Search

Rock salt-type rare-earth monopnictides (REPn) attract much attention because of their extremely large magnetoresistance and topological properties. So far, most studies have been conducted on REPn bulk single crystals. Recent theoretical studies predicted that the topological properties of REPn can be developed by forming their ultrathin film or applying epitaxial strain. However, it has been difficult to grow highly crystalline REPn thin films due to the high vapor pressure of Pn, hampering the thin film growth at high temperature. Here, we grew highly crystalline (001)-oriented LaBi thin films by solid-phase reaction of a La/Bi multilayer precursor. The LaBi thin films showed metallic conduction and nonlinear Hall resistance, indicating the coexistence of electron and hole carriers, consistent with the intrinsically semimetallic nature of LaBi. [ABSTRACT FROM AUTHOR]

Characteristics of stress‐dependent properties of rocks are commonly described by empirical laws. It is crucial to establish a universal law that connects rock properties with stress. The present study focuses on exploring the correlations among permeability, porosity, and compressibility observed in experiments. To achieve this, we propose a novel finite strain‐based dual‐component (FS‐DC) model, grounded in the finite strain theory within the framework of continuum mechanics. The FS‐DC model decomposes the original problem into the rock matrix and micro‐pores/cracks components. The deformation gradient tensor is utilized to derive the constitutive relations. One of the novelties is that the stress‐dependent variables are calculated in the current configuration, in contrast to the reference configuration used in small deformation theory. The model has only a few number of parameters, each with specific physical interpretations. It can be reduced to existing models with appropriate simplifications. Then, model performance is examined against experimental data, including permeability, porosity, compressibility, volumetric strain and specific storage. It proves that the variations of these properties are effectively described by the proposed model. Further analysis reveals the effect of pores/cracks parameters. The validity of the FS‐DC model is examined across a broad range of pressures. The results show that rock properties at high confining pressures (>$>$300 MPa) differ from those observed under relatively low pressures (<$<$200 MPa). This disparity can be attributed to inelastic behaviors of micro‐structure, wherein the rock skeleton undergoes permanent deformation and breakage. [ABSTRACT FROM AUTHOR]

Context: This investigation includes the structural and optoelectronic characteristics of both pure and Er-doped rock salt aluminium nitride (AlN). Upon introducing Er doping into the AlN host, the calculations reveal a rise in the atomic parameter. Incorporating Er into the system leads to enhancements in the static dielectric coefficient ɛ1(0), static reflectivity R(0), as well as static refractive index n(0), at zero frequency. After doping, the peaks of imaginary dielectric tensor, extinction coefficient and absorption coefficient shift towards lower energy levels. Various exchange correlation potentials are incorporated to compare the results of electronic and optical characteristics. Methods: We employed the full potential linearized augmented plane wave (FP-LAPW) approach with WIEN2k code in conjunction with the density functional theory (DFT). To explore the optoelectronic characteristics of both pure as well as doped systems, three distinct exchange correlation potentials are utilized: the Perdew-Burke-Ernzerhof Generalized Gradient Approximation (PBE-GGA), Modified Becke Johnson Generalized Gradient Approximations (mBJ + GGA) and Hubbard potential (GGA + U). [ABSTRACT FROM AUTHOR]

Estimating hydraulic properties of carbonate is challenging due to its wider range of porosity and complex pore structures. To investigate the hydraulic properties of carbonate rocks, a novel approach inspired by quantum genetic optimization in this work is proposed to extract the optimal pore network model (PNM), which is applied to simulate the hydraulic properties. The pore network variables, such as porosity, pore and throat sizes, are considered as the optimal parameters, and the capillary pressure curve, breakthrough drainage pressure and permeability are calculated based on the constructed PNM. The computing time (CPU time) and memory usage (RAM usage) for the PNM extraction using the proposed approach and classical methods are compared. Results indicate that the proposed approach shows better computing efficiency than classical methods. Excellent agreements are found between the experimental and simulation results from the proposed and classical methods. The proposed approach provides promising tools to investigate the hydraulic properties of geomaterials. [ABSTRACT FROM AUTHOR]

In petrophysics, physical rock properties are typically established through laboratory measurements of individual samples. These measurements predominantly relate to the specific sample and can be challenging to associate with the rock as a whole since the physical attributes are heavily reliant on the microstructure, which can vary significantly in different areas. Thus, the obtained values have limited applicability to the entirety of the original rock mass. To examine the dependence of petrophysical measurements based on the variable microstructure, we generate sets of random 2-D microstructure representations for a sample, taking into account macroscopic parameters such as porosity and mean grain size. For each microstructure produced, we assess the electrical conductivity and evaluate how it is dependent on the microstructure's variability. The developed workflow including microstructure modelling, finite-element simulation of electrical conductivity as well as statistical and petrophysical evaluation of the results is presented. We show that the methodology can adequately mimic the physical behaviour of real rocks, showing consistent emulation of the dependence of electrical conductivity on connected porosity according to Archie's law across different types of pore space (microfracture, intergranular and vuggy, oomoldic pore space). Furthermore, properties such as the internal surface area and its fractal dimension as well as the electrical tortuosity are accessible for the random microstructures and show reasonable behaviour. Finally, the possibilities, challenges and meshing strategies for extending the methodology to 3-D microstructures are discussed. [ABSTRACT FROM AUTHOR]

Brittleness is an important rock property that examines the mechanical behavior and failure properties of rocks in engineering applications. Although there is no standard method for measuring rock brittleness, it can be calculated indirectly as a function of rock mechanical properties based on the rock strength ratio. The aim of this study was to investigate the relationship between the Leeb hardness (HL) values and the brittleness properties of rocks using the simple statistical method. For this purpose, 18 sandstone rock samples were collected and tested in the laboratory to determine the HL and physico-mechanical properties of rocks. In addition, the brittleness properties of rocks were examined with S20 brittleness (BI8) test and five different empirical methods (BI4, BI5, BI11, BI13, and BI14) calculated from rock strength ratios. New models were proposed to predict the brittleness of the rocks, taking into account the HL. Based on the statistical analysis, the proposed models were in good agreement with those measured (for all of the data, R2: 0.76–0.77, for sandstone, R2: 0.78–0.81). [ABSTRACT FROM AUTHOR]

The excavation of rock, whether in mining, petroleum, or civil engineering projects, predominantly relies on traditional drilling techniques. Across these applications, drilling bit wear considered as a primary factor impacting the overall cost of rock excavation projects. This wear of drill bits is directly linked to the properties of the rock being drilled. In this study, an investigated relations between drilling bit wear and geomechanical properties have been investigated. To measure drill bit wear, a laboratory-scale drilling rig was employed, based on 30 selected rock units. A comprehensive laboratory testing plan was executed on these rock units, encompassing various rock characteristics such as uniaxial compressive strength (UCS), Brazilian tensile strength (BTS), Cerchar abrasivity index (CAI), equivalent quartz content (EQC), grain size of minerals (GS), and Schmidt rebound number (SRN). Nonlinear regression techniques were employed to predict bit wear based on geomechanical rock properties. Performance evaluation criteria were used to validate the regression models. The results revealed an exponential increase in bit wear values with rising UCS, BTS, CAI, EQC, GS, and SRN. The statistical analysis indicated a strong correlation between rock characteristics and drill bit wear, with CAI emerging as the most influential parameter, having a correlation coefficient of R2 = 0.954. The regression models developed in this study are primarily intended for rock engineers engaged in rock drilling projects. [ABSTRACT FROM AUTHOR]

