Study on mechanical properties and damage features of Rock-Coal-Rock combination models with defects and fillings

In order to study the damage features and mechanical properties of rock-coal-rock combination (RCR) models with defects and filling material, the 2-Dimensional Particle Flow Code (PFC2D) is used for the numerical simulation models. The variations of stress-strain, caused by uniaxial compression, are investigated. The distribution of the stress and displacement fields in horizontal and vertical directions of the models after failure is analyzed. The damage characteristics are discussed from the microscopic aspects of crack development, acoustic emission and contact force distribution. The results show the following: (1)The defects significantly affect the mechanical properties, the propagation of internal cracks, the evolution of displacement and stress and the distribution of stress concentration area. The peak stress-strain and elastic modulus of RCR models with defects decrease as the number of square holes increases. The more defects, the earlier new cracks appear in the coal body and the easier the defective models fail. (2) After filling the holes of the defective models, the number of cracks, crack initiation stress, elastic modulus and peak stress-strain are significantly larger than those of the corresponding model with holes, meaning that they can sustain larger load. The displacement and stress fields of the filled models are similar to the ones of the complete combination model. Hence, the filling material can enhance the mechanical properties of the defective RCR combination models.