Nonlinear Soil Response Research Articles

Determination of hurricane-induced barge impact loads on floodwalls using dynamic finite element analysis

During hurricane events, moored barges are at risk of being propelled by high winds and impacting flood protection walls in the vicinity. Cities like New Orleans, Louisiana are at particular risk for such hazards, due to the preponderance of canals and moored barges throughout the city combined with high hurricane risk. Unfortunately, limited information is available to estimate the magnitude of barge impact loads for the design of floodwalls. In this paper, forces associated with hurricane-wind-propelled barge impacts on floodwalls are quantified using high-resolution dynamic finite element simulations. Such simulations account for highly nonlinear material deformation in the impacting barge, nonlinear soil response, and dynamic interaction between the barge, wall, and soil. The paper presents force histories for a variety of representative impact scenarios which can be used directly in dynamic analysis of floodwalls. Additional guidance is provided for employing the force results in static design scenarios.

Nonlinear Site Models Derived from 1D Analyses for Ground‐Motion Prediction Equations Using Site Class as the Site Parameter

Nonlinear site models are an important part of ground‐motion prediction equations (GMPEs) and can be constructed in a number of ways. If numerous soil‐site strong‐motion records contain the effect of strong nonlinear soil response, the parameters for the nonlinear model can be a part of the regression parameters for GMPEs. It is also possible to derive nonlinear site models by numerical simulation. However, the number of strong‐motion records from Japan that contain the effect of strong nonlinear soil response is still too small to derive nonlinear site terms. We present a model of nonlinear site terms using site class as the site parameter in GMPEs based on a 1D equivalent linear model. The 1D model was constructed based on the shear‐wave velocity profiles from the KiK‐net strong‐motion stations with a wide range of site periods, soil depth, and impedance ratios. The rock‐site strong‐motion records were from different earthquake categories in Japan and the Pacific Earthquake Engineering Research Center dataset. Those records had a wide range of earthquake magnitudes, source distances, and peak ground accelerations. A random effects regression model was fitted to the calculated spectral amplification ratios, accounting for the effect of site impedance ratios, earthquake magnitudes, and source distances of the rock‐site records. We also designed a method to adjust the 1D model so it can be used in a GMPE, accounting for the fact that a 1D model is an overly simplistic assumption for many real strong‐motion recording stations in many parts of the world. Online Material: Tables of nonlinear site model parameters.

Three-Dimensional Nonlinear Soil Response Methods Based on a Three-Component Input Wave Field

AbstractIn a previous study, three-dimensional (3D) linear and simplified nonlinear finite-element soil response methods based on a horizontal-component input seismic wave field were proposed. A seismic wave field means seismic waves propagating in a 3D medium. The method had been developed with the goal of adequately treating short-period (less than a few seconds) seismic surface waves trapped by a deep (several km) underground structure in a shallow soil model. In the present study, along with improvements of the methods, 3D linear and simplified nonlinear soil response methods based on a three-component input seismic wave field are developed, and are applied to estimate seismic soil responses in the three geotechnical zones (the reclaimed, alluvial, and hill zones) of Tokyo during two large earthquakes. The more reasonable soil responses revealed that, in a practical sense, vertical ground motions affected soil responses very little. They also clarified large effects of liquefaction in the reclaimed zo...

Ground Motion Site Amplification Factors for Sites Located within the Mississippi Embayment with Consideration of Deep Soil Deposits

In this study, site amplification factors for the deep soil deposits of the Mississippi embayment are computed using a nonlinear site response analysis program first to develop a model for nonlinear soil response for possible use by ground motion developers and second to address site amplification estimation. The effects of geology, sediment depth, and average shear wave velocity at the upper 30 m of soil ranging 180–800 m/s, as well as the effect of peak ground acceleration at the bedrock on nonlinear ground motion amplification for the upper embayment, are investigated. The site response computations cover various site conditions, sediment depth of 70–750 m, and peak acceleration of input rock motions of 0.01–0.90 g. The amplification (or de-amplification) at various frequencies implied by the sediment depth is greater than that implied just by site classification of the top 30 m of soil.

