It is of great significance to study the failure mode of mining roadways for safe coal mining.The unconventional asymmetric failure(UAF)phenomenon was discovered in the 9106 ventilation roadway of Wangzhuang coal mine...It is of great significance to study the failure mode of mining roadways for safe coal mining.The unconventional asymmetric failure(UAF)phenomenon was discovered in the 9106 ventilation roadway of Wangzhuang coal mine in Shanxi Province.The main manifestation is that the deformation of the roadway on the coal side is much greater than that on the coal pillar side.A comprehensive study was conducted on on-site detection,theoretical analysis,laboratory tests and numerical simulation of the UAF phenomenon.On-site detection shows that the deformation of the coal sidewall can reach 50–80 cm,and the failure zone depth can reach 3 m.The deformation and fracture depth on the coal pillar side are much smaller than those on the coal side.A calculation model for the principal stress of surrounding rock when the axial direction of the roadway is inconsistent with the in-situ stress field was established.The distribution of the failure zone on both sides of the roadway has been defined by the combined mining induced stress.The true triaxial test studied the mechanical mechanism of rock mass fracture and crack propagation on both sides of the roadway.The research results indicate that the axial direction,stress field distribution,and mining induced stress field distribution of the roadway jointly affect the asymmetric failure mode of the roadway.The angle between the axis direction of the roadway and the maximum horizontal stress field leads to uneven distribution of the principal stress field on both sides.The differential distribution of mining induced stress exacerbates the asymmetric distribution of principal stress in the surrounding rock.The uneven stress distribution on both sides of the roadway is the main cause of UAF formation.The research results can provide mechanical explanations and theoretical support for the control of surrounding rock in roadways with similar failure characteristics.展开更多
Subgrade engineering is a fundamental aspect of infrastructure construction in China.As the primary structural element responsible for bearing and distributing traffic loads,the subgrade must not only withstand the su...Subgrade engineering is a fundamental aspect of infrastructure construction in China.As the primary structural element responsible for bearing and distributing traffic loads,the subgrade must not only withstand the substantial pressures exerted by vehicles,trains,and other forms of transportation,but also efficiently transfer these loads to the underlying foundation,ensuring the stability and longevity of the roadway.In recent years,advancements in subgrade engineering technology have propelled the industry towards smarter,greener,and more sustainable practices,particularly in the areas of intelligent monitoring,disaster management,and innovative construction methods.This paper reviews the application and methodologies of intelligent testing equipment,including cone penetration testing(CPT)devices,soil resistivity testers,and intelligent rebound testers,in subgrade engineering.It examines the operating principles,advantages,limitations,and application ranges of these tools in subgrade testing.Additionally,the paper evaluates the practical use of advanced equipment from both domestic and international perspectives,addressing the challenges encountered by various instruments in realworld applications.These devices enable precise,comprehensive testing and evaluation of subgrade conditions at different stages,providing real-time data analysis and intelligent early warnings.This supports effective subgrade health management and maintenance.As intelligent technologies continue to evolve and integrate,these tools will increasingly enhance the accuracy,efficiency,and sustainability of subgrade monitoring.展开更多
Joints are widely distributed structural defects in rock masses,and their geometric characteristics play a decisive role in the overall stability of rocks under complex stress conditions.To clarify the influence of jo...Joints are widely distributed structural defects in rock masses,and their geometric characteristics play a decisive role in the overall stability of rocks under complex stress conditions.To clarify the influence of joint geometry on the mechanical behavior of jointed rock under such conditions,this study investigated the mechanical properties and failure mechanisms of composite jointed rock specimens with varying joint roughness and joint dip angles.Three typical failure modes under triaxial loading were identified,and a mechanical analysis model incorporating joint roughness and dip angle was established.The failure mechanism was revealed,and a discrete element model was developed to analyze the micro-damage evolution process of the specimens.The results show that the mechanical parameters of the specimens exhibit pronounced anisotropy.Both the elastic modulus and peak strength reach their minimum values at a joint dip angle of 60°.Increasing joint roughness significantly reduces the degree of anisotropy and enhances the energy storage capacity of the specimens.A strong linear relationship is observed between the elastic strain energy and the peak deviatoric stress,confirming the applicability of the linear energy storage law in composite jointed rocks.Discrete element simulations revealed the evolution path and dominant types of microcracks between the joint and matrix.The joint dip angle governs the transition of dominant crack types from tensile to shear and then back to tensile.Increased joint roughness significantly suppresses damage localization along the joint and results in an approximately 20%increase in the proportion of shear microcracks within the matrix.These findings clarify the regulatory role of joint geometrical parameters in the damage evolution process.展开更多
The internal microstructures of rock materials, including mineral heterogeneity and intrinsic microdefects, exert a significant influence on their nonlinear mechanical and cracking behaviors. It is of great significan...The internal microstructures of rock materials, including mineral heterogeneity and intrinsic microdefects, exert a significant influence on their nonlinear mechanical and cracking behaviors. It is of great significance to accurately characterize the actual microstructures and their influence on stress and damage evolution inside the rocks. In this study, an image-based fast Fourier transform (FFT) method is developed for reconstructing the actual rock microstructures by combining it with the digital image processing (DIP) technique. A series of experimental investigations were conducted to acquire information regarding the actual microstructure and the mechanical properties. Based on these experimental evidences, the processed microstructure information, in conjunction with the proposed micromechanical model, is incorporated into the numerical calculation. The proposed image-based FFT method was firstly validated through uniaxial compression tests. Subsequently, it was employed to predict and analyze the influence of microstructure on macroscopic mechanical behaviors, local stress distribution and the internal crack evolution process in brittle rocks. The distribution of feldspar is considerably more heterogeneous and scattered than that of quartz, which results in a greater propensity for the formation of cracks in feldspar. It is observed that initial cracks and new cracks, including intragranular and boundary ones, ultimately coalesce and connect as the primary through cracks, which are predominantly distributed along the boundary of the feldspar. This phenomenon is also predicted by the proposed numerical method. The results indicate that the proposed numerical method provides an effective approach for analyzing, understanding and predicting the nonlinear mechanical and cracking behaviors of brittle rocks by taking into account the actual microstructure characteristics.展开更多
Rock-like specimens containing a joint with different inclination angles and roughness were prepared using 3D printing technology.Then,true triaxial compression loading experiments were conducted on those jointed spec...Rock-like specimens containing a joint with different inclination angles and roughness were prepared using 3D printing technology.Then,true triaxial compression loading experiments were conducted on those jointed specimens.The increase in roughness leads to an increase in the axial strength and peak strain.With the increasing inclination angle,the axial strength initially decreases from 30°to 60°and then increases from 60°to 90°.While the peak strain first rises from 30°to 45°and then declines from 45°to 90°.The variation in failure mode results from differences in lateral stress on the joints under different strike directions.Specimens with joint strike parallel to the intermediate principal stress predominantly showed matrix or matrix-joint mixed shear failure,whereas those parallel to the minimum principal stress exhibited matrix shear failure.The analysis results of acoustic emission signals indicate the crack number and shear crack percentage increase with the increasing roughness and first decrease(30°to 60°),then increase(60°to 90°)with the increasing inclination angle.The research results can provide some guidance for the design and support of underground engineering with jointed surrounding rock.展开更多
