Cement-soil composite variable-diameter pile with inner core provided with spiral ribs and construction method of cement-soil composite variable-diameter pile

Abstract

The invention discloses a cement soil composite variable-diameter pile with a spiral rib in an inner core and a construction method thereof, the composite pile comprises a peripheral cement soil pile body and an inner core precast concrete pile, the inner core is a prestressed high-strength concrete pipe pile, and at least one continuous spiral rib is arranged on the outer wall of the inner core in the axial direction. The peripheral cement soil pile body is formed by stirring cement soil in situ, the diameter of the pile body is variable in the depth direction, and the peripheral cement soil pile body comprises at least one diameter expanding section with the diameter larger than that of the standard section. The inner core is implanted into the peripheral cement soil pile body which is not initially set and is coaxial with the peripheral cement soil pile body. Mechanical engagement and side friction resistance of the inner core and the outer core are remarkably enhanced through the spiral rib structure of the inner core, meanwhile, a soft soil layer can be reinforced in a targeted mode through the variable-diameter design of the peripheral pile body, the stress performance and the material consumption are optimized, and the pile has the advantages of being high in bearing capacity, good in pulling resistance, high in construction efficiency, economical, environmentally friendly and the like.

Description

Technical Field

[0001] This invention relates to the field of foundation treatment and pile foundation construction technology in building engineering, specifically to a cement-soil composite variable diameter pile with helical ribs in the inner core, which is suitable for soft soil foundation reinforcement, can significantly improve bearing capacity, and has economic and environmental protection characteristics, as well as its construction method. Background Technology

[0002] In coastal, riverine, and inland lake sedimentary areas, thick layers of soft soil, such as silt, silty clay, and soft clay, are widely distributed. These soft soils are characterized by high natural water content, large void ratio, high compressibility, low shear strength, and poor permeability. For engineering construction on such foundations, such as the construction of highways, railways, ports, and high-rise buildings, foundation reinforcement is essential to meet the requirements for bearing capacity and deformation control.

[0003] Cement-soil mixing piles and prestressed high-strength concrete pipe piles (PHC pipe piles) are two commonly used foundation treatment methods. Cement-soil mixing piles use specialized mixing machinery to forcibly mix soft soil with a solidifying agent deep within the foundation. The physical-chemical reaction between the solidifying agent and the soft soil causes the soil to harden into a high-quality foundation with integrity, water stability, and a certain strength. Its advantages include vibration-free, noise-free, and pollution-free construction, and it can effectively improve the bearing capacity of the foundation. However, the pile strength is relatively low, the bearing capacity is limited, and the quality of the pile is greatly affected by soil uniformity and construction operations. PHC pipe piles, on the other hand, have advantages such as high pile strength, large bearing capacity, fast construction speed, and stable and reliable quality. However, driving them in soft soil can produce a significant soil squeezing effect, adversely affecting the surrounding environment. Furthermore, their high strength performance is often not fully realized due to the low side friction resistance provided by the surrounding soft soil.

[0004] To combine the advantages of both types of piles and overcome their respective disadvantages, various forms of combined or composite piles have emerged in the prior art. For example, a published patent discloses a construction method for a composite foundation of cement-soil mixing piles and prestressed pipe piles. This method involves inserting prestressed pipe piles before the cement-soil mixing piles have initially set, thus forming a composite pile. This process utilizes the cement-soil mixing piles to provide a construction channel and lateral restraint for the pipe piles, while the pipe piles compensate for the low strength of the cement-soil mixing piles.

