scholarly journals Experimental Testing and Numerical Modelling of Mechanical Behaviors of Silty Clay under Freezing-Thawing Cycles

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Tianfei Hu ◽  
Dawei Liu ◽  
Hui Wu
Keyword(s):  
Numerical Modelling ◽  
Experimental Testing ◽  
Axial Strain ◽  
Volumetric Strain ◽  
Triaxial Tests ◽  
Model Parameters ◽  
Silty Clay ◽  
Test Results ◽  
Mechanical Behaviors ◽  
Physical Weathering

Seasonal freezing-thawing cycle is one of the most common physical weathering processes in cold regions, which can significantly affect the mechanical behaviors of soil. In this paper, a series of freezing-thawing (F-T) cycle and consolidated drained triaxial tests have been carried out on silty clay samples collected from Tibetan Plateau. To do so, a modified numerical model was developed taking into F-T effect. Test results showed that the stress-strain curves of original soil specimens presented strain hardening characteristics, accompanied with shear shrinkage. In F-T experienced specimens, volumetric strain in triaxial loading stage was gradually increased, while failure strength was decreased. Elliptic and parabolic functions were selected in numerical modelling to describe volume and shear yield surfaces on a p-q plane, respectively. Moreover, a double-yield surface constitutive model was developed to describe relationships among deviatoric stress, axial strain, and volumetric strain. Furthermore, equations for model parameters with the number of F-T cycles as variable were derived based on the triaxial test results which were then substituted into the established model to take into account the effects of F-T cycles. Finally, numerical results were validated with experimental findings.

Experimental Study on Slaking Deformation of the Remolded Laterite

2014 ◽  
Vol 584-586 ◽  
pp. 1192-1196
Author(s):  
Xiao Wen Liu ◽  
Xiao Yan Chen
Keyword(s):  
Experimental Study ◽  
Stress State ◽  
Axial Strain ◽  
Volumetric Strain ◽  
Reference Value ◽  
Test Results ◽  
Stress Strain ◽  
Modulus Of Deformation ◽  
Logarithmic Relationship ◽  
Wetting Deformation

Through lots of triaxial and a single-line wetting path experiments for slaking deformation of the remolded laterite , behaviors of stress-strain and volumetric strain-axial strain are studied at different level values of wetting stress.The test results indicate that the modulus of deformation and the strength of samples are reduced by wetting, that the value of wetting deformation is relation to the stress state and that the logarithmic relationship between wetting axial strain of the type of laterite and wetting stress levels meets . The test results obtained have an important reference value for actual projects in Jiangxi laterite area.

scholarly journals Comparison of Mechanical Properties of Fiber-Reinforced Sand under Triaxial Compression and Direct Shear

2015 ◽  
Vol 7 (1) ◽  
Author(s):  
Reza Noorzad ◽  
Seyed Taher Ghoreyshi Zarinkolaei
Keyword(s):  
Shear Strength ◽  
Axial Strain ◽  
Triaxial Compression ◽  
Polypropylene Fiber ◽  
Triaxial Tests ◽  
Direct Shear ◽  
Test Results ◽  
Peak Reduction ◽  
Shear Tests ◽  
Direct Shear Tests

AbstractThis research investigates the behavior of sand reinforced with polypropylene fiber. To do this, 40 direct shear tests and 40 triaxial tests were performed on the coastal beaches of Babolsar, a city in the North of Iran. The effect of parameters such as fiber content, length of fiber and normal or confining pressure on the behavior of Babolsar sand have been studied. In this study, four various fiber contents (0, 0.25, 0.5 and 1 percent), three different lengths of fiber (6, 12 and 18 mm) and four normal or confining pressures (50, 100, 200 and 400 kPa) have been employed. The test results show that fiber inclusion has a significant effect on the behavior of sand. In both direct shear and triaxial tests, the addition of fibers improved shear strength parameters (C, '), increased peak shear strength and axial strain at failure, and also limited the amount of post-peak reduction in shear resistance. The comparison of the test results revealed that due to better fiber orientation toward the direction of principal tensile strain in triaxial test as compared to direct shear tests, the fiber efficiency and its effect on soil behavior is much more significant in triaxial specimens.

