Soil-foundation Interaction Research Articles

Analysis of Large-Size Flexible Shallow Foundation Settlement Basing on Foundation-Soil Interaction

The large-size flexible shallow foundation （LFSF） can not be designed fully in accordance with the shallow foundation design specification, for there are differences between LFSF and traditional shallow foundation. Taking the foundation project of Shenzhen Mawan port for example, considering the interaction between foundation and ground base and adopting a non-linear foundation model, the impact of foundation parameters and load conditions on basal pressure and foundation settlement were simulated to value adoption of the height-width ratio by finite element method. Analysis showed that soil physical parameters of elastic modulus, Poisson's ratio had great impacts on basal pressure and foundation settlement, and the accuracy of these parameters should be ensure in modeling. However the effects of expansion angle and cohesion were relatively small. The values of expansion angle and cohesion can refer to design specification. Foundation of this type mainly focus on flexural design.

Model Test and Study on Pile Foundation in Transversely Isotropy Clay

To further verify the feasibility of theoretic calculation, according to similarity theory, the principles and methods of pile foundation-soil interaction in saturated soft clay are determined. It studies acceleration interaction of each test point on the soil surface under the same largest shock force with different frequency on the top of the pile. The results of experiment show that the acceleration interaction trend of each point changes with the change of shock frequency, it shapes like a down N with the shock frequency of 5Hz, like an M with the shock frequency of 10Hz, like a down V under the shock frequency of 15Hz～30Hz. With the shock frequency of 40Hz and 50Hz, it likes a plane curve (hyperbolic curve) shape.

Effects of longitudinal variability of soil on a continuous spread footing

A simple model, describing the soil–foundation interaction for continuous wall footing, and which takes longitudinal variations in soil's properties into account, is presented in this paper. This model has been developed using a finite element representation in which a 1D structure (continuous spread footing) rests on a spatially variable soil, described by Winkler-type springs, characterized by the subgrade reaction coefficient. Geotechnical (pressuremeter tests) and geophysical (VLF-R: Very Low Frequency-Resistivity mode) surveys, performed over a selected study area resting on an alluvial terrace, were used to provide information on the soil's variability, and to reveal the presence of clayey soil. Three kinds of natural variability are considered: natural soil variations, rapid variations in the soil's properties, and shrinkage of clayey soil. A relationship between the coefficient of subgrade reaction and the resistivity was observed. The spatial variability of the coefficient of subgrade reaction was analyzed using geostatistics, and then used in the model to derive differential settlements and bending moment values of a continuous spread footing, which cannot be predicted if the soil is assumed to be homogeneous, or if shrinkage under the continuous wall footing is not taken into account. Results show that, as is often the case in practice, when the longitudinal soil variability is not taken into account, the design may be unsafe.

Simple Method for Dynamic Interaction between Two Rigid Foundations

In the past many researchers studied dynamic stiffness and damping coefficients of surface and embedded rigid foundations of arbitrary shapes in the elastic homogenous half space. Dynamic stiffness and damping coefficients were obtained by using regularly shaped foundations instead of arbitrarily shaped ones. Obviously, the calculating methods were not perfect. In addition, the two parameters mentioned above were calculated only in the case of a single foundation. But the cases of two or more foundations were not presented because the interactions between foundations were not considered in all present papers. This paper eliminates two faults named above by using the assumption of the plane strain and of dynamic foundation-soil interaction factors. The calculating method of dynamic impedances presented by the paper proved to be accurate and practical.

Approximate Boundaries for Finite-Element Models of Static Soil–Foundation Interaction Problems

In this paper, we examine the use of boundary springs as approximate external boundary conditions for the typical soil islands encountered in finite-element (FE) models of soil–foundation interaction problems. We present a set of simple uniformly distributed boundary springs and a set of variable boundary springs that account for the lateral distribution of contact forces between the foundation and the soil. We evaluate the accuracy of the approach for shallow foundations resting on soil islands of different dimensions. It is shown that significantly smaller errors can be achieved with these boundary springs than those obtained when fixed-fixed or fixed-free external boundary conditions are used. We present an iterative approach to determine the boundary springs for cases in which extremely small soil islands are required. Although the approach suggested to determine the boundary springs is best suited to shallow foundations, good results are also obtained for pile foundations. The approach presented applies to a uniform elastic half-space, but extensions to layered media are possible.

