Rock fragmentation is an important indicator for assessing the quality of blasting operations.However,accurate prediction of rock fragmentation after blasting is challenging due to the complicated blasting parameters ...Rock fragmentation is an important indicator for assessing the quality of blasting operations.However,accurate prediction of rock fragmentation after blasting is challenging due to the complicated blasting parameters and rock properties.For this reason,optimized by the Bayesian optimization algorithm(BOA),four hybrid machine learning models,including random forest,adaptive boosting,gradient boosting,and extremely randomized trees,were developed in this study.A total of 102 data sets with seven input parameters(spacing-to-burden ratio,hole depth-to-burden ratio,burden-to-hole diameter ratio,stemming length-to-burden ratio,powder factor,in situ block size,and elastic modulus)and one output parameter(rock fragment mean size,X_(50))were adopted to train and validate the predictive models.The root mean square error(RMSE),the mean absolute error(MAE),and the coefficient of determination(R^(2))were used as the evaluation metrics.The evaluation results demonstrated that the hybrid models showed superior performance than the standalone models.The hybrid model consisting of gradient boosting and BOA(GBoost-BOA)achieved the best prediction results compared with the other hybrid models,with the highest R^(2)value of 0.96 and the smallest values of RMSE and MAE of 0.03 and 0.02,respectively.Furthermore,sensitivity analysis was carried out to study the effects of input variables on rock fragmentation.In situ block size(XB),elastic modulus(E),and stemming length-to-burden ratio(T/B)were set as the main influencing factors.The proposed hybrid model provided a reliable prediction result and thus could be considered an alternative approach for rock fragment prediction in mining engineering.展开更多
Deep Underground Science and Engineering(DUSE)is pleased to release this issue with feature articles reporting the advancement in several research topics related to deep underground.This issue contains one perspective...Deep Underground Science and Engineering(DUSE)is pleased to release this issue with feature articles reporting the advancement in several research topics related to deep underground.This issue contains one perspective article,two review articles,six research articles,and one case study article.These articles focus on underground energy storage,multiscale modeling for correlation between micro-scale damage and macro-scale structural degradation,mineralization and formation of gold mine,interface and fracture seepage,experimental study on tunnel-sand-pile interaction,and high water-content materials for deep underground space backfilling,analytical solutions for the crack evolution direction in brittle rocks,and a case study on the squeezing-induced failure in a water drainage tunnel and the rehabilitation measures.展开更多
Attributed to its superior water-to-solid ratio and quick setting time,the highwater material is widely adopted in underground spaces as a cost-effective and environmentally friendly backfill material.To elucidate the...Attributed to its superior water-to-solid ratio and quick setting time,the highwater material is widely adopted in underground spaces as a cost-effective and environmentally friendly backfill material.To elucidate the bleeding mechanism of high-water material under the high confining pressure,a total of 57 tubular specimens were prepared and tested,critical parameters of which included the water-to-solid ratio,curing time,and lateral confinement pressure.Test results showed that no obvious cracks were observed from the surface of confined highwater material,which is different from that of unconfined high-water material,which featured shear cracks.Moreover,the volume of these confined high-water materials under compaction exhibited a continuous shrinkage associated with the water bleeding.The threshold values of the water bleeding are significantly affected by the water-to-solid ratio,followed by the confining pressure and curing time.When other parameters are constant,the higher confinement is requested for these specimens with a small water-to-solid ratio.Meanwhile,the mass of bleeding water increased with the lateral confinement,showing a quick increase at the initial stage.During the bleeding process,the free water stored in the pores was compacted,the evidence of which is the transformation of the hydration products(calcium aluminate hydrate)from its natural fibrous structure into the rod-shaped or dense agglomerate structures.These research outcomes provide an in-depth insight into the fundamental mechanics of the high-water material under the high lateral confinement when it is used for underground spaces.展开更多
In this study,the design and development of a sensor made of low-cost parts to monitor inclination and acceleration are presented.Αmicro electro-mechanical systems,micro electro mechanical systems,sensor was housed i...In this study,the design and development of a sensor made of low-cost parts to monitor inclination and acceleration are presented.Αmicro electro-mechanical systems,micro electro mechanical systems,sensor was housed in a robust enclosure and interfaced with a Raspberry Pi microcomputer with Internet connectivity into a proposed tilt and acceleration monitoring node.Online capabilities accessible by mobile phone such as real-time graph,early warning notification,and database logging were implemented using Python programming.The sensor response was calibrated for inherent bias and errors,and then tested thoroughly in the laboratory under static and dynamic loading conditions beside high-quality transducers.Satisfactory accuracy was achieved in real time using the Complementary Filter method,and it was further improved in LabVIEW using Kalman Filters with parameter tuning.A sensor interface with LabVIEW and a 600 MHz CPU microcontroller allowed real-time implementation of highspeed embedded filters,further optimizing sensor results.Kalman and embedded filtering results show agreement for the sensor,followed closely by the lowcomplexity complementary filter applied in real time.The sensor's dynamic response was also verified by shaking table tests,simulating past recorded seismic excitations or artificial vibrations,indicating negligible effect of external acceleration on measured tilt;sensor measurements were benchmarked using highquality tilt and acceleration measuring transducers.A preliminary field evaluation shows robustness of the sensor to harsh weather conditions.展开更多
The Edikan Mine,which consists of Fobinso and Esuajah gold deposits,lies within the Asankrangwa Gold Belt of the Birimian Supergroup in the Kumasi Basin.The metasedimentary rocks in the Basins and the faulted metavolc...The Edikan Mine,which consists of Fobinso and Esuajah gold deposits,lies within the Asankrangwa Gold Belt of the Birimian Supergroup in the Kumasi Basin.The metasedimentary rocks in the Basins and the faulted metavolcanic rocks in the Belts that make up the Birimian Supergroup were intruded by granitoids during the Eburnean Orogeny.This research aims to classify granitoids in the Edikan Mine and ascertain the petrogenetic and geochemical characteristics of some auriferous granitoids in the wider Kumasi Basin,Ghana,to understand the implications for geodynamic settings.A multi-methods approach involving field studies,petrographic studies,and whole-rock geochemical analysis was used to achieve the goal of the study.Petrographic studies revealed a relatively high abundance of plagioclase and a low percentage of K-feldspars(anorthoclase and orthoclase)in the Fobinso samples,suggesting that the samples are granodioritic in nature,while the Esuajah samples showed relatively low plagioclase abundance and a high percentage in K-feldspars,indicating that they are granitic.The granitoids from the study areas are co-magmatic.The granitoids in Esuajah and Fobinso are generally enriched in large ion lithophile elements and light rare earth elements than high field strength elements,middle rare earth elements,and heavy rare earth elements,indicating mixing with crustal sources during the evolution of the granitoids.The granitoids were tectonically formed in a syn-collisional+VAG setting,which implies that they were formed in the subduction zone setting.Fobinso granodiorites showed S-type signatures with evidence of extensive crustal contamination,while the Esuajah granites showed I-type signatures with little or no crustal contamination and are peraluminous.Gold mineralization in the study area is structurally and lithologically controlled with shear zones,faulting,and veining as the principal structures controlling the mineralization.The late-stage vein,V3,in the Edikan Mine is characterized by a low vein angle and is mineralized.展开更多
