Recent geological study and survey on the scale of 1: 50000 in northern Guangxi have made some advancements: meta-basic-ultrabasic rocks which occured as bedding injection sheets in the Sanrnenjie formation of the Pro...Recent geological study and survey on the scale of 1: 50000 in northern Guangxi have made some advancements: meta-basic-ultrabasic rocks which occured as bedding injection sheets in the Sanrnenjie formation of the Proterozoic Danzhou group and caused contact metamorphism or hydrothermal alteration in adjacent wallrocks, were originated in extensional environment. Basic rocks belong to deep-sea tholeiite. TLe meta-basic -ultrabasic rocks sufferred intense deformation partitioning, resulting in lenticular network which was composed of mylonite zones in highly de formed field and lensoids in less- or non-deformed field. This structural pattern was explained as "melange" or "non-rooted cool intrusion " by previous workers. The deformation partitioning was mainly pure shearing in the early stage plus simple shearing in the later stage. This evolution was closely related to progressive deformation of the Guangxi orogeny.展开更多
Backfill is often employed in mining operations for ground support,with its positive impact on ground stability acknowledged in many underground mines.However,existing studies have predominantly focused only on the st...Backfill is often employed in mining operations for ground support,with its positive impact on ground stability acknowledged in many underground mines.However,existing studies have predominantly focused only on the stress development within the backfill material,leaving the influence of stope backfilling on stress distribution in surrounding rock mass and ground stability largely unexplored.Therefore,this paper presents numerical models in FLAC3D to investigate,for the first time,the time-dependent stress redistribution around a vertical backfilled stope and its implications on ground stability,considering the creep of surrounding rock mass.Using the Soft Soil constitutive model,the compressibility of backfill under large pressure was captured.It is found that the creep deformation of rock mass exercises compression on backfill and results in a less void ratio and increased modulus for fill material.The compacted backfill conversely influenced the stress distribution and ground stability of rock mass which was a combined effect of wall creep and compressibility of backfill.With the increase of time or/and creep deformation,the minimum principal stress in the rocks surrounding the backfilled stope increased towards the pre-mining stress state,while the deviatoric stress reduces leading to an increased factor of safety and improved ground stability.This improvement effect of backfill on ground stability increased with the increase of mine depth and stope height,while it is also more pronounced for the narrow stope,the backfill with a smaller compression index,and the soft rocks with a smaller viscosity coefficient.Furthermore,the results emphasize the importance of minimizing empty time and backfilling extracted stope as soon as possible for ground control.Reduction of filling gap height enhances the local stability around the roof of stope.展开更多
The Early Cambrian Yuertusi Formation(Є_(1)y)in the Tarim Basin of China deposits a continuously developed suite of organic-rich black mudstones,which constitute an important source of oil and gas reservoirs in the Pa...The Early Cambrian Yuertusi Formation(Є_(1)y)in the Tarim Basin of China deposits a continuously developed suite of organic-rich black mudstones,which constitute an important source of oil and gas reservoirs in the Paleozoic.However,its hydrocarbon generation and evolution characteristics and resource potential have long been constrained by deeply buried strata and previous research.In this paper,based on the newly obtained ultra-deep well drilling data,the hydrocarbon generation and expulsion model ofЄ_(1)y shale was established by using data-driven Monte Carlo simulation,upon which the hydrocarbon generation,expulsion,and retention amounts were calculated by using the diagenetic method.The research indicates that theЄ_(1)y shale reaches the hydrocarbon generation and expulsion threshold at equivalent vitrinite reflectances of 0.46%and 0.72%,respectively.The cumulative hydrocarbon generation is 68.88×10^(10)t,the cumulative hydrocarbon expulsion is 35.59×10^(10)t,and the cumulative residual hydrocarbon is 33.29×10^(10)t.This paper systematically and quantitatively calculates the hydrocarbon expulsion at various key geological periods for theЄ_(1)y source rocks in the study area for the first time,more precisely confirming that the black shale of theЄ_(1)y is the most significant source rock contributing to the marine oil and gas resources in the Tarim Basin,filling the gap in hydrocarbon expulsion calculation in the study area,and providing an important basis for the formation and distribution of Paleozoic hydrocarbon reservoirs.The prospect of deep ultra-deep oil and gas exploration in the Tarim Basin is promising.Especially,the large area of dolomite reservoirs under the Cambrian salt and source rock interiors are the key breakthrough targets for the next exploration in the Tarim Basin.展开更多
The North China Craton(NCC)experienced significant lithospheric thinning of over 100 km during the Mesozoic,accompanied by extensive magmatic activity and extensional tectonics.However,the timing and mechanism of this...The North China Craton(NCC)experienced significant lithospheric thinning of over 100 km during the Mesozoic,accompanied by extensive magmatic activity and extensional tectonics.However,the timing and mechanism of this thinning remain the subjects of debate.This study presents zircon U-Pb ages,Hf isotopic data and whole-rock elemental and Sr-Nd isotopic compositions of the Guanshui monzonites and diorites in the eastern NCC.Zircon U-Pb dating reveals that both rock types formed at ca.130 Ma.The monzonites,characterized by high Mg^(#)(50.9-57.9),low Nb/U ratios(2.53-3.89)and depleted isotopic compositions,suggest derivation from asthenospheric mantle modified by slab-derived fluids.The diorites,distinguished by low SiO_(2)(49.5-50.8),high Mg^(#)(66.7-68.5)and an EM2-type enriched mantle isotopic signature,point to a lithospheric mantle source modified by subducted sediment melts.The coexistence of monzonites and diorites suggests a transition in magma source from lithospheric to asthenospheric mantle,implying that lithospheric thinning may have commenced around 130 Ma.The destruction of the NCC was likely driven by localized,small-scale drip-style detachment processes,rather than wholesale lithospheric removal.展开更多
Forced imbibition,the invasion of a wetting fluid into porous rocks,plays an important role in the effective exploitation of hydrocarbon resources and the geological sequestration of carbon dioxide.However,the interfa...Forced imbibition,the invasion of a wetting fluid into porous rocks,plays an important role in the effective exploitation of hydrocarbon resources and the geological sequestration of carbon dioxide.However,the interface dynamics influenced by complex topology commonly leads to non-wetting fluid trapping.Particularly,the underlying mechanisms under viscously unfavorable conditions remain unclear.This study employs a direct numerical simulation method to simulate forced imbibition through the reconstructed digital rocks of sandstone.The interface dynamics and fluid–fluid interactions are investigated through transient simulations,while the pore topology metrics are introduced to analyze the impact on steady-state residual fluid distribution obtained by a pseudo-transient scheme.The results show that the cooperative pore-filling process promoted by corner flow is dominant at low capillary numbers.This leads to unstable inlet pressure,mass flow,and interface curvature,which correspond to complicated interface dynamics and higher residual fluid saturation.During forced imbibition,the interface curvature gradually increases,with the pore-filling mechanisms involving the cooperation of main terminal meniscus movement and arc menisci filling.Complex topology with small diameter pores may result in the destabilization of interface curvature.The residual fluid saturation is negatively correlated with porosity and pore throat size,and positively correlated with tortuosity and aspect ratio.A large mean coordination number characterizing global connectivity promotes imbibition.However,high connectivity characterized by the standardized Euler number corresponding to small pores is associated with a high probability of non-wetting fluid trapping.展开更多
