scholarly journals Creep Properties of Expansive Soils under Triaxial Drained Conditions and its Nonlinear Constitutive Model

2021 ◽  
Author(s):  
Jingjing Li ◽  
Lingwei Kong
Keyword(s):  
Expansive Soils ◽  
Creep Property ◽  
Volumetric Strain ◽  
Failure Stress ◽  
Creep Model ◽  
Creep Process ◽  
Triaxial Tests ◽  
Nonlinear Creep ◽  
Deviator Stress ◽  
Accelerated Creep

The creep behaviors of expansive soils play an important role in landslide prediction and long-term stability analysis. In this paper, triaxial drained compression creep tests of expansive soils were conducted on the improved stress-controlled triaxial apparatus. The test results show that only transient deformation and attenuation creep occur with low deviator stress, and the increment of axial strain increases exponentially with deviator stress increasing; while deviator stress reaches a certain value, attenuation creep, steady creep and accelerated creep all occur in a creep curve. Meanwhile, the volumetric strain presents the shear shrinkage characteristic at the initial stage of loading, and the shear shrinkage is small. With the extension of loading time, the volumetric strain gradually varies from shear contraction to dilatancy. When entering the accelerated creep stage, the development rate of volumetric strain increases sharply. Besides, isochronous stress-strain curves of expansive soils indicate that their creep process possesses nonlinear characteristics, and the nonlinear degree is related to creep time and stress level. Imitating the empirical formula of cyclic cumulative deformation of clay, a new nonlinear creep model is presented, which may well describe the creep property of expansive soils. Furthermore, critical failure stress could be obtained based on the proposed creep model. The ratio of the critical failure stress to conventional shear failure stress ranges from 70% to 80%, with average of 75.56%, therefore, critical failure stress may be estimated by conventional triaxial tests with the margin of error 5.5% within.

scholarly journals Improved Nonlinear Nishihara Shear Creep Model with Variable Parameters for Rock-Like Materials

2020 ◽  
Vol 2020 ◽  
pp. 1-15 ◽  
Author(s):  
Hang Lin ◽  
Xing Zhang ◽  
Yixian Wang ◽  
Rui Yong ◽  
Xiang Fan ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Shear Strength ◽  
Creep Test ◽  
Creep Property ◽  
Variable Parameter ◽  
Nonlinear Function ◽  
Creep Model ◽  
Creep Process ◽  
Shear Creep

Creep property is an important mechanical property of rocks. Given the complexity of rock masses, mechanical parameters change with time in the creep process. In this work, a nonlinear function for describing the time-dependent change of parameters was introduced and an improved variable-parameter nonlinear Nishihara shear creep model of rocks was established. By creating rock-like materials, the mechanical properties of rocks under the shear creep test condition were studied, and the deformation characteristics and long-term shear strength of rocks during creep were analyzed. The material parameters of the model were identified using the creep test results. Comparison of the model’s calculated values and experimental data indicated that the model can describe the creep characteristics of rocks well, thus proving the correctness and rationality of the improved model. During shear creep, the mechanical properties of rocks have an aging effect and show hardening characteristics under low shear stress. Furthermore, according to the fact that Gk of the nonlinear model can characterize the creep deformation resistance, a method to determine the long-term shear strength is proposed.

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 A novel nonlinear creep model based on damage characteristics of mudstone strength parameters

PLoS ONE ◽  
2021 ◽  
Vol 16 (6) ◽  
pp. e0253711
Author(s):  
Bin Hu ◽  
Aneng Cui ◽  
Kai Cui ◽  
Yang Liu ◽  
Jing Li
Keyword(s):  
Creep Curve ◽  
Damage Evolution ◽  
Combination Method ◽  
Creep Model ◽  
Model Parameters ◽  
Nonlinear Creep ◽  
Strength Parameters ◽  
Nonlinear Characteristics ◽  
Creep Stage ◽  
Accelerated Creep

