Abstract: Affected by the interface effect, the macroscopic pre-cracking deformation of coal-rock combined body under static compression is significantly different from the coal and rock single body. Based on the effective medium model of rock-like material, this paper considers the composition characteristics of the coal-rock combined body, and proposes a pre-cracking macro-elastic model suitable for different types of coal-rock combined body. The parameters obtained from the test curve are determined by the axial crack strain, which is simple and convenient. The data verification of the existing literature shows the rationality, validity and universality of the model. Moreover, the model parameters are discussed and the following conclusion are obtained: (1) The micro-crack difference can be ignored in the pre-cracking stage of coal-rock combined body. (2) By decoupling the matrix of the coal-rock combined body, the model reflects the impact of interface effect on the elastic modulus of the coal-rock combined body. (3) The effective proportion of the rock matrix decreases significantly with the increase of the coal proportion. (4) There is an optimal ratio of elastic modulus of rock body to coal body, which maximizes the effective proportion of rock matrix. This model can provide a new perspective for mine support scheme design and material selection.

Key words: coal-rock combined body, elastic model, effective medium theory (EMT), static compression, microcrack