A cast-in-place concrete pile and a construction method thereof

Abstract

The application discloses a concrete bored pile and a construction method thereof and belongs to the technical field of building construction. The concrete bored pile comprises a reinforcement cage structure arranged in a pile foundation hole and concrete poured into the pile foundation hole. The reinforcement cage structure comprises a plurality of circumferentially distributed ordinary steels. A plurality of steel rings are arranged on the outer sides of the ordinary steels. The ordinary steels are fixed on the steel rings. The lower ends of the ordinary steels are provided with fixing rings. The fixing rings are fixed on the ordinary steels. Slow-bonding prestressed steels are arranged between adjacent ordinary steels. One end of the slow-bonding prestressed steels is fixed on the fixing rings. The other end of the slow-bonding prestressed steels extends upwards to the outside of the pile foundation hole. When the ends of the slow-bonding prestressed steels are pulled and tightened, the slow-bonding prestressed steels are in contact with the inner sides of the steel rings. The technical scheme is used for improving the anti-pulling capacity of the concrete bored pile and avoiding the interference between the reinforcement cage and the hole wall during the lowering process of the reinforcement cage.

Description

Technical Field

[0001] This invention belongs to the field of building construction technology, specifically relating to a concrete cast-in-place pile and its construction method. Background Technology

[0002] Cast-in-place concrete piles are a type of pile foundation widely used in construction, bridges, ports, and other engineering projects. Their construction process typically includes drilling, fabricating and lowering the reinforcing cage, and pouring concrete. In projects subjected to significant uplift loads (such as tension piles and anti-buoyancy piles), the uplift capacity of the cast-in-place pile is a key design indicator. To enhance the uplift bearing capacity of cast-in-place piles, existing technologies often incorporate an outward-expanding structure (such as radially enlarged reinforcing rings, bent reinforcing bars, or enlarged head devices) at the lower end of the reinforcing cage, forming an enlarged head at the pile bottom. This increases the contact area and anchorage force between the pile and the surrounding soil, significantly improving the uplift performance of the cast-in-place pile.

[0003] However, the use of a reinforcing cage with an outwardly flared lower end has significant drawbacks during actual lowering: because the radial dimension of the flared portion is significantly larger than the diameter of the main body of the reinforcing cage, when the cage is hoisted into the pile hole, the flared portion is prone to scraping, jamming, or even colliding with the sidewall of the pile hole, leading to increased lowering resistance and difficulty in lowering. In severe cases, it can even cause the inner wall of the pile hole to collapse or the reinforcing cage to deform, affecting construction efficiency and pile quality. To solve these problems, some construction methods employ measures such as segmented lowering and hole enlargement, but these all significantly increase construction difficulty, extend the construction period, and increase costs, and it is difficult to completely avoid interference problems during the lowering process. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a concrete cast-in-place pile and its construction method, so as to improve the pull-out resistance of the concrete cast-in-place pile and avoid interference between the reinforcing cage and the borehole wall during the lowering process.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A cast-in-place concrete pile includes a reinforcing cage structure disposed within a pile foundation hole and concrete poured into the pile foundation hole. The reinforcing cage structure includes a plurality of circumferentially distributed ordinary reinforcing bars. A plurality of reinforcing rings are sleeved on the outer sides of the plurality of ordinary reinforcing bars, and the plurality of ordinary reinforcing bars are all fixed to the reinforcing rings. A fixing ring is provided at the lower end of each ordinary reinforcing bar, and the fixing ring is fixed to the ordinary reinforcing bar. A loosely bonded prestressing tendon is provided between adjacent ordinary reinforcing bars. One end of the loosely bonded prestressing tendon is fixed to the fixing ring, and the other end of the loosely bonded prestressing tendon extends upward to... Outside the pile foundation hole, when the ends of several of the loosely bonded prestressing tendons are stretched, the loosely bonded prestressing tendons contact the inner side of the reinforcing ring. Each end of the loosely bonded prestressing tendon is provided with a fixing plate. One end of the fixing plate is fixed to the fixing ring, and the other end of the fixing plate is provided with a sliding hole. A transverse insert is provided in the sliding hole. The transverse insert is slidably connected in the sliding hole. One end of the transverse insert is provided with a connecting ring. The connecting ring is fixed to the inward end of the transverse insert and is slidably sleeved on the loosely bonded prestressing tendon.

