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KIRTLAND AIR FORCE BASE ALBUQUERQUE, NEW MEXICO ...

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APPENDIX B<br />

Hardness<br />

The hardness of a rock is a function of the compaction, cementation, and mineralogical composition of<br />

the rock. A relative scale for sedimentary rock hardness is as follows:<br />

Soft—Weathered, considerable erosion of core, easily gouged by screwdriver, scratched by<br />

fingernail. Soft rock crushes or deforms under pressure of a pressed hammer. This term is<br />

always used for the hardness of the saprolite (decomposed rock which occupies the zone<br />

between the lowest soil horizon and firm bedrock).<br />

Medium soft—Slight erosion of core, slightly gouged by screwdriver, or breaks with<br />

crumbly edges from single hammer blow.<br />

Medium hard—No core erosion, easily scratched by screwdriver or breaks with sharp edges<br />

from single hammer blow.<br />

Note the difference in usage here of the words ―scratch‖ and ―gouge.‖ A scratch should be considered a<br />

slight depression in the rock (do not mistake the scraping off of rock flour from drilling with a scratch in<br />

the rock itself), while a gouge is much deeper.<br />

Fracturing<br />

The degree of fracturing of a rock is described by measuring the fractures of joint spacing. After<br />

eliminating drilling breaks, the average spacing is calculated and the fracturing is described by the<br />

following terms:<br />

Very broken—Less than 2 inches<br />

Broke—2 inches to 1 ft<br />

Blocky—1 to 3 ft<br />

Massive—3 to 10 ft<br />

Artificial breaks can be distinguished from natural partings by several criteria. Drilling breaks are<br />

generally relatively sharp edged and the newly exposed rock surfaces are invariably fresher in appearance<br />

(less weathered) than natural breaks. Core pieces on each side of a drilling break usually fit perfectly<br />

back together, whereas natural breaks may exhibit gaps and clay films or seams, oxidation stains, or<br />

mineralization. Do not confuse drill cuttings or drilling mud on a fractured surface with a natural clay<br />

film or seam.<br />

The structural integrity of the rock can be approximated by calculating the RQD of cores recovered. The<br />

RQD is determined by adding the total lengths of all pieces exceeding 4 inches and dividing by the total<br />

length of the coring run, to obtain a percentage:<br />

where:<br />

r<br />

RQD<br />

r<br />

l<br />

100<br />

= Total length of all pieces of the lithologic unit being measured, which are<br />

Kirtland AFB<br />

SOPs for Field Investigations B-19 April 2004

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