Vertical Pile Groups Research Articles

Comparison of static lateral behavior of three pile group configurations using three-dimensional finite element modeling

The lateral resistance of three pile group configurations was investigated using three dimensional (3-D) finite element modeling. The three pile groups considered in the study were a vertical pile group, a battered pile group, and a mix of vertical and battered piles in a group. The study was motivated by the full-scale static load test that was conducted on the M19 pier foundation in the I-10 twin span bridge in Louisiana. The static lateral resistance of the M19 battered pile group was investigated previously using a 3-D finite element simulation and verified with the aid of experimental results. In the present study, the M19 battered pile group model was used as the basis for the vertical and mixed pile groups for developing their 3-D finite element models. The nonlinear material behavior was accounted for using elastoplastic constitutive models such as the concrete damaged plasticity model and the anisotropic modified Cam clay model. The lateral resistance of the pile groups was investigated in terms of load–displacement, axial load, bending moment, pile damage, soil resistance, and p-multipliers. The results show that the battered pile group had the largest lateral resistance, followed by the mixed and vertical pile groups, respectively. The largest lateral load share was carried by the two middle rows in the battered pile group, while it was in the leading row in the vertical and mixed pile groups. The soil resistance profiles show that the vertical pile group mobilized greater soil resistance than the battered and mixed pile groups at the same lateral load. The back-calculated p-multipliers are the highest in the battered pile group case, followed by the mixed and vertical pile groups, respectively.

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 Three Dimensional Comparative Study of Seismic Behaviour of Vertical and Batter Pile Groups

To a practicing foundation engineer, the performance of batter pile under seismic conditions still remains a questionable prospect. The contradictory findings reported by various investigators with regard to the performance of batter piles add to this dilemma. This calls for a rigorous three-dimensional investigation to evaluate seismic behavior of batter pile groups. In this study, a comparative assessment of three-dimensional seismic behavior of a 2 × 2 vertical and batter pile groups having batter angle of 15° was carried out using a full three-dimensional finite element code developed in MATLAB (Sarkar 2009). The effects of centre to centre spacing of piles and soil modulus values were investigated. Idealized soil profiles having constant and triangular variation of soil modulus were adopted for the study. Results of analyses for both the vertical and batter pile groups are presented in terms of dynamic stiffness and kinematic interaction factors. Results indicate better seismic performance of batter pile groups in comparison to that of vertical pile groups. To demonstrate the importance of the findings, a five-storied portal frame structure supported separately on vertical and batter pile groups were considered and analyzed for El-Centro Earthquake (1940) time history. The difference in structural response considering vertical and batter pile groups is highlighted.

Modeling of Batter Pile Behavior under Lateral Soil Movement

Pile foundation is frequently used when structures are located on weak sublayers or are at risk from lateral loadings such as earthquakes. The design of pile foundations has recently become crucial to stop slope movement. To understand the behavior of pile foundations subjected to lateral soil movement, the three-dimensional Fast Lagrangian Analysis of Continua (FLAC3D) program was used to perform numerical simulations, which can reduce the cost of field testing. Vertical piles and batter piles were combined into 3 × 3 pile groups, and the response of batter piles to soil movement was analyzed. The outer batter piles led to an increased bending moment in the middle, vertical pile row. Increasing the pile spacing and the presence of battered piles reduced the pile group’s displacement. The batter pile group’s maximum bending moment was smaller than the vertical pile group’s in sand soil, but 5–8 times higher in clay soil.

Study of static lateral behavior of battered pile group foundation at I-10 Twin Span Bridge using three-dimensional finite element modeling

