A partially variable-diameter precast pile, a construction method thereof and a pile foundation structure
By setting an adjustable diameter structure on the precast pile and adopting differential grouting technology, the problems of inflexibility and high cost of diameter variation in the implantation method were solved, thereby improving the bearing capacity of the soil around the pile and controlling early settlement, thus improving the economy and stability of the project.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- 王树峰
- Filing Date
- 2026-04-10
- Publication Date
- 2026-06-05
AI Technical Summary
The existing precast pile implantation method has a lack of flexibility in variable diameter structures, making it difficult to customize designs according to geological conditions. In addition, it consumes a large amount of cement, resulting in high costs and difficulty in controlling early settlement.
The design incorporates precast piles with variable diameter sections. Adjustable variable diameter structures are installed on the upper, middle, and end of the pile body. Differential grouting technology is used, injecting high-concentration cementitious grout at the variable diameter sections and low-concentration grout at the non-variable diameter sections to ensure that the variable diameter sections are located within the bearing stratum of the pile foundation, forming a trapezoidal stress surface and adding fiber structures.
The precise setting of the variable diameter structure was achieved, which improved the bearing capacity of the soil around the pile, reduced the amount of cement used, controlled early settlement, and improved the economy and stability of the project.
Smart Images
Figure CN122147864A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of prestressed centrifugal forming precast pile technology, and in particular to a partially variable diameter precast pile and its construction method, as well as a pile foundation structure. Background Technology
[0002] Precast piles are a widely used type of pile in building foundation engineering. Currently, the mainstream construction methods for prestressed precast piles mainly include the hammer driving method, the static pressure method, and the insertion method. The hammer driving method and the static pressure method belong to the "soil displacement pile" construction technology, which uses huge impact force or static pressure to directly drive or press the precast pile into the stratum. These methods have obvious drawbacks: First, the huge dynamic force during construction may damage the concrete of the pile body, affecting the structural integrity of the pile; second, the strong soil displacement effect will disturb and squeeze the surrounding soil, posing a threat to nearby underground pipelines, structures, and existing building foundations, thus greatly limiting its application in densely built-up urban areas. The insertion method, as a "non-soil displacement" or "less soil displacement" technology, overcomes the above disadvantages to some extent. This method first drills a precast hole in the stratum, and then inserts the precast pile into the hole. However, the drilling process itself removes and disturbs the original soil, inevitably weakening the natural bearing capacity of the soil around the pile, especially the bearing layer at the pile tip. To compensate for this loss of bearing capacity, existing technologies typically employ two methods: one is to inject grout into the pile hole to solidify the soil using cement grout; the other is to use precast piles with variable diameters that are enlarged at the ends or in parts to increase the pile-soil contact area.
[0003] The existing implantation method still has the following technical defects: (1) The variable diameter structure is simple and inflexible: Due to the limitations of traditional precast molds, the variable diameter position and geometry of existing variable diameter piles are relatively fixed, making it difficult to "customize" the design according to complex and varied geological conditions and different bearing capacity requirements. It is impossible to achieve the precise setting of the variable diameter structure in the key parts of the pile body under stress; (2) The contradiction between bearing capacity compensation and material cost: In order to compensate for the bearing capacity loss caused by drilling, high-concentration cement slurry is usually injected into the entire area around the pile. Although this improves the bearing capacity, it leads to the problem of large cement consumption and high cost, resulting in poor economic efficiency; (3) Poor early settlement control: Especially at the pile end, due to the damage of the bearing layer caused by drilling and the failure of traditional reinforcement methods to achieve efficient synergistic force between the pile end and the soil, the implanted pile is prone to large settlement in the early stage of bearing load, which affects the safety and quality of the project. Summary of the Invention
[0004] The purpose of this invention is to provide a partially variable diameter precast pile and its construction method and pile foundation structure, which can flexibly design the variable diameter position and shape according to geological conditions, and can effectively restore and improve the bearing capacity of the soil around the pile through precise and economical reinforcement methods, thereby solving the technical problems of inflexible variable diameter, high cost and difficulty in settlement control in the existing implantation method construction.
[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: The present invention provides a partially variable diameter precast pile, comprising a pile body, wherein a variable diameter structure is provided on the pile body, the variable diameter structure being provided at least at one of the upper part of the pile body, the middle part of the pile body, and the pile end, and the maximum external dimension of the variable diameter structure being greater than or equal to the diameter of the standard section of the pile body.