[0005] However, existing composite piles still face technological bottlenecks that need to be overcome. Firstly, the performance of the bonding surface between the inner and outer cores is crucial. Traditional smooth pipe piles rely primarily on adhesive force and interfacial friction to bond with the cement-soil mixture. Due to the shrinkage of the cement-soil mixture during solidification, tiny gaps easily form between them, leading to insufficient interfacial friction. Under vertical loads, the pipe pile and cement-soil mixture may slip relative to each other, preventing true synergistic operation. Secondly, the pile's stress distribution is poorly matched to geological conditions. Deep soft soil layers are often not uniform, potentially containing multiple layers of soft soil or interlayers with different properties. Using piles of uniform diameter makes it impossible to locally reinforce the weakest soil layer, resulting in material waste or insufficient local bearing capacity. Thirdly, the level of refinement and automation in construction processes needs improvement, especially in ensuring the verticality of the inner core and the concentricity of the inner and outer cores. Traditional methods relying on manual labor and experience are insufficient to guarantee high-quality pile construction.

[0006] Therefore, there is an urgent need to develop a new type of composite pile and its construction method that can effectively enhance the bonding force between the inner and outer core interfaces, achieve optimal matching between the pile bearing capacity and geological conditions, and has high construction accuracy and high efficiency. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a cement-soil composite variable diameter pile with helical ribs in the inner core and its construction method.

[0008] This invention is achieved through the following technical solution: This invention provides a cement-soil composite variable diameter pile with helical ribs in the inner core, comprising an outer cement-soil pile body and an inner precast concrete pile. The inner core precast concrete pile is a prestressed concrete pipe pile, and its outer wall is provided with at least one continuous protruding spiral rib along the axial direction. The outer cement-soil pile body is a columnar body formed by in-situ mixing of cement and soil. Its pile body diameter is set to be variable along the depth direction, including at least one standard section and at least one enlarged section with a diameter greater than the standard section. The inner core precast concrete pile is coaxially implanted in the outer cement-soil pile body before initial setting, and the spiral rib is embedded and engaged in the cement-soil of the outer cement-soil pile body.

[0009] Furthermore, the cross-section of the spiral rib is trapezoidal, rectangular, or semi-circular, with a height of 10mm to 50mm and a width of 20mm to 80mm; the spiral angle of the spiral rib is 15° to 45°.

[0010] Furthermore, the inner core precast concrete pile is composed of multiple sections of pipe pile connected by end plates and connectors.

[0011] Furthermore, the enlarged diameter section is positioned at a depth corresponding to the soft soil layer of the foundation; the diameter D of the enlarged diameter section...扩 With the diameter D of the standard segment 标 The ratio D 扩 / D 标 It ranges from 1.2 to 2.0.

[0012] This invention also provides a construction method for a cement-soil composite variable-diameter pile with helical ribs in the inner core, comprising the following steps: S1. Precast inner core: Precast prestressed high-strength concrete pipe pile segments with spiral ribs in the factory; S2. Pile location measurement and site leveling: Determine the pile location and level the construction site; S3. Construction of the outer cement-soil pile body: Using a mixing drill with variable diameter and hole expansion function, the pile is driven, sprayed and mixed at the designed pile position. By controlling the opening and closing of the drill bit's expanding wing mechanism, an enlarged diameter section is formed in the preset soft soil layer depth range, forming a variable diameter outer cement-soil pile body that has not yet set. S4. Core Implantation Preparation: After step S3 is completed, immediately move the static pressure pile driver to the pile position and perform leveling and centering to ensure that the pile driving point coincides with the central axis of the outer cement-soil pile body. S5. Core Implantation and Connection: Before the cement and soil in the outer cement-soil pile body initially set, the first precast pipe pile segment is lifted by a static pressure pile driver and vertically inserted into the outer cement-soil pile body, and statically pressed to the set depth; then the second precast pipe pile segment is lifted and firmly connected to the previous segment through end plates and connectors, and static pressure is continued. This process is repeated until all pipe pile segments are implanted to the design elevation, forming a complete precast concrete pile with an inner core. S6. Curing and Shaping: After static curing, once the outer cement-soil pile body has finally hardened, a cement-soil composite variable diameter pile with spiral ribs in the inner core is formed.

[0013] Furthermore, in step S3, the mixing drill includes a drill rod and a variable-diameter mixing drill bit disposed at the bottom end of the drill rod; the variable-diameter mixing drill bit includes at least two radially extendable or oscillating wing cutters; the unfolding angle or extension length of the wing cutters is controlled by hydraulic or mechanical means to achieve cutting and mixing of pile holes of different diameters.

