Cliffside 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 Broad River in Cleveland County, North Carolina. The project consisted of two phases of modifications for the Cliffside Low Head Dam. The first phase included the installation of 40-EA post-tensioned rock anchors. Anchors were 1-inch DCP bar anchors, with 22 anchors located on the spillway and 18 anchors located on the overflow walls. Each anchor has a design load of 76.8 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 four reinforced concrete bulkheads to supplement the existing steel gates at the spill gate structures. Unknown downstream conditions necessitated the need to install the reinforced concrete upstream of the gates in lieu of the original downstream design. The bulkheads were placed using a concrete pump truck and tremie pipe into a permanent sheet piling form. The form was cutoff at the top of gate elevation to restore the normal state for river conditions.

Site Logistics

The project site is located on the Broad River, near the North Carolina / South Carolina border. All-access to the dam spillway and spill gates had to be via barge equipment. Since the overflow walls were only 2 feet in width 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 dam spillway. The crew installed water control boxes, field-fabricated from road plate sheet steel, to act as a temporary water diversion around the work area and allow for safe personnel access to the spillway.

Specific Challenges

Upstream sediment buildup, particularly near the right abutment of the dam, prevented barge equipment access. With minor equipment re-configuration, the crew dredged 408 cubic yards of sediment under USACE Nationwide Permit 3.

Inclement weather during the performance period included two hurricanes.

One anchor borehole in the spillway encountered a direct connection flow path to the upstream pool via an area of heavily deteriorated concrete. In order to complete the anchor installation, the crew installed a plate patch plate over the area. Consolidation grouting for the borehole incorporated the deteriorated concrete.

The as-found condition of the four gates for the Cliffside Low Head Dam showed signs of heavy deterioration in their interior structural members. To support the weight of concrete during installation, Brayman incorporated an engineered reinforcement panel into the bulkheads.

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