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Full workflow

The sequence of a real project, from the on-site survey to the report. The detailed options are in the pages of the individual chapters.

1. The geostructural survey (ISRM)

Rock Mechanics NX represents and processes the geostructural discontinuity survey carried out on site with the compass and clinometer method, according to the ISRM recommendations "Suggested Methods for the Quantitative Description of Discontinuities in Rock Masses" (1978).

For each discontinuity set, the ISRM parameters are described:

Parameter Description Where it counts
Attitude dip direction and dip orientation A6, SMR, stability
Spacing \(s\) mean distance between adjacent discontinuities A3, RQD from \(J_v\)
Persistence continuity of the joint over the face A4 (v1)
Aperture distance between the walls A4 (v2), \(J_a\)
Roughness at small and medium scale A4 (v3), \(J_r\), JRC
Wall weathering degree of degradation A4 (v4), \(J_a\)
Infilling nature and thickness of the material A4 (v5), \(J_a\)
Hydraulic conditions from dry to heavy inflow A5, \(J_w\)

Digital acquisition of the survey

The survey can be acquired in the field with eGeo Compass or processed with GMS (GeoMechanical Survey), which interfaces with the app. The joint sets and attitudes are thus imported without manual re-entry.

2. Intact rock strength and RQD

  • \(S_u\) (uniaxial compressive strength): from a Point Load Test, Schmidt hammer or ISRM estimate.
  • RQD: from borehole cores or estimated from the volumetric joint count \(J_v\) / from the number of joints per metre.

Full definitions and equations in Overview and common parameters.

3. Geomechanical classification

The method (or more than one) is chosen according to the structure and the lithology. All methods draw on the same survey:

The output of each classification is: numerical index → class (I–V or I–IX) → rock-mass quality → characteristic parameters (\(c\), \(\varphi\), \(E\), GSI).

Several classifications compared

It is good practice to evaluate the rock mass with several methods and compare their characteristic parameters: the empirical correlations are calibrated on different contexts, and the scatter of the results is itself an indication of reliability.

4. Stability check

When the survey identifies a kinematically possible mechanism:

  • Planar sliding — a discontinuity with a dip direction close (± 20°) to that of the face and a smaller dip. Tension crack, water in the joints, seismic action and external forces are considered.
  • Sliding 3D — two sets intersecting to form a tetrahedral wedge; sliding along the line of intersection or on a single plane.

For sliding along two joints in the design phase of the intervention (bolts, anchors, mesh), refer to the technical sheet of RockPlane NX.

5. Utilities

6. Export

The calculation report is generated with the survey data, the classifications and the checks, plus the graphical outputs. See Export and report and File formats.

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