the force on the wheel required to achieve 3 feet of penetration ranges 

 from 7,000 pounds to 28,000 pounds. This approach was eliminated because 

 full penetration is not assured, tracking the cable is a difficult process, 

 and the probability of damaging the cable is very high since the cable 

 could be forced into a rock or other hard surface. 



SUBSYSTEM ANALYSIS 



The following sections present force and power analyses and discuss 

 the subsystem candidates which appear to be most appropriate for a deep- 

 ocean cable burial system. 



Excavation Subsystems 



Plowing . Plowing cables into the soil is a relatively simple and 

 quite effective means of burying cables. Plowing has been used extensively 

 and very successfully on land and has had some success underwater. The 

 basic problems with cable plowing are the high force required to move the 

 plow through the soils (drawbar force) and the force required to achieve and 

 maintain plow penetration. Appendix A and Reference 36 discuss drawbar 

 force predictions for a plowshare. 



Appendix A shows that the total drawbar force required to move a 

 plowshare through the soil is larger for clay than for sand, and is 

 velocity dependent . 



F = C F + F 

 TOT V s I 



where FrpQ^ = total resistance 



C = a velocity coefficient determined from Figure A-1 



F = force due to static soil resistance 



^ =SA+SNA^ 



us u c f 



F = an inertial term 



= (1/2)Ps Aj Cjj v2 



S = undrained shear strength 



A = side area of plow 



s ^ 



A^ = frontal area of plow 



N = dimensionless coefficient '\' 1 

 c 



P = soil mass density 



C = drag coefficient Oi 1.5 



V = velocity 



16 