The mechanical anisotropy on extruded AZ31 magnesium alloy bar has been investigated by combining experimental measurement and crystal plasticity modeling.Monotonic tension and compression are conducted in four loadin...The mechanical anisotropy on extruded AZ31 magnesium alloy bar has been investigated by combining experimental measurement and crystal plasticity modeling.Monotonic tension and compression are conducted in four loading directions with the oblique angleϕof 0°,30°,60°and 90°from extrusion radial direction to extrusion direction,and are also simulated by visco-plastic self-consistent model with considering twinning and detwinning scheme at the first time.The simulation results are well in agreement with the corresponding experimental data.Combined with the Schmid factor(SF),the anisotropic mechanical behaviors including yield strength,ultimate strength and strain hardening rate are interpreted with the predicted relative activities of deformation modes,texture evolution and twin volume fraction.With the loading angle varying from 0°to 90°,it is found that prismatic slip becomes the primary deformation mode with the decreasing relative activities of basal slip and extension twinning in tension.While the deformation mechanism is more complex in compression:Extension twinning gets great activation at the beginning of the deformation,especially under compression along 90°;basal slip and pyramidal<c+a>slip dominate the late deformation of compression along 0°and 30°,while basal slip and prismatic slip are dominated modes in compression along 60°and 90°.Additionally,different {10 1 2}twinning behaviors with two or three and one or two pairs of twin variants being activated in tension along 30°and compression along 90°,respectively,have a close correlation with the texture evolution to coordinate plastic deformation.The activation of{10 1 2}twinning,which varies with the loading angleϕ,results in the increased trend of strain hardening rate.Following the exhausting of twinning,non-basal slips with the highest SF become the primary deformation mode subsequently,contributing to the decreasing trend in hardening behavior and the anisotropy of ultimate strength.展开更多
Cold regions often feature complex geological environments where various physical phenomena interact,with a particularly notable thermo-hydro-mechanical(THM)coupling.In this study,fully coupled THM cyclic tests were c...Cold regions often feature complex geological environments where various physical phenomena interact,with a particularly notable thermo-hydro-mechanical(THM)coupling.In this study,fully coupled THM cyclic tests were conducted,followed by fatigue tests,to explore how THM treatment influences the fatigue properties of damaged sandstone.Experimental results indicate that rock fatigue deformation,damage evolution,and failure characteristics are highly sensitive to initial damage caused by coupled THM treatment.Rocks subjected to multiple THM cycles exhibit lower initial irreversible strain,shorter fatigue life,lower critical total dissipated energy,and higher irreversible strain increments,indicating accelerated deterioration.After THM coupling,rock fatigue failure shows complex crack networks,with macroscopic failure modes shifting from shear to tensile failure.Polarized microscopy and acoustic emission analyses reveal that this transition stems from micro-scale transgranular to intergranular fractures.We introduced a fractional order-based damage fatigue model to quantitatively describe the rock viscoelastic parameters after different initial damage treatments.Rock viscoelastic-plastic parameters decrease with increasing coupled THM cycles.Finally,we discussed the feasibility of applying these results to the long-term stability analysis of rock slopes.This study provides unique insights and modeling tools from fully coupled THM experiments to understand the rock fatigue characteristics,offering potential applications for slope stability assessment.展开更多
Given that dolomite is prone to strength degradation and susceptible to water-sand ingress under physicochemical actions,this study aims to investigate these phenomena,along with the sanding mechanism in the Xiaopu Tu...Given that dolomite is prone to strength degradation and susceptible to water-sand ingress under physicochemical actions,this study aims to investigate these phenomena,along with the sanding mechanism in the Xiaopu Tunnel of the Yunnan Dianzhong Water Diversion Project,using a combined experimental and modeling approach for systematic analysis.Triaxial cyclic loading-unloading tests were first conducted on dolomite samples soaked in sulfuric acid solutions of varying concentrations,with synchronous monitoring of their mechanical responses(e.g.,peak strength,deformation modulus,porosity changes).These tests,combined with observations of macroscopic morphology and mass changes during soaking,revealed a four-stage degradation pattern of dolomite in sulfuric acid:water absorption,dynamic equilibrium,dissolution,and stabilization.Key quantitative relationships established that as sulfuric acid concentration increased(from 0%to 15%),the peak strength of dolomite decreased significantly(by 7.49%to 24.99%),while porosity markedly increased(by 45%to 130%).Further post-failure analysis(fracture surface observation)and scanning electron microscopy(SEM)micro-characterization uncovered the intrinsic mechanisms of acid-induced damage:the acid solution not only promoted macroscopic crack propagation and increased fracture surface roughness but also triggered severe structural deterioration at the microscale,including enlarged crystal spacing,dissolution of gel-like substances,formation of intra-crystalline pores,weakened interparticle cementation,and development of macropores.The extent of this deterioration was positively correlated with acid concentration.Based on the experimentally revealed chemo-mechanical coupling damage mechanism between acid and rock,this study established,for the first time,a multi-scale predictive model capable of quantitatively correlating acid concentration,microstructural deterioration,and degradation of macroscopic mechanical properties.The development of this model not only deepens the quantitative understanding of the dolomite sanding mechanism but also provides a crucial theoretical tool for assessing surrounding rock stability and predicting risks in similar water diversion tunnel engineering.Addressing the specific risks of water and H^(+) erosion in the Xiaopu Tunnel,the research findings directly informed the engineering reinforcement strategy:concrete lining is recommended as the primary load-bearing structure,supplemented by surrounding rock surface protection measures,to effectively mitigate the acid-induced damage process and enhance the long-term stability of the surrounding rock.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 research of rock properties based on its inherent microscopic to mesoscopic porous structure has drawn great attention for its potential in predicting the macroscopic behavior of rocks.An accurate reconstruction o...The research of rock properties based on its inherent microscopic to mesoscopic porous structure has drawn great attention for its potential in predicting the macroscopic behavior of rocks.An accurate reconstruction of the threedimensional porous structure is a premise for the related studies of hydraulic and mechanical properties of rocks,such as the transport properties and mechanical responses under pressures.In this paper,we present a computer procedure for reconstructing the 3D porous structure of low-permeability sandstone.Two large-size 3D models are reconstructed based on the information of a reference model which is established from computed tomography(CT)images.A self-developed finite element method is applied to analyze the nonlinear mechanical behavior of the sandstone based on its reconstructed model and to compare the results with those based on the reference model.The good consistency of the obtained mechanical responses indicates the potential of using reconstruction models to predict the influences of porous structure on the mechanical properties of low-permeability sandstone.展开更多
