29th GFWA Prize in Geomechanics

Nehal Vaghjiani, Noel Chen Fun Ker, Tony James Ngo and David Gangell

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 at Universities in Western Australia.

Prizes

Presentations

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 29th Annual Prize in Geomechanics.

Speakers

Nehal Vaghjiani University of Western Australia

“Predicting Jack-up Instability due to Local Scour”

Offshore jack-up platforms are typically used for drilling and construction operations in shallow water sites. The platform typically consists of a hull connected to three steel truss legs, which each have a spud-can foundation attached to the bottom. Recently there has been an increase in use of jack-ups for construction of offshore wind farms which exposes the spudcan foundations to an increased risk of scour (sediment erosion). For these applications sandy soil conditions are commonly encountered. This results in only a small amount of initial leg penetration, and the water depth is relatively shallow so that near-seabed water velocities can be sufficient to scour the seabed. If scour is not managed it can cause instability in a platform and result in failure of the platform.

There is currently limited experimental data regarding scour around jack-up structures on sand. Further to this there is also limited information in design guidelines and previous engineering experience is heavily relied upon for design. To research the scour propagation mechanisms, a reduced-scale model jack-up leg assembly was tested in a recirculating flume. The experiments consider both hydrodynamic and geotechnical factors. The model tests measured the settlement rates of the spudcan during scour events and used image analysis to reveal two separate interaction mechanisms.

Noel Chen Fun Ker Curtin University

“The effectiveness of fly ash towards mitigating sulphate attack present in cemented clay”

There has been a paradigm shift towards sourcing for sustainable alternatives for soil stabilization applications. The sustainable alternatives used would involve adopting more sustainable and environmentally friendly method as part of the soil stabilization techniques towards ensuring the quality of environment is preserved. Therefore, the aim of the research project is to investigate the effect of fly ash in mitigating the effects of sulphate attack present in cemented clay. Fly ash is a waste by-product of coal combustion power plant which can be used as an environmentally friendly additive towards achieving soil stabilisation. Sulphate attack usually occurs when the magnesium sulphate present in soils causes the formation of sulphate ions. The presence of sulphate ions would deteriorate on the exposed concrete structure by mean of induced expansion leading to cracking of structure matrix. The testing conducted throughout the research project would be particle size distribution, OMC and MDD (compaction test), compressive strength (Unconfined Compressive Strength test) test and microstructure of fly ash cemented soil sample (SEM test) before and after exposure to sulphate attack which would contribute towards supporting the research topic. The results collected from the testing would further investigate the effectiveness of fly ash towards controlling the effect of sulphate attack present in cemented clay samples. For instance, to achieve highest compressive strength when cemented clay samples subjected to aggressive nature of sulphate attack. Hence, the need to determine the effectiveness of fly ash towards achieving soil stabilisation when expose to sulphate attack.

Tony James Ngo University of Western Australia

“CPT behaviour in sand”

Despite the popularity of the Cone Penetration Test, uncertainty remains regarding aspects such as factors influencing the stress level dependence of qc in a sand of constant relative density, the effect of the mineralogy and the effect of saturation. This research provides greater clarity on these effects by presenting results from a large series of drained cone penetrometer tests performed under controlled conditions in a laboratory pressure chamber. The experiments involved dry and fully saturated silica and carbonate sands placed at a number of relative densities (Dr) and tested at different stress levels and overconsolidation ratios. The observations are compared with existing relationships proposed between qc and Dr and highlight the approximate nature of such relationships and the need for more specific formulations. The study also examines the effects of soil layering on CPT interpretation and foundation design.

David Gangell Curtin University

“Implementation of biochar into road pavements”

Biochar is a high carbon, charcoal-like substance produced through pyrolysis of organic materials. Pyrolysis is an environmentally friendly chemical process that turns unstable decomposing matter into a stable substance. It has a high surface area, high porosity, low bulk density and high-water retention capabilities, making it ideal for agricultural soil amendment. Until now biochar has typically only been used in agriculture, and with its relatively high cost and low demand, it had limited use and inadvertently been underutilised. Through the chemical modification of anionic bitumen, emulsion biochar can now be utilised in road pavement construction. The modified emulsion allows covalent bonding mechanisms to occur between biochar particles and when it is mixed with aggregate, pavement layers are formed. This concept makes the addition of biochar into road pavement viable resulting in environmentally friendly road construction through carbon sequestration. This project investigates the effect biochar properties on the performance of a bitumen stabilised ferricrete basecourse material. Carbon content, particle size and mix percentage are the biochar variables examined through laboratory performance testing of Unconfined Compressive Strength (UCS) and Repeated Load Triaxial (RLT) tests. UCS testing is indicative of the pavement strength, while RLT testing is carried out to determine the resilient modulus which measures the stiffness of the pavement. Main Roads WA Specification and Austroads Guide to Pavement Technology have been used in conjunction with applicable Australian standards to ensure that the project outcomes are relevant and feasible.

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