[0006] Furthermore, the outer side of the sliding hole of the fixed plate is provided with several elastic limiting ropes. One end of the elastic limiting rope is connected to the fixed plate, and the other end of the elastic limiting rope is provided with a limiting plate. The other end of the elastic limiting rope is fixed to the limiting plate. The middle part of the limiting plate is fixed to the outward end of the transverse insertion rod. The elastic limiting rope is provided with a breakage notch. The elastic limiting rope is used to restrict the position of the transverse insertion rod, so that the inward end of the transverse insertion rod bends the loosely bonded prestressing tendon inward. When the loosely bonded prestressing tendon is stretched and straightened, the elastic limiting rope breaks at the breakage notch.

[0007] Furthermore, one end of the elastic limiting rope slides through the limiting plate, and an end plate is provided on the end of the elastic limiting rope located inside the fixed plate. The end plate is fixed to the elastic limiting rope. A limiting hole is provided at the upper end of the fixed plate, and the limiting hole is connected to the sliding hole. A limiting post is provided inside the limiting hole, and a through hole is provided at the lower end of the limiting post. The elastic limiting rope passes through the through hole. A tension spring is provided on the end of the limiting hole located above the fixed plate. One end of the tension spring is fixed to the upper end of the limiting post, and the other end of the tension spring is fixed to the fixed plate. A locking hole is provided on the inward-facing end of the transverse insertion rod. When the loosely bonded prestressed tendon is stretched and pushes the transverse insertion rod outward to the limit position, the elastic limiting rope breaks at the breakage notch, and the tension spring pushes the limiting post downward, causing the limiting post to slide into the locking hole.

[0008] Furthermore, a guide block is provided inside the sliding hole, the guide block is fixed on the inner wall of the sliding hole, and a guide groove is provided on the transverse insert rod, with the guide block located inside the guide groove.

[0009] Furthermore, a compression spring is provided between the end plate and the fixed plate, with one end of the compression spring abutting against the end plate and the other end of the compression spring abutting against the fixed plate. The portion of the elastic limiting rope located between the outer surfaces of the end plate and the fixed plate is treated with adhesive hardening.

[0010] Furthermore, the fixing ring is provided with a plurality of circumferentially distributed mounting holes, and the outer surfaces of a plurality of ordinary reinforcing bars are fixed in the mounting holes. The ends of the loosely bonded prestressing tendons pass through the mounting holes, and the ends of the loosely bonded prestressing tendons are provided with a stop block, the diameter of which is larger than the diameter of the mounting hole.

[0011] Furthermore, the slow-setting prestressed tendon includes an outer sleeve, inside which are steel strands, and between the steel strands and the outer sleeve is a slow-setting adhesive.

[0012] A construction method for cast-in-place concrete piles includes the following construction steps: S1. After the pile foundation hole is excavated, the steel cage structure is fabricated or assembled on site. S2. Hoist the pre-fabricated steel cage and accurately position it inside the pile foundation hole; S3. Install tensioning equipment on the ground to initially tension the slow-bonded prestressed tendon located at the upper end of the pile hole, so that it is straightened and pushes the transverse insertion rod outward until the elastic limit rope breaks due to tension. S4. Pour concrete into the pile hole and cure it. After the concrete strength reaches the design threshold, use tensioning equipment to perform secondary tensioning on the loosely bonded prestressing tendons until the applied prestress meets the design requirements. Then anchor the upper end of the loosely bonded prestressing tendons. S5. Once the concrete in the pile foundation hole has completely hardened, the construction of the concrete cast-in-place pile is complete.

[0013] The beneficial effects of this invention are as follows: This technical solution, without altering the main structure of the reinforcing cage, achieves a dual pull-out resistance mechanism—no outward expansion at the lower end during lowering of the reinforcing cage, the formation of a radially enlarged body after lowering, and prestressed tendons—through retractable transverse inserts and tensionable, slowly bonded prestressed tendons. This effectively solves the problem of obstructed lowering and significantly improves the pull-out bearing capacity of the cast-in-place pile. Furthermore, by tensioning the slowly bonded prestressed tendons in the pull-out cast-in-place pile, the pile body is placed under compression, thereby significantly enhancing the tensile strength of the pile.

