Rock Surface Research Articles

Whole rock lithogeochemical analysis of the Mount Read Volcanics: a new tool for geochemical exploration

The Mount Read Volcanics (MRV) of western Tasmania is a belt of Middle to Late Cambrian submarine volcanics and volcaniclastics and one of the major base and precious metal provinces within Australia. Exploration success in the MRV has been in decline in recent years due to a variety of challenges including intensely altered rocks with complex stratigraphy and lithofacies variation, and a lack of accessible outcrop. As a result, local and regional mapping of the MRV is often restricted to Group-level stratigraphy, rendering geological mapping ineffective for identifying decametre-scale mine stratigraphy. Surface rock chip and drill hole samples were collected and analysed using commercially available geochemical assays to create a regional geochemical dataset of the MRV, covering the entire province and all major stratigraphic units. From these data, a lithogeochemical methodology was developed, utilizing Ti/Nb and V/Sc systematics that effectively characterizes the samples according to composition and magmatic processes. This method is shown to be robust to biases due to alteration and lithofacies, eliminating the need for highly selective sampling or extensive data filtering. To demonstrate the utility of this method in an exploration context, data from the K-lens of the Rosebery polymetallic volcanic-hosted massive sulfide (VHMS) deposit was used as a case study. Using Ti/Nb–V/Sc systematics, a rock composition classification was developed that allowed for discrimination of the footwall, hanging wall and host stratigraphy of the Rosebery mine sequence. A geochemical fingerprint for the footwall stratigraphy to mineralization was developed, and by correlating this signature to the regional unclassified samples, geochemical analogues for the Rosebery footwall were readily identified. This approach rapidly reduces the exploration search space and provides valuable information for future mineral exploration. The methodology is applicable in other terrains; however, appropriate orientation studies are required to investigate potential biases due to lithofacies, alteration and mineralogical variability.

Understanding the wettability alterations in carbonate reservoirs: Integrating experimental data and a surface complexation model for enhanced predictions

In this study, we developed a laboratory-based model to analyze wettability alteration in the oil–water-rock system. The selected Surface Complexation Model (SCM), based on experimental data, is refined through sensitivity analysis and comparison with experimental measurements, including zeta potential and contact angle. Our analysis indicates that, in addition to magnesium, calcium, and sulfate ions, the adsorption of sodium and chlorine on calcite surfaces, as well as sodium adsorption on oil surfaces, significantly affects electrostatic interactions and surface potential alterations. Consequently, the complexing reactions of these ions were incorporated into the model and adjusted based on sensitivity analysis. Moreover, surface complex reactions exhibit distinct behaviors in neutral, acidic, and alkaline environments. Therefore, different reactions were considered and sensitivity analyzed for oil and rock surfaces in neutral conditions. The model’s reliability was further validated by comparing predicted and experimental zeta potentials. Additionally, disjoining pressures were computed, and contact angles were simulated, demonstrating the model’s accuracy. Key findings include the successful modification of reaction parameters to achieve accurate results across different pH levels and ion concentrations. This confirms the applicability and reliability of the developed SCM for wettability alteration analysis, further supported by stability maps that consider varying ion concentrations and pH levels.

Can rock surface flow derived from outcrops generate surface runoff in a rocky desertified area?

