The use of secant pile walls in the rehabilitation of the Pohick Creek Dam No. 2 (Lake Barton) auxiliaryspillway

摘要

Pohick Creek Dam No. 2, known as Lake Barton, was built in 1978 in Fairfax County, Virginia. This structure was built as a high hazard dam due to its location in an urban environment. In 2004, the Virginia Division of Dam Safety issued a conditional certificate for Operation and Maintenance because the vegetated earthen auxiliary spillway could not pass the Probable Maximum Flood without breaching the structure. Under the authority of the Small Watershed Amendments of 2000 (PL 106-472), the USDA Natural Resources Conservation Service prepared a rehabilitation plan for the dam. The plan provided for building a reinforced concrete wall at the end of the control section and a concrete secant pile wall at the end of the constructed outlet section. Construction was completed in 2010. The secant pile wall was constructed of 79 alternating reinforced and non-reinforced concrete piles drilled an average of 68 feet into the ground. Tieback anchors were utilized to prevent the secant wall from overturning inthe event the downstream material was removed during the design event. A 6.6 foot deep reinforced concrete wall was installed across the 70-foot wide control section and up the side slopes to the elevation of the top of the dam. The footprint of the construction site was 0.7 acres, the construction time was 7 months, and the total construction cost was $2,808,715.