Holtwood Hydro-Electric Generating Station Expansion

TRC was retained as the Geotechnical Engineer-of-Record to execute a geotechnical investigation associated with a 125 MW expansion of PPL Corporation’s Holtwood hydro-electric generating facility on the Susquehanna River. Planned expansion work includes

the excavation of an expanded forebay, construction of a new skimmer wall, a new rubber dam atop the existing dam crest, a new bypass tunnel under the existing diversion wall for the existing Unit No. 1 tailrace, and the excavation of approximately 750,000 cy of rock from the one-mile long channel below the powerhouse.

As part of the investigation, TRC executed a comprehensive subsurface exploration program using our in-house drill rigs that consisted of 35 land-based test borings, 5 water-based test borings and 19 packer tests. Forty percussion test probes, 23 test pits and a variety of geophysical testing (seismic refraction survey, underwater side-scan sonar and down-hole high-resolution acoustical borehole televiewer) were performed by others but planned for and executed by TRC’s field staff.

A comprehensive testing program was subsequently executed in TRC’s soil-mechanics lab to supplement the visual classification of soil samples and measure/verify select engineering properties of the soil and rock.

Supplemental exploration programs consisted of 8 land-based borings and LRFD foundation design services for an access bridge over the Norfolk Southern Railroad. Six additional test borings with acoustic televiewer logging of the core holes were completed in order to characterize the rock within the proposed excavation areas beneath the Route 372 bridge.

A comprehensive geotechnical report was prepared which addressed such pertinent issues as rock cuts and rock stabilization using high-strength rock bolts, foundation systems, earthwork, groundwater control, vibration control, seismic design, and excavation protection.

During construction, TRC provided general geotechnical consultation to assist with the resolution of associated issues should they arise.