scholarly journals Research on Shear Behavior and Crack Evolution of Symmetrical Discontinuous Rock Joints Based on FEM-CZM

Symmetry ◽  
2020 ◽  
Vol 12 (8) ◽  
pp. 1314
Author(s):  
Xianlong Wu ◽  
Gang Wang ◽  
Genxiao Li ◽  
Wei Han ◽  
Shangqu Sun ◽  
...  
Keyword(s):  
Joint Distribution ◽  
Shear Resistance ◽  
Rock Joints ◽  
Cohesive Elements ◽  
Crack Evolution ◽  
Shear Process ◽  
Size Standard ◽  
Discontinuous Joints ◽  
Discontinuous Rock ◽  
Elastic Stage

The discontinuous joints are an essential type of natural joints. The normal force, joint persistency, and distribution exert great influences on the shear resistance of the rock joints. By simulating the uniaxial compression experiment and Brazilian test, the material parameters and the basic size standard for meshing were determined. The symmetrical discontinuous joint distribution of three types were established, the cohesive elements were inserted between the solid elements, and the numerical simulation of the shear test was conducted. The effects of joint distribution, joint continuity, and normal stress on the shear resistance of joint rock were investigated, and the law of crack evolution was analyzed. The results showed that the shear process of discontinuous joints can be divided into four stages: elastic stage, strengthening stage, plastic stage, and residual stress stage. For the scattered joint distribution, the rock bridge can provide more reinforcement for the joints, which enhances the shear resistance of the joints, the stress concentration point at the end of the joint is easy to accumulate more fracture energy, which induces the initiation of the cracks, and under the influence of unbalanced torque, the both-sided joint distribution is more likely to produce tension damage.

scholarly journals A temperature- and stress-controlled failure criterion for ice-filled permafrost rock joints

2018 ◽  
Vol 12 (10) ◽  
pp. 3333-3353 ◽  
Author(s):  
Philipp Mamot ◽  
Samuel Weber ◽  
Tanja Schröder ◽  
Michael Krautblatter
Keyword(s):  
Normal Stress ◽  
Failure Criterion ◽  
Slope Failure ◽  
Rock Slope ◽  
Shear Resistance ◽  
Stress Conditions ◽  
Rock Joints ◽  
Normal Stresses ◽  
Permafrost Rock ◽  
Limestone Sample

Abstract. Instability and failure of high mountain rock slopes have significantly increased since the 1990s coincident with climatic warming and are expected to rise further. Most of the observed failures in permafrost-affected rock walls are likely triggered by the mechanical destabilisation of warming bedrock permafrost including ice-filled joints. The failure of ice-filled rock joints has only been observed in a small number of experiments, often using concrete as a rock analogue. Here, we present a systematic study of the brittle shear failure of ice and rock–ice interfaces, simulating the accelerating phase of rock slope failure. For this, we performed 141 shearing experiments with rock–ice–rock “sandwich”' samples at constant strain rates (10−3 s−1) provoking ice fracturing, under normal stress conditions ranging from 100 to 800 kPa, representing 4–30 m of rock overburden, and at temperatures from −10 to −0.5 ∘C, typical for recent observed rock slope failures in alpine permafrost. To create close to natural but reproducible conditions, limestone sample surfaces were ground to international rock mechanical standard roughness. Acoustic emission (AE) was successfully applied to describe the fracturing behaviour, anticipating rock–ice failure as all failures are predated by an AE hit increase with peaks immediately prior to failure. We demonstrate that both the warming and unloading (i.e. reduced overburden) of ice-filled rock joints lead to a significant drop in shear resistance. With a temperature increase from −10 to −0.5 ∘C, the shear stress at failure reduces by 64 %–78 % for normal stresses of 100–400 kPa. At a given temperature, the shear resistance of rock–ice interfaces decreases with decreasing normal stress. This can lead to a self-enforced rock slope failure propagation: as soon as a first slab has detached, further slabs become unstable through progressive thermal propagation and possibly even faster by unloading. Here, we introduce a new Mohr–Coulomb failure criterion for ice-filled rock joints that is valid for joint surfaces, which we assume similar for all rock types, and which applies to temperatures from −8 to −0.5 ∘C and normal stresses from 100 to 400 kPa. It contains temperature-dependent friction and cohesion, which decrease by 12 % ∘C−1 and 10 % ∘C−1 respectively due to warming and it applies to temperature and stress conditions of more than 90 % of the recently documented accelerating failure phases in permafrost rock walls.

scholarly journals Three-Dimensional Combined Finite-Discrete Element Modeling of Shear Fracture Process in Direct Shearing of Rough Concrete–Rock Joints

