The negative Poisson’s ratio(NPR)bolt is an innovative support element distinguished by its high strength,elongation,and a slightly negative Poisson’s ratio.Unlike conventional prestressed(PR)bolts with a positive P...The negative Poisson’s ratio(NPR)bolt is an innovative support element distinguished by its high strength,elongation,and a slightly negative Poisson’s ratio.Unlike conventional prestressed(PR)bolts with a positive Poisson’s ratio,the NPR bolt exhibits a quasi-ideal plastic response without a prominent yield platform,enabling it to sustain high prestress with a substantial safety margin,which is particularly advantageous for jointed rock masses.However,investigations into the shear resistance mechanisms of NPR bolts under varying prestress levels remain limited.This study conducted full-scale double shear tests to assess the shear strength,deformation behavior,energy absorption,and failure mechanisms of NPR bolts under different prestress conditions.To ensure a fair comparison with PR bolts,a prestress utilization coefficient(PUC)was introduced.The results reveal that at a PUC of 0.25,the NPR bolt achieved peak axial force,shear displacement,and peak shear force values that are 2.41,1.88,and 2.13 times greater than those of the PR bolt,respectively.Shear performance was optimized at a prestress level of 100 kN,with energy absorption reaching 47.1 kJ,which is 2.8 times that of the PR bolt.Furthermore,the necking ratio was significantly reduced,indicating more distributed plastic deformation and delayed failure.Field applications verified the superior performance,resulting in a 27.4%reduction in roof settlement and enhanced structural integrity.These findings confirm that NPR bolts possess excellent shear resistance,energy absorption,and deformation adaptability,and optimizing prestress significantly enhances their support performance,providing a strong basis for geotechnical engineering applications.展开更多
High rock temperature is a great challenge frequently encountered during subsurface resource recovery and deep underground space utilization,and it is still unclear how the granitic rock responds to realtime high temp...High rock temperature is a great challenge frequently encountered during subsurface resource recovery and deep underground space utilization,and it is still unclear how the granitic rock responds to realtime high temperature upon shear loading.To better understand the shear fracture behavior and underlying processes of intact granite exposed to thermal-mechanical coupling loading,direct shear tests were conducted utilizing a newly built testing apparatus at varied normal stresses and high temperatures.Influencesof different temperatures and different heating methods(real-time heating and thermal treatment)on the shear mechanical behavior were compared and discussed.Results indicate that shear stress fluctuationswith some small stress drops occur as shear stress is approaching the peak strength under real-time heating,accompanied by more and earlier AE signal uprushes.This suggests that greater cracking events occur earlier during real-time heating than after thermal treatment,resulting in a lower peak shear strength.Furthermore,the peak shear strength,post-peak stress drop,and cohesion rise from room temperature(RT)to 200℃(the peak strength increases by 8%,5.8%,and 9.9%under normal stress of 5 MPa,15 MPa,and 20 MPa,correspondingly),and subsequently decline from 200℃to 400℃.Temperature has a limited impact on shear stiffness from RT to 200℃,but significantlyreduces it from 200℃to 400℃,with drops of 15%,7.9%,and 10%under normal stress of 5 MPa,15 MPa,and 20 MPa,respectively.Moreover,the shear strength and stiffness under real-time heating are lower than those for the thermally treated specimens.The strengthening of intact granite below 200℃upon shear is associated with loss of water and a more compacted structure,while the weakening effect of temperature on shear strength from 200℃to 400℃is due to the new thermal cracks and less brittle and stiff of minerals.展开更多
This study investigates the width of the secondary eyewall(SE)immediately following its formation in tropical cyclones with surface environmental winds aligned and counter-aligned with environmental vertical wind shea...This study investigates the width of the secondary eyewall(SE)immediately following its formation in tropical cyclones with surface environmental winds aligned and counter-aligned with environmental vertical wind shear(VWS),using idealized numerical experiments.Results reveal that the SE develops greater radial extent when surface winds align with VWS compared to counter-aligned conditions.In alignment configurations,shear-enhanced surface winds on the right flank amplify surface enthalpy fluxes,thereby elevating boundary-layer entropy within the downshear outer-core region.Subsequently,more vigorous outer rainbands develop,inducing marked acceleration of tangential winds in the outer core preceding SE formation.The resultant radial expansion of supergradient winds near the boundary-layer top triggers widespread convective activity immediately beyond the inner core.Progressive axisymmetrization of this convective forcing ultimately generates an expansive SE structure.展开更多
Excavation causes stress redistribution and affects the stress path during the shearing process of rock.The shear strength of rock varies under different stress paths,and the presence of defects reduces the shear stre...Excavation causes stress redistribution and affects the stress path during the shearing process of rock.The shear strength of rock varies under different stress paths,and the presence of defects reduces the shear strength.To further investigate this phenomenon,this study investigates the shear behaviour of rocks with different shear surface integrities under the influenceof different stress paths through laboratory tests and numerical simulations.The results indicate that the shear strength depends on the stress path and a decrease in the shear surface integrity reduces the degree of dependence.The cohesion and friction angle of the Mohr‒Coulomb criterion decrease with weakening of the shear surface integrity.For different stress paths,the direct shear strength is always greater than that of other shear stress paths.The pattern of changes in the acoustic emission count and cumulative count indirectly reflectsthe above findings.Numerical simulations further indicate that the different principal stress states and normal suppression effects during the shearing process lead to changes in the factors of crack propagation,resulting in different mechanical behaviours under various stress paths.For rocks with different integrity levels,the main reason for the different path dependences of shear strength is that the size of the area affected by shear is different.Shear failure will concentrate on the shear plane when the normal inhibition effect is greater.This study explores the mechanism of rock shear behaviour,providing a theoretical basis for establishing more accurate constitutive models and strength criteria.展开更多
The yielding transition of amorphous solids remains a fundamental yet poorly understood issue in materials physics.In this work,we employ oscillatory shear to probe the yielding transition in metallic glasses(MGs)with...The yielding transition of amorphous solids remains a fundamental yet poorly understood issue in materials physics.In this work,we employ oscillatory shear to probe the yielding transition in metallic glasses(MGs)with various thermal histories.We identify three distinct deformation regimes depending on the applied strain amplitudes.Below the yield strainγ_(y),the response is elastic and accompanied by aging,through reversible atomic rearrangements that preserve the material's initial memory of thermal history.Slightly aboveγ_(y),the system undergoes a sharp transition during oscillatory cycles,indicated by a sudden rise in potential energy and non-affine displacement,along with the emergence of a shear band.Well aboveγ_(y),plastic deformation dominates,driving samples of various initial stability toward a common steady state,while thermal histories are erased by irreversible rearrangements and shear band formation.These findings advance the understanding of failure mechanisms in MGs and shed light on tuning their mechanical performance in industrial applications involving cyclic loading.展开更多
