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Mon October 31, 2011 - Southeast Edition
By Kerry Lynn Kirby
Construction of a closing structure at the Union Pacific railroad crossing in St. Charles Parish is the last piece of a large-scale project under way in southeast Louisiana to complete a loop of levees, floodgates and other flood-mitigation structures around the Mississippi River.
Dubbed the Western Tie-In because it ties in a previously unprotected area on the river’s western bank in the western portion of Jefferson Parish and the eastern portion of St. Charles Parish, the project has been broken into eight different contracts to facilitate construction, said Project Manager Jeff Williams, U.S. Army Corps of Engineers’ Team New Orleans.
The $8.37 million Union Pacific crossing contract was originally designed to be let as part of a single contract that included both of the Western Tie-In project’s railroad closing structures, Williams said.
But once an agreement on how construction would affect railroad operation was worked out between the other railroad — Burlington Northern Santa Fe (BNSF) Railway — and U.S. Army Corps of Engineers’ local partner, the state of Louisiana, the contract for that crossing was broken out so that work could proceed while the Union Pacific agreement was negotiated, he said.
Constructing swing gates across active railroad tracks poses a major challenge, said Williams, noting that while both lines are quite active, Union Pacific’s line is its most active in the state.
“Construction work for both contracts has to be done during ’track windows,’ six- to 12-hour time periods when there is no railroad traffic on the tracks. It involves working with a flagman and railroad personnel, and coordinating construction schedules to align work at the tracks with the track windows,” Williams said.
“If you miss a scheduled track window, you need to wait essentially a week [until the next one],” he said.
Boh Bros. Construction Co. is the contractor for the BNSF crossing job, which has been going well and, at about 10 percent complete, is estimated to be finished in December, Williams said. The $4.42 million contract includes construction of a railroad floodgate at the crossing, which is about 0.3 mi. (.5 km) north of U.S. 90 and connects north and south portions of the Davis Pond Guide Levee.
The BNSF gate is one single leaf swing gate, 38 ft. (11.5 m) long and 6 to 8 ft. (1.8 to 2.4 m) tall. The gate opening width is 34 ft. 9 in. (10.6 m).
“Cajun Constructors was awarded the contract for the Union Pacific crossing job, which includes construction of a swing gate at the crossing as well as an elevated ramp crossing La. 18. Work on that job, estimated to be completed in May 2012, is not to the point where it needs to be coordinated with track windows,” Williams said.
The Union Pacific gates are dual swing gates, each 33 ft. (10 m) long and 5 ft. (1.5 m) tall. The gate opening width is 65 ft. 6 in. (20 m).
“The swing gates at both crossings will remain open at all times until a tropical storm is approaching the area,” Williams said.
The Western Tie-In is a component of the Corps’ Hurricane and Storm Damage Risk Reduction System (HSDRRS) for southeast Louisiana.
The HSDRRS includes five parishes in metro New Orleans — with a population of close to 1 million — and consists of 350 mi. (563 km) of levees and flood walls; 73 non-federal pumping stations; three canal closure structures with pumps; and four gated outlets.
The Western Tie-In project consists of a series of approximately 4.5 mi. (7.2 km) of levees and flood walls along the Davis Pond Freshwater Diversion Canal and Outer Cataouatche Canal in portions of Jefferson and St. Charles parishes.
In addition to the two railroad gates and the levees, the Western Tie-In includes a pump station, a navigable closure structure across Bayou Verret for maritime access, an elevated crossing at U.S. 90, and a highway crossing that ties into the Mississippi River Levee.
Once completed, the Western Tie-In will link the Lake Cataouatche earthen levee to the Mississippi River Levee system in Ama, La. Communities benefiting from the Western Tie-In project include Ama, Waggaman, Avondale and Bridge City.
The structural features being built by the Corps are designed to reduce the risk associated with a 100-year storm surge event, or an event that has a one percent chance of occurring in any given year. The Corps modeled with 152 different storms to come up with its risk-reduction plan.
“Because the Corps’ priority is public safety, every effort has been made to move the project along so as to be prepared for a storm surge event. Thus, it has been a “test bed” for different construction methods that facilitate progress, like the splitting of contracts when one component is holding up the start of another,” according to public affairs officer René Poché.
