The Effect of Geological Factors on the Grout Curtain Performance Analysis of Darian Dam Using the Results of Instrumentation Data in the First Impounding

Determining the conditions of underground water level is one of the key factors in geotechnical analyses. In most dam construction projects, electrical and mechanical piezometers are installed for determining groundwater conditions, water level and its seasonal fluctuations, the position of perched and confined aquifer and investigate the conditions of pore water in dam and abutments. Besides, observation wells are located to verify underground water level fluctuations in different seasons and before and after impounding in different parts of the site. In this study, seepage status, water passages, and weaknesses of gout curtain of Darian dam are evaluated. Darian earthfill dam with a height of 176 m built on the Sirvan river is located in the west of Iran. The main methods used to improve the foundation and abutments in Darian dam include grout injections, consolidation, and drainage system. After the first impounding of Darian dam, the grout curtain has not reduced the potential in a considerably of the right side of the dam. In other words, the groundwater level in the upstream and downstream of grout curtain is almost the same. In this regard, the electrical and mechanical piezometers installed in upstream and downstream of grout curtain, iso-piezometric map, true equipotential lines, and phreatic flow line at different instrumentation levels and a downstream crosssection of grout curtain were depicted by obtaining continuous readings of observation wells. The results of instrumentation data and comparison of an iso-piezometric map of observation wells before and after impounding indicate that the grout curtain of Darian dam cuts a geologic unit with low permeability in the right side. By impounding and rise of water in the reservoir and the change in the hydro-geological boundaries, a different condition dominates both sides of this geological unit. Continuous reading of piezometers, observation wells, and drainages adequately explains that inefficiency of grout curtain on the right side is due to the water trapped behind the radiolarite unit.