Anti-drag precast pile with protective flanges and construction method of anti-drag precast pile

Abstract

The invention discloses an anti-drag precast pile with protective flanges and a construction method thereof, and belongs to the field of constructional engineering. A precast pile body is divided into a preset resistance reduction pile section and a preset bearing pile section, a plurality of annular expansion flanges are fixed to the resistance reduction pile section at intervals in the axial direction, a resistance reduction layer is arranged between every two adjacent flanges, and the outer diameter of each flange is larger than that of the corresponding resistance reduction layer. Annular groove spaces are defined by the adjacent flanges and the pile body and filled with soft isolation materials with the strength lower than that of concrete of the pile body, and a soft isolation layer is formed. Grouting holes can be preset in the flanges. During construction, a synchronous pile sinking grouting method is adopted; in the pile sinking process, soft isolation materials are injected into the periphery of a pile, and a flange baffle is used for guiding and filling a groove; or a post-grouting method is adopted, and the soft isolation material is injected through the grouting holes after pile sinking. The resistance reduction layer is protected through the flanges, pile soil is thoroughly isolated through the soft isolation layer, the resistance reduction effect is stable and reliable, and construction is easy and convenient.

Description

Technical Field

[0001] This invention relates to the field of building engineering technology, specifically to a precast pile for reducing negative skin friction on the pile side and its construction method, and more particularly to a friction-reducing precast pile with protective flange and its construction method. Background Technology

[0002] In engineering construction in areas with soft soil, fill, and collapsible loess, pile foundations are often used to transfer loads to deep, stable soil layers. However, when the soil around the pile settles due to consolidation, collapsibility, or other reasons, and the settlement exceeds the settlement of the pile itself, the soil will generate a downward frictional force on the pile's side surface, i.e., negative skin friction. The presence of negative skin friction increases the load on the pile, leading to increased pile foundation settlement and even causing engineering accidents such as cracking or tilting of the superstructure.

[0003] To reduce the adverse effects of negative skin friction, the engineering community has developed various drag reduction technologies, which can be mainly divided into three categories: The first type is the coating / wrapping method, such as applying asphalt or grease to the pile surface, or wrapping it with materials such as plastic film or geotextile, as described in document CN112095580A. This method reduces negative skin friction by introducing a medium with a low coefficient of friction at the pile-soil interface. However, its fatal flaw is that when precast piles are driven using hammer driving or static pressure methods, the pile body experiences severe friction with the surrounding soil. The friction-reducing layer on the pile surface is easily scratched, peeled off, or damaged, resulting in a significant reduction in its friction-reducing effect or even complete failure.

[0004] The second type is the casing / casing method, which physically isolates the soil by setting continuous steel or plastic casings around the pile, as described in document CN102628269A. Although this method can effectively isolate the soil, it is complex in structure, expensive, and the casing itself has many problems such as pull-back, corrosion, and difficulty in fixing during removal or long-term use. The construction process requires high precision.

[0005] The third type is the variable cross-section pile method, which affects the soil stress by changing the shape of the pile, such as wedge-shaped piles with a smaller top and a larger bottom, or enlarged-base piles, as exemplified by the enlarged-base irregular pile of Lanzhou Jiaotong University (CN2025). However, this method involves significant modifications to the main structure of the pile, complex design calculations, and still cannot completely avoid direct contact between the soil and the pile.

[0006] In summary, existing technologies have failed to fundamentally solve the problems of the drag-reducing layer being easily damaged during pile driving and how to construct a stable and long-lasting soil-pile isolation system in a simple, reliable, and economical way. They either passively increase the strength of the drag-reducing layer or involve major modifications such as adding sleeves or changing the shape, but they have always lacked a clever solution that systematically optimizes the structure and process. Summary of the Invention

[0007] This invention aims to overcome the many shortcomings of existing technologies and provide a precast pile structure that is ingenious in structure, easy to construct, and has a stable and reliable drag reduction effect. By integrating the two functions of "protection" and "construction", it achieves a leap from "passive drag reduction" to "active isolation", fundamentally solving the dual technical problems of easy damage to the drag reduction layer and incomplete soil-pile isolation.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A drag-reducing precast pile with protective flanges includes a precast pile body. The pile body includes predetermined drag-reducing pile segments and predetermined bearing pile segments divided along its axial direction. The predetermined drag-reducing pile segments typically correspond to soil layer segments that may generate negative skin friction, while the predetermined bearing pile segments correspond to stable soil layer segments that provide bearing capacity.