[0006] Furthermore, when the variable diameter structure is located at the pile end and / or the middle of the pile body, the maximum external dimension of the variable diameter structure is equal to the diameter of the standard section of the pile body; when the variable diameter structure is located at the upper part of the pile body, the maximum external dimension of the variable diameter structure is greater than the diameter of the standard section of the pile body.
[0007] Furthermore, the variable diameter structure has a trapezoidal profile in the radial section passing through the pile axis.
[0008] Furthermore, the inclination angle of the lower waist in the trapezoidal profile is no greater than 50°.
[0009] Furthermore, the height of the trapezoid is the variable diameter height, which is not less than 10% of the diameter of the standard section of the pile body.
[0010] Furthermore, when the variable diameter structure is installed at the pile end, the variable diameter structure has a fiber structure inside.
[0011] This invention also provides a construction method for partially variable diameter precast piles, which, using the aforementioned partially variable diameter precast piles, includes the following steps: S1. Drill holes according to the maximum external dimensions of the partially variable-diameter precast piles to form initial pile holes; S2. In the pile hole corresponding to the position of the precast pile diameter-changing structure, a hole enlargement operation is performed to form an enlarged hole section that adapts to the shape of the diameter-changing structure. S3. Inject cementitious grout into the pile hole, wherein a variable diameter grouting cement-soil pile is formed in the enlarged hole section, and a variable diameter grouting cement-soil pile is formed in the non-enlarged hole section. The strength of the variable diameter grouting cement-soil pile is higher than that of the variable diameter grouting cement-soil pile. S4. Before the cementitious grout initially sets, the partially variable-diameter precast pile is inserted into the pile hole, and the variable-diameter structure is located in the corresponding enlarged hole section.
[0012] Furthermore, in step S2, the maximum diameter of the enlarged hole section is less than or equal to 1.4 times the maximum external dimension of the pile body.
[0013] Furthermore, in step S3, the strength difference is achieved by injecting a first gelling slurry into the enlarged hole section and a second gelling slurry into the non-enlarged hole section, wherein the concentration of the gelling material in the first gelling slurry is higher than that in the second gelling slurry.
[0014] The present invention also provides a pile foundation structure, including the aforementioned partially variable diameter precast piles implanted in the soil layer, wherein the variable diameter structure is entirely located within the bearing layer of the pile foundation.
[0015] Compared with the prior art, the beneficial technical effects of the present invention are as follows: The present invention relates to a partially variable-diameter precast pile and pile foundation structure. By designing the variable-diameter structure as a modular unit that can be installed at least once in the upper, middle, and end parts of the pile, it breaks the limitation of the traditional single variable-diameter location of precast piles. The construction party can accurately set the variable-diameter structure at the corresponding location of the weak bearing capacity soil layer or the part that needs to be reinforced according to the geological survey report of the specific project, which greatly improves the adaptability of the precast pile to different complex strata conditions. At the same time, the variable-diameter structure itself increases the contact area between the pile body and the surrounding soil, and improves the side friction resistance. By limiting the cross section of the variable-diameter structure to a trapezoidal shape and the inclination angle of the lower waist of the trapezoidal outline not to exceed 50°, an optimized "mortise and tenon" type stress surface is formed, so that the cement-soil reinforcement around the pile is in a more favorable compressive stress state when under stress, thereby transferring the load to the deep soil more efficiently. In particular, when a fiber structure is added inside the variable-diameter structure at the pile end, the bonding and integrity between the pile end and the cement-soil can be further strengthened, which greatly improves the end resistance and anti-settlement performance.
