Analysis of Nonlinear Stress and Strain in Clay under the Undrained Condition

2011 ◽  
Vol 27 (2) ◽  
pp. 201-213 ◽  
Author(s):  
P.-G. Hsieh ◽  
C.-Y. Ou
Keyword(s):  
Soft Clay ◽  
Stress Path ◽  
Small Strain ◽  
Model Parameters ◽  
Soil Behavior ◽  
Total Stress ◽  
Soil Stiffness ◽  
Nonlinear Stress ◽  
Strength Tests ◽  
Laboratory Stress

ABSTRACTThough the total stress undrained analysis approach in geotechnical engineering is widely utilized by practicing engineers, it has some intrinsic imperfections that cause the obtained parameters to have unavoidable empirical correlations. In this study, an undrained soft clay model is developed, which overcomes the imperfections of the conventional total stress undrained approach. In addition, the high soil stiffness at small strain and the concept of yield surface are employed to realistically simulate actual soil behavior. The model parameters can be obtainable directly from conventional laboratory tests. The model is validated through different laboratory stress path tests and strength tests in this paper.

Mechanical Characteristics of Ningbo Marine Deposit Soft Clay under Different Stress Paths

2011 ◽  
Vol 250-253 ◽  
pp. 2093-2097
Author(s):  
Chen Bin ◽  
Jun Neng Ye ◽  
Gan Bin Liu
Keyword(s):  
Effective Stress ◽  
Mechanical Characteristics ◽  
Axial Strain ◽  
Soft Clay ◽  
Stress Path ◽  
Shear Mode ◽  
Test Results ◽  
Total Stress ◽  
Consolidation Pressure ◽  
Marine Deposit

Based on a series of consolidated-undrained stress path tests, the mechanical characteristics of Ningbo marine deposit soft clay under K0 consolidation condition are systematically studied for different consolidation pressure, i.e.,60, 120 and 200kPa, in the GDS stress path triaxial system. Three kinds of stress path, i.e., DE (increase p), DG(constant p) and DF(reduce p), are carried out, and the characteristics of stress-axial strain relation, stress path and strength under different stress paths are compared. The test results show that the effective stress paths under consolidated-undrained shear are mainly related to initial consolidation, and the controlled shear mode has evident effect on the effective stress paths. In addition, the stress path has a certain influence on both the total stress and the effect stress strength.

Determination, Derivation, Influence and Discussions of Parameters for Deformation Analyses with Duncan-Chang Modified E-B Model

2011 ◽  
Vol 90-93 ◽  
pp. 157-164
Author(s):  
Han Peng Liu ◽  
Dong Yuan Wang ◽  
Zhi Jun Ma
Keyword(s):  
Laboratory Tests ◽  
Small Strain ◽  
Hebei Province ◽  
Experimental Results ◽  
Model Parameters ◽  
Horizontal Deformation ◽  
Strain Behavior ◽  
Nonlinear Stress ◽  
Confining Pressures ◽  
New Apparatus

This paper presents a study on influence of model parameters on deformation analyses with Duncan-Chang Modified Nonlinear Stress-strain (E-B) model for an ore mining tailings located in Chengde, Hebei Province of China. How to determine and derive these parameters from the laboratory experimental results was introduced first. Findings from numerical analyses performed with Midas GTS indicate that model parameters K and n most significantly affect the vertical and horizontal deformation respectively. Based on the analysis, the accuracy and effectiveness of these parameters were discussed further. Principles of the model and the parameter derivations suggest the model and parameters work better for small strain cases, hence model parameters shall be better determined with laboratory tests with low confining pressures or using new apparatus to measure small strain behavior of soil to ensure analysis results reliable.

