Soil-foundation System Research Articles

A meta-heuristic optimization-based approach for 3D simplified parametric analysis of embedded soil-foundation systems undergoing coupled horizontal-rocking vibrations

This paper presents a novel modeling approach based on meta-heuristic optimization for constructing adaptive lumped-parameter models to approximate the dynamic response of a shallow foundation in layered soil considering coupled horizontal and rocking vibrations. The developed model is adaptive to complexities of impedance functions for different types of layered soil deposits. The optimal parameters of the proposed model are computed using three optimization algorithms, with the forensic-based investigation outperforming the others and being chosen as the best optimization strategy for numerical investigations. A parametric study of foundation characteristics and soil properties on frequency response curves, including magnification factors and phase angle, is performed to comprehensively verify the proposed model’s appropriateness. The findings reveal that dynamic responses of the proposed simplified systems are perfectly consistent with those computed using existing impedances and worldwide-recognized software in both frequency and time domains. It shall be concluded that the proposed model is compatible with different soil profiles and more effective than existing models in approximating the unbounded behavior of layered soil. Furthermore, it offers great potential to implement the time-history analysis of interacting systems subjected to forced vibrations and seismic motions in commercial software based on the proposed model for engineering practice.

Dynamic Analysis of Block-Type Machine Foundation Using Barkan’s Model for Various Soil Parameters

Machine foundation involves both the static loads and the dynamic loads caused by working of the machine. The machine weighs several tons and is required to restrict amplitudes to only a few microns. Inadequately constructed foundations may result in failures exceeding many times the cost of the capital investment required for properly designed foundations. This necessitated a deeper scientific investigation of dynamic loading and analysis. Method proposed by Barkan (recommended by IS: 2974-1982) for design of machine foundations under harmonic load, still remains the most popular method for vibration analysis of block foundations in Indian industry. Finite Element (FE) is very commonly accepted analysis tool for solution of engineering problems. Effective Pre and Post-processing capabilities make modeling and result interpretation simple. The current paper aims to do the parametric study of dynamic analysis of block foundation using Barkan’s method. For the same, three different machines of 150 rpm, 250 rpm and 450 rpm are taken into account and six different soil types: (a) Medium, Stiff and Hard Clay and (b) Loose, Medium and Dense Sand are considered. Foundation sizes are optimized according to soil cases and each case is analysed using conventional method and FEM model using STAAD Pro. for 0.8, 1 and 1.2 times the soil parameters to cover the confidence range. This study is further extended for the comparison of concrete quantity consumed. The results grossly show that as the clay varies from medium to hard, and sand from loose to dense, the foundation size required, decreases. It was seen that, with the increase in stiffness of soil, natural frequency of machine foundation soil system increases and amplitude of foundation reduces. Also, FEM method of analysis indicates safer amplitude of foundation compared to classical method of analysis, inferring to conventional method being conservative.

Influence of Stone Columns on Seismic Response of Buildings Considering the Effects of Liquefaction

In this paper, the behaviour of a soil-foundation system supported on a stone column-reinforced liquefiable soil strata is investigated through finite element analysis. The numerical analyses are performed on a five story reinforced concrete moment resisting building supported on a raft foundation. The influence of stone column slenderness ratio on liquefaction mitigation is studied by varying the length of stone columns at a constant area replacement ratio. The results are obtained based on the excess pore pressure, free-field soil settlement, foundation settlement, acceleration response, superstructure's inter-story drift, and lateral story displacement for each ground motion. The results showed that the liquefaction of free-field soil had a major impact on the foundation settlement and building lateral deformation. With the inclusion of stone columns, excess pore pressure ratio in the free-field region reduced considerably, which had immediate effects on the building's lateral deformation.

