Intact rocks with layered microstructures,such as gneiss,exhibit strong anisotropy.Although anisotropy in the macroscopic strength of gneiss has been widely reported,the role of microstructures in tensile mechanics re...Intact rocks with layered microstructures,such as gneiss,exhibit strong anisotropy.Although anisotropy in the macroscopic strength of gneiss has been widely reported,the role of microstructures in tensile mechanics remains largely unclear.Utilizing a range of methodologies,it was determined that the tensile strength,deformation,and fracturing behavior of Himalayan gneiss are predominantly influenced by biotite.In contrast to the behavior of other transversely isotropic rocks,the apparent tensile strength of the gneiss first decreased and then increased with anisotropic angleβ,rather than the widely reported monotonic increase or single-shoulder response.The shear sliding of biotite along cleavage planes caused stress concentrations in the surrounding brittle minerals,inducing cracks and reducing the overall tensile strength of the gneiss.Micro-observations of the relationship between cracks and biotite orientation identified three types of biotite crystal fragmentation:tensile fragmentation along cleavage planes,shear fragmentation along cleavage planes,and tensile fragmentation perpendicular to cleavage planes.Tensile and shear fragmentation of biotite along cleavage planes negatively affected the gneiss'macroscopic tensile strength.Conversely,when the tensile stress was parallel to the biotite cleavage planes,tensile fragmentation perpendicular to the cleavage planes increased the macroscopic tensile strength of the gneiss due to plastic deformation and high surface energy.Quantitative analysis of shear stress along biotite cleavage planes revealed the mechanical mechanism behind the reduced tensile strength of the East Himalayan gneisses near an anisotropic angle of 30°.These results elucidated the influence of grain-level anisotropy on the macroscopic tensile mechanical properties of intact layered rocks.展开更多
To efficiently link the continuum mechanics for rocks with the structural statistics of rock masses,a theoretical and methodological system called the statistical mechanics of rock masses(SMRM)was developed in the pas...To efficiently link the continuum mechanics for rocks with the structural statistics of rock masses,a theoretical and methodological system called the statistical mechanics of rock masses(SMRM)was developed in the past three decades.In SMRM,equivalent continuum models of stressestrain relationship,strength and failure probability for jointed rock masses were established,which were based on the geometric probability models characterising the rock mass structure.This follows the statistical physics,the continuum mechanics,the fracture mechanics and the weakest link hypothesis.A general constitutive model and complete stressestrain models under compressive and shear conditions were also developed as the derivatives of the SMRM theory.An SMRM calculation system was then developed to provide fast and precise solutions for parameter estimations of rock masses,such as full-direction rock quality designation(RQD),elastic modulus,Coulomb compressive strength,rock mass quality rating,and Poisson’s ratio and shear strength.The constitutive equations involved in SMRM were integrated into a FLAC3D based numerical module to apply for engineering rock masses.It is also capable of analysing the complete deformation of rock masses and active reinforcement of engineering rock masses.Examples of engineering applications of SMRM were presented,including a rock mass at QBT hydropower station in northwestern China,a dam slope of Zongo II hydropower station in D.R.Congo,an open-pit mine in Dexing,China,an underground powerhouse of Jinping I hydropower station in southwestern China,and a typical circular tunnel in Lanzhou-Chongqing railway,China.These applications verified the reliability of the SMRM and demonstrated its applicability to broad engineering issues associated with jointed rock masses.展开更多
基金supported by the Second Tibetan Plateau Scientific Expedition and Research(STEP)program(Grant No.2019QZKK0904)the National Natural Science Foundation of China(Grant No.42402277)the Fundamental Research Funds for the Central Universities(Grant No.300102264902).
文摘Intact rocks with layered microstructures,such as gneiss,exhibit strong anisotropy.Although anisotropy in the macroscopic strength of gneiss has been widely reported,the role of microstructures in tensile mechanics remains largely unclear.Utilizing a range of methodologies,it was determined that the tensile strength,deformation,and fracturing behavior of Himalayan gneiss are predominantly influenced by biotite.In contrast to the behavior of other transversely isotropic rocks,the apparent tensile strength of the gneiss first decreased and then increased with anisotropic angleβ,rather than the widely reported monotonic increase or single-shoulder response.The shear sliding of biotite along cleavage planes caused stress concentrations in the surrounding brittle minerals,inducing cracks and reducing the overall tensile strength of the gneiss.Micro-observations of the relationship between cracks and biotite orientation identified three types of biotite crystal fragmentation:tensile fragmentation along cleavage planes,shear fragmentation along cleavage planes,and tensile fragmentation perpendicular to cleavage planes.Tensile and shear fragmentation of biotite along cleavage planes negatively affected the gneiss'macroscopic tensile strength.Conversely,when the tensile stress was parallel to the biotite cleavage planes,tensile fragmentation perpendicular to the cleavage planes increased the macroscopic tensile strength of the gneiss due to plastic deformation and high surface energy.Quantitative analysis of shear stress along biotite cleavage planes revealed the mechanical mechanism behind the reduced tensile strength of the East Himalayan gneisses near an anisotropic angle of 30°.These results elucidated the influence of grain-level anisotropy on the macroscopic tensile mechanical properties of intact layered rocks.
基金The authors are grateful to the financial support from the National Natural Science Foundation of China(Grant No.41831290)the Key R&D Project from Zhejiang Province,China(Grant No.2020C03092).
文摘To efficiently link the continuum mechanics for rocks with the structural statistics of rock masses,a theoretical and methodological system called the statistical mechanics of rock masses(SMRM)was developed in the past three decades.In SMRM,equivalent continuum models of stressestrain relationship,strength and failure probability for jointed rock masses were established,which were based on the geometric probability models characterising the rock mass structure.This follows the statistical physics,the continuum mechanics,the fracture mechanics and the weakest link hypothesis.A general constitutive model and complete stressestrain models under compressive and shear conditions were also developed as the derivatives of the SMRM theory.An SMRM calculation system was then developed to provide fast and precise solutions for parameter estimations of rock masses,such as full-direction rock quality designation(RQD),elastic modulus,Coulomb compressive strength,rock mass quality rating,and Poisson’s ratio and shear strength.The constitutive equations involved in SMRM were integrated into a FLAC3D based numerical module to apply for engineering rock masses.It is also capable of analysing the complete deformation of rock masses and active reinforcement of engineering rock masses.Examples of engineering applications of SMRM were presented,including a rock mass at QBT hydropower station in northwestern China,a dam slope of Zongo II hydropower station in D.R.Congo,an open-pit mine in Dexing,China,an underground powerhouse of Jinping I hydropower station in southwestern China,and a typical circular tunnel in Lanzhou-Chongqing railway,China.These applications verified the reliability of the SMRM and demonstrated its applicability to broad engineering issues associated with jointed rock masses.