Rock mass stability is significantly influenced by the heterogeneity of rock joint roughness and shear strength.While modern technology facilitates assessing roughness heterogeneity,evaluating shear strength heterogen...Rock mass stability is significantly influenced by the heterogeneity of rock joint roughness and shear strength.While modern technology facilitates assessing roughness heterogeneity,evaluating shear strength heterogeneity remains challenging.To address this,this study first captures the morphology of large-scale(1000 mm × 1000 mm) slate and granite joints via 3D laser scanning.Analysis of these surfaces and corresponding push/pull tests on carved specimens revealed a potential correlation between the heterogeneity of roughness and shear strength.A comparative evaluation of five statistical metrics identified information entropy(Hs) as the most robust indicator for quantifying rock joint heterogeneity.Further analysis using Hsreveals that the heterogeneity is anisotropic and,critically,that shear strength heterogeneity is governed not only by roughness heterogeneity but is also significantly influenced by the mean roughness value,normal stress,and intact rock tensile strength.Consequently,a simple comparison of roughness Hsvalues is insufficient for reliably comparing shear strength heterogeneity.To overcome this limitation,a theoretical framework is developed to explicitly map fundamental roughness statistics(mean and heterogeneity) to shear strength heterogeneity.This framework culminates in a practical workflow that allows for the rapid,field-based assessment of shear strength heterogeneity using readily obtainable rock joint roughness data.展开更多
Root-inspired anchorage systems in the field of bio-inspired geotechnics are renowned for enhancing the pullout capacity of traditional geotechnical anchorage systems by simulating the morphology and architecture of p...Root-inspired anchorage systems in the field of bio-inspired geotechnics are renowned for enhancing the pullout capacity of traditional geotechnical anchorage systems by simulating the morphology and architecture of plant root systems.However,limited studies have explored their practical applications,particularly in improving slope stability.To fill this gap,this study investigates the reinforcement effect of root-inspired anchors on slope stabilization using transparent soil modeling and 3D-printed anchors,and examines the impact of anchor branching patterns(i.e.branching numbers,branching angle,and branching nodes)on slope bearing capacity,shear band evolution,and temporal and spatial variation of slope deformation.The results show that peak slope bearing capacity increases with branching numbers and branching angles,correlating with the envelope area of the curved shear band.Upper anchors result in step-like deflections in the shear band near the trailing edge,while lower anchors convert the upward concave shear band into an upward convex one,thus increasing the slope bearing capacity.Slope deformation is minimized with intermediate branching parameters,such as a branching number of 4 and a branching angle of 45°.The anchor reinforcement mechanisms,i.e.anchor rod shear resistance,interface friction,anchor pullout capacity,and plate tightening effects,are comprehensively discussed,and the installation effects resulting from compromise slope modeling are identified as the contributors.These findings shed light on the failure process of root-inspired anchors reinforced slopes and provide a preliminary reference for potential applications,especially for the tradeoff between anchor branching,slope deformation,and slope stability.展开更多
High geo-stress and high temperature in deep rock engineering increase the possibility of engineering and geological disasters in discontinuous rocks.However,the influence of thermomechanical coupling on the shear beh...High geo-stress and high temperature in deep rock engineering increase the possibility of engineering and geological disasters in discontinuous rocks.However,the influence of thermomechanical coupling on the shear behavior and damage evolution of prefractured granite remains immature.In this context,true triaxial laboratory tests and discrete element method simulations under different confining pressures(σ3=3 MPa,σ2=4 MPa,andσ3=80 MPa,σ2=100 MPa)and temperatures(25℃-500℃)were carried out on rough granite fractures with two different orientations.Results indicate that high temperature and high confining pressure increase the peak strength of the prefractured specimen,leading to more microcracks in the host rock and more gouges between the surfaces.Thermal strengthening at low temperatures(<300℃)and residual stick-slip only occur under a greater confining pressure for prefractured specimens.High confining pressure suppresses generation of the thermal microcracks in the heating stage.Cracks first initiate in the asperities on the fracture surfaces,and then propagate into the rock matrix during the mechanical loading stage.In addition,prefractured granite with a larger fracture angle is characterized by smaller peak and residual strength,faster residual slip,fewer new cracks on the specimen surface,and a more pronounced thermal strengthening effect on peak strength.The slip tendency analysis indicates that a higher maximum principal stress(s1)and a large fracture angle(45°-75°)generally result in a higher potential for fracture slip or activation.This study will contribute to a better understanding of the fracture shear mechanism under true triaxial thermomechanical coupling conditions and provides new insights into the stability evaluation of deep dynamic geological hazards.展开更多
After the excavation of deep mining tunnels and underground caverns,the stability of surrounding rock controlled by structural planes is prone to structural damage and even engineering disasters due to three-dimension...After the excavation of deep mining tunnels and underground caverns,the stability of surrounding rock controlled by structural planes is prone to structural damage and even engineering disasters due to three-dimensional stress redistribution and multi-directional dynamic construction interference.However,the shear mechanical behavior,fracture evolution mechanism and precursor characteristics of rockmass under true triaxial stress and multi-directional coupling disturbance are not unclear.Therefore,this study carried out true triaxial shear tests on limestone intermittent structural planes under uni-,bi-and tri-directional coupling disturbances to analyze its mechanical behavior,fracture evolution mechanism and precursor characteristics.The results show that as the disturbance direction increase,the shear strength of limestone generally decreases,while the roughness of structural planes and the degree of anisotropy generally exhibit an increasing trend.The proportion of shear cracks on the structural plane increases with the increase of shear stress.The disturbance strain rate before failure shows a U-shaped trend.Near to disturbance failure,there were more high-energy and high-amplitude acoustic emission events near the structural plane,and b-value drops rapidly below 1,while lgN/b ratio increased to above 3.These findings provide experimental recognition and theoretical support for assessing the stability of rockmass under blasting excavation.展开更多
In geotechnical engineering,rock bolts are commonly used for reinforcement,while the surrounding rock mass bears varying degrees of shear loads.The shear rate affects the stability of bolted rock joints,especially in ...In geotechnical engineering,rock bolts are commonly used for reinforcement,while the surrounding rock mass bears varying degrees of shear loads.The shear rate affects the stability of bolted rock joints,especially in projects susceptible to dynamic shear loads.In laboratory experiments,fully-grouted bolts and energy-absorbing bolts were used as research objects,and artificial rock specimens with rough joints were fabricated to analyze the shear characteristics and damage mechanisms of bolted rock joints under cyclic shear conditions and different shear velocities.The results showed that as the shear rate increased,the shear strength of bolted rock joint specimens decreased.Degradation of asperities resulted in no obvious peak shear stress in the specimens.Energy-absorbing bolts exhibited greater deformation capacity,with significant necking phenomena and the ability to withstand larger shear displacements.In contrast,fully-grouted bolts,which have threaded surfaces that provide higher bonding performance,exhibited a reduced capacity for plastic deformation and were prone to breaking under smaller shear displacements.Although the shear stiffness of specimens reinforced by energy-absorbing bolts was slightly lower than that of fully-grouted bolt specimens,they demonstrated greater stability under various shear rates.The absorbed shear energy showed that energy-absorbing bolts had superior coordinated deformation capabilities,thus exhibiting greater absorbed shear energy than fully-grouted bolts.Overall,fully-grouted bolts are more suitable for projects requiring higher rock shear strength and overall stiffness.In contrast,energy-absorbing bolts are more suitable for coping with dynamic or fluctuating load conditions to maintain the relative stability of jointed rock masses.展开更多
