Dynamic Soil-pile Interaction Research Articles

A novel hybrid framework based on modified continued-fraction for pile-soil dynamic interaction of large-scale nuclear power structures

Accurate unbounded domain radiation damping and ground motion input in the near field are important for analyzing the dynamic safety of large-scale nuclear power structures (NPSs). The scaled boundary finite element method (SBFEM) can automatically satisfy the abovementioned radiation condition. However, owing to the coupling of time and space, conventional SBFEM is not competent to the analysis of large-scale structures. In this investigation, a novel coupled method is developed to improve the computational efficiency of unbounded domain dynamic stiffness using a modified continued-fraction technique. Furthermore, a set of systematic and efficient computational procedures for soil-structure interaction (SSI) are implemented based on parallel programming using a special preprocess. The proposed method is verified using three numerical examples, and another numerical application is analyzed for large-scale NPSs with a pile-raft foundation (PRF). The results show that the innovative method has wide engineering applicability with high numerical accuracy and stability, indicating that this method can be applied to the SSI dynamic seismic analysis of large-scale NPSs.

Analysis of seismic response of a large-scale isolated LNG tank considering dynamic soil-pile interaction

Seismic safety is a critical issue for liquefied natural gas (LNG) tanks. It is essential to investigate the effect of the isolation system on the seismic response of LNG tanks, considering dynamic soil-pile interaction, especially for tanks located in the deep soil site. This study aims to quantitatively evaluate the effects of isolation system (e.g., lead-core rubber bearings) on various aspects of a large LNG tank located on a deep soil site under horizontal bi-directional seismic action. Specifically, the evaluation includes outer tank acceleration, inner tank base shear, overturning moment, and pile force distribution. The findings demonstrate that the isolation system can effectively minimize the transfer of inertial interaction from the superstructure to the pile foundation, optimize the internal force distribution within the pile foundation, mitigate the pile group effect, and enhance the safety margin of the structure. Moreover, the isolation system can effectively suppress the transmission of seismic energy in medium and high frequencies, but amplify it in the low-frequency domain. Consequently, it is recommended that it is needed to avoid the site's natural frequency in the design of seismic isolation bearings for LNG tanks.

Acceleration response of part-screw pile composite foundation under long-term train load excitation

This paper investigates the vibration response of a new part-screw pile composite foundation under moving train loads via a model test method. Based on the acceleration signals of the pile and the surrounding soil, a non-linear fitting method is used to establish the relationship between the dynamic attenuation coefficient and the depth of the foundation. Next, the effect of spatial location and train speed on the pile-soil dynamic interaction is investigated by introducing the pile-soil spectral amplitude ratio [Formula: see text]. In addition, the dynamic susceptibility of the part-screw pile to damage under dynamic train loads is revealed with a wavelet packet energy distribution index E DIS. Afterwards, the cumulative deformation evolution characteristics of screw pile composite foundations under long-term train loading were revealed using the frequency domain integration method. The results of this work reveal that the faster the train runs, the larger the pile-soil spectrum amplitude ratio and the more prominent the ‘dynamic concentration effect’ of the part-screw pile. The change in cross-section of the part-screw pile results in a sudden change in the vibration energy transmitted from the top of the pile, which makes the variable section of the part-screw pile more likely to cause dynamic damage or even deformation. The cumulative deformation evolution process of soil between part-screw piles under long-term cyclic train loading can be divided into three stages: slow change period, fluctuation rising period and stable deformation period. The research results have important reference significance for the optimization design of high-speed railway part-screw pile composite foundation and the planning of railway running speed.

Numerical and experimental study on the effect of the installation meth-od on the lateral response of offshore monopiles

