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New tools and directions in offshore site investigation
The offshore environment provides a number of challenges for geotechnical site investigation, among which are the high costs associated with vessel day-rates and an associated need for equipment reliability. New oil and gas developments are increasingly remote, in terms of distance from land and water depths, and seabed conditions often comprise extremely soft sediments within the depth range relevant for infrastructure such as pipelines, subsea foundations and anchoring systems. These factors have combined to provide a gradual shift away from ship-based drilling tools towards seabed-based robotic equipment for drilling, sampling and in situ penetrometer testing. In parallel, a variety of free-fall samplers and penetrometers have been developed, particularly for preliminary investigations to characterise the seabed sediments. An important aspect of the soil response is the extent to which it may be considered drained or undrained during particular operational events. For example, design calculations for the stability and operational movements of pipelines are relatively sensitive to the consolidation response of the soil. Even interpretation of penetrometer data requires an assumption with respect to the degree of consolidation occurring during penetration. The paper provides an overview of recent developments in offshore site investigation equipment, and then focuses on evaluation of consolidation properties.
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Geotechnical Challenges And Lessons Learnt From Bolivia Hill Upgrade Project
This paper presents a case study of geotechnical design and construction challenges of bridge foundations and approaches in a hilly granite formation in northern New South Wales, Australia. Firstly, the geological formation and existing cut slope conditions which have high risks of rock fall is described. The detailed design was based on the available geotechnical information and assumed construction methodology. Reinforced concrete cantilever retaining walls founded on mass concrete were adopted for the bridge southern approach to resolve constructability issues over hilly terrain. Slope treatments using a rock fall fence together with individual boulder stabilisation or removal were also considered. It was found during construction that the actual ground conditions were different to that originally inferred and modifications to pad footing designs were deemed necessary. Additional investigations were undertaken, and the subsurface ground models updated to inform the revised design. For the northern bridge abutment foundation, a piled foundation was introduced to optimise the design with due consideration of temporary piling platform and access along a new geotextile reinforced approach embankment. The revised design was developed in close collaboration with the Contractor and the Principal. The foundation design of Pier 2 was revised using micro-piles to address the presence of a weak rock layer intrusion. In the end, key lessons learnt from this challenging project have been summarised for future project references.
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A three dimensional model for the evaluation of resilient modulus of unbound granular materials
Resilient modulus is an important property that controls the performance of the subgrade and granular materials under repeated loading and is required for mechanistic-empirical pavement design. Technically, resilient modulus can be obtained from the repeated load triaxial test in the laboratory. Due to the time-consuming, complicated and expensive nature of the test, it is common to estimate the resilient modulus from other simpler approaches. Due to the discontinuous nature of the unbound granular materials, discrete element method has been used recently to predict resilient modulus for granular materials. It is clearly necessary that the proposed model be verified by comparing with the experimental results and there appears to be no validation against the experimental resilient modulus for these reported models. In this study, the laboratory repeated load triaxial test was carried out for one of the popular pavement materials used in Victoria, 20 mm class 1 crushed rock. The resilient modulus results were then compared with the result from the model. By restricting the rotational motion to simulate the interlocking effect of the particles, it was observed that the resilient behaviour from the model and the experimental test is almost identical.
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SA-NT Symposium 2020
Geotechnical aspects of renewable energy
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Building Dewatering In The Botany Sands And The Aquifer Interference Policy
The Department of Primary Industries (DPI) Water is responsible for the management of groundwater across NSW. The management of groundwater extraction impacts including those associated with dewatering for building developments which predominate in Sydney within the Botany Sands Groundwater Source is one of the primary roles of the agency. There are an increasing number of residential and commercial developments that need to accommodate construction below the water table for basements and other functions. These have to be built in a way that mitigates adverse impacts on other building developments or other groundwater users, sensitive ecosystems or structures. Parts of Sydney’s development are remarkably high-density and construction must be well planned to prevent such effects as unintentional groundwater mounding, obstruction of natural flows by the completed building, and potential basement inundation caused by periodic elevated water levels.
