Natural Activity Concentrations in some Vegetables, Fertilized Soils and Fertilizers from Far-North Region of Cameroon and Assessment of Radiological Hazards

Ali Zarma, Abiama Ele P., Ema’a Ema’a J.M., Ben-Bolie G.H. and Owono Ateba P.

Samples of vegetable, fertilized soil and chemical fertilizer were collected in different boroughs of Maroua, Far-North Region of Cameroon. Activity concentrations of natural radionuclides such as 226Ra, 232Th and 40K have been determined by gamma-ray spectrometry based on NaI(Tl) detector. Their annual dose rate and representative hazard index were also estimated. The measured results show these radionuclides were present respectively in an average activity concentration value of 10  1, 29  4 and 414  172 Bq.kg−1 in the vegetable samples. In the soil samples, the corresponding values were 8  1, 23  2 and 320  20 Bq.kg−1 respectively while in the fertilizer samples were 12  4, 18  1 and 483  322 Bq.kg−1 respectively. The average value of annual dose was 49  7 μSv.y-1, 0.039  0.014 and 0.040  0.019 mSv.y-1 respectively from vegetables, soils and fertilizers. Concerning representative level index values, the average was 0.61  0.15, 0.50  0.02 and 0.54  0.23, from vegetables, fertilized soils and fertilizers respectively. Obtained values were discussed and compared with internationally recommended limits.

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Study on improving the performance of embankments and retaining walls using geo-anchors: Numerical Evaluation

Muthukumar M.

Soil is considered to be the cheapest material in the construction of embankments, earthen dams, and retaining walls. Hence it becomes necessary to improve the stability of such structures. Various techniques have been adopted to increase the stability. Some of them are soil stabilization, soil reinforcement, grouting, soil nailing etc. Each of these techniques has its own limitations. Geo-anchors, a new method is adopted to increase the stability of steep slopes, to reduce the lateral earth pressures on retaining or sheet pile walls or to stabilise embankments constructed on soft clay. In this method geo-anchors are used which are constructed by lining narrow trenches with high-strength geotextile and by filling the trenches with coarse sand, gravel or crushed rock. The granular material should be compacted in thin layers to increase the effectiveness of the method. A method to calculate the stabilising effect of the geo-anchors for different applications is described. In the present work, numerical analyses have been carried out using PLAXIS to study the performance of geo anchors in embankments and sheet pile walls. The study was carried out by varying the number of geo anchors and the position of the geo-anchors. It is observed that the performance of the geo structures improved by providing geo-anchors. Further the performance of geo-anchors largely dependent on the spacing and the number of geo-anchors. So it is mandatory to carry out the analysis to select the proper spacing and number of geo-anchors for any such earth retaining structures.

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