Search Results (1,628)

This paper systematically analyzes the challenges of stabilizing tunnel excavations in zones with low overburden in urban environments, through an engineering-validated case study of the Kobilja Glava Tunnel. A combined approach involving the New Austrian Tunneling Method (NATM) and the pre-installation of steel pipe umbrellas was applied as the primary pre-support measure under complex geotechnical conditions. The design, drilling, grouting, and formation of the temporary support arch were thoroughly documented, along with the implementation of shotcrete, lattice girders, self-drilling anchors, and reinforcement meshes. A numerical analysis was performed using the PLAXIS 2D software package, encompassing the modeling of deformations, shear forces, axial forces, and bending moments, with precisely defined support parameters. Geodetic monitoring recorded maximum surface settlements of up to 70 mm at an overburden of less than 3 m, while deformations were reduced to 28 mm at an overburden of 20 m. The numerical model confirmed soil plasticization within a 3 m wide zone, with maximum displacements reaching 6.3 cm, consistent with field measurements. Calculated tensile strain and angular distortion were classified according to established building damage criteria, confirming minimal structural impact on adjacent buildings. The applied combination of the NATM and the pipe umbrella pre-support system proved to be an effective and reliable solution for controlling deformations and ensuring excavation stability under conditions of limited rock cover and dense urban development. The obtained results provide a verified framework and practical recommendations for future tunneling projects in similar geotechnical and urban conditions, aiming to enhance safety, stability, and cost-effectiveness. Full article

In situ physical coal fracturing is one of the key technologies for deep coal resource extraction, among which the liquid nitrogen cyclic freeze–thaw (LNCFT) technique demonstrates remarkable fracturing effects and promising application potential in physical coal breaking. To determine economically viable mining and coalbed methane (CBM) extraction cycles, this study builds on previous research and conducts a series of experiments to investigate the effects of different cold condition temperatures and freeze–thaw cycles on the mesoscopic surface structure and macroscopic mechanical properties of deep, water-rich coal-rock samples. A statistical damage constitutive model for saturated coal-rock under coupled freeze–thaw and loading, incorporating a damage threshold, was established to more accurately describe the damage patterns and mechanisms. The results indicate that lower cold condition temperatures lead to greater mesoscopic crack propagation, lower uniaxial compressive strength, and significantly reduced freeze–thaw failure cycles. Under −45 °C, saturated coal-rock samples experienced macroscopic failure after only 23 freeze–thaw cycles, which is 9 and 15 cycles fewer than those under −30 °C and −15 °C, respectively. Furthermore, measurements of wave velocities in three directions before and after testing revealed that freeze–thaw cycles caused particularly pronounced damage in the direction perpendicular to the bedding planes. Additionally, the established coupled statistical damage constitutive model provides a more accurate and intuitive analysis of the entire process from damage to failure under different cold conditions, showing that as the temperature decreases and freeze–thaw cycles increase, the coal-rock’s brittleness diminishes while plastic deformation and ductile failure characteristics are enhanced. In summary, for coal and CBM extraction using the LNCFT technique, it is recommended to extract gas once after approximately 35 cycles of liquid nitrogen injection. This study provides a theoretical basis for the application of liquid nitrogen cyclic freeze–thaw technology in deep coal fracturing. Full article

As a support material for mine roadways, shotcrete (SC) exhibits performance limitations in extreme deep-mining environments characterized by high stress and water seepage. Polyoxymethylene (POM) fiber, with its properties of high strength, high modulus, and corrosion resistance, holds potential for application in surrounding rock support of deep roadways. To investigate the effect of POM fiber on the flexural performance of shotcrete, four-point bending tests were conducted on fiber-reinforced concrete specimens with different fiber lengths and dosages. Combined with ABAQUS numerical simulation, damage simulation analysis was performed on each group of specimens, and the stress propagation state of the fibers was tracked. The results show that the flexural strength of polyoxymethylene fiber shotcrete (PFS) increases with the increase in fiber length and dosage, and the influence of fiber dosage is more significant. POM fiber can effectively inhibit the crack development of shotcrete, enhancing its crack resistance and residual strength. The load-deflection curves indicate that PFS exhibits excellent fracture toughness, with the P9L42 group showing the highest flexural strength improvement, reaching an increase of 94%. The numerical simulation results are in good agreement with the experimental conditions, accurately reflecting the damage state and load-deflection response of each group of concrete specimens. Based on the above research, POM fiber is more conducive to meeting the stability requirements of roadway surrounding rock support, providing a scientific basis for the application of PFS in mine roadway surrounding rock support. Full article

