ORCHARD SUBSTATION EXPANSION
LOCATION: NEW YORK
CLIENT: CONFIDENTIAL
MARKET SECTOR: ENERGY UTILITY
SIZE: 3 Acres
THE OPPORTUNITY
This confidential gas and electric utility service provider required the expansion of the Orchard Substation to service the northern Long Island, New York communities. The Orchard Substation is located on part of the former Glen Cove manufactured gas plant (MGP) Site and abuts a residential neighborhood.
THE CHALLENGE
The existing substation, originally constructed at the bottom of a hill, is bordered by existing houses along the southern and eastern property lines. Because available space was limited, the expansion required excavation into the hillside and the installation of retaining walls, up to 30 feet high, along at the southern and eastern edges of the site. It was necessary to construct the wall in a manner that avoided soil movements that would damage an occupied house that was sited nearly on the property line. The presence of a nearby poorly located, buried gravity sanitary sewer complicated site design and construction constraints.
THE PS&S SOLUTION
Supplemental surveys by PS&S, including an as-built survey of the sanitary sewer by CCTV, were used by our site civil engineers to develop site plans that addressed grading, the required retaining walls and other needed site improvements. After completing a geotechnical investigation, PS&S’s structural and geotechnical engineers collaborated to develop a unique and innovative retaining wall solution. A soldier pile and lagging wall, internally braced using rakers, enabled the excavation and regrading to be completed safely. The vertical steel soldier piles were incorporated into the permanent cast-in-place concrete wall to provide the strength and stiffness needed to be limit soil movements. After construction of the concrete wall the temporary rakers were removed. Prior to construction, the sequence of construction and the associated movements were simulated using a sophisticated finite element computer model. During construction of the concrete wall, unexpected soil contamination was encountered. PS&S responded immediately to revise the foundation system; concrete footings were replaced with auger cast-in-place piles. After the expedited foundation redesign, PS&S’s field engineers documented a field load test program and monitored pile installation activities.