Ön Yüzü Geomembran Kaplı Yüksek Bir KayaDolgu Barajın Deprem ve Geomembranda Yırtık Olması Durumunda Performansının Değerlendirilmesi

Bu makale sızmaya karşı ön yüzü geomembran ile kaplı yüksek bir kaya dolgu barajın deprem olması veya geomembran kaplamada olası bir yırtık olması nedeniyle baraj gövdesinde sızma oluşması durumlarına karşılık stabilite ve sızma analizlerine dayalı barajın performasını ve güvenliğini değerlendirmektedir. Bu nedenle, sonlu elemanlar zamana bağlı değişen sızma analizi ve şev stabilite analizi baraj gövdesindeki kritik kayma yüzeylerini ve güvenlik değerlerini belirlemek için gerçekleştirilmiştir. İlk olarak baraj gövdesindeki suyun sızma yolları ve kayma yüzeylerine etki eden boşluk suyu basınçları zamanla değişen akım hali için numerik sızma analizleri yapılarak belirlenmiştir. Şev stabilitesi açısından kritik durumun, geoemembrandaki yırtığın rezervuar tamamen dolu halde iken nss seviyesinde oluştuğu tespit edilmiştir. Çünkü bu durumda, baraj gövdesinde hidrolik su yüksekliği ve buna bağlı kaya dolguda su sızma basınçları maksimum olmaktadır. Analiz sonuçları göstermiştir ki eğer barajın bulunduğu bölgeye kuvvetli bir deprem etkirse, barajın memba ve mansap şevleri, yüksek güvenlik faktörleri ile kaymaya karşı yeterince güvenli bulunmaktadır. Ayrıca, eğer geomembrane kaplamada bir hasar neticesinde yırtık oluşursa, barajın mansap şevi 2.25 yatay 1 düşey eğimiyle yine yeterince stabil olacağı görülmüştür. Fakat hem kaya dolgu hem de baraj gövdesi altındaki kayaç geçirimli olduğundan, geomembranda bir sızma olursa barajın temelinden sızan suların basıncının sönümlendirilmesi ve güvenle barajın topuğundan uzaklaştırılması amacıyla baraj mansap topuğunda dren veya basınç sönümlendirici bir kuyu tasarlanması tavsiye edilmektedir.

Performance Evaluation of A High Geomembrane Faced Rockfill Dam In Case of Liner Rupture and Earthquake Risks

This paper presents stability and seepage evaluation of a high rockfill dam with a geomembrane seepage barrier by consideringscenarios of a possible occurrence of a large earthquake due to the active faults in the region and also a seepage flow in the dam dueto a possible rupture of the geomembrane liner. For this purpose, finite element transient seepage and pseudo static slope stabilityanalyses were both carried out together to assess the critical potential failure surfaces and safety factors of the rockfill slopes.Therefore, pore water pressures on the failure surfaces were first calculated using the time varying (transient) numerical seepageanalyses method which is essentially important to determine the time dependent variations of seepage paths and water pressureswithin the rockfill as well. In the analyses, it was determined that the most critical slope failure case is when a geomembrane linertears at the time of the highest reservoir water elevation since the hydraulic head is maximum and causes the largest seepage pressurein the rockfill there. Analyses showed that if a strong earthquake struck the region, both the upstream and downstream slopes are safewith sufficiently high safety factors. In addition, in case of a possible tear and leakage on the geomembrane liner, the dam will alsowithstand well with 2.25 horizontal to 1 vertical slopes. However, it is recommended that constructing a downstream toe drain or arelief well will provide an additional safety measure against any heave occurrence or instability of the rockfill since the embankmentand bedrock foundation are pervious causing high seepage pressures at the downstream toe of the dam.

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