End-bearing Pile Research Articles

An analytical solution for integrity detection of a floating pile embedded in saturated viscoelastic half-space

A new mathematical model of a floating pile embedded in a viscoelastic saturated soil for low-strain integrity detection is proposed using the theory of porous media. The saturated surrounding soil is divided into Novak’s thin layers along the pile length and a homogeneous half-space underlying the pile base to consider the effect of excitation frequency on the dynamic stiffness of the soil beneath the pile base. And the corresponding analytical solutions for the dynamic impedance and the reflected wave signal of vertical velocity at the pile head are derived and verified by comparing its reduced solution with the existing solutions for the end-bearing pile. In addition, an extensive parametric analysis is further conducted to investigate the effects of the slenderness ratio of pile, the modulus ratio of pile to the surrounding soil, and the permeability coefficient of saturated soil on the vertical vibration characteristics of the pile–soil interaction system.

Assessing physical mechanisms related to kinematic soil-pile interaction

The kinematic soil-pile interaction is a cornerstone in developing seismic design procedure for piles. How to mathematically quantify this interaction has received intensive research efforts. However, to date, there is no consensus among researchers on the optimal mathematical model with sufficient accuracy and mathematical simplicity. Specifically, existing idealized models are frequently criticized as missing some important physical mechanisms, e.g., shear stresses in soil or continuity. It remains elusive to what extent these physical mechanisms contribute to the overall kinematic response. Herein, the contribution of each physical mechanism is singled out of the overall kinematic response of end-bearing piles with the aid of a continuum solution. Then, a series of parametric study shows that the contribution of each physical mechanism highly depends on the frequency, and the shear stresses in soil may contribute appreciably to the overall kinematic response.

On the Stress-Strain State and Load-Bearing Strength of Argillite-Like Clays and Sandstones

The development of the stress-strain state of the soil mass, represented by argillite-like clays and sandstones, at the base of bored end-bearing piles is examined. A method is developed for conducting experimental studies. Stamp tests showing the load-settlement relation were performed and three phases of development of the stress-strain state were identified. Recommendations are formulated for designing bases comprised of argillite-like clays and sandstones.

Dynamic analysis of axially loaded end-bearing pile in a homogeneous viscoelastic soil

A new approximate analysis technique is developed to obtain the steady-state response of axially loaded pile embedded in a homogeneous, isotropic soil, and resting on a rigid base. In the analysis, the soil is modeled as an axisymmetric linear viscoelastic continuum with frequency independent hysteretic material damping and the pile is modeled as an elastic Euler rod with a circular cross-section. The soil displacement in the vertical direction is expressed as a product of separable functions, while the radial displacement is assumed to be zero for mathematical simplicity; although the effect of the radial displacement is indirectly taken into account by modifying the soil modulus. The Extended Hamilton's principle in conjunction with the calculus of variations is used to obtain the differential equations governing pile and soil displacements and the relevant boundary conditions. The pile and soil displacement equations are solved analytically following an iterative algorithm. The accuracy of the analysis is ensured by comparing the pile responses obtained from this analysis with those obtained by other methods available in the literature. A parametric study is performed to investigate the influence of the pile and soil parameters on the axial dynamic pile-head impedances. The plots developed from the parametric study can be used in the design.

Numerical Study on Buckling of End-Bearing Piles in Soft Soil Subjected to Axial Loads

End bearing piles are commonly used as an efficient foundation system for supporting structures built on soft soils. Although, soft soils can provide some confinement to the pile not to be treated as an Euler column, the excessive large lateral movement may cause the soil to fail under axial loads before reaching the buckling load. Moreover, the buckling resistance of end bearing piles under loading–unloading conditions may be influenced since residual stresses in the structural elements of the piles and the surrounding soil exist even after removing the load. In addition, buckling of end bearing piles under extreme loading conditions of loading–unloading nature may result in residual stresses in the structural elements of the piles and the surrounding soil even after removing the load. In this paper, a 3-D numerical model utilizing the finite difference method was developed to study buckling behavior of end bearing piles. First the model’s calculated buckling load was verified against the theoretical solution for an idealized Euler’s case. Then, a comprehensive parametric study was performed to understand the effect of both the soil stiffness and the flexural stiffness of the pile on the behavior of buckled end bearing piles under both loading and unloading conditions. The results showed that both the lateral stiffness of the supporting soil as well as the flexural stiffness of the pile have a significant impact on the buckling length and hence the buckling load. The flexural stiffness of the pile should match (be relatively close) the stiffness of the soil in order to avoid high values of lateral displacement of the pile’s axis.

