Nonlinear Soil Behavior Research Articles

Shaking table test and numerical simulation of rocking wall frame structure considering dynamic soil-structure interaction

This study investigates the seismic response of a rocking wall frame structure considering dynamic soil-structure interaction (DSSI) through shaking table tests. A comparison with conventional frame structures and structures with fixed-base foundations is made to examine the influence of DSSI effects on various aspects including structural damage distribution, dynamic characteristics, and floor responses. Test results indicate that the presence of a rocking wall reduces structural responses across different site conditions, although the reduction is less significant under soft soil conditions compared to fixed-base foundation conditions. Overall, DSSI diminishes the mitigating effect of the rocking wall on the maximum structural response. Furthermore, a three-dimensional finite element model of the shaking table test is established. The numerical model employs the equivalent linear method to simulate the soil's nonlinear behavior and incorporates the concept of the rocking wall. Comparative analysis between experimental and simulated results demonstrates that the model effectively predicts the dynamic response of the rocking wall frame structure in DSSI systems.

Regional study of site effects on the high-frequency spectral-decay parameter

The high-frequency spectral-decay parameter κ has been used in the field of engineering seismology for several decades. The zero-distance κ value (κ0) is a site parameter in ground motion models and strong motion synthesis. Using surface-borehole pairs of strong motion records from the strong-motion seismograph network KiK-net, we explored the effect of site soil on κ0, specifically the contribution from ground motion directionality. In the target area (138°E−143°E, 36°N–40°N), and records from earthquakes at 50 pairs of stations were collected. All horizontal orthogonal records were rotated from 0° to 180° with an increment of 10° to capture the difference between the average κ0 on two horizontal components and the median value of the rotated κ0 at surface and borehole stations. The same process was applied to Δκ0, the difference between surface station κ0 and borehole station κ0, to measure the contribution by soil column. The nonlinear behavior of soils led to large shear strains, reduced stiffness, and decreased resonance frequency. Thus, the effect of soil nonlinearity on κ is investigated. In the same area, strong ground motion records with peak ground acceleration >100 cm/s2 were selected to identify the soil nonlinearity by the moving time window deconvolution method, and the temporal variation of time-average shear wave velocity and κ at the 50 surface stations were assessed.

Three-Dimensional Site Response Analysis of Clay Soil Considering the Effects of Soil Behavior and Type

To understand changes in bedrock motion at the ground surface, frequency effects, and spatial distribution within the soil, it is important to look at how a site responds to earthquakes. This is important for soil–structure interaction in structural and geotechnical earthquake engineering. This study deals with the effect of classifying clays according to shear wave velocity (stiff/medium/soft) and nonlinearity in behavior (linear/nonlinear) on the analysis of the site response. A 3D soil model with a combination of free fields and quiet boundaries and advanced constitutive models for soil to obtain accurate results was used to conduct this study. A strong TABAS earthquake was used to excite the compliant base of the model after converting the velocity record of TABAS to an equivalent surface traction force using a horizontal force–time history proportional to the velocity–time history. This study reveals that the site response analysis is affected by the type of clay soil and the soil material behavior, with soft clay soil causing higher PGV and PGV values in the linear case and lower values in the nonlinear case due to soil yielding, which causes soil response attenuation. This results in extremely conservative and expensive building designs when linear soil behavior is adopted. On the other hand, the applied earthquake exhibits greater attenuation at longer frequencies and greater amplification at mid and short frequencies. However, at frequencies near the applied earthquake frequency, neither attenuation nor amplification occurs. Furthermore, nonlinear soil behavior is crucial for soil evaluation and foundation design due to higher octahedral shear strain and settlement values, especially in softer soils, resulting from extensive plastic deformation.