The successful deployment of offshore wind turbines requires the utilization of foundation installation methods that are fast, low-cost, and reliable. Offshore wind turbines foundations are commonly installed by impact driving. The noise generated during the driving process is a major constraint as it impacts marine life [1] and induces high stresses which reduce the fatigue lifetime of the foundation. Vibratory pile driving offers a promising alternative to traditional impact driving for the installation of monopiles [2], the limited data on its effects on the mechanical properties of the soil during installation in offshore conditions and consequently the mechanical response of the structure throughout its lifetime has prevented its adoption. During vibratory driving, the repeated and high intensity vibration can cause an increase in pore pressures and a decrease in both the inter-particle soil friction and the effective stress, which can eventually lead to liquefaction [3, 4].
 This research aims at investigating the influence of the installation method on the soil properties around monopiles and how it affects the lateral response of such structures. In order to comprehensively understand the different phenomena involved, this problem is investigated through both numerical modeling and laboratory testing.
 A numerical axisymmetric model based on the finite elements method that reflects on an offshore monopile was developed to describe the installation process using fixed boundaries or Perfectly Matched Layers (PML) [5] to realistically simulate the dynamic soil-pile interaction and ensure radiation of waves towards infinity. This model takes into account the reduction in soil strength around the pile shaft during the installation by impact or vibratory driving, along with the dynamic force applied by the vibro-hammer and the pore water evolution. Cyclic triaxial tests have been conducted on a sand extracted from the North Sea. They are used to calibrate the constitutive equations of the model. The results obtained provide insight into the onset and progression of liquefaction, the distribution of pore water pressures, and the resulting deformation of the soil-pile system and how the boundary conditons and the frequency of the imposed load affect those mechanisms.
 These numerical results are also compared with 1g reduced scale experiments composed of a large cylindrical box filled with dry and saturated sand, in which a fully instrumented model pile (tube 60mm in diameter) is vertically driven. The impact or vibrations are imposed at the pile head by a scaled vibratory hammer or scaled impact hammer. In addition, the relative density and the homogeneity of the sand is carefully controlled using the pluviation method [6] allowing to test the sand at different controlled densities. After the installation phase, the lateral behavior of the pile is investigated by imposing a horizontal force with a piston. The test results will also be compared to similar tests on large diameter piles (2 meters) than are planned for fall 2023.

A scaled boundary finite element method for soil dynamic impedance of pile groups using hybrid quadtree mesh considering horizontal vibration

The numerical modeling of pile-soil dynamic interaction has been a challenging problem in engineering for many years because of the unbounded domain, which typically involves significant computational cost. This paper develops a novel scaled boundary finite element method (SBFEM) that can accurately calculate the soil dynamic impedance of pile groups with end bearing subjected to horizontal vibration. The three-dimensional (3D) problem is first transformed to a two-dimensional (2D) Helmholtz equation in the horizontal plane, exploiting the analytical solution for the vertical modes using separation of variables. The SBFEM is then applied to solve the 2D computational domain, which is divided into bounded and unbounded domains. Based on the SBFEM, an accurate circular artificial boundary condition (ABC) is formulated to simulate the unbounded domain of the soil. A special hybrid quadtree mesh is devised for this problem, where a high-quality structured quadrilateral mesh is generated surrounding the piles. The accuracy of the proposed method is verified using a single pile problem with known analytical solution. The effects of dimensionless frequency, pile numbers, soil depth and relative distance between piles on the soil dynamic impedance are considered.

Influence of defects on the lateral dynamic characteristics of offshore piles considering hydrodynamic pressure

This paper develops an analytical framework to reflect the associative effect of dynamic soil-pile interaction (DSPI) and dynamic water-pile interaction (DWPI) on the lateral dynamic characteristics of offshore concrete piles. The pile is assumed to be an Euler-Bernoul20beam and the soil is described by the Biot's poroelastic theory. The hydrodynamic pressure applying on the pile shaft is calculated based on the radiation wave theory with the consideration of water compressibility. The influence of defects along with the hydrodynamic pressure on the lateral dynamic impedance and natural frequency of offshore piles is thoroughly investigated with the proposed solution. The results show that the hydrodynamic pressure cannot be ignored when analyzing the lateral dynamic characteristics, especially for those offshore piles with deep water depth subjected to high frequency vibration. The damage caused by necking defects is much larger than that of bulging defects, and even a small necking defect can lead to a significant decrease of dynamic stiffness and natural frequency of piles. The lateral dynamic characteristics of piles are more sensitive to the variation of defect radius rather than the defect length.

Effects of rocking impedance and soil shear stress of the free-field on the dynamic response of an end-bearing pile during horizontal earthquakes

An increasing number of pile foundation with large diameter are utilized in civil and offshore engineering in areas of active seismicity. This paper focuses on studying the effects of rocking impedance and soil shear stress of the free-field on the horizontal seismic responses of pile foundation. A substructure model in frequency domain is utilized to simulate pile-soil dynamic interaction during horizontal earthquakes. The soil is considered as viscoelastic media and the pile considered as one-dimensional (1D) rod modelled by Timoshenko beam theory. First, the analytical expressions of the horizontal and rocking impedances for an end-bearing pile are obtained. Further, the earthquake input method for 1D finite element analysis of pile-soil interaction on rigid bedrock during horizontal earthquakes are developed, where the soil shear stress of the free-field is considered. Finally, the proposed model is used to investigate the effects of rocking impedance and soil shear stress of the free-field on the seismic response of the pile with different soil and pile parameters.

