Time-Dependent Ground Movement Behavior in a Metal Mine

Abstract

The deformation monitoring data including the horizontal and vertical displacements from Chengchao Iron-ore Mine were gathered over 10 years. Combined with the field macrofailure characteristics at the ground surface, the time-dependent ground movement behaviors induced by the underground orebody excavation were investigated. Results show that the time-dependent deformation behaviors within the surrounding rock masses are very different with the distance to the mined-out areas increasing. Close to the mined-out areas, the time-dependent deformation behavior can be described by two distinctive stages termed as the “primary steady-state creep” and “progressive” stages. Slightly away from the mined-out areas, the time-dependent deformation behavior can be divided into three distinctive stages termed as the primary steady-state creep, “regressive,” and progressive stages. Far away from the mined-out areas, the surrounding rock mass creeps with a low deformation rate, and the time-dependent deformation behavior is still at the primary steady-state creep stage. The analysis shows that the groundwater can have a remarkable effect on the deformation of the rock masses by causing the movement rate to become faster. The main reason why the regressive stage occurs in the southeastern area of the main transportation tunnel can be attributed to the rainfall, and the period for the maximum deformation rate within the surrounding rock masses corresponds to the rainfall season of the year. The onset-of-failure (OOF) point within the displacement–time curves can be defined as when the failure surface begins to form at the deep part of the rock masses. The time-dependent ground movement behavior of the mine can be divided into four stages: the initial caving of the roof strata, the large-scale caving of the roof strata, when the failure surface begins to form at the deep part of the rock masses around the stack-site and the mine road, and when the failure surface begins to form at the deep part of the rock masses around the southeastern area of the main transportation tunnel.