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PPL Holtwood, LLC Power Plant Expansion

Location: Lancaster County, Pennsylvania Client: Walsh Construction Company

JMT provided multi-disciplinary engineering services associated with a major power plant expansion project.  

JMT was engaged to provide a range of support engineering services as the PPL Holtwood Power Plant underwent a $434 million expansion.  The scope included the design of 9 cofferdams and various other engineering tasks for the construction of a new powerhouse to add 125 megawatts in generating capacity, enhancements to the existing fish lifts to improve the passage for migratory fish, construction of a new skimmer wall bridge, and the installation of inflatable flashboards on the existing spillway.

The primary cofferdam on the project was a cellular cofferdam consisting of three 40' diameter cells and a 14' wide closure wall with vertical rock anchors. This cofferdam was designed to retain up to 50' of the Susquehanna River for excavation and construction of the new powerhouse. As part of the fish lift improvements, JMT designed a braced cellular cofferdam with two 25' diameter cells to allow up to 35' of tailrace dewatering, a braced sheet pile cofferdam to enable up to 40' of dewatering of spillway flows, and a braced sheet pile cofferdam with up to 40' of internal dewatering to construct new fish lift attraction water piping. At the new skimmer wall bridge piers, the cofferdams were four-sided, internally braced sheet pile structures to allow up to 25' of internal dewatering. The river piers included an external clamping system to allow the placement of two 18' depth tremie concrete pours, and the land pier had a tie back wall on the highest sheeting face. Also included on the project were two earthen cofferdams, one at the downstream end of the new powerhouse excavation and the other to allow blasting under the SR 372 bridge structure to be done in the dry.

The constructed cofferdams performed as designed and withstood several high water events without detrimental effects. JMT's good work and ability to provide a quick turn around on design requests led to numerous additional engineering tasks on the project.


**Photos of this project were used with permission from PPL Holtwood, LLC.

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