Force Of Pile Research Articles

The influence of tunnelling on the behaviour of pre-existing piled foundations in weathered soil

A series of three-dimensional (3D) parametric finite element analyses have been performed to study the influence of the relative locations of pile tips with regards to the tunnel position on the behaviour of single piles and pile groups to adjacent tunnelling in weathered soil. When the pile tips are inside the influence zone, which considers the relative pile tip location with respect to the tunnel position, tunnelling-induced pile head settlements are larger than those computed from the Greenfield condition. However, when the pile tips are outside the influence zone, a reverse trend is obtained. When the pile tips are inside the influence zone, the tunnelling-induced tensile pile forces mobilised, but when the pile tips are outside the influence zone, compressive pile forces are induced because of tunnelling, depending on the shear stress transfer mechanism at the pile-soil interface. For piles connected to a cap, tensile and compressive forces are mobilised at the top of the centre and side piles, respectively. It has been shown that the increases in the tunnelling-induced pile head settlements have resulted in reductions of the apparent factor of safety up to approximately 43% when the pile tips are inside the influence zone, therefore severely affecting the serviceability of the piles. The pile behaviour, when considering the location of the pile tips with regards to the tunnel, has been analysed in great detail by taking the tunnelling-induced pile head settlements, axial pile forces, apparent factor of safety of the piles and shear transfer mechanism into account.

Downdrag Force Analysis for Seismic Soil–Pile–Structure Interaction

Earthquake can cause settlement of soil being greater than that of the pile. The pile is pulled down by the soil, and negative friction force is produced on the pile side. The carrying capacity of pile will be reduced because of the negative friction force, which may cause engineering instability. In this paper, the nonlinear and finite difference program FLAC3D was used to evaluate the mechanical behavior of soil–pile interaction under seismic dynamic loading. The response of the pile side friction force, pile axial force, and soil deformation to the seismic loading were analyzed. The distribution of the negative and positive pile side friction forces, the axial force of pile were found to be varied during the period of applying seismic loading. In addition, it was observed that seismic loading had a significant effect on the vertical and horizontal displacement of soil, and the variations of which with the duration of seismic loading were non-monotonic. An increase or a decrease in soil deformation induced by seismic loading appeared alternately due to the alternate dominant function of compression effect and stretching effect.

Study of the progressive collapse mechanism of excavations retained by cantilever contiguous piles

Abstract An increasing number of catastrophic progressive collapses of deep excavations have occurred throughout the world. However, the mechanism by which partial failures evolve into large-scale progressive collapses has rarely been studied. In this paper, long-strip excavations and square excavations retained by cantilever contiguous piles under partial failure were simulated using the explicit finite difference method (FDM). The results show that a partial collapse can cause sharp increases in the internal forces in adjacent intact piles through the horizontal arching effect. Therefore, the concept of a load transfer coefficient is proposed, which is equal to the ratio of increase of the internal force in an intact pile. The relationship between the maximum load transfer coefficient Tmax and the safety factor of the piles determines whether progressive collapse will occur. Furthermore, the influences of a number of important factors on the load transfer mechanism, such as the capping beam, the extent of partial failure, the soil strength, the excavation depth and the corner effect, were examined. A continuous capping beam can reduce the maximum load transfer coefficient Tmax. Within a certain range of the extent of partial collapse, a larger partial collapse extent will produce larger load transfer coefficients and have a greater influence over a larger area. For the same retaining structure, a higher soil strength will result in larger load transfer coefficients. Moreover, when the lateral stiffness of the retaining piles is lower, the maximum load transfer coefficient will be smaller and the range of influence will be larger. In an excavation with a corner effect, when the number of failed piles is above a certain threshold, the maximum load transfer coefficient decreases with an increasing number of failed piles. Therefore, the progressive collapse evolving toward the corner will terminate when the maximum load transfer coefficient decreases below the safety factor. The corner effect can be recognized as a cause of the natural termination of progressive collapse.

