Unified hardening (UH) model for overconsolidated unsaturated soils

2014 ◽  
Vol 51 (7) ◽  
pp. 810-821 ◽  
Author(s):  
Y.P. Yao ◽  
L. Niu ◽  
W.J. Cui
Keyword(s):  
Unsaturated Soils ◽  
Path Dependence ◽  
Three Dimensional ◽  
Constitutive Models ◽  
Stress Path ◽  
Triaxial Tests ◽  
Additional Material ◽  
Basic Model ◽  
Proposed Model ◽  
Unsaturated Clays

Naturally deposited clays are often unsaturated and overconsolidated. Within the frameworks of the Barcelona Basic model (BBM) for normally consolidated unsaturated clays and the unified hardening (UH) model for overconsolidated saturated clays, a three-dimensional constitutive model for overconsolidated unsaturated clays is proposed in this paper. This model can be reduced to the original UH model for overconsolidated saturated clays when suction becomes zero and the BBM when the overconsolidated behaviour disappears. Compared with existing constitutive models for unsaturated clays, the influence of a high overconsolidation ratio (OCR) on wetting deformation can be adequately described. Also, many other characteristics of overconsolidated unsaturated clays can be modelled, including strain-hardening, softening, shear dilatancy, and stress path–dependence behaviour. Compared with the BBM, the proposed model requires no additional material parameter. The validity of the UH model for overconsolidated unsaturated clays has been confirmed by data from two groups of wetting tests performed by the authors and previous triaxial tests in the literature.

Modified state-surface approach to the study of unsaturated soil behavior. Part I: Basic concept

2009 ◽  
Vol 46 (5) ◽  
pp. 536-552 ◽  
Author(s):  
Xiong Zhang ◽  
Robert L. Lytton
Keyword(s):  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Stress Path ◽  
Complex Stress ◽  
Soil Behavior ◽  
Elastic Surface ◽  
Surface Approach ◽  
Basic Model ◽  
Plastic Hardening ◽  
Complex Stress Path

The traditional state-surface approach to the study of unsaturated soil behavior is becoming much less popular these days, as it uses unique constitutive surfaces to represent unsaturated soil behavior. This approach is essentially a nonlinear elastic formation and cannot be used to explain complex stress-path dependency for unsaturated soils. In this paper, a modified state-surface approach (MSSA) is proposed to represent unsaturated soil behavior under isotropic stress conditions in which a conventional void-ratio state surface is considered to be made up of an elastic surface and a plastic hardening surface. The plastic hardening surface remains stationary at all times, whereas the elastic surface remains unchanged when the soil experiences elastic deformation and moves downward when there is plastic hardening occurrence. Using the MSSA, the loading–collapse (LC) and the suction increase (SI) yield curves in the Barcelona basic model (BBM) are derived. The prediction of three typical cases of soils under isotropic conditions and experimental results using the proposed approach confirmed its feasibility, simplicity, and potential for the study of unsaturated soil behavior.

Experimental behaviour and modelling of an unsaturated compacted soil

2000 ◽  
Vol 37 (4) ◽  
pp. 748-763 ◽  
Author(s):  
Celestino Rampino ◽  
Claudio Mancuso ◽  
Filippo Vinale
Keyword(s):  
Unsaturated Soils ◽  
Mechanical Response ◽  
Stress Path ◽  
Silty Sand ◽  
Triaxial Tests ◽  
Experimental Program ◽  
State Variables ◽  
Soil Response ◽  
Optimum Water Content ◽  
Triaxial Cell

This paper reports the experimental study and modelling of the mechanical response of a silty sand used in the core of the Metramo dam, Italy. Specimens were prepared by compacting the soil at optimum water content conditions using the modified Proctor technique. Tests were performed under suction-controlled conditions by a stress path triaxial cell and an oedometer. The experimental program consists of 23 tests carried out in the suction range of 0-400 kPa. The findings indicate the strong influence of suction on compressibility, stiffness, and shear strength. The mechanical properties of the soil improve with suction following an exponential law with decreasing gradient. Furthermore, the soil exhibited collapsible behaviour upon wetting even at low stress levels. Interesting results were also achieved in elastoplastic modelling as well. The results led to characterization of soil behaviour with reference to widely accepted modelling criteria for unsaturated soils, providing noteworthy suggestions about their applicability for granular materials with a non-negligible fine component. Finally, some remarks are made for the extension under unsaturated conditions of the "Nor sand" model for saturated granular soils. The proposed approach yields improved predictions of deviator soil response of the tested soil when Cambridge-type frameworks prove invalid.Key words: unsaturated soils, stress state variables, triaxial tests, oedometer tests, constitutive model.

