Performance Of Pile Foundations Research Articles

Load transfer mechanisms for capped and uncapped non-displacement piles above tunnels: a centrifuge modelling study

This paper presents results from geotechnical centrifuge tests of tunnelling in dry dense sand beneath loaded non-displacement piles, focusing on the effect of a pile cap (representative also of a raft or grade beam) in contact with the soil surface on load transfer mechanisms. Experiments included loading tests to ascertain the foundation capacity and load-displacement response in the presence/absence of an underlying model tunnel. Individual ‘reference’ pile response is compared for cases with and without a pile cap, including pile displacements and load distributions between the head, shaft, and base; the case of ‘friction’ piles with a compressible base are also considered. Results show that uncapped piles with relatively large service loads experience ‘geotechnical failure’ (i.e. large settlements or a significant increase in settlement rate with tunnel volume loss) in order to mobilise base or shaft resistance. Pile caps are shown to reduce settlements and prevent geotechnical failure of both reference and friction piles; they also improve the post-tunnelling foundation performance under loading. The paper provides evidence to enable engineers to consider the beneficial role of shallow elements in contact with the surface on the performance of pile foundations both during and subsequent to tunnelling.

Ultimate Load-Bearing Capacity and Sustainable Performance of Pile Foundations of Yanji Suspension Bridge in Fault Zone Based on Refined Geological Model

Pile foundation is the most important foundation type of long-span bridges, of which the ultimate load-bearing capacity affects the safety and sustainable performance of bridges. When constructing large-span bridges, the bridge site may be close to the adjacent fault zones, which seriously affects the safety and long-term performance of pile foundations, causing the failure and unsustainability of long-span bridges in their life-cycle service life. At present, there are no engineering design rules or methods for assessing the load-bearing capacity of the pile foundation near the fault zones. To study the influence of the fault zone on the loading-bearing capacity and sustainable performance of pile foundations, triaxial compression tests were carried out on the mylonite at the Yanji suspension bridge site near the Xiangfan–Guangji fault zone in Hubei Province. The mechanical properties of mylonite were reflected by the Mohr–Coulomb yield criterion, and a topographic and geological modeling method based on the multi-platform was established. Then, the ABAQUS finite element software was used to study the deformation, stress, failure modes, and sustainable performance of the pile foundation under different bridge load levels, analyze the safety of the pile foundation in the fracture zone, and summarize the ultimate bearing characteristics of the pile foundation. The results show that the whole pile and surrounding rock are basically elastic under the pressure of the designed load, the plastic zone of the pile foundation is mainly concentrated at the pile bottom, and the shear stress concentration zone of the pile is mainly manifested in the joint of the cap and pile and the interface between soft and hard rock. When the load is increased to 4 times the designed load, the stress concentration area of the pile body gradually shifts upward from the pile bottom, and the surrounding rock at the bottom forms an “X-shaped” shear failure zone. After 100 years of operation, the maximum compressive stress of piles reaches 28.6 MPa, which is 120% higher than that at the beginning of the bridge construction, indicating that the sustainable performance of the piles can withstand the effect of the fault zone over the designed service years.

Non-Destructive Evaluation of Material Stiffness beneath Pile Foundations Tip Using Harmonic Wavelet Transform

