Nonlinear Soil Model Research Articles

Comparative study on dynamic responses of ballasted and ballastless tracks at critical velocity

High-speed railways are becoming ubiquitous worldwide, demanding increased operational speeds. Yet, as trains near critical speeds, dynamic stress and embankment displacement escalate, jeopardizing safety. While significant strides have been made in studying these critical speeds, capturing the dynamic characteristics of all track responses remains elusive. This study presents a coupled train-track-ground model employing a 2.5D finite element approach integrated with a nonlinear soil model to investigate the influence of embankment and foundation properties on the critical speeds for both ballasted and ballastless tracks. The research resulted in the development of unified Dynamic Amplification Factor curves that consistently represent the dynamic behavior of various tracks as observed in multiple studies. Additionally, the applicability of simplified theoretical models for calculating critical speeds, such as the elastic half-space foundation and track-foundation models, was assessed. The findings suggest that the simplified models are suitable only under specific conditions. This research provides valuable perspectives on optimizing train speeds and ensuring the safety of diverse track types.

Numerical modeling for controlled compensation grouting

This article analyzes the numerical modeling of the stress-strain state of a gravity structure sand base during grouting works using the controlled compensation grouting technique. The modeling is performed using the finite element method and physical nonlinear soil models that take into account the Coulomb-Mohr strength condition. The modeling is done in the computational software JuliS as well as the universal software complex PC ZSoil. The goal of the research is to study the impacts of compensation grouting parameters on the elevation value of base slab. A model was created for the grout body as an expanding spheroid whose volume changes as cement grout is fed in the soil. The authors developed a grouting sequence for grouting solutions based on the location of grout body in the grouting pillar. It is more efficient to feed the grout starting from the lower grout body. The grouting solution feed mode is selected depending on the soil strength condition and accounting for the prevention of hydraulic fracture. As a result of the research, the initial subsidence of the soil on the daytime surface above the injection zone was obtained, which requires experimental confirmation and is a matter for discussion.

A comparison between static and dynamic load tests of Tapered steel jacking piles in Baskarp sand

In this study, four full scale static compression tests were performed on a tapered steel jacking pile with diameters 76 mm and 89 mm in both dry and saturated soil conditions. Each test consists of multiple sub-tests with respect to determination of in-situ Baskarp Sand No.15 conditions and bearing capacities of the piles. Further, a finite element methodology has been developed to predict the load-displacement response of tapered piles installed in sand, incorporating the effects of jacking installation. The methodology is based on the identification of the failure mechanism and shear strain formation at failure around the pile as well as adoption of soil-soil interface elements. The nonlinear soil model parameters for a fully wished-in-place (fully-WIP) condition were obtained through piezocone penetration tests where various methods were applied to obtain the relative density, among which those providing best fit according to Jamiolokowski et al., (2003) were selected for further assessment. Finally, the hammer tests were performed from which the dynamic bearing capacities and the relation between static and dynamic bearing capacities were obtained.

Investigation of the stress-strain state of foundation structures in determining the vertical stiffness of piles using different software systems

The results of numerical modeling of the interaction between a multi-storey building on a pile foundation and the soil base in the "Lira-SAPR" software are presented. A comparison of the stress-strain state of foundation structures was performed using different methods for determining vertical stiffness (Rz) in single-node FE 57 (this element is designed to model the behavior of a pile together with the surrounding soil, similar to FE 56, and can implement the interaction with the "SOIL" system). Piles were modeled by a chain of single-node FE 57 connected by vertical bars.
 In the first variant, the calculation of the building was performed in the "Lira-SAPR" software. To determine the vertical stiffness in FE 57, a soil model with physical-mechanical characteristics was created, and layering was defined according to the engineering-geological cross-section in the "SOIL" system. The calculation of vertical stiffness took into account mutual influence and the model of the conditional foundation.
 In the second variant, the determination of vertical stiffness (Rz) in FE 57 was carried out using the "Plaxis 3D" software. The overall model of above-ground structures, foundations, and all necessary loads were created in the "Lira-SAPR" software. Subsequently, an export to "Plaxis 3D" was performed, where the soil was previously modeled as a three-dimensional soil mass (with characteristics and strengths of layers similar to those created in the "SOIL" system) using the "Hardening soil" behavior model. After the import into "Plaxis 3D," the analysis of the "Soil-Foundation-Structure" system was conducted, and the obtained values of vertical stiffness (Rz) in FE 57 were exported back to "Lira-SAPR". After the export of "refined" values of vertical stiffness to "Lira-SAPR", a general static analysis and comparison of the stress-strain state of foundation structures with the first calculation variant was performed.
 It was established that the vertical stiffness in FE 57 in the first variant is higher than in the second, accordingly, the total displacements for the first variant are smaller. The importance of using the connection between "Lira-SAPR" and "Plaxis 3D" or other specialized geotechnical software complexes was demonstrated to obtain more accurate results of the interaction of the "Soil-Foundation-Structure" system due to the possibility of using nonlinear soil models to better describe the behavior of the foundation.

