Stability Analysis And Reinforcement Technology Of Mined-out Area In Songjiang Copper Mine

The underground mining in Songjiang Copper Mine has caused discrete mined-out areas about 346×104 m3 in volume. These areas have created security risks during the recovery of residual ores and the mining of tungsten and molybdenum. Based on the production situation and the survey and statistical results of geotechnical and geological field investigations of Songjiang Copper Mine, this paper has established 3D visualization numerical model of the mine with 3DMine, Midas, FLAC3 D and other software, which analyzed the stability and presented the safety grade of the mined-out area with a variety of methods, such as theoretical calculations, numerical simulations and fuzzy comprehensive evaluations; further more, the paper proposed the reasonable and effective control plan of the mined-out areas based on the treatment scheme of mined-out areas at home and abroad on the conditions of the mine situation. The main contents and conclusions of this paper are as follows:(1) Carrying out a detailed and continuous field investigation of rock engineering geological conditions with the method of line observations and a compass, steel tape, geological hammer and other equipment. Based on the investigation of the underground mining situation, we carried out a detailed statistics and analysis of the mined-out areas. Through the field sampling and indoor tests of rock mechanical parameters, we tested the physical mechanical parameters of the main ore of Songjiang Copper Mine, which provided important basic information for the stability analysis and controlling techniques research of mined-out area;(2) According to the level layout and the longitudinal projection of exploration line of ores, and the actual situation of the investigation about mined-out areas, we established a 3D visualization numerical model of the mine with 3DMINE, MIDAS, FLAC3 D and other software;(3) The security grading standards was based on the exposed area and the largest span of roof, by which we completed the stability analysis and safety grade of mined-out areas, and evaluated the security and stability situation of five main-out areas with fuzzy comprehensive evaluations; based on the MIDAS-FLAC3 D software, we completed numerical simulation analysis of underground stress field, strain field and plastic zone of mined-out area in Songjiang Copper Mine with finite elementfinite difference method, the analysis of the stability of existing mined-out area has an important guiding significance for governance of mined-out area and safety production of mine;(4) The results of stability analysis of mined-out area show that the five main mined-out areas can maintain the self-stability in a certain degree at present, the stability of No. 1 and No. 2 mined-out areas are less safer and No. 3, No. 4 and No. 5 mined-out areas are relatively safer. But in the discontinuous regions of +250-1, +170-1, +130-3, +130-5, +90-1, +90-2, +90-4, +50-2, +50-3, +10-3, +10-4 and +10-8 and the 11#~1# exploration line of No. 1 mined-out area, 7#~2# exploration line of No. 2 mined-out area and 3#~1# exploration line of No. 3 mined-out area are not safe, those are the danger zones in the mine, and the monitoring and controlling methods should be strengthened in the process of production;(5) According to the results of stability analysis of mined-out area, and considering the examples of mined-out area treatments at home and abroad, the economic conditions and mining technologies, we can draw the conclusion that different mined-out areas should have different governance programs. In the No.1 mined-out area, we suggest using the method of leaving barrier pillar of 15-20 meters, and No. 2, No. 3 and No. 4 mined-out areas should use the reinforced concrete wall of 1 meter and sand bag of 4 meters; and the No. 5 and other small mined-out areas should use the mud bricks to close the mined-out areas;(6) The results of this paper can guide the production practice of mine. It’s necessary to recommend strengthen the monitoring of mined-out area in the process of mining. It’s important to establish the microseismic monitoring systems and early warning mechanisms, and organize professional personnel to carry out monitoring work, which can provide a guarantee for the safe production of mines.