McMahon & Mann Consulting Engineering and Geology, P.C.

Power and Control Tunnel Bridge Evaluation

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Power and Control Tunnel Bridge Evaluation
Project Details
Location: Lewiston, New York
Client: TVGA Consultants for the New York Power Authority
Client Contact: Mr. Bill Broderick, P.E., NYPA

The Power and Control Tunnel Bridge spans the forebay canal at the Niagara Power Project in Lewiston, NY.  The NYSPA contracted with a team that included McMahon & Mann to assess the condition of this bridge that carries power conduits from the Lewiston-Pump Generating Plant.  Cracking of the superstructure was observed over each of the two piers constructed within the forebay canal, and a survey of the bridge profile revealed that the top of the west pier had heaved approximately 5 inches. The expansion joint at the west end of the bridge was closed and frozen in place, and the measured distance between expansion joints is approximately 6 inches less compared to the original construction. We completed a geotechnical analysis of the rock conditions surrounding the bridge to assess the potential for rock squeeze between the walls of the forebay and heave of the shale foundation beneath the piers. A protocol for evaluating movements of the rock and correlating the movements with respect to time was developed. Rock squeeze is a regional problem and data from other nearby facilities was collected to validate a model for describing the time dependent rock movements.  It was concluded that the rate of rock deformation had decayed, and the anticipated future movements of the rock would not have a significant impact on the performance of the structure.  The bridge bearings were repaired and a monitoring program was implemented to validate the conclusions and verify the safety of the structure.

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