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Tunnelling Boom In Australia: Prospect Of Educating Tunnel Engineers
Australia is in the middle of an infrastructure boom. Nine out of twelve of Australia’s current largest infrastructure projects are tunnelling projects. The value of the planned underground projects in Sydney and Melbourne is over $40 billion. The avoidable social costs of congestion are estimated to increase in all eight Australian capital cities by 2030. To address this problem, the focus is on the development of underground space. Extensive state and federal government infrastructure programs have increased public investment in civil infrastructure programs and are expected to drive growth in the sector over the next 20 years. Despite the number of international companies joining the local market, the issue of recruiting skilled workforce is significant. The professional skills shortage within the local tunnel consulting industry is a major threat to Australia’s underground projects. This paper investigates the benefits of offering tertiary degrees in Australia on tunnelling and development of underground space-related topics. Requirements to establish a tunnel engineering degree with the main focus on current industry skills and knowledge requirements are presented.
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Re-engineering Old Foundations For A New Structure – Greenland Centre
The concept of reusing existing building elements during site redevelopment within urban environments is gaining momentum. With ever-increasing pressure from modern society for engineers to focus on sustainable solutions, the industry is also beginning to recognise other benefits from maintaining, improving or re-engineering existing structures. These include fast tracking decommissioning and construction programs while at the same time saving on demolition and waste disposal costs. Along with the various challenges, such as testing, confirming the integrity of older structures and understanding foundation conditions, one of the major obstacles to effectively reusing existing building elements is the often complex re-engineering required to design and prove a solution is viable. In urban areas where space is at a premium, usually the ‘bigger is better’ approach prevails, and existing columns and footings will be required to support higher applied loads than they were originally designed to carry.
The Greenland Centre in Sydney’s CBD is an example where the re-use of existing structural elements has been successfully adopted, by re-engineering of footing arrangements. The steel portal frame and piled footings of an old 27 storey building were retained, with the piles augmented with new pad footings to increase the footing bearing capacity to support a significantly higher 67 storey building. Finite element analysis was conducted to assess various footing arrangements to optimise the final design so that serviceability limits for the new structure could be achieved. Settlement monitoring and stress, strain measurements have been conducted through construction, with results so far shown to be within the limits predicted in the initial modelling process.
The paper discusses the general issues involved in the reuse of foundations and present results from the Greenland Centre to illustrate the advantages and challenges of reusing existing foundation elements.
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Volume 37, Number 4 — Other
Table of contents, editorial and chairman’s column for Australian Geomechanics, Volume 37, Number 4.
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Failure Processes of Rainfall-Induced Flow Slides Using A Large Scale Model Slope
Flow slides are considered to be universal type landslides as such events are commonly reported in various geological and geotechnical conditions, predominantly attributing mobilised soil flows capable of advancing longer distances at higher speeds. Thus, flow slides are classified as one of the most disastrous landslides. Hence the prior identification of failure mechanism of flow slides is vital in mitigating adverse impacts. A large-scale instrumented model slope was employed to study the failure processes of rainfall-induced flow slides. The model slope was instrumented with pore- water pressure transducers, volumetric water content sensors, digital cameras, and linear variable differential transducers to measure surface displacements. The test was performed on Tsukuba river sand (D50 = 0.55 mm), and the failure behaviour was analysed. The analysis highlighted that the higher moisture contents present in loose soils result in a significant rise in pore-water pressure reducing the shear strength of soil mass. Thus, a sliding surface is generated in the upper slope, and failed slope mass compresses the lower slopes, triggering rapid and catastrophic flow slides. The study concludes that the measurement of pore-water pressure, moisture content, surface displacement, and surface deformation velocities provide notable precursors to rapid flow slides, mitigating adverse impacts of flow slides.
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Some Relationships Between Shrink-swell Index, Liquid Limit, Plasticity Index, Activity And Free Swell Index
Many laboratory experimental methods have been proposed to measure soil reactivity, some methods leading to direct measurement whilst other methods propose indirect estimations. Reactivity measurements based on plasticity properties appear to be commonly used and preferred over many other methods in the identification of soil expansivity, which may be due to the simplicity and easiness of test procedure. In this study, volume change potentials of several clay soil samples, containing different percentages of montmorillonite clay, are evaluated using shrink-swell index (Iss), indirect estimations based on liquid limit (LL), plasticity index (PI), activity (A) and a new approach based on free swell index (FSI). The analysis of test results presented in this paper shows that FSI could be a satisfactory indicator for the classification of the volume change potential of clayey soils.
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Emergency Embankment Stabilisation Works, Pacific Highway, Eungai Creek
The Pacific Highway stretches 900 km from Sydney to Brisbane and has been progressively upgraded and realigned over the last 30 years to reduce travel times and improve safety to road users. The northbound embankment of the highway near Eungai Creek was constructed around 1991 and less than a decade later the highway was upgraded with a second embankment to provide dual carriageway conditions.
Cracking of the northbound pavement occurred as early as 2007. Sealing of the cracks was undertaken, though the cracking continued. In 2017 geotechnical site investigations were undertaken and instrumentation installed in the northbound embankment. Substantial displacement between the concrete pipe sections which formed the culverts beneath the embankment was observed. Monitoring over the subsequent four years indicated relatively minor movement of the toe and crest of the embankment.
Site investigations indicated variable subsurface conditions, with localised zones of firm alluvium within and beyond the embankment footprint, underlain by residual soil and phyllite bedrock. Standpipe piezometers consistently indicated significant artesian groundwater pressures.
A review of the site was undertaken in early 2021 to identify potential deformation and failure mechanisms and provide concept options for the permanent stabilisation of the northbound embankment. Additional investigation, detailed field mapping and survey were undertaken to gain a better understanding of the site and assess whether further deterioration had occurred over recent years. Observed conditions were significantly worse than anticipated such that urgent maintenance and repair works were initiated immediately.
Shortly after completion of the field work, wet weather triggered an embankment failure which required partial closure of the highway. Significant contributors to the failure were the poor condition of the surface drainage which led to saturation and softening of the embankment fill, and artesian groundwater conditions that weakened the foundation soils.
Emergency stabilisation measures were developed for rapid implementation and to allow for the future permanent works. These works comprised the construction of soldier piles along the embankment crest and placement of a rockfill toe berm.
Construction of the emergency stabilisation works has progressed smoothly and allowed the highway to fully reopen and continue to provide its key function as an essential transport artery connecting Australia’s eastern seaboard.