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Point cloud modeling of rock slopes using LIDAR and Structure-from-Motion digital stereophotogrammetry provides,at a minimum, thousands of facets and facet normals that can be used to identify the densities of orientations of rock massdiscontinuities, the geometries of potentially removable blocks, and the character of the excavation face. As part of the EngineeringGeology graduate curriculum at the Civil and Environmental Engineering program at the University of California, Berkeley we teachgraduate students an integrated methodology for [a] gathering point cloud information be laser or camera; [b] computing facets andfacet normals form point clouds for stereonet presentation and geometric analysis of block dimension; [c] extract rock massdiscontinuities from stereonet data to analyze key blocks, assess discontinuous deformation analysis (DDA) behavior, and modelrock slope stability. These new methods require a suite of different software tools discussed in the paper to move through the workflowprocess. Computational rock mechanics provides data sets that are orders of magnitude richer in detail and result in betterunderstanding of rock slope and tunnel key block behavior. Full application of computational rock mechanics methods should reducethe cost of bolting by identifying critical support orientations and design loads.

This study focuses on obtaining differences in rock fracture surface morphology under various loading directions and speeds to infer rock damage mechanics by using micro-electro–mechanical system (MEMS) sensors, which can measure stress, strain, and displacement during loading accurately, providing detailed data for understanding the rock fracture mechanism for physics-informed statistics. Statistical variables analyze directional angle samples of the normal vector central line. The deviation normal distribution coefficient (DNDC) for rock fracture surface normal vectors is defined by the kurtosis coefficient. Brazilian splitting tests calculate the DNDC for Brazilian disk fracture surfaces. The variation in the DNDC with a measurement scale distinguishes morphological differences. Three results are obtained: the DNDC has a scale effect; loading the specimen in another direction before compression causes internal damage; and different loading speeds do not significantly change the DNDC. This research holds promise for a better understanding of rock fractures. [ABSTRACT FROM AUTHOR]

High‐voltage electric pulse rock breaking has excellent potential for exploiting deep geothermal resources. Numerous researchers have conducted experimental studies on this topic, particularly in rock mechanics, where the breakdown occurs. However, there has been limited scholarly research on drilling fluid. Therefore, the study focuses on the drilling fluid suitable for electric pulse drilling, considering the characteristics of electric pulse rock breaking, which differ from traditional rock breaking. The study focused on the impact of various drilling fluid parameters on the effectiveness of electric impulse rock breaking using red sandstone as the experimental material. This was investigated using the finite element method, and indoor electric rock‐breaking tests were conducted in a drilling fluid environment. The results indicate that the plasma channel mainly grows in the permeable layer of the drilling fluid, resulting in shallow rock breaking depth in the drilling fluid environment. The pore permeated by drilling fluid guides the growth of the plasma channel. The higher the conductivity of the drilling fluid, the closer the ion channel of rock breaking by electric pulse is to the rock surface. This results in a smaller crushing volume and shallower damage depth, which is more detrimental to rock breaking by an electric pulse. The viscosity of drilling fluid can impede the breakdown to some extent. In this paper, the influence of drilling fluid parameters on electro‐pulse rock‐breaking technology is preliminarily studied, which has significant reference value for the selection of actual drilling fluid. [ABSTRACT FROM AUTHOR]

Tight sandstone reservoirs, despite their low porosity and permeability, present considerable exploration potential as unconventional hydrocarbon resources. Natural fractures play a crucial role in hydrocarbon migration, accumulation, and present engineering challenges such as late-stage reformation in these reservoirs. This study examines fractures in the seventh member of the Triassic Yanchang Formation's tight sandstone within the Ordos Basin using a range of methods, including field outcrops, core samples, imaging and conventional logging, thin sections, and scanning electron microscopy. The study clarifies the characteristics of fracture development and evaluates the relationship between dynamic and static rock mechanics parameters, including the calculation of the brittleness index. Primary factors influencing fracture development were quantitatively assessed through a combination of outcrop, core, and mechanical test data. Findings reveal that high-angle structural fractures are predominant, with some bedding and diagenetic fractures also present. Acoustic, spontaneous potential, and caliper logging, in conjunction with imaging data, enabled the development of a comprehensive probabilistic index for fracture identification, which produced favorable results. The analysis identifies four key factors influencing fracture development: stratum thickness, brittleness index, lithology, and rock mechanical stratigraphy. Among these factors, stratum thickness is negatively correlated with fracture development. Conversely, the brittleness index positively correlates with fracture development and significantly influences fracture length, aperture, and linear density. Fractures are most prevalent in siltstone and fine sandstone, with minimal development in mudstone. Different rock mechanics layer types also impact fracture development. These insights into fracture characteristics and controlling factors are anticipated to enhance exploration efforts and contribute to the study of similar unconventional reservoirs. [ABSTRACT FROM AUTHOR]

To address the environmental and formation damage caused by traditional hydraulic fracturing in coalbed methane and shale gas extraction, supercritical CO2 (SC-CO2) fracturing technology has emerged as an effective alternative due to its low viscosity, high diffusivity, and waterless nature. This paper reviews recent advancements in experiments and numerical simulations to explore the mechanisms of fracture initiation and propagation in this technology, with a focus on analyzing fracture initiation pressure, propagation patterns, and influencing factors. The findings show that SC-CO2 fracturing can generate complex fracture networks at lower initiation pressures, with stress conditions, temperature, and natural fractures significantly impacting fracture initiation and propagation. Additionally, the paper highlights existing limitations in accurately simulating CO2 flow, phase transitions, and its interactions with natural fractures, offering optimization suggestions and future perspectives. [ABSTRACT FROM AUTHOR]

Determining rock mass mechanical parameters and accurately predicting tunnel deformation during tunnel construction remain challenging tasks. This study introduces a novel approach to calculate the Geological Strength Index by integrating indoor rock mechanics tests with geometric data from three-dimensional dense reconstruction. We utilized the Hoek-Brown strength criterion to develop a theoretical model for predicting tunnel deformation in fractured rock masses. Case studies reveal that the average value of Geological Strength Index for the Xiamen highway tunnel's surrounding rock is 44. With support from the lining structure equivalent to 0.002–0.02 times the initial in-situ stress, the plastic zone thickness decreased by approximately 50%, and radial displacement was reduced by about 40%. Enhancing the lining structure's support pressure significantly reduces the plastic zone radius and radial displacement. As the Geological Strength Index decreases, the nonlinearity between support pressure and plastic zone radius becomes more pronounced, with a similar trend observed for the relationship between support pressure and tunnel radial displacement. The relative deviation between predicted and measured values did not exceed 1.69%. The method accurately captures the effects of rock fragmentation and tunnel construction on plastic zone formation and displacement, offering an effective approach for the rapid and secure assessment of rock tunnel excavation stability using digital technology. [ABSTRACT FROM AUTHOR]