Squeezing phenomena can lead to severe loads in deep tunnels,especially in the presence of a low ratio of surrounding rock strength to overburden pressure.For this reason,it is highly imperative to analyze and identif...Squeezing phenomena can lead to severe loads in deep tunnels,especially in the presence of a low ratio of surrounding rock strength to overburden pressure.For this reason,it is highly imperative to analyze and identify a suitable methodology to estimate the squeezing potential and select a proper support system of rock mass.This study aims to reveal the causes of failure of Tishreen tunnel in the west of Syria and develop remediation measures accordingly so as to bring the tunnel back into service.The tunnel in question was subjected to successive failures such as buckling and spalling of side walls,floor heave,and extremely large convergence reaching the failure state of the tunnel lining.In this study,an effective way was demonstrated to evaluate the squeezing potential of the tunnel lining and appropriate modeling of the long-term response of a tunnel excavated in weak rock.Specifically,the causes of failure of Tishreen tunnel were first evaluated by empirical approaches.Then,a numerical model was developed using a timedependent constitutive model to investigate the time-dependent response of the tunnel lining.On this basis,this study proposed an effective reinforcement schemes including steel ribs,grout injection,ground anchors,and new lining of reinforced concrete.The results show that the Burger viscoplastic model simulates effectively the resulting deformation and creep behavior of squeezing ground.It is also observed that using a combined heavy support system can provide efficient control over squeezing deformation and maintain the serviceability of the tunnel under study.展开更多
Deep Underground Science and Engineering(DUSE)is a new international journal(Online ISSN:2770-1328;Print ISSN:2097-0668)launched by China University of Mining and Technology.The Journal is managed by a renowned intern...Deep Underground Science and Engineering(DUSE)is a new international journal(Online ISSN:2770-1328;Print ISSN:2097-0668)launched by China University of Mining and Technology.The Journal is managed by a renowned international publisher John Wiley&Sons Australia,Ltd.and published quarterly in English.The Journal is devoted to building a mainstream academic exchange platform,focusing on forefront research and striving to become a world class scientifi c and technological journal.展开更多
Chinese coal reservoirs are characterized by low pressure and low permeability,which need to be enhanced so as to increase production.However,conventional methods for permeability enhancement can only increase the per...Chinese coal reservoirs are characterized by low pressure and low permeability,which need to be enhanced so as to increase production.However,conventional methods for permeability enhancement can only increase the permeability in fractures,but not the ultra-low permeability in coal matrices.Attempts to enhance such impermeable structures lead to rapid attenuation of gas production,especially in the late stage of gas extraction.Thermal stimulation by injecting high-temperature steam is a promising method to increase gas production.The critical scientific challenges that still hinder its widespread application are related to the evolution law of permeability of high-temperature steam in coal and the thermal deformation of coal.In this study,an experimental approach is developed to explore the high-temperature steam seepage coupled with the thermal deformation in coal under triaxial stress.The tests were conducted using cylindrical coal specimens of?50 mm×100 mm.The permeability and thermal strain in coal were investigated when high-temperature steam was injected at151.11,183.20,213.65,and 239.76°C.The experimental results reveal for the first time that as the amount of injected fluid increases,the steam permeability shows periodic pulsation changes.This paper introduces and explains the main traits of this discovery that may shed more light on the seepage phenomenon.When the injected steam temperature increases,the amplitude of pulsating permeability decreases,whereas the frequency increases;meanwhile,the period becomes shorter,the pulsation peak appears earlier,and the stabilization time becomes longer.The average peak permeability shows a“U-shaped”trend,decreasing first and then increasing as the steam temperature increases.Meanwhile,with the extension of steam injection time,the axial,radial,and volumetric strains of coal show a stage-wise expansion characteristic at different temperatures of steam injection,except for the radial strains at 151.11°C.A two-phase flow theory of gas–liquid is adopted to elucidate the mechanism of pulsating seepage of steam.Moreover,the influencing mechanism of inward and outward thermal expansion on the permeability of coal is interpreted.The results presented in this paper provide new insight into the feasibility of thermal gas recovery by steam injection.展开更多
Deep Underground Science and Engineering(DUSE)is a new international journal(Online ISSN:2770-1328;Print ISSN:2097-0668)launched by China University of Mining and Technology.The Journal is managed by a renowned intern...Deep Underground Science and Engineering(DUSE)is a new international journal(Online ISSN:2770-1328;Print ISSN:2097-0668)launched by China University of Mining and Technology.The Journal is managed by a renowned international publisher John Wiley&Sons Australia,Ltd.and published quarterly in English.The Journal is devoted to building a mainstream academic exchange platform,focusing on forefront research and striving to become a world class scientifi c and technological journal.展开更多
Coal mining induces changes in the nature of rock and soil bodies,as well as hydrogeological conditions,which can easily trigger the occurrence of geological disasters such as water inrush,movement of the coal seam ro...Coal mining induces changes in the nature of rock and soil bodies,as well as hydrogeological conditions,which can easily trigger the occurrence of geological disasters such as water inrush,movement of the coal seam roof and floor,and rock burst.Transparency in coal mine geological conditions provides technical support for intelligent coal mining and geological disaster prevention.In this sense,it is of great significance to address the requirements for informatizing coal mine geological conditions,dynamically adjust sensing parameters,and accurately identify disaster characteristics so as to prevent and control coal mine geological disasters.This paper examines the various action fields associated with geological disasters in mining faces and scrutinizes the types and sensing parameters of geological disasters resulting from coal seam mining.On this basis,it summarizes a distributed fiber-optic sensing technology framework for transparent geology in coal mines.Combined with the multi-field monitoring characteristics of the strain field,the temperature field,and the vibration field of distributed optical fiber sensing technology,parameters such as the strain increment ratio,the aquifer temperature gradient,and the acoustic wave amplitude are extracted as eigenvalues for identifying rock breaking,aquifer water level,and water cut range,and a multi-field sensing method is established for identifying the characteristics of mining-induced rock mass disasters.The development direction of transparent geology based on optical fiber sensing technology is proposed in terms of the aspects of sensing optical fiber structure for large deformation monitoring,identification accuracy of optical fiber acoustic signals,multi-parameter monitoring,and early warning methods.展开更多
Oil and gas exploration studies have been increasingly moving deeper into the earth.The rocks in deep and ultra-deep reservoirs are exposed to a complex environment of high temperatures and large geo-stresses.The Tari...Oil and gas exploration studies have been increasingly moving deeper into the earth.The rocks in deep and ultra-deep reservoirs are exposed to a complex environment of high temperatures and large geo-stresses.The Tarim oilfield in the Xinjiang Uygur Autonomous Region(Xinjiang for short),China,has achieved a breakthrough in the exploration of deep hydrocarbon reservoirs at a depth of over 9000 m.The mechanical properties of deep rocks are significantly different from those of shallow rocks.In this study,triaxial compression tests were conducted on heat-treated carbonatite rocks to explore the evolution of the mechanical properties of carbonatite rocks under high confining pressure after thermal treatment.The rocks for the tests were collected from reservoirs in the Tarim oilfield,Xinjiang,China.The experiments were performed at confining pressures ranging from atmospheric to 120 MPa and temperatures ranging from25 to 500°C.The results show that the critical confining pressure of the brittle–ductile transition increases with increasing temperature.Young's modulus is negatively correlated with the temperature and positively correlated with the confining pressure.As the confining pressure increases,the failure mode of the specimens gradually transforms from shear fracture failure into“V”-type failure and finally into bulging failure(multiple shear fractures).With increasing temperature,the failure angle tends to decrease.In addition,an improved version of the Mohr-Coulomb strength criterion with a temperature-dependent power function was proposed to describe the failure strength of carbonatite rocks after exposure to high temperature and high confining pressure.The surface of the strength envelope of this criterion is temperature dependent,which could reflect the strength evolution of rock under high confining pressures after thermal treatment.Compared with other strength criteria,this criterion is more capable of replicating physical processes.展开更多