In this study, the static lateral behavior of a battered pile group foundation was investigated using three-dimensional finite element (FE) analysis. The FE model was used to simulate the static lateral load test that was performed during the construction of the I-10 Twin Span Bridge over Lake Pontchartrain, La., in which two adjacent bridge piers were pulled against each other. The pier of interest was supported by 24, 1:6 batter, 34 m long piles in a 6 × 4 row configuration. The FE model of the battered pile group was developed in Abaqus and verified using the results from the field test. The model utilized an advanced constitutive model for concrete, which allowed distinct behavior in tension and compression, and introduced damage to the concrete stiffness. The soil domain comprised of several layers in which the constitutive behavior of clay layers was modeled using the anisotropic modified Cam-clay (AMCC) model, and for sands using the elastic perfectly plastic Drucker–Prager (DP) model. FE results showed good agreement with the results of the lateral load test in terms of lateral deformations and bending moments. The results showed that the middle rows carried a larger share of lateral load than the first and the last rows. The pile group resisted a maximum lateral load of 2494 t at which the piles were damaged within a 6 m zone from the bottom of the pile cap. The edge piles carried larger internal forces and exhibited more damage compared to the inner piles. The soil resistance profiles showed that soil layering influenced the distribution of resistance between the soil layers. A series of p–y curves were extracted from the FE model, and then used to study the influence of the group effect on the soil resistance. The p–y curves showed that the group effect reduced the soil resistance in all rows, with the lowest resistance in the third row. Finally, the p-multipliers were calculated using the extracted p–y curves, and compared to the reported p-multipliers for vertical pile groups.

RESPONSE OF LATERALLY LOADED SINGLE PILE IN SANDY SOIL

Pile foundations are often required to resist lateral loading. Lateral loads come from a variety of sources including wind, earthquakes, waves, and ship impacts. The lateral capacity of a pile is usually much smaller than the axial capacity and as a result groups of piles are often installed to increase the lateral capacity of the entire foundation system. When vertical or plumb pile groups do not provide sufficient lateral resistance the piles can be battered in order to mobilize some of the higher axial capacity to resist the lateral load. Several methods are available for predicting the ultimate lateral resistance to piles in sandy soil. However, these methods often produce significantly different ultimate resistance values. This makes it difficult for practicing engineers to effectively select the appropriate method when designing laterally loaded piles in sandy soil. In this paper, lateral load behavior of single piles in sandy soil was studied, for different L/D ratio by changing the diameter and length of pile. The analysis was carried out considering long free-head pile. The influence of soil type, effect of pile length and pile diameter on the pile response was observed and the results obtained by IS2911Part1 (sec2) and Matlock & Reese were presented.

Model Tests on Horizontal Impedance Functions of Fixed-Head Inclined Pile Groups under Soil Nonlinearity

The effects of soil nonlinearity on the dynamic behavior of fixed-head floating inclined pile groups are investigated experimentally in the form of horizontal impedance functions (IFs) and internal forces in piles. A 2×2 model of inclined pile groups embedded in dry cohesionless soil and subjected to a broad range of lateral harmonic loadings at the pile-cap level are examined. Piles with a spacing-to-the-diameter ratio (s/d) of 5 with practical pile inclinations of 0, 5, and 10° along the direction of loading are reported. Results show a profound impact of local nonlinearity and resonance of soil on the horizontal impedance functions. The inclined pile groups show higher values of horizontal IFs than the vertical pile group, in accordance with the general understanding. Influence of pile inclinations on the horizontal IFs is further examined through the variation of soil reactions along the depth of the piles. Semiempirical expressions for estimating the soil reactions, as a function of pile inclinations, are proposed. As for the internal forces in piles, bending strains for the inclined piles are smaller than the vertical pile; the axial strains show an opposite behavior.

A new BE formulation coupled to the FEM for simulating vertical pile groups

Abstract The aim of this work is to obtain a numerical tool for pile–soil interaction analysis. The soil is modeled as an infinite domain in radial directions. The piles, considered cylindrical, are modeled with the finite element method (FEM), using one-dimensional elements. Displacements and tractions along the shaft are approximated by polynomial functions. The soil is modeled using the boundary element method (BEM) with Kelvin fundamental solutions. Infinite boundary elements (IBEs) are employed for the far field simulation, allowing computational cost reduction without compromising the accuracy. The IBE formulation is based on a triangular boundary element with linear shape functions instead of the commonly used quadrilateral IBEs. By coupling the FEM–BEM formulations, a single system of equations which represents the complete pile–soil interaction problem is obtained.

