Flow and transport properties of fractured crystalline rock are of great interest for different geotechnical ap-plications,such as storage of carbon dioxide,extraction of geothermal energy,or geologic storage of hazar...Flow and transport properties of fractured crystalline rock are of great interest for different geotechnical ap-plications,such as storage of carbon dioxide,extraction of geothermal energy,or geologic storage of hazardous waste.For the long-term safety assessment of geological storage of hazardous waste,the understanding of flow and transport properties through the network of fractures is essential.The flow and transport behaviour can be explored using numerical models to investigate what parameters that affect the results.In this work a pilot study is carried out for multiple realizations of single realistic fractures,using fractal theories,which then are nu-merically sheared using a semi-analytical algorithm.The aperture field is calculated using the average distance of the volume integral of the void that a 1 mm lateral displacement of the sheared surfaces generates.The flow field through the aperture field is solved using Reynolds lubrication equation in linear triangular finite elements.The transport properties,travel length,travel time,transport resistance and specific flow wetted surface,are calculated in a Lagrangian framework using 10,000 particles for each of the 128 flow fields.Evaluating these four metrics,varying initial roughness,4<JRC<10 and normal stress between 0.2 and 20 MPa during shearing,it is concluded that an increase in normal stress generally results in longer travel paths,longer travel times,higher transport resistance and larger specific flow wetted surface while an increase of initial roughness will generally result in longer travel paths,shorter travel times,lower transport resistance and smaller specific flow wetted surface.展开更多
The distinctive characteristics exhibited by the aftershocks of Ms6.0 induced earthquakes in Changning,Sichuan,China,have attracted significant attention.The prevalence of salt rock(halite)in this area is closely asso...The distinctive characteristics exhibited by the aftershocks of Ms6.0 induced earthquakes in Changning,Sichuan,China,have attracted significant attention.The prevalence of salt rock(halite)in this area is closely associated with induced seismic events.The present study was conducted to examine the role of halite in frictional properties.To this end,laboratory measurements were taken for simulated fault gouge composed of halite.Slide-hold-slide(SHS)shear experiments were performed on gouges with grain size<106 mm at constant normal stress from 5 MPa to 30 MPa and constant shear velocity in the range of 1-10 mm/s.Halite gouge shows higher frictional strength and frictional healing rate than most minerals.The results reveal that the fault within halite can potentially generate intense seismic events and more significant aftershocks.An increase in normal stress leads to a reduction in frictional healing,with frictional strength initially increasing and then decreasing.The elevated shear velocity following fault activation facilitates fault dilation,diminishes the frictional strength of the fault,and contributes to fault healing during the inter-seismic period.The aforementioned findings will contribute to a comprehensive understanding of the potential for the healing property of induced seismicity on faults containing halite,particularly in the Changning region of China.展开更多
Landslides frequently occurred in Jurassic red strata in the Three Gorges Reservoir(TGR)region in China.The Jurassic strata consist of low mechanical strength and poor permeability of weak silty mudstone layer,which m...Landslides frequently occurred in Jurassic red strata in the Three Gorges Reservoir(TGR)region in China.The Jurassic strata consist of low mechanical strength and poor permeability of weak silty mudstone layer,which may cause slope instability during rainfall.In order to understand the strength behavior of Jurassic silty mudstone shear zone,the so-called Shizibao landslide located in Guojiaba Town,Zigui County,Three Gorges Reservoir(TGR)in China is selected as a case study.The shear strength of the silty mudstone shear zone is strongly influenced by both the water content and the normal stress.Therefore,a series of drained ring shear tests were carried out by varying the water contents(7%,12%,17%,and 20%,respectively)and normal stresses(200,300,400,and 500 kPa,respectively).The result revealed that the residual friction coefficient and residual friction angle were power function relationships with water content and normal stress.The peak cohesion of the silty mudstone slip zone increased with water content to a certain limit,above which the cohesion decreased.In contrast,the residual cohesion showed the opposite trend,indicating the cohesion recovery above a certain limit of water content.However,both the peak and residual friction angle of the silty mudstone slip zone were observed to decrease steadily with increased water content.Furthermore,the macroscopic morphological features of the shear surface showed that the sliding failure was developed under high normal stress at low water content,while discontinuous sliding surface and soil extrusion were occurred when the water content increased to a saturated degree.The localized liquefaction developed by excess pore water pressure reduced the frictional force within the shear zone.Finally,the combined effects of the slope excavation and precipitation ultimately lead to the failure of the silty mudstone slope;however,continuous rainfall is the main factor triggering sliding.展开更多
During the excavation of large-scale rock slopes and deep hard rock engineering,the induced rapid unloading serves as the primary cause of rock mass deformation and failure.The essence of this phenomenon lies in the o...During the excavation of large-scale rock slopes and deep hard rock engineering,the induced rapid unloading serves as the primary cause of rock mass deformation and failure.The essence of this phenomenon lies in the opening-shear failure process triggered by the normal stress unloading of fractured rock mass.In this study,we focus on local-scale rock fracture and conduct direct shear tests under different normal stress unloading rates on five types of non-persistent fractured hard rocks.The aim is to analyze the influence of normal stress unloading rates on the failure modes and shear mechanical characteristics of non-persistent fractured rocks.The results indicate that the normal unloading displacement decreases gradually with increasing normal stress unloading rate,while the influence of normal stress unloading rate on shear displacement is not significant.As the normal stress unloading rate increases,the rocks brittle failure process accelerates,and the degree of rocks damage decreases.Analysis of the stress state on rock fracture surfaces reveals that increasing the normal stress unloading rate enhances the compressive stress on rocks,leading to a transition in the failure mode from shear failure to tensile failure.A negative exponential strength formula was proposed,which effectively fits the relationship between failure normal stress and normal stress unloading rate.The findings enrich the theoretical foundation of unloading rock mechanics and provide theoretical support for disasters prevention and control in rock engineering excavations.展开更多
