Modeling Of Soil Behavior Research Articles

Simulation of Dynamic Effects on Trunk Pipelines Laid in Difficult Engineering and Geological Conditions

In this paper, we conduct an experimental study of pipeline deformation together with soil to analyze the stress-strain state of the pipeline and compare it with the results of computer simulation. The experimental setup is a box of OSB panels, which is filled with soil. A polypropylene pipe is laid in the ground, onto which strain gauges are attached, which transmit strain measurements to the computer. At the bottom of the box is a board that drives the ground with a jack. The dependence of stresses in the pipe on soil displacements is constructed first for a polypropylene pipe, then the stresses are converted to a steel pipe and compared with the results of computer simulation in Ansys. The discrepancy between the results is small, due to inaccuracy in the selection of models of soil behavior. Further refinement of mathematical models is planned.

A single-stress model for the prediction of yielding of unsaturated cemented soils under isotropic loads

This paper presents a bounding surface model predicting the combined effects of cementation and partial saturation on the mechanical behaviour of soils subjected to isotropic loading. The loss of cementation caused by loading, wetting or drying of a normally consolidated soil is described by a “cementation bonding function”. This states that, under virgin conditions, the ratio between cemented and uncemented void ratios monotonically decreases with increasing levels of scaled stress. The scaled stress is the variable governing the intrinsic behaviour of the soil under both saturated and unsaturated conditions. Combination of the cementation bounding function with a previously proposed model for unsaturated soil behaviour leads to the formulation of a “cemented unified normal compression line” (CUNCL). This describes the virgin behaviour of both cemented and uncemented soils under saturated and unsaturated conditions. Progressive yielding is modelled by assuming that the slope of the generic loading curve tends towards the slope of the CUNCL as the soil state moves from overconsolidated to virgin conditions. The model has been calibrated and validated against existing experimental data demonstrating a good ability to predict the void ratio of cemented soils during isotropic loading, unloading and wetting under both saturated and unsaturated conditions.

Regularities of contact interaction of small-sized supporting elements of walking machines with weakly bearing soils

The results of finite-element modeling of the mechanics of contact interaction of small-sized support elements (feet) of walking machines with weakly bearing soils are discussed. A flat contact task is formulated for rigid feet of a rectangular shape interacting with an elastoplastic supporting surface. Nonlinear models of soil behavior under loading were used. A two-stage iterative algorithm for solving the non-linear problem in the computer system of finite element analysis ANSYS is implemented. The task was solved under conditions of large deformations of the supporting surface. The simulation results showed that a sufficiently large amount of soil is loaded during the interaction of a small foot with a supporting surface. Under normal loading, the greatest stresses and strains occur directly under the foot. Here may be the destruction of the soil. At a standardized depth of 0,5 m, the stress decreases. The top layer of soil remains lightly loaded. In addition to vertical deformations, there is a «squeezing» of soil to the right and left from under the foot. With a tangential load, the stress and strain fields lose their symmetrical nature. The zones of greatest equivalent stresses and strains are shifted towards the action of the tangential load. The greatest ground stresses occur under the foot and on the lateral surface of the foot. In the direction of the tangential load, the entire mass of the soil, including its upper layers, is substantially loaded. Near the foot, in the zone of greatest stresses, a characteristic area appears, where the soil is squeezed up. Here the reverse process of compaction of the soil takes place. It is shown that the use of feet with a small supporting surface leads to an undesirable increase in soil stresses in the contact zone. On the other hand, in small feet, there is a decrease in the soil compaction zone and its upper layer is less loaded. Also, for small feet, the supporting surface is used more efficiently - the stresses along its length are distributed more evenly, and the side surface acts as a grouser.

