Comparison of Projectile Penetration and a Cone Penetrometer as Methods for Measuring Tuff Strength

摘要

Most methods of predicting the effects of underground nuclear explosions require, as input, estimates of the strength of the medium in which the effects occur. At present there is no in situ method of measuring this strength. We have tested two methods that could be adapted for use on the walls of large boreholes in tuffs at the surface at NTS. The first method is depth of penetration of a projectile, where the depth of penetration is inversely proportional to (rhoY)/sup 1/2/, where rho is the bulk density and Y is the unconfined compressional strength. We fired projectiles at tuffs in seven locations in the NTS area. Strength and density were measured on core samples. The measurements showed a great deal of scatter, but mean results from the seven sites gave a reasonable linear fit to both (rhoY)/sup -1/2/ and to strength itself. The second method - force on the tip of a cone penetrometer - has never been investigated in rock. There are many semiempirical relationships between force and various soil properties, but not strength per se. We were able to test a cone penetrometer at only three of the seven projectile locations, and one other location. At most depths, the range of force was large. The mean force observed over a 15 cm depth range does not appear to have any relation to the strength at that depth range. 14 refs., 6 figs., 4 tabs. (ERA citation 10:050052)