Case Study
Blackwall Tunnel, London
Project Value: £35k
3D high definition scans of the northbound tunnel, before and
after its refurbishment.
The Blackwall Tunnel provides a critically important road link
between the north and south banks of the river Thames in east
London. There are actually two separate tunnels at Blackwall,
the first of which opened in 1897 and now carries northbound
traffic along its 1,364m length. (The second tunnel was built
some 70 years later and carries southbound traffic.)
Recent refurbishment works to the old, northbound tunnel were
designed to bring it into line with modern safety standards, and
reduce the number of incidents that in the past had required
frequent closures. (Since the tunnel typically carries around
50,000 vehicles per day, such closures were enormously
disruptive and expensive.) The works included refurbishment of
the four main ventilation shafts and installation of new
lighting, CCTV, ventilation fans and communications systems. An
additional lane also had to be built to take heavy goods
vehicles on the northbound approach, allowing over-height
vehicles to be diverted away from the tunnel before they could
reach the entrance and cause an obstruction. The tunnel was
fully re-opened in November 2011, more than a year ahead of
schedule.
Scope of Works
Apex Engineering Service’ role was to carry out a survey of the
whole length of the tunnel – including the ventilation shafts
and the 239m northern and 263m southern approaches – using 3D
high definition laser scanning technology. Our client required
surveys both before commencement of the works and after their
completion.
Methodology
The initial survey was undertaken by a team of three engineers,
who established control over the entire length of the tunnel and
co-ordinated the key positioning of the ventilation shafts in
relation to one another. For the return visit, the 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.
For the remaining nights, a team of two surveyors completed the
tunnel and ventilation shafts.
Deliverables
Our CAD team delivered grayscale Truviews as well as a 3D
point-cloud on an Ordnanace Survey grid with a tolerance of 5mm
for interrogation by the client. Taking into consideration the
1,866m length of the tunnel (including the northern and southern
approaches), employing 3D high definition laser scanning
technology for these surveys enabled us not only to turn both
jobs around very quickly but to deliver a highly cost effective
package too.
