Deformation Behavior Of Soil Research Articles

Experimental study on the deformation behavior of soils under one-dimensional unloading

Experimental study on the deformation behavior of soils under one-dimensional unloading

The Effect of Oil Contaminated on Collapse Pattern in Gypseous Soil Using Particle Image Velocimetry and Simulation

Gypseous soil covers approximately 30% of Iraqi lands and is widely used in geotechnical and construction engineering as it is. The demand for residential complexes has increased, so one of the significant challenges in studying gypsum soil due to its unique behavior is understanding its interaction with foundations, such as strip and square footing. This is because there is a lack of experiments that provide total displacement diagrams or failure envelopes, which are well-considered for non-problematic soil. The aim is to address a comprehensive understanding of the micromechanical properties of dry, saturated, and treated gypseous sandy soils and to analyze the interaction of strip base with this type of soil using particle image velocimetry (PIV) measurement and Plaxis 3D simulation. The results showed that high-resolution digital cameras captured soil deformation using PIV, displacement fields, and velocity vectors were generated, which helped identify different sand movement zones. Further, PIV showed punching and general shear failure in uncontaminated and soaked contaminated gypsum soils, respectively. Moreover, the Plaxis results corresponded well with the PIV, as material behavior models are essentially simplified representations of the actual behavior of footing and soil. Understanding soil deformation behavior is crucial for accurate engineering calculations and designs, making these findings valuable for geotechnical and construction engineering applications. Doi: 10.28991/CEJ-2024-010-07-016 Full Text: PDF

Seepage effect on progressive failure of shield tunnel face in granular soils by coupled continuum-discrete method

Seepage induced by the difference of hydraulic head between the ground and the shield’s chamber will adversely affect the stability of tunnel face when tunnels are excavated through water-rich stratum. In order to investigate the influence of seepage on the stability of tunnel face, a 3D continuum-discrete method is proposed to simulate the failure of tunnel face. The large deformation behavior of soil is determined by the discrete element method and the fluid flow in soil phase is described by the Darcy fluid model and continuity equation. A series of simulations are carried out to obtain the failure mechanism and critical support pressure of tunnel face. Then the results under dry, undrained and seepage conditions are analyzed and the seepage effect on the stability of tunnel face with different water depth is investigated. Besides, a comparison between the simulation results and solutions in previous researches is conducted. Additionally, the micro-mechanical analysis under dry and seepage conditions are presented. The results show that the coupled method can well evaluate the stability of tunnel face considering seepage effect and provider useful guidance for practical tunnel designs.

Energy-based insight into characterization of shakedown behavior of fully weathered red mudstone

Weathered Red mudstone is widely distributed in Sichuan basin. The compacted weathered red mudstone has been used as subgrade fill materials of high-speed railway in southwestern of China. Dynamic responses of such materials under cyclic loading are critical to long-term stability of subgrade. Shakedown concept is widely employed in characterizing the permanent deformation behavior of soils. According to the evolution of axial strain (Werkmeister’s theory) or unit dissipated energy (Tao’s theory) with loading cycles, the behavior of unbound granular materials can be classified into three categories: plastic shakedown, plastic creep and incremental collapse. However, both theories are more suitable for the unbound granular materials with some limitations when used to separate the plastic creep and incremental collapse behavior. To overcome the limitations of the current theories, 26 cyclic triaxial tests were conducted on a saturated fully weathered red mudstone (SFWRM) to study the evolution of axial strain and unit dissipated energy during cyclic loading. A clear dependency of axial strain, axial strain rate on the unit dissipated energy level under various cyclic stress states were observed. A new criterion which is based on the responses of unit dissipated energy with cyclic stress ratio, was proposed to determine the limit between plastic creep and incremental collapse. Comparing with Werkmeister’s criterion and Tao’s criterion, the proposed criterion showed a better performance in identifying the incremental collapse behavior of the SFWRM.

The effects of changing the deviatoric and spherical stresses during cyclic loading on the drained response of a sand

Changing the deviatoric and spherical stresses could affect the accumulative deformation behaviour of soils under cyclic loading. Drained cyclic triaxial loading tests were performed on saturated sand to study the dependence of cyclic loading-induced axial and volumetric strain accumulations on changing the deviatoric and spherical stresses in between loading cycles. The change in the stresses was simulated by changing cell pressure and axial load along different stress paths. The variation of axial and volumetric strain accumulations before and after changing the stresses is compared and discussed. It is found that changing the stresses could have different impacts on the axial and volumetric strain accumulations, as the accumulations are affected by different mechanisms. The axial strain accumulation after changing the stresses is affected by the average stress ratio and precedent stress history. The volumetric strain accumulation is hardly affected by changing the stresses unless an increase in the average stress ratio is caused. Both axial and volumetric strain accumulations show independence on the stress path of the disturbance. For the samples with decreasing average stress ratio, the strain accumulation direction after changing the stresses cannot be fully described using Modified Cam Clay flow rule.