Three sandstone specimens common in rock engineering were selected to study the differences in the mechanical properties of rocks with different lithologies.The development and expansion of the internal cracks in the ...Three sandstone specimens common in rock engineering were selected to study the differences in the mechanical properties of rocks with different lithologies.The development and expansion of the internal cracks in the specimens were observed by combining the simulation system with the acoustic emission system.Through the combination of dynamic and static stresses,the deformation and damage of rocks under deep rock excavation and blasting were simulated.As the results show,the acoustic emission events of specimens with different lithologies under combined static and dynamic cyclic loading can be roughly divided into three phases:weakening,stabilizing,and surging periods.In addition,the acoustic emission characteristics of specimens with different lithologies show general consistency in different compression phases.The degree of fragmentation of specimens increases with the applied stress level;therefore,the stress level is one of the important factors influencing the damage pattern of specimens.The acoustic emission system was used to simulate the deformation and damage of rocks subjected to deep rock body excavation and engineering blasting.Cyclic dynamic perturbations under sinusoidal waves with a frequency of 5 Hz,a loading rate of 0.1 mm/min,a cyclic amplitude of 5 MPa,and a loading rate of 0.1 mm/min were applied to the three rock samples during the experiments.Among them,the fine-grained sandstones are the most sensitive to the sinusoidal cyclic perturbation,followed by the muddy siltstone and the medium-grained sandstones.On this basis,the acoustic emission energy release characteristics were analyzed,and the waveform characteristics in the damage evolution of the specimen under dynamic perturbation were studied by extracting the key points and searching for the main frequency eigenvalues.展开更多
Microcrack growth during progressive compressive failure in brittle rocks strongly influences the safety of deep underground engineering.The external shear stressτxy on brittle rocks greatly affects microcrack growth...Microcrack growth during progressive compressive failure in brittle rocks strongly influences the safety of deep underground engineering.The external shear stressτxy on brittle rocks greatly affects microcrack growth and progressive failure.However,the theoretical mechanism of the growth direction evolution of the newly generated wing crack during progressive failure has rarely been studied.A novel analytical method is proposed to evaluate the shear stress effect on the progressive compressive failure and microcrack growth direction in brittle rocks.This model consists of the wing crack growth model under the principal compressive stresses,the direction correlation of the general stress,the principal stress and the initial microcrack inclination,and the relationship between the wing crack length and strain.The shear stress effect on the relationship between y-direction stress and wing crack growth and the relationship between y-direction stress and y-direction strain are analyzed.The shear stress effect on the wing crack growth direction during the progressive compressive failure is determined.The initial crack angle effect on the y-direction peak stress and the wing crack growth direction during the progressive compressive failure considering shear stress is also discussed.A crucial conclusion is that the direction of wing crack growth has a U-shaped variation with the growth of the wing crack.The rationality of the analytical results is verified by an experiment and from numerical results.The study results provide theoretical support for the evaluation of the safety and stability of surrounding rocks in deep underground engineering.展开更多
With recent technological advancements,tunnel boring machines(TBM)have developed and exhibited high performance in large diameters and weak ground conditions.Tunnels are crucial structures that significantly influence...With recent technological advancements,tunnel boring machines(TBM)have developed and exhibited high performance in large diameters and weak ground conditions.Tunnels are crucial structures that significantly influence the timelines of highway and railway projects.Therefore,the construction of tunnels with TBMs becomes a preferred option.In this study,a comparative analysis between TBM and the New Austrian Tunneling Method(NATM)for tunnel construction is performed in the construction of the T1 tunnel with a diameter of 13 m,which is the longest tunnel in the E?me-Salihli section of Ankara-izmir High-Speed Railway Project(Türkiye).The selection of TBM type,measures taken in problematic sections,and application issues of TBM are discussed.The impact of correct description of geological and geotechnical conditions on both selection and performance of TBM is presented.An earth pressure balanced type TBM is chosen for the construction of the T1 tunnel.Because of the additional engineering measures taken before excavation in problematic areas,the tunnel was completed with great success within the initially planned timeframe.From this point of view,this study is an important case and may contribute to worldwide tunneling literature.展开更多
Groundwater inrush is a hazard that always occurs during underground mining.Grouting is one of the most effective processes to seal underground water inflow for hazard prevention.In this study,grouting experiments are...Groundwater inrush is a hazard that always occurs during underground mining.Grouting is one of the most effective processes to seal underground water inflow for hazard prevention.In this study,grouting experiments are conducted by using a visualized transparent single-fracture replica with plane roughness.Image processing and analysis are performed to investigate the thermo–hydro–mechanical coupling effect on the grouting diffusion under coal mine flowing water conditions.The results show that higher ambient temperature leads to shorter initial gel time of chemical grout and leads to a better relative sealing efficiency in the case of a lower flow rate.However,with a higher water flow rate,the relative sealing efficiency is gradually reduced under higher temperature conditions.The grouting pressure,the seepage pressure,and the temperature are measured.The results reveal that the seepage pressure shows a positive correlation with the grouting pressure,while the temperature change shows a negative correlation with the seepage pressure and the grouting pressure.The“equivalent grouting point offset”effect of grouting shows an eccentric elliptical diffusion with larger grouting distance and width under lower temperature conditions.展开更多
Due to the invisibility and complexity of the underground spaces,monitoring the propagation and filling characteristics of the grouting slurry post the water–sand mixture inrush in metal mines is challenging,which co...Due to the invisibility and complexity of the underground spaces,monitoring the propagation and filling characteristics of the grouting slurry post the water–sand mixture inrush in metal mines is challenging,which complicates engineering treatment.This research investigated the propagation law of cement-sodium silicate slurry under flowing water conditions within the caving mass of a metal mine.First,based on borehole packer test results and borehole TV images,the fractured strata before grouting were classified into four types:cavity,hidden,fissure,and complete.Second,an orthogonal experimental design was employed to evaluate the impact of four key factors—stratigraphic fragmentation,water flow rate,grouting flow rate,and water-cement ratio—on the efficacy of grouting within a caving mass at the site.The results indicate that the factors influencing grouting efficacy are ranked in the following order of importance:stratigraphic fragmentation>water flow rate>water–cement ratio>grouting flow rate.Ultimately,five propagation filling modes—pure slurry,big crack,small crack,small karst pore,and pore penetration—were identified by examining the propagation filling characteristics of slurry in rock samples,incorporating microscopic material structure analysis through scanning electron microscopy and energy spectrum analysis.The findings of this study provide valuable insights into selecting engineering treatment parameters and methodologies,serving as a reference for preventing and controlling water–sand mixture inrush in metal mines,thereby enhancing treatment efficacy and ensuring grouting success.展开更多
