Project: Blackwall Tunnel Northbound

Works: Refurbishment works and high definition scanning surveys

Survey prior to works commencing and after completion

Area: London

Project Value: £35k

The Blackwall Tunnel is one of the critical highway links in east London, carrying traffic under the River Thames between the boroughs of Greenwich in the south and Tower Hamlets in the north. Actually there are two separate tunnels, the first of which was opened on 22 May 1897 is 1,364m long and now carries northbound traffic. The second followed 70 years later on 2 August 1967 and carries southbound traffic.

The essential safety improvements have brought the 114 year old landmark tunnel, which is used by 50,000 vehicles a day – up to date with modern safety standards, thus reducing the number of incidents that force the tunnel to close in future. The works included the refurbishment of the four main ventilation shafts and the installation of new lighting and CCTV, ventilation fans and communications systems throughout the tunnel. Also an additional lane was constructed for heavy goods vehicles (HGVs) on the northbound approach, to allow over-height vehicles to be diverted away from the tunnel before they reach the entrance and cause an obstruction.

Essential safety works on the northbound Blackwall Tunnel are now complete. The tunnel re-opened to full service on 11 November 2011 and finished more than a year ahead of schedule.

Objectives

To carry out a 3D high definition laser scanning survey to the whole length of the tunnel, including the north and south approaches (239m and 263m long respectively), including the ventilation shafts, to produce a full 3D point cloud for the client to interrogate. These surveys were to be carried out prior to the works commencing and upon completion of all the refurbishment works.

Progress and Outcome

For the initial survey, the locations of the ventilation shafts were key to the design of the refurbishment. This survey was undertaken by a team of three surveyors, who established control over the entire length of the tunnel and co-ordinated the 3D scanned shafts in relation to one another. For return visits, tunnel closures for the survey took place over the course of five nights. A team of four surveyors worked for the first two nights to establish control and survey approximately 50% of the tunnel. The remaining three nights, a team of two surveyors completed the tunnel and ventilation shafts.

A 3D point-cloud was delivered to the client, including grayscale Truviews, on OS Grid with a tolerance of 5mm. Taking in consideration the length of the tunnel is 1,866m, inclusive of the North- and South- approach, these surveys were not only time efficient, but also proved to be cost effective. Both these surveys now offer a detailed record of tunnel conditions prior to and following their refurbishment.

Find out more

Call Vertical Survey Services on +44 7944 664067 or write to us using our email form for more information.