Calculation Methods and Parameters Analysis of Mining Failure Depth of Coal Mining Face
The research on the mining failure depth of coal seam floor is of great significance for the prevention and control of floor water and gas extraction. It is an extremely important part of coal mining process and has always been a key issue for scholars engaged in mining industry research. On the basis of referring to a large number of previous research results, this paper summarizes the calculation methods of floor failure depth caused by coal seam mining, introduces the theoretical methods commonly used for floor mining failure depth at home and abroad, and analyses the sensitivity of its parameters, aims to provide some references for relevant research. Introduction When mining above confined water, floor water-inrush accident caused by floor fracture and aquifer communication caused by mining influence has always been one of the major problems affecting coal mine producing safely. Since 1971, due to frequent floor water-inrush accidents [1-5] , the relevant departments have attached great importance to this problem and established many key issues on floor water-inrush problem. Many scholars and field workers have done a lot of work on floor water inrush, and have gotten remarkable results. Many important theories of floor water inrush have been put forward, the "lower three zones theory [6] ", the "key stratum theory [7] ", the "in-situ fracture and original destruction [8] ", and the "lower four zones theory [9] " etc. These theories provide the necessary theoretical basis for accurately predicting floor water inrush, and they all contain a common research content-determination of floor failure depth. How to accurately calculate the floor failure depth and control its maximum value within the permissible range is still one of the key problems to be solved urgently. Accurate determination of the floor failure depth is helpful to reasonably set up water-proof coal pillars, determine the direction of roadway excavation, evaluate the safety of mining and put forward effective measures to prevent water-inrush accidents, and provide scientific suggestions for safe production of coal mine. It is precisely because of the importance of calculating the floor mining failure depth, the calculation methods have been paidly attention by scholars, and it is also a hot spot in mining engineering research. A number of new research results have begun to emerge, and many scholars use different methods to study it from different perspectives. Based on the previous research results, this paper introduces the main methods of calculation of floor mining failure depth in detail, aims to provide reference for relevant researchers to engage in the research of this field. Calculation Methods and Parameters Analysis The Formula under the Theory of Elasticity [10] According to Mohr-Coulomb failure criterion and elastic mechanics, the maximum failure depth of floor is as follows: ) 1 ( ) 1 1 cos 1 2 ( 2 1 1 1         K R K K K K H n h c   (1)