pile. Thus, because of the limited number of vessels available, the 

 high cost to the Navy, and the required equipment modifications and 

 additions, the use of drilled- in pile foundations on rock is not 

 expected to have great popularity in the near future. 



Tined Foundation 



The various tined foundation concepts all somewhat resemble the 

 AFAR tower bases described earlier; however, the AFAR tower base 

 functions more as a deadweight anchor with teeth. A "tine" is a tooth 

 or prong aligned vertically or slightly inclined and is intended to 

 provide vertical load support and to bite into rock irregularities to 

 provide lateral load resistance. 



Lightweight structures on rock may use only a three-legged arrange- 

 ment (see Figure 5a)-. The center of gravity of the structure must be 

 kept low to limit potential for overturning, and at the same time the 

 frame and payload must be raised to clear the microrelief. Thus, such 

 a foundation unit would probably be nine to 12 feet across with four 

 feet of clearance between the frame and the tine tips; the tines would 

 be solid steel, and the framework would be pipe-sections to assist in 

 lowering the center of gravity. The tines should be inclined outward, 

 possibly up to 20 degrees from the vertical, to reduce the joint bend- 

 ing moment due to initial implant tilt and to lateral loading. The tine 

 collars, the flat, round plates attached about one foot up the tine, 

 function as small footings if the tines should not encounter a solid 

 rock surface. For instance, a tine could break through a weathered 

 basalt surface into a lava tube, or it could bear in pillow basalt and 

 encounter negligible resistance in the sedimentary fill between pillows. 

 Such eventualities must be designed for because it is impossible in 

 many cases to identify the real character of a rock surface even with 

 good quality photographs; for instance, what appears as an integral 

 flow surface may be a pillow lava.-*-" Furthermore, a foundation may not 

 be emplaced precisely at the position sampled and photographed, and 

 bottom conditions change radically within short distances in rock out- 

 crop terrain. 



For larger, heavier, or tall structures, it may be necessary to 

 use a greater number of tines, possibly arranged as illustrated in 

 Figure 5b, dubbed a "multiple" stubby pile configuration. Here each 

 cluster of tines would be articulated with respect to the main frame. 



Alternately, each of the legs or tines could be made to emanate 

 directly from the frame, and then in some way made to bear equally on 

 the supporting strata. For instance, the tines could be floated as 

 pistons in hydraulic cylinders, even remotely adjusted to level the 

 structure, and then locked in place23 (see Figure 5c). Or the tines 

 may be allowed to deform in bending by inserting a limiting moment 

 connection, a set of interleaved flat plates torqued together to pro- 

 duce a joint that will not move until some limiting moment is applied, 

 after which the joint moves plastically until the applied moment 



12 



