This document discusses factors related to rock stability and tunnel design including hydraulic radius, modified stability graphs, numbers and factors for rock stress, joint orientation, gravity adjustment, rockmass quality, and rock quality designation, as well as estimates of induced compressive stress.

1.  L HR  LH 2 ( L  H ) Face hydraulic radius

2. Modified stability graph

3. Modified stability number

4. Rock stress factor - A

5. Joint orientation factor - B

6. Gravity adjustement factor - C

7. Rockmass quality

8. Rock quality designation - RQD

9. Engineering estimate of induced compressive stress