Pile Foundation System Research Articles

Non linear soil structure interaction of space frame-pile foundation-soil system

The study deals with physical modeling of space frame- pile foundation and soil system using finite element models. The superstructure frame is analyzed using complete three -dimensional finite element method where the component of the frame such as slab, beam and columns are descretized using 20 node isoparametric continuum elements. Initially, the frame is analyzed assuming the fixed column bases. Later the pile foundation is worked out separately wherein the simplified models of finite elements such as beam and plate element are used for pile and pile cap, respectively. The non-linear behaviour of soil mass is incorporated by idealizing the soil as non-linear springs using p-y curve along the lines similar to that by Georgiadis et al. (1992). For analysis of pile foundation, the non-linearity of soil via p-y curve approach is incorporated using the incremental approach. The interaction analysis is conducted for the parametric study. The non-linearity of soil is further incorporated using iterative approach, i.e., secant modulus approach, in the interaction analysis. The effect the various parameters of the pile foundation such as spacing in a group and configuration of the pile group is evaluated on the response of superstructure owing to non-linearity of the soil. The response included the displacement at the top of the frame and bending moment in columns. The non-linearity of soil increases the top displacement in the range of 7.8 %- 16.7%. However, its effect is found very marginal on the absolute maximum moment in columns. The hogging moment decreases by 0.005% while sagging moment increases by 0.02%.

Modified generalized pushover analysis for estimating longitudinal seismic demands of bridges with elevated pile foundation systems

In longitudinal multi-mode pushover analysis of bridges with elevated pile foundation systems, the inelastic contributions of the second mode cannot be neglected. Generalized pushover analysis cannot be applied directly in this condition. A modified generalized pushover procedure is developed for estimating seismic demands of bridges with elevated pile foundation systems. Modified generalized pushover procedure, modal pushover analysis and incremental dynamic analysis of a bridge with elevated pile foundation systems are conducted. The results show that the modified generalized pushover procedure can provide reasonable estimations of moments and predict more accurate plastic hinge rotations compared with modal pushover analysis.

An investigation of the changes in the natural frequency of a pile affected by scour

Scour around bridge foundations is one of the leading causes of bridge failure. Up until recently, the monitoring of this phenomenon was primarily based around using underwater instrumentation to monitor the progression of scour holes as they develop around foundation systems. Vibration-based damage detection techniques have been used to detect damage in bridge beams. The application of these vibration based methods to the detection of scour has come to the fore in research in recent years. This paper examines the effect that scour has on the frequency response of a driven pile foundation system, similar to those used to support road and rail bridges. The effect of scour on the vibration characteristics of the pile is examined using laboratory and field testing. It is clear that there is a very clear reduction in the natural frequency of the pile as the severity of scour increases. It is shown that by combining state-of-the-art geotechnical techniques with relatively simple finite element modelling approaches, it is possible to accurately predict the natural frequency of the pile for a given scour depth. Therefore, the paper proposes a method that would allow the estimation of scour depth for a given observed pile frequency.

Case Study of Offshore Pile System Failure in Hurricane Ike

The objective of this paper is to document and study the failure of a driven, steel pipe pile foundation system supporting an offshore platform. The three-pile system failed in overturning because of a pull-out failure of the most critically loaded pile in a hurricane 5 years after installation. The calculated tensile capacity of this pile using the American Petroleum Institute (API) design method is close to the estimated load at failure. This case history is significant because it represents the failure of a large-diameter pile in service when loaded by a storm. Also, this case history generally affirms the current design methods and contradicts a widely held perception that offshore pile designs are significantly conservative. This case history highlights the opportunities to improve design practice by explicitly accounting for pile flexibility when dealing with strain-softening soils and by considering the capacity of the foundation system as well as the capacity of individual piles in design.

Response of Piered Retaining Walls to Lateral Soil Movement Based on Numerical Modeling

The response of individual retaining walls employed as a preferred slope stabilization technique, to lateral loading has been widely explored in the literature. The present study focuses on the response of piered retaining walls, i.e. retaining walls supported by a pile foundation system, to lateral soil movement. Numerical analysis results by MATLAB have revealed wall-soil-pile interaction mechanism with different effective height of wall, spacing, diameter and number of piles, using different soil properties, which quantifies the behavior of piered retaining walls owing to lateral soil movement. Based on a numerical configuration sensitivity study, the relationship between lateral loading and pile/wall deflection, shear and bending moment under different influencing parameters has been established. Optimum effective parameters are accordingly defined and relevant guidance on choosing appropriate piling configuration is provided, which can be of practical use in engineering design.