Modelling seasonal ratcheting and progressive failure in clay slopes: a validation

Seasonal wetting and drying stress cycles can lead to long-term deterioration of high-plasticity clay slopes through the accumulation of outward and downward deformations leading to plastic strain accumulation, progressive failure, and first-time failures due to seasonal ratcheting. Using recent advances in hydromechanical coupling for the numerical modelling of unsaturated soil behaviour and development of nonlocal strain-softening regulatory models to reduce mesh dependency of localization problems, the mechanism of seasonal ratcheting has been replicated within a numerical model. Hydrogeological and mechanical behaviours of the numerical model have been compared and validated against physical measurements of seasonal ratcheting from centrifuge experimentation. Following validation, the mechanism of seasonal ratcheting was explored in a parametric study investigating the role of stiffness and long-term behaviour of repeated stress cycling extrapolated to failure. Material stiffness has a controlling influence on the rate of strength deterioration for these slopes; the stiffer the material, the smaller the seasonal movement and therefore the more gradual the accumulation of irrecoverable strains and material softening. The validation presented provides confidence that the numerical modelling approach developed can capture near-surface behaviour of high-plasticity, overconsolidated clay slopes subject to cyclic wetting and drying. The approach provides a tool to further investigate the effects of weather-driven stress cycles and the implication of climate change on high-plasticity clay infrastructure slopes.

Моделирование разжижения грунтов основания при сейсмическом воздействии с использованием модели UBC3D-PLM

Liquefaction is a phenomenon in which the stiffness and strength of a soil are reduced as a result of seismic effect or other dynamic effects. Liquefaction was the basic reason of the big damages caused by many earthquakes around the world. The basic step in the processes of predicting the soil liquefaction is the modeling of soil behavior. At the present time, numerous soil models are presented. Nevertheless, only some of them can simulate this process. Model UBC3D-PLM is one of these models which can be used. In this paper, the possibilities of this model are considered by modeling on the PLAXIS software package the seismic impact on a building with its different heights. The actual data of Upland earthquake 1990 near Los Angeles city was used. Results of this simulation showed us the difference in the behavior of the soil mass under the impact of an earthquake compared with the elastic behavior, as well as showed us the necessary to use the UBC3D-PLM model to estimate the seismic impact.

Mixed hardening hyper-viscoplasticity model for soils incorporating non-linear creep rate – H-creep model

This paper focuses on the deformation of soils considering the time-dependent stress-strain evolution. In this paper, a new mixed hardening hyper-viscoplasticity model is proposed for the derivation of the time-dependent constitutive behaviour of soils, with the intention to capture the variation in the shapes of the yield loci by pursuing non-associated flow rules and accounting for kinematic hardening effects. The distinctive departure from the existing viscoplasticity models is the application of thermodynamics, based upon the use of internal variables, to postulate free-energy and dissipation potential functions, from which the corresponding yield locus, isotropic and kinematic hardening laws, flow rules and the elasticity law are deduced in a systematic procedure. The kinematic hardening behaviour of the yield locus is considered using the shift stress, resulting from the additional plastic component of the free-energy function. A non-linear creep formulation is postulated to address the limitation of over-estimating long-term settlement and incorporated into the model for more reliable predictions. The major parameters required for the model are identified, along with the summary of descriptions on how the model parameters can readily be determined. Non-associated behaviour is found to be a natural consequence of this approach, whenever the division between dissipated and stored plastic work is not equal. This study aims to provide a theoretical background and a numerical implementation for those who are interested in the advancement of constitutive modelling of soil behaviour under the framework of hyperplasticity. Validity and versatility of the proposed constitutive model are evaluated against triaxial and oedometer test results available in literature.

Simulation of soil liquefaction due to earthquake loading

Liquefaction is a phenomenon in which the strength and stiffness of a soil are reduced as a result of seismic or other dynamic effects. Liquefaction was the main reason of the huge damages caused by many earthquakes around the world. The modeling of soil behavior is the main step in the process of predicting the soil liquefaction. Currently, a large number of soil models are presented. However, only some of them can simulate this process. One of these models which can be used is model UBC3D-PLM. In this paper, the possibilities of this model are considered by modeling the seismic impact on a building with its different heights on the PLAXIS software package. The real data of Upland earthquake 1990 near Los Angeles city was used. Results of the simulation showed the difference in the behavior of the soil mass under the influence of an earthquake compared with the elastic behavior, as well as the need to use the UBC3D-PLM model to estimate the seismic impact.

