Pile Segment Research Articles

Response of tapered piles to axial harmonic loading

This paper presents a new mathematical approach for the analysis of a harmonically vibrating, linear, elastic, tapered pile. The soil consists of a number of horizontal elastic strata that are homogeneous, isotropic, and linearly viscoelastic. The governing differential equation for an arbitrary pile segment is obtained and solved. The solution starts from the pile toe and ends up with the pile head. It will be shown that when the taper angle is increased, the resonant amplitudes of piles decrease. It will also be demonstrated that the resonance amplitudes and resonant frequencies of the floating tapered pile and a uniform pile of the same volume and length vary slightly. However, the resonant amplitude of an end-bearing tapered pile is significantly less than that of the equivalent uniform pile. It will generally be concluded that the use of tapered piles subjected to axial harmonic vibrations is superior to the use of cylindrical piles of the same length and volume. This is very attractive for dynamically loaded piles, encouraging the practical use of tapered piles.

Dynamic response of a pile in a transversely isotropic saturated soil to transient torsional loading

The transient dynamic response of a pile embedded in transversely isotropic saturated soil and subjected to transient torsional loading is studied. The pile–soil system is divided into thin layers, and the Laplace transform is used to solve the governing equations of the soil layer and the pile segment. The matrix equations to describe the stiffness of the pile are deduced from the loading condition at the pile head and the compatibility between the pile and the soil. The displacement of the pile in the time domain is calculated by using the numerical inverse transformation. The pile’s slenderness ratio and its transverse isotropy are calculated numerically.

Skin friction features of drilled CIP piles in sand from pile segment analysis

AbstractNumerical pile segment analysis is conducted in this study with an advanced soil model to investigate the skin friction behaviour of a drilled Cast‐In‐Place (CIP) pile installed in sand. Although the interface between the sand and pile is considered rough, thin elements adjacent to the pile are used to include effects of localized shear.Unit weights of fluid concrete and accompanied changes in stress are considered as the effects of pile installation. Changes in effective stresses are the most prominent effect due to pile installation with a change in direction of the major principal stress from the vertical to the radial direction.Shear behaviour of the sand at the interface during the early shear stage is related to the contractive tendency of the sand at small strain levels. Changes in the stress field around the pile with little changes in volumetric strain take place during the early shear stage. Stress redistributions during the early shear stage depend on the direction of the major principal stress before shear.Results of the pile segment analyses for drilled CIP piles show good agreement with design methods. Parametric studies are used to characterize the effects of sand density and pile diameter on the skin friction behaviour of drilled CIP piles. Copyright © 2007 John Wiley & Sons, Ltd.

Analysis of kinematic seismic response of tapered piles

In the present work, a two-phase analysis is used to assess the lateral movement of a tapered pile due to kinematic seismic loading resulted from earthquakes. First, the free-field horizontal displacement of the ground due to earthquake is estimated using available theory of wave propagation. Second, these estimated soil movements are imposed on the taper pile in a closed-form solution to compute the pile response. The governing differential equation for an arbitrary pile segment is obtained, which includes the free-field horizontal movement estimated from the first phase. The equation is solved explicitly to obtain the horizontal deflection. Parametric studies show that tapered piles tend to be more flexible than uniform piles of the same volume and length under earthquake loading, which is soundly interesting.

Uplift performance of FRP tapered piles in dense sand

The influence of taper angle on the uplift performance of FRP tapered piles in dense sand at various embedment ratios is investigated using a large-scale testing facility (pressure chamber). The current study evaluates the uplift performance of tapered piles relative to the uplift performance of straight-sided wall piles. Thirteen pile installations were performed in a pressure chamber using conventional head driving and a novel toe driving technique. Twenty­six uplift load tests were performed at different radial and vertical confining pressures in order to simulate pile segments at different depths. The results of uplift loading tests are presented and discussed. The results showed that the uplift capacity of tapered piles is slightly higher than that of cylindrical piles with similar average diameter and length. The taper effect on the pile uplift performance is evaluated using the uplift taper coefficient. A hyberbolic relationship is established between the uplift load and displacement that can be used to determine the soil stiffness for use in non­linear analysis. A simplified design approach for uplift capacity of tapered piles is discussed and evaluated.

