Pile Interface Research Articles

Soil–pile separation effect on the performance of a pile group under static and dynamic lateral loads

The effect of soil–pile separation is studied with respect to the performance of a laterally loaded pile group. Full-scale tests, which consist of a combination of a single and a 3 × 5 group pile under static and dynamic lateral loads, present a unique opportunity and allow a rigorous study without arbitrary parameter back-fitting. The coupled soil–pile system is idealized through two-dimensional finite elements with soil models idealized by a hyperbolic-type multiple shear mechanism. Nonlinear spring elements are used to idealize the soil–pile interaction through a hysteretic nonlinear load–displacement relationship. Joint elements with a separation–contact mechanism are used to idealize the separation effect at the soil–pile interface. Ignoring soil–pile separation in static tests overestimates the ultimate lateral load–carrying capacity by 43% for a single pile and 73% for the trailing pile in a closely spaced pile group. Moreover, neglecting soil–pile separation in dynamic tests overestimates the total group load–deflection curve in both the loading and unloading phases.

MAGMATIC AND STRUCTURAL EVOLUTION OF AN ANORTHOSITIC MAGMA CHAMBER: THE POE MOUNTAIN INTRUSION, LARAMIE ANORTHOSITE COMPLEX, WYOMING

The 200 km 2 Poe Mountain intrusion, part of the 1.43 Ga Laramie anorthosite complex in southeast Wyoming, USA, preserves an exceptional range of primary magmatic and secondary deformation-induced structures that document the sequence of events involved in the emplacement, crystallization, and high-temperature deformation of a Proterozoic anorthosite. The intrusion consists of a steeply dipping (40–90°) olivine leucogabbroic to anorthositic margin of layered cumulates (minimum stratigraphic thickness of 5 km) that contains structures typical of mafic layered intrusions. The layered margin grades inward to a core of granoblastic (recrystallized) anorthosite characteristic of Proterozoic anorthosite plutonic suites worldwide. From the lowest to the highest stratigraphic levels, the layered series is divided into the anorthositic layered zone (ALZ) and leucogabbroic layered zone (LLZ). Igneous layering occurs at all scales from laterally discontinuous cm-thick horizons to distinct mappable packages of layered rocks up to several hundred meters thick. Contacts between the layered zones and internal subsections can be traced ~20 km along strike. The layered rocks are strongly laminated, defined by the orientation of tabular plagioclase; the abundance of layers in the ALZ containing blocky megacrysts of plagioclase increases down-section toward the core. Most of the tabular plagioclase appears to have grown within the upper crustal magma reservoir; plagioclase megacrysts were likely entrained from depth. Isolated examples of layer disruption record periodic re-organization of the semi-consolidated cumulate pile in response to slumping. Structures related to the impact of settled blocks, combined with scours and a mixed magma horizon, indicate that layering and lamination formed directly at or near the magma – pile interface, and that a dynamic magma chamber was present throughout the crystallization history of the Poe Mountain intrusion. Because the rejected interstitial liquid in anorthositic cumulates is denser than intermediate-composition plagioclase, the intrusion floor must have been inclined to allow for drainage. A sloping floor formed in the Poe Mountain intrusion owing to the contemporaneous diapiric rise of the relatively buoyant plagioclase-megacryst-rich rocks in the core; diapirism was the driving force for pervasive recrystallization of the core anorthosite and much of the ALZ. The Poe Mountain intrusion demonstrates that the assembly of Proterozoic anorthosites required active, periodically replenished magma chambers where the efficient segregation of plagioclase and removal of dense rejected melt, aided by syn- to post-crystallization deformation, led to the formation of vast expanses of nearly monomineralic cumulates.