Pile foundations are used to support superstructures and play an important role in the safety of these structures. The performance of pile foundations generally depends on the conditions of the pile itself and the material under the pile tip(i.e., bottom), especially for end-bearing piles installed in soft soil volumes. Therefore, to assess the performance of existing pile foundations, it is crucial not only to evaluate the structural integrity of the pile itself, but also to assess the ground conditions, such as subsoil stiffness beneath the pile foundation tip. Accessing the subsoil beneath the pile foundation tip is highly challenging in the field. Hence, there is a need for the development of non-destructive pile evaluation methods that allow the assessment of subsoil stiffness beneath the pile tip without direct access to the subsoil. Various non-destructive methods have been developed for pile performance assessment. However, these conventional non-destructive methods are primarily designed for assessing the structural integrity of the pile itself, and there are no existing non-destructive pile integrity testing methods applicable to evaluate the subsoil stiffness beneath the pile tip. In this study, a non-destructive method is developed to evaluate the subsurface soil stiffness beneath pile tip without direct access. The proposed method involves applying impact loading to the easily accessible pile head and measuring the elastic waves propagated within the pile foundation due to the impact loading. These wave signals are then recorded at the pile head. The measured time–history signals are decomposed using harmonic wavelet transform. This allows the obtainment of well-defined magnitude and phase information over time for various individual frequency components composing the wave. In this study, a method is proposed to assess the stiffness of the subsoil beneath the pile tip by simultaneously utilizing the magnitude and phase information of the measured signals obtained through harmonic wavelet transform. To facilitate this, a step-by-step data analysis procedure for evaluating the subsoil stiffness beneath the pile tip is introduced. To validate the proposed method, numerical simulations were conducted using ABAQUS. The experimental data obtained from the numerical simulations were processed using the proposed method to assess the subsoil stiffness beneath the pile. The determined subsoil stiffness was then compared with the exact soil stiffness used in the numerical simulation to evaluate the validity of the proposed method. Through this analysis, the proposed method demonstrated its effectiveness in assessing the subsoil stiffness beneath piles tip installed in weak soil volume.

Time-dependent deviation of high-speed railway bridge pier-cap-pile foundations in deep soft soils under surcharge loads: a case study

Permanent surcharges or temporary surcharges along high-speed railway lines occur frequently due to irregularities in construction, resulting in lateral deviations of adjacent pier-cap-pile foundations, especially in soft soil areas. The pier-cap-pile foundation deviation caused by surcharge loads in soft soils shows a significant time-dependent characteristic (TDC) that has been disregarded in most previous studies. In this study, an extended Koppejan model, which considers the TDC of soil movements, was developed, and the corresponding user-material subroutine (UMAT) was programmed in ABAQUS software. Then, the UMAT was embedded into a finite element model that was combined with an actual engineering case. Based on the validated model, the time-dependent deformation development of the pier-cap-pile foundation was investigated, and the subsequent service performance and deformation mechanism characterized by the time-dependent additional load were revealed. In addition, a rectification measure with an unloading + high-pressure rotary jetting pile was proposed, and the pile foundation performance after rectification was evaluated. The evaluation results were successfully applied to field rectified construction. The research findings obtained in this study may provide a valuable reference for similar accidents of pile foundation deviation caused by adjacent surcharge loads.

Factors affecting axial and lateral load transfer of hollow fibre-reinforced polymer piles in soft clay

ABSTRACT The growing interest in the long-term performance of pile foundations and their ability to resist the negative effects of water exposure and aggressive environmental conditions has led to considering non-corrosive materials such as fibre-reinforced polymer (FRP). The most common applications are light-bearing structures in waterfront environments, while applications for larger structures have not been widely accepted in industry due to the lack of long-term records and design guidelines available. In this study, a numerical model using the finite element method was developed to simulate small-scale load tests of hollow carbon-fibre reinforced polymer (CFRP) and glass-fibre reinforced polymer (GFRP) piles in soft clay. The findings of this research indicate that the number of FRP layers impacts loading behaviour significantly, while inner tube soil height has a reasonable influence on axial load response and fibre orientation has a minor effect under lateral load conditions.

Influence analysis of overlying soil layer to seismic behavior of inclined liquefiable soil and pile interaction system

The statistical data of earthquake hazard indicate that the liquefaction and large lateral flow deformation of ground is one of the main reasons of pile foundation failure. It is significant to focus on the seismic dynamic behavior of pile foundation in inclined liquefiable soil. Based on the Opensees finite element platform, an integrated finite numerical model of inclined liquefiable soil-pile group-structure interaction is established in this study, according to the shaking table model test of inclined liquefiable soil. The nonlinearity of pile-soil contact and the shear localization of soil layer are considered in the numerical simulation. The comparison of the numerical simulation result with the shaking table test results are verified. In order to discuss the influence of different overlying soil layer on the seismic behavior of soil and pile system, a typical inclined liquefiable soil-pile group-structure interaction finite element model is established by the proposed numerical simulation method. The results show that the overlying soil layer has an obvious influence on the seismic dynamic behavior of the pore pressure, the horizontal displacement of soil and pile. The increase of the thickness of overlying soil can reduce the liquefaction degree of sand and improve the mechanical performance of pile foundation.

