Stachiw 



maintain the effect of the penetration flange rigidity constant, 

 all insert subassemblies that fit inside the penetration flanges 

 were designed to fit with a known clearance between the exterior 

 taper of the insert and the interior taper of the penetration 

 flange. The only point of contact between the penetration flange 

 and the insert subassembly was at the 0-ring sealing surface located 

 on the penetration flange lip. 



FABRICATION OF CONCRETE SPHERES 



Concrete hemispheres were cast in a mold and subsequently 

 cemented together with an epoxy bonding agent. Depending on the 

 type of test, the exterior and interior surfaces were either left 

 untreated or coated with a waterproofing material. The concrete 

 mix used developed after 250 days a strength of 10,000 to 11,000 

 psi as determined by uniaxial compression testing of solid test 

 cylinders associated with spheres. 



The treatment of the exterior surface depended upon the type 

 of test for which the given sphere was intended. For the perme- 

 ability tests, where the rate of water flow through concrete under 

 hydrostatic pressure was under investigation, the exterior surface 

 of the sphere was left untreated, the way it emerged from the 

 mold. For the strain determination tests, on the other hand, 

 where the prime objective of the test was to protect the electric 

 strain gages from seawater, the external surface of the spheres 

 was protected by a thin coat of epoxy resin. 



HYDROSTATIC TESTING 



INSTRUMENTATION - Two different types of instrumentation 

 were employed on the concrete spheres. The permeability experi- 

 ments required instrumentation designed to measure rate of per- 

 meability, while the short- and long-term stress investigations 

 needed only strain measuring instruments. 



Instrumentation for the determination of strains consisted 

 of electric resistance strain gages attached to the concrete sphere, 

 and an automatic strain switch and read-out unit. Two different 

 approaches were used to measure the rate of permeability through 

 concrete in the experimental spheres. One approach relied exclu- 

 sively on electronic transducers and read-out equipment, while the 

 other utilized only mechanical or hydraulic components. The elec- 

 tronic water detector, specially designed for this study, operated 

 on the principle that a rising water level in the sphere would 

 markedly change the resistance between two separated rods placed 

 inside the sphere cavity. As the water rose in the sphere, it 

 would wet more and more of the two vertical rods, decreasing the 

 resistance between them. This voltage change could be amplified, 

 measured, and recorded to provide a resistance versus time record. 

 The other approach used in the measurement of permeability rate 

 consisted of tubing inserted into the sphere, through which accum- 

 ulated water in the sphere's interior could be ejected at desired 



226 