[0016] The construction method of partially variable-diameter precast piles of this invention employs differential grouting technology. High-concentration cementitious grout is injected only into the enlarged borehole section corresponding to the variable-diameter structure to form a high-strength driven variable-diameter enlarged-hole grouting cement-soil pile, while a lower-concentration grout is injected into the standard pile section to form a driven variable-diameter enlarged-hole grouting cement-soil pile. This significantly reduces the total amount of cement and other cementitious materials used while ensuring the strongest reinforcement in the critical variable-diameter area, effectively lowering project costs and solving the high cost problem caused by the high grouting throughout the entire area in traditional implantation methods to compensate for bearing capacity. Furthermore, the construction method requires the precast pile to be implanted before the cement grout initially sets, ensuring a tight and complete bond between the pile body and the cement-soil reinforcement. By requiring the variable-diameter structure to be entirely located within the bearing stratum of the pile foundation and controlling its height to be greater than the implantation depth, the reinforcement is ensured to fully act within the effective bearing stratum, effectively compensating for the soil bearing capacity weakened by drilling, significantly reducing early settlement of the pile foundation, and improving the long-term stability of the structure. Attached Figure Description
[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0018] Figure 1 This is a schematic diagram of the structure of a partially variable-diameter precast pile according to Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the structure of two connected variable diameter structures in a partially variable diameter precast pile according to Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of the structure of a partially variable-diameter precast pile according to Embodiment 2 of the present invention; Figure 4 This is a schematic diagram of the structure of a partially variable-diameter precast pile in Embodiment 3 of the present invention; Figure 5 This is a schematic diagram of the structure of a partially variable-diameter precast pile in Embodiment 4 of the present invention; Figure 6 This is a schematic diagram of the drilling shape and the structure of the grouting body around the pile for a portion of the variable-diameter precast piles in Embodiment 4 of the present invention; Figure 7 This is a schematic diagram of the drilling shape and the structure of the grouting body around the pile for a portion of the variable-diameter precast piles in Embodiment 4 of the present invention; Figure 8 This is a schematic diagram of the structure of a partially variable-diameter precast pile in Embodiment 5 of the present invention; Figure 9 This is a schematic diagram of the drilling shape and the structure of the grouting body around the pile for a portion of the variable-diameter precast piles in Embodiment 5 of the present invention; Figure 10 This is a schematic diagram of the drilling shape and the structure of the grouting body around the pile for a portion of the variable-diameter precast piles in Embodiment 5 of the present invention; Figure 11 This is a schematic diagram of the structure of a partially variable-diameter precast pile according to Embodiment 6 of the present invention; Figure 12 This is a schematic diagram of the drilling shape and the structure of the grouting body around the pile for a portion of the variable-diameter precast piles in Embodiment 6 of the present invention; Figure 13 This is a schematic diagram of the drilling shape and the structure of the grouting body around the pile for a portion of the variable diameter precast piles in Embodiment 6 of the present invention.
[0019] Explanation of reference numerals in the attached drawings: 1. End-diameter variable precast pile; 11. Pile body; 2. Variable diameter structure; 21. Overall height; 22. Variable diameter height; 23. Inclination angle; 24. Variable diameter interval; 3. Fiber structure; 4. Driven pile with variable diameter and enlarged hole, grouted cement-soil pile; 5. Driven pile with enlarged hole and grouted cement-soil pile; 6. Driven pile with grouted cement-soil pile; 7. Ordinary precast pile; 8. Middle-diameter variable precast pile; 9. Upper-diameter variable precast pile. Detailed Implementation
[0020] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.
[0021] In the description of this invention, it should be understood that the terms "length," "width," "inner," and "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.
[0022] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.
[0023] This specification provides an embodiment of a partially variable diameter precast pile, including a pile body, a variable diameter structure provided on the pile body, the variable diameter structure being provided at least at one of the upper part of the pile body, the middle part of the pile body, and the pile end, and the maximum external dimension of the variable diameter structure being greater than or equal to the diameter of the standard section of the pile body.
[0024] When the variable diameter structure is located at the pile tip and / or the middle of the pile body, the maximum external dimension of the variable diameter structure is equal to the diameter of the standard section of the pile body; when the variable diameter structure is located at the upper part of the pile body, the maximum external dimension of the variable diameter structure is greater than the diameter of the standard section of the pile body.
[0025] At this point, the profile of the variable diameter structure on the radial section passing through the pile axis is trapezoidal.
[0026] Furthermore, the inclination angle of the lower waist in the trapezoidal profile shall not exceed 50°, and the height of the trapezoid shall be the diameter variation height, which shall not be less than 10% of the standard section diameter of the pile body.
[0027] In addition, when the variable diameter structure is installed at the pile end, the internal structure of the variable diameter structure is made of fiber.
