Abstract: Gelevard dam is one of the under-construction dams in Iran. Gallery tunnels have been executed to implement the possibility of an appropriate grout curtain, complete sealing of support, and dam foundation. The current paper has studied and analyzed the left bottom gallery (LG3) with a length of 380 meters, 3 meters drilling diameter, and optimal coverage concrete thickness of the gallery. The required armature in the appropriate host rock pile has been determined as average and weak. Accordingly, the optimal thickness of gallery covering concrete has been assumed 30 centimeters on the roof and walls and 45 centimeters on the floor. The geometry of this area has been modeled commensurate with the reality in the software limited elements as much as possible. Results have been presented in graphs, after evaluation of place changes, minimum and maximum tensions, axial force, shear force, and bending moment. The obtained results indicated that 30 centimeters thickness of permanent concrete coverage without armature and 1.5 meters and 3 meters thickness of grout area of the weak host rock is suitable for the host rock with appropriate quality and an average one. The 40-centimeter thickness armature concrete coverage and injection thickness of 4.5 meters can be appropriate as well.