Crack and Bridge monitoring

01

About project

In July 2020 a large cliff fell into a feeding canal for a 125 MW hydro dam (Sultartangavirkjun) resulting in complete shutdown. The Icelandic National Power Company needed to clear the canal as quickly as possible to return to full production, but another large crack was visible in the cliff posing a danger to the workers on site. Monitoring any movement of that crack was vital for ongoing work at the site.

 

We were able to act quickly and set up an effective alarm system using VDV. Within days the problem had been solved. The client could rest assure that had the cliff started to move, people working on the site would have had time to get to safety.

— Hallur Birgisson, VISTA Engineering
02

The challenge

The remaining crack went underneath an old bridge that was planned to be removed. The task was to monitor the crack and the bridge foundation to detect if it was moving. This project had to be executed within four days, including development, assembly, testing and installation.

The crack was in the light brown cliff that went underneath the bridge. 

 

03

The solution

A proper sensor to monitor movement on the bridge pillars was not available in the country at this exact moment so a custom made sensor was built. It consisted of a wire strung between the two pillars connected to a wheel and spring to keep it steady. A high resolution resistor was then used to detect any movement on the wire. This worked out excellent and the sensor detected 1 mm movement. Also a Geokon Crackmeter 4420 was used and installed over the crack.

The custom built sensor that detected up to 1 mm movement in the wire strung between the bridge pillars.
The wire between the two pillars.
Geokon 4420 Crackmeter installed and connected to CR300

A CR300 Datalogger from Campbell was used. Connected to the datalogger was a flashing light and a horn that would go off in the case of either the crack or the bridge pillars would move more than 2 mm. All data was collected and fed into VDV every 1 minute and alarms sent out as text messages and emails.

Warning lights and horn connected to the datalogger
Data from the wire sensor between the two pillars. Higher value equals shorter distance between the pillars. The flick in the data in the last few hours is due to heavy wind and rain that was causing the wire to bounce.

 

04

The results

The client was very satisfied with the result and how quickly it was implemented. With the lights and the horn on site, along with text message alarms, the client could have evacuated the location within few minutes if a movement had been detected. With this solution the security of the workers, working on securing the site, was guaranteed.