System Design Process of Mine Facility Project
Executive Summary
A systemic approach for developing structural components such as infrastructure, surface and sediment, slope and groundwater management for a mining project is the most important requirement. This report evaluates an integrated system of pre-design and detailed design in different phases as well as various optimization methods that help to solve mining problems.The paper is a detailed outline of the design and techniques with a system evaluation of valid processes and feedback loop. The ultimate goal of the research is to interpret the role of design and optimization methods to reduce the need of time, performance and cost while providing safety operational measures. It also provides recommendations based on the study for future considerations of site design and improvement in current principles and models.
Table Of Contents:
Executive Summary 1
Introduction 3
Strategic Design Model 6
Sequencing Model 6
Equipment Allocation Model 7
Methods 7
Preliminary Design 7
Detailed Design 8
Grading and Stabilizing Piles 8
Jet Grouting 9
Barrier wall and Water Collection System 10
Mine Water Treatment 11
System, Evaluation and Validation and Optimization 11
Optimization Algorithms 12
Seminal Work on Optimization 12
Conclusion 14
Recommendations 15
References 16
INTRODUCTION
Underground mining is a complex technology with drawbacks such as poor working conditions, frequently occurring disasters, less amount of light, etc, So, to improve theses conditions a more developed and innovative form of modern mining is required based on new technologies and site designs to overcome the flaws which are a result of traditional mining processes. Underground mining compared to surface mining requires less cost as the waste to extracted ore ratio is too less with more extraction benefits. There are three categories of mining method based on surrounding rocks and ores texture and size: supported, unsupported and caving.
Unsupported-
Pillars- This method works with flat, thin and homogenous ore deposits. Room and pillar fall under this category. Pillars or bolts are stable ceiling support from which ore is recovered through blasting and loaders helps to remove them. The another method extract ores are through retreating (mining to the extent of tunnel collapse).
Stopes- In this method, ores with boundaries are steep dipped. It consists of blasting ores after dividing it into several stopes and extracted through drilling afterward. Ore is extracted from the bottom and stops are again filled.
Fig.1.1: Pillar Mining Fig. 1.2: Stopes Mining
(Source: Hamrin,2001)
Caving- This method doesn’t require blasting rather the rocks are broken down into small pieces that can be recovered easily from the ore deposit.
Longwall caving- It is a type a caving method which is used for long and thin deposits of ores. The rocks are cut out mechanically without blasting from the deposits.
Fig.2: Longwall Mining (Source: Hamrin, 2001)
Sublevel caving- Long and pure deposits which look like veins are extracted with the help of this method. Parallel sublevels or tunnels are used for extracting ore after the blast. However, after the blast the ore is brought down to a hauled level through a chute and crushed into small rocks to transfer it to surface easily through vertically placed shafts.
Block caving- Structurally it is simpler than sublevel and helps in extraction of low-quality ores. The ores are present at the bottom from where they are recovered with the help of draw points. Hydraulic hammers are used to drill large rocks again after the blast. It works on the principle of gravity through which rocks flow at the bottom. Some critical points that influence the extraction are size and filter rate of rocks along with stability in mines.
Fig.3.1: Sublevel caving Fig.3.2: Block caving (Source. Hamrin, 2001).
Strategic Design Model-
Geotechnics is more preferred than OR (operational research) techniques in mining. In case of gold mines, longwall, pillar, stopes, and sublevel caving mining method is used for ore recovery and extraction from orebodies. A strategic design to determine the shape, layout of mine and also to design a 3-D structure of haulage by sublevel and stopes mining method. The stopes are arranged in symmetry with high gradient, low curvature and constraints such as the production of maximum and minimum ores, demand in the market, and quality of ore of area that has been avoided (Brazil and Thomas, 2007).
Sequencing Models-
It is difficult to identify general underground mine site design and sequencing generic blocks formulations in an underground mining design. These formulations objective function is NPV representation while including both the constraints ( precedence and restriction on resource) similar to open pit sequencing model.
Constraints considered are specific to mining method. Some variables are used in this model such as in case of supported method, “yatt =1″ and ” yakt =1″are used for a given mine area (developed/drilled/ extracted) with or without an equipment “k” in a given time period of ‘t'(Sarin and West-Hansen 2005).
