Permanent Strand Anchors and Hollow Bolt Anchors secure rockfall

On 31.12.2002 a rockfall with a volume of about 6,000 m3 occurred at the B99 Katschberg federal road at km 78.4 in Carinthia, Austria. Fortunately, nobody was hurt. In addition, about 2,000 m3 of rock had to be blasted off subsequently.

The causes for the rockfall were described as follows:

  • the existence of a distinctive, mechanically effective fault structure with loosened rock subsoil led to the reduction of the mountain stability;

  • strong weathering of rock in some areas;

  • Passing of mountain water through the loosened rock subsoil and hydraulic crevasse water thrust connected therewith as well as frost blasting near the surface;

  • superimposed load due to overburden loose sediment;

  • sliding off at an average inclination of 40° to 50°.

The stabilization concept required the specific application of fixing and sealing measures such as nailings, nailed (simple or double corrosion protected) shotcrete areas, concrete sealings, retaining walls as well as in-situ concrete ribs and beams back anchored with permanent strand anchors.

In addition, correspondingly dimensioned barriers such as elastic stone barriers and gravity walls were erected. The stabilization measures were accompanied by a geotechnical surveillance and control concept with 2 inclinometer drillings each 40m deep, surface measuring points and pressure cells in order to detect stronger movements at an early stage.

Since the bench edge of the rockfall was located in the immediate vicinity of the A10 Tauern Expressway, the key north-south transport connection between Germany and Italy/Slovenia, the execution of the stabilization measures had to meet special requirements. As scheduled, construction time was 6 months, whereby one lane of the B99 federal road remained open to traffic at all times.


DSI Salzburg delivered about 1,350 m permanent DYWIDAG Strand Anchors with 4-and 5-0.6" prestressing strands St 1570/1770 N/mm2 , ranging between 19 and 31 m in length,about 500 m DYWI® Drill Anchors with accessories as well as about 2,400 m GEWI® steel with accessories as stabilization means.

Technical assistanceRental of technical equipment Stressing

Office Dr.Ernst Garber - Dr.Jörg Dalmatiner, Villach + Graz, Austria

Firma STRABAG AG, Division 33, Rock Technology, Ing. Adolf Astner, Spittal/Drau, Carinthia, Austria

Office Dr.Ernst Garber - Dr.Jörg Dalmatiner, Villach + Graz, Austria