Dynamic Response Of Pile Groups Research Articles

Scattered wave effects on the vertical dynamic response of pile groups embedded in layered soil

This paper presents an analytical solution that provides the response to vertical dynamic loads of pile groups with arbitrary numbers of end-bearing piles. The solution allows accounting for pile–pile interaction effects on pile group response in a robust manner, as both wave diffraction and scattering are explicitly considered. The effects of soil layering are introduced by using the plane strain model to mathematically describe wave propagation in the subsoil. In addition to accounting for realistic soil conditions, the adopted plane strain formulation eliminates the need to calibrate the Winkler spring and dashpot parameters to obtain the impedance of pile groups. The presentation of the solution is accompanied by an arithmetic study focused on exploring the effects of scattered waves on the response of pile groups in layered soil.

Dynamic Responses of Embedded Rock Pile Groups due to Rock Burst considering Coupled Pile-to-Pile Interaction

Abstract This note presents an analytical solution to investigate the dynamic behavior of pile groups of embedded rock due to rock burst, which takes into account the interaction between piles. The energy generated by the rock burst propagates through the soil in the form of stress waves. It is transmitted to the pile foundation through the interaction between the soil around the pile and the pile. For rock-socketed piles, the condition of pile tip fixing is considered. The horizontal dynamic response calculation model of the pile group is established, and the analytical forms of the pile group stiffness and pile group interaction factor are obtained. In addition, the effect of saturated soil parameters on the dynamic response of pile groups are discussed.

Dynamic response of pile group in two-layered soils under scour condition by FEM-ALEM approach

Pile groups for the bridge and jacket foundations in the marine or traffic geotechnical engineering are significantly influenced by the current scour in service. Under the effects of scour and dynamic load, the capability of the pile foundations to resist deformation is reduced and thus causes structural failure. This paper presents a FEM-ALEM coupling approach to study the dynamic interaction between a pile group and layered soils under scour condition. Behaviors of the pile group are analyzed by applying the finite element method. Fundamental solutions of the layered soils under scour condition are obtained by adopting the analytical layer element method. Comparisons with existing solutions are performed to confirm the correctness of the present approach, and numerical examples are provided to discuss the effects of the scour type, scour depth, scour width and layered property of soil on the dynamic behaviors of the pile group. The present coupling approach can be used to evaluate the responses of a pile group embedded in layered saturated soils under scour due to a vertical dynamic load.

Dynamic Analysis on Pile Group Supported Offshore Wind Turbine under Wind and Wave Load

With growing demand for renewable wind energy, the number of offshore wind turbines increased rapidly in recent years. This paper uses the improved Tajimi model and transfer matrix method to analyze the dynamic response of pile group supported offshore wind turbine under wind and wave load. The vibration equation of the structure is established by tower discretization. The calculation result is compared with the numerical simulation result. The horizontal displacement of the structure under loads with different frequencies can be obtained. The wind speed and the foundation impedance are found important to the structure displacement. The pile–pile interaction factor depends on the pile spacing, the pile embedment ratio, and the incidence angle.

Influence of depth of liquefiable soil layer on dynamic response of pile group subjected to vertical load

Influence of depth of liquefiable soil layer on dynamic response of pile group subjected to vertical load

Lateral dynamic response of pile group embedded in unsaturated soil

A mathematical formulation is proposed for the analysis of a pile group embedded in unsaturated soil subjected to horizontal time-harmonic vibration. The unsaturated soil is governed by the motion theory of three-phase poroelastic medium, and the piles with fixed connection to cap are modeled as Timoshenko beam models. By introducing Helmholtz decomposition to the governing equations, the resistance and attenuation function of displacement of the surrounding soil are theoretically derived. Then, the impedances of pile group in frequency domain are evaluated by utilizing the superposition approach based on the dynamic interaction factors. The internal forces of piles induced by both kinematic effects arising from the adjacent pile motion and inertial effect from pile cap, as well as the degree of contribution of the two effects have been investigated. The accuracy of the proposed method was validated by its comparison with a benchmark solution for the corresponding single phase medium problem. A comprehensive parametric study is performed to depict the effects of saturation, permeability, and pile group arrangement, and indicating that the saturation and permeability exert considerable effects on the nearly saturated condition, by contrast, the unsaturated case is much less affected.

