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In this paper we use a multidisciplinary approach including field observations, geological mapping and stress analysis to investigate the structural evolution of the NE-trending Sfina Basin, which located in the foreland basin of the Alpine chain (Maghrebides) in Tunisia. The Sfina Basin structure is the Neogene pull-apart basin, forming along the NE-trending Zaghouan fault, it located in Tunisian Atlas domain and formed in a NE‒SW-trending dextral strike-slip fault systems. Our result has shown that this NE-trending basin is limited in both northern and southern edges by two NE-trending dextral fault segments. During the Late Cretaceous‒Middle Miocene, under NE‒SW extensional regime, the NE-trending transtensional fault segments constituted the boundaries of the Sfina Basin that developed as a dextral releasing stepover. During the Late Miocene‒Early Quaternary, Sfina Basin was inverted under a regional NW‒SE-to-NNW‒SSE compressional event in response to the Africa‒Eurasia convergence with continental collision process. The inversion occurred mainly along Sfina Basin sidewalls by reactivation of the pre-existing NE‒SW-trending weaknesses as right-lateral transpressional shears and led to formation of the NE‒SW-trending major folds structures in the Sfina area. [ABSTRACT FROM AUTHOR]

The present-day lithospheric stress state of the Qinghai-Tibetan Plateau and neighboring areas is controlled by both the lithosphere itself and the underlying mantle. In other words, the stress is affected by the gravitational potential energy (GPE) difference caused by the change in the density distribution within the lithosphere and the drag force on the base of the lithosphere caused by mantle convection. The study of the lithospheric stress state plays an important role in further understanding the dynamic background and mechanism for the evolution of the Qinghai-Tibetan Plateau. In this study, the Crust1.0 crustal density model combined with the S40RTS mantle shear wave velocity variation model was used to calculate the GPE. The EGM2008 gravity field model was used to calculate the drag force from mantle convection at the base of the lithosphere. The lithospheric and joint stress fields of the two sources were obtained by solving the force balance under the thin sheet approximation. This way, we could comprehensively analyze the characteristics of the stress state within the Plateau. Six regions were classified according to the GPE stress field, mantle drag force stress field, the relative magnitude of the two stress fields, and correlation between the two stress fields and surface deformation. The lithospheric stress fields of the Tarim Basin and other stable blocks are mainly controlled by the GPE difference. The lithospheric stress field in the collision zone between the Indian Plate and the Qinghai-Tibetan Plateau is predominantly controlled by the deep mantle drag force. The lithospheric stress field in the interior of the Plateau is controlled by both GPE and mantle drag. The correlation between the lithospheric stress field and surface deformation at the southeast margin of the Qinghai-Tibetan Plateau is poor. It is hypothesized that the presence of lower crustal flow with lower effective viscosity leads to crust-mantle decoupling, and the mantle drag force has a weaker influence on the shallow crust, resulting in the inconsistency between the average lithospheric stress field and surface deformation. [ABSTRACT FROM AUTHOR]

Intraplate earthquakes occur more frequently in the Japanese islands than in other regions. Large intraplate earthquakes in the island arc preferentially occur in strain concentration zones detected by geological and geodetic studies. Crustal heterogeneity plays a crucial role in generating large intraplate earthquakes and strain concentrations. Thus, we elucidated the crustal heterogeneities beneath a strain concentration area on the back‐arc side of the northeastern Japan Arc based on electrical resistivity, which is sensitive to weak zones in the crust. By deploying wideband magnetotelluric surveys, we revealed the three‐dimensional electrical resistivity structure in the crust, suggesting the coexistence of two different types of strain‐concentration mechanisms in the strain‐concentration area. The shallow conductive layers and lower‐crustal conductors appear to act as low‐elastic‐modulus and low‐viscosity areas, respectively, and are responsible for the strain concentration. We found shallow and lower‐crustal conductors in the strain concentration zone revealed by geological studies. Those conductive areas are considered to act as mechanically weak zones and cause stress loading on the brittle pars of pre‐existing faults, resulting in large intraplate earthquakes. The resultant earthquakes presumably contribute to strain accumulation on a geological timescale. In addition, a spatial correlation between the epicenters of large intraplate earthquakes and edges of lower‐crustal conductors implies the contribution of the fluids in the lower crust to the generation of large earthquakes. We also identified vertical conductors ranging from the lower crust to Quaternary volcanoes, which may indicate trans‐crustal magmatic systems under these volcanoes. Plain Language Summary: Intraplate earthquakes occur more frequently in the Japanese islands than in other regions worldwide. Large intraplate earthquakes in this region preferentially occur in high‐deformation zones, as detected by geological studies and global positioning system (GPS) measurements. Heterogeneous structure in the crust plays a crucial role in the generation of large intraplate earthquakes and high crustal deformations. Thus, we revealed the three‐dimensional crustal electrical resistivity structure beneath a strain‐concentration area in the northeastern Japan. The resistivity structure suggests the coexistence of two different mechanisms of high deformation. Shallow conductive layers and lower‐crustal conductors appear to act as low‐stiffness and low‐viscosity areas, respectively, leading to high crustal deformation. We found shallow and deep conductors in the high‐deformation zones revealed by geological studies. As both can act as weak zones, those conductors presumably play a key role in loading on faults, resulting in intraplate earthquakes. Because the epicenters of large intraplate earthquakes are positioned near the edges of lower‐crustal conductors, the fluids in those deep conductors possibly contribute to the generation of large earthquakes. We also revealed vertical conductors ranging from the deep crust to Quaternary volcanoes, which may indicate magma‐rich areas under these volcanoes. Key Points: The electrical resistivity structure suggests the coexistence of two strain‐concentration mechanisms in the strain‐concentration areaThe shallow conductive layers and lower‐crustal conductors act as low‐elastic‐modulus and low‐viscosity areas, respectivelyWeak zones in the crust, imaged as conductors, presumably cause stress loading on faults and contribute to large intraplate earthquakes [ABSTRACT FROM AUTHOR]

Hydraulic fracturing pressure is one of the key criteria in defining the pumping schedule and in dimensioning surface plants for fracturing operations. However, it is difficult to predict at a practical field scale due to the complex determining factors, involving geological, hydrodynamic and rock mechanical parameters. This study proposes a synthetic data-driven workflow, integrating both hydrodynamic and rock mechanical models, to predict the pressure based on fracturing experience in neighboring wells. The data quality and performance of the geological, hydrodynamic and rock mechanical features are evaluated based on a backward elimination strategy and control variate method, using error evolutions as criteria. Relatively small errors (root mean square error 5.1 ~ 5.7 MPa and mean absolute error 5.6 ~ 8.3%) are returned for wells/cases within the same region as the training wells, demonstrating the superior performance of the workflow. The prediction errors increase significantly with increasing distance between training and testing wells – defining the range of applicability of the workflow. The rock mechanical feature (represented by the brittleness index) provides a larger contribution to the prediction than that of the hydrodynamic feature (represented by the proppant accumulation) in most of the testing cases. Young's Modulus exhibits a higher performance (induces the smallest errors in pressure prediction) to characterize the rock mechanical feature of the formation, compared with the brittle mineral ratio and Poisson's Ratio. The data quality of geological stresses and Poisson's Ratio may require improvements based on the irregular error evolutions. The remaining errors and proximity/regional limitations of the data-driven workflow are critically discussed. This new method provides a platform for the prediction of pressures at field-practical scales, which may be significant for both hydraulic fracturing and geological storage of CO2 and H2 in depleted reservoirs with sufficient historical hydraulic fracturing records. Highlights: A data-driven workflow is built to predict fracturing pressure at field scales. Errors increase with the increasing distance between training and testing cases. Contribution of rock mechanical feature is larger than hydrodynamic feature. Young's Modulus performs better in characterizing rock mechanical feature. Lower data qualities of geological stresses and Poisson's Ratio are revealed. [ABSTRACT FROM AUTHOR]

