U.S. Army Corps of Engineers photo
Covering 4,565 sq. mi. (11,823 sq m), Bluestone Dam has the largest drainage area of any dam in West Virginia. Behind the dam is Bluestone Lake.
The U.S. Army Corps of Engineers is midway through a 20-year, $300 million construction project to fully stabilize Bluestone Dam, located on the scenic New River near the town of Hinton in southern West Virginia.
The purpose of the Bluestone Dam Safety Assurance project is to upgrade the dam to bring it up to current engineering standards.
The ongoing stability project, scheduled for completion in 2020, will significantly improve safety, according to Col. Dana R. Hurst, commander and district engineer of the Corps of Engineers’ Huntington District.
Because water from the New River flows into the Kanawha River before flowing into the Ohio River, a dam failure could cause major flooding not only in Hinton, but also in downstream cities like Charleston and Point Pleasant. If the dam failed, the results would be catastrophic, with nearly 100,000 people at risk and an estimated $10 billion in damage, including flooding of more than 50,000 structures.
“This nation cannot take a failure of Bluestone Dam. The consequences are enormous,” Hurst told the Register Herald.
When it was completed in 1949 after five years of construction, the heavy concrete dam was designed to use its massive weight to resist pressure exerted by floodwaters. Constructed by the U.S. Army Corps of Engineers at a cost of $30 million, the gravity dam was part of a flood control system intended to reduce major flood damage along the New and Kanawha Rivers. When heavy rains hit, the Corps could opt to hold back water behind the dam to try to reduce flooding downstream. To date, the Corps estimates that the dam has prevented more than $5 billion in flood damage.
Although the dam has not changed significantly over the years, design standards and threat assessments have. The Dam Safety Assurance review and an Issue Evaluation Study showed that without additional improvements, “Bluestone does not meet current standards,” according to Peggy Noel, a public information officer of the Corps of Engineers Huntington District.
“When the dam was built in the 1940s, the ’state of the art’ assumed higher rock strengths. The new design standards have resulted in lower rock strength.”
New studies also indicate the possibility that a severe storm could result in more water behind the dam than expected in the 1940s, with the potential for major damage if the dam failed. As explained by Lisa Morgan, project manager, the Bluestone Dam was built when weather forecasting was not as advanced as it is now.
“Modeling was state-of-the-art for the time,” she said.
When the dam was planned in the late 1930s, engineers designed it to be able to safely contain runoff from the region’s worst storm on record, which at the time was a 1916 hurricane that dumped more than 13 inches of rain in 24 hours across much of the upper New River watershed.
“They used history to determine flood damage protection. The science of forecasting has improved since then.”
Because of the new technology — and due to the collapse and failure of other dams, the U.S. Army Corps of Engineers started a Dam Safety Assurance Program in the 1990s to ensure that dams built in the early part of the 20th century meet modern design standards and are capable of operating safely. They also increased potential for rainfall to 20 in., based on 50 years of weather observation and flood data, as well as “probably maximum precipitation” models developed by the National Weather Service.
The dam was revitalized in the 1980s and continues to undergo rigorous routine periodic inspections, performed on a fixed schedule. A routine inspection by a diverse group of experts in the late 1990s using modern techniques revealed potential problems, Morgan said.
“The strength and geography of 55 sections was evaluated: some don’t meet the standard. Various scenarios could see load exceed strength. We want to mitigate issues by bringing [the dam] up to the new standard, even though there’s a low probability of a big storm happening.”
The Corps of Engineers determined that the dam should be raised 8 ft. (2.4 m) and that anchors should be installed to secure its base to bedrock. Because analyses made during the review indicated that the bedrock securing the dam might not be as strong as it was assumed to be when the dam was constructed, adding anchors is of critical importance.
Another recommendation is to convert the penstocks originally designed to accommodate hydropower generation (although never used for that purpose) to augment lake discharge during severe flooding.
Preparing for the Worst
Currently, the dam’s pool is at 1,406.5 ft. While there is room for some expansion, a significantly higher elevation could threaten the structure’s stability. Also of concern is the dam’s foundation. Bluestone has 55 monoliths — individual pieces that came together during construction. The rock underneath the dam could cause those monoliths to slide.
A design was created, based on evaluations of the dam conducted between 1998 and 2005. After Hurricane Katrina in 2005, the Corps re-evaluated elements like debris blockage, protection from scour (erosion) and consequences. The effects of disaster are measured by the probability of an event multiplied by consequences — both in terms of potential life lost and economic impact. Based on this formula, the Corps determined that a failure of the Bluestone Dam would be catastrophic.
When the work is complete, Bluestone Dam will be able to hold 1,520 ft. of water. During the project, a lower “interim” operating pool level is being maintained, with a maximum height of 1,499.6 ft. of water. If it rises much higher, the dam could slide and fail.
Phasing in the Plan
The Corps designed a five-phase program, explained Chuck Minsker, public affairs specialist, Huntington District, U.S. Army Corps of Engineers. Taking a staged approach should reduce interim risk while working on long-term goals, Morgan said.
