5. Repair of Earth Structures . 



Damage to earth structures or earth parts of structures generally 

 consists of erosion or removal of the soil. The repair consists primarily 

 of replacing the earth material or the protective layer. If permeability 

 or stability of the structure is a problem, the voids can be filled with 

 concrete or asphalt grout. 



6. Environmental Considerations, 



a. Physical Effects . The nature of the soil pore fluid and .temperature 

 can influence the behavior of clay soils. A loss in shear strength of 

 marine clays may be realized by removal of the salt due to leaching by 

 freshwater. Changes in moisture content can cause swelling or shrinking of 

 clay soils. Decreasing the temperature of a cohesive soil can cause an 

 expansion of the soil. Fine-grained soils are also susceptible to frost 

 heave. 



The most significant environmental effect on the physical properties of 

 soils is liquefaction (resulting in loss of strength) due to a seismic event 

 or water wave action. Liquefaction due to either of these causes could result 

 in failure of the structure. The soil properties generally related to this 

 phenomona are saturation, grain size, relative density, and permeability. The 

 problem is generally associated with loose fine sands and silts below the 

 water level at sites in highly seismic areas or areas subject to high breaking 

 waves. Liquefaction of foundation soils under gravity ocean structures due to 

 water wave forces on the structure has been found in offshore work. Liquefac- 

 tion can generally be minimized or mitigated by densification or treatment of 

 the soils, or by providing drainage (rock drains). A discussion of soil 

 response to both seismic and water wave- induced dynamic loads is presented in 

 Callender and Eckert (in preparation, 1983). 



b. Erosion Effects. The erosion and subsequent deterioration of both 

 natural landforms and manmade coastal structures is of concern. Shore 

 erosion is a major problem along the ocean coastline and the Great Lakes. 

 Erosion is caused principally by storm-induced wave action and associated 

 longshore currents. The processes are further complicated by erosive 

 forces that may come from ice, wind, rain, burrowing animals, or human 

 activity. Shore erosion problems become more critical when beaches become 

 eroded or submerged, and adjoining highly erodible upland areas are subject 

 to direct wave attack (Fig. 12). Unconsolidated sands and silts are 

 generally the most easily eroded, clays and gravels are slightly more 

 resistant, and cemented soils and rock are the least erodible earth 

 materials. The soils may be protected from erosion by various devices such 

 as revetments, seawalls, and bulkheads. Groins may be used to maintain 

 beaches. A detailed discussion of beach erosion is presented in Chapter 4 

 of the SPM (U.S. Army, Corps of Engineers, CERC, 1977). 



7. Uses of Soils in Coastal Construction. 



a. General . Earth can be used for almost any kind of coastal struc- 

 ture. Coastal structures are generally associated with three types of 

 projects: port and harbor development (including marinas), land reclama- 

 tion, and coastal protection. Design considerations and criteria are 



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