Bridging the Gap Between Seismic and Sub-seismic Mirror-Slip Surfaces in Carbonate Fault Gouge

2020 ◽  
Author(s):  
Milo Trainor Moss ◽  
Berend A. Verberne ◽  
Miki Takahashi ◽  
Andre R. Niemeijer
Keyword(s):  
Normal Stress ◽  
Fault Slip ◽  
Shear Displacement ◽  
Displacement Rate ◽  
Structural Development ◽  
Normal Stresses ◽  
Seismic Slip ◽  
Slip Surfaces ◽  
Wide Range ◽  
Triaxial Cell

<p>Specularly light reflective fault plane interfaces known as Mirror-Slip Surfaces (MSS’s) are common in seismically active fault zones around the world and thus their role in controlling fault strength and stability is of great interest. MSS’s have been experimentally produced in simulated carbonate faults at relatively high (10<sup>-1</sup>-10<sup>0</sup> m/s) and low (10<sup>-7</sup>-10<sup>-5</sup> m/s) sliding velocities (resp. HV and LV). However, their role in controlling fault mechanical properties at sub-seismic vs seismic fault-slip velocities remains enigmatic. With the aim to unravel the structural development of MSS’s with increasing shear displacement (rate) and effective normal stress, we conducted HV and LV shear deformation experiments on simulated faults composed of granular calcite. We employed a ring shear set-up in a HV rotary shear apparatus as well as a saw-cut assembly mounted in a triaxial cell, which enabled fault-slip tests under a wide range of slip velocities (v = 10<sup>-7</sup> - 10<sup>-</sup><sup>1</sup> m/s) and effective normal stresses (σ<sub>n</sub> ≈ 10 – 170 MPa). All experiments were carried out under room-dry conditions, at room temperature. Post-mortem microstructure analysis of recovered fragments was carried out through visual inspection, incident light and scanning electron microscopy, as well as using Raman spectroscopy.</p><p>MSSs develop at sub-seismic slip velocities (v = 10<sup>-7</sup> m/s) initially as visibly striated patches after 0.0062 m (σ<sub>n</sub> ≈ 10 MPa), 0.004 m (σ<sub>n</sub> ≈ 50 MPa) and 0.0026 m (σ<sub>n</sub> ≈ 170 MPa) of shear displacement. The area covered by MSSs systematically increases with displacement to form continuous coatings after 0.042 (σ<sub>n</sub> ≈ 10 MPa), 0.0062 m (σ<sub>n</sub> ≈ 50 MPa) and 0.0036 m (σ<sub>n</sub> ≈ 10 MPa).  As displacement rate is increased (10<sup>-5</sup> – 10<sup>-4</sup> m/s) MSSs are no longer observed however continuous MSSs are visible again at seismic slip velocities (>10<sup>-1</sup> m/s). Our microstructural analysis revealed that MSSs are layers of (nano)crystalline calcite some of which contain elongated nanofibrous structures. In addition, discrete, 3 - 20 micron-sized patches of amorphous carbon are produced at seismic slip velocities, and at sub-seismic velocities under high normal stresses (σ<sub>n</sub> > 160 MPa). We could not however identify any microstructural characteristics that are diagnostics of MSSs produced at certain slip rates or normal stress.</p><p>Our interpretation is that MSSs form by sintering of nm-sized particles within ultrafine-grained shear bands. With increasing shear displacement, MSS patches connect into continuous veneers. The formation of (continuous) MSSs at low as well as high sliding velocities in our experiments implies that natural MSSs are unreliable indicators for palaeoseismicity.</p>

scholarly journals Numerical Shear Tests on the Scale Effect of Rock Joints under CNL and CND Conditions

2020 ◽  
Vol 2020 ◽  
pp. 1-15 ◽  
Author(s):  
Xige Liu ◽  
Wancheng Zhu ◽  
Lankun Li
Keyword(s):  
Shear Strength ◽  
Normal Stress ◽  
Scale Effect ◽  
Shear Behavior ◽  
Shear Displacement ◽  
Rock Joints ◽  
Peak Shear Strength ◽  
Normal Stresses ◽  
Shear Tests ◽  
Joint Length