In deep coal mines characterized by high temperature, high humidity, high-salinity water, and elevated ground stress, stress corrosion cracking (SCC) of bolts is widespread, causing frequent instability of roadway surrounding rock and hindering long-term stability. This study systematically examines the failure characteristics of anchorage materials in highly corrosive roadways and clarifies the effects of deep-mine temperature and humidity on material corrosion. Long-term corrosion tests on bolts reveal changes in mechanical properties and macroscopic morphology and elucidate the intrinsic mechanisms of SCC. The results show that with the increase in corrosion time, the yield strength, ultimate load and elongation of the anchor rod decrease by up to 11.8%, 13.6%, and 7.08%, respectively. Under high stress, localized corrosion pits form on bolt surfaces, rupturing the oxide film and initiating rapid anodic dissolution and cathodic hydrogen evolution. Interaction between corroded surfaces and microcracks produced by internal impurities leads to progressive damage accumulation and ultimate fracture of the bolts. These findings provide guidance for corrosion protection of coal mine roadway support materials and for improving the long-term performance of roadway supports. Full article

Understanding the shear behavior of the interface between surrounding rock and backfill is of significant engineering importance for enhancing stope stability in cemented tailings backfill mining. However, the evolutionary mechanisms of shear properties and damage under varying mechanical conditions remain insufficiently studied. This investigation employed tailings and surrounding rock from a Guangdong tailings pond, with basic mechanical parameters determined through laboratory tests. Numerical models of the rock-backfill composite were developed using PFC2D, considering different shear rates (0.3, 0.6, and 0.9 mm/min), lateral confinement levels (0.5, 1.0, and 1.5 MPa), and roughness coefficients. The analysis compared the interface’s peak and residual shear strengths, revealed crack evolution patterns, and explored damage mechanisms using acoustic emission monitoring and energy dissipation theory. Key findings include the following: (1) Shear stress–displacement curves under all conditions exhibited three stages, ascending, shearing-off, and sliding, with distinct peak and residual strengths. (2) Increasing lateral confinement, shear rate, and roughness transformed failure from localized to global sliding, with cracks occurring at the interface and propagating into the backfill. (3) Cumulative acoustic emission events increased with all three factors, with lateral confinement showing the most substantial effect on interface energy accumulation (83% increase). These results provide theoretical support for assessing interface stability in deep backfilled stopes. Full article

Salinity is one of the primary limiting factors in the rice production system in northeast Thailand due to the presence of underground salt rocks, and the situation is expected to deteriorate further in the future since rice is particularly susceptible to salinity. In this study, 382 indigenous lowland rice germplasms were evaluated for salt tolerance under hydroponic conditions at the seedling stage. The stress condition was induced by adding NaCl from 2 dS/m to 22 dS/m. Twenty-two varieties (group 1) were selected based on low leaf salinity scores in 2019 and 2020. Ten varieties, LLR050, LLR054, LLR106, LLR216, LLR309, LLR365, LLR377, LLR402, LLR441, and LLR449, were selected from leaf salt injury scores under hydroponic conditions in 2021 and 2022. The response of ten selected varieties was investigated under both hydroponic and soil media at the seedling stage, as well as soil culture at the tillering and flowering stages. The results revealed that LLR054, LLR365, and LLR216 exhibited low leaf injury scores (less than 4.0) at both the seedling and tillering stages. At the seedling stage, most varieties demonstrated high Na+ accumulation in the root, while high accumulation in the shoot was observed at the tillering stage. Varieties LLR054 and LLR441 displayed low leaf damage scores, root sodium accumulation at the seedling stage, and shoot sodium accumulation at the tillering stage, similar to the tolerant check variety Pokkali. Additionally, LLR365 and LLR216 showed high shoot sodium accumulation but low leaf damage scores at the tillering stage. At the flowering stage, LLR050 and LLR449 maintained high yields and filled seeds per panicle under salt stress. Therefore, early-stage LLR054, LLR441, LLR365, and LLR216 had high tolerance and LLR050 and LLR449 maintained high yields, and these varieties are potential sources of salt tolerance for future rice breeding programs. Full article

