Search Results (309)

Empirical and numerical methodologies for the geomechanical assessment of underground excavations have evolved in recent years to adapt to the geotechnical and structural conditions of natural caves, enabling stability evaluation and ensuring safe conditions for speleological exploration. This study analyzes the evolution of the state of the art of these techniques worldwide, assessing their reliability and application context, and identifying the most suitable methodologies for determining the stability of the Al-Badia lava tube. The research was conducted through bibliographic analysis and rock mass characterization using empirical geomechanical classifications. Subsequently, the numerical boundary element method (BEM) was applied to compare the obtained results and model the stress–strain behavior of the cavity. The results allowed the classification of the Al-Badia lava tube into stable, transition, and unstable zones, using empirical support charts and determining the safety factors of the surrounding rock mass. The study site highlights that empirical methods are rather conservative, and numerical results align better with observed conditions. Full article

In this study, we examined the microclimates at eight entrances to a karst system distributed between an elevation of 812 and 906 m in Southern Spain. The karst system, characterised by subvertical open tectonic joints that form narrow shafts, developed on the slope of a mountainous area with a Mediterranean climate and strong chimney effect, resulting in an intense airflow throughout the year. The airflows modify the entrance temperatures, creating a distinctive pattern in each opening that changes with the seasons. The objective of this work is to characterise the outflows and find simple temperature-based parameters that provide information about the karst interior. The entrances were monitored for five years (2017–2022) with temperature–humidity dataloggers at different depths. Other data collected include discrete wind measurements and outside weather data. The most significant parameters identified were the characteristic temperature (T_y), recorded at the end of the outflow season, and the rate of cooling/warming, which ranges between 0.1 and 0.9 °C/month. These parameters allowed the entrances to be grouped based on the efficiency of heat exchange between the outside air and the cave walls, which depends on the rock-boundary geometry. This research demonstrates that simple temperature studies with data recorded at selected positions will allow us to understand geometric aspects of inaccessible karst systems. Dynamic high-airflow cave systems could become a natural source of evidence for climate change and its effects on the underground world. Full article

The deep carbonate reservoirs in the Tarim Basin, Xinjiang, China, are widely developed with multi-scale complex reservoir spaces such as fractures, pores, and karst caves under the coupling of abnormal high pressure, diagenesis, karst, and tectonics and have strong heterogeneity. Among them, fracture–cavity carbonate reservoirs are one of the main reservoir types. Revealing the petrophysical characteristics of fracture–cavity carbonate reservoirs can provide a theoretical basis for the log interpretation and geophysical prediction of deep reservoirs, which holds significant implications for deep hydrocarbon exploration and production. In this study, based on the mineral composition and complex pore structure of carbonate rocks in the Tarim Basin, we comprehensively applied classical petrophysical models, including Voigt–Reuss–Hill, DEM (Differential Effective Medium), Hudson, Wood, and Gassmann, to establish a fracture–cavity petrophysical model tailored to the target block. This model effectively characterizes the complex pore structure of deep carbonate rocks and addresses the applicability limitations of conventional models in heterogeneous reservoirs. The discrepancies between the model-predicted elastic moduli, longitudinal and shear wave velocities (Vp and Vs), and laboratory measurements are within 4%, validating the model’s reliability. Petrophysical template analysis demonstrates that P-wave impedance (Ip) and the Vp/Vs ratio increase with water saturation but decrease with fracture density. A higher fracture density amplifies the fluid effect on the elastic properties of reservoir samples. The Vp/Vs ratio is more sensitive to pore fluids than to fractures, whereas Ip is more sensitive to fracture density. Regions with higher fracture and pore development exhibit greater hydrocarbon storage potential. Therefore, this petrophysical model and its quantitative templates can provide theoretical and technical support for predicting geological sweet spots in deep carbonate reservoirs. Full article

