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Libraries and Learning Services University of Auckland Research Repository, ResearchSpace Version This is the publisher’s version. This version is defined in the NISO recommended practice RP-8-2008 http://www.niso.org/publications/rp/ Suggested Reference Arulrajah, A., Narsilio, G., Kodikara, J., & Orense, R. P. (2015). Key issues in environmental geotechnics: Australia - New Zealand. Environmental Geotechnics, 2(6), 326-330. doi:10.1680/envgeo.14.00005 Copyright Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated. Previously published items are made available in accordance with the copyright policy of the publisher. For more information, see General copyright, Publisher copyright, SHERPA/RoMEO. Environmental Geotechnics Volume 2 Issue EG6 Key issues in environmental geotechnics: Australia–New Zealand Arulrajah, Narsilio, Kodikara and Orense Environmental Geotechnics December 2015 Issue EG6 Pages 326–330 http://dx.doi.org/10.1680/envgeo.14.00005 Paper 14.00005 Received 16/02/2014; accepted 04/09/2014 Publisher online 06/10/2014 Keywords: energy/environment/recycling & reuse of materials ICE Publishing: All rights reserved Key issues in environmental geotechnics: Australia–New Zealand 1 2 Arul Arulrajah PhD, MEngSc, BSc, FIEAust, CPEng Associate Professor, Swinburne University of Technology, Melbourne, Australia Guillermo Narsilio PhD, MScMath, MScCE, CEng 3 4 Jayantha Kodikara PhD, BSc, CPEng, FIEAust Professor, Monash University, Melbourne, Australia Rolando P. Orense Dr Eng, PE Associate Professor, University of Auckland, Auckland, New Zealand Senior Lecturer, The University of Melbourne, Melbourne, Australia 1 2 3 4 Because of climate change and increasing population in Australia–New Zealand, several key environmental geotechnics issues are emerging. These key issues include the impact of climate change, depletion of natural resources, interest in the use of recycled materials, advances in seeking new energy sources, disaster waste management as well as other sustainability issues. Evaluation of climate change effects, adaptation technologies and interdisciplinary solutions for geo-infrastructure and other key issues and challenges will be discussed in this paper. Introduction Environmental geotechnics issues are emerging in Australia and in New Zealand because of climate change and increasing population in the region. Geotechnical engineers in the region are increasingly expected to meet the requirements for environmentally friendly designs, constructions and innovations. End users in the region increasingly expect the delivery of a project that can be certified as clean and ‘green’, at the lowest additional cost possible. Climate change in the region has resulted in the increased usage of sustainable materials in geotechnical engineering as well as the usage of various alternative clean energy sources such as geothermal and solar energy. Moreover, the series of large-scale earthquakes in New Zealand sparked the need for efficient disaster waste management and recycling measures. Climate change It is widely accepted that the world’s climate is changing as evident from anomalous warming of the earth’s atmosphere on average (Figure 1). Since 1900, the average temperature appears to have risen about 0·8°C and the rate of increase has also increased in the later years, with an about 0·2°C rise in each decade. There is substantial evidence to also suggest that the measured increase in average temperatures is mainly due to the anthropogenic effects of increase in greenhouse gas (GHG) emissions where carbon dioxide is the predominant contributor. Using the anthropogenic effect as the primary driver, the global warming predictions made into the future indicate that temperatures could rise as much 2°C to 4°C by 2100 (Meehl et al., 2012). Along with such changes, significant variations 326 in long-term weather patterns have been forecasted around the globe. For instance, in Australia, along with increased average temperatures, overall reductions in precipitation but with varied rainfall patterns with more intense rainfall events and severe droughts, sea level rises and the likelihood of severe storms and bush fires have been predicted (CSIRO, 2007). In New Zealand, on the other hand, in addition to more marked seasonality in the projected rainfall and wind patterns, other changes expected are decreased frost risk, increased frequency of high temperatures, increased frequency of extreme daily rainfalls, decreased seasonal snow cover and a possible increase in strong winds (MFE, 2008). Such changes could have a severe impact on the resilience of geo-infrastructure such as structural