To investigate the influence of the shear lag effect on the bending shear stress of single-box multicell box gird-ers(MCBG),the shear lag warping additional deflection is selected as the generalized displacement.The g...To investigate the influence of the shear lag effect on the bending shear stress of single-box multicell box gird-ers(MCBG),the shear lag warping additional deflection is selected as the generalized displacement.The governing dif-ferential equations and boundary conditions for the shear lag of the MCBG are derived using the energy variational method.Based on the shear lag warping deformation state of the MCBG and by employing the microelement equilib-rium differential equation and the coordination conditions for shear lag warping deformation,the calculation method for the bending-warping shear stress of the MCBG is de-rived,and the influence of the width-to-span and height-to span ratios on bending-warping shear stress is analyzed.Ex-ample analysis shows that the bending-warping shear stress of the MCBG calculated by the proposed calculation method coincides with the finite element solution,and the warping shear stress satisfies the self-balancing condition of shear warping,thus verifying the accuracy of the proposed method.The warping shear stress exhibits an antisymmetric distribution about the vertical axis of symmetry and has a weakening effect on the shear stress of the elementary beam(EB).The larger the width-to-span ratio is,the larger the proportion of the warping shear stress of the EB.The larger the height-to-span ratio is,the smaller the proportion of the warping shear stress and the more significant the influence of the width-to-span ratio.The more the number of cells is,the smaller the influence of the warping shear stress on the total bending shear stress.The influence of the shear lag ef-fect can be ignored in the calculation of the bending shear stress of three or more cells in the MCBG.展开更多
Evaluation of hydromechanical shear behavior of unsaturated soils is still a challenging issue. The time and cost needed for conducting precise experimental investigation on shear behavior of unsaturated soils have en...Evaluation of hydromechanical shear behavior of unsaturated soils is still a challenging issue. The time and cost needed for conducting precise experimental investigation on shear behavior of unsaturated soils have encouraged several investigators to develop analytical, empirical, or semi-empirical models for predicting the shear behavior of unsaturated soils. However, most of the previously proposed models are for specimens subjected to the isotropic state of stress, without considering the effect of initial shear stress. In this study, a hydromechanical constitutive model is proposed for unsaturated collapsible soils during shearing, with consideration of the effect of the initial shear stress. The model implements an effective stress-based disturbed state concept (DSC) to predict the stress-strain behavior of the soil. Accordingly, material/state variables were defined for both the start of the shearing stage and the critical state of the soil. A series of laboratory tests was performed using a fully automated unsaturated triaxial device to verify the proposed model. The experimental program included 23 suction-controlled unsaturated triaxial shear tests on reconstituted specimens of Gorgan clayey loess wetted to different levels of suctions under both isotropic and anisotropic stress states. The results show excellent agreement between the prediction by the proposed model and the experimental results.展开更多
The mechanical parameters and failure characteristics of sandstone under compressive-shear stress states provide crucial theoretical references for underground engineering construction.In this study,a series of varied...The mechanical parameters and failure characteristics of sandstone under compressive-shear stress states provide crucial theoretical references for underground engineering construction.In this study,a series of varied angle shear tests(VASTs)were designed using acoustic emission(AE)detection and digital image correlation technologies to evaluate the mechanical behaviors of typical red sandstone.AE signal parameters revealed differences in the number and intensity of microcracks within the sandstone,with a test angle(α)of 50°identified as a significant turning point for its failure properties.Whenα³50°,microcrack activity intensified,and the proportion of tensile cracks increased.Asαincreased,the number of fragments generated after failure decreased,fragment sizes became smaller,and the crack network simplified.Cracks extended from the two cut slits at the ends of the rock,gradually penetrating along the centerline towards the central location,as observed from the evolution of the strain concentration field.Both cohesion(c)and internal friction angle(ϕ)measured in VAST were lower than those measured under conventional triaxial compression.展开更多
Mg alloy often undergoes shear deformation during industrial processing.While its anisotropy and tension-compression asymmetry have been thoroughly studied under uniaxial loading,the understanding for shear loading is...Mg alloy often undergoes shear deformation during industrial processing.While its anisotropy and tension-compression asymmetry have been thoroughly studied under uniaxial loading,the understanding for shear loading is still lacking.This study employed a rolled AZ31B plate with typical basal texture to investigate the shear behaviors.Positive and negative simple shear experiments were performed at different angles in the transverse plane,whereby the visco-plastic self-consistent model was calibrated to reveal the deformation mechanisms and predict the mechanical responses at various orientations.Positive-negative shear asymmetry is present because extension twinning preferentially operates in one shear direction but is suppressed in the opposite direction.Simple shear induces multiple twin variants,thus impedes twin growth and slows the consumption of matrix,as compared to in-plane compression.For slip dominated simple shear,the interaction between loading-induced rigid body rotation and slip-induced crystal rotation produces distinct hardening behaviors,namely orthogonally asymmetric mechanical responses at complementary loading angles,which is largely absent in uniaxial loading.Finally,simulation results verify that positive-negative shear asymmetry appears only when the deviatoric normal stress on the sheet plane is non-zero.Positive-negative shear asymmetry persists except for the conditions of shear plane parallel to sheet plane,or shear direction parallel or perpendicular to rolling direction.展开更多
Localized rock failures,like cracks or shear bands,demand specific attention in modeling for solids and structures.This is due to the uncertainty of conventional continuum-based mechanical models when localized inelas...Localized rock failures,like cracks or shear bands,demand specific attention in modeling for solids and structures.This is due to the uncertainty of conventional continuum-based mechanical models when localized inelastic deformation has emerged.In such scenarios,as macroscopic inelastic reactions are primarily influenced by deformation and microstructural alterations within the localized area,internal variables that signify these microstructural changes should be established within this zone.Thus,localized deformation characteristics of rocks are studied here by the preset angle shear experiment.A method based on shear displacement and shear stress differences is proposed to identify the compaction,yielding,and residual points for enhancing the model's effectiveness and minimizing subjective influences.Next,a mechanical model for the localized shear band is depicted as an elasto-plastic model outlining the stress-displacement relation across both sides of the shear band.Incorporating damage theory and an elasto-plastic model,a proposed damage model is introduced to replicate shear stressdisplacement responses and localized damage evolution in intact rocks experiencing shear failure.Subsequently,a novel nonlinear mathematical model based on modified logistic growth theory is proposed for depicting the shear band's damage evolution pattern.Thereafter,an innovative damage model is proposed to effectively encompass diverse rock material behaviors,including elasticity,plasticity,and softening behaviors.Ultimately,the effects of the preset angles,temperature,normal stresses and the residual shear strength are carefully discussed.This discovery enhances rock research in the proposed damage model,particularly regarding shear failure mode.展开更多