Side Shear Setup. II: Results From Florida Test Piles

This paper analyzes the results of a driven pile side shear setup (SSS) test program performed at the University of Florida and described in a companion paper. All pile segments showed SSS, with similar magnitudes in both cohesionless and cohesive soils, and irrespective of depth. Horizontal effective stresses increased after driving, but then stabilized as induced pore pressures dissipated. SSS continued long after pore pressure dissipation due to other aging effects. Pile load tests in all soil types, and standard penetration tests with torque measurement (SPT-T) in cohesive soils, confirmed the approximate semilog-linear time versus SSS behavior and the usefulness of the setup factor A . Staged (repeated) tests significantly increased SPT-T measurements, suggesting a reduction factor of 0.4 for SSS results measured by staged testing. We believe that engineers can now include SSS in routine design, using a minimum setup factor A=0.1 for soils similar to those tested, or higher if supported by dynamic or...

Design and Construction of Three Instrumented Test Piles to Examine Time Dependent Pile Capacity Gain

Abstract Three heavily instrumented test piles were designed, constructed, and installed at a bridge reconstruction site in Newbury, Massachusetts as part of a research initiative into time dependent pile capacity gain. Pile instrumentation consisted primarily of an alternating pattern of piezometers and strain gages, allowing for correlation between pile capacity gain and excess pore pressure dissipation along discrete pile segments. Additional instrumentation within the piles included accelerometers, telltales, and radial pressure cells, allowing monitoring of total pressure at the pile wall. Standard dynamic gages (strain gages and accelerometers) were also attached to the piles during dynamic testing. A total of 86 vibrating wire, 17 electrical resistance, 17 telltales, and 4 piezo-resistive gages were installed within the test piles to record strain, displacement, pressure, and acceleration. This paper describes (i) the initial installation location of the test piles, (ii) the design and layout of the individual test piles, (iii) the selection and installation design of the individual instrumentation within the test piles, and (iv) assembly of the test piles. Sample measurements of the various instruments and a summary of the instrumentation performance are also presented.

Novel toe driving for thin-walled piles and performance of fiberglass-reinforced polymer (FRP) pile segments

Despite the rapidly growing use of pile foundations, it is presently difficult to assure the integrity and uniformity of the cross-sectional area of cast-in-place piles when using normal concrete. Cavities and soil encroachments leading to soil pockets can jeopardize their load-bearing capacity. Moreover, corrosion in reinforced concrete and steel shell piles has been very costly, exceeding US$2 billion in annual repair costs in the United States alone. To address these two challenges, extensive research has been underway at the University of Western Ontario to develop novel technology for the construction of piles. Self-consolidating concrete (SCC), a material that flows under gravity and assures the integrity of piles, is cast into fiberglass-reinforced polymer (FRP) tubes that provide corrosion-resistant reinforcement. A toe driving technique was developed to install the empty FRP shells into the soil, and SCC is subsequently cast into the shells. Driving tests using this new technique were carried out on large-scale model FRP and steel pipe piles installed in dense dry sand enclosed in a pressure chamber. FRP–SCC and steel closed-end piles were also driven using conventional piling at the pile head. Static load tests were conducted on the various pile specimens under different vertical and horizontal confining pressures. The pile specimens were instrumented to investigate their dynamic behaviour under driving and their response to static compressive, uplift, and lateral loading. It is shown that the toe driving technique is very suitable for installing FRP piles in dense soils. Results from the driving tests and static load test indicate that FRP–SCC hybrid piles are a very competitive and attractive option for the deep foundations industry.Key words: FRP, self-consolidating concrete, piles, pile drivability, toe driving, axial load, uplift load, lateral load, large-scale modeling, shaft resistance, dense sand.