Background: To evaluate the stability of jointed rock masses subjected to dynamic disturbance, laboratory dynamic shear test on rock joint is necessary. Developing dynamic shear test equipment for rock joint is currently a pressing issue. Objective: To address this issue, a new apparatus is developed to reproduce the shear-slip process of rock joint subjected to dynamic disturbance under various initial stress state. Methods: The disturbance load, which has a dominant frequency close to that of seismic waves, is generated by an electromagnetic-driven disturbance generator, and its amplitude and duration can be accurately controlled in a stable manner. The initial normal and shear stresses can be applied in the shear test under dynamic disturbance using servo-controlled loading unit, which facilitates the simulation of the real stress state of rock joint. Results: The shear tests under dynamic disturbance show that when an initial shear stress is applied to rock joint, an additional deformation stage of stress recovering can also trigger a slip displacement, which contributes to the destabilization of jointed rock masses. With increasing initial shear stress, the dynamic slip displacement, stress drop and post-disturbing deformation increase. The feasibility of the apparatus to conduct quasi-static direct shear tests with both the constant normal loading (CNL) and constant normal stiffness (CNS) boundaries is also verified. Conclusions: Test results demonstrate that using the new apparatus, shear-slip properties of rock joint subjected to dynamic disturbance can be tested in various initial stress states. [ABSTRACT FROM AUTHOR]

Artificial caverns in salt rock formations play an important role in the net‐zero energy transition challenge, both for covering short‐term fluctuations in energy demand and serving as safe locations for long‐term underground gas storage both for hydrogen and natural gas. Geophysical tools can serve for monitoring geomechanical changes in the salt cavern during selection and development, and during gas storage/extraction activities, but the use of common geophysical monitoring techniques has been very limited in this area. Here, we present experimental work on physical and transport properties of halite rocks within the energy storage context and assess the potential of seismic and electromagnetic data to monitor gas storage activities in salt formations. First, we analysed the stress‐dependency of the elastic and transport properties of five halite rocks to improve our understanding on changes in the geological system during gas storage operations. Second, we conducted two dissolution tests, using cracked and intact halite samples, monitored with seismic (ultrasonic P‐ and S‐waves velocities and their attenuation factors) and electromagnetic (electrical resistivity) sources to evaluate (i) the use of these common geophysical sensing methods to remotely interpret caverning development and (ii) the effect of structural discontinuities on rock salt dissolution. Elastic properties and permeability showed an increasing trend towards rock sealing and mechanical enhancement with increasing pressure for permeabilities above 10−21 m2, with strong linear correlations up to 20 MPa. In the dissolution tests, the ultrasonic waves and electrical resistivity showed that the presence of small structural discontinuities largely impacts the dissolution patterns. Our results indicate that seismic and electromagnetic methods might help in the selection and monitoring of the caverning process and gas storage operations, contributing to the expected increase in demand of large‐scale underground hydrogen storage. [ABSTRACT FROM AUTHOR]

The seismic attributes of water‐rich sandstone contain much information about the rock's physical properties and seismic wave parameters. They are commonly used to predict the rock's physical properties (e.g. porosity). However, the seismic attributes of water‐rich sandstone are affected by porosity, water saturation and thickness. To eliminate the influence of thickness on the porosity prediction of water‐rich sandstone and improve the accuracy of the porosity prediction, the authors propose a Lambert W–R transform method to isolate the contribution of thickness and porosity from seismic attributes. First, a rock physical model is used to calculate the equivalent elastic parameters of water‐rich sandstones with different porosity values and water saturation levels. Second, the seismic attribute dataset of water‐rich sandstone is established by forward modelling the seismic response of the wedge‐shaped water‐rich sandstone model, and the selection of sensitive physical properties is completed. Then, the transformation parameters (ζAhRs and ηAhRs) are obtained by Lambert W–R transformation, which is exponentially related to instantaneous amplitude. ζAhRs and ηAhRs are sensitive to thickness and porosity, respectively. Finally, an interpretative template for porosity prediction of water‐rich sandstone is established by cross‐plot analysis (ζAhRs and ηAhRs) and verified by a practical case. The verification results show that the porosity predicted by the interpretation template is consistent with drilling fluid consumption. However, it is lower than the porosity of logging constrained P‐wave impedance inversion. [ABSTRACT FROM AUTHOR]

Because of their relatively shallow volume of investigation, borehole acoustic measurements can be affected by abnormal near‐wellbore conditions such as irregular calliper, drilling‐induced formation damage and mud‐filtrate invasion, among others. Additionally, borehole‐slowness measurements inherently deliver rock elastic properties spatially averaged across the length of the multi‐receiver array included in the waveform acquisition system. The consequence is that the interpretation of borehole acoustic measurements needs to account for both radial variations of elastic properties and axial spatial averaging effects across thinly laminated formations before conducting seismic‐well log ties and rock physics interpretations. We introduce an inversion‐based interpretation method to estimate radial shear‐slowness variations from frequency‐dependent slownesses in vertical wells penetrating horizontally layered formations. The inversion procedure is efficiently implemented with an optimized two‐dimensional fast‐forward‐modelling method that simulates borehole acoustic modes in the presence of invaded and thinly laminated formations. Furthermore, the inversion method consists of two sequential steps: Firstly, layer‐by‐layer dispersion slownesses are processed to mitigate axial spatial averaging effects on borehole acoustic measurements; secondly, radial variations of elastic properties are estimated from inversion results obtained from the first step. The new inversion‐based interpretation workflow estimates a layer‐by‐layer single‐radial‐step shear slowness model, including altered and virgin radial zones. By considering both radial and axial averaging effects, the implementation of the two‐step inversion‐based interpretation method in thinly laminated and radially invaded formations consistently improves the definition of shear slowness between invaded and virgin radial zones compared to traditional radial‐profiling methods. The accuracy of the estimated shear slowness heavily relies on the sensitivity of dispersion modes to radial variations in formation shear slowness. [ABSTRACT FROM AUTHOR]

Rock specimens of the reservoir's core material from the Chayanda oil and gas condensate field (OGCF) were tested using the Triaxial Independent Load Test System of the Ishlinsky Institute for Problems in Mechanics, Russian Academy of Sciences (TILTS) in order to experimentally study the effect exerted by desalinization of reservoir rocks on their strain, strength, and filtration characteristics. According to the study data, desalinization considerably increases a rock permeability. Strain and strength properties of the studied rocks change toward softening (except for an internal friction angle), nevertheless remaining relatively high. Based on the experimental physical modeling of the pressure reducing process at the bottom of a horizontal well using TILTS, a slight decrease in elastic and strength properties of the Chayanda OGCF reservoir rocks after their desalinization should not affect the stability of the well's walls. The results obtained make it possible to draw the important practical conclusion: when operating the field at the stage of salt washing out due to water filtration under the operation process, a dramatic increase in the risks related to reservoir destruction and higher sand production should not be expected. [ABSTRACT FROM AUTHOR]

To improve the extraction of coal resources, gob‐side entry driving is gradually being promoted and applied. However, as the thickness of the coal seam increases, the deformation control of the roadway becomes more difficult. Aiming at this problem, a combination of theoretical calculation, numerical simulation, and field test was used to analyze the aspects of the stress environment, surrounding rock properties, and support forms. The phenomenon and mechanization of intensified deformation and failure of roadway with increasing coal seam thickness were revealed. The specific results include: (1) The ratio of principal stress at the excavation position controls the maximum failure depth of roadway, and the direction of principal stress determines the location of the maximum failure depth; (2) As the thickness of the coal seam increases, the properties of the surrounding rock at the excavation position decrease, the principal stress ratio increases, and the deflection angle of the principal stress increases, which lead to an intensification of the deformation and failure of the roadway. Based on the deformation and failure characteristics of the roadway and the shortcomings of the original support form, a control strategy and support scheme based on a new support structure called "Anchor Cable with C‐shaped Tube" is proposed, which has achieved better deformation control effect in on‐site application. [ABSTRACT FROM AUTHOR]

Seismic and electromagnetic explorations are two of the most successful geophysical applications for understanding the subsurface earth, and the joint interpretation of seismic and electromagnetic survey data can help to better characterize the rocks because they contain independent and complementary information about the rocks. However, the success of the joint interpretation depends on the understanding of the correlations between the elastic and electrical rock properties and their influencing factors. Confining pressure is an important geological parameter that has been found to give rise to linear elastic–electrical correlations in sandstones. However, it is still poorly known what controls the slopes of the pressure-dependent linear correlations, even though slope is one of the most important parameters determining the linear correlation. We make artificial sandstones with controlled porosity and permeability, respectively, and measure their pressure-dependent elastic (electrical resistivity) and electrical (P -wave velocity) properties simultaneously, as well as porosity. We show that the slopes of the measured electrical resistivity versus P -wave velocity as an implicit function of confining pressure correlate positively with the compliant porosity in all the samples. The results not only reveal the petrophysical parameter that controls the slopes of the pressure-dependent linear elastic–electrical correlations in sandstones, but also provide a basis for the discrimination of the slope-controlling parameter from the simultaneously measured elastic and electrical properties. [ABSTRACT FROM AUTHOR]