Shield tunnel,composed of several segments,is widely used in urban underground engineering.When the tunnel is under load,relative displacement occurs between adjacent segments.In the past,distributed optical fiber sen...Shield tunnel,composed of several segments,is widely used in urban underground engineering.When the tunnel is under load,relative displacement occurs between adjacent segments.In the past,distributed optical fiber sensing technology was used to perform strain monitoring,but there is an urgent need to determine how to transform strain into displacement.In this study,optical frequency domain reflectometry was applied in laboratory tests.Aiming at the shear process and center settlement process of shield tunnel segments,two kinds of quantitative calculation methods were put forward to carry out a quantitative analysis.Meanwhile,the laboratory test process was simulated numerically utilizing the discrete element numerical analysis method.Optical fiber,an atypical geotechnical material,was innovatively applied for discrete element modeling and numerical simulation.The results show that the measured displacement of the dial gauge,the calculated results of the numerical model,and the displacement quantitatively calculated from the optical fiber data agree with each other in general.The latter two methods can potentially be utilized in engineering application of deformation monitoring at shield tunnel joints,but need to be further calibrated and adjusted in detail.展开更多
The Maoping lead–zinc mining area is a significant metal mine site in northeastern Yunnan.In this study,both hydraulic fracturing in situ stress testing and ultrasonic imaging logging were first carried out in the mi...The Maoping lead–zinc mining area is a significant metal mine site in northeastern Yunnan.In this study,both hydraulic fracturing in situ stress testing and ultrasonic imaging logging were first carried out in the mining area.Second,930 focal mechanism solutions and 231 sets of stress data near the mining area were collected.Then,the variations in the type of in situ stress field,the magnitude of in situ stress,the direction of horizontal principal stress,and the ratio of lateral pressure were analyzed to characterize the distribution of the in situ stress field.On this basis,a new method using borehole breakouts and drilling-induced fractures was proposed to determine the stress direction.Finally,the evolution of the mechanical properties of dolomite with burial depth was analyzed and the influence of rock mechanical properties on the distributions of the in situ stress field was explored.The results show that the in situ stress in the mining area isσ_(H)>σ_(V)>σ_(h),indicating a strike–slip stress state.The in situ stress is high in magnitude,and its value increases with burial depth.The maximum and minimum horizontal lateral stress coefficients are stabilized at approximately 1.22 and 0.73,respectively.The direction of the maximum horizontal principal stress is NW,mainly ranging from N58.44°W to N59.70°W.The stress field inferred from the focal mechanism solution is in good agreement with the test results.The proportion of structural planes with dip angles between 30°and 75°exceeds 80%,and the dip direction of the structural planes is mainly NW to NWW.The line density of structural planes shows high density in shallow areas and low density in deep areas.More energy tends to be accumulated in rocks with higher elastic modulus and strength,leading to higher in situ stress levels.These findings are of significant reference for mine tunnel layout,support design optimization,and disaster prevention.展开更多
Fracture surface contour study is one of the important requirements for characterization and evaluation of the microstructure of rocks.Based on the improved cube covering method and the 3D contour digital reconstructi...Fracture surface contour study is one of the important requirements for characterization and evaluation of the microstructure of rocks.Based on the improved cube covering method and the 3D contour digital reconstruction model,this study proposes a quantitative microstructure characterization method combining the roughness evaluation index and the 3D fractal dimension to study the change rule of the fracture surface morphology after blasting.This method was applied and validated in the study of the fracture microstructure of the rock after blasting.The results show that the fracture morphology characteristics of the 3D contour digital reconstruction model have good correlation with the changes of the blasting action.The undulation rate of the three-dimensional surface profile of the rock is more prone to dramatic rise and dramatic fall morphology.In terms of tilting trend,the tilting direction also shows gradual disorder,with the tilting angle increasing correspondingly.All the roughness evaluation indexes of the rock fissure surface after blasting show a linear and gradually increasing trend as the distance to the bursting center increases;the difference between the two-dimensional roughness evaluation indexes and the three-dimensional ones of the same micro-area rock samples also becomes increasingly larger,among which the three-dimensional fissure roughness coefficient JRC and the surface roughness ratio Rs display better correlation.Compared with the linear fitting formula of the power function relationship,the three-dimensional fractal dimension of the postblast fissure surface is fitted with the values of JRC and Rs,which renders higher correlation coefficients,and the degree of linear fitting of JRC to the three-dimensional fractal dimension is higher.The fractal characteristics of the blast-affected region form a unity with the three-dimensional roughness evaluation of the fissure surface.展开更多
This research presents the square root sum of squares response of displacements and tunnel moments under the Kobe and Loma Prieta seismic excitations with a peak ground acceleration of 0.05 g for various dry relative ...This research presents the square root sum of squares response of displacements and tunnel moments under the Kobe and Loma Prieta seismic excitations with a peak ground acceleration of 0.05 g for various dry relative densities of local sand in Bangladesh.For this reason,a one-dimensional gravitational shake table test was performed after calibration to determine the seismic performance of the concrete tunnel-sand-pile interaction model.A vertical 40 kg load was applied on each pile cap along with the seismic excitations.The experimental results obtained were compared with the previous numerical study conducted by using field data so as to better interpret the variations of results.In the case of vertical sand displacement,the ratio between the previous field data obtained through numerical study and the present study is found to be 0.96.Moreover,the experimental results were compared with the 3D full-scale numerical analysis results of Plaxis considering the Mohr-Coulomb constitutive model of sand.Variations of experimental and numerical results show a satisfactory level of alignment with the previously published work.According to the shake table test results,the lateral displacement of the tunnel is greater than the vertical displacement because of the transverse directional seismic excitation on the tunnel body.The minimum difference between lateral and vertical displacements of the tunnel is found to be 31%for a relative density of 27%under the Loma Prieta earthquake.However,this research may be advanced in the future by considering various peak ground accelerations,tunnel-pile clearance,and geometric properties.展开更多
基金National Natural Science Foundation of China,Grant/Award Number:52374153。
文摘Rock fragmentation is an important indicator for assessing the quality of blasting operations.However,accurate prediction of rock fragmentation after blasting is challenging due to the complicated blasting parameters and rock properties.For this reason,optimized by the Bayesian optimization algorithm(BOA),four hybrid machine learning models,including random forest,adaptive boosting,gradient boosting,and extremely randomized trees,were developed in this study.A total of 102 data sets with seven input parameters(spacing-to-burden ratio,hole depth-to-burden ratio,burden-to-hole diameter ratio,stemming length-to-burden ratio,powder factor,in situ block size,and elastic modulus)and one output parameter(rock fragment mean size,X_(50))were adopted to train and validate the predictive models.The root mean square error(RMSE),the mean absolute error(MAE),and the coefficient of determination(R^(2))were used as the evaluation metrics.The evaluation results demonstrated that the hybrid models showed superior performance than the standalone models.The hybrid model consisting of gradient boosting and BOA(GBoost-BOA)achieved the best prediction results compared with the other hybrid models,with the highest R^(2)value of 0.96 and the smallest values of RMSE and MAE of 0.03 and 0.02,respectively.Furthermore,sensitivity analysis was carried out to study the effects of input variables on rock fragmentation.In situ block size(XB),elastic modulus(E),and stemming length-to-burden ratio(T/B)were set as the main influencing factors.The proposed hybrid model provided a reliable prediction result and thus could be considered an alternative approach for rock fragment prediction in mining engineering.
