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Most of the mine roadways in China are located in layered rock mass. To study the mechanical properties of a layered rock mass, the uniaxial compression test was carried out on the layered composite rock mass composed of sand and paraffin. The results showed that the locations of the high‐ and low‐strength rocks were independent of the strength of the layered composite rock. The main failure site was not affected by the combination mode. Failure was mainly concentrated in the low‐strength rock. The strengths of low‐ and high‐strength rocks determined the lower and upper limits of the strength of the layered rock, respectively. When the thickness of the layered high‐strength composite rock was >60%, the layered composite rock strength tended to be high; conversely, layered composite rock strength lowered the rock strength, and with increasing thickness, the layered composite rock strength was significantly enhanced. From the perspective of energy conversion, the effect of the thickness of the high‐strength rock mass on the strength of the layered composite rock mass was analyzed. [ABSTRACT FROM AUTHOR]

Fracture interactions are an important factor that affects rock effective elastic properties. We study the fracture interaction effects by combinations of theoretical modelling, numerical simulations and experiments in this work. First, we propose a simplified differential effective medium scheme and self‐consistent approximation for effective elastic properties of rocks with aligned fractures, and we compare their results to those of non‐interaction approximation. The results show that the predictions by differential effective medium scheme and self‐consistent approximation are lower than those by non‐interaction approximation. This indicates that the differential effective medium scheme and self‐consistent approximation quantify the stress amplification effects but not stress shielding effects. To validate this, we carry out numerical simulations for cases with coplanar cracks and stacked cracks, respectively. We find that the stress shielding effect (stacked cracks) causes a significant increment of effective elastic stiffnesses of fractured rocks. However, the stress amplification (coplanar cracks) has the opposite effect, which induces a slight reduction in rock effective elastic stiffnesses. The differential effective medium scheme quantifies the lower bound for this effect well. Besides numerical simulations, applying theoretical models in experimental measurements also shows a pronounced effect of stress shielding but a small influence of stress amplification on fractured rock elastic properties. This work indicates that the stress shielding is an important effect that affects fractured rock elastic properties. Without considering this effect, the fracture density may be largely underestimated by the seismic or sonic logging inversion. Hence, the models accounting for stress shielding effects need to be developed in the future, which can combine with the above models for the seismic or sonic logging inversion of fracture properties. [ABSTRACT FROM AUTHOR]

Mineral fabric analyses of Permian La Plata and Jurassic Paez arc plutons provide information about the interplay of tectonic deformation and magma emplacement in the southern Colombian Andes. We combined field mapping, microstructural data, AMS fabrics, rock magnetic properties, vorticity analysis, and thermobarometry to study the internal fabrics of the plutons. Our results indicate that the studied plutons have well-developed NE magmatic and mylonitic foliations, with the latter being distinctive for the Permian pluton. These foliations are consistent with the N65°E/63°W Permian and N43°E/82°W Jurassic AMS magnetic fabrics. Magnetic lineations record subhorizontal (Permian) and vertical (Jurassic) magmas upwards in the NE–SW trajectories. The orientations of all the plutonic fabrics indicate structurally controlled magma emplacement consistent with compressional tectonics and bulk NW–SE crustal shortening. Microstructural features recorded in the plutons reveal magmatic to sub-magmatic and solid-state deformation developed at high- to low-temperatures during their syn-tectonic emplacement history. Thermobarometric calculations indicate similar shallow emplacement conditions (~10 km depth) in the La Plata and Paez plutons. The application of vorticity analysis shows that the magnetic fabrics and syn-emplacement of the Permian pluton developed by simple-shear dominated dextral transpression, whereas the AMS fabrics for the Jurassic syn-tectonic intrusion may have been associated with pure-shear contractional deformation. [ABSTRACT FROM AUTHOR]

Brittleness is an important mechanical property of rock. Accurately evaluating rock brittleness and its influence on the TBM tunnelling performance is necessary. In this work, via two practical engineering cases, with the aim of overcoming the difficulty of penetrating extremely hard rock (breccia fused tuff) in the Z huxi project, the influence of rock brittleness on the TBM tunnelling performance was studied via comparative analysis with that Nabang project. Seven commonly used rock brittleness indices based on stress‒strain curves were summarized, and a brittleness evaluation method suitable for extremely hard rock was determined by introducing the normalized specific energy to obtain brittleness indices for two lithologies (breccia fused tuff and biotite hornblende plagioclase gneiss) in two projects. The influences of rock brittleness on penetration and the specific energy were compared and analysed. The results showed that the brittleness indices B 3 and B 5 were more suitable for evaluating rock brittleness. Rock brittleness influenced the TBM tunnelling performance, but this influence gradually decreased with decreasing uniaxial compressive strength ( UCS ), which is obviously less than that of the rock strength. When the UCS was lower than 150 MPa, the TBM tunnelling parameters could be adjusted within a significant margin to eliminate the influence of rock brittleness, which could be ignored when predicting the tunnelling performance. When the UCS was greater than 150 MPa, rock brittleness imposed a notable influence on the tunnelling performance, which must be considered when predicting the tunnelling performance. This research could provide reference data for evaluating the hard rock brittleness index and accurately predicting the TBM tunnelling performance in engineering practice. [ABSTRACT FROM AUTHOR]

Understanding polymer retention is a critical aspect in the field of chemical-enhanced oil recovery (cEOR). This article presents a comprehensive review of polymer retention in reservoir rocks, focusing on the underlying mechanisms, measurement techniques, and the factors influencing this phenomenon. Three main (proposed) mechanisms that contribute to polymer retention are discussed in detail. Polymer adsorption, hydrodynamic retention, and mechanical entrapment are identified as key factors affecting the overall retention of polymers during flow through porous media. Also, herein, we explore the details of these mechanisms, explaining how polymer characteristics and rock surface properties influence the degree of retention. Furthermore, we analyze the influencing factors that affect polymer retention. The rock surface properties, such as surface charge and wettability, play a vital role in determining the interaction between polymers and rocks. The interplay of these factors provides valuable insights into understanding and controlling polymer retention in cEOR applications. This review paper put in a nutshell a comprehensive understanding of the mechanisms, measurement techniques, and influencing factors involved. [ABSTRACT FROM AUTHOR]

In order to master the strength and deformation characteristics, including the macro–micro failure mechanism of soft rock samples with penetrating joints under triaxial loading, a series of numerical triaxial tests have been carried out. The strength and deformation characteristics, failure modes, crack propagation, distribution of force chains, and the influences of joint dip angles and confining pressures have been analyzed and compared with the laboratory test results. The results show that (1) the residual strength ratio of jointed rock samples generally increases first and then decreases with the increase in joint dip angles under the same confining pressure and reaches the maximum value around 23–24°. Poisson's ratio increases with the increase in the confining pressure or the joint dip angle. The elastic modulus increases with the increase in the confining pressure and decreases with the increase in the joint dip angle. (2) The jointed rock samples with different joint dip angles compact with relatively small volumetric strains and then dilate up to failure with relatively large volume expansions. Lower confining pressure and smaller dip angles will lead to a more pronounced dilation phenomenon and less obvious volume shrinkage rules. (3) The low-angle jointed rock samples all exhibit the X-type shear failure. The jointed rock samples with a joint dip angle of 45° exhibit hybrid failure with both slippage and shearing, which are controlled by both the matrix and the joint. (4) The change in the number of cracks includes three stages: the slow crack initiation stage, rapid growth stage, and crack coalescence stage. The total number of shear or tensile cracks all decrease with an increase in the joint dip angles, with the number of tensile cracks being approximately twice that of shear cracks. The tension cracks are mostly horizontal, and the shear cracks are mostly vertical. (5) The number of force chains shows a decreasing trend after the cracks begin to grow. The jointed rock samples for the intact, 15° and 30° cases all form a main force chain during the failure process, while there is no main force chain for the 45° case. [ABSTRACT FROM AUTHOR]

