resistance. Skirts, or cutting edges, used about the periphery of the 

 foundation to hinder undercutting by animals or current scour, should 

 push even 3-inch diameter nodules to the side. Pavements cannot be 

 considered rock foundations because they may lie on unconsolidated 

 material, and appreciable loads may punch through. Again, a spread 

 footing type foundation is the logical selection, and again special 

 consideration will have to be given to the problem of lateral load 

 resistance. The pavement surface should be disturbed as little as 

 possible because the same strong currents which keep these areas free 

 of sediments will rapidly erode and undercut when possible. If leg- 

 ged foundations, hereafter called "tined" foundations, are used in 

 this environment (to resist lateral load), the tines themselves should 

 not be depended on to support vertical load because they may punch 

 through the pavement and find negligible resistance in the underlying 

 sediment. 



Coral 



Occurrence. Perhaps one-half of the shores of the tropical Pacific 

 and Indian Oceans are bordered by coral reef;-'-" and a number of sea- 

 mounts are capped by coral, sometimes reaching thousands of feet in 

 thickness. Coral structures making up a reef vary greatly in size and 

 shape; some are rounded, massive "heads" a few inches to several feet 

 in diameter; others are delicate, branching forms named "staghorn"; 

 there are numerous intermediate varieties. At the outer edges of a 

 typical reef, pieces of living coral up to 20 feet across are torn off 

 by storm waves. These are then either thrown up by the waves onto the 

 reef flat, or they fall down onto the submarine slope outside the 

 breakers. These coral pieces, if they come to rest within reach of 

 sufficient sunlight (maximum depth about 90 f athoms^) , may be subse- 

 quently bound together by living, thriving coral or, more likely, by 

 calcareous algae. In this way a reef grows slowly outward at the 

 margin. 19 Coral maintains a void space of 25 to 50 percent."^ 



The steep slope beyond the breakers may descend at 45 degrees to 

 near vertical for a few fathoms, with a narrow shelf or a more gradual 

 slope beyond. Beyond the shelf, slopes of as much as 45 degree to 200 

 meters depth are not uncommon, and they may reach 600 meters. Then 

 slopes of approximately 25 degrees are common to 1000 fathoms. 



Engineering Significance . Coral slopes are undesirable sites for 

 valuable, bottom-resting installations because of the steep slopes, the 

 irregular microrelief resulting from large blocks, the highly variable 

 strength of typical coral, and the potential for falling blocks from 

 the reef above. Areas of small-sized coral debris and coral sand will 

 occur and can be utilized for small, light-weight installations. The 

 most dependable way to establish an installation on a deep coral slope 

 appears to be to make the structure buoyant and anchor it. 



