Construction method of reinforced concrete film bag cast-in-place pile in soft stratum

Abstract

The invention relates to a soft stratum reinforced concrete film bag cast-in-place pile construction method. The method comprises ten construction steps of cast-in-place pile hole forming, film bag manufacturing, bottom plate component manufacturing, reinforcement cage manufacturing and grouting pipe mounting, bottom plate mounting, film bag fixing, reinforcement cage and film bag lowering, guide pipe dismounting and guide pipe hole plugging, concrete pouring and post-grouting construction. In the process that a reinforcement cage and a film bag are put into a cast-in-place pile hole, clear water is injected into the film bag, bottom wall protection slurry is sucked through a guide pipe, replacement of the clear water and the wall protection slurry is completed, and when concrete is poured, the guide pipe rotates reversely to be separated from a bottom plate, a rubber plug moves to seal a guide pipe hole, the film bag isolates mud sediment and other sundries, and the pile forming quality is improved; and a film bag variable-diameter expansion body is formed through post-grouting, so that the bearing capacity of the pile foundation is improved.

Description

Technical Field

[0001] The present invention relates to the construction of bored cast-in-place piles, and specifically to the construction of reinforced concrete membrane bag cast-in-place piles in soft strata with high water content, high sensitivity, low strength and easy hole shrinkage. Background Art

[0002] When constructing cast-in-place pile foundations in soft strata such as soft soil strata with high water content, silt strata, saline soil strata, and fractured zones, quality problems such as concrete slurry leakage and slurry channeling are extremely likely to occur, and the construction difficulty is great; if not properly handled, safety accidents such as hole collapse may even be caused. Wrapping a membrane bag around the cast-in-place pile can effectively prevent concrete slurry leakage and prevent the influence of soft strata such as soft soil with high water content, silt, saline soil strata, and fractured zones on the quality of the formed cast-in-place pile. The traditional membrane bag is tied to the steel reinforcement cage and lowered together with the steel reinforcement cage, and concrete is poured into the membrane bag. The bottom of the membrane bag is connected to the slurry, and the influence of the slurry circulation of the slurry retaining wall on the inside of the membrane bag still cannot be avoided, which may lead to phenomena such as mud skin and slag inclusion in the pile body, affecting the construction quality of the cast-in-place pile; moreover, the bottom of the membrane bag is not closed, and the pile bottom is a weak part of the cast-in-place pile, which will pose a potential safety hazard to the quality and safety of the pile foundation project; during the lowering process of the membrane bag, there is a large friction between the membrane bag and the pile hole, and it sinks by the self-weight of the steel reinforcement cage and the membrane bag, affecting the lowering efficiency and increasing the risk of collapse after the pile hole is formed; the membrane bag only plays a role of wrapping and blocking around the pile, and does not fully utilize the material properties of the membrane bag.

[0003] In order to improve the construction quality of reinforced concrete membrane bag cast-in-place piles in soft strata, improve the construction efficiency and construction safety of membrane bag cast-in-place piles, and make full use of the material properties of the membrane bag, it is necessary to optimize and improve the corresponding construction methods. Summary of the Invention