Centrifuge modeling of batter pile foundations under earthquake excitation

Although batter pile foundations are widely used in civil engineering structures, their behavior under seismic loadings is not yet thoroughly understood. This paper provides insights about the differences in the behavior of batter and vertical piles under seismic soil-pile-superstructure interaction. An experimental dynamic centrifuge program is presented, where the influences of the base shaking signal and the height of the gravity center of the superstructure are investigated. Various seismic responses are analyzed (displacement and rotation of the pile cap, total shear force at the pile cap level, overturning moment, residual bending moment, total bending moment and axial forces in piles). It is found that in certain cases batter piles play a beneficial role on the seismic behavior of the pile foundation system. The performance of batter piles depends not only on the characteristics of the earthquakes (frequency content and amplitude) but also on the type of superstructures they support. This novel experimental work provides a new experimental database to better understand the behavior of batter pile foundations in seismic regions.

Numerical investigations of pile load distribution in pile group foundation subjected to vertical load and large moment

This paper presents a numerical study of pile force distribution in a pile group foundation subjected to vertical load and large moment. The physical modeling of a pile foundation for a wind turbine is analyzed using 3D finite element software, PLAXIS 3D. The soil profile consists of several clay layers, which are modeled as Mohr-Coulomb material in an undrained condition. The piles in the pile group foundation are modeled as special elements called embedded pile elements. To model the problem of a pile group foundation, a small gap is created between the pile cap and underlying soil. The pile cap is modeled as a rigid plate element connected to each pile by a hinge. As a result, applied vertical load and large moment are transferred only to piles without any load sharing to underlying soil. Results of the study focus on pile load distribution for the square shape of a pile group foundation. Mathematical expression is proposed to describe pile force distribution for the cases of vertical load and large moment and purely vertical load.

Effect of in-situ variability of soil on seismic design of piled raft supported structure incorporating dynamic soil-structure-interaction

Inherent variability of soil considerably affects the seismic design of piled raft supported structures. Conventional design of such structure adopts fixity at base level of superstructure and pile head. However, soil–pile–superstructure interaction largely affects the fundamental frequency and design forces in columns and piles. In contrast, fixed base assumption cannot capture soil structure interaction (SSI) effect. In addition, uncertainty in soil may further leads to a change in the dynamic behavior of the system. This study examines the effect of inherent variability of undrained shear strength of soil in seismic design of structures supported by piled raft foundation embedded in soft clay. Superstructure is modeled as lumped mass stick model and piled raft slab is modeled as rigid plate. Pile is modeled as Euler–Bernoulli beam element and soil resistance is modeled using linear Winkler springs attached to the pile. Dynamic analysis is carried out in time domain to estimate the responses. Monte Carlo simulation technique is used for probabilistic assessment of the fundamental frequency and forces at column and pile attributing a wide range of parametric variation of a representative soil–piled raft–superstructure system. The study shows that the fundamental frequency and forces in column and pile changes significantly due to soil variability.

Centrifuge tests of axially loaded piles in consolidating soil

Axially loaded piles installed in layered soils where the upper soil layer is still consolidating are subjected to the combined interactive action of axial load and drag load. The shift of the location of the neutral plane as a result of the interaction of the axial load and drag load leads to the possibility that such piles need not account for the negative skin friction in determining the maximum pile force for the pile structural design. The results of a series of centrifuge tests on axially loaded piles in consolidating layered soil are presented so that the effect of negative skin friction on pile settlements and locations of the neutral plane of such piles can be better understood. The criteria regarding whether negative skin friction needs to be accounted for in determining the maximum pile force for the pile structural design are established in the present study based on centrifuge test results and findings reported in the literature.

A theoretical analysis of the bearing performance of vertically loaded large-diameter pipe pile groups

This paper aims to present a theoretical method to study the bearing performance of vertically loaded large-diameter pipe pile groups. The interactions between group piles result in different bearing performance of both a single pile and pile groups. Considering the pile group effect and the skin friction from both outer and inner soils, an analytical solution is developed to calculate the settlement and axial force in large-diameter pipe pile groups. The analytical solution was verified by centrifuge and field testing results. An extensive parametric analysis was performed to study the bearing performance of the pipe pile groups. The results reveal that the axial forces in group piles are not the same. The larger the distance from central pile, the larger the axial force. The axial force in the central pile is the smallest, while that in corner piles is the largest. The axial force on the top of the corner piles decreases while that in the central pile increases with increasing of pile spacing and decreasing of pile length. The axial force in side piles varies little with the variations of pile spacing, pile length, and shear modulus of the soil and is approximately equal to the average load shared by one pile. For a pile group, the larger the pile length is, the larger the influence radius is. As a result, the pile group effect is more apparent for a larger pile length. The settlement of pile groups decreases with increasing of the pile number in the group and the shear modulus of the underlying soil.