Dynamic Analysis of the Superstructure-Pile Foundation-Soil Interaction System under Earthquake Based on Fuzzy Theory

Based on frequency domain method, the seismic responses of the superstructure-pile foundation-soil system are studied taking the dynamic soil-structure interaction into consideration. For analyzing the earthquake response of cylindrical pile foundation, earthquake response analysis of three-dimensional system of pile foundation-soil-superstructure simplify two-dimensional question. The dynamic responses of the interaction system under EI-Centro ground motion excitation are evaluated by using secondary development of the large general finite analysis software Abaqus. It is shown that pile foundation is more anti-seismic and that pile foundation flexibility can improve the structural basic cycle. Based on a comprehensive assessment theory, soil-superstructure interaction problem under Earthquake is analyzed by second-level evaluation of comprehensive evaluation. By applying comprehensive evaluation method fuzzy theory model of soil-superstructure interaction is built. It is show that fuzzy mathematics method is appropriate for this kind of soil-superstructure interaction problem.

PERPETUATE Project: The Proposal of a Performance-Based Approach to Earthquake Protection of Cultural Heritage

The paper describes the methodology proposed in the PERPETUATE Project (funded by the Seventh Framework Programme – Theme ENV.2009.3.2.1.1). The methodology proposed in PERPETUATE uses a displacement-based approach for the vulnerability evaluation and design of interventions. The use of safety verification in terms of displacement, rather than strength, orients to new strengthening techniques and helps in the comprehension of interaction between structural elements and unmovable artistic assets. The procedure is based on the following fundamental steps: definition of performance limit states, specific for the cultural heritage assets (considering both structural and artistic assets); evaluation of seismic hazard and soil-foundation interactions; construction knowledge (non-destructive testing, material parameters, structural identification); development of structural models for the seismic analysis of masonry structures and artistic assets and design of interventions; application and validation of the methodology to case studies. Two main scales are considered: the seismic risk assessment at territorial scale and at the scale of single historic building or artistic assets. The final aim of the project is to develop European Guidelines for evaluation and mitigation of seismic risk to cultural heritage assets.

Application and Validation of Practical Tools for Nonlinear Soil-Foundation Interaction Analysis

Practical guidelines for characterization of soil-structure interaction (SSI) effects for shallow foundations are typically based on representing foundation-soil interaction in terms of viscoelastic impedance functions that describe stiffness and damping characteristics. Relatively advanced tools can describe nonlinear soil-foundation behavior, including temporary gap formation, foundation settlement and sliding, and hysteretic energy dissipation. We review two tools that describe such effects for shallow foundations and that are implemented in the computational platform OpenSees: a beam-on-nonlinear-Winkler foundation (BNWF) model and a contact interface model (CIM). We review input parameters and recommend parameter selection protocols. Model performance with the recommended protocols is evaluated through model-to-model comparisons for a hypothetical shear wall building resting on clay and model-data comparisons for several centrifuge test specimens on sand. The models describe generally consistent moment-rotation behavior, although shear-sliding and settlement behaviors deviate depending on the degree of foundation uplift. Pronounced uplift couples the moment and shear responses, often resulting in significant shear sliding and settlements. Such effects can be mitigated through the lateral connection of foundation elements with tie beams.

