"No Dig" – trenchless pipe installation
Rehabilitation of old water mains
The Vienna Waterworks (Municipal Department 31 - MA 31) are responsible for keeping the city supplied with an uninterrupted stream of pure drinking water. This involves maintenance and repair of the existing distribution network and installation of new pipes where needed. Innovative technologies are used for these tasks, in particular trenchless, or "No Dig" techniques for pipe rehabilitation and replacement.
The total length of the water distribution network within the City of Vienna's territory is no less than 3,000 kilometres, and the Vienna Waterworks (Municipal Department 31 - MA 31) are responsible for keeping the whole system in working condition. The oldest pipe sections have been in place for more than a century, but age by itself is not the most crucial issue - what counts is the state of repair of the pipes. Conditions in the network are mainly documented in a digital network information system (NIS), which has been specially developed for this purpose and contains all the relevant data, grouped by pipe sections.
In collaboration with the University of Technology of the City of Graz, MA 31 has implemented a software to assess potential need for renewal in pipe sections on the basis of the data supplied by the NIS system. These IT tools enable MA 31 to manage maintenance, repair and replacement works in a proactive manner based on the current state of each pipe section.
The aim is to minimise network losses, i.e. water leakage, wherever pipes are no longer properly sealed. Apart from other measures continuous repair and replacements efforts have brought down network losses from 25 per cent of the total distributed volume in the early 1970s to less than eight per cent today.
There are above-ground and underground methods for the repair and replacement of pipe sections. MA 31 is a member of the Austrian Association for Trenchless Technology (ÖGL), in which civil engineering companies, technology developers, special equipment manufacturers and trading companies and researchers collaborate. In this context, MA 31 plays an important role as a public contract awarder which applies various new technologies at its constructions sites and evaluates them as to functionality and economic viability. The results of these evaluations are fed back to the developers and manufacturers as a basis for further technological advances.
Aged sewer sections may be rehabilitated through different relining processes, all using trenchless technology:
- Pipe bursting: As the old pipe is progressively widened or burst open from inside, a new length of pipe with a strong, crack-resistant outer shell is pulled into place inside; with this method, the diameter of the replacement pipe can be the same or even wider than that of the original pipe.
- Slip lining: A new length of pipe with a smaller diameter is pulled into the existing pipe, which is usually cleaned beforehand;
- U-lining: A length of PE pipe is prefolded into a U shape and pulled into the old pipe; once in place, the PE pipe is heated so that it expands and regains its circular shape for a snug fit with the bore of the old pipe.
Trenchless or "No-Dig" pipe installation methodology is suitable only for longer sections of pipe, but here it has a number of benefits:
- Reduction of CO2 emissions: much less excavated material has to be removed by lorry;
- Reduced cost: in conventional, open-dig pipe installations, reconstruction of the road surface accounts for 30 per cent of the total cost;
- Shorter installation times;
- Improvement of life quality: disturbances to nearby inhabitants and traffic disruptions are kept to a minimum.
At the moment, 10 to 20 per cent of all pipe rehabilitation and replacement processes in the water mains network, as well as work on sections of building supply lines, are carried out using trenchless technologies.
Facts & Figures
- Total length of water supply network: 3,000 km
- Building supply lines: 102,000 branch lines
DI (FH) Volker Schaffler
Tel. +43 1 4000 84269
Fax +43 1 4000 7997
- Municipal Department Vienna Waterworks (MA 31)
- Vienna Waterworks
- Austrian Assocation for Trenchless Technology
- International Association of Waterworks in the Danube Catchment Area – IAWD