[0004] The purpose of the present invention is to propose a construction method for reinforced concrete membrane bag cast-in-place piles in soft strata in view of problems existing in the construction of membrane bag cast-in-place piles, such as mud skin and slag inclusion in the pile body, slow lowering speed, and failure to fully utilize the material properties of the membrane bag.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions: The present invention relates to a construction method for reinforced concrete membrane bag cast-in-place piles in soft strata, which includes the following construction steps: S1. Boring the cast-in-place pile: Drilling a hole with slurry retaining wall according to the size and depth of the cast-in-place pile hole required by the design; S2. Manufacturing the membrane bag: Manufacturing a membrane bag with a threaded or calabash string variable diameter shape on the outer surface; S3. Manufacturing the bottom plate component: S3.1. Manufacturing the lower plate of the bottom plate, with a clamping groove arranged on the outer periphery of the lower plate, a rectangular movable groove arranged on one side of the upper half and a through conduit hole with a connecting thread arranged at the center, and a clamping spring hook welded on the side of the movable groove away from the center; S3.2. Fabricate the upper plate of the bottom plate. The lower half of the upper plate is provided with the upper half of the corresponding movable groove and the conduit holes on the smooth side. The upper half of the movable groove and the upper half of the movable groove combine to form a movable groove. S4. Fabrication of the steel reinforcement cage and installation of the grouting pipe: S4.1. Fabricate the main reinforcement bars, stirrups and grouting pipes of the steel reinforcement cage according to the design requirements. The grouting pipe is evenly provided with horizontal nozzles with one-way grout stopping membranes along the pipe body. S4.2. Assemble and weld the steel reinforcement cage. Two vertical grouting pipes are symmetrically arranged between the main reinforcement bars. The grouting pipes are fixed to the stirrups, and the tops of the grouting pipes are temporarily blocked. S5. Installation of the bottom plate: S5.1. Pass the lowermost section of the conduit through the conduit hole of the upper plate and connect it to the lower plate through external threads and connecting threads. S5.2. Install a rubber plug in the movable groove. The rubber plug is connected to the side of the movable groove away from the center through a snap ring and hooks provided at the corresponding positions on the sides of the movable groove and the rubber plug. A sliding rod is inserted between the rubber plug and the conduit, so that the snap ring is in a compressed state. S5.3. Closely fit the upper plate and the lower plate. The parts of the movable groove on the upper plate and the lower plate coincide. The outer periphery at the contact of the upper plate and the lower plate is connected and fixed by welding seams. S5.4. Weld the bottom of the main reinforcement bars of the steel reinforcement cage to the bottom plate, and weld anchor nails to the bottom surface of the bottom plate. S6. Fixing of the membrane bag: The membrane bag is fixed to the card slot of the bottom plate at the bottom through rib belts and fixed to the steel reinforcement cage at the upper part. S7. Lowering of the steel reinforcement cage and the membrane bag: S7.1. Lift the combined body of the steel reinforcement cage and the membrane bag to the orifice of the cast-in-place pile hole. S7.2. Extend the conduit, inject clear water into the membrane bag, and make the liquid level of the clear water in the membrane bag higher than the top of the slurry for protecting the wall in the cast-in-place pile hole, so as to form a water head difference inside and outside the membrane bag. S7.3. Gradually lower the steel reinforcement cage and the membrane bag, and suck the slurry for protecting the wall in the cast-in-place pile hole to the ground slurry pit through the slurry suction pump connected to the upper part of the conduit. S7.4. During the process of lowering the steel reinforcement cage and the membrane bag, extend the steel reinforcement cage, the membrane bag, the grouting pipe and the conduit section by section. Fix the membrane bag to the steel reinforcement cage, and synchronously inject clear water into the membrane bag to gradually complete the replacement of clear water and the slurry for protecting the wall until the bottom of the cast-in-place pile hole. S7.5. Inject clear water through the conduit and suck again to complete the secondary hole cleaning of the cast-in-place pile hole. S8. Removal of the conduit and plugging of the conduit hole: Rotate the conduit in the reverse direction to screw it out and lift it from the connecting thread on the bottom plate. The anchor nails embedded in the hard soil layer prevent the bottom plate from rotating. The rubber plug and the sliding rod move towards the conduit hole side under the elastic force of the snap ring. Finally, the upper and lower end frustums of the rubber plug are stuffed into the conduit hole to seal the conduit hole. S9. Concrete pouring: After the conduit is completely separated from the bottom plate, continuous concrete pouring is carried out, and the conduit is lifted synchronously and removed section by section until the entire bored pile hole is filled. S10. Post-grouting construction: Remove the temporary plug at the top of the grouting pipe, and perform high-pressure grouting through the grouting pipe. The high-pressure slurry breaks through the grouting film at the outer end of the horizontal nozzle of the grouting pipe and the concrete protection layer of the pile body in sequence, fills the space of the membrane bag outside the pile body and compacts the surrounding soil, and finally forms a threaded or gourd-string variable-diameter expansion grouting body around the pile.

[0006] Preferably, in S2, the diameter of the membrane bag is 5 - 15 cm larger than the diameter of the bored pile hole.

[0007] Preferably, in S5.4, the number of the fixing nails welded on the bottom surface of the bottom plate is 3 - 4, and the length of the fixing nails is 0.5 m.

[0008] Preferably, in S7.2, the water level in the membrane bag is 0.5 - 1.0 m higher than the top of the slurry for protecting the wall in the bored pile hole.

[0009] Preferably, the post-grouting construction in S10 is carried out after the in-situ concrete strength reaches 85% of the standard strength.

