Improved construction method of soil mass of extra-large-diameter soil pressure balancing shield on soft soil stratum

The invention relates to an improved construction method of a soil mass of an extra-large-diameter soil pressure balancing shield on a soft soil stratum, which particularly solves the construction travelling problem of the extra-large-diameter soil pressure balancing shield. The improved construction method of the soil mass of the extra-large-diameter soil pressure balancing shield on the soft soil stratum comprises the following steps: adopting foam and bentonite slurry as additives in the tunneling construction process, injecting the additives to different positions of an excavation surfaceof a cutter, focusing on the foam and controlling the stability of soil pressure, causing bentonite slurry to play a subsidiary role and reducing the excavation strength of the soil mass, simultaneously adopting a central agitator in a soil warehouse to agitate and mix the soil mass and the additives entering into the soil warehouse and further stabilizing the excavation surface, improving the plastic fluidity, reducing t