Abstract: Tunnel excavation will lead to surrounding rock loose and exert certain load on the structure in the meantime. In the excavation process, the load of structure releases continuously in the stress adjustment process till the structure and rock mass stabilizing. Numerical analysis and model test are carried out to research the load releasing process of the whole section in the construction of ultra-large section railway tunnel. The load fluctuation rules of key points in bench excavation are studied firstly, then concepts of section comprehensive load release rate and difference coefficient of load release that characterizes the state of load release of the whole section are defined; and the load fluctuation rules in the process of construction are summarized via the two parameters. With monitoring of change laws of radial pressure at key points of rock mass in the geomechanical model test, the conclusions obtained by numerical analysis are testified; and the principle that the section must be regarded as a whole is realized to make the study of load release more comprehensive.

Key words: load releasing, construction process, total load releasing rate of section, difference coefficient of load releasing