bluuebunny/crossref_metadata_2025_split huggingface dataset:
Time-resolved optical emission spectroscopy in CO2 nanosecond pulsed discharges
Authors: Ceppelli M , Salden T P W , Martini L M , Dilecce G , Tosi P 
Published: September 2021

Abstract
Nanosecond repetitively pulsed discharges at atmospheric pressure have shown comparatively high performances for CO2 reduction to CO and O2. However, mechanisms of CO2 dissociation in these transient discharges are still a matter of discussion. In the present work, we have used time-resolved optical emission spectroscopy to investigate the CO2 discharge progression from the initial breakdown event to the final post-discharge. We discover a complex temporal structure of the spectrally resolved light, which gives some insights into the underlying electron and chemical kinetics. We could estimate the electron density using the Stark broadening of O and C lines and the electron temperature with C+ and C++ lines. By adding a small amount of nitrogen, we could also monitor the time evolution of the gas temperature using the second positive system bands of N2. We conclude that the discharge evolves from a breakdown to a spark phase, the latter being characterised by a peak electron density around 1018 cm−3 and a mean electron temperature around 2 eV. The spark phase offers beneficial conditions for vibrationally enhanced dissociation, which might explain the high CO2 conversion observed in these plasma discharges.
Survey of deep sub-barrier heavy-ion fusion hindrance phenomenon for positive and negative Q-value systems using the proximity-type potential
Authors: Gharaei R. , Fuji A. , Azadegan B. 
Published: September 2021

Abstract
A systematic survey of the accurate measurements of heavy-ion fusion cross sections at extreme sub-barrier energies is performed using the coupled-channels (CC) theory that is based on the proximity formalism. This work theoretically explores the role of the surface energy coefficient and energy-dependent nucleus-nucleus proximity potential in the mechanism of the fusion hindrance of 14 typical colliding systems with negative

-values, including 11B+197Au, 12C+198Pt, 16O+208Pb, 28Si+94Mo, 48Ca+96Zr, 28Si+64Ni, 58Ni+58Ni, 60Ni+89Y, 12C+204Pb, 36S+64Ni, 36S+90Zr, 40Ca+90Zr, 40Ca+40Ca, and 48Ca+48Ca, as well as five typical colliding systems with positive

-values, including 12C+30Si, 24Mg+30Si, 28Si+30Si, 36S+48Ca, and 40Ca+48Ca. It is shown that the outcomes based on the proximity potential along with the above-mentioned physical effects achieve reasonable agreement with the experimentally observed data of the fusion cross sections

, astrophysical

factors, and logarithmic derivatives

in the energy region far below the Coulomb barrier. A discussion is also presented on the performance of the present theoretical approach in reproducing the experimental fusion barrier distributions for different colliding systems.
Bubble dynamics in Liquid Hole Multipliers
Authors: Tesi A. , Segre E. , Leardini S. , Breskin A. , Kapishnikov S. , Moleri L. , Vartsky D. , Bressler S. 
Published: September 2021

Abstract
In bubble-assisted Liquid Hole Multipliers (LHM), developed for noble-liquid radiation detectors, the stability of the bubble and the electro-mechanical properties of the liquid-to-gas interface play a dominant role in the detector performance. A model is proposed to evaluate the static equilibrium configurations of a bubble sustained underneath a perforated electrode immersed in a liquid.
For the first time bubbles were optically observed in LAr; their properties were studied in contact with different material surfaces. This permitted investigating the bubble-electrodynamics via numerical simulations; it was shown that the electric field acts as an additional pressure term on the bubble meniscus.
The predictions for the liquid-to-gas interface were successfully validated using X-ray micro-CT in water and in silicone oil at STP. The proposed model and the results of this study are an important milestone towards understanding and optimizing the parameters of LHM-based noble-liquid detectors.
Considerations on failure mechanisms of rock slopes involving toppling
Authors: Alejano L R 
Published: September 2021

