Factors influencing overbreak in narrow vein longitudinal retreat mining

Limiting the amount of ore dilution prior to entering the process stream is the goal of any mining operation. Narrow vein longitudinal retreating mining methods are especially susceptible to hanging wall and footwall dilution due to the wall overbreak. Understanding the factors which influence the stability of these walls can help a mining engineer design stopes that minimize dilution. This thesis presents the results of a study to examine these influential factors and reveals the process used to construct an empirical model capable of estimating dilution for a specific stope. This work is centered on a case study of Agnico Eagle Mines Ltd. Lapa mine located in Preissac, Quebec.;Before constructing this numerical model it is necessary to find an adequate means to organize and interpret the copious amounts of data retrieved from the mine site. Data such as geotechnical drill holes, stope reconciliation data, and stope construction details are integrated into a purpose-built geomechanical database. Named the "Data Integrator for Mine Analysis and Design (DIMAND)" the database software package provides easy access to important data and eases the construction of numerical models.;In order to fully understand the influence of stope strike length on unplanned ore dilution, a numerical model is constructed. Due to the geometry of the problem, it is necessary to perform the analysis in three dimensions. The finite difference code FLAC3D is employed to construct a model based on rock mass properties and stope constructions present at Lapa mine. With strain softening behaviour common in rock masses and the Lapa rock mass being one regularly subjected to large strains, a strain-softening constitutive model is employed in the FLAC3D model. This model reveals that larger stope strike lengths are prone to generate larger volumes of dilution into a newly opened stope whereas shorter strike lengths are less prone to dilution. The model also explores the effects of a retreat sequence on overbreak; revealing that primary stopes are slightly more prone to overbreak than secondary stopes.;These studies aided in the development of an empirical model that provides estimates for stope overbreak tonnages. The development of the empirical model is explored in detail from early models with small sample groups and simple mathematical constructions, to the final model which employed 86 stopes and statistical software to identify important relationships between seemingly independent factors. Through the use of this model engineers can now plan stopes with knowledge of how each parameter influences overbreak and production and scheduling personnel can plan production goals with increased confidence.;Possessing a means to properly measure and quantify dilution is an essential part of this study. An in depth review of the various techniques is presented with the concept of Dilution Density being chosen as a means to quantify dilution. In order to determine which factors influence dilution, a review of existing literature, including modelling studies is undertaken. With careful review of the mining practice and geological environment, the most important of these factors are identified. One of these factors, stope strike length in narrow vein retreat mining, is not thoroughly explored by existing publications; and, in order to better understand this factor a numerical model is constructed.