work underway on a water-discharge structure we designed for poor soil conditions
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design of abutment wall extension at Dells hydro station

design of abutment wall extension at Dells hydro station
Xcel Energy

responding to a sandstone abutment failure improves dam safety

In 2011, erosion and rock slides created a shortened seepage path around an existing sandstone abutment at the Dells Hydroelectric Generating Station. This was identified as a Category I Potential Failure Mode. After working with Barr to inspect the freshly exposed rock faces, Xcel’s project team decided to extend the abutment wall upstream to stabilize the adjacent sandstone wall and extend the seepage path around the abutment.

Barr first conducted an options evaluation summarizing the potential dewatering methods and wall configurations available to create the abutment wall extension. After Xcel selected an option with a downstream seepage-collection system, we collected bathymetry data upstream of the abutment and used it to create a 3D model of the rock surface. Our design included the use of vertical soldier piles with post-tensioned tiebacks drilled 15 to 20 feet into the underlying sandstone. This allowed the reinforced concrete wall to be installed without the need for dewatering or a reservoir drawdown. Barr’s structural and geotechnical engineers finalized the drawings and technical specifications. We also provided construction support that included real-time monitoring of abutment movements in order to maintain dam and personnel safety.