Axis-symmetric analysis of layered transversely isotropic saturated elastic soils containing a monopile under time-harmonic vibration

The axis-symmetric dynamic soil-pile interaction analysis is of fundamental significance in geotechnical, seismic and transportation engineering. In addition, soils tend to show an obvious stratification after the long-term deposition. Physical and mechanical properties of soils are generally transversely isotropic due to the orientation of soil particles in deposition. Therefore, the axis-symmetric analysis of layered transversely isotropic saturated elastic soils containing a monopile under time-harmonic vibration is carried out in this study. Firstly, the extended precise integration method (EPIM) is employed to obtain the dynamic fundamental solution for layered transversely isotropic saturated soils, which would be utilized as the kernel function of the boundary element method (BEM). Moreover, by modeling the pile as a one-dimensional bar, the motion equation of the monopile under steady-state vibration is acquired based on the finite element method (FEM). Finally, the coupled BEM-FEM formulation representing the soil-pile interaction is developed and the axis-symmetric solution for layered soils containing a monopile is acquired. Compared with existing results, the accuracy of the proposed method is verified. Numerical examples are conducted to analyze the influence of frequency, transverse isotropy, the stratification of soils and the length-radius ratio of piles on soil-pile interaction behaviors.

Analysis of Horizontal Dynamic Response of a Single Pile in Layered Foundations Based on the Timoshenko–Pasternak Model

To compensate for the deficiencies of the conventional Euler–Bernoulli beam-dynamic Winkler foundation model in analyzing the horizontal dynamic response of a single pile, in this paper, the Timoshenko–Pasternak model, which considers both the soil shear effect and pile shear deformation, is established to reveal the pile-soil dynamic interaction accurately. Based on Timoshenko beam theory and Pasternak foundation theory, the pile horizontal vibration control equation considering pile shear deformation and the soil shear effect is derived based on D’Alembert’s principle. On this basis, the transfer matrix method is applied to consider the layering characteristics of the soil, and the dynamic complex impedance frequency domain analytical solution of the pile top is obtained by using the initial parameter method combined with the pile bottom boundary conditions. A comparison with the existing model solution is carried out to verify the correctness and reasonableness of the model in this paper; finally, the parameters of the pile characteristics and soil properties around the pile are analyzed. The results show that (1) the pile bottom boundary condition and pile length have almost no effect on the pile top impedance after the single pile reaches the critical value of the length-to-diameter ratio. (2) The trend of pile top impedance becomes increasingly evident with increasing dimensionless frequency. (3) The pile top impedance increases with the decrease in the pile-soil elastic modulus ratio, and the changing trend becomes increasingly apparent; meanwhile, the influence of the elastic modulus of the surface soil on the pile top impedance is much more significant than the influence of the underlying soil on it.

A high-accuracy substructure method in the time domain for simulating pile-soil dynamic interaction in horizontal vibration

An accurate and efficient substructure method in the time domain is developed to simulate pile-soil dynamic interaction during horizontal vibration. The present method considers the equilibrium of a linear elastic soil in both the radial and circumferential directions to account for three-dimensional wave scattering, and considers the end bearing pile as a one-dimensional rod. First, an analytical expression for the soil resistance to a horizontal vibration pile in the frequency-domain is obtained. From this, an exact dynamic stiffness relationship between the soil resistance and the pile displacement is constructed at the pile-soil interface. Further, the dynamic stiffness relationship in the frequency domain is transformed into a high-order approximation in the time domain. Then, this high-order approximation is equivalent to a mechanical model system consisting of mass, dashpot and spring elements. Finally, the effectiveness of the present method is verified and the effects of the dynamic stiffness of the soil on the dynamic responses of the pile are investigated.