[0010] Preferably, in S5.2, the sliding rod is a rod with a cylindrical middle part and hemispherical ends at both ends. The length of the sliding rod is the same as the width of the movable groove, and the diameter is the same as the height of the movable groove. The sliding rod rolls left and right in the movable groove.

[0011] Preferably, the conduit used in S5 is composed of multiple conduit units connected spirally end to end. The length of the conduit is 50 - 100 cm longer than the length of the steel reinforcement cage. The bottom of the conduit unit is provided with an external thread, the top is provided with an enlarged end, and the inner side of the enlarged end is provided with an internal thread. The bottom of the conduit is connected to the inner wall of the conduit hole through a connecting thread.

[0012] Preferably, the middle part of the rubber plug used in S5.2 is a cylinder, and the upper and lower ends are symmetric frustums. The diameter of the cylinder of the rubber plug is the same as the width of the movable groove.

[0013] The beneficial effects of the technical solution involved in the present invention compared with the traditional technology are as follows: 1. The membrane bag involved in the present invention is processed in the factory into a threaded or gourd-string shape that changes along the bored pile body. After concrete pouring, high-pressure post-grouting is carried out through the grouting pipe. The membrane bag wraps the expanded grouting body to form a variable-diameter shape such as a threaded shape or a gourd string along the height direction of the pile body, improving the lateral friction resistance between the bored pile and the surrounding soil. The structure is reliable and the construction difficulty is small.

[0014] 2. In the central part of the bottom plate involved in the present invention, a conduit hole is provided and connected to a conduit. During the process of lowering the steel reinforcement cage membrane bag, the mud in the bored pile hole is suctioned through a mud pump, and clear water is injected into the membrane bag. The water head difference between the inside and outside accelerates the lowering efficiency of the steel reinforcement cage and the membrane bag, reduces the construction period, effectively reduces the risk of pile hole collapse, and improves the construction safety of the bored pile.

[0015] 3. In the present invention, clear water is injected through the membrane bag, and the mud in the pile hole is replaced by suctioning the mud outside the membrane bag. There are no sundries such as mud sediment in the membrane bag, reducing phenomena such as pile breaking, mud skin, and slag inclusion, and the forming effect of the bored pile body is good.

[0016] 4. The conduit of the present invention is connected to the bottom plate by threads and sucks the slurry for protecting the wall during lowering. After the steel reinforcement cage is lowered to the bottom of the hole, the bottom of the pile hole can be flushed with high pressure to reduce the sediment at the bottom of the pile; after the conduit is removed by reverse rotation, it is used for concrete pouring, effectively improving the utilization effect of the conduit.

[0017] 5. In the present invention, a movable groove and a rubber plug are provided inside the bottom plate. During the removal of the conduit, the rubber plug immediately seals the conduit hole in the central part of the bottom plate, effectively preventing mud and slag from entering the membrane bag.

[0018] 6. The membrane bag involved in the present invention can effectively avoid the influence of soft strata such as high water content soft soil strata, silt strata, saline soil strata, and fractured zones on the bored pile, and can also be directly used to improve the bearing capacity of the bored pile, with a wide range of applications. Description of the Drawings

[0019] Figure 1 is the construction flow chart of the reinforced concrete membrane bag bored pile in soft strata; Figure 2 is the schematic diagram of the forming device of the reinforced concrete membrane bag bored pile in soft strata; Figure 3 is the schematic diagram of the conduit unit and the upper and lower connection threads; Figure 4 is the schematic diagram of the bottom plate structure; Figure 5 is the bottom view of the lower plate; Figure 6 is the top view of the lower plate; Figure 7 is the sectional view of the lower plate; Figure 8 is the bottom view of the upper plate; Figure 9 is the top view of the upper plate; Figure 10 is the sectional view of the upper plate; Figure 11 is the connection diagram of the bottom plate and the conduit; Figure 12 is the sectional view of the rubber plug in the bottom plate in a contracted state; Figure 13 It is a plan view of the rubber plug inside the bottom plate in a contracted state; Figure 14 It is a three-dimensional view of the rubber plug; Figure 15 It is a schematic diagram of the replacement of mud with clear water when the pile-forming device is lowered; Figure 16 It is a schematic diagram of the start of concrete pouring; Figure 17 It is a sectional view of the rubber plug inside the bottom plate in a state of blocking the conduit hole; Figure 18 It is a plan view of the rubber plug inside the bottom plate in a state of blocking the conduit hole; Figure 19 It is a schematic diagram of the finally formed reinforced concrete membrane bag cast-in-place pile.