Structure dependent changes in pore water pressure due to stress application and consequences on the effective stress

Divergent processes in soils affect the pore systems and alter hydraulic, gaseous and thermal fluxes as soon as the internal soil strength (= the precompression stress) is exceeded. Especially the intense changes of the hydraulic flux properties during soil deformation result in retarded soil settlement due to their dependency on time and stress dependent changes in pore water pressure as well as the water saturation degree. These processes depend besides on texture and bulk density especially on aggregation level, but the linkage between changes in effective stress and soil structure in various soil horizons defined by the precompression stress is still not analyzed and is therefore subject of this investigation. In this study, stress strain and pore water pressure data from almost 900 (predrained to −60 hPa) samples from arable top- and subsoil horizons subjected to oedometer compaction tests are evaluated. Among others, hydraulic stress parameters like the effective stress and χ-factor are calculated and linked to the precompression stress values. Results are presented for 6 differently aggregated soil horizons. Ap horizons with a very weak soil structure document no defined soil rigidity due to a reduced functionality of the pore systems and a stress dependent weakening, while especially the soil deformation behavior of sandy Bw horizons is less controlled by the precompression stress and the calculated effective stresses. The E and Bg horizons indicate anthropogenic impacts on structure properties and the related stress-strain behavior. While it could be documented that the enhanced strain coincides with an increase in the calculated χ-factor, it does not coincide in correspondingly enhanced effective stresses due to the non- equilibrated pore water pressure even after 45 h of increasing stress application. We conclude that further investigations are needed to quantify the highly dynamic interactions between the stress dependent hydraulic conductivity / pore water pressure ratio and the impact on the stress affected pore water pressure reequilibration. Furthermore, the contribution of the sorptive potential in soils with more negative initial matric potential on these changes would elucidate also the physico chemical impacts on soil strength more clearly especially under drier soil conditions.

Undrained Cyclic Loading Response of Subgrade Soil Subjected to Varying Moisture Content and Stress Level

Subgrades that are constructed from fine-grained cohesive soils undergo large settlements; therefore, the study of their deformation behavior is important to avoid early deterioration in the traffic infrastructure. In this study, the deformation behavior of two different types of cohesive subgrade soils at different compaction states has been addressed that considered the effect of influencing factors, such as water content, deviatoric stress, and confining pressure (σ3). The results from the unconsolidated undrained cyclic triaxial tests show that the deformation behavior of soil is highly influenced by the level of applied deviatoric stresses and moisture content on the wet side of optimum (WS) and is slightly affected by σ3 and moisture content on the dry side of optimum (DS). The elastic strain (ɛe) component showed a decreasing trend with an increase in the number of load cycles (N) and then attained a steady value toward a higher N; however, the plastic strain (ɛp) component continuously increased for a given magnitude of applied cyclic deviatoric stresses (σd,c). From the test results, logarithmic strain models were proposed to predict the long-term total (ɛt) strain and ɛp that developed in cohesive subgrade soils, which were subjected to various combinations of variations in moisture content and stresses. The proposed model has been compared with the existing model and shows better prediction ability with a coefficient of correlation (R2) of >95% in most cases.

Evolution law of small strain shear modulus of expansive soil: From a damage perspective

It is of great significance to study the nonlinear evolution law of the small strain shear modulus of expansive soil for analyzing the deformation behavior of soil or geotechnical structure and the seismic site response. Existing studies rarely discuss the damage mechanism of the small strain shear modulus of expansive soil, and the corresponding damage model describing the small strain stiffness decay law is lacking. In this study, a series of resonance column tests were carried out to investigate the effects of mean effective stress, loading and unloading stress paths and vibration cycles on the nonlinear decay law of small strain shear modulus of expansive soil, and the damage mechanism was discussed in detail. Subsequently, a novel damage model describing the decay law of small strain shear modulus of expansive soil was proposed and verified by the results of resonant column tests. The results show that the decay process of the small strain shear modulus with the shear strain is essentially the damage of the soil structure, which can be characterized mathematically by damage model. The mean effective stress and the larger overconsolidation ratio caused by the unloading process can inhibit the damage, while the vibration cycles can cause small reduction in small strain shear modulus and promote the damage. The proposed damage model with clear physical meaning can well describe the evolution law of small strain shear modulus of expansive soil, and has higher accuracy than the traditional model.