Energy is an important resource that supports the development of human society,and energy security is even more relevant to the strength of a country.In order to ensure energy security,countries around the world are t...Energy is an important resource that supports the development of human society,and energy security is even more relevant to the strength of a country.In order to ensure energy security,countries around the world are taking measures to carry out energy transformation and construct new energy systems.As an important part of the new energy system,energy storage technology is highly valued by all countries.Among many large-scale energy storage technologies,salt cavern compressed air energy storage(CAES)technology stands out for its safety and economy,which is recognized and valued by scholars from various countries.For the construction of salt cavern CAES power station,it is very important to ensure the stability of salt cavern.Therefore,scholars have investigated the mechanical properties of salt rocks and the stability of salt caverns for CAES.This paper synthesizes the findings of current research on the creep and fatigue properties of salt rock,highlighting three key points:The factors influencing the creep and fatigue characteristics of salt rock include its composition,stress levels,and temperature.Notably,impurities and surrounding pressure tend to inhibit the deformation of salt rock,whereas elevated temperature and differential stress facilitate its deformation;The mechanisms governing creep and fatigue damage in salt rock are primarily associated with dislocation movement and microcracking;Most existing constitutive models for creep and fatigue are based on viscoelastic-plasticity theory,with fewer models derived from micro-mechanical perspectives.Additionally,this paper reviews studies on the stability of salt cavern CAES reservoirs utilizing numerical simulation methods and offers insights into future research directions concerning the creep and fatigue properties of salt rocks.展开更多
Significant exploration progress has been made in ultra-deep clastic rocks in the Kuqa Depression,Tarim Basin,over recent years.A new round of comprehensive geological research has formed four new understandings:(1)Es...Significant exploration progress has been made in ultra-deep clastic rocks in the Kuqa Depression,Tarim Basin,over recent years.A new round of comprehensive geological research has formed four new understandings:(1)Establish structural model consisting of multi-detachment composite,multi-stage structural superposition and multi-layer deformation.Multi-stage structural traps are overlapped vertically,and a series of structural traps are discovered in underlying ultra-deep layers.(2)Five sets of high-quality large-scale source rocks of three types of organic phases are developed in the Triassic and Jurassic systems,and forming a good combination of source-reservoir-cap rocks in ultra-deep layers with three sets of large-scale regional reservoir and cap rocks.(3)The formation of large oil and gas fields is controlled by four factors which are source,reservoir,cap rocks and fault.Based on the spatial configuration relationship of these four factors,a new three-dimensional reservoir formation model for ultra-deep clastic rocks in the Kuqa Depression has been established.(4)The next key exploration fields for ultra-deep clastic rocks in the Kuqa Depression include conventional and unconventional oil and gas.The conventional oil and gas fields include the deep multi-layer oil-gas accumulation zone in Kelasu,tight sandstone gas of Jurassic Ahe Formation in the northern structural zone,multi-target layer lithological oil and gas reservoirs in Zhongqiu–Dina structural zone,lithologic-stratigraphic and buried hill composite reservoirs in south slope and other favorable areas.Unconventional oil and gas fields include deep coal rock gas of Jurassic Kezilenuer and Yangxia formations,Triassic Tariqike Formation and Middle-Lower Jurassic and Upper Triassic continental shale gas.The achievements have important reference significance for enriching the theory of ultra-deep clastic rock oil and gas exploration and guiding the future oil and gas exploration deployment.展开更多
It is important to analyze the damage evolution process of surrounding rock under different water content for the stability of engineering rock mass.Based on digital speckle correlation(DSCM),acoustic emission(AE)and ...It is important to analyze the damage evolution process of surrounding rock under different water content for the stability of engineering rock mass.Based on digital speckle correlation(DSCM),acoustic emission(AE)and electromagnetic radiation(EMR),uniaxial hierarchical cyclic loading and unloading tests were carried out on sandstones with different fracture numbers under dry,natural and saturated water content,to explore the fracture propagation,failure precursor characteristics and damage response mechanism under the influence of water content effect.The results show that with the increase of water content,the peak stress and crack initiation stress decrease gradually,and the decreases are 15.28%-21.11%and 17.64%-23.04%,respectively.The peak strain and crack initiation strain increase gradually,and the increases are 19.85%-44.53%and 19.15%-41.94%,respectively.The precracked rock with different water content is mainly characterized by tensile failure at different loading stages.However,with the increase of water content,the proportion of shear cracks gradually increases,while acoustic emission events gradually decrease,the dissipative energy and energy storage limits of the rock under peak load gradually decrease,and the charge signal increases significantly,which is because the lubrication effect of water reduces the friction coefficient between crack surfaces.展开更多
The fatigue fracture under cyclic dynamic direct tensions of brittle rock is an important mechanical characteristic index for the evaluation of geological disasters and underground engineering safety.However,most stud...The fatigue fracture under cyclic dynamic direct tensions of brittle rock is an important mechanical characteristic index for the evaluation of geological disasters and underground engineering safety.However,most studies focus on macroscopic fracture mechanical properties,and the mechanism linking the macroscopic fracture with the microcrack growth during the cyclic dynamic direct tensile loading of brittle rocks is rarely studied.In this paper,a micro-macro fracture model explaining the stress-strain constitutive relationship is established at the last impact failure after being subjected to multiple cyclic direct tensile impacts of brittle rocks.This model is based on the wing crack extension model under direct tensile loading,the quasi-static and dynamic fracture toughness relationship,the suggested crack rate and strain rate relationship,the relationship of damage and dynamic tensile fatigue life N,the relationship of dynamic fracture toughness and dynamic tensile fatigue life N.The variations of dynamic mechanical properties of rocks with dynamic tensile fatigue life for different initial crack sizes and angles within the rocks are further discussed.The compressive strength,elastic modulus,crack initiation stress,limit crack extension length and crack extension rate descend and the failure strain ascends with an increment of dynamic tensile fatigue life in rocks.This study's results provide help for the safety and stability of the underground surrounding rocks under blasting working or seismic disasters.展开更多