This study investigated the mechanical responses and debonding mechanisms of a bolt-resin-rock composite anchoring sys-tem subjected to cyclic shear loading.A systematic analysis was conducted on the effects of the in...This study investigated the mechanical responses and debonding mechanisms of a bolt-resin-rock composite anchoring sys-tem subjected to cyclic shear loading.A systematic analysis was conducted on the effects of the initial normal load(Fsd),cyclic shear dis-placement amplitude(ud),frequency(f),and rock type on the shear load,normal displacement,shear wear characteristics,and strain field evolution.The experimental results showed that as Fsd increased from 7.5 to 120 kN,both the peak and residual shear loads exhibited in-creasing trends,with increments ranging from 1.98%to 35.25%and from 32.09%to 86.74%,respectively.The maximum shear load of each cycle declined over the cyclic shear cycles,with the rate of decrease slowing and stabilizing,indicating that shear wear primarily oc-curred at the initial cyclic shear stage.During cyclic shearing,the normal displacement decreased spirally with the shear displacement,im-plying continuous shear contraction.The spiral curves display sparse upwards and dense downward trends,with later cycles dominated by dynamic sliding along the pre-existing shear rupture surface,which is particularly evident in coal.The bearing capacity of the anchoring system varies with the rock type and is governed by the coal strength in coal,resin-rock bonding in sandstone#1 and sandstone#2,com-bined resin strength and resin-rock bonding in sandstone#3(sandstone#1,sandstone#2 and sandstone#3,increasing strength order),and resin strength and bolt-resin bonding in limestone.Cyclic shear loading induces anisotropic interfacial degradation,characterized by es-calating strain concentrations and predominant resin-rock interface debonding,with the damage severity modulated by the rock type.展开更多
Premature adiabatic shear localization caused by strain softening is a roadblock for the application of body-centered cubic(BCC)structured high-entropy alloy(HEAs)in the impact field.A micron-scale orthorhombic-phase(...Premature adiabatic shear localization caused by strain softening is a roadblock for the application of body-centered cubic(BCC)structured high-entropy alloy(HEAs)in the impact field.A micron-scale orthorhombic-phase(O-phase)strengthened TiZrVNbAl alloy was developed to delay adiabatic shear failure and enhance dynamic ductility.The O-phase can not only reduce the slip length,but also promote the pinning and tangling of the dislocations near the phase boundaries.The introduction of the O-phase transformed the strain hardening rate from negative to positive,resulting in a significantly improved dynamic shear resistance.Meanwhile,slip transfer across the O-phase via dislocation cutting mechanisms and a reduction of slip band spacing guaranteed dynamic deformation uniformity.Benefiting from the introduction of the O-phase,the alloy exhibits an excellent stored energy density(∼446 J/cm^(3),surpass the reported BCC-HEAs and typical titanium alloys),a large dynamic fracture strain(∼42%)and a considerable dynamic specific yield strength(∼241 MPa cm^(3)g^(-1)).The present study presents an effective approach for developing BCC-HEAs with excellent dynamic shear resistance and plasticity.展开更多
The growing demand for geothermal energy exploration and deep engineering projects necessitates a deeper understanding of rock behavior under extreme thermal conditions.This study investigates the effect of thermal tr...The growing demand for geothermal energy exploration and deep engineering projects necessitates a deeper understanding of rock behavior under extreme thermal conditions.This study investigates the effect of thermal treatment on the shear behavior of sedimentary sandstone and igneous granite,which are abundant in the Earth's crust.Direct shear tests were conducted on rock joints at room temperature(RT),250℃,and 500℃.The results show that the joints in sandstone and granite exhibit improved compressive and shear strength up to a temperature threshold of 200℃–350℃,followed by significant weakening beyond this range.This study investigated key parameters,including normal and shear stiffness,maximum joint closure,peak and residual shear strengths,internal friction angle,dilation angle,and cohesion.The compressive behavior of both rock types followed a modifiedBandis's equation.The peak shear strength followed Patton's bilinear and Jaeger's nonlinear failure criteria more accurately than the Mohr–Coulomb criterion.The results of this study provide valuable insights into the temperature-dependent behavior of sandstone and granite joints under compressive and shear loads,and their interoperation was strongly dependent on the mineralogical and structural components of the two rock types.These results have advanced our understanding of the temperature-dependent behavior of rock fractures,improving the safety of underground structures under thermal effects.展开更多
Understanding the anchorage performance of en-echelon joints under cyclic shear loading is crucial for optimizing support strategies in jointed rock masses.This study examines the anchorage effects on enechelon joints...Understanding the anchorage performance of en-echelon joints under cyclic shear loading is crucial for optimizing support strategies in jointed rock masses.This study examines the anchorage effects on enechelon joints with various orientations using laboratory cyclic shear tests.By comparing unbolted and bolted en-echelon joints,we analyze shear zone damage,shear properties,dilatancy,energy absorption,and acoustic emission characteristics to evaluate anchoring effects across shear cycles and joint orientations.Results reveal that bolted en-echelon joints experience more severe shear zone damage after cycles,with bolt deformation correlating to shear zone width.Bolted en-echelon joints exhibit faster shear strength deterioration and higher cumulative strength loss compared to unbolted ones,with losses ranging from 20.04%to 72.76%.The compressibility of en-echelon joints reduces the anchoring effect during shear cycles,leading to lower shear strength of bolted en-echelon joints in later stages of shear cycles compared to unbolted ones.Bolts reinforce en-echelon joints more effectively at non-positive angles,with the best performance observed at 0°and-60°.Anchorage accelerates the transition from rolling friction to sliding friction in the shear zone,enhancing energy absorption,which is crucial for rock projects under dynamic shear loading.Additionally,rock bolts expedite the transition of the cumulative AE hits and cumulative AE energy curves from rapid to steady growth,indicating that strong bolt-rock interactions accelerate crack initiation,propagation,and energy release.展开更多
The scaled suction caisson repre sents an innovative design featuring a bio-inspired sidewall modeled after snake skin,commonly utilized in offshore mooring platforms.In comparison with traditional suction caissons,th...The scaled suction caisson repre sents an innovative design featuring a bio-inspired sidewall modeled after snake skin,commonly utilized in offshore mooring platforms.In comparison with traditional suction caissons,this bio-inspired design demonstrates reduced penetration resistance and enhanced pull-out capacity due to the anisotropic shear behaviors of its sidewall.To investigate the shear behavior of the bio-inspired sidewall under pull-out load,direct shear tests were conducted between the bio-inspired surface and sand.The research demonstrates that the interface shear strength of the bio-inspired surface significantly surpasses that of the smooth surface due to interlocking effects.Additionally,the interface shear strength correlates with the aspect ratio of the bio-inspired surface,shear angle,and particle diameter distribution,with values increasing as the uniformity coefficient Cudecreases,while initially increasing and subsequently decreasing with increases in both aspect ratio and shear angle.The ratio between the interface friction angleδand internal friction angle δ_(s) defines the interface effect factor k.For the bio-inspired surface,the interface effect factor k varies with shear angleβ,ranging from 0.9 to 1.12.The peak value occurs at a shear angleβof 60°,substantially exceeding that of the smooth surface.A method for calculating the relative roughness R_(N) is employed to evaluate the interface roughness of the bio-inspired surface,taking into account scale dimension and particle diameter distribution effects.展开更多
基金supported by the State Key Laboratory of Intelligent Construction and Healthy Operation and Maintenance of Deep Underground Engineering(Grant No.SDGZ2505)the Postdoctoral Fellowship Program of the China Postdoctoral Science Foundation(Grant No.GZB20250742)the General Program of the China Postdoctoral Science Foundation(Grant No.2025M773213).
