| Title | VARIABILITY OF GEOTECHNICAL PROPERTIES OF MATERIALS WITHIN WAIRAKEI SUBSIDENCE BOWL, NEW ZEALAND |
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| Authors | W. Koros, J. O’Sullivan, J. Pogacnik, M. O’Sullivan, M. Pender C. Bromley |
| Year | 2015 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | ABAQUS, Subsidence, triaxial test, Shear Strength, Modified Cam-Clay, Mohr-Coulomb, Wairakei geothermal field. |
| Abstract | At Wairakei geothermal field in New Zealand, subsidence has occurred since the onset of production in the 1950’s. A good understanding of the stress-deformation behaviour of materials is important for understanding the phenomenon and being able to predict future subsidence. For many of the materials found in the Wairakei geothermal field simple, linear constitutive laws are sufficient for describing their stress-deformation behaviour. However, evidence shows that the stress-deformation behaviour of the formations responsible for majority of the subsidence at Wairakei is not represented well in this approach. In this work we have selected the Modified Cam-Clay model to describe the behaviour of these formations more accurately. The selection of the Modified Cam-Clay model is justified by considering the geotechnical properties of the materials using data obtained from published triaxial tests, Atterberg limits and particle size analysis data. The consolidation and compression characteristics were also considered and data from samples taken at different depths were analysed using the Mohr–Coulomb model. The Modified Cam-Clay model was then employed in ABAQUS finite element analysis to reproduce the stress-deformation behaviour of a number of laboratory triaxial tests. This allowed the Modified Cam-Clay model parameters to be calibrated giving a clearer understanding of the nonlinear constitutive laws for the materials. The outcomes from this study form the basis for the characterisation of the stress-deformation behaviour and strength properties of materials for purposes of modelling subsidence at borehole WKM 15 within Wairakei subsidence bowl. |