Page 71 - Handbook GEOTEKNIK_Final_Neat

Negative Skin Friction, Q Pile Structure Capacity
nsf

Method of Reducing Negative Skin Friction • Structure capacity should be checked either based on BS8110, BS8004 or MS1314,
depending type of pile
i. By sleeving the pile section within the overlying fill or soft clay

ii. Surround with plastic membrane with a low friction value Type of Pile Reference Structure Capacity
iii. Surround pile with soft asphalt membrane which has a comparatively low frictional value
iv. Coated with bitumen (3mm thick) RC or Spun Piles 0.25*f *A or M /01.5b
c
p
cu

Main Effects of Negative Friction Micropile BS8110 : CL. 3.8.4.3 0.4*f *A + 0.75*A *f y
s
g
cu

i. Increased axial load in pile Borepile BS8004 : CL. 7.4.4.3.1 0.25*f *A p
cu

ii. Increased settlement of pile

iii. Reduced load carrying capacity of pile
Where f : Grout/concrete strength characteristic
cu
Note: f : Yield stress of steel

The maximum downdrag can be estimated by assuming a distribution of frictional y
stresses proposed by Tomlinson A : Area of grout
g
A : Area of steel
s
A : Area of pile
p
M : Crack Moment at 0.05mm crack width (MS1314)
c

54 PUBLIC WORKS DEPARTMENT MALAYSIA GEOTECHNICAL ENGINEERING HANDBOOK 55