Natural fracture data from one of the Carboniferous shale masses in the eastern Qaidam Basin were used to establish a stochastic model of a discrete fracture network and to perform discrete element simulation research...Natural fracture data from one of the Carboniferous shale masses in the eastern Qaidam Basin were used to establish a stochastic model of a discrete fracture network and to perform discrete element simulation research on the size efect and mechanical parameters of shale.Analytical solutions of fctitious joints in transversely isotropic media were derived,which made it possible for the proposed numerical model to simulate the bedding and natural fractures in shale masses.The results indicate that there are two main factors infuencing the representative elementary volume(REV)size of a shale mass.The frst and most decisive factor is the presence of natural fractures in the block itself.The second is the anisotropy ratio:the greater the anisotropy is,the larger the REV.The bedding angle has little infuence on the REV size,whereas it has a certain infuence on the mechanical parameters of the rock mass.When the bedding angle approaches the average orientation of the natural fractures,the mechanical parameters of the shale blocks decrease greatly.The REV representing the mechanical properties of the Carboniferous shale masses in the eastern Qaidam Basin were comprehensively identifed by considering the infuence of bedding and natural fractures.When the numerical model size is larger than the REV,the fractured rock mass discontinuities can be transformed into equivalent continuities,which provides a method for simulating shale with natural fractures and bedding to analyze the stability of a borehole wall in shale.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
Based on laboratory results of time-dependent mechanical behavior tests,we investigated short-term and mechanical creep behavior of sandstone,observed in conventional triaxial compression experiments at room temperatu...Based on laboratory results of time-dependent mechanical behavior tests,we investigated short-term and mechanical creep behavior of sandstone,observed in conventional triaxial compression experiments at room temperature,using a servo-controlled rheology testing machine.Given our short-term experimental test results,we confirmed deviatoric creep stress levels of sandstone.Multiple deviatoric stress levels were applied in steps to each sample.Each deviatoric stress level before the final failed deviatoric stress was maintained for 48 h or longer.Time-dependent variations of axial strains of sandstone samples are discussed and evaluated.During the creep tests,complete tertiary creep curves of sandstone were observed under failed deviatoric stress levels with different confining pressures.Slices of coal in sandstone samples can lead to distinct tertiary creep deformation failure.展开更多
The use of aeolian sand(AS)as an aggregate to prepare coal mine cemented filling materials can resolve the problems of gangue shortage and excessive AS deposits.Owing to the lack of research on the mechanism of cement...The use of aeolian sand(AS)as an aggregate to prepare coal mine cemented filling materials can resolve the problems of gangue shortage and excessive AS deposits.Owing to the lack of research on the mechanism of cemented AS backfill(CASB),the response surface method(RSM)was adopted in this study to analyze the influence of ordinary Portland cement(PO)content(x_(1)),fly ash(FA)-AS(FA-AS)ratio(x_(2)),and concentration(x_(3))on the mechanical and microscopic properties of the CASB.The hydration characteristics and internal pore structure of the backfill were assessed through thermogravimetric/derivative thermogravimetric analysis,mercury intrusion porosimetry,and scanning electron microscopy.The RSM results show that the influence of each factor and interaction term on the response values is extremely significant(except x_(1)x_(3),which had no obvious effect on the 28 d strength).The uniaxial compressive strength(UCS)increased with the PO content,FA-AS ratio,and concentration.The interaction effects of x_(1)x_(2),x_(1)x_(3),and x_(2)x_(3) on the UCS at 3,7,and 28 d were analyzed.In terms of the influence of interaction items,an improvement in one factor promoted the strengthening effect of another factor.The enhancement mechanism of the curing time,PO content,and FA-AS ratio on the backfill was reflected in the increase in hydration products and pore structure optimization.By contrast,the enhancement mechanism of the concentration was mainly the pore structure optimization.The UCS was positively correlated with weight loss and micropore content but negatively correlated with the total porosity.The R^(2) value of the fitting function of the strength and weight loss,micropore content,and total porosity exceeded 0.9,which improved the characterization of the enhancement mechanism of the UCS based on the thermogravimetric analysis and pore structure.This work obtained that the influence rules and mechanisms of the PO,FA-AS,concentration,and interaction terms on the mechanical properties of the CASB provided a certain theoretical and engineering guidance for CASB filling.展开更多
This study aims to investigate the mechanical response and acoustic emission(AE)characteristic of pre-flawed sandstone under both monotonic and multilevel constant-amplitude cyclic loads.Specifically,we explored how c...This study aims to investigate the mechanical response and acoustic emission(AE)characteristic of pre-flawed sandstone under both monotonic and multilevel constant-amplitude cyclic loads.Specifically,we explored how coplanar flaw angle and load type impact the strength and deformation behavior and microscopic damage mechanism.Results indicated that being fluctuated before rising with increasing fissure angle under monotonic loading,the peak strength of the specimen first increased slowly and then steeply under cyclic loading.The effect of multilevel cyclic loading on the mechanical parameters was more significant.For a single fatigue stage,the specimen underwent greater deformation in early cycles,which subsequently stabilized.Similar variation pattern was also reflected by AE count/energy/b-value.Crack behaviors were dominated by the fissure angle and load type and medium-scale crack accounted for 74.83%–86.44%of total crack.Compared with monotonic loading,crack distribution of specimen under cyclic loading was more complicated.Meanwhile,a simple model was proposed to describe the damage evolution of sandstone under cyclic loading.Finally,SEM images revealed that the microstructures at the fracture were mainly composed of intergranular fracture,and percentage of transgranular fracture jumped under cyclic loading due to the rapid release of elastic energy caused by high loading rate.展开更多
The mechanical behaviors and energy dissipation characteristics of heat-treated granite were investigated under repeated impact loading.The granite samples were firstly heat-treated at the temperature of 20℃,200℃,40...The mechanical behaviors and energy dissipation characteristics of heat-treated granite were investigated under repeated impact loading.The granite samples were firstly heat-treated at the temperature of 20℃,200℃,400℃,and 600℃,respectively.The thermal damage characteristics of these samples were then observed and measured before impact tests.Dynamic impact compression tests finally were carried out using a modified split-Hopkinson pressure bar under three impact velocities of 12 m/s,15 m/s,and 18 m/s.These test results show that the mineral composition and the main oxides of the granite do not change with these treatment temperatures.The number of microcracks and microvoids decreases in the sample after 200℃ treatment.The mechanical properties of a sample after 600℃ treatment were rapidly deteriorated under the same impact velocity.The average of peak stress is much smaller than those after 20℃,200℃ and 400℃ treatments.The heat-treated samples have an energy threshold each.When the dissipated energy of a sample under a single impact is less than this threshold,the repeated impacts hardly lead to further damage accumulation even if its total breakage energy dissipation(BED)density is large.Under the same number of repeated impacts,the cumulative BED density of a sample after 600℃ treatment is the largest and its damage evolves most quickly.The total BED density of the sample after 200℃ treatment is the highest,which implies that this sample has better resistance to repeated impact,thus having less crack initiation and growth.展开更多
