Across the world, ballasted railway tracks are utilised extensively due to their cost efficiency, ease of drainage, and capacity to withstand cyclic imposed loadings from heavy trains. In spite of these benefits, the ballast is often considered as a flexible medium; as such, its continuous deterioration is largely disregarded. Geotechnical challenges such as ballast contamination in the form of particle fragmentation, deposition of weathered materials, upward pumping of clay and fines from underlayers, and coal intrusion have led to differential settlements and reduced drainability of tracks, thereby exacerbating track maintenance costs. This study reviews existing works of literature to expound on the mechanisms for ballast contamination and to highlight the fundamental parameters that guide the characterisation and performance evaluation of railway ballasts. The study shows that ballast fragmentation accounts for about 76% of commonly recorded contaminations, while it is also observed as the most critical to track stability. As such, a variety of indices and specifications for ballast gradation have been established worldwide to guide practice in ballast characterisation and performance evaluation. However, the mechanisms of ballast fragmentation and deterioration require further research to guide the improvement of contemporary guidelines, and mitigate the risk of abrupt track failures, especially in developing countries.
This study assessed the aggregate properties that influence track ballast performance along selected Nigerian railway lines. Ballast materials from five selected rail tracks (RT1, RT2, RT3, RT4, and RT5) in Nigeria were collected and assessed in present conditions and after triple-fouling (subjected to degradation, clay, and diesel intrusion). Tests performed include gradation, strength, soundness, and drain-ability tests. Results obtained were compared with the requirements established in five recognized railway ballast standards,where applicable. Initial gradation results indicate that presently, ballast materials from the selected study locations can all be classified as "uniformly graded gravel". However, upon triplefouling, a gradation shift towards the "well graded" classification was observed. Based on EN 13,450, the gradations of RT1, RT2, and RT3 ballast materials were more satisfactory than gradations of RT4 and RT5. Strength test results show that ballast materials from tracks RT1, RT2, and RT3 performed satisfactorily based on the five ballast standards considered. RT4 and RT5 on the other hand, only performed suitably based on the AREMA No. 4 ballast standard. The least resistance to weathering was observed in the RT4 and RT5 samples. Initial drain-ability test
Air is an essential element in the life of humans, and everyone deserves to breathe in clean air. But anthropogenic activities from industrialization and modernization, as well as some natural disasters such as earth quake and volcanic eruption pollute the air. Consequently, air pollution threatens the health of people living in close proximity to the source of pollution by causing or aggravating sicknesses like, heart problem, cancer and respiratory disorder. The dispersion of air from a point source tends to follow the shape of Gaussian or normal statistical distribution. The present paper aims at examining Gaussian plume model as the easiest and simplest model among the lists of air dispersion models evaluated, stating the various issues from the source to the receptors. Gaussian Plume model is mostly used in the analysis of air dispersion with the concentration of a given place, having function of the distance from the source, emission rate and the meteorological data, mostly temperature, wind speed and wind direction, with the help of some various assumptions, in order to estimate how much air has reduced or travelled from the source and the concentration at the ground level. The model uses Briggs coefficients sigma y and z to get both vertical and horizontal dispersion. Plume rise determines dispersion and transportation levels, and thereby affect the distance to maximum ground level concentration and the maximum ground level concentration, the taller the stack or chimney (source), the larger the plume and the lower the concentration at the ground. A week analysis on pollutants generated from Larfarge cement factory Sagamu, Ogun State was carried out. The result shows mathematical simulation of Gaussian plume model of pollutants concentrations from the source and the applicability of the model.
Cement factory produces air pollutants that contaminate and cause adverse effects on the health of dwellers of the affected environment. These pollutants enter the body and become injurious by initiating or aggravating problems in the respiratory, circulatory and nervous systems. During the production of cement, many processes like crushing, raw milling, calcining, burning and cements milling, release pollutants to the immediate environment. This study aimed at estimating the discharge rate of carbon dioxide (CO2) pollutant emitted from the production/combustion unit of Lafarge Cement Factory Sagamu Ogun State. Six points on each of the three major routes that lead to the factory were used as the sampling points for the study. Gaussian plume model method was applied in developing the model equation. Raw data obtained from the field was used to determine the spread of CO2 concentration. The study showed that there were emissions of CO2 within the study area, with an average monthly highest discharge rate of 773.333 ppm on Ikorodu route, and the lowest discharge rate on Abeokuta route (689.875 ppm). Consequently, the findings can be used to formulate and validate models as well as develop co-correlation among the three routes in the study area.
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