Abstract
Probably, the most relevant issue in stability analysis of rock slopes is the correct identification of the potentially occurring failure mechanism, which should be mechanically analyzed to assess stability, later on. Traditional rock slope stability approaches consider planar, wedge, rotational and toppling failure as potential instability mechanisms. Whereas the three first types involve sliding associated to different geometries of the unstable element or mass, toppling often involves also sliding and very complex geometries of multiple elements. In this sense, toppling should be contemplated more like a group of mechanisms than like a simple mechanism such as planar or wedge failure. Toppling could involve moreover one or many blocks. Initial studies classified toppling failure mechanisms in three groups: block, flexural and block-flexural toppling. The stability analysis of rock slopes prone to toppling involves the mechanical analysis of individual slab like blocks, which are considered to present perfect rectangular cross-section. However, the actual shape of these rock elements may not be so regular, so the influence of more realistic irregular shapes is usually not accounted for. In this article, the author will address how some geometry variations may be included in this analysis based on analytical considerations and physical models. Additionally, failure mechanisms observed in rock cuts and open pits often combine toppling with other sliding phenomena in different more or less complex manners. These combined mechanisms involving toppling will be reviewed and some case studies worked out by the author will be presented. Moreover, all along this document, considerations will be put forward regarding the nature of toppling related phenomena where small equilibrium variations may produce a release of a large mechanical energy, which can ultimately produce the destabilization of large slopes or groups of blocks. This suggests that it is wise in these cases to analyze not only the factor of safety, but also the evolution of the potential failure mechanism to understand what is happening and eventually provide sensible and reliable designs or appropriate remedial measures.
Microscopic observations and interpretations of the progressive fracture in Kuru granite under uniaxial compression
Authors: Wan W , Li C C 
Published: September 2021

Abstract
Kuru granite is strong and brittle so that it is prone to strain burst. A series of laboratory tests were carried out to investigate the fracturing process in both pre- and post-peak stages under uniaxial compression. The progressive fracturing in the cylindrical specimens was monitored by acoustic emission (AE) technique. The specimens were loaded to different levels both in pre-peak and post-peak stages. After that, the load was removed and two thin sections, one parallel and the other perpendicular to the loading direction, were prepared from each specimen. The fractures in the specimens were microscopically observed. The geometry of each fracture was quantified by its length, opening and orientation. The results show that noticeable fracture propagation occurs mainly at the stress level above 80% of the Uniaxial Compressive Strength (UCS). In general, intergranular cracks dominate in the whole loading process, but after the peak stress the density of intragranular cracks becomes comparable to the intergranular cracks. The percentage of the intergranular first rises and then drops with an increase in the damage of the material. The variation in the number of intragranular cracks is opposite. The intergranular cracks dominate in the beginning of fracture initiation and during the stage of stable fracture propagation, but the intragranular cracks begin to flourish during the stage of unstable fracture propagation. The propagation of intragranular cracks consumes more energy than intergranular cracks. The fracture propagation in the loading direction becomes dominant with an increase in the damage of the rock and finally the specimen fails in splitting. The microscopic observations reveal the fracturing pattern of the burst-prone rock, which are useful data for the study of the physics of strain burst in rock.
Effect of sloppy sample preparation on results from uniaxial compressive strength tests
Authors: Koelen K , Alber M , Duda M , Backers T 
Published: September 2021

Abstract
The requirements on sample geometry for strength tests are specified in standards and recommendations such as those provided by ASTM, ISRM and DGGT. Various circumstances may lead to deviations from these specifications, e.g., the nature of the rock material, lack of time, economic reasons, underestimation of the importance of precise preparation and inaccurate tools. We investigated the effect of sloppy sample preparation on the experimentally determined Young’s modulus and uniaxial compressive strength in conventional uniaxial compressive strength tests of two rocks, Ruhr sandstone and Solnhofen limestone. Both are known for their high uniaxial compressive strength > 100 MPa and Young’s modulus > 30 GPa. Six end face geometry categories were tested on cylindrical samples with a diameter of 30 mm and a nominal length of 65 mm: (1) two standard end faces with tolerances ± 0.01 mm and ± 0.005 mm, (2) one standard, one inclined end face with inclinations of 0.04°, 0.1°, 0.6° and 1.2°, (3) two inclined end faces with inclinations of 0.04° and 0.6° and three azimuth combinations, (4) two rough end faces, (5) two wedged end faces with wedge angles of 5° and 10°, and (6) two spherical end faces with radii of 35 mm, 40 mm, and 45 mm. At least two samples were tested for one geometry. The strength for standard end face geometries based on seven tests was 171±9 MPa for Ruhr sandstone and 232±38 MPa for Solnhofen limestone. Low tolerance standard end faces showed a slightly better reproducibility than high tolerance standard end faces. The strength of Ruhr sandstone reduced significantly by 61% from 181±20 MPa to 70±7 MPa when the inclination of one end face was increased. For the same geometries, the strength of Solnhofen limestone reduced by 71%. The full ranges of strength and Young’s modulus (excluding spherical geometries which were determined only for Ruhr sandstone) were 27 MPa to 266 MPa and 2 GPa to 48 GPa for Solnhofen limestone, and 70 MPa to 351 MPa and 3 GPa to 41 GPa for Ruhr sandstone. Our results show that low tolerance preparation increases reproducibility, and slight deviations from standard end face geometries and impurities significantly affect experimentally determined Young’s modulus and strength.
A review of the testing approaches in swelling rock conditions at three different institutions
Authors: Selen L. , Panthi K. K. 
Published: September 2021

