Modern warfare demands weapons capable of penetrating substantial structures,which presents sig-nificant challenges to the reliability of the electronic devices that are crucial to the weapon's perfor-mance.Due to...Modern warfare demands weapons capable of penetrating substantial structures,which presents sig-nificant challenges to the reliability of the electronic devices that are crucial to the weapon's perfor-mance.Due to miniaturization of electronic components,it is challenging to directly measure or numerically predict the mechanical response of small-sized critical interconnections in board-level packaging structures to ensure the mechanical reliability of electronic devices in projectiles under harsh working conditions.To address this issue,an indirect measurement method using the Bayesian regularization-based load identification was proposed in this study based on finite element(FE)pre-dictions to estimate the load applied on critical interconnections of board-level packaging structures during the process of projectile penetration.For predicting the high-strain-rate penetration process,an FE model was established with elasto-plastic constitutive models of the representative packaging ma-terials(that is,solder material and epoxy molding compound)in which material constitutive parameters were calibrated against the experimental results by using the split-Hopkinson pressure bar.As the impact-induced dynamic bending of the printed circuit board resulted in an alternating tensile-compressive loading on the solder joints during penetration,the corner solder joints in the edge re-gions experience the highest S11 and strain,making them more prone to failure.Based on FE predictions at different structural scales,an improved Bayesian method based on augmented Tikhonov regulariza-tion was theoretically proposed to address the issues of ill-posed matrix inversion and noise sensitivity in the load identification at the critical solder joints.By incorporating a wavelet thresholding technique,the method resolves the problem of poor load identification accuracy at high noise levels.The proposed method achieves satisfactorily small relative errors and high correlation coefficients in identifying the mechanical response of local interconnections in board-level packaging structures,while significantly balancing the smoothness of response curves with the accuracy of peak identification.At medium and low noise levels,the relative error is less than 6%,while it is less than 10%at high noise levels.The proposed method provides an effective indirect approach for the boundary conditions of localized solder joints during the projectile penetration process,and its philosophy can be readily extended to other scenarios of multiscale analysis for highly nonlinear materials and structures under extreme loading conditions.展开更多
The stability of the“surrounding rock-backfill”com posite system is crucial for the safety of mining stopes.This study systematically investigates the effects of steel slag(SS)content and interface angle on the stre...The stability of the“surrounding rock-backfill”com posite system is crucial for the safety of mining stopes.This study systematically investigates the effects of steel slag(SS)content and interface angle on the strength and failure characteristics of rock and SS-cemented paste backfill composite specimens(RBCS)through uniaxial compression strength tests(UCS),acoustic emission systems(AE),and 3 D digital image correlation monitoring technology(3 D-DIC).The intrinsic mechanism by which SS content influences the strength of SS-CPB was revealed through an analysis of its hydration reaction degree and microstructural characteristics under varying SS content.Moreover,a theoretical strength model incorporating different interface angles was developed to explore the impact of interface inclination on failure modes and mechanical strength.The main conclusions are as follows:The incorporation of SS enhances the plastic characteristics of RBCS and reduces its brittleness,with the increase of SS content,the stress-strain curve of RBCS in the“staircase-like”stag e becomes smoother;When the interface angle is 45°,the RBCS stress-strain curve exhibits a bimodal feature,and the failure mode changes from Y-shaped fractures to interface and axial splitting;The addition of SS results in a reduction of hydration products such as Ca(OH)_(2) in the backfill cementing system and an increase in harmful pores,which weakens the bonding performance and strength of RBCS,and the SS content should not exceed 45%;As the interface angle increases,the strength of RBCS decreases,and the critical interface slip angle decreases first and then increases with the increase in the E S/E R ratio.This study provides technical references for the large-scale application of SS in mine backfill.展开更多
This study proposed a new and more flexible S-shaped rock damage evolution model from a phenomenological perspective based on an improved Logistic function to describe the characteristics of the rock strain softening ...This study proposed a new and more flexible S-shaped rock damage evolution model from a phenomenological perspective based on an improved Logistic function to describe the characteristics of the rock strain softening and damage process.Simultaneously,it established a constitutive model capable of describing the entire process of rock pre-peak compaction and post-peak strain softening deformation,considering the nonlinear effects of the initial compaction stage of rocks,combined with damage mechanics theory and effective medium theory.In addition,this research verified the rationality of the constructed damage constitutive model using results from uniaxial and conventional triaxial compression tests on Miluo granite,yellow sandstone,mudstone,and glutenite.The results indicate that based on the improved Logistic function,the theoretical damage model accurately describes the entire evolution of damage characteristics during rock compression deformation,from maintenance through gradual onset,accelerated development to deceleration and termination,in a simple and unified expression.At the same time,the constructed constitutive model can accurately simulate the stress-strain process of different rock types under uniaxial and conventional triaxial compression,and the theoretical model curve closely aligns with experimental data.Compared to existing constitutive models,the proposed model has significant advantages.The damage model parameters a,r and β have clear physical meanings and interact competitively,where the three parameters collectively determine the shape of the theoretical stress−strain curve.展开更多
The intersection is a widely used traffic line structure from the shallow tunnel to the deep roadway,and determining the subsidence hidden danger area of the roof is the key to its stability control.However,applying t...The intersection is a widely used traffic line structure from the shallow tunnel to the deep roadway,and determining the subsidence hidden danger area of the roof is the key to its stability control.However,applying traditional maximum equivalent span beam(MESB)theory to determine deformation range,peak point,and angle influence poses a challenge.Considering the overall structure of the intersection roof,the maximum equivalent triangular plate(METP)theory is proposed,and its geometric parameter calculation formula and deflection calculation formula are obtained.The application of the two theories in 18 models with different intersection angles,roadway types,and surrounding rock lithology is verified by numerical analysis.The results show that:1)The METP structure of the intersection roof established by the simulation results of each model successfully determined the location of the roof’s high displacement zone;2)The area comparison method of the METP theory can be reasonably explained:①The roof subsidence of the intersection decreases with the increase of the intersection angle;②The roof subsidence at the intersection of different roadway types has a rectangular type>arch type>circular type;③The roof subsidence of the intersection with weak surrounding rock is significantly larger than that of the intersection with hard surrounding rock.According to the application results of the two theories,the four advantages of the METP theory are compared and clarified in the basic assumptions,mechanical models,main viewpoints,and mechanism analysis.The large deformation inducement of the intersection roof is then explored.The J 2 peak area of the roof drives the large deformation of the area,the peak point of which is consistent with the center of gravity position of the METP.Furthermore,the change in the range of this peak is consistent with the change law of the METP’s area.Hence,this theory clarifies the large deformation area of the intersection roof,which provides a clear guiding basis for its initial support design,mid-term monitoring,and late local reinforcement.展开更多
