Gibson Soil Research Articles

Sidewall Shell Contribution to the Lateral Capacity of Offshore Suction Caissons in Clay

The response of suction caisson (bucket) foundations subjected to horizontal head displacement, or head rotation, is parametrically studied by means of three-dimensional finite-element analyses. The undrained clay stratum is either homogeneous or linearly inhomogeneous (Gibson soil). The effect of the nature of the interface between foundation and surrounding soil is explored with two different scenarios: an ideal case of a fully bonded contact (FBC), and a possibly more realistic tensionless and sliding interface of limited shear resistance (TSI). The latter scenario results in a significant reduction of failure loads. Closed-form expressions are developed for the maximum horizontal and moment capacity for a range of bucket aspect ratios in both soil types, and with both interface conditions. They are validated through comparisons with available results from the literature. The contribution of the suction caisson’s cylindrical sidewall shell to the overall response of the system is investigated. It is shown that for an embedment depth exceeding the caisson’s radius the shell provides practically the same lateral bearing capacity as the whole suction caisson, in contrast with the vertical (axial) loading of a caisson with sliding interface in which the role of the shell is much less significant.

A New Load-Transfer Factor to the Slipping Analytical Formulation in Axially Loaded Piles

The load-transfer factor (ζ) in the concentric cylinder approach is often used in analytical formulation in axially loaded piles. The factor is a constant value (in a given pile slenderness ratio and soil condition) devised under the elastic and ‘pre-failure’ perfect pile–soil bonding conditions (a non-slip analytical model). Given most numerical methods have already considered the pile–soil slipping in the ‘pre-failure’ stage, the limitations of non-slip analytical models have recently been discussed, and slipping analytical models have been recommended. Therefore, this research aims to investigate the load-transfer factor in slipping analytical models. This paper reviews that the factor in slipping analytical models is only constant in linear elastic and some Gibson soil conditions. Beyond these conditions, the factor varies as the pile-head load increases in some cohesionless soils. Adopting the existing constant factor in slipping analytical models will deviate the load–displacement results, as supported by numerical results. Therefore, a new equation is proposed to the load-transfer factor, and a new analytical method is proposed by varying the load-transfer factor during loading for improvement. Results presented in this paper demonstrate improved load–displacement results.

Refined model for rectangular thin plates on two-parameter foundations using an iterative procedure

The main purpose of this study is to investigate the influence of soil heterogeneity on the mechanical responses of rectangular plates resting on elastic foundations and to determine reasonable physical model parameters. The bending problem of rectangular thin plates lying on Gibson elastic foundations is solved using an iterative procedure. First, plates and foundations are discussed as a whole system, based on the principle of minimum potential energy. Second, the governing equations and boundary conditions for plates are established. And the equation for the attenuation parameter in the mathematical model is also derived. Then an iterative procedure is used to iterate the two parameters simultaneously, which solves a key issue for the two-parameter foundation model. Third, a double Fourier series with supplementary functions is adopted, and the solution to the bending problem is obtained. The agreements between the numerical results and the literature results prove that the refined model is practical and achievable. The proposed method exhibits a certain universality in analyzing the interactions between rectangular thin plates and elastic foundations. Furthermore, Gibson soil has an influence on the structural responses of rectangular plates on elastic foundations.

Bending Analysis of Circular Thin Plates Resting on Elastic Foundations Using Two Modified Vlasov Models

The influence of soil heterogeneity is studied on the bending of circular thin plates using two modified Vlasov foundation models. The model parameters are determined reasonably using an iterative technique. According to the principle of minimum potential energy and considering transversely isotropic soils and Gibson soils, the governing differential equations and boundary conditions for circular thin plates on two modified Vlasov foundations are derived using a variational approach, respectively. The determination of attenuation parameters is a difficult problem, which has hindered the further application of the Vlasov foundation model. The equation that must be satisfied by the attenuation parameter is determined, and an iterative method is used to solve the problem. A comparative analysis is conducted between two modified Vlasov models and the traditional Vlasov model. The results show that the governing equations and boundary conditions for circular thin plates resting on two modified foundations are consistent with those for a circular thin plate on traditional two-parameter foundation after degradation. The accuracy and reliability of the proposed solutions are demonstrated by comparing the obtained results with those reported in the literature. The heterogeneity of soils, including the transversely isotropic soils and Gibson soils, has a certain effect on characteristic parameters of the foundation models as well as the deformations and internal forces of circular thin plates. The present study could be employed as a reference for future engineering designs.

