Conventional and UAV-Based Aerial Surveys for Long-Term Monitoring (1954–2020) of a Highly Active Rock Glacier in Austria

Rock glaciers are creep phenomena of mountain permafrost. Speed-up has been observed on several rock glaciers in recent years and attributed to climate change. Although rare, related long-term studies are nevertheless essential to bring a climate perspective to creep velocity changes. In the present study, we focused on changes both in the surface creep velocity and volume of the Leibnitzkopf rock glacier (Hohe Tauern Range, Austria) in the period 1954–2020. We applied 3D change detection using aerial images of both conventional (12 epochs between 1954 and 2018) and unmanned aerial vehicle (UAV)-based aerial surveys (2 epochs, 2019 and 2020), and combined this with ground and air temperature data. Photogrammetric processing (structure-from-motion, multi-view stereo) of the multi-temporal dataset resulted in high-resolution digital orthophotos/DOPs (5–50 cm spatial resolution) and digital elevation models/DEMs (10–50 cm grid spacing). Georeferencing was supported by five externally triangulated images from 2018, bi-temporal aerial triangulation of the image data relying on stable ground around the rock glacier, measured ground control points (2019 and 2020), and measured camera locations (PPK-GNSS) of the UAV flight in 2020. 2D displacement vectors based on the multi-temporal DOPs and/or DEMs were computed. Accuracy analyses were conducted based on geodetic measurements (2010–2020) and airborne laser scanning data (2009). Our analyses show high multi-annual and inter-annual creep velocity variabilities with maxima between 12 (1974–1981) and 576 cm/year (2019–2020), always detected in the same area of the rock glacier where surface disintegration was first observed in 2018. Our volume change analyses of the entire landform for the period 1954–2018 do not indicate any significant changes. This suggests little permafrost ice melt and/or general low ice content of the rock glacier. Analyses of the temperature data reveal a close relationship between higher temperatures and rock glacier acceleration despite the high probability of low ice content. This suggests that hydrogeological changes play an important role in the rock glacier system. The paper concludes with a summary of technical improvements and recommendations useful for rock glacier monitoring and a general view on the kinematic state of the Leibnitzkopf rock glacier.

Creep Velocity of Non-Spherical Gravel Particles in Mountainous Regions

The movement of sediment particles is governed by the relative magnitude of acting drag and the resistance offered by the particle. The magnitude of drag force that acts on a sediment particle depends on flow parameters as well as on the surface area of the particle exposed to flow. Similarly, the resistance offered by the particle depends on its weight and the surface area of the particle in contact with the stream bed. In the case of spherical particles, orientation does not play an important role, while in the case of non-spherical particles how particle orients itself play a vital role. Therefore, in the case of non-spherical particles, which is the real situation, the movement velocity of sediment particles will depend on their orientation. Numerous studies have been conducted for spherical particles but literature is lacking information for non-spherical particles. In this study, experiments were conducted on coarse solitary non-spherical gravel particles to observe their creep velocity with their changed orientations under varying flow conditions. The experimental finding unveiled that the creep velocity of these particles not only depended on the shape and size of the particles but also on their orientation relative to the flow direction. It was observed that for a particle of a given size, the orientation of the particle which leads to maximum exposed area i.e O2 orientation resulted in the highest creep velocity. The findings of the study have been illustrated with mathematical relationships and graphical representations for various combinations of input variables.

CREEP RESISTANCE OF FERRITIC-MARTENSITIC STEEL 16Cr12MoWSiVNbB (EP-823)

