Waghorne, EP & Disfani, MM 2019, 'Land subsidence/rebound change after Hazelwood mine rehabilitation', in AB Fourie & M Tibbett (eds), Proceedings of the 13th International Conference on Mine Closure
, Australian Centre for Geomechanics, Perth, pp. 111-122.
As the power stations in the Latrobe Valley, Victoria, reach the end of their economic life, mine closures are anticipated. The closure of ENGIE’s Hazelwood Power Station and associated mine has already occurred and mine rehabilitation and closure planning are well under way.
During mining, pumping from deep, high pressure aquifers was required to reduce mine stability risks. This pumping, combined with water extraction (by others) for domestic supply and agricultural use, has lowered aquifer water pressures across the region. As a result, there has been gradual land subsidence of 0.3 to 0.5 m across the region, with 1 to 2 m close to the mines.
The Hazelwood mine rehabilitation plan includes the construction of an internal lake to balance uplift forces from the aquifers, allowing aquifer pumping at the mine to cease. Over the following decades, the aquifer pressure will recover, and a reduction of in situ effective stresses will occur so that compressible sediments in the strata will swell. Whilst future changes to the land surface are expected to occur slowly it will be important to understand the magnitude of the change and to assess any impacts on community infrastructure.
As there had been limited investigations into the swell properties of the sediments in the Latrobe Valley, an investigation was commenced at the University of Melbourne on the thick compressible coal seams and clay sediments found near the mine. The effect during loading, of creep and chemical/micro-structure changes on the swell properties of brown coal was also studied.
A background of aquifer pressure changes and subsidence in the Latrobe Valley over the last 60 years is provided, with recent test results and discussion of their significance on land subsidence and rebound prediction over the next 50 to 100 years.
Keywords: mine rehabilitation, mine closure, subsidence, rebound, aquifer, strata testing.
Giese, S 2010, Ground Movement Causing Regional Settlement as can be Seen in the Vicinity of Deep Open Cuts in the Rheinish Brown Coal Area, PhD thesis, Rheinisch-Westfälische Technische Hochschule Aachen University, Aachen.
Helm, D 1987, ‘Prediction of subsidence due to groundwater withdrawal in the Latrobe Valley, Australia’, Proceedings of the Sixth International Congress on Rock Mechanics, vol. 1, CRC Press, London.
Krupp, RE 2015, Effects of Groundwater Conservation in the Rhineland Brown Coal Area on the Topography and the Groundwater Levels, and Consequences for Buildings, Agricultural Land, Infrastructure and the Environment, study commissioned by Alliance 90 for The Greens in the Parliament of North Rhein Westphalia, Germany, 138 p.
Mesri, G & Stark, TD 1997, ‘Secondary compression of peat with or without surcharging’, Journal of Geotechnical and Geoengineering, May.
Poland, JF & Working Group 1984, ‘Mechanics of land subsidence due to fluid withdrawal’, in JF Poland (ed.), Guidebook to Studies of Land Subsidence Due to Ground-water Withdrawal, UNESCO, Paris.
Regan, WM & Ash, PJ 1986, ‘Latrobe Valley deep piezometer bores 2996M and 3067M, laboratory test results’, SECV Design Engineering and Environment Department Report No. GDD6.
Tyagi, L & Balkis, J 2018, ‘Impact of chemical bonding and microstructure on the rebound behaviour of brown coal during stressrelief’, research paper, Department of Infrastructure Engineering, University of Melbourne, Melbourne.
Waghorne, EP 2009, ‘Brown coal mining in the Latrobe Valley’, Monograph 12 Australasian Coal Mine Practice, 3rd edn, The Australasian Institute of Mining and Metallurgy, Carlton, pp. 470‒485.
Woskoboenko, F, Stacy, WO & Raisbeck, D 1991, ‘Physical structure and properties of brown coal’, in RA Durie (ed.), The Science of Victorian Brown Coal: Structure, Properties and Consequences for Utilization, Commonwealth Scientific and Industrial Research Organisation, North Ryde, pp. 152‒245.