A new approach for improving lateral performance of pile foundations in seasonally frozen regions

Ground freezing in cold areas can cause brittle damage to deep foundations during seismic loading. This paper presents a novel solution to this problem by replacing local soil around the pile with a temperature-insensitive composite material, namely polyurethane glue-bonded rubber particles-sand mixture (PolyBRUS). Three 1/12 scale reinforced concrete pile foundations embedded in unfrozen, frozen, and frozen with local replacement conditions were prepared, and quasi-static cyclic loading tests were conducted to reveal the adverse effects of seasonal freezing on pile foundations and verify the performance of the proposed solution. The model preparation, including model pile configuration, model construction, sensor configuration, and frozen soil formation, were described in detail. The pile foundation lateral performance data, including failure mode observations, lateral load-displacement hysteresis relations, and moment distributions, were presented. The evolution of secant stiffness and energy dissipation of the pile-soil system with lateral displacement were analyzed and discussed. It was found that the peak lateral load of the model pile in 20 cm-thick seasonal frost is 53% larger than the unfrozen conditions. In contrast, the ultimate displacement in seasonally frozen conditions is 25% less than that in unfrozen conditions. And seasonal freezing can render a pile from ductile to brittle failure. More importantly, the results show that the local replacement with the proposed material can ensure similar lateral behavior for the soil-pile system under both unfrozen and frozen conditions. It is concluded that the proposed local replacement approach offers excellent potential for mitigating the adverse effects of seasonal freezing on the lateral performance of deep foundations in cold regions. In future studies, local replacement zone optimization and large-scale field tests are recommended to further confirm this method's effectiveness and provide design parameters for pilot testing.

Seismic behavior of pile foundations in unsaturated soils

Earthquakes have caused significant damage to civil engineering structures worldwide due to inadequate lateral load capacity and excessive deformation of pile foundations supporting these structures. The seismic performance of pile foundations interacting with unsaturated soils could be affected by changes in matric suction due to the moisture content variation induced by seasonal weather changes or water table fluctuations. Hence, the main objective of this study is to investigate the effects of unsaturated soil conditions on the seismic response of a pile-soil system in silty clay soils. This study utilized a stand-alone finite element computer code called DYPAC (Dynamic Piles Analysis Code) developed using the Beams on Nonlinear Winkler Foundation (BNWF) approach. Free field soil displacements and p-y curve parameters, inputs needed for DYPAC analyses, were updated based on the soil suction variations. This study found that soil suction can significantly influence the seismic performance of piles interacting with unsaturated silty clay soils, especially as the soil becomes drier in the transition zone. The best seismic performance of the pile, which is the minimum lateral pile displacement, happened in the transition zone between fully saturated and nearly dry conditions.

Nonlinear Stochastic Seismic Response Analysis of Three-Dimensional Reinforced Concrete Piles

A reliable assessment and design of engineering structures requires appropriate estimation and consideration of different sources of uncertainty. The randomness of seismic ground motion is one major uncertainty that needs to be considered from the perspective of performance-based earthquake engineering. To properly account for this uncertainty and its corresponding effect on pile foundations, a stochastic seismic response analytical framework based on a probability density evolution method and a stochastic ground motion model is proposed for the nonlinear stochastic seismic response analysis of pile foundations. A three-dimensional finite element model of a reinforced concrete pile with a large diameter embedded in the soil foundation is firstly established and calibrated using the full-scale lateral load test results from the literature, in which the nonlinear behavior of soil, the soil–pile interaction, the concrete damaged plasticity, and the steel yielding of the pile are properly modeled. Then, the calibrated three-dimensional numerical model is employed as an illustrative example for the stochastic seismic response analysis using the proposed framework. The mean, standard deviation, and probability density function of pile settlement and the dynamic reliabilities of the pile concerning various performance requirements are obtained in the present study. The settlements of the pile show great variability under the excitation of various stochastic ground motions, and the maximum mean value of the pile settlements is about 8 mm. The changing shape of the settlement probability density functions in every moment demonstrates that it is unreasonable to use assumed probabilistic distribution models to characterize the seismic responses of pile foundations during a seismic reliability analysis. Based on the proposed method, it is found that the dynamic reliabilities of the selected reinforced concrete pile concerning four different performance levels are 0, 0.1293, 0.8247, and 1, respectively. The proposed stochastic seismic response analytical method in the present study can provide a proper and comprehensive way to quantify various uncertainties and their corresponding effects on the seismic performance of pile foundations. It can also be used to estimate the actual reliability level of pile foundations that are designed by the current codes when they are subjected to seismic loads.