Rock surface flow, formed from exposed rock surfaces, is a unique form of runoff in rocky desertified areas with massive bedrock outcrops. The question of whether the rock surface flow promotes surface runoff formation continues to puzzle us. To address this problem, four sites with notable bedrock outcrops and different land use types were selected from a typical desertified area in Guizhou, China. Straight and concave rock-surface shapes that were the most capable of collecting rainwater were selected at each site. Soil infiltration and water storage capacity experiments were conducted to observe the infiltration and water storage properties of the soil closely adhering to the rock–soil interface (CRSI) of the bedrock outcrops by taking the soils far from the outcrops horizontally (FRSI) as the control, and to further explain the conditions for surface runoff formation via rock surface flow. Our results showed that the CRSI is more prone to producing surface runoff than the FRSI, which is attributed to its lower infiltration (stable infiltration rate of 0.2 to 192.6 mm/min) and water storage capacity (total reservoir 441.6 to 613.6 t/hm2) than that of FRSI (4.50 to 272.8 mm/min, 458.8 to 635.4 t/hm2). This phenomenon would be intensified after receiving the rock surface flow input. Concurrently, concave rock surfaces are more likely to promote surface runoff formation than straight rock surfaces, which are affected by the accumulation of rock surface shapes on rainwater. A discriminating condition for whether rock surface flow produces surface runoff at the CRSI is proposed based on the inversely proportional functional relationship between rainfall (rainfall intensity RI and amount RA) and the effective rock surface rainfall catchment area (ARS). When RI or RA exceeds the critical threshold, the surface runoff with mechanisms of excess infiltration or excess saturation is generated around bedrock outcrops. The discriminating equation will help increase surface runoff prediction accuracy in rocky desertified areas with exposed bedrock outcrops. These results help understand the importance and role of rock surface flow hydrologic processes in karst areas.

Interaction mechanism and factors influencing dynamics of rock-heavy oil-chemical agent interface

The interactions among the rock, oil, and chemical agent are critical for oil recovery. However, the mechanisms underlying this synergistic effect remain unclear. Therefore, this study used custom-made experimental methods to analyze these interactions and behavior of heavy oil on rock surfaces and elucidate the micro-interaction mechanism of the liquid–solid interface. Oil adhesion, flow, and deformation were studied via experiments on oil spreading, oil film emulsification, oil film shrinkage, and oil droplet peeling and deformation. Moreover, the contributions of oil diffusion on rock surface and flow through porous media to oil spread dynamics were detailed for the first time. The influence of the oil flow in porous media on oil recovery and the influencing factors were also studied. Furthermore, the effects of the rock–oil–water interface on the emulsification, shrinkage, and peeling of oil film were studied via chemical agent–oil film interactions. The main mechanisms underlying the effects of chemical agents on heavy oil flow were elucidated. Finally, the morphologies of the oil droplets under weak buoyancy were studied. The degree of deformation of oil droplets was evaluated to analyze the effect of chemical agents on the oil–water interface and factors influencing this process. Therefore, this study offers insights into the oil recovery process by analyzing heavy oil flow through porous media and the effects of chemical agents on rock surfaces and oil–water interfaces and lays the groundwork for chemical agent optimization to enhance oil recovery.

Investigating the Feasibility of EOR While Preloading Parent Wells to Mitigate Fracture Hits: An Experimental and Modeling Study

Summary During a fracturing operation in an infill (child) well, pressure and fluid communication between this well and a nearby parent well, known as fracture hits (FHs), can impair the production performance of both wells. A cost-effective strategy to mitigate the FH is to preload the parent well with water during the fracturing of the child well. It has been hypothesized that the production performance of the parent well can be enhanced by the preloading process if proper additives are used in the injected water. We develop a laboratory protocol to physically simulate primary production and surfactant preloading stages using Montney core and fluid samples under reservoir conditions. We investigate the role of wettability alteration, interfacial tension (IFT) reduction, and surfactant’s chemical stability on the performance of enhanced oil recovery (EOR) during the preloading process. An analytical model is developed to predict the volume of leaked-off surfactant and recovered oil using measured pressure-decline data from the preloading stage. This study only focuses on the interactions of preloading fluid with the parent well’s matrix and does not consider the child-parent well interference. Our results demonstrate that 31.8% of the oil is recovered during primary production from large inorganic pores under solution-gas drive mechanism. Under countercurrent imbibition, a nonionic surfactant leaks off into the smaller organic and inorganic pores and recovers an additional 11.8% oil from a depleted core during preloading. The analytical model estimates oil recovery factors close to the experimental data determined by material balance. Core visualizations demonstrate a population of small oil droplets on the rock surface under reservoir conditions. While IFT is reduced to nearly the same extent by either surfactant, only the wettability-altering surfactant yields incremental oil recovery. Zeta-potential measurements indicate that while neither surfactant alters the rock-water surface charge, the wettability alteration is achieved by modifying the oil-water surface charge even at concentrations above the critical micelle concentration (CMC). Based on the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, the repulsive electrostatic double-layer (EDL) forces are intensified with an increase in surfactant concentration, resulting in enhanced stability of the water film on the rock surface and increased hydrophilicity. Under elevated temperatures, we observe two phenomena, which can adversely affect the performance of a nonionic surfactant: (a) agglomeration of surfactant particles due to reduced solubility in water, reducing pore accessibility, and (b) chemical decomposition of the surfactant, affecting its ability for IFT reduction and wettability alteration.

