DEVELOPMENT & TEST OF BEHAVIOR OF SPHERICAL CONCRETE HULLS UNDER HYDROSTATIC LOADING-PART I. Exploratory Investigation,
 Technical Report R517, Naval Civil Engineering laboratory, Port Hueneme, CA, by J.D. Stachiw and K.O. Gray, March 1967, 69 pages.

Hollow concrete spheres 16 inches in outside diameter have been tested to destruction by exposure to external hydrostatic pressure in seawater to determine the compressive strength and permeability of concrete under such loading. The testing has shown that for the particular mix used, the compressive strength of dry concrete in a spherical hull of 16-inch outside diameter and 1-inch wall thickness under biaxial loading (short-term hydrostatic pressurization to failure at a constant rate) is approximately 48% higher than for identical dry concrete in 3-inch-diameter by 6-inch-long solid test cylinders under uniaxial loading conditions. Concrete spheres in which the wall was thoroughly permeated by seawater failed at stress levels approximately 180/o higher than 3-inch-diameter by 6-inch-long solid test cylinders. The permeability of uncoated spheres to seawater at simulated ocean pressure of 1,500 psi was approximately 6x 10-3 milliliters per hour per square inch of area per I inch of thickness.