Wellbore breakout is one of the critical issues in drilling due to the fact that the related problems result in additional costs and impact the drilling scheme severely.However,the majority of such wellbore breakout a...Wellbore breakout is one of the critical issues in drilling due to the fact that the related problems result in additional costs and impact the drilling scheme severely.However,the majority of such wellbore breakout analyses were based on continuum mechanics.In addition to failure in intact rocks,wellbore breakouts can also be initiated along natural discontinuities,e.g.weak planes and fractures.Furthermore,the conventional models in wellbore breakouts with uniform distribution fractures could not reflect the real drilling situation.This paper presents a fully coupled hydro-mechanical model of the SB-X well in the Tarim Basin,China for evaluating wellbore breakouts in heavily fractured rocks under anisotropic stress states using the distinct element method(DEM)and the discrete fracture network(DFN).The developed model was validated against caliper log measurement,and its stability study was carried out by stress and displacement analyses.A parametric study was performed to investigate the effects of the characteristics of fracture distribution(orientation and length)on borehole stability by sensitivity studies.Simulation results demonstrate that the increase of the standard deviation of orientation when the fracture direction aligns parallel or perpendicular to the principal stress direction aggravates borehole instability.Moreover,an elevation in the average fracture length causes the borehole failure to change from the direction of the minimum in-situ horizontal principal stress(i.e.the direction of wellbore breakouts)towards alternative directions,ultimately leading to the whole wellbore failure.These findings provide theoretical insights for predicting wellbore breakouts in heavily fractured rocks.展开更多
Based on the finite-discrete element method,a three-dimensional numerical model for axial impact rock breaking was established and validated.A computational method for energy conversion during impact rock breaking was...Based on the finite-discrete element method,a three-dimensional numerical model for axial impact rock breaking was established and validated.A computational method for energy conversion during impact rock breaking was proposed,and the effects of conical tooth forward rake angle,rock temperature,and impact velocity on rock breaking characteristics and energy transfer laws were analyzed.The results show that during single impact rock breaking with conical tooth bits,merely 7.52%to 12.51%of the energy is utilized for rock breaking,while a significant 57.26%to 78.10%is dissipated as frictional loss.An insufficient forward rake angle increases tooth penetration depth and frictional loss,whereas an excessive forward rake angle reduces penetration capability,causing bit rebound and greater energy absorption by the drill rod.Thus,an optimal forward rake angle exists.Regarding environmental factors,high temperatures significantly enhance impact-induced rock breaking.Thermal damage from high temperatures reduces rock strength and inhibits its energy absorption.Finally,higher impact velocities intensify rock damage,yet excessively high velocities increase frictional loss and reduce the proportion of energy absorbed by the rock,thereby failing to substantially improve rock breaking efficiency.An optimal impact velocity exists.展开更多
Hydrogen,a genuinely clean energy,is a promising alternative to fossil fuels.Inspired by underground gas storage of methane,establishing underground hydrogen storage(UHS)in depleted oil and gas reservoirs has emerged ...Hydrogen,a genuinely clean energy,is a promising alternative to fossil fuels.Inspired by underground gas storage of methane,establishing underground hydrogen storage(UHS)in depleted oil and gas reservoirs has emerged as a significant research focus.Carbonate reservoirs,where widely-presented fractures can facilitate the high-speed injection and production of gases,are hence ideal candidates for building underground hydrogen storage facilities.During the cyclic injection and extraction processes of UHS,the formation is subjected to stress disturbances,leading to stress sensitivity.Understanding the stress sensitivity patterns of carbonate rocks is crucial for optimizing injection and production strategies.This study reconstructed three-dimensional digital models of fractured carbonate rocks from the L gas field using micro-CT scanning technology.Utilizing the finite element method,we investigated the microscopic permeability characteristics of carbonate rocks and analyzed the impact of stress loading direction and confining stress on stress sensitivity.The findings reveal that the stress loading direction significantly influences the stress sensitivity of fractured carbonate rocks.When a stress of 60 MPa is applied perpendicular to the fracture direction,the permeability reduction ratio can reach 17.32%.In contrast,when the same stress is applied parallel to the fracture direction,the permeability reduction ratio is only 4.82%.Furthermore,a simulation of UHS with cyclic injection and production of H2 in the target block was conducted.When both permeability and porosity stress sensitivity were considered,the working gas volume for UHS decreased by only 3.4%,demonstrating that fractured carbonate reservoirs are feasible candidates for constructing underground hydrogen storage.展开更多
Layered rocks are widely distributed in sedimentary and metamorphic rocks and show anisotropic deformation and strength due to the layered structures with apparent weak surfaces.This study summarizes the findings on t...Layered rocks are widely distributed in sedimentary and metamorphic rocks and show anisotropic deformation and strength due to the layered structures with apparent weak surfaces.This study summarizes the findings on the deformation and damage characteristics of layered rock masses and surrounding rocks.The physicomechanical properties of layered rocks with different properties(e.g.inclination,shear strength,tensile strength,shear stiffness,roughness,and layer spacing)and different lithological and stress conditions are analyzed.The results revealed that with increasing layer inclination angles,the deformation and strength parameters of the rock masses present U-shaped,W-shaped,incremental,decremental,and basically unchanged trends,which are closely related to their strength and stress conditions.The increase in layer strength and confining pressure effectively suppresses the deformation and strength anisotropy caused by layer weakening,and the rock mass shifts from“structure-controlled”to“stress-structure-controlled”deformation mode.Water will increase the anisotropic behavior of layered rock masses due to the degradation of bedding and bedrock performance.The anisotropic behavior of the layered surrounding rocks is analyzed to reveal how it affects the deformation and failure behaviors of tunnels.The asymmetric characteristics of surrounding rock deformation are closely related to the layer weakening,layer thickness,and in situ stress.These findings are crucial for understanding layered rock mass deformation and failure mechanisms,facilitating prediction and control of tunnel deformation.展开更多
Source rocks(shales) exhibit different geometric pore types and considerable anisotropy caused by the preferential orientation of the clay and kerogen layers,which is not accounted for in classical rockphysics models....Source rocks(shales) exhibit different geometric pore types and considerable anisotropy caused by the preferential orientation of the clay and kerogen layers,which is not accounted for in classical rockphysics models.Pore geometry can be effectively studied through the aspect ratio,and in this study,we use the aspect ratio to characterize different pore geometries.Then,we consider a pore connectivity index as well as a lamination index associated with these orientations.An inclusion-based theory(differential effective medium and self-consistent approximation) and the Brown-Korringa equations are used in the modeling approach.The results show that the indices as well as the aspect ratio of the connected pores significantly affect the elastic properties.We propose an inversion method to invert these three parameters simultaneously from experimental vertical P-and S-wave velocities using a global optimization algorithm.The method is applied to well log and seismic data from the Longmaxi shale reservoir in southwest China to verify its pre dictive ability.展开更多
