Geotechnical Investigation of the Silvan (Diyarbakir/Turkey) Dam

Irrigation Tunnel Route

   In this study, it was aimed to investigate the Babakaya Tunnel and Silvan Tunnel routes which will transmit Silvan Dam water to the left bank plains Tigris River from the engineering geological point of view and to determine the tunnel excavation-support systems. Directed to this purpose, geological maps with scales of 1:25 000 and 1:5 000, geological cross-sections with a scale of 1:5 000 of the tunnel routes were prepared. The cores obtained from the boreholes drilled by DSI X. Regional Directorate  were examined and used as laboratory specimens to determine strength values. The results of water-pressure tests carried out in the boreholes used to determine the permeability features of the formations.

            The Babakaya Tunnel passes through Gercus Formation between 0+000 – 0+240 km, Midyat Formation between 0+240 – 3+173 km, Germik Formation between 3+173 – 4+640 km and Silvan Formation between 4+640 – 5+ 130 km.

            The rock mass classification according to RMR and Q systems have been used to obtain the excavation – support requirements and stand up time. According to RMR rock mass classification system for Babakaya Tunnel, Gercus and Midyat formations fell into the fair rock class. According to Q rock mass classification system, Gercus and Germik formations fell into poor rock class, Midyat and Silvan formations fell into the good rock class. In the middle part of the Babakaya Tunnel, there is a large possibility to meet ground water.

            The Silvan Tunnel passes through Silvan Formation between 0+000 – 3+800 km, Germik Formation between 3+800 – 3+900 km, Midyat Formation between 3+900 – 5+550 km, Gercus Formation between 5+550 – 8+250 km, Midyat Formation between 8+250 – 12+175 km, Silvan Formation between 12+175 – 12+550 km and Selmo Formation between 12+550 – 13+500 km.

            According to RMR rock mass classification system for Silvan Tunnel, Silvan, Midyat and Gercus formations fell into the fair rock class, Germik and Selmo formations fell into the poor rock class. According to Q rock mass classification system, Midyat and Silvan formations fell into the fair rock class, Gercus and Germik formations fell into the poor rock class and Selmo Formation fell into the very poor rock class.

            The part of the Silvan Tunnel on the South bank of the Silvan anticline, there will be a water pressure. In order to aolish the influence on the springs and wells used for drinking water purpose, the additional precautions must be taken.

Key Words: RQD, permeability, strength, RMR system, Q system, excavation type, support system