An Analytical Model for Estimating the Vibration Frequency of Structures Located on the Pile Group in the Case of Floating Piles and End-bearing Pile

Exact estimation of vibration fundamental period of structures plays a vital role in their designing procedure. The proposition of a relatively exact expression which considers the effects of a pile group on the fundamental period of the structures was of less interest to previous researchers. This study aims to propose an analytical model and expression so as to estimate the free vibration period of the structures located on a pile group. To reach the objectives of this study, several numerical analyses has been carried out using the method of equivalent spring which takes into account the effects of soil-pile-structure interaction on the fundamental period of the structures. In the next step of the study the effects of a pile group on the fundamental period of the structures have been analyzed analytically. In this analytical study two cases have been considered for the piles which are end-bearing and floating piles. In the case of floating piles a five degrees-of-freedom analytical model and its corresponding expression have been proposed considering the soil-pile-structure system. The numerical modelling has been performed using the direct method due to the neglect of the soil in analytical expression and the results have been compared with those of the proposed analytical expression. The soil mass participation coefficient (λ) has been obtained using the discrepancy between the results of the two different methods to modify the analytical expression. In the case of end-bearing piles an analytical model with three degrees-of-freedom and its corresponding expressions has been proposed. Then the soil has been neglected and a new analytical expression has been proposed using the mass participation coefficients adopted from other researches to calculate the fundamental period of the structures. The comparison between the results of the proposed expression and those of case and numerical studies confirms that the proposed expressions benefit from a relative accuracy and can be used as an initial criterion in designing procedure.

A unified model for analyzing free vibration and buckling of end-bearing piles

Offshore structures are often founded on long, slender piles that extend for a substantial distance above the ground surface. This paper presents a novel unified model to analyze the free vibration and buckling of partially embedded end-bearing piles subjected to axial compressive load. Consideration is given to the tapered piles of variable cross-sectional shape with constant volume. The governing differential equation of the motions is derived, and solved by using the Runge-Kutta method in combination with the Regula-Flasi method. The accuracy of the proposed model is confirmed by comparing the obtained calculations with existing closed-form and numerical solutions. Numerical results for the natural frequency, buckling load and corresponding modal displacements are provided, which are analyzed to highlight the effects of the parameters related to the cross-sectional shape, taper ratio and embedment of the pile, soil stiffness and compressive force as well as the end constraint. The geometry and material parameters that statically and dynamically yield the strongest piles with fixed volume are identified. The analytical model is beneficial for the optimum design of the soil-pile system in engineering applications.

Three-Dimensional Response of Neighboring Buildings Sitting on Pile Foundations to Seismic Pounding

Seismic pounding occurs when the separation gap between buildings and structures is not wide enough, particularly during major earthquake events; this can cause them to collide, causing local damage or, in extreme cases, collapse. This study investigated the impact that this separation gap has on the seismic response of midrise buildings supported on piles while considering seismic soil–pile–structure interaction (SSPSI). To achieve this aim, three 15-story reinforced concrete buildings sitting on pile foundations and with five different separation gaps under excitations from the 1994 Northridge and 1995 Kobe earthquakes were numerically simulated. This study used three-dimensional numerical modeling to simultaneously capture the effects of seismic pounding and SSPSI. Because the considered structure, pile foundation, and soil deposit are three-dimensional in nature, the adopted three-dimensional numerical modeling can provide a more realistic simulation to capture the seismic behavior of the system. The nonlinear behavior of structural elements was included, and the dynamic soil properties were obtained from field data and backbone curves. A contact pair interface with small-sliding surface-to-surface formulation between buildings was used to capture possible seismic pounding, and contact interfaces with a finite-sliding formulation were used to simulate the interaction between the piles and the soil. The results, including lateral building deflections, interstory drifts, structural shear forces, foundation rocking, lateral pile deflections, and the distributions of bending moments and shear forces of the piles, are presented and discussed. The findings of this study will give engineers a better insight into the possible effects of seismic pounding on the seismic performance of buildings, and the response of end-bearing piles in soft soils.

