Lateral Response Of Piles Research Articles

Nonlinear analysis of laterally loaded rigid piles at the crest of clay slopes

This paper proposes a method for nonlinear analysis of a rigid pile under lateral load at the crest of clay slope. It is assumed that the ultimate soil resistance in front of the pile and behind the pile vary nonlinearly with depth. The modulus of horizontal subgrade reaction in front of the pile and behind the pile vary nonlinearly with the pile displacement at ground surface. The horizontal shear resistance at the pile base is considered and a bilinear relationship between the shear resistance and the displacement is used. Three distribution patterns of the soil resistance along a pile are also considered. Based on the force and moment equilibrium, the system equations are derived for a laterally loaded rigid pile in sloping ground with different soil resistance distribution patterns. The proposed method is validated by comparing its results with those from field tests, finite element analyses and a theoretical method. Finally, the method is used to analyze the effect of slope angle, pile-soil adhesion factor, height above ground surface of point of load application, pile diameter and embedded length on the lateral response of rigid piles.

Nonlinear analysis of pile groups subjected to combined lateral and torsional loading

An empirical approach has been developed to analyze the nonlinear response of a pile group with arbitrarily distributed piles subjected to combined lateral and torsional loading. In this approach, the concept of instantaneous twist center is applied to analyze the displacement relationship of pile heads and establish the static equilibrium equations of the pile cap. The horizontal interaction among the individual piles is considered through the generalized p-multiplier. The coupling effect of lateral resistance on the torsional resistance of each pile is quantified using an empirical factor β; the lateral and torsional nonlinear responses of individual piles are modeled by p-y and τ-θ curves, respectively. The proposed approach not only captures the most significant aspect of the group effect and coupling effect in a pile group subjected to combined lateral and torsional loading, but also automatically updates p-multipliers of individual piles based on pile cap displacements. The proposed approach was verified using results of model tests on pile groups subjected to lateral loading, torsional loading, and combined lateral and torsional loading, separately. In general, the pile cap response and the transfer of applied loads in the pile groups agree well with the test results.

Centrifuge modeling of the cyclic lateral behavior of large-diameter monopiles in soft clay: Effects of episodic cycling and reconsolidation

Large-diameter monopiles supporting offshore wind turbines (OWTs) are subjected to intermittent episodes of cycling and reconsolidation during the lifetime. The lateral soil-pile stiffness is likely to degrade during the cycling but tends to recover during the subsequent reconsolidation. The former effect has been widely acknowledged in monopile design, while the latter is less commonly recognized. This study aims to (a) investigate the effects of episodic cycling and reconsolidation on the evolution of cumulative displacement, stiffness and bending moment of large-diameter monopiles in soft clay, and to (b) analyze their consequences to the structural safety of the OWT (i.e., evolving natural frequency fN and thus likelihood of resonance). A series of centrifuge tests were performed to simulate laterally loaded monopiles subjected to multi-stage episodic cycling and reconsolidation. The experimental results show that the lateral soil-pile stiffness degrades during the initial cycling episode, but it entirely recovers during the subsequent reconsolidation to exceed the initial stiffness, with a percentage increase up to 50%. Consequently, the cumulative lateral pile-head displacement and maximum bending moment induced by the 3rd episode of cycling can be 63% and 15% smaller than that due to the 1st episode, respectively. The effects of episodic cycling and reconsolidation on the lateral stiffness, displacement and bending moment of the pile become more pronounced as the cyclic amplitude increases. Despite these observed beneficial effects, the stiffer lateral pile response after the reconsolidation would have increased fN of a typical 6 MW turbine founded on the monopile by up to 13% (i.e., from 0.206 to 0.232 Hz), forcing it to unfavorably approach the 3P frequency limit that could trigger resonance.