Combining elastic full waveform inversion (FWI) with rock physics holds promise for expanding the application of FWI beyond seismic imaging to predicting and monitoring reservoir properties. Distributed acoustic sensing (DAS), a rapidly developing seismic acquisition technology, is being explored for its potential in supporting FWI applications. In this study, we implement a sequential inversion scheme that integrates elastic FWI and Bayesian rock physics inversion, using a vertical seismic profile (VSP) data set acquired with accelerometer and collocated DAS fibre at the Carbon Management Canada's Newell County Facility. Our aim is to establish a baseline model of porosity and lithology parameters to support later monitoring of CO2 storage. Key strategies include an effective source approach for addressing near-surface complications, a modelling strategy to simulate DAS data comparable to field data, and a Gaussian mixture approach to capture the bimodality of rock properties. We conduct FWI tests on accelerometer, DAS, and combined accelerometer-DAS data. While our inversion results accurately reproduce either data set, the elastic models inverted from accelerometer data outperform the other two in matching well logs and identifying the target reservoir. We attribute this outcome to the limited complementarity of DAS data with accelerometer data in our experiment, along with the limitations imposed by single-component measurements on DAS. The porosity and lithology models predicted from accelerometer-derived elastic models are reasonably accurate at the well location and exhibit geologically meaningful spatial distribution. [ABSTRACT FROM AUTHOR]

Grouting reinforcement technology is a vital component of geotechnical engineering, which plays a crucial role in repairing surrounding rock that is damaged and improving its strength. To analyze the impact of grouting on the mechanical properties of rock fractures, specimens of mudstone fractures were selected before and after grouting reinforcement for direct shear tests. The purpose was to investigate the changes in mechanical properties under normal and tangential loading conditions. Furthermore, the microscopic–mesoscopic and macroscopic aspects of grouting reinforcement were discussed to explore its influence on the interface structure, deformation resistance, and strength of the fractured rock mass. By analyzing the test results of the fracture's mechanical properties before and after grouting, a constitutive model and strength criterion were proposed to accurately describe the mechanical behavior of the fracture surface. Building on a numerical software platform, the custom model was compiled with the VC++ integral programming environment and embedded in UDEC software. Finally, these findings were successfully applied to a typical deep roadway surrounding rock grouting reinforcement project, which showcased the practical implications of this paper. The results demonstrate that grouting reinforcement significantly impacts the normal and tangential mechanical properties of the fracture surface and the shrinkage and dilatation mechanical behaviors. The grout filling and cementation process enhances the rock mass fracture's resistance to deformation, effectively preventing the gradual weakening and slip in the fracture field. This improves the overall integrity and stability of the rock mass. The proposed mechanical model effectively captures the compression, shear, shrinkage, and dilatation mechanical behaviors before and after grouting. Similarly, the custom fracture grouting mechanical model could be a useful tool to simulate the behavior of grouting reinforcement in engineering rock masses. [ABSTRACT FROM AUTHOR]

Subcritical crack propagation in stressed carbonate rocks in a chemically reactive environment is a fundamental mechanism underlying many geomechanical processes frequently encountered in the engineering of geo-energy, including unconventional shale gas, geothermal energy, carbon sequestration and utilization. How a macroscopic Mode I crack propagates driven by a reactive fluid pressurizing on the crack surfaces with acidic agents diffusing into the rock matrix remains an open question. Here, the carbonate rock is modeled as an elasto-viscoplastic material with the mineral mass removal process affecting the rock properties in both elastic and plastic domains. A blunt-tip crack is considered to avoid any geometrically induced singularity problem and to allow a numerical analysis on the evolution of the chemical field being linked to the micro-cracking activities in front of the crack tip, affecting the delivery of acid. The model is capable of reproducing an archetypal three-region behavior of subcritical crack growth in a reactive environment. The crack propagation exhibits a prominent acceleration in Region III due to a two-way mutually enhancing feedback between mineral dissolution and the degradation process, which is most pronounced in front of the crack tip. With the consideration of initial imperfections in the rock, the macroscopic crack propagation is further accelerated with a secondary acceleration arising due to self-organization of micro-bands inside the chemically enabled plasticity zone. [ABSTRACT FROM AUTHOR]

Button cutters are the main cutting tools used in Raise Boring Machines (RBMs), particularly in very hard and abrasive ground conditions where their longer lifespan makes them preferable to other types of cutters. Meanwhile, single-disc cutters are the most efficient hard rock cutters and are frequently utilized in Tunnel Boring Machines. Although it is challenging to conduct full-scale linear cutting tests with multi-row button cutters due to laboratory equipment limitations and there are almost none of theoretical and empirical approaches to predict their cutting performances, it is very common and easier to generate data for single-disc cutters by cutting tests or using theoretical or statistical methods. By establishing statistical relationships between experimental cutting performances of button and disc cutters, it may be possible to compare the cutting performance of these roller-type cutters and transition from disc cutter performance to button cutter performance without conducting very difficult cutting tests with button cutters. The basic aim of this study is to investigate correlations between performances of a single-kerf button cutter and a constant-cross-section single-disc cutter. Full-scale linear cutting tests are performed on five different block rock samples with a 305-mm (12 inch)-diameter button cutter having an insert tip width of 11 mm in single- and double-spiral cutting patterns (pitch of 15 mm). Additionally, a series of single-spiral cutting pattern tests are performed on the same block samples with a 330-mm (13 inch)-diameter disc cutter having a tip width of 12 mm. The results indicate that optimum cutting parameters of the button cutter (normal and rolling forces, and coarseness index normalized by depth of cut per revolution, specific energy, and ratio of line spacing to depth of cut per revolution) can be predicted from the optimum cutting parameters of the disc cutter. The correlations are reliably used for predicting field performance of an RBM, which generally validates the approach used in this study. The study also provides a set of relationships between the cutting performance parameters of the disc cutter and the physical–mechanical properties of the rock samples. The relationships obtained in this study can be used for the purpose of predicting field performances of mechanical miners using button and disc cutters. [ABSTRACT FROM AUTHOR]

Non-invasive techniques, such as close-range photogrammetry (CRP) and 3D ultrasonic tomography complemented with optical and scanning electron microscopy and mercury porosimetry, were applied to characterize the carbonate rock samples of the Calcari di Cagliari formation. The integrated approach started with the computation of high-resolution 3D models of the carbonate samples using the CRP technique to produce 3D high-resolution models texturized both with natural colors and intensity. Starting from the 3D models from previous techniques, a 3D ultrasonic tomography on each rock sample was accurately planned and carried out in order to detect the elastic properties of such rocks and relate them to textural heterogeneity or internal defects. The results indicate that the relationship between longitudinal velocity and rock properties is complex even in the same carbonate formation. Understanding the relationship between the geomatic and geophysical responses in the investigated rock properties, such as textural characteristics and especially structure and geometry of pores, type of pores, tortuosity and cementing material, is important for many practical applications and especially in the diagnostic process of the conservation state of monumental structures. The integration of the above non-invasive techniques complemented by petrographical–petrophysical data proved to be a powerful method to associate each lithotype with a different susceptibility to degradation. The results presented in this paper demonstrate that the proposed integrated use of complementary methodologies would guarantee the reproducibility of the measurements both at the laboratory and field scale for the monitoring in time of the rock condition while giving a useful contribution in making decisions on an appropriate remedial strategy. [ABSTRACT FROM AUTHOR]

