Slope stabilisation with multiple anchors monitored by glass fibre technique

Franki Africa – A Keller Company

Slope stabilisation with multiple anchors monitored by glass fibre technique

A new Refinery, with a capacity of 10 Mio. Tons of crude oil per year, is under construction on an area of about
2.300 hectare. Keller Grundbau won the contract to execute the slope stabilization for two locations of the project,
with test loads for the permanent anchors up to 3700 kN. Due to the geographical location of the project, close to
a tectonic fault zone and, moreover, in between 2 volcanos, highly heterogeneous soil conditions, including
pressured groundwater were the main challenges for the drilling works of the permanent ground anchors. To fulfil
the design requirements, multiple strand anchors with three-bond length, up to 16 strands were used, after an
intensive testing program, and manufactured directly at site. The testing included two multiple anchors fully
equipped with glass fibre sensors to investigate the load distribution behaviour with an outstanding resolution. The
main goal was to get the full picture of the strain distribution along the whole length of the anchor, in the strand
as well as in the ground – grout interface. This kind of measurement technique allows a real time monitoring with
an accuracy of the measured strain of ±1.0 µm/m. In the following paper the results of the glass fibre measurement
and the details of the multiple anchor design are discussed.

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