Optimal design of diversion tunnel section for Dajinping hydropower project on the Songlin River

Dajinping project is a diversion type hydropower project planned on the Songlin River trunk,the geological conditions along its tunnel are complicated.During early construction,the tunnel is excavated as circular section arch at the first stage.According to the geologic conditions of surrounding rocks exposed by excavation and the requirements of later construction progress,the design section is optimized under the condition that the tunnel layout,design discharge and unit output will not be changed so as to ensure the stable and safe operation of the project.For tunnel sections with good surrounding rocks,the U-shaped rock-bolted section is selected as a final optimized section instead of the original circular reinforcement concrete lining section.The above method is convenient and practical and satisfies the accuracy requirement.Along with the construction of middle and small-sized hydropower projects,the optimal design can be used as a simple and easy concept to timely adjust the section form during tunnel construction.