Composite rock layers are widely present in mining and tunnel construction projects,and are prone to dynamic tensile failure along bedding planes under dynamic disturbances.To ensure engineering safety,it is necessary...Composite rock layers are widely present in mining and tunnel construction projects,and are prone to dynamic tensile failure along bedding planes under dynamic disturbances.To ensure engineering safety,it is necessary to conduct research on the dynamic tensile characteristics under different working conditions.Considering the difficulty of on-site sampling,composite rock samples were prepared with cement mortar,and dynamic Brazilian splitting tests were carried out using split Hopkinson pressure bar(SHPB)equipment,a high-speed camera,and PFC^(2D)numerical software to explore their dynamic tensile properties under dynamic disturbance under different strength ratios and other factors.The results show that the dynamic tensile strength of samples exhibits a rising trend with the strength ratio and strain rate growth.As the incident angle increases from 0°to 90°,the stress contour deflects transform from center-splitting failure to tension-shear combined failure and back again.The influence of the incident order in different lithology rocks on the dynamic tensile strength of composite samples is controlled by strain rate,and when the strain rate increases to 400 s^(-1),the difference in strength due to the sequence of incident stress waves is within 5%.Based on PFC^(2D),the strength ratio of composite samples has a certain influence on the distribution of microfractures.With strength ratios equaling 1.5 or 2.0,the cracks are mainly concentrated on the softer material side,while a large number of cracks are distributed on both sides of the bedding plane with a strength ratio equal to 1.2.展开更多
This paper addresses a fundamental question in rock mechanics:Are there Class II rocks?The historical development of servo-controlled rock testing machines is reviewed,followed by a brief review of some stiff testing ...This paper addresses a fundamental question in rock mechanics:Are there Class II rocks?The historical development of servo-controlled rock testing machines is reviewed,followed by a brief review of some stiff testing machines.The pioneering work of some researchers is reviewed,and the misconception of classifying rocks into Class I and Class II is discussed.The mechanism of post-peak Class II behavior is discussed based on some recent test results.When a brittle hard rock is tested using a soft testing machine under axial-strain-controlled loading,violent failure can occur when the peak strength is reached,and the post-peak stress-strain curve cannot be obtained.However,a Class II post-peak stress-strain curve can be obtained when the rock is tested under lateral-strain-controlled loading.If a stiff testing machine is used,Class I and Class II post-peak stress-strain curves will be obtained under axial-and lateral-strain-controlled loadings,respectively.It is therefore not appropriate to classify rocks into Class I or Class II rocks.The influences of other conditions,such as rock type,confinement,and specimen height-to-diameter ratio,on the type(Class I or Class II)of post-peak stress-strain curves are also discussed.Finally,some misconceptions in the rock mechanics community,stemming from the concept of“Class II rock”,are discussed.By clarifying these concepts related to Class I and Class II behaviors,this paper seeks to clarify misunderstandings and misapplications related to post-peak strength and deformation properties in the field.展开更多
The internal microstructures of rock materials, including mineral heterogeneity and intrinsic microdefects, exert a significant influence on their nonlinear mechanical and cracking behaviors. It is of great significan...The internal microstructures of rock materials, including mineral heterogeneity and intrinsic microdefects, exert a significant influence on their nonlinear mechanical and cracking behaviors. It is of great significance to accurately characterize the actual microstructures and their influence on stress and damage evolution inside the rocks. In this study, an image-based fast Fourier transform (FFT) method is developed for reconstructing the actual rock microstructures by combining it with the digital image processing (DIP) technique. A series of experimental investigations were conducted to acquire information regarding the actual microstructure and the mechanical properties. Based on these experimental evidences, the processed microstructure information, in conjunction with the proposed micromechanical model, is incorporated into the numerical calculation. The proposed image-based FFT method was firstly validated through uniaxial compression tests. Subsequently, it was employed to predict and analyze the influence of microstructure on macroscopic mechanical behaviors, local stress distribution and the internal crack evolution process in brittle rocks. The distribution of feldspar is considerably more heterogeneous and scattered than that of quartz, which results in a greater propensity for the formation of cracks in feldspar. It is observed that initial cracks and new cracks, including intragranular and boundary ones, ultimately coalesce and connect as the primary through cracks, which are predominantly distributed along the boundary of the feldspar. This phenomenon is also predicted by the proposed numerical method. The results indicate that the proposed numerical method provides an effective approach for analyzing, understanding and predicting the nonlinear mechanical and cracking behaviors of brittle rocks by taking into account the actual microstructure characteristics.展开更多
Layered rocks(LR)exhibit inherent anisotropic stiffness and strength induced by oriented rough weakness planes,along with stress induced anisotropy and friction related plastic deformation occurs during loading.Furthe...Layered rocks(LR)exhibit inherent anisotropic stiffness and strength induced by oriented rough weakness planes,along with stress induced anisotropy and friction related plastic deformation occurs during loading.Furthermore,microcracks located in intact rock matrix(IRM)of LR are also critically important for friction and damage dissipation processes.In this paper,we first present a novel multiscale friction-damage(MFD)model using a two-step Mori-Tanaka homogenization scheme,with the aim of describing the multiscale friction-damage mechanics in LR.Physically,the initiation and propagation of flaws at different scales(i.e.microcracks and weakness planes)induced damage,and the plastic deformation is closely associated with frictional sliding along these flaws.In the thermodynamics framework,the macroscopic stress-strain relations,the local driving forces respectively conjuncted with flaws propagation and plastic deformation are derived.An analytical macroscopic strength criterion is subsequently deduced,which takes into account the variation of inclination angle and confining pressure.Notably,the failure mechanisms of IRM shearing and weakness planes sliding are inherent included in the criterion.As an original contribution,a new multisurface semi-implicit return mapping algorithm(MSRM)is developed to integrate the proposed MFD model.The robustness of MSRM algorithm is assessed by numerical tests with different loading steps sizes and convergence conditions.Finally,the effectiveness of the MFD model is confirmed using data from experiments under conventional triaxial compression,all main features of mechanical behaviors of LR are well captured by the proposed model,including initial anisotropy,stress-induced anisotropy and strain hardening/softening.展开更多
文摘Recent geological study and survey on the scale of 1: 50000 in northern Guangxi have made some advancements: meta-basic-ultrabasic rocks which occured as bedding injection sheets in the Sanrnenjie formation of the Proterozoic Danzhou group and caused contact metamorphism or hydrothermal alteration in adjacent wallrocks, were originated in extensional environment. Basic rocks belong to deep-sea tholeiite. TLe meta-basic -ultrabasic rocks sufferred intense deformation partitioning, resulting in lenticular network which was composed of mylonite zones in highly de formed field and lensoids in less- or non-deformed field. This structural pattern was explained as "melange" or "non-rooted cool intrusion " by previous workers. The deformation partitioning was mainly pure shearing in the early stage plus simple shearing in the later stage. This evolution was closely related to progressive deformation of the Guangxi orogeny.