Simulation of cyclic laterally-loaded piles in undrained clays accounting for soil small-strain characteristics

The performance of pile foundations subjected to cyclic lateral loading is central to offshore geotechnical engineering. Although non-linearity and path-dependence of soil mechanical behavior at small strains are widely recognized, the influences of these local behavior on global response of pile foundations are less explored. This work presents numerical analyses of cyclically-loaded piles in undrained clays that explicitly account for soil small-strain characteristics. By using intergranular strain (IGS) elasticity method, a soil model proposed by the authors for undrained clays during cyclic loading is extended to include non-linear small-strain behavior. Via comparing against element tests, the constitutive relation is shown capable of representing the observed variation of soil stiffness and damping with strain magnitudes, as well as the dependence of such non-linearity on stress paths. Based on the above soil model, finite element simulations are performed to interpret the response of laterally loaded piles from geotechnical centrifuge tests. The impacts of soil small-strain behavior on pile force–displacement relations, hysteric loops, and the ability of a pile–soil system to dissipate energy are investigated. This work highlights that the sensitivity of these foundation responses to small-strain non-linearity of soils can vary considerably, depending on pile geometry features and head constraint conditions.

Soil-pile-quay wall interaction in liquefaction-induced lateral spreading ground

Earthquake-induced soil liquefaction and lateral spreading often causes damage to pile foundations of quays and offshore structures. In this study, the soil-pile-quay wall interaction in liquefaction-induced lateral spreading ground was analyzed from three perspectives—experimental investigation, numerical simulation, and parametric analysis. A large-scale (1 g acceleration) shake-table test was conducted on a 2 × 2 pile group behind a quay wall, and described in terms of sensor arrangement, model configuration, and test results. The test resulted in phenomena such as the quay wall overturning to the water side, and ground settlement. A 2D (two-dimensional) nonlinear FE (finite element) model of a coupled dynamic soil-water system, which considered soil-pile-quay wall interactions, was validated using the experimental data. Based on the validated model, a parametric study was conducted to illuminate the effects of the pile head fixing conditions, pile stiffness, superstructure mass, permeability coefficient, and acceleration. The results indicated that these parameters had a significant influence on the soil-pile-quay wall interaction in the liquefaction-induced lateral spreading ground. Investigating the effects of each of the five parameters on the dynamic performance of pile foundations in this study has guiding implications for tests and numerical simulations.

Effect of Liquefaction Induced Lateral Spreading on Seismic Performance of Pile Foundations

Seismically active areas are vulnerable to liquefaction, and the influence of liquefaction on pile foundations is very severe. Study of pile-supported buildings in liquefiable soils requires consideration of soil-pile interaction and evaluation of the interaction resulting from movement of soil surrounding the pile. This paper presents the results of three-dimensional finite difference analyses conducted to understand the effect of liquefiable soils on the seismic performance of piles and pile groups embedded in stratified soil deposits using the numerical tool FLAC3D. A comparative study has been conducted on the performance of pile foundations on level ground and sloping ground. The soil model consists of a non-liquefiable, slightly cemented sand layer at the top and bottom and a liquefiable Nevada sand layer in between. This stratified ground is subjected to 1940 El Centro, 2001 Bhuj (India) earthquake ground motions, and harmonic motion of 0.3g acceleration. Parametric studies have been carried out by changing the ground slope from 0° to 10° to understand the effects of sloping ground on pile group response. The results indicate that the maximum bending moments occur at boundaries between liquefiable and non-liquefiable layers, and that the bending moment increases with an increase in slope angle. The presence of a pile cap prevents horizontal ground displacements at ground level. Further, it is also observed that the displacements of pile groups under sloping ground are in excess of those on level ground due to lateral spreading. Doi: 10.28991/CEJ-SP2021-07-05 Full Text: PDF

