Building foundation pile lower part expansion reinforcement cage and putting method thereof

Abstract

A building foundation pile lower part expansion reinforcement cage relates to a building foundation pile reinforcement cage, a reinforcement ring opening is arranged in the middle of the reinforcement cage, and the inner end of a reinforcement small cage is fixedly connected with the reinforcement ring opening; the lower end of the reinforcement cage is connected with outer square reinforcements, the two sides of the upper outer square reinforcements are hinged to the upper ends of two upper square reinforcements respectively, the lower ends of the two upper square reinforcements are hinged to the upper ends of two lower square reinforcements respectively, and the lower ends of the two lower square reinforcements are hinged to the two sides of the bottom outer square reinforcements respectively. The upper portions of four lifting steel bars fixedly connected to the bottom outer square steel bar movably penetrate through four holes formed in the middle of the upper outer square steel bar, and limiting lowering rods are arranged at the positions, close to the four holes of the upper outer square steel bar, of the upper portions of the four lifting steel bars correspondingly. The steel bar small cage is located in the hole wall blind hole, and the two upper square steel bars and the two lower square steel bars are distributed in a rhombus shape in the lower part expanding; the anti-sedimentation structure is formed by arranging the small reinforcement cage and changing the lower structure of the reinforcement cage.

Description

Technical Field

[0001] The invention relates to a steel reinforcement cage for a building foundation pile, and in particular to a steel reinforcement cage for a lower portion of a building foundation pile and a method for placing the steel reinforcement cage. Background Art

[0002] The function of the building foundation pile is to bear the weight of the building, that is, to transfer all the upper loads to the soil layer with good bearing performance deeper underground through the foundation pile, so as to meet the requirements of bearing capacity and settlement. The foundation pile itself is a force-transmitting component with certain rigidity and bending resistance. The current method of building foundation pile construction is to prepare for the equipment to enter the site and clean up according to the design, and then dig soil or stone at the set position to form a pile hole, drain and supply air in the pile hole to facilitate further entry into the pile hole, correct the pile hole center and geometric dimensions, then trim the hole wall and use a water pump to pump out the groundwater in the pile hole where groundwater appears, then use early-strength concrete to seal the water outlet, install a wall template on the hole wall of the pile hole, correct the center and geometric dimensions of the pile hole, and then repair the hole wall. The center of the pile hole and the roundness of the template, after pouring the retaining wall concrete, start compacting, curing, and repairing the retaining wall concrete after removing the template, then excavate the next section of the pile hole and carry out the construction cycle as mentioned above; this kind of building foundation pile in a state similar to a rod can better resist the pull-out load and withstand the vibration load in the soil layer with good geological conditions, but for places where the bearing capacity of the foundation soil is not enough to support the superstructure, the pile foundation will cause settlement as the use time increases. The main reason is that the physical and mechanical properties of the foundation soil are not good and cannot effectively support the weight of the building; the existing method is to use pile foundation reinforcement, foundation treatment, structural adjustment, monitoring and maintenance, etc. to reduce or avoid structural safety problems caused by pile foundation settlement. Summary of the invention

[0003] The purpose of the present invention is to disclose a steel cage with an expansion at the bottom of a building foundation pile and a method for placing the same based on the existing deficiencies. By setting a small steel cage and changing the lower structure of the steel cage, an anti-settlement structure is formed by the steel bars at the bottom of the steel cage and the lower diameter expansion of the pile hole.

[0004] In order to achieve the invention objective of the present disclosure, the present invention discloses the following technical solutions: A steel bar cage for expanding the lower part of a foundation pile of a building comprises a steel bar cage, a steel bar ring is arranged in the middle part of the steel bar cage, and the inner end of the steel bar cage is fixedly connected to the steel bar ring; the lower ends of multiple vertical rods at the lower end of the steel bar cage are respectively connected to the four sides of the upper outer square steel bar, the two sides of the upper outer square steel bar are respectively hingedly connected to the upper ends of the two upper square steel bars, the lower ends of the two upper square steel bars are respectively hingedly connected to the upper ends of the two lower square steel bars, the lower ends of the two lower square steel bars are respectively hingedly connected to the two sides of the bottom outer square steel bar, the lower ends of four lifting steel bars are fixedly connected to the middle part of the bottom outer square steel bar, the upper parts of the four lifting steel bars are movably passed through four holes arranged in the middle part of the upper outer square steel bar, limiting lowering rods are respectively arranged at the positions of the four holes of the upper part of the four lifting steel bars close to the upper outer square steel bar, and the same positions of the upper ends of the four lifting steel bars in the steel bar cage are respectively arranged with external expansion steel bars.