基金the funding support from the National Natural Science Foundation of China(Grant Nos.52304101 and 52004206)the China Postdoctoral Science Foundation(Grant No.2023MD734215)。
文摘Backfill is often employed in mining operations for ground support,with its positive impact on ground stability acknowledged in many underground mines.However,existing studies have predominantly focused only on the stress development within the backfill material,leaving the influence of stope backfilling on stress distribution in surrounding rock mass and ground stability largely unexplored.Therefore,this paper presents numerical models in FLAC3D to investigate,for the first time,the time-dependent stress redistribution around a vertical backfilled stope and its implications on ground stability,considering the creep of surrounding rock mass.Using the Soft Soil constitutive model,the compressibility of backfill under large pressure was captured.It is found that the creep deformation of rock mass exercises compression on backfill and results in a less void ratio and increased modulus for fill material.The compacted backfill conversely influenced the stress distribution and ground stability of rock mass which was a combined effect of wall creep and compressibility of backfill.With the increase of time or/and creep deformation,the minimum principal stress in the rocks surrounding the backfilled stope increased towards the pre-mining stress state,while the deviatoric stress reduces leading to an increased factor of safety and improved ground stability.This improvement effect of backfill on ground stability increased with the increase of mine depth and stope height,while it is also more pronounced for the narrow stope,the backfill with a smaller compression index,and the soft rocks with a smaller viscosity coefficient.Furthermore,the results emphasize the importance of minimizing empty time and backfilling extracted stope as soon as possible for ground control.Reduction of filling gap height enhances the local stability around the roof of stope.
基金supported by the CNPC Science and Technology Major Project of the Fourteenth Five-Year Plan(2021DJ0101)the National Natural Science Foundation of China(U19B600302,41872148)。
文摘The Early Cambrian Yuertusi Formation(Є_(1)y)in the Tarim Basin of China deposits a continuously developed suite of organic-rich black mudstones,which constitute an important source of oil and gas reservoirs in the Paleozoic.However,its hydrocarbon generation and evolution characteristics and resource potential have long been constrained by deeply buried strata and previous research.In this paper,based on the newly obtained ultra-deep well drilling data,the hydrocarbon generation and expulsion model ofЄ_(1)y shale was established by using data-driven Monte Carlo simulation,upon which the hydrocarbon generation,expulsion,and retention amounts were calculated by using the diagenetic method.The research indicates that theЄ_(1)y shale reaches the hydrocarbon generation and expulsion threshold at equivalent vitrinite reflectances of 0.46%and 0.72%,respectively.The cumulative hydrocarbon generation is 68.88×10^(10)t,the cumulative hydrocarbon expulsion is 35.59×10^(10)t,and the cumulative residual hydrocarbon is 33.29×10^(10)t.This paper systematically and quantitatively calculates the hydrocarbon expulsion at various key geological periods for theЄ_(1)y source rocks in the study area for the first time,more precisely confirming that the black shale of theЄ_(1)y is the most significant source rock contributing to the marine oil and gas resources in the Tarim Basin,filling the gap in hydrocarbon expulsion calculation in the study area,and providing an important basis for the formation and distribution of Paleozoic hydrocarbon reservoirs.The prospect of deep ultra-deep oil and gas exploration in the Tarim Basin is promising.Especially,the large area of dolomite reservoirs under the Cambrian salt and source rock interiors are the key breakthrough targets for the next exploration in the Tarim Basin.
基金supported by the Jiangsu Innovation and Entrepreneurship Project(JSSCBS20211225).
文摘The North China Craton(NCC)experienced significant lithospheric thinning of over 100 km during the Mesozoic,accompanied by extensive magmatic activity and extensional tectonics.However,the timing and mechanism of this thinning remain the subjects of debate.This study presents zircon U-Pb ages,Hf isotopic data and whole-rock elemental and Sr-Nd isotopic compositions of the Guanshui monzonites and diorites in the eastern NCC.Zircon U-Pb dating reveals that both rock types formed at ca.130 Ma.The monzonites,characterized by high Mg^(#)(50.9-57.9),low Nb/U ratios(2.53-3.89)and depleted isotopic compositions,suggest derivation from asthenospheric mantle modified by slab-derived fluids.The diorites,distinguished by low SiO_(2)(49.5-50.8),high Mg^(#)(66.7-68.5)and an EM2-type enriched mantle isotopic signature,point to a lithospheric mantle source modified by subducted sediment melts.The coexistence of monzonites and diorites suggests a transition in magma source from lithospheric to asthenospheric mantle,implying that lithospheric thinning may have commenced around 130 Ma.The destruction of the NCC was likely driven by localized,small-scale drip-style detachment processes,rather than wholesale lithospheric removal.
基金supported by the National Natural Science Foundation of China(Grant Nos.42172159 and 42302143)the Postdoctora Fellowship Program of the China Postdoctoral Science Foundation(CPSF)(Grant No.GZB20230864).
文摘Forced imbibition,the invasion of a wetting fluid into porous rocks,plays an important role in the effective exploitation of hydrocarbon resources and the geological sequestration of carbon dioxide.However,the interface dynamics influenced by complex topology commonly leads to non-wetting fluid trapping.Particularly,the underlying mechanisms under viscously unfavorable conditions remain unclear.This study employs a direct numerical simulation method to simulate forced imbibition through the reconstructed digital rocks of sandstone.The interface dynamics and fluid–fluid interactions are investigated through transient simulations,while the pore topology metrics are introduced to analyze the impact on steady-state residual fluid distribution obtained by a pseudo-transient scheme.The results show that the cooperative pore-filling process promoted by corner flow is dominant at low capillary numbers.This leads to unstable inlet pressure,mass flow,and interface curvature,which correspond to complicated interface dynamics and higher residual fluid saturation.During forced imbibition,the interface curvature gradually increases,with the pore-filling mechanisms involving the cooperation of main terminal meniscus movement and arc menisci filling.Complex topology with small diameter pores may result in the destabilization of interface curvature.The residual fluid saturation is negatively correlated with porosity and pore throat size,and positively correlated with tortuosity and aspect ratio.A large mean coordination number characterizing global connectivity promotes imbibition.However,high connectivity characterized by the standardized Euler number corresponding to small pores is associated with a high probability of non-wetting fluid trapping.
