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In this paper, the lateral limiting pressure on square pile groups in undrained soil is explored using two−dimensional finite element modelling. A parametric study is conducted to assess the role of pile−soil adhesion, group size and pile spacing on group capacity and corresponding failure mechanisms. Results from the finite element output show that large groups of closely−spaced piles exhibit significant reductions in lateral capacity compared to equivalent single pile values. Significant variations in the load−sharing across the group are also observed, with the corner piles experiencing loads up to 162% above the group average for a 25−pile group. A simplified closed−form design approach is developed using a modified Ramberg−Osgood formulation to predict the lateral group capacity. The proposed approach is shown to provide excellent agreement to the numerical results and a rigorous upper bound prediction of a selection of field data and predictions determined using existing design guidelines.

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... In recent years, the focus of pile design has shifted towards 21 serviceability limit state resulting in the application of non−linear frameworks to pile group analysis 22 (Sheil et al. 2018). Within a non−linear framework, pile settlement is no longer uncoupled from the 23 ultimate capacity and therefore an accurate capacity estimation remains an essential underpinning 24 element of formal pile design calculations (Sheil andMcCabe 2014, 2017). 25 ...

In this paper, the lateral limiting pressure on rectangular pile groups in undrained soil is explored using two−dimensional finite element modelling. The primary aim of the study is to assess the influence of pile group shape effects on the soil limiting pressured offered by the deep ‘flow-around’ failure mechanism, and associated soil failure mechanisms, considering both a small (four piles) and large (36 piles) group. Additional parameters considered in the modelling include pile spacing and pile-soil interface roughness. The finite element results show that group shape has a significant influence on the behaviour of closely spaced pile groups. In particular, the number of piles parallel to the direction of loading is shown to dominate the lateral bearing capacity factor such that significant increases in capacity efficiency can be achieved by slight modifications to the group shape for a given number of piles. The load-sharing across the group, traditionally defined using p-multipliers, was also shown to be highly non-uniform and dependent on group size, pile-soil roughness and group geometry in addition to the pile spacing. The finite element output is presented in the form of design charts for the determination of group p-multipliers whereas a library of existing design solutions is presented for the calculation of the overall group response.

This paper studies the effect of loading eccentricity and pile spacing on the ultimate lateral soil resistance of twin-piles using finite element limit analysis and analytical upper bound plasticity methods. Two kinematic mechanisms corresponding to the failure modes produced by the advanced finite element simulations are postulated with different eccentricity and pile spacing cases. Comparisons have shown excellent agreements between the two approaches. A series of parametric studies are then subsequently performed. Numerical results have shown that loading eccentricity considerably affects ultimate lateral soil resistance, leading to a maximum reduction of 50%. In addition, the curve of normalised pile resistance versus pile spacing ratio is dissimilar to that without considering the effect of loading eccentricity. The proposed solutions and failure mechanisms in this study will provide a deepened insight on the performance of twin-pile group under eccentric loads.

In this paper, the lateral limiting pressure offered by the deep ‘flow-around’ soil failure mechanism for perimeter (ring) pile groups in undrained soil is explored using two−dimensional finite element modelling. A parametric study investigates the role of group configuration, pile−soil adhesion, group size, pile spacing and load direction on group capacity and corresponding soil failure mechanisms. The finite element output show that the plan group configuration (square or circular) has a negligible influence on lateral capacity for closely spaced perimeter pile groups. When compared to ‘full’ square pile groups with the same number of piles, the present results suggest that for practical pile spacing (≳ two pile diameters), perimeter groups do not necessarily increase capacity efficiency, particularly if the piles are smooth. Nevertheless, perimeter groups are shown to be characterized by both the invariance of their capacity to the direction of loading and their highly uniform load-sharing between piles, which are beneficial features to optimize design.

The settlement behaviour of vertically‒loaded pile groups has been the subject of an extensive body of research over the past two decades. In particular, this work has identified the over‒conservatism associated with predictions of pile interaction derived from elastic theory and the corresponding amplification of group settlement relative to single pile values. Researchers have since redoubled efforts to refine settlement predictions for pile groups towards more economical design, largely through more rigorous treatment of soil stiffness nonlinearity. Although foundation design engineers are increasingly employing three‒dimensional continuum analyses to quantify pile interaction on a site−specific basis, simplified design approaches remain an integral part of preliminary foundation design. The purpose of this paper is to undertake a critical examination of these methods with a view to increasing their potential for take‒up by foundation engineering practitioners. A database of simplified models has been collated for the prediction of nonlinear pile interaction that exists within vertically‒loaded pile groups. These models are categorised as either analytical or empirical. The development, limitations, and range of applicability of these models are explored in detail in the context of some published case histories.

