Lateral Pile Research Articles

Geosynthetic-reinforced cushioned piles with controlled rocking for seismic safeguarding

In this study, a cushioned pile foundation reinforced with geosynthetics is proposed to protect buildings and foundations from seismic energy. This composite foundation utilises piles to control foundation settlement while the geosynthetic-reinforced cushion modifies the dynamic structural characteristics and the load transfer mechanism. The seismic performance of this proposed foundation system is evaluated numerically using FLAC3D software. A fully coupled nonlinear dynamic analysis was conducted in the time domain. The variation of shear modulus corresponding to shear strains in the soil is used to simulate the dynamic behaviour of the soil, while the influence of the plasticity index is also captured. The soil-geosynthetic interface utilises the Mohr-Coulomb failure criterion to capture possible sliding and pull-out of the reinforcement layers. 3D numerical predictions of the tensile forces mobilised in the geosynthetic layers, the shear forces, the lateral deformations and maximum and residual inter-storey drifts in the building are presented and discussed in this paper, as well as how the shear forces and bending moments develop in the piles, and the lateral pile displacements. The results indicate that the proposed geosynthetic-reinforced cushioned pile foundation can provide design engineers with an alternative solution for safeguarding buildings constructed on soft soils in earthquake-prone regions.

Bearing Characteristics of Composite Pile Group Foundations with Long and Short Piles under Lateral Loading in Loess Areas

It is very necessary to research the bearing characteristics of composite pile group foundations with long and short piles under lateral load in loess areas, because these foundations are used widely. But few people researched this problem in loess areas up to now worldwide. In this paper, firstly, an indoor test model of a composite pile foundation with long and short piles is designed and then employed to explore the vertical load bearing characteristics and load transfer mechanisms of a single pile, a four-pile group, and a nine-pile group under different lateral loads. Secondly, ANSYS software is employed to analyze the load-bearing characteristics of the test model, and for comparison with the experimental results. The results demonstrate the following. (1) The lateral force versus pile head displacement curves of the pile foundation exhibit an obvious steep drop in section, which is a typical feature of piercing damage. A horizontal displacement limit of the pile foundation is 10 mm and 6mm for the ones sensitive to horizontal displacement. (2) The axial force along a pile and frictional resistance do not coincide, due to significant variations and discontinuities in the collapsibility of loess; a pile body exhibits multiple neutral points. Therefore, composite pile groups including both long and short piles could potentially maximize the bearing capacity and reduce pile settlement. (3) The distribution of stress and strain along the pile length is mainly concentrated from the pile head to a depth of about 1/3 of the pile length. If the lateral load is too large, short piles undergo rotation about their longitudinal axis and long piles undergo flexural deformation. Therefore, the lateral bearing capacity mainly relies on the strength of the soil at the interface with the pile or the horizontal displacement of the pile head.

Variation in lateral load capacity of pile embedded near slope with ground inclination and edge distance

ABSTRACT There are many circumstances in which piles have to be provided on slopes. Experimental model tests in the laboratory have been undertaken to investigate the lateral pile response in sloping ground. The paper discusses about the investigation in a series of 22 laboratory tests in dense sand at 72% relative density. The main motive of the study was to examine the effect of slope angle and edge distance on the pile response. Ground slope was varied as 1V:1.5H, 1V:1.75H and 1V:2H for sloping ground condition. Pile response was obtained for seven different positions of pile from the crest of the slope for a specified relative density. Then pile response for horizontal ground condition was obtained for quantification of effect of sloping ground. Displacement and bending moments in the pile increased significantly when the ground surface changes from horizontal to slope. An increase in the edge distance from the slope crest causes reduction in the pile displacement and maximum bending moment.

Study on deformation influence of shield tunnel passing through existing railway bridge piles

Based on the rail transit of Xuzhou city and considering the actual engineering geological conditions, this paper studies the deformation effect of bridge piles across the railway bridge of shield tunnel. In this paper, the finite element numerical analysis software Midas GTS/NX is used to analyze the influence of the shield tunnel crossing bridge on the deformation of the bridge pile, and the change law of the displacement of the bridge pile under the condition of unreinforcement and reinforcement is obtained. The calculated results show that under the condition of no reinforcement, the settlement deformation of the bridge pile exceeds its own displacement limit due to the side crossing of shield tunnel. The reinforcement scheme of the bridge pile is used to enlarge the size of the original bearing platform section and add the foundation pile, and the simulation is carried out. The results show that the settlement of the bridge pile decreases significantly under the condition of reinforcement. The results prove the rationality of the reinforcement scheme to a certain extent, and provide a certain theoretical basis for the design of similar shield tunnel lateral pier pile.