Numerical Study of High Speed Railway Subgrade Settlement Induced by Underwater Lowering

Groundwater lowering has brought a great impact on high speed railway. It has developed a measurable regional settlement of subgrade and also made a negative impact on piles under subgrade. In this paper, two structure types, namely P-R structure and P-N structure under subgrade have been considered at different groundwater lowering rates. Plaxis 3D is employed to assess subgrade center point's settlement, piles’ negative skin friction, increment of skin friction in piles and piles’ axial force. From the results, we can figure that groundwater lowering indeed has a negative impact on subgrade and the maximum negative skin friction of piles can increases up to 30-40 kN/m. The axial force in piles can be twice as initial conditions.

Comparison of slope stabilization methods by three-dimensional finite element analysis

Man-made factors take an important place in the formation of landslides besides the natural events. Road constructions, establishing new residential areas and interfering natural drainage systems are some of the common reasons that cause landslides. A slope on an intercity road construction site in the western Black Sea region, Turkey, is selected for this study due to the presence of small-scale soil movements, rock falls, tension cracks and occurrence of landslides in the neighborhood. The study area is investigated at three different profiles based on the topography. Slope stability analyses are carried out on these profiles by three-dimensional finite element analyses. As the results of analysis critic levels of the factor of safety and the high soil movements are estimated for one of the profiles. There are a couple of methods developed to prevent potential landslides, ceasing soil movements and securing the construction zones. Stabilizing slopes with piles are widely being used to enhance slope stability of landslide-prone areas. In this study, the behavior of stabilizing piles with and without lateral support is investigated. The bending moments and shear forces of piles and the maximum soil displacements are estimated to evaluate the performance of pile-stabilized slopes. Slope angle reduction is being performed as a remediation option, and an optimal solution is proposed after comparing the result of the analyses.

말뚝의 횡방향 이격거리를 고려한 터널굴착이 인접 단독말뚝 및 군말뚝에 미치는 영향에 대한 연구

ABSTRACT: In the present work, a number of three-dimensional (3D) parametric numerical analyses have been carried out to study the influence of tunnelling on the behaviour of adjacent piles considering the transverse distance of the pile tip fro m the tunnel. Single piles and 5×5 piles inside a group with a spacing of 2.5d were considered, where d is the pile diameter. In the numerical modelling, several key issues, such as the tunnelling-induced pile settlements, the interface shear stresses, the relative shear displacements, the axial pile forces, the apparent factors of safety and zone of influence have been rigorously analysed. It has been found that when the piles are inside the influence zone, the pile head settlements are increas ed up to about 111% compared to those computed from the Greenfield condition. Larger pile settlements and smaller axial pile forces are induced on the piles inside the pile groups than those computed from the single piles since the piles responded as a block with the surrounding gr ound. Also tensile pile forces are induced associated with the upward resisting skin friction at the upper part of pile and the downward acting skin friction at the lower part of pile. On the contrary, when the piles were outside the influence zone, tunnelling-induced compressive pile forces developed. Based on computed load and displacement relation of the pile, the apparent factor of safety of the piles was reduced up to about 45%. Therefore the serviceability of the piles may be substantially reduced. The pile behaviour, when considering the single piles and the pile groups with regards to the influence zone, has been analysed by considering the key features in great details.Keywords: Three-dimensional (3D) numerical modelling and analysis, Single piles, Group piles, Tunnelling, Tunnelling influence zone

The Stress Characteristics of Numerical Analysis on Bridge Pile Foundation in High and Steep Rock Slopes

The bearing mechanism of bridge pile foundation in high-steep rock slopes is much more complex than that in the flat. In the basis of theory research and model experiment made by previous scholars, then the software of finite element method is used on numerical analysis in this paper, which systematically discusses the distribution of body force of pile, the displacement in pile top and situation of pile’s thrusting force distribution caused by the soil (rock) around the pile under the combined load, the negative impact of combined load on pile stability was also discussed, which can guide engineering practice.

