In autumn 2010, it became necessary to effect demanding repairs to
sewer pipes in the city of Reutlingen. The work needed to be carried
out on pipes with diameters of DN 400 to DN 1100. The maintenance
work was needed on a total of seven sections with around 700
running metres. Civil engineers, Gauss + Lörcher Ingenieurtechnik
GmbH based in Rottenburg, chose to carry out the repairs using
hose liners as such liners would make excavation work
unnecessary and because the large nominal widths of the mixed-
water collectors, the direct proximity to other supply liners and other
extreme conditions that made the work more difficult made such
liners look like the best way of realizing the repairs. One factor in
choosing to work with liners was that the sections to be repaired
were located on a very busy road in the city centre and so the
necessary excavation would have resulted in considerable
disruption to traffic.

Because it was able to demonstrate that it was up to the job
and because it submitted the most economical bid, the new Stuttgart
branch of Pfaffinger Rohrnetz & Sanierungstechnik GmbH based in
Passau, with its special expertise and its great experience
demonstrated by its many references, was awarded the contract to
carry out the work. The company decided to use Impreg Liners for
this job as they were regarded as a reliable choice particularly where
larger nominal diameters were concerned. The material´s
homogeneous structure and suitable resin formula produce
consistent high-quality and even material properties. The structural
requirements at site, for instance, only permitted a wall thickness of
nine millimetres. The limited cross-section was necessary to
maintain the collectors´ hydraulic performance capacity particularly
as the liners possessed a considerably better roughness coefficient
than the porous old pipe.

Heavy traffic and little space

Lots of preparation work was necessary before at 7.00 a.m.
on 22 September repairs could be commenced with the cleaning and
inspection of the sewers on the Justinus-Kerner-Straße in
Reutlingen. The sewers were then closed and a water drainage
system put in place to provide protection against flooding while road
safety measures and a traffic control system using traffic lights were
installed.

The heavy traffic that occurs here in the mornings meant that
special measures were required. The Justinus-Kerner-Straße
directly feeds into the B27 and is used constantly by local
commuters and local public transport companies. It´s almost
impossible to close this road as such a closure would only be
possible with the help of complicated diversions and severe
restrictions for residents. In preparation of the work, the grass
verges at the site were cut back and around 15 trees were trimmed
with the help of the city authorities to create the required clearance
profile for heavy-duty vehicles and buses and to enable all commuter
traffic to bypass the construction site. The kerb for the pavement
that was also utilized to this end was provisionally ramped up with
asphalt-coated gravel along a section of around 250 metres.

The extremely limited space along with the daily performance
targets resulting from the overall situation and the unusual weights
that had to be moved at site made special project planning
necessary. The DN 1100 liners weighed tonnes and had to be
supplied to the site in sections on a ready-to-install and just-in-time
basis.

Installation through shaft openings

It´s usually necessary to lift out the shaft cones when liners of
this size are installed, but the excavation that this would have
required would not have satisfied the demands set out in the project
concept. The liners therefore had to be fitted through the 625mm
wide shaft openings. A special aid for pulling in the liners was used
here to prevent the tight openings from damaging the liners. A crane
was used to position the special equipment above the shafts and
insert the folded liners through the tight openings in a controlled
fashion. As the Impreg Liner permits easy handling, the six tonne
heavy and 48 metre long hose liners were pulled into the shaft with
the help of the crane without a hitch. Once the end packing and
supply lines had been fitted, the liners were pressurized and
calibrated. As this was happening, the section of the road that had
been closed for work was cleared and reopened to road users as
the only equipment thatwas then required was the truck-mounted UV
system needed for the curing process.

Once the chain of lights had been switched on, the section
was cured within around four hours. The inlets that had been
previously measured were manually opened and properly
connected. The sewers were then inspected for approval by CCTV
after which the construction site and traffic-flow measures were
cleared.

In spite of the massive dimensions and difficult local conditions, the
work in each of the seven sections was completed within one
working day.

The smooth cooperation between the customer, the civil
engineering office responsible for planning and supervision
(Ingenieurbüro Gauss+Lörcher GmbH) and the construction
company carrying out the work (Pfaffinger Rohrnetz- &
Sanierungstechnik GmbH) meant that the demanding repair task
was concluded without difficulty and demonstrated that technology
using UV curing may also be used on bigger jobs.

More information at www.impreg.de, info@impreg.de and
info@pfaffinger.de, www.pfaffinger.com

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