Settlement of axially loaded piles entirely embedded in rock – analytical and experimental study

Finite element analysis was performed to study the settlement behaviour of axially loaded piles entirely embedded in nonhomogenous rock. The elastic modulus of the rock mass was taken to increase linearly along the pile length starting from a nonzero value at the ground surface. Cases of pile-rock stiffness ratios that have not been considered in the literature were investigated. Such ratios are typical for reinforced concrete piles bored in sedimentary rocks. Results of the numerical analysis were verified through conducting static loading tests on full-scale piles in rock of well-defined physical and mechanical properties. Charts were developed to predict the elastic settlement of piles in rock. An equation was also introduced to incorporate the effect of rock nonhomogeneity in estimating the depth at which settlement becomes insensitive to the increase of pile length. A complementary numerical analysis utilizing a simple piled foundation system showed that the pile load share is sensitive to the rate of increase in rock stiffness along the pile length. The sensitivity is more pronounced for piled foundations resting on rock with high mass stiffness. +On leave from Jordan University of Science and Technology

Networked pseudodynamic testing of bridge pier and precast pile foundation

Using the internet-based network platform NetSLab, the seismic response of bridge pier and precast concrete pile foundation was investigated in this study. NetSLab was developed based on client/server concept along with a data model and communication protocols, and is capable of transferring control and feedback data and signals among geographically distributed laboratories or computers connected by the Internet. In this study, the bridge column was simulated numerically whereas the full-scale prestressed/precast pile model was tested physically with predetermined moment distribution along the pile model and neglecting pile group effects. The hybrid experimental results indicate that the sudden spalling of the thick concrete cover of the precast pile may cause unstable response of the bridge pier and pile foundation system under simulated earthquake loading, particularly when the bridge is subjected to near fault ground motions. The research also demonstrated the enhanced testing capabilities of the networked pseudo dynamic testing concept.

Visualization of soil arching on reinforced embankment with rigid pile foundation using X-ray CT

The purpose of this paper is to study and compare arching in reinforced and unreinforced piled embankments for different fill materials and pile spacings. Toyoura sand, silica sand no.7, silica sand no.8 and dry powder clay are used as fill materials. In this study, X-ray CT method is used as a non-destructive technique to examine the load distribution mechanism quantitatively. Vertical cross sectional images are constructed by the data obtained from CT scanning. It is seen that low density areas represent the shear planes and dilatancy in the arch within the piled embankment. The angle of density change is defined as the angle formed by the arch-shaped shear plane and the horizontal plane within the inter-pile soil. While Toyoura sand has the smallest angle of density change due to the largest peak internal friction angle and the effective particle size, dry powder clay has the largest angle of density change. The earth reinforcement is found to be effective with the use of pile elements for the purpose of stress re-distribution in the fill. Furthermore, the amount of the embankment loading is visualized by three dimensional extraction images. The effectiveness of the proposed method is verified by conducting a comparative study with the current Japanese design model. It is shown that, using X-ray CT method and visualization techniques provide a better understanding of soil arching in a reinforced embankment with rigid pile foundation system.

Gravel Mat로 보강된 말뚝지지 전면기초의 실내모형실험

A piled raft foundation is one of the systems used to reduce the settlement of structures. However, the general design method for a piled raft foundation system assumes that the piles only support external loads, which exclude the bearing capacity of the raft itself. In this study, an experimental model test was performed to evaluate the raft capacity for the external load on the sand. Additionally, a part of the sandy ground under the raft was replaced with a gravel mat to reinforce the piled raft foundation system and increase the bearing capacity. Then, parametric studies of the reinforced ground were performed to determine the displacement and load-sharing ratio of the piled raft foundation system.