In order to improve the reliability of the deployment of production schemes after artificial fracturing in tight reservoirs, it is urgent to carry out research on the description of fractures after artificial fracturing. In this study, taking the Chang 61 oil formation group in the Wangyao South area of Ordos Basin as an example, three different fracture modeling schemes are used to establish the geological model of fractured reservoirs, and the fitting ratios of the respective reservoir models are calculated by using the method of reservoir numerical simulation of the initial fitting, and the optimal fractured reservoir modeling scheme is screened in the end. The research area adopts three types of fracture prediction results based on FMI fracture interpretation data, seismic fracture prediction data, and rock mechanics artificial fracturing simulation data. On this basis, geological models of fractured reservoirs are established, respectively. The initial fitting of reservoir values of each geological model are compared, and the highest initial fitting rate of reservoir values is 88.44%, which is based on rock mechanics artificial fracturing simulation data. However, the initial fitting rate of the reservoir model was the lowest at 75.76%, which was established based on the fracture random modeling results of FMl fracture interpretation data. Under the constraints of seismic geostress prediction results and microseismic monitoring data, the simulation results of rock mechanics artificial fracturing fracture are used as the basis, on which the geological model of artificially fractured reservoirs is thus established, and this scheme can more realistically characterize the characteristics of fractured reservoirs after artificial fracturing in the study area. [ABSTRACT FROM AUTHOR]

Caves have long fascinated humanity, serving as shelters, canvases for artistic expression and now significant attractions in the realm of tourism. Among these remarkable geological formations, the Maltravieso cave in Extremadura, Spain, stands out for its rich archaeological and paleontological heritage, particularly its collection of Paleolithic rock art. Despite its cultural significance, there is a notable dearth of studies addressing the stability of the cave from an engineering perspective. This article presents a pioneering study aimed at assessing the stability of the Maltravieso cave through a multidisciplinary approach: using empirical geomechanical classifications such as the Q Index, Rock Mass Rating (RMR) and the recently formulated Cave Geomechanical Index (CGI), alongside other techniques like Structure from Motion (SfM), 2D numerical modeling and 3D wedge analysis. This research aims to fill the gap in our opinion of cave stability assessment. By combining field data collection with sophisticated analysis methods, this study seeks to provide valuable insights into the geomechanical properties of the Maltravieso cave and validate a simple yet effective methodology for evaluating the stability of natural caves. This work not only contributes to the body of knowledge regarding cave geomechanics but also underscores the importance of preserving these invaluable cultural and geological treasures for future generations. [ABSTRACT FROM AUTHOR]

To explore the precursory information and instability fracture of rocks, we conducted a series of uniaxial compression tests on flawed sandstone. An integrated warning modeling is developed to predict the fracture in flawed sandstone. The results show that both the peak strength and elastic modulus of flawed sandstone demonstrate an "inverted" Gaussian distribution relative to the ligament angle, reaching the minimum values at 60°. The elastic strain energy proportion shows a sharp drop‐off, whereas the proportion of dissipative energy increases in steps. The coalescence modes of flawed sandstone change from a mixed tensile‐shear failure approximately aligned with the axis to an oblique shear failure. An integrated warning model is developed by integrating a Multi‐Output Classifier (MOC) and Grid optimization (GO). The integrated warning model has an accuracy of 97.95%. Additionally, the sensitivity of the model is recorded at 99.26%, confirming its effectiveness in predicting the likelihood of fracturing. Highlights: The cracking process of flawed sandstone is classified based on energy characteristics.The elastic energy ratio and dissipative energy ratio of flawed sandstone are revealed.The precursory indicators are identified using b‐value, AE variance, and AE energy.An integrated warning model is developed in combination with RFA and MOC. [ABSTRACT FROM AUTHOR]

The features of rock shear-slip fracturing are closely related to the stability of rock mass engineering. Granite, white sandstone, red sandstone, and yellow sandstone specimens were selected in this study. The loading phase of "shear failure > slow slip > fast slip" was set up to explore the correlation between fracture type, acoustic emission (AE) features, and energy dissipation during the rock fracturing process. The results show that there is a strong correlation between fracture type, energy dissipation, and AE features. The energy dissipation ratio of tension-shear (T-S) composite, shear, and tensile types is 10:100:1. The fracture types in the shear failure phase are mainly tensile and TS composite types. The differential mechanism of energy dissipation of different rocks during the shear-slip process is revealed from the physical property perspectives of mineral composition, particle size, and diagenetic mode. These results provide a necessary research basis for energy dissipation research in rock failure and offer an important scientific foundation for analyzing the fracture propagation problem in the shear-slip process. They also provide a research basis for further understanding the acoustic emission characteristics and crack type evolution during rock shear and slip processes, which helps to better understand the shear failure mechanism of natural joints and provides a reference for the identification of precursors of shear disasters in geotechnical engineering. [ABSTRACT FROM AUTHOR]

Predicting rock tunnel squeezing in underground projects is challenging due to its intricate and unpredictable nature. This study proposes an innovative approach to enhance the accuracy and reliability of tunnel squeezing prediction. The proposed method combines ensemble learning techniques with Q-learning and online Markov chain integration. A deep learning model is trained on a comprehensive database comprising tunnel parameters including diameter (D), burial depth (H), support stiffness (K), and tunneling quality index (Q). Multiple deep learning models are trained concurrently, leveraging ensemble learning to capture diverse patterns and improve prediction performance. Integration of the Q-learning-Online Markov Chain further refines predictions. The online Markov chain analyzes historical sequences of tunnel parameters and squeezing class transitions, establishing transition probabilities between different squeezing classes. The Q-learning algorithm optimizes decision-making by learning the optimal policy for transitioning between tunnel states. The proposed model is evaluated using a dataset from various tunnel construction projects, assessing performance through metrics like accuracy, precision, recall, and F1-score. Results demonstrate the efficiency of the ensemble deep learning model combined with Q-learning-Online Markov Chain in predicting surrounding rock tunnel squeezing. This approach offers insights into parameter interrelationships and dynamic squeezing characteristics, enabling proactive planning and support measures implementation to mitigate tunnel squeezing hazards and ensure underground structure safety. Experimental results show the model achieves a prediction accuracy of 98.11%, surpassing individual CNN and RNN models, with an AUC value of 0.98. [ABSTRACT FROM AUTHOR]

The natural non-penetrated openings in natural rock masses due to weathering and erosion and the artificial non-penetrated openings formed in deep mining and tunneling have significant effects on the stability and safety of rock engineering. Hence, the uniaxial compression test, 3D particle flow code (PFC3D) simulation, and digital image correlation (DIC) method are used to systematically investigate the influence of the opening penetration ratio (OPR) on the mechanical behaviors and fracture characteristics of rocks containing the non-penetrated opening. Further, the maximum principal strain/stress distributions around the opening on both sides of the specimen are compared to quantitatively analyze the effect of OPR on the crack initiation mechanism from the microscopic perspective. The results show that as OPR increases, the uniaxial compressive strength (UCS) and elastic modulus (E) of sandstone/numerical specimens show a linearly decrease law, and the failure mode exhibits a law of shear failure to tensile-shear mixed failure and then to shear failure. The fracture process analyses show that the two sides of specimens containing non-penetrated opening have different cracking characteristics and belong three-dimensional failure, while the specimen containing penetrated opening are two-dimensional failure. The stress/strain distribution around the opening is altered by the support effect in the non-opening part of specimens. Therefore, as the OPR increases, the crack initiation stress level decreases and the crack initiation crack type around the opening changes from the tensile-shear to tensile. Finally, implications of the study for fracture prevention in underground excavation engineering and early warning of instability in rock engineering are given. These findings enrich the study on the failure mechanism of rock masses containing defects, which is of great importance for rock engineering safety. Highlights: The uniaxial compression strength and elastic modulus of sandstones decrease linearly with increasing opening penetration depth. The cracking behaviors of sandstone with non-penetrated opening are three-dimensional. The pre-existing defect surface of sandstone with non-penetrated opening is cracking first and failure first. The changes in stress/strain distribution around the opening on both sides make differences in the crack initiation mechanism and initiation stresses. The findings are instructive for fracture prevention in underground excavation engineering and early warning of instability in rock engineering. [ABSTRACT FROM AUTHOR]

