Optimum static and dynamic design of displacement chamber of headrace tunnel with bedding parallel shear zones in Siah Bishe Dam, Iran

The Siah Bishe pumped storage project is now under construction. The investigation results, the stability analysis and the support concept for the displacement chamber are discussed in this paper. The geometry of the transversal section and optimum maintenance system have been designed with respect to the unique geological and shear zone conditions encountered in Siah Bishe. The displacement chamber is arranged in sedimentary and volcanic rocks of Triasic and Jurasic ages. Length of the chamber is 50 m and the height is 10 m with relatively north–south trend. The results of geo-engineering surveys and statistical joint-graphics of stereograms reveal at least three discontinuity systems in the rock mass. The transversal section along the chamber was studied to analyze the stability of rock wedges inside the chamber. The frequency and width of bedding parallel shear zones determined the final support concept. Special attention was paid to the design of the transversal section so as to minimize the stress concentration in the critical regions of the wall, bottom of the chamber and corners. The results of analyses show that the chamber is stable in static and dynamic condition with 20 cm thickness of reinforced shotcrete, fully bonded rock bolt with 35 mm diameter, 3.5 m length and steel frame with 82 kg/m I section with 0.85 m spacing.