scholarly journals A sphere packing model for shear bands in dense soils

2021 ◽  
Vol 249 ◽  
pp. 11003
Author(s):  
Calixtro Yanqui
Keyword(s):  
Shear Bands ◽  
Sphere Packing ◽  
Friction Angle ◽  
Plastic State ◽  
Granular Soils ◽  
Biaxial Test ◽  
Strain Behaviour ◽  
Coefficient Of Lateral Pressure ◽  
Soil Stress ◽  
Line Of Discontinuity

The rhombic sphere packing can be used to model the biaxial test on granular soils in a very simple way. According to the angle of assemblage, the packing is dilatant or contractive. Correspondingly, overall stresses are transmitted as chains of forces or oblique forces of contact. The connection of the soil stress-strain behaviour and the packing void ratio is achieved by mapping both of the plots. The mapping shows that dense soils are dilatant and loose soils are contractive, separated by the critical state. It also shows that the bifurcation point and the peak strength are features only of dense soils. The band of strain localization is analysed in the elastic regime, and its inclination is found maximizing the intensity of the mobilized stress ratio. The stresses within the shear band are obtained by assuming a partially coaxial packing rotated to reach the full plastic state. The equilibrium of the overall stress at the line of discontinuity reveals a relationship between the peak friction angle and the coefficient of lateral pressure at rest. As long as these parameters are obtained independently of each other, they allow the validation of the theory.

An experimental examination of the critical state and other similar concepts for granular soils

1995 ◽  
Vol 32 (6) ◽  
pp. 1065-1075 ◽  
Author(s):  
J. Chu
Keyword(s):  
Critical State ◽  
Friction Angle ◽  
Stress Path ◽  
Dense Medium ◽  
Triaxial Tests ◽  
Granular Soils ◽  
Test Results ◽  
Dense Sand ◽  
Strain Behaviour ◽  
Series Of Experiments

Measuring the critical state parameters of dense granular soil by drained triaxial tests is problematic, as significant nonhomogeneous deformations can develop prior to approaching a critical state. This leads to further questions on the verification of the critical state concept for granular soils. In this study a new testing method, which enables the critical state of dense sand to be measured in the homogeneous deformation region, was adopted to measure the critical state of dense sand and to examine the critical state concept. A series of experiments was carried out to measure the critical state for dense, medium dense, and loose sand. The test results show that although a unique critical state curve may exist, the critical state friction angle is not constant but stress level dependent. The other similar concepts, namely, the phase transformation state, the characteristic state, and the steady state, were also examined, and the relationships among these states were established. Key words : critical state, granular soils, stress path, stress–strain behaviour, triaxial test.

Strain localization due to structural softening during pressure sensitive rate independent yielding

2013 ◽  
Vol 184 (4-5) ◽  
pp. 357-371 ◽  
Author(s):  
Laetitia Le Pourhiet
Keyword(s):  
Shear Band ◽  
Strain Softening ◽  
Shear Bands ◽  
Limit Load ◽  
Friction Angle ◽  
Stress Axis ◽  
Flow Rule ◽  
Finite Limit ◽  
Confining Stress ◽  
Pressure Sensitive

Abstract After giving a complete analytical solution for the strain softening model associated to Mohr-Coulomb non associated elasto-plastic flow rule (MC-model), the paper demonstrates that this rheology possesses a finite limit load which allows solving for strength drop as a boundary value problem. The MC-model produces a non-dimensional strength drop, which depends on three parameters: the orientation of the shear band versus the least principal stress axis outside the band α0, the peak friction angle φ and the dilatation angle Ψ. The maximum reduction of strength obtained with that strain-softening model is on the order of the confining stress p0. For this weakest regime, the effective friction of the shear band drops from μini = 0.85 at peak to μss = 0.64 at the end of the softening phase. In this model, which considers thick shear bands, the weakest regime is not obtained for an orientation corresponding to the exact Coulomb orientation. Instead, the orientation of the weakest shear zone systematically deviates from the coulomb orientation by an angle, which rises with its internal friction angle. The characteristic shear strain needed to achieve steady state is quantified semi analytically and in the range of parameters valid for Earth, this strain is found to be of the order of 7–8%. These numbers are typical of what is observed in the laboratory, which give us confidence on that MC-model is a good and probably the simplest model to localize strain in numerical codes aimed at modeling the brittle part of the Earth.