[0005] The lower part of the building foundation pile expands the steel bar cage, the inner end of the steel bar cage is provided with a ring-jointed steel bar ring of the same size as the steel bar ring, the middle part of the steel bar cage is provided with a plurality of reduced diameter steel bar rings arranged at intervals, and the outer end of the steel bar cage is provided with reduced diameter circular ring steel bars, the ring-jointed steel bar ring, the plurality of reduced diameter steel bar rings arranged at intervals and the reduced diameter circular ring steel bars are connected by a plurality of steel bars to form a steel bar cage; steel bar rings are respectively provided on the front and rear surfaces of the steel bar cage, the two steel bar rings are staggered one above and one below, and the ring-jointed steel bar rings of the steel bar cage are connected by steel ties.

[0006] The described building foundation pile lower part expands the steel bar cage, and upper reinforcing steel bars are respectively provided at the positions of the two upper square steel bars near the front and rear rod bodies, and the front and rear sides of the upper outer square steel bars are respectively connected to the outer sides of the upper reinforcing steel bars at the front and rear ends of the two upper square steel bars through connecting rings B; square supporting steel bars are respectively provided at the lower parts of the opposite surfaces of the two upper square steel bars, and the middle parts of the two square supporting steel bars are respectively connected to one end of the support rod, and the other end of the support rod is connected to the upper square steel bars.

[0007] The lower part of the building foundation pile expands the steel bar cage, and the middle part of the two lower square steel bars is provided with lower reinforcing steel bars facing up and down. The upper ends of the two lower square steel bars are connected to the lower ends of the two upper square steel bars through connecting rings C respectively.

[0008] The described lower expanded steel bar cage of the building foundation pile has a slightly smaller bottom inner square steel bar in the middle of the bottom outer square steel bar, the two ends of the bottom inner square steel bar are fixedly connected by the bottom connecting steel bar at the front and back, and the front and back of the bottom outer square steel bar are connected to the lower square steel bar by connecting ring A respectively; the lower parts of the four lifting steel bars are respectively fixedly connected to the four corners of the bottom inner square steel bar; a slightly smaller upper inner square steel bar is arranged in the middle of the upper outer square steel bar, the two ends of the upper inner square steel bar are fixedly connected by the upper connecting steel bar at the front and back, and bent steel bars are respectively arranged on the inner sides of the four corners of the upper inner square steel bar, and four holes are respectively formed on the inner sides of the four corners of the upper inner square steel bar by the bent steel bars, and the upper parts of the four lifting steel bars are movably passed through the four holes.

[0009] The lower part of the building foundation pile expands the steel bar cage, and the lower ends of the four lifting steel bars are respectively covered with rubber sleeves.

[0010] The lower part of the building foundation pile expands the steel cage, which includes a plurality of steel cage ring rods spaced from top to bottom, and a plurality of steel cage vertical rods are spaced on the inner walls of the plurality of steel cage ring rods; the steel cage ring rods and steel cage vertical rods of the steel cage are disconnected in the steel ring mouth.

[0011] The steel bar cage is expanded at the bottom of the building foundation pile, and the upper ends of the expanded steel bars of the four lifting steel bars are fixedly connected to the four corners of the steel bar ring A, and the lower ends of the expanded steel bars of the four lifting steel bars are fixedly connected to the four corners of the steel bar ring B.