Mechanical response of bridge piles in high-steep slopes and sensitivity study

The bridge piles located in high-steep slopes not only endure the loads from superstructure, but also the residual sliding force as well as the resistance from the slope. By introducing the Winkler foundation theory, the mechanical model of piles—soils—slopes system was established, and the equilibrium differential equations of pile were derived. Moreover, an analytic solution for identifying the model parameters was provided by means of power series method. A project with field measurement was compared with the proposed method. It is indicated that the lateral loads have great influences on the pile, the steep slope effect is indispensable, and reasonable diameter of the pile could enhance the bending ability. The internal force and displacements of pile are largely based upon the horizontal loads applied on pile, especially in upper part.

Design of integral abutment bridges for combined thermal and seismic loads

Integral abutment bridges have many advantages over bridges with expansion joints in terms of economy and maintenance costs. However, in the design of abutments of integral bridges temperature loads play a crucial role. In addition, seismic loads are readily transferred to the substructure and affect the design of these components significantly. Currently, the European and American bridge design codes consider these two load cases separately in their recommended design load combinations. In this paper, the importance and necessity of combining the thermal and seismic loads is investigated for integral bridges. A 2D finite element combined pile-soil-structure interactive model is used in this evaluation. Nonlinear behavior is assumed for near field soil behind the abutments. The soil around the piles is modeled by nonlinear springs based on p-y curves. The uniform temperature changes occurring at the time of some significant earthquakes around the world are gathered and applied simultaneously with the corresponding earthquake time history ground motions. By comparing the results of these analyses to prescribed AASHTO LRFD load combinations it is observed that pile forces and abutment stresses are affected by this new load combination. This effect is more severe for contraction mode which is caused by negative uniform temperature changes.

Angle of repose and contact-force distribution in granular pile under variable g

Taking the discontinuity and random character of granular system into account,a kinematic model of particles was established by three-dimensional discrete element method in order to investigate the relationship between angle of repose and gravity. Accumulation process of granular pile was simulated using the model under variable gravity. The angle of repose and probabilistic distribution of contact forces were obtained in the model. Results show that the force-chain formed from contact forces within particle pile has the characteristics of structure of irregular mesh. Contact forces within particle pile are approximately log-normal distributed and there are about 65% of contacts carrying a force lower than the mean. Moreover,there are about70% of contacts whose friction force are fully mobilized and the ratio of tangential force to normal force among the rest of contacts is uniformly distributed. The distributions of contact force of granular piles in different gravity field have similar properties. The contact forces,which are normalized with respect to particle's gravity,of piles with variable gravity have nearly the same distribution. The angle of repose is not affected by the gravity,though granular pile has a randomness property of microscopic structure.

Kinematic and inertial forces in pile foundations under seismic loading

Under seismic excitation, a pile undergoes stresses stemming from both the vibration of the surrounding soil (kinematic interaction) and that of the superstructure (inertial interaction). The relative contributions of kinematic and inertial interaction on the magnitude of seismic forces induced in pile foundations are investigated by means of nonlinear two-dimensional (2D) finite element (FE) analyses. The interaction between the pile and the surrounding soil in three-dimensional (3D) type was idealized in the 2D analysis using soil–pile interaction springs with hysteretic nonlinear load displacement relationships. Parametric analyses are carried out, focusing on normalized seismic forces in the piles as affected by typical characteristics of structures and piles as well as ground nonlinearity. The results of the study provide a new interpretation of the interplay between pile kinematic and inertial seismic forces. The numerical results showed that for relatively short/stiff piles or where structure’s natural frequency is lower than that of the ground, the kinematic interaction can be the prime contributor to the seismic forces in the pile provided that the excitation frequency is not close to the natural frequency of the coupled soil–pile–structure system, fSSI. In a frequency band approaching fSSI, the inertial interaction generally prevails imposing large bending moments at or near the pile head. The results showed also that maximum kinematic seismic force does not always occur at the fundamental frequency of the deposit. For certain relative soil–pile stiffness and excitation amplitudes, the largest peak of the kinematic seismic forces in piles can be occurring at the second mode.