Mudstone interlayer is a weak layer in rock engineering. When it is subjected to continuous stress higher than its damage threshold, due to the dislocation of particles in mudstone crystals and the expansion of cracks, mudstone strength is gradually damaged and deteriorated and the strain gradually increases, thus accelerating the phenomenon of creep damage. In order to describe the characteristics of the whole process of mudstone aging deformation, based on the damage evolution of strength parameters (cohesion and internal friction coefficient) with stress and time in mudstone creep tests, a novel damage nonlinear viscoelastoplastic body (D-NVPB) is proposed through improving traditional plastic element. D-NVPB describes the nonlinear characteristics of the accelerated creep stage of mudstone. With the element combination method, D-NVPB is connected with the Burgers model in series to form a new nonlinear damage creep model (D-NVEP model). The analysis results of creep characteristics theoretically verified the rationality of the model in describing the instantaneous elasticity, viscoelasticity, and nonlinear viscoplastic characteristics of the complete creep curve of mudstone. With the data obtained in the uniaxial compression creep test of mudstone under the action of a stress level of 14 MPa, based on the Levenberg-Marquardt nonlinear least squares method, the fitting calculation was performed through piecewise fitting and overall fitting. The correlation coefficient was 0.9909, which verified the applicability of the model. The obtained model parameters by the identification were used to predict the mudstone creep curve under the stress levels of 13 MPa and 15 MPa. The good prediction results further verified the feasibility of the model. Compared with the traditional creep model, the D-NVEP model can better describe the nonlinear characteristics of the accelerated creep stage and quantitatively display the strength damage evolution process of rock in the creep failure process.

Study on triaxial creep behavior and the damage constitutive model of red sandstone containing a single ice-filled flaw

2020 ◽  
pp. 105678952096143
Author(s):  
Yao Bai ◽  
Renliang Shan ◽  
Tianyu Han ◽  
Haoyu Dou ◽  
Zhe Liu
Keyword(s):  
Constitutive Model ◽  
Creep Behavior ◽  
Creep Property ◽  
Creep Model ◽  
Creep Process ◽  
Red Sandstone ◽  
Creep Curves ◽  
Triaxial Creep ◽  
Dip Angle ◽  
Frozen Red Sandstone

The freezing method is widely used in the construction of vertical shafts in water-rich strata. The formed frozen rock wall is often involved in the creep process, and in particular, the creep behavior of frozen fissured rock mass poses a great threat to construction safety. To better understand the creep instability law of ice-filled, fractured red sandstone under freezing and triaxial stress conditions, a series of triaxial creep tests on frozen red sandstone specimens containing a single, pre-existing flaw at −10°C and under a confining pressure of 4 MPa were carried out with a self-developed DRTS-500 subzero rock triaxial testing system. The multistage loading creep curves were obtained, and the evolution laws of deformation and damage for the frozen specimens in the primary (instantaneous), secondary (steady-state) and tertiary (accelerating) phases were analyzed. The nonlinear visco-elastoplastic constitutive model of red sandstone with a single ice-filled flaw was established according to the fractional calculus theory and the Kachanov damage theory. The results show that the initial creep property, unstable creep property and creep failure mode of frozen single-flaw red sandstone are significantly affected by the flaw dip angle. The proposed creep damage model can accurately describe the complete creep curves of frozen red sandstone with a single ice-filled flaw, especially in the unstable creep stage. The influences of the stress level and flaw dip angle on the creep parameters were analyzed, and sensitivity analyses of the characteristic creep parameters were carried out to verify the reliability and rationality of our creep model. This research can be applied to the assessment of collapse, cracking and other long-term failures and hence can be used as a theoretical basis of design in the freezing engineering of coal mine shafts.