[0009] The predetermined drag-reducing pile segment is provided with multiple annular extended flanges spaced at intervals along the pile shaft axially. The inner diameter of each extended flange is adapted to the outer diameter of the pile shaft and is fixedly fitted onto the pile shaft. A drag-reducing layer is provided on the pile shaft surface located between two adjacent extended flanges. Furthermore, the outer diameter of each extended flange is larger than the maximum outer diameter of the pile shaft segment with the drag-reducing layer.

[0010] As a core technical improvement of this invention, two adjacent extended flanges and the pile body surface together form an annular groove space for accommodating the isolation material. This annular groove space is filled with a soft isolation material whose strength after curing is lower than that of the pile body concrete, forming a soft isolation layer that separates the pile body from the surrounding soil.

[0011] The soft insulating material can be bentonite slurry solidification, foamed concrete, or low-grade mortar, etc. Its strength is much lower than that of the pile body concrete, and usually also lower than that of the surrounding soil. This allows it to absorb and dissipate shear energy through its own shear deformation, plastic flow, or localized failure when the soil settles, rather than effectively transferring the shear force to the internal pile body.

[0012] To facilitate the filling of soft insulating material, grouting holes communicating with the annular groove space can be pre-set on the extended flange. This design provides the structural basis for the "post-grouting method".

[0013] There are multiple options for fixing the extended flange to the pile body to adapt to different pile types, materials and construction conditions, including but not limited to: welding, flange connection, clamp connection or embedded connection.

[0014] The extended flange may be a metal ring or a high-strength composite material ring. The drag-reducing layer may be made of asphalt, grease, polymer film, or composite geomembrane.

[0015] The present invention also provides a construction method for the above-mentioned drag-reducing precast pile with protective flange, comprising the following steps: 1) Determine the predetermined drag-reducing pile segment and the predetermined bearing pile segment of the pile body; 2) At a predetermined position of the predetermined drag-reducing pile segment, the extended flange and the drag-reducing layer are configured; in this step, there is no requirement for the sequential order of the installation of the extended flange and the setting of the drag-reducing layer, and they can be arranged flexibly according to the actual situation; 3) Drive the precast piles into the foundation soil to the design elevation; 4) Fill the annular groove space formed by the two adjacent extended flanges and the pile body surface with soft isolation material, and form a soft isolation layer after it solidifies.

[0016] Step 4) above can be achieved through two parallel preferred methods: Method 1 (Simultaneous Pile Driving and Grouting): During pile driving, after the first extended flange sinks into the soil, soft insulating material is injected around the pile. As the pile continues to sink, subsequent extended flanges continuously "catch" the soft insulating material above and guide it downwards. Utilizing the natural baffle effect of the extended flanges, the soft insulating material gradually fills the spaces within each annular groove. This method requires no pre-processing of the flanges, making construction extremely simple, and the filling effect is intuitive and reliable.

[0017] Method 2 (Post-grouting method): After the pile driving is completed, soft insulating material is injected into the annular groove space by connecting to the pre-set grouting holes on the extended flange. This method allows for controllable grouting timing and ensures better filling quality, making it suitable for projects with high requirements for the insulating layer.

[0018] Compared with the prior art, the present invention has the following significant advantages: 1. Innovative design for protecting the drag-reducing layer: The extended flange is set on the upper part of the bearing pile segment, which has no impact on the relationship between the bearing pile segment and the soil. Only the drag-reducing pile segment is treated. Because the outer diameter of the extended flange is larger than the outer diameter of the drag-reducing layer, during the pile driving process, the flange contacts the soil first and cuts to enlarge the hole, creating a "safe space" for the drag-reducing layer located therein that is not directly rubbed by the soil. This fundamentally solves the problem of the drag-reducing layer being easily damaged, which has plagued this field for many years.

