The Tennessee River sees a high volume of barge traffic carrying mostly coal (11.3 million tons) and crude materials (10.7 million tons) like rock from nearby Vulcan Quarry and sand mined out of the Ohio River near Paducah. Farm products make up about 10 percent, or 3.8 million tons, of the goods shipped. Shipping by water is generally a very efficient process, except when a lock creates a bottleneck.
The existing lock at the Kentucky Dam does just that, creating some of the longest delays for commercial tows in the country. Last year barges queued up more than 9 hours on average, but in January, Don Getty, U.S. Army Corps of Engineers Nashville District project manager of Kentucky Lock Addition, said the average delay was more than 14 hours.
At 600 ft. (183 m), the existing lock is too short for most barges to get through all at once. Tugs often bring 15 barges in a tow to Kentucky Lock. Spanning up to 105 ft. (32 m), the tugs have to break apart to get through and then tie back together — which is dangerous, according to Getty. It also extends the time to 2-1/2 to 3 hours. “Kentucky Lock has some of the longest delay times in the country; last year there was a 9 hour, 35 minute wait, not including the time to get through the lock,” Getty said. Because it takes so long to get through the lock, they average 8 to 10 lockages a day, thus contributing to the delay.
Fortunately for river traffic, a new navigation lock is being built to reduce congestion. At twice the length, the new lock is expected to almost completely eliminate the wait time, especially since the existing lock will remain in operation. “Keeping the existing lock functional is good for water savings with smaller vessels and allows the generation of hydropower with the water saved,” Getty said.
Smaller tugs with barges will continue to lock through the existing lock, while tugs with more barges will lock through the new 1200-ft. (365.8 m) lock, which is landward of existing lock, without the need to break apart. “A single lockage is more efficient,” Getty said. When the new lock is completed, two barges will be able to lock through at the same time, even if they’re traveling in opposite directions.
The U.S. Corps of Engineers placed concrete to top out the first monolith concrete for the Kentucky Lock addition earlier this year, but the idea for this project was conceived in the late 1970s or early 1980s, Getty said. A feasibility study was completed in 1992 to demonstrate that the project is worthwhile and that the benefits exceed the cost. It was authorized by Congress in 1996 (typical of Corps projects), Getty explained and construction began in 1998.
The $862 million project — an engineer’s dream, Getty describes it — consists of 10 major contracts, seven of which have been completed — mostly road and railroad work, Getty explains. Three involved large relocations: a two-lane highway and a single railroad track were moved downstream with new bridges. The two 3,000-ft. (914.4m) bridges (of seven new bridges on the project) cost $200 million. The third relocation consisted of moving some high-voltage lines that were in the way, at a cost of $13 million.
Eight sealed bids were submitted, the low bid winning. Thalle Construction Company, Hillsborough, N.C., was awarded the contract to build the first nine of 61 concrete monoliths that will comprise the two walls of the new lock in 2010, currently at $97 million (the current contract value, not the bid amount). Each monolith will be 40 to 50 ft. (12 to 15 m) long by 100 ft. (30 m) tall.
Having excavated rock and soil, in February, crews completed the first monolith. All nine are scheduled to be completed by spring of 2016. Currently, they are 80 percent complete.
The current contract will require 130,000 cu. yds. (99,392 cu m) of concrete. “That amount is always challenging,” Getty said. Corps requirements on concrete are stringent in order to avoid “concrete growth,” a reaction caused by an alkali-aggregate mix. “Over time it forms a film and grows.” It becomes stressed and degrades. Older locks and dams often have issues and even break apart due to concrete growth, although the existing lock, built in the 1940s, has experienced no concrete growth.
To avoid that reaction, the Corps tested the aggregate and Portland cement for the right mix. “We tested a lot of aggregate, spent several hundred thousand dollars to find suitable sources,” Getty said. They tested at three quarries, one of which is just a mile away but has only two suitable ledges, indicating just how specific the Corps’ requirements are.