[0028] The technical solutions provided by the various embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
[0029] Example 1 like Figure 1 , Figure 2 As shown, in this embodiment 1, the part of the variable diameter precast pile is the end variable diameter precast pile 1. The end variable diameter precast pile 1 includes a pile body 11. The pile end of the pile body 11 is provided with a variable diameter structure 2, and the maximum external dimension of the variable diameter structure 2 is equal to the diameter of the standard section of the pile body 11.
[0030] At this time, the profile of the variable diameter structure 2 on the radial section passing through the pile axis is trapezoidal, and the overall height 21 of the variable diameter structure 2 is greater than the depth of the pile foundation implanted into the bearing layer, preferably not less than 3 meters.
[0031] Furthermore, the diameter change angle of the variable diameter structure 2, that is, the inclination angle 23 of the lower waist in the trapezoidal profile, is not greater than 50°, and the angle of the upper waist is not limited. The inclination angle 23 is the acute angle between the waist of the trapezoid and the straight line perpendicular to the axis of the pile body. The diameter change angle is calculated according to the maximum force formula of the mortise and tenon structure: in, For axial pressure, The contact surface angle is 23°, which is the tilt angle. This refers to the contact area.
[0032] Based on the simulation calculation of the diameter change angle, the height of the trapezoid is the diameter change height 22, and the diameter change height 22 is not less than 10% of the diameter of the standard section of the pile body 11.
[0033] In addition, the variable diameter structure 2 has a fiber structure 3 inside, which can be integrated with the soil around the pile, which can significantly increase the bearing capacity of the pile end and reduce settlement.
[0034] In this embodiment 1, the end-diameter-changing precast pile 1 is constructed using the implantation method. Its bottom diameter-changing structure 2 is placed within the bearing layer of the pile foundation, and its implantation depth must meet the relevant requirements of the "Code for Design of Concrete Pile Foundations" to ensure that its diameter-changing height is greater than the depth of implantation into the bearing layer, thereby fully utilizing the bearing capacity of the diameter-changing structure.
[0035] The construction of the partially variable-diameter precast piles in Example 1 includes the following steps: S1. Drill holes according to the maximum external dimensions of the partially variable-diameter precast piles to form the initial pile holes; S2. In the pile hole corresponding to the position of the precast pile diameter-changing structure 2, a hole enlargement operation is performed to form an enlarged hole section that adapts to the shape of the diameter-changing structure 2. This hole enlargement operation can form one or more enlarged hole sections that adapt to the shape of the diameter-changing structure at the same design position. S3. Inject cementitious grout into the pile hole, wherein a variable diameter grouting cement-soil pile 4 is formed in the enlarged hole section, and a variable diameter grouting cement-soil pile 5 is formed in the non-enlarged hole section. The strength of the variable diameter grouting cement-soil pile 4 is higher than that of the variable diameter grouting cement-soil pile 5. S4. Before the cementitious grout initially sets, insert part of the variable diameter precast pile into the pile hole and position the variable diameter structure 2 in the corresponding enlarged hole section. S5. Configure appropriate counterweights on construction equipment, or use a pile hammer to assist in pile driving.
[0036] Furthermore, in step S2, the maximum diameter of the enlarged borehole section is less than or equal to 1.4 times the maximum external dimension of the pile body 11. The minimum height of the enlarged borehole section is greater than the sum of the product of the diameter variation interval 24 between adjacent diameter variation structures on the pile body and the cosine of the inclination angle 23 multiplied by the diameter variation height, to ensure soil stability after borehole enlargement.
[0037] Furthermore, in step S3, the strength difference is achieved by injecting the first gelling grout into the enlarged hole section and the second gelling grout into the non-enlarged hole section, with the concentration of the cementing material in the first gelling grout being higher than that in the second gelling grout.
[0038] By locally reinforcing key areas where the diameter changes, a balance is achieved between increased bearing capacity and material savings. As an alternative, a grout with a uniform cementitious material concentration can be injected throughout the pile hole to form a cement-soil pile with high overall strength that completely encapsulates the precast pile. This method is suitable for situations with poorer soil conditions that require overall reinforcement.
[0039] Example 2 like Figure 3As shown, the difference between this embodiment 2 and embodiment 1 is that some of the variable diameter precast piles are central variable diameter precast piles 8. The central variable diameter precast pile 8 includes a pile body 11. A variable diameter structure 2 is provided in the middle of the pile body 11, and the maximum external dimension of the variable diameter structure 2 is equal to the diameter of the standard section of the pile body 11. This structure can be set in a part of the pile body with better soil layer, and the pile-soil contact area is increased by changing the diameter shape.
