Elastic Subsoil Research Articles

Pile field numerical analysis at the stage of long-term impacts

The authors propose a combined approach for definition of the shear rigidity of the multilayered soil which is cut through by a pile. The solution for the vertical direction is presented in the view of an axisymmetric problem. As to the horizontal direction, the solution is presented in view of a beam on elastic subsoil with genetically non-linear transition to equivalent horizontal rigidity of the wide pile field in condition of dynamic forces action. The axisymmetric solution provides visual clarity in the analysis of the stress-strain state of the pile and near-pile soil in comparison with the approved analytical methods. To speed up calculations at the stage of the main combination of constant and long-term impacts, the vertical rigidity of the base under the foot of the pile can be calculated analytically as for a stamp on an elastic-plastic base. The horizontal rigidity is considered as for a discrete single bent pile in the medium of an elastic layered half-space at the stage of formation of the stress-strain state of the system under the main combination of static loads. These methods of numerical modeling of deformations of a single pile make it possible to expand the algorithm of analytical calculation of a large pile field, which in turn is modified by the authors by excluding deformations of the pile body due to its natural consideration in the finite element formulation, as well as by introducing the parameter of the limiting radius of the influence of a single pile on the settlement of neighboring piles. The considered numerical approaches to the calculation of the pile field are applicable in a complex calculation taking into account the history of loading at the stage of the main combination of permanent and long-term impacts. At the stages of short-term or special dynamic impacts an integral rigidity of pile cells is proposed, which will be considered in the next publication of the authors.

Pile field numerical analysis at the stage of dynamic impacts

The authors propose a combined approach for definition of the shear rigidity of the multilayered soil which is cut through by a pile. The static solution for the vertical direction is presented in the view of an axisymmetric problem. As to the horizontal direction, the solution is presented in view of a beam on elastic subsoil with genetically non-linear transition to equivalent horizontal dynamic rigidity of the wide pile field. At the stage of formation of the stress-strain state of the system under the main combination of static loads еhe axisymmetric solution provides visual clarity in the analysis of the stress-strain state of the pile and near-pile soil in comparison with the approved analytical methods. The horizontal rigidity is considered as for a discrete single bent pile in the medium of an elastic layered half-space. These methods of numerical modeling of deformations of a single pile make it possible to expand the algorithm of analytical calculation of a large pile field, which in turn is modified by the authors by excluding deformations of the pile body due to its natural consideration in the finite element formulation, as well as by the parameter of the limiting radius of the influence of a single pile on the settlement of neighboring piles. In this publication, the authors describe a methodological approach to constructing a model of a large-size pile field at the second stage of short-term or special dynamic impacts. A transition to the integral rigidity of pile groups is proposed, taking into account the spatial dynamic model of a large-size pile foundation. The numerical problems of modeling a spatial soil array, a wave method for determining the discreteness of the model, methods for replacing the underlying half-space with a contact model are considered.

Genetically nonlinear combined model of pile field under dynamic impacts

The authors propose a combined approach for definition of the shear rigidity of the multilayered soil which is cut through by a pile. The solution for the vertical direction is presented in the view of an axisymmetric problem. As to the horizontal direction, the solution is presented in view of a beam on elastic subsoil with genetically non-linear transition to equivalent horizontal rigidity of the wide pile field in condition of dynamic forces action. The axisymmetric solution provides visual clarity in the analysis of the stress-strain state of the pile and near-pile soil in comparison with the approved analytical methods. To speed up calculations at the stage of the main combination of constant and long-term impacts, the vertical rigidity of the base under the foot of the pile can be calculated analytically as for a stamp on an elastic-plastic base. The horizontal rigidity is considered as for a discrete single bent pile in the medium of an elastic layered half-space at the stage of formation of the stress-strain state of the system under the main combination of static loads. At the final stage of short-term or special load, a transition to the integral shear rigidity of a pile field is proposed.

Stability and Vibrations of Micrononhomogeneous Plate Band Resting on Elastic Subsoil

Stability and Vibrations of Micrononhomogeneous Plate Band Resting on Elastic Subsoil

Impact of genetically nonlinear application of external loads on the stress-strain state and on the principal vibration modes of reinforced concrete frame buildings on elastic subsoil

In this paper authors discuss the impact of genetically nonlinear application of external loads on the stress-stain state and on principal vibration modes of reinforced concrete frame structures on elastic foundation. The reader will find a methodology for integrated numerical and instrumental analysis. Six examples of linear and nonlinear FEA-models calculated in SCAD Office are given in comparison.