Aeolian sand is widely distributed in desert areas, but it has certain challenges in the application of roadbed engineering due to its loose particles and poor stability. Cement-modified aeolian sand has gradually become the mainstream improvement method of aeolian sand materials due to its good sand fixation performance. However, the mechanical properties and failure modes of cement-modified aeolian sand are still unclear. The effective characterization of the damage evolution process of aeolian sand is crucial to understanding its mechanical mechanism. This study focuses on cement-modified aeolian sand as the research subject. Utilizing an unconfined compression apparatus and an acoustic emission monitoring system, this research simultaneously monitors stress–strain data and acoustic emission signals during the deformation and failure process of cement-modified aeolian sand. This investigation analyzes the influence of cement content on mechanical performance parameters, examines the correlation between acoustic emission time–frequency characteristics and damage evolution processes, and subsequently establishes an acoustic-emission-based damage evolution model. The results show that a strong correlation is observed between the stress–strain curve and the acoustic emission (AE) evolution characteristics of the cement-modified aeolian sand. When the applied stress reaches 80% of the peak stress, the AE signals enter a relatively calm period. This characteristic can be regarded as significant precursor information for the deformation and failure of the material. The damage in the cement-modified aeolian sand follows a Weibull distribution. The shape parameter m attains its maximum value at a cement content of 7%. The material’s homogeneity transitions from being comparable to coal rock at lower cement contents to resembling granite at higher contents. These findings can provide a technical basis for using acoustic emissions to characterize damage and identify risks in cement-modified aeolian soils. Full article

Chinese shale reservoirs are typically deep, clay-rich, and highly water-sensitive, which severely limits the effectiveness of conventional hydraulic fracturing. To address this challenge, we propose a microwave-assisted waterless fracturing method and investigate its feasibility through laboratory experiments on core samples from the Gulong shale and tight sandstone formations in the Daqing Oilfield. A coupled model integrating microwave power dissipation, pore water heating, and thermal stress evolution is developed to interpret the underlying mechanisms. Experimental results show that, under microwave irradiation (200 W, 40 s) and initial pore water content of 2.1–6%, fracturing is successfully induced without external fluid injection. The tensile failure of the rock coincides with the peak internal pore pressure generated by rapid vaporization and thermal expansion of pore water, as confirmed by a modified tensile strength measurement method. Fracture patterns observed in SEM and post-treatment imaging align with model predictions, demonstrating that microwave energy absorption by pore water is the primary driver of rock failure. The technique eliminates water-related formation damage and is inherently suitable for deep, water-sensitive reservoirs. This study provides experimental evidence and mechanistic insight supporting microwave-based waterless fracturing as a viable approach for challenging shale formations. Full article