Seismic Analysis and Design of Pile Group Bridge Foundations in Soft and Liquefied Soil

A pile group foundation is a highly indeterminate system with non-linearities caused by soils and pile and cap materials. The cap footing is often sufficiently rigid to develop a linear variation in the pile axial forces induced by the imposed moments. However, a nonlinear foundation–soil interaction analysis is required to perform a reliable evaluation of capacity and displacement demands for seismic design. A detailed nonlinear analysis using advanced numerical techniques, such as the finite element method to model the soil response and soil–foundation interactions during a seismic event, can be complex and time-consuming. The complexity is significantly greater when the foundation supports high and multidirectional dynamic loads induced during seismic events, especially when the foundation soil is soft or predicted to liquefy. Because of time and resource constraints—and for the case of liquefied soils, considering the difficulties and uncertainties associated with developing constitutive models—such an analysis is often neither feasible nor desirable for small to medium-size projects. It is, therefore, necessary to develop simplified and practical analysis methods, with clearly defined applicability and limitations, and with appropriate built-in conservatism, for the seismic analysis and design of such foundations. This paper summarizes the results of a recent study on the subject. Applications of simplified two-dimensional and three-dimensional analysis methods are demonstrated. Effects of the footing rigidity and direction of the applied seismic shear and moment on the response are also presented.

Nonlinear Soil–Abutment–Foundation–Structure Interaction Analysis of Skewed Bridges Subjected to Near-Field Ground Motions

This paper investigates the behavior of skewed highway bridges subjected to earthquake loading with strong velocity pulses. The behavior of bridges with skewed abutments in the longitudinal direction is strongly coupled by transverse loading. The interaction between skewed bridge abutment foundations and backfill has a strong impact on dynamic bridge response. While bridge structures may remain in the linear range during seismic loading, local nonlinear behavior at the abutment–embankment interface can cause significant nonlinear bridge structure response. Skewed bridge models are presented incorporating soil–abutment–structure interaction using nonlinear abutment springs. As a case study, a global three-dimensional nonlinear finite element model of the skewed and seismically instrumented Painter Street overpass in Rio Dell, California, with monolithic abutments was developed. The model used nonlinear foundation–soil interaction based on approach soil properties from geotechnical tests. A soil continuum finite element analysis was performed using constitutive hardening soil material to evaluate abutment backfill passive resistance considering backwall skew. The bridge response resulting from seismic ground motion records was compared with structure response data. The computer models represented fairly well the overall seismic response of the skewed bridge. Bent pile foundations had much less impact on overall bridge response than the abutments. Near-fault ground motions with high-velocity pulses generated asymmetrical impulsive loading and large displacements in transverse directions leading to significant rotation and residual deck displacement. These permanent structure displacements can control the design of the abutment seat width and shear keys and could exceed column displacement capacity and impose additional moment at the column not considered in current design.

Experimental evaluation of vertical response of rigid surface footing on layered soil

The study of the dynamic response of foundations is of significant importance in the machine foundation design and soil-foundation interaction problems, in general. This paper presents experimental investigations in the field studying the effect of layering of soil mass on the dynamic response of foundation under vertical mode of vibration. Model block vibration tests on a rigid surface footing were conducted on different layered soil systems. A concrete block of size 400×400×100 mm was used as the model block and a Lazan type mechanical oscillator was used for inducing vibration in vertical direction. In the investigation two different soils, namely, gravel and fly ash were used. In total 132 tests were conducted on different layered soil beds with different loading combinations. Dynamic response of foundation resting on layered soil system were also analyzed by two simple approximate methods namely, mass spring dashpot model and equivalent elastic half-space theory. Results obtained from the two methods were compared with that obtained from the experimental investigation. It was found from the comparisons that the simple mass-spring dashpot model was capable of predicting the resonance frequency and the resonance amplitude satisfactorily. Elastic half space theory with equivalent soil properties was found to underestimate the displacement amplitude.