Impact of Vertical Vibration on Group Piles During Earthquake Loading: Experimental Findings

This study presents novel research on the impact of vertical vibration on the dynamic response of pile groups embedded in stratified soil under seismic loading conditions. An experimental setup was employed wherein the piled machine foundation was subjected to vertical vibrations at three operating frequencies (10, 20, and 30 Hz) and subsequently exposed to four levels of seismic acceleration (0.1 g, 0.34 g, 0.77 g, and 0.82 g). Piles with a length-to-diameter ratio of 25 were embedded in a stratified soil profile, with an upper loose layer (30% relative density) and a lower dense layer (80% relative density) acting as end-bearing. Measurements and analyses of horizontal and vertical accelerations, and amplification factors were conducted using the Fast Fourier Transform (FFT), spectral acceleration (Sa), and variation of acceleration with depth. The results demonstrated a significant reduction in horizontal acceleration, with a peak ground acceleration (PGA) reduction of up to 64% in average, particularly at higher frequencies such as 30 Hz. The mitigation efficiency at 30Hz improved with increasing PGA, showing reductions of 42, 68, 75, and 63% for seismic accelerations of 0.1 g, 0.34 g, 0.77 g, and 0.82 g, respectively. The analysis further revealed harmonic resonance and higher mode effects at lower frequencies, with nonlinear soil behavior affecting the resonance and amplification patterns. Additionally, the results demonstrate that the far-field accelerations exceeded the near-field accelerations within the pile group, particularly in the surface layer. The results indicated that the initial vibration amplitudes exceeded the safe operating limits outlined in ACI 351.3R-18 under seismic loading, particularly at higher seismic acceleration levels and lower frequencies. Additional modified charts were presented to account for these conditions. The results presented promising evidence for using vertical vibrations as an earthquake-mitigation strategy. However, avoiding operating at frequencies less than 10 Hz is recommended because of the potential resonance and interaction with horizontal accelerations during earthquakes. Doi: 10.28991/CEJ-SP2024-010-010 Full Text: PDF

Multistep procedure for estimating non-linear soil response in low seismicity areas—a case study of Lucerne, Switzerland

SUMMARY The impact of non-linear soil behaviour on seismic hazard in low-to-moderate seismicity areas is often neglected; however, it may become relevant for long return periods. In this study, we used fully non-linear 1-D simulations to estimate the site-specific non-linear soil response in the low seismicity area, using the city of Lucerne in Switzerland as an example. The constitutive model considers the development of pore pressure excess and requires calibration of complex soil models, including the soil dilatancy parameters. In the absence of laboratory measurements, we mainly used the cone penetration test data to estimate the model variables and perform inversion for the dilatancy parameters. Our findings, using Swiss building code-compatible input ground motions, suggest a high probability of strong non-linear behaviour and the possibility of liquefaction at high ground motion levels in the case study area. While the non-linearity observations from strong-motion recordings are not available in Lucerne, the comparison with empirical data from other sites and other methods shows similarity with our predictions. Moreover, we show that the site response modelled is largely influenced by the strong pore pressure effects produced in thin sandy water-saturated layers. In addition, we demonstrate that the variability of the results due to the input motion and the soil parameters is significant, but within reasonable bounds.

Simulation of soil-structure interaction using inelasticity-separated finite element method

The soil–structure interaction (SSI) effect is nonnegligible during the nonlinear seismic response analysis of large-scale or underground structures. However, the computation of nonlinear response of a structure considering SSI effect usually is a time-consuming process because the numerical model should involve the structure itself, a wide-range soil domain and the soil–structure interface, especially for large-scale structure. This study aims to incorporate the inelasticity-separated finite element method (IS-FEM), which is an algorithm recently developed for efficient structural nonlinear analysis, to improve the efficiency of the soil-structure interaction system. To this end, an inelasticity-separated contact element model for modeling the nonlinear behavior of soil and structure interface is developed in this study. To derive the inelasticity-separated governing equation of this model, a reference elastic stiffness is defined so that the normal and shear deformation of any point pair in the presented contact element is decomposed into reference linear and reference nonlinear parts according to this reference elastic stiffness. As a result, the problem of inconsistency between the requirement of IS-FEM for constant initial linear elastic stiffness and the existence of inflection point for the stress versus relative displacement relationship of contact behavior can be solved. Then, the Goodman element formulation for depicting the nonlinear contact behavior is introduced and an interpolation scheme to establish the reference nonlinear deformation field in an element is incorporated. By combining the proposed model with existing inelasticity-separated elements, a global analytical model of the soil–structure interaction system can be established within the framework of IS-FEM. Because the nonlinearity usually occur in some local regions of the global model and the use of the IS-FEM only require performing these operations for a small scale matrix representing local nonlinearity, the computational efficiency of nonlinear structural response analysis considering SSI effect can be improved significantly. The applicability and efficiency of the proposed method is finally verified by two numerical examples.

