Faculty of Engineering, Earth Resources Engineering

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Browsing Faculty of Engineering, Earth Resources Engineering by Author "Dharmaratne, PGR"

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    item: Thesis-Abstract
    Durability of rocks under tropical conditions
    Samaradivakara, GVI; Dharmaratne, PGR; Puswewala, UGA
    Sri Lanka has a basement rock formation of metamorphic origin that the majority is gneissic type, which is intensively used in many of the civil engineering constructions. In addition, foundations of most of the important civil engineering structures are extended up to or into the fresh gneissic rock strata. Sri Lanka has a tropical climate. Therefore the study on durability of gneissic rocks under tropical conditions would be immensely beneficial to the construction industry of the country. The simulation of exact natural weathering conditions is quite complicated. This study concentrates mainly on how heat stress affects deterioration of index properties of gneissic rocks. When the rock mass gets heated, and cooled rapidly due to sudden rainfall, there is a possibility of propagating micro-fractures in the rock mass which will initiate weakening the strength properties of the rock mass. Most of the bridge abutments and dam constructions are associated with basement rock. In such locations rocks mass is alternately subjected to wetting and drying processes. Therefore the deterioration of rock resulting in its breakup, which is termed as "slaking" is also studied in this research. One hundred and sixty rock samples of gneissic rock of diameter 54mm (NX size) are tested in this research. Out of these 132 samples are fresh competent rocks and 28 are weathered to different degrees. These samples are selected from biotite gneiss and quartzo-feldspathic gneiss; the major two gneissic rock formations found in Sri Lanka. Fresh gneissic rock samples were subjected to heating and the weakening of their strength properties were studied upon cooling. Naturally weathered gneissic rock samples belonging to different weathering grades were also tested for their index properties. These were compared with the index properties of artificially weathered fresh gneissic rock samples and some correlations are established. The rate of deterioration of index properties of quartzo-feldspathic gneiss is seen to be more than that of biotite gneiss. Therefore more attention should be paid in the designing of foundations of important civil engineering structures in quartzo-feldspathic gneiss as far as the 'durability, is concerned, based on the project location..
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    item: Thesis-Abstract
    Heat treatment of gems with special emphasis on geuda stones
    Peiris, BPS; Dharmaratne, PGR
    Detailed literature survey is presented on gem minerals, corundum family of gems, colour in gem s tones and heat treatments. Physical and chemical investigations on gem minerals are conducted to understand the nature of treatable stones. Treatable stones are characterized by the presence of different types of impurities in the basic corundum structure. Optimum heating rates, cooling rates and soaking periods are established for geuda and ottu stones. Investigations carried out on over one thousand and twenty samples revealed that certain types of geuda stones can be converted into good blue sapphires while other varieties become light blue or dark blue stones. Removal of bluish and brownish tints in red geuda A comparative stones are not completely satisfactory. Study of the Lakmini furnace with the Toda furnace was carried out to ascertain the more economic one.
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    item: Thesis-Full-text
    Influence of mechanical and aggregate properties of rock on powder factor in rock blasting
    Karunanayake, KDP; Dharmaratne, PGR; Rohitha, LPS
    Quarry metal is a widely used material in any large scale construction industry. Though demand for quarry metal substantially increased due to recently emerged large infrastructure development projects in Sri Lanka such as highway and port city, profit margins of the quarrying has drastically reduced due to high powder factors recorded in recent rock blasting activities of local quarries. Most possible reason for realizing high powder factors could be the introduction of various new explosive agents such as water-gel in to the local mining industry. Importance of analysing the influence of mechanical and aggregate rock properties on powder factor arises in this context to allow seeking suitable rocks those incur minimum blasting expenditure during the production stage. Outcomes of the project can be used to predict powder factor which could be achieved in blasting operations of a certain rock even before starting the quarry operations to minimize its production cost in the long run. Eight quarries operates under the close supervision of qualified Mining Engineers were selected for this study to ensure blasting geometry and configurations have being properly managed during the realized powder factor data recorded time period. Random core samples were obtained from each quarry site and they were tested for Density, Uniaxial Compressive Strength (UCS) and Tensile Strength. Similarly, random aggregate samples were taken and performed the Aggregate Impact Value (AIV) test. Rock Mass Rating (RMR) was determined for each quarry using UCS values and other field data obtained at the site. Explosive consumption and drilling records for recent six month were obtained from each quarry for the calculation of powder factor. Powder factor was plotted against each selected rock property and regression analysis was performed on test results to understand their standalone influence. The only realized best fitting model for the Powder Factor was AIV according to the regression analysis and it is very closely following the quadratic model. Rock property test results and past records of few other quarries were used to validate formulae obtained in this research. Explosive cost and production cost of all the quarries analysed for the same six months period. Results revealed that the production cost is a function of explosive cost since other costs on drilling, machineries and labour are usually incur relatively fixed costs in nature. Hence it can be concluded that the aggregate rock properties, especially Aggregate Impact Value (AIV) influence on powder factor of blasting and furthermore affects economics of the quarry production. More importantly, combined formula derived in this research can be used predicting powder factor of a fresh rock before conducting any blasting activity.