[0014] Other advantages, objectives, and features of the invention will be set forth in the following description and will be apparent to those skilled in the art in some respects, or may be learned by practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0015] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the following figures are provided for illustration: Figure 1 This is a three-dimensional schematic diagram of the steel cage structure in the concrete cast-in-place pile of the present invention; Figure 2 A three-dimensional schematic diagram of the lower end of the steel cage structure in the concrete cast-in-place pile of the present invention, showing the provision of slow-bonding prestressed tendons; Figure 3 This is a three-dimensional schematic diagram of the components such as the transverse insert rod on the fixing ring in the concrete cast-in-place pile of the present invention; Figure 4 This is a three-dimensional schematic diagram from another perspective of the components such as the transverse insert rod on the fixing ring in the concrete cast-in-place pile of the present invention; Figure 5 This is a schematic cross-sectional view of the components such as the transverse insert rod on the fixing ring in the concrete cast-in-place pile of the present invention. Figure 6 This is a schematic diagram of the construction process of the concrete cast-in-place pile of the present invention.

[0016] The following labels are shown in the attached diagram: 1. Ordinary reinforcing bar; 2. Reinforcing bar ring; 3. Fixing ring; 4. Mounting hole; 5. Connecting ring; 6. Horizontal insert rod; 7. Limiting plate; 8. Elastic limiting rope; 9. Break-off notch; 10. End block; 11. Tension spring; 12. Locking hole; 13. Guide groove; 14. Guide block; 15. End plate; 16. Compression spring; 17. Stop block; 18. Sliding hole; 19. Fixing plate; 20. Limiting post; 21. Slow-bonding prestressed tendon. Detailed Implementation

[0017] like Figures 1-6As shown, a cast-in-place concrete pile includes a reinforcing cage structure installed in the pile foundation hole and concrete poured into the pile foundation hole. The reinforcing cage structure includes several circumferentially distributed ordinary reinforcing bars 1. Several reinforcing bar rings 2 are sleeved on the outer sides of the ordinary reinforcing bars 1. The ordinary reinforcing bars 1 are all fixed to the reinforcing bar rings 2. The lower end of the ordinary reinforcing bars 1 is provided with a fixing ring 3, which is fixed to the ordinary reinforcing bars 1. A loosely bonded prestressing tendon 21 is provided between adjacent ordinary reinforcing bars 1. One end of the loosely bonded prestressing tendon 21 is fixed to the fixing ring 3, and the other end of the loosely bonded prestressing tendon 21 extends upward to the pile foundation. Outside the hole, when the ends of several loosely bonded prestressing tendons 21 are stretched, the loosely bonded prestressing tendons 21 contact the inner side of the reinforcing ring 2. The outer side of the ends of the loosely bonded prestressing tendons 21 are provided with fixing plates 19. One end of the fixing plate 19 is fixed to the fixing ring 3. The other end of the fixing plate 19 is provided with a sliding hole 18. A transverse insertion rod 6 is provided in the sliding hole 18. The transverse insertion rod 6 is slidably connected in the sliding hole 18. One end of the transverse insertion rod 6 is provided with a connecting ring 5. The connecting ring 5 is fixed to the inward end of the transverse insertion rod 6 and is slidably sleeved on the loosely bonded prestressing tendon 21.

