The occurrence of residual stresses in helical piles

Residual stresses generated during the pile installation are usually observed and considered in the interpretation of conventional pile load tests. However, in the case of helical piles, residual stresses can be generated by previous loadings. At the end of the unloading stage in tension tests, the shaft resistance is reversed, and the helices are maintained forced against the soil. The occurrence of residual stresses measured at the lower portion of the shaft, close to the helices, was observed in four tension tests performed on instrumented helical piles in Brazil. This paper discusses the outcomes of these tests on helical piles installed in two different sites of tropical residual soil. The results illustrate that the amount of residual stresses is greater for piles with less contribution of shaft resistance in the pile uplift capacity.