When earlier remediation of an embankment on the shore of Bala Lake in Wales failed to address the underlying ground movement, Griffiths delivered a solution that features the world’s first installation of a Smart Anchor Monitoring System developed by DYWIDAG Ltd. The system allows remote surveillance of the asset’s performance, supported by early warning alarm notifications.
The northern section of the A494 is one of the busiest trunk roads in Wales and is crucial to tourism and the local economy of Gwynedd.
Significant erosion had weakened an embankment that carries a section of the road alongside the northern shore of Lake Bala. A scheme to rectify and protect the embankment from further damage was completed in 2008, however, in late 2009 further settlement occurred, and surveys were commissioned by the North and Mid Wales Trunk Road Agent (NMWTRA) to monitor and record the settlement.
The data recorded showed that movement had continued which resulted in the need to reconstruct the vehicle restraint barrier running along the section. Engineers were engaged to investigate the cause of the movement and to provide a detailed design to stabilise the embankment over the entire 180m length.
In 2018, a soil nail trial was carried out using self-drilling soil nails that proved to be partially successful in slowing the ground movement considerably, but not entirely. But in early 2020, the continuing deterioration of the safety barrier foundation rendered the soil nail solution ineffective.
Clive Bayley, Procurement and Contract Manager for NMWTRA said “Our primary concern was the integrity of the vehicle restraint system; temporary traffic lights were installed to close the southbound lane. Due to the importance of the A494, we were keen to identify a permanent solution that would allow the re-opening of the road as early as possible.
On behalf of the Welsh Government the North and Mid Wales Trunk Road Agency (NMWTRA) commissioned Alun Griffiths (Contractors) Ltd under an ECI contract to develop a solution. Working with Ymgynghoriaeth Gwynedd Consultancy (YGC) and DYWIDAG, several options were considered for the remediation of the embankment, with the preferred solution comprising a restrained/anchored reinforced concrete pile cap/retaining wall over a length of approximately 75m, with anchor piles spaced at 2m centres and embedded into the bedrock. The vehicle restraint system and pedestrian barrier were to be supported by the structure with both the highway and footpath regraded and resurfaced.”
Regional Director for Griffiths, Owain Thomas said “The proposed solution would improve the factor of safety of the embankment, reducing any ground movement and resultant cracking in the highway and footpath, and delivering a 120-year design life.”
The innovative solution was to install a reinforced concrete ‘king post’ retaining wall, supported by 36 ground anchors, 12 of which were smart anchors – the use of which is the first in the world.
Using a unique force measurement sensor, the smart anchors can be monitored remotely with real time data being transmitted to a cloud-based system, thus permitting continuous surveillance of the asset’s performance.
The data can be used to verify design predictions, improve modelling quality and provide insights for more tailored design solutions.
Llanycil has advanced ground anchor technology to the next level with the ability to identify minor issues before they become major problems, allowing engineering resources to be focussed on preventative maintenance.
