case. For "shallow anchors" it was found that creep rates were negli- 

 gible when the cyclic load was less than 50 percent of the static 

 capacity. "Deep" anchors failed at lower percentages of their respective 

 static capacities. It is reasonable to assume, however, that in no 

 case will the holding capacity of a "deep" anchor be less than that of 

 a "shallow" anchor simply because the anchor must be pulled through the 

 "shallow" depth range before ultimate pullout. 



Trofimenkov and Mariupolskii (1965) performed what are the only 

 full-scale, repeated loading, pullout tests of anchors. In long-term 

 repeated load tests on anchors embedded in fine and medium sands of loose 

 to medium density, the holding capacities were reduced by up to 50 per- 

 cent. 



The test series mentioned above are the only two known to have 

 been performed on saturated sand where drainage was allowed. Although 

 these results are very limited, at least some tentative design procedures 

 can be developed based on them. For "shallow" embedment, a maximum 

 allowable cyclic load of 50 percent of the static or short-term capa- 

 city is recommended. For "deep" embedment a conservative design should 

 result if the applied cyclic load is less than 50 percent of the static 

 capacity corresponding to the transition between "deep" and "shallow" 

 behavior. 



It is possible that the required reduction factor may be greater 

 with soil in the silt-fine sand range. It is suggested that seafloor 

 soil grain size characteristics be determined whenever a direct embed- 

 ment anchor is to be established in granular soil which will be subjected 

 to repeated loadings. An anchor in granular soil with a characteristic 

 mean grain size D , greater than 0.20mm should be designed with the 

 repetitive loading factor given above. If the soil falls in the silt- 



fine sand range, D _ between .02 mm - .20 mm, it may be necessary to 

 use a different anchoring technique or employ high safety factors 

 (a minimtom of 10) . Another possibility would be to reduce system 

 tautness and thereby reduce the effect of surface wave action and dampen 

 repetitive loading. The approach depends upon system requirements, system 

 importance, and the consequences which would result from a failure. 

 Work is on-going at the University of Massachusettes under a NCEL con- 

 tract to evaluate the long-term repeated load response of anchors embeded 

 in soil in the silt-fine sand range. 



ESTIMATION OF SOIL PROPERTIES 



In order to use the prediction equations which have been given, it 

 is necessary to have estimates of_severa.l soil properties. Aside from 

 the drained strength parameters, c and ^, which were discussed previously, 

 the pertinent soil parameters are the soil buoyant unit weight , y , > the 

 undrained shear strength (for a cohesive soil), c, and the angel of 

 internal friction (for a cohesionless soil) . There are two major pro- 

 blems involved in estimating these quantities. First it is necessary to 

 estimate the distribution of these properties at the proposed anchor 



10 



