Fracture Zone Research Articles

The Brazil Basin Tracer Release Experiment: Observations

Abstract Lightening of bottom water is required to close the abyssal overturning circulation, believed to play an important role in the climate system. A tracer release experiment and turbulence measurement programs have revealed how bottom water is lightened, and illuminated the associated circulation in the deep Brazil Basin, a representative region of the global ocean. Tracer was released on an isopycnal surface about 4000 m deep, over one of the fracture zones emanating from the Mid-Atlantic Ridge (MAR). Tracer that mixed toward the bottom moved toward the MAR across isopycnal surfaces that bend down to intersect the bottom at a rate implying a near-bottom buoyancy flux of 1.5 × 10−9 m2 s−3, somewhat larger than inferred from dissipation measurements. The diffusivity at the level of the tracer release is estimated at 4.4 ± 1 × 10−4 m2 s−1, again larger than inferred from dissipation rates. The main patch moved southwest at about 2 cm s−1 while sinking due to the divergence of buoyancy flux above the bottom layer. The isopycnal eddy diffusivity was about 100 m2 s−1. Westward flow away from the MAR is the return flow balancing the eastward near-bottom upslope flow. The southward component of the flow is roughly consistent with conservation of potential vorticity. The circulation as well as the pattern of diapycnal flux are qualitatively the same as in St. Laurent et al. (2001) but are more robust. The results indicate that diapycnal diffusivity is about twice that invoked by Morris et al. (2001) in calculating the basinwide buoyancy budget. Significance Statement Buoyancy flux into the abyssal waters is required to close the overturning circulation of those waters, an important part of the climate system. This contribution presents a robust view of the strength of that buoyancy flux and the associated circulation.

Next Generation Seismic Source Detection by Computer Vision: Untangling the Complexity of the 2016 Kaikōura Earthquake Sequence

AbstractSeismic source locations are fundamental to many fields of Earth and planetary sciences, such as seismology, volcanology and tectonics. However, seismic source detection and location are challenging when events cluster closely in space and time with signals tangling together at observing stations, such as they often do in major aftershock sequences. Though emerging algorithms and artificial intelligence (AI) models have made processing high volumes of seismic data easier, their performance is still limited, especially for complex aftershock sequences. In this study, we propose a novel approach that utilizes three‐dimensional image segmentation—a computer vision technique—to detect and locate seismic sources, and develop this into a complete workflow, Source Untangler Guided by Artificial intelligence image Recognition (SUGAR). In our synthetic and real data tests, SUGAR can handle complex, energetic earthquake sequences in near real time better than skillful analysts and other AI and non‐AI based algorithms. We apply SUGAR to the 2016 Kaikōura, New Zealand sequence and obtain five times more events than the analyst‐based GeoNet catalog. The improved aftershock distribution illuminates a continuous fault system with extensive fracture zones beneath the segmented, discontinuous surface ruptures. Our method has broader applicability to non‐earthquake sources and other time series image data sets.

Coupled thermal-gas-mechanical phase-field modeling for fracture initiation and propagation in the underground caverns for compressed air energy storage

With the aim of addressing the large-scale engineering fracture problems in an underground cavern for compressed air energy storage (CAES), in this study, a coupled thermal-gas-mechanical (TGM) phase-field modeling for simulating fracture initiation and propagation in the CAES caverns is proposed. This study also focuses on COMSOL Multiphysics strategy of the TGM phase-field fracture modeling. The temperature field, air seepage field, displacement field, initial geostress field, and phase field are fully coupled and solved in COMSOL. A circular preexisting fracture zone is generated and used to initialize the fracture propagation according to the newly specified history strain field. The results indicate that the proposed TGM phase-field modeling and the corresponding COMSOL implementation strategy can simulate the thermodynamic responses and fracture initiation and propagation well. The lateral pressure coefficient and gravitational stress field have a strong impact on the fracture patterns and critical pressure, inducing fractures.