“It’s precise work that will take a long time, although each goal has a time line.” Several major contracts are under way concurrently, she said.
Phase 1 began February 2000 and was completed in 2004, Minsker said. The $19.1 million contract included installation of thrust blocks on the east face of the dam on the downstream side to add strength and keep the dam from sliding. It also included modification of the penstocks to improve outflow, construction of a temporary access bridge below the dam to accommodate construction and the addition of bulkheads.
Phase 2A work, completed February 2007, was a $7.3 million project that included construction of a gate closure for Route 20, improvements to the access road, construction of a fishing pier and the addition of another monolith to the east abutment.
Phase 2B work includes strategic installation of 216 high-strength steel anchors. The anchors are constructed of steel strand cables in which each strand has a 35,000-lb. (15,876 kg) design load, Mike McCray, chief of engineering geology section, explained.
A multi-strand anchor is a group of cables attached to the foundation rock at one end and to the dam by way of an anchor head and bearing plate at the other end. Most of the anchors are composed of 61 strands, which can add up to 2 million lbs. (907,185 kg) of stabilizing force to help hold the dam in place during floods. The cables are lowered through the dam into the foundation rock through a predrilled hole and the cables are bonded into rock. The cables are then stretched, using a specially made hydraulic jack and locked off at their design load.
It takes 20 to 30 days to install one anchor, Morgan estimated, using technology borrowed from the oil and gas industry. Pilot holes are drilled, relying on real-time surveying and 3-D modeling, she explained. Then the holes are drilled out to a 16-in. (41 cm) diameter to a depth of 270 ft. (82.3 m) into the bedrock.
“There are many steps,” she summarized, “such as pressure grouting to make it watertight and installing a sleeve with corrugated pipe for corrosion protection.”
As of early 2011, this phase was 80 percent complete, with 184 anchors installed by Bayman Construction Corp., which won the $60 to 70 million contract. Funding from the American Recovery and Reinvestment Act provided an additional $36 million to the regular budget for the installation of an additional 54 anchors in the spillway and east abutment areas to help stabilize and strengthen the dam, and for the construction of a work platform along the western downstream face (above the spillway area). The work platform allows crews to add anchors without disrupting the operation of the dam.
Phase 3, which has just begun, includes work to increase the discharge ability of the dam’s penstocks. Hurst explained that these can be used to release water at the base and relieve base water pressure and dissipate energy during a large storm event. However, as Morgan noted, there is concern about erosion, so the penstock discharge areas and other areas immediately downstream of the dam will be lined with concrete
The $48.5 million contract for the construction of scour protection and a concrete stilling basin below the penstock discharge area on the east side of the dam was awarded to Shaka Inc., Jeanette, Pa., in September 2010.
“When the penstocks are operated, the streams of water would have enough force to peel away the bedrock. The scour protection is a concrete covering over the bedrock that protects it from the damaging force of the water and uses high-strength concrete that’s designed for high water velocities,” McCray said.
Concrete divider walls, right and left training walls and a concrete stilling basin with concrete baffles will be installed in the area below the penstocks. A baffle system is part of a stilling basin, designed to slow the energy of the water, Morgan said.
“It’s two rows of concrete blocks that take the energy out of the water, so that water doesn’t have the erosive capability as when it first comes through the penstocks,” said Ken Halstead, regional technical specialist of Flood Damage Reduction.
Phases 4 and 5 will be awarded in 4 to 5 years, completing the project. That work will include installing the remaining 60 high-strength anchors over the stilling basin area, the construction of an 8-ft. (2.4 m) pre-cast concrete parapet wall on top of the dam, scour protection in the stilling basin, improvements to the spillway and mitigation features.
At the Midway
“We’re halfway through the project,” Morgan said, “but there is significant construction yet to do. There’s still work to be bid.”
Two different procurement methods are being used: RFP, which allows the Corps to choose contractors based on their credentials and qualifications and invitation for bid, which selects the low bidder.
Recent work has required an average of 31 to 41 workers onsite each day; the maximum number on the project at one time was 60. Current equipment on the job includes a Manitowoc 777, a Hutte 202 directional drill, a Hutte 205 one-piece hydraulic crawler drill rig, a Mud Puppy, generators, air compressors, an IT 28G loader, pumps, a Manitowoc 8500 crawler crane, CK 850 Kobelco crane and a High Shear 1010E grout plant.
Scheduling has been arranged in phases by the type of work, with clauses in the contracts for weather delays built in to the schedule. The pools aren’t impacted by the work, Morgan said. “The lake is a huge draw. We will continue to maintain recreational use during the project.”
A full-time safety officer ensures safety for everyone during construction. Rusty Landry, a certified health, safety and environmental specialist of Bayman Construction, said employees have worked 965 days without a lost-time accident. Although work proceeds safely and on schedule, Morgan reflected that it has been “one of the district’s most challenging projects.” CEG