견고한 점토층에서 실시된 터널근접시공으로 인한 단독말뚝의 거동에 대한 연구

In the current work, a series of three-dimensional (3D) numerical modelling has been performed in order to study the effects of the relative locations of tunnels with respect to the position of pile tips which governs the behaviour of pre-existing, adjacent single piles. In the numerical analyses, several governing factors, such as tunnelling-induced pile head settlements, relative displacements, volume losses, axial pile forces, interface shear stresses and apparent factors of safety have been analysed. When the pile tips are inside the tunnelling influence zone, of which the pile tip location is considered with respect to the tunnel position, tunnelling-induced pile head settlements are larger than the ground surface settlements, resulting in tunnelling-induced tensile pile forces. On the contrary, when the pile tips are outside the influence zone, compressive pile forces associated with downward shear stresses at the upper part of the piles are developed. Based on computed load and displacement relation of the pile, the apparent factors of safety of the piles inside the tunnelling influence zone have been reduced by 36% in average. The shear transfer mechanism based on the relative tunnel locations has been analysed in great detail by considering tunnelling-induced pile forces, interface shear stresses and the apparent factors of safety.

Behavior of pile group with elevated cap subjected to cyclic lateral loads

The pile group with elevated cap is widely used as foundation of offshore structures such as turbines, power transmission towers and bridge piers, and understanding its behavior under cyclic lateral loads induced by waves, tide water and winds, is of great importance to designing. A large-scale model test on 3×3 pile group with elevated cap subjected to cyclic lateral loads was performed in saturated silts. The preparation and implementation of the test is presented. Steel pipes with the outer diameter of 114 mm, thickness of 4.5 mm, and length of 6 m were employed as model piles. The pile group was cyclic loaded in a multi-stage sequence with the lateral displacement controlled. In addition, a single pile test was also conducted at the same site for comparison. The displacement of the pile cap, the internal forces of individual piles, and the horizontal stiffness of the pile group are presented and discussed in detail. The results indicate that the lateral cyclic loads have a greater impact on pile group than that on a single pile, and give rise to the significant plastic strain in the soil around piles. The lateral loads carried by each row of piles within the group would be redistributed with loading cycles. The lateral stiffness of the pile group decreases gradually with cycles and broadly presents three different degradation patterns in the test. Significant axial forces were measured out in some piles within the group, owing to the strong restraint provided by the cap, and finally lead to a large settlement of the pile group. These findings can be referred for foundation designing of offshore structures.

말뚝선단의 위치가 터널근접 시공에 의한 말뚝의 거동에 미치는 영향에 대한 연구

In the current work, a series of three-dimensional (3D) finite element analyses have been performed to study the effects of the locations of pile tips on the behaviour of single piles to adjacent tunnelling. In the numerical modelling, several key issues, such as tunnelling-induced pile head settlements, axial pile forces, interface shear stresses and apparent factors of safety have been studied. When the pile tips are inside the influence zone which considers the relative pile tip location with respect to the tunnel position, tunnelling-induced pile head settlements are larger than those computed from the greenfield condition. However, when the pile tips were outside the influence zone, an opposite trend was observed. When the pile tips were inside the influence zone, tunnelling-induced tensile pile forces developed; however, when the pile tips were outside the influence zone, tunnelling-induced compressive pile forces were mobilised, associated with larger settlements of the surrounding soil than the pile settlements. It has been shown that the increases in the tunnelling-induced pile head settlements have resulted in reductions of the apparent factor of safety by about 50% when the pile tips are inside the influence zone, therefore severly affecting the serviceability of piles. The pile behaviour, when considering the location of pile tips with regards to the influence zone, has been analysed in great detail by taking the tunnelling-induced pile head settlements, axial pile force and apparent factor of safety into account.

Field Test Research of Inclined Large-Scale Steel Pipe Pile Foundation for Offshore Wind Farms

ABSTRACT Huo, S.; Chao, Y.; Dai, G., and Gong, W., 2015. Field test research of inclined large-scale steel pipe pile foundation for offshore wind farms. Relying on the East Sea Wind Farm project in China, the laterally loaded tests using the unidirectional and single cycle loading test methods were conducted on full-size inclined steel pipe piles filled with concrete. The internal force and deformation of piles, the critical bearing capacity, and lateral soil pressure were obtained from the full-scale test. The results show that the location of the maximal bending moment of pile shaft was at the depth of 2.5~3.5 meters beneath the soil surface level and soil resistance of the pile with a positive inclination angle was more than that with a negative inclination angle. The results also indicated that the p-y curves of all test piles increased linearly when the lateral displacement at pile head was smaller than 20 mm.