The impact of normal stress-induced closure on fluid flow and solute transport in a single rock fracture is demonstrated in this study.The fracture is created from a measured surface of a granite rock sample.The Bandi...The impact of normal stress-induced closure on fluid flow and solute transport in a single rock fracture is demonstrated in this study.The fracture is created from a measured surface of a granite rock sample.The Bandis model is used to calculate the fracture closure due to normal stress,and the fluid flow is simulated by solving the Reynold equation.The Lagrangian particle tracking method is applied to modeling the advective transport in the fracture.The results show that the normal stress significantly affects fluid flow and solute transport in rock fractures.It causes fracture closure and creates asperity contact areas,which significantly reduces the effective hydraulic aperture and enhances flow channeling.Consequently,the reduced aperture and enhanced channeling affect travel time distributions.In particular,the enhanced channeling results in enhanced first arriving and tailing behaviors for solute transport.The fracture normal stiffness correlates linearly with the 5th and 95th percentiles of the normalized travel time.The finding from this study may help to better understand the stress-dependent solute transport processes in natural rock fractures.展开更多
The shear characteristics of soil-structure interfaces with different roughness are studied systematically by us-ing the DRS-1 high normal stress and residual shear apparatus. The experimental results indicate that,un...The shear characteristics of soil-structure interfaces with different roughness are studied systematically by us-ing the DRS-1 high normal stress and residual shear apparatus. The experimental results indicate that,under a relatively high normal stress,normal stress and the coefficient of structural roughness are the most important factors affecting the mechanical interface characteristics. The relationship between shear stress and shear displacement of the soil-structure interface is a hyperbolic curve with high regression accuracy. Based on our experimental results,a nonlinear elastic con-stitutive model of the soil-structure interface under relatively high normal stress is established with a definite physical meaning for its parameters. The model can predict the strain hardening behavior of the soil during the shearing process. The results show an encouraging agreement with experimental data from direct shear tests.展开更多
The frictional rupture mechanisms of rock discontinuities considering the dynamic load disturbance still remain unclear.This paper investigates the transitional behaviors of slip events happened on a planar granite fr...The frictional rupture mechanisms of rock discontinuities considering the dynamic load disturbance still remain unclear.This paper investigates the transitional behaviors of slip events happened on a planar granite fracture under cyclic normal stress with diferent oscillation amplitudes.The experimental results show that the activations of fast slips always correlate with unloading of normal stress.Besides,the intensive normal stress oscillation can weaken the shear strength which is recoverable when the normal stress return to constant.The rupture patterns are quantifed by stress drop,slip length and slip velocity.With the efect of small oscillation amplitudes,the slip events show chaotic shapes,compared to the regular and predictable style under constant normal stress.When the amplitude is large enough,the big and small slip events emerge alternately,showing a compound slip style.Large amplitude of the cyclic normal stress also widens the interval diferences of the slip events.This work provides experimental supports for a convincible link between the dynamic stress disturbance and the slip behavior of rock fractures.展开更多
Through high-precision engraving,self-affine sandstone joint surfaces with various joint roughness coefficients(JRC=3.21e12.16)were replicated and the shear sliding tests under unloading normal stress were conducted r...Through high-precision engraving,self-affine sandstone joint surfaces with various joint roughness coefficients(JRC=3.21e12.16)were replicated and the shear sliding tests under unloading normal stress were conducted regarding various initial normal stresses(1e7 MPa)and numbers of shearing cycles(1 e5).The peak shear stress of fractures decreased with shear cycles due to progressively smooth surface morphologies,while increased with both JRC and initial normal stress and could be verified using the nonlinear Barton-Bandis failure criterion.The joint friction angle of fractures exponentially increased by 62.22%e64.87%with JRC while decreased by 22.1%e24.85%with shearing cycles.After unloading normal stress,the sliding initiation time of fractures increased with both JRC and initial normal stress due to more tortuous fracture morphologies and enhanced shearing resistance capacity.The surface resistance index(SRI)of fractures decreased by 4.35%e32.02%with increasing shearing cycles due to a more significant reduction of sliding initiation shear stress than that for sliding initiation normal stress,but increased by a factor of 0.41e1.64 with JRC.After sliding initiation,the shear displacement of fractures showed an increase in power function.By defining a sliding rate threshold of 5105 m/s,transition from“quasi-static”to“dynamic”sliding of fractures was identified,and the increase of sliding acceleration steepened with JRC while slowed down with shearing cycles.The normal displacement experienced a slight increase before shear sliding due to deformation recovery as the unloading stress was unloaded,and then enhanced shear dilation after sliding initiation due to climbing effects of surface asperities.Dilation was positively related to the shear sliding velocity of fractures.Wear characteristics of the fracture surfaces after shearing failure were evaluated using binary calculation,indicating an increasing shear area ratio by 45.24%e91.02%with normal stress.展开更多
Excavation and earth surface processes(e.g.,river incision)always induce the unloading of stress,which can cause the failure of rocks.To study the shear mechanical behavior of a rock sample under unloading normal stre...Excavation and earth surface processes(e.g.,river incision)always induce the unloading of stress,which can cause the failure of rocks.To study the shear mechanical behavior of a rock sample under unloading normal stress conditions,a new stress path for direct shear tests was proposed to model the unloading of stress caused by excavation and other processes.The effects of the initial stresses(i.e.,the normal stress and shear stress before unloading)on the shear behavior and energy conversion were investigated using laboratory tests and numerical simulations.The shear strength of a rock under constant stress or under unloading normal stress conforms to the Mohr Coulomb criterion.As the initial normal stress increases,the cohesion decreases linearly and the tangent of the internal friction angle increases linearly.Compared with the results of the tests under constant normal stress,the cohesions of the rock samples under unloading normal stress are smaller and their internal friction angles are larger.A strength envelope surface can be used to describe the relationship between the initial stresses and the failure normal stress.Shear dilatancy can decrease the total energy of the direct shear test under constant normal stress or unloading normal stress,particularly when the stress levels(the initial stresses in the test under unloading normal stress or the normal stress in the test under constant normal stress)are high.The ratio of the dissipated energy to the total energy at the moment failure occurs decreases exponentially with increasing initial stresses.The direct shear test under constant normal stress can be considered to be a special case of a direct shear test under unloading normal stress with an unloading amount of zero.展开更多