文摘Deep Underground Science and Engineering(DUSE)is pleased to release this issue with feature articles reporting the advancement in several research topics related to deep underground.This issue contains one perspective article,two review articles,six research articles,and one case study article.These articles focus on underground energy storage,multiscale modeling for correlation between micro-scale damage and macro-scale structural degradation,mineralization and formation of gold mine,interface and fracture seepage,experimental study on tunnel-sand-pile interaction,and high water-content materials for deep underground space backfilling,analytical solutions for the crack evolution direction in brittle rocks,and a case study on the squeezing-induced failure in a water drainage tunnel and the rehabilitation measures.
基金Regional Fund of National Natural Science Foundation of China,Grant/Award Numbers:52164011,52464008National Natural Science Foundation of China-Xinjiang Joint Fund,Grant/Award Number:2022D01E31+2 种基金Graduate student scientific research innovation projects in Xinjiang Uygur Autonomous Region,Grant/Award Number:XJ2024G097Xinjiang Uygur Autonomous Region Special Program for Key R&D Tasks,Grant/Award Numbers:2022B01034,2022B01051,2023B01010Xinjiang Uygur Autonomous Region“Tianshan Talent Training”Program,Grant/Award Numbers:2022TSYCCX0037,2023TSYCJC0009,2023TSYCJC0095。
文摘Attributed to its superior water-to-solid ratio and quick setting time,the highwater material is widely adopted in underground spaces as a cost-effective and environmentally friendly backfill material.To elucidate the bleeding mechanism of high-water material under the high confining pressure,a total of 57 tubular specimens were prepared and tested,critical parameters of which included the water-to-solid ratio,curing time,and lateral confinement pressure.Test results showed that no obvious cracks were observed from the surface of confined highwater material,which is different from that of unconfined high-water material,which featured shear cracks.Moreover,the volume of these confined high-water materials under compaction exhibited a continuous shrinkage associated with the water bleeding.The threshold values of the water bleeding are significantly affected by the water-to-solid ratio,followed by the confining pressure and curing time.When other parameters are constant,the higher confinement is requested for these specimens with a small water-to-solid ratio.Meanwhile,the mass of bleeding water increased with the lateral confinement,showing a quick increase at the initial stage.During the bleeding process,the free water stored in the pores was compacted,the evidence of which is the transformation of the hydration products(calcium aluminate hydrate)from its natural fibrous structure into the rod-shaped or dense agglomerate structures.These research outcomes provide an in-depth insight into the fundamental mechanics of the high-water material under the high lateral confinement when it is used for underground spaces.
基金Research Committee,National Technical University of Athens。
文摘In this study,the design and development of a sensor made of low-cost parts to monitor inclination and acceleration are presented.Αmicro electro-mechanical systems,micro electro mechanical systems,sensor was housed in a robust enclosure and interfaced with a Raspberry Pi microcomputer with Internet connectivity into a proposed tilt and acceleration monitoring node.Online capabilities accessible by mobile phone such as real-time graph,early warning notification,and database logging were implemented using Python programming.The sensor response was calibrated for inherent bias and errors,and then tested thoroughly in the laboratory under static and dynamic loading conditions beside high-quality transducers.Satisfactory accuracy was achieved in real time using the Complementary Filter method,and it was further improved in LabVIEW using Kalman Filters with parameter tuning.A sensor interface with LabVIEW and a 600 MHz CPU microcontroller allowed real-time implementation of highspeed embedded filters,further optimizing sensor results.Kalman and embedded filtering results show agreement for the sensor,followed closely by the lowcomplexity complementary filter applied in real time.The sensor's dynamic response was also verified by shaking table tests,simulating past recorded seismic excitations or artificial vibrations,indicating negligible effect of external acceleration on measured tilt;sensor measurements were benchmarked using highquality tilt and acceleration measuring transducers.A preliminary field evaluation shows robustness of the sensor to harsh weather conditions.
文摘The Edikan Mine,which consists of Fobinso and Esuajah gold deposits,lies within the Asankrangwa Gold Belt of the Birimian Supergroup in the Kumasi Basin.The metasedimentary rocks in the Basins and the faulted metavolcanic rocks in the Belts that make up the Birimian Supergroup were intruded by granitoids during the Eburnean Orogeny.This research aims to classify granitoids in the Edikan Mine and ascertain the petrogenetic and geochemical characteristics of some auriferous granitoids in the wider Kumasi Basin,Ghana,to understand the implications for geodynamic settings.A multi-methods approach involving field studies,petrographic studies,and whole-rock geochemical analysis was used to achieve the goal of the study.Petrographic studies revealed a relatively high abundance of plagioclase and a low percentage of K-feldspars(anorthoclase and orthoclase)in the Fobinso samples,suggesting that the samples are granodioritic in nature,while the Esuajah samples showed relatively low plagioclase abundance and a high percentage in K-feldspars,indicating that they are granitic.The granitoids from the study areas are co-magmatic.The granitoids in Esuajah and Fobinso are generally enriched in large ion lithophile elements and light rare earth elements than high field strength elements,middle rare earth elements,and heavy rare earth elements,indicating mixing with crustal sources during the evolution of the granitoids.The granitoids were tectonically formed in a syn-collisional+VAG setting,which implies that they were formed in the subduction zone setting.Fobinso granodiorites showed S-type signatures with evidence of extensive crustal contamination,while the Esuajah granites showed I-type signatures with little or no crustal contamination and are peraluminous.Gold mineralization in the study area is structurally and lithologically controlled with shear zones,faulting,and veining as the principal structures controlling the mineralization.The late-stage vein,V3,in the Edikan Mine is characterized by a low vein angle and is mineralized.
