EXPERIMENTAL INVESTIGATIONS ON STATIC LOADING RATE EFFECTS ON MECHANICAL PROPERTIES AND ENERGY MECHANISM OF COARSE CRYSTAL GRAIN MARBLE UNDER UNIAXIAL COMPRESSION
HUANG Da1，2，3，HUANG Runqiu2，ZHANG Yongxing1，3
(1. College of Civil Engineering，Chongqing University，Chongqing 400045，China；2. State Key Laboratory of Geohazard Prevention and Geoenvironment Protection，Chengdu University of Technology，Chengdu，Sichuan 610059，China；3. Key Laboratory of New Technology for Construction of Cities in Mountain Area，Ministry of Education，Chongqing University，Chongqing 400045，China)
Abstract：Loading rate has an important influence on rock mechanical properties. The influence degree is closely related to the microstructure of rock，loading and unloading paths and states，etc.. Based on the uniaxial compression tests of coarse crystal grain marble with nine strain rate levels in range of static loading rate，the influences of loading strain rate on stress-strain curve，failure pattern，strength，elastic modulus，deformation modulus and strain energy dissipation and release of the marble are investigated；and the energy mechanism of rock damage evolution is discussed. The initial cracking stress and critical dilatancy stress of rock specimens under different loading rates can be obtained by the relations of total volumetric strain and crack volumetric strain with initial cracking stress and critical dilatancy stress. The loading strain rate of about 1×10－3 s－1 is the dividing point. When the strain rate is less than the value，a certain plastic yield or flowing section near the peak of stress-strain curve is still present；but when the strain rate is more than the value，the fold line type near the peak of stress-strain curve is present. The fracture pattern of rock specimen changes from tension-shear to tensile rip and even rip-ejection with the increase of loading strain rate. Generally，the initial cracking stress，critical dilatancy stress，and uniaxial compressive strength increase with the loading strain rate；and the initial cracking stress and critical dilatancy stress are more closer to the peak strength. But when the loading strain rate is 1×10－4–1×10－3 s－1，a relative low value area is present for all values mentioned above，which is related to the microstructure of coarse crystal grain marble. The correlations between the initial cracking stress，critical dilatancy stress，elastic modulus and deformation modulus and the uniaxial compressive strength are linear. Under uniaxial compression，the more the energy dissipation before peak strength is，the higher the strength is；and the more the energy release after the peak strength is，the stronger the tensile through fracture characteristic is，and the more the fractured blocks are. The energy dissipation makes rock damage and the strength loss；and the energy release makes the macrofracture surface be run-through，inducing integral damage.
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2012, Vol. 31 
