and the power requirement is the same. For the cutting wheel trencher, 

 a parallel analysis results in 



For upmilling 



and for climbmilling 



P = 94 hp 



max ^ 



UP 



FWD 



•3,515 lb 

 -4,430 lb 



P = 94 hp 

 max 



UP 



3,350 lb 



F = 4,430 lb 

 FWD 



Climbmilling appears attractive in that, for the same power as upmilling, 

 a drawbar assist of 2,600 to 4,400 pounds is available to overcome the 

 running gear /soil interaction forces, cable drag, and water drag on the 

 machine. The machine must weigh greater than the upward force to keep the 

 trencher from digging itself out of the trench. However, the incidence of 

 stiff clays or rocks may cause the cutting wheel or trencher to climb out 

 of the trench, resulting in instability of the machine and possible 

 damage to the machine and the cable. Shock absorbing, braking, and possibly 

 other control systems must be incorporated into the trencher. It may also 

 be necessary to direct a water stream on the buckets to loosen and remove 

 trenched soil. 



For upmilling, the system can be very light (neutral if desired) 

 since the cutting force provides a significant downward force, but the 

 machine must provide 2,600 to 4,400 pounds of drawbar force in addition 

 to the other forces acting against the system's forward progress. Power 

 requirements in both cases are high due to the high digging rate required 

 for a 1 -knot speed of advance. 



Water Jetting. Although water jet excavation is the most common 

 means employed for pipeline burial, very little analytical or experimental 

 information was encountered in the literature. References 39 and 40 

 discuss research performed on jetting in sand. The trench depth is related 

 to the jet flow parameters by 



= C, 



Q(p + C2) 



1/2 



20 



