Case study: Strong-motion arrays for dams

March 2006

PDF article available

The Porțile de Fier hydroelectric complex is located on the River Danube, where the river leaves the gorge of Porțile de Fier (“Iron Gates”). At this point, the river forms the boundary between Romania and Serbia, where the gorge is known as Đerdap.

Constructed between 1964 and 1972, the Porțile de Fier I dam was the first to be constructed across the Danube, and created a reservoir stretching through the gorge as far as Belgrade. In 1984, with the completion of a second dam 80 km downriver of the first, the hydroelectric complex reached its current configuration.

Hidroelectrica, the state-owned operator of the Romanian project, has commissioned an array of 8 Güralp instruments to study the movement of the dam and monitor its structure.

Landsat satellite image of the Porțile de Fier hydroelectric complex (NASA).

Installation layout

Hardware connections at each station.

The different networking technologies in use.

The array is spread over four sites.

Two CMG-5T strong motion accelerometers are installed on each dam. Each pair is connected to a 6-channel CMG-DM24 digitizer and CMG-DCM data communications module, which interfaces with the local network over a fibre-optic link. Power to the installations is provided by an on-site UPS.

A further installation at St. Petru, near Porțile de Fier I, contains a CMG-5T instrument and a CMG-40T-1 medium motion velocity sensor, with a DM24 and DCM configured similarly to the dam installations. These instruments measure free-field ground motion, which can be compared with the results from the dam structure during analysis. A fibre-optic link connects this installation to the local network.

The final installation, situated near Porțile de Fier II, uses the same hardware as the one at St. Petru. It is connected to the local network over a 500 m radio link at 2.4 GHz.

Installation ideas

CMG-40T-1

The CMG-5T is a low-noise triaxial broadband accelerometer for strong-motion and structural studies.
The CMG-40T-1 is a 1 second response velocity instrument which partners well with the CMG-5T for free-field installations, giving experimenters high resolution information on relatively small earth movements.
The CMG-DCM is capable of interfacing to many different types of network link, including serial modems (direct or using PPP), radio links, VSAT or fibre-optics. The DCM can provide real-time data to network clients using a numbder of protocols, including Scream! and DSS.
For smaller projects, the Güralp Serial Server / UPS combines Ethernet networking with a built-in power supply. Data from these units can be collected at a central PC running Scream! and forwarded to a wider network as appropriate.



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