Résumé Vertisols cover a hydrologically very significant area of semi-arid regions, and thus understanding of water flow and solute accumulation is very relevant to agricultural activity and water resources management. Previous works suggest a conceptual model of desiccation-crack-induced salinization where salinization of sediment in deep section of the vadose zone (up to 4 m) is induced by subsurface evaporation due to convective air flow in desiccation cracks. This thesis presents a conceptual model of water flow and solute transport in vertisols, and its numerical implementation. The model uses a single-porosity material but unconventionally prescribes a boundary condition representing a deep crack in soil and uses the unsaturated hydraulic conductivity as one of the fitting parameters. The numerical model is bound to one location close to a dairy farm waste pond, but the application of the suggested conceptual model could be possibly extended to all semi-arid regions with vertisols. Simulations were conducted using several modelling approaches with an ultimate goal of fitting the simulation results to the controlling variables measured in the field : water content, and chloride salinity of pore water. The development of the model was engineered in numerous steps ; all computed as forward solutions by trial-and-error approach. The crack boundary condition allows chloride to accumulate due to subsurface evaporation on the crack wall, and subsequently rainwater pushes the solute further down the sediment. In order to prescribe the suggested function, HYDRUS 2D/3D code had to be modified by its developers. The main fitting parameters were : the saturated hydraulic conductivity and infiltration distribution of rainwater. The model supports previous findings that significant amount (more than 80%) of water from rain events must infiltrate through the crack rather than through land surface, and that the desiccation cracks are responsible for more than 70% of overall actual evaporation. It was also noted that infiltration from the crack has to be increasing with depth and that the highest infiltration rate should be between 1-3 m below land surface. In conclusion, this thesis supports previous findings about vertisols : especially, the utmost importance of soil cracks as preferential pathways for both water and contaminants, and soil cracks as deep evaporators
hydrus 2d 3d crack in 14
Mots clés : desikační trhliny, salinizace, preferenčni tok, koncepční model, nesaturovaná zóna, vertisol, retenční křivka, HYDRUS, podpovrchový výpar, semiaridní klima, modelování ; desiccation crack, salinization, subsurface evaporation, semi-arid climate, preferential flow, numerical model, vadose zone, vertisols, retention curve, HYDRUS, modelling
The article presents a hybrid monitoring technique for the measurement of the deformation field. The goal is to obtain information about crack propagation in existing structures, for the purpose of monitoring their state of health. The measurement technique is based on the capture and analysis of a digital image set. Special markers were used on the surface of the structures that can be removed without damaging existing structures as the historical masonry. The digital image analysis was done using software specifically designed in Matlab to follow the tracking of the markers and determine the evolution of the deformation state. The method can be used in any type of structure but is particularly suitable when it is necessary not to damage the surface of structures. A series of experiments carried out on masonry walls of the Oliverian Museum (Pesaro, Italy) and Palazzo Silvi (Perugia, Italy) have allowed the validation of the procedure elaborated by comparing the results with those derived from traditional measuring techniques. PMID:28773129
The article presents a hybrid monitoring technique for the measurement of the deformation field. The goal is to obtain information about crack propagation in existing structures, for the purpose of monitoring their state of health. The measurement technique is based on the capture and analysis of a digital image set. Special markers were used on the surface of the structures that can be removed without damaging existing structures as the historical masonry. The digital image analysis was done using software specifically designed in Matlab to follow the tracking of the markers and determine the evolution of the deformation state. The method can be used in any type of structure but is particularly suitable when it is necessary not to damage the surface of structures. A series of experiments carried out on masonry walls of the Oliverian Museum (Pesaro, Italy) and Palazzo Silvi (Perugia, Italy) have allowed the validation of the procedure elaborated by comparing the results with those derived from traditional measuring techniques.
Objectives To demonstrate the effectiveness of in vivo replicas of fractured ceramic surfaces for descriptive fractography as applied to the analysis of clinical failures. Methods The fracture surface topography of partially failed veneering ceramic of a Procera Alumina molar and an In Ceram Zirconia premolar were examined utilizing gold-coated epoxy poured replicas viewed using scanning electron microscopy. The replicas were inspected for fractographic features such as hackle, wake hackle, twist hackle, compression curl and arrest lines for determination of the direction of crack propagation and location of the origin. Results For both veneering ceramics, replicas provided an excellent reproduction of the fractured surfaces. Fine details including all characteristic fracture features produced by the interaction of the advancing crack with the material's microstructure could be recognized. The observed features are indicators of the local direction of crack propagation and were used to trace the crack's progression back to its initial starting zone (the origin). Drawbacks of replicas such as artifacts (air bubbles) or imperfections resulting from inadequate epoxy pouring were noted but not critical for the overall analysis of the fractured surfaces. Significance The replica technique proved to be easy to use and allowed an excellent reproduction of failed ceramic surfaces. It should be applied before attempting to remove any failed part remaining in situ as the fracture surface may be damaged during this procedure. These two case studies are intended as an introduction for the clinical researcher in using qualitative (descriptive) fractography as a tool for understanding fracture processes in brittle restorative materials and, secondarily, to draw conclusions as to possible design inadequacies in failed restorations. PMID:17270267
Lalonde, Sébastien et Guilbault, Raynald. 2008. A new and efficient approach for boundary element 2D crack modeling . In Canadian Society for Mechanical Engineering Forum (CSME) (Ottawa, ON, Canada, June 5-8, 2008)
Perraton, Daniel, Guissi, G., Pierre, P. et Doré, G.. 2008. A new laboratory test for reflective cracking in mode I and/or II . In Pavement cracking mechanisms, modeling, detection, testing and case histories : proceedings of the 6th RILEM International Conference on Cracking in Pavements : Chicago, USA, 16-18 June 2008 (Chicago, IL, USA, June 16-18, 2008)pp. 447-456. Boca Raton : CRC Press. 2ff7e9595c
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