Loading-Rate Dependency of Coal Strength.

Uniaxial compression, uniaxial tension and indirect tension (Brazilian) tests were carried out for coal (anthracite) obtained in a coal mine located about 26 km west of Beijing.Complete stress-strain curves not only in uniaxial compression test but also in uniaxial tension test were successfully obtained. In post-failure region of uniaxial tension test, the curve showed Class I characteristics accompanied with small amount of residual strength. The peak strength obtained by the uniaxial tension test was far less than the indirect tensile test frequently conducted.The strain rate was alternatively increased and decreased to obtain the loading-rate dependency. When strain rate was increased, stress increased abruptly by a certain amount depending on the loading-rate dependency of the rock. The experimental results showed that loading-rate dependency of the coal both under the uniaxial compression and tension stress was relatively smaller than the most rocks that had been tested by the authors.