Discontinuity survey, Rock Mass Rating and the Q-system computed as you enter, point-load to strength conversion, and Markland kinematic tests run against the actual slope you are standing under — planar, wedge and toppling, with the intersections plotted.
Friction angle is the one number people guess. Rough clean joints 35–45°, smooth planar 30–35°, clay-infilled can be under 20°. If it is infilled, measure it — do not assume.
UCS ≈ 22 × Is₅₀ for most rock. It is an estimate, not a substitute for a test — the factor ranges from about 15 to 30 depending on rock type.
| Set | Dip dir | Dip | Spacing | Persist | Rough |
|---|
A scanline finds joints that cross it and misses joints that run beside it. The set most nearly parallel to your traverse is the one most under-counted — and it is often the set that fails the slope. This weights each reading by how badly it was under-sampled.
Weight = 1/sin(angle between the scanline and the joint plane). It is capped because 1/sin runs away near zero and one joint would otherwise swamp the whole diagram — a capped reading is flagged, not hidden.
GSI is judged from the blockiness of the mass and the condition of the joint surfaces. It is an estimate made by eye, and the answer inherits that. Blasting damage D is the parameter engineers most often leave at zero when it should not be.
Two independent routes to RQD rarely agree exactly. If they disagree badly, one of the two measurements is wrong, and that is worth knowing before the design depends on it.