Effect of geometric nonlinearity on the ultimate lateral resistance of piles in clay

In this note we investigate how the assumption of small deformations affects the estimation of the ultimate resistance to lateral pile movements in clay. For that we perform coupled hydro-mechanical finite element analyses, using the Modified Cam Clay model to describe soil behaviour. Validation of the numerical methodology via small-strain analyses is followed by an investigation on how the ultimate resistance diverges from exact plasticity solutions when large displacements are considered. Results suggest that the failure mechanism depends on the pile displacement required to mobilise the ultimate resistance, and that small-strain plasticity solutions provide upper bounds of the ultimate resistance.

Effect of excavation unloading on p-y curves for laterally loaded piles

Field test and numerical analysis were conducted to investigate the soil stress variation and lateral pile response to whole excavations from cone penetration tests (CPTs). The effects of excavation unloading on the performance of CPT cone resistances and p-y curves were examined. The p-y responses were related to the excavation-induced both stratigraphic variation and soil stress relief. Based on CPT profiles, the numerical calculations of the lateral pile responses before and after excavations were obtained and compared using a CPT-based p-y method. Finally, the suggestion on the design of laterally loaded piles considering excavation unloading was given.

Modelling and Assessment of a Single Pile Subjected to Lateral Load

Abstract A three-dimensional finite element technique was used to analyse single pile lateral response subjected to pure lateral load. The main objective of this study is to assess the influence of the pile slenderness ratio on the lateral behaviour of single pile. The lateral single pile response in this assessment considered both lateral pile displacement and lateral soil resistance. As a result, modified p-y curves for lateral single pile response were improved when taking into account the influence lateral load magnitudes, pile cross sectional shape and flexural rigidity of the pile. The finite element method includes linear elastic, Mohr-Coulomb and 16-nodes interface models to represent the pile behaviour, soil performance and interface element, respectively. It can be concluded that the lateral pile deformation and lateral soil resistance because of the lateral load are always influenced by lateral load intensity and soil type as well as a pile slenderness ratio (L/D). The pile under an intermediate and large amount of loading (in case of cohesionless soil) has more resistance (low lateral displacement) than the pile embedded on the cohesion soil. In addition, it can be observed that the square-shaped pile is able to resist the load by about 30% more than the circular pile. On the other hand, pile in cohesionless soil was less affected by the change in EI compared with that in cohesive soil.

TIME DEPENDENT INFLUENCE ON THE LATERAL RESPONSE OF SINGLE PILE SUBJECTED TO LATERAL LOAD

The time dependent response of the pile foundation can be categorized as one of the effective parameters that should be taken into account during analysis and design stage. From the literatures, very few reports are available on lateral response of the pile especially on the effect of soil type. It seems to be no exact solution for laterally loaded pile foundations in consolidating elasto-plastic soil to determine the design parameter such as maximum lateral pile displacement, ultimate lateral soil resistance and p-y relationship. Therefore, this study investigates the effect of soil type with different intensities of loading on the lateral pile deformation and lateral soil pressure with time. Finite element analysis is carried out to evaluate the lateral pile response embedded in cohesionless and cohesive soil subjected to pure lateral load. The simulation include linear elastic model to represent the pile structural material and Mohr-Coulomb elasto-plastic model to represent the surrounding soil. Biot’s equation of consolidation is used to govern the elasto-plastic material. The complete model of the whole geotechnical system are used to assess the lateral pile displacement and lateral soil pressure developed at pile face of 15m pile length and 1m pile diameter. It is shown that the lateral pile displacements increased and the lateral soil pressure was redistributed with time due to consolidation process.

