precise data regarding engineering properties of the various sediment 

 types in the study area are not obtainable. However, certain general 

 observations can be made regarding the engineering properties of possi- 

 ble value in the preliminary planning of engineering works in the coastal 

 and inner shelf environment and in devising sampling plans for specific 

 project sites. 



Clay deposits in the Holocene shelf sediments are most likely to 

 pose foundation problems. Most of these clays are classed as type F 

 lithology. When recovered from cores, they are soft, unconsolidated, 

 highly plastic clays with little apparent strength. Under the Unified 

 Soil Classification, this material is classified as a fat clay (CH) and 

 is rated a poor foundation medium. The clay layer in some places is too 

 thin to cause special problems but elsewhere the deposit is much more 

 than 3 meters thick. Clay deposits occur throughout the study area but 

 are particularly frequent in Long Bay. Though clay often fills small 

 channels, the usual occurrence is in areas showing flat-lying reflectors; 

 thus, there is no pattern by which clay can be identified on seismic 

 reflection profiles. Clay deposits rarely crop out and no known distri- 

 bution pattern or relationship with shelf morphology is present that 

 could be used to predict the presence of clay in specific areas. 



Fine quartz sands (types A, B, and C sediments) comprise the dominant 

 lithology of inner shelf surficial and shallow subshelf deposits. Size 

 gradation data of material from these deposits are included in Appendix B. 



Under the Unified Soils Classification System, most types A, B, and C 

 sediments fit the criteria of poorly graded sand (SP), which has fair to 

 good foundation properties. Other than liquefaction potential previously 

 discussed, the inner shelf, fine sand deposits are probably similar to 

 typical SP class sediments in their response to foundation stresses and 

 slope stability. Two factors, however, in the character of these inner 

 shelf deposits may be of significance. One is the large number of foram- 

 iniferal tests (external skeleton) in the carbonate fraction of some 

 types B and C sediments. These tests are hollow and easily broken so 

 some volume change may occur during the initial loading of a mass of the 

 soil. A second factor which may affect the properties of types B and C 

 sediments is the slight cementation which occurs locally due to dissolu- 

 tion and redeposition of some calcium carbonate grains. These cementation 

 bonds probably increase the in situ strength of the soils but they are 

 easily broken by disturbance. The occurrence of partly cemented sections 

 seems to be spotty both laterally and in depth; therefore, high in situ 

 strength characteristics at one locale may not be typical of the material 

 elsewhere and may be modified during construction operations. 



The degree of cementation of type G sediment varies from well 

 cemented to essentially uncemented. This, along with variations in 

 size and sorting characteristics, can be expected to create substantial 

 variations in engineering properties from place to place and in depth. 

 Although type G rock facies appear quite competent in places, there is 

 typically considerable void space in the unfilled interstices between 



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