Numerical simulation of impact effect for damage assessment of highway bridge abutments

ABSTRACT Bridge abutments are often damaged by girder impacts during major earthquakes. Very limited studies have been conducted. None of the past studies have incorporated abutment damage as an integrated system, i.e. the interaction between the deck and the back wall as well as between abutment and backfill. First, the reliability of the numerical model for damage assessment is validated with the result obtained from the shaking table test. Second, numerical simulations of the impact effect were carried out on four abutments with different shapes and dimensions of wing wall. The developed numerical models can simulate the nonlinear backfill soil, the backfill-back wall interface, and damage to reinforced concrete with the strain rate effect of the concrete and steel reinforcement. Parametric studies were conducted on the influence of the nonlinearity of the backfill soil, back wall-to-backfill friction, constitutive law of concrete, hourglass ratio, and impact energy. The results show that the nonlinear behaviour of the backfill soil and wing wall plays a significant role in the impact force on the back wall behaviour. Since poundings can be repetitive, this study confirms that the velocity of the initial impact of a bridge deck can precisely predict the severity of abutment damage.

Non-linear critical speed in high-speed ballasted railways with ground reinforcement

When constructing or upgrading high-speed railway lines on soft soils, reinforcing the soil foundation becomes crucial. This not only involves small track displacements but also increases the critical speed, thereby ensuring safe and efficient regular operations. Nevertheless, existing studies on the critical speed phenomenon in high-speed railway tracks with ground reinforcement are limited, and they all assume a linear elastic behavior for both the soils and reinforcement materials. The main novelty of this research is that it presents the first study on the effect of non-linear soil behavior on the critical speed of high-speed railway ballasted tracks with soil reinforcement and introduces a novel simplified approach based on an equivalent homogeneous soil layer by replacing the soil layer containing inclusions/columns. To accomplish this, a full 3D non-linear numerical model was developed and experimentally validated. The findings from a detailed and comprehensive parametric analysis demonstrate a significant influence of non-linear behavior on the critical speed, resulting in reductions of up to 30% compared to the linear elastic scenario. Furthermore, it is found that the soil-reinforcement stiffness contrast, the area replacement ratio, and the plasticity index of the soil foundation play a crucial role in the critical speed. Other aspects such as the installation pattern and the thickness of soft soil have a relatively lower impact on the critical speed.

DEM analysis of constrained modulus nonlinearity and damping factor of dry granular soils

The seismic site response analysis requires the dynamic soil properties (i.e., the modulus and damping). While it is well understood that the shear modulus and damping ratio are nonlinearly shear-strain dependent, the knowledge on the constrained modulus and damping ratio of compressional waves is still very limited due to lack of laboratory testing equipment. This study aims to simulate cyclic tests of constrained compression for granular specimens by discrete element method (DEM) to understand the dynamic soil properties of compressional waves, i.e., the nonlinearity in constrained modulus and damping ratio with the compression strain. The evolution in microstructure of granular specimens is revealed to provide micromechanical interpretations for the compressional soil nonlinearity. The results show that the dependency of constrained modulus on compression strain is different in compression and extension stages, and the modulus reduction is only observed in the extension path. The damping ratio of samples under cyclic constrained compression is smaller than that of cyclic shear. The nonlinear soil behavior is more obvious at lower confining pressure and for dense sample. The nonlinearity of constrained modulus depends on the coordination number, contact normal force and fabric anisotropy, while the associated damping ratio is only related to fabric anisotropy.