Hydromechanical behaviour of expansive soils with different suctions and suction histories

2016 ◽  
Vol 53 (1) ◽  
pp. 1-13 ◽  
Author(s):  
Junran Zhang ◽  
De’an Sun ◽  
Annan Zhou ◽  
Tong Jiang
Keyword(s):  
Expansive Soils ◽  
Volumetric Strain ◽  
Expansive Soil ◽  
Experimental Results ◽  
Triaxial Tests ◽  
Test Results ◽  
Soil Water Retention ◽  
Suction Control ◽  
Vapor Equilibrium ◽  
High Suction

This paper presents a number of experimental results of suction-controlled triaxial tests on a compacted weakly expansive soil with different suctions and suction histories. In terms of suction control methods, the high suction level (from 3.29 to 38 MPa) was realized by the vapor equilibrium technique and the low suction level (from 0 to 800 kPa) was controlled by the axis translation technique. Results of the triaxial tests indicate that the specimen with higher suction shows higher strength and lower contractive and higher dilative volumetric strains, and the average skeleton stress ratio (q/p′) at failure decreases with increasing suction in the high suction range (3.29∼38 MPa). Given that suction during shearing is constant (e.g., 200 kPa), the specimen dried to a higher suction and the history shows higher strength and lower contractive volumetric strain. Experimental results also show that high pre-applied suction (i.e., the maximum suction in the history) can lead to peak strength, post-peak softening, and shear dilation. Three different methods (pressure plate, filter paper, and vapor equilibrium) were employed to study the soil-water retention behaviour of the unsaturated expansive soil. Test results indicate that by combining these three different methods, it is possible to determine the SWCC in the entire suction range (0∼367 MPa). Test results of the expansive soil also show that the void ratio keeps decreasing with increasing suction in the entire suction range.

scholarly journals Measuring unsaturated soil deformations during triaxial testing using a photogrammetry-based method

2016 ◽  
Vol 53 (3) ◽  
pp. 472-489 ◽  
Author(s):  
Lin Li ◽  
Xiong Zhang ◽  
Gang Chen ◽  
Robert Lytton
Keyword(s):  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Axial Strain ◽  
Volumetric Strain ◽  
3D Models ◽  
Triaxial Tests ◽  
Triaxial Testing ◽  
Distribution Analysis ◽  
Soil Deformation ◽  
Full Field

When characterizing an unsaturated soil using the triaxial test apparatus, it is required to measure the soil deformation during loading. Recently, a photogrammetry-based method has been developed for total and localized volume change measurements on unsaturated soils during triaxial testing. In this study, more in-depth discussions on the photogrammetry-based method are addressed, such as system setup, the measurement procedure, accuracy self-check, data post-processing, and differences from conventional image-based methods. Also, an application of the photogrammetry-based method on unsaturated soil deformation measurements is presented through a series of undrained triaxial tests with different loading paths. After testing, three-dimensional (3D) models of the tested soils at different loading steps were constructed based on the 3D coordinates of measurement targets on the soil surface. Clear barreling processes for soils during deviatoric loading were observed through the constructed 3D models at different axial strain levels. Soil volume changes and volumetric strain nonuniformities during isotropic and deviatoric loadings were extracted based upon detailed analyses of different soil layers. Through a full-field strain distribution analysis, a shear band evolution process was captured for the soil during deviatoric loading at a low confining stress. The photogrammetry-based method proved to be very powerful for in-depth soil deformation characteristics investigation.

scholarly journals A Strain-Based Percolation Model and Triaxial Tests to Investigate the Evolution of Permeability and Critical Dilatancy Behavior of Coal

Processes ◽  
2018 ◽  
Vol 6 (8) ◽  
pp. 127 ◽  
Author(s):  
Dongjie Xue ◽  
Jie Zhou ◽  
Yintong Liu ◽  
Sishuai Zhang
Keyword(s):  
Axial Strain ◽  
Triaxial Compression ◽  
Sudden Change ◽  
Volumetric Strain ◽  
Confining Pressure ◽  
Percolation Model ◽  
Triaxial Tests ◽  
Transition Behavior ◽  
Orthogonal Experiments ◽  
Stress Dependent

Modeling the coupled evolution of strain and CH4 seepage under conventional triaxial compression is the key to understanding enhanced permeability in coal. An abrupt transition of gas-stress coupled behavior at the dilatancy boundary is studied by the strain-based percolation model. Based on orthogonal experiments of triaxial stress with CH4 seepage, a complete stress-strain relationship and the corresponding evolution of volumetric strain and permeability are obtained. At the dilatant boundary of volumetric strain, modeling of stress-dependent permeability is ineffective when considering the effective deviatoric stress influenced by confining pressure and pore pressure. The computed tomography (CT) analysis shows that coal can be a continuous medium of pore-based structure before the dilatant boundary, but a discontinuous medium of fracture-based structure. The multiscale pore structure geometry dominates the mechanical behavior transition and the sudden change in CH4 seepage. By the volume-covering method proposed, the linear relationship between the fractal dimension and porosity indicates that the multiscale network can be a fractal percolation structure. A percolation model of connectivity by the axial strain-permeability relationship is proposed to explain the transition behavior of volumetric strain and CH4 seepage. The volumetric strain on permeability is illustrated by axial strain controlling the trend of transition behavior and radical strain controlling the shift of behavior. A good correlation between the theoretical and experimental results shows that the strain-based percolation model is effective in describing the transition behavior of CH4 seepage in coal.