Effect of coupling excess pore pressure and deformation on nonlinear seismic soil response

The excess pore pressure (\(\Delta p_w\)) generation and consequent reduction in effective stress lead to the softening of a liquefiable soil deposit that can alter ground motions in terms of amplitude, frequency content and duration. However, total stress models, which are the most currently used, do not take into account coupling of excess pore pressures and soil deformations. To assess this effect, two analyses were made: (1) a Biot hydraulic and mechanical computation of a saturated soil deposit with coupling pore pressures and soil deformations and (2) a mechanical computation of a decoupled model with same initial behaviour. Both analyses were performed with a fully nonlinear elastoplastic multi-mechanism model. As \(\Delta p_w\) depends on the soil properties, two soils were analysed: loose-to-medium and medium-to-dense sand. The results regarding the profile of maximum accelerations and shear strains, the surface accelerations and their corresponding response spectra are analysed. The mean values of the normalized response spectra ratio of surface accelerations between the coupled and decoupled model show a deamplification of low and high frequencies (i.e. at frequencies lower than 1.0 Hz and higher than 10 Hz) that tend to increase with the liquefaction zone size. Coupling of \(\Delta p_w\) and soil deformation is therefore of great importance to accurately model the ground motion response. On the contrary, while peak acceleration predictions could be conservative, the amplification on the low frequencies could be largely underestimated which could be highly prejudicial for flexible buildings.

Numerical validation of analytical solutions and their use for equivalent-linear seismic analysis of circular tunnels

The first part of this paper presents an extensive validation of four analytical solutions for the seismic design of circular tunnels. The validation is performed with a quasi-static finite element (FE) model which conforms to the assumptions of the analytical solutions. Analyses are performed for a wide range of flexibility ratios, slippage conditions at soil–lining interface, assuming both drained and undrained behaviour. Based on the numerical predictions the relative merits of the considered analytical solutions are discussed and recommendations are given for their use in design. The second part of this paper explores the use of equivalent linear soil properties in analytical solutions as an approximate way of simulating nonlinearity. The results of equivalent linear site response analyses are used as an input for the analytical solutions. The comparison of the analytical predictions with nonlinear numerical analysis results is very satisfactory. The results of this study suggest that analytical solutions can be used for preliminary design using equivalent linear properties and the corresponding compatible strain as an approximate way of accounting for nonlinear soil response.

Guidelines for Calibration and Use of the Severn-Trent Sand Model in Modeling Cantilevered Wall-Supported Excavations

AbstractThe Severn-Trent sand model is an advanced elastoplastic constitutive model that accurately reproduces the nonlinear mechanical response of coarse-grained soils at small to relatively high strain levels under monotonic loading. The model, formulated within the framework of critical state soil mechanics, includes advanced plasticity modeling concepts such as kinematic hardening, multisurface plasticity, and bounding surface plasticity. This paper shows how the use of Severn-Trent can be extended in modeling cantilevered wall-supported excavations. Following a brief description of the approach taken to introduce the constitutive model into a finite-difference commercial code, guidelines for the model calibration are discussed. Accounting for the approximation, which affects the evaluations of some variables, several plane-strain numerical analyses are performed. The parametric study aims to evaluate to what extent the response of a cantilevered retaining structure in a dry, normally consolidated Toy...

Broadband Ground-Motion Simulation of an Intraslab Earthquake and Nonlinear Site Response: 2010 Ferndale, California, Earthquake Case Study

Intraslab earthquakes are generated by fault ruptures, which occur at shallow (20–60 km) or deep (>60 km) parts of a subducting tectonic plate slab. In both cases the rupture occurs in the vicinity of a zone with large velocity contrast and increased regional stress caused by the subducting plates. These conditions have significant effects on fault geometry, rupture dynamics, and seismic energy, which in turn affect the amplitude and duration of ground motion. Consequently, intraslab earthquakes can generate larger ground motion than shallow crustal earthquakes of same magnitude. Therefore their study is very important for strong ground motion prediction and seismic‐hazard assessment. In an effort to develop a methodology for simulating strong ground motion from intraslab earthquakes we tested the broadband ground‐motion simulation technique of Graves and Pitarka (2010) in modeling ground motion recorded from the M 6.5 2010 Ferndale, California, intraslab earthquake. The Graves and Pitarka (2010) method was originally developed for simulating crustal earthquakes. To our knowledge this is the first attempt to apply a broadband ground‐motion‐simulation method in modeling ground motion from intraslab earthquakes in the United States. A similar approach (Matsuzaki et al. , 2010) was applied to studying the rupture process of the 2001 Geiyo, Japan, intraslab earthquake using the recipe developed by Irikura and Miyake (2006). In this study we simulate and analyze ground‐motion‐acceleration time history recorded during the earthquake in a zone between Ferndale and Eureka, and Humboldt Bay. The earthquake was very well recorded in a geotechnical array located in the Humboldt Bay soft sediments. The ground‐motion acceleration recorded by the array’s instruments at several depths provided a good opportunity for testing numerical techniques and empirical models of the nonlinear seismic response of soils for input motion with moderate amplitude. A large part of our investigation is focused on modeling the observed nonlinear response …