Studying the mode shape participation factor of wave loads for offshore wind turbine structures

This paper introduces a method for analyzing resonance between Offshore Wind Turbine (OWT) structures and wave loads using Wave Participation Factor ratios (WPFs). Despite temporal fluctuations in WPFs due to wave loads, they prove effective for identifying key modes influencing wave load behavior in both fixed and floating OWT structures. For fixed OWT foundations, nonlinear soil behavior causes some natural frequency variations under wave forces, but they typically remain within a limited range. Lower natural frequency modes show minor WPFs, reducing the risk of resonance with wave loads. Modes with higher natural frequencies have substantial WPFs and are less prone to resonance. However, precautions are needed to avoid rotor-induced wind load resonance. Floating OWT structures have large WPFs in their first six near-rigid body motion modes, while mooring line stiffness leads to substantial variations in these modes. It's crucial to control the first six nonlinear frequencies outside the dominant wave load range. Beyond these six modes, natural frequencies significantly exceed wave load frequencies, reducing resonance concerns. In summary, this study presents an effective method for assessing resonance between OWT structures and loads, providing valuable insights for structural design and operational safety.

Impact of the Nonlinear Soil Behavior on the Movements Prediction of Deep Excavations

Impact of the Nonlinear Soil Behavior on the Movements Prediction of Deep Excavations

Seasonal Variation of VS at Shallow Depth and Nonlinear Behavior of Soil Based on the ARGONET Vertical Array Data

Ground acceleration time histories from earthquakes recorded by the ARGONET vertical array in Cephalonia, Greece, in the period from July 2016 to April 2022, are analyzed seeking evidence for nonlinear behavior of the shallow soil layers. Shear waves velocity, VS, between the shallowest sensor pair of the vertical array, i.e., within the top 5.6 m of the soil column, is derived for each earthquake record using the method of interferometry by deconvolution. The temporal variation of VS values is compared with indicators related to soil moisture and this leads to the identification of a clear difference in the level of the measured values between periods of intense rainfall and the dry summer months. Lower velocities, even lower than the level of VS during rainy periods (7-13% of the annual average), are obtained based on the strongest records of the analyzed sample. These low velocities are considered as indicators of nonlinear soil behavior, the threshold onset of which is difficult to determine without prior correction for the seasonal variation. The applied method can provide a detailed description of VS changes even during a single earthquake. Examples are provided on how nonlinear soil behavior may be manifested by a sudden VS value drop at the arrival of the strongest seismic phases.

Numerical Modelling simulation technology of Nonlinear Multi-Field Coupled Ground Foundation

Contemporary civil engineering practices demand sophisticated computational tools to navigate the complexities of structural systems and their interactions with the ground. This paper introduces a novel numerical modelling simulation technology tailored for nonlinear multi-field coupled ground foundations. Ground foundations, pivotal interfaces between structures and underlying soil, undergo intricate interactions influenced by various physical phenomena, including soil-structure interaction, soil-structure-fluid interaction, and thermal effects. Traditional analytical methods often falter in capturing the nuanced nonlinear behavior of these coupled systems. Consequently, this paper proposes a comprehensive numerical modelling framework integrating advanced computational techniques to accurately simulate the complex interplay of multiple fields within ground foundations. The methodology incorporates finite element analysis, multi-physics coupling algorithms, and advanced constitutive models to capture the nonlinear behavior of soil, structure, and fluid interactions. Through detailed case studies and validation against experimental data, the efficacy and accuracy of the proposed simulation technology are demonstrated, emphasizing its potential to revolutionize the design and analysis of ground foundation systems in civil engineering applications. This paper represents a foundational contribution towards advancing the state-of-the-art in numerical modelling simulation technologies for nonlinear multi-field coupled ground foundations, fostering innovation and optimization in civil engineering practice.

