Postgraduate Research Students

Dr Erwin Mmbando
PhD Civil, Environmental and Mining Engineering
2024

Thesis title: Ensuring geotechnical stability of filtered tailings stacks

Supervisors: Professor Andy Fourie and Dr David Reid, The University of Western Australia, Australia; Associate Professor Johan Wesseloo, Australian Centre for Geomechanics, The University of Western Australia

Tailings storage facilities (TSFs) are important for safe mine waste disposal. To address the stability concerns of hydraulically deposited TSFs, there is a shift towards filtered tailings stack technology. This thesis assessed if filtered tailings can maintain dilative states under increasing loading. To achieve this, this thesis explored the effects of structure and pore chemistry on the critical state behaviour of bauxite residue reconstituted by different methods. Additionally, the effects of the initial void ratio on the critical state behaviour (transitional) of clayey tailings were studied. Finally, a comparison of residual strengths measured in situ and in the laboratory are provided.

Dr Arturo Maldonado
PhD 
2023

Thesis title: The shear strength of bedding planes in shale materials of the Hamersley Group Rocks in the Pilbara

Supervisors: Professor Phil Dight and Dr Kyle Woodward, The University of Western Australia, Australia; Dr Kenneth Mercer, 3rd Rock Consulting, Australia (external supervisor)

The shear strength of bedding planes was measured from direct shear testing of natural and artificial surfaces. All testing was conducted at natural moisture content with very slow shear strain to permit pore pressure dissipation. All stresses were dilation corrected to estimate the basic friction angle of bedding and artificial surfaces. The mineralogy of bedding surfaces presents very good relationship with dilation corrected friction angles, as derived from laboratory testing. In fresh and slightly weathered shales, bedding planes present pre-shearing history that causes low dilation angles. Within moderately and highly weathered shales, bedding planes are coated by decomposed rock.

Dr Teófilo Aquino Vieira da Costa
PhD Civil, Environmental and Mining Engineering
2022

Thesis title: Brazilian banded iron formations: a geological and geotechnical characterisation from hard and fresh to weak and completely weathered rocks

Supervisors: Professor Phil Dight, The University of Western Australia, Australia, Professor Eduardo Marques, Universidade Federal de Viçosa, Brazil, Dr Kenneth Mercer, 3rd Rock Consulting, Australia (previously The University of Western Australia)

Brazilian Proterozoic banded iron formations (BIF), classified as low-grade ore, are called ‘itabirites’ and are divided into quartzitic, dolomitic, amphibolitic and high-grade ore ‘hematitite’, together with the main iron host rock of the Iron Quadrangle mines in Brazil. Their genesis is controversial, but it is agreed that metamorphic and tectonic events as well as the supergene and hypogene enrichment are responsible for modifying the original hard rock characteristics reconcentrating the iron. Weathering processes are responsible for reducing the strength, generating deep and heterogeneous weathered profiles with low strength rocks (weak rocks) reaching 400 m depth.

Based on field investigation and laboratory tests from 15 different mines, the PhD thesis determines the intact rock strength parameters and petrophysical proprieties (macro and micro scales) in different weathering profile levels (horizons and zones), highlighting geological and geotechnical characteristics considering the degree of anisotropy defined by the compositional metamorphic banding (heterogeneity), establishing relationships between petrophysical, rock strength and elastic parameters, proposing empirical correlation equations.

To reach the thesis goals, rock laboratory tests (triaxial, unconfined compressive strength – UCS, P and S wave and Brazilian tests) and soil laboratory tests (Atterberg limits, particle size distribution and soil-water characteristic curves, saturated and unsaturated direct shear tests, triaxial – CIU and permeability tests) were undertaken for each typology in different directions to account for anisotropy. In addition, petrographic thin sections, geological and geotechnical field investigation, and permeability in situ tests were assessed.