scholarly journals An evolutionary modelling approach to predicting stress-strain behaviour of saturated granular soils

2018 ◽  
Vol 35 (8) ◽  
pp. 2931-2952 ◽  
Author(s):  
Alireza Ahangar Asr ◽  
Asaad Faramarzi ◽  
Akbar A. Javadi
Keyword(s):  
Axial Strain ◽  
Volumetric Strain ◽  
Triaxial Tests ◽  
Granular Soils ◽  
Unified Framework ◽  
Stress Strain ◽  
Content Type ◽  
Deviator Stress ◽  
Strain Behaviour ◽  
Model Predictions

PurposeThis paper aims to develop a unified framework for modelling triaxial deviator stress – axial strain and volumetric strain – axial strain behaviour of granular soils with the ability to predict the entire stress paths, incrementally, point by point, in deviator stress versus axial strain and volumetric strain versus axial strain spaces using an evolutionary-based technique based on a comprehensive set of data directly measured from triaxial tests without pre-processing. In total, 177 triaxial test results acquired from literature were used to develop and validate the models. Models aimed to not only be capable of capturing and generalising the complicated behaviour of soils but also explicitly remain consistent with expert knowledge available for such behaviour.Design/methodology/approachEvolutionary polynomial regression (EPR) was used to develop models to predict stress – axial strain and volumetric strain – axial strain behaviour of granular soils. EPR integrates numerical and symbolic regression to perform EPR. The strategy uses polynomial structures to take advantage of favourable mathematical properties. EPR is a two-stage technique for constructing symbolic models. It initially implements evolutionary search for exponents of polynomial expressions using a genetic algorithm (GA) engine to find the best form of function structure; second, it performs a least squares regression to find adjustable parameters, for each combination of inputs (terms in the polynomial structure).FindingsEPR-based models were capable of generalising the training to predict the behaviour of granular soils under conditions that have not been previously seen by EPR in the training stage. It was shown that the proposed EPR models outperformed ANN and provided closer predictions to the experimental data cases. The entire stress paths for the shearing behaviour of granular soils using developed model predictions were created with very good accuracy despite error accumulation. Parametric study results revealed the consistency of developed model predictions, considering roles of various contributing parameters, with physical and engineering understandings of the shearing behaviour of granular soils.Originality/valueIn this paper, an evolutionary-based data-mining method was implemented to develop a novel unified framework to model the complicated stress-strain behaviour of saturated granular soils. The proposed methodology overcomes the drawbacks of artificial neural network-based models with black box nature by developing accurate, explicit, structured and user-friendly polynomial models and enabling the expert user to obtain a clear understanding of the system.

scholarly journals Fatigue and damage properties of frozen silty sand samples subjected to cyclic triaxial loading

2016 ◽  
Vol 53 (12) ◽  
pp. 1939-1951 ◽  
Author(s):  
Enlong Liu ◽  
Yuanming Lai ◽  
Mengke Liao ◽  
Xingyan Liu ◽  
Feng Hou
Keyword(s):  
Stress Ratio ◽  
Axial Strain ◽  
Volumetric Strain ◽  
Silty Sand ◽  
Triaxial Tests ◽  
Axial Stiffness ◽  
Cyclic Triaxial ◽  
Cycle Number ◽  
Number Of Cycles ◽  
Strain Method

Cyclic triaxial tests were conducted to explore the influences of dynamic axial loading on the dynamic features and fatigue of frozen silty sand, using an MTS-810 apparatus from Material Testing Systems (MTS). The temperature was −15 °C, and the cyclic axial loads with different amplitudes at 1.0 Hz were applied under confining pressures of 0.6, 1.4, and 6.0 MPa. The cyclic triaxial test results demonstrate that the residual axial strain of the frozen silty sand samples increases gradually during the initial cycles and then increases with increasing number of cycles at a constant speed until failure. The residual volumetric strain contracts during the initial loading cycles and then dilates until failure. Both the residual strain method and the residual volumetric strain method proposed here can be used to describe the degradation process in frozen silty sand samples subjected to cyclic loading. The dynamic axial stiffness of a frozen sample decreases rapidly in the initial cycles and then approaches a stable value with increasing cycle number. The initial damage increases when the stress ratio increases; the larger the stress ratio, the smaller the number of cycles at failure.

scholarly journals Empirical Method for Evaluating Resilient Modulus of Saturated Silty Clay under Cyclic Loading

