Uplift Behaviour Of Piles Research Articles

Quasi-static tests and numerical simulations of ductile seismic behavior for scoured bridge pile group foundations considering pile uplift

Scour is the main hazard for coastal bridges. Compared to the fully embedded pile group foundation before scour, the scoured pile group foundation is more prone to the inelastic damage and pile uplift when subjected to earthquakes. However, the seismic behavior of the scoured bridge pile group considering both the ductile and uplift behavior of piles is yet to be documented. This study aims to reveal the ductile seismic behavior of the scoured pile group foundation considering the pile uplift behavior. To this end, quasi-static tests were performed on two reinforced concrete (RC) 3 × 2 pile group foundation specimens embedded in homogeneous sand with and without pile uplift. The lateral loads were separately applied to the cap center of the pile group and the top of the pier to reproduce the pile uplift effect on the foundation. The experimental result of these two specimens was comprehensively compared and discussed. Furthermore, the finite element models for the quasi-static tests were developed and validated. The experimental result indicates that the pile group without uplift shows ductile properties, whereas that with uplift exhibits both ductile and self-centering behavior. The uplift of piles reduces the lateral strength and residual lateral deformation of the ductile foundation. Moreover, the pile group with the pile uplift has a more considerable displacement ductility at the first yielding limit state of belowground piles but a smaller displacement ductility at the peak lateral strength and ultimate residual strength limit states. The findings of this study provide insights into the seismic design/assessment of scoured bridges in coastal regions.

Application of a Hydraulic Gradient Technique for Modeling the Uplift Behavior of Piles in Sand

Abstract A scale modeling technique is presented for simulating the uplift behavior of piles in sand, which satisfies stress and strain similitude with full-scale prototypes. A hydraulic gradient approach was used to increase the body forces in the scale model tests, until the stresses became representative of reasonable field-scale conditions. The associated model scaling laws that are used with this technique are presented and discussed. Eight pile pullout tests were conducted, at varying magnitudes of hydraulic gradient; one of these tests was conducted on a pile instrumented with strain gages. From the results of this study, it was concluded that the hydraulic gradient technique can be effectively applied to induce reasonable prototype stresses in a scale model, allowing for reasonable simulation of the uplift behavior of piles in sand. The hydraulic gradient technique was found to be particularly sensitive to the distribution of the hydraulic gradient in the soil profile, which is not surprising, given the nature of the scaling laws for this particular modeling technique. Analysis of the results from the pile instrumented with strain gages indicated that (1) very little shear stress was mobilized in the upper 25 % of the pile, even at applied uplift loads approaching the ultimate pullout force; (2) the largest amount of shear stress for each applied uplift force was typically mobilized at a point somewhere between 60 % and 80 % of the length of the pile; and (3) at failure, the mobilized shear stress distribution was clearly not triangular, as is postulated by commonly used pile uplift design approaches. Post-failure investigations conducted after the completion of each pullout test indicated that the failure shear surface in each of the model tests developed along the pile-soil interface.

THE UPLIFT BEHAVIOR OF PILES WITH ENLARGED BASE IN SAND

THE UPLIFT BEHAVIOR OF PILES WITH ENLARGED BASE IN SAND

Influence of foundation geometry on the uplift behaviour of piles with enlarged bases : Dickin, E A; Leung, C F Can Geotech JV29, N3, June 1992, P498–505

Influence of foundation geometry on the uplift behaviour of piles with enlarged bases : Dickin, E A; Leung, C F Can Geotech JV29, N3, June 1992, P498–505

The influence of foundation geometry on the uplift behaviour of piles with enlarged bases

Centrifugal model tests investigating the influence of shaft to base diameter ratio and bell angle on the uplift capacity of piles with enlarged bases (or belled piers) in sand are reported. Increases in the angle of bell and in diameter ratio both result in a decrease in net uplift capacity and failure displacement. This appears to account for observed differences in uplift capacity between belled piers and anchor slabs. Studies of failure mechanisms around models of belled piers and anchor plates show distinctly different behaviour characteristics between foundation types. The comparatively low uplift capacities observed for belled piers are attributed to a lesser degree of soil mobilization. An empirical design method for belled piers is proposed in which appropriate factors which account for foundation geometry are applied to a simple continuous anchor formula. Key words : piles, sand, uplift capacity, centrifuge, design.

Performance of piles with enlarged bases subject to uplift forces

The influence of embedment, base diameter, and backfill density on the uplift behaviour of piles with enlarged bases embedded in sand was investigated in a centrifuge. Comparitive tests on straight-shafted piles are also reported. For piles in dense sand, sensible agreement was found with earlier research on anchor plates and published field data. However, uplift capacities in loose sand were considerably lower than previously observed for anchor plates. A number of theories for anchors considerably overpredict the observed capacity for belled piers in both dense and loose sand, although in the case of dense sand, reasonable values are obtained using an empirical equation derived from centrifuge tests on anchor plates and a finite element based design approach. The normally conservative vertical slip-surface model is alone in providing reasonable agreement with the surprisingly low observations for piles in loose sand. Key words: piles, uplift capacity, centrifuge tests, sand.