Effect of Pile Arrangements on the Dynamic Coupled Response of Pile Groups

This paper presents both experimental and analytical investigation to monitor the effect of dynamic pile-soil-pile interaction on the nonlinear coupled response of a 6-pile group placing in different arrangements of piles under rotating machine induced vibrations. Another aspect of the present study is the theoretical prediction of parameters responsible for the nonlinear coupled response of the pile foundation. The pile groups comprised of hollow steel piles with an outer diameter of 0.114 m and a length of 3 m. Coupled vibration field tests are performed on the pile groups laid in two different set of pile arrangements (2 $$\times$$ 3 and 3 $$\times$$ 2 pile groups) to obtain the dynamic horizontal and rocking responses of the pile groups under different eccentric moments. For theoretical study, the continuum approach with superposition method is used to determine the nonlinear dynamic responses of the pile groups. The analytical frequency-amplitude responses for both types of vibrating displacements are compared with the dynamic field test results and the variations of the influencing parameters for the nonlinear dynamic response of the soil-pile system are predicted for coupled vibration. For 3 × 2 pile group, the resonant frequencies are found lower and resonant amplitudes are found higher than the values of the 2 × 3 pile group for all eccentric moments. It is also observed that the stiffness and damping of the 3 × 2 pile group shows lesser values than the 2 × 3 pile group even if the input analytical parameters are same for both the pile groups. From the results, it can be concluded that the effect of dynamic pile-soil-pile interaction is more pronounced for 3 × 2 pile group as compared to the 2 × 3 pile group.

Behaviour of pile foundation of G+5 buildings on various soil types of Guwahati at regional scale

The paper presents the results of a parametric study of static and dynamic response of pile groups of G+5 buildings of Guwahati, the capital city of Assam situated in India. Based on a preliminary survey conducted on 500 buildings of the city, it is observed that most of the buildings under survey are G+5 buildings. Guwahati, being a hub of erratic topography, consists of varied soil types. These soil types are grouped into various geo-units on the basis of their grain size distribution obtained from the geotechnical investigations at around 600 boreholes within the city. The study is conducted by modelling a representative G+5 building with piles, grouped in five, fixed at the head by pile caps and embedded in a homogeneous soil stratum in a finite element formulating software, PLAXIS 3D. The results are presented in the form of comprehensive plots, and a comparative study is made to obtain the pattern of pile behaviour, in terms of deflection, bending moment and shear force, in various geo-units of Guwahati. The paper gives an insight to the pile designers of the region, an estimation of the maximum seismically induced deflection, bending moment and shear strength of the pile to maintain the structural integrity of the pile, when the pile is embedded in different types of soil of Guwahati.

The Effect of Vertical Loads and the Pile Shape on Pile Group Response under Lateral Two-Way Cyclic Loading

This paper is presented the lateral dynamic response of pile groups embedded in dry sand under influence of vertical loads and the pile shape in-group, which are subjected to the lateral two-way cyclic loads. The laboratory typical tests with pile groups (2×1) have an aluminum-pipe (i.e. circular, square) pile, embedded length to diameter of pile ratio (L/D=40) and spacing to diameter ratio (S/D) of 3, 5, 7 and 9 are used with different cyclic-load ratio (CLR) 0.4, 0.6 and 0.8. The experimental results are revealed that both the vertical and lateral pile capacity and displacement is significantly affected by the cyclic-loading factors i.e. (number of cycles, cyclic load ratio, and shape of pile) .In this study, important design references are presented. Which are explained that the response of the pile groups under cyclic lateral loading are clear affected by the attendance of vertical load and pile shape. Where, it is reduction the lateral displacement of group piles head and increase lateral capacity about (50) % compared without vertical loads. On the other side, the pile shape is a well affected to the pile response where the level of decline in lateral displacement at the pile groups head in the square pile is more than circular pile about 20 % at the same load intensity.