Building damage during nearby construction: Forensic analysis

The paper presents a case history of a 5-storey building, seriously damaged during construction of a nearby structure. Founded on spread footings on soft clayey soil, the building was functional for nearly 30years. When construction of an adjacent 4-storey RC building begun, its infill walls sustained shear failure. The shear cracks were inclined at 45°, being characteristic of differential settlements, and the neighboring construction was deemed to be the cause of failure. During the present forensic investigation, additional cracks were detected, also inclined at 45° but towards the opposite direction. Internal floor measurements were conducted, revealing that the maximum differential settlement of 5cm is accompanied by 2.4cm of differential settlement to the opposite direction. A number of construction defects were detected, with the most important being the superficial foundation of the building and the absence of tie beams. To quantify the contribution of each factor to the observed failure, the neighboring structures are simulated through finite elements, modeling nonlinear soil response with a Cam-clay model, validated against the conducted measurements. It is shown, that the shear failure of the infill walls is primarily due to construction defects, with the neighboring construction playing a secondary role.

Numerical Solution of Single Pile Subjected to Simultaneous Torsional and Axial Loads

AbstractTorsional loads on pile foundations are induced by the action of eccentric horizontal forces on the supporting structures. Such loading not only initiates twisting at the pile head but also reduces its axial capacity significantly with increased settlement of the foundation. Several theoretical and experimental investigations have already been carried out on piles under torsional load, as evidenced by the available literature on the subject, although contributions on the influence of combined torsional and axial loads on pile foundations are rather limited. This paper presents a novel numerical model (boundary-element method) to analyze the response of a single vertical floating pile subjected to simultaneous torsional and axial loads. The nonlinear stress-strain response of soil has been incorporated in the model by means of the hyperbolic model, whereas the pile material has been idealized as elastic–perfectly plastic. The effect of progressive pile-soil slippage at the interface is considered. ...

Numerical Solution of Single Piles Subjected to Pure Torsion

Torsional load on pile foundations is induced by the action of eccentric horizontal forces on the supporting structures. Such loading not only initiates twist at the pile head, but also reduces its axial capacity significantly associated with increased settlement of the foundation. Inadequate design of piles under torsion may lead to disastrous consequences. Although several theoretical and experimental investigations have already been carried out on piles under torsional load as evidenced from the available literature, there is ample scope for further contributions on the influence of torsional load on pile foundation. This paper presents a novel numerical model (boundary element method) to analyze the response of a single, vertical, floating pile subjected to pure torsional load. The nonlinear stress-strain response of soil has been incorporated in the model by hyperbolic correlation, whereas the pile material has been idealized as elastic–perfectly plastic. The effect of progressive pile-soil slippage at the interface is considered. Apart from predicting the load-displacement response with incremental angle of twist of pile under pure torsion, the profiles for shear stress and angle of twist and the depth of interface slippage are some of the salient features captured by the proposed model. Validation of the model developed by comparing with existing models and experimental data indicate the suitability and accuracy of the solutions developed. However, minor discrepancies in the solution appeared owing to the simplified assumptions of perfectly plastic postpeak soil behavior and the absence of residual stress in the soil owing to pile installation. The proposed model is also applied successfully to selected case studies on concrete piles (L/D ranged from 10–40) in medium-soft clay, medium-dense sand, and layered soil, and a set of design curves have been constructed.