Regulatory provisions for determining parameters of nonlinear mechanical behavior in hardening soil models

Presently, nonlinear mechanical soil models are widely used in the geotechnical practice. They are implemented in geotechnical finite-element software PLAXIS, MIDAS GTS NX, Z-Soil, Optum, etc. Notwithstanding the fact that International regulatory documents mainly recommend nonlinear models for calculating foundations, they do not specify methods for defining their parameters because nonlinear models are actually commercial products of various software manufactures and cannot be normalized in any country. For this very reason, specialists of Gersevanov Research Institute of Bases and Underground Structures (department of JSC "Research center of Construction") developed Standard of Organization STO 36554501-067-2021. The Standard is based on the world experience in assessing nonlinear model parameters defined with using advanced laboratory equipment. The article describes the most significant provisions of this Standard. Thus, depending on the problem to be solved, four groups of models are introduced: I - a model includes volumetric isotropic hardening (Soft Soil); II - a model includes volumetric isotropic hardening and rheological properties of the soil (Soft Soil Creep); III - a model includes double isotropic hardening (Hardening Soil) and IV - a model includes double isotropic hardening and stiffness at small strain (Hardening soil with small strain). Requirements to the necessary and sufficient types and scope of tests, which define model parameters, are reported. Taking into account that only laboratory tests define model parameters, Standard provides requirements for specimens' quality evaluation performed basing on measurements of the volumetric strain under effective natural stress. Specimens of poor and very poor quality cannot be considered. It is shown that power-law coefficient m , which indicates the relationship between soil stiffness and stress-strain-state in the models of III and IV groups can be received from triaxial compression and oedometer tests and shall be prescribed depending on prevailing deformation (shear or compression). Stiffness parameters at small strains can be defined wit in-situ tests (seismoacoustic profiling) or with laboratory tests (resonant column test, seismoacoustic profiling of specimens in triaxial cell equipped with bender element and strain gauges on the local base). The developed Standard specifies requirements for laboratory definition of stiffness at small strains.

Pipe-soil interaction behaviors of deepwater J-lay pipeline on sloping seabed

The pipe-soil interaction behaviors are crucial factors for the J-lay pipeline design, which are mainly investigated on the horizontal seabed in previous studies. This paper develops an innovative method for the static and dynamic analyses of pipe-soil interactions considering the J-lay pipeline on a sloping seabed. This approach simulates the motion processes of the pipeline particles and solves the internal forces of the pipeline elements by the vector mechanics and finite element principle. The position coordinates formulations of pipeline particles are derived to calculate the pipeline locations on the sloping seabed. The non-linear hysteretic soil model and the modified Coulomb friction model are employed to simulate pipe-soil interactions in the vertical seabed plane as well as the axial and lateral directions. Moreover, a large-scale pipe-laying experimental test system is established to carry out the model experiments of a J-lay pipeline on different seabed conditions. The static and dynamic pipe-soil interaction responses are then analyzed by the VFIFE method for a 6-inch gas pipeline J-laying on the negative sloping seabed. The influence of seabed slope type and angle and soil characteristics is further explored on the pipe-soil interaction behaviors, which provide significant evidence for the design of pipe-lay on the sloping seabed.

Dynamic Soil-Structure Interaction Through 2-D Site-Specific Response Analysis

Seismic response of structures involved soil-structure-interaction (SSI) that need to consider both inertial and kinematic interaction. Many underground SSI has been developed such as modelling the structures and soils as continuum with seismic load simplified as pseudo-static or static equivalent. More recent and more realistic SSI model consider non-linear time-history analysis in the form of 2-D site-specific response analysis (SSRA), in which both inertial and kinematic interaction in combination with non-linear soil model, as well as time-history ground-motions are simulated. This paper presents simplified pseudo-static soil-structure interaction finite-element (FE) response of underground box-station structure under prescribed maximum strain displacement as resulted from 1-D site-specific response analysis under various ground-motions characteristics of subduction and shallow crustal earthquakes. More complex model of SSI system of basement is also presented. This basement SSI model incorporates non-linear time-history analysis with dynamic soil properties considered through 2-D SSRA simulating seismic wave propagation from reference base-rock to ground surface. Various base-rock seismic ground-motions are simulated from results of de-aggregation analysis from probabilistic seismic hazard analysis considering both subduction and shallow crustal earthquakes scaled at various ground-motion periods. The analysis adopts dynamic soil model with non-linear modulus and damping using FLAC computer program.