A New Nonlinear Stress-Strain Model for Soils at Various Strain Levels

2013 ◽  
Vol 631-632 ◽  
pp. 782-788
Author(s):  
Cheng Chen ◽  
Zheng Ming Zhou
Keyword(s):  
Compression Test ◽  
Triaxial Compression ◽  
Small Strain ◽  
Empirical Formulas ◽  
Stress Strain ◽  
Strain Behaviour ◽  
Proposed Model ◽  
Nonlinear Stress ◽  
London Clay ◽  
Strain Model

Soils have nonlinear stiffness and develops irrecoverable strains even at very small strain levels. Accurate modeling of stress-strain behaviour at various strain levels is very important for predicting the deformation of soils. Some existing stress-strain models are reviewed and evaluated firstly. And then a new simple non-linear stress-strain model is proposed. Four undetermined parameters involved in the proposed model can be obtained through maximum Young’s module, deformation module, and limit deviator stress and linearity index of soils that can be measured from experiment directly or calculated by empirical formulas indirectly. The effectiveness of the proposed stress-strain model is examined by predicting stress-strain curves measured in plane-strain compression test on Toyota sand and undrained triaxial compression test on London clay. The fitting results of the proposed model are in good agreement with experimental data, which verify the effectiveness of the model.

Deformability and consolidation characteristics of soft Bangkok clay using screw plate tests

1990 ◽  
Vol 27 (5) ◽  
pp. 531-545 ◽  
Author(s):  
D. T. Bergado ◽  
K. C. Chong ◽  
P. A. M. Daria ◽  
M. C. Alfaro
Keyword(s):  
Graphical Method ◽  
Soft Clay ◽  
Stress Path ◽  
Soil Parameters ◽  
Test Results ◽  
Coefficient Of Consolidation ◽  
Plate Test ◽  
Settlement Time ◽  
Oedometer Tests ◽  
Test Embankment

This study centred on the performance of the screw plate test (SPLT) to determine the deformability and consolidation characteristics of soft Bangkok clay. For comparison, a series of stress-path-controlled triaxial consolidation tests (tri) were carried out on good quality samples of Bangkok clay taken from the same testing sites and imposed with the same loading conditions as the screw plate tests. Undrained and drained moduli and coefficients of consolidation were obtained from the stress-path-controlled triaxial consolidation tests and were compared with the corresponding values of the screw plate test. In addition, the ultimate bearing capacity was derived from the pressure–deformation relationships of the screw plate test results. A graphical method was used to compute the coefficient of consolidation from the screw plate tests and from stress-path-controlled triaxial consolidation test results. The compressibility data were also obtained from conventional oedometer tests (oed). Both cv (SPLT)/cv (tri) and cv (SPLT)/cv(oed) ratios compared favorably with the cv (field)/cv (laboratory) ratio obtained from past investigations. The data from pressure–settlement–time relationships of the screw plate tests were used to successfully predict values that compared favorably with the measured values at each stress level. The pressure–deformation–time relationship from stress-path-controlled triaxial consolidation tests were also evaluated, and they indicated behaviour similar to that of the screw plate test results. Soil parameters obtained from screw plate tests were subsequently used to predict the settlement of two test embankments, giving fairly close agreement with the observed values. Key words: soft clay, settlement, deformation, consolidation, screw plate test, triaxial test, embankment, prediction, stress path.

scholarly journals Fractional Stress Relaxation Model of Rock Freeze-Thaw Damage

2021 ◽  
Vol 2021 ◽  
pp. 1-8
Author(s):  
Q. Liu ◽  
W. Chen ◽  
J. K. Guo ◽  
R. F. Li ◽  
D. Ke ◽  
...  
Keyword(s):  
Stress Relaxation ◽  
Fatigue Loading ◽  
Element Model ◽  
Model Parameters ◽  
Rock Stress ◽  
Relaxation Equation ◽  
Freeze Thaw ◽  
Thaw Cycle ◽  
Nonlinear Stress ◽  
Freeze Thaw Cycle