In this paper, a novel three-dimensional grain-based model based on particle flow code (PFC3D-GBM) is used to reconstruct the crystalline structure of granite, which enables the grouping and filling of minerals. Some contacts in the numerical sample are grouped separately and then calibrated with lower microparameters, which represent mesoscopic defects within natural granites. In addition, considering the heterogeneity of the levels of force chain networks in different structures of granites, a multilevel classification of the entire force chain network is accomplished. A uniaxial compression test is conducted to quantify the effect of the microtensile strength σD and volume proportion VD of mesoscopic defects on the macroscopic mechanical behaviour of granites at various points of the force chains. Both the strength and modulus of the sample increase as σD increases. The mean, sum and maximum of the general force chains of the intact structures and defect structures increase with increasing σD. The bearing capacity of various structures also increases. Both the strength and modulus of the sample decrease as VD increases, and the strength of the overall force chain network decreases. The mean, sum and maximum values of the general force chains of the intact structures decrease. Although the number of force chains in the corresponding defect structures greatly increases, the average level of the force chain network decreases. The bearing capacity of the various structures decreases as VD increases. Highlights: A three-dimensional grain-based model is proposed, which enables the multilevel classification and quantitative analysis of the force chain network. The mesoscopic defects within natural granites are reproduced by grouping "weak contacts" with low microstrengths. The influence of the microstrength and volume proportion of defects on granites is explored based on the multilevel force chain network. The bearing capacity of granites is proportional to the microstrength of defects and is inversely proportional to the volume proportion. [ABSTRACT FROM AUTHOR]

Natural fractures are effective storage spaces and the main seepage channels of tight reservoirs, and the spacing and role of structural fractures of different scales in tight reservoirs are also different. However, the opening or height of underground natural fractures is often difficult to determine directly using seismic data or imaging logging, which restricts the characterization, modeling, and analysis of the formation mechanisms of reservoir fractures. This paper uses the morphology of water absorption profiles and conventional logging data to calculate the ratio of the isotope intensity of a single well to natural gamma values from logging and characterize the types of water absorption profiles. The size (opening and height) of the fractures is closely related to the height of the water absorption profile and the fluctuation in the water absorption intensity. The calculated rock mechanics parameters along a single well, combined with the internal friction angle of the rock and the fracture strike, are used to determine the magnitude and direction of the paleostress of the Y290-Y414 Block in the southeastern Ordos Basin during the Himalayan period. By establishing a single-well geomechanical model to simulate the three-dimensional distribution of paleostress and paleostrain during the formation of fractures, a database model for constructing the scale of fractures is established. Through correlation analysis, a model for predicting the strength and thickness of the water absorption profile is established. Finally, the three-dimensional distribution pattern of the scale of structural fractures is predicted, and the reliability of the prediction results is verified using dynamic development data. The research results have certain reference significance for explaining the mechanism of fracture formation, characterizing the scale of underground fractures, and modeling reservoir fractures. Highlights: A model for predicting the height and opening of structural fractures is established. The scale of fractures is closely related to the mechanical structure of the rock layers. The presence of large-scale fractures is the main cause of water channeling and flooding. [ABSTRACT FROM AUTHOR]

Rapid and partial acquisition are features of rock drilling for obtaining rock properties. Most previous research has primarily concentrated on how to quickly obtain rock mechanics parameters, with limited emphasis on extracting rock parameter fields, particularly in three dimensions. This study attempted to develop a numerical integrated method to extract 3D parameter fields of rocks based on a newly developed digital-controlled drilling platform. The importance of incorporating a damage model for accurate simulations of rock drilling through finite element analysis (FEA) was investigated. By calibrating damage parameters through uniaxial compressive strength (UCS) and Brazilian tensile strength (BTS) tests, these parameters can be considered constants in rock drilling simulations across various rock types. The accuracy of rock parameters estimated by the proposed method and the derived analytical model were further demonstrated through comparison with the corresponding standard tests. Furthermore, the 3D parameter field of rocks was obtained by integrating a deep learning method and micro-CT technology. The numerical prediction illustrated the advantages of acquiring a rock parameter field in achieving more accurate simulations of the rock failure process. Besides, our solution can also provide support for the parameter selection of numerical models considering spatial variability for natural rocks. Highlights: A digital-controlled equipment for rock drilling was developed. Equations were derived for extracting rock parameters through the drilling data. A deep learning method was developed to reproduce the three-dimensional parameter field of rocks. The significance of considering the realistic rock parameter field was numerically demonstrated. [ABSTRACT FROM AUTHOR]

Large deformation phenomena in rock engineering are commonly key bottlenecks impeding engineering progress. Correspondingly, large deformation analysis in rock mechanics has a widespread impact on mechanism understanding, prevention, and control guidance. Various large deformation schemes broadly categorized as hypoelastic- and hyperelastic-based models exist in the literature and software. Without an understanding of the capabilities and demerits of these schemes, the diversity in choices inadvertently leads to pitfalls, placing engineering endeavors at a disadvantage. In this work, we review and compare the most prevalent schemes (including PK2-Green, Jaumann, Green–Naghdi, Truesdell, and hyperelastic-based schemes) from perspective of rock mechanics, with an emphasis on their application in rock engineering, and further develop a hyperelastic-based large deformation scheme (marked as Cauchy-Ln scheme) based on Cauchy stress and Hencky logarithm strain. The proposed model realizes the separation of material nonlinearity and geometry nonlinearity. Several typical large deformation phenomena in rock engineering are studied. The relationships between large deformation phenomena and large deformation analyses are clarified under different circumstances. Especially under large strain conditions, the PK2-Green scheme is enfeebled, and the hypoelastic-based scheme should be used with caution. For rock material with an apparent pressure-sensitive effect, the proposed Cauchy-Ln scheme is superior. Highlights: The connections between large deformation phenomenon and large deformation analysis are delineated. Prevalent large deformation schemes are compared from a rock mechanics perspective with an emphasis on application in rock engineering. A newly hyperelastic-based large deformation numerical model, enhancing compatibility with rocks, is developed. [ABSTRACT FROM AUTHOR]

The stability of the oil well wellbore is a prerequisite for selecting the optimal completion method. In this paper, based on experimental testing and theoretical models of rock mechanics parameters in deep oil reservoirs, the in situ stress parameters of deep oil wells are accurately predicted. On this basis, a full life cycle assessment model for wellbore and perforation casing stability was established, and the effects of pressure depletion and changes in the production pressure differential on wellbore stability and casing stability were analyzed. The research results indicate that as the formation pressure decreases, the critical collapse pressure difference around the wellbore significantly decreases. The greater the production pressure difference, the more likely the wellbore is to become unstable. Under the original formation pressure coefficient, if there is no casing, the critical failure pressure difference of the wellbore wall is 55 MPa. After cementing and perforation, when the casing is uniformly stressed and the formation pressure drops to a coefficient of 0.83, the casing will not be damaged even when the wellbore is completely emptied. At this time, there is still a certain safety production pressure difference in the perforated formation. This study can effectively guide the optimization of well completion and safe development in deep oil reservoirs. [ABSTRACT FROM AUTHOR]