Pile foundation analysis and design using experimental data and 3-D numerical analysis

Capacity based design of pile foundations limits the soil-structure interaction mechanism to group bearing capacity estimation, neglecting, in most cases, the contribution of the raft. On the other hand, a straightforward, nonlinear, 3-D analysis, accounting for soil and structural nonlinearities and the effects arising from pile–soil–pile interaction, would be extremely high CPU-time demanding and will necessitate the use of exceptionally powerful numerical tools. With the aim of investigating the most efficient, precise, and economical design for a bridge foundation, a hybrid method, compatible with the notion of sub-structuring is proposed. It is based on both experimental data and nonlinear 3-D analysis. The first step to achieve these targets is a back-analysis of a static pile load test, fitting values for soil shear strength, deformation modulus, and shear strength mobilization at the soil–pile interface. Subsequently, the response of 2 × 2 and 3 × 3 pile group configurations is numerically established and the distribution of the applied load to the raft and the characteristic piles is discussed. Finally, a design strategy for an optimized design of pile raft foundations subjected to non-uniform vertical loading is proposed.

Numerical analysis of the response of battered piles to inclined pullout loads

AbstractThis paper presents a three‐dimensional finite element analysis of the response of battered piles to the combined lateral and vertical pullout loads. Analyses are carried out using an elastoplastic constitutive law based on the non‐associated Mohr–Coulomb criterion. The influence of the contact condition at the pile–soil interface is also investigated. Analyses show that the load's inclination with regard to the pile's axis affects both the lateral and axial response of the battered piles. Analyses also show that the pullout capacity of battered piles is affected by the pile's inclination regarding the vertical axis as well as the load's inclination regarding the pile's axis. The investigation of the influence of the contact condition at the soil–pile interface shows that the possibility of sliding at the soil–pile interface affects the response of battered piles subjected to loads with low inclination regarding the pile's axis. Copyright © 2008 John Wiley & Sons, Ltd.

Vertical dynamic response of pile in a radially heterogeneous soil layer

AbstractAn analysis of a pile vertical response considering soil inhomogeneity in the radial direction under dynamic loads is presented. The solution technique is based on a three‐dimensional axisymmetric model, which includes the consideration of the vertical displacement of the soil. The soil domain is subdivided into a number of annular vertical zones, and the continuity of the displacements and stresses are imposed at both the interface of pile–soil and the interfaces of adjacent soil zones to establish the dynamic equilibrium equations of the pile–soil interaction. Then, the equations of each soil zone and of the pile are solved one by one to obtain the analytical and semi‐analytical dynamic responses at the top of the pile in the frequency domain and time domain. Parametric studies have been performed to examine the influence of soil parameters' variations in the radial direction caused by the construction effect on the dynamic responses of pile. The results of the studies have been summarized and presented in figures to illustrate the influences of the soil parameters as they change radially. The effect of the radius of the disturbed soil zone caused by construction is also studied in this paper. Copyright © 2008 John Wiley & Sons, Ltd.

Axisymmetric finite element analysis of pile loading tests

In this paper a typical soil–structure interaction problem is considered, the case of a vertical pile installed in sand and submitted to an axial compression loading. Results from two full scale pile tests are analysed and the tests are reproduced by numerical simulations via finite elements method (FEM). The choice of the mechanical parameters for the soil and the sand–pile interface and the modelling approach are first described. A new numerical strategy is outlined to account for pile installation effects due to jacking and driving via FEM. The proposed approach is based on the application of existing empirical correlations available for the quantification of residual radial and shear stresses along the pile shaft as well as residual pressures around the pile base after the installation. This approach is proposed as an alternative to more complex methods based on the numerical modelling of the pile penetration problem. The role of the constitutive modelling of the interface is also discussed. Finally, comparative analyses of pile loading tests using FEM are provided and the comparisons between numerical and experimental results are presented and discussed.

Target reliability based design optimization of anchored cantilever sheet pile walls

In this study, the stability of anchored cantilever sheet pile wall in sandy soils is investigated using reliability analysis. Targeted stability is formulated as an optimization problem in the framework of an inverse first order reliability method. A sensitivity analysis is conducted to investigate the effect of parameters influencing the stability of sheet pile wall. Backfill soil properties, soil – steel pile interface friction angle, depth of the water table from the top of the sheet pile wall, total depth of embedment below the dredge line, yield strength of steel, section modulus of steel sheet pile, and anchor pull are all treated as random variables. The sheet pile wall system is modeled as a series of failure mode combination. Penetration depth, anchor pull, and section modulus are calculated for various target component and system reliability indices based on three limit states. These are: rotational failure about the position of the anchor rod, expressed in terms of moment ratio; sliding failure mode, expressed in terms of force ratio; and flexural failure of the steel sheet pile wall, expressed in terms of the section modulus ratio. An attempt is made to propose reliability based design charts considering the failure criteria as well as the variability in the parameters. The results of the study are compared with studies in the literature.

