Farnworth Tunnels Monitoring, Bolton

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Farnworth Tunnels

Project summary:

The project is proposed to enlarge the Farnworth Up Tunnel to accommodate twin railway tracks and overhead line electrification (OLE) equipment. The Farnworth Tunnels are Grade II listed structures located on the Manchester to Preston Line ELR-MVE1 between Kearsley and Farnworth Stations. During the upgrade works to the Up Tunnel, the existing Down Tunnel was used to accommodate current rail traffic. Following the completion of the upgrade to the Up Tunnel, the Down Tunnel is decommissioned.

The brief:

MSG-JV is responsible for providing a monitoring system and database for the duration of the works. As part of this system, we are responsible for calibration, quality assurance, installation, commissioning, maintenance, and instrumentation monitoring. We collect, process, store, interpret, and report the data to our client daily, and the data is supplied in a specified format for inclusion in the Employers Database.

A comprehensive monitoring programme is required to validate design assumptions, confirm anticipated ground/structure movement, and ensure workforce and train safety.

The objectives of the monitoring programme are:

  • To monitor movements in the SCL strengthened Down Tunnel to ensure railway operation standards are not compromised.
  • To monitor any movements in the existing brickwork lining of the Down Tunnel as a result of the partial removal of the brickwork.
  • To monitor track movements on the bi-directional Down line.
  • To provide an automated alarm in the event of the movements exceeding the trigger values settled.
  • Monitoring movement of the A666 as a result of the New Tunnel construction.
  • Monitoring any movement of the existing masonry portal walls during the temporary works and launch/removal of the tunnelling shield.
  • To monitor the Cemetery Road Shed’s structure in the zone of influence.

The challenges:

During the tunnelling under the A666, a major dual carriageway, the TBM encountered over 100 tonnes of running sand which poured into the new tunnel. This created a void above where daylight could be seen. The A666 saw 200mm of settlement during the tunnelling works through unforeseen ground conditions. With state-of-the-art monitoring software and communications, the alert was raised before tunnelling began under the A666.

The predicted settlement at the surface was 100mm; the actual figure proved closer to 300mm once the TBM drive was complete.

Increased monitoring was implemented, and Bolton Council enforced lane closures above the working face. A standby highway gang was called to carry out resurfacing works on four occasions.

Our work:

Carry out 3D automatic monitoring of the existing brickwork lining of the Down Tunnel prior to commencement of works on site as a record of the condition of the wall and during the works. To carry out 3D automatic monitoring of existing portals and the A666 motorway.   

Automatic In-place Inclinometers were installed along the length of the tunnel with 7 bi-axial sensors, each 3 m long, installed in a chain to allow accurate real-time monitoring.

The installation of precise wireless tilt-sensors to monitor deformation of the Cemetery Road Shed structure and CTRL wall in real-time.

Our team:

Our rail survey team and monitoring team attended the site after several consultations with the client, and after all planning and preparation from a technical and health and safety point of view had been completed.

Figure 1 – ATS (Automated Total Station) Monitoring System installed in Down tunnel during SCL strengthening works.

Figure 2 – Rail survey team carrying out control network traverse through Farnworth Tunnels

They carried out complete rail surveys of the tracks and tunnel and installed monitoring prisms in the tunnel that was already undergoing SCL strengthening in preparation for the widening of the Up tunnel.

An ATS (Automated Total Station) monitoring system was installed for the first phase of monitoring of the Down tunnel, as shown in Figure 1.

Subsequent phases of rail surveys were carried out later. And monitoring installations continued as our client prepared for the TBM launch with our dedicated on-site monitoring team.


Figure 3 – Heat map from KRONOS showing settlement on the A666

Figure 4 – Time displacement graphs showing settlement on the A666 at each monitoring location

Figure 5 – Settlement on the A666 and subsequent repaving and remedial works

Figure 6 – ATS monitoring system monitoring Down tunnel during SCL strengthening works


For more information on this project, please contact Andrew Masters at amasters@murphygs.com or +44 203 598 3775

  • Client

    Murphy Group

  • Sector/Market

    InfrastructurePublic Sector

  • Services

    Monitoring – Structural & EnvironmentalBIM

  • Location

    Farnworth, Bolton

Services Used

Vibration Monitoring Services

Monitoring – Structural & Environmental

Whitehall Building Information Modelling (BIM)


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