A substructure method for seismic responses of offshore wind turbine considering nonlinear pile-soil dynamic interaction

The increasing number of wind turbines in areas of active seismicity has attracted scientific interest to evaluate the seismic responses of offshore wind turbine (OWT). The pile-soil dynamic interaction can have significant influence on the seismic responses of OWT. This research aims at investigating the seismic responses of a 5 MW OWT considering nonlinear pile-soil dynamic interaction. The pile is assumed to be rest on the rigid bedrock. The soil nonlinearity is accounted for approximately using an inhomogeneous boundary zone around the pile and a homogeneous zone outside the boundary zone. For simplification purpose, the dynamic analysis of the OWT is divided into two stages. In the first stage, the dynamic resistance factor of soil layer with radially inhomogeneous boundary zone is obtained by using transfer matrix method. In the second stage, a substructure model for dynamic responses of OWT including structure-pile-soil interaction is proposed. A three-dimensional (3D) finite element model (FEM) in Abaqus is used to verify the proposed method. Numerical results show that the proposed model agrees well with the 3D FEM. Finally, the effects of pile-soil interaction on the seismic responses of a 5 MW OWT are investigated.

Vertical vibration of an end bearing pile interacting with the radially inhomogeneous saturated soil

This study aims at portraying the vertical vibration characteristics of an end bearing pile interacting with the saturated soil that is of distinctly inhomogeneous behavior in the radial direction due to the construction disturbance. The pile is considered a one-dimensional bar. The saturated soil is considered by the Biot's two-phase linear theory and its radial inhomogeneity is simulated by the gradual variation of soil properties radially in a linear way. In practical terms, it is partitioned into a number of vertical ring-shaped zones in the radial direction with the soil properties approximately remain the same within the same soil zone. The pile–soil dynamic interaction is then obtained by solving the governing equations of each soil zone and is substituted into the governing equation of the pile to derive the analytical solution for the dynamic impedance at the pile head. The present solution is validated by comparing with other solutions. Meanwhile, it is employed to investigate the effect of the construction disturbance on the vertical vibration of the pile for different pile–soil parameters.

A simplified method for assessing the dynamic behaviour of a pile in layered saturated soils that considers current scour

Piles are commonly used in wharfs and offshore platform foundations. The coupled effects of current scour and dynamic load can reduce the non-deformability of a pile-soil system and ultimately lead to structural instability of structures. This paper develops a simplified method to study the dynamic interaction of layered saturated soils and piles under current scour conditions. Fundamental solutions for the dynamic consolidation of layered soil are obtained by the analytical layer element method (ALEM). The pile is modelled as a one-dimensional bar and solved by the finite element method (FEM). By coupling the ALEM and the FEM, solutions for the dynamic behaviour of the pile in soils are obtained while considering current scour. A flexibility matrix that is assembled by fundamental solutions is modified and expanded to match the stiffness matrix of the pile by the simplified method. This approach can solve pile-soil dynamic interaction problems under varied scouring conditions. The influences of scour type, scour depth, excitation frequency and layered property are examined, and the results show that the dynamic behaviour of the pile can be accurately simulated using the simplified method.

Analysis of the Pile-Soil Dynamic Interaction of Wharf in Marine Environment under the Impact of Earthquake

Zhou, L., 2020. Analysis of the pile-soil dynamic interaction of wharf in marine environment under the impact of earthquake. In: Gong, D.; Zhang, M., and Liu, R. (eds.), Advances in Coastal Research: Engineering, Industry, Economy, and Sustainable Development. Journal of Coastal Research, Special Issue No. 106, pp. 531–535. Coconut Creek (Florida), ISSN 0749-0208.The dynamic interaction of pile-soil structure is an interdisciplinary subject combining structural dynamics and soil dynamics. Under the action of an earthquake load, the soil will cause the movement of ground surface different from that of underlying bedrock. At the same time, the pile-soil structure will also affect the movement of the foundation bottom. Pile foundation is a foundation form with a long history that has many unique functions and is widely used in many fields, such as high-rise buildings, heavy-duty workshops, bridges, and offshore engineering. Pile foundation has become an important type of foundation in engineering construction and is widely used in marine terminals. The dynamic interaction of pile-soil structure in marine environment under earthquake needs to be stimulated, which will have important academic significance and practical value. In this paper, the loads and their effects on the quay structures in the marine environment are analyzed, which reflects the results of the pile-soil dynamic interaction.