Analysis of load sharing characteristics for a piled raft foundation

The load sharing ratio (apr) of piles is one of the most common problems in the preliminary design of piled raft foundations. A series of 3D numerical analysis are conducted so that special attentions are given to load sharing characteristics under varying conditions, such as pile configuration, pile diameter, pile length, raft thickness, and settlement level. Based on the 3D FE analysis, influencing factors on load sharing behavior of piled raft are investigated. As a result, it is shown that the load sharing ratio of piled raft decreases with increasing settlement level. The load sharing ratio is not only highly dependent on the system geometries of the foundation but also on the settlement level. Based on the results of parametric studies, the load sharing ratio is proposed as a function of the various influencing factors. In addition, the parametric analyses suggest that the load sharing ratios to minimize the differential settlement of piled raft are ranging from 15 to 48% for friction pile and from 15 to 54% for end-bearing pile. The recommendations can provide a basis for an optimum design that would be applicable to piled rafts taking into account the load sharing characteristics.

Comparative analysis of methods of pile-bearing capacity evaluation using CPT logs from tropical soils

This study presents the results of a comparative analysis of the performance of eight direct cone penetration test (CPT) methods in predicting the ultimate load-carrying capacity of a 300 mm diameter end-bearing pile, evaluated at defined soil depths using CPT logs obtained for various locations in the south-east and south-south regions of Nigeria. The methods used are the Schmertmann (1978), LCPC (Bustamante & Gianeselli 1982 - Laboratoire Central des Ponts et Chausees), De Ruiter and Beringen (1979), Tumay and Fakhroo (1982), Price and Wardle (1982), Philipponnat (1980), Aoki and De Alencar (1975), and the Penpile methods (Clisby et al 1978). The results of univariate analysis of variance indicated that the interactions between location and treatment (methods of pile capacity prediction), depth and treatment, and location and depth were statistically significant for cohesionless soils, but that the interaction between depth and treatment was not statistically significant for cohesive soils. Also, post-hoc tests (Least square difference and Bonferroni methods) showed that the LCPC and Philipponnat methods are best suited for cohesionless soils, while the LCPC, Tumay and Fakhroo (1982) and De Ruiter and Beringen (1979) methods are recommended for cohesive soils.

Influence of pile radius on the pile head kinematic bending strains of end-bearing pile groups

An analytical solution is developed for the kinematic response of a group of end-bearing fixed-head cylindrical vertical piles embedded in a homogeneous elastic stratum subjected to vertically-propagating harmonic shear waves. Pile-soil interaction, incorporating group effects in a pile group, is represented through a simplified beam-on-dynamic-Winkler-foundation (BDWF) model with realistic frequency-dependent springs and dashpots. Expressions for interaction factors and curvature ratios atop the foundation are presented considering different boundary conditions at the tip of the piles. To investigate the fundamental characteristics of kinematic bending in end-bearing pile groups when kinematic interaction dominates, kinematic bending strains at the head of each pile are expressed in terms of the slenderness ratio. The methodology is verified by comparison against results of a coupled finite element-boundary element (FE-BE) model. Obtained results indicate that kinematic bending strains of end-bearing single piles and piles in a group follow the same trend, with values being almost coincident in the case of slender piles. In addition, boundary conditions at the pile tip markedly affect the kinematic bending at the pile head.

A closed-form solution for kinematic bending of end-bearing piles

Kinematic soil-pile interaction is indispensable for seismic design of pile foundations and superstructures. The current understanding of kinematic pile bending mostly relies on either continuum approaches, requiring complex numerical calculation or iterative decoupling, or Winkler beam approaches, overlooking the continuity and shear stiffness of soils. In this study, a closed-form solution was proposed for the kinematic bending of end-bearing piles. In this solution, the conventional Beam-on-Dynamic-Winkler-Foundation (BDWF) was extended to incorporate the shear resistance of soils via Pasternak model. The proposed solution can provide an explicit analytical formulation for kinematic bending of end-bearing piles which is convenient for engineering practice. In addition, the proposed solution was compared with the conventional BDWF solution and the numerical solution, indicating that the proposed solution can maintain both accuracy and simplicity. At last, a series of parametric study was carried out and showed that the shear resistance of soils may considerably contribute to lowering the kinematic responses but increasing the maximum bending moment at the pile tip.

