Percent Recovery is defined as the ratio of core recovered to the run length expressed as a percentage:

$\text{Percent Recovery}\left(\%\right)=\frac{\text{Length of core recovered}*\hspace{0.17em}100}{\mathit{\text{Length of core run or interval}}}$

Determine the RQD for rock core samples following ASTM Test Procedure D6032, Standard Test Method for Determining Rock Quality Designation (RQD) of Rock Core.

$\text{RQD}\left(\%\right)=\frac{(\sum \text{Length of sound core segements > or = 4inch}es)\hspace{0.17em}*100}{\mathit{\text{Lenght of core run or interval}}}$

As illustrated by the example:

$\text{Percent Recovery =}\frac{\text{(10 in. + 8 in. + 10in. + 7.6 in. + 3.2in. + 4.8 in)}}{\text{48}}=96\%$

$\text{RQD (\%) =}\frac{\text{(10inches+7.5inches+8.0inches*\hspace{0.17em}100)}}{\mathrm{48}}=\text{53\%Fair}$

Mechanical breaks in the core (perpendicular to the length of the core) should not be counted towards RQD reduction. Use segments of 4” or above only by breaks identified as natural fractures or joints within the rock mass. Record the rock type (limestone, shale, sandstone, etc.), degree of weathering (highly, moderate, minimal, unweathered), natural fracture frequency (number of visible joints or natural discontinuities within a typical 12” segment of recovered core) and jointing condition (closed or open), and size of the jointing or discontinuities to use classification criteria as specified in this chapter.

Always note the percent recovery and RQD on boring logs where rock is encountered.