Biyopolimer Katkılı Geosentetik Kil Örtülerde İçsel Erozyon ile Permitivite Tayini

Abstract

Geosentetik kil örtü (GKÖ), düşük hidrolik iletkenliği sayesinde tatlı su rezervuarlarında kaplama malzemesi olarak kullanılabilmektedir. GKÖ üzerinde birikebilecek yüksek seviyedeki su, GKÖ içerisindeki bentonitin geotekstillerin arasından sıyrılarak ani hidrolik iletkenlik artışıyla malzemenin kullanılamaz hale gelmesine neden olabilir. Bu etkileşime içsel erozyon denilmektedir. Bu çalışmada GKÖ’nün bentonit bileşenine sırasıyla ağırlıkça %0.25, 0.5, 1, 2, 5 ve 10 oranlarında kitosan ile Na karboksimetil selüloz biyopolimerleri eklenerek üç eksenli hidrolik iletkenlik deneyleri yapılmıştır. GKÖ içerisinde Na ve Ca içerikli iki farklı bentonit kullanılmış olup içsel erozyonu gözlemleyebilmek için GKÖ’ler, dane boyutu 37.5 mm olan iri daneli yuvarlak çakılların üzerine serilerek yüksek hidrolik yükler altında test edilmişlerdir. Bu koşul, karşılaşılabilecek en kötü senaryolardan birini temsil etmektedir. Deney sonuçlarına göre 10 m’lik hidrolik yük altında test edilen bütün GKÖ’lerde içsel erozyon gözlemlenmiştir. Ayrıca içsel erozyondan hemen önce ölçülen permitivite değerleri karşılaştırılarak kullanılan biyopolimerlerin, GKÖ’lerin hidrolik performansını ne ölçüde değiştirdiği araştırılmıştır. Sonuçlara göre GKÖ’lerdeki bentonite %1 kitosan ve %2 selüloz eklenmesi, GKÖ’lerin permitivitesini 2 mertebeden daha yüksek oranda azaltmıştır. Böylelikle çevre dostu, organik katkı malzemesi olan iki farklı biyopolimerin çevre geotekniği uygulamalarında kaplama malzemesinin hidrolik iletkenliğini azaltmasına bağlı olarak bariyer amaçlı kullanımı teşvik edilebilecektir.

Keywords

• Geosentetik Kil Örtü
• İçsel Erozyon
• Karboksimetil Selüloz
• Kitosan
• Permitivite

Determination of Internal Erosion and Permittivity of Biopolymer-Added Geosynthetic Clay Liners

Abstract

Geosynthetic clay liner (GCL) can be used as a lining material in freshwater reservoirs due to its very low hydraulic conductivity. The high amount of water that can be collected on top of a GCL might force the bentonite in the GCL to be extruded out of the geotextiles and as a result, the sudden increase in the hydraulic conductivity might cause the GCL to loose its hydraulic capability. This interaction is defined as internal erosion. In this study, triaxial permeability tests were conducted on chitosan and Na carboxymethyl cellulose-added GCLs. These two biopolymers were added to the bentonite component of the GCLs with a content of 0.25, 0.5, 1, 2, 5 and 10% by dry weight respectively. Na and Ca bentonites were used in the GCLs and the GCLs that were placed over a rounded coarse gravel with a grain size of 37.5 mm, were tested at high hydraulic heads in order to observe internal erosion. This condition represents one of the worst-case scenarios. Test results indicated that all of the GCLs experienced internal erosion at a hydraulic head of 10 m. Furthermore, the permittivity values of the GCLs just before internal erosion, were measured and the effects of the biopolymers on the GCL’s hydraulic performance were investigated. According to the test results, 1% chitosan and 2% Na carboxymethyl cellulose addition to the bentonite component of the GCLs resulted in more than 2 orders of magnitude decrease in permittivity. Due to the results of this study, the usage of two different biopolymers that are environmentally friendly organic additives can be encouraged to be used as barriers in geoenvironmental application by decreasing the hydraulic conductivity of the lining material.

Keywords

• Carboxymethyl Cellulose
• Chitosan
• Geosynthetic Clay Liner
• Internal Erosion
• Permittivity

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