[0019] 2. "Flange-Insulator Layer" Collaborative Working System: The extended flange not only serves as a protective component but also plays a dual role during service: firstly, it acts as a natural "template," defining the geometric boundaries of the soft insulation layer and ensuring its regular shape; secondly, it acts as an "anchor point," with its root embedded in the soft insulation layer to prevent the insulation layer from slipping off entirely due to its own weight or external forces during long-term use. The flange and the insulation layer form an unbreakable whole.

[0020] 3. Thorough Force Isolation Mechanism: The soft isolation layer completely fills all the pores between the pile and the soil, achieving complete physical isolation. More importantly, its low strength makes it a "sacrificial" energy-dissipating layer. The shear force generated by soil settlement acts on the soft isolation layer, but the low-strength isolation layer dissipates energy through its own deformation or destruction, failing to effectively transfer it to the pile. This achieves true "force" isolation, rather than merely "reducing" friction.

[0021] 4. Flexible and diverse construction techniques: This invention provides two parallel construction methods: "simultaneous pile driving and grouting" and "post-grouting." The former utilizes the baffle effect of the flange to achieve an integrated operation of "pile driving and filling," which is extremely efficient; the latter achieves precise and controllable filling through pre-set grouting holes, ensuring reliable quality. Both methods can be flexibly selected according to project requirements, making it highly adaptable.

[0022] 5. Simple structure, economical and efficient, and widely applicable: The core structure consists only of intermittently arranged annular flanges, making processing and installation convenient. The soft isolation materials used (bentonite, foamed concrete, etc.) are inexpensive. Multiple connection methods, including welding, flanges, clamps, and embedded connections, perfectly adaptable to different types (pipe piles, square piles, solid piles, hollow piles) and different materials (concrete, steel, composite materials) of precast piles, resulting in a wide range of applications and high engineering promotion value. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the overall structure of the drag-reducing precast pile with protective flange in an embodiment of the present invention.

[0024] Figure 2 This is a schematic cross-sectional view of a drag-reducing precast pile with protective flanges in an embodiment of the present invention.

[0025] Figure 3 This is a partial structural diagram of the welded connection between the extended flange and the pile body in an embodiment of the present invention.

[0026] Figure 4 This is a schematic diagram of the extended flange being connected by a clamp in an embodiment of the present invention.

[0027] Figure label: 1-Pile body; 11-Designated drag-reducing pile segment; 12-Designated load-bearing pile segment; 13-Steel end plate; 2-Drag-reducing layer; 3-Extended flange; 31-Weld; 32-Clamping flap; 33-Fastening bolt; 4- Annular groove space; 5- Soft isolation layer. Detailed Implementation

[0028] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in further detail below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and do not constitute any limitation on the scope of the invention.

[0030] Example 1: Basic Structure of Welded Flange like Figure 1 , 2 As shown, this embodiment provides a drag-reducing precast pile with protective flanges, using multi-section prestressed concrete pipe piles as the pile body 1. The pile body 1 includes a predetermined drag-reducing pile segment 11 located at the upper part and a predetermined bearing pile segment 12 located at the lower part. A steel end plate 13 is provided at the end of the pile body 1.

[0031] like Figure 3 As shown, in the predetermined drag-reducing pile section 11, an annular steel extension flange 3 is provided on the outside of the steel end plate 13. The inner diameter of the extension flange 3 is adapted to the outer diameter (600mm) of the pile body 1. After it is fitted onto the pile body 1, it is welded and fixed to the steel end plate 13 of the pipe pile through weld 31. In this embodiment, the extension flange is spliced ​​from 4 arc-shaped metal strips.

[0032] A layer of PE film is wrapped around the pile surface between two adjacent extended flanges 3 as a drag-reducing layer 2. The outer diameter of the extended flange 3 (630 mm) is larger than the maximum outer diameter of the pile section with the drag-reducing layer 2 (604 mm).

