31st GFWA Prize in Geomechanics

Damian Sakellaris, Daniel Cumming , Rajal Kerari and Khulekani Sibanda

The GFWA Prize in Geomechanics is a prize sponsored by the engineering firm GFWA Pty Ltd and awarded by the Australian Geomechanics Society (AGS) for the best presentation by a final year student in the area of Geomechanics from universities in Western Australia.



Two students from The University of Western Australia and two students from Curtin University, each present a short (15-minute max) presentation on their work in geomechanics followed by a brief (5-minute max) question session. The presentations are judged by a selection of experienced industry professionals, with the winner being awarded the 31st Annual Prize in Geomechanics.

About the Presenters

Damian Sakellaris The University of Western Australia

The Effects of Global Scour on a Multi-Legged Spudcan Structure

Spudcans are saucer-shaped structures equipped with a small spigot located on the lower surface, which facilitates the penetration of sediment during their application as load-bearing supports. These structures are commonly employed in offshore environments, specifically on the seabed, to secure platforms and facilitate the construction of structures such as wind turbines. Scour is a phenomenon characterized by the disturbance of fluid flow and the subsequent transportation of sediment by the generation of vortices. This process is observed in the vicinity of the spudcans. There are concerns over scour due to its potential to cause additional spudcan penetration into the seafloor and the formation of scour holes around the structure, hence confounding forecasts related to future embedment and stability. The diverse penetration of the spudcans induces the generation of dynamic stresses, primarily through the creation of moments at the base of the spudcan. This phenomenon amplifies the susceptibility of the structure to potential failure.

The existing body of literature has primarily examined the concept of embedment using standalone spudcans, with a particular emphasis on local scouring mechanisms at different initial penetrations. In practical applications, structures will employ the use of multiple legs in order to enhance the stability of the platforms. This introduces a level of complexity, particularly in relation to global scour and orientation patterns in relation to the flow of water. To address the gaps and limitations observed in prior studies using single-legged spudcan structures, this research aims to provide an analysis of scouring mechanisms developed during unidirectional, idealised flow conditions utilising multi-legged spudcan structures. The experiments involve physical models of scaled down structures used in industry. The structures will not be fixed and will interact with the scouring process via lateral and vertical movements to 6 degrees of freedom measuring variations based on factors such as orientation of structure, embedment, and the number of spudcans. The monitoring of changes is conducted through the utilization of digital photography, video, and 3D photogrammetry techniques. These technologies provide the creation of three-dimensional representations of scour profiles and structural tilting, which can be further analysed to assess the penetration of individual spudcans throughout the test. To comprehend the dynamics of sediment movements and the formation of scouring patterns in the vicinity of the spudcans, the acquired data will undergo analysis and visualization using Photocatch and Paraview software tools.

The experiment found that alongside rippling effects, the scour interaction from upstream spudcans to downstream spudcans would accelerate penetration to a degree faster than all other spudcans. This instability would quickly induce tilting in the structure. Additionally rippling and early effects of scour interaction from spudcan would inhibit penetration. To minimise these effects and maintain the greatest stability it was found that minimising downstream spudcans reduces the effect of global scour and to have any downstream spudcans offset so as to delay accelerations in embedment.

Daniel Cumming The University of Western Australia

Digging into the truth behind Pilbara “White Striping”

“Every challenge becomes an opportunity to propel us towards unprecedented excellence”.

The Pilbara region is the Heavy Haul capital of the World and state of the art engineering and maintenance is required to keep the operations running 24 hours per day and 365 days per year. “White Striping” is a predominant feature in the Pilbara Heavy Haul environment, but its behaviour, initiation and failure mechanism is not fully understood.

White Striping is a white coloured traversal stripe, occurring often in a cluster with an oscillating period between each stripe. Within the Pilbara industry on a surface level, it is associated with unhealthy track. The stripes are a result of varying dynamic loads causing a hammering effect on the sleepers and ballast which will abrade at the stripe locations at maximum dynamic load.

White Striping is hypothesised to be closely related to failing formation and therefore, this paper examines the relationships between formation condition and White Striping with a view to proving that White Striping is a symptom and early warning sign of formation failure. The aim of the research endeavours to improve the planning of track renewals for Pilbara Heavy Haul whilst preventing the consequences of formation failures which have a negative impact on the operation.

The study analyses quantified track geometry data, as well as Ground Penetrating Radar (GPR) data and explores its relationship to a developed White Striping track index model, coined the White Striping Index (WSI). With 7,315 data lots (731.5km) of mainline track within the study, several high-level relationships have been generated.

To unlock the truth behind the phenomenon and identify contributing factors that induce white striping, the study employs a data analytic machine learning algorithm, decision tree classification. This approach creates accurate models that provide valuable insights into the underlying mechanisms of white striping. The analysis strongly links White Striping to poor vertical alignment and ballast fouling, two key leading indicators of the phenomena. The implication of the study confirms the hypothesis, linking White Striping to onsetting formation failure and provides a framework for on-site investigations to help inform maintenance strategies in the Pilbara heavy haul environment.

Rajal Kerari School of Civil and Mechanical Engineering, Curtin University

Cost Implications of Estimation of Slurry Tailings Beach Slope on Tailing Dams

This research investigates the financial and operational ramifications of the estimation of slurry tailings beach slopes on tailing dams. A central objective is quantifying discrepancies arising from imprecise beach slope estimations, especially concerning Capital Expenditure (CAPEX) and Operational Expenditure (OPEX) versus initial forecasts. The CAPEX and OPEX implications of these estimations can profoundly influence project budgets. Inaccuracies in Centrally Thickened Discharge (CTD) facilities could amplify costs by up to 400%, whereas Traditional Tailings Impoundments might cause increases of up to 30%. These disparities are largely due to dependencies on critical assumptions related to non-segregating tailings beach slope modelling, efficient thickening processes, adeptly designed pipelines, and extrapolation of in-situ parameters from disturbed samples in CTD storage schemes. Such factors render CTD facilities more susceptible to cost escalations than conventional Perimeter Impoundments. The results underscore that while there are observable trends between estimated and actual values, the strength and significance of these relationships fluctuate. Such variations hint at external influencing factors not covered in this dataset, affecting CAPEX and OPEX figures. The presented study emphasizes the need for refining these estimates to enhance their reliability and accuracy, offering critical insights into mine operators and professionals to optimize cost structures linked to beach slope predictions.

Khulekani Sibanda School of Civil and Mechanical Engineering, Curtin University

Geomechanical Behaviour of Geopolymer Treated Crushed Rock Base

This study explores the potential of using geopolymer mixtures as environmentally friendly alternatives to conventional Hydrated Cement Treated Crushed Rock Base (HCTCRB) for flexible pavement in road construction. Geopolymers, formed by aluminosilicate precursors and alkaline activators, show promise in enhancing material stiffness and resilience while reducing environmental impact. In this study, various testing methods, including unconfined compressive strength and resilient modulus, were conducted to identify optimal geopolymer mixtures. The results indicate that geopolymer-treated base materials can meet performance requirements outlined by Main Rods of Western Australia (MRWA) and potentially offer sustainable solutions for road construction. The study also suggests that geopolymers offer a more predictable response to applied loads compared to HCTCRB.

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