Approximate analytical solution of tunneling‐induced responses of a soil–foundation system using contact mechanics

AbstractEstimating the tunneling‐induced responses of a soil–foundation system is crucial for safety control in urban underground engineering. In existing analytical research, the soil–foundation interaction is considered based on the Winkler soil model, with minimal focus on the continuum soil model. Hence, in this study, based on the continuum soil model, an approximate analytical solution is derived to predict the tunneling‐induced responses of a soil–foundation system considering the contact effect, where an approximation by replacing the surface of the complex variable solution for an elastic half‐plane with a tunnel with the mathematical expression of Sagaseta's ground loss settlement formula is adopted. A new strategy is proposed to optimize the derivation process, where the normal contact pressure after tunnel excavation is directly determined using the contact mechanics, and the proposed solution is obtained using the superposition principle. Subsequently, the approximation is proven to be accurate when the ratio of the buried depth to the tunnel radius is greater than 2.00. The proposed solution meets the given conditions and is in good agreement with numerical results, which verify the correctness of analytical solution. Furthermore, a parametric study is performed to investigate the influences of the key parameters on the mechanical responses. The results indicate that the proposed solution can quantitatively describe the nonlinear contact characteristics in the soil–foundation system; the contact effect is found to contribute to the discontinuous displacement and stress concentration when subjected to the significant effects of tunnel excavation.

Effect of structural inertia on liquefaction-induced settlements of shallow foundations

The majority of published research on the performance-based design of shallow foundations on liquefiable soil focuses on seismic settlement accumulation by neglecting soil-structure-interaction (SSI) effects. On the other hand, SSI effects prove dominant when the foundation soil is non-liquefiable. Thus, the aim of this paper is to investigate the dynamic response of structure-foundation-soil (SFS) systems by examining the role of structural inertia on the performance of shallow foundations on liquefied soil, through a series of 3D fully coupled nonlinear numerical analyses of SFS systems. As a first step, the nonlinear fundamental period of vibration of the SFS system is correlated to the key system and excitation parameters. Next, in order to isolate the effects of structural inertia, shear-induced seismic settlements of SFS systems in liquefied soil are compared with the respective settlements of conjugate foundation-soil (FS) systems that apply the same static contact pressure on the foundation soil. Finally, approximate relations are proposed for the effects of structural inertia on liquefaction-induced settlements of shallow foundations, based on a multivariable statistical analysis of the numerous parametric numerical estimates.

Fragility Analysis of Helical Piles Supporting Bridge in Different Ground Conditions

This paper examines the seismic performance of a bridge–helical pile foundation based on the seismic fragility analysis, considering the element fragility of a coupled bridge–soil–foundation system. Nonlinear time history analyses were conducted using a finite-element modeling scheme that was validated using the results of large-scale shaking table tests of soil–piles–structure systems involving both liquefiable and nonliquefiable soils. Incremental dynamic analysis was conducted to generate the fragility curves for a two-span bridge supported on helical piles in nonliquefiable and liquefiable sites considering a suite of ground motions. The damage limit states were defined to describe the capacity of the bridge components. In total, 440 nonlinear time-history analyses were performed to evaluate the seismic demand of the helical piles and the bridge-reinforced concrete pier components, and the results were used to establish their fragility curves. The results revealed that the helical piles were the most fragile component in the nonliquefiable and liquefiable tests. The liquefiable soil could decrease the seismic demand on the column lateral deformation and increase the demand dispersion. On the other hand, the reinforced concrete pier exhibited a large drift response in the nonliquefiable soil, causing it to be more vulnerable to seismic hazards than in the case of liquefiable soil.

Seismic response of large offshore wind turbines on monopile foundations including dynamic soil–structure interaction

This paper presents the results of a study on the dynamic and seismic response of the support structures of three reference Offshore Wind Turbines (OWT) of increasing rated power, founded to the seabed through monopile foundations. Thus, the structural behaviour of the NREL 5 MW, IEA Wind 10 MW and IEA Wind 15 MW reference OWTs under seismic input is analysed. To do so, a model based on the aero-hydro-servo-elastic OpenFAST open-software code, modified to include dynamic Soil–Structure Interaction (SSI) and input ground motion, is employed. Dynamic SSI phenomena are incorporated through lumped parameter models fitted to the impedances computed using an advanced boundary elements–finite elements model of the soil–foundation system in which the monopile is discretized as a steel pipe buried in the unbounded seabed. The fore–aft and side-to-side responses of the systems are computed under power production, parked and emergency shutdown operating conditions considering different earthquakes and arrival times. It is found that even low and moderate intensity earthquakes can produce significant increases in the structural demands of large OWTs. There exists a clear tendency for SSI to be beneficial when the size of the OWT increases.

