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Earthquake-induced soil liquefaction can cause soil settlement around piles, resulting in drag load and pile settlement after shaking stops. Estimating the axial load distribution and pile settlement is important for designing and evaluating the performance of axially loaded piles in liquefiable soils. Commonly used neutral plane solution methods model the liquefiable layer as an equivalent consolidating clay layer without considering the sequencing and pattern of excess pore pressure dissipation and soil settlement. Moreover, changes in the pile shaft and the tip resistance due to excess pore pressures are ignored. A TzQzLiq numerical model was developed using the existing TzLiq material and the new QzLiq material for modeling liquefaction-induced downdrag on piles. The model accounts for the change in the pile's shaft and tip capacity as free-field excess pore pressures develop or dissipate in soil. The developed numerical model was validated against data from a series of large centrifuge model tests, and the procedure for obtaining the necessary information and data from those is described. Additionally, a sensitivity study on TzLiq and QzLiq material properties was performed to study their effect on the developed drag load and pile settlement. Analysis results show that the proposed numerical model can reasonably predict the time histories of axial load distribution and settlement of axially loaded piles in liquefiable soils both during and postshaking. [ABSTRACT FROM AUTHOR]

The paper presents a generalised design approach for pile groups subjected to combined (V H M) loading. The Limit Equilibrium method is extended to pile groups under general planar loading, considering the axial load dependency of bending stiffness and strength of reinforced concrete (RC) piles. 3D failure envelopes are analytically derived for different layouts. The key simplifying assumptions are critically discussed, and the failure envelopes are verified against finite element (FE) analysis results. Key features of pile group response, such as plunging vs. non-plunging axial pile response and the role of transverse reinforcement, are identified and quantified. A key novelty of the proposed method lies on the consideration of coupling between the lateral–bending resistance of the piles. The method further incorporates well-recognised features of pile group response regarding the axial load dependency of bending moment capacity and stiffness of the RC piles. The latter results in redistribution of bending moments and shear forces along the piles of the group. These features allow the reproduction of key aspects observed in demanding FE simulations and centrifuge tests, regarding the ultimate resistance under V H M and in addition the load path dependent failure modes. The proposed method offers a practical engineering tool for preliminary design and optimisation. • Analytical failure envelopes of RC pile groups under combined VHM loading. • Full coupling between the lateral–bending resistance of the piles. • Axial load dependent bending moment capacity and stiffness of the RC piles. • Redistribution of bending moments and shear forces along the piles of the group. • Simple design method based on closed form expressions predicting failure modes. [ABSTRACT FROM AUTHOR]

During a high-magnitude earthquake, drag loads can be induced by liquefaction of soils, defined as the additional vertical load caused by the settlement after soil liquefaction around the pile due to yielding and volume decreasing in soft soils layers, causing a downdrag displacement. In several projects, the magnitude of these loads and settlements caused by downdrag in piles is not well defined. In this research, we advance towards estimating this drag loads and their impact on projects. For this purpose, a case study considering the 2010 Maule earthquake was analyzed, comparing methodologies of shaft loads against numerical modelling results using nonlinear finite element method, in order to estimate the range of settlement, shear stress at the soil-structure interface, the axial loading in the pile and the volumetric strain, among others. It can be demonstrated that the studied piles show downdrag with its consequently drag loads, which is shown as the effective mobilization in the surrounding soil of the southeast and northeast piles, with a strain of 0.2% and 0.1% respectively. These strains imply an additional shear stress in the soilstructure interface, with axial loadings of 45 and 36 ton respectively. [ABSTRACT FROM AUTHOR]

Pile-soil interaction has been a subject of interest to many earlier researchers. However, not much work has been done on the effects of structural response of single piles subjected to different combination of axial and lateral loads and hence the respective pile-soil interaction. The main objectives of this paper are to assess the influence of axial load intensities on the lateral single isolated pile response in various pile slenderness ratios. Three-dimensional finite element approach was used to simulate the whole geotechnical system. The finite element included linear elastic model to represent the pile, Mohr-Coulomb to model surrounded soil and 16-nodes interface element to simulate the pile-soil interface. It was found that the lateral deflection is increased with increased the axial load in case of cohesionless soils. While, in case of cohesive soil, reduction in lateral pile displacement is occurred when low axial load is applied (i.e. V less than 4H) and increased when axial load level (i.e. V more than 6H) has been increased. [ABSTRACT FROM AUTHOR]

