larger numbers of load repetitions were not investigated. This is 

 somewhat unfortunate since it has been hypothesized (Larew and Leonards, 

 1962) that there is a finite, ultimate repeated load strength which 

 applies for numbers of repeated loadings approaching infinity. It 

 would be of interest to know how the ultimate strength relates to the 

 900 load repetition strength. 



Data from full scale tests using screw piles subjected to repetive 

 loads on a soft clay land soil, Trafimenkov and Mariupolsuii (1965), 

 indicate that strength reduction could be on the order of 50 percent, 

 a slightly larger reduction than that indicated by the San Francisco 

 Bay mud tests . 



A laboratory study of the repeated load response of anchors embedded 

 in clay was conducted at the University of Massachusetts (Bemben and 

 Kupferman, 1971). The results indicated a very complicated process of 

 upward anchor displacement with time. However, the results do not appear 

 sufficient for quantitative design of practical anchor systems. In 

 general a reduction factor of about 50 percent of the short term capa- 

 city appears adequate for long-term repeated loading of anchors in 

 cohesive soil. It is suggested that this reduction factor be applied 

 directly to other soils when additional testing is not feasible. 



Cohesionless Soil 



The problem of the reduction of sand strength with repeated load 

 application is somewhat more complex. Lee and Seed (1967) investigated 

 the response of a uniform river sand, (grain size .15 to .30 mm) placed 

 at several different relative densities and subjected to 10 load repe- 

 titions. The specimens, tested in the undrained condition, had strength 

 reductions ranging from 50 to 85 percent. In the same report, it is 

 shown that 75 to 90 percent strength reductions occur after 1000 cycles. 



This could be a very dangerous situation. However, one way in 

 which the problem could become less severe would be through partial 

 drainage. Evidence suggests that sand strength is decreased because of 

 a buildup in pore water pressures. If these are not allowed to dissipate, 

 the strength reduction will be extreme. In all field problems, however, 

 at least some pore pressure dissipation will occur and therefore in- 

 crease the repeated load strength. This then becomes a complex porous 

 media flow problem which can be solved only through model and field tests. 



Repeated load model anchor tests have been conducted at the Univer- 

 sity of Massachusetts (Kalajian, 1971) on a loose saturated fine to 

 medium sand. The data are presented as the peak cyclic load normalized 

 by the static holding capacity as a function of the cyclic creep rate. 

 The tests were not continued long enough to establish whether cyclic 

 creep rate dissipated; however, the data provide comparisons between 

 "shallow" and "deep" anchor behavior under cyclic loading. The cyclic 

 creep rate for a "shallow" anchor was considerably less than the creep 

 rate for deeply embedded anchor, probably because of partial dissipation 

 of pore pressures and subsequent densif ication of the sand in the "shallow" 