Regularities of rocks zonal disintegration and methane emissions periodicity in mine roadways

The article presents the results of studies on the establishment of stable relationships between methane emissions into degassing wells and their spatial location, stress-strain state of rock massif and mining operations process. Vibroacoustic and electrometric of mine control methods have been used to establish zoning and alternation of fractured zones in the rock massif during mining operations. Using the finite element method, zones of different permeability in the roof above the longwall face were determined, and a qualitative transition from compressive deformations to tensile deformations was revealed. Based on data from mine experiments at 157 degassing wells, patterns of repeatability of rocks zonal disintegration and periodicity of gas emissions into mine roadways depending on the distance to the moving longwall face have been determined for the first time. It has been established that the concentration of methane gas in a wells with distance from the longwall face changes according to a damped quasi-periodic dependence with recombinant changes in stress-strain states. For wells aimed at the goafs, the period of the quasi-periodic function increases by 40%, the amplitude decreases to 30%. The obtained dependencies make it possible to increase the efficiency of degassing.

Seismic response analysis and resilience study of Qingdao 2nd submarine tunnel using the finite element method

Earthquakes, as considered a highly destructive and unpredictable natural disaster that poses significant challenges for engineers designing underground structures. Incorporating seismic considerations is important to ensure the safety and stability of such structures. Therefore, it is crucial to analyze the response of tunnels to earthquakes and establish an evaluation index for their resilience, which would help guide projects toward improved safety. In this paper, we use numerical simulations to study the seismic impact on the Qingdao 2nd Submarine Tunnel according to different lining thicknesses (25-75 cm) and varying stratum conditions. Through adjustments to lining thickness and stratum conditions, a total of 30 numerical simulation experiments are conducted. These experiments contribute to the creation of the resilience evaluation index. The results of the study indicate the following trends: 1. Increasing lining thickness reduces the stress and deformation along the lining, though the effect stabilizes around 45-cm thickness. 2. Poor surrounding rock conditions lead to increased stress and deformation along the lining, especially near fault fracture zones. 3. The culmination of the study involves the creation of a resilience evaluation index, which serves as a practical guidance for tunnel construction in real-world projects.

Coupled Detachment Faulting and Hydrothermal Circulation at 49.7°E Southwest Indian Ridge Revealed by Seafloor Magnetism

AbstractDetachment faults at slow‐ and ultraslow‐spreading mid‐ocean ridges are essential for lithosphere‐hydrosphere interactions. However, their coupling with subseafloor hydrothermal circulation is poorly understood. Here, we investigated shallow hydrothermal fluid circulations in the active Dragon Horn detachment fault system of the Southwest Indian Ridge using combined near‐bottom magnetic anomaly data and rock magnetic analyses. We observed enhanced magnetic anomalies related to the high magnetization of basaltic country rocks and highly serpentinized (>80%) peridotite, whereas the hydrothermally altered basalts and sulfide deposits had weak magnetization and reduced magnetic anomalies. Therefore, the low‐magnetization zone was interpreted as a proxy for the hydrothermal fluid channel. The spatial distribution of the low‐magnetization zone revealed that the inactive Suye field expanded more than 500 m in diameter horizontally and ∼100 m vertically, and the active Longqi hydrothermal field had a >1 km fluid channel, both centered around the detachment fault fracture zone. Our results establish a robust link between detachment faulting and shallow hydrothermal circulation in which the detachment fault system provides critical fluid paths. Therefore, detachment tectonics are important elements for evolving seafloor hydrothermal fields along the Southwest Indian Ridge and possibly other slow‐ and ultraslow‐spreading mid‐ocean ridges globally.

Effects of Reverse Fault Dislocation Application Method for Tunnelling Through Active Faults

Active faults seriously threaten the structural integrity of mountain tunnels in seismic zones, and reverse faults are the most hazardous. A tunnel project in the western region was used as a reference to analyze the damage mechanism of tunnels under different modes of reverse fault displacement. The ABAQUS finite element analysis software was employed for the numerical simulation, and a quasi-static method was adopted to analyze the displacement and stress response patterns of the tunnel structure traversing the fault under three typical modes of reverse fault displacement. This led to deriving the tunnel structure’s longitudinal damage modes and impact zones based on reverse fault displacement. The study revealed that the damage modes of the tunnel under different fault displacement modes varied, which was reflected in the different degrees of shear and compression. Regardless of the fault displacement mode, the tunnel structure located within the fault fracture zone was severely damaged, with the most severe damage occurring at the interface between the fixed plate and the fault displacement section. Therefore, in the design, special attention should be paid to the displacement resistance performance of the dangerous sections of the tunnel. The research results provide significant reference and guidance for similar projects.