Pile group effects of a composite pile group that consists of a group of subgroups are investigated based on a series of static pushover analysis with the help of the nonlinear three-dimensional finite element method (FEM). The numerical result suggests that there is an interaction between subgroups as well as an interaction within each subgroup; the former interaction effect is very similar to the latter if the distance between subgroups is normalized with respect to an equivalent pile diameter of each subgroup. A simplified method to estimate pile group effects of a composite pile group is then proposed in which the interaction effects within and between the subgroups are both accounted for using the same P-multiplier approach commonly employed for a pile group. The P-multipliers estimated by the proposed method show a fairly good agreement with those estimated from the FEM analyses.

The lateral response of piles embedded in soil is typically analyzed using the beam on nonlinear Winkler springs approach, in which soil–pile interaction is modeled by nonlinear p–y curves (where p is soil resistance and y is horizontal displacement). In this approach, one of the most common methods of accounting for interaction effects in pile groups is to modify the single pile p–y curves using a p-multiplier for each row of piles in the group, with higher values for leading row and lower values for trailing rows. The leading and trailing rows interchange during seismic loading; therefore, sometimes an average p-multiplier is used for all piles in the group. This average p-multiplier is called the group reduction factor. Group reduction factors have been established from experimental data from static loading tests on small pile groups, mostly 3 × 3 groups with free pile head conditions and center-to-center pile spacings of about 3 pile diameters. In this paper, continuum simulations are used to study th...

The use of p-multipliers in the analysis of the lateral loading behavior of pile groups is based on the concept of modifying the single-pile p-y curve to obtain the p-y curve for a pile in a group. The p-multipliers account for the reduced soil resistance mobilized at a given deflection as a result of overlapping of shear zones. Different factors can influence the p-multipliers; however, because of the lack of experimental data, most researchers and design guidelines consider only the normalized pile spacing in the direction of loading in their recommendations. In this study, the effects of pile spacing and clay stiffness on the p-multipliers were investigated using the results of two series of centrifuge tests. The soil profile consisted of four lightly overconsolidated clay layers overlying a dense sand layer. The pile groups had a symmetrical layout consisting of 2 × 2 piles spaced at center-to-center distances of 3.0 and 7.0 pile diameter (D) and were driven into improved (stiff clay) and unimproved soft clay. Ground improvement was done in situ using simulated cement deep soil mixing (CDSM). Computer analyses were performed to back-calculate the p-multipliers. There was very good agreement between the measured and computed responses for both the leading and trailing rows of piles in the unimproved and improved soft clay. The results reveal that increasing the clay stiffness and pile spacing in the direction of loading increase p-multipliers. No pile–soil–pile interaction was observed for the 7D spacing. The proposed set of p-multipliers for the soft clay was found to be in close agreement with some current guidelines, whereas other design guidelines appear to recommend relatively conservative values of p-multipliers for both soft and stiff clay (improved ground).

In this paper, the PLAXIS 3-D Foundation finite element (FE) software package, in conjunction with the nonlinear Hardening Soil (HS) constitutive model, is employed in an extensive parametric study of the angular distortion of piled foundations which has been documented as the most influential settlement characteristic in the cracking of buildings. Numerical results are appraised in the context of acceptable limits for angular distortion recommended in the literature and set out in geotechnical building codes since there is currently no guidance in the literature on appropriate pile cap rigidities to remain safely within these limits. Results from the parametric study were validated by comparing to measured differential settlement characteristics from buildings and full-scale pile groups documented in the literature with good agreement. In addition, the numerical data has been formulated into a set of fully-normalised trends; although a relatively wide range of variables are considered in the parametric study, a consistent trend between the average settlement performance and angular distortion for corresponding pile cap rigidities was evident. These trends present design engineers with a useful resource for estimating the angular distortion of piled foundations.

The displacement finite element, lower and upper bound finite element limit analysis and analytical upper bound plasticity methods are employed to investigate the undrained limiting lateral resistance of piles in a pile row. Numerical analyses and analytical calculations are presented for various pile spacings and pile–soil adhesion factors. The numerical results are shown to be in excellent agreement with each other and also with the theoretical upper bounds produced by the analytical upper bound calculations. Based on the numerical and analytical results, an empirical equation is proposed for the calculation of the ultimate undrained lateral bearing capacity factor. This equation is subsequently used to calculate p-multipliers applicable to the lower part of piles in pile rows, which are compared to multipliers available in the literature (that are constant with depth). The comparison shows significant differences, indicating that the amount of reduction in lateral resistance due to group effects is not constant with depth as routinely assumed in practice.

Design equations are presented for the calculation of the ultimate lateral resistance of two-pile groups
in clay under a general loading direction. Analytical upper bound solutions, numerical upper and lower
bound limit analyses and displacement finite-element analyses are first presented for the case of two
piles loaded parallel to the pile-to-pile axis. Displacement finite-element analyses are subsequently used
to calculate the ultimate lateral resistance for different directions of pile displacement. The design
equations that are proposed, based on the numerical study, take account of the effect of the pile spacing,
the pile–soil adhesion and the displacement or the loading direction on the ultimate lateral resistance.