The Soil-Pile Dynamic Interaction Effect on Bridges with Slab-Beam Deck by Using Finite Element Method

The Soil-Pile Dynamic Interaction Effect on Bridges with Slab-Beam Deck by Using Finite Element Method

Computational simulation of three-dimensional dynamic soil-pile group interaction in layered soils using disturbed-zone model

Computational continuum models of piles embedded in disturbed zones are developed using the Boundary Element Method (BEM) for application to three-dimensional dynamic soil-pile group interaction in layered soils. The enhanced 3D BEM code BEASSI is validated for handling pile group problems by comparison with reference solutions. A general sub-structuring formulation is developed to calculate theoretical accelerance functions. A 3D disturbed-zone computational model is then extended to handle the dynamic response of a typical 2 × 2 pile group. The performance of the model is illustrated through convergence studies and a case study corresponding to full-scale field tests. The results indicate strong frequency-dependent pile-soil-pile interaction by impedance functions, group efficiency ratios, and pile deformations. The findings from this study provide new insights into dynamic soil-pile group interaction, and the general approach can be used to examine other pile and soil conditions.

Experimental application of FRF-based model updating approach to estimate soil mass and stiffness mobilised under pile impact tests

The dynamic response of structures in contact with soil is receiving increasing interest and there is a growing need for more accurate models capable of simulating the behaviour of these systems. This is particularly important in the field of offshore wind turbines, where accurate estimates of system frequency are needed to avoid resonance, and in the structural health monitoring fields, where accurate reference damage models are used. Previous work has shown that there is significant uncertainty in how to specify mobilised soil stiffness for dynamic soil-pile interaction modelling. Moreover, the contribution of soil mass in dynamic motion is often ignored. This paper applies a finite-element iterative model updating approach previously developed by the authors to two experimental piles to ascertain the mobilised soil stiffness and mass profiles from impact test data. The method works by obtaining a frequency response function (FRF) from an impact test performed on a test pile, developing a numerical model of this system, applying initial estimates of soil mass and stiffness, and updating these properties to match the experimental FRF with that generated in the numerical model. A range of elements are investigated including multiple runs of the approach to test repeatability, the influence of different starting estimates for stiffness, the effect of variability in experimental test data, and the influence of the pile length over which masses are distributed. Moreover, potential sources of error are discussed. The method provides reasonably consistent estimates of the soil stiffness and mass acting in the lateral dynamic motion of a given pile tested in this paper. The approach may be useful in the continued improvement of Soil-Structure Interaction (SSI) modelling for dynamic applications.

Dynamic response of a pile embedded in elastic half space subjected to harmonic vertical loading

An analytical method is developed to investigate the dynamic response of a pile subjected to harmonic vertical loading. The pile is modeled as a one-dimensional (1D) elastic rod. The elastic soil is divided into a homogeneous half space underlying the base of pile and a series of infinitesimally thin layers along the vertical shaft of pile. The analytical solution for the soil-pile dynamic interaction problem is obtained by the method of Hankel transformation. The proposed solution is compared with the classical plane strain solution. Arithmetical examples are presented to demonstrate the sensitivity of the vertical impedance of the pile to relevant parameters.

Effect of compressible parameters on vertical vibration of an elastic pile in multilayered poroelastic media

This paper mainly investigates the influences of compressible parameters on the vertical vibration of a pile embedded in layered poroelastic soil media. The pile is treated as a 1D elastic bar by the finite element method, and fundamental solutions for the layered poroelastic soils due to a vertical dynamic load are obtained by the analytical layer element method. Based on the compatibility conditions, the pile-soil dynamic interaction problem is solved. The numerical scheme has been compiled into a Fortran program for numerical calculation. Influences of the pile-soil stiffness ratio, compressible parameters, vibration frequency and the soil stratification are discussed.

Inelastic Response Spectrum for Seismic Soil Pile Structure Interaction

Structures resting on deep foundations like pile groups are subjected to entirely different kind of vibrations than those resting on shallow foundations, due to the inherent variations in the ground motions experienced at various levels of the foundation. The present work tries to generate response spectrum for single-pile supported structures using inelastic dynamic soil-pile interaction analysis. In the numerical model, the soil nonlinearity includes both separation at soil-pile interface and the plasticity of the near-field soil. The radiation boundary condition is also incorporated in the form of a series of far-field dampers which absorb the out-going waves. Inelastic response spectra for the structure, represented by a SDOF system, is generated after applying the synthetic time histories compatible with design (input) response spectra (as per IS 1893:2002-part I) at the base of pile to investigate the effects of ground response analysis including kinematics and inertial interaction between soil- pile system. It is found that a structure supported by pile foundations should be designed for larger seismic forces/ accelerations than those obtained from the design spectrum given in IS 1893:2002-Part I. The verification of the developed MATLAB program is reported towards the end, using results from commercial Finite Element software ABAQUS.