Effect of unsaturated soil on deterministic and probabilistic analysis of the stability of an earth dam in steady state (case study: Seydon dam – Iran)

Document Type : Research Paper

Authors

1 Assistant Professor, Department of Civil Engineering, Technical Faculty, Behbahan Khatam Al Anbia University of Technology,

2 Associate Professor, Department of Civil Engineering, Technical Faculty, Behbahan Khatam Al Anbia University of Technology.

Abstract

The stability and flow rate of earth dams are influenced by several factors, including geometric characteristics, material permeability, and the height of water upstream. To effectively understand the behavior of unsaturated soils in earth dams, it is essential to apply the principles of unsaturated soil mechanics, given the complexities involved. Neglecting uncertainties in geotechnical assessments can lead to incorrect estimates of safety factors for dam slope stability. This research investigates the impact of unsaturated soil conditions on seepage discharge and the safety factor for the downstream of the earth dam under varying scenarios, with a focus on the Seydon Dam in Khuzestan province, Iran. The findings indicate that modeling the dam's soil as a saturated-unsaturated system decreases the computed flow rate through the dam and enhances the downstream slope's safety factor in both probabilistic and deterministic analyses. Additionally, a sensitivity analysis reveals that the earth dam shell's parameters significantly influence downstream slope stability. Spatial variation analysis further indicates that accounting for spatial changes in soil parameters can decrease the safety factor of the downstream slope compared to a standard assessment.

Keywords

Main Subjects


1-   Akbas, S.O. and Kulhawy, F.H., 2010. Characterization and estimation of geotechnical variability in Ankara clay: a case history. Geotechnical and Geological Engineering28, pp.619-631. DOI:10.1007/s10706-010-9320-x
 
2-   Athani, S.S., Solanki, C.H. and Dodagoudar, G.R., 2015. Seepage and stability analyses of earth dam using finite element method. Aquatic Procedia4, pp.876-883. DOI:10.1016/j.aqpro.2015.02.110
 
3- Casagrande, A., 1961. Control of seepage through foundations and abutments of dams. Geotechnique11(3), pp.161-182.
 
4- Djehiche, A., Gafsi, M. and Kotchev, K., 2012. Drainage of Bank Storage in Shallow Unconfined Aquifers. Drainage Systems, p.89.
 
5- Dupuit, J.É.J., 1863. Études théoriques et pratiques sur le mouvement des eaux dans les canaux découverts et à travers les terrains perméables: avec des considérations relatives au régime des grandes eaux, au débouché à leur donner, et à la marche des alluvions dans les rivières à fond mobile. Dunod, éditeur.
 
6- Eslamian, S., Bayat, M., Shams, G. and Hajiannia, A., 2021. 2D and 3D Modeling of Transient Seepage from Earth Dams Thorough Finite Element Model (Case Study: Kordaliya Dam). Water Resources14(48), pp.86-97. DOI:10.30495/wej.2021.4591
 
7- Fredlund, D.G. and Xing, A., 1994. Equations for the soil-water characteristic curve. Canadian geotechnical journal31(4), pp.521-532. DOI:10.1139/t94-061
 
8- Fredlund, D.G., Xing, A., Fredlund, M.D. and Barbour, S.L., 1996. The relationship of the unsaturated soil shear strength to the soil-water characteristic curve. Canadian geotechnical journal33(3), pp.440-448. DOI:10.1139/t96-065
 
9- Guo, X., Dias, D. and Pan, Q., 2019. Probabilistic stability analysis of an embankment dam considering soil spatial variability. Computers and Geotechnics113, p.103093. DOI:10.1016/j.compgeo.2019.103093
 
10- Hasani, H., Mamizadeh, J. and Karimi, H., 2013. Stability of slope and seepage analysis in earth fills dams using numerical models (case study: Ilam Dam-Iran). World Appl Sci J21(9), pp.1398-1402. DOI: 10.5829/idosi.wasj.2013.21.9.1313
 
11- Kacimov, A.R., Al-Maktoumi, A. and Obnosov, Y.V., 2021. Seepage through earth dam with clay core and toe drain: the Casagrande–Numerov analytical legacy revisited. ISH Journal of Hydraulic Engineering27(sup1), pp.264-272. DOI:10.1080/09715010.2019.1633694
 
