow leakage through the normally relatively impermeable materials that comprise aquitards. These preferential flow paths could be activated through aquitards if there are differences between groundwater pressures above and below the aquitard materials.
These findings have implications at scales ranging from individual sites to basins and catchments in which activities occur that affect the subsurface environment by extraction of groundwater or modification to aquitards.
"The research is of benefit to mining and agricultural communities, by improving predictions of barriers to groundwater flow," said Dr Timms.
Funded by the Australian Research Council, through the National Centre for Groundwater Research and Training, the research outcomes are reported in a number of publications.
Professor Andy Baker features in American Water Resources Association ‘Water Resources Impact’, September 2020 edition.
The Connected Waters Initiative (CWI) is pleased to welcome Taylor Coyne to its network as a postgraduate researcher. If you’re engaged in research at a postgraduate level, and you’re interested in joining the CWI network, get in touch! The CWI network includes multidisciplinary researchers across the Schools of Engineering, Sciences, Humanities and Languages and Law.
The Grand Challenge on Rapid Urbanisation will establish Think Deep Australia, led by Dr Marilu Melo Zurita, to explore how we can use our urban underground spaces for community benefit.
On the 21 August 2020, CWI researchers made a submission to the National Water Reform Inquiry, identifying priority areas and making a number of recommendations as to how to achieve a sustainable groundwater future for Australia.
Results published from a research project between the Land Development Department (LDD) Thailand and UNSW has demonstrated how 2-dimensional mapping can be used to understand soil salinity adjacent to a earthen canal in north east Thailand (Khongnawang et al. 2020).