[0020] In the figure, the notations are as follows: 1 - cast-in-place concrete, 2 - expansion grouting body, 3 - steel reinforcement cage, 4 - anchor nails, 5 - bottom plate, 501 - lower plate, 502 - upper plate, 503 - movable groove, 504 - clamping groove, 505 - conduit hole, 506 - connecting thread, 507 - weld seam, 6 - rubber plug, 601 - frustum, 602 - cylinder, 7 - slide bar, 8 - snap ring, 801 - hanging buckle, 9 - clear water, 901 - clear water liquid level, 10 - membrane bag, 11 - rib belt, 12 - cast-in-place pile hole, 13 - retaining mud, 14 - conduit, 1401 - enlarged end, 1402 - internal thread, 1403 - external thread, 15 - soft soil layer, 16 - hard soil layer, 17 - grouting pipe. Specific implementation manner

[0021] In order to deepen the understanding of the present invention, the following will refer to Figures 1 to 19 , and the embodiments of the present invention will be described in detail. The following embodiments are implemented on the premise of the technical solution of the present invention, and detailed implementation manners are given, but the protection scope of the present invention is not limited to the following embodiments.

[0022] In this embodiment, the diameter of the cast-in-place pile hole 12 is 1.5 m, the depth is 20 m, the length of the grouting pipe 17 is 20 m, horizontal nozzles are arranged at intervals of 1 m, the diameter of the steel reinforcement cage 3 is 1.4 m, and the thickness of the protective layer is 5 cm; the diameter of the bottom plate 5 connected to the bottom of the steel reinforcement cage 3 is 1.42 m, and the height is 5 cm, wherein the height of the lower plate 501 is 3.5 cm and the height of the upper plate 502 is 1.5 cm; the diameter of the membrane bag 10 outside the steel reinforcement cage 3 is 1.6 m to ensure the post-grouting expansion space, the length of the membrane bag 10 is 22 m, and rib belts 11 are arranged at intervals of 1 m; the single-section length of the conduit 14 is 2 m, the diameter is 15 cm, the periphery of the cast-in-place pile is a soft soil layer 15, and the bottom of the cast-in-place pile is a hard soil layer 16.

[0023] The construction method of the reinforced concrete membrane bag cast-in-place pile in soft strata, in combination with the attached Figure 1 shown, includes the following construction steps.

[0024] S1, bored pile hole: according to the design requirements of bored pile hole 12 size, depth, mud wall drilling hole; S2, the film bag 10 production: the outer surface of the film bag 10 is a thread or gourd string diameter shape, the diameter of the film bag 10 is 5-15cm larger than the cast-in-place pile hole 12, as shown in the attached Figure 2 As shown; S3, bottom plate 5 (attached Figure 4 ) Component production: S3.1, make the lower plate 501 of the bottom plate 5, as shown in the attached Figure 5 -Attached Figure 7 As shown, a clamping groove 504 is arranged on the outer periphery of the lower plate 501, a rectangular movable groove 503 is arranged on one side of the upper half, a through conduit hole 505 with a connecting thread 506 is arranged at the center, and a clamping spring hook 801 is welded on the side of the movable groove 503 away from the center; S3.2, make the upper plate 502 of the bottom plate 5, as shown in the attached Figure 8 -Attached Figure 10 As shown, the lower half of the upper plate 502 is provided with a corresponding movable groove 503 and a conduit hole 505 on a smooth side; S4, production of steel cage 3 and installation of grouting pipe 17 (attached Figure 2 ): S4.1. The main reinforcement, stirrups and grouting pipe 17 of the steel cage 3 are manufactured according to the design requirements. The length of the grouting pipe 17 is the same as the main reinforcement of the steel cage 3. The grouting pipe 17 is evenly provided with horizontal nozzles with a one-way grouting membrane along the pipe body; S4.2, assemble the welded steel cage, symmetrically set two vertical grouting pipes 17 between the main reinforcements, the grouting pipes 17 are fixed to the stirrups, the horizontal nozzles of the grouting pipes 17 face the outside of the pile hole 12, and are located between the adjacent ribs 11 of the membrane bag 10, and the top of the grouting pipes 17 is temporarily blocked; S5, base plate 5 installation: S5.1. Pass the lowermost section of the conduit 14 through the conduit hole 505 of the upper plate 502 and connect it to the lower plate 501 through the external thread 1403 and the connecting thread 506. Figure 11 As shown; S5.2, combined with Figure 12 -Attached Figure 13 As shown, a rubber plug 6 is installed in the movable groove 503. The middle part of the rubber plug 6 is a cylinder 602, and the upper and lower ends are symmetrical truncated cones 601. The diameter of the cylinder 602 is the same as the width of the movable groove 503. Figure 14As shown, the rubber plug 6 is connected to the side of the movable groove 503 away from the center through a snap ring 8 and a hook 801 provided at the corresponding positions on the side surfaces of the movable groove 503 and the rubber plug 6. A slide bar 7 is inserted between the rubber plug 6 and the conduit 14, so that the snap ring 8 is in a compressed state. The slide bar 7 is a rod body with a cylindrical middle part and hemispherical ends at both ends. The length of the slide bar 7 is the same as the width of the movable groove 503, and the diameter is the same as the height of the movable groove 503. The slide bar 7 can roll left and right in the movable groove 503.