The TFR（Tampered Failure Rate） model was proposed by Bhattacharyya and Soejoeti（1989） for step-stress accelerated life tests, On step-stress completely accelerated test occasions, the paper gives a method of estim...The TFR（Tampered Failure Rate） model was proposed by Bhattacharyya and Soejoeti（1989） for step-stress accelerated life tests, On step-stress completely accelerated test occasions, the paper gives a method of estimating parameters under a normal stress.展开更多
Following a sticky particle model and Its computer simulation scheme proposed In the previous papers, the viscosity and normal stress difference are cakulated when the aggregating colloid is being sheared. The plottin...Following a sticky particle model and Its computer simulation scheme proposed In the previous papers, the viscosity and normal stress difference are cakulated when the aggregating colloid is being sheared. The plotting of the viscosity vs shear strain shows a sigmoidal shape, which Is also observed in experimental results. The normal stress difference is plotted vs shear strain, which has not been reported in the literatures till now.展开更多
Seven reinforced concrete （RC） beams with epoxy-bonded glass fiber reinforced plastic （GFRP） sheets and two control RC beams were experimentally tested to investigate the bond behavior of the interfaces between RC...Seven reinforced concrete （RC） beams with epoxy-bonded glass fiber reinforced plastic （GFRP） sheets and two control RC beams were experimentally tested to investigate the bond behavior of the interfaces between RC beams and GFRP sheets. The variable parameters considered in test beams are the layers of GFRP sheets, the bond lengths and the reinforcement ratios. The results indicate that the flexural strength of the repaired beams is increased, but the ultimate load of beams with GFRP sheets debonding failure is reduced relatively. The bond length is the main factor that results in bonding failure of the strengthened beams. An experimental method of interfacial shear stress is proposed to analyze the distribution of shear stress according to experimental results. The analytical method of shear and normal stresses and a simple equation are proposed to predict the peeling loads. The proposed model is applied to experimental beams. The analytical results show a good agreement with the experimental results.展开更多
Multilayer ceramic coatings were fabricated on steel substrate using a combined technique of hot dipping aluminum(HDA) and plasma electrolytic oxidation(PEO). A triangle of normalized layer thickness was created for d...Multilayer ceramic coatings were fabricated on steel substrate using a combined technique of hot dipping aluminum(HDA) and plasma electrolytic oxidation(PEO). A triangle of normalized layer thickness was created for describing thickness ratios of HDA/PEO coatings. Then, the effect of thickness ratio on stresses field of HDA/PEO coatings subjected to uniform normal contact load was investigated by finite element method. Results show that the surface tensile stress is mainly affected by the thickness ratio of Al layer when the total thickness of coating is unchanged. With the increase of Al layer thickness, the surface tensile stress rises quickly. When Al2O3 layer thickness increases, surface tensile stress is diminished. Meanwhile, the maximum shear stress moves rapidly towards internal part of HDA/PEO coatings. Shear stress at the Al2O3 /Al interface is minimal when Al2O3 layer and Al layer have the same thickness.展开更多
Background: New normality is uncertain in every sense, specifically in education and for many health disciplines. Being immersed in COVID-19 pandemics brought serious consequences for mental health, and is very import...Background: New normality is uncertain in every sense, specifically in education and for many health disciplines. Being immersed in COVID-19 pandemics brought serious consequences for mental health, and is very important to handle emotions and stress coping strategies to obtain positive outcomes. Objective: To identify the most frequent emotions, as well as the adaptation strategies to the new normality faced by the students of nursing. Methods: Qualitative and phenomenological research, with the participation of 20 students from both genders in the middle term of nursing career at Faculty of Higher Studies Iztacala, National Autonomous University of Mexico, from August to November 2021. Information was collected from a focal group for ten sessions;analysis was according to De Souza Minayo, and there was a signed informed consent letter from participants. Results: Four categories emerged with sub-categories. Category I Maximized emotions. Sub-categories: 1) Frustration, anger, disappointment;2) Personal disappointment, hopelessness, uncertainty;3) Depression. Category II Support elements close to the new normality. Sub-categories: 1) Family communication;2) Education for mental and physical health. Category III Stressing situations that exceeded the student. Sub-category: Disease in lovely ones. Category IV Stress coping strategies. Sub-categories: 1) Friends and relatives that help to get better;2) Family values. Informers pointed out to have maximized emotion, and having no self-control on its negative outcomes occurred;in addition, the situation was not favorable at home with several losses of loved ones, as well as a poor economy that threatened students to give up studies. Conclusion: Emotions facing this new normality are very important and should be attended to, their proper handling will result in a new learning of socio-emotional abilities, stress coping strategies development, better adaptation and informed decisions taken.展开更多
A true triaxial apparatus which is composed of three units was presented.The apparatus allows for investigations on deformation and seepage behaviors of a single rock fracture subjected to lateral stress and normal st...A true triaxial apparatus which is composed of three units was presented.The apparatus allows for investigations on deformation and seepage behaviors of a single rock fracture subjected to lateral stress and normal stress.The first unit has three jacks which can apply loads independently in three orthogonal directions.The second unit is used to supply water inflow,control seepage pressure and measure flow velocity in real time.The third unit is for measuring the normal deformation of rock fractures.Some tests for investigating the normal deformation and seepage behaviors of rock fractures subjected to normal and lateral loads on hard granite specimens with an artificial persistent fracture,were introduced.The results show that both the normal deformation and the hydraulic conductivity are influenced not only by the normal stress but also by the lateral stress.It is also shown that the aperture and the hydraulic conductivity decrease with the increasing normal stress but increase with the increasing lateral stress and both the aperture and the hydraulic conductivity obey exponential relationships with the normal stress and the lateral stress.展开更多
