Question

What can be said about stability of slope when the layers are horizontal?

(a) Stable up to 45°

(b) Stable at all angles up to 90°

(c) Unstable up to 45°

(d) Unstable at all angles up to 90°

The question was posed to me in class test.

This intriguing question originated from Causes of Mass Movements topic in division Mass Movements of Engineering Geology

Answer 1

Right answer is (b) Stable at all angles up to 90°

The best explanation: The layers horizontal layers: Such rocks forming the slopes of the natural valleys and artificial cuts are stable at all angles up to 90°. When they fail, it may be due to the presence of secondary jointing or related fractures.