The investigation of upper mantle structure beneath the US has revealed a growing diversity of discontinuities within, across, and underneath the sub‐continental lithosphere. As the complexity and variability of these detected discontinuities increase—for example, velocity increase/decrease, number of layers and depth—it is hard to judge which constraints are robust and which explanatory models generalize to the largest set of constraints. Much work has been done to image discontinuities of interest using S‐waves that convert to P‐waves (or top‐side reflected SS waves). A higher resolution method using P‐to‐S scattered waves is preferred but often obscured by multiply reflected waves trapped in a shallower layer, limiting the visibility of deeper boundaries. Here, we address the interference problem and re‐evaluate upper mantle stratification using filtered P‐to‐S receiver functions (Ps‐RFs) interpreted using unsupervised machine‐learning. Robust insight into upper mantle layering is facilitated with CRISP‐RF: Clean Receiver‐Function Imaging using Sparse Radon Filters. Subsequent sequencing and clustering organizes the polarity‐filtered Ps‐RFs into distinct depth‐based clusters. We find three types of upper mantle stratification beneath the old and stable continental US: (a) intra‐lithosphere discontinuities (paired or single boundary), (b) transitional discontinuities (single boundary or with a top layer), and (c) sub‐lithosphere discontinuities. Our findings contribute a more nuanced understanding of mantle discontinuities, offering new perspectives on the nature of upper mantle layering beneath continents. Plain Language Summary: Early investigations of the mantle rocks in the US indicate intricate layering. However, uncertainties remain regarding the origins of these structures. Here, we re‐examine mantle rock stratification using a fine‐resolution approach. We use short waves that improve our ability to identify the depth of thin layers and sharp transitions in rock properties. Until now, these methods haven't been used due to interference with waves trapped in the near‐surface layers. We address this problem with machine learning and the CRISP‐RF (Clean Receiver Function Images Using Sparse Radon‐Filters) method. CRISP‐RF filters out the waves trapped in the crust and machine learning reveals spatially coherent patterns. Underneath the stable continents, we find evidence for different types of rock layering: (a) reflectors within cold stiff rocks (b) reflectors at depth ranges where the rocks become warmer and flow more readily, and (c) reflectors at depths farther down in the upper mantle. Our approach enables the test of hypotheses about the origins of upper mantle layering beneath continents. Key Points: Upper mantle stratification is constrained using Clean Receiver‐function Imaging using Sparse Radon Filters and machine learningStratification is classified into intra‐lithospheric, transitional and sub‐lithosphericHigh‐resolution constraints allow the evaluation of different causal models [ABSTRACT FROM AUTHOR]

In multiple observed caldera‐forming eruptions, the rock overlying a draining magma reservoir dropped downward along ring faults in sequences of discrete collapse earthquakes. These sequences are analogous to tectonic earthquake cycles and provide opportunities to examine fault mechanics and collapse eruption dynamics over multiple events. Collapse earthquake cycles have been studied with zero‐dimensional slider‐block models, but these do not account for the complicated interplay between fluid and elastic dynamics or for factors such as the heterogeneous fault properties and non‐vertical ring fault geometries often inferred at volcanoes. We present two‐dimensional axisymmetric mafic piston‐like collapse earthquake cycle models that include rate‐and‐state friction, fully‐dynamic elasticity, and compressible viscous fluid magma flow. We demonstrate that collapse earthquake intervals and magnitudes are highly sensitive to inertial effects, evolving stress fields, fault geometry, and depth‐varying fault friction. Given the consistent earthquake cycles observed in most eruptions, this suggests that ring faults can quickly stabilize and often become nearly vertical at depth. We use the well‐monitored 2018 collapse sequence at Kı̄lauea as a case study. Our model can produce many features of Kı̄lauea seismic and geodetic observations, except for a significant amount of interseismic slip, which cannot be readily explained with simple rate‐and‐state friction parameterizations. Plain Language Summary: Many large volcanic eruptions involve caldera collapse, where the rock above a magma reservoir abruptly subsides as the reservoir drains. Collapse can cause large earthquakes and repressurize the magma reservoir, creating a repeating cycle that helps sustain eruptions over days‐months. We develop computational models to understand the rock and magma interactions involved in collapse earthquake cycles, using data from the 2018 eruption of Kı̄lauea. The models can explain many geophysical measurements and show that collapse eruptions are very sensitive to fault geometry and spatially variable rock properties. However, standard friction models do not readily explain large amounts of fault slip measured between collapse earthquakes, suggesting that other complexities should be considered. Key Points: We develop 2D axisymmetric fully‐dynamic caldera collapse earthquake cycle models with rate‐and‐state friction and compressible fluid flowCollapse earthquake sequences are highly sensitive to fault geometry as well as heterogeneous stresses and frictionOur models fit geophysical data except large interseismic slip distances suggesting processes beyond simple rate‐and‐state friction parameterizations [ABSTRACT FROM AUTHOR]

The effect of damage on the brittle deformation of mafic and ultramafic rocks has been investigated by performing triaxial deformation experiments on thermally cracked and intact rock samples. The investigation was performed by recording the axial and lateral strains during deformation while simultaneously capturing the ultrasonic velocity, and electrical resistivity. While the peak strength is presumably controlled by the stiff intrinsic fractures, the crack opening mode also showed critical effects on the attained peak strength. The pore pressure distribution showed an apparent control over the dynamic Young's modulus as the ratio between the dynamic and static modulus of thermally cracked rocks is significantly higher than that of intact rocks. The compliant nature and the higher inelastic volumetric strain of the thermally cracked samples further indicated a possible explanation to the steep dipping plates and the taller topographic heights at the trench outer rise systems of old subduction zones. Plain Language Summary: The presence of fractures strongly influences the physical properties of rocks and not many experiments have been performed to understand the effect those fractures have on the deformation of mafic and ultramafic rocks. We find that, to address the deformation of the subduction zones, it is essential to perform experiments on such rocks under fully saturated conditions. As the incoming, relatively intact, oceanic plate sinks at the convergent boundaries, the plate bends significantly and creates a large number of faults. Therefore, the physical properties of the rock are subject to change and the way that rock deforms changes compared to an undamaged rock. However, so far, no research has been conducted to understand this change fully. Therefore, by performing experiments in the laboratory, we have attempted to understand how damage affects the physical properties and the deformation. By such experiments, we have identified that when fractures are present, the oceanic rocks show strong volume expansions before break by fracture and alter the physical properties. The results we have obtained here by gathering velocity, electrical resistivity, and strain, at the same time, can be related to the geophysical and topographic observations of the trench outer‐rise systems. Key Points: The effect of damage on brittle deformation of mafic and ultramafic rocks has been addressed via experimentsThe ultrasonic velocity, electrical resistivity, and strain are measured simultaneously during deformation of rocksPresence of cracks strongly influence deformation and physical properties which are comparable to outer rise geophysical observations [ABSTRACT FROM AUTHOR]

Estimating penetration rates of Jumbo drills is crucial for optimizing underground mining drilling processes, aiming to reduce costs and time. This study investigates various regression and machine learning methods, including Multilayer Perceptron (MLP), Support Vector Regression (SVR), and Random Forests (RF), to predict the penetration rates (ROP) using multivariate inputs such as operation parameters and rock mass characteristics. The Rock Mass Drillability Index (RDi), incorporating both intact rock properties and structural parameters, was utilized to characterize the rock mass. The dataset was split into 80% for training and 20% for testing. Performance metrics including correlation coefficient (R2), variance accounted for (VAF), mean absolute error (MAE), mean absolute percentage error (MAPE), and root mean square error (RMSE) were calculated for each method to evaluate the accuracy of the predictions. SVR exhibited the best prediction performance for ROP, achieving the highest R2, lowest RMSE, MAE, and MAPE, as well as the largest VAF values of 0.94, 0.15, 0.11, 4.84, and 94.13 during training, and 0.91, 0.19, 0.13, 6.02, and 91.11 during testing, respectively. With this high accuracy, we conclude that the proposed machine learning algorithms are valuable and efficient predictors for estimating jumbo drill penetration rates in underground mining operations. [ABSTRACT FROM AUTHOR]

