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SEM1T @Y ~ 91~L1-95 ;11 =14PM 0 $~( 303 832 81O6:>Y 8/ 8 <br />13 <br />Roof and Ground Control <br />13.1-SUBSIDENCE AND GROUND MOVEMENT <br />1{ORY'.kT STEFAN%O <br />lil.l-dUDSIDENI>E AND FAILURE <br />This treatment of mLs;dentt and ground movement kill be confined to wL- <br />eidence rnnlrol for Gmthng audax damage by aareestng Jw atRmficant panmelers <br />alieclmC Ground movemenle during mmmg Lo opumlce mmmg It,:hmyurx. The <br />ntalenal will lte equally appliubl< [o eraporile mining u well as coal but aril <br />not deal wiW Llo<k uviug or similar eyslema alone (nilurr is deliberately induced <br />nod wrCnoc urolcdion ie not nursery or provided. <br />When m uudtrgruuod oprning is ex461iehed, lha origiud rquilihtium is dis- <br />turbed wiW resulteat elllese tronexntralioni Wbile malty laclnrs errs Iavulrcrl is <br />opening alabilily, the span (W) undoubtedly ie one of W< mast impor4nL factors iu <br />failure- Aaeum;ng it u rclative)y small, the overlying rock etn4 can bridge crass Lhc <br />opening sad little iC eny ntovemenL or eanvergcuee of top sod bottom .ill occur. <br />Hoa~ever, ae We span inucosca, a point io reached wMre We alresa in Ulu overlying <br />rock clrn4 rsxcds some slrcaglh value oI Lhe ror,4, aaJ Ut< my brenLs. If Ute <br />opening span w limited b conic NLcriliral value (-W,) and/or is aL great r1epW <br />(Dl, a pseudo-arch will form, arltiering 54LililY before lvV[ure ocrure Lo lhr. <br />nufacc. "lire Lourtelary of this arch rs thought' la aplwosimslc an clli pst ;u loon <br />...W We major aria verticJ and equal b four limns W. alUiupglt Lhtre hsa been <br />I;Ltlu fit1A rtscarcL W wLs4nfia4 Uric Uteory. However, i( lht u'idW of Ueie <br />opening is Increased at this horizon W come critical value (W,) or the same <br />span Is created rn a ehallorver xam, We overlying atrala roll prugnsstvcly ntpturc <br />to thr lurlarr and Wr rdteraetertslic svLsidtace Trough IS loaned lFtg. IJ-1; <br />TLe area of Qtt aur(ac< aRte[<d is ntudt Rrealer lbut [he orrn of Lhe smm <br />rxlratted, Jependiog on Ilte "angle of draw" (a), wltith is Utc tLaglt between <br />o rerurrl hoc !rom Wt tdge of We oytoing end euother hoe extended to s <br />pmnL aL which subsidence tails out W sero. Thin angle has Lcrn found to be <br />ebuut 15' in lirrropc Lut a rather •redemic, being a fmcLioa uI mxLrum<nt yrecmon <br />in Aaetting aubs;dntce. Siuct We wlniJcntt dI¢L ie ao small al any pmnt bcyood <br />a 25- angle, Win latlcr may he rnneidered the prwclical Lm;L ul tatlxddence. Furtherv <br />nave, mdlcaUOLLS urc that We anglr. al Araw vanes trial dcVUt mid Harms u1 <br />the straw.' lu afield study over a 1.000-ftdegt potash mine m Ncw Alrueu, <br />the maximum angle of Araw was found to be 515`.' <br />6a Inv, otJy n single upemng has been mtutderad. HOw/<rfr, Ure ~r,dU+ of We <br />esurahon applies Lo env complex mmiog system of enlnes, rooms and longwalls <br />as long as We term Itac I..en fully exlratltd and Wt wiJU, n:pn:scnla lltt dtslnttce <br />from ouc solid riL (u anaWcr. It will be naiad tlmL dm nmowa of vcrttxnl displnct- <br />meul vancY !mm point to paint Ort Ulc eudate (SI, but the manmunl npbstdrnct <br />for n given trough occur. s[ Lhc ttnler (S). This latter vxl uc ninv not he rgtw] <br />In lha maxtmwll possible wbsidcam (6_) which uecnn uoly if n cnhcal ur iuycl- <br />cnncal (Pal) widW La.<Lccn crceM<A (1~iA. l;f-U. <br />tiulvcUnliRl wrfxte Jnunac am rend( when eubsidentn rterum. Pnrtars a!fecline <br />the plnounL and lyftn of ground nlal'Calnel. nT.: IIuC1:oCSt and prppC'lir of thr <br />uxm. angle nl draw, width of er<n rn Lion, depett aaJ type u! orcrirurJcn, mrlir.utmor <br />of slieLa mtJ nvfarm, :rod LLt amauol of support Idl In Lhc roh In Europr, <br />11~ <br />