文摘The negative Poisson’s ratio(NPR)bolt is an innovative support element distinguished by its high strength,elongation,and a slightly negative Poisson’s ratio.Unlike conventional prestressed(PR)bolts with a positive Poisson’s ratio,the NPR bolt exhibits a quasi-ideal plastic response without a prominent yield platform,enabling it to sustain high prestress with a substantial safety margin,which is particularly advantageous for jointed rock masses.However,investigations into the shear resistance mechanisms of NPR bolts under varying prestress levels remain limited.This study conducted full-scale double shear tests to assess the shear strength,deformation behavior,energy absorption,and failure mechanisms of NPR bolts under different prestress conditions.To ensure a fair comparison with PR bolts,a prestress utilization coefficient(PUC)was introduced.The results reveal that at a PUC of 0.25,the NPR bolt achieved peak axial force,shear displacement,and peak shear force values that are 2.41,1.88,and 2.13 times greater than those of the PR bolt,respectively.Shear performance was optimized at a prestress level of 100 kN,with energy absorption reaching 47.1 kJ,which is 2.8 times that of the PR bolt.Furthermore,the necking ratio was significantly reduced,indicating more distributed plastic deformation and delayed failure.Field applications verified the superior performance,resulting in a 27.4%reduction in roof settlement and enhanced structural integrity.These findings confirm that NPR bolts possess excellent shear resistance,energy absorption,and deformation adaptability,and optimizing prestress significantly enhances their support performance,providing a strong basis for geotechnical engineering applications.
基金support from the Taishan Scholars Program,Key Research Program of Frontier Sciences,Chinese Academy of Sciences(CAS),Grant No.ZDBS-LY-DQC022Open Research Fund of State Key Laboratory of Geomechanics and Geotechnical Engineering Safety,Grant No.SKLGME023003.
文摘High rock temperature is a great challenge frequently encountered during subsurface resource recovery and deep underground space utilization,and it is still unclear how the granitic rock responds to realtime high temperature upon shear loading.To better understand the shear fracture behavior and underlying processes of intact granite exposed to thermal-mechanical coupling loading,direct shear tests were conducted utilizing a newly built testing apparatus at varied normal stresses and high temperatures.Influencesof different temperatures and different heating methods(real-time heating and thermal treatment)on the shear mechanical behavior were compared and discussed.Results indicate that shear stress fluctuationswith some small stress drops occur as shear stress is approaching the peak strength under real-time heating,accompanied by more and earlier AE signal uprushes.This suggests that greater cracking events occur earlier during real-time heating than after thermal treatment,resulting in a lower peak shear strength.Furthermore,the peak shear strength,post-peak stress drop,and cohesion rise from room temperature(RT)to 200℃(the peak strength increases by 8%,5.8%,and 9.9%under normal stress of 5 MPa,15 MPa,and 20 MPa,correspondingly),and subsequently decline from 200℃to 400℃.Temperature has a limited impact on shear stiffness from RT to 200℃,but significantlyreduces it from 200℃to 400℃,with drops of 15%,7.9%,and 10%under normal stress of 5 MPa,15 MPa,and 20 MPa,respectively.Moreover,the shear strength and stiffness under real-time heating are lower than those for the thermally treated specimens.The strengthening of intact granite below 200℃upon shear is associated with loss of water and a more compacted structure,while the weakening effect of temperature on shear strength from 200℃to 400℃is due to the new thermal cracks and less brittle and stiff of minerals.
基金jointly supported by the National Natural Science Foundation of China[grant numbers U2342202,42175005,and 42175016]the Qing Lan Project[grant number R2023Q06]。
文摘This study investigates the width of the secondary eyewall(SE)immediately following its formation in tropical cyclones with surface environmental winds aligned and counter-aligned with environmental vertical wind shear(VWS),using idealized numerical experiments.Results reveal that the SE develops greater radial extent when surface winds align with VWS compared to counter-aligned conditions.In alignment configurations,shear-enhanced surface winds on the right flank amplify surface enthalpy fluxes,thereby elevating boundary-layer entropy within the downshear outer-core region.Subsequently,more vigorous outer rainbands develop,inducing marked acceleration of tangential winds in the outer core preceding SE formation.The resultant radial expansion of supergradient winds near the boundary-layer top triggers widespread convective activity immediately beyond the inner core.Progressive axisymmetrization of this convective forcing ultimately generates an expansive SE structure.
基金support from the Postgraduate Research&Practice Innovation Program of Jiangsu Province,China(Grant No.KYCX24_2822)the Graduate Innovation Program of China University of Mining and Technology(Grant No.2024WLKXJ205)the National Natural Science Foundation of China(Grant No.52474157).
文摘Excavation causes stress redistribution and affects the stress path during the shearing process of rock.The shear strength of rock varies under different stress paths,and the presence of defects reduces the shear strength.To further investigate this phenomenon,this study investigates the shear behaviour of rocks with different shear surface integrities under the influenceof different stress paths through laboratory tests and numerical simulations.The results indicate that the shear strength depends on the stress path and a decrease in the shear surface integrity reduces the degree of dependence.The cohesion and friction angle of the Mohr‒Coulomb criterion decrease with weakening of the shear surface integrity.For different stress paths,the direct shear strength is always greater than that of other shear stress paths.The pattern of changes in the acoustic emission count and cumulative count indirectly reflectsthe above findings.Numerical simulations further indicate that the different principal stress states and normal suppression effects during the shearing process lead to changes in the factors of crack propagation,resulting in different mechanical behaviours under various stress paths.For rocks with different integrity levels,the main reason for the different path dependences of shear strength is that the size of the area affected by shear is different.Shear failure will concentrate on the shear plane when the normal inhibition effect is greater.This study explores the mechanism of rock shear behaviour,providing a theoretical basis for establishing more accurate constitutive models and strength criteria.
基金supported by the National Natural Science Foundation of China(Grant Nos.52201169 and 52575352)the Key Research&Development Plan of Anhui Province(Grant No.2022a05020016)。
文摘The yielding transition of amorphous solids remains a fundamental yet poorly understood issue in materials physics.In this work,we employ oscillatory shear to probe the yielding transition in metallic glasses(MGs)with various thermal histories.We identify three distinct deformation regimes depending on the applied strain amplitudes.Below the yield strainγ_(y),the response is elastic and accompanied by aging,through reversible atomic rearrangements that preserve the material's initial memory of thermal history.Slightly aboveγ_(y),the system undergoes a sharp transition during oscillatory cycles,indicated by a sudden rise in potential energy and non-affine displacement,along with the emergence of a shear band.Well aboveγ_(y),plastic deformation dominates,driving samples of various initial stability toward a common steady state,while thermal histories are erased by irreversible rearrangements and shear band formation.These findings advance the understanding of failure mechanisms in MGs and shed light on tuning their mechanical performance in industrial applications involving cyclic loading.
