on the piles. The locating could be done acoustically, and the posi- 

 tioning by water jets on the driver. The positioning could also be 

 done by submersibles, either manned or unmanned. However, because of 

 the likelihood of cable entanglement and the expense of submersible 

 operations, this mode was eliminated from consideration. 



Jack- In System 



The jack- in concept for seafloor pile emplacement is shown 

 schematically in Figure 2. This concept was developed to eliminate 

 the need for a large reaction mass against which to jack.^ As indi- 

 cated in Figure 2, the system uses five piles in a regular pentagonal 

 template. At each comer of the template a jacking mechanism controls 

 the position of the pile relative to the template. Piles are driven by 

 jacking on one pile at a time in the sequence shown by the circled 

 numbers in Figure 2. The reaction is derived from the weight of the 

 emplacement system plus the skin friction on the two piles adjacent to 

 the one being driven. 



Several types of jacking mechanism are feasible for this system. 

 One promising concept uses a winch-and cable mechanism. Other possible 

 mechanisms include rack-and-pinion jacks, chain jacks, and hydraulic 

 cylinders. It was concluded that the specific type of jacking mechanism 

 would not influence the choice between the conceptual designs. 



The control system for the jack- in concept would direct the power 

 to one jack at a time. Several repetitions of the jacking sequence 

 will probably be necessary because a given pile may meet a level of 

 resistance that will overcome the available reaction, and that comer 

 of the template will begin to rise. Jacking on that pile should be 

 discontinued when the template reaches a predetermined inclination, and 

 the next pile in the sequence should be jacked. The control system 

 should permit the skipping of a given pile in the event it reaches 

 maximum penetration before the other piles. At the end of driving the 

 power and control subsystems would be detached and retrieved. 



Screw-Pile System 



A screw-pile system is shown schematically in Figure 3. The piles 

 have one or more helical blades at the lower end, and are emplaced by 

 rotating them about the longitudinal axis. The piles would be rotated 

 individually to minimize power requirements. The driving torque would 

 be resisted by lateral forces on the other piles in the template. At 

 least two sequences of pile rotation may be required because the torque 

 might be great enough to overcome the lateral soil resistance in the 

 early stage of driving. Thus, the control subsystem would be quite 

 similar to the jack-in system described above. 