Abstract
The swelling potential of weak rocks is crucial to assess in stability determinations of tunnels constructed for both infrastructure and hydropower. Among the institutions that are involved with extensive research on swelling rock material, the methodologies applied at three different European institutions are reviewed in this manuscript. XRD analysis and oedometer swelling tests are included as index tests at all three institutions whereby the adopted swelling test methodologies at all three institutions are grounded in the ISRM standards. Different mindsets in how to forecast the challenges related to swelling are, however, reflected in the boundary conditions of test procedures and the internal modifications on the test apparatus, the preparation procedure, and in the choice of specimen size/mass. This manuscript reviews the adopted methodologies and highlights the advantages and drawbacks on the testing approaches used. Two of the institutions rely on a general approach which is standardized, and the results are compared. It is highlighted that, both institutions have modified the ISRM standard and the methodologies represents two unique approaches. Institution 3 have a case-specific approach and no test data were available. However, the described methodology differs from the procedures at Institution 1 and 2. Important differences between the testing procedures are both discussed and exemplified by comparing the test results obtained from duplicate samples at two of the institutions.
Mineralogical control on the intact strength of schist in Central Otago, New Zealand
Authors: Ridl R N , Villenueve M C , Bell D H , Macfarlane D F 
Published: September 2021

Abstract
Schist is highly variable in terms of intact strength, mineralogical composition and structure due to the provenance of parent rock and metamorphic conditions during formation. This paper explores the mineralogical and structural control on the intact strength properties of schist. The analysis is initially based on laboratory tests (compressional and petrographic analysis) carried out on quartz-mica schist specimens taken from Central Otago in New Zealand, and is subsequently compared to international experimental studies on schist. The results show that the foliated fabric produces directionally dependent strength anisotropy which shifts with compressional confinement exceeding 10 MPa. Furthermore, the significant variability of intact strength data of up to 48 MPa for the same loading orientation can be constrained if the mineralogical composition and degree of mineral segregation are considered. Review of the petrography of the schist shows that the relative melanocratic (mica, biotite) and leucocratic (quartz, feldspar, calcite, epidote) content of the schist strongly controls its strength due to failure mechanisms associated with the crystal lattice structure. The study results highlight the importance of detailed mineralogical estimates and descriptions of mineralogical segregation during mapping and borehole profiling.
Hydromechanical rock mass characterization using discrete fracture network models – a case study based on terrestrial laser scanning and rock mechanical testing
Authors: Gottron D , Henk A 
Published: September 2021

Abstract
Understanding the anisotropic hydraulic and mechanical properties of fractured rock masses is of great importance for a safe and optimal utilisation of the subsurface. Two sandstone quarries are utilized to obtain fracture network characteristics by Terrestrial Laser Scanning (TLS) producing 3d point cloud data. Semiautomatic analysis of the point clouds provides the probability density functions for each of the fracture parameters used as stochastic input for a Discrete Fracture Network (DFN) model. Rock mechanical laboratory tests are carried out to determine the mechanical properties of the intact rock and fractures. These parameters are then combined in the DFN model to calculate spatially variable tensors for permeability, Young’s modulus and Poisson’s ratio. Thereby, the spatial resolution of the tensor description is adapted to the grid size which can be used in further hydromechanical models. The approach allows to populate these models with more realistic parameters which incorporate also the effect of fractures on the rock mass behaviour. Obtained results are subsequently compared with conventional engineering rock mass classifications. The applied workflow allows for upscaling of rock properties determined in the laboratory to the anisotropic rock mass properties required for further hydromechanical modelling on larger scales, e.g., the reservoir scale.
Classification of natural and engineered rock slopes using UAV photogrammetry for assessing stability
Authors: Bar N , Borgatti L , Donati D , Francioni M , Salvini R , Ghirotti M 
Published: September 2021

Abstract
Ground failure on natural and engineered rock slopes is a geological hazard with potentially fatal consequences to the public or personnel in the mining industry. Aerial reconnaissance with the use of unmanned aerial vehicles (UAV) is rapidly becoming standard practice for geotechnical and engineering geological site investigations, enabling faster and safer data collection on slopes, which are often difficult to access on foot. Data obtained from aerial reconnaissance alongside conventional field investigations assist in the development of an engineering geological model that can form the basis of various stability analyses including kinematic, limit equilibrium and finite element analyses, and even rock fall simulations. This paper presents two case studies in which remote reconnaissance is used as an initial method of site investigation to classify natural and engineered rock slopes. The case studies from San Leo in Italy and an open pit mine in the Caribbean are used to demonstrate the effectiveness of these techniques for developing a preliminary engineering geological model from which stability analyses can be derived to predict future ground behaviour to assist in managing risks associated with the geological hazard.
Assessment of kinematic rock slope failures in Mudurnu Valley, Turkey
Authors: Arslan Kelam A , Akgun H , Bobet A , Kockar MK 
Published: September 2021

