scholarly journals Experimental Study on 3D Roughness and Shear Failure Mechanism of Rock Mass Discontinuity

2018 ◽  
Vol 2018 ◽  
pp. 1-20 ◽  
Author(s):  
Jihong Wei ◽  
Yan Men ◽  
Shaorui Sun ◽  
Huilin Le ◽  
Feng Zhu
Keyword(s):  
Surface Topography ◽  
Physical Model ◽  
Residual Strength ◽  
Failure Modes ◽  
Rock Joint ◽  
Model Construction ◽  
Joint Surface ◽  
Shear Direction ◽  
Direct Shear ◽  
Normal Stresses

A set of systematic experimental methods, including 3D accuracy scanning and identification of discontinuous surface topography, physical model construction, and laboratory direct shear experiment under different directions and normal stresses, was proposed to research the influence of discontinuity roughness on strength and deformation of discontinuity. During physical model construction of discontinuity, three types of discontinuity and rough natural rock joint surface models were constructed and moulded. Meanwhile, many influence factors of discontinuity surface topography, such as asperity inclination angle (AIA), asperity height (AH), normal stress (NS), and shear direction (SD), were considered during the direct shear experiment. On the basis of the experimental results, it can be found that there were two types of failure modes under different loading conditions, which were named “failure by shearing through the asperities” and “failure by sliding over the asperities”. The obvious stress concentration phenomenon, climbing, and cutting effects appeared in the process of the direct shear experiment. In addition, the accurate identification of surface topography of natural rough rock joint surface was carried out using three-dimensional sensing system (3DSS) and self-programming software before and after the experiment. The subsamples with the same surface topography as the original samples were moulded using a self-developed instrument. Then, the mechanical behavior of the original samples and subsamples for the natural rough rock joint surface under different shear directions and normal stresses was studied. The results show that the shear displacement under different shear directions and normal stresses is very large before it reaches the failure state. And the residual strength of the original samples is higher than that of the subsamples. In addition, failure modes of the subsamples are main failure by shearing through the asperities due to the significant difference between peak shear strength and residual strength. The failure modes for parts of the original samples are failure by sliding over the asperities. The change ratio of area for the discontinuity after the experiment depends on surface topography, strength of heave on the surface of discontinuity, and particle size of minerals on the surface of discontinuity.

scholarly journals Shear Mechanical Behaviours and Multistrength Parameter Characteristics of Fault Gouge

2019 ◽  
Vol 2019 ◽  
pp. 1-14 ◽  
Author(s):  
Han Bao ◽  
Qun Qi ◽  
Hengxing Lan ◽  
Changgen Yan ◽  
Wei Xu ◽  
...  
Keyword(s):  
Water Content ◽  
Normal Stress ◽  
Clay Minerals ◽  
Residual Strength ◽  
Failure Modes ◽  
Friction Angle ◽  
Strength Properties ◽  
Fault Gouge ◽  
Normal Stresses ◽  
Fault Gouges

Fault gouge has special mechanical properties and remarkable engineering effects. Using a ring shear test, the strength properties of the differently colored remolded fault gouges of the Shendaogou Fault in Yan’an were studied by changing moisture contents and normal stresses. Chlorite and illite are the main clay minerals in fault gouges; differences in mineral composition make fault gouges appear in different colors. Besides clay minerals, the dried fault gouges disintegration in water is also due to the transformation of gypsum. The gradation of green fault gouge and multicolor fault gouge is better than that of the red fault gouge, while the fault gouges’ strain softening properties become weaker as the coarse grain content increases. Affected by water content and normal stress, the shear planes can be divided into three failure modes: peeling failure, grooved failure, and sliding failure. With the increase of water content, there will be a significant weakening on cohesion and friction angle. A new parameter, the “Normal Stress Threshold (NST),” is introduced as a critical value for the emergence of the strain hardening phenomenon, and the NSTs of different fault gouges are significantly different. The functions obtained from the relation of residual strength, peak strength, and normal stress can be used to calculate shear strength parameters under any normal stresses. In addition, the residual strength of fault gouge is obviously different from clay and loess, which can be qualitatively explained by clay particle contents.