Effect of Scour on the Natural Frequency Responses of the Meteorological Mast in the Taiwan Strait

The meteorological mast (met mast) for the Taiwan Power Company’s offshore wind farm is located in Taiwan Strait near Changhua County. The p–y curve method recommended in the current offshore foundation design codes does not account for the local scour around the pile foundation; it overestimates the lateral pile deformation and underestimates the foundation stiffness. This paper presents a method to correct the initial modulus of subgrade reaction and modify the ultimate lateral resistance caused by the local scour. The natural frequency of the met mast structure is also determined by a numerical model and verified with the measured data in situ. A comprehensive parameter study is performed to analyze the effect of scour on the dynamic responses of the met mast. Two types of foundation model, a coupled-springs foundation model and a distributed-springs foundation model, are considered in the dynamic analysis of the met mast. The results demonstrate that using a distributed-springs foundation model provides a relatively accurate estimate of the natural frequencies of the met mast structure. Furthermore, the scour exerted significant effects on certain modes of the vibration responses. The natural frequencies of the met mast structure can be reduced by approximately 14% due to scour, particularly in the horizontal bending modes. This paper also provides a preliminary strategy for structural monitoring and analysis to detect scour damage on offshore wind turbines with monopile foundations.

Three-Dimensional Response of Neighboring Buildings Sitting on Pile Foundations to Seismic Pounding

Seismic pounding occurs when the separation gap between buildings and structures is not wide enough, particularly during major earthquake events; this can cause them to collide, causing local damage or, in extreme cases, collapse. This study investigated the impact that this separation gap has on the seismic response of midrise buildings supported on piles while considering seismic soil–pile–structure interaction (SSPSI). To achieve this aim, three 15-story reinforced concrete buildings sitting on pile foundations and with five different separation gaps under excitations from the 1994 Northridge and 1995 Kobe earthquakes were numerically simulated. This study used three-dimensional numerical modeling to simultaneously capture the effects of seismic pounding and SSPSI. Because the considered structure, pile foundation, and soil deposit are three-dimensional in nature, the adopted three-dimensional numerical modeling can provide a more realistic simulation to capture the seismic behavior of the system. The nonlinear behavior of structural elements was included, and the dynamic soil properties were obtained from field data and backbone curves. A contact pair interface with small-sliding surface-to-surface formulation between buildings was used to capture possible seismic pounding, and contact interfaces with a finite-sliding formulation were used to simulate the interaction between the piles and the soil. The results, including lateral building deflections, interstory drifts, structural shear forces, foundation rocking, lateral pile deflections, and the distributions of bending moments and shear forces of the piles, are presented and discussed. The findings of this study will give engineers a better insight into the possible effects of seismic pounding on the seismic performance of buildings, and the response of end-bearing piles in soft soils.

Influence of sloping ground on lateral load capacity of single piles in clayey soil

In many practical situations, structures subject to lateral loading are located near slopes. The presence of a slope on deep foundations loaded in a downslope direction can decrease the overall lateral capacity of the system. In this paper, the effect of soil slope, undrained cohesion, pile–soil interface adhesion, pile diameter and pile cap on the lateral load carrying capacity of pile located at the crest of clay slope is studied using PLAXIS-3D. Clay is modelled as linearly elastic perfectly plastic Mohr–Coulomb material, whereas pile is modelled as a linear elastic material. Formation of gap on the extension side of pile–soil interface is also considered. Lateral load capacity of pile for a corresponding prescribed displacement of 5 mm is estimated. An equation to determine the value of lateral pile capacity in terms of undrained cohesion, pile diameter and pile–soil interface adhesion has been formulated from the results.

Modeling the lateral response of pile groups in cohesionless and cohesive soils

A three-dimensional finite element approach was used to assess the lateral pile and pile group response subjected to pure lateral load. The study evaluated three pile group configurations (i.e. 2 × 1, 2 × 2 and 3 × 2 pile groups) with four values of pile spacing (i.e. 2D, 4D, 6D and 8D, where D is the pile diameter). The results of the influence of load intensities, group configuration, pile spacing are discussed in terms of response of load vs. lateral displacement, load vs. soil resistance and corresponding p–y curves. The improved plots can be used for laterally loaded pile design and also to produce the group action design p-multiplier curves and equations. As a result, design curves were developed and applied in the actual case studies and similar expected cases for assessment of pile group behavior using improved p-multiplier. A design equation was derived from predicted design curves to be used in the evaluation of the lateral pile group action. The equation was used with the previous results to predict the expected design curve take in the account different source of p-multiplier. It was found that the group interaction effect led to reduced lateral resistance for the pile in the group relative to that for the single pile. In addition, the present study was compatible with the results of previous results for the first and second trailing row and was less compatible with the result from the previous works in the case of piles in leading row.

