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Rajapakse, J.P.,Gallage, C.,Dareeju, B.,Madabhushi, G.,Fenner, R. Techno-Press 2015 Geomechanics & engineering Vol.8 No.6
Pebble matrix filtration (PMF) is a water treatment technology that can remove suspended solids in highly turbid surface water during heavy storms. PMF typically uses sand and natural pebbles as filter media. Hand-made clay pebbles (balls) can be used as alternatives to natural pebbles in PMF treatment plants, where natural pebbles are not readily available. Since the high turbidity is a seasonal problem that occurs during heavy rains, the use of newly developed composite clay balls instead of pure clay balls have the advantage of removing other pollutants such as natural organic matter (NOM) during other times. Only the strength properties of composite clay balls are described here as the pollutant removal is beyond the scope of this paper. These new composite clay balls must be able to withstand dead and live loads under dry and saturated conditions in a filter assembly. Absence of a standard ball preparation process and expected strength properties of composite clay balls were the main reasons behind the present study. Five different raw materials from industry wastes: Red Mud (RM), Water Treatment Alum Sludge (S), Shredded Paper (SP), Saw Dust (SD), and Sugar Mulch (SM) were added to common clay brick mix (BM) in different proportions. In an effort to minimize costs, in this study clay balls were fired to $1100^{\circ}C$ at a local brick factory together with their bricks. A comprehensive experimental program was performed to evaluate crushing strength of composite hand-made clay balls, using uniaxial compression test to establish the best material combination on the basis of strength properties for designing sustainable filter media for water treatment plants. Performance at both construction and operating stages were considered by analyzing both strength properties under fully dry conditions and strength degradation after saturation in a water bath. The BM-75% as the main component produced optimum combination in terms of workability and strength. With the material combination of BM-75% and additives-25%, the use of Red Mud and water treatment sludge as additives produced the highest and lowest strength of composite clay balls, with a failure load of 5.4 kN and 1.4 kN respectively. However, this lower value of 1.4 kN is much higher than the effective load on each clay ball of 0.04 kN in a typical filter assembly (safety factor of 35), therefore, can still be used as a suitable filter material for enhanced pollutant removal.
Simultaneous tasks as a contributory factor to maritime accidents: A socio-cultural approach
Rajapakse Asanka,Emad Gholam Reza,Lützhöft Margareta,Grech Michelle 한국해운물류학회 2022 The Asian journal of shipping and Logistics Vol.38 No.4
Analyses of accident investigation reports show that attempting to simultaneously perform tasks onboard ships to manage workload has led to many accidents at sea. These accident reports point out that seafarers fail to follow procedures as expected by shipping companies when conducting tasks simultaneously. Only a handful of studies that examined such discrepancies between work as imagined by shipping companies and work as actually done by seafarers exist. This study aims to examine why seafarers engage in simultaneous tasks, which may lead to accidents. In an exploratory qualitative study, face-to-face interviews were conducted with selective and targeted seafarers previously involved in maritime accidents. The collected data were analysed using interpretive and descriptive qualitative methods with a socio-cultural approach. The findings of this study show that the substantial regulatory changes over the years in the maritime industry have resulted in increased occupational workload for seafarers. Some of these regulatory barriers designed to improve safety at sea prompted seafarers to engage in simultaneous tasks to perform excessive paperwork and compensate for insufficient crewing. The research also revealed how a poor speak-up culture onboard might encourage simultaneous tasks leading to accidents at sea. The analysis shows that reasons for engaging in simultaneous tasks at sea are varied and complex. Therefore, complex intervention efforts to discourage seafarers from engaging in simultaneous tasks is needed to mitigate accidents at sea. © 2022 The Authors. Production and hosting by Elsevier B.V. on behalf of The Korean Association of Shipping and Logistics, Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Properties of Hand-made Clay Balls used as a Novel Filter Media
Rajapakse, J.P.,Madabhushi, G.,Fenner, R.,Gallage, C. Techno-Press 2012 Geomechanics & engineering Vol.4 No.4
Filtration using granular media such as quarried sand, anthracite and granular activated carbon is a well-known technique used in both water and wastewater treatment. A relatively new pre-filtration method called pebble matrix filtration (PMF) technology has been proved effective in treating high turbidity water during heavy rain periods that occur in many parts of the world. Sand and pebbles are the principal filter media used in PMF laboratory and pilot field trials conducted in the UK, Papua New Guinea and Serbia. However during first full-scale trials at a water treatment plant in Sri Lanka in 2008, problems were encountered in sourcing the required uniform size and shape of pebbles due to cost, scarcity and Government regulations on pebble dredging. As an alternative to pebbles, hand-made clay pebbles (balls) were fired in a kiln and their performance evaluated for the sustainability of the PMF system. These clay balls within a filter bed are subjected to stresses due to self-weight and overburden, therefore, it is important that clay balls should be able to withstand these stresses in water saturated conditions. In this paper, experimentally determined physical properties including compression failure load (Uniaxial Compressive Strength) and tensile strength at failure (theoretical) of hand-made clay balls are described. Hand-made clay balls fired between the kiln temperatures of $875^{\circ}C$ to $960^{\circ}C$ gave failure loads of between 3.0 kN and 7.1 kN. In another test when clay balls were fired to $1250^{\circ}C$ the failure load was 35.0 kN compared to natural Scottish cobbles with an average failure load of 29.5 kN. The uniaxial compressive strength of clay balls obtained by experiment has been presented in terms of the tensile yield stress of clay balls. Based on the effective stress principle in soil mechanics, a method for the estimation of maximum theoretical load on clay balls used as filter media is proposed and compared with experimental failure loads.
Tissa Rajapakse,Ramanie Samaratunge 서울대학교 국제학연구소 2002 Journal of International and Area Studies Vol.9 No.2
This paper investigates the relationship between the growing significance of trade diplomacy and the changes in the relative bargaining position of the major players, the US and the EU, in GATT multilateral trade negotiations. As the variables of the negotiation equation grew in complexity in the later GATT trade rounds, middle-power trade diplomacy became an important force in influencing negotiation outcomes. It is argued that middle-power trade diplomacy played a significant role in bringing agriculture into the GATT trade negotiation agenda and facilitating the successful completion of the Uruguay Round negotiations.