In order to demonstrate sustainable development principles, the Aquifer Interference Policy (AIP) requires the proponent to account for all groundwater take during both construction and occupation. This may include the proponent taking measures to avoid or prevent the take of groundwater where possible and include mitigation or avoidance strategies to reduce take of water. The proponent should demonstrate that adequate arrangements will be in place to ensure the minimal impact considerations of the AIP are met. The information needed for assessments of the groundwater impacts of proposed developments under the AIP requires a comprehensive evaluation of the hydrogeological environment. This information is required to allow DPI Water to balance the management of the groundwater resource with facilitating sustainable development.
In some instances, the use of secant piled cut-off walls to enclose an entire site may not be the optimum solution without other engineering measures because the walls effectively work like dams to groundwater flow. Alternate methods of construction might be more appropriate and facilitate flows both beneath and around structures. The dewatering considerations are not limited to individual properties as there are significant interferences from major infrastructure projects, as well as other nearby concurrent building developments, which need to be accommodated at the same time. This paper discusses requirements for proponents and their consultants that relate to the assessment of dewatering proposals in Sydney’s Botany Sands Groundwater Source, which is part of the Greater Metropolitan Region Water Sharing Plan area.
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The Influence Of Bagasse Fly Ash Particle Size In Controlling Expansive Soils In Combination With Hydrated Lime
Sugarcane is the second largest export crop in Australia. Industrial production of sugar, from sugarcane, results in bagasse fly ash (BFA), a by-product from the cogeneration in sugar milling operations that generate electricity by steam. The chemical and physical properties of BFA highlight its potential as a promising pozzolan for the stabilization of expansive soils, due primarily to a high content and surface area of the amorphous silicate found in BFA. Silicate in bagasse fly ash reacts extensively with calcium hydrate in lime to produce hydrated products via pozzolanic reactions, this results in a hardening of the material to which BFA and lime have been added. This reaction has been studied to be a function of the size of BFA particles and conditions of the curing process.
This study explored the variables that influence the reaction and evaluated shrinkage and compressive strength of the mixtures to which bagasse fly ash, in the form of different particle size distributions, and hydrated lime are added. The maximum BFA particles sizes considered within this study include 75, 150 and 425 μm; curing times of 7 and 28 days are also explored. A suite of testing, including Atterberg limits, linear shrinkage (LS), and unconfined compressive strength (UCS) tests were completed on the prepared mixtures. The findings indicate that bagasse fly ash with a maximum size of 425 μm yields a higher UCS and lower LS, compared to finer BFA particle mixtures. The ash with a maximum particle size of 425-μm also improves the ductility of treated soils and accelerates their strength gain, compared to soil- lime stabilized samples. The results of the study build towards a better understanding of BFA, and the ways in which such a material maybe engineered to replace concrete in road work projects and other applications involving expansive soils.
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Thornthwaite Moisture Index And Climate Zones In The Northern Territory
The Thornthwaite Moisture Index (TMI) is an established climate parameter for geotechnical engineers to categorise a site and enable estimation of seasonal ground movements associated with soil moisture changes. TMI assessment and mapping for the Northern Territory are presented, using the TMI calculation method commonly used for similar recent studies elsewhere in Australia. The assessment included the analysis of 17 sites within the Northern Territory and one site in Queensland which has enabled development of Climate Zone classifications. Climate data was obtained from the Australian Bureau of Meteorology to calculate the TMI on a ‘year by year’ basis over a target period of 29 years (1990 to 2019). Related work in Queensland (Fox 2002) and Western Australia (Hu et al, 2016) has guided the development of the Northern Territory Climate Zone Map. Further work is required to characterise the soil moisture behaviour in arid zones. A general lack of guidance in AS2870 (2011) for arid areas, including much of the Northern Territory, could be addressed with further research and development.
