Excavation and support construction method for shallow-buried long-and-large-connector accessory structure foundation pit of subway station

The invention discloses a subway station shallow-buried long and large connector accessory structure foundation pit excavation supporting construction method. The method comprises the following steps that firstly, accessory fender posts, top beams and retaining walls are constructed; secondly, an accessory structure foundation pit is excavated for the first time, and a main body side crown beam and a retaining wall are cut off; 3, excavating for the second time and cutting the main body fender post to the elevation of the top surface of the main body structure top plate; fourthly, steel bars are anchored into the top plate of the main body structure, and reinforced concrete brackets are constructed; 5, excavating for the third time to the positions of a main body structure top plate and an accessory interface lintel, installing a steel enclosing purlin, and erecting a second steel support; and sixthly, the soil body between the grid-connected spraying support piles is circularly excavated to the designed elev