scholarly journals A New Unified Solution for Circular Tunnels Based on Generalized SMP Criterion considering the Strain Softening and Dilatancy

2019 ◽  
Vol 2019 ◽  
pp. 1-10
Author(s):  
Qifeng Guo ◽  
Jiliang Pan ◽  
Xinghui Wu ◽  
Xun Xi ◽  
Meifeng Cai
Keyword(s):  
Internal Friction ◽  
Plastic Zone ◽  
Strain Softening ◽  
Friction Angle ◽  
Surrounding Rock ◽  
Internal Friction Angle ◽  
Plastic State ◽  
Circular Tunnel ◽  
Dilatancy Angle ◽  
Elastic Plastic

According to the strain-softening characteristics of rock mass, an ideal elastic strain-softening model is developed, and the surrounding rock of tunnels is subdivided into the plastic broken zone, plastic strain-softening zone, and elastic zone. Based on the generalized spatially mobilized plane criterion, an elastic-plastic analytical solution of a circular tunnel is derived. The effects of intermediate principal stress, strain softening, and dilatancy are considered in the unified solution. The stress, displacement, and plastic zone radius of surrounding rock based on the SMP criterion are compared with those based on the Mohr–Coulomb criterion. Furthermore, the effects of parameters such as the softening modulus, dilatancy angle, and internal friction angle on the deformation and stress of tunnels are discussed. It has been found that the larger the dilatancy angle is, the larger the plastic zone displacement and the radius of the broken zone are. The larger the internal friction angle, the smaller the sizes of the plastic zone, the strain-softening zone, and the broken zone are. The deformation of surrounding rock in the broken zone is more sensitive to the internal friction angle than that in the strain-softening zone. The unified solution based on the SMP criterion provides a well understanding for the elastic-plastic state of tunnels, which can be the guidance for tunnel excavations and support designs.

scholarly journals Experimental Study of the Composition and Structure of Granular Media in the Shear Bands Based on the HHC-Granular Model

2014 ◽  
Vol 2014 ◽  
pp. 1-7
Author(s):  
Guang-jin Wang ◽  
Xiang-yun Kong ◽  
Chun-he Yang
Keyword(s):  
Shear Strength ◽  
Internal Friction ◽  
Granular Media ◽  
Random Distribution ◽  
Shear Bands ◽  
Friction Angle ◽  
Internal Friction Angle ◽  
Coarse Grained ◽  
Composition And Structure ◽  
Coarse Grained Soil

The researchers cannot control the composition and structure of coarse grained soil in the indoor experiment because the granular particles of different size have the characteristics of random distribution and no sorting. Therefore, on the basis of the laboratory tests with the coarse grained soil, the HHC-Granular model, which could simulate the no sorting and random distribution of different size particles in the coarse-grained soil, was developed by use of cellular automata method. Meanwhile, the triaxial numerical simulation experiments of coarse grained soil were finished with the different composition and structure soil, and the variation of shear strength was discussed. The results showed that the internal friction angle was likely to reduce with the increasing of gravel contents in the coarse-grained soil, but the mean internal friction angle significantly increased with the increment of gravel contents. It indicated that the gravel contents of shear bands were the major factor affecting the shear strength.