[0012] A method for placing an expanded steel cage at the bottom of a building foundation pile, the method comprising: A. Excavate a pile hole of the required diameter and depth in the ground soil layer by using equipment in advance and manual methods in the later stage. Then, excavate a blind hole on the pile hole according to the design. During the excavation process of the pile hole and the blind hole on the hole wall, a concrete retaining wall can be made at the same time. Excavate the lower diameter expansion from the lower part of the pile hole toward the surroundings, and finally make a concrete retaining wall at the lower diameter expansion. B. Use a hoist to lift the upper end of the steel cage and slowly lower it into the pile hole. When the rubber sleeves at the lower ends of the four lifting steel bars contact the bottom surface of the lower expansion diameter, the steel cage continues to descend, pushing the upper outer square steel bars and the upper inner square steel bars down along the four lifting steel bars. At this time, the joints of the two upper square steel bars and the two lower square steel bars begin to expand outward until the four bent steel bars of the upper inner square steel bars are pressed on the limiting lowering rods of the four lifting steel bars. At this time, the steel cage stops descending, and then the construction personnel go down to the steel cage and use supports to center the steel cage. Then the personnel go up and use the hoist to put the small steel cage into the inner hole of the steel cage and lower it to the blind hole in the hole wall of the corresponding pile hole. Then the personnel enter the middle of the steel cage to adjust the small steel cage so that the small steel cage is inserted into the blind hole in the hole wall, and then the ring mouth of the small steel cage is fixedly connected by steel tying wire to connect the steel ring and the steel ring mouth of the steel cage. After the two small steel cages are installed in this way, they are ready for the next operation after acceptance confirmation.

[0013] In the method for placing the steel cage for expanding the lower part of the building foundation pile, in step A, the template is installed in sections and the protective wall is made in sections when pouring the protective wall; if groundwater appears during the excavation of the pile hole, the blind hole in the hole wall and the lower expansion, a water pump is used to drain the groundwater, and the water outlet is sealed with early-strength concrete.

[0014] Through the above disclosure, the beneficial effects of the present disclosure are: The present invention discloses a lower expansion steel bar cage for installing a small steel bar cage, wherein a steel bar ring is provided on the steel bar cage, and the lower end of the steel bar cage upright is welded and connected to the upper outer square steel bar to form an integral body. The outer sides of the upper connecting steel bars at both ends of the upper inner square steel bars and the inner sides of both ends of the upper outer square steel bars are hingedly connected by a connecting ring B and two square support steel bars, and the upper and lower ends of the two lower square steel bars are hingedly connected to the two upper square steel bars and the bottom inner square steel bars by connecting rings C and A, respectively. After the rubber sleeves at the lower ends of the four lifting steel bars contact the bottom surface of the pile hole through the aforementioned connection method, the outer expansion steel bars at the upper ends of the four lifting steel bars are pushed deeper into the steel bar cage, and at the same time, the connection between the two upper square steel bars and the two lower square steel bars is pushed forward. Lateral expansion, the limiting lowering rods arranged on the upper part of the four lifting steel bars will also automatically stop when the two upper square steel bars and the two lower square steel bars expand to both sides and reach the set width; after the above-mentioned structure is finalized, the steel bar cage is installed on the steel bar ring, and then concrete can be poured into the pile hole, the blind hole in the hole wall and the lower expansion diameter to obtain a diamond-shaped anti-settling structure formed in front, behind and below the foundation pile; the rubber sleeves arranged at the lower ends of the four lifting steel bars in the present invention can prevent the steel bars from contacting the bottom surface of the pile hole and causing rust; the present invention arranges expansion steel bars at the lower part of the steel bar cage, so that the lower part of the foundation pile is formed in a diamond shape after the concrete is poured, and the side wall protruding columns of the foundation pile are formed after the steel bar cage is poured with concrete, which effectively increases the anti-settling strength of the lower part of the foundation pile of the building. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of the overall three-dimensional structure of the present invention; Figure 2 It is a schematic diagram of the three-dimensional docking structure of the steel cage and the steel cage of the present invention; Figure 3 It is a schematic diagram of the vertical structure of the expanded steel bars at the bottom of the steel cage of the present invention; Figure 4 It is a structural schematic diagram of the steel cage of the present invention in a state of entering a pile hole; Figure 5 It is a schematic diagram of the unfolding structure of the expanded steel bars at the bottom of the steel cage of the present invention; Description of the Figures: In the figure: 1. Steel cage; 2. Small steel cage; 3. Steel ring A; 4. Outward expansion steel; 5. Steel ring B; 6. Lower end of vertical pole; 7. Upper inner square steel; 8. Upper outer square steel; 9. Upper square steel; 10. Square support steel; 11. Lifting steel; 12. Lower square steel; 13. Connecting ring A; 14. Bottom inner square steel; 15. Bottom outer square steel; 16. Reduced diameter circular ring steel; 17. Ring mouth butt steel ring; 18. Steel ring mouth; 19. Steel cage ring rod; 20. Steel cage vertical pole; 21. Bent steel; 22. Upper connecting steel; 23. Limit lowering rod; 24. Connecting ring B; 25. Upper reinforcing steel; 26. Support rod; 27. Connecting ring C; 28. Lower reinforcing steel; 29. ​​Bottom connecting steel; 30. Blind hole in hole wall; 31. Pile hole; 32. Soil layer; 33. Lower expansion; 34. Rubber sleeve. DETAILED DESCRIPTION