This study investigates the instability characteristics of dynamic disasters resulting from disruption caused by extracting resources underground. Utilizing the split Hopkinson pressure bar (SHPB) system, the dynamic ...This study investigates the instability characteristics of dynamic disasters resulting from disruption caused by extracting resources underground. Utilizing the split Hopkinson pressure bar (SHPB) system, the dynamic response mechanism of coal energy evolution is examined, and the energy instability criterion is established. The validity of the instability criterion is explored from the standpoint of damage progression. The results demonstrate that the energy conversion mechanism undergoes a fundamental alternation under impact disturbance. Moreover, the energy release rate as well as the energy dissipation rate undergo comparable changes across distinct levels of impact disturbance. The distinction between the energy release rate and the energy dissipation rate (DRD) increases as coal mass deformation grows. Prior to coal facing instability and failure, the DRD experienced an inflection point followed by a sharp decrease. In conjunction with the discussion on the damage evolution, the physical and mechanical significance of DRD remains clear, which can essentially describe the whole impact loading process. The phenomenon that the inflection point appears and DRD subsequently suddenly decreases can be employed as the energy criterion prior to the failure of instability. Furthermore, this paper provides significant reference for the prediction of dynamic instability of coal under dynamic disturbance.展开更多
To investigate the effects of water and cyclic loading on dolomite’s mechanical properties during deep mining,mechanical experiments on non-pressure water absorption and cyclic loading were conducted.The findings rev...To investigate the effects of water and cyclic loading on dolomite’s mechanical properties during deep mining,mechanical experiments on non-pressure water absorption and cyclic loading were conducted.The findings reveal that the elastic modulus and Poisson ratio of dolomite fluctuate with increasing water content.The mass of water absorption is positively correlated with time and the water absorption stage can be divided into three stages:accelerated,decelerated,and stabilized stages.During this process,the number of pores in dolomite increases,while the pore diameter initially decreases and then fluctuates.Microscopic analysis shows that the proportion of mesopores first increases and then decreases,while micropores exhibit the opposite trend,and the proportion of macropores fluctuates around 0%.A model diagram of structural evolution during water absorption has been developed.Additionally,the softening process of dolomite’s water absorption strength is categorized into three stages:a relatively stable stage,an accelerated softening stage dominated by mesopore water absorption,and a decelerated softening stage characterized by micropore water absorption.A uniaxial damage constitutive model for dolomite under water influence was established based on the Weibull distribution and Mohr-Coulomb strength criterion,and experimental validation indicates its strong applicability.展开更多
Water is a critical factor affecting the mechanical properties of rocks, leading to their degradation. Understanding the creep mechanical behavior of deep roadway surrounding rock under the influence of underground wa...Water is a critical factor affecting the mechanical properties of rocks, leading to their degradation. Understanding the creep mechanical behavior of deep roadway surrounding rock under the influence of underground water is of great significance. Compression and creep experiments on sandstone with varying water contents were conducted using a deep soft rock five-linked rheological experiment system. The experimental conditions, including water content (0%, 0.8%, 1.6%, 2.4% and 3.3%) and confining pressure (0, 6, 9 and 12 MPa), were determined based on pressure-free water absorption tests and in-situ stress measurements. The experimental results show that the compressive strength, creep failure stress, and dilatancy stress of sandstone decrease exponentially with increasing water content, while they increase exponentially with confining pressure. The ratio of lateral to axial instantaneous strain increases nearly linearly with the increase of stress, and the lateral creep strain characteristics of the sample are more significant than the axial ones. The duration of the attenuation creep stage of sandstone decreases with increasing water content and increases with increasing confining pressure. The lateral strain enters the steady-state creep stage before the axial strain, and the onset time of the accelerated creep stage of lateral strain under the failure stress is earlier than that of axial strain. The long-term strength of sandstone was determined based on the lateral steady-state creep rate curve, showing a negative exponential relationship with water content and a positive exponential relationship with confining pressure. A method for determining the long-term strength of rocks based on the ratio of lateral strain to axial strain (μc) is proposed, which is independent of water content. The research results provide a reliable theoretical basis for the analysis of the long-term stability of roadways under the influence of groundwater and the early prediction of creep failure.展开更多
The stability of the roof in coal mining is crucial for ensuring safe extraction.Studying the mechanical behavior of rock beams under various conditions is essential for improving coal mining safety.However,research o...The stability of the roof in coal mining is crucial for ensuring safe extraction.Studying the mechanical behavior of rock beams under various conditions is essential for improving coal mining safety.However,research on the dynamic response of rock beams under sudden unloading remains limited.This study utilized a self-developed bidirectional loading and unilateral unloading test system to simulate how sudden lower strata subsidence induces the fracture of upper hard rock beams.Bottom unloading experiments were performed on rock beams with varying thicknesses and spans.The experiments recorded surface crack development and internal damage evolution using high speed photography and acoustic emission monitoring.The results show that rock beams experience multiple stress reductions after unloading,with the largest reduction occurring in the first stage.Flexural deformation was observed,becoming more pronounced as the thickness-span ratio decreased.Greater thickness increased shear cracks and crack expansion angles,while larger spans promoted tensile cracks,arched crack formation,and notable rock spalling.Acoustic emission analysis showed that signal count and energy increased with thickness and span.Finally,discrete element numerical simulations revealed the critical controlling role of harder rock strata in rock beam failure:when the harder strata are at the top,cracks are sharp,and shear failure is more likely;when they are at the bottom,the overall failure range expands,and cracks tend to form arches.These findings improve the understanding of dynamic rock beam fracture under sudden unloading and offer theoretical guidance for roof stability control in deep mining.展开更多
Aiming at the problem of deep surrounding rock instability induced by roadway excavation or mining disturbance,the true triaxial loading system was used to conduct graded cyclic maximum principal stress σ_(1) and int...Aiming at the problem of deep surrounding rock instability induced by roadway excavation or mining disturbance,the true triaxial loading system was used to conduct graded cyclic maximum principal stress σ_(1) and intermediate principal stress σ_(2) tests on sandstone to simulate the effect of mining stress in actual underground engineering.The influences of each principal stress cycle on the mechanical properties,acoustic emission(AE)characteristics,and fracture characteristics of sandstone were analyzed.The damage characteristics of sandstone under true triaxial cyclic loading were studied.Furthermore,the damage constitutive model of rock mass under true triaxial cyclic loading was established based on AE cumulative ringing count.The quantitative investigation was conducted on cumulative-damage changes in circulating sandstone,which elucidated the mechanism of damage deterioration in sandstone subjected to true triaxial cyclic loading.The results show that the influence of the graded cycleσ_(1) on limit maximum principal strain ɛ_(1max) and limit minimum principal strainɛ_(3max) was significantly greater than that of the limit intermediate principal strain ɛ_(2max).Graded cycleσ_(2) had a greater impact onɛ_(2max) and a smaller impact onɛ_(3max).The elasticity modulus of sandstone decreased exponentially with the increased cyclic load amplitude,while the Poisson ratio increased linearly.b of AE showed a trend of increasing,decreasing,slightly fluctuating,and finally decreasing during cyclingσ_(1).b showed a trend of slight fluctuation,large fluctuation,and finally increase during cyclingσ_(2).Sandstone specimens experienced mainly tensile failure,tensile-shear composite failure,and mainly shear failure with increased initialσ_(2) orσ_(3).This was determined by analyzing the rise angle-average frequency of the AE parameter,corresponding to the rock specimens from splitting failure to shear failure.Besides,the mechanical damage behavior of sandstone under true triaxial cyclic loading could be well described by the established constitutive model.At the same time,it was found that the sandstone damage variable decreased with increasedσ_(2) during cyclingσ_(1).The damage variable decreased first and then increased with increasedσ_(3) during cyclingσ_(2).展开更多