In a recent study, the time-dependent increase in axial load resistance of steel H-piles driven into cohesive soils, due to setup, was systematically quantified using measured field data. A method to estimate the setup based on measurable soil properties was subsequently established. These studies highlighted that the uncertainties of the measurements of soil properties and thus the semi-empirical approach to estimate setup are significantly different from those of the methodology used for measuring the pile resistance during retaps at any time after the end of driving. Recognizing that the two sets of uncertainties should be addressed concurrently, this paper presents a procedure for determining the factored resistance of a pile with due consideration to setup in accordance with the load and resistance factor design that targets a specific reliability index. Using the first-order second-moment method, the suggested procedure not only provides a simplified approach to incorporate any form of setup in design, but it also produces comparable results to the computationally intensive first-order reliability method. Incorporating setup in design and construction control is further shown to reduce foundation costs and minimize retap requirements on piles, ultimately reducing the construction costs of pile foundations. [ABSTRACT FROM AUTHOR]

This paper presents the results of static compression load tests performed on long rock-socked bored piles installed in stratified soils. Three bored piles with 34 m in embedded length were instrumented in order to separate the shaft and base resistance, and to allow the determination of the distribution of shaft resistance along the pile shaft. Conventional methods of estimating shaft resistance were assessed. It was found that more than 78% of the shaft resistance was provided by shaft friction at the end of tests. The base resistance has not been fully mobilized in the test. The recommendations of Chinese technical code (JG94-2008) to estimate the shaft resistance were more conservative for long rock-socketed bored piles. Empirical correlations to estimate the shaft resistance are limited due to different geological conditions. The methods which incorporated parameters directly interpreted from standard penetration test (SPT) results provided the most consistent estimates. [ABSTRACT FROM AUTHOR]

Mobilization of negative skin friction (NSF) along a pile shaft increases the axial load (dragload) and pile head settlement (downdrag) of the pile, which may exceed the structural capacity of the pile and violate its serviceability performance, respectively. Therefore, the dragload estimation is essential for a pile embedded into a settling ground, where NSF is very likely to occur. This paper presents the results of a series of fully coupled consolidation numerical parametric studies of a pile embedded into a consolidating ground. The investigation focuses on the influences of pile geometry, ground compressibility, and loading condition on pile responses. The soil compressibility and time to apply the pile head load are found to have little influence on the degree of skin-friction mobilization in the long term. The long-term neutral plane (NP) lies within the 60-70% range of the pile embedded length when the pile head load is absent. The presence of a head load shifts NP upward, and the amount of upshift increases with decreasing pile diameter and length. A simple design chart is proposed to estimate the skin-friction distribution in the long term in cases where the pile head load is absent. Finally, an illustrative example is provided to demonstrate how the chart is used and performs. The study offers practicing engineers a simple and quick approach to estimating the dragload of a pile subject to NSF. [ABSTRACT FROM AUTHOR]

The analysis of piled raft foundations has improved over the last few decades to account for the combined contribution of raft and piles to provide a more efficient system. Unconnected piled raft foundation (UCPRF) is an economical and efficient system where the piles are separated from the raft by a structural fill cushion. The cushion acts to redistribute the load between raft and piles. In this study, ABAQUS finite element analysis software was used to investigate the load sharing capacity of the system. The effects of cushion, piles number, diameter, and length as well as raft thickness in reducing settlement were investigated. The study showed that UCPRF provides an economical alternative for a connected piled raft foundation subject to vertical axial loads. In the unconnected system, plain concrete piles are adequate, without the need of reinforcement, where their basic function is to strengthen the top and reduce the maximum settlements. [ABSTRACT FROM AUTHOR]