Bedrock geology from Antarctica remains largely unknown since it is hidden beneath thick ice sheets. Geophysical methods such as gravity and magnetic inverse modelling provide a framework to infer crustal rock properties indirectly in Antarctica. However, due to limited availability of rock samples, validation against direct geological information is challenging. We present a new rock property catalogue containing density and susceptibility measurements on 320 rock samples from northern Victoria Land. This catalogue is used to assess the reliability of local and regional scale inverse results, including a new local high resolution magnetic inversion in the Mesa Range region and a previously published regional scale joint inversion of gravity and magnetic data in northern Victoria Land and the Wilkes Subglacial Basin. We compare our density and susceptibility measurements to global and local measurements from the literature to access the correlation to rock types and geological units. Furthermore, the measured values are compared against inverted values. The close correspondence between inverted and measured rock properties allows us to predict locations of rock types where currently such information is missing. The utility of measured susceptibility and density relationships for interpreting inversion output provides a strong incentive to incorporate local rock samples into geophysical studies of subglacial geology across Antarctica. [ABSTRACT FROM AUTHOR]

Rock abrasivity plays an important role in the machine design, construction scheduling, and budgeting of TBM projects. Establishing several faster and simpler estimation equations for the Cerchar Abrasivity Index (CAI) of rocks is, therefore, very important. This study investigated the correlation between the CAI and mechanical properties of rock, rock mass classification parameters, and machine performance. A TBM construction database including 159 tunnel sections is established. Several acceptable and practical estimation equations of CAI are developed using simple and multiple regression analysis (0.66 < R2 < 0.76). In this process, a normalized specific energy is proposed to evaluate the machine performance. The results show that the rock compressive strength and brittleness index are the most dependent parameters to explain CAI, and the estimated rock mass strength also indicates a close correlation. In addition, the contribution of a rock mass classification system and machine performance index for estimating CAI cannot be ignored. Finally, the estimation performance of the developed equations is compared and evaluated, and a new method for selecting an optimal model based on ranking is proposed. Since the input parameters of the proposed equations can be readily available at the project planning stage, they are very practical for TBM designers, tunnel designers, and contractors. Highlights: The correlations between the CAI and rock mechanical properties, rock mass classification parameters, and machine performance are investigated. A normalized specific energy index is proposed for assessing the performance of rocks excavation by TBMs. Several acceptable and practical estimation equations of CAI are developed using simple and multiple regression analysis. A new method for selecting optimal estimation model based on ranking is presented. [ABSTRACT FROM AUTHOR]

The instability failure of engineering rock mass is caused by the full development of cracks under the combined action of the surrounding rock stress environment and frequent stress disturbance. The development and propagation of cracks is essentially a process of cumulative rock damage and progressive failure. Taking the rock damage induced by crack development under multistage stress disturbance as the theme, combined with the engineering site, this work carried out multistage stress disturbance tests considering disturbance amplitude, time and initial stress factors, aiming at exploring damage mechanism of rock at each disturbance factor and the characteristics of microscopic crack development. The increase of various disturbance factors reduce the peak strength and average elastic modulus of the rock, and increase the axial strain increment at each disturbance stage, which weakens the mechanical properties of the rock. The microcracks development presents a process of "local convergence of microcracks to form damage zone, continuous development of microcracks to expand damage zone, propagation of damage zone to form fracture zone, propagation of fracture zone to form macroscopic fracture surface". Furthermore, the increase of the disturbance factors promotes crack development and expansion and induces the generation of tensile cracks. The established acoustic emission (AE) Qt value can reflect the development of microscopic cracks within the rock in real time and is negatively correlated with the rock damage state, which can be used as an index for quantitative evaluation of rock damage. The research results can provide some reference and guidance for the monitoring and evaluation of engineering rock mass damage. Highlights: Conduct multistage stress disturbance tests of sandstone under triaxial compression. Analyze the effect of amplitude, time and initial stress on the mechanical behavior of rock. Explore the fracture characteristics and AE damage characteristics of sandstone. Reveal the damage and microscopic crack mechanism of rock under disturbance factor. [ABSTRACT FROM AUTHOR]

This study investigates the thermal–mechanical behavior of slates in geothermal reservoirs and establishes an anisotropic thermal–mechanical coupling failure criterion. Slate samples obtained from a geothermal site were subjected to a series of direct-shear and triaxial-compression tests at various confining pressures and temperatures. The results showed that the orientation angle within a specific range caused shear sliding failure of the slate, primarily due to foliation strength; beyond this range, intrinsic rock properties led to different failure modes. Elevated temperatures significantly diminished the strength anisotropy of the slate. These findings provided a foundation for the development of an anisotropic thermal–mechanical coupling failure criterion. The validity of the proposed criterion, which incorporates both the orientation angle and thermal degradation effects, was demonstrated through experimental results. A three-dimensional surface diagram was constructed to visualize the relationship between the temperature, orientation angle, and failure principal stress, highlighting the anisotropic thermal-degradation characteristics of the slate under varying confining pressures. This study enhances the understanding of the thermal–mechanical behavior of these materials in geothermal reservoirs. Highlights: This study clarified the thermal effect on the anisotropic strength of slate. This study proposed an anisotropic thermal–mechanical coupling failure criterion for slate. The proposed criterion incorporates both the effects of orientation angle and thermal degradation on the strength. Elevated temperatures diminished the strength anisotropy of the slate. [ABSTRACT FROM AUTHOR]

Since an increasing number of rock engineering structures are constructed in the stratified rock mass, a comprehensive understanding of the mechanical properties of anisotropic rock is crucial for the stability evaluation of these structures. In this study, the combined influences of the dip angle of the bedding plane and intermediate principal stress on the strength and failure behavior of anisotropic rock are experimentally investigated. True triaxial compression tests on a sandstone possessing seven different bedding plane angles (i.e., 0°, 15°, 30°, 45°, 60°, 75°, and 90°) are conducted under six different intermediate principal stresses (i.e., 10 MPa, 60 MPa, 100 MPa, 130 MPa, 160 MPa, and 190 MPa). The effects of intermediate principal stress and bedding plane angle on the stress–strain curve, Young's modulus, strength, and failure mode of the rock are soundly examined and discussed. The results show that both intermediate principal stress and bedding plane angle have a large influence on the deformation properties of the rock. In addition, the peak strength exhibits a typical U-shaped variation with increasing bedding plane angle under low intermediate principal stress condition, and the U-shaped behavior gradually diminishes with the increase in intermediate principal stress. Multiple failure planes can be observed after the failure of the rock specimens, showing asymmetric V-shaped patterns. The failure angle of the tested rock is found to generally increase as the applied intermediate principal stress gradually increases. The results in the present study deepen our understanding of the strength and failure behavior of anisotropic rock under true triaxial loading conditions. Highlights: Peak strength shows a U-shaped variation with increasing bedding plane angle at small σ2. U-shaped behavior of rock strength diminishes with increasing intermediate principal stress. Multiple asymmetric V-shaped failure patterns are observed after the failure of the rock specimen. Failure angle exhibits an increasing trend as intermediate principal stress gradually increases. [ABSTRACT FROM AUTHOR]

The creep behavior of rocks has been broadly researched because of its extensive application in geomechanics. Since the time-dependent stability of underground constructions is a critical aspect of geotechnical engineering, a comprehensive understanding of the creep behavior of rocks plays a pivotal role in ensuring the safety of such structures. Various factors, including stress level, temperature, rock damage, water content, rock anisotropy, etc., can influence rocks' creep characteristics. One of the main topics in the creep analysis of rocks is the constitutive models, which can be categorized into empirical, component, and mechanism-based models. In this research, the previously proposed creep models were reviewed, and their main characteristics were discussed. The effectiveness of the models in simulating the accelerated phase of rock creep was evaluated by comparing their performance with the creep test results of different types of rocks. The application of rock's creep analysis in different engineering projects and adopting appropriate creep properties for rock mass were also examined. The primary limitation associated with empirical and classical component models lies in their challenges when it comes to modeling the tertiary phase of rock creep. The mechanism-based models have demonstrated success in effectively simulating the complete creep phases; nevertheless, additional validation is crucial to establish their broader applicability. However, further investigation is still required to develop creep models specific to rock mass. In this paper, we attempted to review and discuss the most recent studies in creep analysis of rocks that can be used by researchers conducting creep analysis in geomechanics. Highlights: Creep constitutive models for rocks were reviewed, and their main characteristics were discussed. The applications of creep analysis in geomechanics were explained, and some engineering projects were mentioned. The back analysis techniques using long-time measured monitoring data were successfully used for finding rock mass creep parameters. [ABSTRACT FROM AUTHOR]