Mathematical models and solution algorithms for computational design of RC piles under structural effects

The paper presents mathematical models and solution algorithms for RC pile design, through scanning soil stratums from top to downwards with an interactive scanner band. The equilibrium of transferred loads from the superstructure, friction forces and tip bearing forces are considered for the design, which leads to optimum pile length. The most important contribution of this research for designers is supplying an efficient tool to obtain optimum pile length and reinforced concrete design of pile foundation systems. A program package has been developed in MATLAB depending on the proposed algorithm. Soil behaviors depending on external effects, active and passive zone distributions are considered. All possible effects in all freedom degrees are taken into account in design process. Stress and strain distributions due to axial loads, bending moments, shear forces and torsional moments may be monitored. The optimum pile length, cross section dimension and reinforcement details may be found by using developed algorithm. In this study, a dynamic layer object has been produced to find optimum pile length. In solution process, this layer is compressed to a scanner band to find more optimal pile length. This scanner band moves from up to down and stops whenever optimum length is found. During this movement, all bearing capacity controls are carried out considering soil effects. Reinforced concrete design is also achieved depending on external loads. The flowcharts and computer codes developed for pile design is presented in the paper in detail. Finally, numerical solutions of axially and multi-loaded piles as deep foundation systems are presented. The design procedure of given examples are demonstrated through the proposed algorithms. The optimum length, cross section dimension and reinforcement details are presented.

The design of foundations for high-rise buildings

High-rise buildings are usually founded on some form of piled foundation subject to a combination of vertical, lateral and overturning forces. However, conventional methods for assessing stability may not be adequate when designing such foundations because they tend to focus on resistance under vertical loading. This paper sets out an ultimate-limit-state approach for computer-based design of pile foundation systems for high-rise buildings and provides an example application on a 151-storey tower in South Korea.

Time–Frequency Signal Analysis for Nondestructive Evaluation of Pile with Cap

As stress waves decay as they pass through the pile foundation system, it is extremely challenging for all nondestructive testing methods to evaluate the pile integrity of a shaft underneath a structure. In this study, time–frequency signal analysis (TFSA) is used for signal processing and adopted to interpret the pile integrity testing signal. An experimental case with pile lengths of 58m with caps, were tested by the low strain sonic echo method. Traditional time domain analyses can not identify the pile tip response signals 58m lengths. After time-history curves are transformed into a time–frequency domain distribution, the results indicate the pile tip can be located more easily and clearly than the traditional time-domain analyses of pile integrity testing allowed for.

Experimental study on tuned liquid damper performance in reducing the seismic response of structures including soil-structure interaction effect

In this paper, the performance of a tuned liquid damper (TLD) in suppressing the seismic response of buildings is investigated with shake table testing of a four-story steel frame model that rests on pile foundation. The model tests were performed in three phases with the steel frame structure alone, the soil and pile foundation system, and the soil-foundation-structure system, respectively. The test results from different phases were compared to study the effect of soil-structure interaction on the efficiency of a TLD in reducing the peak response of the structure. The influence of a TLD on the dynamic response of the pile foundation was investigated as well. Three types of earthquake excitations were considered with different frequency characteristics. Test results indicated that TLD can suppress the peak response of the structure up to 20% regardless of the presence of soils. TLD is also effective in reducing the dynamic responses of pile foundation.

Seismic performance of pile-to-pile cap connections: An investigation of design issues

Damage in recent earthquakes has resulted in the design of pile foundation systems becoming more conservative, particularly pile-to-pile cap connections. However, the application of current international design practice results in pile cap joint details having congested steel reinforcement in the pile cap and this is extremely difficult to construct in accordance with the designers recommendations. The formation of plastic hinges in the piles remains a serious risk. A review of critical design issues and former research investigations into the soil-structure interaction of pile systems and the findings of a three-dimensional, nonlinear finite element analysis of the system is reported. Significant gaps have been identified between current practice and the performance of piling systems when subjected to seismic events. Preliminary findings indicate potential for alternate connection details to improve performance under seismic action. The paper concludes with a concise summary of current state-of-the-art design approaches and details further research requirements.

Design of raft-pile foundation using combined optimization and finite element approach

This paper describes the application of a structural optimization approach combined with the finite element method for the optimal design of a raft–pile foundation system. The analysis takes into account the non-linear behaviour of the soil medium and the piles. For the optimization process, the sensitivity analysis is carried out using the approximate semi-analytical method while the constraint approximation is obtained from the combination of extended Bi-point and Lagrangian polynomial approximation methods. The objective function of the problem is the cost of the foundation. The design variables are the raft thickness, cross-section, length and number of piles. The maximum displacement and differential displacement are selected as the constraints. The proposed method is shown to achieve an optimum design of raft–pile foundation efficiently and accurately. Copyright © 1999 John Wiley & Sons, Ltd.

