Study on creep characteristics and fractional creep damage constitutive model of limestone under thermal-mechanical action

To study influence of thermal-mechanical action on creep for the geothermal wellbore, Dalian limestone was taken as the research object, and triaxial creep tests were carried out on samples under different temperatures and the effects of different temperatures on the creep deformation, creep rate and long-term strength of limestone are discussed. The test results show that the creep process of limestone under thermal-mechanical action shows three distinct phases. As the temperature increases, the creep time and long-term strength gradually decrease. The macroscopic failure modes of limestone under different temperatures are shear failure and the fracture surface is more obvious. Meanwhile, based on the principle of statistical damage and fractional calculus, the damage body under high temperature is proposed, and a fractional creep damage model that can characterize the triaxial creep mechanical behavior of limestone under different temperatures is constructed. The reasonableness of the model is proved by comparing. The parameters analysis shows that the fractional order δ mainly affects the creep rate, which is expressed in the stable and accelerated phases. The aging damage parameter λ is related to the time coordinate scale. The research results in this paper can provide a certain guiding significance for the long-term stability evaluation of the surrounding rock of the geothermal wellbore.