Infinite Soil Medium Research Articles

3D Finite-Element Dynamic Analysis of Rigid Pavement Using Infinite Elements

A solution algorithm based on three-dimensional (3D) finite-element analysis is presented to study the dynamic response of concrete pavements subjected to moving loads. The pavement is discretized by 20-node isoparametric brick elements. The supporting soil medium is idealized by the elastic continuum model. Kelvin elements are attached to the transmitting boundary separating the near field and far field of the infinite soil medium in the vertical and longitudinal directions. Three-dimensional, 16-node infinite elements are attached to the transmitting boundary in the longitudinal direction to simulate the infinite soil medium in vehicle traverse direction. The moving vehicle is modeled by a mass supported by a linear spring and dashpot assembly simulating the vehicle suspension system. The vehicle-pavement interaction force is modeled with a Dirac-delta function. The dynamic equilibrium equation is solved by applying the Newmark-Beta integration scheme. The effects of vehicle-pavement interaction, pavement thickness, and soil parameters on the dynamic response of pavement are investigated by conducting a parametric study. It has been observed that the dynamic interaction between the moving load and the pavement has a significant effect on pavement response.

Three dimensional vibration analysis of a buried pipeline with slip conditions

Based on the three-dimensional (3D) elasticity theories, an analytical solution for the infinite pipeline surrounded by the infinite soil medium subjected to an incident plane wave is derived. The Coulomb frictional force is applied at the pipeline–soil interface to represent the slip condition between the pipeline and the soil medium. This applied interface interaction can be considered as the viscous damping with some considerations. The normal and shear stress distributions along the cross-section of the pipeline are obtained by solving the obtained equations analytically. Furthermore, the superposition and the corresponding principles are used to obtain the von Misses strains. The critical and maximum amplitude ranges of the incident wave for which slipping and yielding, respectively, occur are estimated. The solutions are presented for ranges of soil densities and pipe thicknesses with perfect/imperfect bonds and different incident wave angles.

АНАЛИЗ ПРИБЛИЖЕННЫХ РЕШЕНИЙ ЗАДАЧИ О РАСШИРЕНИИ СФЕРИЧЕСКОЙ ПОЛОСТИ В ГРУНТОВОЙ СРЕДЕ

The solutions of a problem of a spherical cavity expansion from a point to an infinite soil medium are presented. Compressibility of the soil is described by the impact adiabat in the form of the linear relation combining shock wave velocity and mass velocity behind the wave front. The analytical problem solution under the assumption of medium incompressibility behind the wave front and the numerical solution in complete formulation are obtained. The proximity of both solutions is shown for supersonic velocities of the cavity expansion. Keywords: impact adiabat, spherical cavity expansion, local interaction model, compressible soil medium.

Effect of Soil Locking on the Cylindrical Shock Wave’s Peak Pressure Attenuation

The paper investigates the characteristics of propagating shock waves in soil, resulting from an explosion of a cylindrical line charge. The main purpose of this investigation is to study the full locking parameter's effect on the qualitative and quantitative behavior of the peak pressure attenuation. The soil is modeled as a bulk irreversible compressible elastic plastic medium, including full bulk locking and dependence of the current deviatoric yield stress on the pressure. The Lagrange approach and the modified variational-difference methods are used to simulate the process. A study of the characteristics of the equation of the state of soil was carried out for the case of a cylindrical line charge explosion in an infinite soil medium. The computed results were compared with experimental data. It was found that the full locking model somewhat overpredicts the measured stresses. The dependence of the peak stress attenuation, during the shock wave propagation, on the full locking parameter of the equation of state was studied. When the pressure-volumetric strain relationship beyond the point of full compaction is not steep, the attenuation may be described by a power law that may be expressed as a linear relationship on a logarithmic scale. When this relationship is relatively steep however, the logarithmic dependence of the peak stress on the shock wave coordinate is close to a bilinear function. It was also shown that the shock wave peak stress parameters of this power law for the high pressure range (i.e., short distance of the wave front from the explosive charge) are linearly dependent on the full locking parameter. Also it was shown that the full compaction density affects the exponent of stress-distance power relationship only at the earlier stage of the wave propagation and only when the range of nonlinear elastic compaction is relatively narrow.

