Method for controlling stability of second-layer primary support arch feet of large-span structure in soft stratum arch cover method

The invention discloses a method for controlling the stability of a second-layer primary support arch foot of a large-span structure in a soft stratum arch cover method. The method comprises the steps that S1, pilot tunnel excavation is conducted on an arch foot part; s2, constructing a first-layer primary support and a temporary support of the pilot tunnel at the arch foot part; s3, after the first-layer primary support and the temporary support are constructed to form a ring in a closed mode, longitudinal beams are constructed; s4, the steel frame plate face close to the longitudinal beam is cleaned; s5, longitudinal beam reinforcing steel bars are bound, and longitudinal beam longitudinal main reinforcing steel bars are welded to the first-layer primary support exposed steel frame; s6, a formwork is installed, and concrete is poured on the longitudinal beams in a segmented mode in the longitudinal direction; and S7, after the longitudinal beam molded concrete reaches the preset strength, a second-layer pri