[0014] Furthermore, in step S5, when the static pressure pile driver is pressing the inner core precast concrete pile, the pile driving force is monitored in real time, and the pile driving force is maintained within a preset range by adjusting the static pressure speed, so as to ensure that the verticality deviation of the inner core is less than 0.5%.

[0015] Furthermore, the cement slurry is composed of the following raw materials in parts by weight: 100 parts cement, 20-30 parts fly ash, 5-10 parts bentonite, 50-65 parts water, 0.5-1.5 parts water-reducing agent, and 1-3 parts early-strength agent.

[0016] Furthermore, step S6 is followed by step S7, construction of pile cap and cushion layer: the excess part of the pile head of the composite pile is removed to the design elevation, a reinforced concrete pile cap is constructed, and then a cushion layer and a concrete cushion layer are laid on the pile top and the soil between the piles to form a composite foundation that shares the load.

[0017] The advantages and beneficial effects of this invention are as follows: 1. Significantly Enhanced Interface Bonding: The spiral rib design on the outer wall of the inner core is the most crucial innovation of this invention. It changes the traditional single bonding-friction force transmission mode between smooth piles and cement-soil, introducing a "mechanical interlocking" or "threaded anchoring" mechanism. When subjected to vertical loads, the spiral ribs, like the threads of a screw, form a strong interlock with the surrounding cement-soil, effectively resisting the relative slippage between the inner and outer cores, allowing them to truly "integrate" and work together. This more effectively transfers the pile top load to the surrounding soil and pile end, significantly improving the single pile bearing capacity and pull-out resistance.

[0018] 2. Highly Matched Bearing Capacity to Geological Conditions: The variable diameter design of the outer cement-soil piles allows for site-specific adjustments to the pile's bearing capacity. For the weakest soil layers requiring reinforcement, an enlarged diameter section increases the pile's side surface area, resulting in greater side friction and compensating for bearing capacity losses due to low soil strength. In areas with relatively good soil quality, a standard section is used, saving materials and labor. This variable cross-section design optimizes material allocation, avoiding wasteful "one-size-fits-all" approaches, resulting in significant technical and economic benefits.

[0019] 3. Significantly improved construction accuracy and quality: The construction method proposed in this invention, through the concept of "quick insertion" (inserting the inner core immediately after the outer pile body is completed), and the use of a static pressure pile driver with automatic leveling, laser centering, and real-time monitoring functions, ensures the timeliness of the inner core insertion and the accuracy of verticality and concentricity, greatly reducing quality problems such as eccentricity, tilting, and poor interface bonding caused by improper construction operations.

[0020] 4. High Overall Benefits: This composite pile combines the advantages of high strength and reliable quality of PHC pipe piles with the vibration-free, soil-free, and environmentally friendly construction of cement-soil mixing piles. The spiral rib and variable diameter design significantly improves pile performance without substantially increasing material costs. Combined with a streamlined construction organization, the overall construction efficiency is high, the construction period is short, and it offers excellent economic and social benefits. It is particularly suitable for large-scale urban renewal projects and riverside / coastal development projects with stringent environmental and time requirements. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the structure of the cement-soil composite variable diameter pile with spiral ribs in the inner core of the present invention. Figure 2 This is a schematic diagram of the cross-sectional structure of the cement-soil composite variable diameter pile with helical ribs in the inner core according to the present invention. Figure 3 This is a partially enlarged schematic diagram of the pipe pile segment connection of the present invention; Figure 4 This is a schematic diagram of the variable diameter stirring drill bit structure of the present invention (with the fins extended). Figure 5 This is a schematic diagram of the static pressure implantation process of the inner core of the present invention. Detailed Implementation

[0023] To enable those skilled in the art to better understand the present invention, the technical solution of the present invention will be further described below with reference to specific embodiments.

[0024] Example 1 This embodiment provides a cement-soil composite variable-diameter pile with helical ribs in the inner core, the structure of which is as follows: Figure 1 , Figure 2 As shown.