“A contract covering construction of a mostly east-west earthen levee running parallel to U.S. 90 was split in two for that reason. Because the design was ready for the sand base of the levee, that portion of the structure was split off so that work could begin while design work continued for the earthen levee, which has essentially the same footprint on top of the sand base,” Williams said.
The $10.9 million contract for construction of 2.5 mi. (4 km) of sand levees was awarded to Phylway Construction, which completed the work in July 2010. The sand levees formed sand cells that were unwatered in preparation of the clay levee construction.
An unwatering process was used to remove surface water for building in dry soil conditions and entailed using collector ditches in combination with surface grading to bring water to a collection area where the water could be pumped away using portable pumps, according to Williams.
“Very little unwatering was needed because using sand allowed for easy construction and compaction in wet conditions. Basically, the contractor would dump sand and push as well as compact it in place without having to unwater the area. Three different temporary bridges were constructed across the Outer Cataouatche Canal using this method,” Williams said.
The sand cells constructed under that contract were intended to provide some flood protection from the Davis Pond Freshwater Diversion Structure and from any tidal influences.
“The sand cells worked quite well, and during heavy flooding events, the sand cells held even when water was within six inches of the top elevation,” he said. “Although the project name implied sand cells, in reality it was three different cofferdams strategically placed to allow for access and construction of the (earthen) levee.”
The same unwatering method was used on the complementary $30.22 million contract to build approximately 2.8 mi. (4.5 km) of clay levees — referred to as the East to West Levee — to the 100-year level of protection. That contract was awarded to WRS Compass with completion estimated for October.
“The contractor was required to use unwatering because the job entailed building earthen levees in lieu of sand cells. The contractor subdivided the area into several different sections and used unwatering techniques to remove water in the area he was working,” Williams said. “He would get the levee to a certain elevation before moving on,” Williams said.
“Generally, when constructing earthen levees, borings are taken to understand what kind of soils exist below where the levee is to be constructed,” he continued. “The existing materials are used or removed depending on the required design. This earthen levee was designed using the existing soil conditions.”
The contractor was required to use sand in the inner core part of the levee, which allowed for construction in a wet environment.
“The contractor used large construction equipment to move, shape and compact the sand to required compactions based on the design,” said Williams. “Once the sand reached a compaction rate and certain elevation, the contractor then started using compacted clay placed in even lifts, which basically prevents water from going through the levee.
“The shape and height of the levee was determined during design based on many factors, including existing soil conditions, added materials and water elevations. The 100-year elevation for that levee is 11.5 feet, so the levee was constructed to an elevation of 13.5 feet to allow for 2 feet of settlement over time. This elevation was established by New Orleans hydraulic studies,” he said.
Another stretch of levee tying in both railroad crossings and the new U.S. 90 bridge closing and flood walls across that highway was essentially completed in November 2010.
The $5.33 million contract, awarded to DQSI, entailed raising about 1.3 mi. (2.1 km) of the Davis Pond Guide Levee to the 100-year elevation.
Referred to as the North to South Levee, it was a standard earthen levee, Williams said.
“Not a lot of issues there. Just waiting on grass to grow,” he said, noting that while a lack of rain due to summer drought had helped the project progress, that same lack of rain delayed grass growth.
Construction of a closure structure across Bayou Verret, which is a navigable waterway, is another matter.
“The entire job area is very swampy, marshy wetlands, so while the conditions were no surprise, they present a lot of challenges for construction, Williams said. “Basically, it requires a lot of cranes working off barges because there is not a lot of land access,” said Williams, noting that this is nothing new to contractor Tetra Tech, which was awarded the $28.95 million contract.
The contract entails constructing a sector gate built to the 100-year level of protection and connecting the East to West Levee on the east and west sides of the canal. It also includes construction of flood walls, small levee sections and a bypass channel.
“In southern Louisiana, in general, you’ll find all pile-supported structures because of the terrain,” said Williams.
