CHAPTER 6 



STRUCTURAL FEATURES 



I. INTRODUCTION 



This chapter provides illustrations and information concerning the 

 various structural features of selected coastal engineering projects. This 

 chapter complements information discussed in Chapter 5, Planning Analysis. 



Sections II through IX of this chapter provide details of typical sea- 

 walls, bulkheads, revetments, protective beaches, sand dunes, sand bypassing, 

 groins, jetties, and breakwaters. The details form a basis for comparing one 

 type of structure with another. They are not intended as recommended dimen- 

 sions for application to other structures or sites. Section X, Construction 

 Materials and Design Practices, provides information on materials for shore 

 structures and lists recommendations concerning the prevention or reduction of 

 deterioration of concrete, steel, and timber waterfront structures. 



II. SEAWALLS, BULKHEADS, AND REVETMENTS 



1. 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 rather massive structures because they resist the full force of 

 the waves. Bulkheads are next in size; their primary function is to retain 

 fill, and while generally not exposed to severe wave action, they still need 

 to be designed to resist erosion by the wave climate at the site. Revetments 

 are generally the lightest because they are designed to protect shorelines 

 against erosion by currents or light wave action. Protective structures for 

 low-energy climates are discussed in detail in U.S. Army, Corps of Engineers 

 (1981). 



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

 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-face seawall (Fig. 6-3) is designed for stability against 

 moderate waves. This figure shows the option of using reinforced concrete 

 sheet piles. The tongue-and-groove joints create a space between the piles 

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

 space, a geotextile filter can be used to line the landward side of the sheet 

 piles. The geotextile filter liner provides a sandtight barrier, while per- 

 mitting seepage through the cloth and the joints between the sheet piles to 

 relieve the buildup of hydrostatic pressure. 



6-1 



