Soil-pile Interaction Analysis Research Articles

Analytical method for laterally loaded offshore slender piles near sandy slopes considering slope deformation

This paper presents an analytical method to study the lateral response of offshore slender piles near sandy slopes. A slope deformation model is constructed to evaluate the slope displacement induced by the load transfer of a pile at the slope crest. A modified strain wedge (SW) model is developed by considering the slope deformation and the impact of the slope on the effective overburden pressure. A geometric transformation is employed to facilitate the analysis of the edge distance. The efficiency and accuracy of the method are demonstrated through comparisons of its results with those of six centrifuge piles and four model piles. Finally, the effects of the slope angle and edge distance on the pile response are discussed. This method introduces the slope deformation into the analysis of soil-pile interaction, allowing for comprehensive consideration of the combined effects of slope angle and edge distance.

Effect of Soil-Pile-Structure Interaction on Behaviour of Offshore Jacket Structure

Offshore jacket structures are generally supported on pile foundations. Studies have evaluated the effect of soil-pile interaction on design of foundation; however, effect of soil-pile-structure interaction on behaviour of jacket structure has received little attention. Hence, present study focuses on understanding the influence of soil conditions, soil-pile interaction and foundation modeling approach on deformation characteristics and member forces of jacket structure. Linear static analysis on a typical 4-legged battered jacket structure is performed using STAAD Pro., subjected to dead/live loads and environmental loads. The water depth of 120 m and wave heights of 5 m, 10 m and 15 m are considered for this study. Morison’s equation considering Stokes 5th order wave theory is used for calculation of wave forces on jacket structure. The supports are modelled as skirted pile groups. The piles are represented by springs, with stiffness calculated using soil-pile interaction analysis. The soil conditions used in the study are varied for different compaction states of sand and different consistency states of clay and various parameters such as lateral/vertical deflection, support reactions, forces in leg, beams and bracings have been compared. It is concluded that ignoring soil-pile-structure interaction during analysis of jacket structure would underestimate the lateral/vertical deflections, support reactions, shear force and bending moment for leg, and axial forces in beam and plan bracing of the structure. No substantial impact of the interaction on other member forces is observed. Jacket structure founded on clayey soil exhibits higher deformation and member forces as compared to sand in general. The study is expected to help structural engineers in adopting an appropriate modelling approach, considering soil-pile-structure interaction, to obtain more realistic response for jacket structures.

Pseudo-Static Simplified Analysis Method of the Pile-Liquefiable Soil Interaction considering Rate-Dependent Characteristics

The lateral pressure generated by liquefied soil on pile is a critical parameter in the analysis of soil-pile interaction in liquefaction-susceptible sites. Previous studies have shown that liquefied sand behaves like a non-Newton fluid, and its effect on piles has rate-dependent properties. In this study, a simplified pseudo-static method for liquefiable soil-pile interaction analysis is proposed by treating the liquefied soil as a thixotropic fluid, which considers the rate-dependent behavior. The viscous shear force generated by the relative movement between the viscous fluid (whose viscosity coefficient varies with excess pore pressure and shear strain rate) and the pile was assumed to be the lateral load on the pile. The results from the simplified analysis show that the distribution of bending moment is in good agreement with experiments data. Besides, the effects of various parameters, including relative density, thickness ratio of nonliquefiable layer to liquefiable layer, and frequency of input ground motion, on the pile-soil rate-dependent interaction were discussed in detail.

Axis-symmetric analysis of layered transversely isotropic saturated elastic soils containing a monopile under time-harmonic vibration

The axis-symmetric dynamic soil-pile interaction analysis is of fundamental significance in geotechnical, seismic and transportation engineering. In addition, soils tend to show an obvious stratification after the long-term deposition. Physical and mechanical properties of soils are generally transversely isotropic due to the orientation of soil particles in deposition. Therefore, the axis-symmetric analysis of layered transversely isotropic saturated elastic soils containing a monopile under time-harmonic vibration is carried out in this study. Firstly, the extended precise integration method (EPIM) is employed to obtain the dynamic fundamental solution for layered transversely isotropic saturated soils, which would be utilized as the kernel function of the boundary element method (BEM). Moreover, by modeling the pile as a one-dimensional bar, the motion equation of the monopile under steady-state vibration is acquired based on the finite element method (FEM). Finally, the coupled BEM-FEM formulation representing the soil-pile interaction is developed and the axis-symmetric solution for layered soils containing a monopile is acquired. Compared with existing results, the accuracy of the proposed method is verified. Numerical examples are conducted to analyze the influence of frequency, transverse isotropy, the stratification of soils and the length-radius ratio of piles on soil-pile interaction behaviors.

