The Trans Anatolian Gas Pipeline Project (TANAP) is part of the Southern Gas Corridor, which aims to convey natural gas from the Caspian region via Turkey to Europe. It traverses the whole of Turkey in east-west direction.

The pipeline has a length of 1811 km where the pipe diameter is 56" for the first 1338 km and 48" for the remaining 455 km up to the Greek border. The Sea of Marmara is being crossed by 2x36” pipes.

East of Sivas City, the route runs 92 km through one of the world´s largest gypsum karst terrains covering an area of 2140km². A fantastic place for the geologist but a big challenge for the routing, construction and operation of a pipeline.

Based on the morphology, a karst classification, comprising of 5 karst types, was set up.
The development of a genetic karst model enabled the assignment of specific hazards to each of the identified karst types. These hazards comprise of large near surface cavities ,  collapse dolines, subsidence sinkholes, internal erosion and pinnacled bedrock. Each karst type required a specific risk mitigation depending on type and severity of the hazard, to be considered either by routing or by applying technical measures.

Construction finally proofed that the karst model was correct. This was also underlined by the discovery of a large cave on the right of way during grading works within one of two short route sections with a predicted high risk of large cavities. Detailed ground investigations were necessary to assess the irregular three dimensional shape of the cave and to move the alignment to safe ground.

Experience from BTC and Nabucco Projects which also cross gypsum karst were highly beneficial for the successful completion of the task.