will have permeabilities ranging from 10" 5 to 10" 1 * centimeters per second. 

 Organic and inorganic silts, mixtures of sand, silt and clay, glacial till, 

 and some stratified clay deposits will have permeabilities ranging from 10" 6 

 to 10" 5 centimeters per second. Clays, which are practically impervious and 

 commonly used for core materials in water-retaining embankments, will have 

 permeabilities ranging from 10" 9 to 10~ 7 centimeters per second. 



d. Other Properties and Characteristics . Other soil properties and 

 characteristics that are useful to know for the design of coastal structures 

 include dry density, water content, specific gravity, resistivity and 

 corrosion potential, grain-size distribution, plasticity characteristics, 

 chemical properties, and durability. 



3. Methods of Soil Improvement . 



Methods of soil improvement generally include densification, drainage, 

 changing soil properties at depth by grouting or injection, surface sta- 

 bilization by admixtures, and reinforcement with metal or fabric strips or 

 mesh. Most of these methods have been utilized in one manner or another to 

 improve soils used in the construction of coastal structures. The most 

 widely used, and generally the most practical, are densification and drain- 

 age. A somewhat newer method developed in Europe, and now being more 

 widely used in the United States is reinforced earth (Figs. 8 and 9]. Some 

 of the methods available for improvement of soils are classified according 

 to the basis of soil improvement, as shown in Table 3 (Mitchell, 1976). 



REINFORCED 

 VOLUME 



TETRAPODS, 4.2 YD3 EL 275 



REINFORCED 

 VOLUME 



■DRAINAGE 

 LEVELING PAD BLANKET 

 -ROCKFILL0.1-0.5T 

 RIP RAP, 0.5-1. OT 



Figure 9. Cross section of reinforced earth seawall at LaReunion 

 Island in the Indian Ocean (courtesy of The Reinforced 

 Earth Company) . 



57 