During the underground excavation, various flaws are frequently observed, which significantly decrease the mechanical properties of surrounding rock, as has been proven. As known, grouting technology is a means of reinforcement that efficiently enhances the stability of underground engineering. However, existing studies have mainly focused on increasing the strength of the slurry stone, and relatively less attention has been paid to the poor bonding effect at the interface between the slurry and the rock mass. In this work, we proposed to adopt slurry containing nano-silica sol to reinforce the fractured rock mass. Based on the mechanical model of micro–nano-siliceous slurry reinforcement for single fractured rock masses established in this paper, the effect and the mechanism of micro–nano-siliceous slurry reinforcement for fractured rock were explored through theoretical analysis, laboratory tests, and numerical simulations. Results showed that the application of micro–nano-siliceous slurry increased the friction and the bonding force at the slurry–rock interface, which led to a (σn·Δμ + Δc) reduction of the effective stress. The optimum incorporation rate of the nano-silica sol was determined to be 3% based on these indicators including slurry fluidity, slurry stone rate, and strength and deformation parameters of slurry stone. The peak strength of the sandstone specimens reinforced by the micro–nano-siliceous slurry increased by 16.49% those of the sandstones reinforced by the ordinary slurry, and the elastic energy accumulated by the former was higher. Scanning electron microscope images revealed that the incorporation of nano-silica sol distinctly improved the pore characteristics of the slurry-rock interface. Finally, on the basis of 1790 ventilation roadway of Shiyakou coal mine, the effectiveness and the feasibility of micro–nano-siliceous slurry for reinforcing underground engineering surrounding rocks were verified using numerical simulation. Highlights: This paper developed a new micro–nano-siliceous grouting material. A mechanical model for fractured rock mass reinforced by new slurry was proposed. The optimal incorporation rate of nano-silica sol was determined by various means. This study demonstrated the effectiveness of the new grouting material in reinforcing fractured rock mass by control lab experiments and numerical simulation. The mechanisms of micro–nano-siliceous slurry to improve slurry–rock interface were revealed. [ABSTRACT FROM AUTHOR]

Fragmentation by blasting is a critical process in hard rock mining. The interaction between the rock mass and blast energy influences the outcomes, specifically on the rock mass response to higher stresses and loading rates, and the properties of structures. In this study, LS-DYNA is used to model the nonlinear dynamic fracturing of the rock to understand the effects of rock mass properties on the blast outcomes. The results are verified and compared with the case study, and they show that the formation of damage zones around the charge is highly influenced by rock mass strength and discontinuity properties. [ABSTRACT FROM AUTHOR]

The Nari Caldera on Ulleung Island, an oceanic intraplate volcano, is a significant repository of information on the latest volcanic activity. To interpret the characteristics of the latest volcanic activity, it is essential to understand the caldera structures formed by the most explosive eruption of the Ulleung volcanic edifice. This study presents a three-dimensional (3-D) resistivity model based on audio-magnetotelluric (AMT) data and interprets the caldera structure of Ulleung Island. New land and ocean terrain models were used for the 3-D inversion of the AMT data, and a finer, nonuniform grid was generated for the caldera area. Subsequently, 3-D inversion and imaging were conducted on the AMT data at 25 stations. In the caldera area of Ulleung Island, the 3-D resistivity model is divided into two bodies: a high resistivity body located in the south and a low resistivity body located in the north. This structure is consistent with the location of the two calderas, Seongin Caldera and Nari Caldera, as inferred from geological studies. Furthermore, the high resistivity body located in the south exhibited a bowl shape in the 3-D space. Therefore, we suggest that the high resistivity body located south of the caldera on Ulleung Island is a structure of the Seongin Caldera. The Seongin Caldera has a diameter of approximately 1.5 km and a caldera fill height of approximately 0.8 km, as measured from the resistivity model. Based on the stratigraphy of Ulleung Island and the physical properties of the rock types, the interior of the Seongin Caldera was considered to have been filled with trachytic lavas of the Seonginbong Group. From the high geothermal gradient of Ulleung Island and the stratigraphy of the GH-4 borehole, the low resistivity body extending from the shallow depths of the Nari Caldera to the lower part of the Seongin Caldera could be interpreted as trachytic rocks that underwent hydrothermal alteration. In addition, a low resistivity body contains highly porous and/or weathered rock. This study presents information on the calderas of Ulleung Island that can aid in interpreting the characteristics of the latest volcanic activity. We expect this information to contribute to the preparation for potential volcanic hazards. [ABSTRACT FROM AUTHOR]

In subsurface energy extraction, permeability or conductivity is the vital parameter for quantifying fluid flow in porous media. Three-dimensional digital core technique is widely used to calculate flow parameters and to analyze the internal structure and properties of rocks. However, one major problem is its high computational cost associated with fine-scale simulation of porous media, especially for large and complex rock samples. In this study, we propose to use subvolume properties to increase computational efficiency. Specifically, we first construct digital cores of dune sand and sandstone by CT scanning technology, and divide the whole core into multiple subvolumes and calculate their permeabilities. Then, we reassemble the subvolumes and compute the permeability for the whole core. This approach may lead to underestimation as the connectivity between subvolumes could be lost. To address this issue, we divide the whole core into different-sized subvolumes, and then use curve fitting to deduce the permeability of whole rock sample via extrapolation. The results show that the proposed method has improved accuracy, and is significantly faster than simulating the whole digital core, since the computation on subvolumes can be easily parallelized. This approach provides new ideas for accurate and efficient permeability estimation for digital porous media. [ABSTRACT FROM AUTHOR]

There is a high correlation between rock engineering behavior and the anisotropy index, which is crucial for the safety assessment of rock properties. In rock drilling, rock anisotropy significantly affects the cost and efficiency of the drilling project. Therefore, the anisotropy during the rock drilling process is investigated in this study. First, measurements of horizontal and vertical drilling rates were conducted at a marble quarry. Then, experimental tests were conducted to measure the physical and mechanical properties of collected minor rock blocks corresponding to the major under-drilling marble blocks. Through this process, a total of 40 data sets comprising vertical and horizontal drilling rates and 12 different rock properties were provided. The results showed that the vertical drilling rate correlates more with rock mechanical properties, while the horizontal drilling rate is associated more with physical characteristics. Also, sensitivity analysis confirmed that porosity and dry density are the most and least effective variables on both vertical and horizontal drilling rates, respectively. Based on the analysis of variance, the polynomial equation was found to be the optimum relationship between vertical and horizontal drilling rates. Based on the comparative analysis and using actual data sets, the accuracy of the proposed equation was proved. Finally, a drilling anisotropy index was proposed based on the ratio of vertical to horizontal drilling rates. The results showed that the drilling anisotropy index is more prominent in rock blocks with high-strength properties. Also, it was proved that the drilling anisotropy index has an inverse relation with vertical and horizontal drilling rates. As the vertical and horizontal drilling rates are inherently affected by different rock properties, it can be concluded that the suggested relationship between vertical and horizontal drilling rates and the proposed drilling anisotropy index could be effectively applied to assessing the interaction of drilling rates with rock properties in anisotropic rocks. Practical Applications: This study investigated the relationships between rock properties and vertical and horizontal drilling rates, which is one of the main issues in rock drilling operations. According to the field and laboratory results, the correlation between the physical and mechanical properties of rocks with vertical and horizontal drilling rates was achieved, which can be considered during the drilling operation to enhance the drilling efficiency. Also, a new drilling anisotropy index was proposed, which can help identify a good interaction between drilling tools and the rock environment in anisotropic rocks. In addition, a new relation was proposed between vertical and horizontal drilling rates, which can be applied in practice to predict one of them based on the other. Generally, the outputs of this research could be applied to specifying the relationship between rock properties and vertical and horizontal drilling rates, emphasizing the drilling anisotropy index. In practice, the study outputs can lead to enhanced drilling efficiency and mine productivity in marble quarry mining by providing a deep knowledge of rock interaction with drilling tools while drilling in both the vertical and horizontal directions and choosing proper drilling tools for the under-drilling rock type. [ABSTRACT FROM AUTHOR]

