The timing is perfect for this special issue because its contents are in line with the strategic research directions of the National Natural Science Foundation of China, which on 14th June 2016 announced that it will promote interdisciplinary “Blue” and “Green” research as part of its 13th Five-Year Plan. “Blue” refers to scientific research associated with the oceans such as research on climate change and energy. “Green” covers research projects such as the exploration of green energy and the use of vegetation to protect and save the environment while achieving sustainable development.

Energy, climate change, and waste management are among the crucial global challenges of the 21st century. Following collaboration among researchers and engineers in geotechnical and environmental engineering since the 1980s, a new discipline called geo-environmental engineering has been established with the aim of addressing problems such as waste disposal and the cleaning up of contaminated sites. In more recent years, due to increasing energy demands and depleting natural resources, geotechnics have started to play a major role in the exploration of new forms of energy such as shale gas and methane hydrate, and in energy conservation. This has given birth to a new branch of geotechnical engineering known as geo-energy.

Geo-environmental engineering includes the management of waste to minimize or eliminate harm to the environment. It also contributes to the remediation of contaminated areas and the use of vegetation to improve the stability of slopes and landfill covers. Since the industrial revolution in the 1950s, the quantity of waste generated has increased significantly. In 2013, up to 1.3 billion tons of municipal solid waste (MSW) was produced, and this amount is expected to almost double by 2025 (World Bank, 2013). In the USA, about 65% of MSW goes to landfills (EPA, 2011). Improper design of landfills can lead to the production of leachate, contaminating the groundwater. Also, without a proper gas collection system, methane gas, which is a more potent greenhouse gas than carbon dioxide, can escape into the atmosphere. For the past century, the sea level has risen by about 2 mm per year (Cazenave and Llovel, 2010), further aggravating the problems. At this rate, 40% of the human population may be affected by rising waters within the next century (Parry et al., 2007).

Extensive research work on domestic waste disposal has been carried out over the years, in particular with a new form of earthen landfill cover system making use of unsaturated soil mechanics (Ng and Menzies, 2007). Not only can this new three-layer, environmentally friendly earthen cover system prevent rainfall infiltration, it can also reduce gas emissions from domestic waste underneath (Ng et al., 2015a; 2015b; 2015c; 2015d; 2015e; 2016b; Wong et al., 2016a; 2016b). Research on the use of vegetation to improve slope stability has been accelerating. Recent research has focused on mechanical as well as hydraulic effects including soil suction and root architecture (Kamchoom et al., 2014; Ng and Yu, 2014; Ng et al., 2014b; 2015f; 2015g; 2016a; Liu et al., 2016). Although some new findings have been made and insights acquired, it is clear that much more research is needed to save the Earth.

Energy consumption has grown proportionally with population and economic growth (IEA, 2015). The rapid increase in energy use has raised concerns about exhaustion of energy resources and adverse environmental impacts. Researchers in the new branch of geotechnical engineering, geo-energy, have sought ways to reduce energy consumption through the use of energy piles and energy tunnels. They have also been exploring alternative energy sources such as shale gas and methane hydrate to slow down global warming (Shen et al., 2016). In the past three decades, ground source heat pumps (or energy piles) have been increasingly used and incorporated in geotechnical structures (geo-structures) such as foundations, diaphragm walls, and tunnels in Europe. This technology has proven to reduce energy consumption by 75% for space conditioning (Brandl, 2006). Given that 25% of the world’s energy is spent on space conditioning (EEBPP, 2000), considerable savings can be made. Despite their environmental benefits, ground source heat pumps in the form of energy piles are not widely accepted due to concerns about the effect of temperature on soil-structure interactions (McCartney et al., 2010). Recently, a geotechnical centrifuge was used to investigate extensively the performance of floating energy piles and new insights have been gained (Ng et al., 2014a; 2015h; 2016c).

As well as energy consumption, geo-energy also looks into alternative energy sources such as deep geothermal energy, methane hydrate, and shale gas extraction. The usage of methane hydrate as an energy source began in the early 2000s (Sloan, 1998; Spalding and Fox, 2014). Early exploration in Japan discovered 11 years’ worth of natural gas supply. Globally, methane hydrate can potentially provide enough energy for several hundred years (Buffett and Archer, 2004; IEA, 2012). However, its extraction is challenging, requiring careful design and consideration (Shen et al., 2016). Any design failure could release a huge amount of methane into the atmosphere, and trigger underwater landslides and tsunamis (Spalding and Fox, 2014).

Another newly explored energy source is shale gas, which is often trapped during rock formation at depths exceeding 3000 m. Extraction of shale gas is usually combined with carbon sequestration (Mitchell and Green, 2015). This process involves pumping carbon dioxide at high pressure to displace the shale gas. However, the application of high pressure at this depth can induce earthquakes (McGarr, 2014).

It is clear that geotechnical engineering has been playing a crucial role in the preservation and sustainability of the environment, and will continue to do so in the future. Geotechnical engineers as well as researchers should be aware of this role and should be prepared to provide sustainable geotechnical solutions whenever possible.

All these endeavours have culminated in the 1st International Conference on Geo-energy and Geo-environment (GeGe2015), which took place between 4th and 5th December 2015 at the Hong Kong University of Science Technology (HKUST) (Ng et al., 2015i). The conference provided a platform for sharing scientific breakthroughs and innovations for building a sustainable future. It was jointly organised by the HKUST, Chongqing University, Hohai University, and Zhejiang University in China, and the École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland. Support was received from the Hong Kong Geotechnical Society, the Geotechnical Division of the Hong Kong Institution of Engineers, and TC215 Environmental Geotechnics and TC308 Energy Geotechnics of the International Society for Soil Mechanics and Geotechnical Engineering. Authors who submitted excellent extended abstracts to the GeGe2015 conference were invited to submit full papers for review and publication in this special issue. Following the success of the GeGe2015 conference in providing a platform for sharing scientific knowledge, breakthroughs, and innovations for building a sustainable future, the 2nd GeGe conference will be held at Zhejiang University in 2017 and the 3rd at EPFL in 2019.