The Experts below are selected from a list of 38445 Experts worldwide ranked by ideXlab platform
Asaf Pekdeger - One of the best experts on this subject based on the ideXlab platform.
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the impact of variable temperatures on the redox Conditions and the behaviour of pharmaceutical residues during artificial recharge
2006Co-Authors: Gudrun Massmann, Janek Greskowiak, Uwe Dunnbier, S Zuehlke, Andrea Knappe, Asaf PekdegerAbstract:Summary The redox Conditions below an artificial recharge pond in Berlin were largely dependent on seasonal temperature changes of 0–24 °C in the infiltrate. Aerobic Conditions prevailed in winter, when temperatures were low, while anaerobic Conditions were reached below the pond when temperatures exceeded 14 °C. In contrast to temperature changes, cyclic changes between saturated or Unsaturated Conditions below the pond had only a minor effect on the redox Conditions. However, the intrusion of gaseous oxygen during Unsaturated Conditions caused a temporary reinforced increase in oxidation of particulate organic matter. The effect of variable redox Conditions on the behaviour of a number of pharmaceutically active compounds, namely carbamazepine, phenazone and several phenazone-type PhACs, was investigated. Phenazone is redox sensitive and was generally fully degraded before reaching the first groundwater well, as long as oxygen was present. When Conditions turned anaerobic, phenazone was not fully eliminated. 1-Acetyl-1-methyl-2-dimethyl-oxymoyl-2-phenylhydrazide (AMDOPH) and carbamazepine are very persistent drug residues. However, results suggest that AMDOPH may be slightly degradable under aerobic Conditions too, but further studies will be needed to verify this statement.
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the impact of variably saturated Conditions on hydrogeochemical changes during artificial recharge of groundwater
2005Co-Authors: Janek Greskowiak, Gunnar Nützmann, C D Johnston, Gudrun Massmann, Henning Prommer, Asaf PekdegerAbstract:Artificial recharge of groundwater is often used to either purify partially treated wastewater or to enhance the quality of surface water by percolation through a variably saturated zone. In many cases, the most substantial purification process within the infiltration water is the redox-dependent biodegradation of organic substances. The present study was aimed at understanding the spatial and temporal distribution of the redox reactions that develop below an artificial recharge pond near Lake Tegel, Germany. At this site, like at many artificial recharge sites, the hydraulic regime immediately below the pond is characterised by cyclic changes between saturated and Unsaturated Conditions. These changes, which occur during each operational cycle, result from the repeated formation of a clogging layer at the pond bottom. Regular hydrogeochemical analyses of groundwater and seepage water in combination with continuous hydraulic measurements indicate that NO3-- and Mn-reducing Conditions dominate beneath the pond as long as water-saturated Conditions prevail. Manganese-, Fe- and SO42--reducing Conditions are confined to a narrow zone directly below the clogging layer and in zones of lower hydraulic conductivity. The formation of the clogging layer leads to a steady decrease of the infiltration rate, which ultimatively causes a shift to Unsaturated Conditions below the clogging layer. Atmospheric O2 then starts to penetrate from the pond fringes into this region, leading to: (i) the re-oxidation of the previously formed sulphide minerals and (ii) the enhanced mineralisation of sedimentary particulate organic C. The mineralisation of sedimentary particulate organic C leads to an increased H2CO3 production and subsequent dissolution of calcite.
Jianfu Shao - One of the best experts on this subject based on the ideXlab platform.
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elastoplastic damage modelling of argillite in partially saturated condition and application
2007Co-Authors: Yun Jia, X C Song, G Duveau, Jianfu ShaoAbstract:This paper presents an elastoplastic damage model for argillites in Unsaturated and saturated Conditions. A short resume of experimental investigations is presented in the first part. Based on experimental data and micromechanical considerations, a general constitutive model is proposed for the poromechanical behavior of argillite in both saturated and Unsaturated Conditions. The proposed model is formulated within the framework of poroplasticity and continuum damage mechanics. Main features observed in experimental data are taken into account, in particular the elastic degradation due to microcracks, coupling between plastic deformation and induced damage, influence of water saturation on plastic flow and damage evolution, as well as variation of permeability with induced damage. The performance of the model is examined by comparing numerical simulation with test data in representative load paths. Finally, the model is applied to a hydromechanical coupling analysis of a cavity subjected to excavation and ventilation.
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a coupled elastoplastic damage model for semi brittle materials and extension to Unsaturated Conditions
2006Co-Authors: Jianfu Shao, Yun Jia, Djimedo Kondo, Annesophie ChiarelliAbstract:In this paper, a coupled elastoplastic damage model is proposed for semi-brittle materials. This model is applied to a specific semi-brittle sedimentary rock material. A brief account of experimental investigations is presented in the first part. The data obtained show an important plastic deformation coupled with stress-induced damage corresponding to initiation and growth of microcracks. Influences of mineral compositions and water content on the mechanical behaviour are also investigated. Based on these experimental evidences, the general formulation of the model is presented in the second part of the paper. The effective elastic properties of isotropic damaged material are determined based on relevant considerations from micromechanics. Damage evolution law and plastic damage coupling are described by using the framework of irreversible thermodynamics. A non-associated plastic flow rule is used. The model is extended to partially saturated Conditions in order to study coupled hydromechanical behaviours in drying–wetting processes. Comparisons between numerical simulations and test data are performed for various loading paths. It is shown that the proposed model is able to describe the main features of mechanical behaviour observed in this class of materials.
M B Jogi - One of the best experts on this subject based on the ideXlab platform.
