Abstract: This paper investigates the roof strata stability of complicated mined-out areas and determines the reasonable control methods. Taking the Paomaping Lead-zinc deposit as the engineering background, the theoretical analysis, field investigation and laboratory mechanical experiments are carried out. The critical collapse area of goaf roof is calculated based on the equilibrium arch theory. In view of above researches, using three-dimensional finite element numerical simulation method, the deformation and failure mechanism of roof strata in mined-out area is analyzed and the corresponding control methods are put forward. The results show that the critical caving equivalent circular area of mined-out area is 6 191 m2, and the existing exposed area of the mined-out area is close to the critical failure value and its exposed area should be effectively controlled. The exposed area and span of the mined-out area are the main factors affecting the roof stability. With their expansion, the tensile stress appears in the roof, resulting in unstable failure. Forced caving of roof and surrounding rock will obvi- ously decrease the stability of mined-out area, inducing the roof strata instability. Waste rock backfilling of mined-out area can effectively control the strata deformation, improving the rock mass stress and roof stability.

Key words: mined-out areas, stability analysis, numerical simulation, waste rock backfilling, overburden strata