This paper presents a nonlinear stability analysis of piles under bilateral contact constraints imposed by a geological medium (soil or rock). To solve this contact problem, the paper proposes a general numerical methodology, based on the finite element method (FEM). In this context, a geometrically nonlinear beam-column element is used to model the pile while the geological medium can be idealized as discrete (spring) or continuum (Winkler and Pasternak) foundation elements. Foundation elements are supposed to react under tension and compression, so during the deformation process the structural elements are subjected to bilateral contact constraints. The errors along the equilibrium paths are minimized and the convoluted nonlinear equilibrium paths are made traceable through the use of an updated Lagrangian formulation and a Newton-Raphson scheme working with the generalized displacement technique. The study offers stability analyses of three problems involving piles under bilateral contact constraints. The analyses show that in the evaluation of critical loads a great influence is wielded by the instability modes. Also, the structural system stiffness can be highly influenced by the representative model of the soil. [ABSTRACT FROM AUTHOR]

Jetting is a technique commonly used to install well conductors, which is faster than the conventional drill and cement method. Conductors are designed to support the buoyed weight of the first string of casings (typically, 3-5 days after jetting) and later to provide the lateral stability for the well system against cyclic loading from environmental elements. The axial bearing capacity of a jetted conductor increases with time due to consolidation and thixotropy effects; however, the field data for set-up only extend to about 10 days. Installation of jetted conductors as piles and anchors may be an economic solution for offshore developments. The long-term axial capacity of jetted conductors was investigated through a series of centrifuge modelling and laboratory thixotropy testing. The centrifuge tests simulated jetting installation of four model conductors and measured capacities at set-up times ranging between 10 and 1000 days in a kaolin clay seabed with an undrained shear strength profile similar to that encountered in deepwater Gulf of Mexico. The centrifuge test results were compared to the field data in the Gulf of Mexico. The implications of the centrifuge test results for deepwater Gulf of Mexico conditions are discussed. A method is presented for estimating the long-term axial capacity of jetted conductors in Gulf of Mexico seabed conditions with recommendations for additional studies. [ABSTRACT FROM AUTHOR]

This paper presents the effect of surcharge support pressure on pile load-settlement response during static load testing. A three-dimensional nonlinear finite-element model is developed to investigate the loading sequences of an axial compressive static load test, using surcharge loads as the reaction system. Results of a static load test at a construction site for which the geotechnical data are available were used for verification of the numerical model. The results show that the surcharge pressure on supports has little impact on the ultimate capacity of the pile, as the shaft skin friction is slightly influenced by the surcharge and the effect on the tip resistance is negligibly small. The initial stiffness of the pile, however, might be considerably affected by the surcharge pressure distributed around the pile shaft. The influence on stiffness increases with increase in the pile diameter. The effect of surcharge pressure is more pronounced for piles embedded in frictional soils compared with cohesive soils. Comparing the results with those available in the literature for pile testing using the reaction pile system shows that the pile stiffness is 15 to 25% less affected in the surcharge reaction system. [ABSTRACT FROM AUTHOR]

This paper presents an analytical solution developed to describe the dynamic interaction between a single end-bearing pile subjected to a dynamic axial load on its head, and its surrounding poroelastic soil. The main feature of the solution is that both the two-phase soil and the pile are treated as three-dimensional continua. This allows capturing the propagation of compressional and shear waves in three dimensions, and their effect on pile response. The soil surrounding the pile is treated as porous medium and its response is described with Biot's poroelastic theory, while the pile is treated as linear elastic solid, considering explicitly both vertical and radial pile displacements. The solution yields expressions for the displacement and velocity admittance at the pile head in the frequency domain, and allows computing pile head velocity time histories. These are applied to study the effects of wave propagation in three dimensions on pile response in the frequency- and in the time-domain, and identify the conditions under which these effects may be important for the analysis of piles in practice. [ABSTRACT FROM AUTHOR]