This study aims to achieve rapid drilling of life-support holes, regarding the optimization design of drill bits as the key, among which the simulation analysis of drill bit cutting teeth is an important technical means. Firstly, based on the rock mechanics test results in the study area combined with the corresponding logging information, the analysis and evaluation of the geological conditions in the study area were completed, a complete rock mechanics characteristic profile was established, and the drillability of the rock was calculated to be relatively good. Then, a numerical simulation of parallel cutting of rock with conical teeth was established by experimentally testing rock mechanics parameters and using the discrete element method (PFC2D). The simulation study of the drill bit cutting teeth was completed by parameter calibration, analysis of rock cutting morphology, analysis of the number of rock cutting cracks, and analysis of the specific work of rock cutting and breaking. It was determined that the optimal rock-entering angle of the drill bit cutting teeth in the Shouyang mining area is 14°. Finally, verified by field practice, the optimized drill bit has stable performance, strong cutting ability, and good wear resistance; the maximum instantaneous mechanical drilling speed reaches 58.14 m/h, and it shows a slightly worn state after continuously drilling 582 m in the stratum, meeting the requirements of one-trip drilling and hole formation for life-support holes. This research provides a scientific basis and practical techniques for the construction of life-support holes in the Shouyang mining area and under similar geological conditions. It can provide more effective emergency plans and rescue strategies for possible mine disasters in the future, which is crucial for improving the technical system of emergency rescue for mine accidents and enhancing the emergency rescue capability of surface drilling. [ABSTRACT FROM AUTHOR]

The damage evolution process of layered rock is influenced by its fine structure, lamination direction, and confining pressure, exhibiting significant anisotropic characteristics. This study focuses on shale as the research object, employing indoor tests and theoretical analysis to define damage variables and initial damage based on ultrasonic wave velocity. This research investigates the damage evolution law of layered rock under varying confining pressures and dip angles. The findings reveal that damage variables defined using transverse wave velocity effectively reflect the damage evolution process. Additionally, confining pressure significantly affects damage evolution, with increasing pressure causing a rightward shift in the damage variable–strain curve and an increase in initial damage. The slab inclination angle also influences damage evolution; samples with 45° and 60° inclinations are more susceptible to damage, with initial damage showing a trend of increasing and then decreasing. To accurately describe the relationship between damage variables and strain during the loading process, this paper establishes a segmented damage evolution equation characterized by wave velocity. Initially, an inverse proportional function is employed to characterize the strain before crack closure. Subsequently, a logistic function represents the curve from crack strain to peak strain. This combined approach provides a comprehensive depiction of the damage evolution. This study underscores the importance of considering confining pressure and laminar inclination in the analysis of rock stability and integrity. These results provide critical insights into the damage evolution characteristics of layered rocks, offering valuable references for engineering safety assessments. [ABSTRACT FROM AUTHOR]

Complex underground conditions make it challenging to conduct extensive coring, and it is difficult for laboratories to carry out a large number of rock mechanics experiments due to the limited number of cores. Rock-like specimens are commonly used in the laboratory to replace coal-rock specimens. In this paper, rock-like specimens with different proportions are produced to study the mechanical properties, failure characteristics, and acoustic emission laws of rock-like specimens under uniaxial compression. The results show that when the rock-like specimen does not contain gypsum, the stress of the specimen decreases rapidly after reaching the peak stress, which is similar to the mechanical properties of hard brittle rock. When the rock-like specimen contains gypsum, the stress of the specimen decreases slowly after reaching the compressive limit, and the failure of the specimen is gentle, which is similar to the mechanical properties of soft rock. When the specimen lacks gypsum, the strength of the rock-like specimen is larger, and the strength of the specimen is positively correlated with the proportion of cement. When the specimen contains gypsum, the strength of the rock-like specimen decreases sharply, and the strength of the rock-like specimen is negatively correlated with the proportion of gypsum. The maximum acoustic emission ringing count increases with higher cement content but decreases with increased gypsum content. The cumulative count change of acoustic emissions approximately underwent four stages, aligning well with the four stages of uniaxial compression failure observed in typical rock. The research results have important reference value for the selection of rock-like materials to replace the original rock materials for laboratory research. [ABSTRACT FROM AUTHOR]

With the increasing demand for mineral resources, mining operations are gradually moving into deeper levels, leading to a rise in the severity of the high-temperature thermal hazard caused by geothermal heat in mines. To understand the distribution and characteristics of the temperature field in the surrounding rock of metal mines, this study derived a non-steady-state heat conduction differential equation suitable for the surrounding rock of underground metal mines based on the thermal property changes of rocks at high temperatures, thereby obtaining the distribution characteristics of the thermal insulation ring in the surrounding rock. However, the monitoring technology of the underground rock temperature field is constrained by factors such as long-term power supply of equipment and complex data collection. Therefore, based on high-precision temperature acquisition devices, this study developed and constructed a cloud monitoring system for the temperature field of the surrounding rock, realizing long-term online temperature field monitoring of the 930 m and 945 m horizontal underground roadway in the West Mountain mining area of Sanshandao. The monitoring data indicate that the system has stable data transmission and smooth operation, achieving remote long-term data collection and transmission. This has improved the efficiency of monitoring the temperature field of surrounding rocks in mines, providing a basis for the risk assessment of thermal environmental conditions in deep high-temperature areas of metal mines and the control of the thermal hazard in deep underground engineering. [ABSTRACT FROM AUTHOR]

The deep integration of computer field and coal mining field is the only way to coal mine intellectualization. A variety of artificial intelligence tools have been applied in open-pit and shallow coal mines. However, with the geometric increase of coal demand, the contradiction between supply and demand is becoming more and more serious, and the exploitation of resources from shallow layer (> 600 m) has become an inevitable trend. Well then, as a new engineering scene, the harsh conditions of "three high and one disturbance" seriously threaten the safety of personnel. The superposition of complex mining environment makes the number of input factors increase sharply, which leads to the application of artificial intelligence in deep coal mine roadway engineering. The guidance is not mature, the construction of various databases is missing, and there are still some problems in universality and applicability. To this end, this paper starts with the introduction of the operating characteristics of various artificial intelligence tools, and conducts a comprehensive study of the relevant high-level articles published in top journals. It systematically sorts out the research progress that has successfully solved the five directions of rock mechanics strength, surrounding rock stability, rock-burst, roof fall risks and micro-seismic events. While objectively evaluating the comprehensive performance of different tools, it also expounds its own views on key research and results. Literature review shows that whether as a development tool or a comparative model, the application of ANN in the field of coal mining is more than 98%, and it performs extremely well in the direction of surrounding rock stability and roof fall risk, with an accuracy rate of more than 90%. As the most mature direction of AI tools application, rock mechanical strength has experienced the development process from "SVM → ANN → DL → XGBoost → RF". The dataset is from small samples (< 100) to big samples (> 1000), and the R2 of tree-based models can be stabilized at more than 95%. The research on rock-burst prediction mainly focuses on field factors and micro-seismic monitoring data. Whether it is a small sample or a large-scale data model, the accuracy of BN remains above 85%. The prediction and evaluation of micro-seismic events is a new direction in recent years. The image processing and application of CNN is extremely important. The signal recognition and classification accounts for more than 90%, and the research potential of source location needs to be further explored. In general, the nature of the rock itself is the first choice for almost all influencing factors. At the same time, the update iteration of monitoring methods (micro-seismic, ground sound, separation, deformation, etc.) expands the development of the database, making it possible to obtain the data due to threat to life and cost of equipment, which is very difficult to obtain before. In the process of parameter selection at the input end, the method of combining lithology conditions, geological environment and monitoring data will gradually become the first choice for research. Finally, in the follow-up work collation and on-the-spot investigation, it mainly focuses on the existing problems of deep coal mines, explores the application potential of artificial intelligence in deep coal mine roadway engineering, puts forward the possible research focus and challenging problems in the future, and gives its own opinions. [ABSTRACT FROM AUTHOR]

