Defending the Marina

    Nov. 1, 2002
    The historic city of Cambridge, MD, sits at the mouth of the Choptank River as it enters Chesapeake Bay. The 30-mi.-long Choptank is home to freshwater large-mouth bass upriver and rockfish in the lower saltwater area. As such, Cambridge is headquarters to a substantial amount of commercial and recreational fishing each year.Figure 1.

    Top View of marina showing the location of the 2,300-ft. bulkhead replacement.The original City Marina basin was built in the 1920s, with the original bulkhead replaced by a creosote 3×10 wood bulkhead in 1956. In recent years, City Engineer George Hyde began to carefully check and evaluate the almost-50-year-old 2,300-ft. bulkhead for the 180-slip marina, having detected early signs of erosion and damage. By 2000, there were areas of severe deterioration, with cave-ins behind the shifting walls that were dangerous to boat owners and pedestrians walking the waterfront. The area in summer is bustling with a variety of family activities that include concerts in the park, picnics in the parking lot, and Fourth of July fireworks. Vehicular traffic is heavy in this very active area. Action was needed, and based on Hyde’s recommendation, the city agreed that the bulkhead walls needed to be replaced for the start of the 2002 season. Work was to begin in late summer and be completed during the winter months when boats were in storage. With detailed engineering drawings ready for the all-new third bulkhead (Figure 1), construction bids were due in March 2001. The city had previous experience using vinyl sheet piling on another project, and the bid specification called for complete replacement of the existing wooden bulkhead with vinyl sheet piling.Vinyl sheet piling has become widely accepted as an environmentally inert substitute for traditional products such as copper chromium arsenate- or creosote-treated lumber. Salt water provides an ideal environment for marine borers, which can attack wood piling, and the threat of marine borers has grown rapidly on the East Coast. Ironically, for many years this problem was nonexistent because of water pollution. But as stricter environmental regulations have been enforced, water quality has improved and the borers are making a triumphant comeback. Their return threatens timber piers and bulkheads from Maine to Florida. Vinyl piling is impervious to sunlight, salt water, and marine borers. “We’re a fairly small town with a population of around 12,000,” notes Hyde. “So installation of 2,300 feet of vinyl sheet piling at a cost of $650,000 proved a pretty big project for us.” The award went to Baltimore Pile Driving & Marine Construction Inc. of White Hall, MD, a company that specializes in marine construction.“Since the City of Cambridge used vinyl sheet piling before, we elected to use the same brand for this project,” says Charles “Skip” Wolfe, the project supervisor. “Even though the panels were only 12 feet in length for the first project phase, we ran into a major time-consuming, labor-intensive headache. The panel design we started with required that two 1-foot-wide panel sections be threaded together to form the required 2-foot-wide bulkhead configuration before driving. It didn’t take long to realize that it was very easy to experience joint deflection during driving. This resulted in a decrease in coverage as well as a problem in keeping the two-piece panels plumb. So as we moved into the project’s second phase, we faced an important decision. Panel length would increase to 18 feet. With such a long panel, everything involved in handling and driving would become extremely difficult. We conferred with the city, and after we voiced our concerns, they agreed to let us make the product decision for the second phase. Figure 2.

    Bulkhead cross-section showing installation of the old wall.Figure 3.
    Bulkhead cross-section showing installation of the new wall.“After a thorough evaluation of our options, we switched to using a single, 2-foot-wide, 18-foot-long C-LOC 9900 panel. Driving these rigid, heavy-duty panels was easy with a vibratory hammer. We used our excavator to lift the 180-pound panels in place and thread the new panel into the already-installed sheet, then vibrate it into the ground. There were a few hard spots where we had to use a water jet to assist in driving the panel. In reality, the profile design of the 2-foot-wide C-LOC vinyl panel system proved the better choice. The panels interlock at the rear, away from stress for added strength, giving excellent protection from wave action from large boats and debris. Both commercial and recreational boats anchor at the marina. After all, in this part of the world, it’s crabbing in the summer, oysters in the fall.” Crane Products Ltd. of Columbus, OH, manufactures C-LOC. “To keep the wall straight during installation,” Wolfe explains, “the main thing you need is a jig. Here we used 4-by-6s driven vertically every 16 feet along a string line representing the wall. The 4-by-6 tops were slotted, and approximately 3-foot pieces of the 4-by-6s were lagged to the top of the old wall using the slots. We then attached them to the 4-by-6 vertical slots to establish the needed driving height as well and provide a very straight guide for installing the vinyl sheet panels. We attached the back bottom wales to the verticals and drove the vinyl sheets against them. Outside wales were hung and bolted, and the tie rods installed. The old wall was then removed, and installation was completed with a washed sand backfill. A new concrete pedestrian walkway was then installed behind the new bulkhead.”Because this was a Navy wall bulkhead installation, the key was to assemble the front wale, sheet piling, and back wale into one cohesive structure (Figures 2 and 3). “As the wall was approximately 9 feet above the mud line, and with only one level of tieback rods and deadmen required, we elected to have a top, front, and back wale to stabilize the top of the wall and support the cap board,” explains Wolfe. “We then hung a front and back lower wale to run the tie rods through to the vertically driven deadmen. The tie rod nuts were adjusted as necessary to maintain a straight wall. The wall was capped with a treated 2- by 14-inch board.“While we are a 12-month pile-driving operation,” Wolfe continues, “I prefer to install a wall like this in the wintertime because the tides are lower and you have more bulkhead surface area to work with, especially in installing the bottom tie rods. As part of this job, we learned a lot about differences between vinyl sheet piling panel designs and products. Most brands we looked at use recycled plastic material, or regrind, which if not processed and extruded properly can result in very visible, unattractive surface imperfections. The C-LOC people do a great job in providing a smooth, UV-protected, clay-color surface that complements this historic waterfront for the start of the marina’s ’02 season.”