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King Abdulaziz University (2016)

Geotechnical and Hydrological Evaluation of Wadi Bat-han Diversion Dam (Al-Madinah, Saudi Arabia)

Al-Saied, Ali Belgasem

Titre : Geotechnical and Hydrological Evaluation of Wadi Bat-han Diversion Dam (Al-Madinah, Saudi Arabia)

Auteur : Al-Saied, Ali Belgasem

Université de soutenance : King Abdulaziz University

Grade : Master Thesis 2016

Résumé
Flood is one of the main and frequent geological hazard that may causes serious destruction and loss of life. Dams are one of the most important solutions for flood protection, they can store water or change the course of flooding water to avoid populated areas. Al-Madinah Al-Monawarah is located in a depsression that makes the area of the Holy Mosque and the sourounding areas liable to flooding water from various directions. Bat-han dam in the souther part of Al-Madinah to divert the flooding water away from the Holy Mosque. It is a long earthfill dam (670 m), 9 m high, built in 1420 H (2000) and never maintained ever sence, as a result there are conserns regarding the future dam safety during an event of flood. Bat-han dam was investigated by the Saudi Geological Survey (SGS) in 2014, which includes the dam static slope stability, the auther is a member of that research team. Some of the related geotechnical data were used in this study. The dam soil is mainly compacted sand mixed with gravel or fine material in some areas. The sand is moderatly dense to dense ranging in SPT N values from 20 to 45. Basalt is situated at 2 to 9 m deep, under the dam, and it is fractured in the upper 1 to 2 m allowing the grounwater to seep and move through the rocks. The capacity of the dam reservoir is huge (10.109 million m3), and the spillway can handle water flow of 293 m3/s which is more than the estimated peak discharge (244.9 m3/s) for a return period of 1000 years.As a way of calibration the static slope satbility was repeated here using a different software (SLIDE v5), the obtained factor of safeties FS are adequate and thier values are closed to the ones reported by SGS. As an objective of this research, the slope stability under daynamic forces and soil liquefaction were evaluated, that was not done before. The nearest historical earthquake and the Peak Ground Acelerations (PGA) of the dam site were obtained from a recent seismic study (2015). The estimated earthquake magnitude, M was 5.6 and PGA values of both bed rock and dam foundation are 0.088g and 0.15g respectivelly for a return period of 975 years. These values were implemented to evaluate the dynamic behavoir of dam slopes. It tune out that the slopes are satble (FS= 1.6 to 1.9) even if the PGA is 1.5 and the soil is wet. Part of the soil is fine sand and silt, therefore, the soil liquefaction potential is also possible. A comparison of the stress induced by the historical earthquake (CSR) and the soil resisting to liquify (CRR) was carried out. The resulting FS indicated that the dam is safe and can withstands soil liquefation (FS=5.2 to 6.5). It can be concluded that the dam has the ability to resists soil slope failure under static and dynamic conditions

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Page publiée le 1er décembre 2016, mise à jour le 4 décembre 2017