Experiment on Mine Ground Pressure of Stiff Coal-Pillar Entry Retaining under the Activation Condition of Hard Roof

In mining excavation, the retained entry with stiff coal pillar is situated in the strong mine ground pressure. Influenced by mining abutment stress and dynamic stress (the vibration signal) induced from the hard roof activation, the retained entry may be subjected to roof separation, supporting body failure, severe floor heave, and even roof collapse. Based on a 2D physical model, an experimental method with plane-stress conditions was used to simulate the mechanical behavior of the rock strata during mining. In this experiment, three monitoring systems were adopted to reveal the characteristics of the strong mine ground pressure in the stiff coal-pillar entry retaining. The results show that the hard roof undergoes bending down, fracture, and caving activation successively until it is able to support overlying loads. The abutment stress which is induced from the loading transfer in stiff coal pillar is larger than that in other rocks around the retained entry in amplification, and overlying loads above the worked-out area have a loading effect on the unworked-out area. When the hard roof is situated in the activation state, the dynamic stress is generated from the hard roof activation, which is verified by the great saltation of acoustic emission signals. The results of mining ground pressure in the physical model can clearly illustrate the mechanical behavior of the rock around the retained entry with stiff coal pillar.

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