An onsite batch plant owned by Thalle speeds up delivery of the approved concrete mix. There was no delivery in late February when the project was shut down for two weeks due to 14 in. of snow and cold temperatures. “It’s very unusual to be shut down a whole week,” Getty said. “Normally, we’re working year-round. We have a cold weather system for placing concrete, but it affects production rates.”
Before concrete can be poured, rebar must be placed. Three tower cranes lift number 18 bars of reinforcing steel, each measuring 40 ft. (12.2 m) and weighing 13 lbs. (5.9 kg) per foot.
The 150 workers on site on an average day must contend with traffic locking through the existing side-by-side lock that shares a common center wall. With centerlines only 200 ft. (61 m) apart, the locks will be in close proximity. “It’s still operating,” said Getty. “Our goal is to minimize the impact and closures.” There were brief closures during bridge construction and he anticipates a longer closure when they build the temporary downstream coffer dam.
Because this area encompasses the largest reservoir east of the Mississippi River, it’s important to protect against a pool of loss while work is taking place on the lock. Two coffer dams will be built for protection, one upstream and one downstream. The upstream coffer dam, a short structure close to the land, has been designed and built.
The downstream coffer dam design was recently completed. Work on it is expected to be concurrent with work on the lock. “There’s plenty of room to work together; we’re blessed with enough real estate. We’ll clearly delineate areas to work in.”
While work on the current contract is in the dry, work on the downstream coffer dam will require building in the wet. Getty said the plan is to float in concrete sections — pre-cast segments 200 ft. (61 m) by 30 ft. (9.1 m) — sink them and fill them with tremie concrete (a special mix) and then dewater them and build with traditional concrete. Portions of the concrete floated in will be incorporated in the new walls in order to minimize impact.
“We’re ready to let [the contract for the downstream coffer dam] to bid this summer if we get the funding,” Getty said.
This is a 100 percent federal project, but 50 percent of the funding comes from a special trust fund on the marine industry on diesel fuel: the Inland Waterways Trust Fund. That became problematic, said Getty, because it was insufficiently funded, causing a delay because “the revenues were not near enough to fund the current project, let alone future projects.” Most of the revenue is going to the Olmsted Lock, a $3 billion project in Ohio, he explains.
Fortunately, two huge watershed events changed things. First, the Olmsted Lock’s cost-share changed from 50/50 to 85/15, freeing up $100 million a year. Second, the marine diesel fuel tax that funds the project increased from 20 cents to 29 cents — the first increase since 1995. “We were hurting for funding the last five years, except for $89 million from the American Recovery and Reinvestment Act,” Getty said. “But now the financial bottlenecks have been cleared.”
The biggest challenge has been financing, but Getty said “the future looks extremely bright.” In fact, he reveals, the Corps is working on developing new funding budgets for additional inland navigation projects.
Geology has posed a challenge. The Corps was aware that the area consists of different types of limestone, all of it karstic limestone with horizontal and vertical features, according to Getty. Nevertheless, it was difficult to predict what they’d find and where they’d find it. As crews excavated rock, which they disposed of on site, they frequently encountered clay-filled cavities that they replaced with concrete.
That creates an issue with the current contract issue because of the extensive grouting needed to form a hydraulic water barrier by filling voids below the concrete in the rock. Because they encountered so many cavities, they had an overrun of grout, which added $8 million to the budget. A significant underrun in grout on the coffer dam helped offset that cost.
The rock is extremely hard; Getty said it has compression strength of 30,000 psi. “It’s hard to drill … and drilling is very slow.”
Environmental and wildlife issues posed minor obstacles. During the two months when fish are spawning, in-water work is halted. In addition, when work disturbs the stream bed, crews must relocate mussels.
Crews also will have to restore the integrity of the dam after they have built the upstream lock.
Despite a completion date of 2022-23, Getty considers work a “fast process.” With $392 million spent to date and one monolith, the project is 45 percent complete. Finishing the other 60 monoliths will require an additional 850,000 cu. yd. (649,871 cu m) of concrete.
There are two to six contracts left to award; the number depends on how the financing is configured. “We haven’t designed them all yet,” he said.