The document describes the installation of the longest anchors in Europe on the Mühltobel bridge in Austria. Six 151-meter-long strand anchors were drilled and installed at each of the bridge's two abutments to secure them. The complex drilling process through the abutments and gypsum rock formations below was performed continuously to avoid swelling. The anchors were then grouted and tensioned to reinforce the unstable bridge foundations affected by shifting gypsum layers.

1. Comacchio Drilling Equipment
The longest anchors in Europe: A Case Study

2. The longest anchors in Europe: A
Case Study
Installation of strand anchors on the Mühltobel bridge
Dalaas, Austria
(Project carried out in 2011)
Engineering: GEOTEK Dönz + Mähr GmbH (Austria)
Contractor: GK Construction GmbH (Austria)
Foundations contractor: Greuter AG (Switzerland)

3. 135.7 km rail connection between Innsbruck and Bludenz (Austria)
Arlberg Railway (Arlbergbahn)
Dating back to 1883, the Arlberg Railway is Austria's only east-west mountain railway,
Operated by the Austrian Federal Railways (ÖBB) and frequented by international trains,
including the Orient Express.
One of Europe's most problematic mountain railways, threatened by avalanches,
mudslides, rock falls and floods

4. Mühltobel Bridge
Located in Dalaas, Klostertal, one of the most problematic areas of the Arlberg Railway,
due to gypsum formations. Interrupts the 2 sections of the Mühltobel gallery as passage
for debris.
High gypsum percentage in the layers below the bridge foundations caused
displacements that endangered the bridge structure:
- Left abutment drifted approx. 10 cm from the wing wall of the gallery toward valley
- Right abutment had shear cracks showing overloading of the foundations
- Both abutments were secured by single anchors that were no longer functioning

5. The project
Engineering company
Geotek suggested installing
3 permanent pre-stressed
anchors for each abutment.
Double corrosion protection
steel 1570/1770
8 strands Ø 0.62"
Load capacity Ptk = 2124 kN
Safety class II
Length = 145 m
Bond length = 25 m
Pre-stressing at 700 kN
Test load 1200 kN
Anchor specs:
Reinforced concrete
cross member between
the two abutments
to support the forces in
track axle

6. The project
According to geotechnical report, the stable layer (limestone) in the slope was located at a
depth of approx. 130 m. Requested anchor length: 145 m
Additional ground consolidation with jet grouting was carried out on both abutments (22 m
columns for right abutment, 12 m columns for left abutment).

7. Challenges
Drilling of the holes through the 6 m thick reinforced concrete of both abutments to a
depth of 145 m in very complex geological conditions.
Supply of special anchors in lengths of 151 m, to be placed on a special drum and
transported just in time to the job site.
Installation of the anchors at an incline of just 10° causing strong friction and the risk
of strand anchors getting stuck during insertion.
Mountain job site with temporary electricity and water supply to be specially provided.
Working in day and night shifts of 10/12 hours with permanent supervision of the
contractor.

8. Drilling
Complex geological conditions:
Load bearing rock/marl stratum located under approx. 10 m scree deposits and 110 m
heavily swelling gypsum formations (gipskeuper).
The main risk was related to swelling of the chalk layers due to water inflows, that could
cause the blocking of the anchors inside the borehole. To avoid this, each borehole had
to be drilled working no-stop in day and night shifts.
High borehole accuracy at a depth never performed before, allowed borehole deviation
was set at 2%.

9. Drilling
Drilling was performed using a Comacchio machine MC-F 04.1 (MC 20)
Main features:
188 kW engine power
Double head system:
3600 daNm torque on the lower head
900 daNm torque on the upper head
10000 daN retract / feed force

10. Drilling
Telescopic drilling method: 5" DTH hammer using
114 mm rods
219 mm casings up to 45 m depth
178 mm casings to reach the 145 m depth required
Advantages of the method:
Reducing friction on the first 45 m of borehole
Keeping the casings constantly in movement up to the 145 m depth

11. Anchor installation
Six strand anchors specifically designed and manufactured by Swiss-based DYWIDAG-
Systems International at production plant Koenigsbrunn near Augsburg (Germany).
Longest anchors ever manufactured in Europe (max. production capacity in Switzerland
equal to 75 m).
Double corrosion protected strand anchors in length of 151 m. Each consisting of 6
strands (St1670/1860) with 0.62" nominal diameter, designed to support 1968 kN load at
yield strength and 2232 kN breaking load.

12. Anchor installation
Installation at in incline of only 10° using a special drum
Bond lengths grouted at a length of 25 m, using four 16 mm hoses. Each anchor required
10 tons grout. The sulfate-resisting cement Protego 4R HS from Swiss-based supplier
Holcim was used.
After a curing time of 1 week the first permanent strand anchor was tensioned in the
presence of the experts of Cottbus Technical University. Initially tensioning to more than
1,200 kN, afterwards anchoring was carried out at a working load of 700 kN. Testing was
performed according to DIN 4125.

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26. Thank you