Seabed subsidence monitoring

The Fjordbyen project, or Fjord City, is a large-scale, multi-year land development and reclamation project in Gilhusbukta, Norway. The project will move 4.8 million tonnes of rock mass into the Gilhuskukta Bay of the Drammmensfjord, allowing the construction of civil infrastructure like a public transportation hub, a hospital, and housing for 20,000 people. As a busy shipping port, Gilhusbukta was one of Norway’s most polluted industrial sites, where significant amounts of oil, tar, and creosote had leaked into the fjord. In order for the land in the Drammmensfjord Bay to be safe for construction, tonnes of rock fill had to be dredged from the sea bed and washed of contaminants before deposit back into the seabed [1].

Cautus Geo, a monitoring system integrator and long-time Measurand distributor, was responsible for monitoring the site. To monitor the length of Gilhusbukta Bay, Cautus Geo installed SAAX-type ShapeArray in long trenches dug across the bay in the seabed. Using Cautus Web, Cautus Geo’s own software platform, the data of three distinct SAAX-type ShapeArrays were combined into a single, seamless profile of the seabed. Three profiles made of nine SAAX-type ShapeArrays in total were trenched into the seabed to establish automated subsidence monitoring before million of tonnes of rock fill was dumped into the bay. The longest settlement profile out of the three measured 330 metres long.

In addition to ShapeArray, Cautus Geo has installed 27 piezometers at nine different locations–the deepest are more than 50 metres below the seabed.

“It is important for our customer to have full documentation on the settlements to ensure that the ‘new ground’ is stable and suitable for building,” Atle Gerhardsen, Cautus Geo CEO, said.

Cautus Geo used a battery-operated Data Acquisition System to collect and send to data from the ShapeArray and piezometer installations to Cautus Web. All monitoring data at the site can be used by Cautus Web to quickly present, analyze, and set alarm thresholds to notify project stakeholders of movement via email and SMS message.

Reference:

A. Karlsvik, “Environmental Dredging: The SeaBed Way,” in Seventh International Conference of Remediation of Contaminated Sediments, Dallas, Texas, 2013.