Three-step and upper-step combined excavation construction method for super-large-span tunnel

The invention relates to the technical field of ultra-large-span tunnel construction, in particular to a three-step and upper-step combined excavation construction method for an ultra-large-span tunnel, the stability of surrounding rock can be effectively guaranteed through three-step and upper-step combined excavation construction, meanwhile, a self-propelled hydraulic inverted arch trestle is used in a matched mode, and the construction efficiency is improved. And a common bearing structure of the surrounding rock and the primary support can be formed as soon as possible, so that the safety of tunnel construction is improved. According to the method, the temporary support engineering amount in the tunnel excavation process is reduced, the total construction cost of the engineering is reduced, the construction progress is accelerated, the cost is effectively saved, a common bearing structure of the surrounding rock and the primary support is formed as soon as possible, the temporary support engineering amoun