A Comparative Study Between Lateral and Upward Anchor-Soil and Pipe-Soil Interaction in Dense Sand

2016 ◽  
Author(s):  
Kshama Roy ◽  
Bipul Hawlader ◽  
Shawn Kenny ◽  
Ian Moore
Keyword(s):  
Shear Bands ◽  
Experimental Studies ◽  
Confining Pressure ◽  
Design Guidelines ◽  
Vertical Strip ◽  
Dense Sand ◽  
Progressive Development ◽  
Lateral Resistance ◽  
Strain Behaviour ◽  
Uplift Forces

Buried pipelines are extensively used in onshore and offshore environments for transportation of hydrocarbons. On the other hand, buried anchors have been used for many years to stabilize various structures. In the development of design guidelines for pipelines, theoretical and experimental studies on buried anchors are sometimes used assuming that pipeline-soil and anchor-soil interaction are similar. In the present study, finite element (FE) modeling is performed to simulate the response of pipeline and anchor buried in dense sand subjected to lateral and uplift forces. The similarities and differences between the responses of these two types of structures are examined to justify the application of anchor theory to pipeline behaviour. The stress-strain behaviour of dense sand is modeled using a Modified Mohr-Coulomb (MMC) model, which considers the pre-peak hardening, post-peak softening, density and confining pressure dependent friction and dilation angles. A considerable difference is found between the lateral resistance of pipeline and vertical strip anchor of similar size. Progressive development of shear bands (shear strain concentrated zone) can explain the load-displacement behaviour for both lateral and upward loading.

On a class of non-coaxial plasticity models for granular soils

2005 ◽  
Vol 462 (2067) ◽  
pp. 725-748 ◽  
Author(s):  
H.S Yu ◽  
X Yuan
Keyword(s):  
Simple Shear ◽  
Shear Loading ◽  
Granular Soils ◽  
Strain Rates ◽  
Principal Stresses ◽  
Constitutive Theories ◽  
Strain Behaviour ◽  
Plastic Potential ◽  
Stress States ◽  
Soil Behaviour

The non-coaxiality of the directions of principal stresses and principal plastic strain rates in granular soils under stress rotations has long been observed and recognized in soil tests using both simple shear and hollow cylinder apparatuses. A few constitutive theories have also been proposed in the literature to account for the effect of stress rotations and the subsequent non-coaxial soil behaviour, particularly in the context of shear band analysis. However, the lack of corresponding general numerical methods makes it difficult to investigate the influence of non-coaxial stress–strain behaviour on the results of geotechnical boundary value problems. This paper presents a numerical evaluation of a class of non-coaxial, elastic–plastic models that are developed by combining the conventional plastic potential theory and the double shearing theory. The general non-coaxial constitutive theories are first formulated and then a finite element implementation of the theories is carried out. To evaluate the non-coaxial theories, the problem of simple shear of soils is chosen to investigate the predicted behaviour of soils under simple shear loading conditions where the axes of principal stresses rotate. In particular, the influence of initial stress states and the degree of non-coaxiality are examined. It is found that the numerical results predicted using the non-coaxial model are in general agreement with the experimental observations reported in the literature.

scholarly journals Estimation of the shear strength of a coarse soil with high fines content by parallel gradation method

2019 ◽  
Vol 92 ◽  
pp. 06001
Author(s):  
N'guessan MoÏse Kouakou ◽  
Olivier Cuisinier ◽  
Farimah Masrouri ◽  
Emmanuel Lavallée ◽  
Tangi Le Borgne
Keyword(s):  
Mechanical Properties ◽  
Shear Strength ◽  
Friction Angle ◽  
Granular Soils ◽  
Standard Laboratory ◽  
Fines Content ◽  
Initial Soil ◽  
Coarse Soil

The determination of the mechanical properties of soils containing particles larger than the allowable size of standard laboratory equipments is complex. It is indeed necessary to remove the coarsest fraction to carry out the tests. This scalping poses a problem of reliability of the results at the scale of the structure. Parallel gradation is the method commonly used for estimating the shear strength of heterogeneous granular soils from tests on their finer fraction. However, the effect of high fines content on the estimation of shear strength by this method is not well understood. The results of this study show that the parallel gradation method can predict the friction angle of the initial soil with high fines content when the modelled soil has a similar skeleton as the initial soil. However, the cohesion of the initial soil is overestimated.

