Construction method for connecting section of ultra-large rectangular continuous open caisson underground station in soft soil stratum

The invention provides a soft soil stratum ultra-large rectangular continuous open caisson underground station connecting section construction method which comprises the following steps that after construction of internal structures of two adjacent open caisson sections is completed, an N-Jet construction method is adopted for conducting grouting reinforcement on the bottom and the two sides of a connecting section between the two open caisson sections; a soil layer of the connecting section is excavated step by step until the bottom of the pit of the connecting section is excavated, soil and water retaining plates are erected in the excavation and tunneling direction, the soil and water retaining plates of the section are installed every time excavation of the section is completed, and the soil and water retaining plates are erected on the left side face and the right side face of the connecting section and matched with the well walls of the two open caissons to define a rectangle; all the soil and water ret