Dynamic Eigenvalue Problem of Concrete Slab Road Surface

The paper presents an analysis of the dynamic eigenvalue problem of concrete slab road surface. A sample concrete slab was modelled using Autodesk Robot Structural Analysis software and calculated with Finite Element Method. The slab was set on a one-parameter elastic subsoil, for which the modulus of elasticity was separately calculated. The eigen frequencies and eigenvectors (as maximal vertical nodal displacements) were presented. On the basis of the results of calculations, some basic recommendations for designers of concrete road surfaces were offered.

A parametric study for free vibration analysis of hyperbolic cooling towers on elastic foundation using consistent FEM-Vlasov model

The main purpose of this paper is to apply the modified Vlasov foundation model to free vibration analyses of hyperbolic cooling towers resting on elastic foundations. Moreover, the influence of some characteristic parameters such as thickness, height, curvature and throat level on the frequency response of cooling towers on elastic foundations is investigated. For this purpose, a computing tool coded in MATLAB employing open application programming interface feature of SAP2000 to provide two-way data flow during execution is used to perform the analyses of hyperbolic cooling towers with supporting columns over hollow annular rafts founded on elastic subsoil. The circumferential, lateral and extensional natural frequency parameters of cooling towers are presented in tabular and graphical forms to evaluate the effects of the geometric parameters and soil–structure interaction. As far as numerical examples are considered, it can be concluded that the soil–structure interactive behavior of the tower leads to a remarkable decrease in the frequency parameter of the system compared to the fixed based condition. Moreover, the frequency parameters are considerably affected by altering geometrical parameters.

Centrifuge Tests of Dyke Collapses on Soft Subsoil

This paper presents the results of an experimental investigation on the failure or collapse of dykes with a strong contrast of stiffness between the dyke itself and its foundation layers. In deltaic regions, dykes are commonly built out of stiff sandy or clayey materials and rest on soft foundations layers (e.g. soft clay or peat). Their interaction is largely unexplored and the failure mechanism unknown. The tests presented in this paper aim to highlight the difference in failure mechanisms. The tests consisted mainly of stiff dykes on soft subsoils but a few soft dykes on stiff subsoil were also investigated. The dykes were made out of Speswhite clay or Baskarp sand whereas the subsoil was made out of silicon or clay. The silicon was used to replicate a soft elastic subsoil for which it was possible to control the stiffness. The model was then subjected to increasing gravity up to 100 G-level. The results show that slope failures take place in the dyke when the foundations layers are stiff. It is believed to be the consequence of a build up of pore pressure due to the volumetric contraction of the dyke. On the other hand, soft foundation layers underwent large settlements which in turn deformed the stiff dyke without any slope failure taking place. However, diffused sheared zones were observed in the core of the dyke.

Rayleigh‐wave Resonance Analysis: a Methodological Test on a Viking Age Pit House

AbstractSeismic surface‐waves may show amplitude resonances at certain frequencies depending on the thickness and elastic parameters of near‐surface layers. We investigate if resonance frequencies of Rayleigh‐waves, (seismic surface‐waves polarized in the vertical plane) can be used to prospect archaeological remains of small‐scale buildings such as pit houses. Our test site is a newly detected Viking age village on the island of Föhr (north Germany) where we concentrated on one typical pit house. The results from resonance analysis are compared with magnetic data, ground penetrating radar (GPR) and classical seismic refraction measurements. The method of Rayleigh‐wave resonance mapping used in this paper is based on the idea that Rayleigh‐wave oscillations on top of anthropogenic structures will show different resonances than on undisturbed soil. We perform spectral analysis of these oscillations to provide information related to the seismic site response. We process single vertical component recordings and map the change in resonance frequency that can be related to the archaeological objects. The test showed that the pit house can be mapped by Rayleigh‐wave resonance analysis with a horizontal resolution of ~0.6 m. Corresponding computations of the depth of the pit house agree with the results from GPR, magnetic modelling and refraction seismics. A modelling study helped to understand the connection between subsoil shear‐wave velocity model and the signal generated by the pit house. The progress of seismic field measurement is slow compared to GPR and magnetometry. However, since seismic methods are based on elastic subsoil parameters, it can be applied in cases where magnetic contrasts are low or GPR fails because of high electromagnetic wave absorption. Copyright © 2015 John Wiley & Sons, Ltd.