Freeze-thaw cycle is a type of fatigue loading, and rock stress relaxation under freeze-thaw cycles takes into account the influence of the freeze-thaw cycle damage and deterioration. Rock stress relaxation under freeze-thaw cycles is one of the paramount issues in tunnel and slope stability research. To accurately describe the mechanical behaviour of stress relaxation of rocks under freeze-thaw, the software element is constructed based on the theory of fractional calculus to replace the ideal viscous element in the traditional element model. The freeze-thaw damage degradation of viscosity coefficient is considered. A new three-element model is established to better reflect the nonlinear stress relaxation behavior of rocks under freeze-thaw. The freeze-thaw and stress relaxation of rock are simulated by ABAQUS, the relevant model parameters are determined, and the stress relaxation equation of rock under freeze-thaw cycle is obtained based on numerical simulation results. The research shows that the test results are consistent with the calculated results, indicating that the constitutive equation can better describe the stress relaxation characteristics of rocks under freeze-thaw and provide theoretical basis for surrounding rock support in cold region.

scholarly journals Laboratory Studies of Small Strain Stiffness and Modulus Degradation of Warsaw Mineral Cohesive Soils

Minerals ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 1127
Author(s):  
Emil Soból ◽  
Katarzyna Gabryś ◽  
Karina Zabłocka ◽  
Raimondas Šadzevičius ◽  
Rytis Skominas ◽  
...  
Keyword(s):  
Shear Modulus ◽  
Relative Error ◽  
High Reliability ◽  
Strain Range ◽  
Cohesive Soil ◽  
Small Strain ◽  
Empirical Models ◽  
Soil Behavior ◽  
Fundamental Parameters ◽  
Stiffness Characteristics

The shear modulus and normalized shear modulus degradation curve are the fundamental parameters describing soil behavior. Thus, this article is focused on the stiffness characteristic of 15 different Warsaw cohesive soli represented by the parameters mentioned above. In this research, standard resonant column tests were performed in a wide shear strain range, from a small one, where soil behaves like an elastic medium, to a medium one, where soil has an unrecoverable deformation. Collected data allows the authors to create empirical models describing stiffness characteristics with high reliability. The maximum shear modulus calculated by the proposed equation for Warsaw cohesive soil had a relative error of about 6.8%. The formula for normalized shear modulus estimated G/GMAX with 2.2% relative error. Combined empirical models for GMAX, and G/GMAX allow the evaluation of Warsaw cohesive soil’s shear modulus value in a wide shear deformation range, with a very low value of the relative error of 6.7%.

Measurement and Calibration of the Parameters of Hypoplasticity Model for an Iraqi Soil

2020 ◽  
Vol 857 ◽  
pp. 243-252
Author(s):  
Aysar Hassan Subair ◽  
Ala Nasir Aljorany
Keyword(s):  
Constitutive Model ◽  
Void Ratio ◽  
Initial Stresses ◽  
Model Parameters ◽  
State Variables ◽  
Soil Behavior ◽  
Dense Sand ◽  
Hypoplastic Model ◽  
Material Parameters ◽  
Wide Range

There are many constitutive models that have been used to model the mechanical behavior of soils. Some of these models are either unable to represent important features such as the strain softening of dense sand or required many parameters that can be hard to obtain by standard laboratory tests. Because of that, a more reliable constitutive model, which is capable to capture the main features of the soil behavior with easily obtained parameters, is required. The Hypoplasticity model is considered as a promising constitutive model in this respect. It is considered as a particular class of rate non-linear constitutive model at which the stress increment is expressed in a tensorial equation as a function of strain increment, actual stress, and void ratio. The hypoplastic model required only eight material parameters (critical friction angle critical, maximum and minimum void ratio respectively), granular stiffness hs and the model constants n, α, β). The appealing feature of the hypoplastic model is that the material parameters are separated from the state variables (void ratio and the initial stresses). This feature enables the model to simulate the soil behavior under a wide range of stresses and densities with the same set of material parameters. In this research, a brief description of the Hypoplasticity model is presented. Detailed discussions regarding the measurement and calibration of the model parameters of an Iraqi soil are then exposed. It is concluded that only Consolidated Drained (CD) triaxial test, oedometer test, and the well-known limit density tests are needed to get all the parameters of the hypoplasticity model.