scholarly journals Investigation of Lade-Kim Plastic Potential Applicability under Various Stress Paths for Rockfill Materials

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Liping Chen ◽  
Shihai Bian ◽  
Xiaokai Niu ◽  
Yongbo Zhao
Keyword(s):  
Path Dependence ◽  
Stress Path ◽  
Constant Stress ◽  
Coarse Grained ◽  
Triaxial Tests ◽  
Stress Increment ◽  
Verification Method ◽  
Rockfill Materials ◽  
Plastic Potential ◽  
Increment Ratio

The dilatancy behavior of rockfill materials shows obvious stress path dependence. Lade-Kim plastic potential equation has been proposed for a long time to model the mechanical behavior of sand and concrete materials. However, it lacks the verification of rockfill materials, especially under various stress paths. In this paper, the dilatancy performance of coarse-grained materials under various stress paths is investigated, and then the dilatancy equation description and verification method based on Lade-Kim plastic potential are given. The applicability of Lade-Kim plastic potential for different stress path tests, such as conventional triaxial tests, constant P tests, and constant stress (increment) ratio tests, are verified and evaluated. It is found that Lade-Kim plastic potential is difficult to consider the influence of stress path. Finally, the Lade-Kim plastic potential, together with nonlinear dilatancy equation, is evaluated by changing the dilatancy equation in the framework of generalized plasticity. Lade-Kim plastic potential is suitable for constant stress increment ratio loading experiments and special care should be taken when applied to other stress paths. These works are helpful to understand stress path dependence of dilatancy behavior for rockfill materials and is beneficial for the establishment of stress path constitutive model.

scholarly journals Investigating the Effect of Geocell Changes on Slope Stability in Unsaturated Soil

2020 ◽  
Vol 14 (1) ◽  
pp. 66-75
Author(s):  
Behnam Mehdipour ◽  
Hamid Hashemolhosseini ◽  
Bahram Nadi ◽  
Masoud Mirmohamadsadeghi
Keyword(s):  
Slope Stability ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Bending Strength ◽  
Load Capacity ◽  
Three Dimensional ◽  
Bending Moment ◽  
Soil Conditions ◽  
Vertical Side ◽  
Basic Model

The purpose of this research is to investigate the performance and efficiency of reinforced slope in the stability of geocell layers in unsaturated soil conditions. Slope reinforced with geocell acts like a beam in the soil due to the geocell having a height (three-dimensional). Due to its flexural properties, it has moment of inertia as well as bending strength, which reduces the displacement and increases the safety factor of the slope. Taking into consideration unsaturated conditions of soil contributes a lot to making results close to reality. One of the well-known models among elastoplastic models for modeling unsaturated soils is Barcelona Basic Model, which has been added to the FLAC2D software by codification. Changes in thickness, length and number of geocell layers are remarkably effective on slope stability. The results show that the geocell's reinforcing efficiency depends on the number of layers and depth of its placement. As the depth of the geocell's first layer increases, the lateral and vertical side elevation of the upper part of the slope increases with respect to the elevation. Load capacity increases with increasing geocell length. By increasing the length of the geocell layer, the joint strength, the mobilized tensile strength, and the bending moment are increased. At u/H = 0.2, an increase in the bending momentum of about 20% occurs with increasing geocell thickness. In u/H = 1, the increase in bending momentum is 10.4%. In addition, by increasing the thickness of the geocell, the Value of moment of the inertia increases and, as a result, the amount of geocell reinforcement bending moment increases.

scholarly journals A deformation-dependent soil-water characteristic surface model considering hysteresis

