A Laboratory Shear Cell Used for Simulation of Shear Strength and Asperity Degradation of Rough Rock Fractures

Fault reactivation is an unfavourable incident during drilling and production that may occur due to changes in situ stresses and reservoir pressure. Only a few studies, in their analyses, have included the effects of fault geometrical properties—these are important parameters controlling fault slippage and damage around it. In this paper, the significant influence of fracture morphology on the mechanical behaviour of rock fractures was investigated through experimental studies of shearing rock fractures in the lab. The experiments carried out using a fracture shear cell (FSC): the cell that was modified by adding a number of components to an existing true triaxial stress cell (TTSC) and designing a duplex high pressure cylinder that is capable of applying large normal stresses to the sample at a constant rate. A number of artificial blocks made of mortar material were subjected to shear tests using FSC under a wide range of normal stresses and at different shearing directions. The outputs of uniaxial compressive strength and fracture shear tests in the lab were used to plot the failure envelope of the fractured rock mass and discuss the failure mechanism through shearing. Accordingly, a calibrated, numerical discrete element method (DEM) was used to simulate the shear behaviour of fractures previously tested in the lab. The results of lab tests and DEM simulations will be presented and different failure mechanisms that are expected during shearing will be explained. The results show the significant influence of surface roughness on shear strength and extent of damage zone along the fracture. It was found that the shearing response of fractures depends on the magnitude of normal stress, which indicates the importance of having a good knowledge of in-situ stresses when modelling fault reactivation and damage near the fault zones. The results of lab experiments and numerical simulations were compared and good agreements were observed.

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Prediction of the Shear Failure of Opened Rock Fractures and Implications for Rock Slope Stability Evaluation

Advances in Civil Engineering ◽

10.1155/2019/6760756 ◽

2019 ◽

Vol 2019 ◽

pp. 1-7 ◽

Cited By ~ 2

Author(s):

Yingchun Li

Keyword(s):

Shear Strength ◽

Rock Slope ◽

Shear Failure ◽

Rock Slope Stability ◽

Rock Fractures ◽

Asperity Contact ◽

Direct Shear Tests ◽

Proposed Model ◽

The Stability ◽

New Criterion

Rock slope commonly fails due to the shear failure of rock fractures. Shear strength of rock fractures are reduced substantially once the fracture surfaces are mismatched or opened. We propose a new criterion to predict the shear strength of rock fractures in different opening states. The degree of interlocking representing the true asperity contact area is incorporated into the modified model of Saeb and Amadei. The effect of fracture opening on asperity dilation and degradation is separately considered. The transitional stress that is a critical parameter involved in the model is analytically determined based on energy consideration. The new model is validated with experimental results from direct shear tests on synthetic fractures with regular-shaped asperities. Good agreement between the analytical solution and the experimental data confirms the capacity of the proposed model. Therefore, the model has great potential for assessing the stability of rock slopes where fractures are often opened due to stress relief and engineering disturbances.

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A Semi-Empirical Shear Strength Model for Infilled Rock Fractures with Infills in an Unsaturated State

Geotechnical Frontiers 2017 ◽

10.1061/9780784480472.055 ◽

2017 ◽

Author(s):

Ali Khosravi ◽

Sayedmasoud Mousavi ◽

Mehdi Khosravi

Keyword(s):

Shear Strength ◽

Rock Fractures ◽

Strength Model ◽

Semi Empirical

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Characteristics of shear-induced asperity degradation of rock fractures and implications for solute retardation

International Journal of Rock Mechanics and Mining Sciences ◽

10.1016/j.ijrmms.2018.03.012 ◽

2018 ◽

Vol 105 ◽

pp. 53-61 ◽

Cited By ~ 26

Author(s):

Zhihong Zhao ◽

Huan Peng ◽

Wei Wu ◽

Yi-Feng Chen

Keyword(s):

Rock Fractures ◽

Asperity Degradation

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A split ring annular shear cell for the determination of the shear strength of a powder

Journal of Physics E Scientific Instruments ◽

10.1088/0022-3735/1/6/318 ◽

1968 ◽

Vol 1 (6) ◽

pp. 655-656 ◽

Cited By ~ 16

Author(s):

B Scarlett ◽

A C Todd

Keyword(s):

Shear Strength ◽

Split Ring ◽

Shear Cell ◽

Annular Shear Cell

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Photogrammetric Prediction of Rock Fracture Properties and Validation with Metric Shear Tests

Geosciences ◽

10.3390/geosciences11070293 ◽

2021 ◽

Vol 11 (7) ◽

pp. 293

Author(s):

Lauri Uotinen ◽

Masoud Torkan ◽

Alireza Baghbanan ◽

Enrique Caballero Hernández ◽

Mikael Rinne

Keyword(s):

Shear Strength ◽

Rock Fracture ◽

Friction Angle ◽

Jointed Rock ◽

Roughness Coefficient ◽

Rock Fractures ◽

Shear Tests ◽

Large Sample ◽

Peak Friction Angle ◽

Peak Shear Stress

An accurate understanding of jointed rock mass behavior is important in many applications ranging from deep geological disposal of nuclear waste, to deep mining, and to urban geoengineering projects. The roughness of rock fractures and the matching of the fracture surfaces are the key contributors to the shear strength of rock fractures. In this research, push shear tests with three normal stress levels of 3.6, 6.0, and 8.5 kPa were conducted on two granite samples with artificially induced well-matching tensile fractures with sizes of 500 mm × 250 mm and 1000 mm × 500 mm. The large sample reached on average a −60% weaker peak shear stress than the medium-sized sample, and a strong negative scale effect was observed in the peak shear strength. The roughness of the surfaces was measured using a profilometer and photogrammetry. The scale-corrected profilometer-based method (joint roughness coefficient, JRC) underestimates the peak friction angle for the medium-sized slabs by −27% for the medium sample and −9% for the large sample. The photogrammetry-based (Z′2) method produces an estimate with −7% (medium) and + 12% (large) errors. The photogrammetry-based Z′2 is an objective method that consistently produces usable estimates for the JRC and peak friction angle.

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