Abstract: In the process of transition from caving method to filling method, there is a large scale goaf beneath the top pillar of a filling method transition stope and a large number of loose rocks upon this top pillar. So the stability of the top pillar of the transition stope has a great significance for mining safety. The thickness-to-span ratio of the top pillar is an important factor affecting the top pillar’s stability. The relationship model of the stability and the thickness-to-span ratio of the top pillar of the filling method transition stope have been established with the π theorems to analyze the stability of top pillar. The allowable strain of top pillar has been selected as the criterion of stope stability in the model. According to the allowable strain, the reasonable thickness-to-span ratio has been obtained. This model has been applied to study the size of the top pillar in the test transition stope from sublevel caving method to filling method at Chengchao Iron Mine. The minimum thickness-to-span ratio which is suitable for the engineering condition of Chengchao Iron Mine has been obtained by the finite element method; the maximum thickness-to-span ratio has been obtained by loss rate. As the result of calculation, the thickness- to-span ratio for Chengchao iron is 1.24-1.45. The top pillar instability of the test stope does not happen in the production process. The effectiveness of the model is verified by engineering test.

Key words: size of top pillar；&pi, theorems；thickness-to-span ratio；allowable strain