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The carrying-soil effect is an important factor affecting the success or failure of rectangular pipe jacking construction. Because it is difficult to explore the dynamic evolution process of the carrying-soil effect in the field test, this paper relies on the pipe jacking project of a comprehensive pipe gallery in Suzhou City, and uses ABAQUS 2021 finite element software to simulate the jacking process of rectangular pipe jacking. Based on the theory of plastic mechanics of rock and soil and the related research and application status, the equivalent plastic strain index is introduced as the basis for judging the failure boundary of soil in the numerical simulation results, and the boundary between the carrying-soil area and the surrounding soil is determined, that is, the shear fracture surface. According to the principle of plastic potential energy, the development direction of the fracture surface is consistent with the direction of plastic flow, so as to predict the development direction of the boundary of the carrying-soil area. According to the change in the equivalent plastic strain cloud map with the jacking mileage, the evolution process of the carrying-soil effect is clarified, and the dynamic evolution law of the carrying-soil area is revealed, which is of great significance for predicting the disturbance of the surrounding soil during the construction of rectangular pipe jacking and accurately evaluating the environmental effect of the construction. [ABSTRACT FROM AUTHOR]

Undercutting anchors are structural elements used in construction and geotechnics to stabilize both structures and soils. Their main applications include stabilizing slopes and embankments, reinforcing foundations, and providing support during tunnel construction and other underground works. The authors propose the use of these anchors in rock mass detachment technology. This article presents a comprehensive analysis of the mechanism behind rock mass detachment using an undercutting anchor. Particular attention is given to the influence of parameters such as the fracture energy of the medium and the coefficient of friction between the medium and the anchor head on the detachment process of rock elements during anchor expansion in the drilled hole. Numerical FEM analysis was employed to model the effect of changes in the shape and size of failure cones under varying simulation conditions. The discussed problem is crucial for evaluating the effectiveness of this anchor design under non-standard conditions, particularly in the unconventional destruction of rock media. [ABSTRACT FROM AUTHOR]

Externally applied stress on the rock matrix plays a crucial role in oil recovery from naturally fractured tight reservoirs, as local variations in pore pressure and in-situ tension are expected. The published literature severely lacks in evaluations of the characteristics of hydrocarbons, displaced by water, in fractured reservoirs under the action of externally applied stress. This study intends to overcome this knowledge gap by resolving complex time- and stress-dependent multiphase flow by employing a coupled Finite Element Method (FEM) and Computational Fluid Dynamics (CFD) solver. Extensive three-dimensional numerical investigations have been carried out to estimate the effects of externally applied stress on the multiphase flow characteristics at the fracture–matrix interface by adding a viscous loss term to the momentum conservation equations. The well-validated numerical predictions show that as the stress loading increases, the porosity and permeability of the rock matrix and capillary pressure at the fracture–matrix interface decrease. Specifically, matrix porosity decreases by 0.13% and permeability reduces by 1.3% as stress increases 1.5-fold. Additionally, stress loading causes a decrease in fracture permeability by up to 29%. The fracture–matrix interface becomes more water-soaked as the stress loading on the rock matrix increases, and thus, the relative permeability curves shift to the right. [ABSTRACT FROM AUTHOR]

The plastic flow behavior of soft rock exhibits non-coaxial features under complex stress paths, while traditional plasticity theories are ill-equipped to adequately represent this, which leads to the mechanism of soft rock failure still unclear. To investigate the evolution law of strain increments and non-coaxial characteristics of weakly cemented soft rock, the directional shear tests are conducted using the hollow cylinder apparatus (HCA). The results show that non-coaxiality does not occur when α is distinct from 0° or 90°. The oscillation of the non-coaxial angle is significantly more variable in soft rock experiencing combined tension–torsion (45° < α < 90°), as opposed to those under the influence of combined compression-torsion (0° < α < 45°). The non-coaxiality swiftly dissipates when the sample is approaching the failure state. The stress rate is decomposed into stress magnitude and direction to describe non-coaxial features of plastic strain. And a new method for non-coaxial stress rate is proposed which can express the plastic strain increment directions. The spherical interpolation coefficient method is utilized to describe the continuous change in non-coaxial plastic flow direction between tangential and normal directions of the yield surface. The non-coaxial parameter (Δ) is introduced to quantify the non-coaxial characteristics of soft rock and its validity is confirmed through test results. This method effectively captures the principal stress direction influence on non-coaxial behavior of soft rock and have significance for rock mechanics. [ABSTRACT FROM AUTHOR]

Shear strength (SS) parameters are essential for understanding the mechanical behavior of materials, particularly in geotechnical engineering and rock mechanics. This study proposes a novel hierarchical ensemble model (HEM) to predict SS parameters: cohesion (C ) and angle of internal friction (φ ). The HEM addresses the limitations of traditional machine learning models. Its performance was validated using leave-one-out cross-validation (LOOCV) and out-of-bag (OOB) evaluation methods. The model's accuracy was assessed with R-squared correlation (R2), absolute average relative error percentage (AAREP), Taylor diagrams, and quantile–quantile plots. The computational results demonstrated that the proposed HEM outperforms previous studies using the same database. The model predicted φ and C with R2 values of 0.93 and 0.979, respectively. The AAREP values were 1.96% for φ and 4.7% for C . These results indicate that the HEM significantly improves the prediction quality of φ and C , and exhibits strong generalization capability. Sensitivity analysis revealed that σ_3maxσ3max (maximum principal stress) had the greatest impact on modeling both φ and C . According to uncertainty analysis, the LOOCV and OOB had the widest uncertainty bands for the φ and C parameters, respectively. [ABSTRACT FROM AUTHOR]

The paper presents the results of a comprehensive investigation of the applicability of various intelligence methods for the optimal prediction of rock mass caveability in block caving using effective geomechanical parameters. However, due to the complexity of the prediction of rock mass cavability, artificial intelligence-based methods, including the classification and regression tree (CART), support vector machines (SVM), and artificial neural network (ANN), have been selected. For validating and comparing the results, common MVR was used. Because of the dependency of the modelling generality and accuracy on the number of data, we attempted to obtain an adequate database from the results of numerical modelling. The distinct element method (DEM) used to study the rock mass cavability. The results indicated that ANN is the most accurate modelling technique with a determination coefficient of 0.987 compared with the other aforesaid methods. Finally, the sensitivity analysis showed that joint spacing, friction angle, joint set number, and undercut depth are the most prevailing parameters of rock mass cavability. However, the joint dip has shown the minimum effect on rock mass cavability in the block caving mining method. [ABSTRACT FROM AUTHOR]