2020 ◽  
Vol 195 ◽  
pp. 02014
Author(s):  
Cai Guoqing ◽  
Wu Tianchi ◽  
Li Hao ◽  
Zhao Chenggang ◽  
Tian Jingjing ◽  
...  
Keyword(s):  
Soil Water ◽  
Unsaturated Soils ◽  
Three Dimensional ◽  
Degree Of Saturation ◽  
Image Point ◽  
Surface Model ◽  
Characteristic Surface ◽  
Hydraulic Behaviour ◽  
Proposed Model ◽  
Validation Tests

The soil-water characteristic surface model plays an essential part in predicting the hydraulic behaviour of unsaturated soils. Based on the theory of plasticity bounding surface, this paper presents a three-dimensional soil-water characteristic surface model considering the effects of deformation and hysteresis. Suction and void ratio are adopted as independent variables, while the degree of saturation is adopted as a dependent variable. A new mapping rule is used where the distance between the current position and its image point can be calculated as a difference in the degree of saturation axis. The model is verified by comparing with drying-wetting tests on bentonite/kaolin mix and pearl clay. The efficiency of the proposed model is proven by validation tests.

Unified Three-Dimensional Revision of Modified Cam Clay Model

2007 ◽  
Vol 340-341 ◽  
pp. 1267-1272
Author(s):  
Hang Zhou Li ◽  
Hong Jian Liao ◽  
Kyoji Sassa ◽  
Gong Hui Wang
Keyword(s):  
Three Dimensional ◽  
Yield Function ◽  
Triaxial Tests ◽  
Strength Theory ◽  
Unified Strength Theory ◽  
True Triaxial ◽  
Proposed Model ◽  
Modified Cam Clay ◽  
Stress States ◽  
Cam Clay

According to unified strength parameters obtained from unified strength theory, the slope of critical state line is modified to reflect critical states of different geomaterials under general stress states. Yield function that can consider the effect of the third deviatoricic invariant is proposed, and an elasto-plastic constitutive model is established by adopting non-associated flow rules; furthermore, methods of overcoming singular points on the yield surface are discussed. The proposed model is verified by true triaxial tests of clay, and results show that the model can well predict stress-strain relationships.

Simplified analyses of stress induced anisotropy in remolded soft clay under undrained conditions

2020 ◽  
Vol 2 (105) ◽  
pp. 56-64
Author(s):  
P. Lin ◽  
Z.-x. Li ◽  
A. Garg ◽  
J.S. Yadav
Keyword(s):  
Soft Clay ◽  
Constitutive Models ◽  
Stress Path ◽  
Complex Stress ◽  
Triaxial Tests ◽  
Induced Anisotropy ◽  
Stress Induced Anisotropy ◽  
Undrained Conditions ◽  
Plain Strain ◽  
Properties Of Soil

Purpose: The soil’s anisotropy induced by stress (i.e. stress induced anisotropy) has an important effect on the behavior of soil. This paper focuses on analyzing the anisotropy of remolded Shantou soft clay under compression stress path. Design/methodology/approach: Experiments were executed by using three axle experimental instruments. The data obtained from the plain strain tests were analyzed and the relationship between stress and strain was calculated by using the modified Duncan- Chang and Lade-Duncan models. The models were modified under the condition of plain strain and cohesion. Findings: It was concluded that in complex stress path conditions, the conventional triaxial tests may not fully reflect the actual stress of soil and its response in the Duncan-Chang and Lade-Duncan models. Research limitations/implications: The formulation of Mohr-Coulomb failure criterion in the plasticity framework is quite diffcult. As a result, dilatancy cannot be described. The properties of soil in unload or drained conditions remain to be part of further investigated. Practical implications: Based upon the two stiffness parameters, the modified Duncan- Chang model has captured the soil behaviour in a very conformable way and is recommened for practical modeling. These constitutive models of soil are widely used in the numerical analyses of soil structure such as embankments. Originality/value: Duncan-Chang and Lade-Duncan models widely used in engineering practices are modes based on conventional triaxial cases. Both models have have some inherent limitations to represent the stress-strain characteristics of soils, such as shear-induced dilatancy and stress path dependency and required corrections. In this investigation, the tests are carried out in undrained conditions. It is related to the properties of soil in load conditions.

scholarly journals A constitutive model for hydromechanically coupled behavior of unsaturated soils with hydraulic hysteresis