文摘Squeezing phenomena can lead to severe loads in deep tunnels,especially in the presence of a low ratio of surrounding rock strength to overburden pressure.For this reason,it is highly imperative to analyze and identify a suitable methodology to estimate the squeezing potential and select a proper support system of rock mass.This study aims to reveal the causes of failure of Tishreen tunnel in the west of Syria and develop remediation measures accordingly so as to bring the tunnel back into service.The tunnel in question was subjected to successive failures such as buckling and spalling of side walls,floor heave,and extremely large convergence reaching the failure state of the tunnel lining.In this study,an effective way was demonstrated to evaluate the squeezing potential of the tunnel lining and appropriate modeling of the long-term response of a tunnel excavated in weak rock.Specifically,the causes of failure of Tishreen tunnel were first evaluated by empirical approaches.Then,a numerical model was developed using a timedependent constitutive model to investigate the time-dependent response of the tunnel lining.On this basis,this study proposed an effective reinforcement schemes including steel ribs,grout injection,ground anchors,and new lining of reinforced concrete.The results show that the Burger viscoplastic model simulates effectively the resulting deformation and creep behavior of squeezing ground.It is also observed that using a combined heavy support system can provide efficient control over squeezing deformation and maintain the serviceability of the tunnel under study.
文摘Deep Underground Science and Engineering(DUSE)is a new international journal(Online ISSN:2770-1328;Print ISSN:2097-0668)launched by China University of Mining and Technology.The Journal is managed by a renowned international publisher John Wiley&Sons Australia,Ltd.and published quarterly in English.The Journal is devoted to building a mainstream academic exchange platform,focusing on forefront research and striving to become a world class scientifi c and technological journal.
基金Fundamental Research Funds for the Universities of Henan Province,Grant/Award Number:NSFRF180305。
文摘Chinese coal reservoirs are characterized by low pressure and low permeability,which need to be enhanced so as to increase production.However,conventional methods for permeability enhancement can only increase the permeability in fractures,but not the ultra-low permeability in coal matrices.Attempts to enhance such impermeable structures lead to rapid attenuation of gas production,especially in the late stage of gas extraction.Thermal stimulation by injecting high-temperature steam is a promising method to increase gas production.The critical scientific challenges that still hinder its widespread application are related to the evolution law of permeability of high-temperature steam in coal and the thermal deformation of coal.In this study,an experimental approach is developed to explore the high-temperature steam seepage coupled with the thermal deformation in coal under triaxial stress.The tests were conducted using cylindrical coal specimens of?50 mm×100 mm.The permeability and thermal strain in coal were investigated when high-temperature steam was injected at151.11,183.20,213.65,and 239.76°C.The experimental results reveal for the first time that as the amount of injected fluid increases,the steam permeability shows periodic pulsation changes.This paper introduces and explains the main traits of this discovery that may shed more light on the seepage phenomenon.When the injected steam temperature increases,the amplitude of pulsating permeability decreases,whereas the frequency increases;meanwhile,the period becomes shorter,the pulsation peak appears earlier,and the stabilization time becomes longer.The average peak permeability shows a“U-shaped”trend,decreasing first and then increasing as the steam temperature increases.Meanwhile,with the extension of steam injection time,the axial,radial,and volumetric strains of coal show a stage-wise expansion characteristic at different temperatures of steam injection,except for the radial strains at 151.11°C.A two-phase flow theory of gas–liquid is adopted to elucidate the mechanism of pulsating seepage of steam.Moreover,the influencing mechanism of inward and outward thermal expansion on the permeability of coal is interpreted.The results presented in this paper provide new insight into the feasibility of thermal gas recovery by steam injection.
文摘Deep Underground Science and Engineering(DUSE)is a new international journal(Online ISSN:2770-1328;Print ISSN:2097-0668)launched by China University of Mining and Technology.The Journal is managed by a renowned international publisher John Wiley&Sons Australia,Ltd.and published quarterly in English.The Journal is devoted to building a mainstream academic exchange platform,focusing on forefront research and striving to become a world class scientifi c and technological journal.
基金National Natural Science Foundation of China,Grant/Award Number:42130706。
文摘Coal mining induces changes in the nature of rock and soil bodies,as well as hydrogeological conditions,which can easily trigger the occurrence of geological disasters such as water inrush,movement of the coal seam roof and floor,and rock burst.Transparency in coal mine geological conditions provides technical support for intelligent coal mining and geological disaster prevention.In this sense,it is of great significance to address the requirements for informatizing coal mine geological conditions,dynamically adjust sensing parameters,and accurately identify disaster characteristics so as to prevent and control coal mine geological disasters.This paper examines the various action fields associated with geological disasters in mining faces and scrutinizes the types and sensing parameters of geological disasters resulting from coal seam mining.On this basis,it summarizes a distributed fiber-optic sensing technology framework for transparent geology in coal mines.Combined with the multi-field monitoring characteristics of the strain field,the temperature field,and the vibration field of distributed optical fiber sensing technology,parameters such as the strain increment ratio,the aquifer temperature gradient,and the acoustic wave amplitude are extracted as eigenvalues for identifying rock breaking,aquifer water level,and water cut range,and a multi-field sensing method is established for identifying the characteristics of mining-induced rock mass disasters.The development direction of transparent geology based on optical fiber sensing technology is proposed in terms of the aspects of sensing optical fiber structure for large deformation monitoring,identification accuracy of optical fiber acoustic signals,multi-parameter monitoring,and early warning methods.
