Emmanuel Chanda

Pre-Peak and Post-Peak Rock Strain Characteristics During Uniaxial Compression by 3D Digital Image Correlation

A non-contact optical method for strain measurement applying three-dimensional digital image correlation (3D DIC) in uniaxial compression is presented. A series of monotonic uniaxial compression tests under quasi-static loading conditions on Hawkesbury sandstone specimens were conducted. A prescribed constant lateral-strain rate to control the applied axial load in a closed-loop system allowed capturing the complete stress–strain behaviour of the rock, i.e. the pre-peak and post-peak stress–strain regimes. 3D DIC uses two digital cameras to acquire images of the undeformed and deformed shape of an object to perform image analysis and provides deformation and motion measurements. Observations showed that 3D DIC provides strains free from bedding error in contrast to strains from LVDT. Erroneous measurements due to the compliance of the compressive machine are also eliminated. Furthermore, by 3D DIC technique relatively large strains developed in the post-peak regime, in particular within localised zones, difficult to capture by bonded strain gauges, can be measured in a straight forward manner. Field of strains and eventual strain localisation in the rock surface were analysed by 3D DIC method, coupled with the respective stress levels in the rock. Field strain development in the rock samples, both in axial and shear strain domains suggested that strain localisation takes place progressively and develops at a lower rate in pre-peak regime. It is accelerated, otherwise, in post-peak regime associated with the increasing rate of strength degradation. The results show that a major failure plane, due to strain localisation, becomes noticeable only long after the peak stress took place. In addition, post-peak stress–strain behaviour was observed to be either in a form of localised strain in a shearing zone or inelastic unloading outside of the shearing zone.

An application of integer programming and simulation to production planning for a stratiform ore body

Abstract Planning of underground mines poses considerable difficulties in the areas of safety, environment, ground control and production scheduling. As the industry is faced with more and more marginal reserves, it is becoming imperative to generate mine plans which will provide optimal operating strategies and make the industry more competitive. The problem of production planning in underground mines can be formulated using available operations research techniques and computing power. In this paper a computerized model for short-term production scheduling in a typical block caving mine with a stratiform ore body is presented. By combining simulation with mixed integer programming, it has been possible to model realistically the problem of scheduling draw points for production at the Chingola Mine of Zambia Consolidated Copper Mines Limited. The model is based on a given layout of the mining block which is considered fixed during the planning period. The model is intended for use by planning engineers or mine captains working with personal computers. In comparison with manual scheduling, the computerized model has been found to be faster and generates near-optimal schedules.

A comparative study of truck cycle time prediction methods in open‐pit mining

Purpose – The purpose of this paper is to compare the predictive capability of three methods of truck cycle time estimation in open‐pit mining: computer simulation, artificial neural networks (NNs), and multiple regressions (MRs). The aim is to determine the best method. The most common method currently used is computer simulation.Design/methodology/approach – Truck cycle times at a large open pit mine are estimated using computer simulation, artificial NNs, and MRs. The estimated cycle times by each method are in turn compared to the actual cycle times recorded by a computerized mine monitoring system at the same mine. The errors associated with each method relative to the actual cycle times are documented and form the basis for comparing the three methods.Findings – The paper clearly indicates that computer simulation methods used in predicting truck cycle times in open‐pit mining underestimate and overestimate the results for short and long hauls, respectively. It appears that both NN and regression mo...

Rock Drilling Performance Evaluation by an Energy Dissipation Based Rock Brittleness Index

To reliably estimate drilling performance both tool–rock interaction laws along with a proper rock brittleness index are required to be implemented. In this study, the performance of a single polycrystalline diamond compact (PDC) cutter cutting and different drilling methods including PDC rotary drilling, roller-cone rotary drilling and percussive drilling were investigated. To investigate drilling performance by rock strength properties, laboratory PDC cutting tests were performed on different rocks to obtain cutting parameters. In addition, results of laboratory and field drilling on different rocks found elsewhere in literature were used. Laboratory and field cutting and drilling test results were coupled with values of a new rock brittleness index proposed herein and developed based on energy dissipation withdrawn from the complete stress–strain curve in uniaxial compression. To quantify cutting and drilling performance, the intrinsic specific energy in rotary-cutting action, i.e. the energy consumed in pure cutting action, and drilling penetration rate values in percussive action were used. The results show that the new energy-based brittleness index successfully describes the performance of different cutting and drilling methods and therefore is relevant to assess drilling performance for engineering applications.

Implementation and outcomes of online self and peer assessment on group based honours research projects

Honours research projects in the School of Civil, Environmental and Mining Engineering at the University of Adelaide are run with small groups of students working with an academic supervisor in a chosen area for one year. The research project is mainly self-directed study, which makes it very difficult to fairly assess the contribution of individual students to a group-based research project. Until recently, a paper-based method of self and peer assessment (SPA) for the honours research projects was used to assess the projects. This was unsatisfactory for both students and academic staff, who found that the same mark was often awarded by the peers to each student without feedback. In 2010, therefore, an online SPA tool, SPARK, together with a set of newly developed assessment criteria, were used for SPA by the honours students. The new SPA criteria are based on teamwork and research skills, and the new rating scales reflect standard academic grades. Surveys of the students confirmed that they found the criteria and scales much more suitable for the assessment of group work and design projects.