Rapid and accurate assessment of fracture permeability is critical for subsurface resource and energy development as well as rock engineering stability. Fracture permeability deviates from the classical cubic law under the effect of roughness, geological stress, as well as mining-induced stress. Conventional laboratory tests and numerical simulations are commonly costly and time-consuming, whereas the use of a connectivity metric based on percolation theory can quickly predict fracture permeability, but with relatively low accuracy. For this reason, we selected two static connectivity metrics with the highest and lowest prediction accuracy in previous studies, respectively, and proposed to revise and use them for fracture permeability estimation, considering the effect of isolated large-aperture regions within the fractures under increasing normal stress. Several hundred fractures with different fractal dimensions and mismatch lengths were numerically generated and deformed, and their permeability was calculated by the local cubic law (LCL). Based on the dataset, the connectivity metrics were counted using the revised approach, and the results show that, regardless of the connectivity metrics, the new model greatly improves the accuracy of permeability prediction compared to the pre-improved model, by at least 8% for different cutoff aperture thresholds. [ABSTRACT FROM AUTHOR]

Throughout all the countries in the world, including Vietnam, nations with well-established mining industries have undertaken extensive research on the stability of rock masses when constructing underground tunnels in varied geological conditions. The present study aims to provide a comprehensive overview of the risk assessment related to rock masses during the construction of pit lines in mining operations. Consequently, the standing time of unsupported tunnels is assessed based on different values of the strength index and deformation characteristics of the rock mass. The objective was to perform both experimental and theoretical investigations to analyse how the stand-up time of rock masses surrounding a tunnel affects the unsupported span. The analyses were based on considering the rock parameters, including strain modulus; geological strength index; and allowable displacement values, and consideration of hereditary creep properties. By examining tunnels excavated in rock strata, it was concluded that varying geological strength index values resulted in distinct creep behaviour in the surrounding rock masses. Thus, it was reasonable to compute the unsupported span and stand-up time of tunnels. The research revealed that permissible displacements are significantly influenced by the types of rock materials surrounding the tunnel structure. Recognising the significance of time, the authors introduce a more practical interpretation and evaluation of the stability of rock masses, thus enhancing the precision of commonly available models. [ABSTRACT FROM AUTHOR]

The Great Dyke of Atla Regio (GDAR) is traced for ~3700 km on Venus, as a surface graben (narrow trough) interpreted to overlie a continuous laterally-emplaced underlying mafic dyke (vertical magma-filled crack). The GDAR belongs to a giant radiating dyke swarm associated with Ozza Mons (volcano), Atla Regio plume, and was fed from a magma reservoir ~600 km south of the Ozza Mons centre. A 50-degree counter-clockwise swing of the GDAR at 1200 km from the centre is consistent with a 1200 km radius for the underlying Ozza Mons plume head, and a stress link to the 10,000 km long Parga Chasmata rift system. Our discovery of the GDAR, should spur the search for additional long continuous single dykes on Venus (and Earth), with implications for estimating plume head size, locating buffered magma reservoirs, mapping regional stress variation at a geological instant, and revealing relative ages (through cross-cutting relationships) over regional-scale distances. In this study, the authors trace lateral magma movement in a ~ 3700 km long fracture on Venus. This Great Dyke of Atla Regio is the longest so-far traced on Venus (and in the solar system) and belongs to a giant radiating dyke swarm of the Ozza Mons volcano of the Atla Regio plume. [ABSTRACT FROM AUTHOR]

Under complex geological conditions of fault system, stratum and terrain, an accurate inversion of the in-situ stress field is a challenging and hot issue in the study on engineering geology. Focusing on the accurate inversion of fine in-situ stress field for deep-buried tunnel under complex geological conditions, and the influence of major geological factors on the stress state, we took the Jiangranshan tunnel of the express way from Shuangjiang to Cangyuan in southwest Yunnan as a case to perform the study. We first established the fine geological model of the Jiangranshan tunnel area by integrating the fine DEM data and the geological survey data. Then, taking the measured in-situ stress data in the tunnel site and the measured GPS data of velocity field as the integrated constraints, we carried out the inversion of fine in-situ stress field in the engineering region of Jiangranshan tunnel. On the basis of the inversion results, we analyzed the characteristics of fine in-situ stress field in the tunnel site and the influence of main geological conditions on the current in-situ stress field. Finally, we estimated the engineering geological stability of the surrounding rock mass of the Jiangranshan tunnel. The results show that the simulated displacement velocity field in the Jiangranshan tunnel area is basically consistent with the GPS observation results, revealing that the inversion model adopted in this study can well reflect the current tectonic stress environment of the engineering region. The simulation results show that the level of the in-situ stress field in the western part of the study area is relatively high, while it is low in the eastern part. The direction of the maximum principal stress shows partial deflection in the study area. The influence of the nearly E-W-striking Xiaoheijiang fault--the largest fault in the study area--on the in-situ stress is that it causes the slight deflection of the direction of the maximum principal stress; however, it does not cause abrupt change of the in-situ stress magnitude. The secondary faults and topography show little effect on the in-situ stress field, which is limited to very small area and does not cause notable disturbance of the in-situ stress field. The results reveal that the maximum, intermediate, and minimum principal stresses along the tunnel mainly distribute in 7.47--27.23 MPa, 1.59--15.12 MPa, and 0.01--6.71 MPa, respectively, and does not show obviously abnormal characteristics. The engineering geological stability of the surrounding rock mass of the Jiangranshan tunnel is estimated by the stress intensity index (i.e., the ratio of the maximum tangential stress to the uniaxial compress strength of rock). The estimation results, which are determined by integrating the stress field simulation results and the mechanical properties of the typical rocks obtained from the laboratory tests, show that the stress intensity indexes of the Jiangranshan tunnel mainly range between 0.20--0.48. It indicates that the surrounding rock masses of the Jiangranshan tunnel are mainly in a stable state or in a slight rockburst risk under the current in-situ stress conditions. The conclusion can be drawn from the case study that under the complex geological conditions, the fine geological model suitable for the scale of engineering area can be established by using the fine DEM and actual fault and strata data, which can effectively reveal the characteristics of the in-situ stress field in engineering area and the influence of the main geological conditions. This study provides not only the profound understanding of the in-situ stress field of the Jiangranshan tunnel area, but also the implications for the fine inversion of in-situ stress field under complex geological conditions in Yunnan and other similar areas. In addition, this study can directly support the stability evaluation of the surrounding rock of the deep-buried Jiangranshan tunnel. [ABSTRACT FROM AUTHOR]

Based on the characteristics of real stress distribution in coal mining, the evolution law of plastic zone shape and spatial position were investigated. The stress model of roadway with non-orthogonal state of in-situ stress and mining-induced stress was constructed. The boundary equation of the roadway plastic zone under in-situ stress deflection was deduced. Additionally, the evolution mechanism of the roadway plastic zone was analysed. We found that the shape and spatial position of the roadway plastic zone are jointly determined by in-situ stress deflection angle α , mining-induced stress concentration coefficient K, and equivalent lateral pressure coefficient η ′ when the mechanical parameters (rock cohesion c; internal friction angle φ ) were fixed. Specifically, the plastic zone experiences the cyclic evolution phenomenon, where the plastic zone shape varies from petal–ellipse–circle–ellipse–petal shapes in morphology. In this study, we expound the general evolution law of roadway plastic zone under different geological, working conditions and mechanical parameters. The main controlling factors and mechanism of the shape and spatial position evolution of the plastic zone are revealed. A numerical model was established to study the evolution law of plastic zone during the change of corresponding parameters. The results show that the traditional method of predicting the shape of plastic zone by lateral pressure coefficient is inaccurate. The plastic zone distribution calculated using this method was compared with the roadway deformation measured in 1305 bottom drainage roadway of Hudi mine, and the comparison results were in good accordance. The results of this study have certain universality, and enrich the understanding of the roadway plastic zone. It can provide theoretical reference for roadway excavation and support design under different geological and in-situ stress conditions. Highlights: The non-orthogonal failure behavior of the roadway with the change of complicated stress state is revealed. Plastic zone experiences the cyclic evolution phenomenon, where the plastic zone shape varies from petal-ellipse-circle-ellipse-petal shapes in morphology. Main controlling factors and mechanism of the shape and spatial position evolution of the plastic zone are summarized. The unsymmetrical failure mechanism of roadway under non-orthogonal stress state is revealed. [ABSTRACT FROM AUTHOR]