The First Network of Ocean Bottom Seismometers in the Red Sea to Investigate the Zabargad Fracture Zone

In the last decades, the slow-spreading Red Sea rift has been the objective of several geophysical investigations to study the extension of the oceanic crust, the thickness of the sedimentary cover, and the formation of transform faults. However, local seismology datasets are still lacking despite their potential to contribute to the understanding of the tectonic evolution of the Red Sea. The Zabargad Fracture Zone is located in the Northern Red Sea and significantly offsets the rift axis to the East. Thus, it is considered a key tectonic element to understand better the formation of the Red Sea rift. To fill the gap in the dataset availability, we deployed the first passive seismic network in the Red Sea, within the Zabargad Fracture Zone. This network included 12 Lobster OBSs from the DEPAS pool, 2 OBS developed and deployed by Fugro, and 4 portable seismic land stations deployed on islands and onshore on the Saudi Arabian coast. Our data-quality analysis confirms that the head-buoy cable free to strum, as well as other additional elements of the DEPAS OBSs, generate seismic noise at frequencies $>$ 10 Hz. However, the Fugro OBSs show high-frequency disturbances even if they lack vibrating elements. Comparison between land and OBS stations reveals that noise between 1 and 10 Hz is due to ocean-generated seismic noise, and not due to resonance of the OBS elements. We also found that waveforms of teleseismic earthquakes recorded by the Fugro OBSs, islands, and onshore stations have comparable signal-to-noise ratios. Instead, differences in signal-to-noise ratio for local earthquakes are affected more by site and path effects than instrument settings.

Study on overburden failure characteristics and displacement rule under the influence of deep faults

Deep faults significantly impact the structural stabilities and deformation behaviors of their overburden rocks, which are key factors in underground engineering and geological hazard research. Considering the problem of deep-fault-overburdened breaking during mining of super-thick coal seams and taking the Yaoqiao Coal Mine as the research object, the mining fracture evolution characteristics and overburden displacement law of the non-structured and fault-bearing overburden corresponding to fully mechanized caving mining are compared and analyzed using numerical simulations and physical similarity simulations. The results of this study show the following: 1) The fracture height of the overlying rock presents a specific change law with advancement of the working face; the initial rapid increase to a maximum height of 74 m is achieved when the working face advances to 90 m; with the development of the plastic zone indicating past yield, the fracture height decreases to 54 m and becomes stable, and the final caving angle of the fracture stabilizes at 70°. 2) In coal mining under normal fault conditions, when the working face advances from the upper to lower walls, the roof forms a masonry beam structure that slows down fault activation and crack development. When moving away from the fault, the overburden movements and water-conducting cracks are fewer, and the crack height is lower than that without faults. When approaching the fault, the influence of the faults in the fracture zone increases, and the height of fracture development reaches the maximum value after crossing the fault, highlighting the significant influence of the fault on fracture development. 3) Through a similarity simulation test, it is shown that the overburden caving zone is further compacted by the overburden rock and that the roof collapses in a large range, resulting in rapid upward development of the overburden rock cracks and separation of the central overburden rock cracks that are gradually compacted and closed. These findings are expected to have important theoretical and practical significance for deep underground engineering design, geological disaster prevention, and fault activity monitoring.

Microbial Mineralization-Based Rapid and High-Strength Simultaneous Repair of Surrounding Rock Fracture Zones and Lining Cracks

Grouting technology based on microbial mineralization represents a novel approach to enhancing the properties of rock and soil. Widely studied for its combination of high efficiency and environmental friendliness, this method improves the strength and permeability of rock and soil. In this study, a novel approach involving bioslurry + filling particles was proposed to reinforce sand columns. It was observed that the addition of filling particles provided new nucleation sites for crystallization, significantly enhancing the cementation effect of sand particles. After 3 days of grouting treatment, sand columns containing 10% filling particles exhibited an order of magnitude reduction in permeability with the unconfined compressive strength (UCS) reaching 2.5 MPa, more than twice that of sand columns reinforced with bioslurry alone. Additionally, this study presented a method for the simultaneous repair of sand particles and concrete cracks. Results indicated that after 3 days of the grouting treatment, the interfacial shear strength between sand columns and concrete reached 100 kPa. Moreover, for concrete with crack apertures less than 1 mm, the permeability coefficient was reduced by over 80%, while the recovery ratio of the splitting tensile strength reached 64.2%. These findings highlight the potential of microbial mineralized grouting technology in addressing practical challenges, providing a foundation for the rapid and high-strength simultaneous repair of tunnel-surrounding rock fracture zones and lining cracks.