In the limit equilibrium framework, two- and three-dimensional slope stabilities can be solved according to the overall force and moment equilibrium conditions of a sliding body. In this work, based on Mohr-Coulomb(M-...In the limit equilibrium framework, two- and three-dimensional slope stabilities can be solved according to the overall force and moment equilibrium conditions of a sliding body. In this work, based on Mohr-Coulomb(M-C) strength criterion and the initial normal stress without considering the inter-slice(or inter-column) forces, the normal and shear stresses on the slip surface are assumed using some dimensionless variables, and these variables have the same numbers with the force and moment equilibrium equations of a sliding body to establish easily the linear equation groups for solving them. After these variables are determined, the normal stresses, shear stresses, and slope safety factor are also obtained using the stresses assumptions and M-C strength criterion. In the case of a three-dimensional slope stability analysis, three calculation methods, namely, a non-strict method, quasi-strict method, and strict method, can be obtained by satisfying different force and moment equilibrium conditions. Results of the comparison in the classic two- and three-dimensional slope examples show that the slope safety factors calculated using the current method and the other limit equilibrium methods are approximately equal to each other, indicating the feasibility of the current method; further, the following conclusions are obtained: 1) The current method better amends the initial normal and shear stresses acting on the slip surface, and has the identical results with using simplified Bishop method, Spencer method, and Morgenstern-Price(M-P) method; however, the stress curve of the current method is smoother than that obtained using the three abovementioned methods. 2) The current method is suitable for analyzing the two- and three-dimensional slope stability. 3) In the three-dimensional asymmetric sliding body, the non-strict method yields safer solutions, and the results of the quasi-strict method are relatively reasonable and close to those of the strict method, indicating that the quasi-strict method can be used to obtain a reliable slope safety factor.展开更多
Marciniack–Kuczinski(M–K)model is widely used to predict material's forming limit curve(FLC).The prediction of FLC traditionally neglected through-thickness normal stress.However,it cannot be neglected in some f...Marciniack–Kuczinski(M–K)model is widely used to predict material's forming limit curve(FLC).The prediction of FLC traditionally neglected through-thickness normal stress.However,it cannot be neglected in some forming processes.Much work has been done to study the effect of through-thickness normal stress on FLC with constant through-thickness normal stress or constant ratio of through-thickness normal stress and maximum principal stress.In addition,based on Nakazima test process,the ratio of through-thickness normal stress and maximum principal stress has been derived,which was a function of instantaneous thickness and loading path.Here,initial groove angle in M–K model was not considered.In this paper,uniaxial tension tests and Nakazima tests were performed on 7B04 aluminum alloy.Based on Hill 48 yield criterion and M–K model,the prediction model of FLC was established.The increase of thickness can enhance FLC.Meanwhile,it is necessary to consider through-thickness normal stress and initial groove angle in prediction model.On the left side of FLC,the effect of initial groove angle on FLC is weakened by increasing sheet thickness.On the right side of FLC,the effect of initial groove angle on FLC is strengthened by increasing sheet thickness.On the right side of FLC,the relation between limit strain points with different thicknesses is linear under one certain loading path.Thickness has decisive effect on through-thickness normal stress level and the changing trendy of through-thickness normal stress during calculation is different under different stress condition.展开更多
The injection of large volumes of natural gas into geological formations,as is required for underground gas storage,leads to alterations in the effective stress exerted on adjacent faults.This increases the potential ...The injection of large volumes of natural gas into geological formations,as is required for underground gas storage,leads to alterations in the effective stress exerted on adjacent faults.This increases the potential for their reactivation and subsequent earthquake triggering.Most measurements of the frictional properties of rock fractures have been conducted under normal and shear stresses.However,faults in gas storage facilities exist within a true three-dimensional(3D)stress state.A double-direct shear experiment on rock fractures under both lateral and normal stresses was conducted using a true triaxial loading system.It was observed that the friction coefficient increases with increasing lateral stress,but decreases with increasing normal stress.The impact of lateral and normal stresses on the response is primarily mediated through their influence on the initial friction coefficient.This allows for an empirical modification of the rate-state friction model that considers the influence of lateral and normal stresses.The impact of lateral and normal stresses on observed friction coefficients is related to the propensity for the production of wear products on the fracture surfaces.Lateral stresses enhance the shear strength of rock(e.g.Mogi criterion).This reduces asperity breakage and the generation of wear products,and consequently augments the friction coefficient of the surface.Conversely,increased normal stresses inhibit dilatancy on the fracture surface,increasing the breakage of asperities and the concomitant production of wear products that promote rolling deformation.This ultimately reduces the friction coefficient.展开更多
We examine the reflection and transmission phenomena of quasi-longitudinal plane(QP)waves in an AlN-ZnO laminated composite structure.The structure is designed under the influence of the initial stresses in which one ...We examine the reflection and transmission phenomena of quasi-longitudinal plane(QP)waves in an AlN-ZnO laminated composite structure.The structure is designed under the influence of the initial stresses in which one carrier piezoelectric semiconductor(PSC)half-space is in welded contact with another PSC half-space.The secular equations in the transversely isotropic PSC material are derived from the general dynamic equation,taking the initial stresses into consideration.It is shown that the incident quasi-longitudinal wave(QP-mode)at the interface generates four types of reflected and transmitted waves,namely,QP wave,quasi-transverse(QSV)wave,electric-acoustic(EA)wave,and carrier plane(CP)wave.The algebraic equations are obtained by imposing the boundary conditions on the common interface of the laminated structure.Reflection and transmission coefficients of waves are obtained by implementing Cramer’s rule.Profound impacts of the initial stresses and exterior electric biasing field on the reflection and transmission coefficients of waves are investigated and presented graphically.展开更多