基金National Natural Science Foundation of China,Grant/Award Number:52034010。
文摘Oil and gas exploration studies have been increasingly moving deeper into the earth.The rocks in deep and ultra-deep reservoirs are exposed to a complex environment of high temperatures and large geo-stresses.The Tarim oilfield in the Xinjiang Uygur Autonomous Region(Xinjiang for short),China,has achieved a breakthrough in the exploration of deep hydrocarbon reservoirs at a depth of over 9000 m.The mechanical properties of deep rocks are significantly different from those of shallow rocks.In this study,triaxial compression tests were conducted on heat-treated carbonatite rocks to explore the evolution of the mechanical properties of carbonatite rocks under high confining pressure after thermal treatment.The rocks for the tests were collected from reservoirs in the Tarim oilfield,Xinjiang,China.The experiments were performed at confining pressures ranging from atmospheric to 120 MPa and temperatures ranging from25 to 500°C.The results show that the critical confining pressure of the brittle–ductile transition increases with increasing temperature.Young's modulus is negatively correlated with the temperature and positively correlated with the confining pressure.As the confining pressure increases,the failure mode of the specimens gradually transforms from shear fracture failure into“V”-type failure and finally into bulging failure(multiple shear fractures).With increasing temperature,the failure angle tends to decrease.In addition,an improved version of the Mohr-Coulomb strength criterion with a temperature-dependent power function was proposed to describe the failure strength of carbonatite rocks after exposure to high temperature and high confining pressure.The surface of the strength envelope of this criterion is temperature dependent,which could reflect the strength evolution of rock under high confining pressures after thermal treatment.Compared with other strength criteria,this criterion is more capable of replicating physical processes.
基金Open Project of State Key Laboratory for Geomechanics and Deep Underground Engineering in CUMTB,Grant/Award Number:SKLGDUEK2023National Natural Science Foundation of China,Grant/Award Number:52204101Natural Science Foundation of Shandong Province,Grant/Award Number:ZR2022QE137。
文摘Three sandstone specimens common in rock engineering were selected to study the differences in the mechanical properties of rocks with different lithologies.The development and expansion of the internal cracks in the specimens were observed by combining the simulation system with the acoustic emission system.Through the combination of dynamic and static stresses,the deformation and damage of rocks under deep rock excavation and blasting were simulated.As the results show,the acoustic emission events of specimens with different lithologies under combined static and dynamic cyclic loading can be roughly divided into three phases:weakening,stabilizing,and surging periods.In addition,the acoustic emission characteristics of specimens with different lithologies show general consistency in different compression phases.The degree of fragmentation of specimens increases with the applied stress level;therefore,the stress level is one of the important factors influencing the damage pattern of specimens.The acoustic emission system was used to simulate the deformation and damage of rocks subjected to deep rock body excavation and engineering blasting.Cyclic dynamic perturbations under sinusoidal waves with a frequency of 5 Hz,a loading rate of 0.1 mm/min,a cyclic amplitude of 5 MPa,and a loading rate of 0.1 mm/min were applied to the three rock samples during the experiments.Among them,the fine-grained sandstones are the most sensitive to the sinusoidal cyclic perturbation,followed by the muddy siltstone and the medium-grained sandstones.On this basis,the acoustic emission energy release characteristics were analyzed,and the waveform characteristics in the damage evolution of the specimen under dynamic perturbation were studied by extracting the key points and searching for the main frequency eigenvalues.
基金National Natural Science Foundation of China,Grant/Award Numbers:51708016,12172036R&D Program of Beijing Municipal Education Commission,Grant/Award Number:KM202110016014+1 种基金Government of Perm Krai,Research Project,Grant/Award Numbers:СED-26-08-08-28,С-26/628Graduate Innovation Program of Beijing University of Civil Engineering and Architecture,Grant/Award Number:PG2024035。
文摘Microcrack growth during progressive compressive failure in brittle rocks strongly influences the safety of deep underground engineering.The external shear stressτxy on brittle rocks greatly affects microcrack growth and progressive failure.However,the theoretical mechanism of the growth direction evolution of the newly generated wing crack during progressive failure has rarely been studied.A novel analytical method is proposed to evaluate the shear stress effect on the progressive compressive failure and microcrack growth direction in brittle rocks.This model consists of the wing crack growth model under the principal compressive stresses,the direction correlation of the general stress,the principal stress and the initial microcrack inclination,and the relationship between the wing crack length and strain.The shear stress effect on the relationship between y-direction stress and wing crack growth and the relationship between y-direction stress and y-direction strain are analyzed.The shear stress effect on the wing crack growth direction during the progressive compressive failure is determined.The initial crack angle effect on the y-direction peak stress and the wing crack growth direction during the progressive compressive failure considering shear stress is also discussed.A crucial conclusion is that the direction of wing crack growth has a U-shaped variation with the growth of the wing crack.The rationality of the analytical results is verified by an experiment and from numerical results.The study results provide theoretical support for the evaluation of the safety and stability of surrounding rocks in deep underground engineering.
文摘With recent technological advancements,tunnel boring machines(TBM)have developed and exhibited high performance in large diameters and weak ground conditions.Tunnels are crucial structures that significantly influence the timelines of highway and railway projects.Therefore,the construction of tunnels with TBMs becomes a preferred option.In this study,a comparative analysis between TBM and the New Austrian Tunneling Method(NATM)for tunnel construction is performed in the construction of the T1 tunnel with a diameter of 13 m,which is the longest tunnel in the E?me-Salihli section of Ankara-izmir High-Speed Railway Project(Türkiye).The selection of TBM type,measures taken in problematic sections,and application issues of TBM are discussed.The impact of correct description of geological and geotechnical conditions on both selection and performance of TBM is presented.An earth pressure balanced type TBM is chosen for the construction of the T1 tunnel.Because of the additional engineering measures taken before excavation in problematic areas,the tunnel was completed with great success within the initially planned timeframe.From this point of view,this study is an important case and may contribute to worldwide tunneling literature.
基金National Natural Science Foundation of China,Grant/Award Number:41902292。
文摘Groundwater inrush is a hazard that always occurs during underground mining.Grouting is one of the most effective processes to seal underground water inflow for hazard prevention.In this study,grouting experiments are conducted by using a visualized transparent single-fracture replica with plane roughness.Image processing and analysis are performed to investigate the thermo–hydro–mechanical coupling effect on the grouting diffusion under coal mine flowing water conditions.The results show that higher ambient temperature leads to shorter initial gel time of chemical grout and leads to a better relative sealing efficiency in the case of a lower flow rate.However,with a higher water flow rate,the relative sealing efficiency is gradually reduced under higher temperature conditions.The grouting pressure,the seepage pressure,and the temperature are measured.The results reveal that the seepage pressure shows a positive correlation with the grouting pressure,while the temperature change shows a negative correlation with the seepage pressure and the grouting pressure.The“equivalent grouting point offset”effect of grouting shows an eccentric elliptical diffusion with larger grouting distance and width under lower temperature conditions.