Load transfer of fibre-reinforced polymer (FRP) composite tapered piles in dense sand

This paper describes an experimental study conducted using a large, laboratory-scale testing facility to test pile segments at different stress levels. The objectives of the study were twofold: to examine the load-transfer mechanism of tapered piles in compression, and to evaluate the effect of pile material on pile performance characteristics. The results of axial compressive loading tests on 26 pile load tests were presented using fibre-reinforced polymer (FRP) concrete composite tapered piles and steel piles. Two installation techniques were used, including conventional head driving and toe driving using a new technique. Piles were tested at different confining pressures to represent a pile segment at depths of 4.0 and 8.0 m. The load distribution along the pile shafts was measured and the results were compared with those from an analytical solution in terms of the taper coefficient Kt. The comparison showed reasonable agreement between Ktvalues established from the experiments and those obtained from the analytical solution. The measured toe resistance of tapered and cylindrical piles was compared with those from the analytical solution. A simple rational approach was proposed for the design of tapered piles.Key words: tapered piles, FRP, pile capacity, axial performance, centrifuge modeling, shaft resistance, toe resistance.

Three-Dimensional Analysis of Performance of Laterally Loaded Sleeved Piles in Sloping Ground

Development of urban cities in hilly terrain often involves the construction of high-rise buildings supported by large diameter piles on steep cut slopes. Under lateral loads, the piles may induce slope failure, particularly at shallow depths. To minimize the transfer of lateral load from the buildings to the shallow depths of the slope, an annulus of compressible material, referred to as sleeving, is usually constructed between the piles and the adjacent soil. However, the influence of the sleeving on the pile performance in a sloping ground is not fully studied and understood. To investigate the influence, a 3D numerical analysis of sleeved and unsleeved piles on a cut slope is described in this paper. The influences of relative soil stiffness on the response of sleeved piles are also examined. The load transfer from the laterally loaded sleeved pile to the sloping ground is primarily through a shear load transfer mechanism in the vertical plane. Under small lateral loads, the sleeving can lead to a significant reduction in subgrade reaction on the sleeved pile segment and may considerably increase the pile deflection and bending moments. Under large lateral loads, the influence of the sleeving on pile performance appears to diminish because of the widespread plastic zones developed around the pile.

Dynamic response of a pile in a multi-layered soil to transient torsional and axial loading

The dynamic response of an elastic pile subjected to transient torsional and axial loading is considered. The pile is embedded in a multi-layered elastic soil. The stress field in a soil is simplified by following the existing solutions for a pile subjected to static torsional and axial loading. The dynamic equilibrium equation of soil is solved in the Laplace domain by using analytical techniques. The soil resistance is coupled into a one-dimensional governing equation of a pile segment and an analytical solution is presented. An impedance matrix can then be derived for a pile segment relating end stress resultants to the displacements. Non-homogeneous initial conditions of the pile are considered. The impedance matrices of pile segments are assembled by following the concepts of finite element method to analyse a pile embedded in a multi-layered soil. The treatment of soil base response is also discussed. Time domain solutions are obtained by using a numerical Laplace inversion procedure. The extension of the analysis to linear viscoelastic soils using the correspondence principle in the theory of viscoelasticity is discussed. Selected numerical solutions for a pile embedded in a homogeneous soil and a &squo;Gibson’ soil are presented to portray the influence of pile moduli and slenderness ratios, loading history and soil non-homogeneity on the dynamic response of an elastic pile. Nous étudions la réponse dynamique d’un pilot élastique soumis à une charge de torsion et axiale transitoire. Le pilot est enfoui dans un sol élastique constittué de plusieurs couches. Nous simplifions le champ de contrainte dans un sol en appliquant les solutions existantes pour un pilot soumis à une charge de torsion et axiale statique. L’équation de 1’équilibre dynamique du sol est résolue dans le domaine de Laplace en utilisant des techniques analytiques. Nous couplons la résistance du sol en une équation standard unidimensionnelle pour un segment de pilot et nous présentons une solution analytique. Une matrice d’impédance pent alors être dérivée pour un segment de pilot en liant les résultantes de contrainte en bout aux déplacements. Nous examinons les conditions initiales non homogènes du pilot. Pour analyser un pilot enfoui dans un sol constitué de plusieurs couches, nous assemblons les matrices d’impédance des segments de pilot en suivant les concepts de la méthode d’éléments finis. Nous discutons aussi du traitement de la réponse de base du sol. Les solutions du domaine de temporisation sont obtenues en utilisant une procédure d’inversion numérique de Laplace. Nous discutons de l’extension de l’analyse aux sols à viscoèlasticit&acutee;aire en utilisant le principe de correspondance dans la théorie de viscoélasdcité. Nous présentons de solutions numériques choisies pour un pilot enfoui dans un sol homogène et un sol &squo;Gibson’ pour décrire l’influence des modules de pilot et des coefficients de gracilité, des comportements aux charges et de la non homégénéité du sol sur la réponse dynamique d’un pilot élastique.