基金supported by the Natural Science Fund of China(No.51834003,52274073,52022014).
文摘Energy is an important resource that supports the development of human society,and energy security is even more relevant to the strength of a country.In order to ensure energy security,countries around the world are taking measures to carry out energy transformation and construct new energy systems.As an important part of the new energy system,energy storage technology is highly valued by all countries.Among many large-scale energy storage technologies,salt cavern compressed air energy storage(CAES)technology stands out for its safety and economy,which is recognized and valued by scholars from various countries.For the construction of salt cavern CAES power station,it is very important to ensure the stability of salt cavern.Therefore,scholars have investigated the mechanical properties of salt rocks and the stability of salt caverns for CAES.This paper synthesizes the findings of current research on the creep and fatigue properties of salt rock,highlighting three key points:The factors influencing the creep and fatigue characteristics of salt rock include its composition,stress levels,and temperature.Notably,impurities and surrounding pressure tend to inhibit the deformation of salt rock,whereas elevated temperature and differential stress facilitate its deformation;The mechanisms governing creep and fatigue damage in salt rock are primarily associated with dislocation movement and microcracking;Most existing constitutive models for creep and fatigue are based on viscoelastic-plasticity theory,with fewer models derived from micro-mechanical perspectives.Additionally,this paper reviews studies on the stability of salt cavern CAES reservoirs utilizing numerical simulation methods and offers insights into future research directions concerning the creep and fatigue properties of salt rocks.
基金Supported by the National Natural Science Foundation of China(U22B6002)PetroChina Science and Technology Project(2023ZZ14).
文摘Significant exploration progress has been made in ultra-deep clastic rocks in the Kuqa Depression,Tarim Basin,over recent years.A new round of comprehensive geological research has formed four new understandings:(1)Establish structural model consisting of multi-detachment composite,multi-stage structural superposition and multi-layer deformation.Multi-stage structural traps are overlapped vertically,and a series of structural traps are discovered in underlying ultra-deep layers.(2)Five sets of high-quality large-scale source rocks of three types of organic phases are developed in the Triassic and Jurassic systems,and forming a good combination of source-reservoir-cap rocks in ultra-deep layers with three sets of large-scale regional reservoir and cap rocks.(3)The formation of large oil and gas fields is controlled by four factors which are source,reservoir,cap rocks and fault.Based on the spatial configuration relationship of these four factors,a new three-dimensional reservoir formation model for ultra-deep clastic rocks in the Kuqa Depression has been established.(4)The next key exploration fields for ultra-deep clastic rocks in the Kuqa Depression include conventional and unconventional oil and gas.The conventional oil and gas fields include the deep multi-layer oil-gas accumulation zone in Kelasu,tight sandstone gas of Jurassic Ahe Formation in the northern structural zone,multi-target layer lithological oil and gas reservoirs in Zhongqiu–Dina structural zone,lithologic-stratigraphic and buried hill composite reservoirs in south slope and other favorable areas.Unconventional oil and gas fields include deep coal rock gas of Jurassic Kezilenuer and Yangxia formations,Triassic Tariqike Formation and Middle-Lower Jurassic and Upper Triassic continental shale gas.The achievements have important reference significance for enriching the theory of ultra-deep clastic rock oil and gas exploration and guiding the future oil and gas exploration deployment.
基金financially supported by National Natural Science Foundation of China(No.52304136)Young Talent of Lifting Engineering for Science and Technology in Shandong,China(No.SDAST2024QTA060)Key Project of Research and Development in Liaocheng(No.2023YD02)。
文摘It is important to analyze the damage evolution process of surrounding rock under different water content for the stability of engineering rock mass.Based on digital speckle correlation(DSCM),acoustic emission(AE)and electromagnetic radiation(EMR),uniaxial hierarchical cyclic loading and unloading tests were carried out on sandstones with different fracture numbers under dry,natural and saturated water content,to explore the fracture propagation,failure precursor characteristics and damage response mechanism under the influence of water content effect.The results show that with the increase of water content,the peak stress and crack initiation stress decrease gradually,and the decreases are 15.28%-21.11%and 17.64%-23.04%,respectively.The peak strain and crack initiation strain increase gradually,and the increases are 19.85%-44.53%and 19.15%-41.94%,respectively.The precracked rock with different water content is mainly characterized by tensile failure at different loading stages.However,with the increase of water content,the proportion of shear cracks gradually increases,while acoustic emission events gradually decrease,the dissipative energy and energy storage limits of the rock under peak load gradually decrease,and the charge signal increases significantly,which is because the lubrication effect of water reduces the friction coefficient between crack surfaces.
基金supported by the National Natural Science Foundation of China(Grant Nos.51708016,52438007 and 12172036)the R&D program of Beijing Municipal Education Commission(Grant No.KM202110016014)+1 种基金the Pyramid Talent Training Project of Beijing University of Civil Engineering and Architecture(Grant No.JDYC20200307)the Graduate Innovation Program of Beijing University of Civil Engineering and Architecture(Grant No.PG2025060).
文摘The fatigue fracture under cyclic dynamic direct tensions of brittle rock is an important mechanical characteristic index for the evaluation of geological disasters and underground engineering safety.However,most studies focus on macroscopic fracture mechanical properties,and the mechanism linking the macroscopic fracture with the microcrack growth during the cyclic dynamic direct tensile loading of brittle rocks is rarely studied.In this paper,a micro-macro fracture model explaining the stress-strain constitutive relationship is established at the last impact failure after being subjected to multiple cyclic direct tensile impacts of brittle rocks.This model is based on the wing crack extension model under direct tensile loading,the quasi-static and dynamic fracture toughness relationship,the suggested crack rate and strain rate relationship,the relationship of damage and dynamic tensile fatigue life N,the relationship of dynamic fracture toughness and dynamic tensile fatigue life N.The variations of dynamic mechanical properties of rocks with dynamic tensile fatigue life for different initial crack sizes and angles within the rocks are further discussed.The compressive strength,elastic modulus,crack initiation stress,limit crack extension length and crack extension rate descend and the failure strain ascends with an increment of dynamic tensile fatigue life in rocks.This study's results provide help for the safety and stability of the underground surrounding rocks under blasting working or seismic disasters.
