8/17/2019 2-Negative Skin Friction

1/5

1

 Negative Skin Friction

What is negative skin friction? Negative skin friction is a downward shear drag

acting on the pile surface due to relative

downward movement of soil strata surroundingthe pile.

The following are some of the causes of negative

skin friction•Due to pile or pile segment passing through

compressile soil stratum which consolidates

•Due to placement of a fill on compressile soil

la!er causing the la!er to consolidate

8/17/2019 2-Negative Skin Friction

2/5

"

 Negative Skin Friction

•#owering of ground water tale causing theshrinkage of e$pansive soils.

•%nder consolidated natural or compacted soils.

&f the pile tip is on a stiff or hard stratum' therewill e a relative downward movement of upper

compressile la!er of soil w.r.t. pile ' due to aove

causes' causing a downward drag force.

8/17/2019 2-Negative Skin Friction

3/5

(

 Negative Skin Friction

•)esic stated that downward movement as little as *.+inch ma! e sufficient to moili,e full negative skin

friction.

•The down drag will not affect the geotechnical

capacit! of end-earing piles ut will increase stresses

on the pile and pile cap.

The negative skin friction of a single pile is given !

 Negative skin friction load %nit frictional resistance

/downward0 #ength of the pile aove ottom of the

compressile la!er 2erimeter of the pile cross section

3nd total downward load negative skin friction load 4

live load4 dead load

8/17/2019 2-Negative Skin Friction

4/5

5

 Negative Skin Friction

For a pile group it can e assumed that there is norelative movement etween the piles and the soil

 etween the piles. Therefore the total force acting down

is e6ual to the weight of the lock of soil held etween

the piles' the weight of the piles and the pile cap and

the downward drag along the pile group perimeter due

to negative skin friction

8/17/2019 2-Negative Skin Friction

5/5