During tunnel excavation, stress redistribution is caused by disturbance of the surrounding rock; when the stress exceeds the strength of rock mass, the surrounding rock enters the postpeak deformation stage and then produces the strain-softening effect. This effect will lead to a decrease in rock mass strength, the expansion of the fracture zone, and a decrease in stability. To further study the influence of strain-softening effect on the loose circle of the surrounding rock, the strain-softening factor is introduced into the unified strength criterion. On this basis, the triaxial test with elastic–plastic theoretical analysis is combined, and the strain-softening model based on the unified strength criterion is proposed. Based on this strain-softening model, the stress state of the postpeak plastic zone of the surrounding rock after excavation is studied and analyzed, and the theoretical calculation formula of the loose circle radius considering the strain-softening effect is obtained. Through theoretical calculations and engineering examples, the influence of strain-softening effect and support reaction force on the radius of the surrounding rock loose circle is compared and analyzed. The results show that: (1) the strain-softening effect further deteriorates the mechanical properties of the surrounding rock in the plastic zone, the stability of the surrounding rock is reduced, and the radius of the loose circle is increased, but closer to the measured values; and (2) with the increase of supporting reaction force, the constraint ability of surrounding rock deformation increases and the radius of the loose circle gradually reduces. Therefore, by enhancing the residual strength of the surrounding rock, controlling the radius of the loose circle of the surrounding rock by improving the strength of the supporting structure, and performing primary support on time, the stability of the surrounding rock can be increased. Practical Applications: During tunnel excavation, the process disrupts the surrounding rock, causing stress redistribution. When the local stress surpasses the strength of the rock, it results in damage, forming a loose circle and triggering strain softening. At the same time, both contribute to the expansion of the loose circle, further compromising the stability of the surrounding rock. Analyzing the distribution pattern of loose circles in the tunnel-surrounding rock considering the strain-softening effect, enhancing the residual strength of the surrounding rock, and improving the strength of the supporting structure while implementing the initial support in time can effectively control the expansion of the loose circle and improve the stability of the surrounding rock. This research provides an important theoretical basis and engineering experience for tunnel engineering to ensure construction safety and reduce construction costs. [ABSTRACT FROM AUTHOR]

Fractures are common in rock masses, and the examination of the electrical properties of fractured rocks under the combined scenario of thermal-hydro-mechanical is of great significance for the application of electrical methods for deep underground engineering investigation. The resistivity of limestone specimens containing prefabricated fractures was measured under different combinations of confining pressure, pore pressure and temperature. The formation factor was then calculated. The results showed that the formation factor increased with the increase in confining pressure and decline in pore pressure and temperature. The coupling effect between the three factors in changing resistivity is very significant. After comparing the specimen strain, the fracture specimen formation factor was found to be closely related to the fracture deformation. The difference between confining pressure and pore pressure in changing the rock formation factor was analyzed, and the concept of effective stress for the fractured rock formation factor was proposed. A formation factor model for single-fractured rocks under the thermal-hydro-mechanical coupling was derived, and its accuracy was verified by comparison with experimental results. Finally, the consistency of the effective stress coefficient of fractured rock deformation and the effective stress coefficient of formation factor was analyzed. [ABSTRACT FROM AUTHOR]

Underground engineering frequently encounters the challenges of high temperatures and high confining pressures. The combined effects of temperature and confining pressure can significantly alter the mechanical properties of rock. Evaluating the impact of these factors on rock is a crucial aspect of engineering. This study investigates the mechanical properties of rocks under various temperature and stress conditions, focusing on the deformation and failure characteristics of four typical rock types: granite, red sandstone, gray sandstone, and shale under temperature-confining pressure coupling. The results indicate that high temperatures cause internal structural damage and crack propagation in rocks, leading to a reduction in compressive strength and elastic modulus. Conversely, high confining pressures can inhibit crack propagation and enhance rock deformation capacity. Additionally, significant differences were observed in the mechanical responses of different rocks; red sandstone and shale predominantly exhibited shear failure under the coupled effects of temperature and confining pressure, whereas granite and gray sandstone exhibited bulging failure. Based on the experimental results, an elastic modulus fitting model considering the temperature-confining pressure coupling effect was proposed, and the parameters of the Drucker–Prager criterion were modified. A constitutive model was constructed to accurately reflect the stress–strain state of rocks under the coupled effects of temperature and confining pressure. The constitutive model results show good agreement with the experimental findings. [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]

Rock bursts are among the most severe and unpredictable hazards encountered in deep rock engineering, posing substantial threats to both construction safety and project progress. This study provides a comprehensive investigation into how moisture infiltration influences the propensity for rock bursts, aiming to establish new theoretical foundations and practical methods for their prevention. Through the analysis of meticulous laboratory mechanical experiments and sophisticated numerical simulations, we analyzed the variations in the physical and mechanical properties of rocks under different moisture conditions, with a particular focus on strength, brittleness, and energy release characteristics. The findings reveal that moisture infiltration significantly diminishes rock strength and reduces the likelihood of brittle fractures, thereby effectively mitigating the risk of rock bursts. Additionally, further research indicates that in high-moisture environments, the marked reduction in rock burst tendency is attributed to increased rock toughness and the suppression of crack propagation. This study advocates for the implementation of moisture control measures as a pre-treatment strategy for deep rock masses. This innovative approach presents a viable and effective solution to enhance engineering safety and improve construction efficiency, offering a practical method for managing rock burst risks in challenging environments. [ABSTRACT FROM AUTHOR]

Host rock deformation associated with sill emplacement is used to constrain magma transfer and storage within the upper crust. In contrast to classic models suggesting that the host rock above mafic sills is dominated by elastic bending, recent studies show that bounding faults that limit the uplift area can occur at the peripheries of a mafic sill. However, the accurate dip of this type of fault, named peripheral faults here, is still not well constrained. Their origin is also controversial in some cases. In this study, kinematic modeling and limit analysis are performed to better constrain the structure and mechanical properties of the peripheral faults based on seismic interpretation of a mafic sill from the Tarim Basin, China. The trishear kinematic model successfully reproduces peripheral faulting and associated folding of the host rock by performing a displacement of 58 m on a vertical fault plane with a fault propagation (P) to fault slip (S) ratio of 2.5. The limit analysis also predicts vertical damage at the sill tip by sill inflation. These results suggest that the dip angle of the fault in the case study is 90°, which is more accurate than that from the seismic interpretation with an 88° inward dip. This value may vary in other cases as it depends on the sill geometry (such as diameter and inclination), thickness, depth, and mechanical properties of the host rock. The study supports that peripheral faulting and associated folding can occur at the tips of the mafic sill due to the vertical uplift of the host rock caused by sill inflation. It is also suggested that trishear kinematic modeling and limit analysis are effective methods for studying the geometry of peripheral faults. [ABSTRACT FROM AUTHOR]

During CO2 storage in deep saline aquifers, the presence of residual water has an important influence on the storage efficiency and safety. In this study, natural rock cores taken from deep reservoirs in the Ordos Basin and Fukang, Xinjiang are used as research objects. Nine groups of core‐flooding experiments are performed under different CO2/N2 gas mixture ratios to study the influence of rock properties (mineral composition, permeability, porosity and pore structure) on the residual water. Furthermore, the geophysical and chemical properties of rock cores are analyzed by X‐ray diffraction, electron microscopy, field emission scanning electron microscopy and piezoelectric mercury method. The results show that residual water saturation is a quantitative power function of drainage time. The residual water saturation is positively correlated with the total amount of quartz and feldspar and increases with increasing permeability. Moreover, both the average and median pore throat radius show a strong inverse correlation with irreducible residual water saturation; as these radius increase, the residual water saturation decreases. In contrast, the porosity and maximum pore throat radius display a weaker correlation with irreducible residual water saturation. This study is of great value for engineering practices such as the site selection of CO2 storage projects in saline aquifer and improvement of CO2 storage efficiency. © 2024 Society of Chemical Industry and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Deformation memory effect (DME) is a common property of the rock. A method called Deformation Rate Analysis (DRA) which is based on DME provides a brand-new approach to measuring in situ stress. When rock DME is applied in engineering, it is necessary to solve the problem that which stress peak is corresponding to in situ stress. The standard square samples made of sandstone and granite were selected to investigate the rock DME under different stress paths. Then a memory theoretical model based on multi-surface sliding friction hysteresis is used to analyze the mechanisms of rock DME. The results show that: (1) Rocks always remember the maximum peak stress from preloading, regardless of the sequence of multiple preloading; (2) Multi-memory exists in tests because we found another inflection in DRA curve; (3) The memory model based on sliding friction hysteresis shows the precision of memory information formation increases as the historical maximum peak value gets closer to the measurement load, but multi-memory does not exist in theoretical analysis. The conclusion provides the rule of rock DME under different stress path which would benefits in in situ stress reconstruction. [ABSTRACT FROM AUTHOR]