Rockbursts pose a significant risk in deep gold mines in the Witwatersrand Basin of South Africa as they may damage the excavation, injure workers, and delay production. We analysed the source mechanisms of 75 large mining‐related seismic events (ML 1.5–2.7) that caused damage to stopes in Kloof Gold Mine and used legacy 3D reflection seismic data to delineate the ore body and geological structures that may be correlated with mining‐related seismic events. The 75 seismic events took place at depths of 1600–4200 m below surface. Most events were located close to stopes mining the Ventersdorp Contact Reef ore body. The S‐to‐P‐wave energy ratio (Es/Ep) from the analysed seismic events ranged from 1.1 to 19.9. The source mechanisms of mining‐induced seismic events aid in understanding the dominant modes of failure. Planes of weakness may be the result of mining‐induced stresses or pre‐existing geological structures such as faults and dykes. The Es/Ep ratio, focal mechanism and moment tensor solutions were correlated to the underground mapped and seismically defined geological structures. Approximately 44% of the events showed strong correlation with the known underground mapped and seismically imaged geological structures (faults and dykes), whereas 56% of the events were related to elements of the mining geometry (dip pillars, abutments and remnants). This information enables mining layouts to be modified to minimize the risk of rockbursting. [ABSTRACT FROM AUTHOR]

The study proposes a stochastic approach to quantify the uncertainty of groundwater vulnerability (GV) produced by classical index-overlay methods. In the analysis, the physical-based MODFLOW model has been integrated with the DRASTIC method and modified by the analytical hierarchy process (AHP) technique. Specifically, the flow fields from the MODFLOW model provide the parameters of depth to water and the associated hydraulic conductivity (K) for the DRASTIC method. The integrated loops between the MODFLOW and DRASTIC models enable the evaluations of GV maps by considering sources of uncertainty in geological parameters and stress changes in an aquifer system. In illustrating the approach for practical implementations, the study considers the uncertainty produced by the heterogeneity of K in the Pingtung Plain groundwater basin in southern Taiwan. Different degrees of K heterogeneity were assessed to quantify the impact of the K heterogeneity on the GV mappings. Results show that the integration of parameter uncertainty information from the stochastic-based approach for GV mapping can improve the accuracy and reliability of the GV assessment. The stochastic GV maps have accounted for the source of the K uncertainty. There are significant discrepancies in GV values in the spatial distribution and intensity in all GV classes. The results clarify the potential risk of groundwater contamination in the Pingtung Plain groundwater basin. [ABSTRACT FROM AUTHOR]

The high temperature and high in-situ stress geological environment can significantly affect the mechanical properties, failure modes, and deformation characteristics of deep shale reservoirs. In this study, real-time high temperature triaxial compressive tests simulating the deep shale formation environment (temperature: 25–150 °C, confining pressure: 0–100 MPa) are carried out. The GSI-strength degradation and constitutive models are derived based on the Hoek–Brown criterion. The results show that in low confining pressure conditions, the mechanical behavior of shale is greatly influenced by temperature. Compared with shale at 25 °C, the compressive strength of shale at 150 °C decreases by up to 13.7%, and the elastic modulus decreases by up to 36.9%. The peak strain was increased by a factor of up to 1.4, and the yield stress level was advanced by as much as 7.4%. However, in high confining pressure conditions, the shale plasticity characteristics are significantly enhanced and the failure mode is relatively single. The GSI-strength degradation model can well characterize the variation law of shale strength with confining pressure under high temperature conditions. The statistical damage constitutive model matches the actual stress–strain curve very well, and it can fully reflect the deformation and failure characteristics of deep shale. The findings of this study can help us better understand the variation of mechanical properties of deep shale. [ABSTRACT FROM AUTHOR]

The reactivation of faults is governed by the variation of effective stresses in the fault's plane. These effective stresses are dependent on the total stresses (solely related to the regional geological stresses and lithology) and pore pressure (strongly affected by rock properties, fluid content, and saturation conditions). Injecting fluids into a reservoir formation may change the distribution of pore pressures, which influences the effective stresses and may cause the reactivation of existing faults, which has a wide range of consequences. This study investigated the reactivation of preexisting faults due to fluid injection into hydrocarbon reservoirs at different pressures and temperatures. A 3D model containing a continuous normal fault that divides the domain into two compartments was used. A user-defined constitutive model based on continuum damage mechanics implemented as a Fortran subroutine to predict the behavior of fractured and faulted reservoirs was used. A parametric analysis was performed to examine the influence of geometric parameters, such as the fault dip angle, reservoir characteristics, and fluid injection parameters. A machine learning approach based on artificial neural networks (ANNs) is incorporated to predict the enhanced oil recovery using fluid injection. The results predicted by the ANN were further confirmed by numerical modeling. [ABSTRACT FROM AUTHOR]

The Geological Strength Index (GSI) system is the basis of parameters used in the Hoek-Brown failure criterion for rock mass strength estimation. The author tested this system and here suggests a modified GSI called Geological Strength Index-slope (GSIslope). The modified system combines two different existing approaches: the GSI system and Slope Mass Rating (SMR). The purpose of GSIslope is to allow engineering geologists to quickly evaluate the stability of natural and excavated slopes or open-pit mining in the field. GSIslope is computed by subtracting a constant value of 10 and the multiplication of adjustment factors for discontinuity orientation and slope (F1, F2, and F3, based on the parallelism of discontinuity and slope, discontinuity dip angle, and the difference between the inclination angle of discontinuity and slope) from GSI, and adding field groundwater rating to it. Modified curves are also proposed in this work to determine the accurate ratings of the adjustment factors. The results of this work are compared to the values obtained from equations of continuous-SMR and SMR-value itself for both the adjustment factors and GSIslope values. he comparison showed that the proposed curves and GSIslope equation are valid and easy to use for estimating the adjustment factors' ratings and GSIslope value. [ABSTRACT FROM AUTHOR]

Rockburst exhibits different occurrence time characteristics during drilling and blasting in tunnel excavation, posing challenges to the safe and efficient construction of tunnels. In this study, 25 tunnels with rockburst hazards were examined. By employing the clustering method, we analyzed the characteristics of the most prone time (MPT) for rockburst. Furthermore, we investigated the contribution degree and influence mechanism of stress and geological factors related to the MPT of rockburst. The outcomes revealed that distinct tunnels exhibit diverse rockburst-prone times, leading to varying hazards and losses. The higher the maximum principal stress and the angle between it and the tunnel axis, the earlier the rockburst occurs. Moreover, the MPT of rockburst is influenced by both lithological types, macro and micro rock structures. When the joint intersects with the maximum principal stress at a small angle, rockburst occurs earlier. The stress direction, UCS, attitude of the dominant joint, and stress magnitude stand out as the principal controlling factors. The findings of this research can serve as a basis for assessing the MPT of tunnel rockburst, timing rockburst risk control measures, and selecting appropriate mitigation strategies. • Characteristic of rockburst occurrence time in 25 tunnels is analyzed. • The contribution of stress and geology to the MPT of rockburst is interpreted. • The mechanism of stress and geology on the MPT of rockburst is revealed. [ABSTRACT FROM AUTHOR]

• A computer vision recognition model is established to study the crack coalescence. • The increase of the flaw width changes the angle of crack initiation and the form of crack coalescence. • The magnitude of effective compressive area is positively correlated with the UCS of the specimen. • The CVR model identifies two types of numerical fluctuation signals before crack coalescence. The coalescence of cracks in rock, triggered by external stress or geological activities, plays a pivotal role in determining the mechanical properties and stability of rock structures. Consequently, the prediction method of crack coalescence become critical tools in ensuring the safety and stability of geotechnical engineering facilities. In this paper, based on the strain field data obtained by digital image correlation (DIC), a set of programs was developed to automatically identify the values and percentage changes of different strain intervals in the strain field of the specimen. Then, a computer vision recognition (CVR) model is established to study the process and prediction of crack coalescence in sandstone specimens with open flaws. This method overcomes the limitations, subjectivity and unpredictability of the traditional method of identifying cracks through artificial vision. The results show that the increase of the flaw width causes the displacement trend to be squeezed and deflected along the width direction, thereby changing the angle of crack initiation and exhibiting different forms of crack coalescence. The increase in the inclination angle of the flaw leads to an increase in the effective compressive area (ECA) of sandstone, and the magnitude of ECA is positively correlated with the uniaxial compressive strength (UCS) of the sandstone. Additionally, the CVR model identifies two types of numerical fluctuation signals before crack coalescence, namely the plastic characteristic signal (PCS) in the early stage of the experiment and the early-warning signal (EWS) near the period of crack coalescence, where EWS can be used as a predictive signal for crack coalescence. The research results provide a new algorithm technical support for the process analysis and prediction of crack coalescence, and provide a basis for early warning of rock mass engineering disasters. [ABSTRACT FROM AUTHOR]

