soft layer 



Figure 4. Effect of footing size on stress distribution in a layered soil 

 system. (From SOIL MECHANICS by A. R. Jumikis, 17 Copyright 

 © 1962, by Litton Educational Publishing, Inc., by permission of 

 Van Nostrand Reinhold Company.) 



The location of the structure on or in the sediment will govern the 

 depth to which the survey will be required to extend and the type of para- 

 meters that need to be measured. Depending on the depth requirements, 

 alternative techniques may have to be utilized to assess the foundation para- 

 meters. For example, for a small structure of relatively minor importance, 

 the NCEL in-situ vane shear device could be utilized for strength measure- 

 ments. On the other hand, if a 1,000-foot-long by 100-foot-diameter 

 cylindrical structure is to be founded on the seafloor, vane shear type data 

 would not be adequate. In other cases, the depth to bedrock may be 

 required to be known. The location in the sediment column of the structure 

 also influences the parameters to be measured. For example, lateral loading 

 on the structure due to currents may be less important for structures in 

 the bottom sediments than for structures on the sediment surface. On the 

 other hand, lateral loading due to the sediment weight is of prime importance 

 for a structure in the sediments. Thus the location of the structure in or on 

 the bottom will influence the survey depth and the type of parameters that 

 must be measured. 



In general, the degree of precision of the survey is governed by the 

 relative importance of the structure. For example, the precision required 

 for the survey for a manned bottom installation will be far greater than for 



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