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What is negative skin friction on piles and pile group?Negative skin friction is usually a downward shear drag acting on a pile or pile group because of downward movement of surrounding soil relative to the piles. This shear drag movements are anticipated to occur when a pile penetrates into compressible soil layer that can consolidate. It is reported that, A small relative movement between the soil and the pile of around 10 mm may be adequate for the full negative skin friction to materialize. Moreover, the time of ending the negative skin fiction of piles is estimated to be around 2 years and the degree of consolidation of the soft soils reaches 90%. Finally, this article presents different aspect of negative skin friction on piles and pile group.
Factors that cause negative skin friction on piles and pile group
- Newly placed fill material on compressible soil before the completion of consolidation.
- If fill material is loose cohesionless soil
- When fill material is deposited over layer of soft soil or peat.
- Lowering groundwater which increases the effective stress causing consolidation of soil with resultant settlement and friction force being developed on the pile.
Effect of negative skin friction on piles and pile groups
- Negative skin friction contributes to the uneven settlement of piles or pile group.
- For piles in compressible soils where pile capacity is contributed by both point resistance and shaft adhesion, the problem of negative skin friction should be considered a settlement problem.
- In bearing piles where the settlement of the pile is negligible, negative skin friction becomes a pile capacity problem.