The Q-system was developed between 1971-1974 to classify rock masses around underground openings using field mapping. The Q-value depends on six parameters of the rock and is calculated using an equation that considers factors like the Rock Quality Designation (RQD), joint roughness, joint alteration, and stress reduction factor. RQD was originally defined from drill cores and represents the percentage of intact core pieces longer than 10cm, ranging from 0-100%.

1. Q-system
The Q-system was developed by NGI between 1971 and 1974
(Barton et al. 1974 Tunneling Quality Index (Q).
Classification of the rock mass around an underground opening,
field mapping.
The Q-value in an undisturbed rock mass may be different.
Q-value depend upon six parameter of rock .
Q-value is calculated using the following equation.
Q= RQD Jr Jw
Jn Ja SRF

2. Deere in 1963 (Deere, 1963).
 RQD was originally defined from drill cores.
 RQD will be in %age between 0 and 100 .


6. Table of RQD
RQD = 110 – 2.5Jv (for Jv between 4 and 44)
where Jv is the number of joints per m3