[0018] Before the reinforcement cage is lowered, the loosely bonded prestressed tendons 21 are in a relaxed state. External constraints (such as temporary binding or elastic restraint ropes 8 in subsequent schemes) push the transverse insert 6 inwards, causing the loosely bonded prestressed tendons 21 to bend inwards, thereby reducing the radial profile of the lower end of the reinforcement cage. After lowering, tension is applied to the loosely bonded prestressed tendons 21 to straighten them. During straightening, the loosely bonded prestressed tendons 21 push the transverse insert 6 outwards along the sliding hole 18 through the connecting ring 5, causing the outer end of the transverse insert 6 to extend outwards from the fixing plate 19. Simultaneously, the loosely bonded prestressed tendons 21 contact the inner side of the reinforcement ring 2 to form support. Concrete is then poured, and final tensioning and anchoring are completed. The technical effect is that, without changing the main structure of the reinforcement cage, the retractable transverse insert 6 and the tensionable loosely bonded prestressed tendons 21 achieve a dual pull-out resistance mechanism: no outward expansion at the lower end during lowering of the reinforcement cage, radial expansion after lowering, and prestressed double pull-out resistance. This effectively solves the problem of obstructed lowering and significantly improves the pull-out bearing capacity of the cast-in-place pile. Among them, the tensioning of the slow-bonded prestressed tendons 21 in the pull-out cast-in-place pile puts the pile body under compression, thereby improving the tensile strength of the pile body: the prestress can effectively offset the tensile stress generated by the pile body under the pull-out load, delay or avoid the cracking of concrete under tension, and allow the concrete, which originally has weak tensile strength, to indirectly bear the tensile force through the compression state, giving full play to the excellent compressive performance of concrete, significantly enhancing the overall stiffness of the cast-in-place pile under the pull-out load, and greatly improving the durability of the pile body by inhibiting cracking.

[0019] In one feasible embodiment, the outer side of the sliding hole 18 of the fixing plate 19 is provided with a plurality of elastic limiting ropes 8. One end of the elastic limiting rope 8 is connected to the fixing plate 19, and the other end of the elastic limiting rope 8 is provided with a limiting plate 7. The other end of the elastic limiting rope 8 is fixed to the limiting plate 7. The middle part of the limiting plate 7 is fixed to the outward end of the transverse insert 6. The elastic limiting rope 8 is provided with a breakage notch 9. The elastic limiting rope 8 is used to limit the position of the transverse insert 6, so that the inward end of the transverse insert 6 bends the loosely bonded prestressed tendon 21 inward. When the loosely bonded prestressed tendon 21 is stretched and straightened, the elastic limiting rope 8 breaks from the breakage notch 9.

[0020] Its ingenious design lies in utilizing the tensioning operation that must be performed on the loosely bonded prestressed tendon 21 during construction as the power source to trigger the outward extension of the transverse insert 6. In the initial state, the elastic limiting rope 8 pulls the transverse insert 6 through the limiting plate 7, causing the inward-facing end of the transverse insert 6 to bend the loosely bonded prestressed tendon 21 inward, maintaining the compact profile of the lower end of the steel cage; when the loosely bonded prestressed tendon 21 is tensioned, the prestressed tendon is straightened and generates an outward thrust, which pushes the transverse insert 6 outward through the connecting ring 5. When the tension exceeds the ultimate strength of the breakage notch 9 of the elastic limiting rope 8, the elastic limiting rope 8 automatically breaks from the breakage notch 9, releasing the constraint on the transverse insert 6, allowing the transverse insert 6 to continue moving outward to its limit position. Its technical effect is that it cleverly combines the necessary process of tensioning prestressed tendons with the triggering action of the transverse insert 6, and can automatically complete the activation of the expansion mechanism without additional power or manual intervention, making the construction process simple and reliable; at the same time, the fracture gap 9 ensures the precise control of the fracture position, avoids premature or delayed fracture caused by mistension or uneven force, and improves the stability and consistency of construction.

[0021] In one feasible embodiment, one end of the elastic limiting rope 8 slides through the limiting plate 7, and an end plate 15 is provided on the end of the elastic limiting rope 8 located inside the fixed plate 19. The end plate 15 is fixed to the elastic limiting rope 8. A limiting hole is provided at the upper end of the fixed plate 19, which communicates with the sliding hole 18. A limiting post 20 is provided inside the limiting hole, and a through hole is provided at the lower end of the limiting post 20. The elastic limiting rope 8 passes through the through hole, and a tension spring is provided on the end of the limiting hole located above the fixed plate 19. 11. One end of the tension spring 11 is fixed to the upper end of the limiting post 20 (the upper end is provided with an end block 10, i.e., fixed on the end block 10), and the other end of the tension spring 11 is fixed to the fixing plate 19. The inward end of the transverse insert rod 6 is provided with a locking hole 12. When the loosely bonded prestressed tendon 21 is stretched and pushes the transverse insert rod 6 to move outward to the limit position, the elastic limiting rope 8 breaks from the breakage notch 9, and the tension spring 11 pushes the limiting post 20 downward, so that the limiting post 20 slides into the locking hole 12.