[0016] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings so as to more clearly understand the invention objectives, features and advantages of the present invention. It should be understood that the embodiments shown in the accompanying drawings are not intended to limit the scope of the present invention, but are only intended to explain that the technical solution of the present invention is not limited to one implementation method.

[0017] Combined with Figure 1 , 2The steel cage for expanding the lower part of the foundation pile of the building described in and 3 comprises a steel cage 1, wherein the steel cage 1 comprises a plurality of steel cage ring rods 19 arranged at intervals from top to bottom, a plurality of steel cage vertical rods 20 are arranged at intervals on the inner walls of the plurality of steel cage ring rods 19, a steel ring mouth 18 is arranged in the middle of the steel cage 1, the steel cage ring rods 19 and the steel cage vertical rods 20 of the steel cage 1 are disconnected in the steel ring mouth 18, and the inner end of the steel cage 2 is fixedly connected to the steel ring mouth 18; the lower ends 6 of the plurality of vertical rods at the lower end of the steel cage 1 are respectively connected to the surroundings of the upper outer square steel bars 8, the two sides of the upper outer square steel bars 8 are respectively hingedly connected to the upper ends of the two upper square steel bars 9, the lower ends of the two upper square steel bars 9 are respectively hingedly connected to the upper ends of the two lower square steel bars 12, and the two lower square steel bars 12 The lower ends are hingedly connected to the two sides of the bottom outer square steel bar 15, the lower ends of the four lifting steel bars 11 are fixedly connected to the middle of the bottom outer square steel bar 15, and the lower ends of the four lifting steel bars 11 are respectively covered with rubber sleeves 34. The upper parts of the four lifting steel bars 11 are movably passed through the four holes set in the middle of the upper outer square steel bar 8, and the four holes of the upper part of the four lifting steel bars 11 close to the upper outer square steel bar 8 are respectively provided with limiting lowering rods 23. The same positions on the upper ends of the four lifting steel bars 11 in the steel cage 1 are respectively provided with outward-expanded steel bars 4, and the upper ends of the outward-expanded steel bars 4 of the four lifting steel bars 11 are respectively fixedly connected to the four corners of the steel ring A3, and the lower ends of the outward-expanded steel bars 4 of the four lifting steel bars 11 are respectively fixedly connected to the four corners of the steel ring B5.

[0018] Combined with Figure 1 Or 2, the inner end of the steel cage 2 is provided with a ring-jointed steel ring 17 of the same size as the steel ring 18, the middle part of the steel cage 2 is a plurality of reduced diameter steel rings arranged at intervals, and the outer end of the steel cage 2 is provided with a reduced diameter circular ring steel bar 16, and the ring-jointed steel ring 17, the plurality of reduced diameter steel rings arranged at intervals and the reduced diameter circular ring steel bar 16 are connected by a plurality of steel bars to form the steel cage 2; the front and rear surfaces of the steel cage 1 are respectively provided with steel rings 18, and the two steel rings 18 are staggered one above and one below, and the ring-jointed steel rings 17 of the steel cage 2 are connected by steel tying wires.