foundations, road pavements, buried pipelines and other earthen structures like dams and flood levees (State of Victoria, 2006). Natural slopes can be affected by the intense rainfall, and sea level rise would have adverse effects on the stability of coastal slopes. It follows then that a geo-engineer has two major responsibilities to counter these potential threats for the benefit of the wider community. The first is to develop rational methodologies to evaluate climate change risks to geo-infrastructure and to engineer adaptive technologies to maintain structural resilience, where required. The second is to engineer sustainable geo-related technologies to reduce GHG emissions, in particular the carbon dioxide emissions. Alternative energy Since the industrial revolution, the rate of growth of the human population and associated annual per capita energy consumption has been exponential (Glassley, 2010). Mitigating the environmental Environmental Geotechnics Volume 2 Issue EG6 Key issues in environmental geotechnics: Australia–New Zealand Arulrajah, Narsilio, Kodikara and Orense Offprint provided courtesy of www.icevirtuallibrary.com Author copy for personal use, not for distribution 0·8 Temperature anomaly: °C 0·6 Annual mean 5-year running mean 0·4 0·2 0 −0·2 −0·4 −0·6 1870 1900 1930 1960 1990 2020 Year Figure 1. Global temperature land–ocean index (data source: NASA’s Goddard Institute for Space Studies (GISS)) impacts of an ever-growing human presence on the planet has become inextricably linked with finding renewable energy sources with low GHG emissions, particularly in Australia whose ‘carbon footprint’ per capita is one of the largest in the world mainly because of the use and export of coal. Table 1 summarises all energy resources including fossil fuels, renewable and nuclear sources, together with some of the issues where geotechnical expertise is needed (Santamarina and Cho, 2011). There is no unique solution to reduce GHG emissions, but a combination of measures is needed, including the use of alternative, renewable and sustainable energy sources. There are a number of renewable resources that possess large amounts of energy, some easier to realise than others, and some with a relatively advanced technology (e.g. solar and wind energy). There are of course a number of strategies that can be used with our current resources (e.g. geosequestration of carbon dioxide, smart grid technologies, sustainable transport systems, energy efficiency technologies). Within the Australia–New Zealand (geotechnics) context, geothermal energy is gaining momentum. Geothermal energy can be used for the provision of heating, ventilation and air conditioning (HVAC) to residential, commercial and industrial buildings as well as for power generation (de Moel et al., 2010; Glassley, 2010; Johnston et al., 2011) (see Figure 2). Power is generated on the surface through turbines that are moved (directly or indirectly) by the hot-enough fluid (~175°C) that returns from the ground. New Non-renewable (fossil fuels) Coal Characterisation, subsurface response, mine excavation and instability, gas recovery Renewable Gas Petroleum Hydrates, low-T LNG storage, hydraulic fracturing, optimal extraction Fines and clogging, sand production, borehole instability, EOR, heavy oil and tar sand Solar Nuclear Geothermal Wind Biofuels Drilling, fracture formation, heat transfer, piles, optimization Off/onshore foundations, pseudodynamic loading Land and water use, energy efficiency, and food impact Engineered soils, decommission, leak detect and repair, long-term behaviour and monitoring Table 1. Energy resources and associated geotechnics involvement (modified from Santamarina and Cho, 2011) 327 Environmental Geotechnics Volume 2 Issue EG6 Key issues in environmental geotechnics: Australia–New Zealand Arulrajah, Narsilio, Kodikara and Orense Offprint provided courtesy of www.icevirtuallibrary.com Author copy for personal use, not for distribution (a) (b) Winter Summer Air temp typically 5−15˚C Air temp typically 25–35˚C Cold GSHP Hot Hot GSHP Cold Ground temp typically 18˚C Enhanced rock mass Heat Ground temp typically 18˚C Heat Figure 2. Schematic diagram views of geothermal energy systems: (a) hot dry rock system for power generation and (b) direct heating and cooling system where the primary (ground) circuit is connected to the secondary (building) circuit using a GSHP in winter and summer (typical temperature ranges for Melbourne, Australia; note borehole not to scale) Zealand has advanced considerably on commercial geothermal power plants given its geological conditions (relatively shallow magmatic activity), whereas Australia has embarked in advancing hot