[0022] Its ingenious design lies in utilizing the elastic limiting rope 8 to simultaneously pass through the through hole of the limiting post 20, achieving a dual function with a single rope: both constraining the initial position of the transverse insert 6 through the limiting plate 7, and maintaining the limiting post 20 in an elevated state through the through hole. Initially, the elastic limiting rope 8 passes through the through hole of the limiting post 20 and connects to the end plate 15, the tension spring 11 is in a stretched state, and the limiting post 20 is pulled upward away from the locking hole 12 of the transverse insert 6 by the elastic limiting rope 8; when the elastic limiting rope 8 breaks from the breakage notch 9 during the tensioning process, the tension of the elastic limiting rope 8 disappears, the tension spring 11 contracts and pushes the limiting post 20 downward, causing the limiting post 20 to automatically slide into the locking hole 12 on the transverse insert 6, while the end plate 15 loses its constraint after the elastic limiting rope 8 breaks. Its technical effects are as follows: the same elastic limiting rope 8 achieves dual initial limiting of the transverse insertion rod 6 and the limiting column 20, and triggers the downward locking of the limiting column 20 simultaneously after breakage. The structure is compact and the linkage is reliable. After the limiting column 20 is inserted into the locking hole 12, the transverse insertion rod 6 is mechanically locked, which can resist the vibration and impact during subsequent concrete pouring and use, ensure the long-term stability of the radial expansion body, and significantly improve the long-term safety of the pull-out structure.

[0023] In one feasible embodiment, a guide block 14 is provided inside the sliding hole 18 and is fixed to the inner wall of the sliding hole 18. A guide groove 13 is provided on the transverse insert rod 6, and the guide block 14 is located in the guide groove 13.

[0024] The purpose of setting the guide block 14 and guide groove 13 is to prevent the transverse insert rod 6 from rotating circumferentially during movement, thereby preventing the limiting post 20 from misaligning and entering the locking hole 12 due to rotation. When the transverse insert rod 6 moves axially within the sliding hole 18, the guide block 14 is always embedded in the guide groove 13 of the transverse insert rod 6, forcibly constraining and guiding the movement direction of the transverse insert rod 6, ensuring that it can only move in a straight line and cannot rotate. The technical effect is: to eliminate the risk of alignment failure caused by the rotation of the transverse insert rod 6 to the locking mechanism, and to ensure reliable alignment between the limiting post 20 and the locking hole 12; at the same time, due to the constraint effect of the guide block 14, the diameter of the locking hole 12 can be appropriately larger than that of the limiting post 20, thereby reducing the machining accuracy requirements and improving the assembly tolerance, simplifying the manufacturing process and reducing costs without affecting the locking effect.

[0025] In one feasible embodiment, a compression spring 16 is provided between the end plate 15 and the fixing plate 19, with one end of the compression spring 16 abutting against the end plate 15 and the other end of the compression spring 16 abutting against the fixing plate 19, and the portion of the elastic limiting rope 8 located between the outer surfaces of the end plate 15 and the fixing plate 19 is treated with adhesive hardening.

