Research on excavation supporting measures for the dome of giant cylindrical surge chamber

The excavation and support of large underground caverns in a complex geological environment have brought great challenges to engineering design. The tailwater surge chamber of Baihetan Hydropower Station is a huge project with a maximum excavation diameter of 48 m. Geological factors including high stress, interlayer dislocation zone, and columnar joints impact the cavern's stability, making construction difficult. To investigate the cylindrical surge chamber dome's excavation and support technologies, as well as the stability of the surrounding rock, multiple methods have been applied, including empirical analogy, numerical calculation and field investigation. An excavation and support scheme of “high layered partition, horizontal sector partition, top-down, from inside to outside, area by area excavation and layer by layer support” has been proposed. The anchor observation tunnel in the shape of a “Wang” was innovatively designed. By presetting the new supporting structure of the anti-hanging dome through the anchor cable, the advanced implementation and monitoring of the support of the huge dome system have been accomplished. The research results are helpful to guide and optimize the subsequent excavation and support design of the cavern construction.