2021 ◽  
Vol 337 ◽  
pp. 02009
Author(s):  
Mustafa Mert Eyüpgiller ◽  
Melih Birhan Kenanoğlu ◽  
Mehmet Barış Can Ülker ◽  
Nabi Kartal Toker
Keyword(s):  
Unsaturated Soils ◽  
Constitutive Models ◽  
Coupled Model ◽  
Triaxial Tests ◽  
Elastoplastic Behavior ◽  
Hydraulic Hysteresis ◽  
Constant Suction ◽  
Phase Medium ◽  
Classical Plasticity ◽  
Hydromechanical Behavior

There are several constitutive models developed for understanding coupled hydromechanical behavior of three phase medium of unsaturated soils as well as models for explaining hydraulic hysteresis in water retention. However, very few attempts that merge the two aspects of behavior are available. This study develops a one-way coupled model for understanding the hydromechanical behavior of unsaturated soils. In addition to the hysteresis between main drying and wetting retention curves, the model considers non-uniqueness of retention behavior resulting from void ratio changes due to compression under the stress application. As for the elastoplastic stress strain relationship of soil skeleton, the model is based on the formulation of classical plasticity relying on the critical state concept. Consequently, volumetric deformation due to wetting-drying cycles and its effect on elastoplastic behavior through simultaneously changing matric suction is modeled. Model results are calibrated with the results of isotropic compression stages of triaxial tests at both constant suction and constant water content conditions.

Study on Strength of Shanghai Marine Clay by True Triaxial Test

2012 ◽  
Author(s):  
Jia-ren Sheng ◽  
Chao-jun Wu ◽  
Guan-lin Ye ◽  
Jian-hua Wang
Keyword(s):  
Soft Soil ◽  
Three Dimensional ◽  
Stress Path ◽  
Failure Criteria ◽  
Yangtze River Delta ◽  
Triaxial Tests ◽  
True Triaxial Test ◽  
Marine Clay ◽  
Undisturbed Soil ◽  
True Triaxial

Shanghai locates on the east tip of Yangtze River Delta facing the East China Sea. Shanghai marine clay owns some particular properties. However, the report on the mechanical properties of Shanghai marine clay is rather rare. The three-dimensional strength and deformation characteristics of soft soil are dependent on the stress conditions. In this study, a series of isotropic consolidated drained true triaxial tests are carried out with an automatically controlled mixed rigid-flexible boundary true triaxial apparatus. Undisturbed soil sample is prepared by the block sampling method. 5 drained tests with stress path in the same π plane along different Lode angles are performed. Tests results show that the intermediate stress has large influence on the yielding and failure of Shanghai marine clay. Three dimensional strength of Shanghai marine clay generally obeys the SMP failure criteria.

scholarly journals A new modelling approach for unsaturated soils using independent stress variables

2008 ◽  
Vol 45 (4) ◽  
pp. 511-534 ◽  
Author(s):  
Daichao Sheng ◽  
Delwyn G. Fredlund ◽  
Antonio Gens
Keyword(s):  
Unsaturated Soils ◽  
Constitutive Models ◽  
Smooth Transition ◽  
Compacted Soils ◽  
Hardening Law ◽  
Volume Collapse ◽  
Proposed Model ◽  
Volumetric Model ◽  
Direct Results ◽  
Modelling Approach

Although a number of constitutive models for unsaturated soils exist in the literature, some fundamental questions have not been fully answered. There are questions related to (i) the change of the yield stress with soil suction, (ii) modelling slurry soils, and (iii) the smooth transition between saturated and unsaturated soil states. This paper addresses these questions by proposing an alternative modelling approach. The paper first presents a volumetric model for unsaturated soils. This volumetric model is then used to derive the yield surface in the suction – mean stress space. Hysteresis associated with soil-water characteristic curves is then formulated in the same framework of elastoplasticity. It is shown that volume collapse during wetting and plastic shrinkage during initial drying are both direct results of a suction-dependent hardening law. The proposed model seems to be more flexible in modelling different types of unsaturated soils than most models in the literature. The model can be applied to soils that are dried or loaded from initially slurry conditions, for soils that have low to high air-entry values, and for compacted soils as well.

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