Load-deformation characteristics of minefills with particular reference to arching and stress developments

Pirapakaran, Kandiah (2008) Load-deformation characteristics of minefills with particular reference to arching and stress developments. PhD thesis, James Cook University.

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Abstract

Mining is one of the major export industries in Australia. When the ore is removed from the ground voids are backfilled. There are different types of backfills depending on their nature and usage. Hydraulic and paste fill are most common backfills in industry. The strength and drainage properties of hydraulic fills are required for better design and safety of the mines and miners. Arching is a well known phenomenon identified in geotechnical and mining applications as reduction in the vertical stresses compared to overburden pressure at any depth within the fill. Paste fill is a popular and relatively new minefill that is used for backfilling underground voids created in the process of mining. The binder used in paste fill, typically at dosage of 3% - 5%, contributes significantly to the cost of backfilling. While Ordinary Portland cement (OPC) has been the typical binder in paste fills, there is an increasing trend to replace OPC with blended cements that include OPC mixed with fly ash, slag and lime at different proportions in an attempt to minimize the cost. This research presents a study that utilizes a laboratory model and the two and three-dimensional finite difference packages FLAC and FLAC3D to investigate the arching effects including the consideration of interface elements between rock and backfill, stope geometry and shear strength parameters. An arching effect instrument was developed and was used to investigate the stress developments within circular and square stopes, which were found similar to the results of numerical modelling. Stress values in the circular stopes were approximately 85% of square stopes from the experimental model. Further, an analytical solution was developed from Marston’s solutions for investigating stress developments within rectangular, square/circular and narrow stopes. The research was extended to develop models for narrow and rectangular stopes using FLAC and FLAC3D, respectively. The improved model of narrow stopes was verified against Aubertin et al. (2003) and extended further by incorporating interface elements between rock and backfill. FLAC axi-symmetric model for circular stopes was compared with Rankine (2004) FLAC3D model. Finally, the findings for narrow stopes were verified with Knutsson’s (1981) in situ measurements. Blended cements are generally characterised by very slow early strength development, followed by the attainment of good ultimate strength. Blends comprising of 100% OPC, 75% OPC & 25% fly-ash and 30% OPC & 70% slag were tested, adding 3%, 3.5% and 4% binder to tailings having solids contents of 7%, 80% and 81%. The specimens were subjected to uniaxial compressive strength after curing periods of 7, 14, 28, 56 and 90 days. The short-term flow characteristics of 3.5% paste fill mixes with each type of binder were investigated using yield stress tests. The results provided an understanding of the effect of solids contents, binder contents and curing period in the selection of optimal paste fill mixture. It was observed that slag-based paste fill had higher strength compared to the other two paste fills, however after considering the cost of binders, the 3% slag-based binder with 79% solids content in the paste fill and 3.5% Flyash-based binder with 80% solids content in the paste fill were chosen as optimal mixtures for strength and flow properties. Also, long term strength was investigated on Cannington mine tailings using Portland cement, but only for 79% and 83% solids content in the paste fill.

Item ID: 4789
Item Type: Thesis (PhD)
Keywords: minefill, stresses, backfills, binders, arching effects, interface elements, rock, backfill, stope geometry, shear strength parameters, Ordinary Portland cement, fly ash, slag, lime
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Date Deposited: 21 Jul 2009 02:33
FoR Codes: 09 ENGINEERING > 0914 Resources Engineering and Extractive Metallurgy > 091405 Mining Engineering @ 100%
SEO Codes: 84 MINERAL RESOURCES (excl. Energy Resources) > 8402 Primary Mining and Extraction Processes of Mineral Resources > 840299 Primary Mining and Extraction of Mineral Resources not elsewhere classified @ 70%
97 EXPANDING KNOWLEDGE > 970109 Expanding Knowledge in Engineering @ 30%
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