Influence of soil non-homogeneity on the base shear force of piled structures subjected to harmonic seismic waves

This paper aims at analyzing the effects of soil non-homogeneity on the dynamic behavior of piled structures. In order to fulfil this objective a procedure based on a substructuring model, which includes soil-structure interaction effects, is used to compute the dynamic response of slender and non-slender structures supported on several pile group configurations embedded in four different linear-elastic Gibson soil profiles. A numerical model based on the integral formulation of the elastodynamic problem and Green’s functions for the layered half space is used for the purpose of determining the foundation dynamic response in terms of impedances and kinematic interaction factors. The results obtained in terms of structural base shear force for each one of the variable-with-depth soil profiles are compared to those computed for an equivalent homogeneous soil. A significant influence of the soil profile on the structural harmonic response to seismic waves is observed in terms of maximum shear force at the base of the structure. The homogeneous assumption when modelling depth-varying soil profiles yields, in many cases, non-conservative results when predicting the structural dynamic behavior.

Iterative technique for circular thin plates on Gibson elastic foundation using modified Vlasov model

In this paper, to investigate the influence of soil inhomogeneity on the bending of circular thin plates on elastic foundations, the static problem of circular thin plates on Gibson elastic foundation is solved using an iterative method based on the modified Vlasov model. On the basis of the principle of minimum potential energy, the governing differential equations and boundary conditions for circular thin plates on modified Vlasov foundation considering the characteristics of Gibson soil are derived. The equations for the attenuation parameter in bending problem are also obtained, and the issue of unknown parameters being difficult to determine is solved using the iterative method. Numerical examples are analyzed and the results are in good agreement with those form other literatures. It proves that the method is practical and accurate. The inhomogeneity of modified Vlasov foundations has some influence on the deformation and internal force behavior of circular thin plates. The effects of various parameters on the bending of circular plates and characteristic parameters of the foundation are discussed. The modified model further enriches and develops the elastic foundations. Relevant conclusions that are meaningful to engineering practice are drawn.

Application of regression models for the estimation of the flexible-base period of pile-supported structures in continuously inhomogeneous soils

Although many research efforts have focused on analyzing the effects of soil-structure interaction considering homogeneous soil profiles and relevant achievements have been made under this assumption, reality is much more complex and structures are usually founded on stratified soils. It would be really interesting to be able to continue taking advantage of the knowledge and models available for homogeneous soils by developing strategies enabling to correct their results in order to consider the actual soil stratigraphy. This paper aims at estimating the flexible-base fundamental period of slender and non-slender structures supported on several pile group configurations embedded in different Gibson soils through a substructuring model which takes into account soil-structure interaction effects. The foundation dynamic impedances are obtained through a numerical model based on the integral formulation of the elastodynamic problem and the use of Green’s functions for the layered half space. The results corresponding to each one of these variable-with-depth profiles are compared to those obtained for a homogeneous soil with the same average shear wave velocity in order to assess the effects of soil non-homogeneity. A significant influence of the soil profile on the structural flexible-base period is observed. A polynomial regression model is applied to obtain closed-form formulae and associated charts for estimating the flexible-base period of a pile-supported structure on different soil profiles. Moreover, these formulae can also be used for computing correction factors needed to estimate the fundamental period of structures supported on layered soils from those obtained with simplified models assuming a homogeneous soil profile.

Elastic Stiffnesses of a Rigid Suction Caisson and Its Cylindrical Sidewall Shell

AbstractA finite-element study is presented for the linear-elastic behavior of rigid suction caisson (bucket) foundations installed in either a homogeneous or nonhomogeneous Gibson soil stratum. Cl...

ANALYTICAL STUDY ON PILED-RAFT FOUNDATION CONSIDERING NONLINEAR BEHAVIOR OF GIBSON SOIL

Randolph (1994) was proposed simplified estimated equations to carried out the proportion of load between the components of piled-raft foundation. These equations are based on elastic theory. Therefore, Authors focus on the point of applicability for nonlinear behavior of soil. This paper is a part of study on behavior of piled-raft foundation under considering the nonlinear behavior of ground. Authors already discussed the effect of nonlinear behavior of soil on the equations by Randolph. In addition, as the extension of research, authors also discussed the applicability of these equations for irregular raft shape. However, foundations were rarely set in an ideal homogeneous single soil layer in our previous studies. Therefore, the applicability of these equations are discussed in case of inhomogeneous soil (Gibson soil) in this paper.