Effect of interface friction on tunnel liner internal forces due to seismic S- and P-wave propagation

The effects on the hoop force and bending moment developed in the lining of a circular tunnel of the contact properties of the soil-lining interface are investigated numerically for both cases of S- and P-seismic wave propagation. Development of a robust model for the dynamic simulation of this problem includes: (i) the implementation of a hysteretic model of the non-linear soil response under cyclic loads in the finite element code ABAQUS; and (ii) validation of the analyses results against centrifuge tests from the literature and closed-from elasticity solutions. Accordingly, a parametric study is conducted to quantify the effect of adopting different values of the friction coefficient of the tunnel liner interface, while assuming that the relaxation load is transferred only to the temporary support shell of the tunnel; a hypothesis applicable mainly to tunnels constructed with the NATM method where an unreinforced concrete final lining is usually installed. Practical findings of this study suggest that the full-slip assumption should be used in conjunction with closed-form expressions for preliminary estimates of the tunnel response. On the contrary, for tunnels where the lining is designed to bear the soil loads, numerical tools should be used for the rational assessment of their seismic response. In the latter case, more experimental studies are needed to evaluate the friction properties at the interface, since common expressions correlating the friction coefficient with the friction angle of the surrounding soil do not appear compatible with the centrifuge test results examined herein.

Interaction Analysis of MAT Foundation and Space Frame for the Non Linear Behaviour of the Soil

Structural analysis is one of the most important aspects in structural design, since it gives an idea about the performance of the structure under load. Right from the beginning when the process of development started in the field of soil-structure interaction, an attempt has been made to bring sophistication in the theoretical methods of analysis. In the conventional analysis the stress-strain response of the soil is not considered. The equilibrium equations are satisfied but the compatibility is not considered. But in reality the soil, the foundation and the frame act together as a single compatible unit. The non-linear response of soil is considered for this analysis. The non-linear response of the soil is included in the analysis through multi linear isotropic (MISO) model and the parameters used in the parametric study are relative stiffness factors krs and ksb which are the function of the modulus of the soil, modulus of frame raft materials and geometric properties of the structural elements.

An effective procedure for seismic hazard analysis including nonlinear soil response

This paper presents probabilistic seismic hazard analysis (PSHA) of Tehran, Iran, accounting the effect of nonlinear soil response. It is well-known that soil nonlinearity and its accurate prediction could play important role in seismic hazard study. For this purpose, two different approaches have been carried out for predicting the hazard curves by (1) applying site modifications to the ground motion prediction equation based on generic site classes and use of constant coefficients (2) using a close-form solution that modifies the hazard results at the rock level. Also, efficiency of the Monte Carlo method in modeling of amplification function for the six selected sites in the study area was examined. Results showed important effect of nonlinear soil response mainly for frequencies lower than 8 Hz, which should be considered properly in hazard estimation. As an interesting subject, influence of soil plasticity index (PI) on hazard estimation of clayey sites including the nonlinear soil response was evaluated.

Nonlinear Dimensional Analysis of Trapezoidal Valleys Subjected to Vertically Propagating SV Waves

This paper studies the seismic response of soil basins emphasizing the sensitivity of 2D dynamic response to geometric and material properties. This is accomplished through a formal dimensional analysis accounting for fully inelastic soil response thus augmenting the generalization potential of the results, and provid- ing a novel framework for future research on the subject. It is shown that 2D valley response may be described through the following key dimensionless parameters: (1) the valley shape factor s, expressing the slope inclination; (2) the impedance ratio i, which expresses the stiffness of the soil relative to the bedrock; (3) the wavelength ratio λS, which is a function of soil stiffness and seismic excitation frequency; (4) the rigidity ratio v, expressing the stiffness of the soil relative to its strength; and (5) the resistance ratio r, which expresses the degree of soil nonlinearity. The effectiveness of the dimensional formulation is verified through the numerical analysis of equivalent valleys, assuming elastic and nonlinear soil response. Finally, a parametric study is conducted to gain insight on the effects of the introduced dimensionless parameters on the dynamic response of trapezoidal alleys. It is shown that decreasing thevalley slope or the wavelength ratio promotes wave reflections within the wedge, thus enhancing the possibility of wave interferences and subsequently leading to 2D aggravation on the valley surface. On the other hand, the geometry-dependent parasitic vertical accel- eration increases as the valley slope becomes steeper. As the degree of soil nonlinear- ity increases, 2D phenomena tend to become localized close to the valley edges.

