Abstarct: Bakhtariari Dam is under construction on the Bakhtiari River that it’s located in the Aligoudarz City in Lorestan province. The dam’s diversion system is consisted of two tunnels. During tunnel construction, these tunnels is used as part of dam’s water diversion system, and the other hand it’s used as Bottom tripper or outlet after dam operation. Three kind of rocks’ strength category are existed in tunnel neighborhood (Week, Medium, good strength). Reinforced concrete protection (lining) is final tunnel support system. According to constant lining thickness, the portion of steel (in lining) will be only variable in case of specifying level of lining strength. According to providing tunnel stability, concrete protection (lining) and steel’s portion reduction, level of reinforced concrete is specified in this thesis. In the first step, rock (Tunnel Neighborhood) was classified by rock engineering classification methods. In next step, tunnels’ stability analysis was done by empirical (RMR & Q) & Numerical (By using FLAC2D software) methods. Rock bolt (by 25 mm diameter) with shotcrete was purposed for primary tunnels’ protection system. Water leakage on concrete protection (lining) in under pressure tunnel was caused to change fractures’ width on protection surface then increasing lining permeability. So Fractures’ embellishment & distribution then stress distribution in reinforced concrete protection is changed by increasing water pressure. This phenomena’s Hydro mechanical interplay effect was studied in Shlied theory. Bakhtiari Dam’s underneath tunnel’s reinforced concrete protection was designed baxsed on existing fractures’ width limitation criterion (in lining) and loaded stress on the protection system baxsed on 150 meters water pressure. Finally, the level of reinforced concrete in 3 kind of rock types (Weak, Medium and Good) were predicted by Shlied method as below: Weak 0.63, Medium 0.42 and Good 0.32.