UDEC-based Stability Analysis of the Goafs in Fragment Ore Section

Taking the fragment ore section of orebody No. 105 with the high value in Gaofeng mine in Guangxi province for example, three representative kinds of goafs in all scales were selected on the basis of the differences of goaf scale, surrounding rock conditions and situ stress field, and their stability were calculated by the universal distinct element code (UDEC). The calculation results showed as follows: 1) with the increase of goaf scale, the tensile stress scope in the goaf roof expanded from 12 m to 60 m; 2) the tensile failure mode of joints surfaces was primary, and that of ore block was auxiliary; 3) the maximum principal stress peak could reach 40.3 MPa which exceeded rock body tensile strength 38.07 MPa, but the influence on goaf stability was small because the peak was far away from goaf; 4) the plastic zone in roof changed from 7 m to 12 m because of the increased scale, so the goaf stability became worse gradually; 5) the objective principles that the whole plastic zone distributed on the left part of goaf roof and no plastic zone in pillar provided reference for choosing proper position of filling wellhead.