2020 ◽  
Vol 10 (22) ◽  
pp. 8033
Author(s):  
Gyeongjo Min ◽  
Daisuke Fukuda ◽  
Sewook Oh ◽  
Gyeonggyu Kim ◽  
Younghun Ko ◽  
...  
Keyword(s):  
Friction Coefficient ◽  
Internal Friction ◽  
Fracture Process ◽  
Three Dimensional ◽  
Friction Angle ◽  
Discrete Element ◽  
Shear Resistance ◽  
Internal Friction Angle ◽  
Rock Joints ◽  
Joint Shear

A three-dimensional combined finite-discrete element element method (FDEM), parallelized by a general-purpose graphic-processing-unit (GPGPU), was applied to identify the fracture process of rough concrete–rock joints under direct shearing. The development process of shear resistance under the complex interaction between the rough concrete–rock joint surfaces, i.e., asperity dilatation, sliding, and degradation, was numerically simulated in terms of various asperity roughness under constant normal confinement. It was found that joint roughness significantly affects the development of overall joint shear resistance. The main mechanism for the joint shear resistance was identified as asperity sliding in the case of smoother joint roughness and asperity degradation in the case of rougher joint asperity. Moreover, it was established that the bulk internal friction angle increased with asperity angle increments in the Mohr–Coulomb criterion, and these results follow Patton’s theoretical model. Finally, the friction coefficient in FDEM appears to be an important parameter for simulating the direct shear test because the friction coefficient affects the bulk shear strength as well as the bulk internal friction angle. In addition, the friction coefficient of the rock–concrete joints contributes to the variation of the internal friction angle at the smooth joint than the rough joint.

Evaluation Models for the Peak Shear-Strength and Shear-Resistance Components of Rough Rock Joints

2017 ◽  
Vol 45 (6) ◽  
pp. 20170134 ◽  
Author(s):  
X. B. Zhang ◽  
B. Yi ◽  
Q. H. Jiang ◽  
X. X. Feng ◽  
N. Chen
Keyword(s):  
Shear Strength ◽  
Shear Resistance ◽  
Rock Joints ◽  
Peak Shear Strength ◽  
Resistance Components ◽  
Evaluation Models

scholarly journals Numerical Simulation of Shear Behavior and Permeability Evolution of Rock Joints with Variable Roughness and Infilling Thickness

Geofluids ◽  
2018 ◽  
Vol 2018 ◽  
pp. 1-11 ◽  
Author(s):  
Jingyi Cheng ◽  
Hongwei Zhang ◽  
Zhijun Wan
Keyword(s):  
Rock Joint ◽  
Shear Behavior ◽  
Thickness Ratio ◽  
Rock Joints ◽  
Hyperbolic Function ◽  
Hydraulic Fractures ◽  
Permeability Evolution ◽  
Joint Roughness ◽  
Shear Process ◽  
Variable Roughness

The mechanical properties and permeability evolution of sand-infilled rock joints during the shear process is an important issue in rock engineering, such as it pertains to hydraulic fractures filled with proppant. Shear can disrupt the preexisting hydraulic and mechanical equilibrium conditions, thus affecting fluid flow. In this study, we simulate the shear behavior of rock joints with variable roughness and sand infilling thickness using the discrete element code PFC2D. Rock joint roughness is evaluated by the joint roughness coefficient (JRC), and sand infilling thickness is evaluated by a thickness ratio (i.e., ratio of infill thickness to rock height) ranging from 0.02 to 0.20. The results show that peak shear strength decreases with the thickness ratio in a relation that can be expressed by a hyperbolic function. We also measure the permeability evolution during shearing and find that the permeability of infilled rock joints increases with both the thickness ratio and JRC.

scholarly journals Unloading Effect of the Shear Resistance of Rock Joints

2021 ◽  
Author(s):  
Jianan Yang ◽  
Shuo Wang ◽  
Qiongting Wang ◽  
Wenzheng Xing ◽  
Pengxian Fan
Keyword(s):  
Normal Stress ◽  
Stress Ratio ◽  
Stress Path ◽  
Shear Resistance ◽  
Complex Stress ◽  
Rock Joints ◽  
Roughness Coefficient ◽  
Morphologic Characteristics ◽  
Path Dependent ◽  
Unloading Effect

Abstract To investigate the stress path dependent of rock joints, a comparative experimental study was conducted using cement mortar replicas of artificially split rock joints. In total, 32 replicas were casted and divided into four groups by joint roughness coefficient (JRC). The effects of morphologic characteristics, normal stress levels and stress paths on the shear strength of joints were investigated through tangential loading tests and normal unloading tests. The comparative analysis on the test results indicated that the shear resistance has a distinct unloading effect. The variation trend of shear/normal stress ratio against the normal stress and JRC of the two test conditions were identical. However, under low normal-stress condition, the stress ratio of the joints under normal unloading stress is the higher one; while under higher normal stress, the relationship becomes converse. Compared to that of the tangential loading condition, shear/normal stress ratio of the unloading stress path reduces rapidly as the increasing of normal stress, and the influence of the morphology is masked under lower normal stress. The comparative study revealed a previously unknown unloading effect on the mechanical behavior of rock joints and will aid the estimation of the rock joints’ stability in a complex stress environment.