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Zhen Zhang ◽  
Yong Chen ◽  
Guanbao Ye ◽  
Peilin Xiang ◽  
Yan Xiao ◽  
...  
Keyword(s):  
Cyclic Loading ◽  
Stress Ratio ◽  
Resilient Modulus ◽  
Dynamic Properties ◽  
Damping Ratio ◽  
Empirical Method ◽  
Traffic Load ◽  
Triaxial Tests ◽  
Silty Clay ◽  
Test Results

Resilient modulus of soil is crucial for the design of a structure on a foundation subjected to a cyclic loading (e.g., traffic load or machine vibration load). This paper conducted a series of dynamic triaxial tests of saturated silty clay, considering the influence of the factors of cyclic stress ratio (CSR), static deviatoric stress ratio (SDR), and overconsolidation ratio (OCR) on the resilient modulus and dynamic damping ratio of the soil. A cyclic loading with a form of half sine wave was used to model the traffic loading. The results showed that the soil was prone to failure under a higher SDR, even though the applied CSR was less than the critical CSR. The saturated silty clay performed a strain softening behavior and its dynamic properties deteriorated significantly when higher CSR and SDR and lower OCR were involved. Based on the test results, an empirical method with a form of exponential function was proposed to evaluate the resilient modulus of the soil, considering the combined effects of CSR and SDR and OCR. The proposed method was verified through a comparison with the test results in this study and from literatures, and some recommendations for its application were offered.

scholarly journals Numerical Modelling of Displacement Pile Resistance in Sand Ground. Part 1: Soil Physical Model, Calibration of Model Parameters

2021 ◽  
Vol 16 (1) ◽  
pp. 77-90
Author(s):  
Vaidas Martinkus ◽  
Arnoldas Norkus ◽  
Džigita Nagrockienė
Keyword(s):  
Numerical Modelling ◽  
Physical Model ◽  
Residual Effects ◽  
Model Parameters ◽  
Test Results ◽  
Ground Resistance ◽  
Pile Installation ◽  
Sand Deposit ◽  
Ground Stress ◽  
Pile Resistance

Accuracy of numerical modelling of ground resistance of the displacement pile highly depends on proper evaluation of its states: prior loading and its changes during the loading. Evaluation of initial ground stage, its subsequent changes caused by pile installation and, finally, evolution of the loaded pile resistance are the modelling stages that require validation with specialized test results performed under controlled laboratory conditions. Selection of the proper physical soil model and its parameters should be also done in accordance with the relevant soil tests results. The first paper briefly introduces testing results of a displacement pile prototype. Tests were conducted in the created sand deposit in the laboratory pit. Determining pile resistance and ground stress-strain distribution in the vicinity of the pile allows selecting the physical model for the soil. Numerical calibration of the parameters for the physical model of the selected soil was performed. The second, following paper will introduce analyses of pile resistance. It involves creation of a discrete model and its parameters, numerical modelling of pile resistance against vertical load. The pile ground resistance modelling applying the physical model of the selected soil includes the following stages: evaluation at rest stage and assessment of residual effects of installation and displacement pile loading resistance. Numerical analyses results were validated with displacement pile prototype testing results.

Hydromechanical behaviour of overconsolidated unsaturated soil in undrained conditions

2019 ◽  
Vol 56 (11) ◽  
pp. 1609-1621 ◽  
Author(s):  
Shengshen Wu ◽  
Annan Zhou ◽  
Jie Li ◽  
Jayantha Kodikara ◽  
Wen-Chieh Cheng
Keyword(s):  
Effective Stress ◽  
Unsaturated Soils ◽  
Axial Strain ◽  
Triaxial Compression ◽  
Volumetric Strain ◽  
Degree Of Saturation ◽  
Triaxial Tests ◽  
Conventional Triaxial Compression ◽  
Hydromechanical Behaviour ◽  
Undrained Conditions

Hydromechanical behaviour of an unsaturated silt with various suctions and different overconsolidated ratios (OCRs) was investigated through a series of undrained triaxial tests (constant water contents, CW). All the samples were prepared from the slurry state. Different OCRs (= 1, 2, 4, and 8 in net stress) were achieved by unloading the samples to 400, 200, 100, and 50 kPa from an initial confining net pressure of 400 kPa. Then the samples were dried to various suctions (0, 100, 200, 300, and 400 kPa). Unsaturated samples with different OCRs were then sheared at CW conditions following the conventional triaxial compression (CTC) paths. Full hydromechanical responses including the changes in deviator stress, stress ratio, volumetric strain, suction, and degree of saturation with axial strain were monitored and are presented in this paper. Some key findings include (i) the critical state for unsaturated soils with different OCRs can be well defined by Bishop’s effective stress; (ii) the peak strength in Bishop’s effective stress increases with increase of OCR, but decreases with increase of suction in the undrained condition; and (iii) the volume change of unsaturated soils in undrained conditions is related to OCRs and the volume of pore air.

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