[0025] S5.3. Closely fit the upper plate 502 and the lower plate 501. The part of the movable groove 503 coincides with the upper plate 502 and the lower plate 501. The outer periphery at the contact of the upper plate 502 and the lower plate 501 is connected and fixed by a weld 507. S5.4. The bottom of the main reinforcement of the steel cage 3 is welded to the bottom plate 5, and 3 - 4 anchoring nails 4 with a length of 0.5 m are welded to the bottom surface of the bottom plate 5. S6. Fixing of the membrane bag 10: The membrane bag 10 is fixed at the bottom in the card slot 504 of the bottom plate 5 through the rib belt 11 and fixed on the steel cage 3 at the upper part, as shown in the attachment Figure 2 shown; S7. Lowering of the steel cage 3 and the membrane bag 10 (attachment Figure 15 ) S7.1. Lift the combined body of the steel cage 3 and the membrane bag 10 to the orifice of the cast - in - place pile hole 12. S7.2. Extend the conduit 14. The conduit 14 is spirally connected end - to - end by multiple conduit units. The length of the conduit 14 is 50 - 100 cm longer than that of the steel cage 3. The bottom of the conduit unit is provided with an external thread 1403, the top is provided with an enlarged end 1401, and an internal thread 1402 is provided inside the enlarged end 1401. The bottom of the conduit 14 is connected to the inner wall of the conduit hole 505 through a connecting thread 506. Inject clear water 9 into the membrane bag 10, and the liquid level 901 of the clear water in the membrane bag 10 is 0.5 - 1.0 m higher than the top of the slurry 13 for protecting the wall in the cast - in - place pile hole 12, forming a water head difference inside and outside the membrane bag 10. S7.3. Gradually lower the steel cage 3 and the membrane bag 10, and suck the slurry 13 for protecting the wall in the cast - in - place pile hole 12 to the ground slurry pit through the slurry pump connected to the upper part of the conduit 14. S7.4. During the process of lowering the steel cage 3 and the membrane bag 10, extend the steel cage 3, the membrane bag 10, the grouting pipe 17 and the conduit 14 section by section. Fix the membrane bag 10 to the steel cage 3, and inject clear water 9 synchronously into the membrane bag 10, gradually completing the replacement of the clear water 9 and the slurry 13 for protecting the wall until the bottom of the cast - in - place pile hole 12. S7.5. Inject clear water 9 through the conduit 14 and suck it again to complete the secondary hole cleaning of the cast - in - place pile hole 12. S8. Removal of the conduit 14 and plugging of the conduit hole 505: Combining attachment Figure 17 - attachment Figure 18As shown, the reverse-rotating conduit 14 is unscrewed and lifted from the connecting thread 506 on the bottom plate 5. The fixing nails 4 embedded in the hard soil layer prevent the bottom plate 5 from rotating accordingly. Under the elastic force of the circlip 8, the rubber plug 6 and the slide rod 7 move towards the side of the conduit hole 505. Eventually, the upper and lower frustums 601 of the rubber plug 6 are stuffed into the conduit hole 505 to seal the conduit hole 505.