On the bounding of limit multipliers for combined loading

In the framework of classical plasticity, even when limit multipliers and collapse mechanisms associated with different loads independently acting on a solid or structure are known, not much can be inferred on the limit multiplier of the combined loading. Frame structures under the action of dead loads and seismic forces, soil–foundation interaction problems, tunnels under a variety of loads, deepwater pipelines subject to bending and pressure constitute only a few selected examples for which some sort of superposition rule, as well as bounding techniques, would be extremely useful. The present paper introduces a set of theorems for bounding limit multipliers for combined loads. In particular, ranging from a minimum knowledge about the critical state under a particular loading to a reasonable guess of the kinematics of the problem under combined loads, more and more refined bounds for the overall limit multiplier are derived. The results, to the best of the authors’ knowledge, are novel and a few examples showing their practical value are presented and discussed.

Physical modelling of the push-over capacity of a jack-up structure on sand in a geotechnical centrifuge

Offshore jack-up drilling rigs are subjected to loading from wind, waves, and current in addition to their self-weight. This applies combined loading in all six degrees-of-freedom in space on the footings. Although the foundation–soil interaction is crucial to the overall response of a jack-up structure, current state-of-the-art models to predict jack-up footing behaviour, developed using data from single footing experiments, have not been validated for such multi-footing systems under general combined loading. This paper introduces the experimental development of a three-legged model jack-up and loading apparatus designed to investigate the rig’s response — in particular the footing load paths — under combined loading in three dimensions. Push-over experiments were performed in a geotechnical beam centrifuge on silica sand. Experimental results of two tests on dense sand are discussed, highlighting differences in response and mode of failure depending on the loading direction of the jack-up. The importance of three-dimensional modelling is also stressed by experimentally demonstrating that the symmetric load case is not necessarily conservative.

Three-dimensional numerical analysis of centrifuge experiments on a model jack-up drilling rig on sand

Jack-up drilling rigs are usually founded on three shallow footings. Under wind, wave, and current loading offshore, the footings of these tall multi-footing systems transfer large moment loads in addition to self-weight, horizontal load, and even torsion to the underlying soil. To be able to deploy a jack-up safely at a particular offshore site, the unit’s capacity to withstand a 50 year return period storm is required to be checked in accordance with current guidelines (Site specific assessment of mobile jack-up units, The Society of Naval Architects & Marine Engineers). As the overall system behaviour is influenced significantly by the footing restraint, models that account for the complex nonlinear foundation–soil interaction behaviour are required to be integrated with the structural and loading models. Displacement-hardening plasticity theory has been suggested as an appropriate framework to formulate force-resultant models to predict shallow foundation behaviour. Recent research has extended such a model to account for six degree-of-freedom loading of circular footings on sand, allowing integrated structure–soil analysis in three dimensions. This paper discusses “class A” numerical predictions of experiments on a model jack-up in a geotechnical centrifuge, using the integrated modelling approach, and critically evaluates the predictive performance. The numerical simulations are shown to represent a significant improvement compared with the method outlined in the current guidelines.

Mid-Column Pounding of Multi-Story Reinforced Concrete Buildings considering Soil Effects

In this paper an analysis of seismic pounding of reinforced concrete buildings with non-equal story heights including soil-structure interaction is presented. Two building configurations, configuration A: 10-story and 9-story buildings and configuration B: two 5-story buildings, are considered. The discrete model is used to incorporate foundation-soil interaction and pounding between buildings is incorporated through impact elements that consist of a gap element and a Kelvin-Voigt element. The responses of the buildings are compared in terms of impact forces, interstory displacements and normalized story shear for two near-field and two far-field earthquakes. The buildings under consideration experience the maximum impact forces and interstory displacements due to the near-field earthquakes for both fixed foundation and flexible (soil) foundation cases. Significant reduction in impact forces are observed when the underlying soil effect is considered. The maximum interstory displacements occurred when there is no pounding. In most of the cases, the consideration of soil results in lower normalized story shear.

