The Study On Evolutional Deform Mechanisms Of Boundary Pillar And Its Thickness Optimization Under Multi-factor

With the open-pit mining continued exploitation and depth gradually deepened, open-pit mining is not suitable for the production requirement of the mine, these days, a great many of open-pit mines have started to transfer from open-pit to underground mining. In order to ensure the production capacity of the mine, many mines decided to continue mining during transferring from open-pit to underground mining, which needed to set aside a certain thickness of boundary pillar at the bottom of open-pit, and currently there is no unified calculation method to calculate the thickness of pillar thickness. The engineering background of this paper is Xinqiao mine, using the method of numerical simulation and model test to study on evolutional deform mechanisms of boundary pillar and its thickness optimization.This paper mainly includes the following aspects:(1)Based on ore body model built by3Dmine, DTM model of geography and Midas GTS’coupling, this paper presents the refined geometrical model of transferring open-pit into underground mining. The paper also presents the structural concept of composite boundary pillar according to the actual mine, and adopts FLAC3D simulating the geometrical model of several boundary pillar schemes, in order to obtain the optimal thickness of boundary pillar.(2) Based on unascertained measurement theory, a safety evaluation model of boundary pillar was established. Considering the geologic condition and engineering status of the mine which transferring from open-pit to underground mine.7main factors that influence the stability of boundary pillar were taken into account, including the thickness of boundary pillar, compressive strength of ore, tensile strength of ore, open-pit depth, Joint distribution, the mining method of underground mine and seeper of open-pit. Evaluating the security of boundary pillar,in order to get zhe security level of boundary pillar.(3) To determine the various lithologies similar material ratio in the similarity model test. Barite, sand, cement, gypsum and water as a ratio of the material, physical and mechanical experiments were tested on different proportions of samples, and then selected the success ratio which meet similar principle to simulate surrounding rock on the plate and under disk, filling body and the ore body.(4) Based on Xinqiao open-pit, Using model test to test longitudinal section of the stope,in order to In-depth analysis the deformation and mechanical evolution of the stope during the step excavation.