Research On Damage Evoultion And Fracture Mechanisms Of Mudstone Under High Tempearture

With the social and economic development, the energy demand is increasing andgeotechnical engineering questions related to temperature attract more and more wideattentions, such as geothermal resource development, nuclear waste disposal and undergroundcoal gasification. Research on rock mechanical properties under the coupled action oftemperature and geostress is the basis to solve geotechnical engineering questions related totemperature. This paper mainly studies mudstone in coal strata by means of experimentalmethods and theoretical methods, including MTS810Electro-hydraulic Servo Material TestingSystem and matched High Temperature Furance, Scanning Electron Microscope, X-rayDiffraction Analyser, damage fracture theory and viscoelastic plastic theory. From the macroand mesoscopic scales, damage evolution laws and fracture mechanisms of mudstone underhigh temperature are studied systematically. The main works and research results are as follow:(1) Whole stress-strain curves of mudstone samples at the temperature from normal to800℃are tested systematically and the change laws of elastic modulus, peak strength, peakstress, peak strain and softening modules of mudstone with an increase in temperature areobtained. In addition, analyse the effect of loading speed on mudstone mechanical propertiesand reveal the features of brittle-to-ductility transformation in mudstone with increasingtemperature and strain speed.(2) According to SEM and X-ray diffraction analysis experiment of mudstone samplesfracture, the change features of component structural, component factor of effects on mudstonemechanical property and morphology and development features of crack in sample fracture areobtained. The results show that: component and phase transformation of mudstone sample athigh temperature are important reasons that cause cracks in sample fractures spread, close andform differences of fractures in grain boundary, and thus present change features ofmacroscopic mechanical property in different temperatures, which effectively revealsmicroscopic mechanisms of mudstone macroscopic fracture features in high temperature.(3) Based on rock damage mechanics and statistical strength theory, combiningmechanical properties of mudstone at high temperature, the damage evolution equation andconstitutive model of mudstone considering effects of temperature and loading speed areesTablelished. And aiming at mechanical properties of tested mudstone, the correspondingdetailed parameters of damage equation are given. Furthermore, constitutive model has a goodagreement with experiment results.(4) Through step load creep experiment of mudstone at normal and high (700℃)temperature, we not only obtain the corresponding creep curves and creep empirical equation of mudstone, but also initially esTablelish creep constitutive model of mudstone consideringtemperature effect, including creep equation, unload equation and relaxation equation ofmudstone.To some extent the research results enrich basic theory of rock mechanics and provideimportant basis for research on geotechnical engineering problems under the coupled action oftemperature and geostress.