dry rock technology by way of full-scale pilot power plants. In the latter, ground temperatures needed for the generation of electricity are found a few kilometres below ground surface (much deeper than in New Zealand, but shallower and thus less expensive to drill than other parts of the world); however, the permeability of the rock to allow the injected fluid to heat up is so low that the reservoir needs to be ‘enhanced’ or ‘engineered’ by way of controlled fracturing. One of the most pressing environmental issues arises from the induced microseismicity (from the fracturing) and the geochemistry changes induced in the reservoir and the fluid. Moreover, geothermal fluid extraction for electricity generation can induce regional subsidence. In the Wairakei field in New Zealand, for example, 1–2 m of regional subsidence, in addition to a number of bowl-shaped regions with greater subsidence (including one that reached 15 m), have been observed (Pender et al., 2013). Evaluation and better understanding of such large-scale subsidence requires comprehensive geotechnical investigation on undisturbed samples from depths of up to 1000 m. the energy required for heating and cooling by 66% compared with electrical resistance heating and 42% compared with airsource heat pumps. The use of open-loop geothermal systems, with discharge and interchange of fluids with the ground, poses more environmental concerns than closed loop systems. In both cases, the (environmental) effects of thermal plumes and efficiency are the focus of ongoing research. Although already well-established outside Australasia (Amatya et al., 2012; Banks, 2008; Brandl, 2006; Preene and Powrie, 2009), the other direct form of geothermal energy, for heating and cooling with the use of a ground surface heat pump, is particularly growing in the region. Energy use in buildings accounts for 26% of Australia’s GHG emissions, and heating and cooling account for over half of this energy use (CSIRO, 2010) and thus have a significant impact on the required capacity of electrical infrastructure. In one of the few comparative studies of its type, Stein and Meier (1997) report that residential ground source heat pump (GSHP) systems reduce 328 In the realm of energy research and development, methane hydrates are being considered as a potential fuel for the future. It is believed that there is enough methane in the form of hydrates (methane locked in ice) to supply energy for centuries. The Hikurangi Margin east of New Zealand contains a >50 000-km2 large gas hydrate province. First estimates suggest that the volume of gas in concentrated hydrate deposits is in the order of 700 000 kg/m3 (Pecher and Henrys, 2003), which is more than 100 times New Zealand’s annual gas consumption between 2005 and 2009. Should even only a fraction of New Zealand’s gas hydrates be economically recoverable, they could provide the main source of natural gas for New Zealand for several decades (Pecher and GHR Working Group, 2011). Dissociation (‘melting’) of hydrate can generate large volumes of gas that may weaken the seafloor and trigger submarine landslides and tsunamis. Moreover, extraction of the gas hydrates involves complex physical events (e.g. changes in the soil structure and thermal conductivity, pore fluid and gas migration and other complicated phenomena), which could cause consolidation and shear deformation of the ground due to changes in the effective stress and decrease in soil particle strength (Hyodo et al., 2013). Thus, geotechnical engineers need to investigate the geomechanical properties of methane hydrate-bearing sediments not only for safe and economic exploitation but to understand the risk associated with seafloor instability. Environmental Geotechnics Volume 2 Issue EG6 Key issues in environmental geotechnics: Australia–New Zealand Arulrajah, Narsilio, Kodikara and Orense Offprint provided courtesy of www.icevirtuallibrary.com Author copy for personal use, not for distribution Recycled waste materials The urgent need to lower the carbon footprint of geostructures in the region is increasingly being explored because of the growing depletion of natural resources and disposal cost (Arulrajah et al., 2013a; Hoyos et al., 2011). The requirement to lower carbon footprints in the design and construction of various civil engineering projects is an increasing requirement for clients in many projects. The growing interest in lowering carbon footprints has in recent years led to end users, design consultants and contractors pursuing new technologies that embrace design, materials and construction methods that are environmentally friendly. Construction and demolition (C&D) materials are the