Long Term Production Scheduling Optimisation for a Surface Mining Operation: An Application of MineMax™ Scheduling Software

Since long term production scheduling deals with movement of ore and waste during the life of a mine, it has a significant effect on the cash flow of a mining operation. Therefore, mine planners often seek to optimise the production schedule with respect to a given criterion. The most commonly used criterion in long term scheduling optimisation is to maximise net present value (NPV). The process involves sequencing of ore blocks or parcels to be mined in each period over the life of the mine subject to precedence and other physical constraints imposed by the mining system. The complexity of mine production scheduling in practice entails a computer solution using mathematical programming as the optimisation technique. Linear and mixed integer programming techniques have been used to optimise long term production schedules but most of the computer programs based on these make overly simplifying assumptions and lack the flexibility to handle practical considerations of mine scheduling. MineMax™ scheduling software is applied to long term scheduling for a multielement surface mining operation. MineMax uses mixed integer programming with the branch and bound algorithm as solution strategy. The system allows the planner to generate a mine production schedule in the same manner as manual scheduling, but making use of the interactivity in planning data input, in-built optimisation algorithm and the speed of the personal computer. This study involves investigation into the effects of reblocking and grade intervals on the mining schedule, specifically, the material movement, milling grade and the cash flow over the life of the mine.

An application of goal programming to production planning in the crushed stone industry

ABSTRACT The problems facing the aggragate stone industry in Zambia such as low capacity utilization, failure to meet customer requirements, unnecessarily high operating costs, poor inventory control practices, heavy borrowing and overall poor economic performance are as a result of subjective decision-making related to production planning. This is also true of the industry in nearly all member countries of the SADDC(Southern African Development Co-ordinating Conference) where quarry closures are not uncommon. As a solution to the problem of production planning and control in the crushed stone industry, this paper presents results of an application of the goal programming technique to a Zambian case study engaged in the production of limestone powder for the chemical industry. The formulation of a mathematical model for handling multiple objectives is discussed. The goal programming model can be used by management as a strategic decision support instrument. Results of the study show that over time work is...

Rock cutting performance assessment using strain energy characteristics of rocks

Abstract The intrinsic specific energy, that is the minimum energy consumed by pure cutting action to cut unit volume of rock, along with the rock strain energy, that is the absorbed energy by unit volume of rock in uniaxial compression, were used together to assess rock cutting performance. A series of rock cutting tests using a single polycrystalline diamond compact (PDC) cutter under steady conditions, and uniaxial compressive tests with a single-cyclic loading, otherwise monotonic loading were carried out on rock samples. Different rock types having unconfined compressive strength values of 9–249 MPa were carefully tested to determine the intrinsic specific energy and strain energy values. The results suggest that stress and strain characteristics of the rock obtained from uniaxial compressive tests, in terms of absorbed energy, can be related to cutting performance. Therefore, it was concluded that the strain energy can be used to assess the intrinsic specific energy to evaluate drilling performance in PDC cutting.

Design of pneumatic loading system for monorail application

Electrical Monorails have several advantages over trackless haulage in underground mining, such as ability to negotiate steep vertical and tight horizontal curves, small operating room and less diesel fumes. It has been demonstrated that loading time is the main drawback to high advance rates in monorail application whereby a loader is used to load rocks into monorail containers. A pneumatic loading system can be expected to reduce the loading time. This paper describes a pneumatic loading system for monorail application and provides an overview of the techniques used in lifting broken rocks from the development face into the monorail hopper.

Network Linear Programming Optimisation of an Integrated Mining and Metallurgical Complex

Mining companies seek to mine, route and process ore to make the most efficient use of capital equipment during the life of the mine. The situation analysed in this paper relates to optimisation of medium-term production strategy for a group of mines and metallurgical plants. Typical operations under this scenario involve mining of crude ore from shafts and/or open pits; transportation of ore to the milling plants, run-of-mine stockpiles and leach-pads. The concentrate from the mill(s) is sent to the smelters and refineries, from where the finished metal is sent to the markets. If one assumes that the grade of run-of-mine ore varies according to source and that the milling plants are designed to handle different types of ore, plus the fact that mines and plants may separate by considerable distances, optimisation of the production plan becomes imperative. Most of the publications dealing with the subject of mine production planning are limited to mine scheduling optimisation and do not include metallurgical plants. However, the nature of the problem requires the application of a model that incorporates all the elements of the mineral production system. The methodology outlined in this paper is based on a Network Linear Programming formulation of the production-planning problem for a mining and metallurgical complex. Network LP models are particularly useful in analysing production-distribution type systems such as the one involving a group of mines and metallurgical plants. The problem is formulated using the theory of dual-primal relationships in linear programming. The solution algorithm finds the minimum cost of production and distribution, hence the optimal production and material routing plan for a group of mines and metallurgical plants. The graphs of optimality conditions for each arc in the network could be exploited as a tool for strategic mine planning. The advantages of this formulation are outlined and its application is demonstrated using a hypothetical situation involving an integrated mining and metallurgical complex, specifically six mines, five concentrators, three smelter and two copper refineries. A computer program called Linear Integer Discrete Optimiser (LINDO) is used to solve the network linear programming model. This program allows the user to quickly input an LP formulation, solve it and perform ‘what if’ type analyses.