[0025] Reference Figure 1 The composite pile is mainly composed of an outer cement-soil pile body 1 and an inner precast concrete pile 2, which are coaxially arranged.

[0026] The outer cement-soil pile body 1 is a variable-diameter column formed through in-situ mixing. According to the geological survey report of a certain project, there is a layer of fluid silty clay at a depth of 4m to 8m below the surface. This soil layer has poor mechanical properties. Therefore, in this depth range (4m-8m), the outer cement-soil pile body 1 is designed as an arc-shaped enlarged diameter section 12, with a maximum diameter D. 扩 The diameter is 800mm; while in the relatively good soil layers (such as plastic silty clay) in the depth range of 8m-11m and in the surface fill of 0-4m, the outer cement-soil pile body 1 is a standard section 11 with a diameter of equal diameter, D. 标 It is 500mm. D 扩 / D 标 =1.6, which meets the preferred range of 1.2~2.0; in the bottom section of the outer cement-soil pile body 1 at a depth of less than 11m, the outer cement-soil pile body 1 is designed as a bottom diameter-enlarged section 13, with a diameter D底 The length is 900mm; preferably, the total length of the entire outer cement-soil pile body 1 is 15m.

[0027] Reference Figure 2 and Figure 3 The precast concrete core pile 2 is a factory-prefabricated prestressed high-strength concrete pipe pile (PHC pile) using the prestressed concrete method, with a concrete strength grade of C80. The outer diameter of the pile body is 300mm. Its most significant feature is that continuous spiral ribs 21 are provided axially on the outer wall of the precast concrete core pile 2. Preferably, there are multiple spiral ribs 21. In this embodiment, see Appendix. Figure 2 There are four spiral ribs 21. In more detail, the cross-section of each spiral rib 21 is trapezoidal, with a rib height of 25mm, a rib top width of 15mm, and a rib bottom width of 30mm. The spiral angle of the spiral rib 21 is set to 30°. During prefabrication, the spiral rib 21 is integrally formed with the pipe pile body using a special mold, ensuring the integrity and strength of the structure.

[0028] Reference Figure 1 The total length of the precast concrete core pile 2 is 15m. Since the standard length of a single PHC pipe pile is 10m, it needs to be composed of two pipe piles connected together. (Refer to...) Figure 3 At the connection point of the two pipe pile sections, each end is provided with a steel end plate 22. The spiral ribs 21 of the upper and lower pile sections are broken at the end plate 22. To ensure the reliability of the connection, after the two pile sections are aligned, the bevels of the upper and lower end plates 22 are welded together to form a strong connector 23, ensuring that the connection will not break during subsequent pile driving and use.

[0029] When the precast concrete core pile 2 is inserted into the uncured outer cement-soil pile body 1, the outer wall of the precast concrete core pile 2 and the spiral ribs 21 are completely encased in cement-soil. After the cement-soil hardens, the spiral ribs 21, like the threads of a screw, are deeply embedded and interlocked in the surrounding cement-soil, forming a strong mechanical interlocking structure.

[0030] Example 2 This embodiment details the construction method for building the composite pile described in Embodiment 1, and the process of this method is combined with... Figure 4 and Figure 5 To elaborate.

[0031] S1, Inner Core Prefabrication In the factory, PHC pipe pile steel molds with trapezoidal cross-section spiral ribs 21 are fabricated according to the design drawings. Cleaned prestressed steel bars are inserted into the molds and tensioned, then C80 concrete is poured. After centrifugal molding, normal pressure and high-pressure steam curing, high-strength, high-precision spiral ribbed pipe pile segments (10m / segment in this embodiment) are produced. After passing inspection, they are transported to the construction site for use.

[0032] S2, Pile location measurement and site leveling Before construction, GPS-RTK or a total station was used to accurately lay out all pile positions according to the design drawings, and wooden stakes were driven in to mark them. Then, a bulldozer was used to level the construction site, remove debris, and lay a layer of crushed stone about 30cm thick to ensure the stability of large construction machinery during movement and operation.