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 Study on Cyclic Cumulative Deformation Characteristics and the Equivalent Cyclic Creep Model of Soft Clay

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Wenbo Zhu ◽  
Guoliang Dai ◽  
Weiming Gong
Keyword(s):  
Strain Softening ◽  
Soft Clay ◽  
Cyclic Creep ◽  
Creep Model ◽  
Triaxial Tests ◽  
Strain Accumulation ◽  
Test Results ◽  
Deviator Stress ◽  
Cumulative Deformation ◽  
Stress Ratios

Suction caisson foundations can be used to anchor tension leg platforms. The soil at the bottom of the caisson undergoes both unloading and cyclic loading under wind and wave loads. However, the problem of cyclic cumulative deformation of soft clay under unloading has rarely been addressed. So, the strain cumulative deformation and strain softening characteristics of soft clay are studied by cyclic triaxial tests. The test results show that under low static deviator stress ratios and dynamic deviator stress ratios, the soil has a low level of strain accumulation and softening. As the dynamic deviator stress ratios increase, the cumulative cyclic deformation gradually increases, which rapidly develops in the early stage and tends to stabilize in the later stage. Moreover, the softening index gradually increases and is linearly related to the logarithm of the number of cycles. The cyclic cumulative deformation of the soil increases with increases in unloading stress and dynamic deviator stress, showing a creep characteristic of attenuation and then stabilization. Based on the tests, an equivalent cyclic creep model is established to describe the strain accumulation and softening of soil and verified through comparison with the test results. Then, the model is extended to a three-dimension model, and a finite element subroutine is developed for studying the strain cumulative deformation and strain softening characteristics of soft clay.

Study on Viscoelastic Plastic Damage Model for Mica-Quartzose Schist

2013 ◽  
Vol 300-301 ◽  
pp. 1186-1192 ◽  
Author(s):  
Wen Ling Chen ◽  
Fa Suo Zhao
Keyword(s):  
Damage Model ◽  
Creep Damage ◽  
Damage Variable ◽  
Creep Model ◽  
Creep Process ◽  
Plastic Damage ◽  
Accelerated Creep ◽  
Linear Viscoelastic ◽  
Triaxial Creep ◽  
Plastic Creep

A linear viscoelastic plastic creep model of mica-quartzose schist is established by using the method of establishing combined-linear-component model based on triaxial creep test. The micro-structural changes of mica-quartzose schist during triaxial creep process are observed by using the scanning electron microscope test, based on that, the relation of macro-stress and macro-strain with porosity and damage variable are established through statistical damage theory and simplified mechanical model respectively, the creep damage variable is obtained by further derivation on the basis of above study. The creep damage variable is simplified according to the whole creep process curve, substitutes the simplified creep damage to the estabilished linear viscoelastic plastic creep model of mica-quartzose schist, considering the change of modulus and viscosity during creep process, a viscoelastic plastic damage model of mica-quartzose schist is established. The model parameters are got by segment fitting, the good consistency of the test curves and the fitted curves shows the right and reasonable of the creep model, it also shows that the model can well describe the nonlinear accelerated creep stage. Sensitivity analysis shows that parameter m has greater influence on the accelerated creep deformation than parameter a.

scholarly journals Work input analysis for soils with double porosity and application to the hydromechanical modeling of unsaturated expansive clays

2017 ◽  
Vol 54 (2) ◽  
pp. 173-187 ◽  
Author(s):  
Jian Li ◽  
Zhen-Yu Yin ◽  
Yujun Cui ◽  
Pierre-Yves Hicher
Keyword(s):  
Mechanical Behavior ◽  
Expansive Soils ◽  
Volumetric Strain ◽  
Double Porosity ◽  
Strain Increment ◽  
Degree Of Saturation ◽  
Triaxial Tests ◽  
Expansive Clay ◽  
Expansive Clays ◽  
Boom Clay

