Study on the heights of the “two zones” in overlying strata over Chahasu coal mine gob

Abstract：Determination of the heights of the caved zone and fractured zone (called the two zones) in strata over the mining coal seam is very important for guiding the gas drainage, water prevention and roof control in coal mine.In this paper, the methods of the in-situ rinsing fluid volume, the color TV borehole observation, and theoretical analysis were used to study the heights of two zones of overlying strata in Chahasu coal mine gob.Results demonstrated that: (1) the height of caved zone was about 22.42～29.20 m and the ratio of caved zone to the mining height was about 4.40～6.15.The height of water flowing fractured zone was 63.82～106.5 m and the ratio of water flowing fractured zone to the mining height was about 12.51～23.67.For safety reason, the maximum height of water flowing fractured zone and the maximum caved zone height was determined as 106.50 m and 29.20 m, respectively.So, the fractured zone of the Chahasu coal mine was ultra-high water flowing fractured zone. (2) The heights of two zones obtained from the boreholes in the same coal face were consistently close.The heights of caved zone measured from boreholes in different coal faces were relatively identical, while the heights of water flowing fractured zone varied greatly. (3) There was a significant difference between the results by testing in borehole measurement and through empirical calculation.Important influencing factors while the heights of the two zones calculated should be considered, which could form a positive impact with the actual situation in a good agreement.

Keyword：coal mine gob;overlying strata;the heights of the “two zones”;Chahasu coal mine;