| The micro-contact damage mechanism of rock particles has significant influence on macroscopic rheological behavior of rockfill materials.Under the support of Natural Science Foudation of China project Creep Damage for Particle Contact Effect on Macroscopic Rheological Behavior of Rockfills(NO.11372230),direct shear test and time-dependent creep test under compressive shear stress condition on standard fresh fractured joint and natural irregular joint of limestone specimen were carried out in this paper.By means of 3D optical scanner and acoustic emission detecter,the changes of morphology and fractal dimension of joint surface before and after test,and the charateristics of acoustic emission during loading procedure are observed.The contact damage fractal evolution and micro fracture mechanism during compressive shear test of joint limestone were revealed.The major research achievements are presented as follows:(1)The shear mechanical behavior of rock materials has significant pressure sensitivity.The short-term and long-term shear strength are both proportional to the normal stress,as described by Mohr-Coulomb criterion.(2)A 3D optical scanner was applied to reconstruct the morphology of joint surfaces before and after loading.According to fractal theory,the fractal dimension of limestone joint surface in different loading stages was calculated.The roughness and waviness can be seen as micro and macro fractal measurements of joint surfaces,as well as an approach to study the microcosmic fractal evolution rule during shear fracture of rock joint.(3)The compressive shear mechanical behaviors of natural irregular joint limestone are similar as standard specimen,that the peak shear force is approximately proportional to the normal pressure.The normal pressure kept constant during shear,while the normal displacement kept changing along with loading.The normal displacement curve shows that shear process goes with closure and dilatancy effects.The dilatancy effect increases as normal pressure decreases.(4)The damage and fracture of rocks can produce acoustic emission.The initiation and propagation of shear damage and fracture of limestone could be studied through collecting and analyzing AE signals.Experimental results show that the AE events and loading curve have the same tendency.The specimen that has more AE events are main shear surfaces,on which main damage and fracture occur during loading.(5)The experimental results of shear creep under step loading of regular and irregular limestone specimen show that the creep curve grows stepwise along with loading.The displacement grows fast in the beginning of loading,which is called transient creep stage.The creep rate decreases in weakening creep stage till creep reaches stable state.The identification of experimental creep curve is completed based on the five-element nonlinear viscos-elasticity creep model of rock material,and the model parameters are obtained correspondingly.The experimental data has good agreement with the fitting curve,which shows that the five-element model can describe the behavior of shear creep of rock materials validly and reasonably.(6)Normal displacement during creep kept changing along with time.Dilatancy occurred at the beginning of every loading step as well as the specimens were getting closer under the normal pressure afterwards.Roughness decreases and increases along with loading,which shows that shear surfaces become smooth and rough.The accumulated AE event curve along with time has similar tendency with shear stepwise creep curve. |
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