Abstract: Based on the formation process of caved zone, the dynamic height of caved zone is studied systematically. The studies have shown that the ultimate caving height mainly depends on residual broken expansion coefficient of breaking down rock dispersions, while the residual broken expansion coefficient is determined by the porosity of breaking down rock dispersions. Accordingly, the porosity calculation model is set up by fractal geometry. The relationship between residual broken expansion coefficient and initial broken expansion coefficient of rock is given based on the porosity calculation model. The calculation model of ultimate caved zone height of caving rock filling the whole mined-out area is deduced. At last, the model is verified by an engineering example.

Key words: caved zone, porosity, dynamic height, broken expansion coefficient, fractal