Closure to “Seismic Behavior of Batter Piles: Elastic Response” by A. Giannakou, N. Gerolymos, G. Gazetas, T. Tazoh, and I. Anastasopoulos

Significant advances have been made on this important research topic in the last few years because of Giannakou et al., who have faced, in urgent terms, the matter of whether inclined piles have a beneficial or detrimental role. The discusser agreeswith the authors on the fact that the horizontal drift of a superstructure supported on a group of batter piles is generally smaller than with the exclusively vertical pile group; however, it could not really be generalized that this reduction is appreciable only with tall structures. The discusser has carried out work in his Ph.D. thesis about the inclined piles, studying the behavior of a couple of piles supporting a tall superstructure (hstr 5 10m) and a short superstructure (hstr 5 2m), in different geometrical conditions and seismic excitations than those of the authors, reaching quite different results. Specifically, from results obtained performing FEM three-dimensional analysis with the computer program ADINA (ADINA 2010), and using the base of the model with two real acceleration time histories (El Centro component NS 1940 [amax 5 0:318g]; Bagnoli Irpino Earthquake 1980 [amax 5 0:358g]), the following can be concluded. The reduction of horizontal drift because of inclined piles with regard to vertical piles was more important in short superstructures than tall ones (Figs. 1 and 2). To explain these results, it is useful to keep in mind that under seismic excitation, the horizontal drift of the superstructure mass, um, is made of three parts: horizontal translation of the cap, horizontal translation because of rotation cap, and horizontal deflection of the column. The discusser has found out that the cap's horizontal translation founded on vertical piles tends to be higher than the one with the inclined piles. Instead, the contribution because of the cap rotation can increase or reduce the horizontal drift depending on the sign of the rotation. In the case of the short superstructure, Fig. 3 shows the horizontal displacement of the cap on the inclined piles, uc, the vertical displacement of the pile on the left, vcl, and the vertical displacement of the pile on the right, vcr . For better understanding of the figures, the time considered was limited to the first 3 s. Once the vertical displacements are confirmed, the rotation is obtained by dividing the difference in the vertical displacement at the head of the piles by the distance between the two piles. In Fig. 3, the horizontal oscillation frequency of the cap is quite lower than the one in the vertical direction; the vertical displacement, vcl, also has the opposite sign and basically the same amplitude of vcr. The difference in frequency

Soil-structure-foundation effects on stochastic response analysis of cable-stayed bridges

In this study, stochastic responses of a cable-stayed bridge subjected to the spatially varying earthquake ground motion are investigated by the finite element method taking into account soil-structure interaction (SSI) effects. The considered bridge in the analysis is Quincy Bay-view Bridge built on the Mississippi River in between 1983-1987 in Illinois, USA. The bridge is composed of two H-shaped concrete towers, double plane fan type cables and a composite concrete-steel girder deck. In order to determine the stochastic response of the bridge, a two-dimensional lumped masses model is considered. Incoherence, wave-passage and site response effects are taken into account for the spatially varying earthquake ground motion. Depending on variation in the earthquake motion, the response values of the cable-stayed bridge supported on firm, medium and soft foundation soil are obtained, separately. The effects of SSI on the stochastic response of the cable-stayed bridge are also investigated including foundation as a rigidly capped vertical pile groups. In this approach, piles closely grouped together beneath the towers are viewed as a single equivalent upright beam. The soil-pile interaction is linearly idealized as an upright beam on Winkler foundation model which is commonly used to study the response of single piles. A sufficient number of springs on the beam should be used along the length of the piles. The springs near the surface are usually the most important to characterize the response of the piles surrounded by the soil; thus a closer spacing may be used in that region. However, in generally springs are evenly spaced at about half the diameter of the pile. The results of the stochastic analysis with and without the SSI are compared each other while the bridge is under the sway of the spatially varying earthquake ground motion. Specifically, in case of rigid towers and soft soil condition, it is pointed out that the SSI should be significantly taken into account for the design of such bridges.