A Robust Macroelement Model for Soil–Pile Interaction under Cyclic Loads

The principal focus of this study is the development of a robust macroelement model for soil–pile interaction under cyclic loads. The model incorporates frictional forces and formation of gaps at the soil–pile interface as well as hysteretic behavior of the soil. The plastic envelope of the soil behavior is modeled via the so-called p – y approach, outlined in American Petroleum Institute’s guidelines for design of foundation piles for offshore platforms. The macroelement is an intuitive assembly of various basic elements, each of which incorporating a particular aspect of the soil–pile interaction. The modular structure of this macroelement allows straightforward adaptation of improved constitutive models for its building blocks. Herein, we focus on large-diameter, cast-in-drilled-hole reinforced concrete piles (piers) that are partially or fully embedded in soil. These types of piles are frequently used as support structures in highway construction. Consequently, the numerical robustness of the interact...

Improved numerical algorithms for frictional contact in pile penetration analysis

This paper presents a numerical formulation for frictional contact problems associated with pile penetration. The frictional contact at the soil–pile interface is formulated using the theory of hardening/softening plasticity, so that advanced models for the interface can be dealt with. A smooth discretisation of the pile surface is proposed using Bé zier polynomials. An automatic load stepping scheme is proposed, which features an error control algorithm and automatic subincrementation of the load increments. The numerical algorithms are then used to analyse the installation process of pushed-in axial piles. It is shown that the smooth discretisation of the pile surface is effective in reducing the oscillation in the predicted pile resistances and the automatic load stepping scheme outperforms the classical Newton–Raphson scheme for this type of problem.

Torsional response of pile embedded in a poroelastic medium

The response of a cylindrical elastic pile embedded in a homogeneous poroelastic medium and subjected to torsional loading is studied for the first time. Based on the Muki's model, the pile-porous medium system is decomposed into a fictitious pile system and an extended porous medium system. The one-dimensional, vertical, elastic pile and the three-dimensional poroelastic medium are solved, respectively. Considering the mixed boundary-value conditions at the interface of pile and soil, a Fredholm's integral equation of the second kind for the bar-force is established. The force and the displacement of the pile are calculated by applying numerical quadrature.

Bond strength of concrete plugs embedded in tubular steel piles under cyclic loading

Investigation of the load transfer of concrete plugs to tubular steel piles subjected to tension and compression and cyclic loading has been conducted at Monash University over the past 3 years. The work presented in this paper reports on the results of the combination of pull-out, push-out, and cyclic loading tests carried out on 15 steel tube specimens filled partially with reinforced concrete with variable lengths of embedment. The pull-out force was applied through steel reinforcing bars embedded in the concrete plug, and push-out forces were applied through a thick top circular plate on the top of the concrete plug. Test results included the cyclic loading, ultimate pull-out and push-out forces, slip of concrete plugs, and longitudinal and hoop strains along the piles for some specimens. The tests clearly showed that average bond strength significantly exceeds expectations and is higher than the results of previous investigations using plugs without reinforcement. The test results also indicated that cyclic loading tests reduced the bond strength due to the accumulation of damage to the plug–pile interface. The push-out and pull-out tests conducted under symmetric cyclic loading demonstrated that slip between the concrete plug and the steel tube increased with repeated loading, and the rate of slip growth increased with an increase in the peak load.Key words: tubular steel pile, reinforced concrete plug, bond, cyclic loading.