Dynamic response of pile groups subjected to horizontal loads

This paper presents an analytical method for calculating the dynamic impedance of pile groups comprising an arbitrary number of cylindrical piles connected with a rigid cap. The solution allows consideration of ground waves due to pile vibration that propagate along both the horizontal and vertical planes, as well as the effect of the actual pile section geometry on the reaction from the surrounding soil. For that, we introduce a dynamic pile–soil–pile interaction factor that is defined on the basis of soil reaction developing on receiver piles, instead of the classical displacement-based interaction factor used in past studies. Despite the fact that the solution is applicable to problems where low-to-moderate soil strains are expected to develop, it poses as an attractive, efficient alternative to numerical methods for the analysis of very large pile groups.

Dynamic response of a laterally loaded fixed-head pile group in a transversely isotropic multilayered half-space

The time-harmonic response of a laterally loaded fixed-head pile group embedded in a transversely isotropic multilayered half-space is investigated using a finite element and indirect boundary element coupling method. The piles are solved by the finite element method (FEM), while the soil can be modeled by the indirect boundary element method (BEM) with the aid of the fundamental solution for a transversely isotropic multilayered half-space in a cylindrical coordinate system. The governing equation of the pile-soil-pile dynamic interaction is established by applying the FEM-BEM coupling method. Numerical examples are carried out to validate the presented theory and to investigate influences of the soil׳s anisotropy and layering on the dynamic response of pile groups.

Shaking table model tests on dynamic response of pile groups under liquefaction-induced large ground displacement

A series of shaking table model tests on pile groups in liquefiable ground were designed and conducted. The tests reproduced the macroscopic phenomena of soil liquefaction, soil flow and the large displacement of pile caps. The study focused on the dynamic responses of the ground and pile foundations. Results indicated that for liquefied slope ground with pile groups, soil flow can be classified as partial and overall soil flow. The evolution process and space distribution of the vibration pore water pressure were influenced by soil flow, and the soil mass between piles was relatively difficult to be liquefied. The greater the slope angle, the greater the dynamic earth pressure acting on the pile side and the lateral displacement of pile caps. In the meantime, the inclination of pile foundation weakened the bending moment response of pile shaft. For both inclining and horizontal ground, the maximum bending moment occurred at the interface of the liquefied and non-liquefied layers along the shaft.

Experimental and numerical investigation on the dynamic response of pile group in liquefying ground

The response of pile foundation in liquefiable sand reinforced by densification techniques remains a very complex problem during strong earthquakes. A shake-table experiment was carried out to investigate the behavior of a reinforced concrete low-cap pile group embedded in this type of ground. In this study, a three-dimensional (3D) finite element (FE) analysis of the experiment was conducted. The computed response of the soil-pile system was in reasonable agreement with the experimental results, highlighting some key characteristics. Then, a parametric study was performed to explore the influence of pile spacing, pile stiffness (EI), superstructure mass, sand permeability, and shaking characteristics of input motion on the behavior of the pile. The investigation demonstrated a stiffening behavior appearing in the liquefied mediumdense sand, and the pile group effect seemed negligible. Furthermore, the kinematic effect was closely connected with both EI and sand permeability. Nevertheless, the inertial effect was strongly influenced by the superstructure mass. Meanwhile, high frequency and large amplitude of the input motion could produced greater the pile’s moments. It is estimated that this case study could further enhance the current understanding of the behavior of low-cap pile foundations in liquefied dense sand.

Principle of superposition for assessing horizontal dynamic response of pile groups encompassing soil nonlinearity

Model tests on fixed-head floating piles embedded in dry cohesionless soil (Gifu sand) are carried out under 1-g conditions on a shaking table, to investigate the effects of local soil nonlinearity on the dynamic response of pile groups. Results obtained from these tests are employed to assess the applicability of Poulos׳ superposition method in determining the pile group response under different levels of material nonlinearity. A wide range of head loading amplitudes inducing low-to-high levels of soil strain are employed for a broad range of frequencies. Utilizing the aforementioned superposition method, horizontal impedance functions of a closely spaced 3×3-pile group are computed based on: (1) experimentally-measured values of horizontal impedance functions for a single pile, and (2) experimentally-measured pile-to-pile interaction factors. Comparisons between computed and measured impedance functions show good agreement for low to intermediate loading amplitudes, suggesting that the superposition method is valid even under moderately nonlinear conditions.

