Experimental Investigation of Rate Effects on the Uplift Response of Surface and Skirted Circular Shallow Foundations

Shallow foundations can mobilize uplift resistance due to the negative excess pore pressure generated underneath the foundation. However, quantifying the magnitude of this uplift resistance remains uncertain due to the dependence on uplift rate, with different responses expected for surface foundations and skirted foundations. This paper attempts to reduce this uncertainty through an experimental study conducted in a geotechnical centrifuge where circular surface and skirted shallow foundations in a kaolin clay were uplifted at different velocities. Uplift capacity increased with uplift velocity until undrained conditions are reached, at which point uplift and compression can be described using the same undrained capacity factor. Undrained conditions required an uplift velocity that was approximately three orders of magnitude faster for the surface foundation than for the skirted foundations due to the much shorter drainage path length of the surface foundation. The paper proposes a new form of backbone curve that satisfactorily quantifies the variation in uplift capacity for different drainage conditions and skirt lengths.