[0033] The two adjacent extended flanges 3 and the surface of the pile body 1 together form an annular groove space 4 for accommodating the isolation material. This space will be filled with soft isolation material during subsequent construction.

[0034] Example 2: Diverse Connection Methods for Extended Wings This embodiment demonstrates two different connection methods between the extended flange 3 and the pile body 1, so as to reflect the flexibility and wide applicability of the present invention.

[0035] like Figure 4 As shown, the clamp connection method is as follows: the extended flange 3 consists of two semi-circular clamping plates 32. During installation, the two plates 32 are aligned at predetermined positions on the pile body 1 and locked in place by fastening bolts 33, thus securing them firmly to the pile body. This method is particularly suitable for solid square piles or composite material piles, requiring no welding or pre-processing of the pile body. This connection method facilitates adjustment of the spacing between the extended flanges, for example, adjusting to a spacing of 3m, 5m, etc., offering greater flexibility than welding the extended flanges.

[0036] Flange connection method: A flange is welded to one end of the extended flange 3, and a matching flange is also provided at the corresponding position on the pile body 1. During on-site installation, the two flanges are fastened together with high-strength bolts. This method facilitates adjustment of the flange position according to the actual situation on the construction site and is convenient for disassembly and assembly.

[0037] Other connection methods, such as welding to the steel end plate 13 and embedded connection with a pre-reserved groove during pile prefabrication, are all within the protection scope of this invention.

[0038] Example 3: Extended flange of pre-set grouting hole This embodiment further optimizes the extended flange 3 based on embodiment 1 or 2. The extended flange 3 is a hollow structure, or a partially hollow structure, and grouting holes communicating with the annular groove space 4 are pre-machined on the extended flange.

[0039] The grouting hole can be a threaded hole to facilitate a sealed connection with the grouting pipe. The number of grouting holes can be set to one or more according to the volume of the annular groove space 4 and the grouting requirements. Preferably, multiple grouting holes are evenly distributed along the circumference of the flange 3 to ensure the uniformity of grout filling. This design provides the structural basis for the "post-grouting method".

[0040] Example 4: Synchronous pile driving and grouting method This embodiment, based on the pile structure of Embodiment 1, demonstrates a unique construction method—synchronous pile driving and grouting method.

[0041] The construction process is as follows: 1. Determine the predetermined drag-reducing pile segment 11 and the predetermined bearing pile segment 12 of the pile body 1.

[0042] 2. At the predetermined position of the predetermined drag-reducing pile segment 11, the extended flange 3 is welded and fixed to the steel end plate 13, and the drag-reducing layer 2 is wrapped around the pile body surface between adjacent flanges.

[0043] 3. Start pile driving. After the first (bottommost) extended flange 3 has completely sunk into the soil, bentonite slurry is injected into the pile perimeter through grouting equipment and grouting pipes at the ground opening on the side of the pile.

[0044] 4. Continue driving the pile. As pile 1 sinks, the second extended flange 3 also begins to enter the soil. At this point, a closed annular groove space 4 is formed between the first and second flanges. The bentonite slurry injected above naturally flows into and fills this space under the guidance of gravity and the "scraping" action of the subsequent flanges.

[0045] 5. Following this pattern, grouting is stopped once the flanges of all predetermined drag-reducing pile segments 11 have sunk into the soil. After static curing, the bentonite slurry solidifies, forming a continuous soft isolation layer 5 that wraps around each drag-reducing section of the pile body 1.

[0046] In this embodiment, the flange 3 does not require any pre-set holes. It uses its natural baffle effect to guide the grout filling, realizing the integrated operation of "piling and filling at the same time". The construction process is extremely simple and the filling effect is intuitive and reliable.

[0047] Example 5: Post-grouting method This embodiment is based on the pile structure of Embodiment 3 (i.e., the pre-set grouting holes on the extended flange 3) and demonstrates another construction method - the post-grouting method.

[0048] The construction process is as follows: 1. Determine the predetermined drag-reducing pile segment 11 and the predetermined bearing pile segment 12 of the pile body 1.

[0049] 2. At the predetermined position of the predetermined drag-reducing pile segment 11, an extended flange 3 and a drag-reducing layer 2 are configured.