Numerical investigation of nonlinear soil-structure interaction effects on response of irregular RC buildings

Kathmandu, located in a high seismic zone, predominantly features irregular structures among its building stock. These structures are particularly susceptible to severe damage during seismic events, primarily due to torsional effects. Traditional seismic designs rely particularly on fixed-base conditions that underestimate forces and displacement primarily on soft soil conditions leading to irrational design practices. This study aims to quantify the seismic performance of buildings on various base conditions through fully nonlinear Soil-structure Interaction (SSI). The soil nonlinear behaviour was modelled using the Pressure-Independ-Multi-Yield (PIMY) material with an octahedral shear stress-strain backbone curve. Three distinct soil types were considered, and structures with irregular plan configurations were modelled using finite elements in both Opensees and STKO platforms. Structural performance was analyzed through nonlinear dynamic analysis, and outputs were evaluated based on seismic parameters. Comparing nonlinear SSI with linear SSI and fixed-base conditions revealed a significant increase in structural response, expressed in terms of displacement, drift ratio, and base shear. The magnitude of diaphragm rotation was found to be influenced by a combination of building torsional irregularity and SSI effects. It is suggested that the conventional practice of using the torsional irregularity ratio as a measure of torsional irregularity be revised and enhanced to better account for these influences. It has been quantified that torsional irregularity has a relatively lesser impact on displacements, drifts, and base shear compared to SSI. In all cases, fixed-base conditions consistently exhibited the minimum response. The study explored that linear SSI and fixed-base conditions tend to underestimate structural responses, while nonlinear SSI coupled with dynamic analysis provides a more accurate representation of realistic structural behaviour for seismic design particularly in soft soil cases.

Implications of input ground-motion selection techniques on site response analyses for different tectonic settings

This study investigates how current practices of input ground-motion selection influence site response analysis results and their variability, when considering different tectonic settings. Study sites in Seattle and Boston are chosen to represent tectonic settings with contributions to the seismic hazard from shallow crustal and subduction events, as well as stable continental regions, respectively. Selected input ground-motion suites for one-dimensional site response analysis represent variations in the target spectrum definition, spectral period of interest, seismic source, and ground-motion database. When directly incorporating different types of seismic sources (e.g. shallow crustal versus subduction) into target spectrum definitions and selecting ground motions from the corresponding databases (i.e. consistent with such seismic sources), differences on the estimated site response and its variability are observed. These effects are captured by spectral amplification factors and nonspectral intensity measures (significant duration and Arias intensity) and become particularly apparent for subduction zones. The variability in spectral amplification factors stemming from ground-motion selection techniques is found to be also a function of the characteristics of the site, becoming higher near the fundamental period of the site. Estimated responses at stiffer sites are more significantly influenced by ground-motion selection techniques, whereas the onset of nonlinear soil behavior at softer sites can reduce such variability.

Effects of Source Directivity and Nonlinear Soil Behavior During the January, 1 2024 Noto Earthquake (Mw = 7.5)

The earthquake of January 1, 2024 with the epicenter at Noto Peninsula of Ishikawa Prefecture, Japan, and the moment magnitude Mw = 7.5 obviously represents an intermediate case between weaker earthquakes with relatively small sources, like the 1995 Kobe and 2000 Tottori earthquakes (Mw ~ 6.7-6.8), showing nonlinear soil response and soil softening (reduction of shear moduli) and stronger earthquakes, like the 2003 Tokachi-Oki and Tohoku earthquakes (Mw ~ 8.3-9.0) with extended sources and source directivity effects, accompanied by soil hardening and generation of high peak ground accelerations (PGA) > 1 g. In this research, based on KiK-net vertical array records (11 sites), models of soil behavior in the near-fault zones of the 2024 Noto earthquake are constructed, i.e. vertical distributions of stresses and strains in soil layers changing with time during strong motion, which showed nonlinear soil response and reduction of shear moduli in the near-fault zones. At the same time, the waveforms of acceleration time histories indicate the effects of source directivity, when seismic waves, radiated by the crack tip propagated along a~rather long section of the fault plane, arrived to remote sites almost simultaneously, overlap, harden subsurface soils and generate high accelerations on the surface, PGA ~ 2828 Gal at remote ISK006 station.