The ratio of crack initiation stress to the uniaxial compressive strength(SCI,B/SUC,B) and the ratio of axial strain at the crack initiation stress to the axial strain at the uniaxial compressive strength(B,UCB,CI,A,A...The ratio of crack initiation stress to the uniaxial compressive strength(SCI,B/SUC,B) and the ratio of axial strain at the crack initiation stress to the axial strain at the uniaxial compressive strength(B,UCB,CI,A,A/SSSS) were studied by performing numerical stress analysis on blocks having multi flaws at close spacing's under uniaxial loading using PFC3 D. The following findings are obtained: SCI,B/SUC,B has an average value of about 0.5 with a variability of ± 0.1. This range agrees quite well with the values obtained by former research. For joint inclination angle, β=90°,B,UCB,CI,A,A/SSSS is found to be around 0.48 irrespective of the value of joint continuity factor, k. No particular relation is found betweenB,UCB,CI,A,A/SSSS and β; however, the average B,UCB,CI,A,A/SSSS seems to slightly decrease with increasing k. The variability ofB,UCB,CI,A,A/SSSS is found to increase with k.Based on the cases studied in this work,B,UCB,CI,A,A/SSSS ranges between 0.3 and 0.5. This range is quite close to the range of 0.4to 0.6 obtained for SCI,B/SUC,B. The highest variability of ± 0.12 forB,UCB,CI,A,A/SSSS is obtained for k=0.8. For the remaining k values the variability ofB,UCB,CI,A,A/SSSS can be expressed within ± 0.05. This finding is very similar to the finding obtained for the variability of SCI,B/SUC,B.展开更多
A series of laboratory experiments and PFC numerical simulations for rock-like material specimens containing two unparallel fissures were carried out.On the basis of experimental and numerical results,the stress-strai...A series of laboratory experiments and PFC numerical simulations for rock-like material specimens containing two unparallel fissures were carried out.On the basis of experimental and numerical results,the stress-strain curves,mechanical properties,AE events,cracking behavior and energy characteristics were analyzed to reveal the macro-mechanical behavior and meso-mechanism of pre-fissured specimens under different loading rates.Investigated results show that:1)When the loading rate is relatively low,the stress-strain curves show a brittle response.When the loading rate is relatively high,the curve shows a more ductile response.Both of the peak strength and elastic mudulus increase with the increase of loading rate,which can be expressed as power functions.2)Four crack types are identified,i.e.,tensile crack,shear crack,far-field crack and surface spalling.Moreover,the tensile crack,far-field crack and surface spalling are under tensile mechanism,while the shear crack is under shear mechanism.3)The drops of the stress-strain curves all correspond to the crack initiation or coalescence,which is also linked to a sudden increasing in the accumulated micro-crack curve.4)Both of the maximum bond force and energy have the similar trend with the increase of loading rate to peak strength,which indicates that the trend of peak strength can be explained by the meso-mechanics and energy.展开更多
Geometrical nonlinearity of the soft soil and the deviation of water flow in the soft clay from Darcy's law have been well recognized in practice. However, the theory of consolidation, which can account for both t...Geometrical nonlinearity of the soft soil and the deviation of water flow in the soft clay from Darcy's law have been well recognized in practice. However, the theory of consolidation, which can account for both the geometrical nonlinearity and the non-Darcian flow, has not been reported so far. In this contribution, a model for the consolidation of soft clay which can allow for these two factors simultaneously is proposed. Utilizing the finite difference method, the numerical model for this problem is developed. With the numerical model, the effects of the geometrical nonlinearity and the non-Darcian flow on the consolidation of the soft soil are investigated. The results show that when the self-weight stress is calculated by the same method, the rate of the non-Darcian consolidation for the large-strain case is larger than that for the small-strain case, but the difference between them is limited. However, the difference between the consolidation rates caused by the non-Darcian and Darcian flows is significant. Therefore, when the geometrical nonlinearity of the soft clay is considered in calculating the consolidation settlement, due to the complexity of the large-strain assumption, the small-strain assumption can be used to replace it if the self-weight stress for the small-strain assumption is calculated by considering its sedimentation. However, due to the aforementioned large difference between the consolidation rates with consideration of the non-Darcian flow in soft clay or not, it is better to consider the non-Darcian flow law for both the small and large stain assumptions.展开更多
Anisotropic strength and deformability of the rock mass with non-persistent joints are governed by cracking process of the rock bridges. The dependence of cracking process of jointed rock masses on the two important g...Anisotropic strength and deformability of the rock mass with non-persistent joints are governed by cracking process of the rock bridges. The dependence of cracking process of jointed rock masses on the two important geometrical parameters, joint orientation and joint persistence, was studied systematically by carrying out a series of uniaxial compression tests on gypsum specimens with regularly arranged multiple parallel pre-existing joints. According to crack position, mechanism and temporal sequence, seven types of crack initiations and sixteen types of crack coalescences, were identified. It was observed that both tensile cracks and shear cracks can emanate from the pre-existing joints as well as the matrix. Vertical joints were included and coplanar tensile cracks initiation and coalescence were observed accordingly. For specimen with joint inclination angle ,8=75~, it was found that collinear joints can be linked not only by coplanar shear cracks but also by mixed tensile-shear cracks, and that a pair of them can form a small rotation block. Seven failure modes, including axial cleavage, crushing, crushing and rotation of new blocks, stepped failure, stepped failure and rotation of new blocks, shear failure along a single plane and shear failure along multiple planes, were observed. These modes shift gradually in accordance with the combined variation of joint orientation and joint persistence. It is concluded that cracking process and failure modes are more strongly affected by joint orientation than by joint persistence, especially when joint inclination angle is larger than 45~. Finally, variations of macroscopic mechanical behaviors with the two geometrical parameters, such as patterns of the complete axial stress-axial strain curves, peak strength and elastic modulus, are summarized and their mechanisms are successfully explained according to their different cracking process.展开更多
Fissures play a significant role in predicting the unstable failure of rock mass engineering.For deep rock underground engineering,rock mass containing pre-existing fissures is usually located in triaxial stress state...Fissures play a significant role in predicting the unstable failure of rock mass engineering.For deep rock underground engineering,rock mass containing pre-existing fissures is usually located in triaxial stress state.Therefore,not only pre-existing fissure but also confining pressure affects the failure mechanical behavior of rock material.In this research,the granite specimens containing two non-coplanar open fissures were investigated by a series of conventional triaxial compression tests.First,the effect of bridge angle and confining pressure on strength and deformation characteristics of granite specimens was evaluated.Results show that the triaxial compressive strength,failure axial strain,and crack damage threshold increased nonlinearly with confining pressure.Under high confining pressures,elastic modulus was insensitive to bridge angle.Then,an X-ray micro-CT scanning technique was used to analyze the internal fracture characteristics of granite specimens with respect to various bridge angles and confining pressures.Five typical crack coalescence modes were identified,namely,indirect coalescence,shear coalescence and three types of tensile coalescence.The reconstructed 3-D CT images indicated that under uniaxial or low confining pressures,the bridge angle had a significant effect on crack evolution behavior,while under high confining pressures,shear-dominated failures occurred with the development of anti-wing cracks.展开更多