All test results and Vale’s internal database were assembled and evaluated, and a complete failure envelope for each typology was determined to describe the intact rock and shear strength parameters variance in association with the geological and geotechnical characteristics along the weathering profile.

For each weathering level the following was concluded: for fresh typologies, the anisotropy ratio and index, respectively based on the UCS tests and Vp measures, are low to isotropic except for fresh dolomitic itabirites that present a fair to moderate anisotropy ratio. Even with a moderate dispersion of the UCS results, there is a direct correlation between iron content, bulk density and UCS parameters for hematitite and itabirites, and an inverse correlation with total porosity as expected. For these types, the main characteristics responsible for defining the rock strength and anisotropy are the mineralogy and the rock fabric. On this matter, hard hematitite is the stronger strength typology, followed by fresh quartzitic, amphibolitic and dolomitic itabirites. Hard hematitite also presents extremely high elastic parameters, followed by amphibolitic and quartzitic itabirites, and dolomitic itabirites presented the lower elastic behaviour.

Also, for fresh rocks positioned at the bedrock of the BIF weathering horizon, empirical correlation equations for UCS, Young´s modulus, bulk density and P and S wave velocity were established, which indicate a reliable, straightforward, and low-cost method which can be used to predict, with acceptable accuracy, intact rock strength and elastic parameters.

Moderately weathered typologies, positioned at saprorock and saprolite horizons, even with a small number of tests, showed a fair to moderate anisotropy index due to the higher total porosity and lower bulk density, behaving like a soil when highly weathered (saprolite horizon), or rock when moderately weathered (saprorock horizon). For these types, the heterogeneity is defined mainly by the total porosity, however the mineral composition plays an important role.

The completely weathered rocks are characterised as saprolite or in situ residual soil horizons. For these BIF rock-like soil types, the bulk density, particle size distribution, permeability, total porosity, and water content are the most important parameters for typology shear strength variation. The low anisotropic ratio generally obtained has a minimal effect on the low shear strength values of weathered BIF types. The weathered argillaceous itabirite presents the lowest permeability and highest clay content that induces a matric suction effect (up to 80 kPa) and as an aquiclude can keep the negative porewater pressure (suction) describing an important unsaturated behaviour.

This thesis concludes that for BIF rocks each weathering horizon and level presents a typical intact rock strength, elastic parameters, and intrinsic petrophysical proprieties defining a specific geomechanical behaviour mainly controlled by the binomials iron content/bulk density, total porosity/permeability, and the mineral composition/ bands thickness. Ultimately, the weathering profile horizon and level control slope stability and failure mechanisms not only for long-term excavations but also for temporary slopes from shallow to deep iron ore mines.

To read the thesis in full, visit https://doi.org/10.26182/e8hy-e863

Dr Juan Andrés Jarufe Troncoso
PhD Civil, Environmental and Mining Engineering
2020

Thesis title: Fault slip seismicity in underground mining operations: asperity and barrier shear modelling

Supervisors: Professor Yves Potvin and Associate Professor Johan Wesseloo, Australian Centre for Geomechanics, The University of Western Australia

Mine-induced seismicity is the natural response of the rock mass to underground excavation. It corresponds to rock fracturing caused by high induced stresses and, when not controlled properly, it generates hazards and economical losses to underground projects.

The seismicity manifests itself through different physical mechanisms. In particular, the re-activation or slip of existing faults is the most hazardous and difficult to manage mechanism. This is because of the potentially high magnitude that can be generated by these seismic events, the occasional lack of relations between seismicity and blast times and by the potentially large distance between the seismic event and the blasted zones. This apparent independence between fault slip seismicity and blast imposes a risk to underground excavations that needs to be managed in order to develop safe and sustainable underground projects.

Most numerical methods used to estimate fault slip seismic potential provide a qualitative solution to the seismic potential, indicating periods of higher or lower seismicity, but hardly defining the magnitude of the seismic events that can be obtained.