A mechanical approach for unsaturated expansive soils considering double porosity has been developed based on the porous media theory. In this approach, the adsorbed and the capillary water, as well as the micropores and macropores, are two distinct phases. An interaggregate stress considered as the work-conjugate of the macrostructural strain increment has been defined. Both physicochemical and capillary effects of the pore water have been introduced at the macroscopic level. Other work-conjugate variables relevant for the constitutive modeling of double-porosity unsaturated media have also been identified, consisting of the modified suction as conjugate of the increment of the macrostructural degree of saturation and the microstructural effective stress as conjugate of the microstructural volumetric strain increment. A hydromechanical model for unsaturated expansive clays taking into account the interaction between the micro- and the macrostructures in expansive clays can thus be built. Based on the bounding surface concept, an anisotropic loading – collapse yield surface has been introduced to reproduce the three-dimensional mechanical behavior. To analyze the model capabilities, two series of laboratory tests consisting of multiple wetting and drying cycle tests on Boom clay and triaxial tests on Zaoyang (ZY) expansive clay were simulated. The comparisons between numerical and experimental results show that the model can reproduce with reasonable accuracy the mechanical behavior and the water retention characteristic of unsaturated expansive clays.

scholarly journals A Phenomenological Primary–Secondary–Tertiary Creep Model for Polymer-Bonded Composite Materials

Polymers ◽  
2021 ◽  
Vol 13 (14) ◽  
pp. 2353
Author(s):  
Xiaochang Duan ◽  
Hongwei Yuan ◽  
Wei Tang ◽  
Jingjing He ◽  
Xuefei Guan
Keyword(s):  
Composite Materials ◽  
Creep Behavior ◽  
Reference Model ◽  
Creep Model ◽  
Creep Process ◽  
Validation Dataset ◽  
Testing Conditions ◽  
Proposed Model ◽  
Testing Data ◽  
Bonded Composite

This study develops a unified phenomenological creep model for polymer-bonded composite materials, allowing for predicting the creep behavior in the three creep stages, namely the primary, the secondary, and the tertiary stages under sustained compressive stresses. Creep testing is performed using material specimens under several conditions with a temperature range of 20 °C–50 °C and a compressive stress range of 15 MPa–25 MPa. The testing data reveal that the strain rate–time response exhibits the transient, steady, and unstable stages under each of the testing conditions. A rational function-based creep rate equation is proposed to describe the full creep behavior under each of the testing conditions. By further correlating the resulting model parameters with temperature and stress and developing a Larson–Miller parameter-based rupture time prediction model, a unified phenomenological model is established. An independent validation dataset and third-party testing data are used to verify the effectiveness and accuracy of the proposed model. The performance of the proposed model is compared with that of an existing reference model. The verification and comparison results show that the model can describe all the three stages of the creep process, and the proposed model outperforms the reference model by yielding 28.5% smaller root mean squared errors on average.

Study on the generalized k-Hilfer–Prabhakar fractional viscoelastic–plastic model

2021 ◽  
pp. 108128652110258
Author(s):  
Yi-Ying Feng ◽  
Xiao-Jun Yang ◽  
Jian-Gen Liu ◽  
Zhan-Qing Chen
Keyword(s):  
Constitutive Model ◽  
Three Dimensional ◽  
Sensitivity Analyses ◽  
Creep Process ◽  
Fractional Operator ◽  
Modified Model ◽  
Proposed Model ◽  
Accelerated Creep ◽  
The Laplace Transform ◽  
Classical Models

The general fractional operator shows its great predominance in the construction of constitutive model owing to its agility in choosing the embedded parameters. A generalized fractional viscoelastic–plastic constitutive model with the sense of the k-Hilfer–Prabhakar ( k-H-P) fractional operator, which has the character recovering the known classical models from the proposed model, is established in this article. In order to describe the damage in the creep process, a time-varying elastic element [Formula: see text] is used in the proposed model with better representation of accelerated creep stage. According to the theory of the kinematics of deformation and the Laplace transform, the creep constitutive equation and the strain of the modified model are established and obtained. The validity and rationality of the proposed model are identified by fitting with the experimental data. Finally, the influences of the fractional derivative order [Formula: see text] and parameter k on the creep process are investigated through the sensitivity analyses with two- and three-dimensional plots.

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