Variable-diameter combined steel casing for sandy gravel stratum

The utility model discloses a sand gravel stratum variable-diameter combined steel casing which comprises an inner casing and an outer casing located on the periphery of the inner casing. The protective cylinder limiting connecting piece is used for connecting the inner cylinder and the outer cylinder; the inner cylinder and the outer cylinder are both configured to be of a double-wall pile casing structure, the double-wall pile casing structure is provided with an inner cylinder wall and an outer cylinder wall, and an embedding space is formed between the inner cylinder wall and the outer cylinder wall; the combined steel casing further comprises a plurality of compression-resistant steel pipes embedded into the embedding space. According to the combined steel casing disclosed by the utility model, the double-wall casing structures are sleeved together, and the plurality of compression-resistant steel pipes are embedded in the double-wall embedding spaces of the double-wall casing structures, so that the str