The CT Experimental Investigations On Rheological Mechanical Properties Of Rock

Rock rheological phenomena are ubiquitous in rock engineering construction.The study of rock rheological mechanics is of great value in rock foundation,slope,tunnel and underground engineering.Because the creep and stress relaxation of rock are directly related to the long-term strength of rock and the long-term stability of engineering,it is necessary to study the mechanical properties of creep and stress relaxation of rock to meet the actual needs of current engineering.In view of the shortcomings of micro-specimens and micro-damage research field,this paper takes micro-limestone specimens as the research object,takes "CT Test Research on rheological and mechanical properties of rock" as the main research topic,and makes use of self-developed micro-uniaxial coal-rock testing machine and high-precision micro-CT test system of Taiyuan University of Technology to complete the creep and stress relaxation of limestone under uniaxial compression.A large number of micro-CT images were acquired through dynamic real-time CT scanning experiments of meso-damage extension.Through observing and analyzing the local features of CT images,the evolution of micro-cracks was identified by the change of distance between characteristic points at different locations and density in different regions.The micro-failure laws during creep and stress relaxation of limestone were obtained.In this paper,the research status of rock rheology mechanics and the application of CT technology are introduced firstly.Then,the micro uniaxial coal and rock testing machine,high precision micro CT testing system and their cooperation are explained.The test method and image processing technology are introduced briefly.The creep and stress relaxation CT test of limestone is carried out next.Firstly,the micro limestone specimens were selected and manufactured for the conventional uniaxial compression test.The instantaneous failure strength and ultimate strain of the limestone specimens were measured.Then the creep test under multi-component incremental loading was carried out.The creep characteristics of the limestone specimens were studied.The deformation of the limestone specimens showed deceleration creep and steady creep related to time.Furthermore,the micro-failure law during creep was observed by micro-CT test.The results of CT image analysis show that the creep damage propagation of limestone exists localization phenomenon,and the cracks in the steady creep section accelerate with the increase of stress grade;the cracks are more likely to occur in the low density region,the density of the specimen decreases in the middle and low stress state,and the density changes in the fracture region and non-fracture region under the higher stress state produce differentiation phenomenon,which ultimately leads to the rock failure.In the stress relaxation test of limestone specimens,the stress relaxation test under multi-component loading was carried out first,and the stress relaxation characteristics of limestone were studied.The stress relaxation of limestone undergoes three stages: rapid relaxation,slow relaxation and stable relaxation.Before the specimen is destroyed,the stress relaxation and residual stress ratio increase with the strain level.Under the last strain,the stress decreases rapidly,the stress relaxation increases obviously,and the residual stress ratio decreases instead.Furthermore,the micro-failure law during stress relaxation was observed by micro-CT test.The results of CT image analysis show that the cracks are more likely to occur in the low initial density area when the specimen is initially dilated and then compacted.The stress relaxation damage expansion of limestone increases with the increase of strain level,and the regional differentiation of damage evolution also exists in the high strain level.In this paper,there are still many shortcomings in experimental design and operation,but through the experimental research and theoretical analysis in this paper,the rheological damage law of micro limestone specimens is revealed to a certain extent,which has important research significance.