Numerical Analysis of Laterally Loaded Piles Affected by Bedrock Depth

This study investigates the lateral behavior of pile foundations socketed into bedrocks using 3D finite difference analysis. The lateral load‐displacement curve, pile deflection, and bending moment distribution were obtained for different bedrock depths between 3 and 20 m. It was discovered that bedrocks that have a depth of 7 m (7D) or less influence the lateral behavior of the pile. The p‐y curves were collected at depths of 2.0–4.5 m, and the effect of the bedrock on the curves was evaluated. It was observed that the p‐y curves were significantly affected by the material properties of the bedrock if the rock is located in close proximity (within 3D), but the effect is diminished if the p‐y curves were 3.5 m (3.5D) or farther from the bedrock.

Applicability of Timoshenko, Euler–Bernoulli and rigid beam theories in analysis of laterally loaded monopiles and piles

In various analytical, semi-analytical and numerical studies on laterally loaded piles, the pile is conventionally modelled as an Euler–Bernoulli beam. Modelling large-diameter monopiles and piles using the Euler–Bernoulli beam theory may not be appropriate, because the Euler–Bernoulli beam theory is strictly valid for long, slender piles and does not account for shear deformations, which may have a significant effect on the lateral pile response of large-diameter piles. In order to investigate the effect of shear deformation in the modelling of monopiles and piles, a framework for static analysis of laterally loaded piles is developed, in which the monopile/pile is modelled using the Timoshenko beam theory and the soil as an elastic continuum. A rational soil displacement field is assumed and the differential equations of pile and soil displacements are obtained using calculus of variations. Solutions are obtained analytically and numerically following an iterative scheme. The analysis framework also incorporates the Euler–Bernoulli and rigid beam theories as progressive simplifications of the Timoshenko beam theory. Pile responses obtained using the three beam theories are compared with three-dimensional finite-element analysis to establish the relative accuracies of each beam theory in predicting lateral pile response. Systematic parametric studies are performed to establish which beam theory is most appropriate to model laterally loaded monopiles and piles, particularly the large-diameter piles, and to find out the range of applicability of the different beam theories in predicting lateral pile response. The Timoshenko beam theory can be used for all cases of laterally loaded piles to produce the most accurate results, particularly for piles with hollow cross-sections. The Euler–Bernoulli beam theory produces accurate results for most piles with solid cross-sections. The rigid beam theory can be used for a quick initial estimate of pile head displacement, particularly for piles with high values of relative pile–soil stiffness ratio.

Horizontal Displacement Control in Course of Lateral Loading of a Pile in a Slope

Standard procedures concerning axial and lateral capacity testing of foundation piles usually consist of a single loading cycle. Constant load steps or constant settlement increments may be applied in the test. Such a procedure significantly differs from in-situ conditions of pile loading, which can be cyclic – especially in the case of the constructions, which are subject to wind load. Several tests were performed to observe the behaviour of the driven piles subject to fast cyclic loading in horizontal direction (lateral load). The manner in which the load tests were performed made it possible to determine the displacement of the 40×40 cm pile in the least favourable loading scheme, i.e. the lateral load capacity of the pile oriented towards the embankment slope. The piles were originally designed for the foundation of noise barriers along the highway. Some of the piles were broken in course of driving and a cautious check of their behaviour under load was requested before the assembling of the entire structure. Eight load tests were carried out altogether. While selecting the piles for further load tests, the representativeness of the random sample was taken into account. The piles with diverse cross section and length were chosen, on the basis of the previous low strain tests of their integrity. The subsoil around the piles consisted of medium and coarse sands with the density index ID>0.67. The pile heads were free. The points of support of the reference frame to which the sensors were fastened were located at the distance of 0.6 m from the side surface of the pile loaded laterally. In order to assure the independence of measurement, additional control (verifying) geodetic survey of the displacements of the piles subject to the load tests was carried out. The research conducted at Wroclaw University of Technology made it possible to collect and summarize the results of displacement measurements in course of static load testing of driven piles in a slope. Only selected case studies of cyclic loading in horizontal (lateral) pile load tests are presented in the paper.

3D Dynamic Finite Element Analyses and 1 g Shaking Table Tests on Seismic Performance of Connected and Nonconnected Piled Raft Foundations

Connected and disconnected piled raft foundations have been evaluated under lateral cyclic loading in this study. Connected Piled Raft (CPR) and nonconnected piled (NPR) foundations were considered and evaluated in 1-g shaking table tests. FEM numerical modelling also was employed to evaluate the results. The responses were evaluated and compared using lateral movement of caps, moments and lateral loads along the piles and ground settlements. The results indicate that both nonconnected and connected piled raft foundations effectively reduce the ground settlements, however, connected piled rafts have much higher lateral stiffness and piles contribute to lateral load bearing mechanism more effectively; in connected piled raft, piles bear higher moments and lateral loads and reduce lateral movements more effectively. The cap weight and superstructure (central mass height) effect has been considered through supplementary numerical assessments for CPR case. Superstructure addition tends to increase the pile moment and raft inclination where the frequency effect is also critically important. Also heavier cap experiences higher rotations and associated with higher induced loads to piles.