Tunnel engineering in the cold region often experiences the coupling of the stress field and seepage field, which has complex mechanical behavior and permeability characteristics. This study takes sandstone as the research object and uses the multifunctional RLW-2000 rock triaxial instrument to perform triaxial compression tests on sandstone with different freeze–thaw cycles under seepage pressure and confining pressure. The development law of rock mass cracks under different load combinations is analyzed, and the correlation characteristics between permeability and crack state of freeze–thaw sandstone in the process of seepage–stress–damage are studied. The results show that the permeability decreases gradually due to the compaction of pores and microcracks in the rock at the beginning of loading. As the crack radial strain increases, the internal cracks in the rock begin to grow steadily, and the permeability increases slowly. As the load continues to increase, the accelerated crack propagation leads to a rapid increase in permeability. In addition, under certain freeze–thaw cycles, the initial permeability of sandstone decreases with the increase of confining pressure. Under a certain confining pressure, the initial permeability of sandstone increases with the number of freeze–thaw cycles. Finally, based on the test results, theoretical methods are used to study the characteristics of rock damage under different freeze–thaw cycles, the correlation between the damage variable and, the crack radial deformation is established. The relationship between the permeability and the damage variable is deduced, which reveals the permeability evolution mechanism of freeze–thaw sandstone. These test results can provide a reference for rock stability monitoring under the coupled action of permeability and stress in geological engineering. [ABSTRACT FROM AUTHOR]

Exhumed fossil subduction zones are archives of the deformation conditions and mechanisms from depths not directly accessible. Microstructural analysis of samples exhumed therefrom offers insights into the micromechanics and deformation processes associated with subduction such as earthquakes, slow earthquakes, and aseismic creep. Subducted and exhumed continental metasediments of the Tuscan Metamorphic Units of the Italian Northern Apennines contain a mylonitic foliation and quartz and carpholite dilational hydroshear veins with crack‐and‐seal textures, both developed at blueschist facies conditions (350–400°C, ∼1 GPa). As shown by overprinting relationships and mineral assemblages, these two structure types formed broadly coeval within the stability field of carpholite. Metaconglomerates and metaquartzarenites deformed mainly by dissolution‐precipitation creep and secondary by dislocation creep. Microstructural and electron backscatter diffraction analyses of the veins suggest only limited recrystallization of quartz fibers by subgrain rotation recrystallization, with adjacent metapelite bands acting as decollement horizons, likely by slip on the basal plane of phyllosilicates. We estimated differential stresses of 43–55 MPa and strain rates between 10−13 and 10−14 s−1 from the vein recrystallized quartz fibers. We propose these microstructures and deformation mechanisms to represent a geological evidence of deep episodic tremor and slow slip events in subducted continental metasediments. Pore pressure cyclically reached supralithostatic values triggering tremors causing fracturing of all involved lithotypes. Likely, slow slip was accommodated preferentially by slip on phyllosilicate bands. Aseismic creep occurred mainly by dislocation creep with subgrain rotation recrystallization in vein quartz, slip on the basal plane of phyllosilicates, and dissolution and precipitation creep in the host rock. Plain Language Summary: Rocks exhumed from great depth can help us to investigate processes otherwise non directly accessible. The Italian Northern Apennines comprise exhumed continental sediments that were deformed and metamorphosed at depths of 30–40 km and temperatures of 350–400°C. Broadly coeval continuous and discontinuous deformation is documented as highly deformed zones (shear zones) and veins. We used microstructural analyses and electron microscopy techniques to reconstruct how these rocks deformed and the structures formed. Quartz‐rich metasediments deformed mainly by dissolution and precipitation processes. Weak phyllosilicate‐rich bands accommodated deformation likely by slip on their platy basal planes. Fluid pressure cyclically reached high values that caused failure of the metasediments, with subsequent migration of portion of the fluid and formation of the veins. Veins display only a limited amount of crystal plastic deformation. Quartz paleopiezometry and flow law suggest low differential stresses and average geological strain rates for the deformation of veins. We propose that these structures can be seen as a possible geological record of deep episodic tremor and slow slip events, low intensity and long lasting seismic events associated with slip transients faster than average plate motion. Key Points: Coeval dilational hydroshear veins and mylonites may shed light on deformation mechanisms of deep episodic tremor and slow slip eventsDilational hydroshear veins formed by incremental crack‐seal at supralithostatic pore pressure values and deformed by dislocation creepBlueschist facies mylonites formed mainly by a combination of dissolution‐precipitation creep and slip along phyllosilicate bands [ABSTRACT FROM AUTHOR]

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With the increasing depth of coal mining, the geological stress and structure becomes more and more complex. The elevation of No.8 coal floor significantly undulates in the studied coal mine. Even though a lot of boreholes have been drilled, it remains difficult to predict the spatial distribution features and it becomes challenging to plan the tunnel for the working face. Consequently, there has been a great loss of production in the coal mine, therefore, it is of great significance to study the prediction method for coal floor elevation of the working face. The surface spline function can be regarded as an infinite flat plate deformation in pure bending. The fluctuation of the coal floor can be considered to be the result of multi-period tectonic stress applied on the coal seam, so, the prediction of elevation of the coal floor with surface spline method is feasible. An advantage of surface spline method is that any order differentiable smooth surface can be obtained without regular known lattice and boundary derivatives. In the paper, the complete expression of surface spline function is derived, which is used to predict the elevation of No.8 coal floor of the coal mine. The results show that the trend of elevation of the coal floor can be extrapolated by known data, and the maximum error is 20 m, the minimum error is 0 m, and the error of 80% of the data is less than 3 m. The general trend of the coal floor has been predicted well. However, local peaks and valleys could not be predicted correctly, therefore, the first and second order derivative are projected to predict the peaks and valleys in the head of the tunneling. [ABSTRACT FROM AUTHOR]

Research on the poverty risk caused by geological disasters in disaster-prone areas is a useful exploration to coordinate social economic development with disaster prevention and reduction, and is of great significance to the regional sustainable development. Based on statistical data and spatial data, this paper takes Sichuan Province as the typical research area. Remote sensing and geographic information technology are used to study the poverty risk caused by disasters based on the quantitative evaluation of geological disasters risk and regional development level. The spatial differentiation characteristics of poverty risk caused by disasters are explored on the 1 km × 1 km grid scale. The results indicate that (1) the overall risk of geological disasters in Sichuan Province is relatively high, with high and relatively high risk areas accounting for more than 40% and low and relatively low risk areas accounting for less than 30%. The risks in Mountain and Ravine Areas are significantly higher than other areas. (2) The regional development level in Sichuan Province is relatively high, but with significant spatial differences. The development level of high-altitude areas and remote mountainous areas is quite different from that of the Chengdu Plain in the middle Sichuan Province. The uneven development in the east, middle, and west is a prominent problem. (3) The poverty risk caused by disasters is high, and the spatial pattern presents a characteristic of "high in the west and low in the east" with high positive spatial correlation. High-High Cluster Areas are mainly distributed in western and southwestern Sichuan. Low-Low Outlier Areas are mainly distributed in Chengdu Plain and Hilly Areas of Sichuan Basin. High-Low Outlier and Low–High Outlier Areas occupy a relatively small percentage with scattered distribution. This paper provides some theoretical support for policy formulation and management of coordinated development of regional socioeconomic and ecological environment. [ABSTRACT FROM AUTHOR]

Copyright of Nonferrous Metals (Mining Section) is the property of Beijing Research Institute of Mining & Metallurgy Technology Group 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.)

Copyright of Tunnel Construction / Suidao Jianshe (Zhong-Yingwen Ban) is the property of Tunnel Construction Editorial Office 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.)