Background: Rock slope instability is a complex geotechnical issue that is affected by site-specific rock properties, geological structures, groundwater, and earthquake load conditions. Numerous studies acknowledge these aleatory uncertainties in slope stability assessment; however, understanding the rock behaviour could still be improved. Therefore, this paper aims to summarise the probability methods applied in rock slope stability analysis in mining and civil engineering and develop new probabilistic design and assessment methodologies for four methods, namely empirical/rock mass classifications techniques, kinematic analysis, limit equilibrium (LE), and numerical methods and introduces how to integrate all methods to determine the total probability of failure. The case studies have been conducted based on slopes from Indonesia, a seismically active country, utilising the proposed design methods. Results: Regarding the probabilistic empirical/rock mass classification (RMC) technique, this study has identified that seven of the ten most involved input parameters in RMC naturally exhibit aleatory uncertainty. Thus, the optimal way to present the output probability of RMC is as a confidence interval (CI) or total and conditional probability associated with each rock mass class. In probabilistic kinematic analysis, this study presents a systematic method to compute the probabilities of different types of failure alongside the total probability of occurrence (PtK). The probability of failure (PoF) for jointed generalized Hoek-Brown (GHB) numerical modelling was lower than that obtained through the probabilistic LE approach for a similar slope. However, the PoF of jointed GHB is higher than the LE approach when loaded with 0.1 and 0.15 earthquake coefficients. Conclusions: The variation of PoF across different failure criteria determines how epistemic uncertainty is apparent in the modelling process, while the aleatory uncertainty arises from input parameters. Furthermore, this study introduces the total probability of failure equation as a combination of kinematic and kinetic probabilities (limit equilibrium and numerical modelling). [ABSTRACT FROM AUTHOR]

ABSTRACT The study investigated 50 Permian coals from the Singrauli Coalfields in the Son Valley Basin, India, using advanced petro‐geochemical techniques to assess their source rock properties, energy and utilisation potential and to reconstruct the paleodepositional environment. Petrological analysis indicated vitrinite reflectance values between 0.39% and 0.49%, classifying the Singrauli coals as sub‐bituminous to high volatile bituminous rank and indicating a thermally immature state. The results of geochemical analysis (volatile matter: 36.8%–46.5% and Tmax: 420°C–425°C) further support the above contention. High carbon content (average 77.89%), low sulphur content (average 0.46%) and varying nitrogen and oxygen levels in studied coal enhance its environmental suitability. The hydrogen index (HI: 163–279 mg HC/g TOC) values suggest a predominance of type‐III kerogen with mixed type‐II–III kerogen, further supported by petrographic data. Moreover, geochemical and petrographic data suggested the suitability of Singrauli coals for gasification. The high total organic carbon (TOC ≥ 38 wt%) indicated admirable potential as a source rock for hydrocarbon generation, particularly within the gas‐source rock zone, highlighting their suitability for energy production. Petrographic indices indicated a wet forest swamp origin with a telmatic source and bog region under ombrotrophic to mesotrophic hydrological circumstances. The association of macerals and total sulphur content further supported the conclusion of a freshwater environment during peat deposition. [ABSTRACT FROM AUTHOR]

This study comprehensively investigates H 2 loss resulting from injecting two gas mixtures: I (60% H 2 + 30% CH 4 + 5% N 2 + 5% CO 2) and II (60% H 2 + 30% N 2 + 5% CH 4 + 5% CO 2) into an aqueous solution containing 20,000 ppm sodium chloride and 100 ppm acetic acid (a microbial by-product of acetogenesis) within Bandera clay-rich sandstone reservoirs. Conducted at 42 °C and 1350 psi, various analytical techniques, including X-ray diffraction (XRD), Scanning Electron Microscopy with Energy Dispersive X-ray (SEM-EDX) spectroscopy, Fourier Transform Infrared (FTIR) spectroscopy, porosity and permeability assessments, pH and ion analysis, and gas chromatography, were utilized to assess the relevant properties of rocks, formation water, and gas content before and after 50 days treatment. The results indicate minimal sample reactivity, with dissolution primarily affecting dolomite and albite minerals. On average, porosity increased by 19% in formulation I and 15% in formulation II, while permeability decreased by 4.7% in formulation I and 5.3% in formulation II. In formulation I, H 2 fraction decreased by 2.79%, CH 4 increased by 7.15%, and CO 2 decreased by 9.36%, with N 2 remaining constant, whereas in formulation II, H 2 only decreased by 1.3%, CH 4 increased by 19.22%, and CO 2 decreased by 3.58%, with N 2 remaining consistent. Overall, the N 2 cushion gas condition (i.e., formulation II) slightly outperformed CH 4 in minimizing H 2 losses. This study thus provides significant insights into potential H 2 loss within a microbial-by-product-rich environment for underground hydrogen storage. • Comparative study on H 2 losses using CH 4 or N 2 cushion gas via microbial-byproduct is reported. • Biogeochemical reactions (dissolution/precipitation) induced by the mixtures are very weak. • The presence of acetic acid increased pH from 3.17 to 6.23 and 6.63 for CH 4 and N 2 cushion. • CH 4 cushion resulted in 2.79% H 2 loss compared to N 2 cushion gas (1.3% loss) based on gas chromatography. • Findings provide valuable insights into potential H 2 loss within a microbial rich environment. [ABSTRACT FROM AUTHOR]

China's low-permeability reservoirs possess abundant resources characterized by poor rock properties, strong heterogeneity, and fine pore throats, leading to low displacement efficiency. This study expands the concentration window for achieving ultra-low interfacial tension (ULT) by adding co-surfactants to the primary surfactant. Research indicates that the critical micelle concentration (cmc) and corresponding interfacial tension (γcmc) of the compounded system are lower than those of individual components. When the molar ratio of M to Q is 1:1, the interaction parameter βm reaches its minimum value, indicating the strongest synergistic effect within the system. The compounded system achieves an oil-water interfacial tension as low as 0.0021 mN/m at 0.25% M + 0.025% Q, enhancing recovery efficiency by 0.88% compared to the single component M. Utilizing micro-etching microscopy and natural core physical model experiments, the compounded surfactant system's recovery efficiency increment reaches 19.7%, significantly surpassing water flooding effects. This provides robust support for the efficient development of the Jiyuan X reservoir. [ABSTRACT FROM AUTHOR]

A special type of sandstone in which carbonate rock fragments (CRFs) dominate the composition developed in the Upper Triassic Xujiahe Formation's fourth member (Xu4) in the western Sichuan Basin, known as calcareous sandstone. Calcareous sandstones are widely distributed in the western Sichuan and is the main production target of tight sandstone gas in the Sichuan Basin. In this study, thin sections, porosity–permeability testing, scanning electron microscopy, and X-ray diffraction are applied to examine the characteristics and control factors for high-quality reservoirs in the calcareous sandstones, with a view to providing guidance for natural gas exploration and development in calcareous sandstones. The results show that the calcareous sandstone belongs to litharenite, with an average framework grain composition of 30% quartz, 1% feldspar, and 69% rock fragments, while the Xu4 sandstone has a high quartz content (average content of 71%). Primary intergranular pores are the main storage space, and the reservoir quality is quite poor. Under the influence of different parent rock properties of sandstones, there are obvious differences in the composition of framework grains between the calcareous sandstone and the ordinary Xu4 sandstone, which in turn affects the reservoir storage space, diagenesis, and reservoir quality. High-energy depositional conditions, low content of late cements, and the development of fractures are the main controlling factors for the formation of high-quality reservoirs in Xu 4 calcareous sandstones. [ABSTRACT FROM AUTHOR]

