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zl <br />• 5. ME'ARi1RFS ~ID TO PREVENT SUFSIDtS1CE DAMAGE: <br />Pillar are to be left in the underground to srip~rt ttrc• st~.,ta <br />up to the surface. The ornrpressive strength of average ~-c,a na: <br />been determined to be 3,500 psi. In comparison, the ooa] tram rli~ <br />Hiawatha warn of the Southern Utah Coal Company's Mine No. 1 <br />(SUtYXI) is 3,200 psi. At SUFCD, a ]ayer of about 1 toot cf Wal i.. <br />usually left in mine roofs to increase their stabillity, lr. s,~~i• <br />areas of the tiiawatha seam, these "coal" roofs are stable erough <br />even without bolting. <br />It is expected, that the same conditions prevail rn ttrc It <br />seam. Pillars should be sufficiently stable for an extenrr~ ~, ~~ ~~~;] <br />• of time necessary to protect the surface. Hc..rever, a s,rt~sid n:r <br />monitoring program is recrnmended to rrnxi i tar the s ,bsidNnce. 1 i , ~ or <br />any reason, subsidence should occur, Uten the size of pill.,r~ :rt;y i~~ <br />increased, if necessary, in order to rtigain their stability. <br /> <br />