The Willow Island hydro-electric project is under construction in northern West Virginia, USA, near the town of St. Marys. The Willow Island reservoir has a total surface of 6.65 km² (1,644 ac) and is retained by a 343.8 m (1,128 ft) long dam.
The powerhouse will generate an average annual output of 239 GWh with two horizontal 22 MW bulb turbines. The water will be diverted from the dam and the Willow Island locks that were built in the 1970's to the turbines. In addition to a reinforced concrete powerhouse, an intake approach channel and a tailrace channel are being built for the new hydroelectric project.
An approx. 30.5 m deep rock excavation
For the construction of the new hydroelectric powerhouse, an approx. 30.5 m (100 ft) deep rock excavation had to be built. The excavation support was mainly needed due to a fault line discovered in the rock. Consequently, the design engineer decided to use DYWIDAG Strand Anchors to ensure the stability of the dam during the excavation. DSI USA supplied 28 strand anchors, type 59-0.6".
In order to monitor the forces in the anchors during excavation, three DYNA Force® Sensors were installed on each permanent anchor, totalling 84 sensors. For the first few months during anchor installation, sensor readings were manually taken once a day to monitor the forces acting on the anchors as the excavation progressed. Afterwards, the sensors were connected to several multiplexers using extension cables, and all multiplexers were connected to the readout unit via a main cable. A modem, a controller and a cell SIM card were installed so the data could be accessed from a remote location. A battery and solar panels were used to power the readout unit. The data from the sensors are being remotely taken every three hours, analysed and reported to the owner. The sensor readings are providing valuable information and added safety during the construction of the powerhouse.
In addition, DSI USA also supplied 42 temporary strand anchors with 3-12 strands in lengths between 15.8 m (52 ft) and 25 m (82 ft) to provide temporary soldier pile wall support in the excavation.