Mean Grain Size (0 units) 

 4.8 5.2 5.6 6.0 6.4 6.8 7.2 7.6 8.0 8.4 8.8 9.2 



1,600 



-O A D 



2,000 



2,400 



O D £» 



2,800 



& DO 



~ 3,200 



- 



a. 





Q 3,600 



- 



4,000 





4,400 





4,800 



A 



(0 unit = -log? mean diameter in mm) 



6iOO Q 



eft a 

 o afr 



3D 



Figure 2-3. Mean grain size of carbonate sediment 

 samples versus depth of deposition 

 (from Johnson, Hamilton, and Berger, 1977). 



Normally consolidated sediments are the rule in the deep ocean; 

 there are materials that have never been loaded by overlying material 

 more than they are now. Overconsolidated sediments have had a 

 greater load (overburden) in the past and have since lost it by chemi- 

 cal processes or mechanical erosion. Underconsolidated sediments are 

 young and have not come to equilibrium with the weight of overlying 

 material . 



If one assumes all deep ocean sediments to be normally consoli- 

 dated, one will usually be correct and conservative. A few important 

 exceptions do exist, but these need not concern the engineer unless 

 finding an unusually strong (overconsolidated) sediment would lead to a 

 less conservative design. 



Much of the near shore is overconsolidated . Since this is usually 

 a desirable situation and since it is so common, it would be valuable to 

 find overconsolidated locations and determine their overconsolidation 

 level.* There are no fast rules for locating overconsolidated sediments 

 except that exposed locations (tops of rises, passages) are more likely 

 to be overconsolidated than are protected locations (basins). 



*Overconsolidation ratio (OCR). 



22 