This thesis documents research work on fault slip mechanism and develops a method to explicitly include fault heterogeneities into numerical analysis, providing a tool to calculate maximum expected magnitudes under a probabilistic scheme. These results not only provide the variation of seismic potential over time but also the probability of a large event occurring in a specific mining sequence.

For more details, please visit doi.org/10.26182/5f1f9690635f2

Dr Aida Carolina Borges Carneiro
PhD Civil, Environmental and Mining Engineering
2020

Thesis title: Evaluating alternative tailings management strategies is more than just Net Present Value

Supervisors: Professor Andy Fourie and Professor Richard Durham, The University of Western Australia

The vast amount of waste produced by the mining industry, of which a large proportion is tailings, represents a significant barrier to sustainability. In light of the pressures for change, and as the stewardship of tailings comes under increasing scrutiny, decision makers are looking at the benefits of alternative tailings disposal methods and are urged to adopt a more holistic approach towards the selection of a tailings management option that ensures sound economic, environmental and social performance is achieved.

To this end, life cycle methodologies, such as life cycle costing (LCC) and life cycle assessment (LCA) can be used, and offer valuable concepts for moving towards sustainability.

Against this background, the overarching objectives of the research presented in this thesis was to (i) investigate the life cycle costs associated with various tailings management options and contribute to improving cost data quality and availability in the public domain, (ii) assess the life cycle environmental impacts of alternative tailings disposal methods and contribute to improving mining LCA data quality and availability in the literature, and (iii) develop a methodology to evaluate tailings management options based on a more holistic approach. For these purposes, a hypothetical case involving the management of gold tailings in Western Australia was studied, for which three conceptual project designs were developed for disposing the tailings as a slurry, as thickened, and as filtered tailings. It is important to note that the proposed methodology is robust and capable of being adapted and applied to other cases with equal relevance.

For more details, please visit doi.org/10.26182/5ec3548a81770

Dr Ali Keneti
PhD Civil Engineering
2020

Thesis title: Consideration of rock mass violent failure mechanisms around underground excavations

Supervisors: Dr Roger Dargaville, Monash University and Professor Bre-Anne Sainsbury, formerly Monash University, now Deakin University

This research investigates strainburst failure (as one of the main types of rock mass violent failure mechanism) and the associated risk for underground excavations.

Throughout reviewing selected case study data from around the world, in situ conditions leading to rockburst events in a macro (drive)-scale were identified. The main contributing factors include unfavourable states of stresses, geometry of the excavation (its size and orientation in relation to principal stresses) and the rate and direction of advance. Factors also included unfavourable rock mass characteristics, including mineralogy, contrast in geomechanical properties, and presence of geological intensifiers.

In the second phase, failure mechanisms on a micro-scale were studied. To do this, igneous rock fragments from a strainburst event site were studied under a Scanning Electron Microscope (SEM) in order to characterise their surface features and allow interpretation of the failure/ fracture propagation mechanisms. SEM image analysis indicated that anisotropy, a contrast in geomechanical properties, and adverse effects of the geometry and contact patterns present at the micro-scale as they do at the large scale. It is proposed that these micro-scale features can lead to anisotropic material behaviour and stress concentrations that manifest as strainburst events.

The technique discussed is robust to consider newly available data by site observations to re-evaluate the risk or to assist in microseismic data interpretation.

For more details, please visit bridges. monash.edu/articles/thesis/Consideration_of_Rock_Mass_ Violent_Failure_Mechanisms_around_Underground_ Excavations/12917789

Dr Hongyu Wang
PhD Civil Engineering
2019

Thesis title: The effect of intermediate principal stress on 3D crack growth in compression and rock failure

Supervisors: Professor Phil Dight, Australian Centre for Geomechanics, The University of Western Australia, Professor Arcady Dyskin, The University of Western Australia, Dr Ariel Hsieh, Australian Centre for Geomechanics, The University of Western Australia, Professor Elena Pasternak, The University of Western Australia

Rock is often a brittle heterogeneous material containing a multitude of pre-existing internal cracks, voids and weak micro-surfaces. In compression, these imperfections work as sources of initiation and growth of what is termed ‘wing cracks’. Under load, the growth of wing cracks is believed to cause ultimate failure of rocks. Understanding rock failure behaviour near the excavation boundary is critical for ensuring safety of tunnelling and underground mining, as this can lead to the hazardous condition known as strainbursting.

