Study on the damage localization law in frozen sandstone during uniaxial compression
In recent years,with the advancement of the western development strategy,China has undertaken ex-tensive rock engineering construction in alpine and cold mountainous areas.During the construction process,in-evitable engineering disasters such as slope instability and tunnel collapse have significantly compromised engi-neering safety.These disasters are usually caused by the gradual accumulation of damage and failure of rock un-der external load.In addition,low-temperature environmental factors will lead to the change of mechanical prop-erties of rock,and then affect the load-failure process.Damage localization is the necessary stage and precursor of rock failure under load.In this paper,the damage localization of frozen rock under load is studied,and the in-fluence of initial saturation degree is discussed.Uniaxial compression tests of frozen sandstone specimens with different initial saturation degrees were carried out at-20℃.The digital image correlation(DIC)and acoustic emission(AE)systems were used to collect surface deformation and AE signals during the test.Based on the mechanical test results,the mechanical and deformation characteristics of frozen sandstone are analyzed,and the influence of initial saturation degree on the mechanical properties of rock is demonstrated combined with the change of AE count distribution characteristics.Through the analysis of surface deformation,the surface strain localization mode of the specimen is divided into mode Ⅰ(tensile strain localization),mode Ⅱ(shear strain local-ization)and mode Ⅲ(mixed localization).The initial saturation degree of 40％is the turning point from mode Ⅰ to mode Ⅱ,and mode Ⅲ appears after the initial saturation degree exceeds 90％.All the modes can correspond to the final failure mode of the specimens.Based on the RA-AF analysis,the types of microcrack propagation in the rock during the strain localization process are shown:type Ⅰ(tensile crack),type Ⅱ(shear crack)and type Ⅲ(mixed crack),which are basically consistent with the surface strain localization mode.Finally,combined with the changes of phase composition in the pores of frozen rocks at different initial saturation degrees,the in-fluence of phase composition on the damage localization mode of frozen rocks is analyzed.That is,at low initial saturation degree,the ice content in the pores of frozen sandstone is small,and the external load is mainly borne by the rock skeleton.Because the tensile strength of the rock is usually lower than the shear strength,the rock will be tensile failure,and the damage localization mode is also tensile.At medium saturation degree,the ice content in the pores increases,and cements with the rock skeleton.The tensile strength of the ice helps the fro-zen sandstone resist tensile failure,and the damage localization mode becomes shear.At high initial saturation degree,the pore ice completely fills the microcracks,forcing them to expand,and a mixed damage localization mode is presented.This study helps to deepen the understanding of the mechanical properties of frozen rocks,and can provide important reference for the prediction of failure and instability of rock engineering in cold regions.
NETL
NSTL
万方数据