Evaluation of p-y springs for nonlinear static and seismic soil-pile interaction analysis under lateral loading

In the current state of practice, static/seismic soil-pile interaction is included in design calculations by a set of one-dimensional (1D) uncoupled springs. The guidelines of American Petroleum Institute (API) are often adopted to develop backbone curves for the lateral springs. The purpose of the paper is to assess the reliability of this practice. Twenty-seven static field and laboratory tests, and two dynamic centrifuge tests are simulated to evaluate the performance of the springs. More detailed elaboration on the performance of the springs is provided by simulation of one of the static tests and both of the dynamic tests using also three-dimensional (3D) continuum approach. The evaluation results indicate that API springs do not capture the major mechanisms involved in soil-pile interaction, and this results in erroneous estimation of pile deflections and bending moments. It is shown that the observed errors stem not only from the insufficient characterization of the spring properties (API backbone curves), but also from the inadequate simulation method in which three-dimensional continuum configuration of the supporting soil is represented by a 1D uncoupled spring.

Equivalent-linear pile head impedance functions using a hybrid method

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

Inelastic Response Spectrum for Seismic Soil Pile Structure Interaction

Structures resting on deep foundations like pile groups are subjected to entirely different kind of vibrations than those resting on shallow foundations, due to the inherent variations in the ground motions experienced at various levels of the foundation. The present work tries to generate response spectrum for single-pile supported structures using inelastic dynamic soil-pile interaction analysis. In the numerical model, the soil nonlinearity includes both separation at soil-pile interface and the plasticity of the near-field soil. The radiation boundary condition is also incorporated in the form of a series of far-field dampers which absorb the out-going waves. Inelastic response spectra for the structure, represented by a SDOF system, is generated after applying the synthetic time histories compatible with design (input) response spectra (as per IS 1893:2002-part I) at the base of pile to investigate the effects of ground response analysis including kinematics and inertial interaction between soil- pile system. It is found that a structure supported by pile foundations should be designed for larger seismic forces/ accelerations than those obtained from the design spectrum given in IS 1893:2002-Part I. The verification of the developed MATLAB program is reported towards the end, using results from commercial Finite Element software ABAQUS.

Behavior of Single Pile in Liquefied Deposits during Earthquakes

AbstractAnalysis of pile foundations for earthquake loads requires the consideration of inertial loads that result from the soil-pile-superstructure interaction, as well as the evaluation of kinematic interactions that result from the movement of the surrounding soil and the pile. Such soil-pile interaction analyses must consider the stiffness degradation that results from earthquake loading. In the current study, the soil-pile interaction analysis considers stiffness degradation effects for a range of earthquakes with different amplitudes [maximum horizontal acceleration (MHA)], mean time periods, and different durations of earthquakes. Effects of both kinematic and inertial interactions are evaluated using a seismic-deformation method. A computer program was developed using MATLAB for the analysis. Results of a ground-response analysis obtained from a separate study were used for the soil-pile interaction analysis. Pile response for kinematic interactions were validated with the available theoretical so...