Differential equation of restrained torsion for rectangular-section box bar with honeycomb core was established and solved by using the method of undetermined function.Non-dimension normal stress, shear stress acting...Differential equation of restrained torsion for rectangular-section box bar with honeycomb core was established and solved by using the method of undetermined function.Non-dimension normal stress, shear stress acting in the faceplate and shear stress acting in the honeycomb-core and warping displacement were deduced. Numerical analysis shows the normal stress attenuates quickly along x-axis. Normal stress acting on the cross section at a distance of 20 h from the fixed end is only one per cent of that acting on the fixed end.展开更多
文摘Flow and transport properties of fractured crystalline rock are of great interest for different geotechnical ap-plications,such as storage of carbon dioxide,extraction of geothermal energy,or geologic storage of hazardous waste.For the long-term safety assessment of geological storage of hazardous waste,the understanding of flow and transport properties through the network of fractures is essential.The flow and transport behaviour can be explored using numerical models to investigate what parameters that affect the results.In this work a pilot study is carried out for multiple realizations of single realistic fractures,using fractal theories,which then are nu-merically sheared using a semi-analytical algorithm.The aperture field is calculated using the average distance of the volume integral of the void that a 1 mm lateral displacement of the sheared surfaces generates.The flow field through the aperture field is solved using Reynolds lubrication equation in linear triangular finite elements.The transport properties,travel length,travel time,transport resistance and specific flow wetted surface,are calculated in a Lagrangian framework using 10,000 particles for each of the 128 flow fields.Evaluating these four metrics,varying initial roughness,4<JRC<10 and normal stress between 0.2 and 20 MPa during shearing,it is concluded that an increase in normal stress generally results in longer travel paths,longer travel times,higher transport resistance and larger specific flow wetted surface while an increase of initial roughness will generally result in longer travel paths,shorter travel times,lower transport resistance and smaller specific flow wetted surface.
基金supported by the National Key Research and Development Project(Grant No.2023YFE0110900)the National Natural Science Foundation of China(Grant Nos.42320104003 and 42077247).
文摘The distinctive characteristics exhibited by the aftershocks of Ms6.0 induced earthquakes in Changning,Sichuan,China,have attracted significant attention.The prevalence of salt rock(halite)in this area is closely associated with induced seismic events.The present study was conducted to examine the role of halite in frictional properties.To this end,laboratory measurements were taken for simulated fault gouge composed of halite.Slide-hold-slide(SHS)shear experiments were performed on gouges with grain size<106 mm at constant normal stress from 5 MPa to 30 MPa and constant shear velocity in the range of 1-10 mm/s.Halite gouge shows higher frictional strength and frictional healing rate than most minerals.The results reveal that the fault within halite can potentially generate intense seismic events and more significant aftershocks.An increase in normal stress leads to a reduction in frictional healing,with frictional strength initially increasing and then decreasing.The elevated shear velocity following fault activation facilitates fault dilation,diminishes the frictional strength of the fault,and contributes to fault healing during the inter-seismic period.The aforementioned findings will contribute to a comprehensive understanding of the potential for the healing property of induced seismicity on faults containing halite,particularly in the Changning region of China.
基金funded by the National Science Foundation of China(CN)(Nos.42090054,41922055,41931295)the Key Research and Development Program of Hubei Province of China(No.2020BCB079)。
文摘Landslides frequently occurred in Jurassic red strata in the Three Gorges Reservoir(TGR)region in China.The Jurassic strata consist of low mechanical strength and poor permeability of weak silty mudstone layer,which may cause slope instability during rainfall.In order to understand the strength behavior of Jurassic silty mudstone shear zone,the so-called Shizibao landslide located in Guojiaba Town,Zigui County,Three Gorges Reservoir(TGR)in China is selected as a case study.The shear strength of the silty mudstone shear zone is strongly influenced by both the water content and the normal stress.Therefore,a series of drained ring shear tests were carried out by varying the water contents(7%,12%,17%,and 20%,respectively)and normal stresses(200,300,400,and 500 kPa,respectively).The result revealed that the residual friction coefficient and residual friction angle were power function relationships with water content and normal stress.The peak cohesion of the silty mudstone slip zone increased with water content to a certain limit,above which the cohesion decreased.In contrast,the residual cohesion showed the opposite trend,indicating the cohesion recovery above a certain limit of water content.However,both the peak and residual friction angle of the silty mudstone slip zone were observed to decrease steadily with increased water content.Furthermore,the macroscopic morphological features of the shear surface showed that the sliding failure was developed under high normal stress at low water content,while discontinuous sliding surface and soil extrusion were occurred when the water content increased to a saturated degree.The localized liquefaction developed by excess pore water pressure reduced the frictional force within the shear zone.Finally,the combined effects of the slope excavation and precipitation ultimately lead to the failure of the silty mudstone slope;however,continuous rainfall is the main factor triggering sliding.
基金supported by the National Natural Science Foundation of China(Grant Nos.42372326 and 42090054)supported by the State Key Laboratory of Geohazard Prevention and Geoenvironment Protection Independent Research Project(SKLGP2023Z015).
文摘During the excavation of large-scale rock slopes and deep hard rock engineering,the induced rapid unloading serves as the primary cause of rock mass deformation and failure.The essence of this phenomenon lies in the opening-shear failure process triggered by the normal stress unloading of fractured rock mass.In this study,we focus on local-scale rock fracture and conduct direct shear tests under different normal stress unloading rates on five types of non-persistent fractured hard rocks.The aim is to analyze the influence of normal stress unloading rates on the failure modes and shear mechanical characteristics of non-persistent fractured rocks.The results indicate that the normal unloading displacement decreases gradually with increasing normal stress unloading rate,while the influence of normal stress unloading rate on shear displacement is not significant.As the normal stress unloading rate increases,the rocks brittle failure process accelerates,and the degree of rocks damage decreases.Analysis of the stress state on rock fracture surfaces reveals that increasing the normal stress unloading rate enhances the compressive stress on rocks,leading to a transition in the failure mode from shear failure to tensile failure.A negative exponential strength formula was proposed,which effectively fits the relationship between failure normal stress and normal stress unloading rate.The findings enrich the theoretical foundation of unloading rock mechanics and provide theoretical support for disasters prevention and control in rock engineering excavations.