This study focuses on the monitoring and early warning of landslide hazards induced by blasting caving in the Shizhuyuan polymetallic mine. A 30-channel microseismic monitoring system was deployed to capture the spatiotemporal characteristics of rock mass fracturing during a large-scale directional stratified blasting operation (419 tons) conducted on 21 June 2012. A total of 85 microseismic events were recorded, revealing two distinct zones of intense rock failure: Zone I (below 630 m elevation, P1–P3, C6–C8) and Zone II (above 630 m elevation, P4–P5, C1–C6). The upper slope collapse occurred within 5 min post-blasting, as documented by real-time monitoring and video recordings. Principal component analysis (PCA) was applied to 54 microseismic events in Zone II to determine the kinematic characteristics of the slip surface, yielding a dip direction of 324.6° and a dip angle of 73.2°. Complementary moment tensor analysis further revealed that shear failure dominated the slope instability, with pronounced shear fracturing observed in the 645–700 m height range. This study innovatively integrates spatial microseismic event distribution with geomechanical mechanisms, elucidating the dynamic evolution of blasting-induced landslides. The proposed methodology provides a novel approach for monitoring and forecasting slope instability triggered by underground mining, offering significant implications for disaster prevention in similar mining contexts. Full article

The stability of bottom structures in block caving mines is significantly challenged by impact loads generated from large rockfalls and ore collapses on slopes. This study aims to investigate the mechanical response and failure characteristics of bottom structures under such dynamic and cyclic loading conditions. Discrete element methods (DEMs) were employed to simulate the impact load amplitudes caused by large rockfalls on bottom structures. Specimens with identical mechanical properties to the bottom structure were fabricated at a 1:100 scale, based on the principle of similarity ratio tests. Three distinct types of impact loads were identified and analyzed: overall impact from large-scale slope collapses, localized impact from partial rock and soil mass collapses, and continuous multiple impacts from progressive slope failures. True triaxial tests were conducted to evaluate the mechanical response of the bottom structure under these loading scenarios. The results indicate that while overall and multiple impact loads from slope collapses do not lead to catastrophic failure of the bottom structure, severe damage occurs under a 100 m thickness of ore and large block impacts. Specifically, the inner walls of ore accumulation troughs peel off, and ore pillars between troughs fracture and fail. This study highlights the need for advanced experimental and numerical approaches to accurately predict the stability and failure modes of bottom structures under complex loading conditions. Full article

With the increasing depth of coal mining operations, the repeated extraction of multiple coal seams has led to serious safety threats to mines, including secondary roof fracturing, interlayer separation-induced water hazards, and intense mine pressure. Due to the limited research available on the roof failure laws of gently inclined coal seam groups, this study focuses on the Yindonggou Coal Mine and employs a comprehensive approach combining theoretical analysis, numerical simulation, and field measurement. Theoretical calculations indicate that after the mining of Seam 1, the caving zone height ranges from 6.69 to 11.09 m, and the height of the water-conducting fracture zone ranges from 29.59 to 40.79 m. After Coal Seam 2 is mined, the caving zone extends 24.05–33.47 m above the roof of Coal Seam 1, and the fracture zone develops for up to 74.10–94.94 m. Following the mining of Seam 4, the caving zone expands to 30.73–40.15 m above the roof of Coal Seam 1, and the fracture zone reaches 92.26–113.10 m. The numerical simulation results show that after mining Seam 1, the caving zone height is 8.4 m, and the fracture zone reaches 36 m. After Seam 2 is mined, the caving zone extends to 27 m above the roof of Coal Seam 1 and the fracture zone extends to 89 m. After Seam 4 is mined, the caving zone expands to 40 m above the roof of Coal Seam 1 and the fracture zone develops to 112.6 m. The field measurements validate the following findings: a loss of flushing fluid during drilling indicates that after Coal Seam 4 is mined, the fracture zone develops up to 110.5 m above the roof of Coal Seam 1, and the caving zone reaches 47.5 m. Optical imaging logging shows the fracture zone developing to 114.5 m and the caving zone extending to 48.1 m above the roof of Coal Seam 1. The results demonstrate good consistency among these theoretical calculations, numerical simulations, and field measurements. This study reveals a progressive development pattern of roof failure during the repeated mining of gently inclined coal seam groups, providing a theoretical foundation for water hazard prevention and mine pressure control in deep multi-seam mining operations. Full article