Eccentric decoupling blasting is commonly used in underground excavation.Determination of perimeter hole parameters(such as the blasthole diameter,spacing,and burden)based on an eccentric charge structure is vital for...Eccentric decoupling blasting is commonly used in underground excavation.Determination of perimeter hole parameters(such as the blasthole diameter,spacing,and burden)based on an eccentric charge structure is vital for achieving an excellent smooth blasting effect.In this paper,the Riedel-Hiermaier-Thoma(RHT)model was employed to study rock mass damage under smooth blasting.Firstly,the parameters of the RHT model were calibrated by using the existing SHPB experiment,which were then verified by the existing blasting experiment results.Secondly,the influence of different charge structures on the blasting effect was investigated using the RHT model.The simulation results indicated that eccentric charge blasting has an obvious pressure eccentricity effect.Finally,to improve the blasting effect,the smooth blasting parameters were optimized based on an eccentric charge structure.The overbreak and underbreak phenomena were effectively controlled,and a good blasting effect was achieved with the optimized blasting parameters.展开更多
By adopting cyclic increment loading and unloading method, time-independent and time-dependent strains can be separated. It is more reasonable to describe the reversible and the irreversible deformations of sample sep...By adopting cyclic increment loading and unloading method, time-independent and time-dependent strains can be separated. It is more reasonable to describe the reversible and the irreversible deformations of sample separately during creep process. A nonlinear elastic-visco-plastic rheological model is presented to characterize the time-based deformational behavior of hard rock. Specifically, a spring element is used to describe reversible instantaneous elastic deformation. A reversible nonlinear visco-elastic （RNVE） model is developed to characterize recoverable visco-elastic response. A combined model, which contains a fractional derivative dashpot in series with another Hook’s body, and a St. Venant body in parallel with them, is proposed to describe irreversible visco-plastic deformation. Furthermore, a three-stage damage equation based on strain energy is developed in the visco-plastic portion and then nonlinear elastic-visco-plastic rheological damage model is established to explain the trimodal creep response of hard rock. Finally, the proposed model is validated by a laboratory triaxial rheological experiment. Comparing with theoretical and experimental results, this rheological damage model characterizes well the reversible and irreversible deformations of the sample, especially the tertiary creep behavior.展开更多
For the 110 mining method,it is challenging to accurately calculate the support resistance of the roadway due to the lack of understanding of the dynamic movement of the overlying strata in this method.The consequenti...For the 110 mining method,it is challenging to accurately calculate the support resistance of the roadway due to the lack of understanding of the dynamic movement of the overlying strata in this method.The consequential excessive support results in a significant increase in the cost of roadway support.The authors explored the overlying strata movement and roadway deformation of the gob-entry retaining in the 110 mining method to solve this problem.First,the typical stages of the roof-cutting gob-side entry were defined.Second,the mechanical model and calculation formula of the support resistance on the roof were explored.Then,using numerical simulation software,the starting ranges of the specific supports at different stages were verified and the feasibility of the support scheme was examined.Finally,combined with the field measurement data,the stress and the deformation of the gob roadway at different stages under the influence of two mining processes in the 110 mining method were obtained.The numerical simulation results obtained are consistent with the field test results,providing a theoretical basis for precision support at different stages by the 110 mining method.展开更多
Rockburst is a dynamic phenomenon accompanied by acoustic emission(AE)activities.It is difficult to predict rockburst accurately.Based on the fast Fourier transform(FFT)method and the information entropy theory,the ev...Rockburst is a dynamic phenomenon accompanied by acoustic emission(AE)activities.It is difficult to predict rockburst accurately.Based on the fast Fourier transform(FFT)method and the information entropy theory,the evolution model of dominant frequency entropy was established.The AE energy,frequency and stress were synthetically considered to predict rockburst.Under the triaxial and the single-face unloading tests,the relationship between AE energy and the development of internal cracks was analyzed.Using the FFT method,the distribution characteristics of AE dominant frequency values were obtained.Based on the information entropy theory,the dominant frequencies evolved patterns were ascertained.It was observed that the evolution models of the dominant frequency entropy were nearly the same and shared a characteristic“undulation-decrease-rise-sharp decrease”pattern.Results show that AE energy will be released suddenly before rockburst.The density of intermediate frequency increased prior to rockburst.The dominant frequency entropy reached a relative maximum value before rockburst,and then decreased sharply.These features could be used as a precursory information for predicting rockburst.The proposed relative maximum value could be as a key point to predict rockburst.This is a meaningful attempt on predicting rockburst.展开更多
Permeability is a vital property of rock mass, which is highly affected by tectonic stress and human engineering activities. A comprehensive monitoring of pore pressure and flow rate distributions inside the rock mass...Permeability is a vital property of rock mass, which is highly affected by tectonic stress and human engineering activities. A comprehensive monitoring of pore pressure and flow rate distributions inside the rock mass is very important to elucidate the permeability evolution mechanisms, which is difficult to realize in laboratory, but easy to be achieved in numerical simulations. Therefore, the particle flow code （PFC）, a discrete element method, is used to simulate permeability behaviors of rock materials in this study. Owe to the limitation of the existed solid-fluid coupling algorithm in PFC, an improved flow-coupling algorithm is presented to better reflect the preferential flow in rock fractures. The comparative analysis is conducted between original and improved algorithm when simulating rock permeability evolution during triaxial compression, showing that the improved algorithm can better describe the experimental phenomenon. Furthermore, the evolution of pore pressure and flow rate distribution during the flow process are analyzed by using the improved algorithm. It is concluded that during the steady flow process in the fractured specimen, the pore pressure and flow rate both prefer transmitting through the fractures rather than rock matrix. Based on the results, fractures are divided into the following three types： I） fractures link to both the inlet and outlet, II） fractures only link to the inlet, and III） fractures only link to the outlet. The type I fracture is always the preferential propagating path for both the pore pressure and flow rate. For type II fractures, the pore pressure increases and then becomes steady. However, the flow rate increases first and begins to decrease after the flow reaches the stop end of the fracture and finally vanishes. There is no obvious pore pressure or flow rate concentration within type III fractures.展开更多
Rockburst is one of the major disasters in deep underground rock mechanics and engineering.The precursors of rockbursts play important roles in rockburst prediction.Strainburst experiments were performed under double-...Rockburst is one of the major disasters in deep underground rock mechanics and engineering.The precursors of rockbursts play important roles in rockburst prediction.Strainburst experiments were performed under double-face unloading on sandstone with horizontal bedding planes using an independently designed rockburst testing facility.P-wave propagation time during the tests was automatically recorded by the acoustic emission apparatus.The P-wave velocities were calculated in both two directions to analyze their patterns.To find a characteristic precursor for rockburst,the dynamic evolution of rock anisotropy during the rockburst test is quantified by the anisotropic coefficient k,defined as the ratio of the two P-wave velocities in the directions vertical to and parallel to the bedding planes.The results show that rockburst occurs on the two free surfaces asynchronously.The rockburst failure occurs in the following order:crack generation,rock peeling,particle ejection,and rock fracture.In the process of rockburst under double-face unloading,the potential evolution characteristics of anisotropy can be generalized as anisotropy-isotropy-anisotropy.The suddenly unloading induces damage in the rock and presents anisotropic coefficient k steeply increasing departing from one,i.e.,isotropy.The rocks with horizontal bedding planes will reach the isotropic state before rockburst,which could be considered as a characteristic precursor of this kind of rockburst.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.52475166,52175148)the Regional Collaboration Project of Shanxi Province(Grant No.202204041101044).