The ultimate earth resistance for a group of two side-by-side piles that are laterally loaded in clay is investigated using four different methods of analysis: three numerical (the displacement finite-element
method, and the upper- and lower-bound finite-element limit analysis methods) and one analytical (an
analytical upper-bound plasticity method developed in this paper). The results of the three numerical
methods are shown to be in excellent agreement, while the analytical solution presents a theoretical
upper bound that is very close to the numerical results. The results of the analyses are used to identify
the predominant failure mechanisms for different pile spacings and pile–soil adhesions. They are also
used to develop a design chart and design equations for determination of the ultimate lateral bearing
capacity factor.

This paper presents a finite element parametric study of several variables that affect the stiffness efficiency of rigidly capped pile groups with a view to developing a solution for preliminary design purposes. Previous empirical solutions from linear elastic work had identified a significant dependence of stiffness efficiency on pile group size and group spacing, and in this study, the effect of the pile length-to-diameter ratio, the compressibility of a stiff bearing stratum beneath the pile group and the depth below ground level to the stiff bearing stratum are also considered. Pile groups in a soft clay/silt are modelled using PLAXIS 3D Foundation in conjunction with a soil model that captures the stress dependency of soil stiffness. The trends from the soft soil study have been formulated into a set of equations which can be used to predict the stiffness efficiency of pile groups. This new approach captures more variables than previous simpler empirical prediction methods and performs better when applied to a database of 29 published pile group case histories.

In situations where a raft foundation alone does not satisfy the design requirements, it may be possible to enhance the performance of the raft by the addition of piles. The use of a limited number of piles, strategically located, may improve both the ultimate load capacity and the settlement and differential settlement performance of the raft. This paper discusses the philosophy of using piles as settlement reducers and the conditions under which such an approach may be successful. Some of the characteristics of piled raft behaviour are described. The design process for a piled raft can be considered as a three-stage process. The first is a preliminary stage in which the effects of the number of piles on load capacity and settlement are assessed via an approximate analysis. The second is a more detailed examination to assess where piles are required and to obtain some indication of the piling requirements. The third is a detailed design phase in which a more refined analysis is employed to confirm the optimum number and location of the piles, and to obtain essential information for the structural design of the foundation system. The selection of design geotechnical parameters is an essential component of both design stages, and some of the procedures for estimating the necessary parameters are described. Some typical applications of piled rafts are described, including comparisons between computed and measured foundation behaviour.

A numerical code for the prediction of the settlement of pile groups and piled rafts is presented. The code is based on the interaction factors method; the non-linearity is simulated as suggested by Caputo and Viggiani, that is, concentrating it at the pile-soil interface. In the linear range, the accuracy is checked against known benchmark solutions. A standard procedure, based on the results of load tests on single piles, is suggested for the evaluation of soil properties and for the implementation of the analysis in real cases. Nineteen well-documented case histories are then analysed, calculating for each of them a linear elastic, an equivalent linear elastic and a non-linear solution. Five out of the 19 cases are illustrated in some detail, to allow a deeper insight into the procedure. In all but one of the analysed cases the predicted values of the average settlement are within ±20% of the observed values. The maximum differential settlement is predicted with slightly lesser accuracy. For foundations characterized by a relatively high safety factor, linear and non-linear analyses are essentially equivalent. Some evidence suggests that the low-strain shear modulus, obtained by in situ shear wave velocity measurements, can be successfully employed in the prediction of the settlement. When the safety factor is low, the consideration of non-linearity becomes mandatory.

A 3 x 3 bored pile group consisting of nine cast-in-drilled-hole reinforced concrete shafts and a comparable single-shaft were subjected to reversed cyclic, lateral head loading to investigate group interaction effects across a wide range of lateral displacements. The piles had the same diameter of d=0.61 m and similar soil conditions; however, various equipment constraints led to two differences: (1) a fixed head (zero rotation) boundary condition for the single pile versus minor pile cap rotation in the vertical plane for the group and (2) shaft longitudinal reinforcement ratios of 1.8% for the single pile and 1% for the group piles. To enable comparisons between the test results, a calibrated model of the single pile (1.8% reinforcement) was developed and used to simulate the response of a single shaft with 1% reinforcement. Additional simulations of the pile group were performed to evaluate the effects of cap rotation on group response. By comparing the simulated responses for common conditions, i.e., 1% reinforcing ratio and zero head rotation, group efficiencies were found to range from unity at lateral displacements <0.004xd to 0.8 at small displacements similar to 0.01-0.02xd and up to 0.9 at failure (displacements >0.04xd). Hence, we find that group efficiency depends on the level of nonlinearity in the foundation system. The general group efficiency, although not its displacement-dependence, is captured by p-multipliers in the literature for reinforced concrete, fixed-head piles.

