The investigation of the seepage condition of an upstream cofferdam with computer simulations and field observations (the case study: Inandik Dam-Turkey)

The cofferdam is a structure that prevents water from entering the dam construction area and keeps the excavation area dry during the construction of the dam body. This study investigated the seepage conditions of the upstream cofferdam, which is designed as a clay core earth fill. It was planned impermeability under the upstream cofferdam with a slurry trench. The primary input parameter of the seepage analysis is the permeability coefficient. Permeability tests were conducted under field conditions on alluvial and volcanic rock units at the base of the cofferdam. Laboratory permeability tests were conducted for the permeable and impermeable materials used in the cofferdam construction. The plastic concrete, intended to reduce seepage in the soil beneath the dam body, was designed, and its physical, mechanical, and permeability properties were determined. Following the completion of the upstream cofferdam, seepage that could potentially affect the dam body excavation area was investigated using Rocscience Groundwater and Plaxis LE 2D software. During the excavation of the dam body, the flow rate of water seepage into the excavation pit was measured and compared with the results of the computer software analysis. The results of the field measurements were found to be compatible with those from the numerical analysis programs. It has also been demonstrated that the slurry trench method is an effective way to reduce ground seepage. As a result, it has been observed that the upstream cofferdam and the plastic concrete underneath provide impermeability, allowing the construction of the dam body to be carried out safely. Seepage was brought under control, and necessary measures were taken.