Active faults are a common adverse geological phenomenon that can occur during tunnel excavation and has a very negative impact on the construction and operation of the tunnel.In this paper,the grade IV rock surroundi...Active faults are a common adverse geological phenomenon that can occur during tunnel excavation and has a very negative impact on the construction and operation of the tunnel.In this paper,the grade IV rock surrounding the cross-fault tunnel with poor geological conditions has been chosen for the study.The support capacity of 2^(nd) Generation-Negative Poisson’s Ratio(2G-NPR)bolt in an active fault tunnel has been carried out on the basis of relevant results obtained from the geomechanical model test and numerical investigations of failure model for existing unsupported fault tunnel.The investigation shows that surrounding rock of the tunnel is prone to shear deformation and crack formation along the fault,as a result,the rock mass on the upper part of the fault slips as a whole.Furthermore,small-scale deformation and loss of blocks are observed around the tunnel;however,the 2G-NPR bolt support is found to be helpful in keeping the overall tunnel intact without any damage and instability.Due to the blocking effect of fault,the stress of the surrounding rock on the upper and lower parts of the fault is significantly different,and the stress at the left shoulder of the tunnel is greater than that at the right shoulder.The asymmetrical arrangement of 2G-NPR bolts can effectively control the asymmetric deformation and instability of the surrounding rock.The present numerical scheme is in good agreement with the model test results,and can reasonably reflect the stress and displacement characteristics of the surrounding rock of the tunnel.In comparison to unsupported and ordinary PR(Poisson’s Ratio)bolt support,2G-NPR bolt can effectively limit the fault slip and control the stability of the surrounding rock of the fault tunnel.The research findings may serve as a guideline for the use of 2G-NPR bolts in fault tunnel support engineering.展开更多
Investigations on the dynamic mechanical properties and failure mechanisms of coal under in-situ stress is essential for the prevention of dynamic disasters in deep coal mines.Thus,a modified true triaxial Hopkinson b...Investigations on the dynamic mechanical properties and failure mechanisms of coal under in-situ stress is essential for the prevention of dynamic disasters in deep coal mines.Thus,a modified true triaxial Hopkinson bar was employed to explore the dynamic mechanical behaviors of coal at different confining pressures(0–20 MPa)and strain rates(40–220 s^(-1)).The results show that the dynamic peak stress is positively correlated with lateral static pre-stressσy andσz,but negatively correlated with axial static prestressσx.At approximate strain rates,increasing the lateral static pre-stress facilitates increasing the dynamic peak stress,but the minimum lateral static pre-stress is the primary factor limiting a significant increase in dynamic peak stress of coal.Furthermore,the dynamic differential stress is linearly related to the logarithm of strain rate,and the peak strain varies linearly with strain rate.However,there is no significant correlation between confining pressure and peak strain.Moreover,X-ray CT images and photographic fracture observations of coal samples show the failure patterns under uniaxial and triaxial conditions are splitting failure and shear failure,respectively.The device provides a viable approach for fully comprehending the dynamic mechanical behaviors of rock-like material in complex stress conditions.展开更多
This paper investigates mechanical behaviours of sandstone during post-peak cyclic loading and unloading subjected to hydromechanical coupling effect, confirming the peak and residual strengths reduction laws of sands...This paper investigates mechanical behaviours of sandstone during post-peak cyclic loading and unloading subjected to hydromechanical coupling effect, confirming the peak and residual strengths reduction laws of sandstone with water pressure, and revealing the influence of water pressure on the upper limit stress and deformation characteristics of sandstone during post-peak cyclic loading and unloading.Regarding the rock strength, the experimental study confirms that the peak strength σ_(p) and residual strength σ_(r) decrease as water pressure P increases. Especially, the normalized strength parameters σ_(p)/σ_(pk) and σ_(r)/σ_(re) was negatively and linearly correlated with the P/σ_(3). Moreover, the Hoek-Brown strength criterion can be applied to describe the relationship between effective peak strength and effective confining stress. During post-peak cyclic loading and unloading, both the upper limit stress σ_(p(i)) and crack damage threshold stress σ_(cd(i)) of each cycle tend to decrease with the increasing cycle number. A hysteresis loop exists among the loading and unloading stress–strain curves, indicating the unloading deformation modulus E_(unload) is larger than the loading deformation modulus E_(load). Based on experimental results,a post-peak strength prediction model related to water pressure and plastic shear strain is established.展开更多
Using aeolian sand(AS)for goaf backfilling allows coordination of green mining and AS control.Cemented AS backfill(CASB)exhibits brittle fracture.Polypropylene(PP)fibers are good toughening materials.When the tougheni...Using aeolian sand(AS)for goaf backfilling allows coordination of green mining and AS control.Cemented AS backfill(CASB)exhibits brittle fracture.Polypropylene(PP)fibers are good toughening materials.When the toughening effect of fibers is analyzed,their influence on the slurry conveying performance should also be considered.Additionally,cement affects the interactions among the hydration products,fibers,and aggregates.In this study,the effects of cement content(8wt%,9wt%,and 10wt%)and PP fiber length(6,9,and 12 mm)and dosage(0.05wt%,0.1wt%,0.15wt%,0.2wt%,and 0.25wt%)on fluidity and mechanical properties of the fibertoughened CASB(FCASB)were analyzed.The results indicated that with increases in the three aforementioned factors,the slump flow decreased,while the rheological parameters increased.Uniaxial compressive strength(UCS)increased with the increase of cement content and fiber length,and with an increase in fiber dosage,it first increased and then decreased.The strain increased with the increase of fiber dosage and length.The effect of PP fibers became more pronounced with the increase of cement content.Digital image correlation(DIC)test results showed that the addition of fibers can restrain the peeling of blocks and the expansion of fissure,and reduce the stress concentration of the FCASB.Scanning electron microscopy(SEM)test indicated that the functional mechanisms of fibers mainly involved the interactions of fibers with the hydration products and matrix and the spatial distribution of fibers.On the basis of single-factor analysis,the response surface method(RSM)was used to analyze the effects of the three aforementioned factors and their interaction terms on the UCS.The influence surface of the two-factor interaction terms and the three-dimensional scatter plot of the three-factor coupling were established.In conclusion,the response law of the FCASB properties under the effects of cement and PP fibers were obtained,which provides theoretical and engineering guidance for FCASB filling.展开更多
基金financially supported by the National Natural Science Foundation of China(Nos.52225404,12532020,52394192 and 42321002)Key Research and Development Program Projects of Xinjiang Uygur Autonomous Region(No.2024B03017)Doctoral Startup Foundation of Fuyang Normal University,China(No.2025KYQD0124)。
文摘It is of great significance to study the failure mode of mining roadways for safe coal mining.The unconventional asymmetric failure(UAF)phenomenon was discovered in the 9106 ventilation roadway of Wangzhuang coal mine in Shanxi Province.The main manifestation is that the deformation of the roadway on the coal side is much greater than that on the coal pillar side.A comprehensive study was conducted on on-site detection,theoretical analysis,laboratory tests and numerical simulation of the UAF phenomenon.On-site detection shows that the deformation of the coal sidewall can reach 50–80 cm,and the failure zone depth can reach 3 m.The deformation and fracture depth on the coal pillar side are much smaller than those on the coal side.A calculation model for the principal stress of surrounding rock when the axial direction of the roadway is inconsistent with the in-situ stress field was established.The distribution of the failure zone on both sides of the roadway has been defined by the combined mining induced stress.The true triaxial test studied the mechanical mechanism of rock mass fracture and crack propagation on both sides of the roadway.The research results indicate that the axial direction,stress field distribution,and mining induced stress field distribution of the roadway jointly affect the asymmetric failure mode of the roadway.The angle between the axis direction of the roadway and the maximum horizontal stress field leads to uneven distribution of the principal stress field on both sides.The differential distribution of mining induced stress exacerbates the asymmetric distribution of principal stress in the surrounding rock.The uneven stress distribution on both sides of the roadway is the main cause of UAF formation.The research results can provide mechanical explanations and theoretical support for the control of surrounding rock in roadways with similar failure characteristics.
