CHAPTER 6 

 STRUCTURAL FEATURES 



6.1 INTRODUCTION 



This chapter provides illustrations of various structural features 

 and detailed discussions of selected coastal engineering projects. This 

 chapter complements discussions in Chapter 5, Planning Analysis. 



Sections 6.2 through 6.9 provide details of typical seawalls, bulk- 

 heads, revetments, protective beaches, sand dunes, groins, jetties, and 

 breakwaters. These "details form a basis for comparing one type of struc- 

 ture with another. They are not intended as recommended dimensions for 

 application to other structures or sites. Section 6.10, Construction 

 Materials, discusses materials for shore structures. Section 6.11, 

 Miscellaneous Design Practices, lists recommendations concerning prevention 

 or reduction of deterioration of concrete, steel and timber waterfront 

 structures. 



6.2 SEAWALLS, BULKHEADS, AND REVETIvlENTS 



6„21 TYPES 



The distinction between seawalls, bulkheads and revetments is mainly 

 a matter of purpose. Design features are determined at the functional 

 planning stage, and the structure is named to suit its intended purpose. 

 In general, seawalls are the most massive of the three, because they resist 

 the full force of the waves. Bulkheads are next in size; their function is 

 to retain fill, and they are generally not exposed to severe wave action. 

 Revetments are the lightest, because they are designed to protect shore- 

 lines against erosion by currents or light wave action. 



A curved-face seawall and a combination stepped and curved-face sea- 

 wall are illustrated in Figures 6-1 and 6-2. These massive structures 

 are built to resist high wave action and reduce scour. Both seawalls have 

 sheet-pile cutoff walls to prevent loss of foundation material by wave 

 scour and leaching from overtopping water or storm drainage beneath the 

 wall. The curved-face seawall also has an armoring of large rocks at the 

 toe to reduce scouring by wave action. 



The stepped seawall (Figure 6-3) was designed for stability against 

 moderate waves. The tongue groove provides a space between piles that 

 may be grouted to form a sandtight cutoff wall. Instead of grouting this 

 space, a plastic filter cloth can be used to line the landward side of the 

 sheet piling. The filter-cloth liner provides a sand-tight barrier, and 

 eliminates the buildup of hydrostatic pressure which is relieved through 

 the cloth and the joints between the sheet piles. 



The rubble-mound seawall (Figure 6-4) was built to withstand sev- 

 ere wave action. Although scour of the fronting beach may occur, rock 



