Foundation pit support method for expansion construction from deep foundation pit to shallow foundation pit

The invention relates to the technical field of foundation pit support, and discloses a foundation pit support method for expansion construction from a deep foundation pit to a shallow foundation pit, which comprises the following steps: S1, construction preparation; s2, construction site treatment; s3, pipe piles are pre-buried; s4, mounting a supporting protection plate; s5, the junction of the shallow foundation pit and the deep foundation pit is reinforced; and S6, enclosure is completed. The embedded rod is arranged at the bottom of the prefabricated pipe pile, so that the prefabricated pipe pile can be conveniently embedded, and the first barb and the second barb are arranged outside the prefabricated pipe pile, so that the mounting stability of the prefabricated pipe pile is better, and the construction efficiency of the prefabricated pipe pile is effectively improved; and secondly, a supporting protection plate is arranged between the two prefabricated pipe piles, the connecting stability of the suppo