The use of cemented paste backfill (CPB) is becoming increasingly more common at underground mines worldwide. Part of any CPB design includes the specification of the (typically) shotcrete barricades that retain the CPB within the stope during filling. Newmonts Tanami Operations (NTO) has started an in situ barricade stress monitoring program. The data from this program will provide a basis for comparison of several models that can be used to model the capacity of these barricades. These models vary in complexity from analytical solutions to 3D numerical models. Part of the comparison will include a discussion detailing the required material inputs and how these inputs were obtained. Analysis of this comparison will provide additional understanding on what parameters affect the ultimate capacity of a shotcrete barricade.
Tailings dam failures have and continue to cause large-scale devastation and environmental impacts. Historically these impacts have largely been predicted using Newtonian hydrodynamic modelling principles resulting in a general overestimation of potential consequences. However, since about 2014 the collective mining industry began developing complex tools to better predict the likely impacts of these failures. The industry has focused on leveraging the latest in computational flow dynamics modelling software and computational hardware to preform non-Newtonian tailings dam break assessments. However, as our tools become more sophisticated so does the requirement on input data. This paper discusses the past modelling approaches and the development of non-Newtonian tailings dam break models. The sensitivity of the flow behaviour is presented through four case studies, showing how this selection influences the outcomes and how previous approaches assuming Newtonian characteristics may present an overly conservative result. It is noted that additional knowledge and expertise will become available as non-Newtonian tailings dam break studies become the norm. In the interim, the uncertainty of these analysis needs to be analysed.
?There has been an increasing move towards high-density thickened tailings systems over the last decade, mainly driven by the need to save water, meet environmental regulations and project specific demands. A typical tailings distribution system on a Tailings Storage Facility (TSF) consists of a main pipe with multiple discharges operating simultaneously, to distribute the slurry across an extended length over a specific area of the TSF at a time. A potential limitation of these systems is an uneven distribution of slurry flow rate and solids concentration between multiple spigot discharges, where an inadequate design can lead to laminar pipeline flow conditions resulting in particle segregation, and an increased risk of pipeline blockage. An operation with unbalanced flow rates could result in an uneven distribution of solids that could impact the formation of beach slopes and/or cause difficulties for the dam construction. Paterson & Cooke (P&C) has previously developed several thickened tailings distributed systems, where the discharge points are located on a distribution pipeline which branch off a main pipeline. This previous experience has allowed P&C to develop a methodology for the hydraulic modelling and implementation of these types of systems. This paper presents the methodology for distribution system deposition design review and its implementation of a TSF located in Southern Europe.
In the practice of geotechnical engineering applied to mining, dry stacked tailings heap projects are analysed by limit equilibrium methods and stress-strain analyses. These methods and model assumptions do not consider the influence of the partially drained conditions, strain softening, and transition from overconsolidated to normally consolidated behaviour of the foundation. This situation can lead to calculations of deterministic safety factors that are often overestimated, according to the nature of the foundation. This article proposes a methodology for numerical modelling of the foundation during staged construction of a heap, and considers loading time as a critical variable in calculating the Factor of Safety of the heap dry stacked of elaborating a numerical model considering the foundation and construction. The physical and geotechnical properties of the materials were derived through the model, and are the interpretation of data obtained from a geotechnical investigation and laboratory testing campaign. Stressstrain analyses are performed for different stacking speed scenarios to assess its influence on the safety factor at each loading stage. The analyses are coupled, where the distribution of stresses and deformations within the foundation and the dissipation of porewater pressures over time are simulated. The results show the evolution of the Factor of Safety, the spatial distribution of the regions with excess porewater pressure, allowing the optimisation of both the rate of rise of the dry stack and external batter slope for the project to minimise ground improvement. It is observed that there is a strong dependence of the coefficient of permeability of the foundation soils on the porewater pressure dissipation time. Numerical modelling considering partially drained conditions allows greater understanding of foundation behaviour and performance during the development of the dry stacked heap. The analysis is considered applicable to both soft soil foundation conditions and conversion of existing wet disposal tailings facilities to dry stacking atop, referred to as piggybacking within the mining industry.
This paper presents an optimisation loop that looked to improve how Newmonts Tanami Operations (NTO) determines its required stable stope strengths. In order to do this, a comparison exercise was completed, in which NTOs current stability assessment method was compared to other popular assessment methods ranging from analytical to numerical methods. From this comparison, it was decided to proceed with a different stability assessment method that uses shear stress reduction. The paper then presents how the use of this method was implemented and presents three case studies on how the new stability assessment method has benefited NTO.