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    item: Thesis-Abstract
    Mineralogical, textural and fluid inclusion studies of corundum and spinel in Sri Lanka
    Francis, MDPL; Dharmaratne, PGR
    Corundum and spinel are the most prominent gem minerals found in Sri Lanka that account for more than half its gem exports. Further, Sri Lanka is a major supplier of top quality sapphire. The main objective of this study was to (i) identify as many properties as possible of Sri Lankan corundum and spinel, not recorded so far and (ii) list the properties supposed to be unique to certain terrains such as alkali magmatic terrains in other countries, which were helpful to understand the origin of corundum and spinel of Sri Lanka. For this study samples representative of the Precambrian metasedimentary terrain of Sri Lanka were collected. For detailed investigations, samples from only Balangoda and Kaltota were chosen, because these areas were underlain by different gem-bearing source rocks. Several features unique to alkali magmatic terrains such as plagioclase crust around the crystal, surface features resembling needle - like patterns, radial cracks around zircon inclusions and inclusions of zircon clusters were observed in relation to Sri Lankan corundum. Chemical fmgerprinting, a methodology adopted to determine the origin of corundum, was carried out for a limited number of selected samples of which, two were identified as magmatic. Several microscopic and macroscopic reaction textures provided evidence for the confirmation of metamorphic growth. These reactions were also confrrmed by EPMA analysis. Fluid inclusions representing the Precambrian rocks of Sri Lanka were scrutinized using petrological microscope, Raman microprobe and thermal stage microscope. During this study it was possible to confirm the theory that Sri Lankan fluid inclusions contained more or less pure CO2, and also the theory that the most common daughter minerals were graphite and diaspore. Necking too was observed and the process was similar to what was mostly observed in the corundum of Malawi. A classification of corundum on the basis of fluid inclusions was formulated based on the shape, size and composition of fluid inclusions. The classification led to four categories. Sapphirine too was found as an inclusion, in contact with spinel, in corundum. Hence it was possible to calculate the sapphirine/spinel thermometry. The calculation revealed that the crystallization temperature of Sri Lankan corundum was 761°C (Fe2+ calculation). Finally the features unique to corundum found in other alkali magmatic terrains of the world, which are now identified in Sri Lanka too are taken into consideration. These features were plagioclase crust around corundum, surface features of needle-like pattern, zircon clusters and radial cracks around zircon inclusions in corundum. Two instances found by chemical finger printing to be of magmatic nature indicated the origin as such, while the reaction textures associated with the corundum bearing rock indicated metamorphic origin. These finding proved that the corundum of Sri Lanka displayed a combination of both magmatic and metamorphic properties. Hence the origin of corundum could not be attributed to metamorphism alone with certainty.
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    item: Thesis-Abstract
    Optimization of Sri Lankan underground graphite mining methods, from a view point of rock mechanics and cost
    (2015-06-24) Hettiwatte, MC; Dharmaratne, PGR; Hemalal, PVA
    This research includes the study of the mining method adopted at Bogala Graphite Mines and its suitability compared with other mining methods used in the mining industry. The mining method adopted in Bogala mines has been assessed through this study. It mainly focus on the rock mechanics and financial aspects with comparisons to the mining methods adhered by the Sri Lankan mining industry. The major graphite occurrence discovered more than hundred years has produced highly valued the world over. In Sri Lanka, graphite mineralizations occur in the form of rich veins with steep dips in the South-Western sector of the island, the vast stretch of area which has been famous for graphite mining with thousands of pits in operation during the high demand of the first and second world wars. Where an outcrop is encountered, a pit had been sunk and the steeply dipping vein had been followed to the depths. At Bogala mines, the adoption of Overhand Cut-and-Fill mining method is influenced by the steeply dipping vein environment with rock intercalations and high water inflows with less competent country rock. Although cut–and–fill mining has been traditionally successful ensuring high recovery and safety, only limited studies has been carried out with an engineering input to evaluate this method. With the use of literature and site visits to Bogala mines, the mining method used at Bogala mines, the underground environment and the other mining methods used in the mining industry both internationally and locally have been studied. In evaluating the most suitable mining method, workability, safety and ore dilution and recovery factors of different mining methods were considered and the most suitable method for Bogala mine was evaluated.