Restressable Anchor Heads for a Maximum of Flexibility
Measurements and inspections showed that the forces acting on the dam have increased over time and are expected to become even higher in the coming years. For this reason, a decision was made to anchor the dam into the surrounding slopes using strand anchors and thus to sustainably increase the structure’s load bearing capacity.
The dam on the Bourne River near the city of Choranche south-east of Lyon in the French region Rhône Alpes was built in 1948. The hydroelectric power station of Choranche is an important source of energy for the region with an annual output of 88GWh.
For this purpose, DYWIDAG produced and supplied eight 15m long Type 13-0.62‘‘ DYWIDAG Strand Anchors and eight 17m long Type 22-0.62‘‘ DYWIDAG Strand Anchors to the job site. Afterwards, DYWIDAG installed the anchors vertically on both sides of the dam through the dam flanks and into the bedrock.
In order to be able to adjust the load bearing capacity of the dam to the anticipated increasing future loads, the anchor system had to be de- and restressable with minimum effort. For this purpose, DYWIDAG developed and installed specially designed anchor heads. Each anchor head consists of a wedge plate with an external thread and a load bearing trumpet with an internal thread in order to ensure the adjustability of both elements with each other. This way, the anchor head can be screwed to the desired height, simultaneously regulating the anchor load.
The main advantage of the special anchor heads is the high adjustability of the anchor forces as well as the possibility of executing multiple detentioning and retentioning procedures. In case of a load cell malfunction, the anchor can be fully distressed, and the load cell replaced. DYWIDAG provided, installed and connected all of the load cell systems, including lightning protection and a remote monitoring system.
In addition to installing the anchors, DYWIDAG also carried out the anchor tests and prestressed all of the 16 DYWIDAG Strand Anchors. On two anchors, 4 DYWIDAG DYNA Force Sensors were installed with a readout unit instead of load cells in order to ensure a long-term and safe monitoring of the anchor forces.