[0026] S9. Pouring concrete: As shown in the attached Figure 16 As shown, after the conduit 14 is completely separated from the bottom plate 5, continuous concrete pouring is carried out. The conduit 14 is lifted synchronously and removed section by section until the entire cast-in-place pile hole 12 is filled. S10. Post-grouting construction: As shown in the attached Figure 19 As shown, after the strength of the cast-in-place concrete 1 reaches 85% of the standard strength, the temporary plug at the top of the grouting pipe 17 is removed, and high-pressure grouting is carried out through the grouting pipe 17. The high-pressure slurry breaks through the grouting film at the outer end of the horizontal nozzle of the grouting pipe 17 and the concrete protection layer of the pile body in sequence, fills the space of the film bag 10 outside the pile body and compacts the surrounding soil. Eventually, a threaded or gourd-string variable-diameter expanded grouting body 2 is formed around the pile.

[0027] The above embodiments are only used to explain the technical concept of the present invention, rather than limiting the protection scope of the rights of the present invention. Any non-substantive modification made to the present invention using this concept shall fall within the protection scope of the present invention.

Claims

1. A method for constructing reinforced concrete membrane bag cast-in-place piles in soft strata, characterized in that: The construction steps include: S1, bored pile hole: drilling the bored pile hole (12) with mud wall according to the size and depth required by the design; S2, manufacturing a membrane bag (10): manufacturing a membrane bag (10) whose outer surface is a thread or a gourd string with a variable diameter shape; S3. Production of bottom plate (5) components: S3.

1. Make a lower plate (501) of the bottom plate (5), wherein a clamping groove (504) is arranged on the outer periphery of the lower plate (501), a rectangular movable groove is arranged on one side of the upper half, a conduit hole (505) with a connecting thread (506) is arranged through the center, and a retaining spring hook (801) is welded on the side of the movable groove (503) away from the center; S3.2, manufacturing an upper plate (502) of the bottom plate (5), wherein the lower half of the upper plate (502) is provided with a corresponding upper half of the movable groove and a conduit hole (505) on the smooth side, wherein the upper half of the movable groove and the upper half of the movable groove are combined to form a movable groove (503); S4. Fabrication of steel cage (3) and installation of grouting pipe (17): S4.

1. The main reinforcement, stirrups and grouting pipe (17) of the steel cage (3) are manufactured according to the design requirements. The grouting pipe (17) is evenly provided with horizontal nozzles with a one-way grouting membrane along the pipe body; S4.2, assembling the welded steel cage, symmetrically setting two vertical grouting pipes (17) between the main reinforcements, fixing the grouting pipes (17) to the stirrups, and temporarily blocking the top of the grouting pipes (17); S5. Installation of base plate (5): S5.

1. Pass the lowest section of the conduit (14) through the conduit hole (505) of the upper plate (502) and connect it to the lower plate (501) via the external thread (1403) and the connecting thread (506); S5.

2. Install a rubber plug (6) in the movable groove (503). The rubber plug (6) is connected to the side of the movable groove (503) away from the center through a retaining spring (8) and hooks (801) arranged at corresponding positions on the sides of the movable groove (503) and the rubber plug (6). A sliding rod (7) is inserted between the rubber plug (6) and the guide tube (14), so that the retaining spring (8) is in a compressed state. S5.3, the upper plate (502) and the lower plate (501) are tightly fitted together, the movable groove (503) is partially matched on the upper plate (502) and the lower plate (501), and the outer periphery of the contact part of the upper plate (502) and the lower plate (501) is connected and fixed by a weld (507); S5.4, the bottom of the main reinforcement of the steel cage (3) is welded to the bottom plate (5), and the bottom surface of the bottom plate (5) is welded with embedded nails (4); S6. Fixing the membrane bag (10): The membrane bag (10) is fixed at the bottom in the slot (504) of the bottom plate (5) through the rib belt (11), and the upper part is fixed on the steel cage (3); S7, lowering the steel cage (3) and the film bag (10): S7.

