Canal slope stability: HS 138/45

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 (dip direction/dip)

Hill slope 138°/45°; J1 234°/38°; J2 098°/58°; J3 315°/60°; $\phi = 25^\circ$. In dip/dip direction: HS 45/138, J1 38/234, J2 58/098, J3 60/315.

Single planes

Intersections

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

Interpretation

• J1 dips toward 234°, $96^\circ$ away from the face direction: it runs across the slope and cannot slide out.
• J2 is steeper ($58^\circ$) than the face ($45^\circ$): it does not daylight.
• J3 dips into the hill (315° against 138° + 180° = 318°) at $60^\circ$; toppling needs $\psi \geq 90^\circ - 45^\circ + 25^\circ = 70^\circ$, so it is below the limit.
• The only intersection that points out of the face is J1 x J2, plunging $21.3^\circ$ towards 174°. Its plunge is less than $\phi = 25^\circ$, so the wedge cannot slide.

Conclusion: the rock slope is kinematically stable against plane, wedge and toppling failure and the canal alignment is acceptable. Provide drainage and lining to prevent seepage water from raising pore pressure, and check local loosening.