A series of centrifuge model tests has been conducted to examine the behavior of laterally loaded pile groups in normally consolidated and overconsolidated kaolin clay. The pile groups have a symmetrical plan layout consisting of 2, 22, 23, 33, and 44 piles with a center-to-center spacing of three or five times the pile width. The piles are connected by a solid aluminum pile cap placed just above the ground level. The pile load test results are expressed in terms of lateral load–pile head displacement response of the pile group, load experienced by individual piles in the group, and bending moment profile along individual pile shafts. It is established that the pile group efficiency reduces significantly with increasing number of piles in a group. The tests also reveal the shadowing effect phenomenon in which the front piles experience larger load and bending moment than that of the trailing piles. The shadowing effect is most significant for the lead row piles and considerably less significant for subsequent rows of trailing piles. The approach adopted by many researchers of taking the average performance of piles in the same row is found to be inappropriate for the middle rows, of piles for large pile groups as the outer piles in the row carry significantly more load and experience considerably higher bending moment than those of the inner piles.

This paper presents results from a finite element study on the behaviour of a single pile in elastic–plastic soils. Pile behaviour in uniform sand and clay soils as well as cases with sand layer in clay deposit and clay layer in sand deposit were analysed and cross compared to investigate layering effects. Finite element results were used to generate p–y curves and then compared with those obtained from methods commonly used in practice. Copyright © 2002 John Wiley & Sons, Ltd.

A finite element study has been carried out to determine the pile–soil–pile interaction behaviour for closely spaced pile rows and groups under passive lateral loading from soil movement. A horizontal section close to the piles was studied to determine the effects of pile spacing and soil constitutive law on the load–transfer relationships of the piles. The study has revealed links between the soil stress–strain law, the soil deformation mechanism and the pile load–transfer curves. Interaction behaviour was seen to depend on the prevailing deformation mechanism which in turn was governed by the soil constitutive law. Elastic-plastic and power law soil models were applied. Interaction factors suitable for design use to account for increasing lateral pressure on piles during passive lateral loading have been produced for a range of pile spacings and power law soil exponents. Interaction between piles increased both with reduction of pile spacing and with increase of soil exponent—the less soil stiffness degradation with shear strain, the greater the interaction between piles at a given spacing. This suggests that the passive interaction factors calculated using elastic methods are likely to overestimate the effects of pile–soil–pile interaction.

This paper presents a method of analysis for an off-ground cap supported by piles embedded in a layered soil and subjected to horizontal and vertical loads. The cap is modelled as a thin plate and the piles as elastic beams and the soil is treated as consisting of horizontal layers of different materials. Finite element theory is used to analyse the cap and piles while finite layer theory is employed to analyse the layered soil. Using program APPRAF (Analysis of Piles and Piled RAft Foundations) to carry out the analysis described above, comparisons of the behaviour of capped pile groups are made and factors affecting the displacements of capped pile group foundations are examined. Finally, an example related to three types of soils where the moduli increase with depth is illustrated. The results show that the present method is a powerful and useful way to evaluate the behaviour of capped pile foundations embedded in different types of soils and subjected to both vertical and horizontal loadings.

This paper is a study based on a number of model tests of free- or fixed-headed pile groups, each composed of nine piles, subjected to lateral loading. The model piles made of aluminum were set in dry sand and laterally loaded. The behaviors of the pile groups were then analyzed by the 3-D elasto-plastic finite element method (FEM), which represents a realistic model to simulate the problem. This model includes elasto-plastic soil behavior with no-tension characteristics, as well as thin frictional elements for slippage on the pile-soil interface. Parameter values for the sand used in the analyses were determined from conventional triaxial compression tests. It is shown that the experimental results can be precisely simulated by the analysis.
Furthermore, field tests of a prototype foundation of steel pile group (3 × 3 piles) subjected to lateral loading at its footing were performed. The 3-D FE analyses were conducted to simulate the results. Parameter values for FEM have been adjusted, using the back analysis technique, so as to simulate a load-displacement curve obtained from the single pile loading test. As for the lateral load-displacement relationship and the bending strain distributions along each pile, a good correlation between the experiments and the analyses can be seen in the case of the pile group.

This paper discusses the variation of the P-multiplier (P(m)) used with the p-y curve to assess the response of a pile group under lateral loads, which is a crucial topic for the design of bridge pile foundations. P(m) is influenced by the site geotechnical conditions (i.e., soil profile, type and properties), pile front and side spacings, and pile-group deflection. The presented study shows the needs to incorporate these factors with the recommended sets of P(m) to avoid any compromise or uncertainty when P(m) is treated as a single (unique) value based only on pile spacings. The current study addresses these influential elements using the strain wedge (SW) model technique, suggested P(m) values, and data collected from full-scale pile-group load tests. The experimental results show that P(m) is not unique and must be assessed based on the site geotechnical conditions along with the pile-row front and side spacings. Because the employed P(m) values must be a function of these influential factors, additional full- and model-scale load tests with different pile spacings and soil types might be required. The paper also emphasizes that using other techniques, such as the SW model, in addition to the P-multiplier could increase the confidence in the predicted pile-group lateral response. DOI:10.1061/(ASCE)BE.1943-5592.0000196. (C) 2011 American Society of Civil Engineers.

