(3) Use in Coastal Structures . Stone has many uses in coastal 

 structures, including offshore structures, shore -connected structures, and 

 anchors. Breakwater, jetty and groin design often include several sizes of 

 stone for use in the core and underlayers and for use in the covering or 

 armor layer. Seawalls and revetments may also be constructed from stone. 

 For protection of pier foundations a quarrystone blanket may be laid under 

 the pier in the scour area. 



b. Earth . 



(1) Properties . Earth or soil is a large assortment of materials of 

 various origins. For engineering purposes soils are generally classified as 

 gravel, sand, silt, clay, and organic material; however, most soils are 

 composed of a mixture of two or more of these materials. Although there are 

 several soil classification systems, the most widely used in engineering is 

 the Unified Soils Classification System (USCS) . Gravel is usually considered 

 to range in size from the No. 4 Sieve to 76.2 millimeters (3 inches). Gravels 

 are cohesionless materials. Sand is defined as a grain size between 4.76 

 millimeters and 0.075 millimeter (No. 4 and 200 sieves, respectively) and 

 sands may be further classified as coarse, medium, or fine. Sands are 

 normally cohesionless materials; however, they present an apparent cohesion 

 when damp or moist due to the surface tension effects of pore fluids. Silts 

 and clays are known as fine-grain materials. Silts may also have an apparent 

 cohesion but have relatively poor strength characteristics, limiting their 

 use to certain cases. Clay materials are largely cohesive, have strength 

 characteristics dependent on past stress history, and may be difficult to 

 compact at high moisture contents. Minerals included in the clay composition 

 influence the properties of the soil. Organic materials, formed by the decay 

 of vegetable matter can be entrained in soils and usually have a spongy 

 nature and a fibrous texture. Usually organic soils have high moisture and 

 gas contents and a relatively low specific gravity. 



The major significant engineering properties of soil are shear strength, 

 compressibility, and permeability. The types of problems encountered in the 

 design of coastal structures which utilize these characteristics are slope 

 stability, bearing capacity, settlement, and erosion. Other useful properties 

 of soils in the design of structures include dry density, water content, 

 specific gravity, resistivity and corrosion potential, grain-size distribu- 

 tion, plasticity characteristics, chemical properties, and durability. 



(2) Soil Placement Methods . Soil placement methods are usually 

 determined by the fill location, underwater or above water, and the need for 

 some degree of compaction. Earthfills made from land are usually truck- 

 dumped and bulldozed into place while waterside delivery may be by barge or 

 hydraulic pumping. Fill compaction above the water can be accomplished using 

 mechanical equipment. A fill placed under water will usually require some 

 form of superimposed loading for a period of time to compact it. This 

 loading time depends upon the depth of fill and amount of loading. It 

 usually varies from 0.5 to 2 years. The compactibility of the soil will also 

 impact the loading time. 



(3) Use in Coastal Structures . Earth is commonly used in virtually 

 any port or harbor development, land reclamation, or coastal protection 

 structure. In addition to fill of all kinds, earth is used in making soil- 

 cement as well as fill material for plastic bags and other containing units. 



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