an unmanned Submersible Test Unit (STU), as discussed previously. Since 

 the degree of precision governs the survey technique and procedures, this 

 requirement must be defined prior to conducting the survey. As an example, 

 a bathymetric survey conducted with the LOR AC positioning system and a 

 Precision Depth Recorder (PDR) may be satisfactory for a STU, but would 

 be inadequate for a manned bottom complex. A different survey technique 

 would be required for the latter installation, possibly one using submersibles. 



SITE SURVEY PROCEDURE 



The procedure for surveying a site is divided into two major categories 

 or phases; the preliminary survey phase, and the detail survey phase. The 

 extent to which each survey phase is conducted depends on the purpose of 

 the installation, the operational requirements, the size of the structure, and 

 the degree of importance of the structure. In general, each phase is conducted 

 with a degree of thoroughness which is dependent on the particular installation. 

 It is possible that for a specific structure the existing information will be ade- 

 quate to evaluate and select the site, thus obviating the necessity for further 

 investigations. In other cases, the existing data may be incomplete, requiring 

 only specific information from the detail survey phase. Figure 5 diagram- 

 matically shows the various possible routes that may result in the process of 

 selecting a site. The general site survey procedure, which includes both the 

 preliminary and detail survey phases, will be discussed in this section. 



In certain cases, a site may be preselected, that is, the stipulation is 

 made to place the particular structure at a specific location. For example, 

 it may be stipulated that the structure shall be placed off of San Clemente 

 Island in the vicinity of NOTS Pier. In this case, the previously discussed 

 site survey and selection procedure does not apply. Here, the existing data 

 are evaluated and if necessary, a detail survey is conducted. Regardless of 

 what is found in the evaluation of the existing data or in the detail survey 

 phase, the site "must be made to work" for the structure — the structural 

 design must be accommodated to the constraints of the site. In the previously 

 discussed procedure, the site that would work best for the particular structure 

 is selected after all the data have been evaluated. 



Preliminary Survey 



The preliminary survey phase consists of searching for existing information, 

 personal contacts, and reconnaissance surveys. In the search for existing infor- 

 mation, data on the site parameters including foundation engineering, geological 



13 