Cyclic stress–dilatancy relations and plastic flow potentials for soils based on hypothesis of complementarity of stress–dilatancy conjugates

Soil, rocks and rock masses dilate or compact when sheared, i.e., distortion necessitates volume change. This coupling between distortional strains and volumetric strains, described by stress–dilatancy theories, endows soils with manifestation of peculiar characteristics when they are subjected to shear. Stress–dilatancy theories have become central in describing the mechanical energy dissipation mechanism and further establishing flow rules in constitutive modelling of soils. The classical stress–dilatancy theories, such as Taylor's and Rowe's, are endowed with simplicity and descriptive power, but they were developed for describing the dilatancy behaviour of soils subjected to loading in shear (mobilizing away from isotropic stress state) and needed to be extended for describing plastic dissipation and shear-induced volumetric changes when soils are subjected to cyclic shear. In this paper, hypothesis of complementarity of stress–dilatancy conjugates is proposed as a unifying hypothesis for deriving stress–dilatancy relations for both loading in shear and unloading in shear. Then, plastic potential functions are derived based on the resulting stress–dilatancy relations. In so doing, the resulting stress–dilatancy relations and plastic potential functions are rendered with a quality to be used for the modelling of deformation behavior of soils subjected to both monotonic and cyclic shearing. The theoretical framework is applied first for plane strain and axisymmetric stress–strain conditions; and then extended for the general stress condition considering the Lode angle dependency of the shear strength of soils, using the multilaminate framework and applying the Matsuoka–Nakai spatial mobilized plane.

A coupled hydro-mechanical model for subsurface erosion with analyses of soil piping and void formation

A coupled hydro-mechanical erosion model is presented that is used for studying soil piping and erosion void formation under practical, in-situ conditions. The continuum model treats the soil as a two-phase porous medium composed of a solid phase and a liquid phase, and accounts for its elasto-plastic deformation behaviour caused by frictional sliding and granular compaction. The kinetic law characterizing the erosion process is assumed to have a similar form as the type of threshold law typically used in interfacial erosion models. The numerical implementation of the coupled hydro-mechanical model is based on an incremental-iterative, staggered update scheme. A one-dimensional poro-elastic benchmark problem is used to study the basic features of the hydro-mechanical erosion model and validate its numerical implementation. This problem is further used to reveal the interplay between soil erosion and soil consolidation processes that occur under transient hydro-mechanical conditions, thereby identifying characteristic time scales of these processes for a sandy material. Subsequently, two practical case studies are considered that relate to a sewer system embedded in a sandy soil structure. The first case study treats soil piping caused by suffusion near a sewer system subjected to natural ground water flow, and the second case study considers the formation of a suffosion erosion void under strong ground water flow near a defect sewer pipe. The effects on the erosion profile and the soil deformation behaviour by plasticity phenomena are elucidated by comparing the computational results to those obtained by modelling the constitutive behaviour of the granular material as elastic. The results of this comparison study point out the importance of including an advanced elasto-plastic soil model in the numerical simulation of erosion-driven ground surface deformations and the consequent failure behaviour. The numerical analyses further illustrate that the model realistically predicts the size, location, and characteristic time scale of the generated soil piping and void erosion profiles. Hence, the modelling results may support the early detection of in-situ subsurface erosion phenomena from recorded ground surface deformations. Additionally, the computed erosion profiles may serve as input for a detailed analysis of the local, residual bearing capacity and stress redistribution of buried concrete pipe systems.

Dynamic modulus and damping ratio of compacted loess under long-term traffic loading

Previous studies have centred on the long-term permanent deformation behaviour of soil under traffic loading while neglecting the dynamic parameters as it is affected by cycle number. In this study, forty tri-axial dynamic tests were conducted to assess the effects of cycle number, confining pressure, and dynamic stress on the dynamic modulus and damping ratio of compacted loess. Empirical models of both parameters were established and examined, from which emerged a nearly linear relationship between the dynamic stress-strain points when dynamic stress fell below a given threshold value. The representative dynamic modulus in the linear range initially increased and then decreased. The maximum representative dynamic modulus linearly increased as confining pressure increased, while confining pressure had no clear effect on the damping ratio. As the dynamic stress increased, the damping ratio was initially stable and then gradually increased until becoming stable again at a higher level.

