Many aviation projects involve significant earthworks that can influence overall project success more than any other stage of a development. With major infrastructure owners and operators under pressure to reduce waste, carbon emissions and drive overall project efficiencies, environment and ground engineering specialist Patrick Cox and aviation specialist Richard Gammon look at some of the best ways to reuse ground materials on site.
Expanding or building a major airport typically involves moving large amounts of ground materials to and from the site to create earthworks that will withstand the various performance demands of the new infrastructure development. But this activity can inadvertently generate waste, produce carbon emissions, is expensive and usually programme critical. Substantial haulage of ground materials can have a big negative impact on communities too. Moving materials to and from constrained sites, which are often in urban areas and in proximity to closed landfills or other contaminated land, as is the case with many airports, adds extra logistical challenges and costs.
Global environmental targets and national policies mean infrastructure, and particularly aviation projects, need to meet increasingly tough carbon emission targets. This makes the sustainable onsite reuse of locally available ground materials a top priority for infrastructure owners and operators. Here are four ways to use what’s already on site to reduce ground risk, optimise soil and material reuse, and reduce the transportation of materials off site as waste.
1. Improve what you have
It is possible to improve soil material properties by treating them to increase their strength and performance when under load. There are a number of ground materials improvement techniques, including dynamic compaction and stabilisation, to name but two. We stabilised a proposed helicopter landing site at Lippitts Hill, south east England, avoiding around 2500 lorry movements through a forested area. The steep, sloping site, made of predominantly London Clay, was accessible only by minor roads used by recreational traffic. To meet planning consent requirements, traffic had to be kept to a minimum, creating a strong driver to reuse the clay soil. Our preliminary ground investigations revealed the clay was naturally too wet to properly compact as engineered fill, as required to level out the site. Traditionally, this would have meant disposing of the clay off site and bringing in stone, requiring a large number of lorry movements. Following ground investigation and laboratory testing, we added lime to create acceptable moisture content, followed by slag to mitigate any resulting unfavourable ground conditions. Following further trials, we added water to avoid the lime drying out too much and meet optimum criteria for compaction. All onsite soils were reused, significantly reducing lorry movements while delivering the helicopter landing surface on time and to budget.
2. Make better use of what you have
Poor quality onsite materials can be used where engineering loads and demands are relatively low, such as for banks and slopes to create noise or screening bunds, and for landscaping. A highly effective way to stabilise these materials is to incorporate web, mesh or grid systems, known as geosystems. The Waste and Resources Action Programme’s (WRAP) Axis Business Park project in Liverpool, where onsite materials and geosystems were used to create a bund to reduce noise from a 24-hour warehouse reaching adjacent properties, avoided the off-site disposal of 4,000 tonnes of materials, equating to £236,000 savings in haulage costs, landfill tax and gate costs. The chosen geosystems design also eliminated the need to import large volumes of granular fill material, leading to £112,045 savings. Overall, the chosen geosystems led to savings of around 89 per cent in embodied CO2 and 96 per cent in cost terms. WRAP is a leading UK organisation helping businesses and local authorities reduce waste and recycle more.
3. Redefine what you have
Often, it is the range of ground materials found on a site that can be the biggest problem. When building airport infrastructure on top of landfill for example, the ground conditions may vary greatly in composition and strength, depending on the age of the landfill and the type of waste it contains. The ground may be impacted by soil and groundwater contamination, requiring different treatment solutions some of which will allow for reuse. Some of the waste materials may be degradable, decaying over time, resulting in loss of ground mass strength and volume. This may be critical in its effect on ground settlement given the minimal tolerances acceptable for airport infrastructure. We are increasingly using segregation trials following site investigations as a technique to evaluate the potential to re-use elements of the existing landfill as part of developments. Through the trials it is possible to confirm the suitability of processes to remove unsuitable materials and allow re-use of other more suitable materials, with and without remedial treatment.
4. Reconsider what you have
Many infrastructure owners and operators are interested in how to best to manage excavated ground material on site, without incurring the environmental and financial cost of off-site disposal. Options include the use of a Materials Management Plan (MMP) under the CL:AIRE Definition of Waste: Development Industry Code of Practice (CoP), under which it may be feasible to beneficially reuse material on site without it being classified as waste. An MMP must demonstrate the protection of human health and the environment, suitability of use of the ground material without treatment, certainty of use and quantity of the material. The Environment Agency considers the CoP when deciding whether to regulate materials on site as a waste. By following the CoP, it is unlikely that the ground materials will be classified as waste if used to develop land. This means being able to reuse the material, bypassing waste controls such as applying for an Environmental Permit, which can be costly and time consuming.
MI-ROG: optimising resources guidance
The award-winning Major Infrastructure–Resource Optimisation Group (MI-ROG) is a forum for the UK’s infrastructure operators to collaborate across the circular economy theme, meeting the challenge of major infrastructure delivery in a constrained economy. The group has recently established a working group specifically addressing the need to increase the use of recycled and secondary aggregates in infrastructure development, undertaking a survey of current practice and targets, goals and systems among MI-ROG members and is now establishing potential best practice through a series of working sessions with the aim of developing industry guidance. MI-ROG was set up by AECOM in 2013.
For more info, see the white paper Measuring circular economy performance