Nonlinear Constitutive Soil Models for the Soil–Structure Interaction Modeling Issues with Emphasis on Shallow Tunnels: A Review

Nonlinear Constitutive Soil Models for the Soil–Structure Interaction Modeling Issues with Emphasis on Shallow Tunnels: A Review

Investigation of trench effect on fatigue response of steel catenary risers using an effective stress analysis

The design of Steel Catenary Risers (SCR) heavily relies on the interaction between the riser and seabed in the touchdown zone (TDZ). To accurately estimate the SCR-seabed stiffness, the soil behaviour must be assessed in two main phases: (1) during cyclic SCR motions, which generate excess pore pressure, leading to soil softening and remoulding in the TDZ, and (2) during inactivity periods throughout the SCR’s lifespan, causing dissipation of excess pore pressure associated with the consolidation state. The latter was neglected by the existing non-linear hysteretic soil models, which are based on the total stress approach. In the current study, a global riser analysis was conducted and the consolidation effect was incorporated using an effective stress framework. Long-term soil stiffness was determined by capturing both the remoulding and consolidation effects, which are respectively associated with the damage accumulation during the SCR cyclic motions and soil strength recovery during the intervening pause period. The constructed model was then combined with a new methodology named Hybrid Trench Model to investigate how the consolidation effect contributes to the fatigue performance in different trench depths. Stochastic fatigue analysis showed that the consolidation effect might increase the damage by around 10%-40% over the long-term assessment.

Experimental Study of the Dynamic Performance of Steel Catenary Riser within the Touchdown Zone

This study proposed a novel experimental platform to conduct dynamic loading tests of a truncated model steel catenary riser (SCR) within the touchdown zone (TDZ). The facilities of the platform, including a soil tank, a loading system, and a soil stirring system, were introduced in detail. The parameters of the test were determined through the simulation of an in situ riser. A steel pipe was adopted as the model riser, with its outer diameter equaling that of the prototype SCR. Before executing the dynamic loadings, the model riser developed its static configuration under the submerged weight and applied bending moment. Subsequently, cyclic vertical and lateral displacement loads were applied to the truncated point. The test results showed that when the vertical loading amplitude increased from 200 mm to 300 mm, the stress ranges at the front of the model riser increased by more than 100%, whereas the stress range only differed by less than 5% under different loading periods. Numerical models of the SCR were built based on the vector form intrinsic finite element (VFIFE) method. High similarities between the test and simulation results proved the reliability of the nonlinear soil model and the numerical model. During the test, a seabed trench was developed with a depth of 0.71 D and a width of 0.48 D, and its shape was similar to the in situ trench.

Initial data for Hardening Soil model

Nowadays, civil engineering makes high demands on numeral modelling in geotechnical engineering, notably, to ensure reliability of a structure at minimum cost. Using of codes and standards supported with numerical calculations and soil constitutive models makes the design satisfying this requirement possible. But no matter how complex the model is its fidelity depends on input data. The article describes a method for determining the main characteristics of the Hardening Soil model (including calculating the power parameter m and reducing the deformation characteristics of the soil to the recommended value of the reference pressure). A comparison of two approaches was made: using a table of physical and mechanical characteristics; and the approach based on the analysis of the results of laboratory tests in accordance with the methodology given in the article and further verification of the obtained parameters. The result of the comparison was the complete inconsistency of the first approach for assigning the parameters of the nonlinear soil model and the need to refer to the test protocols was confirmed.

