Assessment of the stabilization problem occured excavation at a dam site in Upstream basen of Ceyhan river

In Turkey, a significant number of hydropower projects are under planning, design, or construction stages. The geological engineering investigations comprise one of the most important parts of the project planning. The necessary geological investigations should be performed before the construction stage of the projects. Based on the investigation results, the locations of the structures are finalized and the design stage of the project begins. The geological risks at project areas increase if there is not sufficient number of geological investigations that cover the entire project area. Accordingly, unexpected geological problems may occur at project areas that may cause project budget increases and/or delay of the completion of the project. Several geological investigations performed at the site before the design of the proposed structures. Test borings and laboratory and in-situ tests were conducted to define the geological conditions at the site. In addition, water pressure tests were performed in the test borings to determine the permeability values of the bedrock formation. Based upon the site investigations, proposed structures were designed and the construction began. The construction of the project started with the excavation of the slopes and access roads. The slope excavation works was ongoing at dam axis area to prepare the slopes for dam body filling works. A landslide occurred which took place at the left bank of the dam axis after heavy rainfalls at the beginning of 2010. The works at the left abutment were stopped due to security reasons. As pointed out above, geological investigations are crucial part of the project planning. The landslide area could not be figured out during the planning stage due to lack of site investigations and misinterpretation of the existing ones. Immediately after the landslide occurred, a site visit performed to the landslide area. The affected areas were observed to define the landslide borders. The situation at the left bank revealed a highly unstable sliding mass, which has considerable amount of deformations and cracks. The reactivation of similar landslides cannot be ignored especially after heavy rain events. Based upon site visit findings, additional investigations (new borings and laboratory tests) were recommended to get more information about the geological conditions. The results of laboratory tests showed that the strength parameter of bedrock (meta-flysch) was around 34 MPa at the landslide area, which is low-medium strength, based on uniaxial compressive strength (UCS) classification. In addition to the aboratory tests, Schmidt hammer tests were performed to define the maximum strength characteristic of the bedrock. The maximum UCS estimated by using the Schmidt rebound value was around 146 MPa, which falls into high-strength rock category.