(1. State Key Laboratory of Geomechanics and Geotechnical Engineering，Institute of Rock and Soil Mechanics，Chinese Academy
of Sciences，Wuhan，Hubei 430071，China；2. University of Chinese Academy of Sciences，Beijing 100049，China)
Abstract：Clump and cluster models based on two-dimensional particle flow code(PFC2D) were constructed through two different algorithms to explore the effects of micro parameters and microstructure(crystal grain size and distribution，pre-existing cracks) on the macro mechanical properties of specimen and to quantify the relationships between them. Meanwhile，the development of micro cracks and the mechanism of micro failure were studied. It was revealed that two algorithms had their own advantages. Macro mechanical properties of marked circular region algorithm changed with the variation of micro parameters nicely. The composition of crystalline gradation was better controlled by the searching algorithm. The uniaxial compressive strength(UCS) and the tensile strength(TS) are in exponential relationship with the clump radius and un-bonded ratio(random pre-existing cracks) and are in power relationship with the bond strength ratio. The elastic modulus and Poisson?s ratio are in linear relationship with the clump radius，bond strength ratio and un-bonded ratio. With the increase of the clump radius，bond strength ratio，bond strength ratio n of cluster and un-bonded ratio，the ratio of uniaxial compressive strength to tensile strength which is mostly affected by bond strength ratio increases a lot. The ratio of tensile cracks is mostly affected by the bond strength ratio，followed by the clump radius. Under the uniaxial compression，the failure of specimen is dominated by the tensile cracks which mainly extend along the axial direction. However，the angle between the dominant orientation of shear cracks and axis is 20 degree to 40 degree. Brazil test failure is dominated by tensile cracks across the center of specimen. The evolution of micro cracks and failure modes are different for cluster and clump models. Compared with the cluster model，the shear crack ratio of clump model is bigger and crack crushing zone is wider. Moreover，the fracture surface is more rough and uneven.
HAZZARD J F，PAUL Y R，MAXWELL S C. Micromechanical modeling of cracking and failure in brittle rocks[J]. Journal of Geophysical Research Solid Earth，2000，105(B7)：16 683-16 697.
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2016, Vol. 35 