Understanding the Dynamics of Matrix-Fracture Interaction: The First Step Toward Modeling Chemical EOR and Selecting Suitable Fracturing Fluid in Unconventional Oil/Gas Recovery

Summary The effects of chemical additives on mitigating water blocking and improving oil recovery were experimentally examined for gas-water and oil-water systems in spontaneous imbibition cells. In these attempts, two factors are critically important: (1) understanding the physics of the interaction, whether it is co- or countercurrent, and (2) characteristics of the chemical additives to suitably orient the interaction for specific purposes (accelerate/decelerate matrix-fracture interactions). Co- and countercurrent imbibition experiments were conducted on sandstone rock samples using various oil samples (viscosities between 1.37 cp and 54.61 cp) as well as gas (air). The selected new-generation chemical additives included deep eutectic solvents, cationic/anionic/nonionic surfactants, and inorganic and organic alkalis. We observed that the functionality of the chemicals varied depending on the fluid type, interaction type (co- or countercurrent), and application purposes. For instance, chemicals such as the cationic surfactant cetyltrimethylammonium bromide (CTAB) significantly reduced water invasion into the gas-saturated sandstone cores during fracturing, while chemicals such as the nonionic surfactant Tween® 80 provided considerable oil recovery improvement in the oil-saturated sandstone cores. The surface tension and wettability of the rock surface are crucial factors in determining the suitability of chemicals for mitigating water blockage. In terms of oil recovery, certain chemical additives, such as O342 and Tween 80, may result in a lower recovery rate in the early stage because of their strong ability in interfacial tension (IFT) reduction but could lead to a higher ultimate recovery factor by altering the wettability. Additionally, the introduction of chemicals resulted in notable spontaneous emulsification, especially in countercurrent imbibition, thereby enhancing oil recovery. The spontaneous emulsification and its stability are influenced by factors such as oil drop size, boundary condition, interaction type, IFT, wettability, as well as rock surface charges. The results have implications for understanding the physics and dynamics of matrix-fracture interactions in co- and countercurrent conditions. In addition, they serve as the first step toward selecting appropriate chemical additives in hydraulic fracturing fluid design and enhancing oil recovery in unconventional reservoirs.

CO2-foam flood with wettability alteration for oil-wet carbonate reservoirs

Carbon dioxide (CO2) flooding in carbonate reservoirs often suffers from poor sweep efficiency, attributed to unfavorable mobility ratio, gravity segregation, and reservoir heterogeneity. CO2-foam injection is a promising strategy to control CO2 mobility. The stability of CO2-foam is affected by reservoir wettability. This study aims to systematically investigate the effectiveness of CO2-foam flood coupled with wettability alteration in an initially oil-wet carbonate rock at a pressure below the minimum miscibility pressure. Three types of surfactants, including a nonionic surfactant Soloterra 843, a cationic surfactant CETAC-30, and a zwitterionic surfactant LMDO, were evaluated as potential foaming agents. Contact angle tests were conducted to assess the wettability alteration capability of these surfactants. Bulk foam stability tests and foam rheology tests were conducted under reservoir conditions. Finally, foam core flood experiments were performed using oil-wet carbonate core samples. Results from contact angle experiments indicated that only CETAC-30 was effective at altering rock wettability from oil-wet to water-wet by removing the negatively charged organic acid components from the rock surface. Foam stability and rheological tests revealed that LMDO exhibited highly stable CO2-foam in the absence of crude oil. However, the presence of crude oil adversely affected CO2-foam stability for all the surfactants. Core flooding experiments demonstrated that injecting wettability alteration surfactant, CETAC-30, in form of foam could not only alter the wettability of rocks, but also enhance the foam strength. Continuous gas injection (without foam) increased oil recovery by 14.4 % due to the near-miscibility of CO2 and oil. Both CETAC-30 and LMDO surfactants increased the oil recovery by about 35 % after waterflood, but the wettability altering surfactant showed the highest mobility reduction factor (MRF). These findings provide valuable insights into the complex interplay between near-miscibility, wettability alteration and foam strength in carbonate reservoirs, offering a basis for optimizing CO2-foam flooding strategies for enhanced oil recovery and carbon sequestration.

