° s = ^^ tan 6 (in) 



where K = coefficient of lateral pressure on pile wall 

 s 



<5 = effective friction angle of soil on nile wall (rad). 



For the calcareous sand, 6 was taken as 0.-^4 rad (25 deg) and JO as 0.4. 

 Such high values are appropriate for calcareous materials only when the 

 oiles are installed by drilling and grouting (McClelland, 1974). Avail- 

 able large scale test information (Angemeer et al . , 1973, 1975) indicates 

 that caoacities of driven Diles in calcareous sands may be as little as 

 one-fourth of those indicated by Eauation 10. Pile load tests are 

 reouired to accurately Dredict the canacity of driven Diles on this tvoe 

 material. The size and difficulty of installation of a pile anchor -for 

 the OTEC nower plant dictates that the soil resistance available be 

 maximized. Therefore, this study assumes that the technoloay will be 

 developed to provide the drilled and grouted pile option in water de n ths 

 to 6,000 m. In reality, the installation of larae anchor piles in deen 

 water aooears more technically feasible by the drilling and groutinn 

 techniaue than by the driving techniaue. 



Results . Computed nullout capacities are shown in Figures 25, 2P, 

 27, and 28 for respective soil categories. The reader should note that 

 capacities were calculated independently of lateral load. Aqain, cal- 

 culations were for a sinole, unrestrained oile subjected to a slowlv 

 applied vertical load. Note that a 110 m lona, 4.9 m diameter nile 

 would provide sufficient Dullout resistance in the deep ocean environ- 

 ment. An 85 m long, 7.6 m diameter oile would hold in the Gulf Stream 

 environment. These pile lengths and diameters are probably within 

 present offshore capabilities. 



Effect of Repetitive Loading 



Definition . Repetitive loadinq is defined as successive, slow 

 applications and relaxations of a load. In other words, shock loads are 

 excluded. Repetitive load is a reasonable approximation of what an 

 actual OTEC anchor will encounter. 



Discussion. Several authors (Matlock, 1970; Oill and Demars, 1970) 

 have noted that static load displacements may be increased by as much as 

 50 percent under repetitive loadina. At initial displacements lamer 

 than 20 percent of pile diameter, Matlock (1970) noted a continuous and 

 progressive deterioration of soil resistance with cycling. Fiaure 24, 

 presenting displacement data for a 2.4 m diameter nile, indicates the 

 24 m long pile will deflect 0.5 m under the static loadina, or about 21 

 percent of the pile diameter. The lonner, 48 m pile will deflect only 

 0.26 m or about 11 percent of the diameter. If this relationship hol^s 

 for piles of other diameters and in other soils, then piles lonaer than 

 10 diameters (or, alternatively, reductions in the lateral loads annlied 

 to the piles) will be necessary to prevent progressive deterioration of 

 soil resistance. 



54 



