Monitoring and numerical analysis of pore water pressure changes Eyvashan dam during the first dewatering period

The performance of dams due to high operating costs and irreparable damages caused by failures in the construction phase and during the dewatering and exploitation period should verified and monitored by proper behavioural analysis. Dewatering the dams will result in the saturation of the embankment and supports and, consequently, the reduction of the stability coefficient. Therefore, in order to allow an earth dam to tolerate the new conditions easily and without problems, the rate of dewatering should be within the range. In this study, pore water pressure in the body of Eyvashan earth dam was evaluated. The water level inside the clay core due to changes in the reservoir water level during the first dewatering and using the actual specifications of the materials by Geostudio and Plaxis software and compared with the results of the instrumentation in the dam body. In order to adapt the observed and predicted data, a multi-variable regression was used and the coefficient of determination was used and respectively the value of R2=0.9834 and R2=0.9863 was obtained which shows a very good agreement between the observed and predicted data. Indicating that the cache water pressure values and their occurrence are in good agreement with the initial design conditions and that the barrier behaviour is stable in terms of pore water pressure. Installed piezometers upstream of the core show a higher pressure than the downstream, due to the high saturation state of the phreatic line. Also, the height of pressure in the downstream of cut off in the results of numerical modelling and in the observed results has suddenly decreased, which indicates the correct function of the injection cut off.