Bulkheads are very similar in design and construction as standard retaining walls. The primary difference in definition between a bulkhead and retaining wall is that a bulkhead is retaining earth on one side, and is partially surrounded by water on the other. Materials used in the construction of bulkheads vary, but generally are the same as those used for the construction of the piers. Timber construction generally uses a pressure-treated marine grade material. A creosote material was used for some years, but it has been discouraged lately. Creosote grade material does not last as long, deteriorates and needs constant maintenance and replacement.
Masonry is often used as a bulkhead material. Masonry can take the form of brick, block, or poured concrete. This type of construction, unlike the piers, should rest upon a footer that carries the weight of the wall. Provisions should also be incorporated in the masonry wall to provide tiebacks up into the earth. Masonry bulkheads, much like retaining walls, generally have a granular backfill and a drainage system that would allow water that accumulates and drains from behind the wall. Brick and block masonry walls are used in residential applications; they require considerable maintenance and generally have a very short life expectancy. Displacement of the brick or block and the lateral pressures being exerted from the earth behind the wall cause breaking of the mortar joints. Tiebacks can be installed through the faces of the brick and block areas utilizing steel channels or wooden planks secured back through the earth with tie rods. This method, at best, is temporary.
Riprap or rubble is often used as a bulkhead system where the height of the bulkhead does not have to be above 2 or 3 feet. Riprap, by definition, is simply the “haphazard arrangement of loose, irregularly sized or broken stones used as protection from erosion along the shoreline of a lake, stream, or waterfront.” The material can be installed in low-lying applications to retain the earthen surface and prevent erosion. However, the applications are limited to low-lying applications, due to the inability to stack this material to a sufficient height and depth to prevent movement from lateral forces.
The construction of wooden bulkheads is much the same as that of any other retaining wall system. On the waterways, the supporting structures could be driven piles, which are sometimes referred to as “tie piles.” Attached to the earthen side of the piles is a horizontal-supporting member referred to as a “whale.” These horizontal members are also called “rangers” or “whalers.” The whalers are attached to the piers with galvanized fasteners, generally in 3 to 4 locations, depending upon the height of the retaining system. The size of the whalers depend upon the spacing between the piers and the amount of earth retained behind the bulkhead. Attached to the horizontal whalers is a sheathing material, generally of dimensional pressure-treated lumber. This dimensional lumber can range from 2 x 6 to 2 x 8 and are attached to the whalers. Gravel backfill should be installed behind the bulkhead system with a geotextile fabric that permits dirt from accumulating into the granular backfill. This provides a weeping system so that the water and moisture that accumulates at the rear of the bulkhead can drain away.
The largest problem with the bulkhead systems is erosion of the backfill area. As the backfill begins to erode, the granular surface is affected, as is the drainage. The increase in hydrostatic pressure, coupled with the lateral forces of the earth itself, tend to push the units over.
Wave and water action on the front side of the bulkhead area also creates a number of problems. It is important that the structural material be constructed of a marine grade pressure-treated lumber, or creosote material; as pieces begin to deteriorate, break, etc., they should be replaced promptly. Damage and rot to the sheathing boards and whalers is time-consuming and fairly expensive, since the entire earthen surface and granular backfill behind it will need to be removed. In general, the cost of repair or replacement of an existing bulkhead system utilizing pressure-treated lumber is based on per linear foot of bulkhead, depending upon the height of the bulkhead system and can be expensive. As with retaining walls, the bulkhead system should not be displaced, leaning, cracked or broken. The earthen surface on the retaining side of the bulkhead system should be to the top of the bulkhead so that surface water runs down over the top of the bulkhead and does not accumulate behind the wall.
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