Slope stability analysis is widely recognized as a crucial aspect in rock mechanics engineering, playing a fundamental role in the design of various rock and soil structures like mining slopes, roads, and tunnels. Over time, several methods have been proposed to address stability concerns, including limit equilibrium methods, numerical approaches, and artificial intelligence techniques. In this study, we conducted stability analysis of mine wall slopes using a neuro-fuzzy integrated approach (ANFIS). Using data from the Choghart iron mine, we developed two neuro-fuzzy networks to analyze the safety and stability of circular failures under static loading conditions. Six parameters were identified as the most significant inputs in the circular failure model, with safety factor (SF) and stability (S) state as outputs, analyzed under two different scenarios. The results obtained indicate that the stability and safety analysis networks exhibit low error and high correlation, with an average error for the safety factor and stability of 0.05 and 0.013, respectively, demonstrating the network's high generalization capability. Additionally, the artificial intelligence outputs of test data identified the southern wall of the mine as the most critical section, calculating the safety factor and stability of this area to be 0.81 and 0.66, respectively. [ABSTRACT FROM AUTHOR]

Compressed air energy storage in artificial caverns can mitigate the dependence on salt cavern and waste mines, as well as realize the rapid consumption of new energy and the "peak-cutting and valley-filling" of the power grid. At the same time, the safety and stability of the surrounding rock of gas storage has attracted extensive attention. Based on finite element simulation, a numerical model of shallow-buried double-chamber for compressed air energy storage is established, and the influence of working pressure, cavern type, pillar space, and cavern diameter on the mechanical behavior of surrounding rock is analyzed. It is discovered that the cavern type significantly affects the response of the surrounding rock, whose deformation and plastic strain in the horseshoe-shaped cavern is significantly larger than that in the circular cavern. For circular caverns, the pillar space of 2~3 times the cavern diameter is only suitable for low working pressure, and the plastic strain and deformation of surrounding rock increases sharply with the increase of working pressure. It is more appropriate to select the pillar space that is 4 times the cavern diameter when the working pressure is greater than 16 MPa. With the increase in the cavern diameter, the maximum deformation of the surrounding rock accelerates rapidly. [ABSTRACT FROM AUTHOR]

A new compilation of Bouguer gravity anomaly data has been used, together with forward and inverse modeling, to reappraise the structure, volume, and state of isostasy of the Cornubian batholith of SW England. We show the individual plutons that comprise the batholith are, on average, ∼10–11 km thick, are outward-sloping in their upper 2–3 km, and are underlain by roots which protrude downward into the middle crust. The batholith volume is estimated within the range of 76,367 ± 17,286 km³, significantly larger than previous estimates. Granite outcrops correlate with elevated topography, and mass balance calculations show that the mass deficiency of the granites relative to their host metasedimentary rocks is approximately equal to the mass excess of the topography relative to air. The existence of roots beneath individual plutons is in general agreement with predictions of an Airy model of isostasy and a depth of compensation that is within the crust rather than at the Moho. In addition, a middle crust compensation depth is compatible with the origin of the granites by heating and melting of metasedimentary rocks and with data from experimental rock mechanics which suggest that at the melting temperature and pressure of granite formation, deformation is likely to be plastic and controlled by glide along dislocations. During pluton emplacement the middle crust would, therefore, have acted as a mechanically weak layer, effectively decoupling the topography from any support it might otherwise have received from the lower crust and/or upper mantle. [ABSTRACT FROM AUTHOR]

In view of the instability issues of surrounding rock in super-large-section chambers, this study takes the super-large-section chambers of the underground agitation station at Jinfeng Gold Mine as the research object, establishes a rock quality index model for the mining area using the mine's geological drilling database, and based on this model, determines the optimal location for the agitation station construction to be at the 150 m level. Through laboratory tests, field investigations, and ground stress measurements, the parameters and stress distribution characteristics of the surrounding rock were determined. The stability of the chamber after excavation was analyzed using the Phase2 rock mechanics software for numerical simulation. Based on the analysis results and the engineering analogy method, a joint support scheme was proposed for the surrounding rock, which includes pipe-slit bolts, hanging mesh, wet shotcrete, resin bolts, long anchor cables, grouting behind walls, and anti-heave reverse arch concrete. The reinforcement effect was evaluated through numerical simulation and field application monitoring, and the results showed that the maximum deformation of the reinforced chamber was 31 mm, the maximum principal stress was 25 MPa, no damage occurred to the bolts (cables), and all safety factors of the concrete lining units were greater than 1.2. The support structure was in a reasonable and effective stress state, indicating that the chamber remained stable after reinforcement, with good support effects. The research findings have important reference value for similar engineering projects. [ABSTRACT FROM AUTHOR]

The hard rock roof in coal mines is prone to failure, causing catastrophic disasters due to highly concentrated stresses. Acidification can effectively degrade the resulting mechanical properties of hard rocks. Therefore, quantitative assessment and understanding of the tensile properties and microscopic characteristics of acidified limestone is essential for rock engineering. In this work, Brazilian splitting tests (BSTs) were carried out on acid-immersed limestone specimens and the resulting properties were determined by digital image correlation (DIC), 3D scanning, and nanoindentation. The effects of varying pH values on tensile properties, splitting surface morphology, and nanoindentation characteristics were investigated. The results indicate the tensile strength decreases with the decrease in pH value, while the splitting failure mode gradually transitions from I-shaped tensile to Y-shaped tensile-shear failure mode. Further, DIC results indicate that the maximum principal strain increases gradually. The evaluation of the splitting surface also showed that the roughness, relative fluctuation height, angle, area ratio of the splitting surface, and the range of indentation depth increase as the pH value decreases, while the relative fluctuation height increases the most. Nanoindentation confirms that the micromechanical parameters (hardness, modulus, and fracture toughness) degrade to varying degrees due to the acidification. Finally, the correlation between tensile strength and micromechanical parameters was developed for a better understanding of the microscopic deterioration mechanism in acidified limestone. Highlights: Acidification significantly affects the tensile strength and failure mode of limestone specimens. Micromechanical properties are gradually decreased as pH decreases. Tensile strength and micromechanical parameters are correlated. Acidification modifies the pore structure and micromechanical properties, reducing tensile strength. [ABSTRACT FROM AUTHOR]

To investigate the influence of joints on the rockburst process in the surrounding rock of deep tunnels, a free-face true-triaxial test was conducted on the rockburst of the jointed surrounding rock of a tunnel. The rockburst ejection failure process (i.e., failure mode, rock strength, and deformation characteristics), rockburst debris characteristics, and acoustic emission evolution characteristics of red sandstone specimens under different joint conditions were investigated. The experimental results indicate that the failure modes of red sandstone specimens with a joint condition perpendicular to the tunnel direction generally exhibit 'internal shear and external splitting', which can suppress the occurrence of rockbursts, whereas the failure mode of red sandstone specimens with a joint condition parallel to the tunnel direction is mainly shear fracture, which can also promote the occurrence of rockbursts. The variation trend of the peak strength and the joint angle of the specimen exhibits a 'U' type shape, and the debris pertaining to the joint specimen's rockburst exhibits fractal characteristics. With the increase of the joint inclination angle, the fragment's ejection kinetic energy exhibits a trend of decreasing first and subsequently increasing. There are significant differences in the total number pertaining to impacts of acoustic emissions during rockburst under different joint conditions. The distribution range pertaining to the dominant frequency signal of the acoustic emission signal at the time of rockburst is mainly a low-frequency signal, and the intermediate-frequency, high-frequency, and ultra-high-frequency signals also exist, thus indicating that the rockburst damage exhibits strong complexity. Finally, the strain rockburst mechanism of jointed rock is significantly different from that of jointless intact rock. The rockburst mechanism is mainly divided into two typologies: shear fracture and slab buckling-shear fracture. The research results contribute to a deeper understanding of the underlying mechanisms of rockburst disasters in jointed rock formations. Highlights: Successfully performed a free-face true-triaxial rockburst test in the jointed surrounding rock of a tunnel. The presence of different joints under true-triaxial conditions significantly alters the mechanism of strain-induced rockburst. Joints perpendicular to the tunnel direction reduce the occurrence of rockbursts, whereas joints parallel to the tunnel direction promote the occurrence of rockbursts. With the increase of the joint inclination angle, the fragments' ejection kinetic energy exhibits a trend of decreasing first and subsequently increasing, where the joint inclination angle of 30° is the transition's inflection point. [ABSTRACT FROM AUTHOR]