Gas reservoir development and the estimation of rock properties heavily rely on lithology classification, which can be difficult, time-consuming, and prone to errors. In this study, a novel deep learning-based approach has been developed for the rapid, accurate, and efficient prediction of lithology in a gas field from conventional well-log data. The well-logs, referred to as numerical well-logs (NWLs), are transformed into two-dimensional images through two proposed approaches: shallow images (SIs) and deep images (DIs). In these images, the pixels effectively represent the relationships between different logs. For this purpose, we developed residual convolutional neural networks (ResCNN) named SIs-ResCNN 2D and DIs-ResCNN 2D. The feed data for DIs-ResCNN 2D are images created and referred to as DIs, which are initially formed from a vector in which the order of logs is somehow repeated, ensuring that each pairwise combination occurs only once. This resulted in the incorporation of the connection between the logs within the pixels of the generated images, alongside the integration of unique binary combinations of the logs. We compared the proposed models, including DIs-ResCNN 2D, DIs-ResCNN 2D, and NWLs-ResCNN 1D with baseline methods such as random forest (RF), K-nearest neighbor (KNN), and support vector machine (SVM). Based on the evaluation metrics, DIs-ResCNN 2D outperformed the other proposed and baseline methods on the test dataset. A balanced DIs-ResCNN 2D model achieved 93% accuracy and F1-score of 80% on a test well, highlighting the importance of data balancing during CNN model training. [ABSTRACT FROM AUTHOR]

As the weak structure and main seepage channel of rock mass, the discrete fracture network (DFN) has a significant influence on the physical and mechanical properties of rock mass. In this paper, based on the rectangular joint model, two algorithms are proposed to realize the precise modeling of the DFN in any polyhedron. First, the equivalence of DFN modeling with the rectangular joint model and the elliptical joint model is theoretically deduced. On this basis, the chain splicing algorithm suitable for the rectangular joint model is proposed, which can generate the DFN model according to the actual distribution of joint spacing, trace, and bridge length. Aiming at the concave boundary in the model domain, the segmentation‐stitching operation is put forward, and the continuity of the joint when passing through the interface is ensured. Finally, the effectiveness of the above algorithm is verified by several simple cases, and the relationship between the size of the geometrical representative elementary volume (REV) and discontinuity parameters is discussed. The results show that when the mean values of the joint distribution parameters are the same, even if the distribution rules are different, the number of joints generated in the same spatial region is approximately equal. The size of the geometrical REV is independent of the spacing and bridge length and is approximately three to five times the mean of the trace. The relevant algorithms and conclusions in this paper can be used as the basis for subsequent rock mass stability analysis and seepage calculation. [ABSTRACT FROM AUTHOR]

This paper proposes a semi‐analytical solution for the ultimate bearing capacity qu of both smooth and rough circular shallow foundations on rock mass. Specifically, a three‐dimensional (3D) Hoek–Brown (HB) is adopted, in conjunction with equilibrium equations under axisymmetric conditions, to derive the governing equations. The method of characteristics is utilized to solve the stress and failure characteristics mesh to determine the qu. The proposed solution is verified by using it to analyze test foundations. Comparison with an HB criterion‐based solution is performed to highlight the importance of 3D strength. Furthermore, parametric studies are performed to investigate the effects of rock mass properties (intact rock constant mi${m}_{\mathrm{i}}$, geological strength index GSI, intact rock unconfined compressive strength σc) and foundation diameter (B) on the qu, failure surface size, and vertical stress distribution on the foundation base. The results indicate that ignoring the 3D strength and the rock mass weight would lead to underestimation of qu. Besides, the ultimate bearing capacity factor Nσ${N}_{{\sigma}}$ (ratio of qu to σc) increases with mi${m}_{\mathrm{i}}$, GSI and B but decreases with σc${\sigma }_{\mathrm{c}}$. The failure surface size is significantly affected by mi${m}_{\mathrm{i}}$, GSI, B, σc${\sigma }_{\mathrm{c}}$ and rock mass unit weight. The stress distribution on the foundation base has higher variance (higher possibility of stress concentration) at smaller σc${\sigma }_{\mathrm{c}}$, GSI, and larger B, rock mass unit weight. [ABSTRACT FROM AUTHOR]

The investigation on damage creep properties of rock under freeze–thaw conditions are essential for assessing the long‐term stability of rock mass engineering in cold regions. This research analyzed the damage characteristics of rock under the coupled effect of freeze–thaw cycles and loading; the damage variable under the coupled effect of freeze–thaw cycles and loading was proposed. A damage creep constitutive model was developed, and the determination method for the model parameters was proposed. The rationality of the model was calibrated using test data, and the calculation results of the proposed model were compared with classical Nishihara model. Additionally, the research analyzed the variation of model parameters with the number of freeze–thaw cycles and discussed the damage creep mechanisms of rock under the coupled effect of freeze–thaw cycles and loading. Highlights: The creep mechanism of rock under the coupled effect of freeze–thaw cycles and loading was proposed.The damage variable under the coupled effect of freeze–thaw cycles and loading was proposed.A damage creep constitutive model was established based on nonlinear rheological and damage theory.The variation of model parameters with the number of freeze–thaw cycles were analyzed. [ABSTRACT FROM AUTHOR]

A method for in-situ stress measurement via fiber optics was proposed. The method utilizes the relationship between rock mass elastic parameters and in-situ stress. The approach offers the advantage of long-term stress measurements with high spatial resolution and frequency, significantly enhancing the ability to measure in-situ stress. The sensing casing, spirally wrapped with fiber optic, is cemented into the formation to establish a formation sensing nerve. Injecting fluid into the casing generates strain disturbance, establishing the relationship between rock mass properties and treatment pressure. Moreover, an optimization algorithm is established to invert the elastic parameters of formation via fiber optic strains. In the first part of this paper series, we established the theoretical basis for the inverse differential strain analysis method for in-situ stress measurement, which was subsequently verified using an analytical model. This paper is the fundamental basis for the inverse differential strain analysis method. [ABSTRACT FROM AUTHOR]

The content of this study combines city safety, optimum excavation situation, mining, geology, and civil engineering principles. Tunnel boring machines (TBM) are the most commonly used machines in the excavation of urban tunnels. These machines prevent the inward movement of the tunnel face and control the amount of settlement formed on the ground by applying pressure to the tunnel face. The most important question here is to determine the amount of pressure to be applied to the tunnel face. There are many widely accepted formulas used in the calculation of the face pressure and these formulas generally attempt to limit the settlements on the ground by using parameters such as groundwater level, overburden thickness, physical and mechanical properties of the surrounding rocks, etc. In this study, a new formula was developed. This new formula calculates the face pressure required to be applied by EPB to the tunnel face in order to prevent damage to a structure located on the route and within the area to be affected by tunnel excavation, instead of only preventing settlements on the surface. In the formula, produced within the scope of this study, in addition to other studies, 3D distances of the structure to which the deformation limitation will be made to prevent damage is also one of the parameters. [ABSTRACT FROM AUTHOR]

The bearing capacity of strip footings placed adjacent to the rock slopes subjected to pseudo-static horizontal earthquake body forces has been investigated by using the upper bound (UB) finite element limit analysis (FELA) in combination with a mesh adaptive strategy. The generalized Hoek–Brown (GHB) failure criterion is applied to describe the strength properties of rock masses, which can be treated as its native form without the smoothing of the yield surface while employing the second-order cone and power cone programming to solve the optimization models. Based on the UB FELA method, the seismic bearing capacity factor is determined considering the effect of different governing parameters, namely the horizontal earthquake acceleration coefficient kh, the normalized slope height H/B, the rock strength ratio σci/γB, the geological strength index GSI and the material constant mi. For design purpose, a series of non-dimensional charts are provided, and typical failure mechanisms are also discussed in detail. [ABSTRACT FROM AUTHOR]

It is of great significance to study the flexural properties and behaviour of rock in rock mechanics and engineering applications, such as tunneling, mining and underground space development. However, there are few studies related to the flexural properties of rock considering different elastic parameters in tension and in compression. This study focuses on rock flexural strength subjected to bending loading. A series of four-point bending tests (FPBTs) on prismatic beams of granite were carried out. The flexural strength of rock was theoretically determined under different assumptions based on the elastic and elastic‒plastic theory considering different elastic properties of rock in tension and in compression. Then, a comparison was made between the indirect tensile strength measured by the Brazilian test and the flexural strength acquired from the FPBT. The effects of specimen shape and heterogeneity on the flexural behaviour of rock were analysed by FEM-based numerical simulation. The results show that the calculated flexural strengths considering the elastoplastic and bimodulus properties of rock are lower than those without considering the properties and are closer to the Brazilian tensile strength of rock. The flexural strengths of rock increase with increasing ratios of height to thickness. Heterogeneity plays a crucial role in the flexural properties of rock. The more homogeneous the rock is, the higher its flexural strength. The findings in this paper facilitate a better understanding of the flexural properties of rock. [ABSTRACT FROM AUTHOR]