Base characteristics of ferritic-martensitic heat resisting steels with 12 % of chrome are parameters of their strength and creep resistance at temperatures of 600 – 750 °С. Steel 16Cr12MoWSiVNbB (EP-823) is considered as the basic material for manufacturing environments fuel rods (TVEL) of a developed reactor with natural safety of BRESTtype. In the literature, there are data about its mechanical characteristics for tensile tests in a range of temperatures of 20 – 750 °С and the limited characteristics of rupture strength. Data on its creep velocity is absent. Laws of creep of steel EP-823 were investigated on metal of three heats with weight of 3 kg. The compression tests at air were applied for cylindrical samples of 5 ÷ 6 mmat temperatures of 600 – 760 °С and stresses of 70 – 310 MPa. The base of compression tests did not exceed 11 hours. The structure after quenching and tempering consisted of tempered martensite and 6 – 12 vol. % of delta-ferrite, the grain size was less 20 μm. It is shown, that the description of creep tests results in double logarithmic (log (σ) – log (έ)) coordinates provides the best concurrence of results of approximation and experiment, than in half-logarithmic (σ – log (έ)). The analysis of parametrical dependences on Hollomon’s PS = (T/1000)[CS – log (έ) and to Larsen-Miller’s PE = (T/1000)[СE – log (σ)] has allowed to find the equations for creep velocity for the set pressure level of 100 – 220 MPa in the form of log (έ) = –19,355 + 9,17 (T/1000) log (σ) and ultimate strength of creep under the set admissions for creep velocity of 0,01 – 1 %/hour in the form of log (σ) = 4,304 – – 0,109 (T/1000) [20 – log (έ)]. Calculations of ultimate strength of creep and creep velocity on pair models and models of Hollomon (Larsen-Miller) give close results, but the preference should be given the second ones as these models consider all three varied factors. Data of control tests under the scheme of a tensile in the same conditions are cited. It is shown, that between results of tests on compression and on tensile at definition of durability characteristics, there is the linear dependence expressed by the equation σ0.2 at compression = 1.3σ0.2 at tensile. At the analysis of creep it has been established, that creep velocity for steel of one grade (09Cr12W3NbB) and for one heat at different type of loading (tensile or compression) have similar values while creep velocities for steel of one grade (EP-823), but of different heats even at one type of loading – compression, can differ substantially.

An Empirical Constitutive Correlation for Regular Jugged Discontinuity of Rock Surfaces

This paper presents a physical investigation and mathematical analysis on mechanical behavior of the regular jugged discontinuity. In particular, we focus on the creep property of structural plane with various slope angles under different normal stress through shear creep tests of structural plane under shear stresses. According to the test results, the shear creep property of structural plane was described and the creep velocity and long-term strength of the structural plane during shear creep were also investigated. An empirical formula is finally established to evaluate shear strength of discontinuity and a modified Burger model was proposed to represent the shear deformation property during creep.

The Effect of Creep Flow on Two-Dimensional Isoflux Microchannels

Micro channel convective heat transfer and friction loss characteristics are numerically evaluated for gaseous, two-dimensional, steady state, laminar, constant wall heat flux flows. The effects of Knudsen number, accommodation coefficients, second order slip boundary conditions, creep flow, and thermal/hydrodynamic developing flow are considered. These effects are compared through the Poisuelle number and Nusselt number. Numerical values for the Poisuelle and Nusselt numbers are obtained using a continuum based three-dimensional, unsteady, compressible computational fluid dynamics algorithm that has been modified with slip boundary conditions. To verify the numerical results, analytic solutions for the hydrodynamically and thermally fully developed Poisuelle and Nusselt numbers have been derived. The fully developed analytic Poisuelle and Nusselt numbers are given as a function of Knudsen number, the first and second order velocity slip and temperature jump coefficients, the Brinkman number, and the ratio of the thermal creep velocity to the mean velocity. Excellent agreement between the numerical and analytical data is demonstrated. Second order slip terms and creep velocity are shown to have significant effects on the Poisuelle and Nusselt numbers.

Temporally-ordered CDW creep in pure and doped NbSe3

Below T=40 K, charge-density wave (CDW) transport in NbSe3 is characterized by two well-defined driving force thresholds ET and ET*. Between these thresholds the CDW moves extremely slowly with creep-like temperature and driving force dependencies. At the same time, the CDW exhibits coherent oscillations with a frequency proportional to the CDW current and having very narrow spectral widths, suggesting that the collective motion is temporally ordered. We have extended our initial work to doped crystals containing isoelectronic (Ta) and nonisoelectronic (Ti) impurities, and to crystals of different thicknesses. These experiments show that the qualitative features are extremely robust, and that the functional form of the creep velocity versus driving force and temperature is consistent across all samples for currents ranging over five orders of magnitude. The temperature dependence is consistent with processes having an energy comparable to the CDW gap, but the field and impurity dependencies are inconsistent with all predicted functional forms for creep in CDWs and related systems, and with our earlier picture of amplitude collapse at each impurity. We compare our results to measurements of creep-like behavior in other CDW and SDW systems, and discuss possible mechanisms.