基金supported by the National Natural Science Foundation of China for Distinguished Young Scholars(Grant No.42225206)National Natural Science Foundation of China(42207180,42477209,42302320).
文摘Subgrade engineering is a fundamental aspect of infrastructure construction in China.As the primary structural element responsible for bearing and distributing traffic loads,the subgrade must not only withstand the substantial pressures exerted by vehicles,trains,and other forms of transportation,but also efficiently transfer these loads to the underlying foundation,ensuring the stability and longevity of the roadway.In recent years,advancements in subgrade engineering technology have propelled the industry towards smarter,greener,and more sustainable practices,particularly in the areas of intelligent monitoring,disaster management,and innovative construction methods.This paper reviews the application and methodologies of intelligent testing equipment,including cone penetration testing(CPT)devices,soil resistivity testers,and intelligent rebound testers,in subgrade engineering.It examines the operating principles,advantages,limitations,and application ranges of these tools in subgrade testing.Additionally,the paper evaluates the practical use of advanced equipment from both domestic and international perspectives,addressing the challenges encountered by various instruments in realworld applications.These devices enable precise,comprehensive testing and evaluation of subgrade conditions at different stages,providing real-time data analysis and intelligent early warnings.This supports effective subgrade health management and maintenance.As intelligent technologies continue to evolve and integrate,these tools will increasingly enhance the accuracy,efficiency,and sustainability of subgrade monitoring.
基金supported by the National Natural Science Foundation of China(Nos.52304108,52274148)China University of Mining and Technology-Beijing Undergraduate Innovation Training Program(No.202515011).
文摘Joints are widely distributed structural defects in rock masses,and their geometric characteristics play a decisive role in the overall stability of rocks under complex stress conditions.To clarify the influence of joint geometry on the mechanical behavior of jointed rock under such conditions,this study investigated the mechanical properties and failure mechanisms of composite jointed rock specimens with varying joint roughness and joint dip angles.Three typical failure modes under triaxial loading were identified,and a mechanical analysis model incorporating joint roughness and dip angle was established.The failure mechanism was revealed,and a discrete element model was developed to analyze the micro-damage evolution process of the specimens.The results show that the mechanical parameters of the specimens exhibit pronounced anisotropy.Both the elastic modulus and peak strength reach their minimum values at a joint dip angle of 60°.Increasing joint roughness significantly reduces the degree of anisotropy and enhances the energy storage capacity of the specimens.A strong linear relationship is observed between the elastic strain energy and the peak deviatoric stress,confirming the applicability of the linear energy storage law in composite jointed rocks.Discrete element simulations revealed the evolution path and dominant types of microcracks between the joint and matrix.The joint dip angle governs the transition of dominant crack types from tensile to shear and then back to tensile.Increased joint roughness significantly suppresses damage localization along the joint and results in an approximately 20%increase in the proportion of shear microcracks within the matrix.These findings clarify the regulatory role of joint geometrical parameters in the damage evolution process.
基金supported by the National Natural Science Foundation of China(Grant No.11802332)the China Scholarship Council(Grant No.202206435003)the Fundamental Research Funds for the Central Universities(Grant No.2024ZKPYLJ03).
文摘The internal microstructures of rock materials, including mineral heterogeneity and intrinsic microdefects, exert a significant influence on their nonlinear mechanical and cracking behaviors. It is of great significance to accurately characterize the actual microstructures and their influence on stress and damage evolution inside the rocks. In this study, an image-based fast Fourier transform (FFT) method is developed for reconstructing the actual rock microstructures by combining it with the digital image processing (DIP) technique. A series of experimental investigations were conducted to acquire information regarding the actual microstructure and the mechanical properties. Based on these experimental evidences, the processed microstructure information, in conjunction with the proposed micromechanical model, is incorporated into the numerical calculation. The proposed image-based FFT method was firstly validated through uniaxial compression tests. Subsequently, it was employed to predict and analyze the influence of microstructure on macroscopic mechanical behaviors, local stress distribution and the internal crack evolution process in brittle rocks. The distribution of feldspar is considerably more heterogeneous and scattered than that of quartz, which results in a greater propensity for the formation of cracks in feldspar. It is observed that initial cracks and new cracks, including intragranular and boundary ones, ultimately coalesce and connect as the primary through cracks, which are predominantly distributed along the boundary of the feldspar. This phenomenon is also predicted by the proposed numerical method. The results indicate that the proposed numerical method provides an effective approach for analyzing, understanding and predicting the nonlinear mechanical and cracking behaviors of brittle rocks by taking into account the actual microstructure characteristics.
基金Projects(52074259,52204132)supported by the National Natural Science Foundation of ChinaProject(104023002)supported by the Yunlong Lake Laboratory of Deep Underground Science and Engineering Project,China+2 种基金Project(BK20220157)supported by Natural Science Foundation of Jiangsu Province of ChinaProject(2023JJ40285)supported by Hunan Provincial Natural Science Foundation of ChinaProject(22B0469)supported by Scientific Research Foundation of Hunan Provincial Education Department,China。
文摘Rock-like specimens containing a joint with different inclination angles and roughness were prepared using 3D printing technology.Then,true triaxial compression loading experiments were conducted on those jointed specimens.The increase in roughness leads to an increase in the axial strength and peak strain.With the increasing inclination angle,the axial strength initially decreases from 30°to 60°and then increases from 60°to 90°.While the peak strain first rises from 30°to 45°and then declines from 45°to 90°.The variation in failure mode results from differences in lateral stress on the joints under different strike directions.Specimens with joint strike parallel to the intermediate principal stress predominantly showed matrix or matrix-joint mixed shear failure,whereas those parallel to the minimum principal stress exhibited matrix shear failure.The analysis results of acoustic emission signals indicate the crack number and shear crack percentage increase with the increasing roughness and first decrease(30°to 60°),then increase(60°to 90°)with the increasing inclination angle.The research results can provide some guidance for the design and support of underground engineering with jointed surrounding rock.
