بررسي پايداري شيرواني سد خاكي تحت شرايط بارگذاري مختلف با استفاده از روش قطعي و احتمالاتي

Study on the slope stability of embankment dam under different load conditions using deterministic and probabilistic methods (Case study: Namrood dam)

بر اين اساس در تحقيق حاضر اقدام به محاسبه ضريب­ هاي ايمني پايداري شيرواني سد خاكي نمرود در استان تهران به عنوان مطالعه موردي در شرايط مختلف بارگذاري شامل تراوش ماندگار و پايان ساخت در حالت قطعي و احتمالاتي ­گرديد. براي انجام تحليل احتمالاتي از بسته نرم­افزاري Geo-studio و روش تحليل قابليت اطمينان شبيه ­سازي مونت­كارلو استفاده شد. همچنين اثر اعمال بار زلزله بر پايداري سازه سد نيز مورد بررسي قرار گرفت. نتايج نشان داد كه در شرايط موجود سد احتمال شكست مقطع­ه اي بحراني سد نمرود ناچيز بوده به گونه ­اي كه بيشترين مقدار احتمال شكست برابر با 0/00007 بدست آمد. در ادامه اقدام به مطالعه ميزان حساسيت خصوصيات احتمالاتي فراسنجه ­هاي موثر ورودي بر احتمال پايداري شيرواني سد گرديد. نتايج تحليل حساسيت نشان داد كه با افزايش بار زلزله به ميزان 15 درصد، احتمال شكست سد به ميزان 100 درصد افزايش يافت. همچنين نتايج نشان داد كه نوع توزيع فراسنجه ­هاي موثر اثر چنداني بر احتمال شكست سازه سد ندارد به گونه ­اي كه با تغيير نوع توزيع فراسنجه وزن مخصوص از حالت نرمال به لگ­نرمال، احتمال شكست سد تنها به ميزان 1/88 درصد كاهش مي ­يابد.

Slope stability analysis is one of the most important parts of an emabankment dam design. However, the current conventional methods, which are based on the use of stability coefficients obtained from the deterministic methods, are not capable to explicitly analyze the uncertainity of effective parameters especially geotechnical parameters. This leads to an incorrect estimate of the potential stability of the dam structure. Accordingly, in the present study, the slope stability coefficient of Namrood dam as a case study was calculated for different load conditions, including permanent leakage and completion of construction by using deteministic and probabilistic methods. Geo-studio software package and Monte Carlo simulation techniques were used for analysis. The effect of earthquake load on the stability of the dam structure was also investigated. The results showed that, the failure probability of the critical sections of Namrood dam was negligible, so that the maximum probability of failure was calculated as 0.00007. Then, sensitivity analysis were carried out on the value and type of distribution of effective parameters. Results showed that with the increase in the earthquake load by 15%, the probability of dam failure increased by about 100%. Finally, results showed that by considering lognoramal instead of normal distribution for unit weight of soils, the probability of dam failure only decreased for 1.88%.