POROSITY CORRELATION

An additional feature of displays of the type presented in Figure 3 is that the slopes of the straight lines, at least for samples of similar material character, are inversely correlated with the porosity of the samples. This observation is highlighted in Figures 3c and 3d. Figure 3c shows results from a series of fused glass-bead samples (Berge et al., 1995) of uniform composition that was fabricated, with lower porosities being achieved by varying temperatures and length of sintering times. The porosities are distributed almost perfectly in Figure 3c, with the lower porosity lines having higher slopes and higher porosity lines having lower slopes. The experimental error in the stated porosity measurements $\simeq \pm 0.6 \%$, so that the main discrepancy observed here with misalignment between the samples at $\phi=36.0\%$ and $\phi=36.5\%$ suggests that this display may provide a more sensitive means of determining the porosity. Figure 3d shows similar behavior for very low porosity granite (Nur and Simmons, 1969), having $\phi \simeq 1\%$;as the pressure is increased, the porosity in the material is steadily decreased mostly due to crack closure.