Dynamic Response of 2 Piles in Series and Parallel Arrangement

In the present study, dynamic analysis of laterally loaded vertical pile group is carried out by keeping in the mind the three dimensional nature of the soil-pile system. Piles and soil are modelled using three-dimensional finite element techniques treating them as linear elastic. The interface of soil and pile under the lateral load has been accounted for by incorporating interface elements in the modelling. The special type of transmitting boundary using Kelvin element is used to transfer the propagating waves from near field to the far field. Group of two piles in series and parallel configuration have been considered for present study. Individual piles are considered monolithic with pile cap. Parametric studies have been performed to examine the effects of pile spacing and soil modulus on the response of pile group.

Dragload and downdrag performances of inclined pile group embedded in consolidating soil

The performance of inclined pile group embedded in consolidating soil under surcharge load was investigated by experiment in comparison with vertical pile group and single pile under the same conditions; dragload, downdrag, and layered soil settlement were measured. A three-dimensional numerical model was built via FLAC3D software, and verified by the experimental results. Influence factors, such as consolidation time, pile spacing, and pile tilt angle were analyzed. The results show that dragload of inclined pile group increases with the increase of consolidation time and pile spacing or the decrease of pile tilt angle. Downdrag of inclined pile group increases with the increase of consolidation time, pile spacing and pile tilt angle.

A three-phase model for evaluating the seismic resistance of soils reinforced by a network of symmetrically inclined piles

Abstract The stability analysis of a piled embankment under seismic loading is considered, with a special emphasis on the optimization of the reinforcement layout by splitting the initial group of vertical piles into two symmetrically inclined arrays of parallel inclusions. The bidirectionally-reinforced soil thus obtained is appropriately described, at the macroscopic scale, by a three-phase model, conceived as an extension of the two-phase model previously developed for unidirectionally-reinforced soils. The model is implemented in a finite element formulation and related numerical code, which is used for simulating the behavior of the piled embankment up to failure. The results of these simulations, which favourably compare with upper bound yield design calculations, clearly indicate that the seismic resistance of the embankment can be considerably increased from symmetrically inclining the piles, even without taking the potential benefits of their flexural resistance into account.

Response of vertical pile group subjected to horizontal cyclic load in soft clay

The environment prevalent in ocean necessitates the piles supporting offshore structures to be designed against lateral cyclic loading initiated by wave action. Such quasi-static load reversal induces deterioration in the strength and stiffness of the soil-pile system introducing progressive reduction in the bearing capacity as well as the pile head displacement. To understand the effect of lateral cyclic load on lateral capacity of pile group in soft clay, a series of laboratory experiments were performed on model piles in soft cohesive soil. This paper presents the experimental observations made and the relevant conclusions drawn there from.

Three dimensional numerical simulations for non-breaking solitary wave interacting with a group of slender vertical cylinders

In thus paper we validate a numerical model for wave-structure interaction by comparing numerical results with laboratory data. The numerical model is based on the Navier-Stokes (N-S) equations for an incompressible fluid. The N-S equations are solved by a two-step projection finite volume scheme and the free surface displacements are tracked by the volume of fluid (VOF) method The numerical model is used to simulate solitary waves and their interaction with a group of slender vertical piles. Numerical results are compared with the laboratory data and very good agreement is observed for the time history of free surface displacement, fluid particle velocity and wave force. The agreement for dynamic pressure on the cylinder is less satisfactory, which is primarily caused by instrument errors.

Three dimensional numerical simulations for non-breaking solitary wave interacting with a group of slender vertical cylinders

In this paper we validate a numerical model for wave-structure interaction by comparing numerical results with laboratory data. The numerical model is based on the Navier-Stokes (N-S) equations for an incompressible fluid. The N-S equations are solved by a two-step projection finite volume scheme and the free surface displacements are tracked by the volume of fluid (VOF) method. The numerical model is used to simulate solitary waves and their interaction with a group of slender vertical piles. Numerical results are compared with the laboratory data and very good agreement is observed for the time history of free surface displacement, fluid particle velocity and wave force. The agreement for dynamic pressure on the cylinder is less satisfactory, which is primarily caused by instrument errors.

