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Articles by S. Narra
Total Records ( 5 ) for S. Narra
  S. Narra
  The aim of this study is to investigate effects of FGD gypsum on virgin clay (>43%) soils in Lusatia, Germany carried out from year 2005 till year 2008. A thorough understanding of various processes controlling persistence, retention and leaching of contaminants is required for proper long-term management and disposal of industrial wastes such as Fly Ash (FA), Flue Gas Desulphurization (FGD) gypsum etc., which are major coal combustion by-products resulting from electric power generation. The FGD gypsum is selected as a substitute for calcium carbonate in amelioration of virgin clay soils in Lusatia. Pot experiments have been evaluated with the wild rye species where as the investigations at open cast mining pit Nochten were evaluated with two different kinds of Poplar clones (Hybrid 275 and Weser 6). Slight reduction in pH with strong increase in electrical conductivity has been observed with increasing the FGD gypsum concentrations. Electrical conductivity obtained was more then 2 mS cm-1 with 16 times the FGD gypsum concentration. Even though the pH and the electrical conductivity did not give positive results, germination success achieved was good, with which the average biomass produced was also good. Nutritional elements lied in between optimum ranges. Accumulation of heavy metals reduced with the 100% FGD gypsum substitution compared to that of 100% lime. The Poplar clones showed good growth at open mining field Nochten. Proportional growth was observed. Significant differences in diameters and heights with respect to different variants were not observed. However, a difference with respect to biomass has been observed. Acceptance of the FGD-gypsum has been clearly observed with biomass produced under both the Poplar clones. Acceptance of FGD gypsum observed was comparatively higher with the Hybrid 275 compared to the Weser 6, which could be correlated to the genotype of the Hybrid 275.
  S. Narra
  The objective of this study is to investigate the influence of different consolidation curve models on the initial void ratio values and through which on the obtained pre-consolidation stress. Further, this study verifies the dependence of pre-consolidation stress on the initial void ratio value measured at 1 kPa. This was done in order to check the trend between the consolidation curve models and the deviation in pre-consolidation stresses. Three different Oedometer tests have been carried out which were denoted as undisturbed, disturbed and disturbed-rewetted. The curves were fitted using two different curve models (Assouline and Van Genuchten models) and the graphical calculation of the pre-consolidation stress was done using two different methods (Casagrande and Silva methods). The curve models are applied on the compaction data obtained from the soil classified as loamy sand. A good consolidation curve fit to the data (R2 ranging between 0.97 and 0.99) has been verified for a wide range of applied stresses (0 to 2500 kPa), including stresses less than the pre-consolidation stress. Huge differences in the initial void ratio values (Δe ranging between 0.003 and 0.423) have been observed with different curve models and with which a huge difference in pre-consolidation stresses (ΔP ranging between 0 and 57 kPa) have been observed. This study clearly showed that the pre-consolidation value obtained was mainly dependent on the curve fitting model and also on the calculating method. This study also showed a dependence of pre-consolidation stress over the void ratio measured at 1 kPa.
  S. Narra
  The objective of this study is to understand the water induced consolidation process at agriculturally used reclaimed soil. The approach of the study is to reproduce the situation occurring when the soil is subjected to water induced compaction at defined loads typical in the top soil (0 to 20 kPa). The water induced compaction process is characterized by sudden change in the voids or pores of the soil that are loaded at their natural water content and flooded. Compression properties are measured with Oedometer tests using sieved sandy loam, taken from a non weathered Saalian glacial till layer, as the meta-stable test soil. Pre-consolidation load calculated for the dry samples overestimated the simulated overburden pressure, whereas, the wetted samples showed a high congruence. In both cases, the point of greatest curvature estimated in the earlier step of deviation gave values that are more realistic to the loads from which the unloading started. The results indicated that both dry compaction and water-induced compaction induce primarily plastic deformation.
  S. Narra
  The objective of this study is to investigate the development of clay soil structure with the amendment of Flue Gas Desulphurization (FGD) gypsum as a substitute for lime in Lusatia, Germany. Development of the clayey soil structure has been evaluated using parameters shear stress and penetration resistance. The sand-clay mixtures (65% sand-35% clay) representatives to the field conditions were subjected to undergo 1, 5, 10 and 20 drainage cycles (swelling and shrinking processes). Shear lines were established based on 12 load stages using box shear machine. Penetration resistance has been accomplished using modified penetrometer. Shear lines distinguished a new structure development with good crystal growth after 10 drainage cycles with FGD gypsum, where as with lime the clayey soil was rather lubricative. Penetration resistance decreased from 30 to 5 MPa with FGD gypsum amendment where as with lime amendment it reduced to 10 MPa only. From water retention characteristics it could be observed that samples were well drained indicating reduction in water holding capacity of clay due to amelioration achieved by FGD gypsum. Observations showed that FGD gypsum is more effective in amelioration compared to lime.
  S. Narra
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