Remedial works to upstream face rip-rap protection.
location
Scotland, UK
Type
Reservoir
Overview
Megget Reservoir, the highest embankment dam in Scotland, supplies 64,000 million litres of water to Edinburgh and the Lothians. Since first filling in 1983, severe wind and wave attack caused repeated damage to the upstream rip-rap, leading East of Scotland Water to seek a permanent solution. Hesselberg Erosion Protection delivered the UK’s first successful demonstration of asphaltic pattern grouting on an embankment dam.
Challenge
The rip-rap protection was failing under severe wave loading, demanding regular maintenance and raising concerns over long-term durability. Conventional repair methods would not address the underlying issue and reconstruction was not a viable option on grounds of cost or programme. The client needed a solution that could strengthen the rock armour in place while maintaining hydraulic performance.
Solution
Working with RH Cuthbertson & Partners, Hesselberg Hydro developed and trialled an innovative asphaltic pattern grouting technique. Full-scale site trials proved that bituminous grout could increase the strength of the rock layer while retaining porosity. On this basis, the contract was awarded through open tender. The works upgraded 27,000 m² of rip-rap on a 2.5 metre grid, using more than 10,500 tonnes of mastic produced on site under mobile laboratory control. Grout was applied hot from purpose-built skips, relying on gravity penetration for even distribution.
“East of Scotland Water has benefited from Hesselberg's [and MJ Gleeson’s] involvement in this project. Their practical experience in successfully pattern grouting sea defence works throughout Europe has added to our confidence in accepting this as a robust long term solution to the Megget problem.”
Engineering Design Manager, East of Scotland Water (Scottish Water)
Result
The project was completed on time and within budget in October 1998. The upgraded upstream face has since endured multiple severe wind events without further damage and with no maintenance required. Megget became the first successful demonstration of asphaltic grouting for an embankment dam in the UK, proving the technology’s long-term value. East of Scotland Water endorsed the solution as a robust and cost-effective answer to the dam’s protection needs.