Comprehensive construction method for forming die and sinking die of local deep pit prefabricated slab at deep foundation pit bottom in overtown beach geology

The invention discloses a blank mold and sinking mold comprehensive construction method for a local deep pit prefabricated slab at the bottom of a deep foundation pit in the overtopping beach geology. Pit-in-pit construction and raft plate excavation are carried out together, then project deepening is carried out, a pit-in-pit die sinking construction technology is adopted, a pit-in-pit part is thrown in advance, a large-face raft plate is constructed in advance, joints of raft plate construction are guaranteed, the construction period and cost are saved, and meanwhile the safety of pit-in-pit structure construction can be guaranteed. The construction efficiency is greatly improved, the process steps are extremely simple, sinking mold manufacturing can be carried out on the ground, and underground sinking mold building is more reliable. Construction is conducted at the original position of a project, the construction producing area can be saved, distribution of the working face is more scientific, joints of r