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

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

Abstract

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.  

Keywords

• Rockfill Dam,Geomembrane Liner,Slope Stability,Transient Flow

References

1. Koerner , R. M., & Wilkes, J. A. (2012). 2010 ICOLD Bulletin on Geomembrane Sealing Systems for Dams. Geosynthetics.
2. ICOLD. (2010). Geomembrane Sealing Systems for Dams - Design Principles and Return of Experience.Bulletin 135. France.
3. ICOLD. (2011). Small Dams-design, Surveillance and Rehabilitation. International Commission on Large Dams, Bulletin 143. France.
4. Bhowmik, R., Shahu, J., & Datta, M. (2017). Failure analysis of a geomembrane lined reservoir embankment. Geotextiles and Geomembranes, vol. 46, p. 52-65.
5. Poulain, D., Peyras, L., & Meriaux, P. (2011). Feedback and guidelines for geomembrane lining systems of mountain reservoirs in France. Geotextiles and Geomembranes, Vol. 29, p. 415-424.
6. Mendoza, C., Gisbert, A., Izquierdo, A., & Bovea, M. (2009). Safety factor nomograms for homogeneous earth dams less than ten meters high. Engineering Geology, vol. 105, p. 231-238.
7. Tolooiyana, A., Abustana, I., Selamata, M., & Ghaffari, S. (2009). A comprehensive method for analyzing the effect of geotextile layers on embankment stability. Geotextiles and Geomembranes, Vol.27, p. 399-405.
8. Briancon, L., H., G., & D., P. (2002). Slope stability of lining systems- experimental modelling of friction at geosynthetic interface. Geotextiles and geomembranes, Vol. 20, P. 147-172.

9. Earth, G. (2019). 3 3, 2019 tarihinde Google Earth: http://www. google.com.tr/int/tr/earth adresinden alındı
10. Erlingsson, S., & Hauksson, D. R. (2009). Analysis of a geomembrane face rockfill dam during earthquake loading. Proceedings of the 17th International Conference on Soil Mechanics and Geotechnical Engineering, p. 1678-1681.
11. Jones, D. R., & Dixon, N. (2003). Stability of Landfill Lining Systems: Report No. 1. R&D Technical Report P1-385/TR1. Research Contractor: Golder Associates (UK) Ltd. In conjunction with Loughborough University Consultants Ltd.
12. MTA-Turkey. (2016). Dinar active fault map. http://www.mta.gov.tr/v2.0/default.php?id=yeni_diri_fay_haritalari: http://www.mta.gov.tr/v2.0/default.php?id=yeni_diri_fay_haritalari adresinden alınmıştır
13. Gülkan, P., & Kalkan, E. (2002). Attenuation modeling of recent earthquakes in Turkey. Journal of Seismology, Vol. 6, p. 397-409.
14. Giroud, J. a. (1989). Leakage through liners constructed with geomembranes – Parts I and II. Geotextiles and Geomembranes, 8(1-2), p. 27-67 and 71-111.
15. Giroud, J. P. (1997). Equations for calculating the rate of liquid migration through composite liners due to geomembrane defects. Geosynthetics International, Vol. 4(3-4), p. 335-348.
16. Foose, G. J., Benson, C. H., & Edil, T. B. (2001). Predicting leakage through composite landfill liners. Journal of Geotechnical and Geoenvironmental Engineering, ASCE, Vol. 127(6), p. 510-520.
17. Touze-Foltz, N., & Giroud, J. P. (2005). Empirical equations for calculating the rate of liquid flow through composite liners due to large circular defects in the geomembrane. Geosynthetics International, Vol.12 No.1, p. 205-207.
18. Girard, H., Fischer, S., & Alonso, E. (1990). Problems of friction posed by the use of geomembranes on dam slopes-examples and measurements. Geotext. Geomembranes, Vol. 9, p. 129-143.
19. Wu, W., Wang, X., & Aschauer, F. (2008). Investigation on failure of a geosynthetic lined reservoir. Geotexit and Geomembranes, Vol. 26, p.363-370.
20. Moraci, N., Cardile, G., Gioffrè, D., Mandaglio, M. C., Calvarano, L. S., & Carbone, L. (2014). Soil geosynthetic interaction: Design parameters from experimental and theoretical analysis. Transportation. Infrastructure. Geotechnology., p. 165-227.
21. Weber, C. T. (2008). Leakage through defects in geomembrane liners under high hydraulic heads. Texas: The University of Texas at Austin.
22. Weber, C. T., & Zornberg, J. (2008). Numerical analysis of leakage through geomembrane lining systems for dams. The First Pan American Geosynthetics Conference & Exhibition. Cancun, Mexico.
23. SLIDE. (2010-2016). Comprehensive slope stability analysis software. Rocscience Inc., 39 University Ave Ste 780 Toronto, Ontario M5G 1Y8.
24. Leps, T. (1970). Review of the shearing strength of rockfill. J. of Soil Mech. and Found. Div., Vol. 96(SM4), p. 1159-1170.
25. Barton, N., & Kjærnsli, B. (1981). Shear strength of rockfill. J. of the Geotech. Eng. Div., Vol. 107(GT7), p. 873-891.
26. Marachi, N. D., Chan, C. K., & Seed, H. B. (1972). Evaluation of properties of rockfill materials. J. Soil Mech. Found. Div., Vol. 98(SM1), p. 95-114.
27. Eurocode, 7. (2013, June 13-14). Geotechnical Design. Dublin.
28. Bishop, A. W. (1955). The Use of the slip circle in the stability analysis of slope. Geotechnique, Vol. 5, P. 7-17.
29. Charbeneau, R. J. (2000). Groundwater .hydraulics and pollutant transport. New Jersey: Prentice Hall.