[0019] Combined with Figure 1Or 2, upper reinforcing steel bars 25 are respectively provided near the front and rear rod bodies of the two upper square steel bars 9, and the front and rear sides of the upper outer square steel bars 8 are respectively connected to the outer sides of the upper reinforcing steel bars 25 at the front and rear ends of the upper ends of the two upper square steel bars 9 through connecting rings B24; square support steel bars 10 are respectively provided at the lower parts of the opposite surfaces of the two upper square steel bars 9, and the middle parts of the two square support steel bars 10 are respectively connected to one end of the support rod 26, and the other end of the support rod 26 is connected to the upper square steel bars 9; the middle parts of the two lower square steel bars 12 are provided with lower reinforcing steel bars 28 facing up and down, and the upper ends of the two lower square steel bars 12 are respectively connected to the front and rear ends of the lower ends of the two upper square steel bars 9 through connecting rings C27; a slightly smaller bottom inner square steel bar 15 is provided in the middle part of the bottom shaped steel bar 14, the front and rear ends of the bottom inner square steel bar 14 are fixedly connected by the bottom connecting steel bar 29 respectively, and the front and rear ends of the bottom outer square steel bar 15 are connected to the lower square steel bar 12 respectively by connecting rings A13; the lower parts of the four lifting steel bars 11 are fixedly connected to the four corners of the bottom inner square steel bar 14 respectively; a slightly smaller upper inner square steel bar 7 is arranged in the middle of the upper outer square steel bar 8, and the front and rear ends of the upper inner square steel bar 7 are fixedly connected by upper connecting steel bars 22 respectively, and bent steel bars 21 are respectively arranged on the inner sides of the four corners of the upper inner square steel bar 7, and four holes are respectively formed on the inner sides of the four corners of the upper inner square steel bar 7 by the bent steel bars 21, and the upper parts of the four lifting steel bars 11 are movably passed through the four holes.

[0020] Combined with Figures 1 to 5 The present invention discloses a method for placing a reinforcement cage under a building foundation pile, the method comprising: A. The pile hole 31 is deeply excavated in the ground soil layer 32 by using a pre-equipped auger. After the pile hole 31 is excavated, it is checked that there is no overflow, void and loose soil at the bottom of the pile hole 31. The places where overflow, void and loose soil are found are repaired. Then, according to the design, a blind hole 30 and a lower diameter expansion 33 are excavated on the pile hole 31. If groundwater appears during the excavation of the pile hole 31, the blind hole 30 and the lower diameter expansion 33, a water pump is used to drain the groundwater, and the water outlet is sealed with early-strength concrete. The above process adopts a segmented construction method, that is, the concrete retaining wall can be made simultaneously during the excavation process of the pile hole 31 and the blind hole 30. The lower diameter expansion 33 is excavated from the lower part of the pile hole 31 toward the surroundings, and finally a concrete retaining wall is made at the lower diameter expansion 33. B. Use a hoist to lift the upper end of the steel cage 1 and slowly lower it into the pile hole 31. When the rubber sleeves 34 at the lower ends of the four lifting steel bars 11 contact the bottom surface of the lower expansion diameter 33, the steel cage 1 continues to move downward, pushing the upper outer square steel bars 8 and the upper inner square steel bars 7 down along the four lifting steel bars 11. At this time, the joints of the two upper square steel bars 9 and the two lower square steel bars 12 begin to expand outward until the four bent steel bars 21 of the upper inner square steel bars 7 are pressed on the limiting lowering rods 23 of the four lifting steel bars 11. At this time, the steel cage 1 stops moving downward, and the two upper square steel bars 9 and the two lower square steel bars 12 also expand outward in place, and then the construction personnel The personnel go down to the steel cage 1 and use stones or steel bar top rods and other supports to center the steel cage 1. The supports make the steel cage 1 in the middle position in the pile hole 31, which is commonly known as centering. Then the personnel go up and use the sling to put the steel cage 2 into the inner hole of the steel cage 1 and lower it to the blind hole 30 of the hole wall corresponding to the pile hole 31. Then the personnel enter the middle of the steel cage 1 to adjust the steel cage 2 so that the steel cage 2 is inserted into the blind hole 30 of the hole wall. Then, the ring mouth of the steel cage 2 is fixedly connected with the steel ring 17 and the steel ring mouth 18 of the steel cage 1 by steel tying wire. After the two steel cages 2 are installed in this way, they are ready for the next operation after acceptance confirmation. C. Before pouring concrete, check the bottom of the lower expansion diameter 33 of the pile hole 31 again to confirm that there is no loose soil or water accumulation before starting the operation; at the same time, use a slump tube to test the slump of the concrete, and the slump is controlled between 6 and 9CM; D. Use a concrete delivery pump to deliver concrete to the discharge barrel, and then introduce it through the string barrel to the top of the lower expansion 33 to start discharging. When the thickness reaches about 40CM, use a rope-bound inserted vibrator to put it into the pile hole 31 and the blind hole 30 on the hole wall, and vibrate the concrete with the inserted vibrator until there are no bubbles in the concrete. Vibrate to make the concrete dense, and then discharge it again to a thickness of about 40CM and then vibrate it in the above manner. At the same time, lift the string barrel, discharge, and vibrate in a continuous cycle until the pile hole 31 is filled with concrete of the required elevation.

