As is well-known

the effective vertical stress of surrounding soil element of pile foundation is not identical to the dead weight of overburden soil plus the applied surcharge load. This is because the vertical shearing is developed on pile-soil interface due to the large pile-soil relative stiffness. The analytical solutions for the effective vertical stress

the unit positive (negative) shaft resistance

the total shaft resistance and the axial force (dragload)

subject to axial and surcharge loads

are derived by means of equilibrium analyses. Those solutions are calibrated by the reported test result of a single pile in saturated clay. It is shown that those solutions are reasonable and it is necessary to consider the vertical shearing of pile-soil interface. Under the surcharge load

the vertical shearing weakens the effective vertical stress

the unit negative shaft resistance and the dragload. The negative shaft resistances at the pile tip of the cases ? = -0.01

-0.02 and -0.04 are reduced to 91%

83% and 71% that of the case ? = 0

respectively. Meanwhile

the induced dragload at the pile tip of the cases ? = -0.01

-0.02 and -0.04 are reduced to 93%

87% and 76% that of the case ? = 0

respectively. The dragload is reduced slight smaller than the negative shaft resistance since it is also controlled by the cross-sectional geometries. This indicates that pile settlement is always overestimated independent of the vertical shearing.