[0040] Example 3 like Figure 4 As shown, the difference between this embodiment 3 and embodiment 1 is that some of the variable diameter precast piles are upper variable diameter precast piles 9. The upper variable diameter precast pile 9 includes a pile body 11. A variable diameter structure 2 is provided on the upper part of the pile body 11. The maximum external dimension of the variable diameter structure 2 is greater than the standard section diameter of the pile body 11, but smaller than the drilling size during construction, so as to facilitate implantation.
[0041] Example 4 like Figures 5 to 7 As shown, the partial diameter-changing precast piles in this embodiment 4 include ordinary precast piles 7 and end diameter-changing precast piles 1. The bottom of the ordinary precast piles 7 is spliced with end diameter-changing precast piles 1. Specifically, the end diameter-changing precast piles 1 include pile bodies 11. The pile ends of the pile bodies 11 are provided with diameter-changing structures 2, and the maximum external dimension of the diameter-changing structures 2 is equal to the diameter of the standard section of the pile body 11.
[0042] At this point, the profile of the variable diameter structure 2 on the radial section passing through the pile axis is trapezoidal.
[0043] Furthermore, the diameter change angle 23 of the diameter change structure 2, that is, the inclination angle 23 of the lower waist in the trapezoidal outline, is not greater than 50°, and the angle of the upper waist is not limited. The inclination angle 23 is the acute angle between the waist of the trapezoid and the straight line perpendicular to the pile axis. The height of the trapezoid is the diameter change height 22, and the diameter change height 22 is not less than 10% of the diameter of the standard section of the pile body 11.
[0044] In addition, the variable diameter structure 2 has a fiber structure 3 inside.
[0045] In the construction of the precast piles with variable diameter in Example 4, holes are first drilled according to the design requirements, with the hole size larger than the maximum external size of the pile body. The hole is then enlarged at the pile body section corresponding to the variable diameter structure 2 at the pile end. Then, cement slurry with a high cement concentration is injected into the hole of the variable diameter structure to form a high-strength pile 4 with variable diameter enlargement and grouting. Cement slurry with a lower cement concentration is injected into the non-variable diameter hole to form pile 5 with variable diameter enlargement and grouting. Finally, before the cement slurry initially sets, the assembled precast piles are driven into the pile hole by their own weight or auxiliary counterweight. Through this method, a higher-strength cement-soil reinforcement can be formed at the variable diameter structure, effectively compensating for the soil bearing capacity weakened by drilling, saving cement consumption, and controlling early settlement.
[0046] In this embodiment 4, the pile perimeter reinforcement formed after construction includes 6 grouted cement-soil piles in the pile hole, 4 grouted cement-soil piles with variable diameter and enlarged hole, and 5 grouted cement-soil piles with enlarged hole. The 6 grouted cement-soil piles in the pile hole form a continuous cement-soil body enveloping the entire precast pile. The 4 grouted cement-soil piles with variable diameter and enlarged hole are located within the enlarged hole section corresponding to the pile end variable diameter structure 2, formed by high-concentration cement grout, possessing the highest strength, and tightly enveloping the variable diameter structure 2 and fiber structure 3, constituting a local reinforcement core. The 5 grouted cement-soil piles with enlarged hole are located in the non-enlarged hole section, formed by lower-concentration cement grout, with lower strength than the 4 grouted cement-soil piles with variable diameter and enlarged hole, and are integrated with the 6 grouted cement-soil piles in the corresponding sections. Together, these three form a composite reinforcement system with a strength gradient, achieving a balance between strengthening key components and overall economy.
[0047] Example 5 like Figures 8 to 10 As shown, the partial diameter-changing precast piles in this embodiment 5 include a middle diameter-changing precast pile 8 and an end diameter-changing precast pile 1. The bottom of the middle diameter-changing precast pile 8 is spliced with the end diameter-changing precast pile 1. Specifically, the middle diameter-changing precast pile 8 includes a pile body 11, and a diameter-changing structure 2 is provided in the middle of the pile body 11.
