A Piecewise Yield Failure Criterion including the Critical State for Brittle Rock

The critical state of rock is an important index for measuring the changes in rock characteristics. However, this state is not unique because of the different researcher assumptions. Based on the theory of the partial differential equation proposed by Vutukuri, according to Mohr’s envelope, a piecewise yield failure criterion (referred to as the Mohr–Wedge criterion), including the critical state for brittle rock, is obtained by introducing the wedge model to solve this equation. The Mohr–Wedge (M–W) criterion consisting of nonlinear and linear components includes the critical state for brittle rock. When the minimum principal stress σ3 is lower than the confining pressure σk, the maximum principal stress σ1 varies nonlinearly with σ3; otherwise, σ1 varies linearly with σ3. This variation conforms to rock deformation features under triaxial compression. In this study, we investigate the rationality of this critical state by an analogy method and illustrate that the critical state mentioned in this criterion is related to the microcracks in the potential failure zone of the rock. Alternatively, the primary object of this study is to reveal the applicability of predicting the yield state for this criterion. The method used in our study is compared to the Mohr–Coulomb (M-C) criterion, the Hoek–Brown (H-B) criterion, and the Exponential (Exp.) criterion by the yield surfaces on the deviatoric plane. Notably, there is a vertex consistent region for the four criteria, but except for this region, the yield state of rock predicted by the four criteria is quite different, depending on the extent of the parameters for the criteria and the magnitude of the slopes of the yield surfaces. The results show that the M-W criterion has certain applicability for predicting the rock yield state by using the multiple data of rock triaxial compression tests in the published literature.

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A Parabolic Failure Criterion for Transversely Isotropic Rock: Modification and Verification

Mathematical Problems in Engineering ◽

10.1155/2019/8052560 ◽

2019 ◽

Vol 2019 ◽

pp. 1-12

Author(s):

Ding-Jian Wang ◽

Huiming Tang ◽

Peiwu Shen ◽

Yi Cai

Keyword(s):

Experimental Data ◽

Failure Criterion ◽

Triaxial Compression ◽

Transversely Isotropic ◽

Confining Pressure ◽

Prediction Errors ◽

Compression Tests ◽

Predictive Capacity ◽

Data Set ◽

Transversely Isotropic Rock

It is of great significance to develop a failure criterion that can describe the orientation-dependent behavior of transversely isotropic rocks. This paper presents a simplified parabolic model that is successful in predicting the strengths of rocks under different confining pressures and bedding angles. The model is a modified version of the normal parabolic criterion for intact rocks. The two orientation-dependent parameters (σcβ and kβ) in the model show trigonometric relationships with the bedding angle, and they can be readily determined through uniaxial and triaxial compression tests. The shape of the failure envelope is determined by kβ, and σcβ only affects the level of rock strength. With application to 446 experimental data, the predicting results by the parabolic criterion are highly consistent with the experimental data, and the predictive capacity of the proposed criterion is better than those of the McLamore-Gray and Tien-Kuo criteria. Besides, the prediction errors for the high confining pressure condition and the bedding-sliding failure mode are smaller than those for the low confining pressure and the non-bedding-sliding failure. Moreover, the prediction error almost remains steady with the decrease of data set, indicating that the proposed criterion is of high precision even if the experimental data are limited.

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Unloading Triaxial Experimental Study on Stress Path of Excavated Soil Slope

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.243-249.2797 ◽

2011 ◽

Vol 243-249 ◽

pp. 2797-2801 ◽

Cited By ~ 1

Author(s):

Yan Gang Zhang ◽

Kun Yong Zhang ◽

Wang Lin Li ◽

Qiao Zhen Shi

Keyword(s):

Principal Stress ◽

Triaxial Compression ◽

Constitutive Models ◽

Confining Pressure ◽

Stress Path ◽

Soil Mass ◽

Soil Slope ◽

Compression Tests ◽

Excavation Process ◽

Major Principal Stress

The current research was implemented to study the practical unloading stress path that the slope mass experienced during the excavation process, which is very important in the stress and strain numerical analysis. Series of unloading tests were carried out under different confining pressure. During the test process, the minor principal stress was kept decreasing, while the major principal stress was kept unchanged to simulate the stress path in some locations of the soil slope, such as at the top of the slope. The corresponding conventional triaxial compression tests were also carried out as comparison. It is shown that there are many differences between the unloading and loading tests. Through analyzing, the tests results could be applied in the development of unloading constitutive models of excavation soil mass. Also, such unloading tests data are valuable in calibration and verification of the current existing popularly used models.