基金supported by National Natural Science Foundation of China(Grant Nos.52074312 and 52211530097)CNPC Science and Technology Innovation Foundation(Grant No.2021DQ02-0505).
文摘Wellbore breakout is one of the critical issues in drilling due to the fact that the related problems result in additional costs and impact the drilling scheme severely.However,the majority of such wellbore breakout analyses were based on continuum mechanics.In addition to failure in intact rocks,wellbore breakouts can also be initiated along natural discontinuities,e.g.weak planes and fractures.Furthermore,the conventional models in wellbore breakouts with uniform distribution fractures could not reflect the real drilling situation.This paper presents a fully coupled hydro-mechanical model of the SB-X well in the Tarim Basin,China for evaluating wellbore breakouts in heavily fractured rocks under anisotropic stress states using the distinct element method(DEM)and the discrete fracture network(DFN).The developed model was validated against caliper log measurement,and its stability study was carried out by stress and displacement analyses.A parametric study was performed to investigate the effects of the characteristics of fracture distribution(orientation and length)on borehole stability by sensitivity studies.Simulation results demonstrate that the increase of the standard deviation of orientation when the fracture direction aligns parallel or perpendicular to the principal stress direction aggravates borehole instability.Moreover,an elevation in the average fracture length causes the borehole failure to change from the direction of the minimum in-situ horizontal principal stress(i.e.the direction of wellbore breakouts)towards alternative directions,ultimately leading to the whole wellbore failure.These findings provide theoretical insights for predicting wellbore breakouts in heavily fractured rocks.
基金Supported by Major Instrument Project of National Natural Science Foundation of China(52327803)Major Project of National Natural Science Foundation of China(52192622).
文摘Based on the finite-discrete element method,a three-dimensional numerical model for axial impact rock breaking was established and validated.A computational method for energy conversion during impact rock breaking was proposed,and the effects of conical tooth forward rake angle,rock temperature,and impact velocity on rock breaking characteristics and energy transfer laws were analyzed.The results show that during single impact rock breaking with conical tooth bits,merely 7.52%to 12.51%of the energy is utilized for rock breaking,while a significant 57.26%to 78.10%is dissipated as frictional loss.An insufficient forward rake angle increases tooth penetration depth and frictional loss,whereas an excessive forward rake angle reduces penetration capability,causing bit rebound and greater energy absorption by the drill rod.Thus,an optimal forward rake angle exists.Regarding environmental factors,high temperatures significantly enhance impact-induced rock breaking.Thermal damage from high temperatures reduces rock strength and inhibits its energy absorption.Finally,higher impact velocities intensify rock damage,yet excessively high velocities increase frictional loss and reduce the proportion of energy absorbed by the rock,thereby failing to substantially improve rock breaking efficiency.An optimal impact velocity exists.
基金National Natural Science Foundation of China,52304048Ye Tian,China Postdoctoral Science Foundation,2022M722637,Ye Tian。
文摘Hydrogen,a genuinely clean energy,is a promising alternative to fossil fuels.Inspired by underground gas storage of methane,establishing underground hydrogen storage(UHS)in depleted oil and gas reservoirs has emerged as a significant research focus.Carbonate reservoirs,where widely-presented fractures can facilitate the high-speed injection and production of gases,are hence ideal candidates for building underground hydrogen storage facilities.During the cyclic injection and extraction processes of UHS,the formation is subjected to stress disturbances,leading to stress sensitivity.Understanding the stress sensitivity patterns of carbonate rocks is crucial for optimizing injection and production strategies.This study reconstructed three-dimensional digital models of fractured carbonate rocks from the L gas field using micro-CT scanning technology.Utilizing the finite element method,we investigated the microscopic permeability characteristics of carbonate rocks and analyzed the impact of stress loading direction and confining stress on stress sensitivity.The findings reveal that the stress loading direction significantly influences the stress sensitivity of fractured carbonate rocks.When a stress of 60 MPa is applied perpendicular to the fracture direction,the permeability reduction ratio can reach 17.32%.In contrast,when the same stress is applied parallel to the fracture direction,the permeability reduction ratio is only 4.82%.Furthermore,a simulation of UHS with cyclic injection and production of H2 in the target block was conducted.When both permeability and porosity stress sensitivity were considered,the working gas volume for UHS decreased by only 3.4%,demonstrating that fractured carbonate reservoirs are feasible candidates for constructing underground hydrogen storage.
基金support of the National Natural Science Foundation of China(Grant No.42207199)Zhejiang Provincial Natural Science Foundation of China(Grant Nos.ZCLMS25D0201 and LQ23D010002).
文摘Layered rocks are widely distributed in sedimentary and metamorphic rocks and show anisotropic deformation and strength due to the layered structures with apparent weak surfaces.This study summarizes the findings on the deformation and damage characteristics of layered rock masses and surrounding rocks.The physicomechanical properties of layered rocks with different properties(e.g.inclination,shear strength,tensile strength,shear stiffness,roughness,and layer spacing)and different lithological and stress conditions are analyzed.The results revealed that with increasing layer inclination angles,the deformation and strength parameters of the rock masses present U-shaped,W-shaped,incremental,decremental,and basically unchanged trends,which are closely related to their strength and stress conditions.The increase in layer strength and confining pressure effectively suppresses the deformation and strength anisotropy caused by layer weakening,and the rock mass shifts from“structure-controlled”to“stress-structure-controlled”deformation mode.Water will increase the anisotropic behavior of layered rock masses due to the degradation of bedding and bedrock performance.The anisotropic behavior of the layered surrounding rocks is analyzed to reveal how it affects the deformation and failure behaviors of tunnels.The asymmetric characteristics of surrounding rock deformation are closely related to the layer weakening,layer thickness,and in situ stress.These findings are crucial for understanding layered rock mass deformation and failure mechanisms,facilitating prediction and control of tunnel deformation.
基金funded by the National Natural Science Foundation of China (No. 42374128)by the Fundamental Research Funds for the Central Universities (No. B240201110)。
文摘Source rocks(shales) exhibit different geometric pore types and considerable anisotropy caused by the preferential orientation of the clay and kerogen layers,which is not accounted for in classical rockphysics models.Pore geometry can be effectively studied through the aspect ratio,and in this study,we use the aspect ratio to characterize different pore geometries.Then,we consider a pore connectivity index as well as a lamination index associated with these orientations.An inclusion-based theory(differential effective medium and self-consistent approximation) and the Brown-Korringa equations are used in the modeling approach.The results show that the indices as well as the aspect ratio of the connected pores significantly affect the elastic properties.We propose an inversion method to invert these three parameters simultaneously from experimental vertical P-and S-wave velocities using a global optimization algorithm.The method is applied to well log and seismic data from the Longmaxi shale reservoir in southwest China to verify its pre dictive ability.
