Arching in granular materials with particular reference to inclined mine stopes

Determination of stress distribution, giving due consideration to arching mechanism within minefill stopes, is of great importance because of its influence on the ground stability, ore recovery and cost effectiveness. Most previous studies on stress determination and arching effects have been applied to vertical stopes, whereas research is lacking on inclined stopes. The objective of this study is to investigate the effect of inclination on arching action on stress distributions, with particular interest on the stress distribution at the base and on the side walls of the stope. Three separate modeling techniques are carried out to achieve the goal of the study, which are numerical, analytical and experimental methods. The studies develop analytical solutions from Marston's theory for inclined stopes with parallel and non-parallel walls, incorporating arching effects within the backfill, and propose a new analytical method developed from Pascal's triangle and binomial series for vertical stress determination in vertical and inclined minefill stope. Good agreement is seen between the two analytical methods for vertical and inclined stopes. The results show that with the same overburden pressure yz and base width B, the stress magnitude experienced by fill material can vary significantly with wall inclination. It is shown that lateral earth pressure coefficient, K and interfacial friction angle, δ has significant influence on vertical stress profile. K and δ should be taken as either K = K₀ and δ = 2/3 (0) or K = Kₐ and δ = (0) to better describe the state of stress within the minefills in underground stopes. A laboratory model is designed to simulate mine backfilling in an inclined stope and determine the average vertical stress at any depth within the fill. Stope inclination, wall roughness, relative density and aspect ratio are varied independently to study their influence on the stress distribution and arching effects. The highest vertical stress is observed at inclination about 80⁰ to the horizontal and shear stress experienced by the footwall increases with increasing stope inclination and wall roughness. The average interfacial friction angle can be used in analytical expression to predict the vertical stress within a stope with dissimilar wall characteristics. The study undertaken has also developed approximate solutions for the stress distribution within inclined stopes based on FLAC simulation. Three separate models are conducted in the simulation. They are laboratory model stope, a prototype minefill stope, and laboratory stope incorporated into rock mass to simulate minefill environments. There is good agreement among the analytical, numerical and the laboratory model results. Lateral earth pressure coefficient, K is better described by Kₐ for inclined minefill stopes.