Learning from a Well-documented Geotechnical Cold Case: The Two Towers of Bologna, Italy

ABSTRACT The Garisenda Tower and the Asinelli Tower, also widely known as the Two Towers, are the best preserved and famous medieval towers in the city of Bologna (Northern Italy). Standing one close to the other, right in the heart of the city centre, the Two Towers are delicate remains of the old towered city, which counted more than 75 towers in the 12th century. The foundations of historic towers and the surrounding soil often hide major hazards for the long-term preservation of these heritage structures. The initial fundamental step to this aim is indeed a deep understanding of their original conception, foundations and subsoil. However, the idea that also such elements are an integral part of the overall structure, and thus subjected to the same conservation rules, is relatively new. The present paper outlines the investigation criteria applied to the soil-foundation systems of the Two Towers of Bologna and describes the authenticity of their characteristics, through the interpretation of new experimental data and the analysis of historical documents. A geotechnical perspective on this type of monuments turns out to be crucial in order to effectively understand the soil-structure interaction mechanisms, which govern their safety conditions over time. This study also aims to better understand the reasons why the Two Towers of Bologna, despite their numerous similarities, have reached completely different structural configurations. The methodology described to investigate this case study, which required the integration of several aspects, can be usefully applied to any historic tower.

SPH-DEM modeling of the seismic response of shallow foundations resting on liquefiable sand

In this study, the seismic response of shallow foundations resting on a liquefiable soil layer is modeled using a coupled smoothed particle hydrodynamics (SPH)-discrete element method (DEM) scheme. In this framework, the soil deposit is represented by an assembly of DEM particles and the fluid domain is lumped into a set of SPH particles carrying local fluid properties. The averaged forms of Navier-Stokes equations dictate the motion of the fluid-particle mixture and the interphase forces are estimated using well-known semi-empirical equations. A saturated soil-foundation system with an average contact pressure of 50 kPa was created using the coupled scheme. The foundation block was composed of a collection of DEM particles glued together by high-stiffness bonds. No-penetration boundary condition was applied to all sides of the foundation block to allow for fluid-foundation interaction. The model was subjected to a strong base acceleration and the response was analyzed and compared to the free-field. The ground settlement in the soil-foundation system mostly originated from co-seismic deviatoric deformations while volumetric strains were the main contributing factor at the free-field. In addition, the impact of soil permeability on the seismic response of the soil-foundation system was examined by changing the pore fluid viscosity. According to the results, as the soil permeability decreased, smaller excess pore pressures developed beneath the footing thanks to the slower migration of pore fluid from the sides and bottom, and a larger magnitude of soil strength and stiffness was maintained in the expansive zone. As a result, the system with the lowest permeability experienced the smallest foundation settlement while the foundation acceleration amplitude was the highest in this case. The results also showed that the percentage of post-shaking settlement appreciably increased in the lower-permeability deposits. The results of this study were compared with the published centrifuge studies that showed good qualitative consistency. • A SPH-DEM scheme is utilized to model the seismic response of shallow foundations on liquefiable soils. • Averaged form of Navier-Stokes equations are used to describe the pore fluid motion in the mixture. • The foundation block was composed of a collection of DEM particles glued together by high-stiffness bonds. • No-penetration boundary condition was applied to all foundation sides to allow for fluid-foundation interaction. • The results of this study qualitatively agree with published centrifuge studies.

SSI effects on seismic settlements of shallow foundations on sand

The gradual extension of performance-based design in geotechnical engineering has focused the attention on the seismic performance of foundations, typically, in terms of settlement, tilt and bearing capacity degradation. The aim of the present paper is to explore the role of superstructure inertia on the performance of shallow foundations through a series of non-linear numerical analyses of structure-foundation-soil systems, performed with the Finite Difference Code FLAC3D. The NTUA-Sand constitutive model is used to simulate the nonlinear cyclic soil response. The parametric analyses focus upon the effect of key soil-structure interaction parameters, such as the frequency characteristics of the structure – foundation (SFS) system and that of the free-field soil profile, as well as, the structural and excitation properties. Initially, the nonlinear fundamental period of vibration of the SFS system is correlated to the above key parameters of the system and the seismic excitation. In the sequel, to isolate the SSI effects, settlements of SFS systems are compared with the respective settlements of equivalent foundation-soil systems (FS). Simplified relations are finally developed for the analytical calculation of SSI effects on foundation settlements, based on a multi-variable statistical analysis of the available numerical predictions.