Comparison of Site Periods Derived from Different Evaluation Methods

Abstract As a part of our microzonation research activities for the city of Ottawa, the fundamental site period, T 0 , was investigated based on different methods, including (1) the horizontal-to-vertical spectral ratio (HVSR) using microtremor ambient-noise measurements; (2) equivalent single-layer (ESL) modeling, as noted in the current National Building Code of Canada (2005); (3) earthquake weak motion observations; (4) multilayer soil modeling; and (5) finite element modeling for linear and nonlinear soil. The differences between these methods are discussed. We have discovered that T 0 based on the HVSR method systematically deviated from T 0 based on the equivalent single-layer modeling method. The variance was more than 30% for periods longer than 2 s, corresponding to impedance boundary depths of more than 75 m in the study area. The effect of the shear-wave velocity gradient on T 0 was investigated by applying multilayer soil modeling, which confirms that the actual velocity-depth gradient shifts the evaluated T 0 to shorter periods compared to equivalent single-layer modeling. The effects of soil nonlinearity on T 0 were examined using a finite element method analysis. The dependency of T 0 on the level of shaking is well defined at higher levels of shaking when the peak ground acceleration (PGA) exceeds 80 Gal because the soft soil behaves nonlinearly. It has been concluded that, for the case of nonlinear soil response, damping plays an important role in reducing the fundamental frequency. These findings will be used in our future research activities directed at providing fundamental period maps for the city of Ottawa, including fundamental period maps for the strong motion design earthquake.

２００３年宮城県沖スラブ内地震における表層地盤の非線形応答とその強震動への影響

We investigate nonlinear soil responses based on strong motion records at a large number of observation sites during the 2003 Miyagi-oki intraslab earthquake (Mw 7.0). First, we examine the efficiency of S-H/V (horizontal-to-vertical spectral ratio for the S-wave portion at the ground surface) method to identify the nonlinearity by comparing the results with those by the standard S-wave surface-to-borehole spectral ratio method. In the examination we propose a new quantitative index to measure the degree of the nonlinear soil response, DNL, which evaluates the gap between the spectral ratio for strong ground motion and that for weak ground motion. The DNL values by the S-H/V method as well as those by the surface-to-borehole spectral ratio method increase with observed peak ground acceleration (PGA) values at surface (100∼1000 cm/s2), reflecting the increase of the degree of nonlinearity. However, both DNL values at sites with large S-wave velocity of the surface layer (>300 m/s) do not show any increase even for large PGA values (∼800 cm/s2), indicating linear site response. From these facts we conclude that the S-H/V spectral ratio method is also efficient to identify the nonlinearity. Second, in order to examine the effects of nonlinear soil response on strong ground motions, we make the broadband strong motion simulation for the 2003 Miyagi-oki earth.quake by means of the empirical Green’s function (EGF) method. The synthetic waveforms for the horizontal components at the ground surface significantly overestimate the observed ones at stations with large DNL values; the synthetic PGA values are about two times greater than the observed ones. We confirm that the overestimation is attributed to the ignorance of the nonlinear soil response in the EGF simulation. Finally we briefly discuss the potential of the DNL value for studying the nonlinear soil response.

Nonlinear Soil Response and Its Effects on Strong Ground Motions during the 2003 Miyagi-Oki Intraslab Earthquake

Nonlinear Soil Response and Its Effects on Strong Ground Motions during the 2003 Miyagi-Oki Intraslab Earthquake