We investigate whether varying wavefield contributions are the likely cause to variation in microtremor horizontal-to-vertical spectral ratio (MHVSR) amplification shape between six sites in the relatively homogeneous geologic setting of Windsor, Ontario. We quantify the MHVSR shape in terms of peak broadness and its fitness using mathematical functions to identify potential wave type contributions. We develop a technique that uses particle motion plots of cross-correlated microtremor recordings to establish the dominant wave types contributing to the microtremor wavefield within three important frequency bandwidths (below, spanning, and above the fundamental peak frequency). We investigate the variability in the inverted shear-wave velocity (VS) depth profile by performing 21 MHVSR inversions with varying Rayleigh, Love, and body wave contributions. The impact to seismic site characterization is that the depth and VS of the resonator (half-space) layer are overestimated consistently by an average of 28% compared to the often-default-assumed Rayleigh ellipticity forward amplification model. Our study demonstrates the importance of correctly identifying wave type contributions of the microtremor wavefield for the proper estimation of VS depth profiles, especially to obtain correct thickness of the sediment layer and resonator VS and thereby the average VS of the upper 30 m (VS30). [ABSTRACT FROM AUTHOR]

X-ray computed tomography has established itself as a crucial tool in the analysis of rock materials, providing the ability to visualise intricate 3D microstructures and capture quantitative information about internal phenomena such as structural damage, mineral reactions, and fluid–rock interactions. The efficacy of this tool, however, depends significantly on the precision of image segmentation, a process that has seen varied results across different methodologies, ranging from simple histogram thresholding to more complex machine learning and deep-learning strategies. The irregularity in these segmentation outcomes raises concerns about the reproducibility of the results, a challenge that we aim to address in this work. In our study, we employ the mass balance of a metamorphic reaction as an internal standard to verify segmentation accuracy and shed light on the advantages of deep-learning approaches, particularly their capacity to efficiently process expansive datasets. Our methodology utilises deep learning to achieve accurate segmentation of time-resolved volumetric images of the gypsum dehydration reaction, a process that traditional segmentation techniques have struggled with due to poor contrast between reactants and products. We utilise a 2D U-net architecture for segmentation and introduce machine-learning-obtained labelled data (specifically, from random forest classification) as an innovative solution to the limitations of training data obtained from imaging. The deep-learning algorithm we developed has demonstrated remarkable resilience, consistently segmenting volume phases across all experiments. Furthermore, our trained neural network exhibits impressively short run times on a standard workstation equipped with a graphic processing unit (GPU). To evaluate the precision of our workflow, we compared the theoretical and measured molar evolution of gypsum to bassanite during dehydration. The errors between the predicted and segmented volumes in all time series experiments fell within the 2 % confidence intervals of the theoretical curves, affirming the accuracy of our methodology. We also compared the results obtained by the proposed method with standard segmentation methods and found a significant improvement in precision and accuracy of segmented volumes. This makes the segmented computed tomography images suited for extracting quantitative data, such as variations in mineral growth rate and pore size during the reaction. In this work, we introduce a distinctive approach by using an internal standard to validate the accuracy of a segmentation model, demonstrating its potential as a robust and reliable method for image segmentation in this field. This ability to measure the volumetric evolution during a reaction with precision paves the way for advanced modelling and verification of the physical properties of rock materials, particularly those involved in tectono-metamorphic processes. Our work underscores the promise of deep-learning approaches in elevating the quality and reproducibility of research in the geosciences. [ABSTRACT FROM AUTHOR]

The Double-Yield (D-Y) model is a widely used method for predicting the mechanical properties of caved rock. However, determining the numerical simulation parameters for this model typically requires extensive trial and error. In this paper, a new approach for parameter inversion of the D-Y model is proposed and applied to a real case study involving repeated mining in multiple coal seams. The proposed framework combines FLAC3D, a finite element numerical simulation software, with a new computational tool developed using MATLAB® App Designer. By applying this framework to the case study, the accuracy and efficiency of parameter determination in the mining area are improved. In addition, a 3D finite element model of multiple coal seams is generated based on the geological information of the case study, and the stress evolution is analyzed. The simulation results are then validated through field measurements, providing valuable reference information for safe and efficient production. Overall, this improved method for parameter inversion of the D-Y model, along with the combined numerical simulation and field measurement approach, enhances the understanding of stress evolution in multiple coal seams and contributes to safer and more efficient mining operations. Highlights: An in-depth analysis was conducted to examine how variations in Double-Yield parameters impact the numerical simulation curve. A breakthrough approach for parameter inversion of the Double-Yield (D-Y) model is introduced, and the computational tool is developed. A 3D finite element model is crafted to analyse the dynamic stress evolution during repeated mining of multiple coal seams. The accuracy of simulation outcomes is bolstered by validation against field measurements of mining-induced stress. [ABSTRACT FROM AUTHOR]

Accurate determination of rock strength is always a crucial problem to ensure the stability of rock engineering, which can be estimated from experimental data at a small scale through size effect models. Previous studies examined the scaling behaviors of rocks from a deterministic perspective, ignoring the strength variabilities around the mean values. In this study, the bonded particle model–μdiscrete fracture network (BPM–μDFN) modelling has been utilized to analyze size effect and associated strength variability for rocks considering microstructure and strain rate. The numerical results demonstrate that the size effect is more significant for rocks with increasing micro-crack intensity, while it becomes less obvious with increasing micro-crack size or increasing strain rate. In addition, the strength variability of rocks is largely influenced by the internal microstructure and strain rate. Finally, a modified empirical size effect model incorporating model parameters of internal microstructure and strain rate is proposed to predict the scaling behaviors of rock considering internal microstructure and strain rate, which can capture the numerical results soundly. The findings of this study could enhance our understanding of rock strength determination from a small scale and provide a guide to design rules for rock engineering. Highlights: The scale-dependent properties of rocks can be captured by the BPM-μDFN models considering internal micro-structures and strain rates. The strength variability of rocks decreases with increasing specimen size for rocks with different internal micro-structures under various strain rates. A novel scaling model is proposed for rocks based on the classical size effect model. [ABSTRACT FROM AUTHOR]

The ability to accurately measure the static Young's modulus is crucial for understanding subsurface storage reservoirs. However, obtaining this data can be difficult and costly. Much previous research focused on the impact of one or two factors on geomechanical properties at a single scale, but a more comprehensive understanding is needed. A data-driven Bayesian approach was used to quantify the uncertainty of Young's modulus using cost-effective experimental measurements of six rock properties—porosity, clay content, permeability, the ratio of framework grain content to cement content (FGC/CC), mean grain size, and sample size. We further use the comprehensive geomechanical model to examine the impact of six rock properties on Young's modulus. We found that the pore abundance and the relative amount of framework grains and cements play significant and competing roles in rock's elastic properties. Furthermore, the surrogate model yields the minimum uncertainty and reflects nonlinear and non-monotonic trends between Young's modulus and secondary rock properties. The surrogate model can estimate Young's modulus distribution of common sedimentary rocks, reducing the cost associated with traditional laboratory testing. Overall, this work elucidates the elastic mechanical behavior of rocks at various core scales in response to other secondary rock properties in the deep subsurface. Highlights: An optimized surrogate model was constructed from the Bayesian framework and six rock properties of five sedimentary rock facies. Both surrogate and deterministic models studied in this work can predict the uncertainty of Young's modulus of sandstone at the core scale. The effects of six rock properties on Young's modulus were quantified using their impact factors. Porosity and mineralogical heterogeneity play competing and significant roles in affecting the elastic behavior of the rock materials. Nonlinear and non-monotonic correlations were found between Young's modulus and compositional ratio. [ABSTRACT FROM AUTHOR]

