Appendix C 



POWER ANALYSIS OF AUGER TRENCHING 



To estimate the power required to auger a trench in the seafloor 

 consider a single vertical auger with the following characteristics 



Outside diameter, D = 4 in. 

 o 



Inside diameter, D. = 2 in. 

 Length, I = 36 in. 

 Pitch, p = 3.6 in. 



hoH 



Figure C-1. Auger configuration. 



With a 3 

 "slug" 



, 6-inch pitch, 10 revolutions of the auger are required for a 

 of soil cut from the bottom of the trench to reach the top. 



Assumptions: 



Half of the auger cuts new material 

 The same forces apply as for trenching 

 (bearing resistance and friction) 



A 



where S 

 N 



u 



TOT 



= S 



A. N + 

 f c 



= undrained shear strength = 4 lb/in 



= frontal area of the auger blade 



= dimensionless constant (^ 3) 



= side area of the auger 



= 4.7 in. 



1 - 2 



— TT D a = lib in. 



Then 



68 