12- Kacimov, A.R. and Brown, G., 2015. A transient phreatic surface mound, evidenced by a strip of vegetation on an earth dam. Hydrological Sciences Journal60(2), pp.361-378. DOI:10.1080/02626667.2014.913793
13- Kacimov, A.R., Yakimov, N.D. and Šimůnek, J., 2020. Phreatic seepage flow through an earth dam with an impeding strip. Computational Geosciences24(1), pp.17-35. DOI:10.1007/s10596-019-09879-8
 
14- Kulhawy, F.H., 2017. Foundation engineering, geotechnical uncertainty, and reliability-based design. In Geotechnical Safety and Reliability (pp. 174-184). DOI:10.1061/9780784480731.015
 
15- Mouyeaux, A., Carvajal, C., Bressolette, P., Peyras, L., Breul, P. and Bacconnet, C., 2018. Probabilistic stability analysis of an earth dam by Stochastic Finite Element Method based on field data. Computers and Geotechnics101, pp.34-47. DOI:10.1016/j.compgeo.2018.04.017
 
16- Pham, T.N., Yang, D., Kanae, S., Oki, T. and Musiake, K., 2001. Application of RUSLE model on global soil erosion estimate. Proceedings of hydraulic engineering45, pp.811-816. DOI:10.2208/prohe.45.811
 
17- Phoon, K.K. and Kulhawy, F.H., 2008. Serviceability limit state reliability-based design. In Reliability-based Design in Geotechnical Engineering (pp. 356-396). CRC Press.
 
18- Rocscience Inc. (2018): Slide2 version 2018 8.021-2D limit equilibrium slope stability analysis. http://www.rocscience.com
 
19- Rahardjo, H. and Fredlund, D.G., 1995, September. Pore pressure and volume change behavior during undrained and drained loadings of an unsaturated soil. In Proceedings of the First International Conference on Unsaturated Soils (pp. 165-170).
 
20- Rezaeeian, A., Davoodi, M. and Jafari, M.K., 2019. Determination of optimum cross-section of earth dams using ant colony optimization algorithm. Scientia Iranica26(3), pp.1104-1121. DOI:10.24200/sci.2018.21078
 
21- Salmasi, F., Norouzi, R., Abraham, J., Nourani, B. and Samadi, S., 2020. Effect of inclined clay core on embankment dam seepage and stability through LEM and FEM. Geotechnical and Geological Engineering38, pp.6571-6586. DOI:10.1007/s10706-020-01455-7
 
22- Shan, Y., Chen, S. and Zhong, Q., 2020. Rapid prediction of landslide dam stability using the logistic regression method. Landslides17, pp.2931-2956. DOI:10.1007/s10346-020-01414-6
 
23-  Siacara, A., Napa-García, G.F., Beck, A.T. and Futai, M.M., 2024. Reliability analysis of an earth dam under rainfall effects. International Journal of Geosynthetics and Ground Engineering10, pp.1-17. DOI:10.1007/s40891-024-00571-1
 
24- Siacara, A.T., Napa-García, G.F., Beck, A.T. and Futai, M.M., 2021. Reliability analysis of earth slopes using direct coupling. In Challenges and Innovations in Geomechanics: Proceedings of the 16th International Conference of IACMAG-Volume 1 16 (pp. 1001-1008). Springer International Publishing. DOI:10.1007/978-3-030-64514-4_110
 
25- Stark, T.D. and Jafari, N.H., 2018. San Luis dam case history: Seepage and slope stability analyses and lessons learned. In IFCEE 2018 (pp. 317-329). DOI:10.1061/9780784481622.025
 
26- Stello, M.W., 1987. Seepage charts for homogeneous and zoned embankments. Journal of geotechnical engineering113(9), pp.996-1012. DOI:10.1061/(ASCE)0733-9410(1987)113:9(996)
 
27- Van Genuchten, M.T., 1980. A closed‐form equation for predicting the hydraulic conductivity of  unsaturated soils. Soil science society of America journal44(5), pp.892-898. DOI: 10.2136/ sssaj1980. 03615995004400050002x
28- Wang, Y., 2014. Probabilistic assessments of the seismic stability of slopes: Improvements to site-specific and regional analyses (Doctoral dissertation).
 
29- Water and Electricity Organization of Khuzestan Province (2010) Water resource planning studies (final report), The first stage of Seydon reservoir dam project.
Volume 47, Issue 4
January 2025
Pages 51-67
  • Receive Date: 07 July 2024
  • Revise Date: 19 October 2024
  • Accept Date: 21 October 2024
  • Publish Date: 20 January 2025