Study On The Roof Safety Thickness And Treatment Methods Of Underground Goaf In Pingshuo East Open Pit Mine

Pingshuo east open pit mine was composed of multiple private enterprises before the resource integration. This phenomenon happened seriously as there are lots of small coal mines, which were mined disorderly. A certain number and unknown goafs are left in the stope. With the processing of the surface mining and the increasing time of the exposure rocks, the geological hazards like ground subsidence, rock collapses, cracks caused by roof caving threat the safety of workers and equipment seriously. So determining the roof safety thickness quantitatively will guarantee the safety of the mining production.Through detailed field geological survey on the east open pit mine and drilling exploration method to find out the mining goaf size and shape characteristics. To calculate the roof safety thickness with theoretical analysis of goaf roof failure mechanism. The mining goaf blasting model is established by the dynamic finite element software of ANSYS / LS-DYNA. To analysis the top and bottom plates' and side walls' stress in different span and buried deep with this model. The mining goaf roof stress distribution characteristic is proposed through the simulation experiments by Midas software under the condition of the different span with static load. At last, the treatment method of east open pit coal mine goaf is proposed. The main research results are as follows:(1) The engineering rock mechanics parameters can be calculated by using the engineering reduction of the rock in the east open pit. The compressive strength is 8.01 MPa, and the tensile strength is 0.45 MPa.(2) The recommended values of roof safety thickness of goafs are proposed through five kinds of classical theory calculation formulas. The roof safety thickness is 7.4m, 11.4m, 15 m, 18.5m, 23.7m, 31.5m respectively when the span is 10 m, 15 m, 20 m, 25 m, 30 m, 40 m.(3) Through the comparison of goaf roof safety thickness under different spans, blasting impact loads and equipment pressure loads, it shows the safety thickness of roof is 12 m, 16 m, 21 m, 25 m, 30 m, 42 m when the span is 10 m, 15 m, 20 m, 25 m, 30 m, 40 m,(4) Put forward the goaf treatment steps, and choose appropriate detection method combined with the practical situation of the east open-pit mine. Dividing the goaf into 3 kinds according to the relationship between the H0,hm,h and subdividing the goaf into three cases according to the stability conditions of the mine rock and the difficulty degree of goafs treatment. Put forward efficient and safe treatment method: caving method for different categories, and it was used to manage a gob caving process, treatment effect was obvious achieved.Determine the roof safety thickness under the different spans in the underground goafs through the research, handle the goafs which the safety thickness is not meet the requirement with the caving method to eliminate the hidden dangers.