[0026] The compression spring 16 is in a compressed state, applying an outward elastic force to the end plate 15. However, due to the constraint of the elastic limiting rope 8, the end plate 15 cannot move outward. The part of the elastic limiting rope 8 that has been hardened with adhesive will not bend or deform and will remain straight. When the elastic limiting rope 8 breaks at the breakage notch 9, the elastic force of the compression spring 16 is released, pushing the end plate 15 to move outward. The end plate 15 pulls the hardened section of the elastic limiting rope 8 (which is in the form of a rigid rod) outward, thereby quickly clearing the broken rope fragments from the sliding hole 18 and the falling area of ​​the limiting post 20. The technical effect is as follows: by applying adhesive hardening treatment to a specific section of the elastic limiting rope 8, it remains a rigid straight rod after breaking, avoiding the entanglement, bending or jamming that may occur after the traditional soft rope breaks (avoiding the problem that the limiting post 20 is blocked from moving downward due to being stretched and unable to retract after breaking); the compression spring 16 pushes the hardened section outward as a whole, reliably clearing obstacles that may hinder the downward movement of the limiting post 20, thereby ensuring the smooth triggering of the locking mechanism.

[0027] In one feasible embodiment, the fixing ring 3 is provided with a plurality of circumferentially distributed mounting holes 4, the outer surfaces of a plurality of ordinary steel bars 1 are fixed in the mounting holes 4, the ends of the loosely bonded prestressing tendons 21 are provided through the mounting holes 4, and the ends of the loosely bonded prestressing tendons 21 are provided with a stop block 17, the diameter of the stop block 17 being larger than the diameter of the mounting hole 4.

[0028] The outer surface of the ordinary reinforcing bar 1 is fixed in the mounting hole 4 on the fixing ring 3, thus connecting it to the fixing ring 3. After the end of the loosely bonded prestressing tendon 21 passes through the mounting hole 4, it is secured below the fixing ring 3 by a stop block 17 with a diameter larger than the mounting hole 4, thereby anchoring the lower end of the loosely bonded prestressing tendon 21 to the fixing ring 3. The technical effect is that by utilizing the cooperation of the mounting hole 4 and the stop block 17, the ordinary reinforcing bar 1 and the loosely bonded prestressing tendon 21 are integrated and fixed on the same fixing ring 3, resulting in a compact structure. At the same time, it ensures that the lower end of the loosely bonded prestressing tendon 21 has a reliable anchoring point during tensioning, preventing slippage and simplifying the manufacturing process of the lower end of the reinforcing cage.

[0029] In one feasible embodiment, the slow-setting prestressing tendon 21 includes an outer sleeve containing steel strands, with a slow-setting adhesive filling the space between the steel strands and the outer sleeve.

[0030] When untensioned, the steel strands can slide relative to the outer sleeve or remain free. During tensioning, the steel strands are stretched, and the retarded adhesive inside the outer sleeve allows the steel strands to move before curing. After tensioning, the retarded adhesive gradually cures over time, bonding the steel strands to the outer sleeve to form a bonded prestressed tendon. The technical advantages are: the retarded adhesive provides the convenience of unbonded tendons during construction (single-strand tensioning, low friction loss), while providing the durability and anchorage reliability of bonded tendons after curing, avoiding the long-term slippage risk of traditional unbonded prestressed tendons, and protecting the steel strands from corrosion.

[0031] A construction method for cast-in-place concrete piles includes the following construction steps: S1. After the pile foundation hole is excavated, the steel cage structure is fabricated or assembled on site. S2. Hoist the pre-fabricated steel cage and accurately position it inside the pile foundation hole; S3. Install tensioning equipment on the ground and perform initial tensioning on the slow-bonded prestressed tendon 21 located at the upper end of the pile hole, so that it is straightened and pushes the transverse insertion rod 6 to move outward until the elastic limit rope 8 breaks due to tension. S4. Pour concrete into the pile hole and cure it. After the concrete strength reaches the design threshold, use tensioning equipment to perform secondary tensioning on the loosely bonded prestressed tendon 21 until the applied prestress meets the design requirements. Then anchor the upper end of the loosely bonded prestressed tendon 21. S5. Once the concrete in the pile foundation hole has completely hardened, the construction of the concrete cast-in-place pile is complete.