Dynamic response of pile foundations with flexible slabs

An elasto-dynamic model for pile-soil-pile interaction together with a simple plate model is used in this study to assess the effect of flexible foundation slabs on the dynamic response of pile groups. To this end, different pile configurations with various slab thicknessesare considered in two soil media with low and high elastic moduli. The analyses include dynamic impedances and seismic responses of pile-group foundations. The presented results indicate that the stiffness and damping of pile foundations increase with thickness of the foundation slab; however, the results approach those for rigid slab as the slab thickness approaches twice the pile diameter for the cases considered in this study. The results also reveal that pile foundations with flexible slabs may amplify the earthquake motions by as much as 10 percent in the low to intermediate frequency ranges.

Dynamic response of pile groups in series and parallel configuration

Basic problem of pile foundation is three dimensional in nature. Three dimensional finite element formulation is employed for the analysis of pile groups. Pile, pile-cap and soil are modeled using 20 node element, whereas interface between pile or pile cap and soil is modeled using 16 node surface element. A parametric study is carried out to consider the effect of pile spacing, number of piles, arrangement of pile and soil modulus on the response of pile group. Results indicate that the response of pile group is dependent on these parameters.

Dynamic Response of Pile Groups under Vertical Forces in Saturated Soil

Based on Biot’s wave propagation equation and boundary conditions, this paper builds up pile group and soil system used for calculation in 3 dimension models, though mass conservative and motion equation. The results of ground surface movement are obtained under the effect of vertical dynamic force though Newmark direct integration. Compared with the measured results, the numerical outcomes conform accurately. The calculating results show that vibration of ground surface can be affected by several parameters such as soils’ possion ratio, permeability coefficient, different types of pile groups and so on. Different factors have different effects on ground’s surface vibration in both far field and near field.

Dynamic impedances of pile groups with embedded caps in homogeneous elastic soils using CIFECM

Significant research has been reported on the dynamic analysis of pile groups. However, in most of the cases, the effect of pile cap is neglected despite the fact that there may be additional interactions due to the presence of the cap. This paper presents the dynamic impedances for the pile groups with caps embedded in isotropic homogeneous elastic soils. A general three-dimensional finite element procedure is developed. The system is sub-structured into bounded near-field and an unbounded far-field. The pile-soil system of the near-field is modeled using solid finite elements, and the unbounded elastic soil system of the far-field is modeled using the consistent infinitesimal finite element cell method (CIFECM) in the frequency domain. The method has shown excellent agreement with the published results for dynamic response of pile groups with a free-standing pile-cap. The dynamic impedances of pile groups with embedded cap are presented. Each pile group is capped with a thick pile-cap, embedded in the near-field soil domain. The dynamic impedances of 2×2 pile groups are presented, for different spacing of piles and thickness of the pile-cap with different embedment ratios. It was found that even for a small embedment ratio, the dynamic interactions due to cap can be significant.

Analysis of pile groups in a poroelastic medium subjected to horizontal vibration

This work investigates the dynamic response of pile groups embedded in a poroelastic medium subjected to horizontal loading. The dynamic response is analyzed using the Muki and Sternberg Method. The load transfer problem is formulated in terms of a second-kind Fredholm integral. The dynamic impedance of the pile groups is computed using the pile–soil–pile dynamic interaction factors. The shear force, bending moment and pore pressure is obtained using the superposition method. Numerical results indicate that the pile flexibility ratio and the pile distance have considerable influence on the dynamic response of the piles and the poroelastic medium.

Dynamic response of pile groups embedded in a poroelastic medium

The dynamic response of pile groups embedded in a homogeneous poroelastic medium and subjected to vertical loading is considered. The piles are represented by compressible beam-column elements and the porous medium uses Biot's three-dimensional elastodynamic theory. The dynamic impedance of pile groups can be computed directly by using pile–soil–pile dynamic interaction factors. The axial forces and pore pressures along the length of pile groups are computed by superposition method, which greatly reduces the computational time for the direct analysis of pile groups. Parametric studies are conducted for various conditions of pile groups. The superposition method is proposed for the dynamic response analysis of pile groups that is computationally feasible for practical applications.