Study on Method to Set Safety Coal and Rock Pillar for Fully Mechanized Top Coal Caving Mining Under Water Body

In order to rationally leave the safety coal and rock pllars under the water body for the fully mechanized top coal caving mining in the ultra thick seam, b ased on the calculation formula of the " two zone" heights suitable for the fully mechanized top coal caving mining face under the middle hard and soft weak overburden strata regressively obtained with the site measure information, the left method of the " effective water insulated thickness method" and the " min safety thickness metho d" were provided to the safety coal and rock pillar protective layer for the fully mechanized top coal caving mining under water body.The left value of the sand preventio n safety coal and rock pillar and water prevention safety coal and rock pillar protective layer under the middle watery water body and rich watery water body was individ ually provided.Based on the basis, the left method of the coal and rock pillars under the middle hard and soft weak overburden strata water body was completed for the fully mechanized top coal caving mining.