Importance ranking of rock properties is important in allocating investigation resources, and then performing probabilistic analysis efficiently. Traditional global sensitivity analysis (GSA) can be employed to perform this ranking; however, it neglects (1) the epistemic uncertainties in the probability models and their parameters due to small sample sizes of inputs, and (2) the mutual dependence of inputs. This paper overcomes these limitations by introducing a stratified Bayesian multimodel inference (BMMI) coupled with moment independent GSA to estimate the imprecise sensitivity indexes (SIs) with complex copula-dependent inputs. The methodology initially identifies candidate marginal models and the uncertainties in their parameters by BMMI, which is employed to construct a model set comprising an ensemble of marginals estimated via the reweighting approach. Subsequently, this model set is used to quantify the uncertainties in the copula-based dependent structure using BMMI. The final step is to estimate the inaccurate SIs using the Monte Carlo–based moment independent GSA framework, which propagates an ensemble of joint densities to represent the overall uncertainty. The methodology is generalized in a way that it can be used for any number of complexly dependent inputs and eliminates the need to estimate conditional probability density functions (PDFs) and a precise copula otherwise required in mapping-based and traditional GSA. The methodology is demonstrated for two slopes, i.e., an infinite soil slope (two inputs) and a rock slope (four inputs). The methodology was accurate for both examples, and more informative than traditional GSA because it estimates the bounds of SIs reflecting the effect of epistemic uncertainties associated with dependent inputs with their point estimates from traditional GSA lying in their bounds. [ABSTRACT FROM AUTHOR]

Digital rock physics is based on imaging, segmentation and numerical computations of rock samples. Due to challenges regarding the handling of a large 3-dimensional (3D) sample, 2D algorithms have always been attractive. However, in 2D algorithms, the efficiency of the pore structures in the third direction of the generated 3D sample is always questionable. We used four individually captured µCT-images of a given Berea sandstone with different resolutions (12.922, 9.499, 5.775, and 3.436 µm) to evaluate the super-resolution 3D images generated by multistep Super Resolution Double-U-Net (SRDUN), a 2D algorithm. Results show that unrealistic features form in the third direction due to section-wise reconstruction of 2D images. To overcome this issue, we suggest to generate three 3D samples using SRDUN in different directions and then to use one of two strategies: compute the average sample (reconstruction by averaging) or segment one-directional samples and combine them together (binary combination). We numerically compute rock physical properties (porosity, connected porosity, P- and S-wave velocity, permeability and formation factor) to evaluate these models. Results reveal that compared to one-directional samples, harmonic averaging leads to a sample with more similar properties to the original sample. On the other hand, rock physics trends can be calculated using a binary combination strategy by generating low, medium and high porosity samples. These trends are compatible with the properties obtained from one-directional and averaged samples as long as the scale difference between the input and output images of SRDUN is small enough (less than about 3 in our case). By increasing the scale difference, more dispersed results are obtained. [ABSTRACT FROM AUTHOR]

This study analyzes how adding europium and transition metals (Cu, Ag, and Au) at a 12.5% concentration to magnesium oxide (MgO) affects its physical characteristics and potential uses. To do so, the full potential linearized augmented plane wave (FP-LAPW) method, based on spin-polarized density functional theory (SP-DFT), is used to derive the results. Wu and Cohen's generalized gradient approximation (GGA-WC) described the exchange-correlation potential. The modified Becke-Johnson exchange potential (TB-mBJ) was also used to improve the findings of optoelectronic properties. When Eu and TM (Cu, Ag, and Au) impurities are co-doped into the nonmagnetic (NM) semiconductor MgO, the structural optimization results show that the lattice constants increase, and the bulk modulus decreases with increasing the atomic number of transition metals. The resulting dilute magnetic oxides (DMOs) are stable in the spin-polarized ferromagnetic (FM) phase, and the formation energy values confirm their stability in the F m 3 ̄ m cubic structure, with the lowest value belonging to Eu 0. 1 2 5 TM 0. 1 2 5 Mg 0. 7 5 0 O. Similarly, calculations of electronic properties using the WC-mBJ functional demonstrate that all compounds have an indirect half-metallic bandgap at L- Γ equal to 2.53, 2.49, and 1.39 eV for Eu 0. 1 2 5 Cu 0. 1 2 5 Mg 0. 7 5 0 O, Eu 0. 1 2 5 Ag 0. 1 2 5 Mg 0. 7 5 0 O, and Eu 0. 1 2 5 Au 0. 1 2 5 Mg 0. 7 5 0 O, respectively. They have an integer magnetic moment of 6 μ B . The density of states shows that at the Fermi level, the 4f-Eu, d-TM, and p-O states give rise to new energy levels. This indicates that the f–p–d hybridization provides this system with its FM properties. Also, these compounds' dielectric function and absorption spectra are calculated and analyzed to learn more about their optical properties. The results provide insight into the optical behavior of the materials. It is observed that the co-doped compounds exhibit greater optical absorbance than their un-doped MgO counterparts do. This theoretical investigation opens the way to preparing high magnetic moment DMOs using TM and rare earth as dopants suitable for spintronic and UV devices. [ABSTRACT FROM AUTHOR]

Assessing the dynamic properties of rocks remains a foundational pursuit in the field of rock engineering, providing crucial insights into their mechanical behaviors across a spectrum of loading conditions, including static, cyclic, and dynamic scenarios. This paper expounds upon the utilization of the nonresonance (NR) torsional shear test and its implications for understanding rock responses, particularly in the context of low and medium loading rates. The NR method serves as a pivotal tool for investigating model rock materials subjected to loading conditions characterized by low frequencies and amplitudes. Renowned for its efficacy, this method allows the simultaneous determination of two critical dynamic parameters: shear modulus (G) and damping ratio (D), all at a specific loading frequency. It has been ascertained that the loading rate increased as the loading frequency and applied amplitude of loading increased. With increasing loading rate, the shear modulus consequently increased while the damping ratio decreased. It is observed that the dynamic responses of both ramp and sinusoidal loading waveforms increase concurrently with the amplitudes of the applied torque and loading frequencies. The sinusoidal waveform exhibits greater dynamicity than the ramp waveform at a certain loading rate. Furthermore, this study delves into the intricate analysis of the nonlinear viscoelastic dynamic response exhibited by rocks, utilizing the modified hyperbolic (MH) model and the Ramberg–Osgood (RO) model as analytical tools. The findings derived from curve fitting exercises unequivocally underscore the superior applicability of the Ramberg–Osgood model, particularly in characterizing modulus reduction behavior. Conversely, the modified hyperbolic model emerges as the preferred choice for comprehensive damping ratio analyses. This study enhances the comprehension of rock dynamics and responses under diverse loading conditions, contributing valuable understanding to rock engineering. Insights into loading and strain rate effects aid informed decisions and preventive measures for rock deformation and collapse risks. Practical Applications: This research suggests vital findings regarding the response of intact model materials to various dynamic loading conditions, providing significant insights for comprehending the mechanical response of rock structures exposed to cyclic loading conditions, which have the potential to create weaknesses in rocks resulting in untimely failures. The research can be utilized to assess the response of rocks in the context of seismic incidents, specifically those characterized by shear waves at particular frequencies. This study evaluates the response of rocks during earthquakes by establishing a correlation between the amplitude of torsional shear loading and the peak ground displacement linked to seismic events. In addition to its seismic implications, this research aids in advancing accurate predictive models and instruments that assess the stability and integrity of rock formations under different loading rates—a consequence of the symbiosis between frequency and amplitude. Professionals may ensure efficient risk mitigation, make well-informed decisions, and execute preventative measures concerning rock collapse and deformation by virtue of their comprehensive awareness of the delicate relationship between loading rate and dynamic rock properties. Incorporating the findings into engineering design standards and codes can bring about substantial improvements, augmenting the overall reliability and protection of rock structures. [ABSTRACT FROM AUTHOR]