Scour protection effects on the dynamic response of jacket structures under extreme load events

A well-validated Finite Element (FE) model of a jacket structure (OC4 jacket) with pile foundation together with a Computational Fluid Dynamic (CFD) model (OpenFOAM-based) set-up for extreme waves on the structure are applied to perform systematic comparative analyses of the dynamic response of the structure to extreme wave loads with and without scour effects. The pile foundation model is considered by implementing a non-linear soil model to the foundation using load-deflection (p-y) approach to capture the non-linear behaviour of the soil for large pile foundation displacements. The results show that, the scour protection improves the foundation bearing capacity and consequently, decreases the failure probability in terms of both serviceability and ultimate limit states. Moreover, it enhances the dynamic response of the structure under extreme load events caused by breaking waves. Accordingly, an innovative solution for scour protection of offshore-fixed bottom structures has been introduced by “Biodegradable Soft Rock” (sand filled containers produced from bio-degradable geotextile product) which is the newest development in this section.

Evaluation of capacity of power hammer machine foundation from high strain dynamic load test: Field test and axisymmetric numerical modeling

The power hammer machines induce harmful vibrations in different parts of the foundation which may result in excessive dynamic settlement. While designing the hammer machine foundation, variety of static and repetitive impact load tests are generally conducted to ensure both the stability and serviceability of the foundation system. The static load test (SLT) is performed in the case of such foundations to obtain the ultimate capacity. However, the SLT is unable to predict the reliable response of the machine foundation. Hence, the current study is aimed to investigate the static and dynamic resistance of power hammer machine foundation by employing the high strain dynamic load test (DLT). The test procedure involves measuring the acceleration, axial force and settlement at the top of the machine foundation. Additionally, the soil resistance pertaining to damping is assumed to disappear with the zero-velocity at the first moment, which is identical to the unloading point method (UPM). Also, the field test and axisymmetric finite element analysis by considering the nonlinear soil model were performed to evaluate the stress settlement curve (SSC) from both SLT and DLT. The results reveal that the capacity of the machine foundation subjected to repetitive dynamic loads increases gradually and then tend to remain stable in case of additional impact loads. The SLTs showed 3–4 % higher static resistance than the first DLT and 8–9 % reduction in contrast to the second DLT. Moreover, the residual plastic deformation of the soil beneath the machine foundation was recorded to rapidly increase at the beginning of hammer tamping while it decreased steadily with further increasing of the hammer blows.

Influence of building-site resonance and building properties on site-city interaction: A numerical investigation

Recently, the concept of ground motions within dense urban areas being significantly affected by upper building clusters has been widely accepted. However, multiple interactions between upper buildings and underlain soil layer have increased the complexity of the problem. In this study, we focused on the analysis of ground motion changes with respect to free-field motion caused by upper building clusters, and the seismic interaction between building clusters and underlain soil, named site-city interaction (SCI). Emphasis was placed on the influence of building-site resonance and building properties on SCI effects. Hence, a two-dimensional (2D) numerical finite element model coupled with a non-linear elastic-plastic soil model and a linear multiple degree-of-freedom building model was developed in the OpenSees framework.Numerical results showed that the SCI effects were strongly influenced by the building-site resonance effects and building properties. For special cases, the ground motion was reduced by more than 60% with respect to the free-field motion. Furthermore, the SCI effects decreased as the degree of soil non-linearity increased, whereas the ground motion caused by SCI effects reduced by more than 20% of the free-field motion. However, owing to the non-linear effects, several unexpected amplifications were observed at certain frequency bands.Overall, the results of this study present an insight into the relationship between building properties, building-site resonance effects and SCI effects, and provide a reference for further SCI analysis of real-life applications.

Numerical investigation of the effect of slope angle and height on the stability of a slope composed of sandy soil

Slope stability issues are very frequently in civil engineering applications and are commonly encountered in huge and significant projects such as dams, highways and tunnels, etc. This study examines the impact of slope height (H) and slope angle (β) on the stability of loose granular soil slope underlined by dense granular soil layer. For this purpose, a number of finite element analyses were conducted on a full-scale soil slope. The computer program Plaxis 2D code was used which is based on the finite element method (FEM). The granular soils were described by non-linear hardening soil model, which is an advanced elastoplastic stress-strain constitutive soil model. Six different slope angles were investigated and for each angle, six different heights were chosen. In total, twelve series of numerical analyses were executed. In the first six series, it was assumed that there is no surcharge load on the top of the slope. In the second six series, the effect of surcharge load was also investigated. According to numerical analysis results, it was found that the slope height and slope angle have a considerable effect on the safety factor (FS) of the slope. It was also noticed that most of the failure surfaces of the slope were circular and classified as face slope failure. It was observed that by increasing slope height and the slope angle, the FS of the slope decreases and vice versa. In addition, curves and charts have been proposed to easily estimate the FS of loose granular soil slope.