The scale effect of rock joint shear behavior is an important subject in the field of rock mechanics. There is yet a lack of consensus regarding whether the shear strength of rock joints increases, decreases, or remains unchanged as the joint size increases. To explore this issue, a series of repeated and enlarged numerical joint models were established in this study using the particle flow code (PFC2D). The microparameters were calibrated by uniaxial compression tests and shear tests on the concrete material under the constant normal loading (CNL) condition. Three different normal stresses were adopted in numerical shear tests with joint specimen lengths ranging from 100 mm to 800 mm. In addition to the commonly used CNL, the constant normal displacement (CND) condition was established for the purposes of this study; the CND can be considered an extreme case of the constant normal stiffness (CNS) condition. The shear stress-shear displacement curves changed from brittle failure to ductile failure alongside a gradual decrease in peak shear strength as joint length increased. That is, an overall negative scale effect was observed. Positive scale effect or no scale effect is also possible within a limited joint length range. A positive correlation was also observed between the peak shear displacement and joint length, and a negative correlation between shear stiffness and joint length. These above statements are applicable to both repeated and enlarged joints under either CNL or CND conditions. When the normal stress is sufficiently high and shear dilatancy displacement is very small, the shear behavior of rock joints under CNL and CND conditions seems to be consistent. However, for shear tests under low initial normal stress, the peak shear strength achieved under the CND condition is much higher than that under the CNL condition, as the normal stresses of enlarged joints increase to greater extent than the repeated ones during shearing.

Friction on PDC Cutters at High Normal Stress

2002 ◽  
Vol 124 (3) ◽  
pp. 146-153 ◽  
Author(s):  
John R. Smith ◽  
Jeffrey B. Lund ◽  
Robert K. Galloway
Keyword(s):  
Normal Stress ◽  
Mineral Oil ◽  
Normal Stresses ◽  
Friction Coefficients ◽  
Wide Range ◽  
Pdc Bit ◽  
The Face ◽  
Frictional Forces ◽  
High Normal Stress ◽  
The Impact

The impact of frictional forces on the overall forces when drilling with a PDC bit has previously been implied by models and by single cutter and bit tests. This report describes new experiments to measure friction between three different bit surface materials and two different rocks over a wide range of normal stresses in up to four different fluids. Polished PDC cutters are shown to have lower frictional forces on the face of the cutter than standard cutters in both water and mineral oil. The measured friction coefficients were generally higher than reported in previous studies.

Normal stresses in concentrated non-Brownian suspensions

2013 ◽  
Vol 715 ◽  
pp. 239-272 ◽  
Author(s):  
T. Dbouk ◽  
L. Lobry ◽  
E. Lemaire
Keyword(s):  
Normal Stress ◽  
Pore Pressure ◽  
Volume Fraction ◽  
Hard Spheres ◽  
Particle Volume Fraction ◽  
Radial Profile ◽  
Normal Stresses ◽  
Particle Volume ◽  
Wide Range ◽  
Normal Stress Differences

AbstractWe present an experimental approach used to measure both normal stress differences and the particle phase contribution to the normal stresses in suspensions of non-Brownian hard spheres. The methodology consists of measuring the radial profile of the normal stress along the velocity gradient direction in a torsional flow between two parallel discs. The values of the first and the second normal stress differences, ${N}_{1} $ and ${N}_{2} $, are deduced from the measurement of the slope and of the origin ordinate. The measurements are carried out for a wide range of particle volume fractions (between 0.2 and 0.5). As expected, ${N}_{2} $ is measured to be negative but ${N}_{1} $ is found to be positive. We discuss the validity of the method and present numerous tests that have been carried out in order to validate our results. The experimental setup also allows the pore pressure to be measured. Then, subtracting the pore pressure from the total stress, ${\mbrm{\Sigma} }_{\mathbf{22} } $, the contribution of the particles to the normal stress ${ \mbrm{\Sigma} }_{\mathbf{22} }^{\mathbi{p}} $ is obtained. Most of our results compare well with the different experimental and numerical data present in the literature. In particular, our results show that the magnitude of the particle stress tensor component and their dependence on the particle volume fraction used in the suspension model balance proposed by Morris & Boulay (J. Rheol., vol. 43, 1999, p. 1213) are suitable.