Forced vibrations of laterally loaded piles

An analytical approach for the determination of the response of a single circularcylindrical pile subjected to a lateral dynamic load is presented. The kinetic and the potentialenergies of the pile-foundation system are minimized by variational principle to obtain thegoverning field equations of the pile-foundation system along with the appropriate boundaryconditions. A non-dimensional parameter γ, associated with the characteristics of the pile, thefoundation and the loading is used to represent the elastic medium. This parameter γ can bedetermined by using an iterative procedure. The classical finite difference method is used tosolve the governing field equations of the pile-foundation system. The validation of the proposedmodel is demonstrated by applying to several published field pile load tests. Parametric studieswith regard to the frequency response of the pile head and the resonant frequency of the pile-foundation system are presented.

Analysis of Piles Subjected to Embankment Induced Lateral Soil Movements

Damage to piles supporting structures, bridge abutments, and utilities can occur as a result of the construction of nearby embankments. This is because the lateral displacements resulting from these construction activities can induce forces and moments in the piles. The resulting stresses can be significant particularly when soft soil deposits are present and the lateral soil displacements are large. This paper describes a simplified numerical procedure based on finite-element method for analyzing the response of single piles to lateral soil movements. The flexural bending of the pile is modeled by beam elements. The complex phenomenon of the pile-soil interaction is modeled by hyperbolic soil springs. A framework for determining the soil parameters for use in the analysis is summarized here. Comparisons are made between the observed behavior of full-scale tests and centrifuge model tests and those computed by the proposed numerical method. Based on parametric studies, empirical design solutions for pile foundation systems at the base of a sloped embankment are presented.

A piled raft interaction model

Based on the considerations of pile interaction as published by Randolph and Wroth (1978) and Van Impe (1991), a modified interaction model for a piled raft foundation system anda layered soil profile is proposed. Attention is payed particularly to the pile soil interaction radius and the relative stiffness of the pile group and raft. The paper shows the application of the model for a case study in France.

Fast foundation for soft clay : Hilton, J R; Rager, R E; Novotny, R L Civ Engng, N YV63, N3, March 1993, P62–65

This article describes the detailed foundation work and high-capacity piling design for a flue gas desulfurization (FGD) retrofit system for the Lambton Generation Station in Ontario, Canada. Morrison Knudsen Corporation (MK) designed the FGD pilings and foundations as part of a joint venture between Joy Technologies and MK for design and construction of the facilities. Engineering commenced in October 1990, pile driving began in March 1991, and by November all of the 1,777 steel pipe piles had been driven and most of the rebar and concrete placed. By December 1991, only 14 months after contract award, nearly all substructure construction was completed. A major engineering challenge was to design a deep-seated pile foundation system where downdrag was a consideration in the presence of soft clays and a significant depth to bedrock. The design effort was further impacted by the heavy loads imposed on the foundations and the demands of a fast-track schedule. To achieve design and schedule goals, a full-scale pile testing program was conducted along with a geotechnical investigation. Based on study and test data, pile designs were confirmed and driving criteria were established. Using hammers of various driving energies, the piles were driven into bedrock after preaugering to a depth of 80 feet, and an integral monolithic mat foundation system was installed.

動的な水平載荷を受ける群杭基礎の挙動に関する実験的研究

This paper deals with the dynamic behavior of a pile-foundation system. Static loading test of a pile in the horizontal direction and dynamic loading test of a 3×3 pile group in the same direction were carried out. The small steel piles used in these tests were 152.4mm diameter, and 7m length. The static cyclic load is applied by a push-pull type hydraulic jack. After the static test, a reinforced concrete foundation (1. 5m×1. 5m×O. 5m) was made on the pile group. The dynamic load is applied by using the vibration generator which is set on the foundation. From these tests, some responses of the pile foundation, the restoring force characteristics, and the strains of pile shafts were obtained. As some significant test results, it was recognized that the resonant frequency and the dynamic stiffness decrease, and the displacement and rocking amplitude increase as the embedment effects of the pile foundation decrease.