The core of sustainable mining is the preservation of the ground stability, and in situ stress measurement is crucial as most of the stability issues are directly associated with the in situ and induced stresses. Deformation rate analysis and acoustic emission are reliable and low-cost methods of stress measurement leveraging stress memory in rocks. However, owing to rock heterogeneity and complex geological stress history, the accurate determination of in situ stresses is often challenging. This study proposes a simple, accurate, and improved method for determining the in situ stresses in rocks called the Secant Modulus Method (SMM). The effectiveness of SMM is determined through uniaxial cyclic loading and unloading experiments on different types of soft and hard crystalline rocks. The influence of the loading modes, strain rates, and time delay is also investigated. Additionally, its utility for in situ stress measurement is explored. The SMM method proved effective in determining both applied and in-situ stresses, with no effect from variations in loading conditions, loading rates, and time delays. Moreover, the in situ stresses measured using the SMM were in good agreement with the overcoring method. [ABSTRACT FROM AUTHOR]

Taking mining area 2502 in the Huayan mine field which was affected by strong geological tectonic stress as an engineering background, the water jet technology is studied through in-site survey, laboratory test, theoretical analysis, numerical simulation, and field industrial test. The research results are as follows: the burst tendency of No. 5 coal seam can be reduced to a certain extent after softening with water, and then the water jet technology is used to prevent rock burst of roadways; the typical characteristics of rock-burst accidents mainly cause heaving floor and serious deformation of two sides. The occurrence mechanism of rock burst in roadway ribs has two different forms, and they are static load dominant type and dynamic load dominant type. The abutment stress concentration value is higher than a certain concentration static load, it will affect the coal and rock medium in the floor, and the coal and rock medium in the floor will be transformed into a plastic state and then occur rock burst; the water jet technology for roadway ribs can effectively prevent rock burst of roadway ribs and floor based on the dynamic and static loads superposition theory and Terzaghi theory. Based on the results of numerical simulation, the specific parameters of water jet technology for roadway ribs in 250204 tailgate are as follows: the diameter and length of initial borehole are 110 mm and 20.0 m, the diameter and length of water jet section are 500 mm and 15.0 m, and the spacing between adjacent water jet boreholes is 3.0 m; the monitoring result of signal intensity by EMR indicates that the decreasing amplitude of signal intensity of EMR is about 60.2% on the side of coal-pillar rib, and the decreasing amplitude of signal intensity of EMR is about 68.6% on the side of solid-coal rib; the convergences monitoring result indicates that the convergence ratio of roadway height is about 3.2%, and the convergence ratio of roadway width is about 2.3% in the pressure relief roadway part; the water jet technology is not only helpful to the prevention of rock burst for the roadway ribs but also can play a good prevention of rock burst for roadway floor. The research results provide a theoretical foundation and a new guidance for preventing rock burst in roadway ribs and floor with similar engineering geological conditions. [ABSTRACT FROM AUTHOR]

Ordovician limestone in North China coalfield has the characteristics of karst fissure development and strong water yield. Coal mines in North China have been threatened by Ordovician limestone water for a long time. Taking the mining of 32 coal seam in the first eastern mining area of Qianyingzi coal mine in Anhui Province in China as the engineering geological prototype, this paper uses the self-developed fluid solid coupling similarity model test device to carry out the similarity model test of overburden stress and pore water pressure response of coal mining under Ordovician limestone nappe aquifer. Based on the variation law of pore water pressure and overburden stress in a stope, it can be seen that the variation law of pore water pressure in confined aquifer is jointly affected by two factors: the vertical distance between the monitoring point and coal seam and the horizontal distance between the monitoring point and DF200 fault. According to the analysis of experimental results, the maximum height of a water flowing fracture zone in the stope is fifteen times the mining thickness. Compared with the theoretical calculation results of empirical formula, the coupling effect of seepage field and stress field and the geological structure characteristics of the stope promote the development of a water flowing fracture zone. The research results of this paper have important theoretical and practical significance not only for the safe mining of Qianyingzi coal mine but also for the safe mining of the coal mine facing the double threat of roof Ordovician limestone confined aquifer and reverse fault. [ABSTRACT FROM AUTHOR]

The Delaware Basin, Texas is currently a hot‐spot of induced seismicity and ground deformation due to fluid extraction and injection associated with horizontal drilling techniques; however, the driving mechanism behind the seismicity and deformation remains under debate. Using vertical and east‐west horizontal surface deformation measurements derived from Sentinel‐1 interferometric synthetic aperture radar (InSAR), we show that the subsurface responds differently to oil and gas activity in the northern and southeastern portions of the basin. In the north, where there is little seismicity, deformation patterns display long‐wavelengths and equidimensional patterns. In contrast, the southeast region hosts most of the seismicity and displays spatial deformation patterns with narrow linear features that strike parallel to the maximum principal horizontal stress and to trends in seismicity, suggesting movement along normal faults. We model a linear deformation feature using edge dislocations and show that the InSAR observations can be reproduced by slip on normal faults contained within the Delaware Mountain Group (DMG), the formation that hosts local wastewater injection and the majority of earthquakes. Our model consists of three parallel, high‐angle normal faults, with two dipping toward one another in a graben structure. Slip magnitudes reach up to 25 cm and are spatially correlated with injection wells. Measured seismicity can only explain ∼2% of the fault motion predicted by our fault model, suggesting that slip leading to the deformation is predominantly aseismic. We conclude that seismic and aseismic fault motion in the southeastern Delaware Basin is likely driven by wastewater injection near critically‐stressed normal faults within the DMG. Plain Language Summary: In the Delaware Basin, TX, widespread oil and gas operations have been linked to an increase in earthquake frequency and ground deformation. We use satellites to measure the ground deformation and show that the northern and southern portions of the basin respond differently to the pumping and injection of fluids. The southern portion displays narrow linear displacement patterns, whereas the northern region displays wide and equidimensional features. The relationship of the narrow features in the southern portion of the basin to local stress conditions and earthquake locations suggests downward slip on faults. Using analytic models in a small study area, we develop a three‐fault slip model that is consistent with ground displacement measurements, the location and sense of slip of the largest local earthquakes, and wastewater disposal wells. Our findings suggest that wastewater disposal in the Delaware Mountain group is reactivating pre‐existing normal faults, leading to induced earthquakes and non‐seismic slip. Key Points: Linear deformation features in the southeastern portion of the Delaware Basin are attributed to aseismic slip on normal faultsIdentified faults create graben structures that likely belong to a larger graben networkAseismic and seismic fault movement in Texas' Delaware Basin can be linked to wastewater injection in the Delaware Mountain group [ABSTRACT FROM AUTHOR]

The control and prevention of rock burst in a steeply inclined coal seam are essential. In order to figure out the effects of filling and mining sequence on rock burst in the steeply inclined coal seam, B3+6 and B1+2 coal seams in Wudong coal mine are chosen as the research objects, and an in-house experiment system of similarity simulation is established in this study. Combined with numerical simulation, the characteristics of collapse, stress distribution, and displacement variations can be measured, which provide useful information to study the effects of the filling body and mining sequence on rock burst. Experimental results show that the key reason for rock burst in a steeply inclined coal seam is the stress concentration of the rock pillar between B3+6 and B1+2 coal seams instead of the stress-lever-effect of a deeper rock pillar. The filling body can support the middle rock pillar, share the geological structure stress in the horizontal and vertical direction, eliminate the stress concentration zone largely, and prevent the occurrence of rock burst. When multiple working faces are working, the opposite side of the coal seam should be mined first to release the energy in the rock in advance, thus preventing the rock burst effectively. The research results provide fundamental information for better understanding the reason for rock burst and preventing rock burst in the steeply inclined coal seam. [ABSTRACT FROM AUTHOR]

Ultra-deep (7500–9000 m) Ordovician tight limestone heterogeneous fractured-vuggy reservoir is an important target of FuMan Oilfield in Tarim Basin. The strike-slip fault controlled reservoir is related to formation fracture and dissolution caused by geological stress. The seismic wave-field anomaly characteristics with different energy and irregular waveform are displayed in the seismic profile. Accurate identification of fractured-vuggy reservoirs wrapped in tight limestone is the direct scheme to improve production efficiency. Therefore, a new combination method flow of seismic wave-field anomaly recognition is proposed. In this process, the seismic data must be preprocessed initially, and on this basis, robust formation dip scanning is carried out. Secondly, the dip data is applied to the transverse smoothing filter to obtain the formation background data. Eventually, the seismic wave-field anomaly data is the residual between background data and original seismic data. This method has been applied in blocks with different structural characteristics and can effectively improve the resolution of strike-slip fault controlled reservoirs. Based on the results, the drilling success rate is increased to more than 95%, and the high-yield rate of oil tests is increased to 75% in 2021. Multiple applications indicate that the method is robust and can be popularized. [ABSTRACT FROM AUTHOR]

