List of Titles

Investigation of an Australian soft rock permeability variation

- Tolooiyan, Ali, Dyson, Ashley, Karami, Mojtaba, Shaghaghi, Tahereh, Ghadrdan, Mohsen

Authors: Tolooiyan, Ali , Dyson, Ashley , Karami, Mojtaba , Shaghaghi, Tahereh , Ghadrdan, Mohsen
Date: 2020
Type: Text , Journal article
Relation: Bulletin of Engineering Geology and the Environment Vol. 79, no. 6 (2020), p. 3087-3104
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Description: In this study, permeabilities of Victorian Brown Coal (VBC) as an Australian soft rock are determined for a range of depths of a continuous coal seam located at the batter crest of the Yallourn brown coal open-cut mine in Victoria, Australia, by implementing a Lugeon packer testing procedure. Permeability values are determined both analytically and by numerical simulation and are compared with laboratory test results. Field testing resulted in permeabilities several orders of magnitude higher than laboratory testing, suggesting the existence of fractures common to lignite structures on a greater scale than can be observed in the laboratory. The variation of depth-based field and laboratory permeabilities is discussed, as well as the necessary conditions required for the numerical modelling of packer testing within VBC. © 2020, Springer-Verlag GmbH Germany, part of Springer Nature.
Description: Department of Economic Development, Jobs, Transport and Resources, DSDBI The second and third authors are funded by the Australian Government Research Training Program (RTP) and the GHERG scholarship programme.

Application of ground penetrating radar (GPR) to detect joints in organic soft rock

- Tolooiyan, Ali, Dyson, Ashley, Karami, Mojtaba, Shaghaghi, Tahereh, Ghadrdan, Mohsen

Authors: Tolooiyan, Ali , Dyson, Ashley , Karami, Mojtaba , Shaghaghi, Tahereh , Ghadrdan, Mohsen
Date: 2019
Type: Text , Journal article
Relation: Geotechnical Testing Journal Vol. 42, no. 2 (2019), p.
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Description: The detection of joints and discontinuities is of particular importance to the stability of a broad range of geostructures, including slopes and underground and open-pit mines. As a common example, the mechanical response of soft rocks observed within open-pit mines is significantly influenced by the existence of joint networks, resulting in a complex stress distribution that governs the stability factor of safety as well as the failure mechanism. In this article, surface geophysics scanning by ground penetrating radar (GPR) is presented for the detection of vertical joints at one of the largest open-pit coal mines in Australia. The optimum soil velocity, point interval, and antenna frequency for joint detection in Victorian Brown Coal (VBC) are presented in comparison with electromagnetic properties of known organic soils. Furthermore, the performance of an assorted set of post-processing signal filtering techniques to successfully identify the underground coal fractures are detailed, along with obstructions affecting the feasibility of GPR vertical joint discovery in this light organic soft rock.

Elastoplasticity of Victorian brown coal and its interaction with interseam clay

- Karami, Mojtaba

Authors: Karami, Mojtaba
Date: 2021
Type: Text , Thesis , PhD
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Description: 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.
Description: Doctor of Philosophy

Maximising the efficiency of Menard pressuremeter testing in cohesive materials by a cookie-cutter drilling technique

- Tolooiyan, Ali, Dyson, Ashley, Karami, Mojtaba, Shaghaghi, Tahereh, Ghadrdan, Mohsen, Tang, Zhan

Authors: Tolooiyan, Ali , Dyson, Ashley , Karami, Mojtaba , Shaghaghi, Tahereh , Ghadrdan, Mohsen , Tang, Zhan
Date: 2021
Type: Text , Journal article
Relation: Engineering Geology Vol. 287, no. (Jun 2021), p. 106096
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Description: Menard pressuremeter testing has been widely used in geotechnical engineering applications for 40 years and is an important technique in determining in-situ horizontal stress distributions. In this study, Menard pressuremeter testing is combined with a "cookie-cutter" insertion technique to determine horizontal stresses for a soft-rock in an operational Australian mine. The method presents an alternative to the Self-Bored Pressuremeter, with cookie-cutter drill rods allowing for sample recovery and further laboratory testing. The method accommodates for the presence of gravel and hard layered materials that present a risk of damage to cutting shoes of Self-Bored Pressuremeter devices. The combination of a sonic drill rig, coupled with the cookie cutter rods produces a close tolerance pocket resulting in "pseudo self boring pressuremeter tests". The undrained shear strength, unload-reload shear modulus and in-situ horizontal stress are presented from pressuremeter tests conducted in the region for the first time. The undrained shear strength was observed in the range of 0.47-0.57 MPa, the unload-reload shear modulus between 17.43 and 18.25 MPa, the lift-off pressure in the range of 0.35-0.61 MPa. The K-0 of coal was equal to 1, with interseam materials ranging from 2.1 to 3.5. Results of the cookie-cutter insertion method are compared with conventional drilling methods, with the cookie-cutter insertion test providing results in good agreement with both advanced triaxial laboratory tests and FEM numerical analysis. Cookie-cutter pressuremeter tests were conducted on cohesive soils at Australia's second-largest open-pit mine, with pressuremeter test results presented for Victorian brown coal for the first time.

Investigating the elastoplasticity of an Australian soft rock based on laboratory test results

- Karami, Mojtaba, Tolooiyan, Ali

Authors: Karami, Mojtaba , Tolooiyan, Ali
Date: 2020
Type: Text , Journal article
Relation: Engineering Geology Vol. 276, no. (2020), p.
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Description: For the stability and deformation analysis of open-cut mines using numerical methods, one critical step is to identify and simulate the elastoplasticity of geomaterials comprising the open-cut batters. The Victorian Brown Coal (VBC) in Australia is a non-textbook geotechnical material with a hardening feature in compression leading to brittle failure while showing a sharp post-peak softening behaviour. In order to study different aspects of elastoplasticity including the hardening and post-peak softening behaviour of the VBC, a series of laboratory tests including one-dimensional oedometer and triaxial tests were carried out on undisturbed VBC specimens taken from 30 m to 50 m below the ground level in one of the largest VBC open-cut mines in Victoria. By post-processing of the triaxial and oedometer test results, a yielding phenomenon was identified at the boundary between the fully elastic and elastoplastic domains. The magnitude of the material stiffness in the elastic domain was found to be independent of the confining pressure in triaxial tests while governed by the chemical bonding of the coal particles. The post-yield behaviour, however, was a frictional hardening and ruled by the magnitude of the confining pressure leading to a failure envelope sensitive to the organic content of the material. In this paper, a unified failure envelope is defined for the VBC using the Hvorslev-type normalisation process. Furthermore, a nonlinear elastoplastic constitutive model was examined to describe the elastoplasticity of VBC in triaxial condition, which led to a good agreement between the experimental and numerical modelling results. © 2020 Elsevier B.V.
Description: Financial support for this research has been provided by Earth Resources Regulation of the Victorian State Government Department of Economic Development, Jobs, Transport and Resources . The authors wish to acknowledge the support provided by the staff of the Yallourn Open Cut Brown Coal Mine, Energy Australia . The first author is funded by the Australian Government Research training program and Geotechnical and Hydrological Research Group (GHERG) scholarship programme at Federation University Australia . The authors are also grateful for the technical advice and assistance of Mr. Wayne Powrie (GHERG, Federation University Australia).

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