scholarly journals An Experimental Study on the Deformation and Strength Characteristics of Q3 Loess under a Plain Strain Anisotropic Consolidation Condition

2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Yu Zhang ◽  
Yang Zhao ◽  
Jin Liu ◽  
Tian-Yi Meng ◽  
Sheng-Jun Shao ◽  
...  
Keyword(s):  
Stress State ◽  
Principal Stress ◽  
Confining Pressure ◽  
Intermediate Principal Stress ◽  
Stress Tests ◽  
Volume Deformation ◽  
Initial Stress State ◽  
K Value ◽  
Vertical Loading ◽  
Confining Pressures

To study the strength, deformation characteristics, and intermediate principal stress of intact loess, vertical loading stress tests with different initial stress state k value were conducted under different confining pressures. Plane strain tests were carried out by the transformed true triaxial apparatus of Xi’an University of Technology. The study shows that loess tends to be in a plastic failure state in different confining pressures and k values, and the stress-strain relationship curve is of a hardening type. Results reveal that loess lateral and volume deformations have nonlinear relationships with its vertical deformation, and volume deformation shrinks in the process of shearing. The effect of confining pressure on soil deformation is greater than k value. The intermediate principal stress coefficient decreases with the increase of the confining pressure and transforms from increasing to decreasing with the increase of k value (ranging from 0.2 to 0.4). In brief, the loess failure strength is closely related to k value, confining stress, and spherical stress state. When k value increases, cohesion effect reduces, whereas internal friction angle increases linearly. The influence of k value on soil strength and deformation is closely related to confining pressure.

Effects of Complex Initial Stress State Parameters on Dynamic Shear Modulus of Loess

2011 ◽  
Vol 243-249 ◽  
pp. 2601-2606 ◽  
Author(s):  
Zhi Jie Wang ◽  
Ya Sheng Luo ◽  
Hong Guo
Keyword(s):  
Stress State ◽  
Shear Modulus ◽  
Principal Stress ◽  
Initial Stress ◽  
Triaxial Tests ◽  
Dynamic Shear Modulus ◽  
Dynamic Shear ◽  
Initial Stress State ◽  
Foundation Soil ◽  
Stress States

The foundation soil of the buildings and structures is often in complex initial stress states. The dynamic torsional shear triaxial tests are carried out on undisturbed and remodeling loess under different complex initial stress states by using the remolded DTC-199 torsional cyclic load triaxial apparatus, and the effects of each complex initial stress state parameter on dynamic shear modulus of loess are discussed. Results show that, other conditions being the same, the influence of angles of initial principal stressα0on dynamic shear modulusGdof loess show a trend of the biggerα0is, the smallerGdis. The effect laws of efficient of initial intermediate principal stressb0onGdof loess are not obvious. When the dynamic shear strain is larger, the bigger initial deviator stress ratioη0is, the smallerGdof loess is. The influence of initial average principal stresspm0on loess is significant. The biggerpm0is, the biggerGdof loess is.Gdof undisturbed loess is greater than that of remodeling loess under the complex initial stress states.

scholarly journals The suction,yield and strength characteristics of unsaturated intact loess based on true tri-axial tests

2019 ◽  
Vol 7 (3) ◽  
Author(s):  
Jinjin Fang
Keyword(s):  
Principal Stress ◽  
Stress Ratio ◽  
Shear Failure ◽  
Confining Pressure ◽  
Intermediate Principal Stress ◽  
True Triaxial ◽  
Yield Stress Increase ◽  
Isotropic Consolidation ◽  
The Relationship ◽  
Intact Loess

To simulate the failure of loess under undrained condition in the actual engineering,a series of isotropic consolidation and shear tests with different intermediate principal stress ratio b under constant water content were performed on intact loess with various initial suctions using the true tri-axial apparatus for unsaturated soil. The relationship between the saturations and initial suctions,the characteristics of yield,suction and strength of unsaturated intact loess were studied. The results show that the initial suctions and the suctions after the isotropic consolidation decrease with the increase of saturations. The suctions increase with the increase of the intermediate principal stress ratio b at the true triaxial shear failure. The net mean yield stress increase with the increase of the initial suction. The yield suction is a constant,but not always equal to the maximum suction that the soil specimen experienced in the history. The strength of soil increase with the increase of the net confining pressure,initial suction and the intermediate principal stress ratio b.