基金funding provided by the Swedish Nuclear Fuel and Waste Management Co.(SKB)。
文摘The impact of normal stress-induced closure on fluid flow and solute transport in a single rock fracture is demonstrated in this study.The fracture is created from a measured surface of a granite rock sample.The Bandis model is used to calculate the fracture closure due to normal stress,and the fluid flow is simulated by solving the Reynold equation.The Lagrangian particle tracking method is applied to modeling the advective transport in the fracture.The results show that the normal stress significantly affects fluid flow and solute transport in rock fractures.It causes fracture closure and creates asperity contact areas,which significantly reduces the effective hydraulic aperture and enhances flow channeling.Consequently,the reduced aperture and enhanced channeling affect travel time distributions.In particular,the enhanced channeling results in enhanced first arriving and tailing behaviors for solute transport.The fracture normal stiffness correlates linearly with the 5th and 95th percentiles of the normalized travel time.The finding from this study may help to better understand the stress-dependent solute transport processes in natural rock fractures.
基金Projects 50534040 supported by the National Natural Science Foundation of China2002CB412704 by the Major State Basic Research and Development Program of China
文摘The shear characteristics of soil-structure interfaces with different roughness are studied systematically by us-ing the DRS-1 high normal stress and residual shear apparatus. The experimental results indicate that,under a relatively high normal stress,normal stress and the coefficient of structural roughness are the most important factors affecting the mechanical interface characteristics. The relationship between shear stress and shear displacement of the soil-structure interface is a hyperbolic curve with high regression accuracy. Based on our experimental results,a nonlinear elastic con-stitutive model of the soil-structure interface under relatively high normal stress is established with a definite physical meaning for its parameters. The model can predict the strain hardening behavior of the soil during the shearing process. The results show an encouraging agreement with experimental data from direct shear tests.
基金supported by Fundamental Research Funds for the Central Universities(22dfx06)Natural Science Foundation of Guangdong Province-Joint Program for Ofshore Wind Power(2022A1515240009).
文摘The frictional rupture mechanisms of rock discontinuities considering the dynamic load disturbance still remain unclear.This paper investigates the transitional behaviors of slip events happened on a planar granite fracture under cyclic normal stress with diferent oscillation amplitudes.The experimental results show that the activations of fast slips always correlate with unloading of normal stress.Besides,the intensive normal stress oscillation can weaken the shear strength which is recoverable when the normal stress return to constant.The rupture patterns are quantifed by stress drop,slip length and slip velocity.With the efect of small oscillation amplitudes,the slip events show chaotic shapes,compared to the regular and predictable style under constant normal stress.When the amplitude is large enough,the big and small slip events emerge alternately,showing a compound slip style.Large amplitude of the cyclic normal stress also widens the interval diferences of the slip events.This work provides experimental supports for a convincible link between the dynamic stress disturbance and the slip behavior of rock fractures.
基金support from the National Natural Science Foundation of China(Grant Nos.52174092 and 52104125)the Fundamental Research Funds for the Central Universities,China(Grant No.2022YCPY0202)is gratefully acknowledged.
文摘Through high-precision engraving,self-affine sandstone joint surfaces with various joint roughness coefficients(JRC=3.21e12.16)were replicated and the shear sliding tests under unloading normal stress were conducted regarding various initial normal stresses(1e7 MPa)and numbers of shearing cycles(1 e5).The peak shear stress of fractures decreased with shear cycles due to progressively smooth surface morphologies,while increased with both JRC and initial normal stress and could be verified using the nonlinear Barton-Bandis failure criterion.The joint friction angle of fractures exponentially increased by 62.22%e64.87%with JRC while decreased by 22.1%e24.85%with shearing cycles.After unloading normal stress,the sliding initiation time of fractures increased with both JRC and initial normal stress due to more tortuous fracture morphologies and enhanced shearing resistance capacity.The surface resistance index(SRI)of fractures decreased by 4.35%e32.02%with increasing shearing cycles due to a more significant reduction of sliding initiation shear stress than that for sliding initiation normal stress,but increased by a factor of 0.41e1.64 with JRC.After sliding initiation,the shear displacement of fractures showed an increase in power function.By defining a sliding rate threshold of 5105 m/s,transition from“quasi-static”to“dynamic”sliding of fractures was identified,and the increase of sliding acceleration steepened with JRC while slowed down with shearing cycles.The normal displacement experienced a slight increase before shear sliding due to deformation recovery as the unloading stress was unloaded,and then enhanced shear dilation after sliding initiation due to climbing effects of surface asperities.Dilation was positively related to the shear sliding velocity of fractures.Wear characteristics of the fracture surfaces after shearing failure were evaluated using binary calculation,indicating an increasing shear area ratio by 45.24%e91.02%with normal stress.
基金This research was funded by the Fundamental Research Funds for the Central Universities,CHD(Grant Nos.300102210307 and 300102210308)the National Natural Science Foundation of China(Grant Nos.41831286 and 41972297)the Natural Science Foundation of Shaanxi Province(Grant No.2020JQ-369).