Ethoxylated molybdenum disulphide based nanofluid for enhanced oil recovery

Despite advances in renewable energy sources, the world's current infrastructure and consumption patterns still heavily depend on crude oil. Enhanced oil recovery (EOR) is a crucial method for significantly increasing the amount of crude oil extracted from mature and declining oil fields. Nanomaterials have shown great potential in improving EOR methods due to their unique properties, such as high surface area, tunable surface chemistry, and the ability to interact at the molecular level with fluids and rock surfaces. This study examines the potential use of incorporating ethoxylated molybdenum disulfide with a unique three-dimensional flower-like morphology for overcoming the challenges associated with oil recovery from reservoirs characterized by complex pore structures and low permeability. The synthesized nanomaterial features a chemical composition that encompasses a polar ethoxy group linking molybdenum disulfide nanosheets and an alkylamine chain. The ethoxy group promotes interactions with water molecules through hydrogen bonding and electrostatic forces, disrupting the cohesive forces among water molecules and reduction surface tension at the oil–water interface. As a result, the nanomaterial achieves an ultra-low interfacial tension of 10−3 mN/m. Core flooding experiments demonstrate a significant oil recovery of approximately 70% at a concentration as low as 50 ppm. This research paves the way for the design and synthesis of advanced extended surfactant-like nanomaterials, offering a promising avenue for enhancing oil recovery efficiency.

Synthesis and properties of AM/AMPS/MMA and cationic monomer copolymer flooding agent

Abstract A novel hydrophobic association copolymer (PAMA) was synthesized by incorporating acrylamide (AM), 2-acrylamide-2-methylpropanesulfonic acid (AMPS), cationic monomer (MEDDA), and methyl methacrylate (MMA). The properties of MMA copolymers with varying contents were analyzed using infrared spectroscopy, nuclear magnetic resonance spectroscopy, and scanning electron microscopy. Optimal overall performance of the solution was achieved when the MMA content reached 1.4 % w/w. Compared to pure PAAM (without MMA), the PAMA-1.4 % polymer exhibited superior viscoelasticity, temperature resistance, and shear resistance. This enhancement in PAMA performance can be attributed to the significant inhibition of intermolecular water film formation within the polymer matrix by MMA, effectively improving and regulating solution solubility while strengthening molecular chain interactions and enhancing the structural network strength of PAMA polymers. Additionally, the inclusion of MMA transformed rock surfaces from non-wetting to wetting conditions, thereby greatly improving oil displacement efficiency. In displacement experiments, PAMA-1.4 % performed better in terms of enhanced oil recovery, the recovery rate of 0.1 % w/w PAMA-2.4 % solution is only 7.78 %, while the recovery rate of 0.1 % w/w PAMA-1.4 % solution is 13.06 %.