Performance of Existing Piled Raft and Pile Group due to Adjacent Multipropped Excavation: 3D Centrifuge and Numerical Modeling

Excavation induces stress changes and soil movement on existing floating piled rafts and elevated pile groups. Limited investigation of the effects of deep excavations has resulted in an incomplete understanding of pile foundation performance at the serviceability state. A series of three-dimensional (3D) centrifuge model tests and numerical simulations are conducted in this study to investigate the influence of raft contact on the response of an existing 2×2 piled raft in comparison to that of an elevated pile group when subjected to an adjacent multipropped deep excavation in dry sand. After rising g, an applied axial load was supported by 18% by the raft and 82% by the piles in the piled raft foundation prior to excavation. Owing to stress release and soil movement caused by the 8-m-deep excavation, the pile head load increased by 21% and 3% for the pile closer to the excavation for the piled raft and pile group foundations, respectively. Analysis of pile–soil relative settlement and raft contact pressure shows that a gap formed between the raft and ground surface in the piled raft, resulting in a load transfer from the raft to the embedded piles. A 20% larger settlement was seen in the piled raft foundation than in the pile group, to further mobilize shaft and end bearing resistances for the maintenance of vertical equilibrium. Moreover, 30% additional pile bending moment was induced due to excavation.

Influence of foundation flexibility on seismic fragility of reinforced concrete high-rise buildings

This study investigated the effect of foundation type and layout on the seismic vulnerability of tall reinforced concrete buildings using fragility curves. To this end, the seismic fragility of 12-, 18-, and 24-story buildings sitting on shallow and pile foundations (i.e., with rigid and flexible pile caps) were evaluated. The uncertainty in the structural and soil properties was assessed by using the Latin Hypercube Sampling method and the seismic uncertainty was incorporated using several near- and far-field earthquakes. The results showed that the use of flexible pile caps reduced the seismic fragility and base shear of superstructures compared to the piled structures with rigid pile caps. Furthermore, the flexible pile caps improved the seismic performance of pile foundations by reducing the earthquake-induced pile head forces and deflection. The findings of this study can help the engineers to select the appropriate foundation layout to optimize the seismic performance of buildings.

Influence of higher-order modes of slender tall pier bridge columns on the seismic performance of pile foundations

Numerous highway bridges have been constructed with slender tall piers over 40 m in Southwest China, due to the mountainous topography. Current researches on this type of bridges mainly focus on the higher mode effects on the seismic behavior of pier columns, while the responses of group pile foundations are generally neglected. The objective of this paper is to investigate how the dynamic demand of group piles are influenced by the higher-order modes of slender tall pier columns. To better understand the influence of higher order modes, two analysis scenarios, representing (1) the equivalent single-degree-of-freedom (SDOF) system neglecting higher mode effects of piers, and (2) the multi-degree-of-freedom (MDOF) system of the original bridge, are developed and analyzed. Fiber elements are utilized considering the potential nonlinear behavior of pier columns and piles, while nonlinear p-y, t-z and q-z springs are employed simulating the properties of soil layers in these numerical models. Using displacement of pile cap as damage index, the effects of higher-order modes on pile foundations are investigated through both incremental dynamic analysis (IDA) and fragility analysis procedures. The results show that the seismic demands of pile foundations could be significantly underestimated when the contribution of higher-order modes of columns are neglected. The damage of piles is observed prior to that of the pier columns, indicating that damage state of pile foundations should be carefully considered during seismic design, and only focusing on the pier columns would lead to unconservative results. Furthermore, p-y springs are shown to perform nonlinearly under strong excitations, which implies that modeling the soil layers with linear springs is insufficient and should be better considered with these nonlinear springs.

