The Brittle-Ductile Transition Character of Rocks and Its Effect on Rockbursts

2004 ◽  
Vol 261-263 ◽  
pp. 171-176
Author(s):  
Guang Zhang ◽  
Jing Xi Chen ◽  
Bin Hu
Keyword(s):  
Stress State ◽  
Stress Path ◽  
Triaxial Tests ◽  
Affecting Factors ◽  
True Triaxial ◽  
Brittle Ductile Transition ◽  
True Triaxial Tests

The brittle-ductile character is one of the important mechanical indexes of rocks and also one of the important affecting factors of rockburst. Both conventional and true triaxial tests have shown that the brittle-ductile character of rocks varies with the variation in rocks stress state and stress path, but these two kinds of tests have revealed totally different laws of brittle-ductile transition. This present paper analyses the results from two tests firstly and then summarizes the effect of rock’s brittle-ductile transition character on rockburst and finally points out the deficiency in present studies of rockburst.

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

Anisotropic Behavior of Geomaterial under Three-Dimensional Stress States

2010 ◽  
Vol 160-162 ◽  
pp. 1425-1431
Author(s):  
Kun Yong Zhang ◽  
Yan Gang Zhang ◽  
Chi Wang
Keyword(s):  
Stress State ◽  
Principal Stress ◽  
Three Dimensional ◽  
Complex Stress State ◽  
Triaxial Tests ◽  
Induced Anisotropy ◽  
Principal Stresses ◽  
True Triaxial ◽  
Stress Effects ◽  
Stress Induced Anisotropy

Most soil constitutive models were developed based on the traditional triaxial tests with isotropic assumption, in which the load is applied as the major principal stress direction and the other two principal stresses are symmetric. When such isotropic models are applied to practical analysis, stress induced anisotropy under complex stress state and the middle principal stress effects are often neglected, thus there are many disagreements between the calculated results and the infield testing data. To simulate the practical loading process, true triaxial tests were carried out on geomaterial under three-dimensional stress state. It was found that the stress induced anisotropy effects are remarkable and the middle principal stress effects are obvious because of the initial three-dimensional stress state. Such kind of stress-induced anisotropy could have important impact on the numerical analysis results and should be taken into consideration when developing the constitutive model.

Simulation of triaxial and true triaxial tests on natural and reconstituted Pisa clay

Géotechnique ◽  
2002 ◽  
Vol 52 (9) ◽  
pp. 649-666 ◽  
Author(s):  
L. Callisto ◽  
A. Gajo ◽  
D. Muir Wood
Keyword(s):  
Triaxial Tests ◽  
True Triaxial ◽  
True Triaxial Tests

Macro–micro responses of crushable granular materials in simulated true triaxial tests

2015 ◽  
Vol 17 (4) ◽  
pp. 497-509 ◽  
Author(s):  
Wei Zhou ◽  
Lifu Yang ◽  
Gang Ma ◽  
Xiaolin Chang ◽  
Yonggang Cheng ◽  
...  
Keyword(s):  
Granular Materials ◽  
Triaxial Tests ◽  
True Triaxial ◽  
True Triaxial Tests

scholarly journals Research on the Reasonable Strengthening Time and Stability of Excavation Unloading Surrounding Rock of High-Stress Rock Mass

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Wensong Xu ◽  
Wentao Xu ◽  
Yunhai Cheng
Keyword(s):  
Rock Mass ◽  
Plastic Zone ◽  
Failure Process ◽  
High Stress ◽  
Stable State ◽  
Surrounding Rock ◽  
Triaxial Tests ◽  
Uniaxial Compression Test ◽  
True Triaxial ◽  
True Triaxial Tests

This study is aimed at better understanding the deformation and failure mechanism of surrounding rock during excavation unloading of a high-stress rock mass and determining the reasonable reinforcement time for the surrounding rock. To fulfill this aim, true triaxial tests were carried out on different loading and unloading paths during the unilateral unloading of a high-stress rock mass. The variational condition for minimization of plastic complementary energy is obtained, the optimal reinforcement time is determined, and the range of the plastic zone in the surrounding rock reinforced by anchor mesh-cable-grouting is compared and analyzed. The results are as follows: (1) Based on the Mohr-Coulomb yield criterion and the deformation reinforcement theory of surrounding rock, the stable state with the minimum reinforcement force is obtained. (2) After the true triaxial tests on the unilateral unloading of the third principal stress were carried out under different confining pressures, loading continued to be performed. Compared with rock failure without confining pressure, in the conventional uniaxial compression test, the failure of samples is dominated by composite splitting-shear failure; the unilateral unloading stress-concentration failure is a progressive failure process of splitting into plates followed by cutting into blocks and then the ejection of blocks and pieces. (3) The relationship between the time steps of the surrounding rock stability and the excavation distance is obtained. The supporting time can be divided into four stages: presupport stage, bolt reinforcement stage, anchor cable reinforcement stage, and grouting reinforcement stage. (4) In the range of within 5 m behind the tunneling face, the plastic zone of the surrounding rock with support is reduced by 7 m as compared with that with no support. In the range of over 5 m behind the tunneling face, the plastic zone of the roadway floor with support is reduced by 2.6 m as compared with that without support, and the deformation is reduced by 90%. These results can serve as a reference for controlling the behavior of surrounding rock during excavation unloading of high-stress rock masses.

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