Approach 



A logical sequence is involved in designing a foundation. This 

 report will generally follow this same sequence. The report begins 

 with a discussion and description of seafloor foundations in order to 

 provide a background for the reader and to establish certain definitions. 



The first step in the design procedure is to define the installation 

 in terms useful to the foundation engineer and to determine what 

 "satisfactory performance" actually is in quantitative terms. The 

 second step is the determination of the influential site properties and 

 the evaluation of each. These first two steps are combined in this 

 report under the section, "Design Conditions". This is followed by 

 the sections covering actual design procedure, which is an iterative 

 process in which a foundation configuration is selected and sized and 

 then is checked for such parameters as adequate bearing capacity and 

 resistance to lateral forces and overturning. An inadequacy in any one 

 parameter requires a change in the size or configuration and a reitera- 

 tion. The emplacement technique, which is discussed in a subsequent 

 section, is considered in the same manner, since a large number of 

 foundation performance difficulties have resulted from improper 

 emplacement. This report deals with only one class of installation; 

 thus, a number of assumptions are made concerning the design considera- 

 tions, site properties, and their interrelationships. These assumptions 

 are necessary because little data will typically be available concerning 

 sites for structures in this category. In all cases, the assumptions 

 should be reasonable or conservative as "worst likely" situations are 

 assumed. This approach also serves the purpose of simplifying the 

 design procedure. 



FOUNDATIONS 



Physical Characteristics 



The foundation is that portion of an installation which transfers 

 the loads of the structure to the seafloor. Its design is largely 

 dependent upon the properties of the underlying soil, or rock, and 

 other environmental factors such as topography and bottom currents. 

 Virtually all foundations for structures fitting into the category 

 covered by this report, should utilize some form of a footing founda- 

 tion. Figure 1 illustrates a multiple spread footing foundation. This 

 particular foundation utilizes three footings, a determinate number 

 which ensures even distribution of the load among the individual footings, 

 and also has a reasonably large distance between the three to increase 

 stability against overturning. The ball and socket joints allow the 

 individual footing to articulate and thus to conform to the topography 

 giving a more uniform distribution of bearing pressures on the seafloor. 



The important physical characteristics of this system (structure 

 and foundation) are illustrated in Figure 1. This particular founda- 



