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Articles by Thamer Ahmed Mohammed
Total Records ( 3 ) for Thamer Ahmed Mohammed
  Azlan A. Aziz , Faisal Hj. Ali , Choong Foong Heng , Thamer Ahmed Mohammed and Bujang B.K. Huat
  Residual soils occur in most countries of the world but the greater areas and depths are normally found in tropical humid areas. In these places, the soil forming processes are still very active and the weathering development is much faster than the erosive factor. Most residual soil exhibit high suctions for most of the year. The absence of positive pore water pressure except immediately after rain, makes conventional soil mechanics for saturated soil not so relevant. Ignorance or lack of understanding of the geotechnical behavior of soil in the partially or unsaturated state has caused a lot of damages to infrastructures, buildings and other structures. For instance, the collapsibility and volume change of partially saturated soils in connection with the drying or wetting causes a lot of damage in foundation, roads and other structures. It is also observed that many shallow slope failures involve a slumping (collapse) type of failure. As such, the development of extended soil mechanics, which embraces the soil in the unsaturated state or subjected to soil suction, is essential. This study examines the collapsibility and volume change behavior specifically of an unsaturated residual soil under various levels of applied matric suction (ua-uw) and net mean stress (σ-ua) in a predetermined stress path. The volume change of the soil is found to be sensitive to both the applied matric suction and net mean stress. The soil is found to exhibit a collapsibility behavior upon a reduction in applied matric suction at constant net mean stress.
  Thamer Ahmed Mohammed , M. Nooshin , Megat Johari Megat Mohd. Noor and A. Liaghat
  Problem Statement: Nitrogen fertilizer is recognized as an important factor in crop’s yield level, however more application of N fertilizers in the soil have some adverse effects on environment and especially on ground water contamination. Perception and recognition the factors influencing nitrate transport through soil profile is helpful for fertilizer management to minimize adverse impacts on environment and nitrate leaching below the root zone. Approach: In this study, 9 large cylindrical lysimeters with 1 m height and 0.5 m diameter were filled with clay loam soil and planted with maize to investigate nitrate leaching under different types of N-fertilizer, chemical fertilizer, activated sludge and organic manure. Nitrate concentration in the soil and drainage water samples were analyzed by spectrophotometer method and the mass of nitrate was calculated in soil and drainage water. Crop productions for different treatments were compared too. Results: Results showed that cumulative mass of nitrate leaching from organic fertilizer was greater than the other treatments (229 kg ha-1). Organic manure had the greatest nitrate accumulation in soil (15.17 mg kg-1), which was significantly greater than chemical fertilizer. Conclusions/Recommendations: experimental results showed that manure application could result in NO3--N accumulation increase in the deeper soil profiles compared with activated sludge. Results showed that maize production was significantly higher under activated sludge fertilizer. Observations made in the current study suggested activated sludge fertilizer due to a higher crop production with same level of ground water contamination, especially in clay loam soils.
  Manal M. Abood , Thamer Ahmed Mohammed , Abdul Halim Ghazali , Ahmed Rodzi Mahmud and Lariyah Mohd Sidek
  Sedimentation of impounding reservoirs is a complex phenomenon and it is governed by many factors and these factors are related to river morphology and hydraulics, hydrology of the catchment, catchment characteristics and landuse. Sedimentation of a reservoir is important, because it may affect storage capacity, production of hydropower, navigation, water supply and turbine operation and dam safety. The monitoring of reservoir sedimentation can help to take the precautionary measures for effective maintenance. But, the lack in modern instrumentations, manpower and financial allocations are the main obstacles encountered to implement such monitoring plan. The advancement in mathematical modeling and computer technology can help to overcome these obstacles. There are many mathematical models used to predict the sedimentation in an impounding reservoir. The models can be divided to 1 Dimensional (1D), 2 Dimensional (2D) and 3 Dimensional (3D). In the present study, evaluation of these models is presented with special emphasis on 1D model. The weakness and strength is highlighted and models with accurate prediction are recommended.
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