A new method for layout layer optimization of long horizontal boreholes for gas extraction in overlying strata: A case study in Guhanshan coal mine, China

AbstractThe gases released by underground coal mining pose a threat to mine safety, lead to resource wastage, and contribute to environmental pollution. Employing long horizontal boreholes (LHB) for gas extraction proves to be an effective solution. However, accurately determining the LHB's position within the overlying rock strata is challenging due to complex mining and geological conditions. This study introduces a novel “zone‐position” method for identifying the optimal LHB placement, utilizing both physical simulation tests and theoretical analysis. The approach comprises two steps. Initially, it identifies the appropriate LHB layout zone within the overlying strata. It delineates four subzones within the fractured zone, among which the stable fractured subzone (SFSZ) is identified as the most favorable for LHB placement. The boundaries of the SFSZ are also defined. Subsequently, the method focuses on pinpointing the LHB's precise location within the SFSZ, proposing a criterion that considers gas accumulation, strata permeability, and LHB stability. Application of this method in engineering projects demonstrates that the gas extracted by LHBs accounts for about 60% of the total gas emission. Furthermore, the volume of gas extracted at the optimal LHB location reaches up to 5.52 m3 min−1, triple that of other locations.

Genesis of a sediment-hosted vein-type Cu deposit in the Lanping Basin, SW China: New insights from geology and LA–ICP–MS analysis of fluid inclusions

Sediment-hosted Cu deposits, including stratiform and epigenetic vein-type Cu deposits, are the second largest source of Cu worldwide. However, many facets of these vein-type Cu deposits, such as the nature and origin of ore fluids and geodynamic mechanisms that produced these fluids, remain controversial, limiting our interpretations of the ore genesis and hampering the selection of exploration strategies. Numerous sediment-hosted vein-type Cu deposits are present in the Lanping Basin, SW China, of which the Jinman deposit is the largest. Copper orebodies at Jinman consist of Cu-sulfide–quartz–carbonate veins and altered wall-rocks hosted mainly in faults and fracture zones in metamorphosed and deformed clastic rocks. The deposit was formed in three stages, pre-, syn- and post-ore, with the first two stages producing hydrothermal veins. The veins in pre-ore stage consist of quartz + ankerite ± sericite ± pyrite, whereas those in syn-ore stage consist of Cu-sulfides + quartz + carbonate ± sericite. During the syn-ore stage, tennantite, quartz, and ankerite crystallized early, then bornite was precipitated, followed by chalcopyrite and chalcocite and finally calcite. Only minor sericite was formed during the post-ore stage. Two major types of fluid inclusions—CO2-rich and aqueous inclusions—are present in both pre- and syn-ore quartz, whereas only aqueous inclusions are present in syn-ore calcite. In pre- and syn-ore quartz and calcite, CO2-rich inclusions have higher homogenization temperatures (275–323 °C) and pressures (307–3495 bar) and lower salinities (0.22–2.7 wt% NaCl eqv.) than aqueous inclusions (164–299 °C, 6.5–80.4 bar and 3.7–20.9 wt% NaCl eqv.). However, the small variations in Cs/Na and Cs/(Na + K) ratios [log Cs/Na = –3.3 ∼ –1.9, log Cs/(Na + K) = –3.3 ∼ –2.1] of the fluid inclusions suggest a same source for the ore fluids. We propose that during both stages, CO2-rich inclusions resulted from unmixing of initial deep-seated, single-phase CO2-rich fluids, whereas aqueous inclusions likely represent the fluids that evolved from these unmixed fluids by extensive CO2 degassing. This interpretation, combined with microthermometric results of CO2-rich inclusions, suggests a mesothermal, low-salinity H2O–NaCl–CO2 ore fluid system. The fluid inclusions from Jinman have similar compositions to those of metamorphic fluids, suggesting a metamorphic origin for the ore-forming fluids. The evolution of fluid compositions suggests that fluid degassing likely acted as a major mechanism for Cu precipitation. We propose that the ore fluids were generated through metamorphic devolatilization of basement of the Lanping Basin in the Biluoxueshan–Chongshan metamorphic zone under a compressional or transpressional regime caused by Cenozoic India–Asia collision. The Jinman deposit has many similarities to orogenic gold deposits worldwide and thus can be thought of as an orogenic deposit. Based on a compilation of the geological characteristics of global sediment-hosted epigenetic vein-type Cu deposits, we suggest that other sediment-hosted epigenetic vein-type Cu deposits with similar genesis to the Jinman deposit are likely present in other regions worldwide. This highlights the exploration potential of this type of deposit in these regions and the need for further research.

