Measurement of pile uplift forces due to soil heave in expansive clays

Abstract

Piled foundations are widely used to limit the movement of foundations in expansive clays. These piles are subjected to large uplift forces as the clay swells (and downdrag forces when it shrinks). The appropriate method to estimate these forces is not well understood, and estimates from various methods presented in literature result in large variations. The uplift force generated in piles by soil heave was derived from strain measurements in full-scale field tests where a pile was installed in a highly expansive soil profile and flooded for several months. The results were compared to available theoretical estimates to comment on the most appropriate procedure to estimate the generated tension in the pile. The results showed that the use of an elastic solution related to the expected soil heave combined with a limiting shaft friction estimated from total stress capacity methods provided the most appropriate match to the measured results both in terms of the magnitude of the developed tension in the pile and shape of the tension profile along the depth of the pile.