Three‐dimensional finite element analyses of passive pile behaviour

AbstractPiles may be subjected to lateral soil pressures as a result of lateral soil movements from nearby construction‐related activities such as embankment construction or excavation operations. Three‐dimensional finite element analyses have been carried out to investigate the response of a single pile when subjected to lateral soil movements. The pile and the soil were modelled using 20‐node quadrilateral brick elements with reduced integration. For compatibility between the soil–pile interface elements, 27‐node quadrilateral brick elements with reduced integration were used to model the soil around the pile adjacent to the soil–pile interface. A Mohr–Coulomb elastic–plastic constitutive model with large‐strain mode was assumed for the soil. The analyses indicate that the behaviour of the pile was significantly influenced by the pile flexibility, the magnitude of soil movement, the pile head boundary conditions, the shape of the soil movement profile and the thickness of the moving soil mass. Reasonable agreement is found between some existing published solutions and those developed herein. Copyright © 2005 John Wiley & Sons, Ltd.

Computer simulation of the dynamic layered soil–pile–structure interaction system

A three-dimensional finite element analysis of the soil–pile–structure interaction system is presented in this paper. The analysis is based on data from shaking table model tests made in the State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, China. The general finite element program ANSYS is used in the analysis. The surface-to-surface contact element is taken into consideration for the nonlinearity state of the soil–pile interface, and an equivalent linear model is used for soil behavior. A comparison of the results of the finite element analysis with the data from the shaking table tests is used to validate the computational model. Furthermore, the reliability of the test result is also verified by the simulation analysis. It shows that separation, closing, and sliding exist between the pile foundation and the soil. The distribution of the amplitude of strains in the pile, the amplitude of contact pressure, and the amplitude of sliding at the soil–pile interface are also discussed in detail in this paper.Key words: soil–pile–structure interaction, shaking table model test, computer simulation, ANSYS program.

Fiber Reinforced Polymer Composite–Wood Pile Interface Characterization by Push-Out Tests

Structural restoration of spliced or damaged wood piles with fiber reinforced polymer (FRP) composite shells requires that shear forces be transferred between the wood core and the encasing composite shells. When a repaired wood pile is loaded, shear stresses develop between the wood pile and the FRP composite shell through the grouting material. Alternatively, shear force transfer can be developed through mechanical connectors. The objective of this study was to characterize the interfaces in wood piles repaired with FRP composite shells and grout materials. Two interfaces were studied: wood pile/grout material and a grout material/innermost FRP composite shell. A set of design parameters that control the response of both interfaces was identified: (1) extent of reduction of cross section of wood pile due to deterioration (necking); (2) type of grout material (cement-based or polyurethane); (3) use of mechanical connectors; and (4) addition of frictional coating on the innermost shell. Push-out tests by compression loading were performed to characterize the interfaces and discriminate the effect of the design parameters. The outcome of the push-out tests was evaluation of the shear stress and force versus slip response and characterization of the failure mechanism. A set of repair systems that represent different combinations of the design parameters was fabricated and the interfaces evaluated. It was found that the combination of cement-based grout and polymer concrete overlay on the innermost shell provided the most efficient shear force-slip response. A simplified piecewise linear model of shear stress versus slip at the wood/grout and grout/FRP composite interfaces with and without mechanical connectors is proposed to synthesize the experimental response.

Three-dimensional finite element nonlinear dynamic analysis of pile groups for lateral transient and seismic excitations

The effects of material nonlinearity of soil and separation at the soil–pile interface on the dynamic behaviour of a single pile and pile groups are investigated. An advanced plasticity-based soil model, hierarchical single surface (HiSS), is incorporated in the finite element formulation. To simulate radiation effects, proper boundary conditions are used. The model and algorithm are verified with analytical results that are available for elastic and elastoplastic soil models. Analyses are performed for seismic excitation and for the load applied on the pile cap. For seismic analysis, both harmonic and transient excitations are considered. For loading on the pile cap, dynamic stiffness of the soil–pile system is derived and the effect of nonlinearity is investigated. The effects of spacing between piles are investigated, and it was found that the effect of soil nonlinearity on the seismic response is very much dependent on the frequency of excitation. For the loading on a pile cap, the nonlinearity increases the response for most of the frequencies of excitation while decreasing the dynamic stiffness of the soil–pile system.Key words: pile groups, plasticity, separation, dynamic stiffness, seismic response.