The Mengshan granitoid complex is located in the central part of Jiangnan Orogen and belongs to the western part of Jiangxi Province, where several phases of granitic magmatism record the crustal evolution of the late-Indosinian. However, its petrogenesis remains uncertain, largely due to controversies over its origin, evolutionary process and tectonic setting during intrusion. In this study, the lithological features and contact relationships observed in the systematic field geological investigations indicate that the late magmatic phases of the Mengshan granitoid complex are mainly composed of medium–fine-grained biotite monzogranite and fine-grained monzogranite, both of which developed primary fine-grained muscovite. Petrological, petrographic, geochemical and zircon U-Pb-Hf isotopic studies were further carried out on these rocks. Zircon U-Pb isotopic analyses suggest that the medium–fine-grained biotite monzogranite mainly formed at 220.7 ± 1.0 Ma to 218.0 ± 0.8 Ma, and that the fine-grained monzogranite formed at 211.5 ± 2.9 Ma to 212.9 ± 1.0 Ma. Whole-rock geochemical analysis results suggest that these rocks are rich in Cs, Rb, and U, and deficient in Ba, Sr, and Ti, and that they have properties characteristic of rocks with high silica, low P content and high K calc-alkali. Mineralogical and geochemical analysis results suggest that they are S-type granites. The εHf(t) values of the early-stage medium–fine-grained biotite monzogranite and late-stage fine-grained monzogranite range from –4.7 to 0.3 and from –3.2 to 0.7, respectively. Geochemical and isotopic data suggest that these granitoids were derived from the partial melting of Proterozoic continent basement rocks, and that minor mantle materials were involved during their generation. The presence of the early Mesozoic Mengshan granitoid complex reflects a reduplicated far-field converge effect of the collision of the North China and South China blocks and the subduction of the Palaeo-Pacific plate into the South China block. The thickening of the Earth's crust facilitated crustal delamination, underplating of mantle-derived magma, and crustal heating, triggering intense partial melting of the lithosphere and magma enrichment. [ABSTRACT FROM AUTHOR]

Curved mountain belts are spectacular natural features that contain crucial 3D information about the tectonic evolution of orogenic systems in the absence of other kinematic markers. The Mesozoic units exposed in the Mexican Fold and Thrust Belt in northeastern Mexico show a striking curvature, whose kinematic history has not been studied. The existing tectonic models of the region simply assumed the shape of the tectonic units as an inherent feature to the orogen. We investigated the kinematic history of this curvature through paleomagnetism and rock magnetism analyses, coupled with an exhaustive review of available published literature. The studied data sets indicate a protracted history of (re)magnetizations that occurred during the Late Jurassic‐Paleocene times at least during the Late Jurassic, Cretaceous and early Eocene. More significantly, they show significant counterclockwise rotations in the northern flank of the curvature and moderate clockwise vertical axis rotations along its southern flank. This data set suggests that the Sierra Madre Oriental was a linear belt that experienced oroclinal bending or buckling during the Cretaceous to early Eocene period (120–50 Ma). Plain Language Summary: The geological history of the American Cordillera is complex due to its extensive geological history. We have investigated a section of this Pacific‐Panthalassa region: the remarkable curved sector of the Mexican Fold and Thrust Belt in northeastern Mexico. This winding area, known as the Sierra Madre Oriental, potentially holds important clues about the evolution of the North American crust. To contribute to a better understanding of this area and to complement the scarce geophysical and geological studies, we used the magnetic properties of rocks and reviewed existing published research to investigate. We've uncovered a complex history of rock magnetizations with at least two main events dating back to the Late Jurassic and Cretaceous periods. Our findings also reveal that these mountain ranges were rotated from their original position on vertical axes, suggesting they were originally linear and were bent or buckled during the period from approximately 120 to 50 million years ago. Key Points: With Paleomagnetism we explore the nature of the striking curvature of the Northeastern section of the Mexican Fold‐and‐Thrust BeltOur study shows evidence of Orocline bending or Buckling during the major horizontal crustal shortening event of the Mesozoic in Mexico [ABSTRACT FROM AUTHOR]

We perform a joint analysis of gravity and magnetic data sets in the Tyrrhenian Sea region to infer the rock physical properties of several volcanic seamounts. We propose a moving‐window application using Poisson's theorem, which relates the total gradient of the magnetic field to the total gradient of the first‐order vertical derivative of the gravity field data. In volcanic environments, where strong intensity of remanent magnetization is expected, the total gradient of the magnetic field is particularly useful since it is almost independent on the direction of the total‐magnetization. The moving‐window approach resulted necessary due to the heterogeneous magnetization distribution of the volcanoes. First, we perform synthetic tests based on realistic seamount models which exhibit inhomogeneous magnetization intensity and orientation. Using the total gradients, we demonstrate that our approach can provide an appropriate magnetization‐to‐density ratio in different subareas of seamounts. The results of the correlation analysis for the Palinuro, Marsili, Vavilov, and Magnaghi seamounts provide interesting information on the variability of magnetization associated with different epochs of formation and demagnetization effects due to hydrothermal alteration processes. Plain Language Summary: We analyzed gravity and magnetic data sets to determine the rock properties of the main seamounts in Southern Tyrrhenian Sea. This study shows that the correlation analysis based on a window‐by‐window approach is an efficient tool for studying potential field anomalies in areas where inhomogeneous distribution of magnetization is expected. We also show that, by studying the total gradients of the magnetic field and the first order vertical derivative of the gravity field, the correlation analysis is almost insensitive to the direction of the remanent magnetization. We obtain interesting information on the variability in magnetization for each seamount and identify possible areas of demagnetization due to hydrothermal alteration processes. Key Points: We may infer the rock magnetization of seamounts by the correlation analysis of gravity and magnetic anomaliesThe study of the potential field total gradients is particularly useful when the source has strong remanent magnetizationWe found inhomogeneous magnetization in the Palinuro, Marsili, Magnaghi and Vavilov seamounts, likely due to hydrothermal activity [ABSTRACT FROM AUTHOR]

The shaft resistance of rock-socketed piles (RSPs) is primarily influenced by the interactions between the pile, rock and any soft interface materials. This study presents a fundamental experimental and numerical investigation to predict the shaft resistance of model RSPs in soft rocks through a comprehensive shear strength framework incorporating the major variables such as roughness and smear fabric. By calibrating the Discrete Element Method (DEM) results with the experimental outcomes, this study evaluates the load-resistance attributes of RSPs in three different soft rocks for a wide range of roughness and smear configurations. The interface roughness effect of the RSPs in terms of the friction coefficient was correlated with the ultimate shaft resistances, uniaxial compressive strength and Young's modulus of the rock. The study then incorporated the effect of smear fabric (placement, thickness and area proportion) in the shear strength framework of clean shafts. Comprehensive review of the DEM results revealed that the socket roughness effect diminishes at a critical roughness factor (RF) of 0.4, beyond which the smear predominantly influences the shaft capacity. Following this, the effects of roughness and smear fabric were incorporated into a single equation representing the interface shear strength of RSPs, where the existence of smear results in a maximum reduction of up to 75% of the ultimate shaft resistance. The distinctive feature of this unified interface shear strength framework lies in its integration of the new smear fabric parameter and the linkage to the mechanical properties of soft rocks, which is the limitation of the earlier studies. It thereby sets a strong base for future studies aimed at advancing the pile-rock interface models. Highlights: Reports the experimental and numerical test results for various rocks in terms of different roughness and smear configurations. Formulates a friction coefficient to correlate the ultimate shaft resistances with the interface roughness and mechanical properties of soft rocks. Evaluates the effects of smear fabric on the shaft resistance of different soft rocks in terms of different area proportions and thicknesses. Proposes a unified interface shear strength framework to predict the shaft resistance of rock-socketed piles in soft rocks. [ABSTRACT FROM AUTHOR]

