| The fault, joint and fissure are very developed in the Jinchuan large scale Ni orefield owing to the effect of many times of structural movement in the geological historic period. Moreover, this area is still in the structure active period at present time, which also has very disadvantageous influence on the stability of surface and underground engineering. After the beginning of deep mining of ore body II in the orefield, the mining influence becomes more and more violent because of the simultaneous mining on several level and the progressive carrying out the expansion and reformation of production ability. The fracture, expansion and creep deformation of wall rock in tunnel are very evident. The completeness and stability of rock body are very bad. The surface fissure expands, surface sinking intensifies, stress value increases. The stability control problem of deep tunnel and mining area becomes more and more prominent. The emergency problems are to put forward the timely rationalization proposal to ensure safety in mining production and to provide the scientific foundation for selection of mine engineering design and support method of tunnel.In this paper, we aim at the lithomechanics and engineering problems in deep mining process of ore body II in Jinchuan Ni orefield basing upon the important scientific project 《The Study on the Stress Field and Lithomechanics of Jinchuan Orefield》 of Jinchuan Company(Group) and scientific project of tackling key problems《The Study on the Lithomechanics under Deep High Intensity Mining Conditions of Jinchuan Mine》. First, the geological condition of Jinchuan Ni orefield and deep deformation characteristics of rock body are systematically surveyed, analyzed and studied; second, the crustal stress measurements in Jinchuan Ni orefield in recent scores of years are gathered, put in order and analyzed, then select the representative area for the survey on the spot based upon the working mentioned above in order to achieve the important data of deep crustal stress of orefield and carry out the comparison, analysis, study of surface and deep crustal stress characteristics of orefield. Afterwards, we select the level1000m,1150m west of F17of ore body II and the level1200m east of F17for the survey on the spot according to the deep mining situation of ore body II in Jinchuan Ni orefield. Finally, the stability of deep large area continuous mining mine pillar and deep tunnel is analyzed with the software FLAC3D in combination with the deep stress distribution and deformation characteristics of ore body II. Thus, we have achieved the following important results:1. We propose that the variation of maximum principal stress value in company with the depth change is nonlinear, which is varied approximately in the cube form. The slope of shallow variation curve is gentle. The maximum principal stress increases rapidly in company with the depth. Nevertheless, the slope of deep variation curve is steep. The maximum principal stress increases slowly in company with the depth. The inflection point of stress variation from the deep to the shallow is approximately at the depth underground400m.2. According to the study, the deep crustal stress distribution of orefield is in close relation not only to geological structure but also evidently influenced by the mining disturbance, which causes the difference of maximum principal stress direction of the deep from that of the shallow. The shallow maximum principal stress direction is mainly in NNE-NE, whereas the deep one is mainly in SSW-SW, ie, it is more complicated.3. The deep maximum principal stress dip angle of ore body II is evidently different from middle-shallow ones. The maximum principal stress dip angle of middle-shallow measuring point is gentle, the maximum principal stress is basically in nearly horizontal state. The deep maximum principal stress dip angle of ore body increases clearly. In this measurement, most deep maximum principal stress data are inclined and the dip angles approach or exceed40°, which shows that the dominance of horizontal stress has been weakened progressively in the deep mining area. The difference between maximum and minimum principal stress value increases, ie, the shear stress increases. The increase of shear damage intensity has a very disadvantageous influence on the stability of deep mining workings.4. Basing upon the deep crustal stress measurement of ore body, the stability of horizontal and vertical mine pillar of dual-level mining in deep large area continuous mining of ore body II is compared, analyzed and studied with the software FLAC3D.5. The analysis of and probe into damage and support mechanism of deep tunnel under high crustal stress show that the wall rock P progressively increases in company with the increase of tunnel depth, the horizontal P higher than vertical P of tunnel, the tunnel unsymmetrical deformation damage serious, the side extruding deformation of one wall often more intense than the other in the tunnel, the shear slide body formed on both sides of tunnel in the area mainly under the vertical P, the irregular fracture on side wall and arch roof pressure damage take place easily, tunnel bottom distension evident. Because of the high crustal stress in Jinchuan Ni orefield, ore and rock fracture, the tunnel crustal P control is limited by the tunnel support form alone. Therefore, we propose the tunnel crustal P control measures combining manual P discharge and tunnel support, which have the important guide and reference significance for the tunnel deformation control and the protection of tunnel stability. |
PDF Full Text Request