Underground space frame structure and construction method thereof

1 . An underground space frame structure, comprising: vertical support piles and multi-layer horizontal components connected to the vertical support piles; wherein the vertical support piles are arranged according to designed positions of the vertical support piles to form a column net;

wherein each of the vertical support piles is a reinforced concrete bored pile; each of the vertical support piles comprises a pile body; the pile body of each vertical support pile is composed of a reinforcement cage and concrete; the pile body of each vertical support pile comprises: an upper pile body, a lower pile body, and an expansion section located between the upper pile body and the lower pile body; the upper pile body of each pile body is a rectangular body, and the lower pile body of each pile body is a cylindrical body; a cross-sectional area of the expansion section is greater than a cross-sectional area of the upper pile body and a cross-sectional area of the lower pile body in each pile body; and the upper pile body, the expansion section, and the lower pile body of each pile body are coaxially arranged from top to bottom in that order and formed in one body; and

the multi-layer horizontal components are connected to the vertical support piles by connecting the multi-layer horizontal components to a side of the upper pile body of each vertical support pile layer by layer from top to bottom.

2 . The underground space frame structure as claimed in claim 1 , wherein the multi-layer horizontal components comprise a waterproof board and at least one layer of horizontal beams and floor slabs; a top surface of the expansion section of each pile body is flush with a top surface of the waterproof board; the expansion section and the lower pile body of each pile body are disposed below the top surface of the waterproof board; and the upper pile body of each pile body is disposed above the top surface of the waterproof board; and

the at least one layer of horizontal beams and the floor slabs are connected to the side of the upper pile body of each vertical support pile.

3 . The underground space frame structure as claimed in claim 2 , wherein the expansion section of each pile body comprises an upper frustum and a lower cylindrical body, the upper frustum and the lower cylindrical body are coaxially arranged, a diameter of the upper frustum gradually increases from top to bottom, a bottom diameter of the upper frustum is equal to a top diameter of the lower cylindrical body, and a thickness of the waterproof board is equal to a thickness of the upper frustum.

4 . The underground space frame structure as claimed in claim 3 , wherein in each pile body, a rectangle defined by a projection of a rectangular cross-section of the upper pile body on a top surface of the upper frustum is inscribed in a circle of the top surface of the upper frustum, and a circle defined by a projection of a circular cross-section of the lower pile body on the top surface of the upper frustum is inscribed in the rectangle defined by the projection of the rectangular cross-section of the upper pile body.

5 . The underground space frame structure as claimed in claim 4 , wherein the reinforcement cage of each pile body comprises: longitudinal rebars and transverse stirrups; and the longitudinal rebars are vertically arranged and continuously laid out along a length direction of each pile body.

6 . The underground space frame structure as claimed in claim 5 , wherein the longitudinal rebars are arranged in a rectangular shape in the upper pile body of each pile body according to the rectangular cross-section of the upper pile body; the longitudinal rebars are arranged in a circular shape in the lower pile body of each pile body according to the circular cross-section of the lower pile body; and transition parts of the longitudinal rebars are bent in the expansion section of each pile body.

7 . The underground space frame structure as claimed in claim 6 , wherein in each pile body, a central point of the rectangular cross-section of the upper pile body is taken as a center, the longitudinal rebars in the expansion section closer to an outside have greater inward bending degrees relative to the longitudinal rebars in the expansion section closer to the center; and the longitudinal rebars in the expansion section at tangent positions between the circular cross-section of the lower pile body and the rectangular cross-section of the upper pile body are not bent.

8 . The underground space frame structure as claimed in claim 6 , wherein the longitudinal rebars on a load-bearing side of each pile body and the longitudinal rebars on a side opposite to the load-bearing side of each pile body are strengthened.

9 . A construction method for the underground space frame structure as claimed in claim 1 , wherein the construction method comprises:

S1: before excavating a foundation pit, using a drilling rig to construct a plurality of pile holes according to the designed positions of the vertical support piles;

S2: after obtaining each pile hole, placing the reinforcement cage into each pile hole, pouring the concrete into each pile hole to construct the vertical support piles, and forming the column net based on the vertical support piles;

S3: after concrete curing is completed, excavating the foundation pit at a designed position of the foundation pit;

S4: during excavating the foundation pit, constructing horizontal beams and floor slabs layer by layer on the upper pile bodies of the vertical support piles from top to bottom, and reserving a construction passage on the floor slabs;

S5: after the excavating of the foundation pit is completed, placing a waterproof board on a bottom surface of the foundation pit; wherein a top surface of the expansion section of each pile body is flush with a top surface of the waterproof board, the expansion section and the lower pile body of each pile body are disposed below the top surface of the waterproof board, and the upper pile body is disposed above the top surface of the waterproof board; and

step S6: blocking the construction passage reserved on the floor slabs.