Impact of nanoparticle movement on oil mobilization: Particles adsorbed at the oil–water interface versus particles dispersed in bulk fluid

Active colloid particles have been used in many fields due to their good performance in enhancing mass transport or modifying interfacial energy. Previous studies have shown that both nanoparticles adsorbed at oil–water interface and those dispersed in bulk fluid could enhance oil recovery during the oil production process. It is challenge to directly compare these results and clarify the effect of nanoparticle’s location on oil detachment from rock surface because different kinds of nanofluids were used in those work. Herein, the oil mobilization performance by nanoparticles adsorbed at oil–water interface and dispersed in the bulk phase were investigated from the pore-scale to core-scale by using one material. Two fluorescent quantum nanodots with different affinities for oil and water phases were synthesized using the same materials but with different compositions and solvents. Their locations were observed under the laser confocal microscopy. The nanoparticles adsorbed at the oil–water interface not only presented a lower interface tension, but also demonstrated a notable capability to change the wettability from oil-wet to water-wet due to its strong tendency to rock surface. The particles-laden interface can also increase the stability and shear viscosity of formed emulsions. Furthermore, it featured a larger swept area of 6.6 % in microfluidic flooding and a higher displacement efficiency of 1.7 % in the core flooding experiments. All these findings indicate that the particle-adsorbed at the oil–water interface is more favorable for enhanced oil recovery.

A Multilevel Classification Strategy for the Identification of Discontinuities from 3D Point Clouds of Complicated Rock Surfaces

A Multilevel Classification Strategy for the Identification of Discontinuities from 3D Point Clouds of Complicated Rock Surfaces

Assessment of the influence of natural thermal cycles on dolomitic limestone rock columns: A 10-year monitoring study

Rock instabilities hazards can lead to major risks. Even if different external factors such as precipitation, seismic activity or freezing, are known to trigger rockfalls, it is more and more assumed that thermal cycling has a role in rock mass deformation, displacement and, moreover cracking initiation or propagation. Here we present 10 years monitoring of a 50-meter-high dolomitic cliff, located above an important highway in the south of France to support this thinking. Local rock surface temperature and joint apertures were recorded on eleven sensors. Their evolution is studied separately and together to characterise the influence of temperature variation on joint apertures. During small time periods, a reversible and proportional behaviour is observed, that can be attributed to thermoelasticity, but over the whole period, a significant drift in displacements is measured, meaning that at least a viscoplastic or fatigue behaviour should be considered.

Exploring the use of zwitterionic liquids for hydrogen desorption and release from calcite rock oil reservoirs. A theoretical study

A theoretical model is presented to describe the processes of release and desorption of molecular hydrogen from the depths of calcite rock oil fields via surfactants such as zwitterionic liquids. This model is based on molecular mechanics and dynamics, for which we built a supercell with a calcite crystalline unit cell in order to model the {1,0,4} surface and volume of the calcite rock; 42 H2 molecules adsorbed and interacting strongly with the calcite surface stone were analyzed in this work; the effect of crude oil is simulated with an asphaltene macromolecule model. Finally, a branched geminal zwitterionic liquid (ZL) molecule is applied to initiate the process of hydrogen desorption and release. The aqueous medium of the oil field is simulated by the dielectric constant of water. The most stable molecules were obtained using forcite computational code. While the interaction energies were calculated by classical molecular mechanics using Dreiding force field. The dynamics of the H2 desorption and release process from calcite rock of oil well is studied using the classical molecular dynamics. The purpose of the work is to theoretically demonstrate that ZL substances are capable of releasing and desorb hydrogen from the calcite surface in the depths of oil fields. The results indicate that ZL polar groups form cation-π interactions with the asphaltene benzene rings structure, and that, the carbonated chains of the former trap the latter to release molecular hydrogen. Finally, the aqueous medium desorbs hydrogen from the calcite surface and transports it to the surface of the oil field.

Strain rate-dependency of thermal infrared radiation of sandstone subjected to dynamic loading: Insights from a lab testing