A Coupled Macroscopic and Mesoscopic Creep Model of Soft Marine Soil Using a Directional Probability Entropy Approach

To mitigate the risk of structural failure in coastal engineering caused by soft marine soil creep, this study presents a coupled macroscopic and mesoscopic creep model of soft marine soil to predict long-term deformation behavior of the soil. First, the mesoscopic characteristics of soft marine soil (e.g., pore, particle, and morphological characteristics) under different external pressures were obtained using a scanning electron microscope. Then, both the mesoscopic and macroscopic characteristics of soil were quantified using directional probability entropy and then used as inputs to develop the model. The model predictions agree with the experimental data. In addition, the experimental results indicate linear negative correlations between porosity and pore ratio with stress—the relationships between the fractal dimension of pore distribution and probability entropy of particle orientation under stress are generally nonlinear. Further, results of sensitivity analysis indicate that the probability entropy of particle orientation is one of the most critical parameters governing long-term creep deformation behavior of soft marine soil.

Soil stress measurement by load cell probes as influenced by probe design, probe position, and soil mechanical behaviour

Knowledge of soil stress induced by vehicle traffic is a premise for assessment of soil compaction risks, but obtaining absolute values of soil stress is not trivial because stress transducer probe readings are influenced by probe characteristics and soil properties. However, little research has quantified the magnitude of the deviations between measured and “true” stress (defined as soil stress in the absence of a probe). The objectives of this study were to use a finite element model to quantify how stress readings by cylindrical probes are influenced by probe design (material properties, dimensions), probe spacing in multi-probe set-ups, probe installation depth, and soil mechanical behaviour. We show that soil stress is typically overestimated by transducer probes. Overestimation decreased with probe diameter to height ratio, and increased with the ratio of probe to soil elastic modulus. Overestimation was smaller but dependent on soil strength under plastic soil conditions and higher but independent of soil strength under elastic soil behaviour. Probes interfere with each other when the vertical gap between adjacent probes is closer than about three times probe diameter. Moreover, we found that measured stress is influenced by soil depth and size of the loaded area. Some of the factors influencing stress readings are easily controlled (e.g. probe material properties, dimensions and spacing). However, other sources of deviations between measured and true soil stress are more difficult to account for. Our findings show that the ratio of measured to true soil stress is dependent on soil deformation behaviour as well as on relationships between probe depth, radius of loaded area and ratio of soil stress to applied surface stress implies that the ratio of measured to true stress is not constant when measuring soil stress at various depths in situ under field conditions. We therefore suggest that future studies should especially address how stress readings are affected by soil mechanical behaviour, soil depth, the size of the loaded area, and interactions among these factors.

Prediction of pressuremeter modulus (EM) using GMDH neural network: a case study of Kenny Hill Formation

Soil investigation (SI) work is a process of collecting subsurface ground profile information in evaluating soil engineering properties for a construction project. The standard penetration method (SPT) is widely accepted worldwide as a feasible and relatively inexpensive method over other field tests. Pressuremeter test (PMT), on the other hand, is costly and more popular in situ method in interpreting soil deformation behavior. Considering SPT is available in almost site investigation works for all sizes of project, it was tempting to establish the correlation between SPT and PMT results, specifically in local geologic setting. The study was conducted in Kenny Hill Formation, Kuala Lumpur, Malaysia. The correlation established in this study is between pressuremeter modulus (EM) and SPT blow count (N60). In addition to in situ methods, the physical properties of soil extruded from boreholes were tested in geotechnical laboratories to determine soil properties, such as particle size distribution, liquid limit, and plastic limit. These parameters need to be considered during prediction of EM. Group method of data handling (GMDH) neural network has been used to achieve this objective. The mean absolute error (MAE) results show that the GMDH neural networks produce values of 8.04 and 8.59 for training and testing. The root mean square error (RMSE) yields 10.61 and 10.84 for training and testing, respectively. Further, the results of the coefficients of determination (R2) are 0.794 and 0.726 for training and testing demonstrates a good correlation exists between predicted and measured values. Based on the GMDH results, N60, sand, and clay are required input variables for determination of EM.

Investigation of small- to large-strain moduli correlations of normally consolidated granular soils

The establishment of correlations between the small-strain shear modulus (Go) and other soil parameters (such as the oedometer constrained modulus, Moedo) at large deformations constitutes an important step toward more precise modeling of soil deformation behavior. In this study, the shear wave velocities (Vs) of 22 different granular soils of various physical characteristics were measured experimentally using the piezoelectric ring-actuator technique (P-RAT) incorporated in the conventional oedometer cell. For each sample tested, the development of Moedowith the development of relative density (Id), as well as the void ratio (e), was recorded. Then, the obtained Vsand Moedo/Gotrends were correlated to the physical parameters of the tested granular soils with the development of e and Id. A practical application employing the achievements in geotechnical engineering design was also evaluated. Based on the proposed correlations, geotechnical designers can easily estimate in situ stress–settlement behavior from the predicted Moedoand Idvalues using simple in situ measurements.

