British Water Members' Handbook 2017 2017 Edition | Page 59

In 2012, main contractors MVB approached Asset International
Limited and Uponor Project Services to examine the complex
design of the Lee Tunnel twin culvert pipeline outfall.
The Asset/Uponor designed twin culvert pipeline outfall
project was divided into a land section, which was installed
by MVB and a marine section, which was installed by marine
contractor, Commercial Marine & Piling Ltd (CMP) alongside
Uponor.
The Asset and Uponor PS partnership set about using their
combined design expertise for land and marine applications
to re-engineer the project by creating a landmark design -
the biggest plastic outfall ever installed in UK and one of the
biggest in terms of diameter worldwide.
The proposal to overcome this enormous challenge; inclusive
of 880 metres of 3000mm diameter Weholite pipes laid as a
twin culvert along with twelve large-scale Weholite Modular
HDPE boxes; also the provision of installation, supervision, site
services and health and safety management.
The project was divided into a land section comprising of
105m of twin culvert laid at 10m depths. This section had
the added complication of needing to break through the
tidal protection wall that stops the Thames flooding Europe’s
largest treatment works at Beckton. This issue was overcome
by utilising a giant 7m x 11m x 5m Weholite Modular box to
house a 3000mm spool section to complete the installation.
The operation to install the remaining 335 metres of twin
culvert section into the River Thames was carried out by
marine contractor CMP, alongside the Asset and Uponor PS
partnership. This ambitious marine project was complicated
still further by the fact the pipes needed to be submerged
under an existing jetty structure and sections of the project
were often isolated by the tide (which in the Thames have a
rise and fall of up to 7 metres), with no access from land.
All the Weholite pipes and modular boxes were
manufactured and prefabricated at Asset’s south Wales
factory. The pipes were then delivered to site in 18 metre
lengths, where they were welded into strings of up to 90
metres. The 50 tonne strings were then lifted onto the water
using three mobile cranes in tandem and prepared for
towing to the submersion site, located around 3km up river.
Part of this preparation involved utilising Uponor’s patented
grouting process which eliminates the need for heavy
concrete collars to ballast the strings. This traditional way
of installing marine pipelines can often be extremely risky
during submersion. Filling the hollow Weholite profile with an
inexpensive and pumpable grout is much safer and affords
for a much quicker preparation time. With no concrete
collars a smaller trench is needed, the dredging operation
is minimised and the volume of excavation is therefore
drastically reduced. Since submarine excavations are more
expensive than on dry land the advantages of Weholite
are transparent. By using the grouting system, Weholite
submersion is much easier to control and ultimately safer.
Once the pipe strings were ready, they were towed
individually up river by tugboat and then submerged.
Specialist divers were used to bolt up the innovatively
designed quick connect flanges that joined each pipe string.
The project also included installation of over 11,000 m2 of
steel sheet piling to allow the dredging of the river bed so the
pipes could be laid free from obstruction. Over 28,000 m3 of
riverbed materials were dredged and much of the dredged
materials were reused to backfill the pipes once installed. This
provided an environmental advantage by vastly reducing the
amount of materials to be taken off site, thereby saving on the
carbon footprint.
Emmanuel Costes, construction manager at MVB,
commented: “We were very happy with the Weholite
technology employed in the implementation of the Lee
Tunnel Outfall pipeline. The specifications of the project were
very particular, however the solutions provided by the Asset
International/Uponor collaboration were impressive, ticking
all of the boxes that this complex, and in many cases unique,
project demanded.”
The scale and scope of the installation means that not only
has it become the UK’s largest plastic outfall pipeline, but it
also represented the UKs first ever sub-sea installation of a
sectional installed multi-directional sewage pipeline.
For more information about Weholite call Asset International
Ltd 01633 273081 or visit www.weholite.co.uk
01633
01633 273
273 081
081