Rocks are generally deformed and fractured upon various scales of strain rates. Understanding the strain rate effects on the thermal infrared radiation (IR) characteristics of rock materials is crucial for predicting and detecting rock failure. In the study, uniaxial compression experiments were conducted on sandstone samples at different strain rates using an Instron hydraulic servo testing machine and a split Hopkinson pressure bar (SHPB) system. Meanwhile, a thermal infrared camera was utilized to capture and record the changes in the IR temperature on the rock surface. The spatial and temporal evolution of thermograms, IR temperature distribution histograms, and average IR temperature (AIRT) during testing were obtained and analyzed. A quantitative correlation between strain rate and the variation in AIRT (ΔT) was established. Furthermore, the dissipation of heat energy (Q) in the sandstone samples during SHPB tests was estimated. Results indicated that at relatively lower strain rates (ranging from 10−6 to 10−2 s−1), the ΔT of rock sample exhibited slight dependence on strain rate. However, a significant rate sensitivity emerged when the strain rate exceeded a specific threshold (approximately 137.09 s−1 for the tested sandstone). The rate-dependent behavior of ΔT across the investigated range of strain rate (up to 102) can be characterized by an allometric power model. Notably, during SHPB testing, the proportion of Q was negligible despite the pronounced rate dependency of heat energy. The abrupt rises in ΔT and Q under dynamic loading conditions can be elucidated by the increasing occurrence of shear cracks and energy-level jumps stimulated by impact disturbance.

Numerical Simulation Study of Factors Influencing Ultrasonic Cavitation Bubble Evolution on Rock Surfaces during Ultrasonic-Assisted Rock Breaking

Numerical Simulation Study of Factors Influencing Ultrasonic Cavitation Bubble Evolution on Rock Surfaces during Ultrasonic-Assisted Rock Breaking

Anisotropy of surface morphology of carbonate rocks after reaction with acid

In acid fracturing, acid is injected into artificial fracture to dissolve the rock, and the rock surface is shaped into the non-uniform morphology. This non-uniform morphology is the main cause of fracture conductivity after acid etching. The effects of acid type, flow rate, contact time and rock type on the non-uniform morphology of acid-etched rock surface have been studied. However, when the direction of acid flow is determined, the difference of dissolution characteristics in different directions of rock surface is not investigated. In this paper, acid rock reaction experiment and analysis of rock surface morphology after acid etching are carried out by using rock samples with flat surface. The difference of morphological characteristic parameters of rock surface in different directions under the condition of acid flow is discussed. It was found that the mean drop height, drop height range and roughness coefficient increase with the increase of acid rock reaction rate on flat rock surface. The morphological characteristic parameters of acid-etched rock face of limestone are greater than those of dolomite, which is conducive to forming acid-etched channels. According to the statistics of all experimental data, the larger average drop height of rock surface is distributed in the direction of parallel acid flow, the larger drop height range is distributed in the direction of vertical acid flow and other directions, and the larger roughness coefficient is distributed in other directions.

The potential of in situ cosmogenic 14CO in ice cores as a proxy for galactic cosmic ray flux variations

Abstract. Galactic cosmic rays (GCRs) interact with matter in the atmosphere and at the surface of the Earth to produce a range of cosmogenic nuclides. Measurements of cosmogenic nuclides produced in surface rocks have been used to study past land ice extent as well as to estimate erosion rates. Because the GCR flux reaching the Earth is modulated by magnetic fields (solar and Earth's), records of cosmogenic nuclides produced in the atmosphere have also been used for studies of past solar activity. Studies utilizing cosmogenic nuclides assume that the GCR flux is constant in time, but this assumption may be uncertain by 30 % or more. Here we propose that measurements of 14C of carbon monoxide (14CO) in ice cores at low-accumulation sites can be used as a proxy for variations in GCR flux on timescales of several thousand years. At low-accumulation ice core sites, 14CO in ice below the firn zone originates almost entirely from in situ cosmogenic production by deep-penetrating secondary cosmic ray muons. The flux of such muons is almost insensitive to solar and geomagnetic variations and depends only on the primary GCR flux intensity. We use an empirically constrained model of in situ cosmogenic 14CO production in ice in combination with a statistical analysis to explore the sensitivity of ice core 14CO measurements at Dome C, Antarctica, to variations in the GCR flux over the past ≈ 7000 years. We find that Dome C 14CO measurements would be able to detect a linear change of 6 % over 7 ka, a step increase of 6 % at 3.5 ka or a transient 100-year spike of 190 % at 3.5 ka at the 3σ significance level. The ice core 14CO proxy therefore appears promising for the purpose of providing a high-precision test of the assumption of GCR flux constancy over the Holocene.