Rational modelling of elastic soil behaviour in 3D condition

A simple and rigorous formulation of elastic component of elastoplastic model for geomaterials is presented. Although linear relation between elastic volumetric strain and mean principal stress in log scale is assumed in most of the usual models, linear relation between each principal stress and the corresponding principal elastic strain in log scale is assumed. Incorporating Poisson's ratio, three principal stresses vs. three elastic principal strain relation is obtained. Also, assuming coaxially between stresses and elastic strains, this relation can be transformed to stress- elastic strain relation in general coordinate. The material parameters of the proposed model of the elastic component are the same as those of the usual models, i.e., swelling index κ and Poisson's ratio ν. This proposed model can describe typical unloading behaviour of various shear tests and constant stress ratio unloading tests reported before.

State-of-the-Art Modelling of Soil Behaviour Under Blast Loading

A comprehensive literature review has been carried out on existing models that characterize soil response under the impact of blast shock waves. Various models in the literature are reviewed and discussed in terms of their equations of state that account for the effect of high pressure, failure models that control the yield behaviour, and strength models that represent the effect of high strain-rates, along with a comparison of their advantages and limitations. Then, the application of different soil models to blast-induced liquefaction is elucidated and compared. Consequently, this review provides a comprehensive understanding of the fundamental and unique aspects of modelling soil response subjected to such transient impulsive loading on the grounds of increasing global interest in blast response of soils.

Atypical soil hardening during the Tohoku earthquake of March 11, 2011 (Mw = 9.0)

Based on the records of KiK-net vertical arrays, models of soil behavior down to depths of ~100–200 m in the near-fault zones during the Tohoku earthquake are examined. In contrast to the regular pattern observed during strong earthquakes, soft soils have not broadly demonstrated nonlinear behavior, or a reduction (with the onset of strong motions) and recovery (after strong motions finished) of the shear modulus in soil layers. At the stations where anomalously high peak ground accelerations were recorded (PGA > 1g), the values of the shear modulus in soil layers increased with the onset of strong motions and reached a maximum when motions were the most intensive, which indicated hardening of soils. Soil behavior was close to linear, here. The values of the shear moduli decrease along with a decrease in intensity of strong ground motions, and at soft soil stations, this was accompanied by a stepwise decrease in the frequency of motion.

A micro finite-element model for soil behaviour: numerical validation

A micro finite-element (μFE) model capable of handling arbitrary shapes and deformable grains has been developed by the authors. The basis of this μFE model is to use a virtualised soil fabric obtained from micro computed tomography (μCT) of real sand to simulate grain-to-grain interaction in a framework of combined discrete–finite-element method. By incorporating grain deformation into the model, the contact response emerges from the interaction of contacting bodies and each irregular contact area will produce a unique response. A detailed numerical description of grain morphology and contact topology of a natural sand and the subsequent simulation are presented in the original paper. The present study focuses on the numerical validation of the constitutive contact behaviour against existent theories, for a single sphere and an assembly of spheres. The ability of the model to simulate elastic–plastic behaviour making use of the deformability of the grains is demonstrated. The unloading–reloading behaviour associated with the geometrical arrangement of the grains for a granular assembly under triaxial compression is examined in terms of energy dissipation quantities.

A micro finite-element model for soil behaviour

This paper describes a numerical model that virtualises the fabric of a natural sand obtained from micro computed tomography (μCT) to simulate the mechanical response of the material, termed here a micro finite-element (μFE) model. The grain-to-grain interactions under loading are modelled in a framework of combined discrete–finite-element method. The basis of this approach is that using a true representation of soil fabric and deformable grains will enable a more realistic representation of the physics of granular behaviour. Each individual grain is represented in a numerical mesh and modelled as a continuum body allowed to deform according to a prescribed constitutive model with appropriate friction contact conditions. An important feature of this model is the ability to compute the map of stress distribution inside the grains. A case study of an intact sand subjected to oedometer compression is presented to demonstrate the insights that can be gained into the stress transmission mechanisms and yield initiation within the grains. The displacement field, inertia tensor and active contact number are used to quantify grain kinematics as the virtual fabric deforms. By coupling contact dynamics with contact topology, this approach provides a robust numerical tool to infer important grain scale parameters that link the micro phenomena to the macro response of soil.