The mechanical behavior of composite granular rocks is a multifaceted phenomenon with broad relevance in various geomechanical applications. Traditional homogenization models and continuum mechanics-based numerical methods often fall short of accurately capturing the intricacies of granular materials. Granular materials exhibit heterogeneity and arching mechanisms governing the force networks that ensure system stability. Unlike continuum-based approaches, discrete element methods (DEM) have an advantage in assessing effective material properties by considering material heterogeneity and grain-level physical interactions. This study evaluates effective elastic properties using DEM with flat-joint contact law for composite binary mixtures with a stiff inclusion embedded within a matrix material. We examine variations in the elastic properties across different structural and laminated geometrical distributions of inclusion materials. Our findings closely adhere to the Voigt-Reuss and Hashin–Strikman bounds within their specific conditions, demonstrating the promising application of DEM in the analysis of composite materials. In addition, our research provides an in-depth analysis of the distinctive stress-evolution and damage-evolution characteristics exhibited by various geometrical configurations of inclusions under unconfined compressive loading. These results offer invaluable insights into the mechanical behavior of composite granular rocks and underscore the potential applications of DEM in addressing rock physics modeling problems encountered in petroleum engineering. Highlights: The study's findings validate the use of discrete element modeling in predicting the effective mechanical behavior of composite rocks. Effective elastic properties of composite rocks estimated using the discrete element method are well constrained by Hashin–Shtrikman and Voigt–Reuss bounds. The research uncovers different behaviors in elastic moduli for isotropic and laminated inclusion scenarios. Stress and strain exhibit distinct patterns of evolution within materials possessing different properties. The study highlights distinct material behaviors under different loading conditions and composite compositions, shedding light on how composition, geometry, and loading direction influence crack formation and sample failure. [ABSTRACT FROM AUTHOR]

In this research, the finite-element numerical software COMSOL Multiphysics is used to simulate the electric pulse rock-breaking process, and the novel numerical model takes into account the multiple fields of electrical, thermal, and mechanical physics. The electric field strength inside the rock under the action of the electric pulse is updated by the full coupling function of COMSOL (version 6.1) software, and the electric damage variable χ is used to describe the process of electric breakdown inside the rock, to simulate the formation of plasma channel in the process of electric pulse rock-breaking. The voltage change curves and plasma channel trajectories in the electric breakdown process of the model in this paper are compared with the literature to verify the accuracy of the model. The formation process of plasma channels captures the temperature and stress changes during the whole process of electric pulse rock-breaking, to reveal the mechanism of the electric pulse rock-breaking process. With the presence of conductive particles inside the rock, the particles can effectively promote the formation of plasma channels, increase the area of electrical damage, and improve rock-breaking efficiency. Before the formation of the plasma channel, the internal temperature of the rock is about 600 K, and the stress is about 10−2 MPa; when the channel is formed, the energy of the electric pulse is mainly concentrated in the plasma channel, and the temperature of the plasma channel rises to 104 K. When the maximum stress exceeds the critical stress of the rock, the rock undergoes fracture. Furthermore, an appropriate increase in the rise time of the electric pulse increases the speed and area of rock-breaking, subsequently improving the efficiency of rock fracture. The results of the numerical modeling in this paper help to better understand the mechanism of the electric pulse rock-breaking process, which is of great engineering significance for the development of new electric pulse rock-breaking technology in the realm of geotechnical engineering. [ABSTRACT FROM AUTHOR]

Engineering disasters, such as rockburst and collapse, are closely related to structural instability caused by insufficient bearing capacity of geological materials. Uniaxial compressive strength (UCS) holds considerable significance in rock engineering projects. Consequently, this study endeavors to devise efficient models for the expeditious and economical estimation of UCS. Using a dataset of 729 samples, including the Schmidt hammer rebound number, P-wave velocity, and point load index data, we evaluated six algorithms, namely Adaptive Boosting (AdaBoost), Gradient Boosting Decision Tree (GBDT), Extreme Gradient Boosting (XGBoost), Light Gradient Boosting Machine (LightGBM), Random Forest (RF), and Extra Trees (ET) and utilized Bayesian Optimization (BO) to optimize the aforementioned algorithms. Moreover, we applied model evaluation metrics such as Root Mean Square Error (RMSE), Mean Absolute Error (MAE), Variance Accounted For (VAF), Nash-Sutcliffe Efficiency (NSE), Weighted Mean Absolute Percentage Error (WMAPE), Coefficient of Correlation (R), and Coefficient of Determination (R²). Among the six models, BO-ET emerged as the most optimal performer during training (RMSE = 4.5042, MAE = 3.2328, VAF = 0.9898, NSE = 0.9898, WMAPE = 0.0538, R = 0.9955, R² = 0.9898) and testing (RMSE = 4.8234, MAE = 3.9737, VAF = 0.9881, NSE = 0.9875, WMAPE = 0.2515, R = 0.9940, R² = 0.9875) phases. Additionally, we conducted a systematic comparison between ensemble and traditional single machine learning models such as decision tree, support vector machine, and K-Nearest Neighbors, thus highlighting the advantages of ensemble learning. Furthermore, the enhancement effect of BO on generalization performance was assessed. Finally, a BO-ET-based Graphical User Interface (GUI) system was developed and validated in a Tunnel Boring Machine-excavated tunnel. [ABSTRACT FROM AUTHOR]

Hydraulic fracturing is a mature and effective method for deep oil and gas production, which provides a foundation for deep oil and gas production. One of the key aspects of implementing hydraulic fracturing technology lies in understanding mechanics response characteristics of rocks in deep reservoirs under complex stress conditions. In this work, based on outcrop core samples, high-stress triaxial compression tests were designed to simulate the rock mechanics behavior of deep reservoirs in Bozhong Sag. Additionally, this study analyzes the deformation and damage law for rock under different stress conditions. Wherein, with a particular focus on combining energy dissipation theory to further understand damage law for deep reservoirs. The experimental results show that regardless of stress conditions, the process of deformation/failure of deep-seated reservoirs goes through five stages: Fracture compaction, new fracture formation, stable fracture expansion, unstable fracture expansion, and post-peak residual deformation. Under different stress conditions, the energy change laws of specimens are similar. The energy dissipation process of rocks corresponds closely to the trend of deformation-failure curve, then displays distinctive stage characteristics. Wherein, in stage of rock fracture compaction, the input energy curve is approximately coincident with the elastic strain energy curve, while the dissipation energy curve remains near zero. With the increase of strain, the growth rate of elastic strain energy increases gradually, but with the deformation entering the crack propagation stage, the growth rate of elastic strain energy slows down and the dissipation energy increases gradually. Finally, in the post-peak stage, rock fracture releases a lot of energy, which leads to the sharp decline of elastic strain energy curve. In addition, the introduction of damage variable D quantifies the analysis of the extent of failure for rocks. During the process of increasing strain, rock damage exhibits nonlinear growth with increasing stress. [ABSTRACT FROM AUTHOR]

