Authors: De Sousa, ER; Fowler, MJ; Swarbrick, GE


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De Sousa, ER, Fowler, MJ & Swarbrick, GE 2013, 'Three-dimensional pore pressure prediction in dual phase conditions for slope stability assessment', in PM Dight (ed.), Slope Stability 2013: Proceedings of the 2013 International Symposium on Slope Stability in Open Pit Mining and Civil Engineering, Australian Centre for Geomechanics, Perth, pp. 1103-1110,

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This paper presents an approach for modelling both liquid and steam pore pressures for prediction of slope stability of proposed mine slopes at the Lihir gold mine in Papua New Guinea. A three-dimensional FEFLOW model has been developed of the Louise Amphitheatre including a centrally located geothermal zone. The model comprises a detailed lithological representation and some structural zones. The complex interaction of surface infiltration, ocean boundaries, geothermal upflow, dewatering, drainage to existing pits and groundwater and steam relief are represented in the model. The model is calibrated by some 200 vibrating wire piezometers that measure both pressure and temperature. The model predicts both groundwater flow and heat transport for annual pit development. A unique post processing method has been developed to rapidly estimate steam pressures based on the flow and heat predictions. A detailed model assessment process has been developed in order to judge the reliability or otherwise of modelling output. The output of the process is a three-dimensional pore pressure grid that identifies zones of both liquid and steam pressures. The results can be subsequently viewed or utilised elsewhere, such as inputs for slope stability analyses. Comparison with conventional dual phase modelling using TOUGH2 is favourable. Stability analyses are used to confirm slope designs and target locations and times where steam relief is required.

De Sousa, E.R. (2013) When layering is not enough – Converting geology block models into groundwater models, in Proceedings of MODFLOW and More 2013: Translating Science into Practice, 2–5 June 2013, Colorado, USA, Integrated GroundWater Modeling Center.
De Sousa, E.R. and Fowler, M.J. (2013a) Improving open pit boundary conditions in FEFLOW with IfmOpenPits, in Proceedings 40th International Congress of the IAH, 15–20 September 2013, Perth, Australia, International Association of Hydrogeologists.
De Sousa, E.R. and Fowler, M.J. (2013b) When cross section modelling is not enough – Improving pore pressure modelling with use of full 3D models, in Proceedings 40th International Congress of the IAH, 15–20 September 2013, Perth, Australia, International Association of Hydrogeologists.
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Harbaugh, A.W. (2005) MODFLOW-2005, the U.S. Geological Survey modular ground-water model - the Ground-Water Flow Process: U.S. Geological Survey Techniques and Methods 6-A16.
Pruess, K., Oldenburg, C., Moridis, G. (1999) TOUGH2 User’s guide, Version 2.0. Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, US.

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