基金supported by the National Natural Science Foundation of China (Nos.42422705,42207175,42177117 and 42577170)the Ningbo Youth Leading Talent Project (No.2024QL051)+1 种基金the Chinese Academy of Engineering Science and Technology Strategy Consulting Project (No.2025-XZ-57)the Central Government Funding Program for Guiding Local Science and Technology Development (No.2025ZY01028)。
文摘Rock mass stability is significantly influenced by the heterogeneity of rock joint roughness and shear strength.While modern technology facilitates assessing roughness heterogeneity,evaluating shear strength heterogeneity remains challenging.To address this,this study first captures the morphology of large-scale(1000 mm × 1000 mm) slate and granite joints via 3D laser scanning.Analysis of these surfaces and corresponding push/pull tests on carved specimens revealed a potential correlation between the heterogeneity of roughness and shear strength.A comparative evaluation of five statistical metrics identified information entropy(Hs) as the most robust indicator for quantifying rock joint heterogeneity.Further analysis using Hsreveals that the heterogeneity is anisotropic and,critically,that shear strength heterogeneity is governed not only by roughness heterogeneity but is also significantly influenced by the mean roughness value,normal stress,and intact rock tensile strength.Consequently,a simple comparison of roughness Hsvalues is insufficient for reliably comparing shear strength heterogeneity.To overcome this limitation,a theoretical framework is developed to explicitly map fundamental roughness statistics(mean and heterogeneity) to shear strength heterogeneity.This framework culminates in a practical workflow that allows for the rapid,field-based assessment of shear strength heterogeneity using readily obtainable rock joint roughness data.
基金supported by the High-end Foreign Expert Introduction Program(Grant No.G2022165004L)the Sichuan Transportation Science and Technology Project(Grant No.2018-ZL-01)China Railway 20th Bureau Science and Technology Project(Grant No.YF1900SD07B).
文摘Root-inspired anchorage systems in the field of bio-inspired geotechnics are renowned for enhancing the pullout capacity of traditional geotechnical anchorage systems by simulating the morphology and architecture of plant root systems.However,limited studies have explored their practical applications,particularly in improving slope stability.To fill this gap,this study investigates the reinforcement effect of root-inspired anchors on slope stabilization using transparent soil modeling and 3D-printed anchors,and examines the impact of anchor branching patterns(i.e.branching numbers,branching angle,and branching nodes)on slope bearing capacity,shear band evolution,and temporal and spatial variation of slope deformation.The results show that peak slope bearing capacity increases with branching numbers and branching angles,correlating with the envelope area of the curved shear band.Upper anchors result in step-like deflections in the shear band near the trailing edge,while lower anchors convert the upward concave shear band into an upward convex one,thus increasing the slope bearing capacity.Slope deformation is minimized with intermediate branching parameters,such as a branching number of 4 and a branching angle of 45°.The anchor reinforcement mechanisms,i.e.anchor rod shear resistance,interface friction,anchor pullout capacity,and plate tightening effects,are comprehensively discussed,and the installation effects resulting from compromise slope modeling are identified as the contributors.These findings shed light on the failure process of root-inspired anchors reinforced slopes and provide a preliminary reference for potential applications,especially for the tradeoff between anchor branching,slope deformation,and slope stability.
基金support from the National Key Research and Development Program of China(Grant No.2022YFE0137200)supported by the Taishan Scholars Program and Open Research Fund of State Key Laboratory of Geomechanics and Geotechnical Engineering Safety(Grant No.SKLGME023003).
文摘High geo-stress and high temperature in deep rock engineering increase the possibility of engineering and geological disasters in discontinuous rocks.However,the influence of thermomechanical coupling on the shear behavior and damage evolution of prefractured granite remains immature.In this context,true triaxial laboratory tests and discrete element method simulations under different confining pressures(σ3=3 MPa,σ2=4 MPa,andσ3=80 MPa,σ2=100 MPa)and temperatures(25℃-500℃)were carried out on rough granite fractures with two different orientations.Results indicate that high temperature and high confining pressure increase the peak strength of the prefractured specimen,leading to more microcracks in the host rock and more gouges between the surfaces.Thermal strengthening at low temperatures(<300℃)and residual stick-slip only occur under a greater confining pressure for prefractured specimens.High confining pressure suppresses generation of the thermal microcracks in the heating stage.Cracks first initiate in the asperities on the fracture surfaces,and then propagate into the rock matrix during the mechanical loading stage.In addition,prefractured granite with a larger fracture angle is characterized by smaller peak and residual strength,faster residual slip,fewer new cracks on the specimen surface,and a more pronounced thermal strengthening effect on peak strength.The slip tendency analysis indicates that a higher maximum principal stress(s1)and a large fracture angle(45°-75°)generally result in a higher potential for fracture slip or activation.This study will contribute to a better understanding of the fracture shear mechanism under true triaxial thermomechanical coupling conditions and provides new insights into the stability evaluation of deep dynamic geological hazards.
基金support received from the National Natural Science Foundation of China(Nos.52274145,52469019,and 52109119)the Guangxi Natural Science Foundation(No.2025GXNSFAA069165)the Chinese Postdoctoral Science Fund Project(No.2022M723408).
文摘After the excavation of deep mining tunnels and underground caverns,the stability of surrounding rock controlled by structural planes is prone to structural damage and even engineering disasters due to three-dimensional stress redistribution and multi-directional dynamic construction interference.However,the shear mechanical behavior,fracture evolution mechanism and precursor characteristics of rockmass under true triaxial stress and multi-directional coupling disturbance are not unclear.Therefore,this study carried out true triaxial shear tests on limestone intermittent structural planes under uni-,bi-and tri-directional coupling disturbances to analyze its mechanical behavior,fracture evolution mechanism and precursor characteristics.The results show that as the disturbance direction increase,the shear strength of limestone generally decreases,while the roughness of structural planes and the degree of anisotropy generally exhibit an increasing trend.The proportion of shear cracks on the structural plane increases with the increase of shear stress.The disturbance strain rate before failure shows a U-shaped trend.Near to disturbance failure,there were more high-energy and high-amplitude acoustic emission events near the structural plane,and b-value drops rapidly below 1,while lgN/b ratio increased to above 3.These findings provide experimental recognition and theoretical support for assessing the stability of rockmass under blasting excavation.
基金partially funded by the National Natural Science Foundation of China(Grant Nos.52179098 and 41907251)the State Scholarship Fund of China(Grant No.202306650001).
文摘In geotechnical engineering,rock bolts are commonly used for reinforcement,while the surrounding rock mass bears varying degrees of shear loads.The shear rate affects the stability of bolted rock joints,especially in projects susceptible to dynamic shear loads.In laboratory experiments,fully-grouted bolts and energy-absorbing bolts were used as research objects,and artificial rock specimens with rough joints were fabricated to analyze the shear characteristics and damage mechanisms of bolted rock joints under cyclic shear conditions and different shear velocities.The results showed that as the shear rate increased,the shear strength of bolted rock joint specimens decreased.Degradation of asperities resulted in no obvious peak shear stress in the specimens.Energy-absorbing bolts exhibited greater deformation capacity,with significant necking phenomena and the ability to withstand larger shear displacements.In contrast,fully-grouted bolts,which have threaded surfaces that provide higher bonding performance,exhibited a reduced capacity for plastic deformation and were prone to breaking under smaller shear displacements.Although the shear stiffness of specimens reinforced by energy-absorbing bolts was slightly lower than that of fully-grouted bolt specimens,they demonstrated greater stability under various shear rates.The absorbed shear energy showed that energy-absorbing bolts had superior coordinated deformation capabilities,thus exhibiting greater absorbed shear energy than fully-grouted bolts.Overall,fully-grouted bolts are more suitable for projects requiring higher rock shear strength and overall stiffness.In contrast,energy-absorbing bolts are more suitable for coping with dynamic or fluctuating load conditions to maintain the relative stability of jointed rock masses.