Nonlinear Soil Spring Model Applied to Simplified Pushover Analysis of Soil-Pile Interaction

An approximate solution to the earthquake problem occurring in the seismic performance of pile-to-pile cap connections has been performed by applying a statically or cyclically lateral load to the superstructure, which is assumed to reflect the effect of the earthquake. In this case, the develop-ment of soil spring values based on the p-y method was adopted to approximate such a solution of soil spring stiffness and modeling in a two-dimensional static incremental (pushover) analysis. The soil was modeled using nonlinear pile elements and the applied loads were simulated as a combination of vertical distributed and lateral loads acting on the pile cap. The nonlinear soil springs associated with the p-y and t-z springs were utilized along the circular reinforced concrete pile. The pile was embedded in two different soil layers, which were varied with depth. A numerical application of the simplified model for soil-pile interaction based on this method was carried out with the more complex finite element analysis, demon-strating a significant lateral displacement reduction due to the soil confinement surrounding the pile. Keywords: nonlinear, soil spring, soil-pile interaction, finite element, pushover analysis, earthquake

The 2002 Canadian Geotechnical Colloquium: The role of soil–pile interaction in foundation engineering

Soil–pile interaction (SPI) plays an important role in the analysis and design of foundations and structures. Geotechnical engineers have recognized this role, and many studies have focused on several aspects of the topic in the past four decades. As the third millennium begins, geotechnical engineers are challenged to provide more reliable and efficient foundation solutions to support larger, heavier, and more complicated structures. SPI must be thoroughly understood to properly address the issues that arise when designing foundations to meet these challenges. This presentation investigates some of the important features of SPI as they relate to some innovative applications in foundation engineering. Specific problems examined here include design of tapered piles where understanding SPI and interface conditions is utilized to develop efficient design procedures; construction of fibre-reinforced polymer (FRP) and thin-walled pipe piles using an innovative device that exploits the understanding of aspects of SPI during driving for efficient installation; and Statnamic pile load testing where analysis of SPI is used to establish the characteristics of the pile static behaviour from the dynamic loading event.Key words: tapered, piles, driving, fibre-reinforced polymer, Statnamic, load testing.

Interactive behavior of soil–pile-superstructure system in transient state to liquefaction by means of large shake table tests

Shaking table tests were conducted by means of a large-scale laminar box with 4 m in length, 2 m in width and 2 m in height in order to investigate behavior of a soil-pile-superstructure system in liquefiable ground. A model two-storey structure, supported by a pile group, was set in a saturated sand deposit, and subjected to a sinusoidal base motion with increasing amplitude. Discussions are focused on the transient behavior until soil liquefaction occurs. Main interests are characteristics of springs used in a sway-rocking model and a multi-freedom lumped mass (MFLM) model that are frequently used in soil–pile interaction analysis. The spring constant in the sway-rocking model is represented by restoring force characteristics at the pile head, and that in the MFLM system is represented by an interaction spring connecting the pile to the free field. The transient state prior to soil liquefaction is shown to be important in the design of a pile because dynamic earth pressure shows peak response in this state. The reduction of the stiffness due to excess porewater generation and strain dependent nonlinear behavior is evaluated.

Observed Seismic Lateral Resistance of Liquefying Sand

This paper presents results from a study of the dynamic response of pile foundations in liquefying sand during seismic loading. The study included a series of dynamic centrifuge tests of pile-supported structures and the back-calculation of time histories for the lateral resistance p and relative displacement y between a pile and the free-field soil. Details of the centrifuge experiments and the procedures used to back-calculate p and y time histories are described. The back-calculated p-y time histories provide a concise representation of the experimental results and can be compared to the equivalent p-y behavior predicted by soil-pile interaction analysis methods. The observed p-y behavior provides insight into the mechanisms of soil-pile interaction in liquefying sand, showing characteristics that are consistent with the undrained cyclic loading behavior of saturated sand, including the effects of relative density, cyclic degradation, pore-pressure generation, prior displacement (strain) history, and p...

Elastoplastic analysis of soil-pile interaction : Cheung, Y K; Lee, P K K; Zhao, W B Comput GeotechV12, N2, 1991, P115–132

Elastoplastic analysis of soil-pile interaction : Cheung, Y K; Lee, P K K; Zhao, W B Comput GeotechV12, N2, 1991, P115–132

Elastoplastic analysis of soil-pile interaction

A finite element analysis of soil-pile interaction is presented in this paper. Goodman's interface elements and four elastic and elastoplastic constitutive models of soil are used. The calculated results are compared with field measurements. The necessity for considering the elastoplastic behaviour of soil coupled with interface elements and the effects of overconsolidation in the analysis of the soil-pile interaction problems is demonstrated.