基金supported by the National Natural Science Foundation of China(Nos.52271123,52101154)the Basic Research Program of Jiangsu(No.BK20231496)+2 种基金the Natural Science Foundation of Jiangsu Higher Education Institutions of China(No.23KJA130001)the Graduate Innovation Program of China University of Mining and Technology(No.2024WLJCRCZL048)the Postgraduate Research and Practice Innovation Program of Jiangsu Province(No.KYCX24_2700).
文摘The mechanical anisotropy on extruded AZ31 magnesium alloy bar has been investigated by combining experimental measurement and crystal plasticity modeling.Monotonic tension and compression are conducted in four loading directions with the oblique angleϕof 0°,30°,60°and 90°from extrusion radial direction to extrusion direction,and are also simulated by visco-plastic self-consistent model with considering twinning and detwinning scheme at the first time.The simulation results are well in agreement with the corresponding experimental data.Combined with the Schmid factor(SF),the anisotropic mechanical behaviors including yield strength,ultimate strength and strain hardening rate are interpreted with the predicted relative activities of deformation modes,texture evolution and twin volume fraction.With the loading angle varying from 0°to 90°,it is found that prismatic slip becomes the primary deformation mode with the decreasing relative activities of basal slip and extension twinning in tension.While the deformation mechanism is more complex in compression:Extension twinning gets great activation at the beginning of the deformation,especially under compression along 90°;basal slip and pyramidal<c+a>slip dominate the late deformation of compression along 0°and 30°,while basal slip and prismatic slip are dominated modes in compression along 60°and 90°.Additionally,different {10 1 2}twinning behaviors with two or three and one or two pairs of twin variants being activated in tension along 30°and compression along 90°,respectively,have a close correlation with the texture evolution to coordinate plastic deformation.The activation of{10 1 2}twinning,which varies with the loading angleϕ,results in the increased trend of strain hardening rate.Following the exhausting of twinning,non-basal slips with the highest SF become the primary deformation mode subsequently,contributing to the decreasing trend in hardening behavior and the anisotropy of ultimate strength.
基金supported by the National Natural Science Foundation of China(Grant No.42372326)supported by the State Key Laboratory of Geohazard Prevention and Geoenvironment Protection Independent Research Project(Grant No.SKLGP2023Z015)supported by the Sichuan Science and Technology Program(Grant No.2024YFFK0416).
文摘Cold regions often feature complex geological environments where various physical phenomena interact,with a particularly notable thermo-hydro-mechanical(THM)coupling.In this study,fully coupled THM cyclic tests were conducted,followed by fatigue tests,to explore how THM treatment influences the fatigue properties of damaged sandstone.Experimental results indicate that rock fatigue deformation,damage evolution,and failure characteristics are highly sensitive to initial damage caused by coupled THM treatment.Rocks subjected to multiple THM cycles exhibit lower initial irreversible strain,shorter fatigue life,lower critical total dissipated energy,and higher irreversible strain increments,indicating accelerated deterioration.After THM coupling,rock fatigue failure shows complex crack networks,with macroscopic failure modes shifting from shear to tensile failure.Polarized microscopy and acoustic emission analyses reveal that this transition stems from micro-scale transgranular to intergranular fractures.We introduced a fractional order-based damage fatigue model to quantitatively describe the rock viscoelastic parameters after different initial damage treatments.Rock viscoelastic-plastic parameters decrease with increasing coupled THM cycles.Finally,we discussed the feasibility of applying these results to the long-term stability analysis of rock slopes.This study provides unique insights and modeling tools from fully coupled THM experiments to understand the rock fatigue characteristics,offering potential applications for slope stability assessment.
基金funded by Ordos Science and Technology Plan (Grant No. TD20240003)the National Natural Science Foundation of China (52174096, 52304110)+1 种基金Ordos Science and Technology Bureau (Grant No. IMRI23005)Ordos Science and Technology Plan (Grant No. YF20240021)
文摘Given that dolomite is prone to strength degradation and susceptible to water-sand ingress under physicochemical actions,this study aims to investigate these phenomena,along with the sanding mechanism in the Xiaopu Tunnel of the Yunnan Dianzhong Water Diversion Project,using a combined experimental and modeling approach for systematic analysis.Triaxial cyclic loading-unloading tests were first conducted on dolomite samples soaked in sulfuric acid solutions of varying concentrations,with synchronous monitoring of their mechanical responses(e.g.,peak strength,deformation modulus,porosity changes).These tests,combined with observations of macroscopic morphology and mass changes during soaking,revealed a four-stage degradation pattern of dolomite in sulfuric acid:water absorption,dynamic equilibrium,dissolution,and stabilization.Key quantitative relationships established that as sulfuric acid concentration increased(from 0%to 15%),the peak strength of dolomite decreased significantly(by 7.49%to 24.99%),while porosity markedly increased(by 45%to 130%).Further post-failure analysis(fracture surface observation)and scanning electron microscopy(SEM)micro-characterization uncovered the intrinsic mechanisms of acid-induced damage:the acid solution not only promoted macroscopic crack propagation and increased fracture surface roughness but also triggered severe structural deterioration at the microscale,including enlarged crystal spacing,dissolution of gel-like substances,formation of intra-crystalline pores,weakened interparticle cementation,and development of macropores.The extent of this deterioration was positively correlated with acid concentration.Based on the experimentally revealed chemo-mechanical coupling damage mechanism between acid and rock,this study established,for the first time,a multi-scale predictive model capable of quantitatively correlating acid concentration,microstructural deterioration,and degradation of macroscopic mechanical properties.The development of this model not only deepens the quantitative understanding of the dolomite sanding mechanism but also provides a crucial theoretical tool for assessing surrounding rock stability and predicting risks in similar water diversion tunnel engineering.Addressing the specific risks of water and H^(+) erosion in the Xiaopu Tunnel,the research findings directly informed the engineering reinforcement strategy:concrete lining is recommended as the primary load-bearing structure,supplemented by surrounding rock surface protection measures,to effectively mitigate the acid-induced damage process and enhance the long-term stability of the surrounding rock.
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the financial supports from the National Natural Science Foundation for Distinguished Young Scholars of China(51125017)the National Natural Science Foundation of China(51374213)the National Basic Research Pro-gram of China(Grant 2010CB226804,2011CB201201).