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Inverse analysis–based interpretation of sand behavior from triaxial compression tests subjected to full end restraint

Canadian Geotechnical Journal ◽

10.1139/t09-015 ◽

2009 ◽

Vol 46 (7) ◽

pp. 768-791 ◽

Cited By ~ 13

Author(s):

Youssef M.A. Hashash ◽

Qingwei Fu ◽

Jamshid Ghaboussi ◽

Poul V. Lade ◽

Christopher Saucier

Keyword(s):

Principal Stress ◽

Failure Criterion ◽

Laboratory Testing ◽

Inverse Analysis ◽

Triaxial Compression ◽

Boundary Value ◽

Octahedral Plane ◽

Compression Tests ◽

Soil Behavior ◽

Triaxial Compression Tests

Current laboratory testing often imposes or assumes uniform stress and strain distribution in a specimen for convenient data reduction to interpret soil behavior. This paper presents an inverse analysis framework, Self-learning Simulations (SelfSim), to interpret the drained behavior of sand from triaxial compression tests with fully frictional loading platens. The frictional platens result in significant bulging of and nonuniform stresses and strains within sand specimens. SelfSim treats the specimen as a boundary value problem (BVP) and extracts these nonuniform stresses and strains from within each specimen using external load and displacement measurements. The extracted behavior shows significant principal stress rotation, variation of intermediate principal stress, and nonuniform volume change throughout the specimen. Mobilized friction angles are interpreted on the two-dimensional slip surface associated with the Mohr–Coulomb failure criterion, on the octahedral plane associated with the Drucker–Prager failure criterion, and on the spatially mobilized plane (SMP) associated with the Matsuoka–Nakai failure criterion. The extracted stress–strain behavior is used to examine the sand’s stress-dilatancy characteristics. Proposed integration of SelfSim inverse analysis with laboratory testing opens the way for new and efficient approaches to soil behavior characterization under general loading conditions, needed for the solution of general geotechnical boundary value problems, from readily available laboratory tests.

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Triaxial Testing of Geosynthetics Reinforced Tailings with Different Reinforced Layers

Materials ◽

10.3390/ma13081943 ◽

2020 ◽

Vol 13 (8) ◽

pp. 1943

Author(s):

Fu Yi ◽

Changbo Du

Keyword(s):

Triaxial Compression ◽

Friction Angle ◽

Confining Pressure ◽

Test Results ◽

Compression Tests ◽

Strength Index ◽

Stress Strain ◽

High Confining Pressure ◽

Zhang Model ◽

Triaxial Compression Tests

To evaluate the shear properties of geotextile-reinforced tailings, triaxial compression tests were performed on geogrids and geotextiles with zero, one, two, and four reinforced layers. The stress–strain characteristics and reinforcement effects of the reinforced tailings with different layers were analyzed. According to the test results, the geogrid stress–strain curves show hardening characteristics, whereas the geotextile stress–strain curves have strain-softening properties. With more reinforced layers, the hardening or softening characteristics become more prominent. We demonstrate that the stress–strain curves of geogrids and geotextile reinforced tailings under different reinforced layers can be fitted by the Duncan–Zhang model, which indicates that the pseudo-cohesion of shear strength index increases linearly whereas the friction angle remains primarily unchanged with the increase in reinforced layers. In addition, we observed that, although the strength of the reinforced tailings increases substantially, the reinforcement effect is more significant at a low confining pressure than at a high confining pressure. On the contrary, the triaxial specimen strength decreases with the increase in the number of reinforced layers. Our findings can provide valuable input toward the design and application of reinforced engineering.

