According to the current practice, the unit shaft resistance of piles based on ground parameters is calculated with the the α-method or the β-method, for total or effective stress conditions respectively. Indeed, these two methods are included in the prEN1997-3:2021 draft standard. And while the physics behind these methods is adequate for calculating the shaft resistance of piles in clays and sands for total and effective stress analysis respectively, the main difficulty in applying the effective stress approach in clays is to estimate the radial effective stress acting on the pile. In the present paper this is addressed by a proposed earth pressure at-rest coefficient, applicable to cohesive-frictional soils and both horizontal and vertical pseudo-static conditions. Comparison examples show excellent agreement of the analytically derived shaft resistance capacities with the respective numerical ones. Regarding seismic conditions it is noted that, for the case of axially loaded piles the horizontal component of the seismic excitation does not affect the shaft resistance capacity of piles, while the vertical component could be neglected as acting favorably. Finally, it is mentioned that the proposed method is a general c-φ procedure, applicable also for purely cohesive and cohesionless soils.