scholarly journals Development of a polyaxial platen for testing true triaxial behavior of rocks

2021 ◽  
Author(s):  
Prasoon Garg ◽  
Bhardwaj Pandit ◽  
Brijes Mishra ◽  
G.L. Sivakumar Babu
Keyword(s):  
Stress State ◽  
Principal Stress ◽  
Axial Stress ◽  
Intermediate Principal Stress ◽  
Intact Rock ◽  
Triaxial Stress ◽  
Triaxial Tests ◽  
True Triaxial ◽  
True Triaxial Tests

Mining at greater depths can lead to stress-induced failure, especially in areas of high horizontal in-situ stress. The induced stresses around the opening are known to be in a poly-axial stress state where, σ_1≠ σ_2≠ σ_3 with special case of σ_3= 0 and σ_1, σ_2 ≠ 0 at its boundary. The conventional triaxial testing does not represent the actual in-situ strength of the rock in regions of high horizontal stress, as it ignores the influence of intermediate principal stress (σ_2). The typical poly-axial testing (biaxial and true-triaxial tests) of intact rock mostly requires sophisticated and expensive loading systems. This study investigated the mechanical behavior of intact rock under a poly-axial stress state using a simple and cost-effective design. The apparatus consists of biaxial frame and a confining device. The biaxial frame has two platens that apply equal stress in both directions (σ_1=σ_2) on a 50.8 mm cubical specimen when placed inside the uniaxial loading device. The confining device performed separate biaxial tests under constant intermediate principal stress (σ_2 = constant) and true-triaxial tests when used along with the biaxial frame. This study then compared the failure modes and peak strength of Berea Sandstone specimens with other biaxial/triaxial devices to validate the design of the poly-axial apparatus. We also performed uniaxial tests on both standard cylindrical samples and prismatic specimen of different slenderness ratios. These tests provided a complete understanding of the failure mode transition from standard uniaxial compressive tests to triaxial stress conditions on cubical specimen. Additionally, this study determined best-fitted strength envelopes for biaxial and triaxial stress state. Based on regression analysis, we found a quadratic polynomial to be a good fit to biaxial strength envelope. For true-triaxial strength envelope, we found the 3D failure criterion by Nadai (1950) to be a good fit with R^2 of 0.964

Analysis of Small Non-Sand Concrete Pile Grouting Pressure Based on Unified Strength Theory

2012 ◽  
Vol 166-169 ◽  
pp. 3095-3099
Author(s):  
Huai Feng Tong
Keyword(s):  
Stress State ◽  
Principal Stress ◽  
Limit State ◽  
Intermediate Principal Stress ◽  
Plastic State ◽  
Strength Theory ◽  
Unified Strength Theory ◽  
Grouting Pressure ◽  
Concrete Pile ◽  
The Relationship

Analysis of stress state of soil around the pile and grouting pressure of small non-sand concrete pile is given based on the expansion elastic theory of cylindrical cavity and the unified strength theory, the grouting pressure formula is obtained in the elastic limit state and elastic-plastic state of soil around the pile considered the intermediate principal stress, and the relationship is obtained between the grouting pressure and the plastic radius; When the soil around the pile is in different stress state, the correlativity of crack and densification of grouting is analyzed, and the relationship between the grouting pressure and the plastic radius is discussed with the right coefficient of the intermediate principal stress and initial press under different values. The obtained results have provided efficient analysis means for grouting optimal design of post-processing technology with small non-sand concrete pile.

scholarly journals A New Calculation Method for the Soil Slope Safety Factor

2017 ◽  
Vol 2017 ◽  
pp. 1-6
Author(s):  
Fu Zhu ◽  
Wanxi Zhang ◽  
Mingzhi Sun
Keyword(s):  
Stress State ◽  
Principal Stress ◽  
Safety Factor ◽  
Lateral Pressure ◽  
Pressure Coefficient ◽  
Intermediate Principal Stress ◽  
New Method ◽  
Soil Slope ◽  
Lateral Pressure Coefficient ◽  
Slope Safety

