An Uri premiere – underground
With the construction of tourism resort, the need for utilities (drinking water, storm water and wastewater sewer lines, electricity) has risen, so many new infrastructure lines must be installed. To handle storm water and wastewater, Andermatt Swiss Alps AG and Abwasser Uri are jointly building a brand new sewer that replaces the old combined sewer system by a modern dual system.
In the future, storm water (surface water) will no longer flow through the wastewater treatment plant; instead, a new sewer line will carry it directly to the Schöllenen Gorge. Wastewater will continue to be carried to the wastewater treatment plant. “In the past, storm water was not carried off separately from wastewater. The new dual system has the advantage of relieving the sewage treatment plant of large amounts of rainwater. This makes wastewater treatment more cost effective”, explains Urs Herger, Project Manager at Andermatt Swiss Alps AG.
The sewer lines coming from the village are very deep when they pass by the resort four to six metres below grade. The wastewater sewer is roughly 50 cm in diameter, and the storm sewer up to 2 m in diameter. “We are using a new method to lay the pipes; it’s being used for the first time in canton Uri”, tells Herger. “The pipes are not set in concrete as before, but covered with liquefied earth. To make this earth, we take the excavated soil, mix it with bentonite (a type of clay), cement and water, and then we pour the slurry back into place. Because of the liquid consistency, the pipes are completely encased.” This method offers several advantages: From an environmental point of view, soil contamination is kept very low; because the pipes are encased very well, the pressure is equalized all around; the liquefied soil dries so fast that you can walk on it after only two hours; and should something ever happen to a pipe, the strengthened soil can simply be excavated to provide access. No more laborious jack hammering through concrete to repair the pipes.
Laying the pipes presents some special challenges. “To keep the trenches dry, groundwater has to be pumped away – in extreme cases, as much as 8 to 10,000 litres per minute. We clean and neutralize the water before discharging it into the Reuss. These operations are regularly checked by environmental auditors for construction works and by the Swiss Federal Office for the Environment.” In about a year, all the pipes in the present stage will have been laid. “But we’ve already reached the first milestone, because without laying the new lines the start of construction for the second hotel would not have been possible. The old combined sewer line ran through the construction site of the hotel. The new lines are now located outside the footprint of the hotel. We will achieve the second milestone when all the lines are in the ground so we can start building the bridge between the roundabout and the resort. These works are presently in full swing. We are confident that we can meet our tight schedule.”
The current “pipe-laying stage” of the works costs some five million francs. The costs are being split between Abwasser Uri and Andermatt Swiss Alps AG on a pro rata basis.
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