Tension Capacity of Crushed Limestone-Cement Grout.

The feasibility of using crushed limestone instead of sand in cement grout is examined in this work. This study entails performing several tests, including the Brazilian test, the compressive strength test, and the stress-strain correlation test. The curing times used were 7, 14, and 28 days for mixtures with various proportions of cement to limestone (1:1, 1:2, and 1:4). The conventional sand-cement grout laboratory tests were prepared using a similar methodology to examine the effectiveness of the suggested substitute. The findings show that the limestone-based grout has sufficient strength, but that it is less than that of the typical sand material. The values of the tensile strength and elastic modulus were determined. A focus was made on the tensile strength and stress-strain relationship. A special laboratory set-up was used to look at the progress of failure using strain gauges fitted to the cylindrical samples both vertically and horizontally. The angular shape of the particles' ability to interlock is responsible for the material's increase in strength. According to this study, crushed limestone can be used as a substitute for sand in circumstances where sand supply is constrained. The suggested grout can be used in the shotcrete of tunnels and rock surfaces.

Exploring Machine Learning Techniques for Open Stope Stability Prediction: A Comparative Study and Feature Importance Analysis

The stability of underground excavations is essential for ensuring the safety of mining operations. Classical stability assessment methods, established in empirical formulas and rock mass classification systems, have long been employed for evaluating stope stability in underground mining. Stability graphs, a popular empirical approach, utilize factors like rock stress, joint orientation, and surface orientation to calculate stability numbers critical for stope design. However, modern advancements in machine learning present new opportunities for enhancing predictive capabilities and understanding complex relationships influencing stope stability. Building upon research demonstrating the feasibility of using machine learning for stability prediction, our study investigates and compares several machine learning algorithms. By analyzing a dataset comprising stope dimensions and geomechanical properties, we explore the potential of machine learning models such as Random Forest, Support Vector Machine, AdaBoost, XGBoost, LightGBM, and Artificial Neural Network in predicting stope stability. Evaluation metrics including accuracy, precision, recall, and F1 score are employed to assess model performance, with the Artificial Neural Network emerging as the most effective. Furthermore, SHapley Additive exPlanations (SHAP) analysis enhances interpretability by explaining the contribution of individual features to model predictions.

Damage evolution and fracture characteristics of coal rock impacted by self‐excited pulse water jet under different stress loading conditions

AbstractIn this paper, based on smoothed‐particle hydrodynamics‐finite element method, numerical models of plunger squeezing water at a sinusoidal velocity were established to simulate self‐excited pulse water jet (SEPWJ). RHT constitutive model was adopted to describe the damage and failure of coal rock impacted by water jet. The morphological evolutions of broken pits and timeliness of rock‐breaking efficiency of SEPWJ and continuous water jet (CWJ) under the conditions with and without stress loadings were obtained and compared. The evolution laws of damage and stress inner coal rock induced by jet impact, and the failure mechanism were revealed. And the influences of different stress loading magnitudes on the fracture characteristics of coal rock were investigated. The results show that the morphologies of broken pits formed by self‐excited pulse jet undergo changes in a semi‐circular, U‐shaped, V‐shaped, and bullet shaped in sequence under the stress‐free loading condition. When applying one‐dimensional (1D) and 2D stress loadings, the shallow but wide broken pits with laminar main cracks along the stress loading direction and the inverted trapezoidal bowl broken pits are formed, respectively. With the increase of 1D stress, the depth and width of broken pits slightly decrease as a quadratic parabolic function and linearly increase, respectively. And the broken pit width and area both show an exponential slow decreasing trends with the increasing 2D stress. SEPWJ can induce higher stresses to cause the earlier occurrence of initial damage and the shorter duration of damage accumulation to coal rock than CWJ, which leads to a better rock‐breaking effect. The surface and deeper coal rock elements are broken mainly due to compressive shear stresses. The 2D stress loading delays the initial damage occurrence and prolongs the damage accumulation duration due to inhibitory effect of stress loading on jet impact.