STABILITY ANALYSIS OF AN EMBANKMENT DAM DURING RAPID DRAWDOWN OF WATER IN RESERVOIR

Abstract

This paper focuses on stability analysis carried out on fictional embankment dam with clay core on impervious bed and calculating results using SLIDE V.6.0 and PLAXIS softwares. The stability of embankment slopes was checked by five different analysis methods: Fellenuis, Bishop, Janbu, Morgenstern-Price and Spencer methods respectively. It is assumed that rapid drawdown rate 3m/day and reservoir water level falling down to 3 m within 8 days. The stability of the upstream slope of the dam decreased dramatically but still in stable during drawdown condition. The factor of safety was greater than 1.3 for all reservoir condition. It was concluded that the factor of safety against sliding of the dam slopes decreases slightly within the short period after the start of rapid drawdown of water in the reservoir, then starts to increase. This is caused by dissipation of excess pore water pressure with time which leads to increase the effective stresses in the soil and hence increase its shear strength.

Keywords

• Slide
• Embankment Dam
• Rapid Drawdown
• Stability.

BİR DOLGU BARAJIN REZERVUARINDAKİ SUYUN ANİ ÇEKİLMESİ SIRASINDAKİ STABİLİTE ANALİZİ

Abstract

Bu çalışma, geçirimsiz yatak üzerinde kil çekirdekli kurgusal dolgu barajının stabilite analizine ve SLIDE V.6.0 ve PLAXIS yazılımları kullanılarak sonuçların hesaplanmasına odaklanmaktadır. Dolgu şevlerinin stabilitesi beş farklı analiz yöntemi ile kontrol edilmiştir: sırasıyla Fellenuis, Bishop, Janbu, Morgenstern-Price ve Spencer yöntemleri. Suyun ani çekilme hızının 3m/gün olduğu ve rezervuar su seviyesinin 8 günde 3 m'ye düştüğü varsayılmaktadır. Gözlem sonuçlarına göre barajın memba eğiminin stabilitesi önemli ölçüde azalmıştır, ancak suyun çekilmesi durumunda hala stabildir. Rezervuar su seviyesinin tüm durumları için güvenlik faktörü 1.3'ten büyüktür. Rezervuarda ani su çekilmesinin başlamasından sonra kısa sürede baraj yamaçlarının kaymasına karşı güvenlik faktörünün bir miktar azaldığı, ardından artmaya başladığı sonucuna varılmıştır. Bu, zemindeki efektif gerilmelerin artmasına ve dolayısıyla kayma mukavemetinin artmasına yol açan aşırı boşluk suyu basıncının zamanla azalmasından kaynaklanmaktadır.

Keywords

• Şev
• Dolgu baraj
• Ani su çekilmesi
• Stabilite

References

1. Abbas, M.J., Aljanabi, A.Q., Mutiny AZ, 2017. Slope stability analysis of an earth dam, Diyala Journal of Engineering Sciences, Vol. 10, No. 01, pp. 106-117.
2. Alonso, E.. Pinyol, N.. 2009. Slope stability under rapid drawdown conditions. First Italian Workshop on Landslides, s. 11–27. http://hdl.handle.net/2117/11200.
3. Bishop, A.W., 1955. The use of slip circle in the stability analysis of slopes. Geotechnique 5(1):7–17.
4. Bishop, A.W., Morgenstern N, 1960. Stability coefficients for earth slopes. Geotechnique 10(4):164–169.
5. Çalamak, M., Selamoğlu, M., Yanmaz, A. M., 2015. Toprak Dolgu Barajlarda Hazne Seviyesindeki Ani Düşmenin Şev Stabilitesine Etkilerinin Değerlendirilmesi, 4. Su Yapıları Sempozyumu, 278-287.
6. Devi, L.N.D.D., Anbalagan, R., 2017. Study on Slope Stability of Earthen Dams by using GEOSTUDIO Software, International Journal of Advance Research, Ideas and Innovations in Technology. Volume 3, Issue 6, 408-414.
7. Erdağ, A,. 2020. Suya Doygun Olmayan Zemin Şevlerinde Yağış Yoğunluğunun Stabiliteye Etkisi, Gazi Üniversitesi, Fen Bilimleri Enstitüsü, Yüksek Lisans Tezi, 97 sf., Ankara.
8. Fattah, Y.M., Omran, A.H., Hassan, A.M., 2017. Flow and stability of Al-Wand earth dam during rapid drawdown of water in reservoir. Acta Montanistica Slovaca. Vol 22, Number 1, 43-57.

9. Fellenius, W., 1936. Calculation of stability of earth dams. In: Proceedings of the second congress of large dams, vol 4, pp 445–463.
10. GEO-SLOPE International Ltd, 2007. Calgary, Alberta: Rapid Drawdown with Multi-Stage, Canada, 2007, www.geoslope.com (Erişim Tarihi: 19.12.2020).
11. Himanshu, N., Burman, A., 2017. Seepage and Stability Analysis of Durgawati Earthen Dam: A Case Study. Indian Geotech J, 49(1):70–89.
12. Janbu, N., 1954. Applications of composite slip surfaces for stability analyses. In: Proceedings of the European conference on the stability of earth slopes, Stockholm, vol 3, pp 39–43.
13. Khassaf, I.S., Abdoul-Hameed, R.M., Al-deen, S.N.N., 2013. Slope Stability Analysis under Rapid Drawdown Condition and Siesmic Loads of Earth Dam (Case Study: Mandali Dam), International Journal of Innovative Research in Science, Engineering and Technology. Vol. 2, Issue 12, 7114-7118.
14. Khattab, A.A.S., 2010. Stability Analysis of Mosul Dam Under Saturated and Unsaturated Soil Conditions. Al-Rafidain Engineering, Vol 18, No 1, 13-27.
15. Laxminarayana, A., Naresh, M., 2017. Analysis of Embankments with Different Fill Materials using Plaxis-2D, International Journal of Engineering Trends and Technology (IJETT) – Volume 45 Number 6, 280-284.
16. Morgenstern, N.R., Price, V.E., 1965. The analysis of the stability of general slip surfaces. Geotechnique 15(1):79–93.
17. Ramachandra, R.A., Khaled H.H., 1999. Flood Frequency Analysis, CRC-Press. (ISBN: 9780849300837).
18. Reddi, L.N., 2003. Seepage in Soils Principles and Applications, Hoboken (NJ): John Wiley & Sons.
19. Rocscience Inc, 2010. Slide Version 6.0-2-D Limit Equilibrium Slope Stability Analysis, www.rocscience.com, Toronto, Ontario, Canada.
20. Rocscience, 2018. Tutorial 13 Rapid Drawdown (B-bar method). https://www.rocscience.com/(Erişim Tarihi: 19.12.2020).
21. Sherard, J.L., Woodward, R.J., Gizienski, S.F., 1963. Earth and Earth Rock Dams: Engineering Problems of Design and Construction. John Wiley and Sons, New York, ABD.
22. Spencer, E., 1967. A method of analysis of the stability of embankments assuming parallel inter-slice forces. Geotechnique 17(1):11–26.
23. USBR, 1987. Design of Small Dams. United States Bureau of Reclamation, Washington, ABD.