Stabilization of Pier 70, A10 Tauern Motorway
During ASFINAG remedial action at the A10 Tauern Motorway, overall structural repair began on the 30 year old “Valley Bridge Larzenbach” structure near Hüttau between the motorway junctions of Bischofshofen and Eben.
Geotechnical work at pier 70, which had become necessary due to landslides, was carried out by PORR Technobau und Umwelt AG.
Although the bridge pier rests on two 9m deep, 5m Ø wells, it slid several centimeters downhill during the past 30 years.
10 St 1670/1860 8 strand Ø 15.7mm Permanent Double Corrosion Protected (DCP) DYWIDAG Strand Anchors and restressable anchor heads were installed in order to stop the pier’s sliding.
Two challenges had to be met during construction work. As the tieback anchoring of the forces in the bridge pier was only possible in very deep strata, Permanent Double Corrosion Protected (DCP) DYWIDAG Strand Anchors with anchor lengths of approx. 80m had to be installed. At this length, the weight of an anchor that had not been pre-grouted is approx. 750kg. The heavy weight of each anchor complicates handling on site and during installation. In addition, installation had to be carried out in very steep terrain that was difficult to access.
Due to these conditions, the anchors were supplied on site on special drums (one drum per anchor). Handling of the compact drums on site was very easy, and the anchors could be transported quickly to the point of installation despite the steep terrain. Installation of the anchors was optimized using a compressed air brake that was specially adjusted to the drums.
After anchor installation and placement of a concrete beam, all of the anchors were equipped with load cells for monitoring anchor forces. Before locking off the anchors, a suitability test was carried out. Due to the extremely long free length of the anchors, an elongation of more than 350mm was to be expected. The stroke of a single jack is not enough to accommodate the anticipated strand elongation.
In addition, re-gripping at each load cycle is very complex and hard to carry out (necessary clearance for wedge set).
Consequently, DSI decided to use special insertion devices in order to be able to couple two Tensa 2,600kN Jacks via a special connecting plate. Thus, a total strand elongation of up to 500mm can be achieved. In combination with a cable winch meter provided by DSI, on-site elongation recordings were eased and the time required for the performance test could be reduced to a reasonable amount.
Stabilization of the pier was successfully completed in November 2009.