[0032] Specifically, the process begins with excavating the pile foundation hole and fabricating or assembling the reinforcing cage structure on-site. At this stage, the loosely bonded prestressed tendons 21 are relaxed and bent inward. The reinforcing cage is then hoisted and lowered into the pile foundation hole. Since the lower end does not flare outward, the lowering process is smooth. Next, tensioning equipment is deployed on the ground to initially tension the loosely bonded prestressed tendons 21 located at the upper end of the pile foundation hole, straightening them and pushing the transverse insert 6 outward until the elastic limiting rope 8 breaks due to tension, causing the transverse insert 6 to extend outward. Concrete is then poured into the pile foundation hole. Once the concrete strength reaches 75% or more of the design strength (meeting the post-tensioning requirements of JGJ 387-2017 "Technical Specification for Loosely Bonded Prestressed Concrete Structures"), the loosely bonded prestressed tendons 21 are tensioned a second time to the design prestress value and anchored. Finally, construction is completed after the concrete in the pile foundation hole has completely hardened. Its technical effects are as follows: by coordinating step-by-step tensioning (initial tensioning triggers the expansion mechanism, and secondary tensioning applies the design prestress) with the concrete pouring sequence, it ensures that the transverse insert 6 has extended outward to form an enlarged head before pouring, and can effectively apply prestress before the concrete sets, avoiding prestress loss due to early tensioning of the concrete. At the same time, it ensures that the steel cage is lowered without interference, which significantly improves construction efficiency and the pull-out resistance of the pile.

[0033] It should be noted that this technical solution sets up two completely independent tensioning processes. The stress objects, implementation purposes, and stress-bearing substrates of the two processes are completely different: the initial tensioning in S3 is only used to unlock the expansion mechanism of the transverse insert rod 6 at the bottom of the pile. The tensioning load only overcomes the breaking tension of the elastic limit rope 8. The stress-bearing components are only the lower end fixing plate 19 of the steel cage, the transverse insert rod 6, and the loosely bonded prestressing tendon 21. No design prestress is applied, and no concrete bearing support is required. It can be completed before pouring concrete. The initial tensioning only realizes the unlocking and expansion of the mechanism. There is no effective prestress retention, and there is no problem of premature loss of prestress. In S4, secondary tensioning is the core process for applying the design prestress for pull-out resistance. It strictly follows the mandatory requirements of JGJ 387-2017. Tensioning and anchoring are carried out after the concrete has cured to 75% of its design strength. At this time, the concrete forms a continuous and complete bearing matrix, and the prestress generated by tensioning can be completely transferred to the concrete to offset the tensile stress generated by the pull-out load, inhibit concrete cracking, and fully realize the improvement of the pull-out bearing capacity of the cast-in-place pile. This is consistent with the general construction logic and timing of existing slow-bonded prestressed pull-out piles.

[0034] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made to it in form and detail without departing from the scope defined by the claims of the present invention.

Claims

1. A cast-in-place concrete pile, comprising a reinforcing cage structure disposed within a pile foundation hole and concrete poured into the pile foundation hole, characterized in that: The steel cage structure includes several circumferentially distributed ordinary steel bars (1). Several steel rings (2) are sleeved on the outer side of the ordinary steel bars (1). The ordinary steel bars (1) are all fixed on the steel rings (2). The lower end of each ordinary steel bar (1) is provided with a fixing ring (3). The fixing ring (3) is fixed on the ordinary steel bar (1). A slow-bonding prestressing tendon (21) is provided between adjacent ordinary steel bars (1). One end of the slow-bonding prestressing tendon (21) is fixed on the fixing ring (3). The other end of the prestressing tendon (21) extends upward to the outside of the pile hole. When the ends of several of the loosely bonded prestressing tendons (21) are tensioned, the loosely bonded prestressing tendons (21) contact the inner side of the reinforcing ring (2). The outer side of the ends of the loosely bonded prestressing tendons (21) are provided with fixing plates (19). One end of the fixing plate (19) is fixed to the fixing ring (3). The other end of the fixing plate (19) is provided with a sliding hole (18). A transverse insert (6) is provided in the sliding hole (18). (6) The transverse insert (6) is slidably connected to the sliding hole (18). One end of the transverse insert (6) is provided with a connecting ring (5). The connecting ring (5) is fixed to the inward end of the transverse insert (6) and is slidably sleeved on the loosely bonded prestressed tendon (21). The outer side of the sliding hole (18) of the fixing plate (19) is provided with several elastic limiting ropes (8). One end of the elastic limiting rope (8) is connected to the fixing plate (19), and the other end of the elastic limiting rope (8) is provided with a limiting plate (7). The other end of the elastic limiting rope (8) is fixed to the limiting plate (7). The middle part of the limiting plate (7) is fixed to the outward end of the transverse insert (6). The elastic limiting rope (8) is provided with a breakage notch (9). The elastic limiting rope (8) is used to limit the position of the transverse insert (6) so that the inward end of the transverse insert (6) bends the loosely bonded prestressed tendon (21) inward. When the loosely bonded prestressed tendon (21) is stretched straight, the elastic limiting rope (8) breaks at the breakage notch (9).

