Experimental And Numerical Investigation Into Behaviour Of Fly Ash Composite Material In The Subbase Of Surface Coal Mine Haul Road

Abstract

Surface mining will continue to play major role in meeting the demand of fossil fuel. India’s power generation will be about 1, 65,000 MW this 11th five year plan out of which the share of coal would be 75%. Majority of the coal demand is met from surface mining due to its speed and ease of operations. The current coal production from surface mines in India is about 390 MT (85%) that will have to be increased substantially to meet the demand. Opencast mine economy depends on the cost of haul road design, construction and its maintenance in addition to other factors. These roads are used by heavy earth moving equipments. With a poorly laid, constructed and maintained haul road, production suffers, accident and breakdown occurs. The haul road has received inadequate attention although production, usage of heavy machineries have increased manifold. The surface of the haul road depends on the behaviour of material beneath it. Strengthening of the base and subbase layers beneath the surface of the surface coal mine haul road are of vital importance to improve upon its performance. The materials that are used in haul road construction, typically sourced locally. It is envisioned that suitable material would address this issue. Solid wastes from the surface mining as well as combustion of coal pose serious environmental problems of vital concern to the producers and users of coal as well as the general public. Opencast mining involves displacement of large amount of overburden dumps materials as mine waste to excavate coal from the earth. The overburden dumps formed outside the open pits not only occupy huge land area but also alter the surface topography and contribute to the environmental degradation. Fly ash is at present an unavoidable coal combustion byproduct. The major challenge with this production of the fly ash is in its huge land coverage, adverse impact on environment, etc. The problem with safe disposal of fly ash is a major issue as India is poised to generate huge volume of fly ash due to the high ash (40% to 50%) content of the coal. In most of the surface mines, the material used in the haul road is not adequate to support the wheel loads. Fly ash posses many attributes to be used as an engineering material in those sections/layers. The prospects of utilizing fly ash that would have been dumped as waste is explored, investigated, experimented and evaluated in the investigation. Different compositions of fly ash, mine overburden and lime have been prepared. The geotechnical properties such as compaction characteristics, California bearing ratio, unconfined compressive strength, Brazilian tensile strength, ultrasonic pulse velocity, morphology, phase characteristics, chemical compositions and leaching behaviour have been determined. The effects of lime content and curing period on the geotechnical characteristics of the fly ash composites are highlighted. Numerical investigation have been carried out to evaluate the behaviour of fly ash composite materials in reducing strain in the haul road of surface coal mine. There were significant improvements in the stress-strain behaviour of developed composites. All the composites resulted in enough strength values to be used as subbase material. Curing periods and lime content have varying influence in the strength development of the composites. The composites with 30% fly ash and 9% lime gave the best performance in reducing the stress-strain values at different section of haul road pavement. There were no traces of toxic elements in the developed composites.