Torsional loads on pile foundations are induced by the action of eccentric horizontal forces on the supporting structures. Such loading not only initiates twisting at the pile head but also reduces its axial capacity significantly with increased settlement of the foundation. Several theoretical and experimental investigations have already been carried out on piles under torsional load, as evidenced by the available literature on the subject, although contributions on the influence of combined torsional and axial loads on pile foundations are rather limited. This paper presents a novel numerical model (boundary-element method) to analyze the response of a single vertical floating pile subjected to simultaneous torsional and axial loads. The nonlinear stress-strain response of soil has been incorporated in the model by means of the hyperbolic model, whereas the pile material has been idealized as elastic-perfectly plastic. The effect of progressive pile-soil slippage at the interface is considered. Apart from predicting the load-displacement response and incremental angle of twist of piles under combined torsional and axial loading, the shear-stress profiles and the effect of vertical loads on the torsional capacity of the piles are some of the salient features captured by the proposed model. Validation of the proposed model by means of a comparison with existing models and experimental data indicates the suitability and accuracy of the solutions developed. The proposed model is also applied successfully to selected case studies on piles in clay, sand, and layered soil, and important conclusions are drawn. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

By using the axisymmetric quasi-lower bound finite-element limit analysis, the bearing capacity factors and have been computed for axially loaded piles, with the shaft embedded in a fully cohesive soil medium and the tip placed over cohesive frictional soil strata. The results were obtained for various combinations of , , and ; the subscripts and refer to lower and upper soil strata, respectively. The factors and increase continuously with increases in and ; the rate of increase of and with , however, decreases with an increase in . For , the factor hardly depends on . [ABSTRACT FROM AUTHOR]

The shaft friction capacity of a piled foundation is commonly linked to the effective stresses acting on the pile, and hence it is assumed that if the surrounding soil liquefies following an earthquake event, the shaft friction capacity of a pile drops to zero. In this paper an investigation into the axial load transfer during a liquefaction event based on dynamic centrifuge test results is presented. A free-standing pile group with the pile cap clear of the ground surface is considered, to clarify the mechanism of load transfer. The pile group was instrumented to measure axial loading at several locations along the pile length, and was embedded in a saturated soil profile where a dense permeable base layer was overlain by a layer of loose, liquefiable sand. The results show that shaft friction continues to be maintained during an earthquake in both loose and dense soil. In the case of loose soils, the apparent shaft friction capacity is proposed with reference to the shear taking place at the pile/soil interface, which causes a local reduction in the pore pressures. [ABSTRACT FROM AUTHOR]

In the design practice for sand compaction piles (SCPs), it is usually assumed that the state of in situ soil does not change during installation. In fact, there is evidence to suggest that extensive remolding of the preferred soil fabric can occur within the zone immediately surrounding the SCP during its installation. Properties of the soil within this heavily disturbed zone can effect pore pressure dissipation and hence the time after which the ultimate strength of the composite ground is available. In this study, the effect of the smear zone around SCPs is modeled using triaxial tests. SCPs of 25-80 mm diameter were installed in 100-mm-diameter cylindrical samples. The sand columns were installed by predrilling a hole and then backfilling it with well-compacted sand. The smear zone was created by using a rough casing to drill the hole. The effect of the smear zone on SCP was investigated by observing the change in pore pressure during consolidation and undrained shear strength of the composite ground. Although both the shear-induced pore pressures and the undrained shear strength of the composite samples could reasonable be predicted, wide scatter still existed in the relationship between the stress concentration factor and the area replacement ratio. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Offshore piles are subjected to complex loading regimes that include both rapidly applied static and cyclic loads. This paper describes an experimental investigation conducted to assess the factors influencing the response of offshore piles to these loading conditions. The tests were performed using instrumented model piles installed in soft clay. During cyclic loading, the piles demonstrated a transition from stable to unstable behavior when the applied loads reached a specific load threshold. Stable behavior was defined when increments of plastic displacement decreased as the number of load cycles increased. During stable behavior, radial effective stresses at the pile-soil interface remained constant. During unstable behavior, pore pressures at the pile-soil interface rose as the number of cycles increased. This resulted in reduced radial effective stresses and progressively increasing displacement rates. Because of the presence of these excess pore pressures, the shaft resistance recorded during static load tests, performed after unstable cyclic loading, were lower than those measured on piles where the pore pressure was fully equalized. However, the axial resistance was seen to be rate dependent. Fast loading of the pile resulted in reductions of pore water pressure at the soil-pile interface and enhanced shaft resistance, which might overcome the negative effect caused by cyclic loading. [ABSTRACT FROM AUTHOR]