This paper describes the results of several numerical experiments performed with a three dimensional finite element model of a laterally loaded pile. The experiments are used to investigate the effect of several factors on the p-y curves derived from the model. The three dimensional finite element model utilizes a plasticity model for soil with interface elements which allow gap formation; the model has been described by Brown and Shie (1). P-y curves are widely used in design because of the relative simplicity of the beam on elastic foundation approach and the ability of design p-y curves to represent nonlinear soil behavior. However, it is recognized that this procedure does not represent the soil as a continuum and that the relative importance of some possibly significant factors may be obscured. The procedures used to develop p-y curves are largely empirical.P-y curves derived from the three dimensional finite element model are used in this study to investigate the effect on the soil response of pilehead fixity, in-situ soil stresses, pile/soil interface friction, and sloping ground. The results provide the type of information needed to intelligently utilize the p-y method in the design process.

A program of research on laterally loaded piles for offshore structure has included field test with an instrument pile, laboratory model testing, and development of correlation for design. The work has been sponsored by a group of five oil companies.
Three loading condition are considered to be particularly pertinent to the design of laterally loaded pile in soft normally consolidated marine clay. These are (1) short time static loading, (2) cyclic loading such as would occur during the progressive build-up of the storm, and (3) subsequent reloading with forces less than previously maximums.
Good general agreement exist between conventional static-loading ultimate-resistance concept and experimental results, provide due allowances are made for the reduced vertical restraint at shallow depth, where it is insufficient to cofine plastic flow to horizontal planes. Force-deformation characteristic based on approximate theory produce satisfactory agreement between computed and experimental behavior of the pile-soil system.
The mechanism of cyclic loading characteristic are qualitatively illustrated by typical results from laboratory model studies. Deterioration in resistance because of cyclic loading is most severe at shallow depth and with large lateral deflection of the pile. A correlation based primarily on result with the instrumented pile tested at Sabine, Texas, gives satisfactory prediction of pile deflection and moment over a wide range of loading condition.
Estimates of response for reloading after cycling at a higher load made by considering that most of the lateral soil resistance is estimated for deflection smaller than those previous attained.
The correlation are summarized and recommendation given for their use in design.
Introduction
The ability to make reasonable estimates of the behavior of laterally loaded piles is an important consideration in the design and construction of many offshore installations. This is particularly true in the Gulf of Mexico where large lateral forces are produced by winds and waves associated with hurricane and where the foundation materials in the critical zone near the mudline are often found to be very weak clays.
A program of research on laterally loaded piles sponsored by five oil companies is the primary basis for the correlation in this paper. At this time it is intend only that the results be summarized in a form directly in design, but publication of the background research is planned for the near future.
Requirement for Analysis and Design
There are many different ways in which piles or caissons may be subjected to effect of lateral forces. One such case is show in Fig 1a represent a pile and a leg of a jacket-type structure.
The structural analysis problem amounts to that of a complex beam-column on an inelastic foundation. For pile separated by spacing of several diameter or more, the Winkler assumption is useful to facilitate the analysis. This means that the soil is considered as a series of independent layers in providing resistance p to pile deflection y (Fig 1b)

Two-dimensional (2D) finite-element analyses were carried out to study undrained soil deformation around piles displaced laterally through soil. The load-transfer p-delta curves produced were found to be applicable for design during passive lateral loading but not for active lateral loading of pile groups. The p-delta curves characterize the local soil-shear deformation around the pile, whereas p-y curves used in the subgrade-reaction method of active lateral-pile-loading design also include the effects of global soil displacement. Hence, determination of p-y curves from basic soil parameters requires consideration of both the local and global soil behavior and the pile-group geometry and loading. Because p-delta curves stiffen with reducing pile spacing, whereas active load-transfer curves soften, there is a significant stiffness disparity between the two forms of load-transfer curves for closely spaced pile groups. Care should be taken in choosing the appropriate form of reaction curve for design.

A large-scale group of steel pipe piles and an isolated single pile were subjected to two-way cyclic lateral loading. The tests were conducted in a submerged firm to dense sand that was placed and compacted around the piles. All of the piles were extensively instrumented so that the variation in soil resistance within the group could be determined. The response of the piles in the group was also compared with the response of the isolated single pile. The loss of efficiency of the piles in the group was related principally to "shadowing" (i.e., the loss of soil resistance of piles in the trailing rows). Piles in the leading row supported a large proportion of the group load and behaved similarly to the isolated single pile. Two-way cyclic loading had little effect on the distribution of load to the piles in the group, but tended to densify the sand around both the single pile and the group piles.

