Figure 8 shows a plot of velocity squared versus acceleration for a 

 typical penetrometer test. When extra-hydrodynamic forces are acting 

 on the object, such as those encountered in penetrating the seafloor, 

 the plot will deviate from the hypothetical straight line. The right 

 loop of the graph represents the straight-line hydrodynamic region, 

 and the gross deviation of the left loop represents the object 

 penetrating the soil. Consequently, a velocity-squared or acceleration 

 value at the point of deviation may be used as a mark to distinguish 

 the solely water data and the water-soil data (penetration data) . The 

 sign convention of Figure 8, and subsequent plots, is positive 

 acceleration downward. 



Ostensibly, the right loop of the test plots does not represent a 

 straight line. The reasons for the error are two-fold. One, the 

 paying of the retrieval line introduced unsteady decelerations as 

 represented by the oscillating plot. Two, the non-zero start is a 

 residual error resulting from integration, calibration, and ship motion. 

 The numerical integrations begin at the end of the penetration test 

 (where acceleration is known to be zero) . Consequently, the error 

 accumulates and manifests itself as residual velocity at the beginning 

 of free-fall. Also, the modulus of the drum spring is not a constant 

 and is approximated bilinearly; therefore, the conversion from drum 

 movement to acceleration values contains a small error. Lastly, ship 

 and winch line movement impart an initial velocity which is recorded 

 in the initial free-fall measurements. In many of the tests, the 

 oscillatory error caused by the above factors did not camouflage 

 the gross deviation occurring at the soil-water interface* In some 

 tests, however, it was difficult to discern the one oscillation that 

 marked soil entrance. 



The results of the penetration data reduction are shown in 

 Table 8. Figures 9 through 12 are acceleration versus soil depth 

 plots for the two test sites, showing the similar objects on the 

 same graph. 



ANALYSIS 



General 



The limited field and laboratory testing program which has been 

 described yielded detailed penetration records in the form of 

 deceleration versus soil depth plots (Figures 9 through 12) and a set 

 of soil property data for each of the two sites investigated. It 

 was the intention of the analysis phase of this investigation to 

 present techniques for relating these two forms of data and thereby 

 to suggest approaches for: 



(1) Predicting penetration response given the soil characteristics 

 at a site; and 



(2) Predicting the soil properties at a site given the results 

 of a penetration test. 