Borehole breakout is an important geological phenomenon that provides a significant reference for the estimation of the direction and magnitude of in situ stress. To better understand the water content effect on borehole breakouts, a series of experiments on red sandstone was conducted. The standard cylindrical samples and cubic samples containing a circular hole were loaded under uniaxial compression in four water states including dry, unsaturated, short-term saturated, and long-term saturated. Then, the water effect was discussed in terms of rock strength and deformation, initiation stress of borehole breakout, failure evolution process, geometries of breakout, fragments, and acoustic emission (AE) signals. In the water-bearing state, rock properties significantly deteriorate with the decline of strength, the enhancement of plastic deformation, and the restrain of the brittle failure mode. For cubic samples, the axial stress required for borehole breakout increases under the short-term saturated condition but decreases after the long-term immersion. In addition, obvious extrusion deformation of borehole walls toward the borehole space is observed in saturated samples, resulting in vague V-shaped void notches. Before the overall failure, more obvious AE signal fluctuation occurs in the water-bearing state and AE locations reveal a larger fracture concentration region. Two mechanisms are proposed to explain the water content effects on the borehole breakout initiation stress, involving strength weakening effect and stress redistribution mechanism. The shrinkage of borehole breakout geometries is discussed further on the influence on the in situ stress estimation. Highlights: The influence of water content on sandstone properties and borehole breakout is comprehensively investigated. Short-term immersion results in a slight rise of borehole breakout initiation stress, while it declines again after long-term immersion. Double mechanisms are proposed to explain the water content effect on borehole breakout initiation. Water induces the shrink of both breakout depth and angular span, which may further affect the in situ stress estimation. [ABSTRACT FROM AUTHOR]

Mud logging data, which quantify the energy expended in rock breaking during drilling, are routinely acquired during drilling. These data offer a practical means to estimate the geomechanical properties of rocks, particularly confined compressive strength (CCS), avoiding the need for costly and destructive laboratory tests. Thus, in this study, predictive models for CCS were developed utilizing mudlogging data and employing various machine learning (ML) algorithms, including multi-layer perceptron neural network (MLPNN), least squares support vector machine (LSSVM), Gaussian process regression (GPR), and random forest (RF). Data were compiled from reservoir sections of two vertical wells (Well A and Well B) of an oil field in southwest Iran. CCS values were estimated using petrophysical logs and empirical correlations, calibrated with laboratory test results, and organized into a database of input and output features. 80% of Well A data were allocated for training, with 20% reserved for testing. The Tukey method was then used to remove outliers from the training subset, ensuring a high-accuracy and generalizable model. Subsequently, tuned ML algorithms based on the problem condition were applied to develop predictive CCS models using the training data. These models were then rigorously assessed using the test data. The outcomes of these steps revealed that the GPR-based model exhibited the lowest Root Mean Square Error (RMSE, train: 0.8499 MPa and test: 6.3886 MPa) and the highest coefficient of determination (R2, train: 0.9993 and test: 0.9597) among developed ML models. Further scrutiny employing over-fitting index and regression error characteristic curve techniques underscored the high accuracy and the generalizability of the GPR model on unseen data. Application of the GPR model on Well B demonstrated remarkable accuracy (RMSE = 2.3107 MPa) and its real-time predictive capability from minimal mudlogging data variables, providing a reliable and cost-effective solution for CCS prediction in vertical wells. Highlights: 4 machine learning models predict confined compressive strength (CCS) from mud-log data 17 outliers detected with high mechanical specific energy values in CCS prediction Gaussian process regression (GPR) delivers the most precise CCS predictions Depth and weight on bit are the most and least influential input features on CCS Partial-dependence plots reveal key input influences on CCS predictions" [ABSTRACT FROM AUTHOR]

The study aims to utilize the convergence–confinement method (CCM) by considering non-hydrostatic stress assumptions in the analysis of the surrounding rock in a circular tunnel. The rock mass properties should adhere to the criteria of the non-linear Hoek–Brown failure criterion. Through a thorough theoretical analysis approach, an analytical solution was derived to determine the stress and displacement induced by tunnel excavation, particularly in the elastic and plastic zones. This solution, applicable under anisotropic stress conditions, involves accounting for confinement loss incrementally for computational feasibility. The implementation of this analytical solution, facilitated by a straightforward spreadsheet, was validated against existing data to evaluate the impact of non-linear failure criteria on ground reaction behavior. The study scrutinizes the mechanical response at the tunnel's inner curve and assesses stress–displacement distribution across the tunnel cross-section. A comparison between the proposed solution and published results demonstrates a consistent and promising correlation. [ABSTRACT FROM AUTHOR]

The joint inclination angle is a crucial factor influencing the mechanical behavior of rock masses and greatly affects the stability of rock mass engineering. The article utilizes cement mortar to fabricate jointed rock models with mechanical properties that closely resemble those of real rock formations. The compressive plate speed of the loading test machine is 0.005 mm/s, and the axial static loading rate ranges from 0.5 to 1.0 MPa/s. To investigate the influence of joint inclination angles on the macroscopic mechanical properties of the rock, the study initially employs indoor full-field observation and the non-contact technology known as Digital Image Correlation (DIC). Experiments are conducted on rock specimens with varying joint inclination angles of 30°, 45°, 60°and 90°. Following this, numerical simulations employing the Discrete Element Method (DEM) are conducted to analyze the microfracture process. The model test and numerical simulation results demonstrate good agreement, particularly regarding the failure modes. It is found that the most common failure mode for jointed rock is a composite form of shear and tension. As the joint inclination angle increases, tensile failure becomes more prominent. The Young's modulus EJR/ER and peak strength σJR/σR ratios between jointed and jointless rock vary with the joint inclination angle, exhibiting a "V" shaped curve. A joint inclination angle of 45° results in minimum strength and modulus in the macro mechanical properties. The joint inclination angle has a negligible effect on the rock mass's residual strength, maintaining an approximately constant ratio of 0.14 between residual and peak strength σr/σp. [ABSTRACT FROM AUTHOR]

In this research, rock mass deformation modulus (Emass), classification of rock mass, cohesion (c) and internal friction angle (Φ), and intact rock properties of the Khersan 2 dam site were investigated. Factors affecting mechanical properties were investigated and compared with the results of previous studies. To assess the shear strength and the Hoek and Brown failure criteria parameters, the triaxial test was performed on samples under saturated conditions. The Q-system and rock mass rating (RMR) were calculated for five-metre sections of boreholes. Results of the Mohr–Coulomb failure criterion showed that the limestones have a mean Φ of 40 degrees and a mean cohesion of 1 MPa, marl limestones have an average of 30 degrees and cohesion of 0.50 MPa, and anhydrite and gypsum showed an average of 26 degrees and 0.10 MPa. The results showed that c and Φ increase with the increase in the shear box size. Based on the RMR and Q-system the site was classified in good class. The mean of Emass showed that the dilatometry test gives the lowest value. Linear and logarithmic relationships were established between RMR89 with compressional wave velocity (Vp) (R2 = 0.95 and RMSE = 1.63) and Q-system (R2 = 0.95 and RMSE = 2.05), respectively. [ABSTRACT FROM AUTHOR]

Around the world, deep borehole disposal is being evaluated for intermediate level-waste (ILW), high-level waste, and spent nuclear fuel. To facilitate a disposal concept options analysis for ILW in Australia, desktop and lab-based geoscientific investigations, together with generic post-closure safety assessments of deep borehole disposal of long-lived ILW, have been undertaken. This paper reports on geoscientific data obtained on crystalline rock and rock salt as model rocks for geological disposal. Petrophysical and mineralogical properties for these rocks have been investigated to provide realistic data for evaluation and input to post-closure safety assessments. For crystalline rock samples originating from depths between 700 to 1900 m, very low hydraulic conductivity (2 × 10−12 to 3 × 10−11 m/s) and very low porosity (0.02% to 1.2%) were obtained. The noble gas isotopic composition of fluid inclusions from the same depth interval confirmed the rock had been devoid of recent interaction with meteoric water, thus providing potentially suitable conditions for geological disposal. Rock salt from a 802-m (heterogeneous sample with 40% halite) and a 1100-m (sample with 98% halite) depth also had a low hydraulic conductivity (5 × 10−10 to 5 × 10−9 m/s at 802 m and 10−11 to 2 × 10−10 m/s at 1100 m) and very low porosity (~0.8% for the heterogenous sample and ~0.2% for the pure halite sample). Post-closure safety assessments based on numerical modeling provided bounding conditions around the thermal evolution of the disposal environment in crystalline rock for low heat generating ILW (50 W per 180-L vitrified waste canister), including exploring the sensitivity of temperature evolution within the borehole and rock environment to parameters such as heat load, borehole depth, geothermal gradients, and rock thermal conductivity. The coupling of heat transport with radionuclide migration to account for buoyancy-driven transport was shown to have a limited impact on radionuclide migration. For a disposal borehole in crystalline rock, the radionuclide concentrations and annual dose rates from key radionuclides (99Tc and 79Se) for a 500-m, 1000-m, or 3000-m deep borehole were negligible (i.e., many orders of magnitude smaller than the threshold dose the International Atomic Energy Agency considers insignificant for humans, 0.01 mSv/year). For disposal in rock salt, a suite of numerical model scenarios explored the effectiveness of the engineered barriers, including the glass matrix, primary package, and overpack, assuming diffusion-dominated transport. These scenarios illustrated that the performance of the disposal system was insensitive to the presence or absence of engineered barriers, as dose rates at late time (>105 years) were nearly identical for all scenarios. These results indicate that the natural barrier provided by the salt is very effective at containing radionuclides, while the engineered barriers serve mainly to delay the arrival of the peak dose. While the results are preliminary, the post-closure safety assessments, supported by measured data from crystalline rock and rock salt, give confidence that deep borehole disposal of long-lived ILW would result in dose rates considered insignificant for humans within a few meters from the borehole. [ABSTRACT FROM AUTHOR]