Time Domain Dynamic Analysis of Floating Piles under Impact Loads

In this study, the differential quadrature method (DQM), a mathematically simple, accurate, and computationally efficient numerical tool, was employed to analyze the response of single piles under dynamic axial loading. The dynamic behavior of the piles and surrounding soil were modeled using the one-dimensional (1D) or three-dimensional (3D) axisymmetric elasticity theory, respectively. The governing equations subjected to the related boundary and initial conditions were discretized in both the spatial and temporal domains via DQM. The behavior of the floating piles embedded in a half-space layer of homogeneous and Gibson soils under uniform and sinusoidal impact loads was studied. The piles and the soil behavior were assumed to be linear elastic and linear viscoelastic, respectively. To compare and verify the results obtained from the DQM approach, the problems were also solved via a finite-element-based commercial software program in some cases. The approach was found to have high accuracy and numerical stability. Finally, the effects of the different parameters of the soil and pile on the pile-head settlement time history were investigated.

Three-dimensional upper-bound analysis for ultimate bearing capacity of laterally loaded rigid pile in undrained clay

A new three-dimensional upper-bound combined failure mechanism is presented to analyze the lateral ultimate capacity of rigid piles embedded in various soil conditions, involving homogeneous soils, layered soils, and Gibson soils. The wedge curved failure surface function composed by rotating the Newton interpolation polynomial is adopted near the ground surface, and a plane strain collapse mechanism is employed at depth. Furthermore, the energy dissipation of the transition interface is introduced to keep a kinematically admissible velocity field between the wedge and the plane strain mechanism. An empirical equation is then proposed based on the upper-bound solutions for the homogeneous soils, and extended to the layered soils and Gibson soils. Meanwhile, the three-dimensional arbitrary Lagrangian–Eulerian (ALE) analysis is employed to investigate the distribution of limiting pressures along the pile shaft for different soil parameters. It is found that the upper-bound solutions based on the rigid-plastic assumption only exhibits a good agreement with the finite element (FE) results for a very high soil rigidity index of 10 000, due to a Possion’s ratio of approximate but less than 0.5 in such a typical undrained FE analysis. For such a Possion’s ratio, an inevitably slight elastic volumetric change induces the unexpected cavity flow at the deep section of the pile. It leads to the soil rigidity affecting the profile distribution of the bearing capacity, although it is not true for a real undrained analysis. Finally, a centrifuge test is analyzed by the upper-bound method to further testify the rationality of the new failure mechanism.

Displacement Ductility Capacity Assessment for a Fixed-Head Pile in Cohesionless Soil

AbstractThis study develops assessment formulas for the displacement ductility capacity of a fixed-head pile in cohesionless soils. The derivations of the formulas are based on an ideal model of a semiinfinite nonlinear pile in a Gibson soil, whose subgrade reaction modulus increases linearly with depth, to link the displacement ductility capacity of the pile with the pile–soil system parameters. The parameters in the formulas include the sectional overstrength ratio and curvature ductility capacity, as well as a modification factor for considering soil nonlinearity. The modification factor is a function of the displacement ratio of the pile’s ultimate displacement to the effective soil yield displacement, which is constructed through a number of numerical pushover analyses. The format of the formulas is similar to that for a pile in cohesive soils. For the case of linear soil, the formulas provide a lower-bound estimate of pile ductility capacity; the displacement ductility capacity of a pile in cohesion...

A Unified Treatment of Axisymmetric Adhesive Contact on a Power-Law Graded Elastic Half-Space

In the present paper, axisymmetric frictionless adhesive contact between a rigid punch and a power-law graded elastic half-space is analytically investigated with use of Betti's reciprocity theorem and the generalized Abel transformation, a set of general closed-form solutions are derived to the Hertzian contact and Johnson–Kendall–Roberts (JKR)-type adhesive contact problems for an arbitrary punch profile within a circular contact region. These solutions provide analytical expressions of the surface stress, deformation fields, and equilibrium relations among the applied load, indentation depth, and contact radius. Based on these results, we then examine the combined effects of material inhomogeneities and punch surface morphologies on the adhesion behaviors of the considered contact system. The analytical results obtained in this paper include the corresponding solutions for homogeneous isotropic materials and the Gibson soil as special cases and, therefore, can also serve as the benchmarks for checking the validity of the numerical solution methods.

