3. F - The soil side wall friction is evaluated in a manner 

 Identical to that of Smith . This evaluation may be represented by 

 the equation 



where c = soil unit shearing resistance produced along vertical 

 surfaces of the object 



dA = differential vertical surface area of obiect 

 V -^ 



It is somewhat difficult to determine exactly what values should 



be used for c . In some cases the soil will not be in contact with 



s 

 the object at every point, while in other cases the soil will be in 



contact but will be either practically undisturbed or totally remolded. 



In this analysis it was assumed that the soil was in contact with 



every vertical surface below the seafloor. For the low velocities 



involved this is probably a good assumption, but it is probably not 



applicable for very high velocity penetration. In terms of disturbance, 



two sets of calculations were performed, one using undisturbed or 



original strengths and the other, disturbed strengths. The strengths 



used were those obtained with the NCEL in situ vane device^ at 



locations adjacent to the penetration test sites. Plots of these 



strengths are included in Figures 13 and 14. The linear fits of these 



data were used to simplify the integration of Equation 13. In 



compliance with the recommendations of Schmid-* , consideration was 



given to the effect which object velocity might have on soil shearing 



resistance. The preliminary soil tests indicated that shearing 



velocity might have a rather strong effect on the mobilized strength 



(Figures 3 through 7) . Also the regression analysis indicated that 



velocity terms were quite important in determining the acceleration 



response. To incorporate time dependent shearing characteristics, 



the shear strength was allowed to vary with velocity as follows: 



c = c + uv (14) 



s so 



where c = "static" soil strength (as measured in standard tests) 

 so 



y = soil viscosity coefficient 



For the soils tested , values of \i were not known for the pertinent 

 velocity ranges. Therefore, several values of u were randomly selected 

 and inserted in the equations to determine what sorts of results they 

 would yield. The values of y used were 0, 0.5, 1.0, and 3.0 Ib-sec/ft . 



14 



