Study On Evolution Law Of Allometric Growth Of Mining Overburden Separated Strata

In the mining of sedimentary coal measure stratum, the separated strata in theoverburden is an inevitable phenomenon with increasing width of mining. And theseparated strata in the mining overburden affect the occurrence of mining subsidencein some way. However, the evolution of the separated strata in the overburden isextremely complex. It varies in size and growth rate in the development process.It hasthe characteristics of allometric growth. Therefore, the research on the evolution law ofallometric growth of the separated strata in the mining overburden can improve themining subsidence theory. And it has important theoretical value and engineeringsignificance.In this dissertation, the separated strata in the mining overburden is for the study.The similar material simulation experiments and RFPA numerical simulation softwareare applied for the analysis of the separated strata in the mining overburden from crackto close. The allometric growth characteristics of the separated strata in the overburdenare extracted from the analysis result, combined with the allometric growth theory, andestablished the allometric growth relational model of the different separated strata andthe single separated strata of the different development stage, and analyses theallometric growth relationship of the different separated strata and a single separatedstrata of the different development stage. The main findings are as follows:(1) In mining overburden, when the subsidence velocity of the lower strata islarger than the subsidence velocity of the upper strata, the separated strata generatesalong the crack. The developmen of the separated strata go through the crack stage,development stage and the closing stage. In the crack and development stage, thesubsidence velocity of the upper strata is less than the subsidence velocity of the lowerstrata. In the closing stage, the subsidence velocity of the upper strata is larger than thesubsidence velocity of the lower strata.(2) When the maximum principal stress and minimum principal stress of miningoverburden are over the critical value, the separated strata generates. The crack tip ofthe separated strata is in tension shear state. And there have mode I crack stress andmode II crack stress. When KIis greater than or equal to KIc, the crack at crack tipextend. (3) The length of the separated strata increase with the increasing of time.Itsvelocity increase firstly but then decrease, and finally tend to zero. It is largest by thistime. The width of the separated strata increase with the increasing of time, until thewidth of the development to the maximum. Then quickly closed, the closing time isshort. The closing velocity of the separated strata is larger compared with developmentstage.(4) The allometric growth theory is applied for research of the different separatedstrata and the single separated strata. It is obtained a logarithm linear relationshipbetween the length of the different separated strata. It has a constant ratio relationbetween the relative growth rate of the upper strata and the relative growth of the lowerstrata in the single separated strata. And it is accord with the allometric growthrelationship that the relative growth rate ratio is constant between part to part in thesystem.