[0021] The preferred embodiments of the present disclosure have been described in detail above, but it should be understood that after reading the above teachings of the present disclosure, those skilled in the art may make various changes or modifications within the scope of protection of the present disclosure. These equivalent forms also fall within the scope defined by the claims attached to this application.

[0022] Parts of the present invention not described in detail are prior art.

Claims

1. A steel cage for expanding the lower part of a building foundation pile, comprising a steel cage (1), characterized in that: A steel bar ring (18) is provided in the middle of the steel bar cage (1), and the inner end of the steel bar cage (2) is fixedly connected to the steel bar ring (18); the lower ends (6) of the plurality of vertical rods at the lower end of the steel bar cage (1) are respectively connected to the periphery of the upper outer square steel bar (8), the two sides of the upper outer square steel bar (8) are respectively hingedly connected to the upper ends of two upper square steel bars (9), the lower ends of the two upper square steel bars (9) are respectively hingedly connected to the upper ends of two lower square steel bars (12), and the lower ends of the two lower square steel bars (12) are respectively hingedly connected to the bottom outer square steel bars (8). The lower ends of the four lifting steel bars (11) are fixedly connected to the middle of the bottom outer square steel bar (15), and the upper parts of the four lifting steel bars (11) are movably inserted into four holes set in the middle of the upper outer square steel bar (8). The four lifting steel bars (11) are provided with limiting lowering rods (23) at the positions of the four holes of the upper outer square steel bar (8) close to the upper outer square steel bar (8), and the upper ends of the four lifting steel bars (11) in the steel cage (1) are provided with outward expansion steel bars (4) at the same positions.

2. The steel reinforcement cage for the lower part of the building foundation pile according to claim 1 is characterized in that: The inner end of the small cage (2) is provided with a butt-jointed steel bar ring (17) of the same size as the steel bar ring opening (18); the middle part of the steel bar small cage (2) is provided with a plurality of spaced-apart reduced-diameter steel bar rings; the outer end of the steel bar small cage (2) is provided with a reduced-diameter circular ring steel bar (16); the butt-jointed steel bar ring (17), the plurality of spaced-apart reduced-diameter steel bar rings and the reduced-diameter circular ring steel bar (16) are connected by a plurality of steel bars to form the steel bar small cage (2); the front and rear surfaces of the steel bar cage (1) are respectively provided with steel bar ring openings (18); the two steel bar ring openings (18) are staggered one above the other; the butt-jointed steel bar rings (17) of the steel bar small cage (2) are connected by steel tying wires.

3. The steel reinforcement cage for the lower part of the building foundation pile according to claim 1 is characterized in that: Upper reinforcing steel bars (25) are respectively provided near the front and rear rod bodies of the two upper square steel bars (9); the front and rear sides of the upper outer square steel bars (8) are respectively connected to the outer sides of the upper reinforcing steel bars (25) at the front and rear ends of the upper ends of the two upper square steel bars (9) through connecting rings B (24); square support steel bars (10) are respectively provided at the lower parts of the opposite surfaces of the two upper square steel bars (9); the middle parts of the two square support steel bars (10) are respectively connected to one end of the support rod (26), and the other end of the support rod (26) is connected to the upper square steel bars (9).

4. The steel reinforcement cage for the lower part of the building foundation pile according to claim 1 is characterized by: A lower reinforcing steel bar (28) facing up and down is arranged in the middle of the two lower square steel bars (12), and the upper ends of the two lower square steel bars (12) are connected to the lower ends of the two upper square steel bars (9) through connecting rings C (27) at their front and rear ends.