[0048] Meanwhile, the end-diameter-changing precast pile 1 also includes the pile body 11. The pile end of the pile body 11 is provided with a diameter-changing structure 2. At this time, the maximum external dimensions of the diameter-changing structure 2 of the middle diameter-changing precast pile 8 and the diameter-changing structure 2 of the end-diameter-changing precast pile 1 are the same, and both are equal to the standard section diameter of the pile body 11.
[0049] Among them, the diameter-changing structure 2 of the precast pile 8 with diameter changing in the middle and the precast pile 1 with diameter changing at the end are both trapezoidal in shape on the radial section passing through the pile axis. Furthermore, the diameter-changing angle 23 of the diameter-changing structure 2, that is, the inclination angle 23 of the lower waist of the trapezoidal outline, is not greater than 50°, and the angle of the upper waist is not limited. The inclination angle 23 is the acute angle between the waist of the trapezoid and the straight line perpendicular to the pile axis. The height of the trapezoid is the diameter-changing height 22, and the diameter-changing height 22 is not less than 10% of the diameter of the standard section of the pile body 11.
[0050] In addition, the internal structure 2 of the diameter-changing precast pile 1 has a fiber structure 3.
[0051] In this embodiment 5, the construction method for the partially variable-diameter precast piles is similar to that in embodiment 4. For the two variable-diameter structures at the middle and end, hole enlargement operations are performed at the corresponding two positions in the pile hole to form an enlarged hole section adapted to the shape of the variable-diameter structure. Subsequently, differential grouting is performed to form a high-strength pile 4 with variable-diameter enlarged hole grouting in the enlarged hole section and a pile 5 with enlarged hole grouting in the non-enlarged section. Finally, the pile is implanted. This method can simultaneously strengthen two key parts, namely the good soil layer in the middle of the pile body and the bearing layer at the pile end, further improving the overall bearing capacity of the pile foundation.
[0052] In this embodiment 5, the pile perimeter reinforcement formed after construction includes grouting cement-soil piles 6, grouting cement-soil piles 4 and grouting cement-soil piles 5. The grouting cement-soil piles 6 form a continuous cement-soil body enveloping the entire precast pile. The grouting cement-soil piles 4 are located in the enlarged sections corresponding to the diameter-changing structures 2 in the middle of the pile body and the diameter-changing structures 2 at the pile end. They are formed with high-concentration cement grout, have the highest strength, and tightly envelop each diameter-changing structure 2, forming a local reinforcement core. The grouting cement-soil piles 5 are located in the non-enlarged sections, formed with lower-concentration cement grout, and have lower strength than the grouting cement-soil piles 4. They merge with the grouting cement-soil piles 6 in corresponding sections. Together, they form a composite reinforcement system with a strength gradient, achieving a balance between multiple reinforcements of key components and overall economy.
[0053] Example 6 like Figures 11 to 13 As shown, the partial variable diameter precast piles in this embodiment 6 include upper variable diameter precast piles 9 and end variable diameter precast piles 1. The bottom of the upper variable diameter precast piles 9 is spliced with end variable diameter precast piles 1. Specifically, the upper variable diameter precast piles 9 include pile bodies 11. A variable diameter structure 2 is provided on the upper part of the pile body 11, and the maximum external dimension of the variable diameter structure 2 is greater than the diameter of the standard section of the pile body 11.
[0054] Meanwhile, the end-diameter-changing precast pile 1 also includes a pile body 11, and the pile end of the pile body 11 is provided with a diameter-changing structure 2, and the maximum external dimension of the diameter-changing structure 2 is equal to the diameter of the standard section of the pile body 11.
[0055] At this point, the diameter-changing structures 2 of the upper diameter-changing precast pile 9 and the end diameter-changing precast pile 1 both have trapezoidal profiles on the radial section passing through the pile axis. Furthermore, the diameter-changing angle 23 of the diameter-changing structure 2, that is, the inclination angle 23 of the lower waist in the trapezoidal profile, is not greater than 50°, and the angle of the upper waist is not limited. The inclination angle 23 is the acute angle between the waist of the trapezoid and the straight line perpendicular to the pile axis. The height of the trapezoid is the diameter-changing height 22, which is not less than 10% of the diameter of the standard section of the pile body 11.
[0056] In addition, the internal structure 2 of the diameter-changing precast pile 1 has a fiber structure 3.
