2011
Coleraine, Northern Ireland
Northern Ireland Railways
Skye Rope Access
URS
Rockfall Protection on A2 Seacoast Road, Downhill
View of the catch fence installed
View of the catch fence installed
Works completed in 2011
Challenge
The A2 Seacoast Road and adjacent railway line run along a narrow, exposed coastal corridor in Northern Ireland, just west of Coleraine. At Downhill, both transport routes pass directly beneath a steep basalt cliff, creating a significant rockfall hazard in an area of outstanding natural beauty.
This location has a well-documented history of rockfall incidents. The most critical event occurred in 2002, when falling rock caused a train derailment. Following this, a concrete crash barrier was installed alongside the railway line to prevent further debris reaching the tracks. However, the ongoing risk to both road users and rail passengers remained a major concern.
A detailed geotechnical assessment commissioned by the Northern Ireland Department for Regional Development identified the root cause of the instability. The cliffs consist of heavily jointed basalt, similar to the geological formations found at the Giant’s Causeway. Over time, weaker layers within the rock mass have weathered and eroded, leaving overlying sections unstable and prone to failure.
The 60-metre-high slope below the cliff is formed of wind-blown sands covered with grass, which acts as a natural pathway for falling rocks. Once detached, rock blocks can travel rapidly downslope toward the road and railway. Some blocks measured up to 1 cubic metre in size, weighing approximately 2,700 kg, and were capable of reaching speeds of up to 15 m/s (33 mph) before impact.
These conditions created a high-risk environment requiring a robust rockfall mitigation solution to protect critical infrastructure and ensure public safety.
Solution
To address the rockfall hazard at Downhill, URS / Scott Wilson was commissioned to carry out a comprehensive site investigation and develop an effective rockfall protection solution for both road and rail infrastructure.
The engineering approach combined detailed geological mapping, slope stability analysis, and advanced rockfall trajectory modelling. This enabled accurate prediction of rockfall behaviour, including block size, velocity, and impact energy, ensuring the design solution could withstand worst-case scenarios.
The final rockfall mitigation strategy focused on both prevention and protection. Measures were designed to stabilise unstable sections of the basalt cliff where feasible, while also incorporating engineered systems to intercept and contain falling rocks before they could reach the A2 road or railway line.
The solution was carefully designed to handle high-energy impacts from large rocks while working within the constraints of a narrow coastal corridor. Construction planning ensured minimal disruption to traffic and rail operations, a critical requirement for this busy transport route.
In addition, the project placed strong emphasis on environmental integration. As the site is located within an area of outstanding natural beauty, all works were designed to blend with the surrounding landscape and minimise visual impact.
The completed rockfall protection system at Downhill significantly reduces the risk of rockfall incidents affecting both the A2 Seacoast Road and the adjacent railway. By combining advanced geotechnical analysis with engineered mitigation measures, the project delivers a long-term solution that enhances safety, protects infrastructure, and preserves the natural environment.
Used Products
