Για τον προσδιορισμό της πορομετρικής καμπύλης των γεωυφασμάτων διατίθενται σήμερα τρία πρότυπα (ASTM D6767, EN ISO 12956 και ASTM D4751) που θεωρούνται “διεθνούς” αποδοχής. Το πιο πρόσφατο από αυτά (ASTM D6767) εγκρίθηκε το 2002, ορίζει μέθοδο με βάση τη ροή σε τριχοειδή και αποτελεί το κύριο αντικείμενο της παρούσας διατριβής. Ελέγχθηκαν 52 μη υφασμένα γεωυφάσματα κατασκευασμένα από ίνες πολυπροπυλενίου τόσο κατά ASTM D6767 όσο και κατά EN ISO 12956 (υγρό κοσκίνισμα) και ASTM D4751 (ξηρό κοσκίνισμα). Τα αποτελέσματα που προέκυψαν συγκρίθηκαν τόσο μεταξύ τους όσο και με φυσικές ιδιότητες των γεωυφασμάτων, με τιμές μεγεθών που παρέχουν οι κατασκευαστές αυτών των προϊόντων και με τιμές μεγεθών που υπολογίζονται θεωρητικά. Τα μεγέθη πόρων και οι πορομετρικές καμπύλες που προκύπτουν εργαστηριακά με εφαρμογή κάθε μίας από τις τρεις μεθόδους είναι διαφορετικά. Αυτό οφείλεται στις διαφορετικές παραδοχές ή υποθέσεις κάθε μεθόδου αλλά και στις διαδικασίες που προβλέπει η κάθε μέθοδος. Ειδικότερα, οι δύο βασικές υποθέσεις του προτύπου ASTM D6767 αφορούν τη γωνία επαφής, θ, μεταξύ ρευστού και στερεού (τίθεται ίση με μηδέν) και τη μορφή της διατομής των πόρων των γεωυφασμάτων (κυλινδρική). Λόγω της δομής των μη υφασμένων γεωυφασμάτων οι δύο παραπάνω υποθέσεις δεν είναι δυνατόν να επαληθευθούν. Για τον λόγο αυτό στην εξίσωση προσδιορισμού των μεγεθών πόρων του προτύπου ASTM D6767 εισάγεται διορθωτικός συντελεστής. Από την επεξεργασία των αποτελεσμάτων της παρούσας διατριβής προέκυψε ότι ο συντελεστής αυτός πρέπει να έχει τιμή ίση με 1/3 (για τη συγκεκριμένη συσκευή που χρησιμοποιήθηκε και τις διαδικασίες που εφαρμόστηκαν για την εκτέλεση των δοκιμών) ώστε τα αποτελέσματα να προσεγγίζουν ικανοποιητικά αυτά της δοκιμής κατά EN ISO 12956. / Three internationally accepted standards (ASTM D6767, EN ISO 12956 and ASTM D4751) are available today for determing the pore size distribution of geotextiles. The most recently approved standard (2002) is ASTM D6767 which defines a method based on capillary flow. Laboratory testing according to this standard is the main subject of this thesis. Fifty two nonwoven geotextiles, made of polypropylene fibers, were tested according to the three standardized methods (ASTM D6767, EN ISO 12956 – wet sieving and ASTM D4751 – dry sieving). Comparisons were made between the results obtained from each standardized method as well as between measured pore sizes and geotextile physical properties, manufacturer provided pore sizes and values obtained theoretically. Different pore sizes and pore size distribution curves are obtained when different laboratory standard methods are applied. This is due to the different assumptions on which each method is based and also due to the procedures that each method specifies. The two main assumptions of the Standard ASTM D6767 concern the contact angle, θ, between liquid and solid (equal to zero) and the pore shapes of the geotextiles (cylindrical). Due to the structure of the nonwoven geotextiles the effect of these assumptions is different to quantify. Accordingly, the computation of pore sizes according standard ASTM D6767 is based on the introduction of a correction coefficient in the pertinent equation. The results obtained during this correction coefficient should have a value equal to 1/3 for the particular device used and the procedures applied. Use of this correction coefficient fields results that approximate very well the results obtained from wet sieving tests according to Standard EN ISO 12956.

Made available in DSpace on 2017-07-21T19:26:10Z (GMT). No. of bitstreams: 1 Jocenei Antonio Oliveira.pdf: 2309316 bytes, checksum: 8527d62e93fbe03d332c4ffaa65aedda (MD5) Previous issue date: 2014-06-10 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Soil water retention properties can be described by so-called soil-water characteristic curve (SWCC) or retention curve (WRC). This curve expresses the relationship between matric potential and soil moisture based on weight or volume. Through the attainment and subsequent analytical interpolation of the WRC, it’s possible the indirect estimative of the pore-size distribution (PSD) curve of any porous system. Sometimes, obtaining the WRC may be a time-consuming process or involve the use of equipment not available in some laboratories. Thus the development of an alternative method to obtain the WRC and after the PSD becomes desirable, since these are properties of extreme importance to characterize porous media. The main objective of this study is to create and adapt methodology for obtaining PSD using computer simulation in tomographic images with micrometer resolution. In this study, there were used samples of sand and glass beads of different grain sizes for the generation of the PSD curve using a Haines’ funnel on balance. After WRC achievement, these were adjusted through an analytical model and then there were built experimental PSD curve. PSD were also determined by adaptation of a computer program using tomographic images of these samples. The results of obtained WRC associated with geometric models to predict the entry point of air have only revealed the idea about how may occur drying of the samples, showing only morphological considerations are not sufficient to describe this situation. The investigated porous systems homogeneity was able to be visualized by comparing the PSD curves in terms of their widths. / Propriedades de retenção da água no solo podem ser descritas pela chamada curva característica de água no solo ou curva de retenção (CR). Esta curva exprime a relação entre potencial mátrico e a umidade do solo à base de massa ou volume. Mediante o levantamento da CR e posterior interpolação analítica, pode-se estimar indiretamente a curva de distribuição de poros (CDP) de um sistema poroso qualquer. Algumas vezes, a obtenção da CR pode ser um processo demorado ou envolver a utilização de equipamentos não disponíveis em alguns laboratórios. Desta forma, o desenvolvimento de uma metodologia alternativa para a obtenção da CR e posteriormente da CDP se faz desejável, uma vez que se trata de propriedade de extrema importância para a caracterização de um meio poroso. O objetivo principal deste trabalho é criar e adaptar metodologia para a obtenção de CDPs utilizando simulação computacional em imagens tomográficas com resolução micrométrica. No presente estudo, foram utilizadas amostras de areias e esferas de vidro de diferentes granulometrias para o levantamento das CRs usando um funil de Haines adaptado. Depois de obtidas as CRs, essas foram ajustadas através do modelo de ajuste de van Genuchten e obtidas as CDPs (primeira derivada da CR). Também foram obtidas CDPs mediante a adaptação de um programa computacional que utiliza informações de imagens tomográficas dessas amostras. Os resultados das CDPs levantadas pelos dois métodos mostram alguma concordância. Verificou-se, no entanto, que apenas considerações sobre a morfologia dos poros não são suficientes para descrever a forma com que as amostras são drenadas.