Soils on the southern border of the cryolithozone of European part of Russia (the Subpolar Urals) and their soil organic matter fractions and rheological behavior

Soil organic matter (SOM) plays an important role in the functioning of mountain ecosystems. This article contains the results of a study on SOM of high-latitude soils of the Subpolar Urals and its influence on the deformation behavior of soils. The first approach of this study was to define the soils of the Subpolar region to identify the main soil types and their morphological and chemical properties. We investigated soil types of mountain-forest, subalpine and alpine tundra vegetation zones, as well as soil types with permafrost. We investigated SOM using the method of physical fractionation, which isolates three fractions of SOM: free particulate organic matter (fPOM<1.6), occluded particulate organic matter (oPOM<1.6) and heavy mineral-associated fraction (MaOM>1.6). The deformation behavior of soils was studied using rheometry. Based on the results, SOM mainly consisted of heavy-fraction MaOM<1.6, accounting for 57–99%. The light fractions of free fPOM<1.6 and occluded oPOM<1.6 organic matter were considerably smaller (0.14–23.9%). However, the direct dependence of the organic carbon concentration on the content of light fractions fPOM<1.6 (0.89, p < 0.05) and oPOM<1.6 (0.84, p < 0.05) for the first mineral horizons was revealed. There also was a significant negative correlation between the carbon content and the heavy-fraction MaOM>1.6 (−0.86, p < 0.05). Rheological studies showed that the stability, resilience and interparticle bonds in soils also depend on the contents of light fractions of SOM: fPOM<1.6 (0.52–0.85, p < 0.05) and oPOM<1.6 (0.46–0.60, p < 0.05).

Experimental Study on the Response of Unsaturated Silt Due to Change in Drainage Conditions During the Triaxial Test Process

An experimental series is performed to study the response of unsaturated silt compacted on the dry and wet side of optimum water content due to change in drainage conditions during the triaxial test process. Soil samples were compacted at water content of 15% and 25% maintaining degree of compaction at 85%. The drainage conditions for pore air and pore water pressure was changed for isotropic consolidation, monotonic shear and water infiltration processes. The isotropic consolidation was performed by keeping pore air pressure drained and pore water pressure undrained. During monotonic shear both pore air and water pressures were undrained, whereas, the water infiltration was carried in fully drained conditions. The water infiltration was carried by keeping deviatoric stress and axial strain constant on the specimen. It was observed that the drainage conditions affect the deformation behavior of soil and results in a rapid decrease in specimen volume. Moreover, the stress paths for the specimens with constant deviatoric stress moved towards the failure line whereas the stress paths for the specimens with constant axial strain moved along the reference failure line.

Anisotropic and Noncoaxial Behavior of K0-Consolidated Soft Clays under Stress Paths with Principal Stress Rotation

AbstractDuring embankment construction, the deformation behavior of soil will vary with increasing fill height because the principal stresses applied on soil elements in K0-consolidated subsoil wil...

Experimental Analysis of Strength and Deformation Behavior of Soils Reinforced with Building-Derived Materials

Recycling of construction and demolition waste (CDW) materials and reusing them in construction is an effective way to dispose of them. Simultaneously, CDW can be used as a substitute for materials whose natural resources are getting depleted. This paper is focused on reusing building-derived materials (BDM), the primary subset of CDW, in geotechnical applications. In order to study the mechanical characteristics of soil blended with different percentages of BDM, a series of triaxial compression tests are conducted at different confining pressures to evaluate their strength and stress–strain behavior. Results from tests conducted with locally available sand and red soil admixed with varying proportions of BDM indicate that 17–23% by weight of soil is the optimum BDM content to be used as an admixture. Increase in confining pressures leads to strain hardening. To describe strength characteristics, the hyperbolic model is adopted to analyze the response at smaller strains. Parameters like cohesion, friction angle, peak stress are obtained from experimental results. The model indicates that failure ratio and tangential modulus depend upon peak load obtained from the experiments. The hyperbolic model results are found to be in good agreement with the experimental results.

Unified hardening law for soils and its construction

The hardening law in an elastoplastic constitutive model should be independent of the stress path for loading conditions. Based on the deformation behavior of soils along two orthogonal stress paths (i.e., constant mean stress shear path and isotropic compression path), a new hardening law, unified hardening law, is proposed to describe the shear contraction and dilatancy in an identical framework. Against Green’s Formula and test data, we prove that the unified hardening law meets the requirement on the independence of loading path, theoretically and experimentally. The constitutive model developed by employing the unified hardening law is further verified by comparing it with the measured stress-strain relation of clay and sand under different loading paths.