This paper presents the results of bi-directional load cell testing conducted on two pre-production 1.5-meter diameter bored concrete piles as part of the METRONET Byford Rail Extension project in Perth. The testing aimed to assess the geotechnical capacity, load-displacement response, and shaft friction parameters of the piles within colluvial and alluvial deposits near the Darling Scarp. The information obtained from the pre-production testing has been valuable in supporting the foundation design of a 46-span rail viaduct structure, which will comprise a total of 131 1.8-meter diameter piles.

Bi-directional load cell testing involves the installation of load cells within the piles, allowing for the direct measurement of load distribution along the pile length and determination of its ultimate pile capacity. The load-displacement response obtained through the testing, provides insights into the pile-soil interaction and facilitates the establishment of shaft friction parameters. In Perth, bi-directional load cell testing of large diameter piles is not yet common practice.

Increased utilization of bi-directional load cell testing in large diameter pre-production piles, may provide economic value to future projects. The insights gained from the testing enhance the accuracy of shaft friction design parameters and contribute to improved safety in design, ensuring reliable and cost-effective foundation solutions. The successful application of bi-directional load cell testing in this study, emphasizes its potential as a valuable tool for geotechnical engineering practices in Perth and beyond.

Around 80% of Australian residents live near its beautiful coastline. Unfortunately, coastal land and infrastructure are at a greater risk than ever due to the unprecedented increase in coastal erosion rates driven by the climate change-induced rise in the mean sea level (MSL). Traditional erosion control measures, such as mechanical compaction, cement-based structures, synthetic binders, and soil replenishment, struggle to meet modern sustainability demands. In contrast, natural beach rocks exhibit remarkable resistance to erosion, formed through complex processes involving nearshore microbial life. The nearshore microbial life produces macromolecules of the polymeric substances that capture the metals and precipitate stable crystal units upon the availability of nutrients under specific conditions, forming erosion-resistant beach rocks. Such beach rocks in nature take years to decades to form through numerous complex geochemical pathways. It is not only critical to unpin these geochemical reactions but also to engineer them to expedite the rates of formation.

This study explores the microbial ureolytic pathway of crystal precipitation, often termed biocementation, and its potential for coastal erosion mitigation. In this study, the scaled wave action was simulated in a flume, and the biopolymer-biocement composite treatment was compared for its performance against erosion control with the trending plain biocement and biopolymer treatments. The study also devised a biopolymer-biocement composite mimicking the natural phenomena and compared it with the plain biocement and plain biopolymer routes of soil improvement. The cost and environmental impact of the treatments are accounted for.
Findings indicate that plain biocementation leads to brittle failure under coastal waves, and biopolymer protection wears off quickly upon hydration. Both treatments only delay erosion beyond a certain wave energy threshold. In contrast, the biopolymer-biocement composite provides dual protection: dampening wave forces with the viscous biopolymer matrix and offering binding strength with brittle biocement. This composite treatment costs about half as much as an equally erosion-resistant plain biocemented sample and produces 50% less ammonia. This study elucidates the resilience mechanisms of beach rocks and proposes a promising methodology for field-scale testing. The research contributes to geotechnical and geoenvironmental engineering by offering nature-inspired solutions for coastal infrastructure conservation.

Discontinuities such as bedding planes, fractures (joints), faults and shear zones, normally exist in porous geological media. These discontinuities have less shear and tensile strength, and depending on their hydraulic conductivity, they may facilitate fluid flow (which happens more commonly) or act as barriers to the seepage. The discontinuities can typically be idealised by two surfaces due to their negligible volume as compared to the domain. It is common for other materials to fill the spaces between the faces of the discontinuities. The existence of the discontinuities plays a fundamental role in the analysis of the fluid flow and deformation of porous media. The ability to accurately dealing with fractures in porous media is of interest to several fields related to geotechnical applications and subsurface resources such as reservoir engineering, aquifers performance, geothermal energy extraction, among others.

Reliable and predictable installation of suction bucket jacket foundations is critical for the operation of offshore wind turbines, but may be challenging in soil stratigraphies where penetration resistance is high, as there are limits to achievable suction pressure due to cavitation and buckling of relatively thin skirted buckets. Installation mitigation measures are often considered to overcome these challenges and optimise the suction buckets. However, the understanding of mitigation measures is limited.

Pressure cycling the suction bucket involves by reversing the pump during installation, aiming to reduce the required suction. Pressure cycling as a potential strategy to overcome installation challenges and limit the required suction is investigated, which may also present opportunity for optimised suction bucket design. The cycling can be termed as 1. one-way whereby only the suction is reduced (but not reversed) in each cycle and 2. two-way whereby the bucket is moved up in each cycle before penetrating further. The pressure cycling strategy was examined in the centrifuge samples – prepared from uniform clay, sand, clay layer over sand, and a sandwiched clay layer sample, complemented with data from field trial installations in sand and layered soils in an offshore windfarm – to investigate the effectiveness, factors affecting, and effect of the pressure cycling strategy.

Of the pressure cyclic installations, one-way cycling of the bucket in the centrifuge and field was found to be ineffective in both sand and clay, as expected. Two-way cycling of the bucket in clay significantly reduced the required suction after completely remoulding the soil at the interface with monotonic installation. This was due to the reduction in lateral stress on the skirt wall of the bucket where the mobilised friction was lower than remoulded shear strength due to dissipation of the excess pore water pressure. The two-way pressure cycling was found to be ineffective in sand due to alternating flow in the soil plug, whereas in layered soil, the strategy was effective and reduced the suction significantly where 1. the thickness and strength of clay is significant 2. the plug lift suction was not attained before the cycling. The existing prediction models for (monotonic) suction bucket installation were extended by incorporating cyclic CPT observations to predict the pressure cyclic installation in clay and sand. Results that obtained were observed to reasonably agree with the pressure cyclic installation in uniform and layered soils.

Pressure cyclic installation has the potential to affect the extraction resistance, hence this was also analysed. The pressure cycled suction buckets were extracted at different times after the installation in different states of sand and in over consolidated clays. In clay, the immediate extraction resistance after pressure cycling was about 50% lower than the extraction after monotonic installation. However, with a delay of about 90 days, the capacity is two times that immediately after installation without pressure cycling. In sand, the immediate capacity after pressure cyclic installation was about 10% lower than the capacity measured after monotonic installation. However, with a delay of 4 days in dense sand, the capacity of the pressure cyclically installed bucket was observed to be more than the immediate capacity of a suction bucket installed without pressure cycling.