Causes and prevention of powered support jammed in fully-mechanized top coal caving mining face in ultra thick seam with watery roof

According to the problem of a large area roof cuting powered support anmed accident requently occured in aill-mechanized top coal caving miningface in ulra thick seam with a watery roof of Ccuinmu Mine,with the analysis on the mine pressure data of the coal mining face,the causes ofthepowered suppor ammed were obtined and the prevention and control countermeasures were provided. The study resuts showed that the causes ofthelarge area powered supors jame:occurred in No.302fully-mechanized top coal caving mining face in Cuimu Mime mainly were that 1 the suppor stengthofNo.12 rulymechanizedtop cadl caving mning face was low,2 the support eficiency of No.302 ful -mechanized top coal caving minin face was low.mainly the actual seting load was 3%.of the rated value onlythe released pressureof the saiety vave was 75% 87% of thedesigned value only and the unbalanced coeficient was 17%43%,3 the roof water would not only redtce the compressive strength of the rock but would reduce te ficton coeficient between the roctk lumps and the posstblity of the strueture stailitylost ccured in theroof would ad 24%. Afier the danger area division conducted.,the support strength improved of thepowered supports pre-wamning,ratonal coal aving and mining techoique and the technical measures to ensure the working status of the powered suppor. the powered support jammed problems were solved in Cuimu Mine.