Table 2. Comparison of Field-Measured Penetrations 

 to Penetrations Calculated From Data Taken 

 in 70 Feet of Water 



Test No. 



Measured Penetration, 



P (inch) 

 m 



Calculated Penetration, 



P (inch) 

 c 



P /P 

 m c 



1 

 2 

 3 

 4 



41.8 

 24.3 

 24.3 

 24.3 



41.0 

 28.3 

 28.8 

 24.0 



1.02 

 0.86 

 0.84 

 1.01 



DISCUSSION 



The purposes of the testing described in this report were (1) to 

 demonstrate that the concept of using the Doppler principle to instrument 

 a penetrometer was workable and that accurate data could be obtained and 

 (2) to see if velocity and penetration performance were as expected. 



The test data show that clear traces of velocity versus time, 

 which are paramount in analyzing the data, can be obtained. Traces 

 similar to those shown in Figure 4 would leave no hope of determining 

 changes in deceleration, which are important in determining changes in 

 strength. Conversely, traces similar to Figure 5 would give a good idea 

 of deceleration changes. The interference in Figure 4 was caused by the 

 receiving system and was not the fault of the sound source on the penetrom- 

 eter. With all transmitting and receiving systems working properly, 

 traces with quality equal to Figure 5 should always be obtained. 



The tests reported give an indication of the accuracies that can be 

 obtained with the Expendable Doppler Penetrometer. For the tests 

 performed in 100 feet of water (see Table 1), the calculated penetrations 

 are from poor velocity records similar to Figure 4, and the measured 

 penetrations were from poorly defined mud lines on the penetrometer 

 body. As a result the measured penetrations averaged 12% more than the 

 calculated values. Better average agreement was obtained for the tests 

 in 70 feet of water (see Table 2) , where divers were used to mark the 

 depth of penetration of the penetrometer. The measured values averaged 

 about 7% less than the calculated values. A 7% error represents about a 

 2-foot error when penetration is 30 feet - the penetration expected in 

 soft clays. This is satisfactory accuracy for determining penetrability. 



It is not possible from the data to determine how accurately strengths 

 can be estimated. The data in Figure 5 shows that changes in penetration 

 resistance can be measured. These changes are indicative of strength 

 changes. However, because the seafloor at the site where the data of 

 Figure 5 was gathered is sand, no in-situ strength data are available. 



16 