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Polycrystalline diamond compact (PDC) bit is one of the most widely used drill bits for improving the rate of penetration in deep oil and gas well and geothermal well. However, the dynamic rock fragmentation mechanics characteristics of PDC bits are still unclearly. A coupled fragmentation mechanics model of PDC cutter-rock interaction is established by combining the mixed fragmentation modes with dynamic strength. The coupling influence laws of cutter angle, cutting depth, dynamic strength ratio, breaking modes on the horizontal force coefficient (HFC), vertical force coefficient (VFC) and specific energy are analyzed. The model of this paper can optimize cutter inclination angle, cutting depth and minimum specific energy. With the increase of the cutter inclination angle, the dynamic VFC changes into two modes. The definition of the dynamic modes depends on the dynamic strength ratio. As the cutting angle increases, the cutting force increases. The cutting force increases nonlinearly with increasing cutting depth. The specific energy of rock fragmentation increases nonlinearly with increasing cutting depth. With the increase of dynamic strength, the specific energy of rock fragmentation increases nonlinearly. When the input-energy increases, the rate of penetration response is divided into three stages. The results have important guiding significance for the PDC bit design and drilling parameters optimization to increase the rate of penetration and the efficiency of exploration and development. [ABSTRACT FROM AUTHOR]

Copyright of Dokuz Eylul University Muhendislik Faculty of Engineering Journal of Science & Engineering / Dokuz Eylül Üniversitesi Mühendislik Fakültesi Fen ve Mühendislik Dergisi is the property of Dokuz Eylul Universitesi Muhendislik Fakultesi Fen ve Muhendislik Dergisi and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

After tunnel excavation and unloading, the stress state of the rock mass is redistributed, resulting in varying radial stresses at different radial depths in the rock mass. Rock mechanics tests showed that the confining pressure, especially for soft rock, had a substantial impact on the mechanical properties of the rock which at various radial depths varied with the confining pressure. Therefore, the Mohr-coulomb strength criterion was used in this study to elastic-plastic analysis of deeply buried tunnels that took into account the coupling impact of strain-softening and confining pressure using the finite difference method. Then, regardless of whether the confining pressure is taken into account, the rock mass's plastic zone radius and deformation value were compared, which were considerably impacted by confining pressure: the effect is more pronounced when the rock strength is lower and the initial geostress is higher. The rock mass's strain-softening behaviors and its confining pressure effect should be highlighted while soft rock tunnel support structures were designed with the condition of high initial geostress in order to prevent the rock mass's distinct deformation of the rock mass caused by the calculation results distortion or even serious consequences like large deformation, damage or failure. [ABSTRACT FROM AUTHOR]

High sidewall cavern splitting failure is a critical engineering phenomenon that occurs during excavation and unloading under true three-dimensional high in-situ stress conditions. This issue significantly impacts the safety of underground cavern construction and excavation, yet its formation mechanism remains unclear. This research utilizes the high sidewall cavern of the main powerhouse at the Pubugou Hydropower Station as a case study to establish an elastic-plastic damage-softening model of splitting failure based on strain gradient theory and to develop a corresponding calculation program. The numerical simulation results effectively elucidate the formation conditions and failure mechanisms of high sidewall caverns. Through comprehensive numerical simulations under various working conditions, we systematically investigate the conditions for generation and the influencing factors of splitting failure. Our study successfully uncovers the generation conditions and formation mechanisms of high sidewall cavern splitting failure. A crucial condition for this failure is that the initial maximum principal stress of the underground cavern aligns parallel to the tunnel axis direction, with a magnitude between 0.21 and 0.7 times the compressive strength. The primary mechanical cause of splitting failure during excavation and unloading is the stress oscillation at the cavern's sidewall. [ABSTRACT FROM AUTHOR]

As a crucial reserve for natural gas, the safe operation of underground gas storage facilities is paramount for seasonal peak shaving and emergency supply security. Focusing on the Lei X gas storage facility in the Liaohe Basin of China, this study delves into the mechanical integrity of gas storage facilities and assesses the upper limit pressure for safe operation. Leveraging seismic logging data, we conducted an analysis and statistical evaluation of boundary faults and top cover characteristics, integrating regional stress fields and rock mechanics to evaluate fault activation pressure and cover failure risk using a fault activation pressure assessment method. This research elucidates the maximum safe operating pressure for underground gas storage facilities. The research findings suggest that the sealing layer of the Lei X gas storage reservoir exhibits a predominant hydro-fracturing pattern. Under the existing stress field conditions, the sealing layer demonstrates favorable sealing properties, and the boundary faults remain relatively stable. Moreover, through data extraction and quantitative analysis, this study clearly determined the critical pressure at which each fault is activated and the pressure at which the sealing layer undergoes hydro-fracturing during cyclic injection and the production of gas storage. Considering the activation pressure and fracturing pressure data for the sealing layer, a secure operating pressure of 15.0 MPa was calculated for gas storage operations. This study offers crucial theoretical support for enhancing injection and production efficiency, as well as ensuring the safe operation of Lei X gas storage and providing technical guidance for future adjustments to injection and production schemes. [ABSTRACT FROM AUTHOR]

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

For jointed rock mass with anisotropy and discontinuity, the structure of the surrounding rock is constantly developing and changing during tunnel excavation. It is difficult to reasonably predict localized deformation of jointed rock mass by using the existing rock mechanics theory. In this paper, the failure characteristic of pre-holed jointed rock mass with three joint angles is experimentally investigated by adopting the digital image correlation and acoustic emission methods. To avoid the influence of measurement error on Digital Image Correlation (DIC) from discontinuous deformation, parametric studies and an optimized algorithm are also included in DIC tests. Results indicate that the perpendicular-jointed condition (0° joints) is the most dangerous situation because of its comparatively lower strength and brittle failure mode with a shift energy release. For rocks with different jointed angles, localized deformation emerges after the material enters the plasticity. Significant localization occurs after the failure with cracks surrounding the center hole and pre-existing joints. [ABSTRACT FROM AUTHOR]

The phenomenon of peripheral rock instability is more common in crushed bedrock roadways, and the fundamental reason for this lies in the significantly different characteristics of its peripheral rock stress field. Taking the newly dug belt inclined shaft of PingDingShan TianAn Coal Co., Ltd. No. 6 Mine as the engineering background, a mechanical model of a broken perimeter rock roadway was established by using classical rock mechanics theory. Stress distribution around the roadway of the broken perimeter rock medium was systematically analyzed, and radial and tangential stress formulas of the broken perimeter rock were deduced. Through the formula calculation, it was deduced that there was a stress drop in the intact surrounding rock outside the disturbed zone, and the radial stress of the intact surrounding rock in its deep part was relatively increased, while the tangential stress was relatively decreased. The existence of crushed surrounding rock increased the minimum principal stress and decreased the maximum principal stress of the unfractured surrounding rock, which proves that a well-maintained disturbed zone can play a lining role. Thus, a "U-shaped steel + inverted arch + bottom arch linkage beam + floor bolt compensation" support program was proposed. This joint support program easily forms a closed support structure, which is more effective in controlling the deformation of tunnel perimeter rock. The support structure can effectively resist the deformation of the surrounding rock and enhance bottom drum resistance. Through numerical simulation, it was concluded that the horizontal displacement of the two gangs was reduced by 70%, and the displacement of the top and bottom plates was reduced by 77% after optimization of the support, which effectively controlled the stability of the broken surrounding rock. [ABSTRACT FROM AUTHOR]