文摘The research of rock properties based on its inherent microscopic to mesoscopic porous structure has drawn great attention for its potential in predicting the macroscopic behavior of rocks.An accurate reconstruction of the threedimensional porous structure is a premise for the related studies of hydraulic and mechanical properties of rocks,such as the transport properties and mechanical responses under pressures.In this paper,we present a computer procedure for reconstructing the 3D porous structure of low-permeability sandstone.Two large-size 3D models are reconstructed based on the information of a reference model which is established from computed tomography(CT)images.A self-developed finite element method is applied to analyze the nonlinear mechanical behavior of the sandstone based on its reconstructed model and to compare the results with those based on the reference model.The good consistency of the obtained mechanical responses indicates the potential of using reconstruction models to predict the influences of porous structure on the mechanical properties of low-permeability sandstone.
基金support of the National Natural Science Foundation of China(51604275)the Key Laboratory of Urban Under Ground Engineering of Ministry of Education(TUE2018-01)+1 种基金Yue Qi Young Scholar Project of China University of Mining&Technology,Beijingthe Fundamental Research Funds for the Central Universities(2016QL02).
文摘Natural fracture data from one of the Carboniferous shale masses in the eastern Qaidam Basin were used to establish a stochastic model of a discrete fracture network and to perform discrete element simulation research on the size efect and mechanical parameters of shale.Analytical solutions of fctitious joints in transversely isotropic media were derived,which made it possible for the proposed numerical model to simulate the bedding and natural fractures in shale masses.The results indicate that there are two main factors infuencing the representative elementary volume(REV)size of a shale mass.The frst and most decisive factor is the presence of natural fractures in the block itself.The second is the anisotropy ratio:the greater the anisotropy is,the larger the REV.The bedding angle has little infuence on the REV size,whereas it has a certain infuence on the mechanical parameters of the rock mass.When the bedding angle approaches the average orientation of the natural fractures,the mechanical parameters of the shale blocks decrease greatly.The REV representing the mechanical properties of the Carboniferous shale masses in the eastern Qaidam Basin were comprehensively identifed by considering the infuence of bedding and natural fractures.When the numerical model size is larger than the REV,the fractured rock mass discontinuities can be transformed into equivalent continuities,which provides a method for simulating shale with natural fractures and bedding to analyze the stability of a borehole wall in shale.
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Projects 50709008 and 50539110 are supported by the National Natural Science Foundation of China.
文摘Based on laboratory results of time-dependent mechanical behavior tests,we investigated short-term and mechanical creep behavior of sandstone,observed in conventional triaxial compression experiments at room temperature,using a servo-controlled rheology testing machine.Given our short-term experimental test results,we confirmed deviatoric creep stress levels of sandstone.Multiple deviatoric stress levels were applied in steps to each sample.Each deviatoric stress level before the final failed deviatoric stress was maintained for 48 h or longer.Time-dependent variations of axial strains of sandstone samples are discussed and evaluated.During the creep tests,complete tertiary creep curves of sandstone were observed under failed deviatoric stress levels with different confining pressures.Slices of coal in sandstone samples can lead to distinct tertiary creep deformation failure.
基金financially supported by the National Natural Science Foundation of China (NO.52174095)。
文摘The use of aeolian sand(AS)as an aggregate to prepare coal mine cemented filling materials can resolve the problems of gangue shortage and excessive AS deposits.Owing to the lack of research on the mechanism of cemented AS backfill(CASB),the response surface method(RSM)was adopted in this study to analyze the influence of ordinary Portland cement(PO)content(x_(1)),fly ash(FA)-AS(FA-AS)ratio(x_(2)),and concentration(x_(3))on the mechanical and microscopic properties of the CASB.The hydration characteristics and internal pore structure of the backfill were assessed through thermogravimetric/derivative thermogravimetric analysis,mercury intrusion porosimetry,and scanning electron microscopy.The RSM results show that the influence of each factor and interaction term on the response values is extremely significant(except x_(1)x_(3),which had no obvious effect on the 28 d strength).The uniaxial compressive strength(UCS)increased with the PO content,FA-AS ratio,and concentration.The interaction effects of x_(1)x_(2),x_(1)x_(3),and x_(2)x_(3) on the UCS at 3,7,and 28 d were analyzed.In terms of the influence of interaction items,an improvement in one factor promoted the strengthening effect of another factor.The enhancement mechanism of the curing time,PO content,and FA-AS ratio on the backfill was reflected in the increase in hydration products and pore structure optimization.By contrast,the enhancement mechanism of the concentration was mainly the pore structure optimization.The UCS was positively correlated with weight loss and micropore content but negatively correlated with the total porosity.The R^(2) value of the fitting function of the strength and weight loss,micropore content,and total porosity exceeded 0.9,which improved the characterization of the enhancement mechanism of the UCS based on the thermogravimetric analysis and pore structure.This work obtained that the influence rules and mechanisms of the PO,FA-AS,concentration,and interaction terms on the mechanical properties of the CASB provided a certain theoretical and engineering guidance for CASB filling.
基金This work was financially supported by the National Natural Science Foundation of China(Nos.42077231 and 51574156).
文摘This study aims to investigate the mechanical response and acoustic emission(AE)characteristic of pre-flawed sandstone under both monotonic and multilevel constant-amplitude cyclic loads.Specifically,we explored how coplanar flaw angle and load type impact the strength and deformation behavior and microscopic damage mechanism.Results indicated that being fluctuated before rising with increasing fissure angle under monotonic loading,the peak strength of the specimen first increased slowly and then steeply under cyclic loading.The effect of multilevel cyclic loading on the mechanical parameters was more significant.For a single fatigue stage,the specimen underwent greater deformation in early cycles,which subsequently stabilized.Similar variation pattern was also reflected by AE count/energy/b-value.Crack behaviors were dominated by the fissure angle and load type and medium-scale crack accounted for 74.83%–86.44%of total crack.Compared with monotonic loading,crack distribution of specimen under cyclic loading was more complicated.Meanwhile,a simple model was proposed to describe the damage evolution of sandstone under cyclic loading.Finally,SEM images revealed that the microstructures at the fracture were mainly composed of intergranular fracture,and percentage of transgranular fracture jumped under cyclic loading due to the rapid release of elastic energy caused by high loading rate.
基金This study was financially supported by the National Natural Science Foundation of China(51579062,51379147),which is gratefully appreciated.
文摘The mechanical behaviors and energy dissipation characteristics of heat-treated granite were investigated under repeated impact loading.The granite samples were firstly heat-treated at the temperature of 20℃,200℃,400℃,and 600℃,respectively.The thermal damage characteristics of these samples were then observed and measured before impact tests.Dynamic impact compression tests finally were carried out using a modified split-Hopkinson pressure bar under three impact velocities of 12 m/s,15 m/s,and 18 m/s.These test results show that the mineral composition and the main oxides of the granite do not change with these treatment temperatures.The number of microcracks and microvoids decreases in the sample after 200℃ treatment.The mechanical properties of a sample after 600℃ treatment were rapidly deteriorated under the same impact velocity.The average of peak stress is much smaller than those after 20℃,200℃ and 400℃ treatments.The heat-treated samples have an energy threshold each.When the dissipated energy of a sample under a single impact is less than this threshold,the repeated impacts hardly lead to further damage accumulation even if its total breakage energy dissipation(BED)density is large.Under the same number of repeated impacts,the cumulative BED density of a sample after 600℃ treatment is the largest and its damage evolves most quickly.The total BED density of the sample after 200℃ treatment is the highest,which implies that this sample has better resistance to repeated impact,thus having less crack initiation and growth.