To address the stability control challenges of the “support-surrounding rock” system in fully mechanized top-coal caving faces within steeply dipping coal seams, this study employs an integrated approach combining theoretical analysis and numerical simulations, revealing the three-dimensional boundary morphology of the top-coal limit equilibrium zone and establishing a quantitative framework for boundary delineation. The results show that the boundary spatial morphology of the limit equilibrium zone in the fully mechanized caving stope in steeply dipping coal seams is an “asymmetric arc-shaped ribbon-like curved surface”. Along the inclined direction of the working face, the boundary distribution presents an “asymmetric circular-arc arch”, with the vault located in the middle-upper part of the working face. Along the strike direction of the working face, the distance from the boundary to the longwall face shows a gradually increasing pattern from top to bottom. Upon comparing the results from the numerical simulation, theoretical calculation, and field monitoring, a consistent overall pattern emerges. This consistency validates the rationality of the analytical representation of the boundary of the top-coal limit equilibrium zone. The research findings hold significant importance in predicting the stability of the “support-surrounding rock” system and the top-coal cavability. They can offer a scientific foundation for guiding the stability control practices of the support–surrounding rock within this type of mining stope. Full article

Interest in using warm-season grasses, including switchgrass (SG) (Panicum virgatum L.), as a bioenergy crop has increased in Europe. This study evaluated the effects of harvesting regimes with two cuts per year on the productivity, chemical composition and biochemical methane potential of the SG cultivars ‘Dacotah’, ‘Foresburg’ and ‘Cave in Rock’ in environments with cool and moderate climates in Europe with minimal fertilizer application. The results of two harvest years suggest that the biomass yield, chemical composition and energy potential depend on the grass cultivars and harvesting time. Significant effects (p < 0.05) of the harvest date and cultivar were observed for most of the measured parameters for biomass and silage quality. All three SG cultivars harvested on August 8 produced the lowest (p < 0.05) volume of methane per kg of biomass (181–202 normal litres (NL) per kg⁻¹ volatile solids (VS)) compared to the biomass of the respective cultivar harvested on 14 July (287–308 NL kg⁻¹ VS) or on October 3, as regrowth after the first cut made in mid-July (274–307 NL kg⁻¹ VS). The stands of all three SG cultivars, when the first harvest was completed in mid-July, achieved a higher annual area-specific methane yield than those harvested first in August (1128–1900 Nm³ ha⁻¹ and 888–1332 Nm³ ha⁻¹, respectively). Depending on the harvest regime and cultivar, the annual gross energy presented as a lower heating value varied from 31.8 GJ ha⁻¹ to 68.0 GJ ha⁻¹. It is concluded that SG growing under the cool temperate climate of Northern Europe could be an interesting alternative crop for methane production. Our study proves that the cultivar choice also plays an important role. Full article

Based on Brillouin optical time-domain reflectometry (BOTDR) technology, this study integrates laboratory tensile tests and similarity simulation experiments to systematically investigate the relationship between overlying strata collapse and fiber strain during coal seam mining. An analytical expression was established to describe the correlation between overlying strata displacement and fiber strain. The horizontal fiber monitoring results indicate that fiber strain accurately captures the evolution of overlying strata collapse and exhibits strong agreement with actual displacement height. When the working face advanced to 115 m and 155 m, the rock strata primarily underwent stress adjustment with minimal failure. At 195 m, the collapse zone expanded significantly, resulting in a notable increase in fiber strain. By 240 m, severe roof failure occurred, forming a complete caving zone in the goaf. The fiber strain curve exhibited a characteristic “double convex peak” pattern, with peak positions closely corresponding to rock fracture locations, further validating the feasibility of fiber monitoring in coal seam mining. Vertical fiber monitoring clearly delineated the evolution of the “three-zone” structure (caving zone, fracture zone, and bending subsidence zone) in the overlying strata. The fiber strain underwent a staged transformation from compressive strain to tensile strain, followed by stable compaction. The “stepped” characteristics of the strain curve effectively represented the heights of the three zones, highlighting the progressive and synchronized nature of rock failure. These findings demonstrate that fiber strain effectively characterizes the collapse height and evolution of overlying strata, enabling precise identification of rock fracture locations. This research provides scientific insights and technical support for roof stability assessment and mine safety management in coal seam mining. Full article