Seismic stability analysis of piled embankments: A multiphase approach

AbstractThe seismic stability analysis of an embankment lying over a soft foundation soil reinforced by a group of vertical piles is performed within the framework of the upper bound kinematic approach of yield design. The analysis is based on a previously developed ‘multiphase’ model of the reinforced ground, which explicitly accounts for the shear and bending resistances of the piles. Making use of appropriate failure mechanisms involving shear zones across which the reinforcements are continuously deforming, along with ‘plastic hinge’ surfaces, upper bound estimates to the critical seismic coefficient of the structure are derived. The results, which are confirmed by the simulations obtained from a finite element elastoplastic code, give clear evidence of the key role played by the bending strength capacities of the piles in ensuring the stability of the pile reinforced embankment. Copyright © 2009 John Wiley & Sons, Ltd.

Lateral Behavior of Vertical Pile Group Embedded in Stabilized Earth Slope

An experimental study of the lateral behavior of vertical pile groups embedded in reinforced and nonreinforced sandy earth slopes was carried out. The model tests include studies of group configurations, pile spacing, embedment length of pile, relative densities of sand, and location of pile groups relative to the slope crest. Several configurations of geogrid reinforcement with different lengths, widths, and number of layers were used to reinforce a sandy slope of 1 (V): 1.5 (H). Pile groups of 2×2 and 3×3 along with center-to-center pile spacing of 2D, 3D, and 4.5D and piles with embedment length to diameter ratios of L∕D=12 and 22 were considered. Based on test results, geogrid parameters that give the maximum lateral capacity improvement are presented and discussed.

Influence of soil–structure interaction on the response of seismically isolated cable-stayed bridge

Soil conditions have a great deal to do with damage to structures during earthquakes. This paper attempts to assess the influence of dynamic soil–structure interaction (SSI) on the behavior of seismically isolated cable-stayed bridge supported on a rigidly capped vertical pile groups, which pass through moderately deep, layered soil overlying rigid bedrock. In the present approach, piles closely grouped together beneath the towers are viewed as a single equivalent upright beam. The soil–pile interaction is idealized as a beam on nonlinear Winkler foundation using continuously distributed hysteretic springs and viscous dashpots placed in parallel. The hysteretic behavior of soil springs is idealized using Bouc–Wen model. The cable-stayed bridge is isolated by using high-damping rubber bearings and the effects of SSI are investigated by performing seismic analysis in time domain using direct integration method. The seismic response of the isolated cable-stayed bridge with SSI is obtained under bi-directional earthquake excitations (i.e. two horizontal components acting simultaneously) considering different soil flexibilities. The emphasis has been placed on assessing the significance of nonlinear behavior of soil that affects the response of the system and identify the circumstances under which it is necessary to include the SSI effects in the design of seismically isolated bridges. It is observed that the soil surrounding the piles has significant effects on the response of the isolated bridge and the bearing displacements may be underestimated if the SSI effects are ignored. Inclusion of SSI is found essential for effective design of seismically isolated cable-stayed bridge, specifically when the towers are very much rigid and the soil condition is soft to medium. Further, it is found that the linear soil model does not lead to accurate prediction of tower base shear response, and nonlinear soil modeling is essential to reflect dynamic behavior of the soil–pile system properly.

Interaction Diagram and Load Effects for Vertical Pile Groups with Application to the AASHTO LRFD

In this paper, a procedure is proposed for calculating the interaction diagram of a vertical pile group subject to axial load and biaxial moments; equations are then applied to the AASHTO LRFD code. Several cases are presented, depending on the efficiency of the pile group, and it is shown that the interaction diagram can be a pentahedron, a hexahedron, an octahedron, a nonahedron, or a decahedron. It is shown how the use of convex analysis and computational geometry leads to a rational calculation of the load effects and of the relationship between load effects and an interaction diagram. When the design entails evaluating several design alternatives, the methods of computational geometry yield a fivefold to tenfold computational saving with respect to considering all load combinations. A simple numerical example shows the application of the proposed procedure in a typical design setting, and highlights the advantages of the proposed procedure.