Due to the high in situ stresses, dynamic disasters occurred frequently in the Huainan mining area, China. Our understanding of the in situ stresses in this area is still insufficient. In this study, the in situ stresses of 18 sections in two boreholes in the Xinji No. 1 coalfield were measured using the hydraulic fracturing method, and the distribution of in situ stresses in the Huainan mining area were investigated. The relationship between in situ stress and geological structure in the Huainan mining area was summarized and the limitation of fault friction strength on in situ stress was discussed. The result showed that the maximum horizontal principal stress (σH) at Xinji No. 1 mine was 13.95–25.23 MPa, the minimum horizontal principal stress (σh) was 12.16–21.17 MPa. The average azimuth of the maximum horizontal principal stress was N83.61°E. The statistical results showed that the in situ stresses in Huainan mining area were characterized by a strike-slip faulting regime. Both the horizontal and vertical principal stresses increased approximately linearly with the increase of burial depth. The orientation of the maximum principal stress in the study area is closely related to the tectonic movement and the ratio of maximum principal stress to minimum principal stress was primarily limited by the friction strength of the faults. The outcomes of this research can provide some reliable engineering parameters and benefit the roadway layout and support design in the Huainan mining area. [ABSTRACT FROM AUTHOR]

In recent years, multi-stage hydraulic fracturing for shale oil reservoirs is developing toward a shorter cluster spacing and a larger number of clusters per stage. The objective is to improve the stimulation performance by reducing the fracturing stages and creating more hydraulic fractures in terms of cost-efficiency in geological engineering. Field tests demonstrate the uneven distribution of fluid volume among clusters and only a few perforation clusters contribute to productivity. The extreme limited entry (XLE) completion is an effective method to improve the efficiency of perforation clusters. However, the influence of several controlling parameters on the cluster effectiveness during XLE completion remains elusive. Therefore, a 3D field-scale hydraulic fracturing model for XLE completion based on the lattice method is developed for the case of shale oil reservoirs of Changqing oilfield in China. In this model, perforation friction, geological factor such as stress difference between adjacent clusters, and filtration of fracturing fluid are considered. The numerical results are compared with field data (i.e., injection pressure and cluster efficiency) obtained from the fracturing construction and the step-down test. The influences of injection rate, cluster spacing, cluster number, and stress difference between adjacent clusters on the fracture morphology, cluster efficiency and injection pressure of XLE completion are discussed in detail. The results show that perforation friction is the most critical factor that affects the efficiency of perforation cluster during XLE completion. A guide chart of cluster efficiency under various differential geological stresses between adjoining clusters is proposed. According to this guide chart, the required perforation friction under different cases can be obtained, and then the related perforation parameters (i.e., perforation diameter and number) can be determined. The research results provide theoretical guidance for optimization of XLE completion in geological reservoirs. [ABSTRACT FROM AUTHOR]

The variation of the in situ stress state is closely related to various factors. In situ stress state is also an important indicator to guide mining production. The study of in situ stress measurement and its distribution characteristics has always been a basic and very important work in mine production. In this study, the deep mines of Linyi Mining Area were considered as the research object. In this regard, the stress distribution law of each mine was studied. We found that the relationship between principal stresses was σH > σ v > σh, which belongs to the strike-slip stress regime. In this stress regime, the lateral Earth pressure coefficient was greater than one, and the magnitude of the three principal stresses all showed an increasing trend with the increase of depth. The maximum horizontal stress direction of the Gucheng Coal Mine, Guotun Coal Mine, and Pengzhuang Coal Mine was NW-SE under the influence of regional geological structure, while the maximum horizontal stress direction of Wanglou Coal Mine was NE-SW under the influence of local geological structure. Besides, the relationship between mine in situ stress and mine geological structure, the impact of original rock stress on stope stability, and the effect of original rock stress on floor water inrushing were also investigated. We believe that the research results are beneficial to mine disaster prevention and safety production. [ABSTRACT FROM AUTHOR]

The study of the relationship of in-situ stress and permeability is of great necessity to understand the formation mechanism of high-permeability coal reservoir. However, characteristics of in-situ stress and its relationship with permeability in low-rank CBM blocks of China is poorly understood. This study employs permeability and in-situ stress test experiment to analyze the vertical variation law of in-situ stress and permeability and the control mechanism of in-situ stress on permeability in the Binchang block of southwestern Ordos Basin. It is concluded that the permeability varies from 0.11–6.84 mD, and the entire coal reservoir is in a state of relative tension in the Binchang block. The extended Somerton stress–permeability model composed of six stress parameters and the geological model of in-situ stress–permeability were established. The modeling results indicate that permeability is most sensitive to the maximum horizontal stress and its derived parameters, and least sensitive to vertical stress. This model indicates that highly permeability develop in the two-stage turning burial depth section (480–800 m), which is consistent with the minimum value of stress parameters such as the lateral pressure coefficient, which indicate that the relative tension stress zone in the depth profile provides structural conditions that are conducive to the development of permeability. [ABSTRACT FROM AUTHOR]

Maintaining surrounding rock mass stability of roadways is essential to the safety of deep coal mining. In this study, the No. 2-2092 roadway of the No. 2-209 mining face in Ganhe coal was taken as the target roadway for field analysis. The selected region can be considered a typical area with dominating geological tectonic stress, based on the geological survey and in situ stress results. A mechanical model of roadway overburdens was developed to analyse the large deformation and stress field distribution. It is found that the large deformation is caused by the combined superposed stress field including laterally transferred stress formed in structures at overlying strata, mining-induced advanced abutment pressure, and the regional in situ stress. Thus, a Two-Direction Hydrofracturing Technique (TDHT) was proposed to reduce the pressure of the No. 2-2092 roadway by altering the roof structure in the influenced zones. Compared with the original roadway without fracturing, it is found that the roof to floor convergence has dropped by nearly 47% after fracturing; the displacement of sidewalls has reduced by almost 31%, demonstrating the effectiveness of the proposed method in pressure relief. Results from this study can provide guidance on controlling the large deformation of roadways in deep underground mines. [ABSTRACT FROM AUTHOR]

In this paper, the elasto-hydrodynamic (EHD) performance of partial journal bearings has been studied. A numerical analysis has been conducted using the ANSYS Workbench (17.2) platform to investigate the performance of partial journal bearings. The lubricant used is considered Newtonian and incompressible fluid that flows steadily under laminar conditions, while the bearing material is assumed to be elastic, isotropic with smooth surface conditions. In the current FSI analysis, the lubricant flow has been predicted according to the finite_ volume method, while the finite element method has been adopted to compute the deformation and stress in the bearing surface. A wide range of operating and design conditions have been considered including the eccentricity ratio (0.1 ≤ ε ≤ 0.82), and arc bearing angle bearing (90ᵒ≤ θ ≤180ᵒ), while the values of bearing length to diameter ratio (L /D) and rotation speed (N) have been fixed at=0.77 and 1500r.p.m, respectively. The hydrodynamic pressure, performance characteristic of journal bearing, stress, and deformation have all been computed. It was found that the arc bearing angle and eccentricity ratio has a clear effect on the elastohydrodynamic properties of the partial bearings especially at high values of them. [ABSTRACT FROM AUTHOR]