A study of the effect of driving on pre‐bored piles

AbstractA finite element model for pile‐driving analysis is developed and used to investigate the behaviour of pre‐bored piles, which are then driven the last 1.25 or 2.25 m to their final design depth. The study was conducted for the case of saturated clays. The model traces the penetration of the pile into the soil and accommodates for large deformations. The non‐linear behaviour of the clay in this study is predicted using the bounding‐surface‐plasticity model, as applied to isotropic cohesive soils. The details of the 3‐D numerical modelling and computational schemes are presented. A significant difference was observed in the pile displacement during driving, and in the computed soil resistance at the pile tip, particularly at the earliest driving stages. No difference in soil resistance at the soil pile interface along the pile shaft was detected between the pre‐bored piles whether driven 1.25 or 2.25 m. Copyright © 2002 John Wiley & Sons, Ltd.

Seal Slab/Steel Pile Interface Bond from Full-Scale Testing

In 1997, the Florida Department of Transportation (FDOT) funded a study to evaluate interface bond from full-scale tests. This paper presents results from model and full-scale tests to assess the interface bond between a cast-in-place concrete seal slab and steel H-piles in cofferdams, which are usually required in the construction of bridge foundations over waterways. Three seal slab placement conditions--freshwater, saltwater, and bentonite slurry--were evaluated and results compared against controls where no fluid was displaced by the concrete. The results show that significant bond stresses developed even in the worst placement condition. Recommendations made for revising current values in specifications have already been implemented by FDOT.

Structures à amortissement non classique: Caractérisation vibratoire par modes propres complexes

ABSTRACT Vibration analysis of damped structures cannot always be determined from the only real modes. Real structures generally involve different types of damping: various materials, local dampers (foundations, bridge pile interface…), soil-structure interaction… It is then often necessary to consider non proportional damping leading, with respect to modal approaches, to complex eigenvalues and eigenvectors. For a non classically damped structure, the modal features (eigenfrequencies, eigenmodes) depend on the mass and stiffness distribution, but also on the damping properties of the structure. This paper gives some theoretical information about non classical damping and complex modes estimation. It presents some comparisons between a standard modal approach (real modes) and a complex modes approach. These results show the great interest of the latter method for the vibratory characterization of non classically damped structures.

The Effects of Soil Yielding on Seismic Response of Single Piles

ABSTRACT In the seismic analysis of pile foundations the soil is often assumed to be an elastic material and the pressure at the soil pile interface is not limited during the analysis. This may result in a considerable error, as the computed pressure from an elastic analysis may go well beyond the ultimate lateral pressure of real soil. In fact, significant yielding at the soil-pile interface has been observed during real earthquakes, and also in laboratory tests. The yield zone is usually near the ground surface where the effect of inertial force due to the superstructure is higher. This yielding redefines the pile response, and in general cannot be ignored. In order to examine the effects of soil yielding on the internal pile response during earthquakes an approximate analysis is described in this paper which is an extension of a static method developed by the second author (1982) for the analysis of piles subjected to lateral soil movement. This method is then used to investigate the effects of soil yielding on the internal response of piles through a comparative study in which real earthquakes are used. It is shown that for strong earthquakes and heavily loaded piles the soil yielding may considerably increase the amount of maximum pile moment developed in the pile. A marked difference in the effects of yielding on the pile moment and shear is observed and discussed.

Cylindrical guided waves for inspection of clay-steel pile interface

The feasibility of detecting damage at the steel pile-clay interface using cylindrical guided waves is investigated in this paper. It is shown that cylindrical guided waves (or cylindrical Lamb waves) can easily detect such damage. A special coupler between the steel pile and ultrasonic transducer has been used to launch non-axisymmetric (or flexural) cylindrical guided waves in the steel pile. This investigation shows that the cylindrical guided waves can propagate along the steel pile embedded in clay and are sensitive to the interface damage between pile and clay.