Failure mode: HS N45E/70, bedding N55E/45

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 and assumptions

All planes strike as given and are taken to dip on the side that appears in the figure: Hill slope N45°E/70° SE = 70/135; Bedding N55°E/45° SE = 45/145; J1 N47°W/31° SW = 31/223; J2 N77°E/36° SE = 36/167; J3 N20°E/10° SE = 10/110. The friction angle is not stated, so $\phi = 30^\circ$ is assumed.

Single planes

Intersections

Result

• Bedding dips $10^\circ$ off the face direction at $45^\circ$: $30^\circ < 45^\circ < 70^\circ$, so it daylights and can slide: plane failure.
• J3 dips only $10^\circ$, below $\phi$: stable. J1 dips across the slope (88° from the face direction).
• The Bedding x J2 intersection plunges $32.6^\circ$ towards 195°, in the face (apparent dip $53.8^\circ$) and above $\phi$: wedge failure is also possible.

Possible mode of failure: plane failure along the bedding planes (main), with wedge failure formed by bedding and J2. Reduce the cut angle below $45^\circ$ and provide bolting and drainage.