STATIC ANALYSIS OF THE CYLINDRICAL TANK RESTING ON VARIOUS TYPES OF SUBSOIL

The paper presents analyses of deformations and stress of the circular rotationally symmetric tanks. The reinforced concrete tanks – water reservoirs – resting on elastic subsoil have been analyzed. The elastic subsoil has been modeled using three basic subsoil models: half-space model, two-parametric model and one-parametric (Winkler) subsoil model. Particular modifications have been applied to the basic models which yield in seven models presented. The cylindrical tank has been analyzed in the interaction with the subsoil, while the elastic subsoil has been characterized by different parameters. The differences in modeling using individual calculation models have been highlighted. The results from analytical and numerical solutions have been presented and compared in graphs and tables. The method for the calculation of settlement of the circular foundation plate was verified experimentally. The settlement of the circular plate was measured while the silo was fully loaded by its contents. The experimentally obtained values have been compared with the calculation results. In the conclusion the recommendations for the suitable model subsoil for these types of structures have been presented.

Numerical modelling of semi-coercive beam problem with unilateral elastic subsoil of Winkler’s type

A non-linear semi-coercive beam problem is solved in this article. Suitable numerical methods are presented and their uniform convergence properties with respect to the finite element discretization parameter are proved here. The methods are based on the minimization of the total energy functional, where the descent directions of the functional are searched by solving the linear problems with a beam on bilateral elastic “springs”. The influence of external loads on the convergence properties is also investigated. The effectiveness of the algorithms is illustrated on numerical examples.

Unilateral elastic subsoil of Winkler’s type: Semi-coercive beam problem

The mathematical model of a beam on a unilateral elastic subsoil of Winkler’s type and with free ends is considered. Such a problem is non-linear and semi-coercive. The additional assumptions on the beam load ensuring the problem solvability are formulated and the existence, the uniqueness of the solution and the continuous dependence on the data are proved. The cases for which the solutions need not be stable with respect to the small changes of the load are described. The problem is approximated by the finite element method and the relation between the original problem and the family of approximated problems is analyzed. The error estimates are derived in dependence on the smoothness of the solution, the load and the discretization parameter of the partition.

2D dynamics of a stratified elastic subsoil layer

2D dynamics of a stratified elastic subsoil layer

2D dynamics of a stratified elastic subsoil layer

The aim of this contribution is to propose a 2D model for an elastic stratified subsoil layer, which takes into account the effect of inhomogeneity on the dynamic behaviour of a medium. The obtained equations describe the subsoil response to the time-dependent foundation soil loadings, and can be applied to the analysis of dynamic subsoil-structure interactions. It is shown under which conditions the effect of microproperties of a medium on its dynamic response cannot be neglected.

A probabilistic analysis of foundation settlements

This paper deals with a settlement analysis of shallow foundations resting on a layered subsoil. Three basic sources of randomness are discussed: random shape of the subsoil (location of an interface between two strata), random material parameters and random loads. The numerical analysis is based on the finite element method coupled with stochastic versions of the perturbation and the Neumann expansion methods. Both methods lead to a simple evaluation of the response variability in terms of the mean value and the covariance matrix for foundation settlements. More sophisticated analyses introduce the probability of failure as a measure of safety. In this context, failure means either exceeding the bearing capacity or exceeding allowable displacements. The probability of failure is usually evaluated by means of FEM-oriented gradient algorithms or some versions of the Monte Carlo simulation techniques. Numerical examples are presented for a raft foundation resting on an elastic subsoil. The obtained results compare the scale of random fluctuations of soil properties or loading with the scale of foundation settlement fluctuations.

On the interactions between a structure and a stratified elastic subsoil

On the interactions between a structure and a stratified elastic subsoil

2047 基礎地盤の近似伝達関数を含む構造物系における複素固有値問題(構造,第1回 日本建築祭 研究発表会 学術講演要旨集)

2047 基礎地盤の近似伝達関数を含む構造物系における複素固有値問題(構造,第1回 日本建築祭 研究発表会 学術講演要旨集)