Static and Dynamic Reliability Analysis of Laterally Loaded Pile Using Probability Density Function Method

Pile foundation is one of the common foundation forms in marine geotechnical engineering, especially in wind power engineering. Its operation safety is seriously affected by many uncertainties, such as the randomness of ground motion in intensity and frequency. The stochastic reliability analysis method can better characterize these uncertainties in the evaluation of the safety performance of pile foundation. The probability density functions (PDFs) of stochastic systems are important prerequisites for reliability analysis. However, for geotechnical problems, the coupling between parametric and excitation randomness and the nonlinear mechanical properties of rock and soil make it very difficult to obtain the associated PDFs. Instead, the probability density evolution method (PDEM) is introduced and is used to investigate the static and dynamic reliability of laterally loaded piles as an example of a geotechnical problem. Compared with Monte Carlo stochastic simulations, PDEM-based computing is shown to be highly efficient when applied to the seismic design of pile in geotechnical engineering, and its calculation efficiency is 20 times of the former for the seismic dynamic reliability of pile foundation. This study provides a new reference for the efficient design and safety evaluation of offshore pile foundation engineering based on static and dynamic reliability of multiple random factors.

Monotonic and Cyclic Frictional Resistance Directionality in Snakeskin-Inspired Surfaces and Piles

AbstractInterface friction is a governing parameter in the performance of piled foundations and other applications. Piles and other foundation elements typically mobilize a similar interface fricti...

Optimal Testing Locations in Geotechnical Site Investigations through the Application of a Genetic Algorithm

Geotechnical site investigations are an essential prerequisite for reliable foundation designs. However, there is relatively little quantitative guidance for planning optimal investigations, including the choice of testing location. This study uses a genetic algorithm to find the ideal testing locations of various numbers of boreholes with respect to pile foundation performance. The optimization has been done separately for single-layer and multi-layer soils, which infer what is best for obtaining soil material properties and delineating layer boundaries, respectively. A sensitivity analysis was conducted to find the genetic algorithm parameters that result in high quality solutions within a reasonable timeframe. While boreholes arranged in a regular grid pattern provide good performance in many cases, there are instances where optimized locations provide a cost saving of A$2 million, or 4.2% of the construction cost. A set of recommended testing guidelines is provided.

Fragility-based sensitivity analysis on the seismic performance of pile-group-supported bridges in liquefiable ground undergoing scour potentials

Characterizing the effect of varying model parameters on the seismic performance of bridges is a desirable assistance to retrofits of existing bridges and designs of new bridges, especially for those in complex geotechnical conditions where scour and liquefaction potentials are involved. This paper aims to rank the sensitivity of fourteen structural and soil parameters for seismic performance assessment of pile-group-supported bridges in liquefiable ground undergoing scour potentials. To this end, a fragility-based Tornado diagram method for sensitivity analyses is proposed first in this study. An experimentally validated soil-foundation-bridge coupled finite element model considering scour and liquefaction effects is adopted and excited by a set of real ground motions for fragility analyses. Results indicate that the effect of scour depth slightly influence the most sensitive parameters, mainly including column height and diameter and pile diameter, for the performance of bridge components (i.e., bearing, column and pile). However, the increase of scour depth does downgrade the relative sensitivity of column-associated ones (e.g., column height and axial compressive ratio) and soil-related ones (i.e., loose and dense sand relative densities), while upgrade that of the pile-associated ones (e.g., pile diameter, center-to-center distance and longitudinal reinforcement ratio). In addition, to abide the capacity design principle that columns should fail before pile foundations, designs or retrofits of bridges using relatively larger pile diameter, column height, material strengths and longitudinal/transverse reinforcement ratios, together with smaller column diameter and pile center-to-center distance are recommended for mitigating scour and liquefaction effects on the seismic performance of pile foundations.

Shake Table Modeling of Pile Foundation Performance in Laterally Spreading Frozen Ground Crust Overlying Liquefiable Soils

AbstractOne of the most important lessons learned from Alaska’s major earthquakes is that lateral spread of frozen ground crust overlying liquefiable soils induced extensive bridge foundation damag...