scholarly journals Scour Effects on the Lateral Behavior of a Large-Diameter Monopile in Soft Clay: Role of Stress History

2019 ◽  
Vol 7 (6) ◽  
pp. 170 ◽  
Author(s):  
Ben He ◽  
Yongqing Lai ◽  
Lizhong Wang ◽  
Yi Hong ◽  
Ronghua Zhu
Keyword(s):  
Large Diameter ◽  
Soft Clay ◽  
Small Diameter ◽  
Initial Stiffness ◽  
Stress History ◽  
Soil Stiffness ◽  
Hypoplastic Model ◽  
History Effects ◽  
Conservative Estimation ◽  
Lateral Behavior

Scouring of soil around large-diameter monopile will alter the stress history, and therefore the stiffness and strength of the soil at shallow depth, with important consequence to the lateral behavior of piles. The existing study is mainly focused on small-diameter piles under scouring, where the soil around a pile is analyzed with two simplified approaches: (I) simply removing the scour layers without changing the strength and stiffness of the remaining soils, or (II) solely considering the effects of stress history on the soil strength. This study aims to investigate and quantify the scour effect on the lateral behavior of monopile, based on an advanced hypoplastic model considering the influence of stress history on both soil stiffness and strength. It is revealed that ignorance about the stress history effect (due to scouring) underestimates the extent of the soil failure wedge around the monopile, while overestimates soil stiffness and strength. As a result, a large-diameter pile (diameter D = 5 m) in soft clay subjected to a souring depth of 0.5 D has experienced reductions in ultimate soil resistance and initial stiffness of the p-y curves by 40% and 26%, and thus an increase of pile head deflection by 49%. Due to the inadequacy to consider the stress history effects revealed above, the existing approach (I) has led to non-conservative estimation, while the approach (II) has resulted in an over-conservative prediction.

Initiation and failure mechanism of base instability of excavations in clay triggered by hydraulic uplift

2015 ◽  
Vol 52 (5) ◽  
pp. 599-608 ◽  
Author(s):  
Y. Hong ◽  
C.W.W. Ng ◽  
L.Z. Wang
Keyword(s):  
Failure Mechanism ◽  
Simple Shear ◽  
Triaxial Compression ◽  
Soft Clay ◽  
Constitutive Models ◽  
Model Parameters ◽  
Hydraulic Pressure ◽  
Percentage Increase ◽  
Basal Resistance ◽  
Dimensionless Groups

Excavations in clay overlying an aquifer may cause catastrophic basal failure due to hydraulic uplift. Although case histories with hydraulic uplift failures are reported worldwide from time to time, the initiation and failure mechanism of the base instability are not well studied and understood. To address these two issues, dimensional analysis is firstly conducted to propose dimensionless groups (DGs) possibly relevant to this subject. Effects of these DGs on the initiation and failure mechanism of base instability are then investigated, by carrying out a series of finite element analyses, in which constitutive models and model parameters have been previously validated against centrifuge test results. It is revealed that the initiation and failure mechanism of base instability due to hydraulic uplift is mainly governed by a ratio of excavation width over the thickness of soft clay inside excavation (B/D). As excavation becomes narrower (i.e., B/D decreases), the hydraulic pressure (Pi) required to initiate uplift movement of clay inside excavation increases significantly (maximum percentage increase = 50%), due to increased effect of downward shear stress acting along soil–wall interface on basal resistance. Based on the parametric study, a calculation chart is developed for estimating Pi of excavations with varied B/D and undrained shear strength of clay. At basal failure caused by hydraulic uplift, the dominant failure mode changes from simple shear in relatively narrow excavations (i.e., B/D < 4) to combined modes of triaxial compression, triaxial extension, and simple shear in relatively wide excavations (i.e., B/D > 4).

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