Variational elastic solution for axially loaded piles in multilayered soil

SUMMARYMost analytical or semi‐analytical solutions of the problem of load‐settlement response of axially loaded piles are based on the assumption of zero radial displacement. These solutions also are only applicable to piles embedded in either a homogeneous or a Gibson soil deposit. In reality, soil deposits consist of multiple soil layers with different properties, and displacements in the radial direction within the soil deposit are not zero when the pile is loaded axially. In this paper, we present a load‐settlement analysis applicable to a pile with circular cross section installed in multilayered elastic soil that accounts for both vertical and radial soil displacements. The analysis follows from the solution of the differential equations governing the displacements of the pile–soil system obtained using variational principles. The input parameters needed for the analysis are the pile geometry and the elastic constants of the soil and pile. We compare the results from the present analysis with those of an analytical solution that considers only vertical soil displacements. The analysis presented in this paper also provides useful insights into the displacement and strain fields around axially loaded piles. Copyright © 2011 John Wiley & Sons, Ltd.

Boundary element analysis of axially loaded piles embedded in a multi-layered soil

In a field, piles are likely installed in a multi-layered soil. Analysis of axially loaded piles in a multi-layered soil is complicated and deserves more attention. A boundary element method is used in this study to analyze an axially loaded single pile in a multi-layered soil using the solution for vertical and horizontal axisymmetric ring loads in a multi-layered elastic medium. Good and reasonable agreement is obtained between the proposed and published solutions for a single pile in a homogenous soil, a finite soil, and a Gibson soil. The proposed solution is also used to evaluate an axially loaded single pile in a multi-layered (8 layers) soil.

Stiffness of a Flexible Circular Footing Embedded in an Elastic Half-Space

This paper addresses the problem of a circular footing of finite but nonzero stiffness embedded in an isotropic nonhomogeneous elastic half-space. The problem is solved by coupling the scaled boundary finite-element method with axisymmetric shell finite elements. The coupling of the two methods is validated by comparing computed solutions with analytical solutions for a flexible footing subjected to a uniformly distributed vertical load embedded in an elastic full-space. Based on the finding that the bending stiffness of the footing dictates the response for vertical and moment load cases, whereas the normal stiffness of the footing dominates the horizontal response, a convenient method for estimating dimensionless elastic stiffness coefficients is presented graphically. New results are presented for homogeneous and Gibson soil profiles and Poisson’s ratios of 0.2 and 0.499, to represent both sand and clay. An example demonstrating a practical application of these results is also provided.

Vertically Loaded Single Piles in Gibson Soil

The available closed-form solutions for vertically loaded piles have been, strictly speaking, limited to homogeneous soil, or nonhomogeneous soil with the shear modulus as a power of depth. The latter solutions —based on a zero shear modulus at ground surface—are generally sufficiently accurate for normally consolidated soil. For overconsolidated soil, however, there is generally a nonzero shear modulus at the surface, which may affect pile response. In this note, rigorous closed-form solutions are established to account for the nonhomo- geneity of soil profile with nonzero shear modulus at ground surface. The solutions are developed using a load transfer approach, and are shown to give satisfactory results in comparison with a more rigorous continuum- based numerical approach, when the proposed load transfer factors are adopted.

Effects of variable shear modulus on wave‐induced seabed response

The shear modulus of a seabed is an important soil parameter in the analysis of the wave‐seabed interaction problem. However, most previous investigations have only considered a porous seabed with uniform shear modulus, despite strong evidence of shear modulus varying with soil depth have been reported in the literature. In this study, the seabed is treated as varying linearly with soil depth (i.e., Gibson soil). The wave‐induced seabed response is found to be affected significantly by variable shear modulus.

Wave-induced pore pressure around a buried pipeline in Gibson soil: finite element analysis

The water wave-induced pore pressure on a pipeline buried in a porous seabed is investigated. Unlike conventional investigations, shear modulus of the seabed is considered to vary with soil depth in this study. The boundary value problem describing soil stresses as well as pore water pressure under periodical wave loading is solved numerically by using a Finite Element Method. Employing the principle of repeatability, the lateral boundary conditions are obtained first and verified with previous analytical solutions. Then, the wave-sealed-pipe interaction problem can be solved to obtain the wave-induced soil response. The effects of variable shear modulus, geometry of the pipe and the degree of saturation on the wave-induced pore pressure are found to be significant.

Approximate Displacement Influence Factors for Elastic Shallow Foundations

Displacement influence factors for calculating the magnitudes of drained and undrained settlements of shallow foundations are approximated by simple numerical integration of elastic stress distributions within a spreadsheet. Influence factors for circular foundations resting on soils having homogeneous (constant modulus with depth) to Gibson-type (linearly increasing modulus) profiles with finite layer thicknesses are obtained by summing the unit strains from incremental vertical and radial stress changes. The effects of foundation rigidity and embedment are addressed by approximate modifier terms obtained from prior finite-element studies. Results are compared with closed-form analytical and rigorous numerical solutions, where available. A new solution for Gibson soil of finite thickness is presented.