The occurrence of rockburst is related to the surrounding rock stress and geological rock mass strength. Rockburst occurs frequently during the construction at a deep tunnel in southwest China (a tunnel with a depth of approximately 2080 m, and a length of 13 km), leading to casualties, damage to construction equipment, and schedule delays. The application of the rockburst criteria based on the stress-strength/strength-stress ratio shows that they are not suitable for the construction stage. This paper suggests a simple and feasible rockburst intensity criterion based on the Geological Strength Index (GSI) for the construction stage. In this criterion, the strength of the rock mass exposed during excavation is estimated by the Hoek-Brown criterion and is used to reflect the geological conditions of the surrounding rock, considering the influences of the joint conditions and engineering disturbance. The maximum principal stress along the tunnel is obtained by the in situ stress inversion. The ratio of the rock mass strength to the maximum principal stress (σcm/σ1) is taken as the evaluation index. The criterion is as follows: σcm/σ1 > 1.2, none rockburst; 0.75 < σcm/σ1 ≤ 1.2, slight rockburst; 0.4 < σcm/σ1 ≤ 0.75, moderate rockburst; and σcm/σ1 ≤ 0.4, intense rockburst. The engineering applications show the reliability of this rockburst intensity criterion. The results of this paper provide a reference for rockburst intensity evaluation during the construction stage of deep tunnels. [ABSTRACT FROM AUTHOR]

The study on induced stress of hydraulic fracturing is an important part of hydraulic fracturing design, temporary plugging and steering fracturing design, and completion design in oil and gas development. Based on fracture continuum method (FCM), cohesive unit method, and finite volume method (FVM), the propagation behavior of multiple hydraulic fractures (HFs) in fractured‐porous media reservoir is simulated from the perspective of fluid and geological stress coupling. The influence of natural fractures (NFs) on stress distribution and stress inversion sensitive factors are studied. NFs in the model are equivalent to physical models controlled by tension and shear bonds. The proposed model can deal with any number of NFs, which greatly improves the computational efficiency of the model. Then PKN analytic solution and Abaqus software results were used to verify the correctness of our model. The results show that the NF will make the reservoir stress show strong heterogeneity after fracturing, and the prominent feature is the regional stress mutation. The sudden change of stress shows the sudden increase or decrease in stress; with the increase in the initial stress difference, the stress inversion becomes more difficult. When the stress difference exceeds 3 MPa, the stress inversion area is almost 0. The stress interference increases with the decrease in cluster spacing. The stress inversion region between HFs decreases, while the external stress inversion region increases; Biot coefficient has great influence on stress and stress inversion. With the decrease in Biot coefficient, stress inversion region will decrease obviously. When the Biot coefficient is 0.4, there is no stress inversion area in the whole reservoir. Poisson's ratio has little influence on stress inversion. When Poisson's ratio changes between 0.1 and 0.3, the change range of stress is within 1 MPa, and the stress inversion area is almost unchanged. Our results can be helpful for understanding the stress distribution after hydraulic fracturing in fractured‐porous media. [ABSTRACT FROM AUTHOR]

Neutron scattering and neutron imaging have emerged as powerful methods for experimentally investigating material deformation and fluid flow in the interior of otherwise inaccessible or opaque structures. This paper describes the design and provides example uses of a pressure cell developed for investigating such behaviors within geological materials. The cell can accommodate cylindrical samples with diameters up to 38.1 mm and lengths up to 154 mm. Ports in the cell and a pressure isolating sleeve around the sample allow the independent application of confining pressure up to 69 MPa and axial pressure up to 34.5 MPa. Two material versions of the cell have been manufactured and used to date. An aluminum version is typically used for temperatures below 40 °C, because of its relative transparency to neutrons, while a titanium version, which is comparatively more neutron attenuating, is used for experiments requiring triaxial pressurization under conditions up to 350 °C. The pressure cells were commissioned at the VULCAN engineering diffractometer at the Oak Ridge National Laboratory (ORNL), Spallation Neutron Source, and have since been used at the ORNL high flux isotope reactor CG1-D imaging beamline, National Institute of Standard and Technology (NIST) BT-2, and NIST NG6 imaging beamlines. [ABSTRACT FROM AUTHOR]

Access tunnel in the main powerhouse of Shuangjiangkou hydropower station was deep buried with high in situ stress and complex geological conditions. Microseismic monitoring technology was established to monitor microcrack evolution process inside the surrounding rock in early excavation stage. Serious falling blocks in the left spandrel of the tunnel were predicted in a timely manner by delimiting major damage areas in the tunnel. Based on comparative analysis on microseismic activity law and field failure characteristics of the access tunnel, a quantitative index was supposed between slight rockburst like falling blocks and microseismic events. Moreover, the change law of daily average apparent stress difference and b value were analyzed based on microseismic event data. In addition, a three-dimensional numerical simulation software (RFPA3D) was used to simulate the damage distribution around the tunnel, and a relationship between spatial position of tunnel damage and direction of the maximum principal stress was qualitatively analyzed. The study results showed that advance speed of the tunnel working face was an important factor affecting the state of stress redistribution in surrounding rock mass, and the change law of b values of microseismic events could be used to predict activity state inside the surrounding rock effectively, which reflected mechanical properties and stress state of surrounding rock. In particular, field falling blocks became more serious with increasing b value, and field surrounding rock was relatively stable with minor b value. A risk of surrounding rock instability was relatively high with small b values. It provided an efficient method of predicting and assessing slight rockburst like falling blocks. The study results can provide significant guidance for field construction and later construction planning. [ABSTRACT FROM AUTHOR]

Hydraulic fracturing has been widely applied to stimulate the natural gas and oil production from unconventional reservoirs. To optimize the design of hydraulic fracturing in this application, an accurate estimation of the initiation and propagation of hydraulic fractures is indispensable. However, it still remains challenging as a result of the complex stress state and geological conditions. On account of their ability to complete control some significant factors and efficient observation of fracture geometry, laboratory-scale hydraulic fracturing experiments have received abundant research attention in recent years. This paper presents a review of the state of the art of laboratory-scale hydraulic fracturing experiments, focusing on the scaling analysis, experimental setup, fracturing fluids, and sample preparation. A discussion of the directions for future research is also provided with the intention of stimulating the development of the experimental technique for investigating hydraulic fracturing. [ABSTRACT FROM AUTHOR]

The use of Right dihedral method, Lisle graph, and Mohr diagram allows the analysis of the paleostress. Fault slip data were measured for eighteen data of two stations located within Chia Gara structure in Dohuk area in the High Folded Zone, Northern Iraq. Depending on Mohr diagram, Bott equation, and vertical thickness, the magnitudes of the paleostress at the time of the tectonic activity were determined. Firstly, Georient Software was used to estimate the orientation of the paleostresses (σ1, σ2 and σ3). Secondly, using the rupture -friction law, taking into account the depth of the overburden, the vertical stress (σv) was calculated to determine the magnitude of the paleostresses in the study area. The values in station one (hinge area, eight data) were σ1=7100, σ2=4121.5, and σ3=1143 bars, whereas the values in station two (the north limb of structure, ten data) were σ1=3740, σ2=1585, and σ3=570 bars. The high magnitudes of the principal stress axes may refer to the active tectonic events which led to the deformation of the area during the Mesozoic Era and the Tertiary period. The study area shows the existence of two types of the faults, the first type is the reactivated faults, the poles of which lie between the sliding line and Mohr envelope. The second type is the inactive faults, with poles lying on the great circle of Mohr diagram. [ABSTRACT FROM AUTHOR]

The dynamics of continental subduction is largely controlled by the rheological properties of rocks involved along the subduction channel. Serpentinites have low viscosity at geological strain rates. However, compelling geophysical evidence of a serpentinite channel during continental subduction is still lacking. Here we show that anomalously low shear-wave seismic velocities are found beneath the Western Alps, along the plate interface between the European slab and the overlying Adriatic mantle. We propose that these seismic velocities indicate the stacked remnants of a weak fossilised serpentinite channel, which includes both slivers of abyssal serpentinite formed at the ocean floor and mantle-wedge serpentinite formed by fluid release from the subducting slab. Our results suggest that this serpentinized plate interface may have favoured the subduction of continental crust into the upper mantle and the formation/exhumation of ultra-high pressure metamorphic rocks, providing new constraints to develop the conceptual and quantitative understanding of continental-subduction dynamics. The dynamics of continental subduction is largely controlled by the rheological properties of rocks involved along the subduction channel. Here, the authors reveal a prominent, yet previously undetected, low-velocity body beneath the Western Alps, along the plate interface between the European slab and the overlying Adriatic mantle, which they interpret as a serpentinite layer. [ABSTRACT FROM AUTHOR]

