Evaluation of Phreatic surface in earth dams by numerical analysis method (Case Study: The Panzdahe Khordad dam)

In this paper, the location of the phreatic curve, the effects of the reservoir water level fluctuations and change of upstream and downstream slope on the phreatic curve, the water pore pressure and the safety factor of the dam body were analyzed after simulating the Panzdahe Khordad dam applying FLAC software. The safety factor reached 1.54 and 1.69 due to an increase in the slope of the upstream and downstream as much as 5 and 10 degrees respectively, at a constant level of water. And due to a decrease in the upstream and downstream as much as the same amount, the safety factor dropped down to 1.39 and 1.30 respectively. With an increase of the water level, the pore pressure and the possibility of the existence of phreatic line increased. Besides, a larger area of the body was saturated and with the development of the plastic zone, the safety factor dropped to 1.01. The results of this research indicate that with a decrease of the embankment volume, the safety factor declined dramatically which can sabotage the stability of the dam with regards to the annual water level fluctuations in upstream. Therefore, the current slope of the dam is adequate.