1. Hanging the steel cage (3) and membrane bag (10) assembly to the opening of the cast-in-place pile hole (12); S7.2, extend the catheter (14), inject clean water (9) into the membrane bag (10), and make the clean water level (901) in the membrane bag (10) higher than the top of the wall protection mud (13) in the bored pile hole (12), so that a water head difference is formed inside and outside the membrane bag (10); S7.3, the steel cage (3) and the membrane bag (10) are gradually lowered, and the wall slurry (13) in the bored pile hole (12) is sucked into the ground slurry pool through a slurry pump connected to the upper part of the guide tube (14); S7.4, during the lowering process of the steel cage (3) and the membrane bag (10), the steel cage (3), the membrane bag (10), the grouting pipe (17) and the guide tube (14) are connected in sections, the membrane bag (10) and the steel cage (3) are fixed, and clean water (9) is simultaneously injected into the membrane bag (10), and the replacement of the clean water (9) and the wall protection mud (13) is gradually completed until the bottom of the bored pile hole (12) is reached; S7.5, injecting clean water (9) through the conduit (14), and suctioning again to complete the secondary cleaning of the bored pile hole (12); S8, removal of the conduit (14) and sealing of the conduit hole (505): the conduit (14) is rotated in the opposite direction to be unscrewed from the connecting thread (506) on the bottom plate (5) and lifted up, the embedding nail (4) embedded in the hard soil layer prevents the bottom plate (5) from rotating accordingly, the rubber plug (6) and the slide rod (7) move toward the conduit hole (505) under the elastic force of the retaining spring (8), and finally the upper and lower end cones (601) of the rubber plug (6) are filled in the conduit hole (505), thereby sealing the conduit hole (505); S9, pouring concrete: after the guide tube (14) is completely separated from the bottom plate (5), continuous concrete pouring is performed, and the guide tube (14) is simultaneously lifted and removed section by section until the entire cast-in-place pile hole (12) is filled; S10, post-grouting construction: remove the temporary plugging at the top of the grouting pipe (17), and perform high-pressure grouting through the grouting pipe (17). The high-pressure grouting liquid successively breaks through the stopper membrane at the outer end of the horizontal nozzle of the grouting pipe (17) and the concrete protective layer of the pile body, fills the space of the membrane bag (10) outside the pile body and compacts the surrounding soil, and finally forms a threaded or gourd-shaped variable diameter expansion grouting body (2) around the pile.

2. The method for constructing reinforced concrete membrane bag cast-in-place piles in soft strata according to claim 1, characterized in that: The diameter of the S2 middle membrane bag (10) is 5 to 15 cm larger than the bored pile hole (12).

3. The method for constructing reinforced concrete membrane bag cast-in-place piles in soft strata according to claim 1, characterized in that: In S5.4, the number of embedded nails (4) welded on the bottom surface of the bottom plate (5) is 3 to 4, and the length of the embedded nails (4) is 0.5 m.

4. The method for constructing reinforced concrete membrane bag cast-in-place piles in soft strata according to claim 1, characterized in that: The clear water level (901) in the S7.2 middle film bag (10) is 0.5 to 1.0 m higher than the top of the wall protection slurry (13) in the bored pile hole (12).

5. The method for constructing reinforced concrete membrane bag cast-in-place piles in soft strata according to claim 1, characterized in that: The S10 post-grouting construction is carried out after the strength of the cast-in-place concrete (1) reaches 85% of the standard strength.

6. The method for constructing reinforced concrete membrane bag cast-in-place piles in soft strata according to claim 1, characterized in that: The slide bar (7) in S5.2 is a rod body with a cylindrical middle and hemispherical ends. The length of the slide bar (7) is the same as the width of the movable groove (503), and the diameter is the same as the height of the movable groove (503). The slide bar (7) rolls left and right in the movable groove (503).

7. The method for constructing reinforced concrete membrane bag cast-in-place piles in soft strata according to claim 1, characterized in that: The catheter (14) used in S5 is composed of multiple catheter units connected end to end in a spiral manner. The length of the catheter (14) is 50 to 100 cm longer than the steel cage. The bottom of the catheter (14) unit is provided with an external thread (1403), the top is provided with an enlarged end (1401), and the inner side of the enlarged end (1401) is provided with an internal thread (1402). The bottom of the catheter (14) is connected to the inner wall of the catheter hole (505) by a connecting thread.

8. The method for constructing reinforced concrete membrane bag cast-in-place piles in soft strata according to claim 1, characterized in that: The rubber stopper (6) used in S5.2 has a cylindrical body (602) in the middle and symmetrical frustums (601) at the upper and lower ends. The diameter of the cylindrical body (602) of the rubber stopper (6) is the same as the width of the movable groove (503).

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