Equipment Allocation Models-
Equipment allocation models are applied on the system of transportation in underground mines. The mines have a complex machine such as conveyor belts, alternate systems, etc, which work independently and are needed to be analyzed that helps in determining locations. The design based on this model makes use of a tool to analyze event simulation eg, a conveyor belt system and longwall method of mining is used to transport ores from the bottom line to the surface while mediating cost with high performance (Mc Nearny and Nie, 2000). Various optimization models are used to place equipment in mines with the help of constrained system model as compared to other models.
METHODS
Preliminary design-
The main structural components of the preliminary design are as follows:
Tailing Piles- Three tailing piles namely, TP-1, 2 and 3 were stabilized by a layer of soil, whose height ranges from 13- 36 m and width about 0.3 km² made up of reactive pyrite (iron sulphide) which reacts with water in the presence of oxygen hence producing iron and sulphate under low pH conditions i.e., acidic which helps to solubilize various metals. Tailings were provided with slopes with less steeps with the help of a movable equipment, high surface runoff and base foundation for better stability in the seismic and steady state.
Water retention: The retention of surface water was done in a pond which receives water from ventilator tunnel of mines through a decant. The fines that are deposited in pond consists of the high amount of metals.
Groundwater containment: Groundwater below the surface of tailings has reduced quality due to high level of metals. A barrier wall was constructed to convey water to a lime treatment plant with leftover sludge being disposed of automatically.
Hydraulic control: Air plugs were attached to the mine ventilator equipped with valve to reduce airflow and thus reducing sulfide oxidation. Valves control airflow in mines and evenly create hydraulic environment.
Control of surface water: Metal discharge seeps into groundwater contaminating it. Channels with interception were constructed to convey surface water and control its run on.
Controlling sediment: Sediments such as precipitates of iron and its constituents seeps from tailing piles into adjacent spaces causing ferricrete, flocculent. Relocation has solved this problem by diverting water flow.
Detailed Design-
The detailed design provides a broader outlook of the underground mine structural components. They are as follows:
Grading and stabilizing Piles:
Tailing slopes helps to rise the steep of slopes with the help of the diking method (single/double). The piles are coated with alluvium (silt, sand, gravel) 11m to 25 m to raise steeps. An intermediate bench should be included with one-third length of slope in tailing piles so the jet grout equipment can be easily accessed in the bottom of tailing pile.
Fig. 4: Tailing Piles
Fig.5: Waste rock pile
Jet grouting:
Structures made on soft soils have low soil strength. So, to improve the soil strength jet grouting method is used. (Wang et al. 2013). In this method, high-velocity fluids are injected with the help of a small nozzle to mix the removed soil with grout forming a cemented column. The columns formed were placed above and below with non‐liquefiable material with liquefiable saturated tailing kept in the middle. This soilcrete design increases the shear strength to some extent and provides space between the column blocks for easy drainage. Several forces act on column blocks, the forces acting on the layer of thick liquefiable material helps to analyze stability through cross-sectional studies.
Fig.6: Jet grout block
Barrier wall and water collection system:
Groundwater collection system model is considered to be the first step in designing process of the site. MODFLOW is used to construct the detailed design process for groundwater system. MODFLOW is a 3-D numerical code with a finite difference which allows even flow of groundwater in a large area. To develop the model a telescoped area is used with small grid cells. The model was then categorized into a five layer simulation for tailings, alluvium, and bedrock.
A vault is attached to a broke trench pipe with downright collection higher than upright inside the water trap. The variation in upright and downright water elevation controls water trap, by maintaining pipe and its envelope when groundwater level is a low hence, restraining oxygenation. In the downright gradient of the water trap a permeability plug is attached that keeps the flow conditions at low level in the upright side of water trap.
Fig.7: Trench water trap
Mine water treatment-
Mine water treatment plants are constructed to minimize power requirements, cost reduction, improved net zero carbon and sustainability. External power sources are used to provide energy to the mines with the help of generators that are designed to bear daily loads of underground mines. Concepts to reduce power are critical for a design which includes:
By developing a gravity based treatment system.
Providing power to lime feed system through hydraulic head.
Drive motors based on variable frequencies.