[0033] S3, Construction of peripheral cement-soil piles The dedicated triaxial or multiaxial mixing drill rig is moved to the first pile location, and the drill rod 31 is adjusted to be vertical using a theodolite and its own verticality adjustment system. The core component of this drill rig is the variable diameter mixing drill bit 32, the structure of which is as follows: Figure 4 As shown. The drill bit 32 is equipped with three sets of swingable wing-expanding cutters 321, and the opening angle of each set of wing-expanding cutters 321 is controlled by a hydraulic cylinder.

[0034] The drilling rig is started, and the drill rod 31 rotates forward and sinks at a set speed. Before sinking to a depth of 4m (i.e., the construction area of ​​the standard section 11 with equal diameter), the control system keeps the expanding blade 321 in the retracted state, at which time the cutting diameter of the drill bit is 500mm. At the same time, through the ground slurry preparation system, cement slurry is prepared according to the formula (100kg cement, 25kg fly ash, 8kg bentonite, 60kg water, 1kg polycarboxylate superplasticizer, 2kg triethanolamine early strength agent), and pumped under high pressure to the slurry nozzle 322 at the bottom of the drill rod 31. The slurry is continuously sprayed and stirred at a pressure of 0.5MPa to carry out the construction of the standard section 11 with equal diameter of the outer cement-soil pile body 1.

[0035] When the sinking depth reaches 4m, in the depth range of 4m-8m, the control system drives the expanding blade 321 to expand outward in the set manner to carry out the construction of the arc-shaped expansion section 12 of the outer cement-soil pile body 1.

[0036] After the drill bit sinks to 8m, the control system controls the expanding blade 321 to retract. The drill bit continues to sink to a depth of 11m in the retracted state to carry out the construction of the second standard section 11 of equal diameter of the outer cement-soil pile body 1.

[0037] When the drill bit descends to 11m, in the depth range of 11m-15m, the control system drives the expanding blade 321 to expand outward in the set manner to carry out the construction of the bottom diameter expansion section 13 of the outer cement-soil pile body 1.

[0038] Finally, drill rod 31 is reversed and lifted. During the lifting process, the extension and retraction of the expanding blade 321 are controlled according to each depth range, and grouting and mixing continue throughout the process to ensure uniform mixing of cement and soil. After being lifted to the ground surface, a non-cured variable-diameter outer cement-soil pile body 1 is formed at the original pile location, consisting of a standard section 11 of equal diameter, an arc-shaped expanded diameter section 12, another standard section 11 of equal diameter, and a bottom expanded diameter section 13.

[0039] S4. Core Implantation Preparation Reference Figure 5 The moment the mixing drilling rig completes construction and moves to its new location, a pre-positioned static pressure pile driver 4, equipped with an automatic control system and a high-precision laser alignment instrument 42, moves to the pile position. The operator activates the pile driver's automatic leveling system via the control platform to ensure the machine is level. Simultaneously, the laser alignment instrument 42 is activated, aligning the emitted laser beam with the center point of the pile position. The hydraulic system is then used to fine-tune the machine's position, ensuring that the center point of the pile driving platform's clamp 41 coincides with the central axis of the surrounding cement-soil pile 1, with the deviation controlled within 10mm.

[0040] S5, Core Implantation and Connection After preparations are complete, the core implantation begins. First, a crane is used to lift the first (10m long) PHC pipe pile segment with spiral ribs 21 into the clamp 41 of the static pressure pile driver 4. The clamp 41 holds the pipe pile tightly, and the verticality is checked again by the bidirectional plumb bob and sensor on the pile driver to ensure that the verticality deviation is less than 0.5%.

[0041] The static pressure system is activated, and the clamp 41 slowly presses down the pipe pile, precisely inserting it into the center of the outer cement-soil pile body 1. The pile driving speed is maintained at a constant speed of approximately 1.0 m / min, and the pile driving force is monitored in real time. Static pressure is stopped when the top of the first pile section is about 1.2 m above the ground (to facilitate pile splicing operations).

