Negative Skin Friction in a pile foundation is likely to occur when
- AThe pile is driven into dense sand.
- BThe surrounding soil settles more than the pile itself.Correct
- CThe pile is subjected to an upward pull.
- DThe water table is at the ground level.
Solution
Concept
Negative Skin Friction in Pile Foundations
Formula
N/A
Step-by-step solution
1. Review the definition and cause of negative skin friction in pile foundations. 2. Recall that negative skin friction develops when the surrounding soil settles faster than the pile. 3. Select Option (b) as the correct choice.
Explanation
Negative skin friction happens when the soil around a pile moves or settles downward faster than the pile itself. Instead of supporting the pile through upward friction, the settling soil pulls the pile downward, adding extra load to the foundation.
Shortcut
To remember Negative Skin Friction in pile foundations, use the memory rule "Soil Down = Drag Down": - Soil Settles Faster: Surrounding soft or soft-consolidating soil moves downward more than the pile itself. - Drag Force: Instead of supporting the pile with upward friction, the relative downward movement of the soil pulls/drags the pile downward, adding an extra load.
Common mistake
A common mistake is selecting option C by confusing negative skin friction with uplift forces or tensile forces acting on the pile. Another frequent mistake is selecting option D by assuming negative skin friction is primarily caused by water table fluctuations rather than relative downward movement/settlement of compressible surrounding soil.
Correct answer: B) The surrounding soil settles more than the pile itself.