RESULTS 



Table 1 shows the bulk density of the two 

 types of porous media as determined by the 

 four methods: (1) large gravimetric sample; 

 (2) small gravimetric samples; (3) the Troxler 

 density probe; and (4) the ratio of the tank 

 weight with dry sand to the volume of the tank 

 occupied by the porous medium. This table 

 shows that there is negligible difference in bulk 

 density between the two tanks. 



Most calibration curves show a linear rela- 

 tionship between neutron counts and percent 

 moisture from zero to about 45 percent. A 

 linear extrapolation of the calibration curve be- 

 yond 45 percent is not accurate because there is 

 a curvilinear relationship between neutron 

 counts and percent moisture beyond this point. 

 For this study the factory furnished the 

 authors with a calibrated curve used to convert 



neutron measurements to percent moisture by 

 volume (fig. 6). Data from the control tank and 

 the sample tank for a given water level were 

 plotted on a master graph with depth of meas- 

 urement on the ordinate and moisture content 

 on the abscissa. An examination of the master 

 graphs for each water level showed that the 

 voids were far enough apart on the access tube 

 to prevent an overlap in effects. Therefore, 

 each master graph was redrawn as two graphs: 

 one for data from the two tanks for depths of 

 measurement which bracketed the small void; 

 and another graph for data that bracketed the 

 large void. Data points were connected to form 

 two smooth curves which represent the soil 

 moisture content at any depth in both the con- 

 trol tank and the sample tank when the water 

 level was at a given depth. The effect of the void 



Table 1. — A comparison of bulk density (in Ib./ft.^ ) in each tank for coarse and find sand as 

 determined by four methods 



Small 

 sample 



Large 

 sample 



Troxler density 

 probe 



Tank wt./voL 



COARSE SAND 



Control tank 

 Sample tank 



98.9 

 99.2 



99.8 101.5 

 99.6 100.2 



99.9 

 99.9 







FINE SAND 





Control tank 



101.6 



100.9 ( ' ) 



102.4 



Sample tank 



100.9 



101.3 ( ' ) 



101.7 



^The Troxler density probe was not available for measurements in the fine material. 



6 