2. A concrete cast-in-place pile according to claim 1, characterized in that: One end of the elastic limiting rope (8) slides through the limiting plate (7), and an end plate (15) is provided on the end of the elastic limiting rope (8) located inside the fixed plate (19). The end plate (15) is fixed to the elastic limiting rope (8). The upper end of the fixed plate (19) is provided with a limiting hole, which is connected to the sliding hole (18). A limiting post (20) is provided inside the limiting hole. The lower end of the limiting post (20) is provided with a through hole, through which the elastic limiting rope (8) passes. The limiting hole is located at the end above the fixed plate (19). A tension spring (11) is provided on the upper part. One end of the tension spring (11) is fixed to the upper end of the limiting post (20), and the other end of the tension spring (11) is fixed to the fixing plate (19). A locking hole (12) is provided on the inward end of the transverse insert (6). When the loosely bonded prestressed tendon (21) is stretched and pushes the transverse insert (6) to move outward to the limit position, the elastic limiting rope (8) breaks from the breakage notch (9), and the tension spring (11) pushes the limiting post (20) downward, so that the limiting post (20) slides into the locking hole (12).

3. A concrete cast-in-place pile according to claim 2, characterized in that: The sliding hole (18) is provided with a guide block (14), which is fixed on the inner wall of the sliding hole (18). The transverse insert (6) is provided with a guide groove (13), and the guide block (14) is located in the guide groove (13).

4. A concrete cast-in-place pile according to claim 2, characterized in that: A compression spring (16) is provided between the end plate (15) and the fixing plate (19). One end of the compression spring (16) abuts against the end plate (15), and the other end of the compression spring (16) abuts against the fixing plate (19). The portion of the elastic limiting rope (8) located between the outer surfaces of the end plate (15) and the fixing plate (19) is treated with adhesive hardening.

5. A concrete cast-in-place pile according to claim 1, characterized in that: The fixing ring (3) is provided with several circumferentially distributed mounting holes (4), and the outer surfaces of several ordinary steel bars (1) are fixed in the mounting holes (4). The end of the slow-bonding prestressed tendon (21) passes through the mounting hole (4) and is provided with a stop block (17) at the end of the slow-bonding prestressed tendon (21). The diameter of the stop block (17) is larger than the diameter of the mounting hole (4).

6. A concrete cast-in-place pile according to claim 1, characterized in that: The slow-setting prestressed tendon (21) includes an outer sleeve, in which steel strands are provided, and a slow-setting adhesive is filled between the steel strands and the outer sleeve.

7. A construction method for a concrete cast-in-place pile according to any one of claims 1-6, characterized in that: The construction steps include the following: S1. After the pile foundation hole is excavated, the steel cage structure is fabricated or assembled on site. S2. Hoist the pre-fabricated steel cage and accurately position it inside the pile foundation hole; S3. Tensioning equipment is set up on the ground to initially tension the slow-bonded prestressed tendon (21) located at the upper end of the pile hole, so that it is straightened and pushes the transverse insertion rod (6) to move outward until the elastic limiting rope (8) breaks due to the tension. S4. Pour concrete into the pile hole and cure it. After the concrete strength reaches the design threshold, use the tensioning equipment to perform secondary tensioning on the slow-bonded prestressing tendon (21) until the applied prestress meets the design requirements. Then anchor the upper end of the slow-bonded prestressing tendon (21). S5. Once the concrete in the pile foundation hole has completely hardened, the construction of the concrete cast-in-place pile is complete.

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