slope for relief of hydrostatic pressures, unless the width of the slope is less than about 15 

 feet and the subsoil is exceptionally porous. Toe thrust should be resisted by a cutoff wall 

 trenched about 2 feet deep along the toe of the slope, and a thickened edge beam at the top 

 of the slope should be provided to resist uneven loading along the shoulder. With careful 

 placement, a good stiff mix may be poured on a slope of 1 on 1.5. For steeper slopes, 

 airblown mortar (Gunite) must be used. Perimeter slopes have been paved with asphaltic 

 concrete, but they usually fail in a few years because of softening in water or uneven 

 settlement of the base material. Asphaltic paving should be used only above the extreme 

 high water level. 



An old-fashioned revetment system that permits perimeter slopes to be built steeply at 

 low cost (where adequate small stone is available) is that of rockfilled wire mesh gabions 

 (Smythe, 1961). Normally used only for flowing watercourses and dry bank retaining walls, 

 this construction is also suitable for marina perimeter stabilization. Heavy duty wire mesh 

 baskets with rectangular sides and of convenient size for such construction are 

 manufactured commercially and shipped to the site in coUasped form. They come 

 galvanized for freshwater use and galvanized plus polyvinyl-cloride-coated for saltwater use. 

 The filled baskets may be placed vertically on top of each other; for better stability they 

 should be canted back to about a 4 to 1 batter slope. Battering may also be done by setback 

 of successive rows for a terraced appearance. The gabioned slope should be backed by a 

 layer of filter cloth to prevent the pumpout of material from the eartiibank behind it. As 

 yet the experience record for such construction in marinas is minimal and its permanence is 

 unknown. The various uses of gabion in marina construction are shown in Figure 46. 



Where surging is anticipated, due to partially attenuated wave action reaching the interior 

 basins of a marina, consideration should be given to low reflectivity perimeter stabilization, 

 especially at the inner ends of basins. A beach is the best type of surge absorber, followed 

 by the flat riprapped slope built with large stones. Concrete slopes, either poured-in-place or 

 of block construction, are almost as reflective as vertical walls. 



Most vertical bulkheads are more expensive to construct than an armored slope. Where 

 land and water areas are limited or costly, ehmination of the waste space occupied by the 

 slope may be an economic requirement. 



Of the many types of vertical perimeter walls currently in use, the least costly to build is 

 usually a tied-back pile-type timber bulkhead. Where construction in the dry is possible, the 

 simplest construction usually consists of round or square piling tied to tie piles or deadmen 

 and sheathed on the landward side to a depth well below the seaward toe of the wall. The 

 pile size used for the tieback system and thickness of the sheathing must be determined by 

 engineering analysis. Plastic filter cloth can be used to prevent loss of material through 

 cracks in the sheathing (Fig. 47). Where timber is economical, the tiebacks may be made 

 with timber planks (Fig. 48). 



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