This research investigates three-dimensional (3D) crack growth using biaxial compression testing with various load ratios of frozen resin samples, containing 3D internal defects of different types. The triggering nature of the intermediate principal stress was discovered. When its magnitude is above a certain threshold (5–8.5% of the major principal stress), it changes the mechanism of propagation of real 3D cracks, allowing them to grow extensively to the sizes causing catastrophic rock failure. This phenomenon is confirmed by numerical studies using the finite element method (FEM).

The research findings highlight the role of the intermediate principal stress. While not participating in the classical failure criteria, it is crucial in that it is capable of changing the mechanics of brittle fracturing in compression. This concept provides an insight into the mechanisms of rock failure in compression and will enable building models for the successful monitoring and prediction of dangerous rock failures.

For more details, please visit doi.org/10.26182/5ee02cd4192e9

Dr Michele Salvoni
PhD Civil and Resource Engineering
2017

Thesis title: Rock damage assessment in a large unstable slope from microseismic monitoring – MMG Century Mine case study

Supervisors: Professor Phil Dight, Australian Centre for Geomechanics; Professor Arcady Dyskin, The University of Western Australia Movements, instability and failures in open pit mines can pose important geotechnical problems, leading to major impacts on the safety of personnel and the mining operations. In particular, large slope-scale rockslides represent a significant challenge, as these types of instabilities require accurate observations and monitoring. However, in many cases engineers can only rely on surface displacements for their interpretation of the failure mechanism because there is no information on the extension of the deformation into the slope. More recently, several attempts have been made to monitor the volume of rock of unstable slope in open pit and natural slopes, using the microseismic technique. Nevertheless, the link between ground deformations, failure mechanism and microseismic data was rarely addressed in the details of these studies.

In this paper, a case study of the SW Wall instability at Century mine (Queensland, Australia) is discussed. Since 2009, the pit wall has been affected by several multibatter failures, associated with continuous bedding planes. Geotechnical investigations, supported by numerical modelling, have interpreted those instabilities as potential development of deep-seated failure. Consequently, in early 2013, the slope angle at the base of the slope was reduced and a buttress was left to avoid further progression of the instability into the lower section of the wall. Slope performance while mining has been primarily managed through surface monitoring (geodetic prisms and groundbased radar). However, as there were still concerns, a microseismic monitoring program was proposed by MMG geotechnical personnel and subsequently implemented….

Dr Daniel Cumming-Potvin
PhD Civil and Resource Engineering
2018

Thesis title: An extended conceptual model of caving mechanics

Supervisors/Advisors: Associate Professor Johan Wesseloo, Australian Centre for Geomechanics; Professor Richard Durham, The University of Western Australia; Professor Dick Stacey (external advisor), University of the Witwatersrand

The Duplancic conceptual model is the industry accepted model of caving and is the framework within which most results from numerical modelling and cave monitoring are interpreted. The Duplancic conceptual model implies that the damage ahead of the cave back decreases continuously with increasing distance from the cave surface. A review of literature revealed a number of studies which indicated that the damage ahead of the cave may be discontinuous. These studies came from a variety of sources including site observations, numerical modelling, physical modelling and analysis of microseismicity.

