Harrison County, the Gulfport/Biloxi resort area of the Mississippi Gulf Coast, is rebuilding eight miles of pedestrian and bicycle “boardwalk” that were destroyed by Hurricane Katrina. Although this steel and wood design boardwalk had withstood numerous hurricanes without any damage, Katrina proved its downfall. Work commenced on the $10-million Pedestrian Pathway project this past June and will continue until expected completion in December 2009.
“Hurricane Katrina certainly had a far higher storm surge than any other hurricanes or tropical storms we've had on the coast,” explained Bobby Weaver, director of the Harrison County Sand Beach Authority. “First, we had to understand why it came loose the way it did.” About 84 percent of the boardwalk was uprooted, according to Weaver.
“There was no vertical wall along the south face to prevent wave action from getting under the walkway,” was the factor that Harrison County engineers and Bill Mitchell of Brown & Mitchell, Inc. (BMI) identified as the cause of the failure. Weaver described how sand had filled in many areas below the boardwalk, but there were enough pocketed areas that the storm surge was able to push the boardwalk upward. The force sheared the anchored bolts from the top of the concrete seawall.
“We knew we had to build a vertical wall to prevent the wave action so there would be no way for waves to penetrate the structure and lift it up,” Weaver concluded.
With post-Hurricane Katrina FEMA funding through the Stafford Act approved, Harrison County contracted consulting engineers BMI to design the new boardwalk of concrete. The county was able to get the concrete structure approved as a replacement within the range of mitigating cost. BMI had designed portions of the previous boardwalk, so they knew what they were up against.
“Harrison County has 26 miles of beach. Eight miles have a boardwalk for pedestrians and bicyclists,” said Larry Landry, resident engineer with Brown and Mitchell Engineers. The remainder of the distance is comprised of sidewalk adjacent to US 90, which runs just north of the seawall and is part of the MDOT (Mississippi Department of Transportation) right-of-way. “The eight miles are not continuous, but broken into 51 sections varying in length from 200 feet to half a mile.”
The specifications for the new pedestrian walkway call for the use of standard MDOT mix for bridges.
Coleman Hammons Construction Co. won the bid this past spring as the prime contractor for the project. The first step of the contract was to remove the eyesore – remaining steel and timbers of the previous boardwalk – within 75 days. Coleman Hammons subcontracted O'Brien Construction for the removal, giving Coleman Hammons and their framing/concrete placement contractor, H.C. Jones Construction, time to mobilize.
To speed production, a series of crews prepares for the actual concrete placement. Excavations reach 6 to 8 feet down to the bottom of the seawall, according to Neil Blair of Coleman Hammons Construction. “The new wall will sit on the last step of the seawall.”
Because U.S. 90 has a number of parking bays along the seawall, the width of the pedestrian pathway varies between 9 and 12 feet.
One crew saw cuts the top of the seawall and the step to create a straightfinish; two crews from H.C. Jones frame the new walls; one crew from O'Brien backfills with sand after the wall is poured; then the Jones crews come back in to frame and place the slab walkway. The slab is 7 inches thick in the pedestrian area, but reinforced to 12 inches along the edges. Buzzard Rebar is providing the steel reinforcement, and Bayou Concrete, a MMC company, is supplying the concrete for over 40,400 lineal feet of wall and walkway.
The contractor has rented one 6-inch Thompson pump and two 3-inch Wacker pumps to keep the water level down in the trench. Aside from Hurricane Gustav this past September, water infiltration has been an issue along the job site. Surprisingly, the water has been leaching from the land direction rather than from the ocean. More than water, the greater issue with Hurricane Gustav was the amount of trash that washed into the seawall area, according to Blair.
“One of the reasons we started building at the Pass Christian side was the logistical issues with the highway contractor reconstructing and paving Hwy. 90/Beach Boulevard,” said Weaver. “We wanted to start in an area where the highway work didn't impede our efforts and we wouldn't interfere with highway work.”
After completing the sections between Pass Christian and Long Beach, the walkway construction will move over to the longer sections in the more heavily trafficked areas of Gulfport and Biloxi. Superior Asphalt will be completing highway work in that area; during the winter months, there will not be as many tourists trying to access the beach.
Moses Electrical is roughing-in electrical boxes for pedestal streetlights to be installed at a later date. When completed, wooden benches will provide respite at the ends of each section, and wooden stairs will lead down to the white sandy beach.