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STABLE-SHORELINE STRUCTURES These structures are constructed parallel with the shoreline to protect it from erosion or other wave damage.A seawall is a vertical or sloping wall that offers protection to a section of the shoreline against erosion and slippage caused by tide and wave action. A seawall is usually a self-sufficient type of structure, such as a gravity-type retaining wall. Seawalls are classified according to the types of construction. A seawall may be made of riprap or solid concrete. Several types of seawall structures are shown in figure 1-16.A bulkhead has the same general purpose as a seawall; namely, to establish and maintain a stable shoreline. However, while a seawall is self-contained, relatively thick, and is supported by its own weight, the bulkhead is a relatively thin wall. Bulkheads are classified according to types of construction, such as the following:
Figure 1-17.Steel
sheet-pile bulkhead.
1. Pile-and-sheathing bulkhead 2. Wood sheet-pile bulkhead 3. Steel sheet-pile bulkhead 4. Concrete sheet-pile bulkhead Most bulkheads are made of steel sheet piles, such as shown in figure 1-17,
and are supported by a series of tie wires or tie rods that are run back to a
buried anchorage (or deadman). The outer ends of the tie rods are anchored to a
steel wale that runs horizontally along In stable soil above the groundwater level, the anchorage for a bulkhead may consist simply of a buried timber, a concrete deadman, or a row of driven and buried sheet piles. A more substantial anchorage for each tie rod is used below the groundwater level. Two common types of anchorages are shown in figure 1-18. In view A, the anchorage for each tie rod consists of a timber cap, supported by a batter pile, which is bolted to a bearing pile. In view B, the anchorage consists of a reinforced concrete cap, supported by a pair of batter piles. As shown in the figure, tie rods are supported by piles located midway between the anchorage and the bulkhead. Bulkheads are constructed from working drawings like those shown in figure 1-19. The detail plan for the bulkhead shows that the anchorage consists of a row of sheet piles to which the inner ends of the tie rods are anchored by means of a channel wale. The section view shows that the anchorage will lie 58 feet behind the bulkhead. This view also suggests the
Figure 1-18.Two types of tie-rod anchorages for bulkheads. order of construction sequence. First, the shore and bottom will be excavated to the level of the long, sloping dotted line. The sheet piles for the bulkhead and anchorage will then be driven. The intervening dotted lines, at intervals of 19 feet 4 inches, represent supporting piles, which will be driven to hold up the tie rods. The piles will be driven next, and the tie rods then set in place. The wales will be bolted on, and the tie rods will be tightened moderately (they are equipped with turnbuckles for this purpose).Backfilling to the bulkhead will then begin. The first backfilling operation will consist of filling over the anchorage, out to the sloping dotted line. The turnbuckles on the tie rods will then be set up to bring the bulkhead plumb. Then the remaining fill, out to the bulkhead, will be put in. Finally, outside the bulkhead, the bottom will be dredged to a depth of 30 feet. To make it possible for ships to come alongside the bulkhead, it will be fitted with a timber cap and batter fender piles, as shown in figure 1-20. These piles, installed at proper intervals, will provide protection against the impact of ships and will protect the hulls of ships from undue abrasion.
Figure 1-19.Working drawings for steel sheet-pile bulkhead.
Figure 1-20.Cap and fender pile for bulkhead.
Figure 1-21.Types of wharfage structures. |
 
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