[0057] In this embodiment 6, the construction method for the partially variable-diameter precast piles is similar to that in embodiment 5. Differentiated hole drilling and enlargement are required for the two variable-diameter structures at the ends. The maximum diameter of the enlarged hole generally does not exceed 1.4 times the maximum diameter of the pile body. High-concentration cementitious grout is injected into the enlarged hole section corresponding to the variable-diameter structure at the pile end to form a high-strength pile 4 with variable-diameter enlarged hole grouting. Lower-concentration cementitious grout is injected into the enlarged hole section at the upper part of the pile body and all non-enlarged hole sections to form pile 5 with enlarged hole grouting. Finally, the above-mentioned grouting body is integrated with the pile 6 with grouting in the pile hole that encloses the entire pile body to form a continuous composite reinforcement system. This system forms a local high-strength reinforcing core at the pile end, significantly improving the end resistance. At the upper part of the pile body, the increased variable-diameter contact surface and the reinforced soil work together to effectively increase the side friction resistance. Furthermore, the reinforcement of the pile end and the upper part of the pile body are combined to form a synergistic force mechanism, which is suitable for engineering scenarios with higher requirements for bearing capacity and settlement control.
[0058] In this embodiment 6, the pile perimeter reinforcement formed after construction includes 6 grouted cement-soil piles in the pile driving hole, 4 grouted cement-soil piles with variable diameter and enlarged hole, and 5 grouted cement-soil piles with enlarged hole. The 6 grouted cement-soil piles in the pile driving hole are continuous cement-soil bodies enveloping the entire precast pile. The 4 grouted cement-soil piles with variable diameter and enlarged hole are located within the enlarged hole section corresponding to the pile end variable diameter structure 2, formed by high-concentration cement grout, possessing the highest strength, and tightly enveloping each variable diameter structure 2, forming a local reinforcement core. The 5 grouted cement-soil piles with enlarged hole are located in the non-enlarged hole section and the upper part of the pile body. The 5 grouted cement-soil piles with enlarged hole are formed by lower-concentration cement grout, with lower strength than the 4 grouted cement-soil piles with variable diameter and enlarged hole. They merge with the 6 grouted cement-soil piles in the corresponding sections, and the three together constitute a composite reinforcement system with a strength gradient, achieving a balance between multiple reinforcements of key parts and overall economy.
[0059] Example 7 The construction method of the partially variable diameter precast pile in this embodiment 7, using the aforementioned partially variable diameter precast pile, includes the following steps: S1. Drill holes according to the maximum external dimensions of the partially variable-diameter precast piles to form the initial pile holes; S2. In the pile hole corresponding to the position of the precast pile diameter-changing structure 2, a hole enlargement operation is performed to form an enlarged hole section that adapts to the shape of the diameter-changing structure 2. This hole enlargement operation can form one or more enlarged hole sections that adapt to the shape of the diameter-changing structure at the same design position. S3. Inject cementitious grout into the pile hole, wherein a variable diameter grouting cement-soil pile 4 is formed in the enlarged hole section, and a variable diameter grouting cement-soil pile 5 is formed in the non-enlarged hole section. The strength of the variable diameter grouting cement-soil pile 4 is higher than that of the variable diameter grouting cement-soil pile 5. S4. Before the cementitious grout initially sets, insert part of the variable diameter precast pile into the pile hole and position the variable diameter structure 2 in the corresponding enlarged hole section. S5. Configure appropriate counterweights on construction equipment, or use a pile hammer to assist in pile driving.
[0060] Furthermore, in step S2, the maximum diameter of the enlarged borehole section is less than or equal to 1.4 times the maximum external dimension of the pile body 11. The minimum height of the enlarged borehole section is greater than the sum of the product of the diameter variation interval 24 between adjacent diameter variation structures on the pile body and the cosine of the inclination angle 23 multiplied by the diameter variation height, to ensure soil stability after borehole enlargement.
[0061] Furthermore, in step S3, the strength difference is achieved by injecting the first gelling grout into the enlarged hole section and the second gelling grout into the non-enlarged hole section, with the concentration of the cementing material in the first gelling grout being higher than that in the second gelling grout.
