ionoftheexcavatedfaceThecoalseamminedbythesublevelcavingmethodwasverticalanditsaveragethicknesswas.m.Withtheaimofcarryingoutthetestintheworstconditions,thetestzoneusedwasinanareawithaseamthicknessoflessthan.m.Athree-segmentsteelsetsupportwasused,thegallerybeingof.minwidthatthelowpartand.mhigh.InFig.sketchesoftheexcavatedfaceswiththe-pick(.m)and-pickcuttingheads(.m)areshown.Thecoalseamwas.and.mthick,respectively.Itwasformedbytwoveins:ontherightthecoalwassoft(σc<MPa),whileontheleftthecoalwascstrong(σc=–MPa)withoutrockbetweenthem.CTheleftwallwasofsiltstone(sometimessandstone)withacompressivestrengthofssMPa,fracturecspacingofσc=–cmandanRMR(RockMassRatio,Bieniawski,)valueofapproximately–.TheSiOcontentintherockwasandthemeangrainsizemm.TheSchimazekindexwasatanaveragevalueofFs.N/mm.Therightwallwasalsosandysiltstone,butmorefracturedanditbrokebecauseofthediscontinuities似,大约是kW,但是工作用时间少了,同时可以观察到过量负荷持续了一个更长时间。
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