文摘Excavation and earth surface processes(e.g.,river incision)always induce the unloading of stress,which can cause the failure of rocks.To study the shear mechanical behavior of a rock sample under unloading normal stress conditions,a new stress path for direct shear tests was proposed to model the unloading of stress caused by excavation and other processes.The effects of the initial stresses(i.e.,the normal stress and shear stress before unloading)on the shear behavior and energy conversion were investigated using laboratory tests and numerical simulations.The shear strength of a rock under constant stress or under unloading normal stress conforms to the Mohr Coulomb criterion.As the initial normal stress increases,the cohesion decreases linearly and the tangent of the internal friction angle increases linearly.Compared with the results of the tests under constant normal stress,the cohesions of the rock samples under unloading normal stress are smaller and their internal friction angles are larger.A strength envelope surface can be used to describe the relationship between the initial stresses and the failure normal stress.Shear dilatancy can decrease the total energy of the direct shear test under constant normal stress or unloading normal stress,particularly when the stress levels(the initial stresses in the test under unloading normal stress or the normal stress in the test under constant normal stress)are high.The ratio of the dissipated energy to the total energy at the moment failure occurs decreases exponentially with increasing initial stresses.The direct shear test under constant normal stress can be considered to be a special case of a direct shear test under unloading normal stress with an unloading amount of zero.
文摘The TFR（Tampered Failure Rate） model was proposed by Bhattacharyya and Soejoeti（1989） for step-stress accelerated life tests, On step-stress completely accelerated test occasions, the paper gives a method of estimating parameters under a normal stress.
文摘Following a sticky particle model and Its computer simulation scheme proposed In the previous papers, the viscosity and normal stress difference are cakulated when the aggregating colloid is being sheared. The plotting of the viscosity vs shear strain shows a sigmoidal shape, which Is also observed in experimental results. The normal stress difference is plotted vs shear strain, which has not been reported in the literatures till now.
文摘Seven reinforced concrete （RC） beams with epoxy-bonded glass fiber reinforced plastic （GFRP） sheets and two control RC beams were experimentally tested to investigate the bond behavior of the interfaces between RC beams and GFRP sheets. The variable parameters considered in test beams are the layers of GFRP sheets, the bond lengths and the reinforcement ratios. The results indicate that the flexural strength of the repaired beams is increased, but the ultimate load of beams with GFRP sheets debonding failure is reduced relatively. The bond length is the main factor that results in bonding failure of the strengthened beams. An experimental method of interfacial shear stress is proposed to analyze the distribution of shear stress according to experimental results. The analytical method of shear and normal stresses and a simple equation are proposed to predict the peeling loads. The proposed model is applied to experimental beams. The analytical results show a good agreement with the experimental results.
基金Project(10572141) supported by the National Natural Science Foundation of China
文摘Multilayer ceramic coatings were fabricated on steel substrate using a combined technique of hot dipping aluminum(HDA) and plasma electrolytic oxidation(PEO). A triangle of normalized layer thickness was created for describing thickness ratios of HDA/PEO coatings. Then, the effect of thickness ratio on stresses field of HDA/PEO coatings subjected to uniform normal contact load was investigated by finite element method. Results show that the surface tensile stress is mainly affected by the thickness ratio of Al layer when the total thickness of coating is unchanged. With the increase of Al layer thickness, the surface tensile stress rises quickly. When Al2O3 layer thickness increases, surface tensile stress is diminished. Meanwhile, the maximum shear stress moves rapidly towards internal part of HDA/PEO coatings. Shear stress at the Al2O3 /Al interface is minimal when Al2O3 layer and Al layer have the same thickness.
文摘Background: New normality is uncertain in every sense, specifically in education and for many health disciplines. Being immersed in COVID-19 pandemics brought serious consequences for mental health, and is very important to handle emotions and stress coping strategies to obtain positive outcomes. Objective: To identify the most frequent emotions, as well as the adaptation strategies to the new normality faced by the students of nursing. Methods: Qualitative and phenomenological research, with the participation of 20 students from both genders in the middle term of nursing career at Faculty of Higher Studies Iztacala, National Autonomous University of Mexico, from August to November 2021. Information was collected from a focal group for ten sessions;analysis was according to De Souza Minayo, and there was a signed informed consent letter from participants. Results: Four categories emerged with sub-categories. Category I Maximized emotions. Sub-categories: 1) Frustration, anger, disappointment;2) Personal disappointment, hopelessness, uncertainty;3) Depression. Category II Support elements close to the new normality. Sub-categories: 1) Family communication;2) Education for mental and physical health. Category III Stressing situations that exceeded the student. Sub-category: Disease in lovely ones. Category IV Stress coping strategies. Sub-categories: 1) Friends and relatives that help to get better;2) Family values. Informers pointed out to have maximized emotion, and having no self-control on its negative outcomes occurred;in addition, the situation was not favorable at home with several losses of loved ones, as well as a poor economy that threatened students to give up studies. Conclusion: Emotions facing this new normality are very important and should be attended to, their proper handling will result in a new learning of socio-emotional abilities, stress coping strategies development, better adaptation and informed decisions taken.
基金Projects(50809069,10872207) supported by the National Natural Science Foundation of ChinaProject(2009CAD017) supported by Outstanding Youth of Hubei Province,China
文摘A true triaxial apparatus which is composed of three units was presented.The apparatus allows for investigations on deformation and seepage behaviors of a single rock fracture subjected to lateral stress and normal stress.The first unit has three jacks which can apply loads independently in three orthogonal directions.The second unit is used to supply water inflow,control seepage pressure and measure flow velocity in real time.The third unit is for measuring the normal deformation of rock fractures.Some tests for investigating the normal deformation and seepage behaviors of rock fractures subjected to normal and lateral loads on hard granite specimens with an artificial persistent fracture,were introduced.The results show that both the normal deformation and the hydraulic conductivity are influenced not only by the normal stress but also by the lateral stress.It is also shown that the aperture and the hydraulic conductivity decrease with the increasing normal stress but increase with the increasing lateral stress and both the aperture and the hydraulic conductivity obey exponential relationships with the normal stress and the lateral stress.