[0042] At this point, the second (5m long) pipe pile segment is hoisted. Construction workers quickly clean the surface of the end plates 22 of both pile segments, exposing their metallic luster. The second pile segment is lifted, aligning its lower end plate with the upper end plate of the first pile segment. Alignment is aided by guide grooves and positioning pins on the end plates, ensuring the axes of the two pile segments are consistent. After verification, certified welders use carbon dioxide gas shielded welding to perform symmetrical, layered welding along the bevel of the end plates, forming a robust connector 23. After the weld cools, a visual inspection is conducted to ensure there are no defects such as porosity or slag inclusions.

[0043] After welding, the static pile driver 4 is started again to drive the two connected pile sections in together. The pile driving force is monitored in real time. If the pile driving force suddenly increases or exceeds the set range, the pile driving speed is appropriately reduced to ensure smooth implantation. Finally, the top of the pile is driven to the design elevation. At this point, the inner core precast concrete pile 2 has been completely implanted into the outer cement-soil pile body 1, and the spiral ribs 21 on it have also been completely embedded and squeezed the surrounding cement-soil.

[0044] S6, Curing and Shaping After the inner core is implanted, a warning line is set up around the pile location to prevent mechanical crushing. The pile is then left to cure, allowing the cement-soil to undergo a hydration reaction in the underground humidity and temperature environment, gradually hardening. Typically, after 28 days of curing, the cement-soil reaches its design strength. At this point, the cement-soil composite variable-diameter pile with spiral ribs in the inner core is complete and can proceed to the next step.

[0045] S7. Construction of pile caps and foundation layers After the composite piles reach their design strength, a hydraulic pile saw is used to cut off and remove any excess pile heads that exceed the design pile top elevation. Then, a reinforcing cage is tied to the pile top, a circular steel mold is erected, C35 concrete is poured, and compacted to form the pile cap. Finally, a 30cm thick layer of graded crushed stone is laid between the pile caps and on the soil between the piles throughout the construction area, and compacted with a plate vibrator. A 15cm thick layer of C20 plain concrete is then poured on top of the cushion layer, smoothed, and finished to serve as the surface for the subsequent foundation slab. At this point, the entire composite foundation construction is complete.

[0046] The cement-soil composite variable diameter pile with spiral ribs in the inner core and its construction method provided by this invention effectively solve the key problems existing in the prior art, such as weak interface bonding, mismatch between performance and geological conditions, and low construction efficiency, through innovative structural design and matching precise construction technology. It has achieved significant progress in pile foundation engineering technology and has extremely high promotion and application value.

[0047] For ease of explanation, spatial relative terms such as “up,” “down,” “left,” and “right” are used in the embodiments to describe the relationship of one element or feature shown in the figures relative to another element or feature. It should be understood that, in addition to the orientations shown in the figures, spatial terms are intended to include different orientations of the device in use or operation. For example, if the device in the figures is inverted, an element described as being “down” of other elements or features would be positioned “up” of those other elements or features. Therefore, the exemplary term “down” can encompass both up and down orientations. The device may be positioned in other ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0048] Moreover, relational terms such as “first” and “second” are used merely to distinguish one component from another that has the same name, without necessarily requiring or implying any such actual relationship or order between the components.

[0049] The above description is only a preferred embodiment of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A cement-soil composite variable-diameter pile with helical ribs in the inner core, characterized in that: This includes the outer cement-soil pile body and the inner precast concrete pile; The inner core precast concrete pile is a prestressed concrete pipe pile, and its outer wall is provided with at least one continuous protruding spiral rib along the axial direction. The outer cement-soil pile body is a columnar body formed by in-situ mixing of cement and soil. Its pile body diameter is set to be variable along the depth direction, including at least one standard section and at least one enlarged section with a diameter greater than the standard section. The inner core precast concrete pile is coaxially implanted in the outer cement-soil pile body before initial setting, and the spiral rib is embedded and engaged in the cement-soil of the outer cement-soil pile body.