[0050] 3. Drive the precast piles into the foundation soil to the design elevation.

[0051] 4. After the pile driving is completed, connect the grouting pipe to the grouting hole on the flange 3, start the grouting equipment, and inject foamed concrete grout into the annular groove space 4. When the grout overflows from the flange joint or the pre-set vent hole on the flange, stop grouting and seal the hole.

[0052] After the foamed concrete has cured, a soft isolation layer 5 is formed.

[0053] In this embodiment, the post-grouting method ensures the compactness and controllability of the filling, and is suitable for projects with high requirements for the quality of the isolation layer.

[0054] Example 6: Variants of Soft Insulation Materials In any of the above embodiments, the soft insulating material 5 can be replaced according to geological conditions and design requirements. For example, bentonite slurry can be used in water-rich strata; foamed concrete can be used in strata requiring a certain level of later strength; and low-grade mortar can be used in large-scale projects that are sensitive to cost. These variations do not depart from the core concept of the present invention.

[0055] The present invention relates to a drag-reducing precast pile with protective flange and its construction method. The components are easy to process and assemble, the construction technology is mature and reliable, and the materials used are widely available and inexpensive. It can be widely used in pile foundation construction in fields such as building construction, transportation engineering, and water conservancy engineering, and has extremely high industrial applicability and promotion value.

[0056] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A drag-reducing precast pile with protective flanges, comprising a precast pile body, characterized in that, The pile body includes predetermined drag-reducing pile segments and predetermined bearing pile segments divided along its axial direction; the predetermined drag-reducing pile segments are provided with multiple annular extended flanges at intervals along the axial direction of the pile body; the inner diameter of the extended flanges is adapted to the outer diameter of the pile body and is fixedly sleeved on the pile body; a drag-reducing layer is provided on the surface of the pile body located between two adjacent extended flanges; the outer diameter of the extended flanges is larger than the maximum outer diameter of the pile body segment where the drag-reducing layer is provided.

2. The drag-reducing precast pile with protective flange according to claim 1, characterized in that, The two adjacent extended flanges together with the pile body surface form an annular groove space. The annular groove space is filled with a soft isolation material whose strength after curing is lower than that of the pile body concrete, forming a soft isolation layer that isolates the pile body from the surrounding soil.

3. The drag-reducing precast pile with protective flange according to claim 2, characterized in that, The soft insulating material is bentonite slurry solidified material, foamed concrete, or low-grade mortar.

4. The drag-reducing precast pile with protective flange according to claim 2, characterized in that, The extended flange is provided with a grouting hole that communicates with the annular groove space.

5. The drag-reducing precast pile with protective flange according to claim 1, characterized in that, The extended flange is fixed to the pile body by welding, flange connection, clamp connection or embedded connection.

6. The drag-reducing precast pile with protective flange according to claim 1, characterized in that, The extended flange is a metal ring or a high-strength composite material ring.

7. The drag-reducing precast pile with protective flange according to claim 1, characterized in that, The drag-reducing layer is made of asphalt, grease, polymer film, or composite geomembrane.

8. A construction method for a drag-reducing precast pile with protective flange as described in any one of claims 1 to 7, characterized in that, Includes the following steps: 1) Determine the predetermined drag-reducing pile segment and the predetermined bearing pile segment of the pile body; 2) The extended flange and the drag-reducing layer are configured at predetermined positions in the predetermined drag-reducing pile segment; 3) Drive the precast piles into the foundation soil to the design elevation; 4) Fill the annular groove space formed by the two adjacent extended flanges and the pile body surface with soft isolation material, and form a soft isolation layer after it solidifies.

9. The construction method according to claim 8, characterized in that, In step 4), after the first extended flange sinks into the soil during the pile driving process, soft isolation material is injected around the pile. The baffle effect of the extended flange is used to guide the soft isolation material to gradually fill into the spaces of each annular groove.

10. The construction method according to claim 8, characterized in that, In step 4), after the pile driving is completed, soft insulating material is injected into the annular groove space by connecting it to the pre-set grouting hole on the extended flange.

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