Challenges in expanding a utility network and hence services to communities are many and varied, and not least they often include negotiating the local geographical hurdles and blockages – and to do so economically, and in timely fashion.

The problems are compounded when multiple utilities need to be improved for communities.

One such set of challenges faced the communities of Klosterneuburg and Korneuburg in Austria when both needed improvements to multiple utility services. They are two municipalities in Lower Austria, the largest federal state in Austria – and where the energy and environmental services utility company, EVN, is based.

The geographical challenge in the particular case of these towns – and a hurdle for each one of the utility services needing to be boosted – was the River Danube.

The towns sit on opposite sides of the famous large river.

EVN’s solution was to construct a single tunnel culvert under the river bed and then to thread a bundle of utility service pipelines through the tight circular space.

The range of utilities to be run through the tunnel are for potable water supplies, gas, electricity, natural heat and also telecommunications. In bundling them together, through the culvert and linking the towns to the greater network, EVN improved the security of supplies and services in the region as well as supporting sustainable energy supplies and the economy.

PIPEJACK TUNNEL

The culvert to hold the bundle of utilities was built below the Danube by pipejack tunnelling. A 40-tonne micro TBM bored the 460m-long culvert tunnel between relatively shallow shafts beyond each river bank. The pits were constructed with concrete pile walls, and approached by sloping cuts, excavated with braced sheet pile supports.

But it was not a straight run for the tunnel to pass under the river. The tunnel alignment has a slight curve with a horizontal radius of 1600m. Over the drive, the depth of cover varies from approx. 5m beyond the portals, near the river banks, to up to 11m below the middle of the river bed.

Behind the micro TBM were jacked a sequence of 2m i.d. concrete pipes to form the tunnel culvert passing under the river. The utility pipelines would be carefully fed through the tunnel – while being arranged together but kept separate in the packed bundle. Once fed through, the remaining sections of pipelines within the tunnel would be sealed into place – but only after a testing phase.

The tests were needed for the assembly of pipelines to ensure that none had defects or problems before they were to sit, permanently in place, in the vital new – but difficult to access – underground link in the expanded network of utilities.

The project was successfully executed by a joint venture of Austrian contractor BT Bau GmbH and Smet- Tunnelling nv, part of Dutch contractor Smet Group.

UTILITY PIPELINES

Locally, either side of the Danube, EVN has groundwater well fields to tap for potable water supplies. It also has power plants on either side of the river. Connecting each utility together is strategically, and operationally, advantageous.

In a statement, EVN spokesperson Stefan Zach, said, “This can be of essential importance in the event of a well field failure. Especially in challenging times like these, it shows how important regional supply security is.”

The new drinking water connector would be two pipelines supplied by AGRU Kunststofftechnik GmbH. The pipelines are high-performance PE 100-RC of o.d. 560mm SDR 111, able to operate at up to 16 bar pressure.

The piping supply package also included fittings.

EVN has power plants on each side of the river. Zach said: “The biomass plants on both sides of the Danube can stand in for the other plant at any time in the event of a breakdown or revision.”

He added: “Since we also have large well fields and springs on both sides of the Danube, the tunnel enables the drinking water reserves to be interconnected.”

On the Korneuburg side of the river, therefore, pipelines were laid from the power plant and from a well field to run toward the river. However, more trenchless tunnelling was needed before reaching the river – to pass below a railway line and also the A22 highway.

In addition to the two water and two district heating pipelines, the project also involved carrying a steel, high-pressure natural gas pipeline and also cables for electricity and optical fibre telecoms.

 AGRU also supplied protective pipelines to house the electricity cables and telecom optical fibre cables, respectively. Almost 2900m of o.d. 160mm SDR 121 pipelines, plus fittings, were supplied in total to help protect the cables.

Each of the water, natural heat and telecom pipes were welded together with 18m-long pipe rods of o.d. 560mm, which AGRU says considerably reduced the welding effort which used mechanically manufactured heating coil sleeves in the connection zones.

A variety of different pipelines – by type, size, and material therefore – had been assembled and aligned together on the banks of the Danube. Their positions were maintained using with carriage (cradle) frames, placed along their length at set intervals. The bundle of pre-welded pipelines, also supported by the carriages, was then pulled along a rail system that had been specially-installed on the run up to the river bank, passing down the approach cutting and into the pit, from where the pipelines then disappeared into the culvert tunnel, below the river.

Once the utility pipelines were in place in the tunnel, for the testing phase of the assembly the concrete culvert tunnel was sealed at its portals. The testing process involved filling the sealed space with water and then the pipelines were examined for possible defects.

Zach, said: “After a positive conclusion of the examination, the tunnel was filled with a concrete suspension and sealed permanently.”

The concrete-sealed arrangement is “maintenance free”, he added.

The company has invested about Euro10 million in the project.