Based on the unified strength theory, a new method to calculate the plane soil slope safety factor was derived that considers the effect of intermediate principal stressσ2and at-rest lateral pressure coefficientK0. Calculation examples from the literature were used to compare the new calculation method and the current slice method; the results showed that both provided good consistency. The new method can provide a reference for slope stability evaluation. The new method was used to calculate the soil slope safety factors for different values of intermediate principal stress parameterb, double shear stress parametersuτ′, and static lateral pressure coefficientK0. The results showed that the safety factorFsincreased whenbwas increased;Fsfirst increased and then decreased whenuτ′was increased; andFsincreased whenK0was increased. These results show that the intermediate principal stress as well as the stress state and its changes cannot be ignored during soil slope stability analysis. The slope soil characteristics and stress state should be considered to determine the unified strength theoretical parameters and static lateral pressure coefficient, maximize the potential of slope soil strength, and effectively reduce the costs of soil slope engineering.

scholarly journals Earth Pressure of Three-Dimensional Stress States under Different Strength Criteria and Its Application

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Yu Zhang ◽  
Jin Liu ◽  
Te-Jia Fan ◽  
Chen-Yang Xu ◽  
Tian-Yi Meng ◽  
...  
Keyword(s):  
Stress State ◽  
Principal Stress ◽  
Three Dimensional ◽  
Earth Pressure ◽  
Measured Data ◽  
Intermediate Principal Stress ◽  
Stress Effect ◽  
Passive Earth Pressure ◽  
The Earth ◽  
Stress States

To solve the Earth pressure problems in practical engineering, such as retaining walls and foundation pits, we derive active and passive Earth pressure formulas in accordance with the relationship between intermediate principal stress and excavation under three-dimensional stress states. The formulas are derived on the basis of the Mohr–Coulomb, spatially mobilized plane (SMP), σ 3 SMP, Lade–Duncan, axisymmetric compression- (AC-) SMP strength, and generalized Mises (Gen-Mises) criteria and then extended to clay. We also compare the calculated Earth pressure with the measured data. Results indicate that the Earth pressure considering medium principal stress contribution under a three-dimensional stress state is consistent with the actual engineering. The calculated active Earth pressure in the Mohr–Coulomb strength criterion is larger, and the passive Earth pressure is smaller than the practical one because the intermediate principal stress effect is not considered. The calculated results of the SMP, σ 3 SMP, Lade–Duncan, AC-SMP strength, and Gen-Mises criteria are close to the measured data, among which the result of the Gen-Mises criterion is closer. The Earth pressure calculated using the Lade–Duncan criterion is no longer appropriate to describe the Earth pressure under medium principal stress condition in this study. The results of this study have theoretical significance for retaining structure design under a three-dimensional stress state.

scholarly journals Failure in Confined Brazilian Tests on Sandstone

2021 ◽  
Vol 11 (5) ◽  
pp. 2285
Author(s):  
Tyler Hagengruber ◽  
Mahmoud Reda Taha ◽  
Esteban Rougier ◽  
Earl Knight ◽  
John Stormont
Keyword(s):  
Principal Stress ◽  
Experimental Tests ◽  
Confining Pressure ◽  
Intermediate Principal Stress ◽  
Brazilian Test ◽  
Test Results ◽  
Strong Function ◽  
Strength Data ◽  
Minimum Principal Stress ◽  
Coulomb Criterion

Strength of rocks in the confined tension region, where the minimum principal stress is tensile, has only infrequently been measured and is not well understood. Quasi-static confined Brazilian tests under a range of confining stresses (2.76 to 27.58 MPa) where used to determine the strength of sandstone in the confined tension region. The test results indicate that the strength in the confined tension region was a strong function of the intermediate principal stress: increasing the intermediate principal stress significantly increased the strength of the sandstone. The strength data were well fit by the Mogi–Coulomb criterion, which accounts for the intermediate principal stress. Unconfined Brazilian strength data were not well fit to the Mogi–Coulomb criterion derived from the confined Brazilian test data, consistent with a transition from tensile to shear processes dominating failure with increasing confining pressure. Observations of post-failure fracture surfaces reveal more indication of shear processes with increasing confining pressure. Numerical simulations from combined finite-discrete element method are compared to the experimental results and reflect similar conditions for failure compared to the experimental tests in the confined tension region.

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