Hydrophobic granular soils are under investigation for constructing roads on frost-susceptible soils in China and the US, in preference to cementitious stabilisation. Hydrophobic granular soils have also been proposed for replacing other geotechnical engineering elements requiring low permeability or resistance to root growth or cracking. In the UK, road building remains a key component of reducing the climate impact of transport whilst maintaining supply chains. Simultaneously, hydraulic risks to infrastructure brought about by climate change are increasing in severity; as of 2016, a 1% chance exists every year that monthly winter rainfall in the UK will be 20% to 30% higher than previously recorded. The scope for hydrophobic granular soils to make a positive impact on UK climate resilient construction practices is therefore considerable.

The first step towards understanding the hydromechanical behaviour of an unsaturated soil is to characterise its water retention properties. For hydrophilic soils, traditional techniques for example psychrometry or tensiometry allow us to construct the retention curve with little difficulty. However, the nature of the water phase within hydrophobic granular soils prevents us from using these methods. This project will explore new methods to construct a water retention curve for hydrophobic granular soils by combining experimental observations of the water phase in the material with numerical simulations of the resulting water pressure. This will be the first investigation of its kind to relate the water pressures in the soil to what is present in situ directly. The outcomes from this project will contribute to novel geotechnical engineering solutions but also to agricultural practices, where hydrophobic granular soils threaten and prevent crop growth. The project therefore addresses multiple UN Sustainable Development Goals, including #2 (no hunger); #9 (industry, innovation, and infrastructure); and #15 (life on land). As hydrophobic granular soils have been proposed for use in water sequestration, the project also relates to UN SDGs #6 (clean water and sanitation) and #14 (life below water).