Ground Pressure Damage Evolution Mechanism of Extraction Level Excavations Induced by Poor Undercutting in Block Caving Method

Under the condition of bad undercutting, ore pillars are easily left in undercut level in block caving method. In order to reveal the evolution mechanism of ground pressure damage induced by bad undercutting, according to the actual engineering and physical parameters of the mine, a numerical simulation model was established by finite difference software FLAC3D. In the simulation process, the extraction level excavations were excavated first according to the post-undercutting method, and the process of the undercutting were divided into three steps. In the first step, a pillar of 15 m × 5 m was formed. The stress state of extraction level excavations and overlying ore body after each step was monitored and analyzed separately, and it was compared with the actual situation of ground pressure disaster on site. The results show that: Under the influence of high horizontal in situ stress, with the development of undercutting, the special stress state in the extraction level excavations are gradually formed, which is that the compressive stress concentrates on the upper part and the tensile stress concentrates on the lower part. With the development of undercutting, the remaining ore pillar form a certain range of tension stress release area above the undercut level, which makes it difficult for overlying ore and rock to cave in, thus causing the phenomenon of “less ore and no ore” in the draw bells.