文摘Modern warfare demands weapons capable of penetrating substantial structures,which presents sig-nificant challenges to the reliability of the electronic devices that are crucial to the weapon's perfor-mance.Due to miniaturization of electronic components,it is challenging to directly measure or numerically predict the mechanical response of small-sized critical interconnections in board-level packaging structures to ensure the mechanical reliability of electronic devices in projectiles under harsh working conditions.To address this issue,an indirect measurement method using the Bayesian regularization-based load identification was proposed in this study based on finite element(FE)pre-dictions to estimate the load applied on critical interconnections of board-level packaging structures during the process of projectile penetration.For predicting the high-strain-rate penetration process,an FE model was established with elasto-plastic constitutive models of the representative packaging ma-terials(that is,solder material and epoxy molding compound)in which material constitutive parameters were calibrated against the experimental results by using the split-Hopkinson pressure bar.As the impact-induced dynamic bending of the printed circuit board resulted in an alternating tensile-compressive loading on the solder joints during penetration,the corner solder joints in the edge re-gions experience the highest S11 and strain,making them more prone to failure.Based on FE predictions at different structural scales,an improved Bayesian method based on augmented Tikhonov regulariza-tion was theoretically proposed to address the issues of ill-posed matrix inversion and noise sensitivity in the load identification at the critical solder joints.By incorporating a wavelet thresholding technique,the method resolves the problem of poor load identification accuracy at high noise levels.The proposed method achieves satisfactorily small relative errors and high correlation coefficients in identifying the mechanical response of local interconnections in board-level packaging structures,while significantly balancing the smoothness of response curves with the accuracy of peak identification.At medium and low noise levels,the relative error is less than 6%,while it is less than 10%at high noise levels.The proposed method provides an effective indirect approach for the boundary conditions of localized solder joints during the projectile penetration process,and its philosophy can be readily extended to other scenarios of multiscale analysis for highly nonlinear materials and structures under extreme loading conditions.
基金Project(52308316)supported by the National Natural Science Foundation of China,Project(BBJ2024088)supported by the Fundamental Research Funds for the Central Universities(PhD.Top Innovative Talents Fund of CUMTB),China。
文摘The stability of the“surrounding rock-backfill”com posite system is crucial for the safety of mining stopes.This study systematically investigates the effects of steel slag(SS)content and interface angle on the strength and failure characteristics of rock and SS-cemented paste backfill composite specimens(RBCS)through uniaxial compression strength tests(UCS),acoustic emission systems(AE),and 3 D digital image correlation monitoring technology(3 D-DIC).The intrinsic mechanism by which SS content influences the strength of SS-CPB was revealed through an analysis of its hydration reaction degree and microstructural characteristics under varying SS content.Moreover,a theoretical strength model incorporating different interface angles was developed to explore the impact of interface inclination on failure modes and mechanical strength.The main conclusions are as follows:The incorporation of SS enhances the plastic characteristics of RBCS and reduces its brittleness,with the increase of SS content,the stress-strain curve of RBCS in the“staircase-like”stag e becomes smoother;When the interface angle is 45°,the RBCS stress-strain curve exhibits a bimodal feature,and the failure mode changes from Y-shaped fractures to interface and axial splitting;The addition of SS results in a reduction of hydration products such as Ca(OH)_(2) in the backfill cementing system and an increase in harmful pores,which weakens the bonding performance and strength of RBCS,and the SS content should not exceed 45%;As the interface angle increases,the strength of RBCS decreases,and the critical interface slip angle decreases first and then increases with the increase in the E S/E R ratio.This study provides technical references for the large-scale application of SS in mine backfill.
基金Project(52074299)supported by the National Natural Science Foundation of ChinaProjects(2023JCCXSB02,BBJ2024083)supported by the Fundamental Research Funds for the Central Universities,China。
文摘This study proposed a new and more flexible S-shaped rock damage evolution model from a phenomenological perspective based on an improved Logistic function to describe the characteristics of the rock strain softening and damage process.Simultaneously,it established a constitutive model capable of describing the entire process of rock pre-peak compaction and post-peak strain softening deformation,considering the nonlinear effects of the initial compaction stage of rocks,combined with damage mechanics theory and effective medium theory.In addition,this research verified the rationality of the constructed damage constitutive model using results from uniaxial and conventional triaxial compression tests on Miluo granite,yellow sandstone,mudstone,and glutenite.The results indicate that based on the improved Logistic function,the theoretical damage model accurately describes the entire evolution of damage characteristics during rock compression deformation,from maintenance through gradual onset,accelerated development to deceleration and termination,in a simple and unified expression.At the same time,the constructed constitutive model can accurately simulate the stress-strain process of different rock types under uniaxial and conventional triaxial compression,and the theoretical model curve closely aligns with experimental data.Compared to existing constitutive models,the proposed model has significant advantages.The damage model parameters a,r and β have clear physical meanings and interact competitively,where the three parameters collectively determine the shape of the theoretical stress−strain curve.
基金Project(52204164)supported by the National Natural Science Foundation of ChinaProject(2021QNRC001)supported by the Young Elite Scientists Sponsorship Program by CAST,China。
文摘The intersection is a widely used traffic line structure from the shallow tunnel to the deep roadway,and determining the subsidence hidden danger area of the roof is the key to its stability control.However,applying traditional maximum equivalent span beam(MESB)theory to determine deformation range,peak point,and angle influence poses a challenge.Considering the overall structure of the intersection roof,the maximum equivalent triangular plate(METP)theory is proposed,and its geometric parameter calculation formula and deflection calculation formula are obtained.The application of the two theories in 18 models with different intersection angles,roadway types,and surrounding rock lithology is verified by numerical analysis.The results show that:1)The METP structure of the intersection roof established by the simulation results of each model successfully determined the location of the roof’s high displacement zone;2)The area comparison method of the METP theory can be reasonably explained:①The roof subsidence of the intersection decreases with the increase of the intersection angle;②The roof subsidence at the intersection of different roadway types has a rectangular type>arch type>circular type;③The roof subsidence of the intersection with weak surrounding rock is significantly larger than that of the intersection with hard surrounding rock.According to the application results of the two theories,the four advantages of the METP theory are compared and clarified in the basic assumptions,mechanical models,main viewpoints,and mechanism analysis.The large deformation inducement of the intersection roof is then explored.The J 2 peak area of the roof drives the large deformation of the area,the peak point of which is consistent with the center of gravity position of the METP.Furthermore,the change in the range of this peak is consistent with the change law of the METP’s area.Hence,this theory clarifies the large deformation area of the intersection roof,which provides a clear guiding basis for its initial support design,mid-term monitoring,and late local reinforcement.
基金Projects(51934007,12072363,52004268) supported by the National Natural Science Foundation of ChinaProject(22KJD440002) supported by the Natural Science Fund for Colleges and Universities in Jiangsu Province,China。
文摘This study investigates the instability characteristics of dynamic disasters resulting from disruption caused by extracting resources underground. Utilizing the split Hopkinson pressure bar (SHPB) system, the dynamic response mechanism of coal energy evolution is examined, and the energy instability criterion is established. The validity of the instability criterion is explored from the standpoint of damage progression. The results demonstrate that the energy conversion mechanism undergoes a fundamental alternation under impact disturbance. Moreover, the energy release rate as well as the energy dissipation rate undergo comparable changes across distinct levels of impact disturbance. The distinction between the energy release rate and the energy dissipation rate (DRD) increases as coal mass deformation grows. Prior to coal facing instability and failure, the DRD experienced an inflection point followed by a sharp decrease. In conjunction with the discussion on the damage evolution, the physical and mechanical significance of DRD remains clear, which can essentially describe the whole impact loading process. The phenomenon that the inflection point appears and DRD subsequently suddenly decreases can be employed as the energy criterion prior to the failure of instability. Furthermore, this paper provides significant reference for the prediction of dynamic instability of coal under dynamic disturbance.