Verification of a framework for cyclic p-y curves in clay by hindcast of Sabine River, SOLCYP and centrifuge laterally loaded pile tests

Pile foundations supporting offshore structures, such as jacket platforms, are subjected to cyclic lateral loading. The capacity and deformation of these pile foundations under cyclic lateral loading are important and challenging design aspects. The purpose of this paper is to present verification of a framework for analysing the lateral pile response under cyclic loading in clay, based on fundamental soil behaviour measured in the laboratory at the element level. This framework can account for site-specific cyclic soil properties, summarized in classic contour diagrams, and the site-specific cyclic loading characteristics in design. This is a step-change improvement from current codes and standards recommendations which are based on a series of tests on a single pile at a single site (i.e. the Sabine River tests, Matlock 1962, 1970). The paper first provides a brief summary of the framework and outlines the important assumptions and calculation procedures. The paper then presents a comprehensive validation exercise of the framework through back-analyses of three sets of 1-g and centrifuge tests, covering different soil conditions (strength profile, OCR and plasticity) and loading sequences. This hindcast demonstrates the model's capabilities to capture the essential behaviours of pile foundations under cyclic lateral loading and its added value as a design tool, when compared with current practice.

Nonlinear solutions for laterally loaded piles

A nonlinear analysis framework for laterally loaded piles is presented that is as accurate as equivalent three-dimensional nonlinear finite element analysis, but computationally one order of magnitude faster. The nonlinear behavior of sands and clays are account for by using hyperbolic modulus–reduction relationships. These nonlinear–elastic constitutive models are used to calculate the reduced modulus at different points in the soil based on the soil strains induced by lateral pile displacement. The reduced modulus at different points in the soil domain are spatially integrated to calculate the reduced soil resistance parameters associated with the differential equation governing the lateral pile displacement. The differential equations governing the lateral displacements of pile and soil under equilibrium are obtained by applying the principle of virtual work to a continuum-based pile–soil system. These coupled differential equations are solved using the one-dimensional finite difference method following an iterative algorithm. The accuracy of the analysis is verified against equivalent three-dimensional nonlinear finite element analysis, and the validity of the analysis in predicting the field response is checked by comparisons with multiple pile load test results. Parametric studies are performed to gain insights into the lateral pile response.

Nonlinear solutions of lateral response for single pile under the combined action of axial and lateral loads

For the study of the laterally loaded pile under axial load, most of the past research always confined the surrounding soil of pile in the linear elastic and elastic-plastic. In order to consider the nonlinear property of soil around the pile more realistically and improve the design of single piles under combined vertical and lateral loads, a nonlinear analysis method based on the hyperbola p-y curve model is applied to calculate the lateral response of pile. The relevant computer program is developed by MATLAB language, and the relevant solving algorithm is presented. The reliability of this approach was verified through comparisons with the measured data from model tests. The calculation results indicate that the approach was more convenient and accurate than the existing methods. The proposed method is applicable for laterally loaded pile under axial load in preliminary engineering design.

Influence of installation method on static lateral response of displacement piles in sand

The influence of the installation method on the static lateral response of displacement piles is presented using the results from reduced-scale field tests on piles in medium dense siliceous sand. In contrast to the importance of the installation method on shaft friction, it is shown that lateral response of piles to static lateral loading is largely insensitive to the installation method. The tests show that the lateral responses of impact-driven piles with different installation frequencies and jacked piles are very similar, while vibro-installed piles exhibit a somewhat stiffer response, reflecting effects of compaction. A comparison of load test results with the predictions obtained from two design methods reveals the suitability of a method that correlates the lateral soil response to the cone penetration test end resistance.

