A new research project launched by Heriot-Watt University and Virginia Tech is aiming to strengthen the resilience of seawalls.
The PIONEER project is being funded by the Engineering and Physical Sciences Research Council (EPSRC) and hopes to be the first step in an international collaboration to strengthen coastal sea defences globally.
Around 148 million people worldwide are exposed to coastal flooding events, which are predicted to surge in frequency and severity in the coming decades as climate change drives sea levels higher.
The research being conducted by Heriot-Watt and Virginia Tech will investigate how the soil behind sea walls is impacted by repeated wetting and drying cycles over time from waves overtopping the sea walls. It’s hoped this will highlight areas where the design and resilience of sea walls could be strengthened.
Dr Melis Sütman, an assistant professor in geotechnical engineering at Heriot-Watt’s school of energy, geoscience, infrastructure and society, said, “The sea level around the UK has already risen by around 1.5 millimetres a year on average from the start of the 20th century. And even in the best case climate change scenario, the sea level will continue to rise. So our coastal defence structures will be of paramount importance to defend our shorelines – not only for the UK, but also for the United States on the other side of the Atlantic.”
Heriot-Watt University explained that, under a low emissions scenario, by the year 2300, the sea level for London and Cardiff is predicted to rise between 0.5 metres and 2.2 metres and up to 1.7 metres for Edinburgh and Belfast. Under a high emissions scenario, this increases to between 1.4 metres and 4.3 metres for London and Cardiff, and between 0.7 metres and 3.6 metres for Edinburgh and Belfast.
In the US, the coastal sea level by 2050 is predicted to be between 0.25- 0.30 meters higher than in 2020 – and as much as the rise measured over the last 100 years before that, from 1920 to 2020, it added.
Dr Sütman continued, “According to the Intergovernmental Panel on Climate Change, unavoidable sea level rise will bring cascading and compounding impacts resulting in flooding and damage to coastal infrastructure that cascades into risks to livelihoods, settlements, health, well-being, food, and water security in the near to long-term.”
She added that rising sea level also has strong economic consequences. For example, the investment needed to protect London is expected to exceed £20 billion. Whilst at Staten Island in New York City, $165 million is being invested to build an 8.5km seawall along the coastline to build resilience to sea level rise and extreme events.
The research will involve testing wave overtopping scenarios on interfaces that mimic the interaction between sea walls and the backfill soils. At Heriot-Watt, tests will take place in the lab on a small-scale device that the university says it has developed as a world first.
A thermo-hydro-mechanical direct shear interface device will be utilised, with it allowing numerous scenarios to be tested and measured. This includes, for example, different water contents, overtopping frequencies and lengths and different properties of the both the soil behind the wall and the wall itself.
Dr Sütman said, “It means that we can create a soil and structure interface – or a concrete interface – in the lab in the size of 60 by 60 millimetres, so very small, and we can apply almost every possible temperature and water content change to this interface. Because this is a small-scale device, the setup is easier – and it’s cheaper – so we’ll be able to investigate many different parameters in a relatively short amount of time.”
Virginia Tech will then conduct its set of experiments on a full-sized wall that is 5 metres in height. Dr Sherif Abdelaziz, associate professor of geotechnical engineering at the Charles E Via, Jr. department of civil and environmental engineering at Virginia Tech, commented, “Our large-scale tests will investigate how the soil and wall are affected by different levels of temperature, suction, water pressure and other parameters. Heriot-Watt will then perform additional lab-scale tests to investigate the conditions we record at full-scale. So our investigations on each side of the Atlantic will very much go hand-in-hand.”