To investigate the seepage and deformation failure characteristics of deep unloaded rock mass under cyclic loading and unloading disturbance, a series of triaxial cyclic loading and unloading tests were conducted on granite. These tests were performed under varying seepage pressures and unloading conditions to analyze the mechanical properties, seepage behavior, and fracture failure characteristics of the material. The findings indicate the following: (1) An increase in seepage pressure and unloading magnitude results in pronounced radial expansion characteristics in the rock specimens following cyclic loading and unloading. Additionally, the axial, radial, and volumetric residual strains exhibit a nonlinear acceleration in growth as the number of cyclic loading and unloading applications increases. (2) The elastic modulus of rocks exhibits two distinct phases: an initial rapid decline followed by a steady-state decrease. Concurrently, Poisson’s ratio demonstrates an initial decrease, which is subsequently followed by a consistent increase. Furthermore, when considering the effects of unloading, the inflection point of the Poisson’s ratio curve will occur earlier. (3) The interplay between seepage pressure and unloading conditions markedly exacerbates the damage and degradation of the rock. Specifically, under conditions of 70% unloading and a seepage pressure of 4 MPa, the peak stress of the rock specimen is reduced by 21.90%, and the peak intensity permeability increases by 446.70%. (4) Under conditions of high confining pressure and elevated seepage pressure, V-shaped conjugate shear fracture surfaces are likely to develop during the cyclic loading failure of granite, accompanied by a limited number of secondary shear cracks. Concurrently, tensile failure surfaces that are parallel to the maximum principal stress are also observed under the influence of unloading. Full article

Permeability evolution is one of the key parameters influencing the efficient exploitation of deep unconventional energy resources, as it reflects the dynamic development of pore-fracture structures under complex engineering effects. Using fractal geometry to describe the pore-fracture system, rock permeability enhancement can be quantitatively evaluated. In this study, fractured coal specimens were analyzed under simulated mining-induced stress relief and CH₄ release conditions based on fractal geometry theory. The permeability-enhancement rate was derived and verified through CT (Computed Tomography) characterization of the pore-fracture network. The fractal dimension of the fracture aperture distribution and the tortuosity of fracture paths were determined to establish a fractal permeability-enhancement model, and its sensitivity was analyzed. The results indicate that permeability evolution undergoes four distinct stages: a stable stage, a slow-growth stage, a rapid-growth stage, and a stable or declining stage. The mining-induced stress relief and gas desorption effects significantly accelerate permeability enhancement, providing new insights into the mechanisms governing gas flow and pressure relief in deep coal seams. The proposed model, highly sensitive to the fracture aperture ratio (λ_min/λ_max), reveals that a smaller aperture span leads to greater permeability enhancement during the damage and fracture stage. These findings offer practical guidance for predicting permeability evolution, optimizing gas drainage design, and enhancing the safety and efficiency of coal mining and methane extraction operations. Full article

The decline in the injectivity of injection wells is a serious problem in geothermal systems. In this article, we analyse the mechanisms responsible for the reduction in permeability in Lower Jurassic sandstones during the injection of cooled formation brine. Flow experiments were conducted on rock cores using three types of brines with varying degrees of contamination. The studies included microscopic analysis, scanning electron microscopy (SEM) and mercury intrusion capillary pressure (MICP) before and after the experiments. The results showed that the main factor in the decrease in permeability is the formation of a filter cake from secondary iron minerals on the front surface of the core. Filter cake formation was observed in all samples, with ferrous sediment penetrating to a maximum depth of 1.5 cm from the core front. In addition, the mobilisation of clay particles was observed, which accumulate in pore constrictions, causing additional flow restriction. Mercury porosimetry revealed significant increases in hysteresis values in the front zone (from 16.5 to 42%), indicating complex pore connectivity changes without substantial porosity reduction. The rate of injectivity decline correlates strongly with the fluid flow velocity. The results of the study provide a scientific basis for optimising reinjection processes in geothermal systems and developing strategies to prevent formation damage. Full article

The process of exploiting hydrocarbon deposits is subject to many complications, some of which can make exploitation very difficult or impossible. These factors include damage to the wellbore zone by drilling fluid, which impedes the flow of reservoir fluid from the production zone to the well. This article presents the results of research conducted to develop drilling fluid compositions with the best possible ability to form a tight sealing sediment on the borehole wall. In addition to traditional carbonate blockers, modern organic agents were used as bridging agents. Research was conducted on the selection of the drilling fluid composition, the rheological parameters of which would ensure the suspension of the solid phase in the form of various types of blockers. After preparing the base drilling fluid, its composition was modified by adding different configurations of blockers. The sets of blockers added to the fluid varied in both chemical structure and particle size. Such modified fluids were then subjected to tests of technological properties, such as rheological parameters, API filtration, and pH. In the next stage, sealing tests of the filter cake formed by the tested fluids were carried out on the surface of the rock core using the PPT—Pore Pressure Transmission Test. Based on the obtained results, it can be concluded that the new type of organic blockers used allows the rapid formation of a tight filter cake on the borehole wall, and thus significantly reduces drilling fluid filtration. During PPT, the sediment formation time (t_pmax) for OB2 was 45 min; for the combination of OB1 and the carbonate inhibitor, it was 8 min; and for the carbonate inhibitor alone, it was 150 min. Full article

