necessary to use the results of short-term field tests to obtain design 

 holding capacities. This may be a good means of reducing uncertainties; 

 however, it is necessary to modify the measured capacities to account 

 for suction forces, or unconservative design values will result. 

 Figure 3 may be used to account for the suction effect. Using D/B and 

 an estimate of c (1 psi should be a reasonable value in most cases) , a 

 reduction factor, R, is obtained. This is inserted into the equation 

 given on the figure and the design short-term holding capacity, F , is 

 calculated. An estimate of the soil unit weight, Y, , is needed and may 

 be assumed equal to 25 pcf in most cases. 



4. Determine Type of Loading . Most anchor trial tests, salvage 

 work, and other projects which require a reaction force for a short 

 period of time are considered to be short term static loadings. Surface 

 vessels and buoys generally exert a long-term repeated loading condition, 

 although certain designs may convert the repeated load into a virtual 

 long term static condition. Subsurface buoys, suspended arrays, and 

 other suspended structures exert long term static loads. 



(a) If the loading is short term static, the design holding capacity 

 is F as determined in Step 3c or 3d. 



(b) If the loading is long term repeated, the design holding capa- 

 city is one-half F from 3c or 3d. This capacity refers to the charac- 

 teristic peak repeated load. 



5. Determine Long-Term Holding Capacity . If the loading is long 

 term static, the long term or drained capacity must be estimated. 



(a) The drained friction angle, (j), may be obtained from a triaxial 

 or similar shear test on a high quality sample. If such a test is not 

 performed then a conservative value of 25 may be assumed for most co- 

 hesive soils. _ _ 



(b) Figure 4 is entered with <^ and D/B, and the parameter N is 

 obtained. 



(c) The drained holding capacity F is obtained from Equation 6 

 (substituting F^^ for F ). 



(d) F from Step 5c is compared with F from Step 3c or 3d and the 

 lower value is used as a design holding capacity. If the anchored 

 system is critical or manned the result should be multiplied by 0.6 to 

 account for possible creep effects. 



6. Determine Short-Term Holding Capacity for Cohesionless Soil . 

 Steps 6 through 9 assume the soil has been determined to be cohesionless. 

 The procedure to be followed in estimating the short-term holding capacity 

 depends upon whether good quality cores or in-situ strength data have 

 been obtained or a field test has been performed. 



Core or in-situ data available. If this information is availabe. 



14 