Material point method for large-deformation modeling of coseismic landslide and liquefaction-induced dam failure

In this study, Material Point Method (MPM) is improved to simulate coseismic slope stability and liquefaction-induced embankment failure under earthquake loading. First, by using elastic or elastoplastic models, topographic amplification and different slope failure modes are analyzed considering the effects of slope geometry, soil properties and excitation frequencies etc. The MPM model is then applied to predict a cascading slope failure process, including triggering, shear band formation, runoff and final deposition. Finally, a fully nonlinear bounding surface soil model is implemented in the two-phase soil-water coupled MPM framework to investigate the liquefaction mechanism and associated dam failure using two case histories. The numerical results are generally comparable with the post-failure profiles obtained from field investigation, which highlight the advantage of MPM in handling liquefaction-induced large deformation. The MPM shows great promise to quantitatively assess risk and consequence associated with seismic slope failure and soil liquefaction, thereby, advance the performance-based engineering design and analysis.

Effect of Soil Properties and Input Motion on Site Amplification Using Validated Nonlinear Soil Model

Three-dimensional (3-D) nonlinear site response analyses are conducted using finite element models of actual soil profiles from ten nuclear power plant (NPP) sites in the United States to investigate the effects of soil properties and input motions on site amplification. The modeling approach developed in this study combines several novel elements, such as 3-D analysis (including vertical motions), nonlinear inelastic behavior of soil (strain-dependent shear modulus reduction and hysteretic damping), formulation of nonreflecting boundary conditions at the base, and generation of realistic outcrop ground motions for specific sites. All these elements of the modeling approach are first validated using actual data from five earthquakes at three downhole array stations recorded in the Kiban-Kyoshin network (KiK-net), Japan. The same approach is then used to develop site models of ten NPP sites in the United States and corresponding ground motions that are spectrally matched to the site hazard spectra. Eight sets of three-component input motions are used in the study and are categorized on the basis of presence or absence of a near-field pulse in the seed ground motions used for spectral matching. It is found that all sites retain a definite site amplification function regardless of the input motion, provided that the seed motion is spectrally matched to the site hazard spectra. The magnitude of site amplification and frequencies at which they occur depend upon soil properties, particularly the shear wave velocity profile and the constitutive relationship (strain-dependent shear modulus reduction and hysteretic damping) of soil. Amplification of spectral acceleration in the vertical direction (up-down motion) is found to be just as much as, if not more than, the amplification in the horizontal direction. Peak shear strain is found to be about 20% larger for near-field motions compared to far-field motions whereas maximum horizontal site amplification for far-field motions is found to be consistently larger than that of near-field motions, even though the differences between the two remain within the scatter resulting from individual ground motions.

Estimation of the response of piled raft using nonlinear soil and interface model

ABSTRACT In this research paper, the complex interaction mechanism between different components of CPRF was simulated through 3D finite element analyses using the nonlinear interface and soil model for three case histories. The interface behaviour between concrete and soil was accounted using combined adhesion and friction model. The nonlinear soil behaviour was included using cap plasticity model, which has stress-dependant shear and compression yield surface, and captures the effect of stress history and stress path. The computed response parameters for the three case histories resulted in reasonably close agreement with the field measurements and led to significant improvement in the estimation of the load sharing of piles. The comparison of the results with the different methods showed that the stiffer interface results in a higher pile-raft coefficient and lesser settlement. The pile and soil stiffness found to vary with their position below the raft due to the different interactions.

Experience in designing the foundations of a multi-storey building on the eluvial soils of the Urals using a model of non-linear soil deformation

The article describes an example of the first design of the foundation of a high-rise building in the Middle Urals using a non-linear soil model that reflects the real deformation properties of the soil. The use of an effective model that reflects the real deformation properties of the soil has allowed to reduce the cost of the foundation by more than two times while increasing of its reliability.

About actual contradiction in geotechnical design and optimal way of it resolution

The paper describes serious and fundamental contradiction in geotechnical design, which manifested itself to the greatest extent when designing the foundations of high-rise buildings in the third quarter of the 20th century has begun to form from the late of the 19th century to the 20th years of the 20th century. Prime cause of this contradiction is in complex physical structure of soils, complex nature of their formation and, therefore, in complex form of their deformation. The article also notes the high technical and economic efficiency of using realistic physically nonlinear soil models in the design of geotechnical parts of buildings and structures. In this case such a designing is most effective when using the parameters of nonlinear models determined from data of in-situ tests.