Prediction of squeezing potential of rock masses around the Suruç Water tunnel

Squeezing problems were observed during the initial stages of excavating the Suruç tunnel which is Turkey’s longest and the world’s fifth longest irrigation tunnel at a length of 17.2 km. The tunnel is built to serve irrigation needs in the Suruç Plain. This research included prediction of squeezing potential along the Suruç tunnel. The diameter of the excavation is 7.9 m, and the final diameter of the tunnel will be 7 m. The tunnel runs mainly through formations of limestone and marl. Field studies included rock mass characterization (using the RMR, RMI, Q, GSI, and RMQR systems), discontinuity surveying, core drilling, and sampling for laboratory testing. Rock mass parameters were calculated using empirical equations. Empirical and semi-empirical approaches were used for evaluation of the squeezing potential. The convergence-confinement method and Plaxis 8.2 software were used for estimation of critical strain, tunnel support pressure, and tunnel convergence. Finally, squeezing potentials were estimated for all geological units. Localized squeezing risks were found in the tunnel. The performance of the new rock mass classification system, RMQR, to estimate the rock squeezing risks was also examined. Observations during the excavation indicated that predictions of the new squeezing risk regions were successful.