- Title
- Elastoplasticity of Victorian brown coal and its interaction with interseam clay
- Creator
- Karami, Mojtaba
- Date
- 2021
- Type
- Text; Thesis; PhD
- Identifier
- http://researchonline.federation.edu.au/vital/access/HandleResolver/1959.17/179474
- Identifier
- vital:15622
- Abstract
- Batter instability is one of the major geotechnical concerns in open-cut mining of recent decades. A key factor in undertaking any stability assessment of batters and determining their Factor of Safety (FoS) against instability is understanding the geotechnical properties of the material comprising the batters. These geotechnical properties usually include stiffness and strength under various loading conditions such as compression, extension and creep. This thesis presents a comprehensive study of the geotechnical properties of materials comprising the batters in the Yallourn open-cut mine in Victoria, Australia, located at one of the largest sources of brown coal in the world. The materials studied in this research are Victorian Brown Coal (VBC) and fine-grained interseam material (containing mainly silt and clay particles). The presented study is based on four key steps undertaken during the research project: 1. Field investigation This step included drilling boreholes at the mine floor and mine crest and recovering samples of VBC and interseam for laboratory testing. Sample trays were logged to provide lithology data required for model generation for numerical modelling undertaken by other PhD students. 2. Laboratory testing This step involved a wide range of laboratory tests on undisturbed samples of VBC and interseam material to investigate soil characteristics, stiffness and strength of tested materials. 3. Data analysis and parameter determination This step included analysing the laboratory test results, preparing stress-strain plots and determining material properties such as pre-consolidation pressure, stiffness and strength. 4. Numerical analysis and model calibration This step included selecting proper constitutive models and determining the models’ parameters based on laboratory tests. The capability of models was then examined by verifying numerical model simulation against laboratory test results. The laboratory tests indicated that VBC shows a hardening feature in compression, leading to brittle failure, while also showing a sharp post-peak softening behaviour. The tests also showed that the interseam material is heavily over-consolidated with a dilative hardening feature. The stiffness and shear strength of the interseam were found to be sensitive to the applied strain rate. The conducted creep tests (applying constant shear stress for a selected period) under triaxial undrained conditions resulted in developing pore water pressure leading to creep failure. Based on the laboratory test results and the obtained geotechnical features of the tested materials, Hardening Soil (HS) and Soft Soil Creep (SSC) models were chosen to describe the geotechnical behaviour of both VBC and interseam material. Both models were calibrated using test results and employed in simulated laboratory tests, including oedometer and triaxial Consolidated Undrained (CU) tests using the Finite Element Method (FEM). This study indicates that, although most of the models’ parameters were determined successfully based on laboratory test results, engineering judgement and back calculating were required to find the best fit for the numerical simulations. The numerical modelling of oedometer and triaxial tests showed that the nonlinear hardening behaviour of VBC and interseam material was captured by the HS model. The stress path in triaxial CU tests and the stress-strain curve in unloading-reloading were simulated well by the HS model. The strain-rate dependency and creep behaviour of interseam material were simulated well by the SSC model, indicating that this model can predict the long-term behaviour of interseam material.; Doctor of Philosophy
- Publisher
- Federation University Australia
- Rights
- All metadata describing materials held in, or linked to, the repository is freely available under a CC0 licence
- Rights
- Copyright Mojtaba Karami
- Rights
- Restrict access 24 months starting 16 December 2021
- Subject
- Elasto-Plasticity; Victorian Brown Coal; Finite Element; Triaxial Test
- Thesis Supervisor
- Baumgartl, Thomas
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