Failure mode from stereonet: HS 40/050

Method (lower-hemisphere stereonet, equal-angle): plot the great circle of the slope face and of each discontinuity, draw the friction circle of radius $\phi$, and mark intersections of great circles. Then apply the kinematic tests below.

Data (dip/dip direction)

HS 40/050; J1 46/040; J2 28/200; J3 70/103; J4 39/348; $\phi = 25^\circ$.

Single planes

Intersections

(The other 2 intersections plunge into the hill, away from the face, and cannot slide.)

Result

• J1 dips almost with the slope but is steeper ($46^\circ > 40^\circ$), so it does not daylight.
• J2 dips back into the hill at $200^\circ$ (far from the face) and is not toppling-type since it is gentle.
• J3 and J4 individually do not daylight in a sliding sense.
• The intersection J3 x J4 plunges $32.4^\circ$ towards $026^\circ$, which is between $\phi = 25^\circ$ and the face apparent dip $37.5^\circ$ and points out of the face.

Possible mode of failure: wedge failure formed by joints J3 and J4, sliding along their line of intersection. (Plane and toppling failure are not kinematically possible.)