基金Project(IMRI23005)supported by Ordos Science and Technology Bureau,ChinaProjects(52174096,52304110)supported by the National Natural Science Foundation of China。
文摘To investigate the effects of water and cyclic loading on dolomite’s mechanical properties during deep mining,mechanical experiments on non-pressure water absorption and cyclic loading were conducted.The findings reveal that the elastic modulus and Poisson ratio of dolomite fluctuate with increasing water content.The mass of water absorption is positively correlated with time and the water absorption stage can be divided into three stages:accelerated,decelerated,and stabilized stages.During this process,the number of pores in dolomite increases,while the pore diameter initially decreases and then fluctuates.Microscopic analysis shows that the proportion of mesopores first increases and then decreases,while micropores exhibit the opposite trend,and the proportion of macropores fluctuates around 0%.A model diagram of structural evolution during water absorption has been developed.Additionally,the softening process of dolomite’s water absorption strength is categorized into three stages:a relatively stable stage,an accelerated softening stage dominated by mesopore water absorption,and a decelerated softening stage characterized by micropore water absorption.A uniaxial damage constitutive model for dolomite under water influence was established based on the Weibull distribution and Mohr-Coulomb strength criterion,and experimental validation indicates its strong applicability.
基金Projects(52174096, 52304110) supported by the National Natural Science Foundation of China。
文摘Water is a critical factor affecting the mechanical properties of rocks, leading to their degradation. Understanding the creep mechanical behavior of deep roadway surrounding rock under the influence of underground water is of great significance. Compression and creep experiments on sandstone with varying water contents were conducted using a deep soft rock five-linked rheological experiment system. The experimental conditions, including water content (0%, 0.8%, 1.6%, 2.4% and 3.3%) and confining pressure (0, 6, 9 and 12 MPa), were determined based on pressure-free water absorption tests and in-situ stress measurements. The experimental results show that the compressive strength, creep failure stress, and dilatancy stress of sandstone decrease exponentially with increasing water content, while they increase exponentially with confining pressure. The ratio of lateral to axial instantaneous strain increases nearly linearly with the increase of stress, and the lateral creep strain characteristics of the sample are more significant than the axial ones. The duration of the attenuation creep stage of sandstone decreases with increasing water content and increases with increasing confining pressure. The lateral strain enters the steady-state creep stage before the axial strain, and the onset time of the accelerated creep stage of lateral strain under the failure stress is earlier than that of axial strain. The long-term strength of sandstone was determined based on the lateral steady-state creep rate curve, showing a negative exponential relationship with water content and a positive exponential relationship with confining pressure. A method for determining the long-term strength of rocks based on the ratio of lateral strain to axial strain (μc) is proposed, which is independent of water content. The research results provide a reliable theoretical basis for the analysis of the long-term stability of roadways under the influence of groundwater and the early prediction of creep failure.
基金Project(TD20240003)supported by the Ordos Science&Technology Plan,ChinaProjects(52174096,52304110)supported by the National Natural Science Foundation of China。
文摘The stability of the roof in coal mining is crucial for ensuring safe extraction.Studying the mechanical behavior of rock beams under various conditions is essential for improving coal mining safety.However,research on the dynamic response of rock beams under sudden unloading remains limited.This study utilized a self-developed bidirectional loading and unilateral unloading test system to simulate how sudden lower strata subsidence induces the fracture of upper hard rock beams.Bottom unloading experiments were performed on rock beams with varying thicknesses and spans.The experiments recorded surface crack development and internal damage evolution using high speed photography and acoustic emission monitoring.The results show that rock beams experience multiple stress reductions after unloading,with the largest reduction occurring in the first stage.Flexural deformation was observed,becoming more pronounced as the thickness-span ratio decreased.Greater thickness increased shear cracks and crack expansion angles,while larger spans promoted tensile cracks,arched crack formation,and notable rock spalling.Acoustic emission analysis showed that signal count and energy increased with thickness and span.Finally,discrete element numerical simulations revealed the critical controlling role of harder rock strata in rock beam failure:when the harder strata are at the top,cracks are sharp,and shear failure is more likely;when they are at the bottom,the overall failure range expands,and cracks tend to form arches.These findings improve the understanding of dynamic rock beam fracture under sudden unloading and offer theoretical guidance for roof stability control in deep mining.
基金Project(2022m07020007)supported by the Key Research and Development Projects of Anhui Province,ChinaProjects(52174102,52074006,51404011,51874002,51974009)supported by the National Natural Science Foundation of China+1 种基金Project(2024cx1017)supported by the Graduate Innovation Fund of Anhui University of Science and Technology,ChinaProject(2024AH040067)supported by the Natural Science Research Project of Anhui Educational Committee,China。
文摘Aiming at the problem of deep surrounding rock instability induced by roadway excavation or mining disturbance,the true triaxial loading system was used to conduct graded cyclic maximum principal stress σ_(1) and intermediate principal stress σ_(2) tests on sandstone to simulate the effect of mining stress in actual underground engineering.The influences of each principal stress cycle on the mechanical properties,acoustic emission(AE)characteristics,and fracture characteristics of sandstone were analyzed.The damage characteristics of sandstone under true triaxial cyclic loading were studied.Furthermore,the damage constitutive model of rock mass under true triaxial cyclic loading was established based on AE cumulative ringing count.The quantitative investigation was conducted on cumulative-damage changes in circulating sandstone,which elucidated the mechanism of damage deterioration in sandstone subjected to true triaxial cyclic loading.The results show that the influence of the graded cycleσ_(1) on limit maximum principal strain ɛ_(1max) and limit minimum principal strainɛ_(3max) was significantly greater than that of the limit intermediate principal strain ɛ_(2max).Graded cycleσ_(2) had a greater impact onɛ_(2max) and a smaller impact onɛ_(3max).The elasticity modulus of sandstone decreased exponentially with the increased cyclic load amplitude,while the Poisson ratio increased linearly.b of AE showed a trend of increasing,decreasing,slightly fluctuating,and finally decreasing during cyclingσ_(1).b showed a trend of slight fluctuation,large fluctuation,and finally increase during cyclingσ_(2).Sandstone specimens experienced mainly tensile failure,tensile-shear composite failure,and mainly shear failure with increased initialσ_(2) orσ_(3).This was determined by analyzing the rise angle-average frequency of the AE parameter,corresponding to the rock specimens from splitting failure to shear failure.Besides,the mechanical damage behavior of sandstone under true triaxial cyclic loading could be well described by the established constitutive model.At the same time,it was found that the sandstone damage variable decreased with increasedσ_(2) during cyclingσ_(1).The damage variable decreased first and then increased with increasedσ_(3) during cyclingσ_(2).
