(1. College of Mining Engineering，Taiyuan University of Technology，Taiyuan，Shanxi 030024，China；2. Key Laboratory of In-situ Property-improving Mining of Ministry of Education，Taiyuan University of Technology，Taiyuan，Shanxi 030024，China)
Abstract：To investigate the deformation and structure variation of lignite under the thermal-mechanical action，experiments were performed to the lignite samples of 50 mm in diameter and 100 mm in length with the high temperature and trixial stress testing platform. The structure variation was studied with Micro-CT，mercury intrusion and liquid nitrogen adsorption methods. Several fundamental characteristics of lignite deformation were obtained when the temperature rose from 23 ℃ to 400 ℃ at a rate of 3 ℃/min under the triaxial constant stress of 7 MPa. The deformation process of lignite can be divided into three stages：a slowly swelling stage with the temperature rising from 23 ℃ to 170 ℃，a rapidly compressing stage with the temperature rising from 170 ℃ to 289 ℃ and a relatively slowly compressing stage with the temperature rising from 289 ℃ to 400 ℃. The critical temperature of the brittle-ductile transition for lignite is about 180 ℃. During the constant load and temperature process，the final value of the axial strain increased firstly then decreased with the largest value of 2.5% at 200 ℃ and the smallest value of about 1.3% at 100 ℃. The largest total radial strain is about 19% and the largest total volume strain is about 41% at 400 ℃. The lignite deformation has great effect on its structure evolution. The total porosity of lignite increased firstly then decreased with the temperature rising. The largest total porosity is 21.46% at 200 ℃ while the smallest total porosity is only 7.61% at 23 ℃. The diameter of the main fissures increased with the temperature rising. The lignite porosity in the heating process has good fractal characteristics. The fractal dimension value decreased firstly then increased while the value of lnA0 increased firstly then decreased with the temperature rising.
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2017, Vol. 36 