基金Project(51608541)supported by the National Natural Science Foundation of ChinaProject(2015M580702)supported by the Postdoctoral Science Foundation of ChinaProject(201508)supported by the Postdoctoral Science Foundation of Central South University,China
文摘In the limit equilibrium framework, two- and three-dimensional slope stabilities can be solved according to the overall force and moment equilibrium conditions of a sliding body. In this work, based on Mohr-Coulomb(M-C) strength criterion and the initial normal stress without considering the inter-slice(or inter-column) forces, the normal and shear stresses on the slip surface are assumed using some dimensionless variables, and these variables have the same numbers with the force and moment equilibrium equations of a sliding body to establish easily the linear equation groups for solving them. After these variables are determined, the normal stresses, shear stresses, and slope safety factor are also obtained using the stresses assumptions and M-C strength criterion. In the case of a three-dimensional slope stability analysis, three calculation methods, namely, a non-strict method, quasi-strict method, and strict method, can be obtained by satisfying different force and moment equilibrium conditions. Results of the comparison in the classic two- and three-dimensional slope examples show that the slope safety factors calculated using the current method and the other limit equilibrium methods are approximately equal to each other, indicating the feasibility of the current method; further, the following conclusions are obtained: 1) The current method better amends the initial normal and shear stresses acting on the slip surface, and has the identical results with using simplified Bishop method, Spencer method, and Morgenstern-Price(M-P) method; however, the stress curve of the current method is smoother than that obtained using the three abovementioned methods. 2) The current method is suitable for analyzing the two- and three-dimensional slope stability. 3) In the three-dimensional asymmetric sliding body, the non-strict method yields safer solutions, and the results of the quasi-strict method are relatively reasonable and close to those of the strict method, indicating that the quasi-strict method can be used to obtain a reliable slope safety factor.
基金the support from the National Natural Science Foundation of China(51575028)the Fundamental Research Funds for the Central Universities(YWF-18-BJ-J-75)。
文摘Marciniack–Kuczinski(M–K)model is widely used to predict material's forming limit curve(FLC).The prediction of FLC traditionally neglected through-thickness normal stress.However,it cannot be neglected in some forming processes.Much work has been done to study the effect of through-thickness normal stress on FLC with constant through-thickness normal stress or constant ratio of through-thickness normal stress and maximum principal stress.In addition,based on Nakazima test process,the ratio of through-thickness normal stress and maximum principal stress has been derived,which was a function of instantaneous thickness and loading path.Here,initial groove angle in M–K model was not considered.In this paper,uniaxial tension tests and Nakazima tests were performed on 7B04 aluminum alloy.Based on Hill 48 yield criterion and M–K model,the prediction model of FLC was established.The increase of thickness can enhance FLC.Meanwhile,it is necessary to consider through-thickness normal stress and initial groove angle in prediction model.On the left side of FLC,the effect of initial groove angle on FLC is weakened by increasing sheet thickness.On the right side of FLC,the effect of initial groove angle on FLC is strengthened by increasing sheet thickness.On the right side of FLC,the relation between limit strain points with different thicknesses is linear under one certain loading path.Thickness has decisive effect on through-thickness normal stress level and the changing trendy of through-thickness normal stress during calculation is different under different stress condition.
基金supported by National Nature Science Foundation of China (Grant No.42177157)the Science and Technology Program of Liaoning Province (Grant No.2023JH1/10400003)the Applied Basic Research Programof Liaoning Province (Grant No.2023JH2/101300153).
文摘The injection of large volumes of natural gas into geological formations,as is required for underground gas storage,leads to alterations in the effective stress exerted on adjacent faults.This increases the potential for their reactivation and subsequent earthquake triggering.Most measurements of the frictional properties of rock fractures have been conducted under normal and shear stresses.However,faults in gas storage facilities exist within a true three-dimensional(3D)stress state.A double-direct shear experiment on rock fractures under both lateral and normal stresses was conducted using a true triaxial loading system.It was observed that the friction coefficient increases with increasing lateral stress,but decreases with increasing normal stress.The impact of lateral and normal stresses on the response is primarily mediated through their influence on the initial friction coefficient.This allows for an empirical modification of the rate-state friction model that considers the influence of lateral and normal stresses.The impact of lateral and normal stresses on observed friction coefficients is related to the propensity for the production of wear products on the fracture surfaces.Lateral stresses enhance the shear strength of rock(e.g.Mogi criterion).This reduces asperity breakage and the generation of wear products,and consequently augments the friction coefficient of the surface.Conversely,increased normal stresses inhibit dilatancy on the fracture surface,increasing the breakage of asperities and the concomitant production of wear products that promote rolling deformation.This ultimately reduces the friction coefficient.
文摘We examine the reflection and transmission phenomena of quasi-longitudinal plane(QP)waves in an AlN-ZnO laminated composite structure.The structure is designed under the influence of the initial stresses in which one carrier piezoelectric semiconductor(PSC)half-space is in welded contact with another PSC half-space.The secular equations in the transversely isotropic PSC material are derived from the general dynamic equation,taking the initial stresses into consideration.It is shown that the incident quasi-longitudinal wave(QP-mode)at the interface generates four types of reflected and transmitted waves,namely,QP wave,quasi-transverse(QSV)wave,electric-acoustic(EA)wave,and carrier plane(CP)wave.The algebraic equations are obtained by imposing the boundary conditions on the common interface of the laminated structure.Reflection and transmission coefficients of waves are obtained by implementing Cramer’s rule.Profound impacts of the initial stresses and exterior electric biasing field on the reflection and transmission coefficients of waves are investigated and presented graphically.
文摘Differential equation of restrained torsion for rectangular-section box bar with honeycomb core was established and solved by using the method of undetermined function.Non-dimension normal stress, shear stress acting in the faceplate and shear stress acting in the honeycomb-core and warping displacement were deduced. Numerical analysis shows the normal stress attenuates quickly along x-axis. Normal stress acting on the cross section at a distance of 20 h from the fixed end is only one per cent of that acting on the fixed end.
