Abstract
This paper briefly reviews the application of various techniques including empirical, analytical and numerical methods in analyzing the surface subsidence associated with sub-level caving. Recent developments in empirical and analytical methods are first introduced. The application of numerical modelling in the characterization of surface subsidence and caving mechanisms is demonstrated using a relatively simple conceptual sub-level cave model and three numerical approaches i) a continuum finite element (FEM) ii) a discontinuum distinct element (DEM) and iii) hybrid finite/discrete element (FDEM) with fracture; the advantages and limitations of each method are discussed. A new deformation monitoring data interpretation technique using the inverse velocity method to predict the time of failure is briefly introduced and its application to sub-level caving is presented using the FDEM numerical method. Recent developments in the field of the discrete fracture network (DFN) and synthetic rock mass, (SRM), approaches and their use in improving our understanding of caving mechanisms are presented. Finally, a new approach to modelling sub-level caving considering intact rock fracture using a DEM UDEC-Trigon method is introduced and preliminary results presented.
1. INTRODUCTION
Cave mining methods generally include mining operations where after undercutting the orebody caves naturally based on gravity flow; these methods include block caving, panel caving and sub-level caving [1]. Sub-level caving is a cost-effective mining method that enables a high degree of mechanization and automation. Mining using sub-level caving induces a large area of deformation on the hanging wall with a more limited area of damage on the footwall. Various parameters influence the observed hanging wall surface subsidence including depth of active mining, geometry and dip of the orebody, the mechanical properties of the intact rock and the characteristics of pre-existing discontinuities and geological structures. In general, mining using sub-level caving results in two types ground surface deformation zones: (i) the discontinuous zone and (ii) the continuous zone. These two surface deformation zones can be recognized as [2]:
• Discontinuous deformation zone characterized by formation of visible cracks on the ground surface and large horizontal and vertical deformations. Surface disturbance such as tension cracks, topographic steps and chimney caves are normally observed in this zone. The disturbance is more extensive in the hanging wall, although the footwall is also affected by the mining activity.
• Continuous deformation zone characterized by uniform settlement and lowering of the ground surface which can only be detected by periodic monitoring with in general no visible surface cracking.