Piles composed of more than one material in their cross section have been used for more than 100 years. Originally this was limited to driven steel shell or pipe piles filled with portland-cement concrete. More recent developments include various types of drilled elements such as micropiles that consist of various combinations of steel shells, portland-cement grout, and steel reinforcing bars. The structural analysis or design of piles with multicomponent cross sections under axial load requires that the axial stress be apportioned to the various components. Traditionally this has been done using an approximate one-dimensional model that implies the components interact with each other only axially, not radially, and that there is no radial interaction with the ground around the pile. This note presents a new three-dimensional model that explicitly and rigorously considers not only the Poisson effects caused by axial load and the triaxial stress field that develops within and between components of a pile as a result but also how this stress field is affected by radial stresses in the adjacent ground. This new model is based on the theory of linear elasticity and yields a closed-form solution that can be either evaluated independently or incorporated within a more general analytical model for axial pile capacity. Examples of calculated results obtained using this new model are presented and suggest that Poisson effects are relatively small in magnitude so that the traditional one-dimensional model is adequate for routine use in most cases. [ABSTRACT FROM AUTHOR]

Most of the current design methods for driven piles were developed for closed-ended pipe piles driven in either pure clay or clean sand. These methods are sometimes used for H piles as well, even though the axial load response of H piles is different from that of pipe piles. Furthermore, in reality, soil profiles often consist of multiple layers of soils that may contain sand, clay, silt or a mixture of these three particle sizes. Therefore, accurate prediction of the ultimate bearing capacity of H piles driven in a mixed soil is very challenging. In addition, although results of well documented load tests on pipe piles are available, the literature contains limited information on the design of H piles. Most of the current design methods for driven piles do not provide specific recommendations for H piles. In order to evaluate the static load response of an H pile, fully instrumented axial load tests were performed on an H pile (HP 310×110) driven into a multilayered soil profile consisting of soils composed of various amounts of clay, silt and sand. The base of the H pile was embedded in a very dense nonplastic silt layer overlying a clay layer. This paper presents the results of the laboratory tests performed to characterize the soil profile and of the pile load tests. It also compares the measured pile resistances with those predicted with soil property- and in situ test-based methods. [ABSTRACT FROM AUTHOR]

Tapered piles in comparison to cylindrical piles can be beneficial in terms of the load capacity. In this paper, estimation of the load capacity for tapered piles using cone penetration test (CPT) resistance was investigated. Fourteen calibration chamber load tests using different pile types and six CPTs were conducted under various soil conditions. From the calibration chamber test results, the total, base, and shaft load capacities were analyzed in terms of soil conditions and taper angle. To evaluate CPT-based load capacity of tapered piles, normalized base and shaft resistances were obtained from normalized unit load-settlement curves. Based on the normalized base and shaft resistances, design equations that can be used to evaluate the base and shaft resistances of tapered piles were proposed. The proposed method is valid for sands of medium to dense conditions, while it may result in unconservative predictions for loose sands. To check the accuracy of the proposed method, field load tests using both cylindrical and tapered piles were conducted and compared with the predictions using the proposed method. A simplified approach using an equivalent cylindrical pile was also investigated and compared. [ABSTRACT FROM AUTHOR]

The capacity of a pile-soil system can be obtained by pushover analysis using the beam-on-nonlinear-Winkler foundation model. When the pile section enters the plastic state, the plastic hinge method is usually adopted to model its postyielding flexural behavior. The propagation of the plastic zone in a pile can be traced using a series of plastic hinges distributed along the pile that is embedded in the soil. This study proposes a proper model for arranging the distributed plastic hinges along the depths of the pile that are prone to yielding. A modified definition of plastic curvature is proposed herein in order to correctly simulate the nonlinear flexural behavior of a pile. Examples are presented to show the effectiveness of the proposed model. [ABSTRACT FROM AUTHOR]