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shear strength of geomembrane soil interface under Unsaturated Conditions
2006Co-Authors: I R Fleming, Jitendra Sharma, M B JogiAbstract:Abstract Interface shear tests on non-textured geomembrane–soil interfaces were performed using a modified direct shear apparatus installed with a miniature pore pressure transducer (PPT). Using the PPT, pore-water pressure changes in the vicinity of geomembrane–soil interface were measured during shear, thus making it possible to analyse test results in terms of effective stresses. When plotted in terms of total stresses, interface shear strength envelopes, consistent with those published in the literature, were obtained. However, the results were difficult to interpret using effective stresses, particularly those obtained at high normal stresses. It was found that at low normal stress values the shear strength of a geomembrane–soil interface in terms of effective stresses could be predicted using Unsaturated soil mechanics concepts. At high normal stresses, it was found that the failure mechanism changed from soil particles sliding at the surface of the geomembrane to soil particles becoming embedded into the geomembrane and plowing trenches along the direction of shear. A plowing failure mechanism resulted in the mobilization of significantly higher shear strength at the geomembrane–soil interface. It was found that at higher placement water content for the soil, near saturated Conditions prevail at the geomembrane–soil interface, resulting in lower effective stresses, a shallower plowing mechanism and lower values of mobilized interface shear strength.
Daichao Sheng - One of the best experts on this subject based on the ideXlab platform.
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From saturated to Unsaturated Conditions and vice versa
2018Co-Authors: Martí Lloret-cabot, Simon J. Wheeler, Jubert A. Pineda, Enrique Romero, Daichao ShengAbstract:Representing transitions between saturated and Unsaturated Conditions, during drying, wetting and loading paths, is a necessary step for a consistent unification between saturated and Unsaturated soil mechanics. Transitions from saturated to Unsaturated Conditions during drying will occur at a nonzero air-entry value of suction, whereas transitions from Unsaturated to saturated Conditions during wetting or loading will occur at a lower nonzero air-exclusion value of suction. Air-entry and air-exclusion values of suction for a given soil will differ (representing hysteresis in the retention behaviour) and both are affected by changes in the dry density of the soil or by the occurrence of plastic volumetric strains. The paper demonstrates, through model simulations and comparison with experimental data from the literature (covering drying, wetting and loading tests), that the Glasgow Coupled Model (GCM), a coupled elasto-plastic constitutive model covering both mechanical and retention behaviour, represents transitions between Unsaturated and saturated behaviour in a consistent fashion. Key aspects of the GCM are the use of Bishop’s stress tensor for mechanical behaviour, the additional influence of degree of saturation on mechanical yielding, inclusion of hysteresis in the retention behaviour, and the role of plastic volumetric strains (and not total volumetric strains) in the description of the water retention response. The success of the GCM in representing consistently transitions between saturated and Unsaturated Conditions, together with subsequent mechanical and retention responses, demonstrates the potential of this coupled constitutive model for numerical modelling of boundary value problems involving saturated and Unsaturated Conditions.
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development of a model test system for studying the behaviour of a compaction grouted soil nail under Unsaturated Conditions
2017Co-Authors: Qiong Wang, Xinyu Ye, S W Sloan, Shanyong Wang, Daichao ShengAbstract:A laboratory model test system was developed to study grouted nail-soil interactions under Unsaturated Conditions. A large soil specimen (730 mm high, 600 mm wide, and 1,000 mm long) was used in the installation of soil nails and sensors with minimal boundary effects. Sensors for measuring earth pressure, soil suction, and volumetric water content (dry density) were buried inside the soil specimen at different locations. Other sensors for measuring grouting pressure, pull-out displacement, and pull-out force were installed in the loading system. A loading and linear guide system was designed to apply a uniform overburden pressure using an air-filled rubber bag, which also simultaneously measured the soil surface displacement. Stockton Beach sand was studied and compacted in the box in layers. After application of the overburden pressure, a grouted nail was installed by injecting grout into a specially designed latex balloon. Pull-out testing was conducted seven days after grouting, which allowed the grout to cure to a suitable strength. The results obtained are presented in terms of the evolution of displacement, earth pressure, suction, dry density, and pull-out force. The recorded data were analysed to explore the earth pressure and density gradient of the surrounding soil. The quality of the results obtained demonstrates the performance of the developed testing system. The results can be further analyzed for theoretical and numerical developments involving compaction-grouted soil nails.
Maria Auset - One of the best experts on this subject based on the ideXlab platform.
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a review of visualization techniques of biocolloid transport processes at the pore scale under saturated and Unsaturated Conditions
2007Co-Authors: Arturo A Keller, Maria AusetAbstract:Abstract Field and column studies of biocolloid transport in porous media have yielded a large body of information, used to design treatment systems, protect water supplies and assess the risk of pathogen contamination. However, the inherent “black-box” approach of these larger scales has resulted in generalizations that sometimes prove inaccurate. Over the past 10–15 years, pore scale visualization techniques have improved substantially, allowing the study of biocolloid transport in saturated and Unsaturated porous media at a level that provides a very clear understanding of the processes that govern biocolloid movement. For example, it is now understood that the reduction in pathways for biocolloids as a function of their size leads to earlier breakthrough. Interception of biocolloids by the porous media used to be considered independent of fluid flow velocity, but recent work indicates that there is a relationship between them. The existence of almost stagnant pore water regions within a porous medium can lead to storage of biocolloids, but this process is strongly colloid-size dependent, since larger biocolloids are focused along the central streamlines in the flowing fluid. Interfaces, such as the air–water interface, the soil–water interface and the soil–water–air interface, play a major role in attachment and detachment, with significant implications for risk assessment and system design. Important research questions related to the pore-scale factors that control attachment and detachment are key to furthering our understanding of the transport of biocolloids in porous media.