2. The cement-soil composite variable diameter pile with helical ribs in the inner core according to claim 1, characterized in that: The cross-section of the spiral rib is trapezoidal, rectangular, or semi-circular, with a height of 10mm to 50mm and a width of 20mm to 80mm; the spiral angle of the spiral rib is 15° to 45°.

3. The cement-soil composite variable diameter pile with helical ribs in the inner core according to claim 1, characterized in that: The inner core precast concrete pile is composed of multiple sections of pipe pile connected by end plates and connectors.

4. The cement-soil composite variable diameter pile with helical ribs in the inner core according to claim 1, characterized in that: The enlarged diameter section is positioned at a depth corresponding to the soft soil layer of the foundation; the diameter D of the enlarged diameter section... 扩 With the diameter D of the standard segment 标 The ratio D 扩 / D 标 It ranges from 1.2 to 2.

0.

5. The construction method of the cement-soil composite variable diameter pile with helical ribs in the inner core according to claim 1, characterized in that... This includes the following steps: S1. Precast inner core: Precast prestressed high-strength concrete pipe pile segments with spiral ribs in the factory; S2. Pile location measurement and site leveling: Determine the pile location and level the construction site; S3. Construction of the outer cement-soil pile body: Using a mixing drill with variable diameter and hole expansion function, the pile is driven, sprayed and mixed at the designed pile position. By controlling the opening and closing of the drill bit's expanding wing mechanism, an enlarged diameter section is formed in the preset soft soil layer depth range, forming a variable diameter outer cement-soil pile body that has not yet set. S4. Core Implantation Preparation: After step S3 is completed, immediately move the static pressure pile driver to the pile position and perform leveling and centering to ensure that the pile driving point coincides with the central axis of the outer cement-soil pile body. S5. Core Implantation and Connection: Before the cement and soil in the outer cement-soil pile body initially set, the first precast pipe pile segment is lifted by a static pressure pile driver and vertically inserted into the outer cement-soil pile body, and statically pressed to the set depth; then the second precast pipe pile segment is lifted and firmly connected to the previous segment through end plates and connectors, and static pressure is continued. This process is repeated until all pipe pile segments are implanted to the design elevation, forming a complete precast concrete pile with an inner core. S6. Curing and Shaping: After static curing, once the outer cement-soil pile body has finally hardened, a cement-soil composite variable diameter pile with spiral ribs in the inner core is formed.

6. The construction method of the cement-soil composite variable diameter pile with helical ribs in the inner core according to claim 5, characterized in that... In step S3, the mixing drill includes a drill rod and a variable diameter mixing drill bit disposed at the bottom end of the drill rod; the variable diameter mixing drill bit includes at least two radially extendable or oscillating wing cutters; the unfolding angle or extension length of the wing cutters is controlled by hydraulic or mechanical means to achieve cutting and mixing of pile holes of different diameters.

7. The construction method of the cement-soil composite variable diameter pile with spiral ribs in the inner core according to claim 5, characterized in that... In step S5, when the static pressure pile driver is pressing the inner core precast concrete pile, the pile driving force is monitored in real time, and the pile driving force is maintained within a preset range by adjusting the static pressure speed to ensure that the verticality deviation of the inner core is less than 0.5%.

8. The construction method of the cement-soil composite variable diameter pile with helical ribs in the inner core according to claim 5, characterized in that... The cement slurry is composed of the following raw materials in parts by weight: 100 parts cement, 20-30 parts fly ash, 5-10 parts bentonite, 50-65 parts water, 0.5-1.5 parts water-reducing agent, and 1-3 parts early strength agent.

9. The construction method of the cement-soil composite variable diameter pile with helical ribs in the inner core according to claim 5, characterized in that... The process after step S6 includes step S7, construction of pile cap and cushion layer: the excess part of the pile head of the composite pile is chiseled off to the design elevation, a reinforced concrete pile cap is constructed, and then a cushion layer and a concrete cushion layer are laid on the pile top and the soil between the piles to form a composite foundation that shares the load.

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