Dan River CCP Low Head Dam Modifications

Brayman Construction was awarded a contract to provide specialized construction services in support of a dam improvement project located on the Dan River near Eden, North Carolina. The project consists of two phases of modifications for the Dan River Low Head Dam. The first phase included the installation of 27EA- Post Tensioned Dam Anchors. Anchors were 1-1/4 DCP Bar Anchors. Nineteen anchors were located on the Spillway (SW), and eight anchors were located on the South Bulkhead (SB). Each anchor has a design load of 113 KIPS. Each hole was core drilled to a diameter of 5 inches using a Commacchio GEO 305 compact drill rig. Anchor recesses were drilled using a stand-mounted core rig. The second phase of the project included the installation of two reinforced concrete bulkheads to supplement the existing steel gates at the spill gate structure. Unknown downstream conditions necessitated the installation of the reinforced concrete upstream of the gates in lieu of the original downstream design. The bulkheads were placed using a concrete pump truck and hopper tremie into a permanent sheet piling form. The form was cut off at the original top of the gate elevation to restore river conditions to their normal state.

Site Logistics

The project site is located on the Dan River, near the North Carolina/Virginia border. All-access to the dam spillway and spill gates had to be via barge or marine equipment. Work on the South Bulkhead was accessed by private land, giving care to maintain the neighboring land owner’s road and property. Since the South Bulkhead was only 3 feet wide at the top, a temporary platform had to be constructed for drilling access. The crew also fabricated a drilling platform on the barge in order to access anchors on the downstream side of the dam spillway. Sheet piling was driven on the dam spillway as a temporary diversion to dewater the work area and allow for safe personnel access to the spillway.

Challenges

The crew battled unusually wet weather conditions in all seasons, which produced extreme variations in river levels. Work schedules had to be developed using constant monitoring of the weather and upstream conditions. The river current near the low head dam necessitated additional marine equipment to safely navigate the water to complete the work.

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