5. The steel reinforcement cage for the lower part of the building foundation pile according to claim 1 is characterized in that: A slightly smaller bottom inner square steel bar (14) is arranged in the middle of the bottom outer square steel bar (15), and the front and rear ends of the bottom inner square steel bar (14) are respectively fixedly connected by bottom connecting steel bars (29), and the front and rear ends of the bottom outer square steel bar (15) are respectively connected to the lower square steel bar (12) by connecting rings A (13); the lower parts of the four lifting steel bars (11) are respectively fixedly connected to the four corners of the bottom inner square steel bar (14); a slightly smaller upper inner square steel bar (7) is arranged in the middle of the upper outer square steel bar (8), and the front and rear ends of the upper inner square steel bar (7) are respectively fixedly connected by upper connecting steel bars (22), and bent steel bars (21) are respectively arranged on the inner sides of the four corners of the upper inner square steel bar (7), and the bent steel bars (21) respectively form four holes on the inner sides of the four corners of the upper inner square steel bar (7), and the upper parts of the four lifting steel bars (11) are movably inserted into the four holes.

6. The steel reinforcement cage for the lower part of the building foundation pile according to claim 5 is characterized by: The lower ends of the four lifting steel bars (11) are respectively covered with rubber sleeves (34).

7. The steel reinforcement cage for the lower part of the building foundation pile according to claim 1 is characterized by: The steel cage (1) comprises a plurality of steel cage ring rods (19) arranged at intervals from top to bottom, and a plurality of steel cage vertical rods (20) are arranged at intervals on the inner walls of the plurality of steel cage ring rods (19); the steel cage ring rods (19) and the steel cage vertical rods (20) of the steel cage (1) are disconnected within the steel ring opening (18).

8. The steel reinforcement cage for the lower part of the building foundation pile according to claim 1 is characterized by: The upper ends of the outwardly expanded steel bars (4) of the four lifting steel bars (11) are respectively fixedly connected to the four corners of the steel bar ring A (3), and the lower ends of the outwardly expanded steel bars (4) of the four lifting steel bars (11) are respectively fixedly connected to the four corners of the steel bar ring B (5).

9. A method for placing a reinforcement cage under a building foundation pile, characterized by: The placing method is applicable to the lower expansion steel cage of the building foundation pile as described in any one of claims 1 to 8, and the placing method comprises: A. A pile hole (31) of a required diameter and depth is excavated in a ground soil layer (32) by using equipment in advance and then manually in the later stage. Then, a blind hole (30) is excavated on the pile hole (31) according to the design. During the excavation process of the pile hole (31) and the blind hole (30), a concrete retaining wall can be made at the same time. A lower expansion (33) is excavated from the lower part of the pile hole (31) toward the surrounding area. Finally, a concrete retaining wall is made at the lower expansion (33); B. Use a lifting device to lift the upper end of the steel cage (1) and slowly lower it into the pile hole (31). When the rubber sleeve (34) at the lower end of the four lifting steel bars (11) contacts the bottom surface of the lower expansion diameter (33), the steel cage (1) continues to move downward, pushing the upper outer square steel bars (8) and the upper inner square steel bars (7) down along the four lifting steel bars (11). At this time, the joints of the two upper square steel bars (9) and the two lower square steel bars (12) begin to expand outward until the four bent steel bars (21) of the upper inner square steel bars (7) press on the limiting lowering rods (23) of the four lifting steel bars (11). At this time, the steel cage (1) stops moving downward. Then, the construction personnel go down into the steel cage (1) and use the support to center the steel cage (1). Then, the personnel go up and use the lifting device to put the steel cage (2) into the inner hole of the steel cage (1) and lower it to the blind hole (30) of the hole wall corresponding to the pile hole (31). Then, the personnel enter the middle of the steel cage (1) to adjust the steel cage (2) so that the steel cage (2) is inserted into the blind hole (30) of the hole wall. Then, the ring mouth of the steel cage (2) is fixedly connected with the steel ring (17) and the steel ring mouth (18) of the steel cage (1) by steel tying wire. After the two steel cages (2) are installed in this way, they are ready for the next operation after acceptance confirmation.

10. The method for placing a reinforcement cage for expanding the lower part of a building foundation pile according to claim 9, characterized in that: When pouring the retaining wall in step A, the template is installed in sections and the retaining wall is produced in sections; if groundwater appears during the excavation of the pile hole (31), the blind hole (30) in the hole wall and the lower expansion (33), the groundwater is pumped out using a water pump, and the water outlet is sealed using early-strength concrete.

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