Understanding the coupled evolution mechanisms of stress, fracture, and seepage fields in overburden strata is critical for preventing water inrush disasters during fully mechanized mining in deep coal seams, particularly under complex hydrogeological conditions. To address this challenge, this study integrates laboratory experiments with FLAC3D numerical simulations to systematically investigate the multi-field coupling behavior in the Luotuoshan coal mine. Three types of coal rock samples—raw coal/rock (bending subsidence zone), fractured coal/rock (fracture zone), and broken rock (caved zone)—were subjected to triaxial permeability tests under varying stress conditions. The experimental results quantitatively revealed distinct permeability evolution patterns: the fractured samples exhibited a 23–48 × higher initial permeability (28.03 mD for coal, 13.54 mD for rock) than the intact samples (0.50 mD for coal, 0.21 mD for rock), while the broken rock showed exponential permeability decay (120.32 mD to 23.72 mD) under compaction. A dynamic permeability updating algorithm was developed using FISH scripting language, embedding stress-dependent permeability models (R² > 0.99) into FLAC3D to enable real-time coupling of stress–fracture–seepage fields during face advancement simulations. The key findings demonstrate four distinct evolutionary stages of pore water pressure: (1) static equilibrium (0–100 m advance), (2) fracture expansion (120–200 m, 484% permeability surge), (3) seepage channel formation (200–300 m, 81.67 mD peak permeability), and (4) high-risk water inrush (300–400 m, 23.72 mD stabilized permeability). The simulated fracture zone height reached 55 m, directly connecting with the overlying sandstone aquifer (9 m thick, 1 MPa pressure), validating field-observed water inrush thresholds. This methodology provides a quantitative framework for predicting water-conducting fracture zone development and optimizing real-time water hazard prevention strategies in similar deep mining conditions. Full article

The archaeological complex of the Benzú rock shelter and cave, located in Ceuta (Spain), represents a heritage site of significant scientific and historical value that is currently at risk due to natural processes and, in particular, the activity of a nearby quarry. This site has been occupied from the Palaeolithic to the Bronze Age and consequently has been the subject of systematic research since 2002, focusing on its stratigraphic sequence, lithic technology, exploitation of marine resources, and the connection between both shores of the Strait of Gibraltar. With the aim of preserving this endangered heritage, a methodology based on advanced digital technologies such as photogrammetry, 3D laser scanning, and GNSS georeferencing has been implemented. These tools have enabled the creation of high-precision, three-dimensional models of the rock shelter and the cave, which are useful for both documentation and monitoring of their structural condition. In addition, fracture networks have been identified, revealing a high degree of geotechnical vulnerability, exacerbated by blasting activities at the nearby quarry. The project has produced a digital twin of the site in an open access format, serving not only for preventive conservation but also for its enhancement through virtual tours, augmented reality, and accessible outreach activities. This digitalization has been essential to facilitate the access to heritage, particularly in areas that are physically difficult to access. Finally, the integration of these digital resources into institutional policies for the sustainable management of heritage is proposed, highlighting the importance of interdisciplinary approaches that combine archaeology, geotechnology, and scientific communication. The experience at Benzú is presented as a replicable model for the protection, interpretation, and dissemination of heritage sites located in fragile and threatened environments. Full article