Dynamic centrifuge modelling has been used to observe amplification of lateral displacements and unstable collapse in pile groups under the action of significant axial load and in liquefiable soils with low stiffness. The popular pseudostatic non-linear p-y analysis method has here been developed to account for such instability effects using the Riks post-buckling analysis method, here implemented in ABAQUS. The numerical method was validated against centrifuge model tests presented in the companion paper and pre-collapse amplification effects and collapse loads were found to be well predicted. The model was extended to examine the response of 2 × 2 pile groups formed from 0·5 m diameter piles with bending properties typical of steel and reinforced concrete and with initial deflections indicative of those that may occur during lateral spreading as a result of strong shaking. These analyses demonstrated the vulnerability of the flexible concrete piles to significant amplification and unstable collapse even at moderate loads, while for the stiffer and stronger steel piles, amplifications are only 10-20% even at maximum typical working loads, and therefore practically negligible in the design of piles in liquefiable soils. [ABSTRACT FROM AUTHOR]

Current research work into the behaviour of piled foundations in liquefiable soils has concentrated on the response to lateral inertial and kinematic loads. It has recently been demonstrated in the literature, however, that an alternative mechanism exists, whereby piles carrying significant axial loads may become unstable as lateral soil restraint is lost owing to earthquake-induced soil liquefaction. In the work presented here and in a companion paper, this effect is examined in greater depth, particularly regarding the integration with and effects on the lateral response of piles such that the two effects can be treated under a unified framework. Dynamic centrifuge testing was used to investigate pile instability by examining the behaviour of pile groups with lateral deflections. Amplification of these deflections was observed to occur during liquefaction, although currently available simple idealisations of soil behaviour were found greatly to over-predict these amplifications when compared with the experimental observations. The response of the soil to such large-deformation events was determined for use in more sophisticated numerical modelling presented in the companion paper. Relative pile-soil flexibility was found to have a strong influence on amplifications occurring in the tests. Ultimately, at high axial load or amplification, unstable collapse (bifurcation) was found to occur both during earthquake shaking, and afterwards owing to excess pore pressure migration altering the strength of the supporting soil surrounding the piles. [ABSTRACT FROM AUTHOR]

The paper examines, using numerical modelling, the problem of the limit shaft resistance of non-displacement piles installed in sands. The modelling makes use of an advanced, two-surface-plasticity constitutive model. The constitutive model predicts the soil response in both the small- and the large-strain range, while taking into account the effects of the intermediate principal effective stress and of the inherent anisotropy of the sand. Finite element analyses of shearing along the pile shaft are performed in order to examine the development of limit unit shaft resistance and the changes in stress state around the shaft upon axial loading of the pile. Special focus is placed on the operative value of the lateral earth pressure coefficient when limit shaft resistance is reached. The analyses offer useful insights regarding the factors controlling the value of unit shaft resistance in sands. The simulations predict a significant build-up of horizontal effective stress for dense sands. Based on these simulations, we propose a relationship between the lateral earth pressure coefficient for use in the calculation of the limit shaft resistance of the pile and the initial density and stress state of the sand. [ABSTRACT FROM AUTHOR]

This paper considers load transfer from an axially loaded long elastic bar into a multilayered poroelastic half-space. The problem is analyzed by decomposing the bar-half-space system into an extended half-space governed by Biot’s theory of poroelasticity and a one-dimensional fictitious bar. The interaction problem is formulated in the Laplace transform domain. Vertical displacement of the bar is approximated by an exponential series with a set of arbitrary functions. The arbitrary functions are determined by using a variational method. The vertical displacement influence function of a multilayered half-space subjected to a buried uniform vertical patch load is required in the variational formulation. The required influence function is obtained by employing a previously developed exact stiffness matrix method. Time domain solutions are computed by using a numerical Laplace inversion scheme. Selected numerical results are presented to portray the influence of the bar length–radius ratio, layer configuration, poroelastic material parameters, and loading time history on the time dependent response of a bar. [ABSTRACT FROM AUTHOR]