Numerical Procedure for Predicting Pile Capacity—Setup/Freeze

In geotechnical engineering practice, the increase over time of pile capacity after installation is sometimes referred to as pile setup or freeze. Pile setup, which is often associated with piles driven into saturated clays and silts, is mainly attributed to soil consolidation around the pile. Field observations have shown that pile setup is significant and continues to develop for a long time after pile installation. Pile foundations are usually expensive. Therefore, taking a small percentage of pile setup into consideration will result in cost reduction and savings in piling projects. This paper presents a general numerical procedure to predict pile setup by simulating the behavior of the pile during its different life stages: installation, subsequent consolidation, and loading. The Hierarchical Single Surface modeling approach, the strain path method, and the nonlinear finite element analysis of porous media were used in the analyses. The procedure was verified by successfully predicting the field behavior of pile segment models installed into soft marine clay. Numerical experiments were also conducted to demonstrate the applicability of the numerical procedure to full-scale driven piles. Piles with diameters of 0.3 m and 0.5 m and a length of 10 m were considered in the analyses.

Load tests on short pile segments : Redel, C Proc eighth asian regional conference on soil mechanics and foundation engineering, Kyoto, 20–24 July 1987V1, P405–410. Publ Japan: Japanese Society for Soil Mechanics and Foundation Engineering, 1987

Load tests on short pile segments : Redel, C Proc eighth asian regional conference on soil mechanics and foundation engineering, Kyoto, 20–24 July 1987V1, P405–410. Publ Japan: Japanese Society for Soil Mechanics and Foundation Engineering, 1987

Principles of side resistance development in rock socketed piles : Williams, A F Proc 3rd Australia-New Zealand Conference on Geomechanics, Wellington, 12–16 May 1980, V1, P87–94. Publ Wellington: New Zealand Institution of Engineers, 1980

An understanding of the principles associated with the aide resistance of rock socketed piles has been developed by considering the pile-rock interface as a confined joint. The approach indicates that relative displacement between the pile and rock will occur by either sliding of one surface on the other or by shearing through the concrete or rock asperities. In either case, a dilation has been shown to occur across the interface which has given rise to significant stresses normal to the pile. The side resistance has been found to be a function of the normal stresses and the strength properties of the concrete and rock. The validity of the concepts developed has been investigated by field testing several piles 1 to 1.2 m diameter and 2 to 2.5 m long in highly to moderately weathered mudstone. The stresses acting normal to each pile have been calculated from measurements of strain in the pile segments, and the socket dilations have been measured by displacement transducers installed in the rock mass. These measurements showed agreement with the postulated principles and have allowed investigation and design procedures to be rationally developed. Further, the developed principles simply explain the work strengthening or work weakening observed during field testing of side resistance piles.

Bending of Piles Determined by Inclinometer Measurements

This paper deals with the bending of slender precast concrete piles which are driven in segments 10 to 14 m in length and spliced in the field by means of rigid steel couplings. The requirements of the Swedish Building Code for allowable bending of these piles are reviewed and the method of inspecting the bending is described. The inspection is performed by lowering a slope inclinometer through a pipe, which is cast centrically in the pile and attached to special couplings by which access all through the pile is obtained.By the inclinometer the inclination and the direction of the inclination is measured. The results are used for determining the location of the pile in the ground and the bending of the pile. Mathematical expressions for this are derived.In Swedish practice, when judging a pile, the bending of the pile segments is treated separately from the bending of the pile over the pile splices, as the latter involves the question of squareness of the joint couplings in casting. The bending of a segment is judged in terms of change of inclination per metre of pile and of bending radius over the length of the segment. A typical example is given on how to present and evaluate the measuring results.