A large-scale group of nine steel-pipe piles in a closelyspaced arrangement was subjected to two-way, cyclic, lateral loading with water above the ground surface. The test was conducted in stiff, overconsolidated clay at a site in Houston, Texas. All of the piles in the group were extensively instrumented to allow the results to be compared with those from other piles in the group and from the testing of an isolated, single pile. The results emphasize the highly nonlinear nature of the pile-soil-pile interaction. A substantial reduction in ultimate soil resistance was measured in the group piles relative to that of a similarly loaded single pile for both the first cycle and for 100 cycles of load.

Penetration of a pipe into cohesive soil is an important consideration in offshore pipeline engineering, especially as such penetration affects on-bottom stability of the pipeline. If the soil is described as a perfectly plastic cohesive material then the calculation of the limit load at a given penetration reduces to a plane strain problem in plasticity theory. Upper and lower bound solutions to this penetration problem are presented. The maximum range between the bounds occurs at one radius penetration. The difference between the upper and lower bounds varies from about ten per cent for the rough pipe case to approximately 25% for the smooth pipe case. Parametric studies demonstrate the effect of embedment depth, pipe-soil adhesion, soil surface heave, and increasing soil strength on the vertical limit load. The solutions presented are shown to compare favorably with test data.
La pénétration d'un conduit dans un sol cohérent représente un aspect important de la construction des pipelines au large, surtout parce qu'une telle pénétration affecte la stabilite du pipeline sur le fond de la mer. Si le sol est décrit comme étant une matiére coherente parfaitement plastique le calcul du chargement limite pour une pénétration donnée se réduit à un problème de déformation plane dans la théorie de la plasticité. L'article présente des solutions donnant des valeurs plus élevées et plus ré-duites pour ce problème de plasticité. L'écart maximum entre ces limites correspond à un pénétration d'un rayon. La différence entre les limites supérieures et inférieures varie d'entre environ 10% pour un conduit a surface lisse et environ 25% pour un conduit à surface rugueuse. Des études parame-triques démontrent I'effet exercé par la profondeur d'enrobage, I'adbesion du conduit au sol, le soulevément de la surface du sol et la résistance croissante du sol sur le chargement limite vertical. Les solutions présentees sont en trés bonne concordance avec les essais effectués.

In the analysis of the undrained loading of laterally loaded piles an important quantity is the ultimate lateral resistance at depth to purely horizontal movement. If the soil is modelled as a perfectly plastic cohesive material then the calculation of this quantity reduces to a plane strain problem in plasticity theory, in which the load is calculated on a long cylinder which moves laterally through an infinite medium. An exact calculation of the load on such a cylinder is presented. If this load is non-dimensionalized with respect to the soil strength and the diameter of the pile, it is found that the load factor varies between for a perfectly smooth pile and for a perfectly rough pile. This result is discussed in the context of previous calculations for the lateral load capacity of piles and is compared with approximate calculations using cavity expansion theory and a wedge failure near the soil surface.
La résistance latérale limite en profondeur au seul mouvement horizontal représente un paramètre important de l'analyse du chargement non-drainé des pieux chargés latéralement. Si le sol est modelisé comme une matériau cohérent parfaitement plastique le calcul de ce paramètre devient un problème de déformation plane dam la théorie de la plasticité, dans laquelle la charge se calcule sur un long cylindre qui se déplace latéralement dans un milieu infini. L'article presente un calcul prtcis de la charge d'un tel cylindre. Si cette charge est rendue sans dimensions eu égard à la résistance du sol et du diamètre du pieu on trouve que le facteur de chargement varie entre pour un pieu parfaitement lisse et pour un pieu parfaitement rugueux. L'article discute ce résultat dans le contexte des calculs précédents de la capacité de chargement des pieux et le compare avec des calculs approximatifs employant la theorie de l'expansion des cavités et un coin de rupture prés de la surface du sol.

This paper presents the results of static lateral load tests carried out on 1x2, 2x2, 1x4, and 3x3 model pile groups embedded in soft clay. Tests were carried out on piles with length to diameter ratios of 15, 30, and 40 and three to nine pile diameter spacing. The effects of pile spacing, number of piles, embedment length, and configuration on pile-group interaction were investigated. Group efficiency, critical spacing, and p multipliers were evaluated from the experimental study. The experimental results have been compared with those obtained from the program GROUP. It has been found that the lateral capacity of piles in 3x3 group at three diameter spacing is about 40% less than that of the single pile. Group interaction causes 20% increase in the maximum bending moment in piles of the groups with three diameter spacing in comparison to the single pile. Results indicate substantial difference in p multipliers of the corresponding rows of the linear and square pile groups. The predicted field group behavior is in good agreement with the actual field test results reported in the literature.