基金supported by the National Natural Science Foundation of China(NSFC)(41941018)the Program of China Scholarship Council(202106430031)。
文摘Active faults are a common adverse geological phenomenon that can occur during tunnel excavation and has a very negative impact on the construction and operation of the tunnel.In this paper,the grade IV rock surrounding the cross-fault tunnel with poor geological conditions has been chosen for the study.The support capacity of 2^(nd) Generation-Negative Poisson’s Ratio(2G-NPR)bolt in an active fault tunnel has been carried out on the basis of relevant results obtained from the geomechanical model test and numerical investigations of failure model for existing unsupported fault tunnel.The investigation shows that surrounding rock of the tunnel is prone to shear deformation and crack formation along the fault,as a result,the rock mass on the upper part of the fault slips as a whole.Furthermore,small-scale deformation and loss of blocks are observed around the tunnel;however,the 2G-NPR bolt support is found to be helpful in keeping the overall tunnel intact without any damage and instability.Due to the blocking effect of fault,the stress of the surrounding rock on the upper and lower parts of the fault is significantly different,and the stress at the left shoulder of the tunnel is greater than that at the right shoulder.The asymmetrical arrangement of 2G-NPR bolts can effectively control the asymmetric deformation and instability of the surrounding rock.The present numerical scheme is in good agreement with the model test results,and can reasonably reflect the stress and displacement characteristics of the surrounding rock of the tunnel.In comparison to unsupported and ordinary PR(Poisson’s Ratio)bolt support,2G-NPR bolt can effectively limit the fault slip and control the stability of the surrounding rock of the fault tunnel.The research findings may serve as a guideline for the use of 2G-NPR bolts in fault tunnel support engineering.
基金the National Key Research and Development Program of China(Nos.2019YFE0118500 and 2019YFC1904304)National Natural Science Foundation of China(Nos.52104107 and U22A20598)Natural Science Foundation of Jiangsu Province(No.BK20200634).
文摘Investigations on the dynamic mechanical properties and failure mechanisms of coal under in-situ stress is essential for the prevention of dynamic disasters in deep coal mines.Thus,a modified true triaxial Hopkinson bar was employed to explore the dynamic mechanical behaviors of coal at different confining pressures(0–20 MPa)and strain rates(40–220 s^(-1)).The results show that the dynamic peak stress is positively correlated with lateral static pre-stressσy andσz,but negatively correlated with axial static prestressσx.At approximate strain rates,increasing the lateral static pre-stress facilitates increasing the dynamic peak stress,but the minimum lateral static pre-stress is the primary factor limiting a significant increase in dynamic peak stress of coal.Furthermore,the dynamic differential stress is linearly related to the logarithm of strain rate,and the peak strain varies linearly with strain rate.However,there is no significant correlation between confining pressure and peak strain.Moreover,X-ray CT images and photographic fracture observations of coal samples show the failure patterns under uniaxial and triaxial conditions are splitting failure and shear failure,respectively.The device provides a viable approach for fully comprehending the dynamic mechanical behaviors of rock-like material in complex stress conditions.
基金supported by the National Natural Science Foundation of China(Nos.52274118 and 52274145)the Construction Project of Chenzhou National Sustainable Development Agenda Innovation Demonstration Zone(No.2021sfQ18).
文摘This paper investigates mechanical behaviours of sandstone during post-peak cyclic loading and unloading subjected to hydromechanical coupling effect, confirming the peak and residual strengths reduction laws of sandstone with water pressure, and revealing the influence of water pressure on the upper limit stress and deformation characteristics of sandstone during post-peak cyclic loading and unloading.Regarding the rock strength, the experimental study confirms that the peak strength σ_(p) and residual strength σ_(r) decrease as water pressure P increases. Especially, the normalized strength parameters σ_(p)/σ_(pk) and σ_(r)/σ_(re) was negatively and linearly correlated with the P/σ_(3). Moreover, the Hoek-Brown strength criterion can be applied to describe the relationship between effective peak strength and effective confining stress. During post-peak cyclic loading and unloading, both the upper limit stress σ_(p(i)) and crack damage threshold stress σ_(cd(i)) of each cycle tend to decrease with the increasing cycle number. A hysteresis loop exists among the loading and unloading stress–strain curves, indicating the unloading deformation modulus E_(unload) is larger than the loading deformation modulus E_(load). Based on experimental results,a post-peak strength prediction model related to water pressure and plastic shear strain is established.
基金financially supported by the National Natural Science Foundation of China(No.52174095)the Top Innovative Talents Cultivation Fund for Doctoral Postgraduates(No.BBJ2023054).
文摘Using aeolian sand(AS)for goaf backfilling allows coordination of green mining and AS control.Cemented AS backfill(CASB)exhibits brittle fracture.Polypropylene(PP)fibers are good toughening materials.When the toughening effect of fibers is analyzed,their influence on the slurry conveying performance should also be considered.Additionally,cement affects the interactions among the hydration products,fibers,and aggregates.In this study,the effects of cement content(8wt%,9wt%,and 10wt%)and PP fiber length(6,9,and 12 mm)and dosage(0.05wt%,0.1wt%,0.15wt%,0.2wt%,and 0.25wt%)on fluidity and mechanical properties of the fibertoughened CASB(FCASB)were analyzed.The results indicated that with increases in the three aforementioned factors,the slump flow decreased,while the rheological parameters increased.Uniaxial compressive strength(UCS)increased with the increase of cement content and fiber length,and with an increase in fiber dosage,it first increased and then decreased.The strain increased with the increase of fiber dosage and length.The effect of PP fibers became more pronounced with the increase of cement content.Digital image correlation(DIC)test results showed that the addition of fibers can restrain the peeling of blocks and the expansion of fissure,and reduce the stress concentration of the FCASB.Scanning electron microscopy(SEM)test indicated that the functional mechanisms of fibers mainly involved the interactions of fibers with the hydration products and matrix and the spatial distribution of fibers.On the basis of single-factor analysis,the response surface method(RSM)was used to analyze the effects of the three aforementioned factors and their interaction terms on the UCS.The influence surface of the two-factor interaction terms and the three-dimensional scatter plot of the three-factor coupling were established.In conclusion,the response law of the FCASB properties under the effects of cement and PP fibers were obtained,which provides theoretical and engineering guidance for FCASB filling.