excess or waste materials associated with the construction and demolition of buildings and structures, including concrete, brick and reclaimed asphalt (Sustainability Victoria, 2010). In Australia, approximately 8·7 million tons of demolition concrete, 1·3 million tons of demolition brick, 3·3 million tons of waste excavation rock, 1·0 million tons of waste glass and 1·2 million tons of reclaimed asphalt pavement are stockpiled annually (Arulrajah et al., 2013a). Following the 2010–2011 Canterbury (New Zealand) earthquake sequence, Christchurch City was significantly damaged, with widespread liquefaction in the eastern suburbs of the city. Ongoing rebuilding efforts indicate that an estimated 4 million tons of building debris will be generated from demolition and building repair works and up to 4 million tons from horizontal infrastructure (i.e. roads, water, sewer and stormwater pipes) repairs. In addition to the large amounts of C&D materials, an excess of 510 000 tons of liquefied sand and silt was generated following the earthquakes (CERA, 2012). Reuse options for C&D or commercial and industrial waste in geotechnical engineering applications are increasingly being sought in the region as their reuse provides substantial benefits in terms of increased sustainability and reduced environmental impact. The usage of C&D materials in pavement applications is a sustainable option that has been explored in recent years globally and is rapidly gaining momentum in acceptability in the region (Arulrajah et al., 2013a; Landris, 2007; Poon and Chan, 2006; Puppala et al., 2011; Sivakumar et al., 2004; Tam and Tam, 2007; Wartman et al., 2004). Ultimately, only through further research can a framework for using new and different categories of waste materials in geotechnical engineering applications be established. Several researchers have investigated the usage of various recycled C&D materials in laboratory applications (Azam and Cameron, 2013), and furthermore, road pavements and footpaths are increasingly being constructed in the region using recycled C&D materials (Arulrajah et al., 2013b). Figure 3 shows a road pavement base constructed using recycled glass blends. Depending on their nature and severity, disasters such as earthquakes, bushfires and floods can create large volumes of debris and waste, the majority of which ends up as C&D wastes. As the waste volumes from a single event can be the equivalent of many times the annual waste generation rate of the affected community and can overwhelm existing solid waste management facilities Figure 3. Laying of pavement base layer composed of glass blends (Arulrajah et al., 2013b) and personnel, management of disaster waste is very important. Following the Christchurch earthquakes, a new, low-engineered disposal site was set up in Burwood to dispose of all presorted and unrecyclable demolition wastes (Brown, 2012). Inert wastes (concrete, asphalt, brick, natural fill) were taken to Lyttelton Port and used for land reclamation. Ground improvement techniques that use in situ soil are being tested as liquefaction countermeasure to try to find a use for the 510 000 tons of grey sand that has been collected. Similarly, road filler made from cement mixed with silt from liquefied sites has also been trialled. Other forms of recycled materials that are rapidly generating research interest in the region include various forms of commercial wastes, industrial wastes, municipal solid wastes and organic wastes. Conclusions Various key issues associated with environmental geotechnics, such as climate change, disaster wastes and recycling materials, have emerged and posed as major challenges to geo-engineers in Australasia. These issues have stimulated advanced research and application of adaptation technologies in an environmentally sustainable manner as well as the development of interdisciplinary solutions that require shared knowledge among the different basic and applied sciences and technologies. Thus, geo-professionals in the region need refined and/or new sets of skills in theoretical modelling and experimentation capabilities and to extend their classical soil and rock mechanics background while interacting with researchers in other disciplines to come up with safe and sustainable design, construction, operation and maintenance of geo-infrastructures. REFERENCES Amatya BL, Soga K, Bourne-Webb PJ and Laloui L (2012) Thermo-mechanical performance of energy piles. 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Your contribution will be forwarded to the author(s) for a reply and, if considered appropriate by the editorial panel, will be published as a discussion in a future issue of the journal.