About this tool Check whether planar sliding or toppling failure is kinematically possible for a rock slope, given the slope face orientation and a discontinuity set. Enter dip and dip direction for both the slope face and the discontinuity, plus the friction angle.
Planar failure is checked using the Markland (1972) criteria: the discontinuity must strike sub-parallel to the face (±20°), daylight on the face (dip < slope dip), and have a dip exceeding the friction angle. Toppling is checked using Goodman & Bray (1976) criteria.
This is the standard first-pass check for rock slope design in quarries, road cuttings, and open pit mines. A full analysis requires stereonet plotting and consideration of wedge failures from intersecting discontinuity sets.
How to use this tool 1. Enter slope face dip and dip direction — the orientation of the designed or existing slope face.
2. Enter discontinuity dip and dip direction — from face mapping, scanline surveys, or core orientation data.
3. Enter the friction angle — basic friction angle of the discontinuity surface. Use tilt test or published values if lab data is unavailable.
Technical information Planar: dip direction within ±20° of face AND dip < face dip AND dip > φ'
Toppling: dip direction ~180° from face (±20°) AND (90° − dip) + φ' < face dip
After Markland (1972) for planar failure and Goodman & Bray (1976) for toppling. Wedge failure analysis requires two discontinuity sets and is best done with a stereonet.
Limitations This tool checks kinematic feasibility only — it does not calculate a factor of safety. A kinematically feasible failure mode may still be stable if cohesion, rock bridges, or reinforcement provide additional resistance.
Wedge failure (from two intersecting discontinuity sets) is not analysed. For a complete kinematic analysis, use a stereonet (e.g. Dips by Rocscience) with all mapped discontinuity sets.
The ±20° directional tolerance is a conventional simplification. Some practitioners use ±30° for a more conservative screening. Adjust based on the variability of the discontinuity orientations.
Revision history 4 August 2026: Initial release
Disclaimer This tool is provided for educational and general information purposes only. It is not a substitute for professional engineering advice, design or verification.
Diggy and its contributors are not licensed engineering consultants and no results generated by this tool should be used directly for construction, design or safety-critical decisions.
All values and outputs are based on published empirical correlations and should be independently checked and confirmed by a qualified geotechnical engineer before use.
By using this tool, you accept full responsibility for how you interpret and apply the information provided.
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