System test, evaluation & validation and optimization-
A mining process system is a system which consists of inputs and outputs that are illustrated by an engineering framework of the system so, optimization is amenable. Optimization of the system starts with reducing inputs while increasing outputs, i.e., profits. System’s performance can be improved by adjusting the feedback of output level.
Fig. 8: Mining process system with feedback loop
Optimization algorithms-
George Bernard Dantzig was the first one to introduce an algorithm to solve LP (linear programming ) problems. The formulation is :
x is restricted to a certain value type; LP problems can be exaggerated to variants of x. These variants of LP are used to optimize underground mine system planning design process (Newman et al. 2010).
Mine planning is the basis on which operational performances, system design operations are run on set targets of upstream and downstream stages. Mine system planning execution is carried over throughout the lifecycle of mining operations.
Seminal work on optimization-
Optimization of mine planning system and evaluation is done through a 3D block model containing geological and geotechnical data that shows mine design process and delineate characteristics of mineral deposit into blocks of mine (Sandanayake et al., 2015). These blocks can be arranged in different orders according to deposit size and granules on the basis of given data.
Fig. 9.1: A 3-D block model (Osanloo et al.,2008) Fig. 9.2: 3-D illustration of underground mine (Bley and Terblanche)
CONCLUSION
Underground mines are different in their designs, layouts and operational models are not used frequently as compared to open pit. This report provides an overview of some improvised innovative designs and construction practices of underground mine planning system. The goal is to advance current practices of mine designing and their possible remedies for drawbacks of the site. However, frequent involvement of stakeholders, proper communication with them and time to time collaboration is required to enhance design processes.
Underground mine planning and design optimization is required for new advancements as mining provides various permutations on the basis of mining method and processes. These optimization processes are somewhat complex and difficult to solve due to intrinsic problems.
RECOMMENDATIONS
More detailed models with improved techniques are required. Lighting should be provided through LED lights to conserve energy and reduce cost. Manual motion and photo sensors should be used inside a mine. All the rooms should be separated into zones to provide easy management and regulation of mine system design. Proper ducting, hydraulic airflows, ventilation, etc, are required to pertain even distribution of heat, water and air. Customizing models with faster problem-solving techniques are needed. Such modified and improvised models are yet to be practically implemented in the underground mining process.
REFERENCES
Brazil, M. and Thomas, D. (2006). Network optimization for the design of underground mines. Networks, 49(1), pp.40-50.
Fourie, A. and Tibbett, M. (2016). Mine closure 2016. Nedlands, Western Australia, Australia: Australian Centre of Geomechanics.
MCNEARNY, R. and NIE, Z. (2000). SIMULATION OF A CONVEYOR BELT NETWORK AT AN UNDERGROUND COAL MINE. Mineral Resources Engineering, 09(03), pp.343-355.
Musingwini, C. (2016). Presidential Address: Optimization in underground mine planning- developments and opportunities. Journal of the Southern African Institute of Mining and Metallurgy, 116(9), pp.809-820.
Newman, A., Rubio, E., Caro, R., Weintraub, A. and Eurek, K. (2010). A Review of Operations Research in Mine Planning. Interfaces, 40(3), pp.222-245.
Sandanayake, D., Topal, E. and Asad, M. (2015). Designing an optimal stope layout for underground mining based on a heuristic algorithm. International Journal of Mining Science and Technology, 25(5), pp.767-772.
SARIN, S. and WEST-HANSEN, J. (2005). The long-term mine production scheduling problem. IIE Transactions, 37(2), pp.109-121.
Bley, A. and Terblanche, S.E. Not dated. An improved formulation of the underground mine scheduling optimization problem when considering selective mining.
Wang, ZF, Shen, SL, Ho, CE & Kim, YH 2013, ‘Jet Grouting: an Overview’, Geotechnical Engineering Journal of the SEAGS & AGSSEA, vol. 44 No. 4, December.
Osanloo, M., Gholamnejad, J., and Karimi, B. 2008. Long-term open pit mine production planning: a review of models and algorithms. International Journal of Mining, Reclamation and Environment, vol. 22, no. 1. pp. 3-35.
Hamrin, H. 2001. Underground mining methods and applications.