“Like a lot of the area north of U.S. 90, the job area also posed environmental concerns,” Williams said. “Concerns that by controlling floodwaters they’d actually end up starving the wildlife were addressed in the design phase by pretty standard measures like adding sluice gates, a bypass channel and culverts.”
The job is about 60 percent complete, with an estimated finish in January 2012. Interim mitigation features include temporary retaining structures and sheet pile.
A $38.48 million contract, awarded to James Construction Group, calls for building a highway bridge over a flood wall at the intersection of the East to West Levee and U.S. 90.
The job includes the highway bridge at U.S. 90 and flood walls across the highway, which are being constructed together, as well as detour roads.
“The job requires building detour roads for access — one north of U.S. 90 and one south of U.S. 90 — because it is a major highway and main evacuation route. Traffic is to be detoured for a significant portion of the construction period,” Williams said.
The 19-ft.-tall (5.7 m) bridge was designed with a 2,100-linear-ft. (640 m) span, although it will be 2,740 linear ft. (835 m) with approaches.
“Conditions in the job area proved much worse than expected. It’s very swampy and not stable at all. It was just basically muck,” said Williams.
“Working in those conditions required working with the engineer and designing a stabilization method,” he said. “And the Corps had to work with the contractor to resequence construction. Special cement injection equipment is being used to address soil stabilization issues and to strengthen the base for the detour roads.”
The worse-than-expected conditions added “significant time growth to the expected finish,” Williams said.
The project is 20 percent complete, with completion estimated for May 2012.
Interim mitigation features include Hesco Baskets — metal baskets filled with a geotechnical fabric that are interconnected and filled with sand. Hesco Baskets are being used as an interim measure for the Union Pacific crossing as well.
The Western Tie-In project entails approximately 17,000 cu. yds. (12,997 cu m) of concrete — 12,000 cu. yds. (9,174 cu m) for bridge construction and 5,000 cu. yds. (3,822 cu m) for flood walls. Roughly 37,000 sq. ft. (3,437 sq. m) of sheet pile is being used in the flood wall construction.
The majority of the embankment material, about 95 percent, was hauled in from nearby borrow pits.
The Western Tie-In area starts at the intersection of the Outer Cataouatche Canal and U.S. 90, site of the U.S. 90 Pump Station Relocation job.
A $6.99 million contract, awarded to Healtheon Inc., entails constructing a relatively small 150 cfs (cubic feet per second) pump station to transfer water from the Inner Cataouatche Canal to the Outer Cataouatche Canal, Williams said.
The pump station’s intake basin receives water from four 54-in.-diameter (137 cm) culverts that are part of the Inner Cataouatche Canal system, he said. The intake basin is more than 20 ft. (6 m) deep with an area of 20 by 50 ft. (6 by 15.2 m).
“Thus far, the most challenging construction feat was the excavation to construct the intake basin,” Williams said. “The 28-foot-deep by 45-foot-by-75-foot-area excavation required a very strong temporary retaining structure to resist the large forces caused by the adjacent levee while also maintaining slope stability.”
“The water is pumped out of this basin via two vertical lift pumps, each 75 cfs,” Williams said. “The pumps will automatically turn on to drain water from the system when the water surface elevation (WSEL) reaches minus 6.6 at the pump station. From the pumps, the water is relayed to the Outer Cataouatche Canal via twin 42-inch-diameter steel pipes that are raised to pass over the levee and are founded on pile bents, with the piles more than 50 feet long. As the water discharges from the pipes, rip rap protects the canal against erosion,” Williams said.
“The pump’s electrical equipment is housed within a building that rests upon ground and a slab built up to a 5.0 elevation,” Williams continued. “The pump station does not have a permanent backup power source but is capable of receiving one in the event of an impending storm event.
“While construction of the pump station is typical earthwork, reinforced concrete placement and steel work, the electrical and mechanical equipment to be installed requires much foresight and careful installation,” Williams explained.
The project is about 27 percent complete and estimated to be finished in March 2012.
“While the Corps is a very visible lead federal agency, the Western Tie-In project involves not only the Corps and its contractors, but also state partners, local municipalities and other federal agencies,” Poché stressed.
“This project exemplifies that team effort,” he said. CEG