Experimental Comparison Study on Behavior of Combined Piles Composite Foundation

2011 ◽  
Vol 90-93 ◽  
pp. 264-270 ◽  
Author(s):  
De Quan Zhou ◽  
Hong Li Liu
Keyword(s):  
Economic Effects ◽  
Composite Foundation ◽  
Experimental Comparison ◽  
Plastic State ◽  
Loading Test ◽  
Total Load ◽  
Soil Stress ◽  
S Curve ◽  
Control Principle ◽  
Plate Loading

The combined pile composite foundation has the advantages of good technical and economic effects, yet there are no mature analysis methods to practise in design and test at present. This paper has studied the three and four-element composite foundation by the plate loading test, in which the pressure cells, pressure manometers and sensors are laid on the top of the piles and soil. The results show that the stress on the top of piles and soil increases with the increase of total load, the increasing rate being directly proportional to the strength or relative rigidity of piles and soil. The various increasing rates of piles and soil stress versus load make great difference between the three and four-element composite foundation in the variation of the load sharing ratio and the stress ratio versus load. The settlement of the combined piles composite foundation varies gradually with pressure, and the p-s curve may be simulated by hyperbola curve so as to establish the failure criterion and obtain tangent modulus. As the pressure increases, the inter-pile soil enters plastic state earlier than the piles, so the latter have to bear majority of the load, which makes the settlement rise. The composite foundation should be designed according to settlement-control principle.

A Gradient-Dependent Flow Theory of Plasticity: Application to Metal and Soil Instabilities

1989 ◽  
Vol 42 (11S) ◽  
pp. S295-S304 ◽  
Author(s):  
H. M. Zbib ◽  
E. C. Aifantis
Keyword(s):  
Shear Banding ◽  
Shear Bands ◽  
Flow Theory ◽  
Higher Order ◽  
Critical Conditions ◽  
Granular Soils ◽  
Wavelength Selection ◽  
Theory Of Plasticity ◽  
Dependent Flow ◽  
Flow Theory Of Plasticity

We propose a gradient-dependent flow theory of plasticity for metals and granular soils and apply it to the problems of shear banding and liquefaction. We incorporate higher order strain gradients either into the constitutive equation for the flow stress or into the dilantancy condition. We examine the effect of these gradients on the onset of instabilities in the form of shear banding in metals or shear banding and liquefaction in soils under both quasi-static and dynamic conditions. It is shown that the higher order gradients affect the critical conditions and allow for a wavelength selection analysis leading to estimates for the width or spacing of shear bands and liquefying strips. Finally, a nonlinear analysis is given for the evolution of shear bands in soils deformed in the post-localization regime.

The Shear Dilation and Shear Band of Coarse Grained Soil Based on Discrete Element Method

2015 ◽  
Vol 744-746 ◽  
pp. 679-685 ◽  
Author(s):  
Zhi Hua Zhang ◽  
Guo Dong Zhang ◽  
Xue Liang Li ◽  
Zhi Hua Xu
Keyword(s):  
Discrete Element Method ◽  
Shear Bands ◽  
Confining Pressure ◽  
Discrete Element ◽  
Coarse Grained ◽  
Biaxial Test ◽  
Confining Stress ◽  
Shear Dilation ◽  
Coarse Grained Soil ◽  
Element Method

Based on the triaxial test of coarse grained soil, using the discrete element method to simulate the biaxial test by using PFC2D as the discrete element method (DEM) tools, and generate particles by a gradation which is similar with that in laboratory. Through self-programming, depends on the macro-reaction in lab to find out the mesoscopic parameters and deformation characteristics of coarse grained soil, then calibrate the value of friction coefficient correspond to that in laboratory, and at last find out the shear bands. The results show that the value of sample volumetric increment ratio (VIR)dεv/dεis positive (shear shrinkage) at first and then negative (shear dilation) when confining stress is 300kPa, when the confining pressure is greater than 300kPa, samples have been on the shear shrinkage.

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