FEM modelling of soil behaviour under compressive loads

Artificial compaction is one of the most dangerous forms of degradation of agricultural soil. Recognized as a phenomenon with multiple negative effects in terms of environment and agricultural production, soil compaction is strongly influenced by the size of external load, soil moisture, size and shape of footprint area, soil type and number of passes. Knowledge of soil behavior under compressive loads is important in order to prevent or minimize soil compaction. In this paper were developed, by means of the Finite Element Method, various models of soil behavior during the artificial compaction produced by the wheel of an agricultural trailer. Simulations were performed on two types of soil (cohesive and non-cohesive) with known characteristics. By applying two loads (4.5 kN and 21 kN) in footprints of different sizes, were obtained the models of the distributions of stresses occuring in the two types of soil. Simulation results showed that soil stresses increase with increasing wheel load and vary with soil type.

Mesh-Less Smoothed Particle Hydrodynamics in Modeling of Soil Behavior

In some cases there is no possibility for modelling of the soil behavior by traditional finite element method or other mesh-based techniques. It has been found that as a completely Lagrangian and mesh-free technique, smoothed particle hydrodynamics (SPH) provides advanced approaches for simulation of soil materials. The advantages of SPH are its high power, simplicity of concept, relative simplicity in combination with modern physics, and particularly its potential in the study of large deformations and failures.

A unified mechanical and retention model for saturated and unsaturated soil behaviour

The coupled mechanical and water retention elasto-plastic constitutive model of Wheeler, Sharma and Buisson (the Glasgow coupled model, GCM) predicts unique unsaturated isotropic normal compression and unsaturated critical state planar surfaces for specific volume and degree of saturation when soil states are at the intersection of mechanical (M) and wetting retention (WR) yield surfaces. Experimental results from tests performed by Sivakumar on unsaturated samples of compacted speswhite kaolin confirm the existence and form of these unique surfaces. The GCM provides consistent representation of transitions between saturated and unsaturated conditions, including the influence of retention hysteresis and the effect of plastic volumetric strains on retention behaviour, and it gives unique expressions to predict saturation and de-saturation conditions (air-exclusion and air-entry points, respectively). Mechanical behaviour is modelled consistently across these transitions, including appropriate variation of mechanical yield stress under both saturated and unsaturated conditions. The expressions defining the unsaturated isotropic normal compression planar surfaces for specific volume and degree of saturation are central to the development of a relatively straightforward methodology for determining values of all GCM parameters (soil constants and initial state) from a limited number of laboratory tests. This methodology is demonstrated by application to the experimental data of Sivakumar. Comparison of model simulations with experimental results for the full set of Sivakumar’s isotropic loading stages demonstrates that the model is able to predict accurately the variation of both specific volume and degree of saturation during isotropic stress paths under saturated and unsaturated conditions.

Atypical soil behavior during the 2011 Tohoku earthquake (М w = 9)

To understand physical mechanisms of generation of abnormally high peak ground acceleration (PGA; >1g) during the Tohoku earthquake, models of nonlinear soil behavior in the strong motion were constructed for 27 KiK-net stations located in the near-fault zones to the south of FKSH17. The method of data processing used was developed by Pavlenko and Irikura, Pure Appl Geophys 160:2365–2379, 2003 and previously applied for studying soil behavior at vertical array sites during the 1995 Kobe (М w = 6.8) and 2000 Tottori (М w = 6.7) earthquakes. During the Tohoku earthquake, we did not observe a widespread nonlinearity of soft soils and reduction at the beginning of strong motion and recovery at the end of strong motion of shear moduli in soil layers, as usually observed during strong earthquakes. Manifestations of soil nonlinearity and reduction of shear moduli during strong motion were observed at sites located close to the source, in coastal areas. At remote sites, where abnormally high PGAs were recorded, shear moduli in soil layers increased and reached their maxima at the moments of the highest intensity of the strong motion, indicating soil hardening. Then, shear moduli reduced with decreasing the intensity of the strong motion. At soft-soil sites, the reduction of shear moduli was accompanied by a step-like decrease of the predominant frequencies of motion. Evidently, the observed soil hardening at the moments of the highest intensity of the strong motion contributed to the occurrence of abnormally high PGA, recorded during the Tohoku earthquake.

