Particle crushing, shear banding, interface abrasion and migration of crushing products all have the potential to influence the behaviour of displacement piles in sands. This paper considers these particulate processes, reporting experiments with model displacement piles installed in uniform pressurised sand and parallel interface ring shear tests. The findings offer new insights into the mechanics of displacement piles in sands.

08.01.15 KB Ok to add accepted version to spiral, embargo period expired

The uplift capacity of helical anchors normally increases with the number of helical plates. The rate of capacity gain is variable, considering that the disturbance caused by the anchor installation is generally more pronounced in the soil mass above the upper plates than above the lower plates, because the upper soil layers are penetrated more times. The present investigation examines the effect of the number of helices on the performance of helical anchors in sand, based on the results of centrifuge model tests. Uplift loading tests were performed on 12 different types of piles installed in two containers of dry sand prepared with different densities. The measured fractions of the uplift capacity related to each individual helical plate of multi-helix anchors were compared with the fractions predicted by the individual bearing method. The results of this investigation indicate that in double- and triple-helix anchors, the contributions of the second and third plate to the total anchor uplift capacity decreased with the increase of sand relative density and plate diameter. In addition, these experiments demonstrated that the variation of the anchor load–displacement behavior with the number of helices also depends on these parameters.

Palavras-chave: estaca metálica helicoidal, capacidade de carga à tração, fundações profundas, controle durante execução, areia, modelagem física em centrífuga.

The empirical torque correlation factor (KT), which relates the uplift capacity to the installation torque of helical piles, is routinely used as an on-site instrument for quality control with this type of foundation. This paper presents a theoretical relationship between uplift capacity and installation torque of deep helical piles in sand. An experimental program, including centrifuge and direct shear interface tests, was carried out to validate this expression. The experimental results were compared with the values predicted by the suggested approach and showed good agreement. As the developed model depends on the residual interface friction angle (δr) between the helix surface and the surrounding sand, results of δr, extracted from different sand samples, are presented for use in this suggested relationship on site. Also, the values of KT found in this work were compared with those of field and laboratory tests on helical piles in sand reported in the literature. From this analysis, it was found that the measured values of KT decrease with an increase in pile dimensions and, in most of cases, with an increase in sand friction angle. These results were explained by the presented model.