lateral movement. A conventional flat-plate foundation, even with cut- 

 ting edges , will not often meet these requirements on an irregular rock 

 surface. 



Several rock foundation concepts have been briefly examined to 

 determine their practicality. These are all variations of: (1) the 

 embedded anchor, (2) the so-called tined foundation, (3) the crushable 

 element foundation, and (4) the common deadweight anchor. 



Embedded Anchor 



The embedded anchor system provides vertical load, lateral load, 

 and moment resistance, and it is workable in very irregular microrelief 

 and on steep slopes. Propellant-embedded anchors have been installed 

 with varying degrees of success in coral and in massive seafloor 

 basalt (see Figures 3a and 3b) . Successful installation of anchor 

 projectiles in hard brittle rocks, such as a competent basalt, may prove 

 difficult because these rocks may shatter during the projectile penetra- 

 tion and the projectile find no purchase, or because, as has happened, ^^ 

 the projectile may crack during penetration. Further development of 

 rock anchor projectiles and testing of their performance in various 

 seafloor rock types are required before conclusions can be drawn. The 

 propellant-embedded anchor is expected to find little purchase in 

 pillow basalts because of the discrete nature of the blocks. 



The use of the propellant-embedded projectile as a foundation ele- 

 ment requires that the structure be tied down tightly; to accomplish 

 this the capability must be developed to connect the structure and the 

 embedded anchor projectile and then tighten the two together. Alter- 

 natively, the anchor launching unit and the structure could be made 

 one; a properly designed non-sensitive structure would probably survive 

 the shock wave and acceleration due to the slow-burning projectile 

 propellant. Unfortunately, few structures important enough to be 

 installed are non-sensitive. Further, a certain number of attempts will 

 occur where the anchor misfires or the projectile does not embed proper- 

 ly; in these cases, the structure-anchor assembly would have to be 

 raised to the surface to correct the malfunction. Preliminary analysis 

 indicates that use of the propellant-embedded anchor as a tie-down for 

 a seafloor foundation on rock involves a high probability of failure. 



Alternately, a drilled- in and grouted pile provides a rigid found- 

 ation in a wide material range from a manganese pavement over dense 

 sand to an integral basalt flow. The structure can be attached to the 

 head of a standard anchor pile, and the drill-string passed through the 

 center of the assembly (see Figure 4) . This system does not require the 

 capability to relocate a position on the seafloor, and it is consider- 

 ably more capable of accommodating microrelief than any other system 

 discussed herein. The use of drilled-in piles in deep water requires 

 the services of an offshore drillship at $15,000+ per day; and, of the 

 four drillships available to reach 6000 feet, all would require signif- 

 icant modification to be able to handle the structure and drill-in the 