Validation and Calibration of a Laboratory Experimental Setup for Cross-Well Radar in Sand

Abstract Cross-well radar (CWR) uses electromagnetic wave antennas lowered into sampling wells, to image the dielectric properties of soil and detect scattering objects such as contaminants (in this case, dense nonaqueous phase liquids (DNAPLs)). To better understand the physics of CWR in soils, it is necessary to experimentally evaluate the behavior of antennas and electromagnetic (EM) waves. A proto-type model of an infinite soil medium was experimentally simulated by constructing a pilot-scale facility, referred to as SoilBED. The most important issue in any experimental research is the repeatability, reproducibility, and reliability of the results. This paper evaluates different factors affecting experimental data collection in order to achieve the required specifications to collect reproducible and reliable data. Antenna depth and insertion problems, soil disturbance, and boundary condition effects were experimentally evaluated. Other (desired or undesired) transmission couplings were studied, and efforts were conducted to eliminate the undesired paths. The calibrated and validated setup can be and is used for different purposes other than DNAPL detection, such as soil and antenna characterization, theoretical simulation validation, and inverse scattering by various materials in dry or saturated soil backgrounds.

Frequency domain analysis of soil-structure interaction

In practical soil-structure analysis a number of basic issues need to be addressed. First, the soil-structure interaction problems are generally of a very large size. A suitable transformation should therefore be used to reduce the size of the problem. Second, analysis in the frequency domain, which is the preferred method for problems involving wave propagation in an infinite soil medium, usually requires the application of discrete Fourier transformation. The use of such transformation often leads to unacceptable errors caused by aliasing or overlapping. Analytical techniques that address these issues are presented here. A set of Ritz vectors based on the concept of component mode synthesis is developed for the transformation of the interaction problem. The method of artificial damping, developed by two of the authors, and reported earlier, is applied in the solution to avoid the problem of aliasing. The effectiveness of these techniques is illustrated by means of some examples of soil-structure interaction.

Effect of raft flexibility and soil media on the dynamic response of a framed structure

In this paper, a numerical model is outlined for a three-dimensional (3D) dynamic soil-structure system using 3D frame elements for modelling the superstructure, the combination of thick plate elements and plane stress elements for modelling the raft foundation and the coupled method of 3D finite elements and infinite elements to model the infinite soil medium. After verifying the accuracy of the present method, a general study on the effects of raft flexibility and soil media on the dynamic response of a 3D frame structure including dynamic interaction effects is also performed. The associated numerical results from this study have demonstrated that (1) the present model is very suitable to solve the dynamic frame-foundation-soil interaction problems; (2) the combination of thick plate element and plane stress element should be used to model the raft in the analysis when the system is subjected to the excitation of horizontal earthquakes; (3) the flexibility of a raft must be included in the dynamic analysis of a 3D frame-foundation-soil system so that a realistic solution can be obtained; (4) the layer characteristics of soil media underneath the raft have significant effects on the dynamic response of a 3D frame structure and the softer soil layer will result in greater response of the frame.

Dynamic response of elastic blocks by time domain BEM and FEM

The dynamic behavior of massive elastic blocks bonded to an infinite soil medium (halfspace), and subjected to horizontal and vertical transient loads, is explored. The blocks, and, in some cases, a small portion of the underlying soil, are modeled by plane strain finite elements, whereas the remaining part of the halfspace is treated by a time domain boundary element method (BEM). Comprehensive investigations are performed to provide a quantitative assessment of the effects of various system parameters on the dynamic response of blocks. Thus, different soil stiffnesses, blocks of variable sizes and the effect of an embedment of the block into the soil, are considered. In addition, investigations taking into account an elastic inclusion in the interior of the halfspace or a second block (structure-soil-structure interaction effects) are discussed. Besides these studies, the finite element method (FEM)-BEM coupling approach presented permits an extension to consider nonlinear effects, as the entire formulation is given directly in the time domain.

Assessment of Computational Practices in Dynamic Soil‐Structure Interaction

This paper presents a comparative study of the most widely used numerical methods in dynamic soil‐structure interaction (SSI). The developments follow in parallel treatments of representative SSI problems solved by frequency, the time‐domain boundary element method (BEM) and finite element method (FEM) formulations. Such treatments serve to enunciate the advantages and limitations of BEM and FEM formulations, and allow critical comparison of their differences and suitability to solve steady‐state and transient elastodynamic problems. Further, the in‐parallel presentation serves as a means of identifying possible sources of computational and modeling errors associated with several factors, such as improper modeling of the finite size structure and the supporting infinite soil medium, consideration of structural inertia, and appropriate coupling between boundary and finite element methods. Even though the examples are representative dynamic soil‐structure interaction problems, the remarks and observations are expected to be of value in the numerical treatment of structural dynamic problems solved through BEM and FEM formulations.