SIMULATION NUMERIQUE DE L’INFILTRATION EN COLONNE DE SOL AVEC PRISE EN COMPTE DE L’HYSTERESIS

Κατά την αριθμητική προσομοίωση δύο πειραμάτων διυγράνσης σε στήλη εδάφους στο εργαστήριο, (ένα σε μία χονδρή και ένα σε μία λεπτόκοκκη άμμο), εξετάστηκαν οι ακόλουθες περιπτώσεις: επίλυση της εξίσωσης της κατακόρυφης μονοδιάστατης κίνησης του νερού στο έδαφος, με θεώρηση και μη της υστέρησης της σχέσεως μύζησης-υγρασίας. Η καλύτερη σύμπτωση μεταξύ αριθμητικών και πειραματικών αποτελεσμάτων, επιτυγχάνεται στην περίπτωση που η υστέρηση λαμβάνεται υπόψη στην προσομοίωση (εξέλιξη των μετώπων υγρασίας και μύζησης στο έδαφος, καθώς και της καμπύλης αθροιστικού όγκου).Effectuant la simulation numerique de deux essays d’infiltration en colonne de sol au laboratoire (le premier essai correspondant a un sable grossier et le second a un sable fin), deux cas different ont ete etudies: resolution numerique de l’equation du transfert vertical d’eau avec et sans prise en compte de l’hysteresis de la relation succion-teneur en eau. Le meilleur accord entre les resultats numeriques et experimentaux, s’obtient dans le cas ou l’hysteresis est prise en compte dans la simulation (profils hydriques et de succion, volume d’eau infiltre dans le sol)

A field study of the coupled effects of aquifer stratification, fluid density, and groundwater fluctuations on dispersivity assessments

A number of experimental studies have tackled the issue of solute transport parameter assessments either in the laboratory or in the field. But yet, the behavior of a plume in the field under density driven forces, is not well known due to possible development of instabilities. Some field tracer tests on the fate of plumes denser than native groundwater such as those encountered under waste disposal facilities, have pointed out the processes of sinking and splitting at the early stage of migration. The process of dispersion was widely investigated, but the range of dispersivity values obtained from either experimental tests, or numerical and theoretical calculations is still very large, even for the same type of aquifers. These discrepancies were considered to be essentially caused by soil heterogeneities and scale effects. In the meantime, studies on the influence of sinking and fingering have remained more scarce. The objective of the work is to analyze how transport parameters such as dispersivities can be affected by unstable conditions, which lead to plume sinking and fingering. A series of tracer tests were carried out to study under natural conditions, the transport of a dense chloride solution injected in a shallow two-layered aquifer. Two types of experiments were performed: in the first type, source injection was such that the plume could travel downward from one layer to the other of higher pore velocity, and in the second one, the migration took place only in the faster layer. The results suggest some new insights in the processes occurring at the early stages of a dense plume migration moving in a stratified aquifer under groundwater fluctuations, which can be summarized through the following points: (i) Above a stability criterion threshold, a fingering process and a multi modal plume transport take place, but local dispersivities can be cautiously derived, using breakthrough curves matching. (ii) When water table is subject to some cycling or rising, the plume can be significantly distorted in the transverse direction, leading to unusual values of the ratio between longitudinal and transverse dispersivities. (iii) Under stable conditions, for example in the case of straightforward injection in the faster aquifer layer, longitudinal dispersivity is greater than the transverse component as usually encountered, and the obtained transport parameters are closed to macro dispersivity values, which reach their asymptotic limit at very short distances. (iv) The classical scale effect about the varying dispersivity at short distances could be a process mainly due to the distance required for a plume stabilization. (c) 2005 Elsevier Ltd. All rights reserved

Multidimensional B-spline parameterization of the detection probability of PET systems to improve the efficiency of Monte Carlo simulations.

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