Lateral Performance for Long Pile Subjected to Simultaneous Axial and Lateral Loads in Dense Sand: An Experimental Study

The present study focus on the investigation ofthe response of single pile when subjected to both axial and lateral loads simultaneously in dense sand. To study this issue, laboratory model was locally improved to examine the piles under this kind of loading. The dense sand provided using raining technique. The slenderness ratio of the tested pile is ( L/D=45). On the other hand, the vertical and horizontal loads are divided into 5 stages to assess the influence of load intensities on the lateral pile response. It can be concluded that the lateral pile response is affected by changing the load intensities

Lateral Response and Failure Mechanisms of Rigid Piles in Soft Soils Under Geosynthetic-Reinforced Embankment

Previous studies regarding geosynthetic-reinforced pile-supported (GRPS) embankments over soft soils have mainly focused on load transfer mechanisms and design approaches. However, little attention was given to the lateral performance of rigid piles in GRPS embankment systems. This paper presents the results of 3D finite element analyses to examine and compare the lateral response and failure mechanisms of floating and end-bearing piles in soft soils under geosynthetic reinforced embankments. The effects of geosynthetic reinforcement and pile length on the stability of the embankments are also investigated. The results indicate that the induced lateral responses in the piles are distinctly different for floating and end-bearing piles. Failure of the floating pile is primarily caused by the inclination of the pile. However, for end-bearing piles, bending failure is clearly established as the principal mode of failure. The benefit of the geosynthetic layers in improving the stability of piled embankments is not particularly apparent. Moreover, the increase in pile length is significant in enhancing the stability of GRPS embankments. Specifically, when the normalized pile length varies from 0.75 to 1.15, the critical height of embankment increases from 6.2 to 11.8 m. However, the effect of pile length becomes negligible when the normalized pile length exceeds 1.15. The lateral movement and failure modes of GRPS embankments are strongly dependent on pile length. Therefore, it is essential to consider this aspect when analyzing the stability of the GRPS embankment.

A general analytical solution for lateral soil response of non-circular cross-sectional pile segment

• An analytical solution is proposed for the lateral soil response of non-circular pile. • A general method is proposed for the conformal mapping of arbitrary hole. • It allows the shape effect of pile with arbitrary cross section to be considered. • Closed-form expressions for the lateral stiffness of non-circular pile are given. This paper presents a general analytical solution for the two-dimensional laterally loaded non-circular cross-sectional pile segment-soil system based on the complex variable elasticity theory. By using the conformal mapping technique, the non-circular cross section of pile in the physical plane is mapped onto the unit circle in the phase plane. Then, using the complex variable theory developed by Muskhelishvili, the stress function, and hence the stress and displacement distributions of soil around the non-circular cross section dimension pile is readily derived. Subsequently, the analytical solution is used to determine the stiffness of two-dimensional pile-soil system. A series of closed form equations for the lateral stiffness of commonly used non-circular cross-sectional piles, such as square, rectangular, X-shaped cross-sectional piles, are derived through parametric studies. The proposed new analytical solution extends the classic elastic solution proposed by Baguelin et al. and it allows the shape effect of pile with arbitrary cross section to be considered.

Effects of scour-hole dimensions on lateral behavior of piles in sands

Scour is a process of soil erosion around foundations caused by currents and waves, which can severely compromise the performance of the foundations. The scour process forms a scour hole around the foundation. The existence of the scour hole has been considered by many design standards for pile foundations such as those from the US Federal Highway Administration (FHWA) and American Petroleum Institute (API). However, these standards recommend different procedures to evaluate lateral responses of piles subjected to local scour that forms three dimensions of scour hole. This paper presents a series of three-dimensional finite element (FE) parametric analyses to examine the feasibility of the standard methods (FHWA and API) as well as an analytical solution proposed by the authors through varying scour-hole dimensions, soil properties, and pile properties. The results showed that the analytical solution provided conservative results while the standard methods provided mixed results compared with the FE analyses. The loss of pile lateral capacity due to scour was more significant in dense sands than in loose sands (approximately 10% more). For a given relative scour depth, the increase in pile diameter increased the scour-induced loss of pile lateral capacity.

