comprising the seawall can readjust and settle without causing structural 

 failure. Figure 6-5 shows an adaptation of the rubble-mound seawall shown 

 in Figure 6-4; the stage placement of A and B stone utilizes the bank 

 material to reduce the stone required in the structure. 



JTf^^ 



Note: 



Dimensions and details to be 

 determined by particular site 

 conditions. 



Large Riprap Stone 



Figure 6-5. Rubble-Mound Seawall (Typical-Stage Placed) 



Three structural types of bulkheads (concrete, steel and timber) are 

 shown in Figures 6-6 through 6-8. Cellular steel sheet-pile bulkheads are 

 used where rock is near the surface, and adequate penetration is impossible 

 for the anchored sheet-pile bulkhead illustrated in Figure 6-7. When verti- 

 cal or nearly vertical bulkheads are constructed and the water depth at the 

 wall is less than twice the anticipated maximum wave height, the design 

 should provide for riprap armoring at the base to prevent scouring. Exces- 

 sive scouring may endanger the stability of the wall. 



Structural types of revetments used for coastal protection in exposed 

 and sheltered areas are illustrated in Figures 6-9 through 6-13. There 

 are two types of revetments: the rigid, cast-in-place concrete type illus- 

 trated in Figure 6-9, and the flexible or articulated armor unit type illus- 

 trated in Figures 6-10 through 6-13. A rigid concrete revetment provides 

 excellent bank protection, but the site must be dewatered during construc- 

 tion to pour the concrete. A flexible structure also provides excellent 

 bank protection, and can tolerate minor consolidation or settlement with- 

 out structural failure. This is true for the riprap revetment and to a 

 lesser extent for the interlocking concrete block revetment. Both the 

 articulated block structure and the riprap structure allow for the relief 

 of hydrostatic uplift pressure generated by wave action. The underlying 

 plastic filter cloth and gravel or a crushed-stone filter and bedding 

 layer provide for relief of pressure over the entire foundation area 

 rather than through specially constructed weep holes. 



Interlocking concrete blocks have been used extensively for shore 

 protection in the Netherlands and England, and have recently become popular 



6-6 