Equivalent-linear pile head impedance functions using a hybrid method

Majority of available solutions for determination of pile head dynamic stiffness and damping for use in substructure analysis of soil-pile interaction are based on linear elastic soil behavior and perfect contact at soil-pile interface. This paper presents a hybrid numerical-analytical methodology for equivalent-linear (EL) characterization of pile head impedance functions under inelastic soil-pile interaction. Inelastic continuum modeling, frequency-domain substructure formulation and closed-form derivation of impedance functions, based on Winkler assumption, are ingredients of the proposed approach. Results from three-dimensional (3D) nonlinear finite element (FE) analyses of single piles under dynamic pile head loading are used as input to the derivation algorithm. A new mathematical procedure for polynomial representation of the impedance functions is introduced, which allows for derivation of the EL impedances for “short-type” lateral behavior of an end-bearing pile, especially in the rock-socketed piles. The back-calculated impedances demonstrate variation of the pile head stiffness and damping in frequency domain as the inelasticity increases. They also reveal significant influence of inelastic interface (gap) and soil deformation on reduction of pile head stiffness, in particular radiation damping.

Analytical Study on RC Framed Structures on effect of Performance of Different types of Piles in Seismic Region

This thesis includes Analytical Study on RC Framed Structures on effect of Performance of Pile Foundation in Seismic Region. For our design section of a RC framed residential high rise building we are comparing mass irregularities and vertical irregularities with respect to Time period, Frequency, Displacement, Storey Drift Ratio and Storey Shear for Friction pile and End Bearing Pile.

Pile-Driving Mechanics at the Base as Informed by Direct Measurements

AbstractDetermination of the base contribution to total pile capacity is an important aspect in the design of end-bearing piles. For driven piles, dynamic load testing and signal matching are the p...

Displacement interaction among energy piles bearing on stiff soil strata

This study presents an analysis of the displacement interaction among general configurations of energy piles bearing on stiff soil strata that are subjected to thermal loads. This work integrates recent analyses investigating the displacement interaction among predominantly floating energy piles subjected to thermal loads in deep uniform soil deposits. To address this challenge, design charts for energy piles resting on either infinitely or finitely rigid soil strata are presented, applied and validated for the analysis of the vertical displacement of predominantly end-bearing energy pile groups subjected to thermal loads using the interaction factor method.

Reply to the discussion by Noor on “Drag load on end-bearing piles in collapsible soil due to inundation”

Reply to the discussion by Noor on “Drag load on end-bearing piles in collapsible soil due to inundation”

Discussion of “Drag load on end-bearing piles in collapsible soil due to inundation”

Discussion of “Drag load on end-bearing piles in collapsible soil due to inundation”

Resistance of inner soil to the vertical vibration of pipe piles

The resistance offered by the inner soil to the vertical oscillation of an end-bearing pipe pile is studied analytically. The differences in the resistance to pile vibrations associated with the inner soil and the outer soil are underlined via example applications and theoretical considerations. Simplified, reduced solutions are also derived, to further investigate the wave propagation mechanisms governing the problem.

Drag load on end-bearing piles in collapsible soil due to inundation

Collapsible soils may experience sudden and excessive settlement when inundated. The use of pile foundations that penetrate the collapsible soil layer to reach a firm stratum is widely used in practice. However, when the ground is inundated, large and sudden settlement of the surrounding soil may take place, causing negative skin friction on the pile’s shaft, which may lead to catastrophic failure. In the literature, research dealing with negative skin friction for piles in collapsible soil is lagging due to the complexity of modeling collapsible soil analytically. Alternatively, results of sophisticated experimental investigation may produce valuable information to predict the negative skin friction and accordingly the drag load on these piles. This paper presents the results of an experimental investigation on a single end-bearing pile in collapsible soil. The investigation is tailored to measure the soil collapse before and during inundation and the associated drag load on the pile. The theory proposed by Hanna and Sharif in 2006 for predicting negative skin friction on piles due to consolidation of the surrounding soft clay was extended to predict the negative skin friction for these piles in collapsible soils. A proposed design procedure is presented.