A numerical investigation of influence of low-plasticity fines in sand on lateral response of piles

Experimental evidence suggests that sands containing non-plastic or low-plasticity fines may show either decreasing or increasing shear strength with increasing fines content in certain situations. Accordingly, the presence of low-plasticity fines can significantly affect the ultimate lateral soil resistance; thus low-plasticity fines can affect the lateral response of piles. In this study, a quantitative method is proposed for determining the effect of low-plasticity fines in sand on the lateral response of piles in sand by combining a strain wedge model and a unified critical state compatible (UCSC) framework. An equivalent granular state parameter is employed in the UCSC framework to define the soil state uniquely in the strain wedge. The proposed quantitative method is incorporated in a finite element program. A series of numerical analyses are performed on a laterally loaded pile embedded in various relative densities of the base (clean) sand, to which various quantities of low-plasticity fines are added. The effect of low-plasticity fines on the lateral response is investigated. Furthermore, the effect of the low-plasticity fines on the response of the strain wedge is discussed.

Effect of Tunneling on Adjacent Piled Foundation in Clay

Soil movements arising from tunnel excavation may induce severe stresses on adjacent piled foundations. This paper investigates the behavior of piles due to nearby tunneling in soft clay using centrifuge modeling technique. Centrifuge modeling has an advantage that the consolidation time of the clay under forced gravity field can be expedited significantly to study the long term performance of a pile due to tunneling. The types of piles investigated in the present study include floating pile, socketed pile and end bearing piles with different pile head conditions. The test results on the induced axial and lateral pile responses due to tunneling are presented in this paper and the implications of the findings to engineering practice are highlighted.

Evaluation of lateral response of single piles to adjacent excavation using data from cone penetration tests

Excavation inevitably induces stress changes in the surrounding soil, which causes significant lateral movements, additional forces, and bending moments in the existing pile foundations. To prevent or minimize damage to adjacent piles, this paper presents an actual full-scale instrumented study to examine the lateral response of existing piles to an adjacent test pit excavation. Cone penetration tests (CPTs) near the test piles before and after excavation are conducted and compared. A simple p–y evolution model for lateral piles during excavation is proposed. The proposed model is defined by the pre-excavation and post-excavation p–y curves from CPT data, which can provide better predictions by comparison with the field measured results. Additionally, for analysis of the pile behaviour after excavation, the observed lateral bearing capacity of full-scale tests are compared with those computed by the pre-excavation and post-excavation p–y curves. The post-excavation p–y curve can generally give a satisfactory prediction of the residual pile bearing capacity after excavation. The calculated results from the free-field cone parameters have a serious overestimation and are detrimental to the service design of pile foundations.

Variation in lateral load capacity of pile embedded near slope with ground inclination and edge distance

ABSTRACT There are many circumstances in which piles have to be provided on slopes. Experimental model tests in the laboratory have been undertaken to investigate the lateral pile response in sloping ground. The paper discusses about the investigation in a series of 22 laboratory tests in dense sand at 72% relative density. The main motive of the study was to examine the effect of slope angle and edge distance on the pile response. Ground slope was varied as 1V:1.5H, 1V:1.75H and 1V:2H for sloping ground condition. Pile response was obtained for seven different positions of pile from the crest of the slope for a specified relative density. Then pile response for horizontal ground condition was obtained for quantification of effect of sloping ground. Displacement and bending moments in the pile increased significantly when the ground surface changes from horizontal to slope. An increase in the edge distance from the slope crest causes reduction in the pile displacement and maximum bending moment.