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Smarter Transport Infrastructure Embracing Granular Waste And Recycled Rubber – A Circular Economy Perspective
Transport infrastructure in Australia is predominantly composed of compacted granular materials used as base, sub-base, ballast, sub-ballast and capping layers for roads and railways. Replacing traditional natural rockfill with granular wastes and other forms of recycled materials such as rubber is becoming increasingly crucial in a circular economy seeking reduced capital and maintenance costs for sustainable infrastructure. Recent extension of ports and reclamation of low- lying land has also considered compacted granular waste as an alternative structural fill. In Australia, ballasted rail tracks offer the most common mode of transportation including both commuter and freight networks. However, ballast and other granulates progressively degrade under dynamic and impact loads. The degree of degradation will be accelerated due to the growing demand for elevated speeds of passenger trains and heavy axle freight trains. It is, therefore, necessary to develop novel and cost-effective technologies to enhance the longevity and performance of transport infrastructure through amended design and construction. Over the past two decades, numerous studies have been conducted under the leadership of 1st Author to investigate the ability of recycled rubber mats/pads, as well as waste tyre cells and granulated rubber to improve the stability of substructure materials for both railways and roads. This keynote paper presents an overview of these novel methods and materials based on comprehensive laboratory tests using iconic testing facilities. Test results from comprehensive laboratory tests and field studies have indicated that the use of energy-absorbing rubber inclusions can substantially improve overall stability. The findings reflect the following: (i) the inclusion of recycled- rubber based synthetic energy absorbing layers significantly attenuates the magnitude of the dynamic load with depth and particle breakage, (ii) an alternative solution by using coal wash-rubber crumb mixtures as capping layer is also introduced in this study, and the compressibility of the rubber is captured by cyclic compression triaxial tests, (iii) the installation of under ballast mats (UBM) for railways significantly reduces permanent vertical and lateral deformation of the track as well as reducing ballast degradation, (iv) waste tyre cells infilled with granular aggregates effectively increase the stiffness and bearing capacity of the capping layer and assist in mitigating excessive lateral displacement, and (v) field tests indicate geogrids and shock-mats are efficient methods to reduce the substructure displacement and particle breakage. These research outcomes provide promising approaches to transform traditional transport infrastructure design practices to cater for future high axle rolling stock and for enhanced longevity and reduced maintenance of all modes of transport corridors.
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The New UK Contaminated Land Regime
This paper attempts to produce an overview of the new UK contaminated land regime. Detailed consideration is given to a number of aspects of the new regime. The methodology by which it is proposed to implement the regime is discussed, including definitions of terms included in the Act. The concept of the “Appropriate Person” is described, as the definition of the person responsible for the contamination. This regime places renewed emphasis on land owners and local authorities being aware of potentially hazardous sites under their ownership. This in turn requires a much greater level of awareness and understanding of site risk assessment amongst these parties. With this in mind, this paper also describes a new Windows-based application to address the risk assessment of contaminated land, building on the methodology advocated by the Environment Agency. The application has four analysis tiers, and the ongoing development of these tiers is described.
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Working Towards Net Zero Emissions – Role Of Geo-Professionals
The global movement in climate change protection is to work towards Net Zero Emissions by around 2050. Net zero emissions refers to reducing greenhouse gas emissions to zero, or as close to zero as possible and offsetting any remaining emissions (e.g. clean energy projects).
This paper outlines some of the steps geo-professionals should take to understand the project Sustainability and Resilience requirements, and areas where we can influence design and construction to meet or exceed those requirements. Sustainability, in relation to geotechnical and geo-environmental work, is an integrated process that balances the social, environmental and financial aspects of planning, design and construction, while managing risk, safety, quality and durability to acceptable standards. Resilience is the ability to cope with uncertain yet extreme events and climate change that may occur over the life cycle of the infrastructure, and to allow expeditious recovery and reconstitution of critical services with minimum impact to public safety and health, the economy, and national security. Geo-professionals are at the forefront of being able to contribute towards sustainable and resilient infrastructure in areas ranging from innovative investigation techniques, use of alternative sustainable resources, reuse of existing foundations, minimising waste, and efficient designs to minimise construction time and materials. Some examples are given in this paper to illustrate where geotechnical designs have contributed to achieving sustainable outcomes.