The study area covers Avanos‐Ozkonak and its surroundings north of Nevsehir province. An attempt was made to determine the relationship between tectonic lineaments and springs in the area. It was found that there is a close relationship between the location of springs and tectonic lineaments. In recent years, lineaments have been used in mineral exploration studies and geothermal areas. Remote sensing methods have also been used in this study. The relationship between tectonic lineaments (faults and fractures) and spring formations obtained from field studies and satellite‐based studies was evaluated. Metamorphic rocks belonging to the Kirsehir massif and Paleocene–Middle Eocene aged units were subjected to polyphase deformation. As a result of these deformations, faults and cracks were formed. This situation has given aquifer properties to the rocks. At the same time, many springs were formed by faults and cracks. This study determined the relationship between 342 springs identified during field works and tectonic lineaments. Approximately 89% of the springs identified in the field were found to be located on the tectonic lineaments obtained from the satellite imagery. Some springs discharged from discontinuities on the formation boundaries. [ABSTRACT FROM AUTHOR]

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In the recent past, several weathering indicators have been developed to describe its state of weathering. The state of rock weathering is a useful indicator to estimate the integrity of tropically weathered rock material and mass which weatherability plays an important role in a tropical region. Through a ground assessment tool, the strength and durability of the rock mass could be estimated and complex or adopted to simplify the early prediction of the complex engineering parameter. This paper presents several models of the Weathering Index (WI) using selected significant parameters using statistical analysis. For this purpose, several sites have been chosen to represent granitic rock mass. Forty (40) numbers of samples were collected and tested comprising from four (4) sites in Malaysia. Several laboratory tests have been conducted such as Point Load Index (Is(50)), dry density, Slake Durability 1 (SD1), Slake Durability 2 (SD2) and moisture content. The field and laboratory data sets are used to determine the WI by using simple regression and MLR analysis Significant parameters found to be useful in determining the WI are selected namely SD1, dry density, Is(50), and block volume. These parameters were selected based on stepwise analysis using Statistical Package for the Social Sciences (SPSS). Following the models' implementation, the models were evaluated and the best prediction model was selected after considering statistical coefficients, such as coefficient of determination (R2), variance account for (VAF), and root mean squared error (RMSE), as well as utilizing a straightforward ranking approach. The findings of this study could contribute to the more accurate prediction of WI using a more simplistic field and laboratory parameters. Therefore, the WI is useful during the initial stages and planning of rock excavation work and provides a good description of weathering grade and rock mass properties, which will affect excavatability in granitic areas. [ABSTRACT FROM AUTHOR]

The randomness and complexity of rock mass fissure development seriously affects the strength and stability of the rock mass. In order to analyse the influence of different numbers of rock bridges on the strength of rock mass, uniaxial compression and numerical simulation tests of fissured sandstone is carried out to study the influence law of different numbers of rock bridges on the mechanical properties and failure characteristics of rock. The results show that the number of rock bridges affects the damage mode of the rock mass, and when the fissure inclination and the inclination of rock bridges is constant, the damage microcrack development status of rocks with different numbers of rock bridges is different; the increase of the number of rock bridges has an optimising effect on the mechanical properties of the rock mass, and the peak stress and elastic modulus increase with the increase of the number of rock bridges. Under uniaxial compression, shear coalescence occurred in the intact rock specimens, while the fracture-containing specimens changed from shear damage to mixed shear-tension damage with the increase of the number of rock bridges. The damage of the rock specimens containing only 0 and 1 rock bridge are mainly caused by the extended shear cracks at the tip of the prefabricated cracks and the penetrating rock bridges; the rock specimens containing 2 rock bridges produced tensile cracks at the same time as shear cracks are formed, and the damage of the specimens is caused by the joint extension of shear and tensile cracks. When the total length of the co-linear cracks is the same, the higher the number of rock bridges, the smaller the stress intensity factor of the rock mass, and the less likely the specimen will be damaged. [ABSTRACT FROM AUTHOR]

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The thermomechanical coupling of rocks refers to the interaction between the mechanical and thermodynamic behaviors of rocks induced by temperature changes. The study of this coupling interaction is essential for understanding the mechanical and thermodynamic properties of the surrounding rocks in underground engineering. In this study, an improved temperature-dependent linear parallel bond model is introduced under the framework of a particle flow simulation. A series of numerical thermomechanical coupling tests are then conducted to calibrate the micro-parameters of the proposed model by considering the mechanical behavior of the rock under different thermomechanical loadings. Good agreement between the numerical results and experimental data are obtained, particularly in terms of the compression, tension, and elastic responses of granite. With this improved model, the thermodynamic response and underlying cracking behavior of a deep-buried tunnel under different thermal loading conditions are investigated and discussed in detail. [ABSTRACT FROM AUTHOR]

Proper characterization of the unsaturated hydraulic properties in rocks is significant for predicting fluid flow in soil, hydrogeologic, and petroleum science and engineering problems. In this study, we contributed rigorous analysis of the unsaturated hydraulic properties of three reservoir rock samples (Berea Sandstone, Guelph Dolomite, and Indiana Limestone). An improved version of the standard evaporation method (HYPROP) was developed to cater specifically to rock samples. The improved HYPROP setup enables measurements of local water pressures within rock samples without disturbing the upper portion of the samples. The obtained results were compared with those obtained using the conventional pressure plate method and a state-of-the-art nuclear magnetic resonance (NMR) method. Observed data were analyzed in terms of four different unimodal and bimodal hydraulic functions. The HYPROP data were found to be relatively close to the pressure plate data of two carbonate rocks. The NMR-based data were reasonably consistent with the HYPROP data, with differences likely due in part to the fact that they were obtained using two different 5-cm long plugs taken from the same core. Heterogeneity along the rock cores from which the samples were taken could be a major reason for the observed differences, and hence should be considered in reservoir analyses. [ABSTRACT FROM AUTHOR]

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Friction properties of rock are closely connected with the anisotropy. The anisotropy of rock friction can provide a valuable assessment for geotechnical and geological engineering. In this study, the rotary friction tests were conducted to analyze the water effect on the friction property and the friction anisotropy of the four types of rock. The drilling response model (DD-model) was employed to characterize the rotary friction behavior of the rocks. The parameters of this model include the three types of friction parameters: 1/ς, μ, and f, where 1/ς and μ are constant, and f is a variable. A quantitative method is proposed for assessing the anisotropy of rock friction. The results of the rotary friction tests indicate that the relation between torque force and thrust force conforms to the DD-model. The changes of two friction constants 1/ς and μ from dry state to water-saturated state suggest that the water effect on the friction strength of the rocks exhibits significant anisotropy. The friction strength determined by the friction variable f increases first, then decreases, and finally stabilizes with the increasing of depth. AIf is an anisotropy index calculated by the proposed method. The percentage difference of the average value of AIf between water-saturated and dry states shows the degree of the water effect on the friction anisotropy of the rocks, mudstone (MU) > granite (GR) > fine sandstone (FS) > argillaceous siltstone (AS). The quantitative model is hopefully constructed for characterizing the relation between the anisotropic friction strength of rock and the moisture state in future. [ABSTRACT FROM AUTHOR]