Nonlinear consolidation finite element analysis of a layered soft soil foundation under multistage loading based on the continuous drainage boundary

To comprehensively consider the impacts of stratification, residual pore water pressure, soil nonlinearity, and boundary permeability on consolidation settlement of soft soil foundations for accurate prediction, a continuous drainage boundary condition is proposed in this study that reflects the residual pore pressure under multistage loading, and a nonlinear elastic constitutive model based on the double logarithmic model is adopted to account for the nonlinear consolidation behaviour of soils. A UMAT subroutine is developed based on the proposed boundary condition and nonlinear elastic constitutive model. Subsequently, the developed subroutine is compared with the built-in linear elastic soil constitutive model in ABAQUS and engineering examples. The application of continuous drainage boundaries in stratified foundations is analysed, as well as the influence of factors such as the loading rate and soil nonlinearity on consolidation settlement. The results indicate that, compared to the built-in model, the subroutine developed in this study can be employed to more accurately calculate the nonlinear consolidation of multilayered foundations under multistage loading. By adjusting the loading rate parameter αk, consolidation under different loading conditions can be predicted. Additionally, the proposed boundary condition simplifies the calculations for soft soil foundations with sand layers, providing a novel computational approach for the design of construction loading schemes and long-term settlement predictions in soft soil foundations.

A Comparative Study of Embedded Wall Displacements Using Small-Strain Hardening Soil Model

Traditional analysis of embedded earth-retaining walls relies on simplistic lateral earth pressure theory methods, which do not allow for direct computation of wall displacements. Contemporary numerical models rely on the Mohr–Coulomb model, which generally falls short of accurate wall displacement prediction. The advanced constitutive small-strain hardening soil model (SS-HSM), effectively captures complex nonlinear soil behavior. However, its application is currently limited, as SS-HSM requires multiple input parameters, rendering numerical modeling a challenging and time-consuming task. This study presents an extensive numerical investigation, where wall displacements from numerical models are compared to empirical findings from a large and reliable database. A novel automated computational scheme is created for model generation and advanced data analysis is undertaken for this objective. The main findings indicate that the SS-HSM can provide realistic predictions of wall displacements. Ultimately, a range of input parameters for the utilization of SS-HSM in earth-retaining wall analysis is established, providing a good starting point for engineers and researchers seeking to model more complex scenarios of embedded walls with the SS-HSM.

Displacement analysis of a geogrid-reinforced retaining wall with modular precast concrete facing

Reinforced earth retaining walls are widely used in transportation projects, such as embankments, bridge access roads, and bridge abutments. When the wall height is large, the weight of the embankment soil and vehicle loads can cause large wall displacements, thereby affecting the serviceability of the wall system. Although many retaining wall projects use wall-facing structures assembled from precast concrete components, most domestic studies have focused on continuous reinforced concrete wall-facing structures. Therefore, to understand the displacement behavior of reinforced retaining walls when the wall height is large, we investigated the displacement behavior of an earth retaining wall in the My Phuoc-Tan Van overpass project, Binh Duong Province. This study uses a finite element simulation that considers the nonlinear behavior of backfill soil, foundation soil, geotextiles, and the interaction between precast concrete units.

Non-linear behaviour of soil–pile interaction phenomena and its effect on the seismic response of OWT pile foundations. Validity range of a linear approach through non-degraded soil properties

The effect of non-linear and inelastic behaviour of the soil–pile interaction on the seismic response of offshore wind turbine pile foundations embedded in sandy soils is analysed. For this purpose, the responses obtained assuming three different Beam on Dynamic Winkler Foundation (BDWF) models are compared: a Plastic Non-Linear Model (PNLM), an Elastic Non-Linear Model (ENLM) and a simple elastic linear model with non-degraded properties of soil (NDLM). The influence of non-linearity and plasticity assumption is studied by evaluating the effects of the kinematic and inertial interaction within soil–pile interaction. Two soil stiffness levels are analysed: very loose and medium dense sand. The seismic response under ten earthquakes is computed in terms of mean envelopes of internal forces along the pile length. The non-linearity and inelastic influence of soil–pile interaction is quantified by means of relative differences with respect to the linear elastic model. Results show that the non-linear and inelastic models acquire relevance when the contribution of the inertial interaction dominates, leading to lower maximum responses than the linear elastic model. If the inertial interaction is not significantly activated, similar results between the three models are obtained, being the linear elastic model enough to reproduce the soil–pile dynamic interaction.