基金Project(11102224)supported by the National Natural Science Foundation of ChinaProject(201206370124)supported by the China Scholarship Council,China
文摘The ratio of crack initiation stress to the uniaxial compressive strength(SCI,B/SUC,B) and the ratio of axial strain at the crack initiation stress to the axial strain at the uniaxial compressive strength(B,UCB,CI,A,A/SSSS) were studied by performing numerical stress analysis on blocks having multi flaws at close spacing's under uniaxial loading using PFC3 D. The following findings are obtained: SCI,B/SUC,B has an average value of about 0.5 with a variability of ± 0.1. This range agrees quite well with the values obtained by former research. For joint inclination angle, β=90°,B,UCB,CI,A,A/SSSS is found to be around 0.48 irrespective of the value of joint continuity factor, k. No particular relation is found betweenB,UCB,CI,A,A/SSSS and β; however, the average B,UCB,CI,A,A/SSSS seems to slightly decrease with increasing k. The variability ofB,UCB,CI,A,A/SSSS is found to increase with k.Based on the cases studied in this work,B,UCB,CI,A,A/SSSS ranges between 0.3 and 0.5. This range is quite close to the range of 0.4to 0.6 obtained for SCI,B/SUC,B. The highest variability of ± 0.12 forB,UCB,CI,A,A/SSSS is obtained for k=0.8. For the remaining k values the variability ofB,UCB,CI,A,A/SSSS can be expressed within ± 0.05. This finding is very similar to the finding obtained for the variability of SCI,B/SUC,B.
基金Project(BK20150005) supported by the Natural Science Foundation of Jiangsu Province for Distinguished Young Scholars,ChinaProject(2014YC10) supported by the Fundamental Research Funds for the Central Universities,China
文摘A series of laboratory experiments and PFC numerical simulations for rock-like material specimens containing two unparallel fissures were carried out.On the basis of experimental and numerical results,the stress-strain curves,mechanical properties,AE events,cracking behavior and energy characteristics were analyzed to reveal the macro-mechanical behavior and meso-mechanism of pre-fissured specimens under different loading rates.Investigated results show that:1)When the loading rate is relatively low,the stress-strain curves show a brittle response.When the loading rate is relatively high,the curve shows a more ductile response.Both of the peak strength and elastic mudulus increase with the increase of loading rate,which can be expressed as power functions.2)Four crack types are identified,i.e.,tensile crack,shear crack,far-field crack and surface spalling.Moreover,the tensile crack,far-field crack and surface spalling are under tensile mechanism,while the shear crack is under shear mechanism.3)The drops of the stress-strain curves all correspond to the crack initiation or coalescence,which is also linked to a sudden increasing in the accumulated micro-crack curve.4)Both of the maximum bond force and energy have the similar trend with the increase of loading rate to peak strength,which indicates that the trend of peak strength can be explained by the meso-mechanics and energy.
基金Projects(51109092,11272137)supported by the National Natural Science Foundation of ChinaProjects(2013M530237,2014T70479)supported by China Postdoctoral Science FoundationProject(SJLX15-0498)supported by Jiangsu Provincial Graduate Students Research and Innovation Program,China
文摘Geometrical nonlinearity of the soft soil and the deviation of water flow in the soft clay from Darcy's law have been well recognized in practice. However, the theory of consolidation, which can account for both the geometrical nonlinearity and the non-Darcian flow, has not been reported so far. In this contribution, a model for the consolidation of soft clay which can allow for these two factors simultaneously is proposed. Utilizing the finite difference method, the numerical model for this problem is developed. With the numerical model, the effects of the geometrical nonlinearity and the non-Darcian flow on the consolidation of the soft soil are investigated. The results show that when the self-weight stress is calculated by the same method, the rate of the non-Darcian consolidation for the large-strain case is larger than that for the small-strain case, but the difference between them is limited. However, the difference between the consolidation rates caused by the non-Darcian and Darcian flows is significant. Therefore, when the geometrical nonlinearity of the soft clay is considered in calculating the consolidation settlement, due to the complexity of the large-strain assumption, the small-strain assumption can be used to replace it if the self-weight stress for the small-strain assumption is calculated by considering its sedimentation. However, due to the aforementioned large difference between the consolidation rates with consideration of the non-Darcian flow in soft clay or not, it is better to consider the non-Darcian flow law for both the small and large stain assumptions.
基金Project(11102224)supported by the National Natural Science Foundation of ChinaProject(2009QL05)supported by the Fundamental Research Funds for the Central Universities of China
文摘Anisotropic strength and deformability of the rock mass with non-persistent joints are governed by cracking process of the rock bridges. The dependence of cracking process of jointed rock masses on the two important geometrical parameters, joint orientation and joint persistence, was studied systematically by carrying out a series of uniaxial compression tests on gypsum specimens with regularly arranged multiple parallel pre-existing joints. According to crack position, mechanism and temporal sequence, seven types of crack initiations and sixteen types of crack coalescences, were identified. It was observed that both tensile cracks and shear cracks can emanate from the pre-existing joints as well as the matrix. Vertical joints were included and coplanar tensile cracks initiation and coalescence were observed accordingly. For specimen with joint inclination angle ,8=75~, it was found that collinear joints can be linked not only by coplanar shear cracks but also by mixed tensile-shear cracks, and that a pair of them can form a small rotation block. Seven failure modes, including axial cleavage, crushing, crushing and rotation of new blocks, stepped failure, stepped failure and rotation of new blocks, shear failure along a single plane and shear failure along multiple planes, were observed. These modes shift gradually in accordance with the combined variation of joint orientation and joint persistence. It is concluded that cracking process and failure modes are more strongly affected by joint orientation than by joint persistence, especially when joint inclination angle is larger than 45~. Finally, variations of macroscopic mechanical behaviors with the two geometrical parameters, such as patterns of the complete axial stress-axial strain curves, peak strength and elastic modulus, are summarized and their mechanisms are successfully explained according to their different cracking process.
基金Project(42077231) supported by the National Natural Science Foundation of China。
文摘Fissures play a significant role in predicting the unstable failure of rock mass engineering.For deep rock underground engineering,rock mass containing pre-existing fissures is usually located in triaxial stress state.Therefore,not only pre-existing fissure but also confining pressure affects the failure mechanical behavior of rock material.In this research,the granite specimens containing two non-coplanar open fissures were investigated by a series of conventional triaxial compression tests.First,the effect of bridge angle and confining pressure on strength and deformation characteristics of granite specimens was evaluated.Results show that the triaxial compressive strength,failure axial strain,and crack damage threshold increased nonlinearly with confining pressure.Under high confining pressures,elastic modulus was insensitive to bridge angle.Then,an X-ray micro-CT scanning technique was used to analyze the internal fracture characteristics of granite specimens with respect to various bridge angles and confining pressures.Five typical crack coalescence modes were identified,namely,indirect coalescence,shear coalescence and three types of tensile coalescence.The reconstructed 3-D CT images indicated that under uniaxial or low confining pressures,the bridge angle had a significant effect on crack evolution behavior,while under high confining pressures,shear-dominated failures occurred with the development of anti-wing cracks.
基金Projects(11802058,52074262)supported by the National Natural Science Foundation of ChinaProjects(BK20170670,BK20180651)supported by the Jiangsu Youth Foundation,China+2 种基金Project(2020QN06)supported by the Fundamental Research Funds for the Central Universities,ChinaProject(SKLGDUEK1803)supported by the State Key Laboratory for Geomechanics and Deep Underground Engineering,ChinaProject supported by the Mass Entrepreneurship and Innovation Project of Jiangsu,China。
文摘Eccentric decoupling blasting is commonly used in underground excavation.Determination of perimeter hole parameters(such as the blasthole diameter,spacing,and burden)based on an eccentric charge structure is vital for achieving an excellent smooth blasting effect.In this paper,the Riedel-Hiermaier-Thoma(RHT)model was employed to study rock mass damage under smooth blasting.Firstly,the parameters of the RHT model were calibrated by using the existing SHPB experiment,which were then verified by the existing blasting experiment results.Secondly,the influence of different charge structures on the blasting effect was investigated using the RHT model.The simulation results indicated that eccentric charge blasting has an obvious pressure eccentricity effect.Finally,to improve the blasting effect,the smooth blasting parameters were optimized based on an eccentric charge structure.The overbreak and underbreak phenomena were effectively controlled,and a good blasting effect was achieved with the optimized blasting parameters.
