Question

Indicate probable reasons why slopes in cohesionless soils may exist, or be made at inclinations steeper than the soil's angle of repose.

Answer 1

Slightly wet cohesionless soil exhibit a very high angle of repose because surface tension between the water and the soil grain tends to hold the grain in place.

• Think about building a sand castle on the beach. If the sand is totally dry, it is impossible to build a pile of sand with a steep face like a castle wall.
• If the sand is somewhat wet however one can build a vertical wall.
• If the sand is too wet then it flows like a fluid and can't remayin posiuas a wall.
• ( When the material become saturated with water the angle of repose is reduced to very small value and the material tend to flow like a fluid. this is because the water gets between the grain and eleminates grain to grain frictional contact.)