scholarly journals Shear Resistance of Rock Joint under Nonuniform Normal Stress

2020 ◽  
Vol 2020 ◽  
pp. 1-8
Author(s):  
Hang Lin ◽  
Hu Wang ◽  
Yifan Chen ◽  
Rihong Cao ◽  
Yixian Wang ◽  
...  
Keyword(s):  
Shear Strength ◽  
Stress Distribution ◽  
Normal Stress ◽  
Rock Joint ◽  
Distribution Patterns ◽  
Shear Resistance ◽  
Nonuniform Distribution ◽  
Rock Joints ◽  
Linear Superposition ◽  
Normal Stress Distribution

Many factors influence the shear resistance of rock joints. Among them, the above overburden load is the most important factor. The uneven thickness of the overburden causes the joints to be subjected to the nonuniform distribution load. While the peak shear strength shows nonlinear relationship with normal stress, linear superposition cannot be used to calculate the overall shear resistance of joint under nonuniform normal stress distribution. In this paper, the nonlinear shear strength model, JRC-JCS model, is applied to study the overall shear resistance of the joint under four nonuniform distribution patterns of normal stress. The results show that when the normal stress is distributed in a nonuniform way, the shear resistance provided by rock joint as a whole decreases with the increase of the normal stress distribution interval. Given the nonuniform distribution of normal stress along the joint, the shear resistance obtained by the Mohr-Coulomb linear model is overestimated. In order to give full play to the overall shear performance of the joint, the shear strength at different positions on the joint should be as close as possible. Then, the shear strength of joint parts can enter peak state condition simultaneously, at which time the shear strength is fully exerted.

scholarly journals A temperature- and stress-controlled failure criterion for ice-filled permafrost rock joints

2018 ◽  
Author(s):  
Philipp Mamot ◽  
Samuel Weber ◽  
Tanja Schröder ◽  
Michael Krautblatter
Keyword(s):  
Failure Criterion ◽  
Slope Failure ◽  
Rock Slope ◽  
Shear Failure ◽  
Shear Resistance ◽  
Stress Conditions ◽  
Rock Joints ◽  
Normal Stresses ◽  
Permafrost Rock ◽  
Limestone Sample

Abstract. Instability and failure of permafrost-affected rock slopes have significantly increased coincident to warming in the last decades. Most of the observed failures in permafrost-affected rock walls are likely triggered by the mechanical destabilisation of warming bedrock permafrost including effects in ice-filled joints. The failure of ice-filled rock joints has only been observed in a small number of experiments, often using concrete as a rock analogue. Here, we present a systematic study of the brittle shear failure of ice and rock-ice interfaces, simulating the accelerating phase of rock slope failure. For this, we performed 141 shear experiments with rock-ice-rock sandwich samples at constant strain rates provoking ice fracturing (10−3 s−1), under relevant stress conditions ranging from 100 to 800 kPa, i.e. 4–30 m rock overburden, and at temperatures from −10 to −0.5 °C, typical for recent rock slope failures in alpine permafrost. To create close to natural but reproducible conditions, limestone sample surfaces were ground to international rock mechanical standard roughness. Acoustic emission (AE) was successfully applied to describe the fracturing behaviour, anticipating rock-ice failure as all failures are predated by an AE hit increase with peaks immediately prior to failure. We demonstrate that both, the warming and unloading (i.e. reduced overburden) of ice-filled rock joints lead to a significant drop in shear resistance. With a temperature increase from −10 °C to −0.5 °C, the shear stress at failure reduces by 64–78 % for normal stresses of 100–400 kPa. At a given temperature, the shear resistance of rock-ice interfaces decreases with decreasing normal stress. This can lead to a self-enforced rock slope failure propagation: as soon as a first slab has detached, further slabs become unstable through progressive thermal propagation and possibly even faster by unloading. Here, we introduce a new Mohr-Coulomb failure criterion for ice-filled rock joints that is valid for joint surfaces which we assume similar for all rock types, and which applies to temperatures from −8 to −0.5 °C and normal stresses from 100 to 400 kPa. It contains a temperature-dependent friction and cohesion which decrease by 12 %/°C and 10 %/°C respectively due to warming and it applies to temperature and stress conditions of more than 90 % of the recently documented accelerating failure phases in permafrost rock walls.

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