Rocky Pen Run Dam
Location
Stafford, Virginia
Client
County of Stafford
Services Provided
Comprehensive Design Reviews
$25M Cost Savings in Value Engineering
Retained for Foundation and Dam
Construction Field Engineering Services
Project Overview
Schnabel was retained by the Stafford County Department of Utilities as a partner to URS Corporation for the design and construction of the Rocky Pen Run Dam Project, a 130-ft high, 1,000-ft long earthen embankment with a 160-ft wide labyrinth abutment spillway and converging concrete chute. The reservoir provides more than five billion gallons of water supply to meet growing demand in the county.
Schnabel was retained to work in close association with Stafford County and URS Corporation (dam designer) to provide value engineering input and reviews throughout the project, and to provide comprehensive contract administration and resident field engineering services, field construction observation, and in-situ and laboratory quality assurance testing services for this $100 million water supply development project. The site conditions for the dam were initially judged to be best suited to development of a roller compacted concrete (RCC) dam. During preliminary design, Schnabel offered RCC design recommendations savings of about $5 million. Also, due to inconsistent and difficult to interpret foundation investigation findings, Schnabel convinced our partners that an initial foundation excavation and treatment contract would be advisable.
During the initial foundation contract, Schnabel triggered a reanalysis of earth fill and RCC options due to deeper and more weathered foundation rock than originally anticipated. That analysis led to a decision to change to an earth dam design, with estimated savings of $10 million in construction cost. Schnabel later found that detailed topographic mapping revealed more storage than originally anticipated. Schnabel analyses showed that lowering the pool by four feet and providing a labyrinth spillway as opposed to the proposed gated spillway would save an additional $10 million without measureable loss of safe yield.
Dam construction is under way, with completion scheduled for late 2013.