Brayman was contracted to provide specialty construction services in support of the Dam Safety Assurance (DSA) Phase 3 Project at Bluestone Dam. Bluestone Dam is a conventional concrete gravity dam situated on the New River approximately one-half mile upstream of the confluence with the Greenbrier River. As a flood risk management project designed and built by the USACE in 1948, the main body of the dam comprises 55 concrete monoliths. The structure has an overall length of 2,048 feet and reaches a maximum height of 165 feet above the stream bed.
The DSA Phase 3 Project involved installation of concrete divider walls, right and left training walls, a concrete stilling basin with concrete baffles, and a scour protection slab in the area below the existing penstocks on the east side of the downstream face of the dam, as well as the installation of additional high capacity dam anchors. The scope required 70,000 cubic yards of rock excavation in front of and below dam foundation, placement of 108,000 cubic yards of mass concrete, and 8,000,000 pounds of reinforcing steel, in order to construct the scour protection slab, divider and training walls. Installation of 240 three-inch diameter post-tensioned threaded rock anchors totaling 17,580 feet, and 112 17-strand high capacity anchors tie the scour protection slab to rock. The bar anchors ranged in length from 72 feet to 82 feet and were drilled to a tolerance of 1:100. The strand anchors were directionally drilled to meet a tolerance of 1:150. To allow excavation at the toe of the dam, an earthen cofferdam was built to hold back the river. During rock excavation, a potential slip plane along an existing fault was identified in the line drilled face immediately beneath the cofferdam. As part of the remedial effort, 15-each hollow bar anchors, 38mm (1.5-inch) up to 31-feet in length were installed with a hydraulic top-hammer drill rig in order to support the rock excavation and the earthen cofferdam. A prism target was mounted on each bar to facilitate daily monitoring with conventional surveying equipment. The cofferdam was also instrumented with an automatic data acquisition system (ADAS) with vibrating wire piezometers, a river level gauge, in place inclinometers (IPIs), as well as conventional inclinometers and other survey monuments.
Due to the large volume of concrete, erection and operation of an on-site wet batch concrete plant was necessary. The concrete plant meets the US Army Corps of Engineers’ specifications for aggregate rewash and rescreening with cooling equipment to maintain a maximum mass concrete temperature of 65°F. The rock excavation is processed on-site to a 4-inch minus material and utilized as backfill for the structure. Quality control management involved oversight of all construction documentation, quality control staff, and materials testing including an AASHTO accredited on-site project laboratory. A significant change order, completed in 2012, included installation of an additional 12-each tie-down anchors located on the stilling basin east training wall. The two 26-strand, eight 42-strand, and two 52-strand guide wall anchors were directionally drilled to depths between 105-feet and 130-feet, reamed from 13-inch to 15-inch diameter, and meet tolerances of 1:150.