Abstract: The inhomogeneous composition of rock is described by using the random parameter assignment method of rock mineral cell unit which is based on the contents (sort and ratio) of the rock forming minerals. The hybrid models with two mineral cell units and three mineral cell units that simulate inhomogeneous rock are used to carry out numerical test to research the influence of inhomogeneity on macroscopic stress-strain curve. Besides, based on the rock mineral composition (sort and ratio), the parameter of inhomogeneity degree is defined. The influence of inhomogeneity degree on the macroscopic mechanical parameters (elastic modulus and ultimate strength) are analyzed according to results of the numerical test. The research result indicates that mechanical property of homogeneity rock is determined by the mechanical properties of the units, while inhomogeneous rock is determined by both the mechanical properties of the units and the rock mineral composition. When the parameter of inhomogeneity degree is small, the weakening effect of elastic modulus caused by inhomogeneity is small, and vice versa. The influence on ultimate strength is the same as that on elastic modulus.

Key words: rock, mineral cell unit, macroscopic mechanical properties, inhomogeneity degree