Upper-span rail transit foundation pit reinforcing device

The invention relates to the field of engineering construction, in particular to an overpass rail transit foundation pit reinforcing device which comprises a bottom plate fixedly connected to the bottom of a foundation pit, four side plates are vertically mounted at the top of the bottom plate, and a closed area is defined by the four side plates; connecting slopes are formed at the two ends of each side plate, every two adjacent connecting slopes are matched with each other, extension grooves are vertically formed in the tops of the side plates, the two ends of each extension groove are open, and every two adjacent extension grooves are communicated with each other. An extension groove is formed in the side plate, an extension plate is slidably mounted in the extension groove, sealing slopes are formed at the two ends of the extension plate, every two adjacent sealing slopes are matched with each other, and an extension part used for driving the extension plate to vertically move is mounted in the side plate