Investigation of change coal seam floor permeability based on pressurized water testing

The permeability performance of the coal seam floor is an important basis for the assessment and prevention of water inundation disasters in the floor, and the water pressure test is an important means to obtain this parameter. The traditional water pressure test has limitations such as large construction volume, low testing accuracy and small data volume, and cannot meet the testing requirements of rock strata permeability performance under the condition of deep thick base plate impermeable layer. This paper presents an efficient and precise improved water pressure test method and applies it to the study of in-situ permeability performance changes of floor rock strata affected by mining activities. The improved water pressure test method of single borehole, movable double embolization and graded circulation was adopted to conduct tests on the unmined and mined affected areas of the No. 9 coal seam floor of Xipang Mine, Dongpang Well. The P-Q curves, permeability and other parameters of each rock layer of the floor were obtained. Combined with the Mann-Whitney U test, The variation laws of permeability performance of different rock strata affected by mining activities were systematically analyzed. Research shows that the improved water pressure test method is significantly superior to the traditional method in terms of test efficiency, borehole utilization rate, etc. The permeability performance of coal seam floor is significantly affected by mining activities. Mining activities reduce the permeability recovery capacity of rock strata, and the permeability performance of different strata shows differentiated responses to mining activities. The improved water pressure test method proposed in this paper provides a technical means for the refined testing of the permeability performance of the floor rock strata. The research results are helpful for accurately identifying the weak areas of the floor and assessing the risk of water hazards, which has important engineering guidance value for promoting the safe and efficient mining of deep coal.