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Case History | Iceland

Kárahnjúkar Hydropower Project

In the summer of 2008, construction traffic was active in the base of the canyon downstream of Iceland’s new Kárahnjúkar Dam. This activity prompted the owner, Landsvirkjun, to monitor a previously identified tension crack and a potentially unstable rock wedge at the canyon edge. The tension crack was instrumented such that an alarm could be raised if it opened, potentially endangering the work crews below.

The instrumentation was comprised of two GEOKON Model 4420 Vibrating Wire Crackmeters, connected to a Campbell Scientific CR850 Datalogger and monitored over the Internet, using Vista Engineering’s Vista Data Vision software. In addition, the datalogger was programmed to sound a siren and control traffic lights on the roadway in the canyon, changing a green light to red in the event of the crack opening beyond a pre-set threshold—thus stopping traffic from entering the area where a rock fall may occur.

At noon, one day in late August 2008, the monitoring system indicated that the crack had opened by about 1 mm, triggering an alarm response and alerting personnel. A few days later, an additional 1 mm opening was detected. Two hours later, it reported the crack had further opened by 4 mm and two hours later, by an additional 23 mm. This data was transmitted to the headquarters of Vista Engineering in Reykjavík, some 400 km away, where it was posted to the internet for review in near real-time by all concerned parties.

Following the initial 1 mm movement, the owner decided to close off the tunnels leading to the canyon. As had been predicted by the consultant, Verkís, the rock slope condition worsened, due to increased water pressure in the crack and vibration from spillway water, resulting in the subsequent collapse of the rock wedge into the canyon. After the ensuing rock pile was removed, normal traffic flow resumed after additional safety measures were put in place.

The success of this program convinced the owner to continue monitoring the remaining wedges on each side of the collapsed area, in addition to monitoring a crack directly below the spillway. Hence, the existing crackmeters were moved to new locations, 5 new gages were added and the data acquisition system’s capacity was expanded to accommodate the additional sensors.

The monitoring project in the canyon remains active today.

Photo of Kárahnjúkar Dam.
Kárahnjúkar Dam:

A tension crack is monitored directly below the spillway.