A static lateral load test was performed on a full-scale 3 X 3 pile group driven in saturated low-plasticity silts and clays. The steel pipe piles were attached to a concrete pile cap which created a "fixed-head" end constraint. A gravel backfill was compacted in place on the backside of the cap, Lateral resistance was therefore provided by pile-soil-pile interaction, as well as base friction and passive pressure on the cap. In this case, passive resistance contributed about 40% of the total resistance. The log-spiral method provided the best agreement with measured resistance. Estimates of passive pressure computed using the Rankine method significantly underestimated the resistance while the Coulomb method overestimated resistance. The cap movement required to fully mobilize passive resistance in the gravel backfill was about 6% of the cap height. This is somewhat larger than reported in other studies likely due to the underlying clay layer. The p-multipliers developed for the free-head pile group provided reasonable estimates of the pile-soil-pile resistance for the fixed-head pile group once gaps adjacent to the pile were considered.

Full-scale lateral load tests on a group of bored and a group of driven precast piles were carried out as part of a research project for the proposed high-speed rail system in Taiwan. Standard penetration tests, cone penetration tests (CPT), and Marchetti Dilatometer tests (DMT) were performed before the pile installation. The CPT and DMT were also conducted after pile installation. Numerical analyses of the laterally loaded piles were conducted using p-y curves derived from preconstruction and postconstruction DMT and by applying the concept of p multipliers. Comparisons between preconstruction and postconstruction CPT and DMT data and evaluation of the results of computations show that the installation of bored piles softened the surrounding soil, whereas the driven piles caused a densifying effect.

A static lateral load test was performed on a full-scale pile group to determine the resulting pile-soil-pile interaction effects. The 3 X 3 pile group at three-diameter spacing was driven into a profile consisting of soft to medium-stiff clays and silts underlain by sand. The piles were instrumented with inclinometers and strain gages. The load carried by each pile was measured. A single pile test was conducted for comparison. The pile; group deflected over two times more than the single pile under the same average load. Group effects significantly reduced load capacity for all rows relative to single pile behavior. Trailing rows carried less than the leading row, and middle row piles carried the lowest loads. Maximum moments in the group piles were 50-100% higher than in the single pile. P-multipliers were 0.6, 0.38, and 0.43 for the front, middle, and back row piles, respectively. Good agreement between the measured and computed Pile group responses was obtained using the p-multiplier approach. Design curves are presented to estimate p-multipliers over a range of pile spacings.

Pile-supported marine structures are designed for significant amounts of lateral load. In this paper, the influence of parameters like flexural rigidity of pile material, embedment length of pile, and arrangement of piles with respect to the direction of loading on the behavior of laterally loaded pile groups has been studied through an experimental program. The results obtained from lateral load tests carried out on model pile groups arranged at different spacings and embedded in a marine clayey bed are presented and discussed. The results indicate that the lateral load capacity of the pile group depends mainly on the rigidity of pile soil system for different arrangements of piles within a group. This is further substantiated by a simplified finite element analysis bringing in the differences in passive resistance. The group efficiencies under lateral loading obtained from the present investigation are found to be in good agreement with the predictions of earlier researchers.

An isolated single pile and a large-scale test group of 16 prestressed concrete piles spaced at 3 diameters were subjected to a static lateral loading using a fixed-headed production group for reaction. The foundation consisted of sand overlying a partially cemented sand at the Roosevelt Bridge replacement, Stuart, Fla. Ten piles of the test group, six piles of the reaction group, and a single pile were instrumented with strain gauges and inclinometers. The piles were 76 cm(2), and approximately 16.5 m long. Standard penetration tests (SPT), cone penetration tests (CPT), DMT, and PMT in-situ tests were used to establish the soil profile and py curves. Subsequent to testing, the strain gauges and inclinometer data were reduced to ''measured'' p-y curves. The p-y curves developed from SPT correlations and PMT results provided an accurate soil representation. The single pile was subjected to 320 kN, while the pile groups were loaded to about 4,800 kN. The testing results show that the nonlinear characteristics of cracked prestressed concrete piles dominate analyses and data reduction. Consequently, the FLPIER program, with its nonlinear concrete capabilities, could predict properly the ''postcracking'' response. The group interaction was accurately modeled by p-y (actually p, only) multipliers, which were determined as 0.8, 0.7, 0.3, and 0.3 for the leading, middle leading, middle trailing, and trailing rows, respectively, with the overall group p-y multiplier being 0.55.

A three-dimensional collapse mechanism is described for analysis of the ultimate strength of laterally loaded piles under undrained conditions. The analysis is based on the upper-bound method of plasticity theory. The mechanism combines a deforming conical soil wedge in the near surface with plane strain deformation at depth. Four optimization parameters are employed, which define the geometrical extent and spatial variation of the Soil deformation. The mechanism is capable of rationally accounting for many complexities such as strength nonhomogeneity, soil-pile adhesion. and suction on the back of the pile. Lateral force and pile top moment loading can both be accommodated. Parameter studies showing the effects of these features are presented along with comparisons of model predictions with recent centrifuge test results. An empirical prediction equation is fit to analytical results for typical soil conditions to provide a more convenient form of the analysis method. The empirical fit is demonstrated for cases of linearly increasing strength and for two-layered soil systems.