基金Project(242102320036)supported by the Science and the Technology Development Plant of Henan Province,ChinaProject(52278367)supported by the National Natural Science Foundation of China。
文摘Composite rock layers are widely present in mining and tunnel construction projects,and are prone to dynamic tensile failure along bedding planes under dynamic disturbances.To ensure engineering safety,it is necessary to conduct research on the dynamic tensile characteristics under different working conditions.Considering the difficulty of on-site sampling,composite rock samples were prepared with cement mortar,and dynamic Brazilian splitting tests were carried out using split Hopkinson pressure bar(SHPB)equipment,a high-speed camera,and PFC^(2D)numerical software to explore their dynamic tensile properties under dynamic disturbance under different strength ratios and other factors.The results show that the dynamic tensile strength of samples exhibits a rising trend with the strength ratio and strain rate growth.As the incident angle increases from 0°to 90°,the stress contour deflects transform from center-splitting failure to tension-shear combined failure and back again.The influence of the incident order in different lithology rocks on the dynamic tensile strength of composite samples is controlled by strain rate,and when the strain rate increases to 400 s^(-1),the difference in strength due to the sequence of incident stress waves is within 5%.Based on PFC^(2D),the strength ratio of composite samples has a certain influence on the distribution of microfractures.With strength ratios equaling 1.5 or 2.0,the cracks are mainly concentrated on the softer material side,while a large number of cracks are distributed on both sides of the bedding plane with a strength ratio equal to 1.2.
基金the Natural Science and Engineering Research Council of Canada(RGPIN/4052-16,ALLRP 560390-20).
文摘This paper addresses a fundamental question in rock mechanics:Are there Class II rocks?The historical development of servo-controlled rock testing machines is reviewed,followed by a brief review of some stiff testing machines.The pioneering work of some researchers is reviewed,and the misconception of classifying rocks into Class I and Class II is discussed.The mechanism of post-peak Class II behavior is discussed based on some recent test results.When a brittle hard rock is tested using a soft testing machine under axial-strain-controlled loading,violent failure can occur when the peak strength is reached,and the post-peak stress-strain curve cannot be obtained.However,a Class II post-peak stress-strain curve can be obtained when the rock is tested under lateral-strain-controlled loading.If a stiff testing machine is used,Class I and Class II post-peak stress-strain curves will be obtained under axial-and lateral-strain-controlled loadings,respectively.It is therefore not appropriate to classify rocks into Class I or Class II rocks.The influences of other conditions,such as rock type,confinement,and specimen height-to-diameter ratio,on the type(Class I or Class II)of post-peak stress-strain curves are also discussed.Finally,some misconceptions in the rock mechanics community,stemming from the concept of“Class II rock”,are discussed.By clarifying these concepts related to Class I and Class II behaviors,this paper seeks to clarify misunderstandings and misapplications related to post-peak strength and deformation properties in the field.
基金supported by the National Natural Science Foundation of China(Grant No.11802332)the China Scholarship Council(Grant No.202206435003)the Fundamental Research Funds for the Central Universities(Grant No.2024ZKPYLJ03).
文摘The internal microstructures of rock materials, including mineral heterogeneity and intrinsic microdefects, exert a significant influence on their nonlinear mechanical and cracking behaviors. It is of great significance to accurately characterize the actual microstructures and their influence on stress and damage evolution inside the rocks. In this study, an image-based fast Fourier transform (FFT) method is developed for reconstructing the actual rock microstructures by combining it with the digital image processing (DIP) technique. A series of experimental investigations were conducted to acquire information regarding the actual microstructure and the mechanical properties. Based on these experimental evidences, the processed microstructure information, in conjunction with the proposed micromechanical model, is incorporated into the numerical calculation. The proposed image-based FFT method was firstly validated through uniaxial compression tests. Subsequently, it was employed to predict and analyze the influence of microstructure on macroscopic mechanical behaviors, local stress distribution and the internal crack evolution process in brittle rocks. The distribution of feldspar is considerably more heterogeneous and scattered than that of quartz, which results in a greater propensity for the formation of cracks in feldspar. It is observed that initial cracks and new cracks, including intragranular and boundary ones, ultimately coalesce and connect as the primary through cracks, which are predominantly distributed along the boundary of the feldspar. This phenomenon is also predicted by the proposed numerical method. The results indicate that the proposed numerical method provides an effective approach for analyzing, understanding and predicting the nonlinear mechanical and cracking behaviors of brittle rocks by taking into account the actual microstructure characteristics.
基金jointly supported by Science and Technology Projects in Guangzhou(Grant No.SL2023A04J01079)Zhejiang ProvincialWater Conservancy Science and Technology Plan Project(Grant No.RC2405)Thematic Five of the Second Scientific Expedition of Qinghai-Tibet Plateau(Grant No.2019QZKK0905).
文摘Layered rocks(LR)exhibit inherent anisotropic stiffness and strength induced by oriented rough weakness planes,along with stress induced anisotropy and friction related plastic deformation occurs during loading.Furthermore,microcracks located in intact rock matrix(IRM)of LR are also critically important for friction and damage dissipation processes.In this paper,we first present a novel multiscale friction-damage(MFD)model using a two-step Mori-Tanaka homogenization scheme,with the aim of describing the multiscale friction-damage mechanics in LR.Physically,the initiation and propagation of flaws at different scales(i.e.microcracks and weakness planes)induced damage,and the plastic deformation is closely associated with frictional sliding along these flaws.In the thermodynamics framework,the macroscopic stress-strain relations,the local driving forces respectively conjuncted with flaws propagation and plastic deformation are derived.An analytical macroscopic strength criterion is subsequently deduced,which takes into account the variation of inclination angle and confining pressure.Notably,the failure mechanisms of IRM shearing and weakness planes sliding are inherent included in the criterion.As an original contribution,a new multisurface semi-implicit return mapping algorithm(MSRM)is developed to integrate the proposed MFD model.The robustness of MSRM algorithm is assessed by numerical tests with different loading steps sizes and convergence conditions.Finally,the effectiveness of the MFD model is confirmed using data from experiments under conventional triaxial compression,all main features of mechanical behaviors of LR are well captured by the proposed model,including initial anisotropy,stress-induced anisotropy and strain hardening/softening.
