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

Yıl 2019, Sayı: 16, 460 - 470, 31.08.2019

Uğur Şafak Çavuş Murat Kilit

https://doi.org/10.31590/ejosat.549123

Öz

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.

Anahtar Kelimeler

Kaya Dolgu Baraj, Geomembrane Kaplama, Şev Stabilitesi, Zamanla Değişen Akım

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

Öz

This paper presents stability and seepage evaluation of a high rockfill
dam with a geomembrane seepage barrier by considering scenarios of a possible
occurrence of a large earthquake due to the active faults in the region and
also a seepage flow in the dam due to a possible rupture of the geomembrane
liner. For this purpose, finite element transient seepage and pseudo static
slope stability analyses 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 seepage analyses method which is essentially important to determine
the time dependent variations of seepage paths and water pressures within the
rockfill as well. In the analyses, it was determined that the most critical
slope failure case is when a geomembrane liner tears at the time of the highest
reservoir water elevation since the hydraulic head is maximum and causes the
largest seepage pressure in the rockfill there. 
Analyses showed that if a strong earthquake struck the region, both the
upstream and downstream slopes are safe with sufficiently high safety factors.
In addition, in case of a possible tear and leakage on the geomembrane liner,
the dam will also withstand well with 2.25 horizontal to 1 vertical slopes.
However, it is recommended that constructing a downstream toe drain or a relief
well will provide an additional safety measure against any heave occurrence or
instability of the rockfill since the embankment and bedrock foundation are
pervious causing high seepage pressures at the downstream toe of the dam.  

Anahtar Kelimeler

Rockfill Dam, Geomembrane Liner, Slope Stability, Transient Flow

Kaynakça

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