Extreme challenges for 55 km of a cast drinking water pipeline
Extreme temperatures from -40 °C to +30 °C, challenging gradients, a very narrow time frame and transport logistics which, because of the remoteness of the site, presented some serious snags: all this was expected by cast iron pipe manufacturers Tiroler Rohre (TRM) in Mongolia who are providing a drinking water supply for the city of Altai with its 30,000 inhabitants. This will run through a 55 km long drinking water pipeline which has to overcome an altitude of 500 m. The conditions place high demands not only on the project management team but also and in particular on the logistics, the installation and the piping material itself. Finally, in places the cast iron pipes must withstand pressures of 50 bars as well as seismic activity.
But, with some sophisticated planning and with utmost know how, even these challenges can be overcome as is being proved by the latest international project of the Tiroler Rohre GmbH company. “We are supplying and laying the cast iron pipes as well as the water purification system and pumping stations”, explains Andreas Weiler, the International Sales Director for TRM who is in charge of the project.
Transport presents the greatest challenge
Mongolia faces enormous challenges when it comes to securing its fresh water resources. Therefore, for supplying drinking water to the 30,000 inhabitants of the city of Altai they need experienced specialists for geologically demanding construction sites and the appropriate extremely robust material. They found what they were looking for in the experts from TRM who started planning the project in the late summer of last year. As the prime contractor, TRM has overall responsibility for delivering all the materials, such as ductile cast iron pipes in nominal size DN 250 for example, and also for planning, executing and supervising the construction work. With ÖSTAP Engineering & Consulting company from Vienna an experienced partner was able to be gained.
By far the greatest hurdle when constructing the drinking water pipeline is logistics: transporting materials from the factory in the Tyrol to the construction site represents a considerable effort and expense for the transporter. For this, the Spedition Strieder company with its many years of experience in transporting ductile iron pipes was able to offer the best solution: the pipes travel by rail to the Mongolian capital of Ulaanbaatar, from where they are taken by road – in some cases dirt roads – on to the construction site. Andreas Weiler has accompanied the transport part of the way which, in total, amounts to just about 1,000 km.
Cast iron pipes must withstand earthquakes
The water for the drinking water supply will be taken from the reservoir near the village of Taishir, then it will be treated and pumped 500 m upwards to the city of Altai at an altitude of 2,200 m. The material requirements for this are enormous. Because of the major height difference, the pressure in the pipeline increases to more than 50 bars in places. “This high pressure can easily be absorbed with cast iron pipes, but with other materials one would have to incorporate pressure reduction stages”, explains Andreas Weiler. The fact that these requirements are not met by just any material has been confirmed in a preliminary study – the cast iron pipe proved to be the best solution. Mongolia lies in a highly seismically active area where earthquakes are a frequent occurrence. Therefore, it is extremely important that the joints of the cast iron pipes can absorb tremors and earth movements.
Temperatures as low as -40°C, which prevail in the Mongolian winter and cause the ground to freeze to a depth of up to 3.5 m, make it necessary to lay the pipes 4 m deep.
A tight time window for the construction work
And it is not only the altitude distance that poses a great challenge, the extreme climate has a part to play as well. If a certain amount of preliminary work could still be completed in autumn 2018, the watchword soon became: wait. Because winter in Mongolia lasts a long time. The time framework for the construction work is accordingly cut very narrow and only leaves room for manoeuvre from May to October. Temperatures as low as -40°C, which cause the ground to freeze to a depth of 3.5 m, make it necessary to lay the pipes 4 m deep. Also, the depth to which the reservoir freezes is greater than one would expect in Central Europe: water extraction is done at a depth of 14 m.
The weather does not only hold extreme temperatures in store, sandstorms also make the construction work more difficult. “When we are actually assembling the pipes, it is important that everything is a clean as possible so that the seal sits in the right position. If the sockets are totally dirty and full of sand, then they have to be cleaned”, says the project director, thinking of the additional time and effort expended because of the Mongolian weather phenomena.
Completion is in sight
Currently the construction work is fully underway and should be completed in the middle of 2020, thus ensuring the supply of clean drinking water for around 30,000 people. At the moment the population is being supplied with water of uncertain quality from deep wells. The entire project, with a contract value of 14 million euros, is financed by an Austrian development aid loan.
Patricia Pfister, Fachmagazin zek kommunal