Quality evaluation of layerlike backfilling and flow pattern of backfill slurry in stope

J. Cent. South Univ. Technol. (2007)04- -0580-04DOl: 10.1007/s11771-007-0111-3空SpringerQuality evaluation of layerlike backfilling and flow pattern ofbackfill slurry in stopePENG Xin(彭欣), uI Xi-bing(李夕ZHANG Qin-li(张钦礼), WANG Xim min(王 新民)(School of Resourcs and Safety Engineering, Central South University, Changsha 410083, China)Abstract: Sabilily condition and quality cvaluaion frmula of ayerike bakiling ro, Q≥C, where e danotcs is qualiy indexdepending on allowable compressive or tensilc strength and integrity of backilling, and Ctechnical indcx depending onmining method and backiling tchmology, were iferred acording to simply spported beam thcorcm. Technicl tratmentmeasures for istable backiling roof, incuding optimum of apropiale filing materials and dosage for exellnt flow propentyard redusction of backfil cost. [t is proved that stope equation of backfll stury in a stope to be lled is r hexp[-+(2n3}, where his hcight of cone and r2 is mean square, and that optimum ddtrainage point of backill slurry can be determined by the equation andsizes of stope. Case study indicates that the resuts can givc a theorctial support for quality evaluation and control of layerlikebackilling.Key words: layerike backilling; quality evaluation; flow pattern; simply supported beamicft by exploiting activities atfter orebody or rock below1 Introductionbackfllig was excavated. Distribution of secondarystress within layerlike backillig can be analyzed byMineral resources are important material foundationsimply supported beam theorem. Gravity load (P)of both national economy and humankind life. It is .exerted on beam is simply represented by unit weight ofrequired to recover mineral resources as soon as possiblebackflling (/tm )) times the height of frst layeron the condition of exploitation safty by its scarcity andbackilling (tm), ie. P=y, as shown in Fig.2, in view ofnon-renewable feature. Backilling has becomne one ofthe fact that dfferent layers are formed independently.mining methods with great prospects owing to highThe maximum tensile stength of retangle layerlikerecovery rate and reliable saety!-4. Cut and fil stopingbackilling roof (8) is computed as follows according tois especially helpful for usage of large trackless vehiclessimply supported beam thcorem:and then has been widely employed in undergroundmines. Reliability of layerlike backiling varies with8,=k|S) P(1)flling technology and quality, and hidden dangers wouldexist while orebody of next sublevel is mined if layerlikewhere k is a computation constant related to length(L)backilling is poor in quality. It is necessary, therefore, toersus width(B) of the beam and can be selected fromdevelop quality evaluation approaches of layerlikeTable 1.backflling, in order to keep backfill effects and increasesafety and cconomic benefit of exploitation of mineralTable 1 Computation constant k of rectangle simply supporedresources by adoption of appropriate managementbeammeasures for backfilling with different qualties.L/B1.01.52.0.04.02 Stability condition of layerlike backillingk 0.2874 0.4872 0.6102 0.7134 0.7410 0.7500roofSubstituting P=yi into Eqn.(1) and convcrting unitStructurc of layerlike backfilling is shown in Fig.1,of lensile strength into MPa, Eqn(1) becomcs:where B and 1 denote the exposition span of backillig_kBZyand the height of first layer baklling, tespectively.(2Backlling roof subsides downwards to rectangle space中国煤化工M.HCNMHGCorresponding author: PENG xin, Doctoral candidatr; Tel: +86-751-6618780; E- mail pxhn@tom.comPENG xin, et al: Quality evaluation of layerlike backilling and flow pattern of backfll slurry in slope581expressed by height () of the first layer backillig(direct roof of next level stope). Relationships betweenallowable compressive strengths and tensile strengths ofsome samples are illustrated in Fig.3.2r0卜8Fig.1 Layered structure of layerlike backilling6tP.yl↓↓↓↓↓↓↓↓↓↓↓↓0.20.40.60.81.01.21.4 16Tensile strength/MPaFig.3 Rclationship bctwccn compressive strcngth and tensilcstrengthFig.2 Load analysis of simply supported beamEqn.(2) implics that the maximum tensile strcngthPlots on |8, -8{ diagram are arranged almost as ain the center of layerlikc backilling roof dccrcascs withstraight line. |8.,H8。relation can be written as follows ifincreasing the height of the first layer backilling.the slope of the straight line is approximated as K.Stability condition of backilling roof is given as|8.~=K18|(4) .follows if allowable tensile strength of backilling is oreprescntcd by |8|:l8.|=-l3,|kB2γ3)Substituting Eqn.(5) into Eqn.(3), the followingequation can be obtained:The following is a case study of some mine[5-6),where cut and-fill mining was adopted, average length (L)|8μi≥kB*yK(6)and width (B) of a stope are 60 m and 12 m, and unitLet C=kB"yK and Q-18l1, thcnweight () and allowable tensile strength (8&|) ofQ≥C .(7)cemented backilling are 1.98 t/m’ and 0.28 MPa,respectively. Height of the first layer backillingwhere 2 denotes the quality index depending onallowable compressive or tensile strength and integrity ofcorresponding to stable roof should be satisfiedbakckiling, and C the technical index depending ont2kB'y= 7.6(m)mining method and backfilling tcchnology.10086|Eqn.(7) is quality cvaluation criterion, indicatingthat backfilling roof is stablc if Q云C, and thawhere k is 0.75 when L/B=5.It is practically difficult that individual backillingbackilling roof may collapsc if Q