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Experimental Investigation and Micromechanical Modeling of Elastoplastic Damage Behavior of Sandstone

Materials ◽

10.3390/ma13153414 ◽

2020 ◽

Vol 13 (15) ◽

pp. 3414

Author(s):

Chaojun Jia ◽

Qiang Zhang ◽

Susheng Wang

Keyword(s):

Damage Evolution ◽

Triaxial Compression ◽

Damage Model ◽

Confining Pressure ◽

Micromechanical Modeling ◽

Compression Tests ◽

Integration Algorithm ◽

Damage Behavior ◽

Plastic Strain Increment ◽

Elastoplastic Damage

The mechanical behavior of the sandstone at the dam site is important to the stability of the hydropower station to be built in Southwest China. A series of triaxial compression tests under different confining pressures were conducted in the laboratory. The critical stresses were determined and the relationship between the critical stress and confining pressure were analyzed. The Young’s modulus increases non-linearly with the confining pressure while the plastic strain increment Nϕ and the dilation angle ϕ showed a negative response. Scanning electron microscope (SEM) tests showed that the failure of the sandstone under compression is a coupled process of crack growth and frictional sliding. Based on the experimental results, a coupled elastoplastic damage model was proposed within the irreversible thermodynamic framework. The plastic deformation and damage evolution were described by using the micromechanical homogenization method. The plastic flow is inherently driven by the damage evolution. Furthermore, a numerical integration algorithm was developed to simulate the coupled elastoplastic damage behavior of sandstone. The main inelastic properties of the sandstone were well captured. The model will be implemented into the finite element method (FEM) to estimate the excavation damaged zones (EDZs) which can provide a reference for the design and construction of such a huge hydropower project.

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The mechanics of subglacial sediment: an example of new “transitional” behaviour

Canadian Geotechnical Journal ◽

10.1139/t09-136 ◽

2010 ◽

Vol 47 (7) ◽

pp. 775-790 ◽

Cited By ~ 33

Author(s):

Fatin Altuhafi ◽

Béatrice A. Baudet ◽

Peter Sammonds

Keyword(s):

Critical State ◽

Triaxial Compression ◽

Interesting Case ◽

Strain History ◽

Compression Tests ◽

Specimen Density ◽

The Difference ◽

Triaxial Compression Tests ◽

Normal Compression

A series of isotropic compression tests and drained and undrained triaxial compression tests have been performed on glacial sediment from Iceland. Langjökull sediment, which is well graded, is thought to have reached a critical grading during deposition and transportation. Multiple parallel normal compression lines (NCLs) were found, but a unique critical state line (CSL) could be identified. This is unlike other so-called “transitional” soils, whose grading varies between reasonably well graded to gap graded, which tend to have distinct NCLs and critical state lines depending on the specimen density. It is thought that in the case of the Langjökull sediment studied, its particular strain history that involved incessant shearing during deposition accounts for the difference in behaviour. This provides the interesting case of a soil that has been crushed to a critical grading in situ, which depends on the mineralogy of the grains, which was then sampled and tested. Despite the unique grading, samples with a range of different void ratios can be prepared and the combination of grading and density seems to set a fabric that cannot be changed by compression, resulting in multiple parallel NCLs. At the critical state, however, the fabric has been destroyed and the CSL is unique.

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Microcracking and the failure of polycrystalline ice under triaxial compression

Journal of Glaciology ◽

10.3189/s0022143000009606 ◽

1992 ◽

Vol 38 (128) ◽

pp. 65-76 ◽

Cited By ~ 1

Author(s):

P. Kalifa ◽

G. Ouillon ◽

P. Duval

Keyword(s):

Triaxial Compression ◽

Peak Stress ◽

Confining Pressure ◽

Triaxial Tests ◽

Strain History ◽

Compression Tests ◽

Brittle Transition ◽

Polycrystalline Ice ◽

Strain Components

AbstractTriaxial and uniaxial compression tests have been carried out at –10°C on granular ice in order to study the role of microcracking on failure in the ductile-brittle transition zone. In the triaxial tests, the effect of confining pressure and strain rate on the crack population, as well as on strength and strain at the peak stress, was investigated. In the uniaxial tests, we measured the evolution of elastic and non-elastic components of deformation with the stress-strain history. The concept of effective stress, with a single scalar damage variable, was used to calculate the effect of microcracking on the strain components.

