CHAPTER II 

 SOILS AND THEIR CHARACTERISTICS 



IN considering any harbor or river improvement necessitating 

 the employment of dredges, as previously shown, it is important 

 to carefully examine the nature of the soil to be excavated. Such a 

 study will influence the selection of the machines and the arrange- 

 ment of the work. By using the most efficient machines and arrang- 

 ing the work in the most convenient way the improvement under 

 consideration will be done in the most economical manner, namely 

 at the smallest cost. Hence the great importance of a thorough, 

 knowledge of the soil to be excavated. 



It would be impossible to describe all the various soils that 

 may be encountered in dredging. They are found in so many varieties 

 and so mixed together that it is difficult to trace each to its respective 

 group. However, for sake of classification only the most character- 

 istic soils will be reviewed here, indicating the type of dredge con- 

 sidered the most appropriate for working in each soil. The soils 

 will be reviewed in the following order: Rock, disintegrated rock 

 and conglomerates, gravel, hardpan, clay and loam, sand and silt. 



Rock. The ordinary dredging operations usually consist of 

 clearing the bottom of canals, rivers, bays, harbors, etc. Since 

 these basins are formed by alluvial deposits accumulated there for 

 centuries, as a rule, they form strata of great thickness, and solid 

 rock is very seldom encountered. But even in the few cases in 

 which rock is found, owing to the fact that for a long timo it has 

 been exposed to the destructive action of fresh or salty water, it is 

 generally found in such a disintegrated condition, as to be consid- 

 ered a loose soil instead of real rock. However, in removing obstruc- 

 tions to navigation or in widening and deepening harbors and 

 channels, solid ledges of rock are encountered. It is removed, as 

 stated, either by hammering or blasting. 



Disintegrated Rock and Conglomerates. The rock that has 

 been disintegrated by the action of water or other means and still 



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