scholarly journals Brief communication: The influence of mica-rich rocks on the shear strength of ice-filled discontinuities

2020 ◽  
Vol 14 (6) ◽  
pp. 1849-1855
Author(s):  
Philipp Mamot ◽  
Samuel Weber ◽  
Maximilian Lanz ◽  
Michael Krautblatter
Keyword(s):  
Shear Strength ◽  
Failure Criterion ◽  
Rock Slopes ◽  
Surface Charges ◽  
Permafrost Rock ◽  
Rock Types ◽  
Negative Surface ◽  
The Stability ◽  
Stress Dependent ◽  
Dependent Failure

Abstract. A temperature- and stress-dependent failure criterion for ice-filled rock (limestone) joints was proposed in 2018 as an essential tool to assess and model the stability of degrading permafrost rock slopes. To test the applicability to other rock types, we conducted laboratory tests with mica schist and gneiss, which provide the maximum expected deviation of lithological effects on the shear strength due to strong negative surface charges affecting the rock–ice interface. Retesting 120 samples at temperatures from −10 to −0.5 ∘C and normal stress of 100 to 400 kPa, we show that even for controversial rocks the failure criterion stays unaltered, suggesting that the failure criterion is transferable to mostly all rock types.

scholarly journals Brief communication: The influence of mica-rich rocks on the shearstrength of ice-filled discontinuities

2020 ◽  
Author(s):  
Philipp Mamot ◽  
Samuel Weber ◽  
Maximilian Lanz ◽  
Michael Krautblatter
Keyword(s):  
Failure Criterion ◽  
Rock Slopes ◽  
Mica Schist ◽  
Surface Charges ◽  
Permafrost Rock ◽  
Rock Types ◽  
Negative Surface ◽  
The Stability ◽  
Stress Dependent ◽  
Dependent Failure

Abstract. A temperature- and stress-dependent failure criterion for ice-filled rock (limestone) joints was proposed in 2018 as an essential tool to assess and model the stability of degrading permafrost rock slopes. To test the applicability to other rocks, we now conducted experiments with mica schist/gneiss which provide the maximum expected deviation of lithological effects on the shear strength due to strong negative surface charges affecting the rock-ice interface. Retesting 120 samples from −10 to −0.5 °C and 100 to 400 kPa, we show that even for controversial rocks the failure criterion stays unaltered, suggesting that the failure criterion is transferable to mostly all rock types.

scholarly journals Analysis of the shear failure of surface methane capture boreholes for improving the drainage period efficiency: A lithological perspective

2019 ◽  
Vol 38 (1) ◽  
pp. 92-110
Author(s):  
Hongjie Xu ◽  
Zezhong Fang ◽  
Shuxun Sang ◽  
Huihu Liu ◽  
Hai Ding ◽  
...  
Keyword(s):  
Shear Strength ◽  
Shear Failure ◽  
Borehole Stability ◽  
Protective Measures ◽  
Direct Shear Tests ◽  
Rock Types ◽  
Lower Shear ◽  
The Stability ◽  
Rock Specimens ◽  
High Quartz

The shear failure of surface methane capture boreholes (SMCBs) is the main reason for the life cycle shortening of surface methane capture boreholes but lacks a comprehensive lithological analysis. To improve the surface methane capture borehole stability and drainage period efficiency, it is of great importance to investigate the influence of lithology on the shear failure of surface methane capture boreholes. The results of direct shear tests and geological investigations show that the shear displacement increases as the grain size decreases. A jump in mechanical properties occurs at the lithological boundaries and is mainly controlled by the composition of the rock specimens. The change in cohesion is the main possible reason for the step change of the shear strength. High quartz and low clay contents may effectively improve the shear strength and failure resistance of rock. Boreholes may potentially experience preferential casing failure in the section of the weaker mudstone and siltstone due to larger shear displacements and lower shear strengths of those rock types. Protective measures at these sections may improve the stability of the borehole casing. The detection results at the close of the borehole verify the prediction.

Stress- and temperature dependent application of joint-constitutive-models for rock-ice mechanical systems and its implementation in a comprehensive distinct element code

2020 ◽  
Author(s):  
Regina Pläsken ◽  
Groß Julian ◽  
Krautblatter Michael ◽  
Mamot Philipp
Keyword(s):  
Distinct Element ◽  
Mechanical Systems ◽  
Failure Criteria ◽  
Rock Joints ◽  
Numerical Representation ◽  
Rock Slopes ◽  
Temperature Dependent ◽  
Distinct Element Code ◽  
Stress Dependent ◽  
Dependent Failure