A physical modelling programme was undertaken to investigate the fracturing and propagation of the cave. The testing was performed at the University of Pretoria’s Geotechnical Centrifuge facility to correctly account for the body forces of the problem. The experiments were two-dimensional to allow for visual observations of the failure process. The results showed the cave propagating through a series of fractures oriented parallel to the cave surface. The cave back progressed vertically via ‘jumps’ to the next successive parallel fracture. This caving mechanism is termed ‘fracture banding’. Field monitoring data from three mines was used to confirm the existence of the damage discontinuity ahead of the cave.

The microseismicity from three mines was examined and multiple examples of discontinuity were found. Bands of events alternated with areas where few events were observed, indicating failure in a similar manner to the parallel fracturing of the physical model. Videos of open hole dipping from two mines were reviewed and the location of significant shears, dislocations and the cave back were recorded…

Dr David Reid
PhD
2017

Thesis title: Laboratory and centrifuge assessment of the geotechnical effects of polymer treatment

Supervisor: Professor Andy Fourie, The University of Western Australia

A laboratory and centrifuge study was carried out to assess the effects of polymer treatment (PT) on the geotechnical behaviour of a low plasticity slurry, when compared to an untreated material. The study indicated that PT resulted in lower densities at a given vertical effective stress, higher rates of consolidation, increased permeability, a modified critical state line, increased undrained strength at a given density, and had negligible effect on cyclic resistance and post-cyclic strength. Centrifuge testing confirmed the lower densities and higher rates of consolidation of PT material, while giving uncertain strength results from penetrometer testing.

Dr Kyle Woodward
PhD Civil and Resource Engineering
2015

Thesis title: Identification and delineation of mining induced seismic responses

Supervisors: Professor Yves Potvin and Dr Johan Wesseloo, Australian Centre for Geomechanics

The phenomenon of seismicity is observed in many hard rock underground mines around the world. Seismic events pose a significant geotechnical challenge due to their potential to damage underground excavations. This translates to a risk to mining personnel, equipment, and infrastructure. The management of seismic hazard is an essential component in minimising the political, social, and economic risks associated with the mining industry. The effective management of seismic hazard is underpinned by a sufficient understanding of the magnitude, spatial, and temporal characteristics of seismicity.

The numerous interrelated factors that influence seismic event occurrence make it difficult to establish cause and effect correlations, and increase the importance of being able to quantify the spatial and temporal characteristics of seismicity. Developing the methods used to assess seismic characteristics improves the management of seismic hazard through an enhanced understanding of rock mass responses to mining and enables the quantification of seismic hazard. This thesis contributes a method of assessing spatial and temporal characteristics of seismicity through the identification and delineation of individual seismic responses. The methods and concepts established in this thesis enable improvements to be made to the management of seismic hazard. 

View at The University of Western Australia’s Research Repository: https://research-repository.uwa.edu.au/en/publications/identification-and-delineation-of-mining-induced-seismic-response

Dr Daniel Heal
PhD Civil and Resource Engineering
2010

Thesis title: Observations and analysis of incidences of rockburst damage in underground mines

Supervisor: Professor Yves Potvin, Australian Centre for Geomechanics, The University of Western Australia

Dr Marty Hudyma
PhD Civil and Resource Engineering
2008

Thesis title: Analysis and interpretation of clusters of seismic events in mines

Supervisor: Professor Yves Potvin, Australian Centre for Geomechanics, The University of Western Australia

Dr John Albrecht
PhD Civil and Resource Engineering
2005

Thesis title: Delineating rockburst damage to underground development subjected to seismic loading

Supervisor: Professor Yves Potvin, Australian Centre for Geomechanics, The University of Western Australia

Dr Michelle Owen
PhD Civil Engineering
2004

Thesis title: Exposure model – detailed profiling quantification of the exposure of personnel to geotechnical hazards in underground mines

Supervisors: Professor Yves Potvin, Australian Centre for Geomechanics, The University of Western Australia; Dr Barry Brady

Dr Paul Duplancic
PhD Civil and Resource Engineering
2002

Thesis title: Characterisation of caving mechanisms through analysis of stress and seismicity