基金Project(BK20150005)supported by the Natural Science Foundation of Jiangsu Province for Distinguished Young Scholars,ChinaProject(2015XKZD05)supported by the Fundamental Research Funds for the Central Universities,China
文摘By adopting cyclic increment loading and unloading method, time-independent and time-dependent strains can be separated. It is more reasonable to describe the reversible and the irreversible deformations of sample separately during creep process. A nonlinear elastic-visco-plastic rheological model is presented to characterize the time-based deformational behavior of hard rock. Specifically, a spring element is used to describe reversible instantaneous elastic deformation. A reversible nonlinear visco-elastic （RNVE） model is developed to characterize recoverable visco-elastic response. A combined model, which contains a fractional derivative dashpot in series with another Hook’s body, and a St. Venant body in parallel with them, is proposed to describe irreversible visco-plastic deformation. Furthermore, a three-stage damage equation based on strain energy is developed in the visco-plastic portion and then nonlinear elastic-visco-plastic rheological damage model is established to explain the trimodal creep response of hard rock. Finally, the proposed model is validated by a laboratory triaxial rheological experiment. Comparing with theoretical and experimental results, this rheological damage model characterizes well the reversible and irreversible deformations of the sample, especially the tertiary creep behavior.
基金Project(51674265) supported by the National Natural Science Foundation of ChinaProjects(2018YFC0603705,2016YFC0600901) supported by the State Key Research Development Program of ChinaProject supported by the Yueqi Outstanding Scholar Award Program of China University of Mining&Technology,Beijing,China。
文摘For the 110 mining method,it is challenging to accurately calculate the support resistance of the roadway due to the lack of understanding of the dynamic movement of the overlying strata in this method.The consequential excessive support results in a significant increase in the cost of roadway support.The authors explored the overlying strata movement and roadway deformation of the gob-entry retaining in the 110 mining method to solve this problem.First,the typical stages of the roof-cutting gob-side entry were defined.Second,the mechanical model and calculation formula of the support resistance on the roof were explored.Then,using numerical simulation software,the starting ranges of the specific supports at different stages were verified and the feasibility of the support scheme was examined.Finally,combined with the field measurement data,the stress and the deformation of the gob roadway at different stages under the influence of two mining processes in the 110 mining method were obtained.The numerical simulation results obtained are consistent with the field test results,providing a theoretical basis for precision support at different stages by the 110 mining method.
基金Project(2017YFC0804201)supported by the National Key Research and Development Program of ChinaProject(51574246)supported by the National Natural Science Foundation of China+1 种基金Project(2011QZ01)supported by Fundamental Research Funds for the Central Universities,ChinaProject(C201911362)supported by the National Training Program of Innovation and Entrepreneurship for Undergraduates,China。
文摘Rockburst is a dynamic phenomenon accompanied by acoustic emission(AE)activities.It is difficult to predict rockburst accurately.Based on the fast Fourier transform(FFT)method and the information entropy theory,the evolution model of dominant frequency entropy was established.The AE energy,frequency and stress were synthetically considered to predict rockburst.Under the triaxial and the single-face unloading tests,the relationship between AE energy and the development of internal cracks was analyzed.Using the FFT method,the distribution characteristics of AE dominant frequency values were obtained.Based on the information entropy theory,the dominant frequencies evolved patterns were ascertained.It was observed that the evolution models of the dominant frequency entropy were nearly the same and shared a characteristic“undulation-decrease-rise-sharp decrease”pattern.Results show that AE energy will be released suddenly before rockburst.The density of intermediate frequency increased prior to rockburst.The dominant frequency entropy reached a relative maximum value before rockburst,and then decreased sharply.These features could be used as a precursory information for predicting rockburst.The proposed relative maximum value could be as a key point to predict rockburst.This is a meaningful attempt on predicting rockburst.
基金Project（BK20150005） supported by the Natural Science Foundation of Jiangsu Province for Distinguished Young Scholars, China Project（2015XKZD05） supported by the Fundamental Research Funds for the Central Universities, China
文摘Permeability is a vital property of rock mass, which is highly affected by tectonic stress and human engineering activities. A comprehensive monitoring of pore pressure and flow rate distributions inside the rock mass is very important to elucidate the permeability evolution mechanisms, which is difficult to realize in laboratory, but easy to be achieved in numerical simulations. Therefore, the particle flow code （PFC）, a discrete element method, is used to simulate permeability behaviors of rock materials in this study. Owe to the limitation of the existed solid-fluid coupling algorithm in PFC, an improved flow-coupling algorithm is presented to better reflect the preferential flow in rock fractures. The comparative analysis is conducted between original and improved algorithm when simulating rock permeability evolution during triaxial compression, showing that the improved algorithm can better describe the experimental phenomenon. Furthermore, the evolution of pore pressure and flow rate distribution during the flow process are analyzed by using the improved algorithm. It is concluded that during the steady flow process in the fractured specimen, the pore pressure and flow rate both prefer transmitting through the fractures rather than rock matrix. Based on the results, fractures are divided into the following three types： I） fractures link to both the inlet and outlet, II） fractures only link to the inlet, and III） fractures only link to the outlet. The type I fracture is always the preferential propagating path for both the pore pressure and flow rate. For type II fractures, the pore pressure increases and then becomes steady. However, the flow rate increases first and begins to decrease after the flow reaches the stop end of the fracture and finally vanishes. There is no obvious pore pressure or flow rate concentration within type III fractures.
基金Projects(41941018,51704298)supported by the National Natural Science Foundation of ChinaProject(2021JCCXSB03)supported by the Fundamental Research Funds for the Central Universities,China。
文摘Rockburst is one of the major disasters in deep underground rock mechanics and engineering.The precursors of rockbursts play important roles in rockburst prediction.Strainburst experiments were performed under double-face unloading on sandstone with horizontal bedding planes using an independently designed rockburst testing facility.P-wave propagation time during the tests was automatically recorded by the acoustic emission apparatus.The P-wave velocities were calculated in both two directions to analyze their patterns.To find a characteristic precursor for rockburst,the dynamic evolution of rock anisotropy during the rockburst test is quantified by the anisotropic coefficient k,defined as the ratio of the two P-wave velocities in the directions vertical to and parallel to the bedding planes.The results show that rockburst occurs on the two free surfaces asynchronously.The rockburst failure occurs in the following order:crack generation,rock peeling,particle ejection,and rock fracture.In the process of rockburst under double-face unloading,the potential evolution characteristics of anisotropy can be generalized as anisotropy-isotropy-anisotropy.The suddenly unloading induces damage in the rock and presents anisotropic coefficient k steeply increasing departing from one,i.e.,isotropy.The rocks with horizontal bedding planes will reach the isotropic state before rockburst,which could be considered as a characteristic precursor of this kind of rockburst.
