Failure mode: HS 75/230, BP 68/045

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 75/230; BP 68/045; J1 49/215; J2 55/265; J3 65/199; $\phi = 32^\circ$.

Single planes

Intersections

(The other 3 intersections plunge into the hill, away from the face, and cannot slide.)

Result

• J1 dips $49^\circ$ at 215°, only $15^\circ$ from the face direction. $32^\circ < 49^\circ < 75^\circ$: plane failure along J1.
• BP dips $68^\circ$ at 045°, opposite to the face (230° - 180° = 050°) and steeper than $90^\circ - 75^\circ + 32^\circ = 47^\circ$: toppling failure.
• J1 x J2, J2 x J3 (and marginally J1 x J3) intersect with plunges above $32^\circ$ but below the face apparent dip: wedge failure is also possible because the face is very steep.

Conclusion: the main modes are plane failure along J1 and toppling of bedding slabs (BP), with secondary wedge sliding. The slope needs to be flattened to less than about $45^\circ$ (J1 dip is $49^\circ$) and reinforced.