[0062] The construction method of the partially variable-diameter precast piles in Example 7 achieves a balance between increased bearing capacity and material savings by locally reinforcing the key parts of the diameter change. As an alternative, a grout with a uniform cementitious material concentration can be injected into the entire pile hole to form a cement-soil pile with high overall strength that completely encapsulates the precast pile. This method is suitable for situations with worse soil conditions and the need for overall reinforcement.
[0063] Example 8 The pile foundation structure of this embodiment 8 includes the aforementioned partially variable-diameter precast piles implanted in the soil layer, with the variable-diameter structure 2 located entirely within the bearing layer of the pile foundation.
[0064] Specifically, the variable diameter structure 2 is located in a target soil layer or bearing layer with high bearing capacity selected according to geological conditions, and the height of the variable diameter structure 2 in the pile axis is greater than the depth of the pile body implanted into the target soil layer at its location.
[0065] The pile foundation structure in this embodiment 8 ensures that the variable diameter reinforcement section acts entirely within the effective bearing soil layer, thereby fully utilizing its "mortise and tenon" bearing capacity and effectively transferring the upper load to the deep soil, significantly improving the vertical bearing capacity and settlement resistance of the pile foundation.
[0066] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.
Claims
1. A partially variable-diameter precast pile, characterized by, The pile body (11) includes a variable diameter structure (2) on the pile body (11). The variable diameter structure (2) is located at least at one of the upper part of the pile body, the middle part of the pile body and the pile end. The maximum external dimension of the variable diameter structure (2) is greater than or equal to the standard section diameter of the pile body (11).
2. The partially variable diameter precast pile according to claim 1, characterized in that, When the variable diameter structure (2) is set at the pile end and / or the middle of the pile body, the maximum external dimension of the variable diameter structure (2) is equal to the standard section diameter of the pile body (11); when the variable diameter structure (2) is set at the upper part of the pile body, the maximum external dimension of the variable diameter structure (2) is greater than the standard section diameter of the pile body (11).
3. The partially variable diameter precast pile according to claim 1, characterized in that, The variable diameter structure (2) has a trapezoidal profile on the radial section passing through the pile axis.
4. The partially variable diameter precast pile according to claim 3, characterized in that, The inclination angle (23) of the lower waist in the trapezoidal profile is no greater than 50°.
5. The partially variable diameter precast pile according to claim 3, characterized in that, The height of the trapezoid is the variable diameter height (22), and the variable diameter height (22) is not less than 10% of the standard section diameter of the pile body (11).
6. The partially variable diameter precast pile according to any one of claims 1-5, characterized in that, When the variable diameter structure (2) is installed at the pile end, the variable diameter structure (2) is provided with a fiber structure (3).
7. A construction method for partially variable diameter precast piles, characterized in that, The method of using partially variable diameter precast piles as described in any one of claims 1-6 includes the following steps: S1. Drill holes according to the maximum external dimensions of the partially variable-diameter precast piles to form initial pile holes; S2. In the pile hole, corresponding to the position of the precast pile diameter-changing structure (2), a hole enlargement operation is performed to form an enlarged hole section that is adapted to the shape of the diameter-changing structure (2); S3. Inject cementitious grout into the pile hole, wherein a pile diameter-expanding grouting cement-soil pile (4) is formed in the enlarged hole section, and a pile diameter-expanding grouting cement-soil pile (5) is formed in the non-enlarged hole section. The strength of the pile diameter-expanding grouting cement-soil pile (4) is higher than the strength of the pile diameter-expanding grouting cement-soil pile (5). S4. Before the gelling grout initially sets, the partially variable diameter precast pile is inserted into the pile hole, and the variable diameter structure (2) is located in the corresponding enlarged hole section.
8. The construction method of a partially variable diameter precast pile according to claim 7, characterized in that, In step S2, the maximum diameter of the enlarged hole section is less than or equal to 1.4 times the maximum external dimension of the pile body (11).
9. A construction method for a partially variable diameter precast pile according to claim 7, characterized in that, In step S3, the strength difference is achieved by injecting a first gelling slurry into the enlarged hole section and a second gelling slurry into the non-enlarged hole section, wherein the concentration of the gelling material in the first gelling slurry is higher than that in the second gelling slurry.
10. A pile foundation structure, characterized in that, The precast pile with variable diameter as described in any one of claims 1-6 is embedded in the soil layer, wherein the variable diameter structure (2) is located entirely within the bearing layer of the pile foundation.