Wedge Failure Kinematic Screen
Screens for wedge sliding on the line of intersection of two discontinuities in a rock slope. You supply the intersection line (plunge and trend), the slope face and a friction angle, and it returns a Yes/No for each sliding condition plus an overall feasibility verdict.
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Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.
How to use this calculator
- Compute the intersection line first with the Kinematic Wedge Intersection Calculator to get its plunge ψi and trend αi.
- Enter ψi and αi, the slope face dip ψf and dip direction αf, and the friction angle φ.
- Read the daylight / frictional / direction criteria and the overall kinematic verdict.
How it works
A wedge slides along the line where its two bounding discontinuities meet, which behaves like a single plunging line. Sliding is possible only when all three hold: the intersection daylights in the face (ψi < ψf); the plunge exceeds the friction angle (ψi > φ); and the trend plunges out of the slope, within ±90° of the face dip direction.
The direction check uses the acute wrap difference Δα between the intersection trend and the face dip direction. Because release only needs the outward-facing half-space, the wedge window is the full ±90°, not the tighter ±20° used for planar sliding.
Worked example
Intersection plunging 35° out of a 60° face. For ψi = 35°, αi = 185°, ψf = 60°, αf = 180° and φ = 30°: Δα = 5°. Daylights (35 < 60) = Yes; frictional (35 > 30) = Yes; direction (5 ≤ 90°) = Yes. Verdict: Kinematically feasible.
Common mistakes
- Entering one discontinuity's dip instead of the intersection line — you must first resolve the line of intersection of the two planes.
- Mixing up plunge/trend of the intersection with dip/dip-direction of a plane.
- Assuming a feasible screen equals instability; a full wedge limit-equilibrium analysis is still required.
Frequently asked questions
How do I get the intersection plunge and trend?
Use the Kinematic Wedge Intersection Calculator, which takes the two discontinuities' dip and dip direction and returns the plunge and trend of their line of intersection.
Why is the direction limit ±90° here but ±20° for planar sliding?
For a wedge, the intersection only has to daylight somewhere on the outward half of the slope, so any trend within ±90° of the face dip direction emerges from the face.
What if the intersection plunges steeper than the face?
Then it does not daylight (ψi ≥ ψf) and the wedge is kinematically locked — it cannot slide out of the slope regardless of friction.
Is this a factor of safety?
No. It is a first-pass Markland-type kinematic screen; follow a feasible result with a full wedge stability analysis including water and shear strength.
Related tools
- Plane Failure Kinematic Screen
- Toppling Kinematic Screen
- Kinematic Wedge Intersection Calculator
- RQD Calculator
- Bench Face Height Calculator
- Berm Width Calculator
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