The impact of fractures and planar structures on the quality of the Upper Jurassic Mozduran reservoir, Kopet Dagh basin (Northeast Iran)

In this study, based on stereographic projections, two sets of planar structures were identified in the Mozduran reservoir, a prolific reservoir in Northeast Iran. The first set includes shallow structures, consisting of stylolites, solution seams, dense veins, and bedding planes. These structures were created by both sedimentary and diagenetic processes and do not have much effect on reservoir quality. The second set includes structures are related to deformation, and these have a substantial impact on increasing the reservoir quality. To investigate the relationships between the types of fractures and their respective influences on reservoir quality, the production logging tool (PLT) gas production rate data was utilized. This analysis revealed that in fractured zones 2 and 4 of Mozduran reservoir, where fractures and flat structures have increased the quality of the reservoir, the PLT gas production rate also increases. Conversely, in areas where filled fractures and diagenetic processes have negatively affected reservoir quality, the PLT gas production rate decreases. This pattern indicates the contrasting impact of planar features on reservoir quality. Moreover, a higher frequency of fractures corresponds to a higher permeability in the Mozduran reservoir of Well #B, whereas a lower frequency of fractures corresponds to lower permeability in that reservoir in Well #A. These relationships confirm the positive influence of fractures on the Mozduran reservoir quality. The study results reveal that deformation variables in the examined reservoir have greater impacts on its quality than the sedimentary and diagenetic porosity/permeability components, but those impacts can have both positive and negative consequences.

Uniaxial compressive stress-strain model of Molybdenum tailings concrete after high-temperature exposure

To investigate the effect of high-temperature exposure on the mechanical properties of molybdenum tailings concrete, 75 cubes and 150 prisms of molybdenum tailings concrete were tested, by considering five heating temperatures (20, 200, 400, 600, and 800 ℃) and five replacement ratios (0, 25, 50, 75, 100%). The failure modes, mass loss rate, and mechanical properties of the specimens were analyzed in detail. The experimental results indicate that with an increasing heating temperature, the color of the blocks became lighter, accompanied by gradually intensifying phenomena such as skin peeling and crack propagation. At 800 ℃, many small cracks at the fracture site of the blocks after splitting failure, and obvious fracture zones in the block under axial compression failure were observed. With an increasing temperature, the mass loss rate and peak strain of the molybdenum tailings concrete show a linear growth trend, reaching the maximum amplitude at 800 ℃ (7.85% and 192.5%), whilst the molybdenum tailings concrete splitting tensile strength, peak stress, and elastic modulus showed a decreasing trend, reaching the maximum amplitude (404%, 61.7%, and 84.9%). By increasing replacement ratios, the mass loss rate of the molybdenum tailings concrete shows a linear growth trend, with a maximum increase of 1.07%. The mechanical properties of the concrete at all temperatures show a trend of first increasing and then decreasing. A 25% replacement ratio can improve the deterioration of the molybdenum tailings concrete after high-temperature exposure, with the maximum amplitude increase of the peak stress, peak strain, and elastic modulus being 24.3%, 12.4%, and 21%, respectively. Based on the test data, the prediction formulas of the mechanical properties of molybdenum tailings under different high-temperature and molybdenum tailings replacement ratios are fitted. The existing constitutive equations are modified to establish the stress-strain constitutive model of molybdenum tailings concrete after high-temperature exposure, of which results are in good agreement with the test data.

Detecting DC Electrical Resistivity Changes in Seismic Active Areas: State-of-the-Art and Future Directions

In this paper, a critical review of the geoelectrical monitoring activities carried out in seismically active areas is presented and discussed. The electrical resistivity of rocks is one of the geophysical parameters of greatest interest in the study of possible seismic precursors, and it is strongly influenced by the presence of highly fractured zones with high permeability and fluid levels. The analysis in the present study was carried out on results obtained over the last 50 years in seismic zones in China, Japan, the USA and Russia. These past works made it possible to classify the different monitoring strategies, analyze the theoretical models for interpreting possible correlations between anomalies in resistivity signals and local seismicity, and identify the main scientific and technological gaps in the literature. In addition, great attention has been paid to some recent works on the study of the correlations between focal mechanisms and the shapes of anomalous patterns in resistivity time series. Finally, some future scenarios for the development of new activities in this field have been identified.

