28th GFWA Prize in Geomechanics

While piles have been used extensively throughout history to support many structures, there is still uncertainty about their changes in axial capacity over time. Many studies have previously attempted to address this change in capacity, and although it has been established that it varies between different soils, there is no clear understanding of the mechanisms. This thesis focuses on driven piles in clay, and is a continuation of a previous project where small-scale (D = 12.5mm) piles in clay “chambers” are being tested to quantify the increases in their capacity. Four types of clays are tested–Kaolin, Onsøy, Brunei and Bayswater–and results of these chamber tests (in particular, the ageing factor D10) will be compared with previous field tests as well as current field tests in Bayswater, Perth.

Most of the energy production on a global scale comes from fossil fuels. This form of energy consumption causes an increasing burden on the economy and the environment. Globally, these effects on the environment have been observed through climate change, posing a greater need for renewable energy technology. A promising technology in the renewable energy field is the energy pile used to heat and cool buildings. Not only can the concrete piles serve to provide structural purposes for the building, but also can be used as heat exchangers between the building and the ground. During the hot seasons, the ambient temperature is warm whereas the ground temperature becomes cooler at greater depths below the ground surface. Conversely, the ground temperature is warmer during the cold seasons compared to the ambient temperature. As a result, the energy pile heat exchanger can transfer the heat from the building to the ground during hot seasons, and transfer the heat from the ground to the building during cool seasons. The concrete material used for the piles is an ideal medium to absorb and conduct thermal energy. Despite this, the ground soil must also have a high thermal conductivity to transfer heat efficiently between the pile and the ground. In this research, bio-cementation through microbially induced calcite precipitation (MICP) has been used to improve the thermal conductivity of the soil surrounding energy piles. Bio-cementation results in the precipitation of calcite crystals which binds the soil particles together, creating a bridge for heat energy to be transported. To improve the formation of these bridges, different cementation solutions via MICP have been used with varying amounts of Calcium Chloride and Magnesium Chloride. It was found that using 100% Calcium Chloride in the MICP cementation solution results in the most optimum thermal conductivity. In an attempt to improve the thermal conductivity of bio-cemented soil, further testing was then conducted to observe the effects of adding varying quantities of fibres, which are normally used to improve the mechanical properties of the soil, to bio-cemented soil including glass fibre, steel fibre, polyethylene fibre and carbon fibre.

The rate of recent tailings dam failures has brought the design of these facilities into the spotlight, and in particular the properties of the tailings they are made from. To determine the stress conditions which cause failure and the nature of failure, the lab scale direct simple shear device was used. The tests were performed under constant shear drained conditions on a range of materials. The results showed silty sand materials failing suddenly, with minimal amounts of strain developing prior to failure, while clay like materials failed much slower, with strains developing slowly throughout the experiment.

Recently there has been a paradigm shift towards putting in more effort and emphasis in sourcing for sustainable alternatives for ground improvement applications. Such sustainable alternatives would involve adopting environmentally friendly natural materials as part of the ground improvement techniques with minimal impact on the quality of the environment. Thus, the aim of the research project is to investigate the effect of sugarcane bagasse ash (SBA) as an admixture on the mechanical behaviour of soil bentonite slurry cut-off walls.

Slurry Walls are low permeability vertical barrier system typically used for groundwater and contamination control and SBA is a natural by-product from the combustion of sugar industry which can be utilised in as an environmentally friendly admixture for soil stabilisation. The mechanical properties of the amended backfill that has been investigated are workability (Slump Test), hydraulic conductivity (Falling Head Test), compressibility (One dimensional consolidation test) and SEM analysis to investigate the microstructural composition of SBA particles. Results collected from the tests would investigate the effect of adding SBA admixture to SB Slurry Walls and whether if it helps to improve the overall mechanical properties – ie, to be able to achieve low permeability range and compressibility range to minimise differential movements. Thus, determining the suitability of SBA as an admixture option for the stabilisation of slurry cut-off walls.