The coupled bridge foundation-superstructure finite-element code FLPIER was employed to predict the lateral response of the single piles and 3 X 3 to 7 X 3 pile groups founded in both loose and medium dense sands. The p-multiplier factors suggested by McVay et al. for laterally loaded pile groups with multiple pile rows were implemented for the predictions. The soil parameters were obtained through a back-analysis procedure based on single pile test results. The latter, as well as the numerical predictions of both the single and group tests, are presented. It was found that the numerical code FLPIER did an excellent job of predicting the response of both the single piles and the 3 x 3 to 7 x 3 pile groups. The latter involved the predictions of lateral load versus lateral deflection of the group, the shears and bending moments developed in the individual piles, and the distributions of-the lateral loads in each pile row, which were all in good agreement with the measured results.

A non-linear three-dimensional finite element procedur is developed and applied for the analysis of pile group foundations. The numerical procedure allows for elastic, non-linear elastic and elastic-plastic hardening behaviour of sand. In order to include the interaction effects involving relative slip and debonding, the thin-layer interface element is used. The predictions for displacements and loads obtained from the numerical procedure are compared with laboratory model test results of a pile group. Displacements, stresses and forces distribution in various components of the pile group are also examined. Furthermore, the effects of the non-linear soil response and relative motions at the interface are indentified and discussed.

The OpenSees finite element framework was used to simulate the response of 3×3 and 4×3 pile groups founded in loose and medium dense sands. Several numerical static pushover tests were conducted to investigate the interaction effects for pile groups. The results were then compared with those from centrifuge study. It is shown that our simulations can predict the behaviour of pile groups with good accuracy. Special attention was given to the three dimensional distribution of bending moment. It was found that bending moment develops in the plane perpendicular to the loading direction. In addition, bending moment data from simulations was used to derive p–y curves for individual piles, which were used to illustrate different behaviour of individual piles in the same group. Copyright © 2003 John Wiley & Sons, Ltd.

Using the results from three full-scale lateral pile group load tests with spacing ranging from 3.3 to 5.65, computer analyses were performed to back-calculate p-multipliers. The p-multipliers, which account for reduced resistance due to pile-soil-pile interaction, increased as pile spacing increased from 3.3 to 5.65 diameters. Extrapolation of the test results suggests that group reduction effects can be neglected for spacings greater than about 6.5 for leading row piles and 7 to 8 diameters for trailing row piles. Based on analysis of the full-scale test results, pile behavior can be grouped into three general categories, namely: (a) first or front row piles, (b) second row piles and (c) third and higher row piles. P-multiplier versus normalized pile spacing curves were developed for each category. The proposed curves yield p-multipliers which are higher than those previously recommended by AASHTO (2000), the US Army (1993) and the US Navy (1982) based on limited test data, but lower values than those proposed by Reese et al (1996) and Reese and Van Impe (2001). The response (load vs. deflection, maximum moment vs. load, and bending moment vs. depth) for each row of the pile groups computed using GROUP (Reese et al, 1996) and Florida Pier (Hoit et al, 1997) generally correlated very well with measurements from the full-scale tests when the p-multipliers developed from this test program were employed.

A series of static lateral load tests were conducted on a group of fifteen piles arranged in a 3x5 pattern. The piles were placed at a center-to-center spacing of 3.92 pile diameters. A single isolated pile was also tested for comparison to the group response. The subsurface profile consisted of cohesive layers of soft to medium consistency underlain by interbedded layers of sands and fine-grained soils. The piles were instrumented to measure pile-head deflection, rotation, and load, as well as strain versus pile depth. The average load resisted by each group pile was lower than the load resisted by the single pile at the same deflection. The lead row resisted loads similar to a single pile with the second row and third and subsequent rows resisting successively smaller loads. Maximum bending moments in the trailing row piles were larger and occurred at greater depths than the lead row piles. Group effects became more pronounced at larger deflection levels due to increased overlap of the shear zones that resisted the lateral motion of the piles thereby reducing the soil resistance. LPILE Plus version 4.0 (Reese et al., 2000) was used to model the single pile test. The initial input soil parameters were adjusted to obtain a good match between the measured and computed results. This refined soil profile was then used to model the pile group in GROUP version 4.0 (Reese et al., 2000). User-defined p-multipliers were adjusted to match the measured and calculated results. For deflections up to 38 mm, p-multipliers were 1.0, 0.87, 0.64, 0.81, and 0.70 for Rows 1 to 5, respectively. For larger deflections, the p-multipliers decreased to an average value of 1.0, 0.81, 0.59, 0.71, and 0.59. Thesis (M.S.)--Brigham Young University. Dept. of Civil and Environmental Engineering, 2004. Includes bibliographical references (p. 215-220).

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