Shear strength and dilative characteristics of an unsaturated compacted completely decomposed granite soil

2010 ◽  
Vol 47 (10) ◽  
pp. 1112-1126 ◽  
Author(s):  
Md. Akhtar Hossain ◽  
Jian-Hua Yin
Keyword(s):  
Shear Strength ◽  
Normal Stress ◽  
Matric Suction ◽  
Water Retention Curve ◽  
Direct Shear ◽  
Normal Stresses ◽  
Soil Water Retention Curve ◽  
Strength Data ◽  
Decomposed Granite ◽  
Completely Decomposed Granite

Shear strength and dilative characteristics of a re-compacted completely decomposed granite (CDG) soil are studied by performing a series of single-stage consolidated drained direct shear tests under different matric suctions and net normal stresses. The axis-translation technique is applied to control the pore-water and pore-air pressures. A soil-water retention curve (SWRC) is obtained for the CDG soil from the equilibrium water content corresponding to each applied matric suction value for zero net normal stress using a modified direct shear apparatus. Shear strength increases with matric suction and net normal stress, and the failure envelope is observed to be linear. The apparent angle of internal friction and cohesion intercept increase with matric suction. A greater dilation angle is found at higher suctions with lower net normal stresses, while lower or zero dilation angles are observed under higher net normal stresses with lower suctions, also at a saturated condition. Experimental shear strength data are compared with the analytical shear strength results obtained from a previously modified model considering the SWRC, effective shear strength parameters, and analytical dilation angles. The experimental shear strength data are slightly higher than the analytical results under higher net normal stresses in a higher suction range.

Crack propagation and coalescence characteristics of rock-like specimen containing preexisting flaws subjected to internal hydraulic pressure and shear force

2021 ◽  
Author(s):  
Yong Li ◽  
Weiqiu Kong ◽  
Weishen Zhu ◽  
Guannan Wu ◽  
Zhiheng Wang ◽  
...  
Keyword(s):  
Crack Initiation ◽  
Crack Propagation ◽  
Shear Force ◽  
Cement Mortar ◽  
Hydraulic Pressure ◽  
Shear Direction ◽  
Direct Shear ◽  
Horizontal Shear ◽  
Shear Tests ◽  
Direct Shear Tests

<p><strong>Abstract:</strong> Based on laboratory direct shear tests and discrete element theory, the crack propagation and coalescence mechanism and numerical simulation of cement mortar specimens considering the combined actions of internal hydraulic pressure and shear force were carried out. We completed the filling of the internal hydraulic pressure in the cement mortar specimens with preexisting flaws, and performed the direct shear tests on the specimens. In the numerical analysis, the pipe domain model in the two dimensional particle flow code (PFC2D) was modified owing to the high brittleness and low permeability of the cement mortar particles in the numerical model. We also modified the calculation rules of the interaction between the fluid and cement mortar particles, and proposed an improved fluid-solid coupling model which is more suitable for the high brittle cement mortar. Under the action of internal hydraulic pressure, a tensile region existed at the tip of the preexisting flaws of the cement mortar specimen, which can also explain the crack initiation and propagation along the horizontal shear direction during the stage of crack initiation. However, the fissure water pressure was not completely dissipated because of the high brittleness of the cement mortar and the existence of a large number of micro-cracks in the failure area, which finally resulted in a relatively concentrated horizontal compressive stress, and roughly formed a compressive region with a smaller stress along the horizontal shear direction.</p>

scholarly journals Scale Dependence of Waviness and Unevenness of Natural Rock Joints through Fractal Analysis

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-18
Author(s):  
Yingchun Li ◽  
Shengyue Sun ◽  
Hongwei Yang
Keyword(s):  
Surface Roughness ◽  
Rock Joint ◽  
Fractal Dimensions ◽  
Window Size ◽  
Scale Dependence ◽  
Rock Joints ◽  
Joint Surface ◽  
Triangular Prism ◽  
Natural Rock ◽  
Waviness And Unevenness

The scale dependence of surface roughness is critical in characterising the hydromechanical properties of field-scale rock joints but is still not well understood, particularly when different orders of roughness are considered. We experimentally reveal the scale dependence of two-order roughness, i.e., waviness and unevenness through fractal parameters using the triangular prism surface area method (TPM). The surfaces of three natural joints of granite with the same dimension of 1000 mm×1000 mm are digitised using a 3D laser scanner at three different measurement resolutions. Waviness and unevenness are quantitatively separated by considering the area variation of joint surface as grid size changes. The corresponding fractal dimensions of waviness and unevenness in sampling window sizes ranging from 100 mm×100 mm to 1000 mm×1000 mm at an interval of 100 mm×100 mm are determined. We find that both the fractal dimensions of waviness and unevenness vary as the window size increases. No obvious stationarity threshold has been found for the three rock joint samples, indicating the surface roughness of natural rock joints should be quantified at the scale of the rock mass in the field.

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