<p>Rock mechanics and its numerical representation alone are challenging tasks – if you add ice to that equation, it becomes an even more complex thing to do. Nevertheless, aiming for a better understanding of rock slopes in permafrost conditions and their mechanical behaviour depending on the scale and mechanisms of interest, integrating rock and joint characteristics, also including ice can become relevant. Krautblatter et al. (2013) suggests a rock-ice mechanical model, that describes the dominating effects for the stability of high-alpine rock slopes in permafrost conditions. This study aims to select ice filled rock joints as one of the relevant effects of Krautblatter et al. (2013) and combines it with findings of the laboratory test and derived temperature dependent failure criteria of Mamot et al. (2018). We present data and strategies for implementing temperature-dependent failure criteria for ice-filled rock interfaces into numerical distinct element code and their calibration by a comparison with preceding laboratory tests. Additionally, methods for temperature transfer within the model are suggested as well as for integrating stress-dependent application of different failure criteria in the numerical formulation. Here we show a benchmark joint-constitutive-model for rock-ice mechanical systems and its implementation in a comprehensive distinct element code.</p>

Slope Stability Analysis under the Condition of Seepage

2012 ◽  
Vol 204-208 ◽  
pp. 241-245
Author(s):  
Yang Jin
Keyword(s):  
Finite Element Method ◽  
Shear Strength ◽  
Slope Stability ◽  
Negative Impact ◽  
Strength Reduction ◽  
Soil Slope ◽  
Failure State ◽  
Calculation Results ◽  
The Stability ◽  
Shear Strength Reduction

The stability of soil slope under seepage is calculated and analyzed by using finite element method based on the technique of shear strength reduction. When the condition of seepage or not is considered respectively, the critical failure state of slopes and corresponding safety coefficients can be determined by the numerical analysis and calculation. Besides, through analyzing and comparing the calculation results, it shows that seepage has a negative impact on slope stability.

scholarly journals Experimental Study on the Softening Characteristics of Sandstone and Mudstone in Relation to Moisture Content

2017 ◽  
Vol 2017 ◽  
pp. 1-14 ◽  
Author(s):  
Gui-chen Li ◽  
Chong-chong Qi ◽  
Yuan-tian Sun ◽  
Xiao-lin Tang ◽  
Bao-quan Hou
Keyword(s):  
Moisture Content ◽  
Vertical Displacement ◽  
Surface Porosity ◽  
Shear Tests ◽  
Moisture Contents ◽  
Dynamic Finite Element ◽  
Rock Types ◽  
Underground Roadway ◽  
The Stability ◽  
Kinetics Of

The kinetics of fluid-solid coupling during immersion is an important topic of investigation in rock engineering. Two rock types, sandstone and mudstone, are selected in this work to study the correlation between the softening characteristics of the rocks and moisture content. This is achieved through detailed studies using scanning electron microscopy, shear tests, and evaluation of rock index properties during exposure to different moisture contents. An underground roadway excavation is simulated by dynamic finite element modeling to analyze the effect of moisture content on the stability of the roadway. The results show that moisture content has a significant effect on shear properties reduction of both sandstone and mudstone, which must thus be considered in mining or excavation processes. Specifically, it is found that the number, area, and diameter of micropores, as well as surface porosity, increase with increasing moisture content. Additionally, stress concentration is negatively correlated with moisture content, while the influenced area and vertical displacement are positively correlated with moisture content. These findings may provide useful input for the design of underground roadways.

scholarly journals Perception on aggregation induced multicolor emission and emission centers in carbon nanodots using successive dilution, anion exchange chromatography, and multi-way statistics

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Mohsen Kompany-Zareh ◽  
Saeed Bagheri
Keyword(s):  
Anion Exchange ◽  
Quantum Confinement Effect ◽  
Anion Exchange Chromatography ◽  
Exchange Chromatography ◽  
Carbon Nanodots ◽  
Surface Charges ◽  
Negative Surface ◽  
Amine Groups ◽  
Optical Behavior ◽  
Optical Structure

AbstractExploration in the way of understanding the optical behavior and structure of carbon nanodots has been increased due to their vast application. Their emission dependency on excitation wavelengths is the more prevalent and controversial subject. In this report we considered the optical structure of hydrothermally synthesized carbon nanodots using citric acid and 2,3-diaminopyridine as precursors. The presence of different emission centers experimented through anion exchange chromatography which resulted in fractions with more unique optical structures. The quantum confinement effect and energy exchange between different types of carbon nanodots, due to aggregation in higher concentration levels, was studied applying a stepwise dilution experiment. Analysis of the experimental data was done through the parallel factor analysis and the trajectory pattern recognition which resolved more about optical interactions and the presence of different emission centers in different particles. Results from infrared spectroscopy confirmed the dominating density of carboxyl functional groups on the nanodots with negative surface charges and higher influence of amine groups on dots with positive surface charges.

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.

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