Creep Response of Model Pile in Clay

Abstract

The shaft creep response of a model pile inserted in a specimen of clay is studied under constant pile loads at varying percentages of the ultimate shaft resistance. The top and lateral surfaces of the clay specimen could deform freely. The specimens were consolidated under varying vertical and horizontal effective stress combinations. The results of the tests using eight normally consolidated clay specimens with three different thicknesses and steel model piles of three different diameters and of smooth and rough surfaces show that the total displacement of a friction pile consists of a relatively small immediate displacement followed by a significant time‐dependent shaft creep. The immediate settlement was mostly elastic and recoverable upon reloading. Consolidation of the clay due to load transfer from the axially loaded pile was negligible, as negligible volume change was recorded during constant pile load tests. The time‐dependent displacement of the pile is attributed primarily to the slip between the pile and the soil. The rate of the slip displacement is found to continuously decrease with time. A parabolic equation is found to represent the creep response best. The creep response as characterized by the parameters of this relationship is dependent on the load ratio (ratio of the axial load to the ultimate shaft resistance) and the pile diameter for a given pile‐soil system; however, it is independent of surface roughness and the state of soil stresses. The horizontal effective stresses in the clay determines the shaft resistance and, therefore, the load ratio for a given axial load.