Elastic modulus＇s evolution law of coal under high temperature and triaxial stress

Abstract：Utilizing the ＂600 ℃ and 20 MN servo-controlled rock triaxial testing machine with high temperature and high pressure＂ developed,performed experiments to research the elastic modulus＇s evolution law of anthracite and gas coal with the temperature increasing from room temperature to 600 ℃ under a pressure equivalent to the in-situ stress at 500 m.The anthracite was extracted from Jincheng coal field and the gas coal was extracted from Xinglongzhuang coal mine.Both the anthracite and the gas coal were shaped into 400 mm in height and 200 mm in diameter.The difference of elastic modulus between anthracite and gas coal was also analyzed.In addition,the mutation critical temperature and influence of pyrolysis on the coal elastic modulus was discussed.The research results indicate that：the process during which the elastic modulus of coal changes with temperature can be divided into three stages,that is,steadily decreasing stage in mid-low temperature,drastically decreasing stage in mid-high temperature and slowly decreasing stage in high temperature;the gas output for coal＇s pyrolysis influences on coal＇s elastic modulus severely,as the temperature increases,the anthracite＇s elastic modulus shows negative exponential relations with the rate of pyrolysis gas;the confine pressure,temperature and pyrolysis influence the coal＇s elastic modulus together,and the temperature and pyrolysis are main factors influencing the coal＇s elastic modulus when the confine pressure remains unchanged.and the coal＇s elastic shows different characteristics under different temperature stage;the law of coal＇s elastic modulus varying with temperature is more complicated than that of sandstone＇s.However,the elastic modulus of coal also has a mutation critical temperature.The difference lies in the large variance of critical temperature between different ranks of coal.