基金The National Natural Science Foundation of China,Grant/Award Number:42130706。
文摘Due to the invisibility and complexity of the underground spaces,monitoring the propagation and filling characteristics of the grouting slurry post the water–sand mixture inrush in metal mines is challenging,which complicates engineering treatment.This research investigated the propagation law of cement-sodium silicate slurry under flowing water conditions within the caving mass of a metal mine.First,based on borehole packer test results and borehole TV images,the fractured strata before grouting were classified into four types:cavity,hidden,fissure,and complete.Second,an orthogonal experimental design was employed to evaluate the impact of four key factors—stratigraphic fragmentation,water flow rate,grouting flow rate,and water-cement ratio—on the efficacy of grouting within a caving mass at the site.The results indicate that the factors influencing grouting efficacy are ranked in the following order of importance:stratigraphic fragmentation>water flow rate>water–cement ratio>grouting flow rate.Ultimately,five propagation filling modes—pure slurry,big crack,small crack,small karst pore,and pore penetration—were identified by examining the propagation filling characteristics of slurry in rock samples,incorporating microscopic material structure analysis through scanning electron microscopy and energy spectrum analysis.The findings of this study provide valuable insights into selecting engineering treatment parameters and methodologies,serving as a reference for preventing and controlling water–sand mixture inrush in metal mines,thereby enhancing treatment efficacy and ensuring grouting success.
基金National Natural Science Foundation of China,Grant/Award Numbers:41977218,42222707State Key Laboratory for GeoMechanics and Deep Underground Engineering,Grant/Award Number:SKLGDUEK2117。
文摘Shield tunnel,composed of several segments,is widely used in urban underground engineering.When the tunnel is under load,relative displacement occurs between adjacent segments.In the past,distributed optical fiber sensing technology was used to perform strain monitoring,but there is an urgent need to determine how to transform strain into displacement.In this study,optical frequency domain reflectometry was applied in laboratory tests.Aiming at the shear process and center settlement process of shield tunnel segments,two kinds of quantitative calculation methods were put forward to carry out a quantitative analysis.Meanwhile,the laboratory test process was simulated numerically utilizing the discrete element numerical analysis method.Optical fiber,an atypical geotechnical material,was innovatively applied for discrete element modeling and numerical simulation.The results show that the measured displacement of the dial gauge,the calculated results of the numerical model,and the displacement quantitatively calculated from the optical fiber data agree with each other in general.The latter two methods can potentially be utilized in engineering application of deformation monitoring at shield tunnel joints,but need to be further calibrated and adjusted in detail.
基金National Key Research and Development Program of China,Grant/Award Number:2022YFC2904100National Natural Science Foundation of China,Grant/Award Number:5220409Beijing Noval Program,Grant/Award Number:20230484242。
文摘The Maoping lead–zinc mining area is a significant metal mine site in northeastern Yunnan.In this study,both hydraulic fracturing in situ stress testing and ultrasonic imaging logging were first carried out in the mining area.Second,930 focal mechanism solutions and 231 sets of stress data near the mining area were collected.Then,the variations in the type of in situ stress field,the magnitude of in situ stress,the direction of horizontal principal stress,and the ratio of lateral pressure were analyzed to characterize the distribution of the in situ stress field.On this basis,a new method using borehole breakouts and drilling-induced fractures was proposed to determine the stress direction.Finally,the evolution of the mechanical properties of dolomite with burial depth was analyzed and the influence of rock mechanical properties on the distributions of the in situ stress field was explored.The results show that the in situ stress in the mining area isσ_(H)>σ_(V)>σ_(h),indicating a strike–slip stress state.The in situ stress is high in magnitude,and its value increases with burial depth.The maximum and minimum horizontal lateral stress coefficients are stabilized at approximately 1.22 and 0.73,respectively.The direction of the maximum horizontal principal stress is NW,mainly ranging from N58.44°W to N59.70°W.The stress field inferred from the focal mechanism solution is in good agreement with the test results.The proportion of structural planes with dip angles between 30°and 75°exceeds 80%,and the dip direction of the structural planes is mainly NW to NWW.The line density of structural planes shows high density in shallow areas and low density in deep areas.More energy tends to be accumulated in rocks with higher elastic modulus and strength,leading to higher in situ stress levels.These findings are of significant reference for mine tunnel layout,support design optimization,and disaster prevention.
基金National Key Research and Development Program of China,Grant/Award Number:2021YFC2902103National Natural Science Foundation of China,Grant/Award Number:51934001Fundamental Research Funds for the Central Universities,Grant/Award Number:2023JCCXLJ02。
文摘Fracture surface contour study is one of the important requirements for characterization and evaluation of the microstructure of rocks.Based on the improved cube covering method and the 3D contour digital reconstruction model,this study proposes a quantitative microstructure characterization method combining the roughness evaluation index and the 3D fractal dimension to study the change rule of the fracture surface morphology after blasting.This method was applied and validated in the study of the fracture microstructure of the rock after blasting.The results show that the fracture morphology characteristics of the 3D contour digital reconstruction model have good correlation with the changes of the blasting action.The undulation rate of the three-dimensional surface profile of the rock is more prone to dramatic rise and dramatic fall morphology.In terms of tilting trend,the tilting direction also shows gradual disorder,with the tilting angle increasing correspondingly.All the roughness evaluation indexes of the rock fissure surface after blasting show a linear and gradually increasing trend as the distance to the bursting center increases;the difference between the two-dimensional roughness evaluation indexes and the three-dimensional ones of the same micro-area rock samples also becomes increasingly larger,among which the three-dimensional fissure roughness coefficient JRC and the surface roughness ratio Rs display better correlation.Compared with the linear fitting formula of the power function relationship,the three-dimensional fractal dimension of the postblast fissure surface is fitted with the values of JRC and Rs,which renders higher correlation coefficients,and the degree of linear fitting of JRC to the three-dimensional fractal dimension is higher.The fractal characteristics of the blast-affected region form a unity with the three-dimensional roughness evaluation of the fissure surface.
文摘This research presents the square root sum of squares response of displacements and tunnel moments under the Kobe and Loma Prieta seismic excitations with a peak ground acceleration of 0.05 g for various dry relative densities of local sand in Bangladesh.For this reason,a one-dimensional gravitational shake table test was performed after calibration to determine the seismic performance of the concrete tunnel-sand-pile interaction model.A vertical 40 kg load was applied on each pile cap along with the seismic excitations.The experimental results obtained were compared with the previous numerical study conducted by using field data so as to better interpret the variations of results.In the case of vertical sand displacement,the ratio between the previous field data obtained through numerical study and the present study is found to be 0.96.Moreover,the experimental results were compared with the 3D full-scale numerical analysis results of Plaxis considering the Mohr-Coulomb constitutive model of sand.Variations of experimental and numerical results show a satisfactory level of alignment with the previously published work.According to the shake table test results,the lateral displacement of the tunnel is greater than the vertical displacement because of the transverse directional seismic excitation on the tunnel body.The minimum difference between lateral and vertical displacements of the tunnel is found to be 31%for a relative density of 27%under the Loma Prieta earthquake.However,this research may be advanced in the future by considering various peak ground accelerations,tunnel-pile clearance,and geometric properties.
