The compressive capacity of helical piles in sand and clay is investigated by means of field testing and numerical modeling. The numerical models are conducted using the computer program ABAQUS and are calibrated and verified using full-scale load testing data. The calibration was accomplished by using reasonable assumptions regarding soil–pile interaction and soil parameters reported from the literature. The model was verified by comparing its predictions with observed load–displacement curves obtained from full-scale pile load tests. The verified numerical model was used to perform a parametric study considering different pile configurations and soil parameters to evaluate the compressive capacity and load-transfer mechanism of helical piles. The compressive capacity obtained from the numerical models is compared with that obtained from existing theoretical methods for calculating the capacity. It is found that the predictions of theoretical equations for piles in cohesionless soil vary largely depending on the choice of bearing capacity factors and proper failure criteria. The interaction of closely spaced helices on the capacity of a helical pile is also evaluated. A bearing capacity reduction factor, R, and helix efficiency factor, EH, are proposed to evaluate the compressive capacity of helical piles in cohesionless soil considering an industry-acceptable ultimate load criterion corresponding to settlement equal to 5% of helix diameter, D.

The axial compression performance of large-capacity helical piles is of significant interest because they can offer an efficient alternative to conventional piling systems in many applications such as in oil processing facilities, transmission towers, and industrial buildings. This paper presents the results of seven full-scale axial compression load tests conducted on 6.0 and 9.0 m large-capacity helical piles and a 6.0 m driven steel pile. The results are considered essential to qualify and quantify the performance characteristics of large-capacity helical piles in cohesive soils. The test piles were close-ended steel shafts with an outer diameter of 324 mm. The test helical piles were either single or double helix, with a helix diameter of 610 mm and interhelix spacing that varied between 1.5 and 4.5 times the helix diameter. The subsurface soil properties at the test site were determined using field and laboratory testing methods. The 6.0 m piles were tested 2 weeks after installation, while the 9.0 m piles were tested 9 months after installation. The load–settlement curves were presented to better understand the behaviour of test piles. An ultimate capacity criterion was proposed to estimate the ultimate load of large-capacity helical piles. The test helical piles developed ultimate resistances up to 1.2–1.8 times that of the driven pile. The load-transfer mechanisms of large-capacity helical piles were studied, and it was found that soil disturbance during pile installation had a significant effect on the pile failure mechanism regardless the value of the interhelix spacing to helix diameter ratio. The mobilized soil strength parameters were back-calculated and compared with the estimated intact soil strength parameters.

The increasingly popular performance-based design approach requires that soil–structure interaction (SSI) analysis become an integral part of the seismic evaluation. This is particularly important for structures with substantial embedment. The primary objectives of this study are twofold: (i) evaluate the SSI effects for buildings with a basement and (ii) evaluate the ability of two analytical methods to account for SSI effects in seismic design — an analytical solution for kinematic SSI and a nonlinear finite element model. Scaled model shaking table tests were performed on a model building with an embedded basement founded in a synthetic stiff clay deposit enclosed in a laminar soil container. The model structure used in this study comprised a simple single-degree-of-freedom structure with a modular box foundation designed to permit consideration of structures with different basement embedment depths. The experimental results showed that the ratio of effective period of the soil–structure system to that of the structure ([Formula: see text]) decreased for the long-period structure and increased for the short-period structure, with increasing embedment. The results confirm the ability of the analytical techniques to predict with reasonable accuracy the SSI effects for buildings with embedded parts.

The dynamic performance of helical piles is of significant interest because such piles can offer an efficient alternative to conventional piling systems in many applications where the foundation is subjected to dynamic loads. This paper presents the results of full-scale dynamic vertical load tests on a 9.0 m double-helix, large-capacity helical pile and a driven steel pile of the same length and shaft geometry. Comparing the results is considered necessary to evaluate, qualitatively and quantitatively, the dynamic performance characteristics of large-capacity helical piles. The test piles were closed-ended steel shafts with an outer diameter of 324 mm. The piles were subjected to harmonic (quadratic) loading of different force intensities acting within a frequency range that covered the resonant frequencies of the tested pile-soil-cap systems. The dynamic and static properties of the subsurface soil adjacent to the test piles were determined using the seismic cone penetration technique and the conventional soil boring and testing methods. In addition, field observations are compared with calculated responses using the program DYNA 6 to better understand the pile-soil interaction for the case of helical piles. The effects of soil nonlinearity and pile-soil separation were accounted for in the analysis by employing a weak boundary zone around the piles in the analytical model. The experimental results show that the dynamic behaviour of helical piles is essentially the same as that of driven steel piles with the same geometric properties (without the helix plates). In addition, it was demonstrated that the program DYNA 6 can accurately simulate the behaviour of both helical and driven piles.Résumé : La performance dynamique de pieux hélicoïdaux est d'intérêt significatif puisqu'ils peuvent offrir une alternative efficace aux systèmes de pieux conventionnels dans plusieurs applications où la fondation est soumise à des sollicitations dynamiques. Cet article présente les résultats d'essais de chargement dynamique vertical à l'échelle réelle sur un pieu hélicoïdal à double hélice, de grande capacité, de 9,0 m, et d'un pieu foncé en acier de même longueur et de même géométrie de l'arbre. La comparaison des résultats s'avère nécessaire pour évaluer, qualitativement et quantitativement, les caractéristiques de la performance dynamique de pieux hélicoïdaux de grande capacité. Les pieux d'essai étaient faits d'un arbre d'acier à embouts fermés avec un diamètre externe de 324 mm. Les pieux ont été soumis à des sollicitations harmoniques (quadratiques) de différentes intensités de force agissant à l'intérieur d'une gamme de fréquences qui couvre les fréquences résonnantes des systèmes pieu-sol-cap testés. Les propriétés dynamiques et statiques du sol de fondation adjacent aux pieux d'essai ont été déterminées à l'aide de la technique sismique de pénétration du cône ainsi que par des méthodes conventionnelles de forage et d'essais de sol. De plus, les observations de terrain sont comparées aux résultats calculés avec le progr...

Hollow-bar micropile construction, also known as self-drilled, is becoming a popular option because it allows faster installation processes and ground improvement at the same time. This paper presents a field study and numerical investigation on the behaviour of single hollow-bar micropiles embedded in a stiff silty clay deposit. Four hollow-bar micropiles were installed using an air-flushing technique employing large drilling carbide bits. Five axial tests were conducted on the four micropiles, comprising three compression and two tension monotonic axial tests. The results of the field tests are presented and analyzed in terms of load–displacement curves. A two-dimensional axisymmetric finite element model (FEM) was created and calibrated using the field test results. The calibrated FEM was utilized to select an appropriate failure criterion for hollow-bar micropiles depending on the load-transfer mechanism of the micropiles. In addition, the model was employed to carry out a parametric study to investigate the effect of the installation methodology, hollow-bar micropile geometry, and shear strength of the surrounding soils on the micropile capacity. Based on the outcomes of the parametric study, an equation is proposed to estimate the axial capacity of hollow-bar micropiles in cohesive soils.