Reconstruction of the Subsurface of Al-Hassa Oasis Using Gravity Geophysical Data

Al-Hassa city, located in Eastern Saudi Arabia, boasts the world’s largest oasis and the most expansive naturally irrigated lands. Historically, a total of 280 natural springs facilitated significant groundwater discharge and irrigation of agricultural land. Furthermore, the water in certain springs formerly had a high temperature. The spatial variability of the water quality was evident. At the same time, Al-Hassa Oasis is situated on the northeastern side of the Ghawar field, which is the largest conventional onshore oil field in the world in terms of both reserves and daily output (approximately 3.8 mmb/d). The aforementioned traits suggest an intricate subsurface that has not yet been publicly and thoroughly characterized. Due to the presence of significant cultural noise caused by agricultural and nearby industrial activities, a robust, easy-to-use, and accurate geophysical method (gravity) was used to cover an area of 350 km2, producing the 3D subsurface model of the study area. A total of 571 gravity stations were collected, covering the whole Al-Hassa Oasis and parts of the nearby semi-urban areas. The gravity data were corrected and processed, and a 3D inversion was applied. The resulting 3D geophysical subsurface modeling unveiled an intricate subterranean configuration and revealed lateral variations in density, indicating the presence of a potential salt dome structure, as well as fracture zones that serve as conduits or obstacles to the flow of the subsurface fluids. This comprehensive modeling approach offers valuable insights into the subsurface dynamics of the broader study area, enhancing our understanding of its qualitative tectonic and hydraulic features and their impacts on the area’s natural resources, such as groundwater and hydrocarbons.

Detection methods for strength deterioration and structural characteristics of fractured rock based on digital drilling

Fractures ubiquitously exist in strata, and large-scale fractures can cause low bearing capacity and poor stability in rock masses and can sometimes lead to hazards such as roof falls and collapses in mines and tunnels. The foundation of the control of surrounding rocks and effective prevention of such hazards is to be able to accurately determine the structural characteristics of fractures and strength parameters of rocks. Traditionally, testing is carried out mainly through indoor compression tests and borehole inspection, which require drilling of the surrounding rock on site and core testing indoors. The effective in situ and accurate detection of the structure and strength properties of surrounding rock has become a challenge. Digital drilling testing of rock mass is a new approach to solve the above problems and future research direction. In this study, a multifunctional rock mass digital drilling test system is used to perform tests on different types of fractured rocks. The response of drilling parameters to fracture parameters is analysed, and a strength deterioration evaluation index for fractured rock based on drilling parameters is established. Then, the response mechanism of the strength deterioration rate while drilling in the fracture zone is defined, and a model for identifying fracture parameters based on drilling is established. Furthermore, an in situ detection method for fractured rock properties based on digital drilling is proposed. The results of the validation test show that the average difference ratio between the equivalent compressive strength measured by the drilling test and the laboratory compressive test is 3.97 %. The strength degradation of the fractured rock is significant, with a maximum strength degradation rate of 82.1 % obtained through drilling. The average identification accuracies of the fracture position and width are 2.56 mm and 0.85 mm, respectively. The identification accuracy of rock properties while drilling is high, which proves the effectiveness of the prediction model while drilling. This study can provide a theoretical and methodological basis for the accurate in situ prediction of rock properties in underground engineering fields, such as mine roadways, transportation tunnels, and hydraulic tunnels.

Two-stage exhumation of high-pressure rocks by corner flow and mud volcanism within an active subduction zone – A case study from serpentinite mud volcanoes along the Mariana convergent margin