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Mechanical Properties of Bentonite-Sand Mixtures Under Triaxial Stress Condition

MRS Proceedings ◽

10.1557/proc-353-307 ◽

1994 ◽

Vol 353 ◽

Cited By ~ 1

Author(s):

M. Umedera ◽

A. Fujiwara ◽

N. Yasufuku ◽

M. Hyodo ◽

H. Murata

Keyword(s):

Mechanical Properties ◽

Shear Strength ◽

Water Content ◽

Triaxial Compression ◽

Confining Pressure ◽

Strength Properties ◽

Compression Tests ◽

Optimum Water Content ◽

Triaxial Compression Tests ◽

Optimum Water

AbstractA series of triaxial compression tests is being conducted under the drained condition on bentonite and sand mixtures, known as buffer, in saturated and optimum water content states to clarify the mechanical properties of the buffer.It was found that the mechanical properties of bentonite and sand mixtures are strongly influenced by water and bentonite contents: shear strength in a saturated state is less than that in an optimum water content state; shear strength decreases rapidly with increasing bentonite content. Strength properties are much dependent on confining pressure.

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Experimental Study on Shear Strength Considering Initial Void Ratio and Plasticity Index

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.405-408.63 ◽

2013 ◽

Vol 405-408 ◽

pp. 63-67

Author(s):

Xing Chen Wang ◽

Ri Qing Xu ◽

Jian Feng Zhu

Keyword(s):

Shear Strength ◽

Void Ratio ◽

Triaxial Compression ◽

Confining Pressure ◽

Deviatoric Stress ◽

Plasticity Index ◽

Test Results ◽

Compression Tests ◽

Functional Relationships ◽

Initial Void Ratio

A series of drained triaxial compression tests under different conditions were performed to quantitatively study the influence of the initial void ratio and plasticity index on the shear strength of remolded saturated clays. The test results show that both the peak stress friction angle and peak deviatoric stress decrease with increasing initial void ratio and plasticity index of the soil under the same confining pressure; whereas, they increase with increasing confining pressure of the soil under the same initial void ratio and plasticity index. A new synthesized physical parameter λ, which simultaneously represent both the type and the condition of remolded saturated clays, is defined based on the test results in this work. The functional relationships among the parameters φd and peak deviatoric stress in Mohr-Coulomb equation and the parameter λ are established to develop a modified Mohr-Coulomb equation by considering physical properties of soil. In this equation, only two input parameters, i.e., λ and the confine pressure, are needed to predict the shear strength of the soil. In order to check the accuracy of the proposed equation, laboratory tests were conducted to evaluate against the predicted results. The results show that the peak shear strength of remolded saturated clays can be well described by the proposed equation. Key words: shear strength; Mohr-Coulomb equation; remolded saturated clays; initial void ratio; plasticity index.

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Mobilized strength components of Athabasca oil sand in triaxial compression

Canadian Geotechnical Journal ◽

10.1139/t99-040 ◽

1999 ◽

Vol 36 (4) ◽

pp. 718-735 ◽

Cited By ~ 29

Author(s):

Ron CK Wong

Keyword(s):

Critical State ◽

Triaxial Compression ◽

Shear Banding ◽

Shear Bands ◽

Compression Tests ◽

Oil Sand ◽

Shear Dilation ◽

X Ray Imaging ◽

Microscopy Techniques ◽

Triaxial Compression Tests

Dense uncemented Athabasca oil sand specimens exhibit unusually high peak strength, dilation with severe softening, and residual strength in drained triaxial compression tests. Computer tomography scanning, X-ray imaging, and scanning electron microscopy techniques are used to examine the microstructural features of the sheared specimens, such as interlocked structure, shear-banding pattern, and porosity distributions inside and outside shear bands. The characteristics of these microstructural features are used to explain the macrodeformation responses observed in the triaxial compression tests. Mobilization of strength components derived from interlocked structure, dilation, rolling, and critical state are analyzed for pre-peak, post-peak softening, and residual states.Key words: oil sand, interlocked structure, shear dilation, shear band, critical state.

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