A methodology for the identification of physical parameters of soil-foundation-bridge pier systems from identified state-space models

A methodology for the identification of the physical parameters of a model describing the transverse dynamics of soil-foundation-pier systems founded on piles is presented in this paper, starting from identified state-space models of the systems obtained from results of dynamic experimental tests and identification techniques available in the literature. By assuming the order of the model to be compliant with that of a numerical one suitably developed to capture the dynamics of the bridge pier, the procedure allows the identification of the stiffness, mass and damping matrices of the analytical model from which the physical parameters of the real system (e.g. masses, pier stiffness matrix and soil-foundation impedance) can be extracted by directly comparing the components of the identified and analytical matrices. The procedure allows the direct definition of the numerical model that best fits the experimental data without the need of any model calibration, and permits the identification of the soil-foundation compliance taking into account its intrinsic frequency-dependent behaviour. Firstly, the dynamics of the analytical model is formulated adopting the continuous-time first-order state-space form. The model includes the frequency-dependent behaviour of the soil-foundation system through the introduction of a lumped parameter model able to reproduce the typical soil-foundation impedances of pile foundations. Then, an identification strategy of the physical parameters of a generic realistic soil-foundation-pier system is proposed starting from the discrete-time state-space model identified from dynamic tests. The procedure is illustrated with some applications, simulating results of forced vibration and ambient vibration tests executed on a known system whose parameters are then identified according to the proposed approach. The procedure revealed to be effective to identify the stiffness, mass and damping matrixes of the known system, and consequently its physical parameters.

A boundary element approach for the evaluation of SSI effects in presence of pile foundations under steady-state conditions

Simplified procedures, capable of predicting the main effects of soil-structure interaction (SSI), involving minimum computational effort are desired in engineering practice. Besides, user-friendly approaches can be incorporated into guidelines or practical recommended procedures. Nevertheless, approximate solutions need to be carefully validated through rigorous analytical or numerical methods, as well as by the comparison with experimental results or field measurements. In the case of piles, the flexibility of the soil-foundation system plays a fundamental role in structural design and the evaluation of the pile group effects still represents a crucial task in practical problem. In this paper, a Boundary Element approach based on the Stiffness Matrix Method (Kausel in Fundamental solutions in elastodynamics. A compendium, Cambridge University Press, England, 2006) is employed to investigate the key features of SSI, by comparison with the actual field data collected by Stewart et al. (Empirical evaluation of inertial soil-structure interaction effects. Rep. No. PEER-98/07, Pacific Earthquake Engineering Research Center, 1998) from instrumented sites and structures.

Practical Design of Machine Foundation Subjected to Harmonic Loading by Rotating Equipment with Varying Frequency

This paper presents a practical design of machine foundation subjected to varying harmonic loads. The dynamic analysis of machine foundation is performed using an analytical method. The varying harmonic loads are generated by varying the speed of the machine as per the performance requirements of the plant, which essentially results in operating the machine at or near the resonance. The vertical vibration and coupled horizontal and rocking vibrations are represented using Lysmer’s and Hall’s analogs, respectively. The equations of motions are formulated considering the vertical motion and coupled horizontal and rocking motion of the foundation soil system in the lumped parameter approach. The analytical formulation is capable of considering the moments generated due to the eccentricity of loads (i.e., static weights of the machine and foundation). A computer program is developed using FORTRAN to obtain the practical solutions for the machine foundation soil system. The maximum amplitudes of the vertical and horizontal displacements of the case study example are 22.5 and 110.68 μm, respectively, for the operating frequencies ranging from 2.5 to 12.1 Hz. The performance of the induced draught fan foundation is evaluated using the General Machinery Vibration Severity Chart, the guidelines given in the publication Foundations for Machines: Analysis and Design, and the American Concrete Institute standard ACI 351.3R-04. These charts and guidelines help in assessing the performance of the machine foundation system during operation of the plant. Based on the results, the performance of the machine foundation system is rated as “good” to “very good” and “fair” to “slightly rough” category based on the obtained vertical and horizontal amplitudes of the displacements respectively. Based on the measured data, it is noted that the evaluated performance parameters are well within the operating parameters of the machine foundation system.