To resolve the critical issues of severe deformation, structural failure, and maintenance difficulties in the advanced reuse zone of gob-side-entry retaining roadways under pillarless mining conditions in ultra-long fully mechanized top-coal caving isolated mining faces, this study proposes a surrounding rock control technology incorporating pressure relief through roof cutting. Taking the 3203 ultra-long isolated mining face at Nanyang Coal Industry as the engineering case, an integrated methodology combining laboratory experiments, theoretical analysis, numerical simulations, and industrial-scale field trials was implemented. The deformation and failure mechanism of flexible formwork walls in gob-side-entry retaining and the fundamental principles of pressure relief via roof cutting were systematically examined. The vertical stress variations in the advanced reuse zone of the retained roadway before and after roof cutting were investigated, with specific focus on the strata pressure behavior of roadways and face-end hydraulic supports on both the wide coal-pillar side and the pillarless side following roof cutting. The key findings are as follows: ① Blast-induced roof cutting reduces the cantilever beam length adjacent to the flexible formwork wall, thereby decreasing the load per unit area on the flexible concrete wall. This reduction consequently alleviates lateral abutment stress and loading in the floor heave-affected zone, achieving effective control of roadway surrounding rock stability. ② Compared with non-roof cutting, the plastic zone damage area of surrounding rock in the gob-side entry retained by flexible formwork concrete wall is significantly reduced after roof cutting, and the vertical stress on the flexible formwork wall is also significantly decreased. ③ Distinct differences exist in the distribution patterns and magnitudes of working resistance for face-end hydraulic supports between the wide coal-pillar side and the pillarless gob-side-entry retaining side after roof cutting. As the interval resistance increases, the average working resistance of hydraulic supports on the wide pillar side demonstrates uniform distribution, whereas the pillarless side exhibits a declining frequency trend in average working resistance, with an average reduction of 30% compared to non-cutting conditions. ④ After roof cutting, the surrounding rock deformation control effectiveness of the track gateway on the gob-side-entry retaining side is comparable to that of the haulage gateway on the 50 m wide coal-pillar side, ensuring safe mining of the working face. Full article

Facing the problems in determining the distribution range of karst areas and detecting karst caves under the restrictions of complex building and human exploration environments on the urban surface, taking the karst detection of Tianmeixin village and its southern pond in the north extension section of Guanghua Intercity Railway Line 18 as the application research object, based on the formation mechanism of karst and the existing geophysical detection methods, the electrical resistivity tomography method with a large detection range and the cross-well seismic computed tomography method with a high detection accuracy are used to carry out application research on concealed karst cave detection, which are two geophysical technical detection methods with strong adaptability and anti-interference ability. The results show that the optimized combination of geophysical exploration techniques can effectively overcome the limitations of the environment, draw the main karst development areas, reveal the interface between rock and soil, and accurately characterize the size and shape of karst caves. The electrical resistivity tomography method was used to find a number of potential water conduction channels in the middle zone between Tianmeixin village and the south river. The overall distribution characteristics of karst in Tianmeixin village were summarized, and the key detection areas were drawn. This conclusion was verified by several sets of cross-well seismic computed tomography profiles, which provided a reference for the layout of the subsequent cross-well seismic computed tomography imaging method and greatly reduced the workload of drilling, shortened the construction period, saved on detection costs, and reduced the impact on the production and life of residents. Full article

Fine material in caving mining can impact dilution, inrushes, and downstream processing. This work describes the application of a new model to improve the accuracy of the prediction of fine material in block caving mining by coupling a stress model and a fragmentation model, integrating the shear strain effect. This combination seeks to offer a better representation of the secondary fragmentation process than previous models have attained. This approach was implemented through a flow simulator using cellular automata to model the gravitational behavior of broken material during extraction. Physical experiments were then replicated in the flow simulator to couple both models and estimate rock fragmentation under stress. Adding the shear strain effect to the new model showed demonstrable improvements in fine fragmentation estimations, optimizing the results under different confinement conditions. The errors obtained did not exceed 6.8% for 0.8 MPa of confinement, 6.5% for 3 MPa, and 3.8% for 5 MPa, also maintaining a low margin of error for medium and coarser fragments, such as d₅₀ and d₈₀. This improvement in predicting the appearance of fine material supports more accurate planning and the implementation of more focused measures to be taken at drawpoints. Full article

Late contact-era depictions of inter-group conflict in southern African rock art include references to the image-makers and their opponents, who must also have been able to view the images. Performance theory allows researchers to go beyond the conventional question about who made the images by also addressing for whom the images were made. This case study uses performance theory to explore several details of the well-known conflict scene at Ventershoek (Jammerberg, Free State Province, South Africa). In it, ‘San hunter-gatherers’ appear to contest the possession of cattle, traditionally the property of ‘Bantu agro-pastoralists’. It is argued that, in addition to depicting conflict, the image-makers painted allusions to their ritualised, spirit-world mediation of conflict, their opponent’s use of protective war medicine and, potentially, lateralised symbols of cattle ownership that would have been comprehensible to audiences on both sides. It is argued further, from performance theory and the painted details, that the Ventershoek conflict scene contributed to the image-makers’ social construction of reality concerning their relationships with other groups. Full article