Abstract: Safety and mechanical characteristics of rock-bolted crane girders are important to construction
of large underground powerhouses. For the underground powerhouse in the Jinping-I hydropower station
located in a high geo stress area, mechanical characteristics of its bolts and attachment of its two crane
girders to the surrounding rock are analyzed with safety monitoring at its excavation stage and a stage of 2
years later, and safety of its rock-bolted crane girders is evaluated. The results indicate that a larger
deformation and deep relaxation of the surrounding rock could be caused by excavation and unloading of
high geo-stress. And the stresses in the girder bolts that are generally at a high level, take a
long time (roughly one year after the excavation) to reach stability. All the bolt stresses are below the yield
strength of steel, and most of the joint openings between the girders and their surrounding rock are less
than 5mm, with a maximum of 9.9mm.