基金The National Natural Science Foundation of China (No. 52368020)Gansu Provincial Universities Young Doctor Support Project (No. 2024QB-047)Gansu Province postdoctoral Fund (No. 386824)。
文摘To investigate the influence of the shear lag effect on the bending shear stress of single-box multicell box gird-ers(MCBG),the shear lag warping additional deflection is selected as the generalized displacement.The governing dif-ferential equations and boundary conditions for the shear lag of the MCBG are derived using the energy variational method.Based on the shear lag warping deformation state of the MCBG and by employing the microelement equilib-rium differential equation and the coordination conditions for shear lag warping deformation,the calculation method for the bending-warping shear stress of the MCBG is de-rived,and the influence of the width-to-span and height-to span ratios on bending-warping shear stress is analyzed.Ex-ample analysis shows that the bending-warping shear stress of the MCBG calculated by the proposed calculation method coincides with the finite element solution,and the warping shear stress satisfies the self-balancing condition of shear warping,thus verifying the accuracy of the proposed method.The warping shear stress exhibits an antisymmetric distribution about the vertical axis of symmetry and has a weakening effect on the shear stress of the elementary beam(EB).The larger the width-to-span ratio is,the larger the proportion of the warping shear stress of the EB.The larger the height-to-span ratio is,the smaller the proportion of the warping shear stress and the more significant the influence of the width-to-span ratio.The more the number of cells is,the smaller the influence of the warping shear stress on the total bending shear stress.The influence of the shear lag ef-fect can be ignored in the calculation of the bending shear stress of three or more cells in the MCBG.
文摘Evaluation of hydromechanical shear behavior of unsaturated soils is still a challenging issue. The time and cost needed for conducting precise experimental investigation on shear behavior of unsaturated soils have encouraged several investigators to develop analytical, empirical, or semi-empirical models for predicting the shear behavior of unsaturated soils. However, most of the previously proposed models are for specimens subjected to the isotropic state of stress, without considering the effect of initial shear stress. In this study, a hydromechanical constitutive model is proposed for unsaturated collapsible soils during shearing, with consideration of the effect of the initial shear stress. The model implements an effective stress-based disturbed state concept (DSC) to predict the stress-strain behavior of the soil. Accordingly, material/state variables were defined for both the start of the shearing stage and the critical state of the soil. A series of laboratory tests was performed using a fully automated unsaturated triaxial device to verify the proposed model. The experimental program included 23 suction-controlled unsaturated triaxial shear tests on reconstituted specimens of Gorgan clayey loess wetted to different levels of suctions under both isotropic and anisotropic stress states. The results show excellent agreement between the prediction by the proposed model and the experimental results.
基金Project(52374150)supported by the National Natural Science Foundation of ChinaProject(2021RC3007)supported by the Science and Technology Innovation Program of Hunan Province,China。
文摘The mechanical parameters and failure characteristics of sandstone under compressive-shear stress states provide crucial theoretical references for underground engineering construction.In this study,a series of varied angle shear tests(VASTs)were designed using acoustic emission(AE)detection and digital image correlation technologies to evaluate the mechanical behaviors of typical red sandstone.AE signal parameters revealed differences in the number and intensity of microcracks within the sandstone,with a test angle(α)of 50°identified as a significant turning point for its failure properties.Whenα³50°,microcrack activity intensified,and the proportion of tensile cracks increased.Asαincreased,the number of fragments generated after failure decreased,fragment sizes became smaller,and the crack network simplified.Cracks extended from the two cut slits at the ends of the rock,gradually penetrating along the centerline towards the central location,as observed from the evolution of the strain concentration field.Both cohesion(c)and internal friction angle(ϕ)measured in VAST were lower than those measured under conventional triaxial compression.
基金supports of the National Key Research and Development Program of China(Grant No.2023YFB3710900)the National Natural Science Foundation of China(Grant Nos.52071211 and 52071208)。
文摘Mg alloy often undergoes shear deformation during industrial processing.While its anisotropy and tension-compression asymmetry have been thoroughly studied under uniaxial loading,the understanding for shear loading is still lacking.This study employed a rolled AZ31B plate with typical basal texture to investigate the shear behaviors.Positive and negative simple shear experiments were performed at different angles in the transverse plane,whereby the visco-plastic self-consistent model was calibrated to reveal the deformation mechanisms and predict the mechanical responses at various orientations.Positive-negative shear asymmetry is present because extension twinning preferentially operates in one shear direction but is suppressed in the opposite direction.Simple shear induces multiple twin variants,thus impedes twin growth and slows the consumption of matrix,as compared to in-plane compression.For slip dominated simple shear,the interaction between loading-induced rigid body rotation and slip-induced crystal rotation produces distinct hardening behaviors,namely orthogonally asymmetric mechanical responses at complementary loading angles,which is largely absent in uniaxial loading.Finally,simulation results verify that positive-negative shear asymmetry appears only when the deviatoric normal stress on the sheet plane is non-zero.Positive-negative shear asymmetry persists except for the conditions of shear plane parallel to sheet plane,or shear direction parallel or perpendicular to rolling direction.
基金supported by the China Scholarship Council Program(Grant No.202008320274)it is also supported by Technical University of Munich.
文摘Localized rock failures,like cracks or shear bands,demand specific attention in modeling for solids and structures.This is due to the uncertainty of conventional continuum-based mechanical models when localized inelastic deformation has emerged.In such scenarios,as macroscopic inelastic reactions are primarily influenced by deformation and microstructural alterations within the localized area,internal variables that signify these microstructural changes should be established within this zone.Thus,localized deformation characteristics of rocks are studied here by the preset angle shear experiment.A method based on shear displacement and shear stress differences is proposed to identify the compaction,yielding,and residual points for enhancing the model's effectiveness and minimizing subjective influences.Next,a mechanical model for the localized shear band is depicted as an elasto-plastic model outlining the stress-displacement relation across both sides of the shear band.Incorporating damage theory and an elasto-plastic model,a proposed damage model is introduced to replicate shear stressdisplacement responses and localized damage evolution in intact rocks experiencing shear failure.Subsequently,a novel nonlinear mathematical model based on modified logistic growth theory is proposed for depicting the shear band's damage evolution pattern.Thereafter,an innovative damage model is proposed to effectively encompass diverse rock material behaviors,including elasticity,plasticity,and softening behaviors.Ultimately,the effects of the preset angles,temperature,normal stresses and the residual shear strength are carefully discussed.This discovery enhances rock research in the proposed damage model,particularly regarding shear failure mode.