NON-LINEAR ANALYSIS OF AN INTEGRAL BRIDGE

This study describes the implementation of a 2‐D finite element model of an integral abutment bridge (IAB) system which explicitly incorporates the nonlinear soil response. The superstructure members have been represented by means of three‐node isoparametric beam elements with three degrees of freedom per node. The soil mass is idealized by eight node isoperimetric quadrilateral element at near field and five node isoparametric infinite element to simulate the far field behavior of the soil media. The non‐linearity of the soil mass has been represented by using the Duncan and Chang hyperbolic model. The applicability of this model was demonstrated by analyzing a single span IAB. This study has shown that the soil nonlinearity has significant effect on the response of the structure, where the displacement that have been obtained on basis of nonlinear analysis is 1.5–2.0 times higher than that obtained from linear analysis. The stress magnitudes in the nonlinear analysis are also higher where in some point the difference reached almost 3 times. Santrauka Straipsnyje aprašoma, kaip taikomas 2‐D baigtiniu elementu metodas tilto sistemai su integraliniais ramtais analizuoti, apimant ir netiesine grunto elgsena. Antžemines tilto dalies laikantieji elementai modeliuojami taikant triju mazgu izoparametrinius strypinius elementus su trimis laisves laipsniais kiekviename mazge. Grunto masyvui modeliuoti taikomi aštuoniu mazgu izoparametriniai ketursieniai elementai arti tilto esančioje aplinkoje ir penkiu mazgu izoparametriniai begaliniai elementai, imituojantys grunto terpes elgsena nuo tilto nutolusiose srityse. Grunto masyvo elgsenos netiesiškumas ivertinamas Duncan ir Chang hiperboliniu modeliu. Jo tinkamumas aiškinamas analizuojant vieno tarpatramio integralini tilta. Atlikti tyrimai parode, kad grunto savybiu netiesiškumas turi didele itaka tilto konstrukciju elgsenai. Tilto poslinkiai, nustatyti taikant netiesine analize, yra 1,5–2,0 karto didesni už poslinkius, nustatytus taikant tiesine analize. Atlikus netiesine analize nustatyti itempiai taip pat yra didesni, o kai kuriais atvejais skirtumas siekia beveik tris kartus.

Coherence of Mach fronts during heterogeneous supershear earthquake rupture propagation: Simulations and comparison with observations

We study how heterogeneous rupture propagation affects the coherence of shear and Rayleigh Mach wavefronts radiated by supershear earthquakes. We address this question using numerical simulations of ruptures on a planar, vertical strike‐slip fault embedded in a three‐dimensional, homogeneous, linear elastic half‐space. Ruptures propagate spontaneously in accordance with a linear slip‐weakening friction law through both homogeneous and heterogeneous initial shear stress fields. In the 3‐D homogeneous case, rupture fronts are curved owing to interactions with the free surface and the finite fault width; however, this curvature does not greatly diminish the coherence of Mach fronts relative to cases in which the rupture front is constrained to be straight, as studied by Dunham and Bhat (2008a). Introducing heterogeneity in the initial shear stress distribution causes ruptures to propagate at speeds that locally fluctuate above and below the shear wave speed. Calculations of the Fourier amplitude spectra (FAS) of ground velocity time histories corroborate the kinematic results of Bizzarri and Spudich (2008a): (1) The ground motion of a supershear rupture is richer in high frequency with respect to a subshear one. (2) When a Mach pulse is present, its high frequency content overwhelms that arising from stress heterogeneity. Present numerical experiments indicate that a Mach pulse causes approximately anω−1.7high frequency falloff in the FAS of ground displacement. Moreover, within the context of the employed representation of heterogeneities and over the range of parameter space that is accessible with current computational resources, our simulations suggest that while heterogeneities reduce peak ground velocity and diminish the coherence of the Mach fronts, ground motion at stations experiencing Mach pulses should be richer in high frequencies compared to stations without Mach pulses. In contrast to the foregoing theoretical results, we find no average elevation of 5%‐damped absolute response spectral accelerations (SA) in the period band 0.05–0.4 s observed at stations that presumably experienced Mach pulses during the 1979 Imperial Valley, 1999 Kocaeli, and 2002 Denali Fault earthquakes compared to SA observed at non‐Mach pulse stations in the same earthquakes. A 20% amplification of short period SA is seen only at a few of the Imperial Valley stations closest to the fault. This lack of elevated SA suggests that either Mach pulses in real earthquakes are even more incoherent that in our simulations or that Mach pulses are vulnerable to attenuation through nonlinear soil response. In any case, this result might imply that current engineering models of high frequency earthquake ground motions do not need to be modified by more than 20% close to the fault to account for Mach pulses, provided that the existing data are adequately representative of ground motions from supershear earthquakes.