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Thermal Matric Potential Abstracts
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Chan, D., Kodikara, J., et al. 2007, Data Analysis and Laboratory Investigation of the Behaviour of Pipes Buried in Reactive Clay, Common Ground: 10th Australia New Zealand Conference on Geomechanics, Brisbane, Carillon Conference Management Pty Ltd for the Australian Geomechanics Society. pp. 206-211.
Buried pipe failures due to ground movement is a common problem which leads to the loss of water or gas supply in urban areas. Statistical analysis of pipe asset data indicates that pipe failure is correlated to ground movement caused by the shrinking and swelling of reactive soils due to seasonal climatic variations. This problem was studied in a large scale laboratory experiment, where a two meter long polyethylene pipe is buried in a box filled with reactive clay soil. The clay soil was subjected to capillary wetting conditions by supplying water to the bottom of the box, simulating seasonal climatic change by increasing the soil moisture content. Deformation of the pipe during soil movement was measured by a series of strain gauges attached to the pipe. Soil temperature, moisture content and suction were measured using the thermocouples, theta probes and thermal matric sensors respectively. This paper reports the statistical analysis of field data and the experimental setup for studying buried pipe failures.
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Salt, M., Jaksa, M., et al. 2007, Water Balance Modelling for Phytocovers and Conventional Final Covers at Landfill Closure, Common Ground: 10th Australia New Zealand Conference on Geomechanics, Brisbane, Carillon Conference Management Pty Ltd for the Australian Geomechanics Society. pp. 392-397.
At landfill completion, regulators require waste be covered to protect humans and the environment and minimise leachate. Cover criteria have become more stringent and prescriptive, with Australian regulators requiring a compacted clay barrier to prevent leaching. However, research overseas has shown that the compacted clay barrier is compromised over time. Research suggests alternative covers based on natural systems (whereby moisture is stored in the soil and lost by evapotranspiration) may be as protective as conventional covers.
The aim of this study was to compare the predicted water balance from a conventional and phytocover final cover using WAVES, a one-dimensional, daily time-step model which predicts soil water balance and plant growth. Overseas trials used models that assume plant growth does not vary between years. WAVES is believed to be more appropriate for Australian conditions due to the high climatic variability. As part of this study, the water balance losses as a percentage of precipitation were compared to those found overseas and Australian field trials.
Preliminary modelling suggests that the conventional cover, consisting of 900 mm soil over a 600 mm compacted clay barrier, will dry throughout its depth in the first year after placement, resulting in preferential cracking and increased permeability. A 1.5-2 m phytocover can achieve equivalent drainage to a conventional cover. To improve the accuracy of modelling, in particular for estimating runoff, adjustments may need top be made to the input parameters but quantification of these adjustments for Australian conditions will require field validation.
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Wong, J.S.C., Yuen, S.T.S., et al. 2007, The Australian Alternative Covers Assessment Program (A-ACAP), Eleventh International Waste and Landfill Symposium, Cagliari, Italy, CISA, Environmental Sanitary Engineering Centre. 1-5 October 2007
A long-term field and laboratory research program is underway to investigate phytocover alternatives to conventional landfill cover designs for Australian landfills (the Australian Alternative Covers Assessment Program, or A-ACAP). The major goals of A-ACAP are to demonstrate that phytocovers can perform to the satisfaction of local regulators and to develop guidelines for their application, design and construction. Five full-scale experiments are currently in progress or under construction in the states of New South Wales, Victoria, South Australia, Western Australia and Queensland. These 5 sites represent a wide range of Australian climatic conditions for monitoring of phytocover performance and investigation of potential limitations in an Australian context. Central to the project's experimental approach is the use of side-by-side comparisons of both conventional covers and candidate phytocovers in each state across mainland Australia. The field program will be supported by laboratory and glasshouse experiments to investigate gaseous transport and methane oxidation related to soil physical and biochemical properties, as well as the suitability of native flora for assisting with water balance goals, providing soil stabilization and vegetative cover, and promoting a functional soil microbial ecosystem in the root zone to optimize methane oxidation. The A-ACAP study will assist the waste management industry and Australian state regulatory agencies, working together, to establish field-based criteria for the design, installation and monitoring of alternative covers. This paper will present an overview of the project and discuss project implementation to date.
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