w^55ss;;^^HZ 



Small Stone 

 B 



Water Level 



Note: Dimensions and details to be 

 determined by particular site 

 conditions. 



Large Riprap Stone 

 A 



'/J^/i^/ki/JJ^ 



Figure 6-5. Rubble-mound seawall (typical stage placed). 



Bulkheads are generally either anchored vertical pile walls or gravity 

 walls; i.e., cribs or cellular steel-pile structures. Walls of soldier beams 

 and lagging have also been used at some sites. 



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

 shown in Figures 6-6, 6-7, and 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 vertical 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. Excessive scouring can 

 endanger the stability of the wall. 



The structural types of revetments used for coastal protection in exposed 

 and sheltered areas are illustrated in Figures 6-9 to 6-12. There are two 

 types of revetments: the rigid, cast-in-place concrete type illustrated in 

 Figure 6-9 and the flexible or articulated armor unit type illustrated in 

 Figures 6-10, 6-11, and 6-12. A rigid concrete revetment provides excellent 

 bank protection, but the site must be dewatered during construction so that 

 the concrete can be placed. A flexible structure also provides excellent bank 

 protection and can tolerate minor consolidation or settlement without 

 structural failure. This is true for the quarrystone or riprap revetment and 

 to a lesser extent for the interlocking concrete block revetment. Both the 

 articulated block structure and the quarrystone or riprap structure allow for 

 the relief of hydrostatic uplift pressure generated by wave action. The 

 underlying geotextile filter and gravel or a crushed-stone filter and bedding 

 layer relieve the pressure over the entire foundation area rather than through 

 specially constructed weep holes. 



Interlocking concrete blocks have been used extensively for shore protec- 

 tion in Europe and are finding applications in the United States, particularly 

 as a form of relatively low-cost shore protection. Typically, these blocks 

 are square slabs with shiplap-type interlocking joints as shown in Figure 6- 

 11. The joint of the shiplap type provides a mechanical interlock with 

 adjacent blocks. 



6-6 