Effect of negative phase of pulse loading on response of machine foundations vibrating under harmonic loads

Analysis of a machine foundation system subjected to harmonic and pulse loading is investigated by modeling it as a linear elastic-perfectly plastic single degree of freedom (SDOF) system. Pulse loading, an idealization of explosion/blast, is represented by modified Friedlander's equation having both positive and negative phases. Analytical expressions are derived for equations of motion to obtain the response of SDOF system under combined action of harmonic and pulse loading in the form of displacement-time plots. Results show noteworthy influence of negative phase of pulse loading on the displacement of SDOF system and suggest that this should not be neglected by idealizing the explosion with the help of a triangular pulse loading. The developed solution and the displacement-time histories can help in the analysis and design of a soil-foundation system undergoing combined harmonic and pulse loading (such as a machine foundation).

Performance evaluation of friction dampers for building with soil-structure interaction

From ancient times, earthquakes have been considered the most devastating natural disaster. Many times, the damages caused by earthquakes are irrecoverable due to the static design of building structures. For the reduction of these damages, friction dampers are widely used as passive energy dissipation devices. As the friction dampers are designed with fixed base assumption, the effect of soil-structure interaction is totally neglected. Hence, the present study deals with the design methodology of friction damper incorporating soil-structure interaction effect. The slip load of friction dampers has been calculated by assuming a fixed base and flexible base (i.e. the linear and nonlinear behavior). The different models of a soil-foundation system were constructed using multilinear elements. The pushover analysis has been carried out to design the friction damper and the comparison of the same has also been done. Finally, a numerical study over different models was carried out to evaluate the performance of the friction dampers. The response was compared based on storey drift, member forces, and energy dissipated by friction dampers. It was found that the design of friction dampers by considering the non-linearity of soil leads to a realistic approach to seismic design.

Application of machine learning algorithms to performance prediction of rocking shallow foundations during earthquake loading

The objective of this research is to develop preliminary predictive models for the performance of rocking shallow foundations using machine learning algorithms and supervised learning technique. Data from a rocking foundation database, consisting of dynamic base shaking experiments conducted on centrifuges and shaking tables, have been used for the development of multivariate linear regression (MLR) model using stochastic gradient descent optimization and distance-weighted k-nearest neighbors (k-NN) regression model. Seismic energy dissipation in soil, permanent settlement of foundation, and the maximum acceleration transmitted to the structure are considered as the performance parameters of rocking foundations, while the input features to machine learning algorithms include critical contact area ratio and rocking coefficient of soil-foundation system, and peak ground acceleration and Arias intensity of earthquake ground motion. It is found that both MLR and weighted k-NN models perform satisfactorily in capturing the complex relationships between the performance parameters and input features of rocking foundations, and that both models perform better than simple statistical models. Based on multiple k-fold cross validation tests across all performance parameters and the mean absolute percentage errors, it is found that the weighted k-NN model consistently outperforms the MLR model in terms of accuracy for the problem considered.