Water content is an important factor affecting the rock-breaking efficiency of tunnel boring machine (TBM) disc cutters. However, limited efforts have been made to study the fracturing mechanism of sandstone excavation by TBM disc cutters under varying water content conditions. To investigate the breakage behavior of water-soaked sandstone by TBM disc cutters, five sets of penetration tests on sandstone specimens with different water content levels were performed. The tests were conducted using a modified RYL-600 computer-controlled rock shear rheometer. An acoustic emission (AE) monitoring system was utilized throughout the entire process to track the AE activity of the specimens. The force–depth curves of the penetration process at various water content levels were investigated. The effects of water content on AE characteristics, rock fracture properties, and specific energy were analyzed. The results indicate that AE activity can be divided into three stages: quiet period, slow rise period, and active period. With increasing water content, peak penetration force, consumed energy, and specific energy decrease gradually, while chip volume increases. Water promotes mutual penetration of surface and internal cracks of the specimen, resulting in the formation of larger chip volumes. These findings provide theoretical guidance for designing and improving TBM cutter head parameters in water-rich soft rock formations. [ABSTRACT FROM AUTHOR]

Geothermal energy is increasingly important for the global environment and for the sustainable development of our society. Electrical surveys are widely employed for the exploration of geothermal energy, because the electrical geophysical properties provide useful information about the fluids at depth. However, although quantitative interpretation of electrical survey data relies on the knowledge about the effects of temperature on the electrical properties of fluid-bearing rocks, it remains poorly understood about how temperature affects the electrical conductivity of clay-free porous rocks. We bridge this knowledge gap by measuring the electrical conductivity and porosity of five brine saturated clean Berea sandstones with temperature ranging between 25 and 140 °C, and analysing all the factors that impact the rock conductivity. We showed that the effects of surface conductivity on the temperature-dependent electrical conductivity can be negligible, whereas the temperature induced variation in the porosity and pore structure quantitatively characterized in terms of cementation exponent can be more significant. We also found that temperature affects the electrical conductivity of brine saturated Berea sandstones by impacting the brine conductivity, and the pore structure and porosity of the samples, with their importance in a descending order. The results have provided new insights into how temperature affects the electrical conductivity of clay-free porous rocks, and will help to improve the quantitative interpretation of electrical survey data for the exploration of geothermal energy. [ABSTRACT FROM AUTHOR]

The use of UAV represents a very useful tool for rock mass characterization, particularly in large, unsafe, and not accessible areas characterized by a complex geometry. This investigation was mainly focused on mapping discontinuities and characterizing rock masses using UAV photogrammetry, machine learning, including different algorithms, and intact rock laboratory analyses, respectively. To this aim different outcrops from those described as a part of the basement of the Acoculco Caldera Complex, composed by a series of folded limestones were selected. The results indicate that geomechanical and physical properties, together with outcrop information are very important to assign suitable properties to large rock units. In turn, the great number of plots of discontinuity orientation extracted from the 3D point cloud data by the used of our code written in python language allowed to easily identify the presence of a total of seven discontinuity sets, some of them related to the bedding sequence and some others related to shear and tensile stress due to folding. Highlights: • Discontinuity orientation extracted from the 3D point cloud data, allowed to easily identify the presence of discontinuity sets. • A detailed characterization of intact rock and discontinuities is presented and discussed. • This manuscript is accompanied by a code written in python programming language, placed in a public repository. • Detailed characterization of the properties of the rock mass is necessary to build different conceptual models in the area. [ABSTRACT FROM AUTHOR]

Seismic surveys along subduction zones have identified anomalously high ratio of P‐ to S‐wave velocity (VP/VS) in the subducting oceanic crust that are possibly due to the presence of pore water. Such interpretations postulate that the pore structure is homogeneous at the scale of the seismic wavelength. Here we present the first statistical evidence of a heterogeneous pore structure in oceanic crust at scales larger than laboratory samples. The spatial correlation of measured bulk density profiles of the crustal section of the Samail ophiolite suggests that the pore structure is heterogeneous at scales smaller than ∼1 m. Wave‐induced fluid flow cannot follow the loading during the seismic wave propagation at this estimated heterogeneity, which implies that fluid‐filled microscopic pores and cracks have a limited impact on the observed high VP/VS anomalies in the subducting oceanic crust. Large‐scale cracks may therefore play an important role in shaping these anomalies. Plain Language Summary: Seismic studies along subduction zones have identified unusually high ratios of P‐ to S‐wave velocity (VP/VS) in the subducting oceanic crust, which indicates the presence of water‐filled cracks and pores. The close link between pore water and local seismic activity highlights the importance of quantitatively interpreting these seismic anomalies in terms of pore characteristics. Previous interpretations have assumed that the microscopic pore structure is quite homogeneous, even at macroscopic scales as large as the seismic wavelength. However, our analysis of a bulk density profile of the crustal section of the Samail ophiolite, Oman, which is a fossilized oceanic plate preserved on land, indicates that the pore structure is more heterogeneous than previously assumed. This means that the fluid flow within the unit volume that represents the macroscopic physical properties of the rock cannot follow the wave‐induced loading during seismic wave propagations. This results in a relatively small impact of water on the seismic velocity, as inferred from theoretical models that predict the effective elastic properties of rock containing fluid‐filled cracks. Therefore, microscopic cracks may not have a large impact on the high VP/VS values of subducting oceanic crust, whereas large‐scale cracks may play a more significant role. Key Points: The bulk density of the crustal section of the Samail ophiolite is more spatially heterogeneous than previously assumedThe effect of fluid‐saturated microcracks on low‐frequency seismic velocities is modeled as an unrelaxed condition for this heterogeneityThe high VP/VS anomaly in the subducting oceanic crust can be explained by both microcracks and large‐scale cracks [ABSTRACT FROM AUTHOR]

In the design of large-diameter rock-socketed piles, the ultimate bearing capacity of intact rocks under the pile tip (qb) is often required to be predicted, especially for rock-socketed end-bearing piles. Existing approaches for calculating qb establish an empirical relation with the macroscopic parameters of rock layers, but the research on the microscopic parameters inside intact rocks is insufficient. This study provides a theoretical method for calculating qb from a micro perspective and implements it in MATLAB, in which the integral stress of the Mindlin solution within the circular region at the pile base was selected as the stress state of the theoretical calculation regions, and the tension– or compression–shear mixed mode I–II criterion was selected as the failure criterion of micro-cracks inside intact rocks. Six model piles with measured ultimate end-bearing capacities were analyzed to validate the proposed solution. The results showed that the failure ranges of intact rocks under an identical base load for analytical analyses are comparable with those obtained by model tests, which confirms the rationality of the theoretical approach. Then, the failure zone of intact rocks under different working loads of pile base was explored. Finally, parametric studies were conducted using the proposed solution to explore the effects of rock properties and pile dimensions. [ABSTRACT FROM AUTHOR]

The object of research is the dynamic processes that occur in the drill string during the deepening of the hole in deep wells. The work is aimed at solving the problem for an idealized system in the form of rod systems while preserving its main oscillatory properties. The nature of oscillatory processes that occur in the drill string during drilling with downhole motors is considered, in some cases it turns out to be very complicated. In the general case, the dynamic process changes according to an aperiodic law, which is superimposed by processes of an oscillating nature with an increasing (damping) nature of the amplitudes of different frequencies. The influence of the torque characteristics of the downhole motor and bit on the development of oscillatory processes in the drill string during well drilling has been theoretically determined. The results of theoretical and experimental studies of oscillatory processes and their interaction with the use of proposed models of hole deepening in the future make it possible to create a simulation model. This model would include taking into account the mode parameters of drilling, the mechanical properties of the rocks to be drilled and the layout of the drill string bottom (DSB). The obtained research results can be applied in practice in the process of designing the structure of the drill string bottom (DSB) with the use of downhole motors, in particular, screw motors, the use of which leads to energy stress, the complication of work processes and structural schemes. As a result, the nature of vibrations changes and the vibration loads on parts of the downhole motor, bits and elements of the drill string are reduced. In the future, it is necessary to take into account the hydrodynamics and the type, as well as the design and parameters of the applied downhole elements for the development of their dynamic models. [ABSTRACT FROM AUTHOR]