Computer · Soil Mechanics

Which of the following statements is/are correct regarding negative skin friction on piles? I. Negative skin friction is a downward drag acting on a pile due to the downward movement of the surrounding compressible soil relative to the pile. II. The magnitude of negative skin friction for cohesive soil is given by 'p × c × Lf' (where p = perimeter of the pile, c = cohesion of soil in the zone of Lf, and Lf = depth of fill or soil moving vertically).