engleski

Evaluation of utilization coefficient during exploitation of thin plates in the case of Lipovec natural stone from Croatia

The calculation of the utilization (integrity) of the rock mass in the natural stone quarry near Zagreb in Croatia is shown. The thinly bedded limestone of Middle Triassic age with market name Lipovec limestone is dark grey, almost black or in some parts of the bluish colour. Limestone is petrographicaly determined as bituminous wackestone limestone. The deposit is layered with layer thicknesses from 3 to 20 cm, which causes the exploited slabs to depend on the thickness of the layers. The calculations of the utilization coefficients depend on discontinuities (cracks and layers) in the deposit, their systems and their distance. The paper will present the estimation of the utilization of the rock mass by calculating the linear, surface and volume coefficients of utilization. The present method is suitable for the estimation of exploitation reserves during geological surveys. The utilization of rock mass significantly influences the profitability of exploitation of thin layer deposits. Market value of stone is further influenced by its decorative nature, and its physical, mechanical, and chemical properties. The deposit of Lipovec Stone is built of thinly bedded limestone with a total thickness of over 20 meters. The beds are almost horizontal and very slightly bent and their position measured in the field is 130°/7°. The thickness of the layers is in the range from 3 to 20 cm. Bed surfaces are generally open, and limestone is very easily separated along the bedding planes. Clay and marl components are visible along layered surfaces. The deposit is intersected by micro- and macrocracks that are mainly vertical or subvertical. Most of the rock mass in the deposit is suitable for the exploitation and production of natural stone in the form of thin and thicker stone elements or slabs. Prices of slabs vary depending on the thickness of the slabs. Thinner slabs usually have a much greater economic value than the thicker one. The stone is suitable for the construction of decorative walls and in general as a covering of internal and external vertical and horizontal surfaces. Exploitation and stone element processing is relatively simple, and is done by using steel rods, pliers, wedges, and blades. After the exploitation, the slabs are fitted to the wooden pallets in the measurements of one cubic meter for the market. Calculation of utilization coefficients is primarily used on deposits where large “healthy” blocks are exploited, less on deposits such as Lipovec Stone. On such deposits discontinuities play a major role and should be taken into account when calculating the utilization coefficients. Thin layers, which give thin slabs of natural stone, and cracks due to system complexity have a great impact on reducing the final volume coefficient of utilization, and is therefore less economic value of the deposit. In order to get more accurate data on the utilization of prospected deposit, three utilization coefficients of the rock mass could be calculated. These are linear, surface, and volume coefficients of rock mass utilization. According to calculations of the coefficient of utilization it can be concluded that a large part of the quarry could be fully utilized. According to the calculations of coefficients of linear utilization, efficiency varies between 85 and 90%, which is not real. Much more realistic results were obtained when calculating the surface coefficient of utilization whose results ranged from 70 to 80%. According to the results, when new dimension is introduced, utilization decreases proportionately. This is evidenced by the results of the volume utilization which are between 60 and 70%. As for the quarry itself, except for the calculations, it was concluded that the usability could be even greater than it is today, with the change of exploitation technique itself, but also with the technology of stone removal. Advanced technologies could greatly reduce the percentage of useless parts of the deposit, but from the economic side, it would mean new potential investments and costs.

utilization coefficient, stone exploitation, thin plates, Lipovec natural stone

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