Crater blasting is widely used for rock excavation. In deep rock engineering projects, blasting is done in a high stress environment. To study the effects of high geological stresses on rock blasting, crater blasting tests on sandstone using an exploding electric wire were conducted under three different static load conditions. The evolution of the strain fields and the propagation of cracks on the surfaces of samples were recorded and subsequently analysed by digital image correlation. The rock fracturing mechanisms are discussed. The experimental results indicate that (1) the areas of major principal strain on the sample surfaces are circular under conditions of no static stress and symmetric biaxial stress loads, but the strain area is elliptical under a uniaxial load; (2) after blasting, the static stress state changes the crack initiation mode, crack propagation, and the distribution of the cracks in the crack network; and (3) static stress can increase the size of the blasting crater. [ABSTRACT FROM AUTHOR]

A systematic analysis on gas occurrence in geological structure zone is crucial to coalbed gas exploitation, gas disaster prevention and outburst risk prediction. To study the geological control of fold structure on gas occurrence and its contribution on coalbed gas outburst, a typical case taken from Qinan coal mine was investigated by laboratory tests, theoretical analysis and on-site exploration. Thereby, a comprehensive understanding was made from the influence of fold structure on tectonic stress, coal structure and gas occurrence based on integrated factors outburst hypothesis. The results indicate that burial depth from 470 to 675 m has a slight influence on the fundamental properties of 72 coal seam, whereas the existence of Wanglou anticline is more relevant to affect vitrinite reflectance, gas adsorption and emission capacity with a positive correlation. By comparing the field data of gas content, pressure and emission quantity, it can be discovered that gas occurrence in 81 mining area appears to be primarily controlled by fold structure. Similar trends can be found in drilling cuttings index, indicating that geological stress increases with the distance approaching Wanglou anticline. In this case, a detailed description of tectonic stress in studying area is conceptually presented. Based on physical, pore structure and surface analyses, further knowledge on structural transformation by fold structure demonstrates adsorption and seepage pores are well developed with complex and disordered surface morphology, providing an evidence on the geological formation mechanism of tectonic coal in Wanglou anticline zone. Moreover, a conceptual description is proposed to explain the generation, migration and preservation mechanism of gas occurrence in the fold zone, which is consistent with roof and floor lithological properties as well as gas content data. Additionally, the locations of six gas outburst accidents were investigated to verify the relationship with fold structure. Based on the above results, theoretical analysis for coal mine outburst is discussed, which highlights the effect of tectonic stress on gas occurrence and coal structure as well as their contributions to gas outburst. [ABSTRACT FROM AUTHOR]

Copyright of Petroleum Geology & Recovery Efficiency is the property of Petroleum Geology & Recovery Efficiency 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.)

Spatio-temporal fluctuation of climatic variables with the terrain characteristics and their inter-relationship is a priority for predicting flash-flood-induced landslide hazards over the fragile Himalayas. The present study addressed this anxiety by assimilating satellite data products and auxiliary datasets in the Bhagirathi River basin of the Indian Himalayas. Snow Covered Area (SCA) is a critical indicator of the ecosystem that influenced the flash flood along different terrain features such as Altitude, Hill-Gradient, and Aspect. GIS-based multi-criteria decision analysis (GIS-MCDA) technique is used to analyze the possible landslide zones and flood extent along the river basin, and MODIS Terra (MOD10A2) data products derived annual SCA is 4278 km2 for the year 2021, the analysis of geospatial maps at 25° intervals of Altitude, hill-gradient, and Aspect. The SCA distribution reveals that apart from the Altitude, the Aspect of the hill gradient significantly impacts snow accumulation. Hill-Gradient, ranging from 13.06 to 19.52, occupies 24.7% of the total area, and 45.3 to 51.83 are found without snow. The highest variation of SCA is along the Western direction (9.19%), followed by North-East (8.79%), while the least (3.78%) variance is in the Southwest direction. Additionally, it was found that many bridges, roads, and other properties are under threat in this study area, even with a moderate flash flood. Findings from this study provide the spatiotemporal status of SCA in various geological stress conditions during the last decades and probable landslide zones. This will be a preliminary pathway to policymakers in rehabilitation and early evacuation of human lives due to flash flood occurrence. [Display omitted] • Spatio-temporal pattern of SCA estimated along the terrain characteristics. • Climate change induced flash-flood influencing socioeconomic development. • The landslide susceptibility analysis through GIS-MCDA distressed high-risk zones. • This study may provide a pathway to policymakers in hazardous conditions. [ABSTRACT FROM AUTHOR]

The underground powerhouse of Lianghekou hydropower station is deeply buried with high ground stress and complicated geological conditions. To delineate rock mass damage zones and analyze the stability of underground powerhouse subjected to excavation disturbance, an ESG monitoring system was applied to carry out real-time monitoring against the inner micro-fracture activity of surrounding rock mass. In order to solve the problem that the deformation of surrounding rock mass cannot be monitored due to the failure of multipoint displacement meters, the engineering analogy method is adopted to forecast the deformation of surrounding rock mass by comparing the similar projects of Houziyan and Baihetan hydropower stations. Research results show: (1) The failure of surrounding rock mass was stress-driven failure, and was primarily characterized by a medium degree of stress-induced failure. (2) During the monitoring period, microseismic (MS) events clustering area formed, which was both related to blasting excavation disturbance of the bus tunnel and the formed crossed free surfaces. (3) The seismic source parameters during the deformation of surrounding rock mass in similar projects were analyzed, and the variation characteristics of the frequency, energy, b -value, central frequency, apparent stress, and apparent volume of MS events were summarized. (4) The engineering analogy method was adopted to forecast that the deformation period of surrounding rock mass of Lianghekou hydropower station is from April 25 to May 2, 2016. The present achievements can provide some references for similar deep underground excavation engineering. [ABSTRACT FROM AUTHOR]

Early detection of rockburst risk areas is a prerequisite for ensuring safe production in coal mines. A reliable and efficient detection method is essential for identifying stress distribution and disturbances in coal and rock masses during mining. In this study, we employed seismic traveltime tomography to study the three-dimensional velocity structure of a continuous mining and excavation area of a coal mine by inverting a number of P-wave arrival times from the induced micro-earthquakes (M < 2.0). The response characteristics and stress evolution of the inversion areas at different mining stages were investigated by examining the obtained time-lapse velocity structure. The microseismic (MS) dataset was partitioned into two clusters in a temporal sequence, with each cluster containing 367 relocated events. A series of checkerboard and restoring resolution tests, as well as field investigations, confirmed the resolution, robustness, and reliability of the tomographic results. In addition, absolute velocity change patterns were proposed to assess and predict rockburst risk areas caused by mining activities. The results showed that high-velocity zones could be attributed to roof subsidence, stress transfer after coal and rock mass rupture, and areas with special geological conditions in isolated working face situations. The coupled effects of stress evolution and geological conditions may lead to more pronounced stress concentrations during the mining process. Furthermore, induced events occur not only in areas between high and low stress but also near the isoline edges of pattern changes. Our established velocity patterns have significant potential for predicting hazardous areas with a timeliness of up to 10 days. [ABSTRACT FROM AUTHOR]

The properties of anchored surrounding rock may vary considerably under complex geological and stress conditions, especially dynamic loading in deep mining. Therefore, comprehensive study of the reinforced mechanism is required to prevent failures associated with deep mining. In this paper, with sandstone as matrix and steel bar as bolt, the dynamic compression test of reinforced rock was carried out by using a 50 mm rod diameter split Hopkinson pressure bar (SHPB) test device. The mechanical and energy characteristics of reinforced rock under dynamic loading were analyzed. The results show that the dynamic strength of reinforced sample is greater than that of unreinforced sample and increases with the increase of the strain rate. The reflected energy and absorbed energy increase with the increase of incident energy, while the transmitted energy increases slightly. The higher the strain rate, the larger the energy dissipation rate and the higher the degree of fragmentation. It shows that the energy dissipation characteristic reflects the internal damage process to some extent. Compared with the results of unreinforced samples, the reflected energy of reinforced samples significantly increases and the absorbed energy will significantly decrease. It can be seen that the bolt can reduce absorbed energy of surrounding rock, thereby improving the stability of roadway surrounding rock. The results may provide reference for the stability of deep roadway and support design. [ABSTRACT FROM AUTHOR]