scholarly journals Rock Stress Measurements for Unlined Pressure Tunnels: A True Triaxial Laboratory Experiment to Investigate the Ability of a Simplified Hydraulic Jacking Test to Assess Fracture Normal Stress

2021 ◽  
Author(s):  
Henki Ødegaard ◽  
Bjørn Nilsen
Keyword(s):  
Normal Stress ◽  
Test Method ◽  
Sudden Increase ◽  
Normal Stresses ◽  
True Triaxial ◽  
Step Rate ◽  
Stress Measurements ◽  
Fracture Closure ◽  
Rate Test ◽  
Hydraulic Jacking

AbstractTo avoid hydraulic failure of unlined pressure tunnels, knowledge of minimum principal stress is needed. Such knowledge is only obtainable from in situ measurements, which are often time-consuming and relatively costly, effectively limiting the number of measurements typically performed. In an effort to enable more stress measurements, the authors propose a simplified and cost-effective stress measuring method; the Rapid Step-Rate Test (RSRT), which is based on existing hydraulic testing methods. To investigate the ability of this test to measure fracture normal stresses in field-like conditions, a true triaxial laboratory test rig has been developed. Hydraulic jacking experiments performed on four granite specimens, each containing a fracture, have been performed. Interpretation of pressure-, flow- and acoustic emission (AE) data has been used to interpret fracture behaviour and to assess fracture normal stresses. Our experimental data suggest that the proposed test method, to a satisfactory degree of reliability, can measure the magnitude of fracture normal stress. In addition, a clear correlation has been found between fracture closure and sudden increase in AE rate, suggesting that AE monitoring during testing can serve as a useful addition to the test. The rapid step-rate test is also considered relevant for field-scale measurements, with only minor adaptions. Our findings suggest that the RSRT can represent a way to get closer to the ideal of performing more testing along the entire length of pressure tunnel, and not only at key locations, which requires interpolation of stress data with varying degree of validity.

scholarly journals Time-Dependent Response of a Recycled C&D Material-Geotextile Interface under Direct Shear Mode

Materials ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 3070
Author(s):  
Fernanda Bessa Ferreira ◽  
Paulo M. Pereira ◽  
Castorina Silva Vieira ◽  
Maria de Lurdes Lopes
Keyword(s):  
Shear Stress ◽  
Stress Relaxation ◽  
Shear Displacement ◽  
Time Dependent ◽  
Shear Behaviour ◽  
Displacement Rate ◽  
Shear Mode ◽  
Direct Shear ◽  
Constant Displacement ◽  
Shear Box

Geosynthetic-reinforced soil structures have been used extensively in recent decades due to their significant advantages over more conventional earth retaining structures, including the cost-effectiveness, reduced construction time, and possibility of using locally-available lower quality soils and/or waste materials, such as recycled construction and demolition (C&D) wastes. The time-dependent shear behaviour at the interfaces between the geosynthetic and the backfill is an important factor affecting the overall long-term performance of such structures, and thereby should be properly understood. In this study, an innovative multistage direct shear test procedure is introduced to characterise the time-dependent response of the interface between a high-strength geotextile and a recycled C&D material. After a prescribed shear displacement is reached, the shear box is kept stationary for a specific period of time, after which the test proceeds again, at a constant displacement rate, until the peak and large-displacement shear strengths are mobilised. The shear stress-shear displacement curves from the proposed multistage tests exhibited a progressive decrease in shear stress with time (stress relaxation) during the period in which the shear box was restrained from any movement, which was more pronounced under lower normal stress values. Regardless of the prior interface shear displacement and duration of the stress relaxation stage, the peak and residual shear strength parameters of the C&D material-geotextile interface remained similar to those obtained from the conventional (benchmark) tests carried out under constant displacement rate.