Effects of Seasonal Freezing on Bridge Column–Foundation–Soil Interaction and Their Implications

Several seismic regions around the world experience seasonal freezing that can drastically alter the soil-foundation-structure interaction and structural response under earthquake loads. This paper analytically investigates the effects of seasonal freezing on lateral load response of a bridge column supported by a cast-in-drilled-hole (CIDH) foundation shaft. Accounting for the temperature effects on materials, the analyses were conducted at ambient temperatures of 23° C, −1° C, −7° C, −10° C, and −20° C, and the results obtained at 23° C and −10° C were validated using experimental data. In comparison to the response at 23° C, the response of the column-shaft system in the range of −1° C to −20° C exhibited 40%–188% increase in the effective elastic stiffness, 17%–63% reduction in the lateral displacement capacity, 0.54–0.82 m upward shift in the maximum moment location, 25%–30% increase in the column shear demand, and 25%–80% increase in shear and 19%–68% reduction in the length of the plastic region in the CIDH shaft.

Static analysis of soil/pile interaction in layered soil by BEM/BEM coupling

In this article we propose to use the boundary element method (BEM) to analyze soil–foundation interactions. The soil structure is modeled as several dissimilar strata placed one on top of the other, composing a sandwich-like profile. Any of these layers may contain components of the foundations. Each region occupied by a soil layer or by a foundation component is handled as a 3D isotropic, elastic and homogeneous domain, and is analyzed by BEM. As a consequence of the positioning of the various subregions in this model, the technique of successive rigidity can be applied directly, resulting in a considerable reduction in the volume of data being stored and manipulated throughout the analysis.

Nonlinear interactive analysis of cooling tower–foundation–soil interaction under unsymmetrical wind load

This paper deals with physical and material modelling of a cooling tower–foundation–soil system. The physical modelling has been carried out using solid 20-noded isoparametric element to model the cooling tower, annular raft foundation and soil media. The cooling tower–foundation–soil system was analysed under vertical and lateral load generated due to self-weight and wind loads. The soil nonlinearity has been taken into consideration using hyperbolic nonlinear elastic constitutive law. The response of the structure has been investigated with respect to displacement and stresses. Moreover, an attempt has been made to study the effect of the linear and nonlinear interactive analyses compared with conventional analysis. It was seen that the interactive analysis of the cooling tower–foundation–soil media plays a major role in releasing the stresses in the cooling tower, particularly at the bottom ring beam.

A semi-analytical approach for analyzing ground vibrations caused by trains moving over elevated bridges

A semi-analytic approach is presented for the three-dimensional analysis of ground vibrations induced by trains moving over elevated bridges. The train is modeled as two sets of moving loads, with one for the front wheels and the other for the rear ones, the elevated bridge as a series of elastically supported beams, and the ground as a viscoelastic half space. Three key elements are considered in the solution: (1) the analytic solution for the vibration of an elastically supported beam under a series of moving loads, (2) the impedance of the foundation–soil system, and (3) Green's function for an elastic half space under a harmonic point load. Such an approach allows us to consider the structural dynamics of the elevated bridge, the foundation–soil interaction, and the wave propagation characteristics in the half space. From the numerical examples studied, the proposed approach was demonstrated to be accurate and efficient. The framework of analysis described herein can be generalized to solve problems with complex foundations and layered soils.

New developments on BE/BE multi-zone algorithms based on krylov solvers: applications to 3D frequency-dependent problems

In this paper, new developments concerning the use of BE/BE coupling algorithms for solving 3D time–harmonic problems are reported. The algorithms are derived by considering different iterative solvers. Their chief idea is to work with the global sparse matrix of the coupled system, however without considering the many zero blocks associated with the non–coupled nodes of different subregions. The use of iterative solvers makes it possible to store and manipulate only the block matrices with non–zero coefficients. Preconditioned iterative solvers based on the Lanczos, bi-conjugate gradient, and GMRES (generalized minimal residual) methods are used to derive the BE/BE coupling algorithms. A description of the formulation of these solvers, which are completely general and can be applied to any non–singular, non–hermitian systems of equations, is provided. The performance of the algorithms is verified by solving some foundation–soil interaction problems. Important parameters for estimating the efficiency of the algorithms as required CPU times, matrix sparsity, and accuracy of the obtained responses are presented in the results of the paper.