Lateral Response of a Single Pile under Combined Axial and Lateral Cyclic Loading in Sandy Soil

According to practical situation, there have been limited investigations on the response of piles subjected to combined loadings especially when subjected to cyclic lateral loads. Those few studies led to contradictory results with regard to the effects of vertical loads on the lateral response of piles. Therefore, a series of experimental investigation into piles in dense sand subjected to combination of static vertical and cyclic lateral loading were conducted with instrumented model piles. The effect of the slenderness ratio (L/D) was also considered in this study (i.e. L/D= 25 and 40). In addition, a variety of two-way cyclic lateral loading conditions were applied to model piles using a mechanical loading system. One hundred cycles were used in each test to represent environmental loading such as offshore structures. It was found that under combined vertical and cyclic lateral loads the lateral displacement of piles decreased with an increase in vertical load whereas it causes large vertical displacements at all slenderness ratios. In addition, for all loading conditions the lateral, vertical (settlement and upward) displacements and bending moments increased as either the magnitude of cyclic load or the number of cycles increases.

Effect of excavation unloading on p-y curves for laterally loaded piles

Field test and numerical analysis were conducted to investigate the soil stress variation and lateral pile response to whole excavations from cone penetration tests (CPTs). The effects of excavation unloading on the performance of CPT cone resistances and p-y curves were examined. The p-y responses were related to the excavation-induced both stratigraphic variation and soil stress relief. Based on CPT profiles, the numerical calculations of the lateral pile responses before and after excavations were obtained and compared using a CPT-based p-y method. Finally, the suggestion on the design of laterally loaded piles considering excavation unloading was given.

Modelling and Assessment of a Single Pile Subjected to Lateral Load

Abstract A three-dimensional finite element technique was used to analyse single pile lateral response subjected to pure lateral load. The main objective of this study is to assess the influence of the pile slenderness ratio on the lateral behaviour of single pile. The lateral single pile response in this assessment considered both lateral pile displacement and lateral soil resistance. As a result, modified p-y curves for lateral single pile response were improved when taking into account the influence lateral load magnitudes, pile cross sectional shape and flexural rigidity of the pile. The finite element method includes linear elastic, Mohr-Coulomb and 16-nodes interface models to represent the pile behaviour, soil performance and interface element, respectively. It can be concluded that the lateral pile deformation and lateral soil resistance because of the lateral load are always influenced by lateral load intensity and soil type as well as a pile slenderness ratio (L/D). The pile under an intermediate and large amount of loading (in case of cohesionless soil) has more resistance (low lateral displacement) than the pile embedded on the cohesion soil. In addition, it can be observed that the square-shaped pile is able to resist the load by about 30% more than the circular pile. On the other hand, pile in cohesionless soil was less affected by the change in EI compared with that in cohesive soil.

Interpretation of pile lateral response from deflection measurement data: A compressive sampling-based method

The performance of piles under lateral loading, i.e., the lateral response of piles, may be evaluated by in situ lateral loading tests. Inclinometers are frequently installed along the pile depth to measure the pile lateral deflection during the loading tests. Other pile responses, such as the bending moment and shear force, may be further obtained through high-order differentiation of the deflection measurement data with respect to depth. As inclinometers measure the pile deflection at a number of pre-specified depths, the deflection measurement data are discrete. Performing high-order derivatives on discrete deflection data is tricky and sometimes provides misleading results, particularly when the pile response is nonlinear. This paper proposes an innovative approach for interpreting the lateral response of piles from discrete deflection measurement data. The proposed method is based on a new sampling theorem in digital signal processing called compressive sensing/sampling (CS). The method is illustrated using a real case history in the USA, and the results show that the proposed method can provide reasonable interpretations of the lateral response of piles. A sensitivity study is also carried out to systematically explore the performance of the proposed method.

Lateral response of single piles in cement-improved soil: numerical and theoretical investigation

This study aims to investigate the lateral response of a single precast concrete pile reinforced with cement-improved soil through a series of theoretical studies and 3D finite element analyses using a concrete damage-plasticity model. Application of cement-improved soil around a pile can obviously reduce both lateral deflections and bending moments in the pile and can significantly increase the lateral capacity of the pile. Increasing soil resistance to limit pile deflection and preventing or delaying the development of tension-induced damage in the pile are reinforcement mechanisms. A modified p–y curve model is proposed to predict the lateral response of single piles in cement-improved soil.