基金The financial support from the National Natural Science Foundation of China(Nos.52174092,42472338,and 51904290)the Natural Science Foundation of Jiangsu Province,China(No.BK20220157)+1 种基金the Fundamental Research Funds for the Central Universities,China(No.2022YCPY0202)the Open Fund of Key Laboratory of Safety and High-efficiency Coal Mining,Ministry of Education(Anhui University of Science and Technology)(No.JYBSYS202311)。
文摘This study investigated the mechanical responses and debonding mechanisms of a bolt-resin-rock composite anchoring sys-tem subjected to cyclic shear loading.A systematic analysis was conducted on the effects of the initial normal load(Fsd),cyclic shear dis-placement amplitude(ud),frequency(f),and rock type on the shear load,normal displacement,shear wear characteristics,and strain field evolution.The experimental results showed that as Fsd increased from 7.5 to 120 kN,both the peak and residual shear loads exhibited in-creasing trends,with increments ranging from 1.98%to 35.25%and from 32.09%to 86.74%,respectively.The maximum shear load of each cycle declined over the cyclic shear cycles,with the rate of decrease slowing and stabilizing,indicating that shear wear primarily oc-curred at the initial cyclic shear stage.During cyclic shearing,the normal displacement decreased spirally with the shear displacement,im-plying continuous shear contraction.The spiral curves display sparse upwards and dense downward trends,with later cycles dominated by dynamic sliding along the pre-existing shear rupture surface,which is particularly evident in coal.The bearing capacity of the anchoring system varies with the rock type and is governed by the coal strength in coal,resin-rock bonding in sandstone#1 and sandstone#2,com-bined resin strength and resin-rock bonding in sandstone#3(sandstone#1,sandstone#2 and sandstone#3,increasing strength order),and resin strength and bolt-resin bonding in limestone.Cyclic shear loading induces anisotropic interfacial degradation,characterized by es-calating strain concentrations and predominant resin-rock interface debonding,with the damage severity modulated by the rock type.
基金supported by the YEQISUN Joint Funds of the National Natural Science Foundation of China(Grant No.U2241234)the National Natural Science Foundation of China(Grant No.52301127).
文摘Premature adiabatic shear localization caused by strain softening is a roadblock for the application of body-centered cubic(BCC)structured high-entropy alloy(HEAs)in the impact field.A micron-scale orthorhombic-phase(O-phase)strengthened TiZrVNbAl alloy was developed to delay adiabatic shear failure and enhance dynamic ductility.The O-phase can not only reduce the slip length,but also promote the pinning and tangling of the dislocations near the phase boundaries.The introduction of the O-phase transformed the strain hardening rate from negative to positive,resulting in a significantly improved dynamic shear resistance.Meanwhile,slip transfer across the O-phase via dislocation cutting mechanisms and a reduction of slip band spacing guaranteed dynamic deformation uniformity.Benefiting from the introduction of the O-phase,the alloy exhibits an excellent stored energy density(∼446 J/cm^(3),surpass the reported BCC-HEAs and typical titanium alloys),a large dynamic fracture strain(∼42%)and a considerable dynamic specific yield strength(∼241 MPa cm^(3)g^(-1)).The present study presents an effective approach for developing BCC-HEAs with excellent dynamic shear resistance and plasticity.
基金the ORSP at Abu Dhabi University,UAE,for funding this project(Grant No.19300751).
文摘The growing demand for geothermal energy exploration and deep engineering projects necessitates a deeper understanding of rock behavior under extreme thermal conditions.This study investigates the effect of thermal treatment on the shear behavior of sedimentary sandstone and igneous granite,which are abundant in the Earth's crust.Direct shear tests were conducted on rock joints at room temperature(RT),250℃,and 500℃.The results show that the joints in sandstone and granite exhibit improved compressive and shear strength up to a temperature threshold of 200℃–350℃,followed by significant weakening beyond this range.This study investigated key parameters,including normal and shear stiffness,maximum joint closure,peak and residual shear strengths,internal friction angle,dilation angle,and cohesion.The compressive behavior of both rock types followed a modifiedBandis's equation.The peak shear strength followed Patton's bilinear and Jaeger's nonlinear failure criteria more accurately than the Mohr–Coulomb criterion.The results of this study provide valuable insights into the temperature-dependent behavior of sandstone and granite joints under compressive and shear loads,and their interoperation was strongly dependent on the mineralogical and structural components of the two rock types.These results have advanced our understanding of the temperature-dependent behavior of rock fractures,improving the safety of underground structures under thermal effects.
基金financially supported by the National Natural Science Foundation of China (No.42172292)Taishan Scholars Project Special Funding,and Shandong Energy Group (No.SNKJ2022A01-R26)funded by the China Scholarship Council (CSC No.202006220274)。
文摘Understanding the anchorage performance of en-echelon joints under cyclic shear loading is crucial for optimizing support strategies in jointed rock masses.This study examines the anchorage effects on enechelon joints with various orientations using laboratory cyclic shear tests.By comparing unbolted and bolted en-echelon joints,we analyze shear zone damage,shear properties,dilatancy,energy absorption,and acoustic emission characteristics to evaluate anchoring effects across shear cycles and joint orientations.Results reveal that bolted en-echelon joints experience more severe shear zone damage after cycles,with bolt deformation correlating to shear zone width.Bolted en-echelon joints exhibit faster shear strength deterioration and higher cumulative strength loss compared to unbolted ones,with losses ranging from 20.04%to 72.76%.The compressibility of en-echelon joints reduces the anchoring effect during shear cycles,leading to lower shear strength of bolted en-echelon joints in later stages of shear cycles compared to unbolted ones.Bolts reinforce en-echelon joints more effectively at non-positive angles,with the best performance observed at 0°and-60°.Anchorage accelerates the transition from rolling friction to sliding friction in the shear zone,enhancing energy absorption,which is crucial for rock projects under dynamic shear loading.Additionally,rock bolts expedite the transition of the cumulative AE hits and cumulative AE energy curves from rapid to steady growth,indicating that strong bolt-rock interactions accelerate crack initiation,propagation,and energy release.
基金supported by the National Natural Science Foundation of China(Grant Nos.52371301 and 52471289)。
文摘The scaled suction caisson repre sents an innovative design featuring a bio-inspired sidewall modeled after snake skin,commonly utilized in offshore mooring platforms.In comparison with traditional suction caissons,this bio-inspired design demonstrates reduced penetration resistance and enhanced pull-out capacity due to the anisotropic shear behaviors of its sidewall.To investigate the shear behavior of the bio-inspired sidewall under pull-out load,direct shear tests were conducted between the bio-inspired surface and sand.The research demonstrates that the interface shear strength of the bio-inspired surface significantly surpasses that of the smooth surface due to interlocking effects.Additionally,the interface shear strength correlates with the aspect ratio of the bio-inspired surface,shear angle,and particle diameter distribution,with values increasing as the uniformity coefficient Cudecreases,while initially increasing and subsequently decreasing with increases in both aspect ratio and shear angle.The ratio between the interface friction angleδand internal friction angle δ_(s) defines the interface effect factor k.For the bio-inspired surface,the interface effect factor k varies with shear angleβ,ranging from 0.9 to 1.12.The peak value occurs at a shear angleβof 60°,substantially exceeding that of the smooth surface.A method for calculating the relative roughness R_(N) is employed to evaluate the interface roughness of the bio-inspired surface,taking into account scale dimension and particle diameter distribution effects.