Fast simulation of railway bridge dynamics accounting for soil–structure interaction

A novel numerical methodology is presented to solve the dynamic response of railway bridges under the passage of running trains, considering soil–structure interaction. It is advantageous compared to alternative approaches because it permits, (i) consideration of complex geometries for the bridge and foundations, (ii) simulation of stratified soils, and, (iii) solving the train-bridge dynamic problem at minimal computational cost. The approach uses sub-structuring to split the problem into two coupled interaction problems: the soil–foundation, and the soil–foundation–bridge systems. In the former, the foundation and surrounding soil are discretized with Finite Elements (FE), and padded with Perfectly Match Layers to avoid boundary reflections. Considering this domain, the equivalent frequency dependent dynamic stiffness and damping characteristics of the soil–foundation system are computed. For the second sub-system, the dynamic response of the structure under railway traffic is computed using a FE model with spring and dashpot elements at the support locations, which have the equivalent properties determined using the first sub-system. This soil–foundation–bridge model is solved using complex modal superposition, considering the equivalent dynamic stiffness and damping of the soil–foundation corresponding to each natural frequency. The proposed approach is then validated using both experimental measurements and an alternative Finite Element–Boundary Element (FE–BE) methodology. A strong match is found and the results discussed.

Effect of Existing Building Walls on the Geotechnical Behavior of Foundation under Earthquake Loading

— Structure’s systems are subjected to additional loads due to earthquakes that may be produces progressive failures. The building illustrates dissimilar categories of failure mechanism for the minor to major earthquake conditions. These structures categorized to the most susceptible type of building has experienced serious hazard or even full failure for the period of seismic activities, therefore their investigation is a complex thing to do. Consequently, this research aims at studying the behaviour of large-scale model of structures constructed with and without brick walls under seismic conditions. The effect of building walls on the performance of the structure during earthquake loading is investigated numerically using PLAXIS 3D software. An eight story building with basement designed on a mat foundation is simulated as three-dimensional model in case of brick walls existing and without brick walls case. The effect of existence such wall building on the stability of foundation soil system is discussed in the form of lateral, horizontal deformation, and foundation acceleration. The studied showed that the reduction of extreme horizontal displacement and bending moment for building foundation with brick walls reached to 43%, and 68% respectively compared to the building without walls. The consideration of wall as filling for super structure significantly reduce the foundation acceleration by as much as 72% of its initial value, which lead to considerable effect of increasing the foundation stability.

Effect of Existing Building Walls on the Geotechnical Behavior of Foundation under Earthquake Loading

— Structure’s systems are subjected to additional loads due to earthquakes that may be produces progressive failures. The building illustrates dissimilar categories of failure mechanism for the minor to major earthquake conditions. These structures categorized to the most susceptible type of building has experienced serious hazard or even full failure for the period of seismic activities, therefore their investigation is a complex thing to do. Consequently, this research aims at studying the behaviour of large-scale model of structures constructed with and without brick walls under seismic conditions. The effect of building walls on the performance of the structure during earthquake loading is investigated numerically using PLAXIS 3D software. An eight story building with basement designed on a mat foundation is simulated as three-dimensional model in case of brick walls existing and without brick walls case. The effect of existence such wall building on the stability of foundation soil system is discussed in the form of lateral, horizontal deformation, and foundation acceleration. The studied showed that the reduction of extreme horizontal displacement and bending moment for building foundation with brick walls reached to 43%, and 68% respectively compared to the building without walls. The consideration of wall as filling for super structure significantly reduce the foundation acceleration by as much as 72% of its initial value, which lead to considerable effect of increasing the foundation stability.

Wavelet-based operating deflection shapes for locating scour-related stiffness losses in multi-span bridges

Scour erosion poses a significant risk to bridge safety worldwide and affects the stiffness of the soil-foundation system, resulting in global changes in the dynamic behavior of the bridges. In this paper, a new approach to detect scour at multiple locations is proposed, using wavelet-based Operating Deflection Shape (ODS) amplitudes. A numerical model of a bridge with four simply supported spans resting on piers is used to test the approach. Scour is modelled as a reduction in vertical foundation stiffness under one or multiple bridge piers. A fleet of passing trucks, modelled as half-car vehicles, are used to excite the bridge to enable structural accelerations be calculated at each support. The approach is shown to be effective with acceleration measurements at each support location in a multi-span bridge. Using a fleet of passing vehicles, the temporal accelerations measured at each support are averaged and transformed into the frequency–spatial domain, in order to estimate the wavelet-based ODS for a given scour case. A damage indicator is postulated based on differences between the ODS of healthy and scoured bridge cases. The damage indicator enables visual identification of the location of scoured piers considering a range of natural frequencies of the system.