Formation damage caused by wellbore fluids remains a key concern in carbonate reservoirs, where pore plugging and filtrate invasion can severely reduce permeability. This study investigates the influence of filtrate-control components in cellulose-based polymeric fluids on the potential for formation damage in carbonate rocks and evaluates the performance of HPA starch as an alternative to cellulose, focusing on its comparative effects on formation permeability. Experimental tests were performed using Indiana Limestone cores to measure filtration behavior and permeability recovery after exposure to different polymeric solutions. The results revealed distinct mechanisms associated with each additive: PAC LV controlled fluid loss mainly by adsorption and pore plugging, while HPA starch formed more deformable and permeable structures. Glycerin, when used alone, did not induce formation damage but increased fluid viscosity, favoring more stable dispersion of the polymeric phase. Micronized calcite enhanced external cake consolidation through particle bridging. The combined use of PAC LV, glycerin, and calcite provided the most efficient filtration control and minimized formation damage. These findings contribute to understanding the isolated and synergistic roles of filtrate-control agents and support the design of optimized polymer-based fluids for well intervention and abandonment operations. Full article

Accurate and comprehensive characterization of high-steep slopes is crucial for real-time risk prediction, disaster assessment, and damage evolution monitoring. The study focused on a high-steep rocky slope along the Yanjiang Expressway in Sichuan Province, China. A novel digital reconstruction method was introduced, which integrates terrestrial laser scanning (TLS) and unmanned aerial vehicle (UAV) photogrammetry through a Transformer-based method combining GeoTransformer with the Maximal Cliques (MAC) algorithm. The results indicated that TLS excels in capturing fine-scale features, whereas UAV demonstrates superior performance in large-scale terrain reconstruction. However, multi-sensor data exhibit heterogeneity in terms of partial overlap, large outliers, and density differences. To address these challenges, the GeoTransformer-MAC framework extracts geometrically invariant features from cross-source point cloud (CSPC) to establish initial correspondences, followed by rigorous screening of high-quality locally consistent correspondences to optimize transformation parameters. This method achieves accurate digital reconstruction of the high-steep rock slope. Global and local error analyses verify the model’s superiority in both overall slope characterization and fine-scale feature representation. Compared with the TLS-only model and the conventional method, the Transformer-based method improves the slope model integrity by 85.58%, increases the data density by 9.71%, and improves the accuracy by nearly threefold. This study provides a novel approach for the digital modeling of complex terrains, which serves the refined identification and modeling of geohazards for high-steep slopes in complex mountainous regions. Full article

The advancing speed of the coal mining face has a significant impact on the mining-induced stress and energy accumulation of the surrounding rock. To explain the influence mechanism from a mesoscopic perspective, this study conducted a uniaxial compression test on the coal–rock combination body under different quasi-static loading rates, and analyzed their mechanical properties, failure characteristics, acoustic emission characteristics and energy evolution characteristics. The main findings are as follows: The uniaxial compressive strength and elastic modulus of the coal–rock combination body show a variation law of first increasing and then decreasing with the increase in loading rate, while the degree of impact failure significantly increases gradually as the loading rate rises. With the increase in loading rate, there is a tendency that the AE parameters concentrate from the first two stages to the latter two stages. The post-peak residual elastic energy density of the coal–rock combination body increases gradually with the increase in loading rate. The formation of the advancing speed effect of mining-induced stress concentration and elastic energy accumulation in coal–rock masses is caused by the “competitive” interaction between fracture propagation and coal matrix damage when the coal component in the coal–rock combination is deformed under stress. Full article