During International Ocean Discovery Program (IODP) Expedition 366 cores were recovered from three serpentinite mud volcanoes containing clasts that originate from the subduction-channel along the Philippine Sea Plate – Pacific Plate boundary. The drilled and sampled mud volcanoes (Yinazao, Fantangisña, and Asùt Tesoru) are located at distances of 55 to 72 km from the Mariana Trench. Mafic rock clasts, embedded within a serpentinite mud matrix, from the flanks and summits of both Asùt Tesoru and Fantangisña Seamounts were analyzed for reconstruction of their metamorphic and deformational overprint in order to reveal the tectono-metamorphic conditions at the metamorphic peak within the subduction channel and the subsequent low-grade overprint during exhumation. Several seamounts comprise clasts of lower plate metabasites with different metamorphic overprint (from low-grade sub-greenschist facies to lower blueschist facies). The metabasites are also associated with clasts of fossiliferous carbonates and cherts with different degrees of metamorphic and deformational overprint, that also originated from the Pacific lower Plate. This implies that these rocks were exhumed from different depths within the subduction channel before being regurgitated within a serpentinite mud matrix. The blueschist facies metamorphic rocks, being affected by metamorphic pressures in the range of 11 to 13.8 kbar at minimum, were very likely exhumed from greater depth within the subduction channel before being captured by uprising, localized serpentinite mudflows, indicating evidence that corner flow is actually taking place along the Mariana convergent margin, and that the high-pressure rocks were exhumed by corner flow in an active subduction zone. Final exhumation, however, is related to the embedding of the rocks within a serpentinite mud matrix and the buoyant ascent of serpentinite mudflows along forearc fracture zones extending from the plate boundary to the upper plate sea floor.

Elastic–plastic criterion solution of deep roadway surrounding rock based on intermediate principal stress and Drucker–Prager criterion

AbstractExcavation‐induced rock failure and deformation near an underground opening boundary is closely associated with the intermediate principal stress, strain softening and rock mass dilation. By combining theoretical analysis and numerical simulation to explore the mechanical evolution of the roadway surrounding rock during excavation. The elastic–plastic criterion solutions for surrounding rock stress, displacement, and the plastic zone of a circular roadway were deduced by including the intermediate principal stress, strain softening and rock mass dilation, based on the Drucker–Prager criterion and the nonassociated flow rule. Furthermore, ABAQUS finite element software was utilized for numerical simulations to scrutinize the influence of mechanical parameters on stress redistribution, surface displacement, and plastic range. The results of the numerical simulations verify the reliability of the theoretical analysis and affirm the high consistency of the results with the theoretical solution. The research findings indicate that the strength of surrounding rock is significantly influenced by the intermediate principal stress, and the deformation and failure of rock mass are primarily impacted by rock mass dilation, while strain softening mainly affects the thickness of the fractured zone. Moreover, the study reveals that enhancing the residual strength of the surrounding rock can improve its resistance to deformation and failure. Furthermore, the excavation of the roadway is observed to increase the original rock stress in the surrounding rock, but increasing the ground support strength effectively controls the deformation and failure of surrounding rock. Ultimately, the research outcomes offer valuable references for engineering calculations and ground support design of surrounding rock in deep roadways.

Experimental and numerical investigation of the damage state of Ti-6Al-4V alloy sheet in the tensile test, hydraulic bulging, and hydroforming processes

There has not been any damage prediction using Johnson-Cook’s (JC) hardening and damage model in the hydraulic bulging (HB) and hydroforming (HF), which are the advanced manufacturing processes, of the Ti-6Al-4V (Ti64) alloy. In the presented study, the damage behavior of the Ti64 alloy sheet in the HB and HF processes was investigated both experimentally and numerically for the first time to address the existing research gap. In this context, firstly, tensile tests (TT) were carried out on samples with different stress triaxiality values at three different tensile speeds, and the fracture morphologies of the samples were examined to evaluate whether it was appropriate to use the JC hardening and damage model. Since the fracture surfaces generally exhibit a ductile fracture morphology and are affected by stress triaxiality and strain rate, it was determined that it would be appropriate to use the JC hardening model and damage criterion to predict the damage of the Ti64 alloy in finite element analysis (FEA). Then, JC model parameters were determined by fitting the stress-strain curve obtained from the FEA and experimental tensile tests. In the HB experiments, bulging height and thickness thinning were predicted by FEA with an accuracy of 97% and 96.85%, respectively. In the HF experiments, the experimental burst pressure, die inlet radius, and base radius were predicted correctly at a rate of 92.5%, 95.5%, and 97.8%, respectively. Also, the thickness of the sample showed good agreement with the FEA results. The fracture zones in each process exhibited good agreement with the experimental results. Thus, it has been demonstrated that the JC damage criterion can be successfully applied in FEA if the Ti64 titanium alloy is damaged in various processes.