The Influence of Seismic Parameters on Site Response

Geotechnical earthquake engineers have been trying to determine the most appropriate solution techniques for ground response analysis under earthquake loadings. This paper presents the importance of the adequate soil behavior model to simulate earthquake site response analysis. The influence of nonlinearity and linearity of soils on the site response is also investigated. Many methods have been proposed for the analysis of one-dimensional ground response such as nonlinear methods and equivalent linear with reduced modulus. Using 13 well known earthquake records and geotechnical information of sand in the Qeshm Island (Iran) and classification of earthquakes based on seismic parameters, the influence of each parameter on the Response spectra and Fourier Spectrum of surface of ground becomes evident. Analysis was done using two softwares; EERA (equivalent linear analysis) and NERA (nonlinear analysis) and compared. Finally, output of the software is compared with the reference result on site.

Mechanical Behavior of Clean Sand at Low Confining Pressure: Verification with Element and Model Tests

AbstractConfining pressure significantly influences the mechanical behavior of soil. Understanding geotechnical problems related to low confining pressures requires precise modeling of soil behavior at low confining stress. Yet laboratory tests, including element tests under low confining pressure, are so far quite limited. In this note, a series of element tests under low confining pressure (5–20 kPa) were carried out to investigate the effect of low confining pressure on the mechanical behavior of loose and medium dense Toyoura sand. Element tests include undrained cyclic loading tests, as well as drained and undrained strain-controlled monotonic loading tests. The results show that loose sand under low confining pressure behaves much like dense sand under higher pressure. Model tests of slope failure flow under microgravity, carried out to supplement the element test results, also confirmed the previously mentioned mechanical behavior. The results obtained in this paper provide a more fundamental under...

Role of admissibility criteria in limit equilibrium slope stability methods based on finite element stresses

A number of limit equilibrium slope stability methods have been developed where the factor of safety is calculated based on stresses computed using an independent finite element analysis. The internal stress distribution is usually generated using the ‘switch on’ gravity technique assuming linear elastic soil behavior. Young’s modulus and Poisson’s ratio are often assigned at random with little knowledge of how the values could impact the slope stability calculations. The results from a number of slope stability studies are provided to summarize the differing opinions regarding the sensitivity of the factor of safety to the selection of Poisson’s ratio and Young’s modulus. It would appear that the different views amongst researchers can be related to the method used to search for the critical slip surface. The factor of safety is reported to vary by less than 5% in studies where the grid and radius searching procedure is used and by more than 20% in studies where the dynamic programming searching procedure is used. The different levels of sensitivity can be related to the soil behavior model adopted in the stress – deformation analysis and the interaction of the searching procedure with the internal stress distribution in the slope.

A View of Pressuremeter Testing in North America

The pressuremeter was introduced to North America by Ménard in 1957. It consists of a cylindrical probe which is inserted into the ground in a borehole, by self-boring or by pushing, and is expanded against the soil or rock to obtain a pressure-expansion curve. Interpretation methods based on cavity expansion theory applied to realistic models of soil behavior allow derivation of in situ lateral stress, stiffness, strength and volume change characteristics of the material being tested. Since its introduction, the pressuremeter test (PMT) has been a popular topic of research but has not gained wide acceptance in geotechnical engineering site characterization practice which, in North America, is still dominated by the Standard Penetration Test (SPT) and more recently by the piezocone (CPTu). Over the same period, the PMT has become the dominant tool for site investigation and foundation design in France. There, the PMT is used empirically based on a very large amount of load testing and experience. This paper examines the use of the PMT in North American practice, discusses its strengths and weaknesses, identifies trends in its use for site characterization and geotechnical design and identifies possible reasons for its lack of adoption by industry. We conclude that the PMT is not competitive with other techniques such as the CPTu and SPT for general site characterization where such tests are possible but that the PMT offers great potential to provide geotechnical design parameters in problematic materials such as hard, very dense or gravelly soils, residual, saprolitic or lateritic soils, soft and fractured rocks, frozen ground and ice. The PMT also has application in all soils where high consequences of failure require very detailed analysis and design. We also emphasize the need for improvements in the education of geotechnical practitioners on the use of the pressuremeter.