Abstract
Slope instabilities are one of the most frequent natural hazards capable of causing severe failures both at regional and large scales. Mudurnu, which is settled on a steep valley, is affected by regional rock slope instabilities. These instabilities constitute a hazard and create an important risk to the community since they threaten human lives, settlement areas, and historically-important structures. In order to minimize the hazard and risk associated with slope instabilities, rock masses along the valley were characterized and the potential failure mechanisms were defined. The west side of the valley, which is the focus of the research, is characterized by Cretaceous pelagic discontinuous limestone, and is prone to complex failures. The aim of the study is to characterize the rock mass along the valley, divide the area into geomechanically-uniform sectors, define possible modes of failure (kinematics) and ultimately quantify the potential failure (kinetics) and the associated risk. For the study, in addition to the field work and scan-line survey measurements, an Unmanned Aerial Vehicle (UAV) was utilized to collect high-resolution images from problematic locations that were not accessible. Then, a point cloud of the area was generated. The images were interpreted and the resulting structural representation of the rock mass was compared with information gathered from the scan-line survey in the field. Afterwards, it was used to identify the possible modes of failure along the valley. Since seismic activity in the area is significant due to the proximity of the North Anatolian Fault Zone (NAFZ), which is the most active fault system in Turkey, dynamic loading was also considered for the stability analyses.
3D Numerical Analysis for Rock Support Design of an Underground Powerhouse Cavern in Complex Geological Conditions
Authors: Yildiz E , Thermann K , Kamuf I 
Published: September 2021

Abstract
A new underground powerhouse that combines a run-of river scheme with a pumped storage scheme is planned in course of the Renewal of Forbach HPP in Germany. The powerhouse cavern is designed to have a maximum span and height of 18.9 and 42 m, and a total length of 123 m. The rock mass conditions were found favourable in general. However, comprehensive investigations revealed weakness planes crossing the cavern. The support system was determined by joint evaluation of empirical methods, wedge analysis and the 2-D finite element analyses. Due to the complicated geometry of the cavern and the orientation of the weakness planes, the effect of weakness zones on the stability and deformations could not be evaluated by only 2-D analyses. Implementing an additional 3-D analysis and comparison of the results with the common 2-D approach allowed a more realistic assessment of the rock behaviour, especially under the existence of the weakness zones through the cavern. A very detailed 3-D finite element model for the whole cavern is still not practical, so a relatively larger mesh was adopted. Nevertheless, a reduced model for a limited part of the cavern was also analysed by using a finer mesh. Obtained results were similar indicating the suitability of the adopted numerical models for the rock support assessment. The deformations and the size of the plastic zones were identified as significantly larger for weakness zones passing through the cavern. For these intersection areas additional rock support measures including pre-stressed anchors were therefore planned.
A simple tool for forecasting the mechanical response of anchored wire mesh panels
Authors: Pol Antonio , Gabrieli Fabio , Bost Marion 
Published: September 2021

Abstract
Anchored wire meshes are applied worldwide as protective structures against rockfall. The mechanical performance of a wire mesh is evaluated through laboratory tests, but these are generally not representative of the field conditions. This paper presents a simple tool to predict the force-displacement response of an anchored mesh panel to an out-of-plane load, extending the experimental standard punch test characteristic values (ISO 17745, ISO 17746, UNI 11437) to field conditions. Discrete element simulations are used to provide analytical relations that account for the effect of the different problem’s variables on the ultimate resistance and maximum deflection of a mesh panel. The numerical results are subsequently used to define a master curve permitting the force-displacement response of a generic anchored mesh panel to be forecasted. Finally, the master curve is validated against ex-post simulations, and practical implications are discussed.
A consistent framework for coupling modern reservoir flow simulator with mechanics
Authors: Ferrari A. , Pizzolato A. , Petroselli S. , Monaco S. , Ottaviani D. 
Published: September 2021

Abstract
This work presents a numerical framework, for the analysis of coupled fluid and geomechanical processes related to subsurface operations, built upon ABAQUS of SIMULIA, an industrial-standard software for mechanical analysis, and Echelon, a GPU-based reservoir simulator. By using porosity updates, the proposed framework can address both the impact of pore pressure changes on rock compaction as well as the the feedback of skeleton deformations on multiphase flow. Our solution is validated by means of various test cases. The results agree with analytical and reference solutions, showing that the proposed implementation of the iterative algorithm correctly accounts for strong coupling between mechanics and flow in porous media.