Response of full-scale piles to EPBM tunnelling in London Clay

The installation and working test performance of four full-scale instrumented driven piles and their subsequent response to twin tunnels constructed below the pile bases are described. One pair was designed to be largely friction piles and the other pair end-bearing. Their locations relative to the new tunnels were carefully chosen to optimise understanding of pile responses at varying offsets from the centre-lines. The site conditions and the greenfield response to earth pressure balance machine tunnelling at the site were described in a companion paper that reported an expanding displacement field around the tunnels rather than the contracting fields usually observed. The field monitoring results indicated that, during construction, zones of influence existed around tunnels, where the ground and piles were subjected to different degrees and senses of relative vertical displacement. Redistributions of load along the pile lengths occurred as the tunnel boring machines approached, passed beneath and continued beyond the pile bases; lateral pile deflections and bending moments were also induced. Based on the results from this field study, implications for the capacity of existing piles (and design of new piles) subjected to tunnelling-induced movements are assessed for cases of expanding and contracting displacement fields.

Lateral cyclic response of an aluminum model pile in sand

ABSTRACTLateral cyclic load tests were performed on an aluminum model pile in dry sand. Two levels of loading were adopted to represent different service load conditions. The maximum number of loading cycles was 1,000. From the test results, it was found that the even though in the service load condition, the pile response was still affected by cyclic effects and a larger load level would produce more significant influence. In a global point of view, the lateral displacement and maximum moment increased with loading cycles, while the secant stiffness within a cycle decreased with cycles. The cyclic effect was more significant on the lateral displacement than on the moment. In a local point of view, cyclic loading would degrade the equivalent subgrade stiffness for the soil shallower than about seven times diameter. In addition, the secant subgrade stiffness within a cycle increased with loading cycles. Some experimental relationships of lateral pile response and loading cycles were built and compared with those in the literature.

Wave-induced liquefaction of the seabed around a single pile considering pile–soil interaction

ABSTRACTThe analysis of wave-induced liquefaction of seabeds is of profound importance for offshore structures such as wind turbines and oil platforms. The seabed around pile foundations is subjected to two effects, vertical wave loads and the lateral pile–soil interactions induced by the rocking of super structures. This paper numerically studies the excess pore pressure responses of the seabed around a pile when both effects are considered. Numerical analysis is conducted using an in-house developed, effective stress-based, three-dimensional finite element code. The mechanical behaviors of the seabed are simulated by a kinematic hardening constitutive model that can describe the cyclic mobility of soils. Comparing the results of the seabed around a pile and the seabed with no pile foundation shows that the excess pore pressures accumulate faster when both of the effects are considered. Water depth plays an essential role in determining whether the effect of pile–soil interaction on excess pore pressures can be neglected. In deep waters, the excess pore pressure response mainly derives from the effect of the pile rocking, while the influence of vertical wave pressure on the seabed is relatively small. However, in shallow waters, both of the effects are significant.

Construction and verification of a unified p–y curve for laterally loaded piles

Estimation of the lateral pile load capacity is the key design procedure for structures where lateral loads are predominant, such as bridges, tall buildings and offshore platforms. In the process of laterally loaded pile design, the p–y curve method is the mainstream method and preferred by designers compared to the elastic continuum or finite element analysis. The traditional p–y curves are derived from some specific field tests and limited data, which do not reflect the overall conditions. In this study, a unified p–y curve based on the stress increment perspective was constructed by introducing Vesic cavity expansion theory and considering the actual stress state of the surrounding soils. The proposed p–y curve combines the contributions of the expansion-induced soil radial stress increment, vertical stress increment and lateral soil resistance caused by deep pile rotation. To validate the proposed method, case examples of lateral pile load tests in various soil conditions were prepared and used to compare the p–y curves from the test results and proposed methods. The p–y curves calculated from the proposed method show reasonable agreement with measured results and give a good prediction in large deformation analysis.