conditions and fog-room conditions are given in 

 Appendix C. The control block from Sphere 7 was 

 not retrieved as the Turtle was not rigged for a 

 retrieval operation. 



Permeability 



The method used to determine the permeability 

 of seawater through the concrete walls produced a 

 fairly accurate indication of in-situ permeability 

 behavior of the spheres. This method used the change 

 in number (reduced number) of chain links to 

 calculate the gain in weight of the sphere due to sea- 

 water intake. The accuracy of the quantitative results 

 depend on several approximations; these are 

 discussed in Appendix D. The accumulative effect of 

 these approximations is estimated to be a maximum 

 of ± 0.8 cu ft of seawater. This error can be reduced 

 to ± 0.3 cu ft by comparing the change in link counts 

 from actual inspections instead of using the calcu- 

 lated link count from zero days. 



Table 5 gives the total quantity of seawater 

 intake, Q, for the different time intervals between 

 emplacement and inspections. Seawater intake 

 includes the seawater absorbed by the concrete and 

 the seawater that permeated through the concrete. 

 Figure 12 shows the Q versus time behavior. Three 

 items of interest are observed. One item is that the 

 uncoated concrete spheres have a greater Q than the 

 coated spheres; after 431 days, the coated spheres 

 showed an average Q of about 2.6 cu ft and the 

 uncoated spheres about 3.6 cu ft. Another item is 

 that the spheres which have been inspected twice 

 showed a considerable decrease in the rate of sea- 

 water intake. The last item is that Q increased for 

 specimens at greater depth, but the increase was not 

 pronounced. 



The actual quantity of seawater permeating the 

 wall, Q , was estimated by subtracting the quantity of 

 absorbed seawater from the total seawater intake. 

 Earlier work on 66-inch-OD spheres [8] showed that 

 the concrete (same concrete as used in this study) 

 absorbed approximately 3 percent by weight (or 7 

 percent by volume) of seawater. This corresponds to 

 2.0 cu ft of seawater absorbed by the concrete. Table 

 5 shows the CL values for the different time intervals. 

 At 431 days, the average CL for the coated spheres was 

 0.8 cu ft and for the uncoated spheres was 1.6 cu ft. 



Reference 8 reports permeability results from 

 two 66-inch-OD concrete spheres subjected to 

 seawater hydrostatic pressure tests. The permeability 

 data are shown in Table 6. D'Arcy's permeability 

 coefficient, K^,, was determined from the data as an 

 average of 0.13 x 10'^^ ft/sec. D'Arcy's permeability 

 coefficient can be expressed as follows for the 

 spheres: 



(1) 



where K^ = permeability coefficient, ft/sec 



Q = quantity of permeability 

 seawater, cu ft 



T = time, sec 



t = wall thickness, ft 



A = exterior surface area, cu ft 



h = depth (or pressure head), ft 



Using the K^. value of 0.13 x 10 ft/sec as a 

 baseline, the data from the spheres in the ocean can 

 be compared to that from the pressure vessel tests. 

 Table 5 lists the K^. values for the ocean spheres. In 

 all cases, the permeability coefficient was lower for 

 the spheres in the ocean than for the spheres in the 

 pressure vessels. The average K^, values for the 

 coated spheres were 0.06x10"'^ ft/sec at 163 

 days and 0.02x10"'^ ft/sec at 431 days, and 

 for the uncoated spheres were 0.11x10''^ ft/sec 

 at 163 days and 0.06x10"^^ ft/sec at 431 days. 

 Other Kj. values were those attained between the time 

 interval of 163 to 431 days; for the coated spheres, 

 no increase in CL, was observed, so K^ was zero, and 

 for the uncoated spheres the average K^, was 

 0.04 X 10'^^ ft/sec. 



The permeability data from the pressure vessel 

 tests showed that a straight line curve of Q versus 

 log T fit the data with fair accuracy. The empirical 

 semi-log relations^ for one sphere (specimen CWL-9A) 

 at a simulated depth of 2,5 20 ft was: 



(ip = 0.34 log loT - 0.11 



(2) 



' Equations 2 and 3 are presented in this report with time, T, in days. These equations are different 

 from those in Reference 8 which give time, T, in hours. 



13 



