GEO-Instruments has played a key role in a two-year project to help protect the natural beauty at one of the UK's most spectacular national parks.
The Visual Impact Provision (VIP) is a large-scale infrastructure improvement scheme designed to reduce the number of overhead electricity lines at Eryri National Park in Wales - also known as Snowdonia.
GEO-Instruments has provided surveying and automated monitoring services to support the VIP tunnelling works, running from Minffordd to Llandecwyn across Eryri.
The project involved the construction of a new tunnel to replace 3km of National Grid overhead power lines and pylons. The 400kV cables will run underground beneath the Dwyryd estuary, with the tunnelling phase of the project completed earlier this month.
Constructed using a tunnel boring machine (TBM), the tunnel runs from the project site near Minffordd to the east side of the estuary, where eventually the underground cables will re-connect with overhead lines.
The tunnel route passes underneath Network Rail tracks at three locations as well as the Ffestiniog heritage railway.
GEO-Instruments has helped to implement tailored monitoring schemes at each of these crossings, helping the project team assess any movement and protect the railway infrastructure during tunnelling.
Monitoring the Rail crossings presented several technical challenges, requiring different approaches to capture movement and assess any potential impact on the tracks.
At one of the crossings, a network of more than 30 automated wireless tiltmeters was installed on the railway sleepers. The sensors provided accurate, high-frequency tilt data 24 hours a day.
With access to the railway tracks heavily restricted, installation works were planned and prepared carefully and carried out in a single night shift to minimise disruption to railway operations.
At another crossing, a combination of three ShapeArrays were used to monitor 110 metres of track. Installed onto the running rails, the combined array monitored for vertical movement of the track during and after TBM passage.
Track Geometry surveys were also carried out on night shifts to record the cant, twist and gauge of the rails using a specialised track trolley. This survey is undertaken before and after tunnelling works to identify and compare any changes.
The Ffestiniog railway is a historic narrow-gauge railway that runs more than 13 miles from Porthmadog to Blaenau Ffestiniog.
Given the railway’s historic significance, detailed monitoring was essential. GEO-Instruments’ monitoring package included pre- and post-works condition surveys, a trackshoe survey and a 3D monitoring survey.
The 3D survey required teams to install prism targets onto the tracks and establish a baseline. After this, the prisms were measured manually by the client using an ATS at regular intervals to identify any movement caused by the tunnelling works.
The project monitoring data is collected and displayed through GEO-Instruments' QuickView monitoring platform.
During tunnelling, the software tracked and displayed the current position and Zone of Influence of the TBM in relation to the surface monitoring points. This gave project teams a clear picture of the machine’s progress alongside the effect tunneling works were having on the surface assets.
The platform is also being used by the client’s monitoring team to manage and visualise data across the wider project, bringing information from multiple monitoring activities together in one place.
Through a combination of automated monitoring, specialist surveying and real-time data visualisation, GEO-Instruments has helped the project team monitor critical railway infrastructure throughout this major tunnelling scheme.
Ken Critchley, Project Manager on the project said:
"We're proud to be involved in the VIP scheme and it's mission to help preserve the natural beauty of Eryri national park."
Read more about our experience monitoring for National Grid projects.