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.

Residual shear strength of fine-grained soils and soil–solid interfaces at low effective normal stresses

2015 ◽  
Vol 52 (2) ◽  
pp. 198-210 ◽  
Author(s):  
Hisham T. Eid ◽  
Ruslan S. Amarasinghe ◽  
Khaled H. Rabie ◽  
Dharma Wijewickreme
Keyword(s):  
Shear Strength ◽  
Large Strain ◽  
Laboratory Research ◽  
Normal Stresses ◽  
Interface Shear ◽  
Residual Shear Strength ◽  
Fine Grained ◽  
Solid Interface ◽  
Wide Range ◽  
Shear Area

A laboratory research program was undertaken to study the large-strain shear strength characteristics of fine-grained soils under low effective normal stresses (∼3–7 kPa). Soils that cover a wide range of plasticity and composition were utilized in the program. The interface shear strength of these soils against a number of solid surfaces having different roughness was also investigated at similar low effective normal stress levels. The findings contribute to advancing the knowledge of the parameters needed for the design of pipelines placed on sea beds and the stability analysis of shallow soil slopes. A Bromhead-type torsional ring-shear apparatus was modified to suit measuring soil–soil and soil–solid interface residual shear strengths at the low effective normal stresses. In consideration of increasing the accuracy of assessment and depicting the full-scale field behavior, the interface residual shear strengths were also measured using a macroscale interface direct shear device with a plan interface shear area of ∼3.0 m2. Correlations are developed to estimate the soil–soil and soil–solid interface residual shear strengths at low effective normal stresses. The correlations are compared with soil–soil and soil–solid interface drained residual shear strengths and correlations presented in the literature.

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 STRUCTURAL DEVELOPMENT AND RESEARCH OF TECHNOLOGICAL PARAMETERS OF MACHINES FOR CENTRIFUGAL -PLANETARY VIBRATION TREATMENT

2020 ◽  
pp. 41-50
Author(s):  
Leonid Yaroshenko ◽  
Igor Kupchuk ◽  
Mykhailo Zamrii
Keyword(s):  
High Efficiency ◽  
Metal Removal ◽  
Three Dimensional ◽  
High Hardness ◽  
Working Environment ◽  
Repeated Loading ◽  
Structural Development ◽  
Technological Parameters ◽  
Advantages And Disadvantages ◽  
Wide Range

The paper analyzes current state and prospects of further development of technology and equipment for mechanization and automation of finishing and cleaning of details. It is stated that the most effective for this purpose are the methods of abrasive machining, which include bulk galvanizing, vibration, centrifugal-rotary and centrifugal-planetary processing. These methods reduce the complexity and cost of processing, which in some cases reaches 20% of the total cost of manufacturing parts. Each of these methods has a different level of efficiency, certain advantages and disadvantages, the level of versatility and scope of effective application. The processes of vibration processing are quite deeply studied, for its industrial mass-produced technological equipment, but they have certain shortcomings that limit their use for further widespread implementation. Centrifugal-rotary processing is a more productive process of three-dimensional finishing and cleaning treatment, but its scope is limited by the possibility of processing parts that are not complex, usually flat. The most productive methods of finishing and cleaning of details include centrifugal-planetary volume processing which high efficiency is caused by repeated loading of particles of working load by inertial forces that creates preconditions for the solutions of a wide range of technological problems, for example, processing of details of difficult form, small weight and the sizes from materials of high hardness or viscosity that represents a serious problem for other methods of volume processing. The constructive scheme is offered in the work and the influence of the composition of the abrasive free-granular working environment on the productivity of the machine for centrifugal-planetary processing of details is investigated. The kinetics of metal removal from the surface of machined parts using different types of abrasive working environment is analyzed. The results of comparative machining of parts in a torus vibrating machine and a machine for centrifugal-planetary machining are given. It is shown that the simultaneous use of centrifugal-planetary and vibration processing methods allows to increase the intensity of the process while ensuring high quality machining of parts of relatively complex shape. The constructive scheme of the machine which allows to implement the specified combined method of processing is offered and described.

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