The paper presents the results of a series of field tests performed to study the causes of friction fatigue experienced by displacement piles. Four instrumented model piles were installed at a dense sand test-bed site. The test series was designed to impose different levels of cyclic loading during pile installation. Static and cyclic load tests were subsequently performed to study the differences in the axial capacities developed for ostensibly monotonic and cyclic installations. The test results indicated that the mobilized horizontal effective stress regime that controls pile side friction primarily depends on the in situ sand state, as reflected by the cone penetration test (CPT) qc resistance. A zone of highly stressed sand that produced a concentration of high shear resistance was mobilized in the vicinity of the pile base. The horizontal effective stress that acted on the pile shaft reduced in response to cyclic loading, with the largest reductions occurring for high-intensity cyclic loading or when the pile had experienced only a few load cycles during installation. Although cyclic loading caused a reduction in the horizontal effective stress that acted on the pile shaft, the elevated stress built up in the vicinity of the pile base during installation remained higher than that remote from the base. The elevated stress in the vicinity of the pile base only dissipated after cyclic tension loading had been applied. [ABSTRACT FROM AUTHOR]

The article explores the shear performance of bored tapered piles in Melbourne mudstone. The shear performance has been evaluated numerically in order to assess their feasibility against cylindrical piles. It was discovered that taper has a significant advantage for axial load capacity as compared to cylindrical piles.

Piles driven into clay are often subjected to indirect loading as a result of the surcharge applied on the surrounding area. During the drained period, both the piles and the soil undergo downward movements caused by the axial and the surcharge loading, respectively. Depending on the relative movement of the pile–soil system, positive and negative skin friction develop on the pile’s shaft. Negative skin friction is the drag force that may be large enough to reduce the pile capacity and/or to overstress the pile’s material causing fractures or perhaps structural failure of the pile, and/or possibly pulling out the pile from the cap. A numerical model that uses the finite element technique combined with the soil responses according to Mohr–Coulomb criteria was developed for case simulation. The computer program CRISP (developed by Cambridge University) was used in this study. The numerical model was first tested against the results predicted by the bearing capacity theories for pile foundations in clay subjected to axial loading. Upon achieving satisfactory results, the numerical model was then used to generate data for piles subjected to surcharge loading. The predicted values were compared well with the field data and the empirical formulae available in the literature. Based on the results of the present investigation, design charts and procedures are presented to predict the location of the neutral plane and to estimate the drag force acting on the pile’s shaft for a given pile–soil–loading conditions. In the case of excessive drag force, coating the pile’s shaft with a thin layer of bitumen is advisable to eliminate or minimize the drag force. The design procedure presented herein would provide the means to establish the need and the extent of the pile coating. Furthermore, it demonstrates the role of the factor of safety on both pile capacity and the depth of the neutral plane. [ABSTRACT FROM AUTHOR]

Piles used for jacket type foundation of offshore wind turbine are subjected to highly cyclic tension and compressive loading. The pile capacity under cyclic tension loading decreases with increased number of loading cycles due to reduction of the pile shaft resistance. A numerical simulation scheme is presented, which allows the calculation of the pile capacity degradation (CDM) due to cyclic loading for driven steel piles. The volume compaction of soil near the pile surface during the cyclic loading is determined from the cyclic simple shear test results and then applied to the pile-soil system. From the limited number of tests available, interaction diagrams have been developed, which give the number of load cycles leading to failure dependent on the mean load and the amplitude of the cyclic load portion, which are both related to the static pile capacity. However, such diagrams cannot account for different soil conditions or pile geometry and pile stiffness. The calculation results for different piles in sandy soil under cyclic axial loading are presented and compared with existing interaction diagrams. Finally, recommendations regarding further investigations and improvements of the method are given. [ABSTRACT FROM AUTHOR]