Structural construction of prestressed high-strength concrete X-shaped pile and manufacturing method of pile section of prestressed high-strength concrete X-shaped pile

Abstract

The invention discloses a structure construction of a prestressed high-strength concrete X-shaped pile and a manufacturing method of pile sections of the prestressed high-strength concrete X-shaped pile, a pile body of the X-shaped pile comprises a plurality of pile sections, the adjacent pile sections are connected through a connecting device, and each pile section comprises a web area located in the center and four flanges arranged around the web area at intervals; and the adjacent flanges are in transition connection through inner arc surfaces. Two reinforcement schemes are adopted, according to the first scheme, a plurality of longitudinal stress ribs, longitudinal prestressed ribs and two sets of annular stirrups distributed in a staggered mode are included, and the longitudinal prestressed ribs surround the annular stirrups and are arranged in the annular stirrups. According to the second scheme, a plurality of longitudinal stress ribs, longitudinal prestressed ribs, a set of spiral stirrups and two sets of unilateral stirrups distributed in a staggered mode are included, the spiral stirrups are arranged in the web area, and the longitudinal prestressed ribs surround the spiral stirrups and are arranged in the spiral stirrups. The X-shaped pile is high in material utilization rate, excellent in bearing performance, stable in quality and high in adaptability.

Description

Technical Field

[0001] This invention relates to the field of prestressed high-strength concrete pile technology, specifically a structural design of a prestressed high-strength concrete X-shaped pile and a method for manufacturing its pile sections. Background Technology

[0002] In the field of building foundation engineering, circular piles are the most widely used traditional concrete piles. However, circular piles have significant limitations in terms of material utilization and bearing capacity matching. With the same amount of concrete, the pile-soil contact area of ​​a circular pile is smaller than that of piles with other cross-sections, resulting in lower pile side friction and consequently lower vertical bearing capacity and tensile bearing capacity compared to piles with other cross-sections.

[0003] While traditional cast-in-place concrete piles can adapt to complex construction scenarios, they suffer from poor performance stability and long construction cycles. Cast-in-place piles require on-site formwork, pouring, and curing, and are greatly affected by ambient temperature and humidity, making them prone to defects such as insufficient density and cracks. Furthermore, the curing period typically requires 7-14 days, severely restricting project progress.

[0004] In summary, traditional circular piles suffer from low material utilization and insufficient bearing capacity, while traditional cast-in-place concrete piles face problems of unstable performance and low construction efficiency. Neither can meet the modern engineering requirements for piles that are "efficient, strong, and economical". Summary of the Invention

[0005] The purpose of this invention is to provide a structural design for a prestressed high-strength concrete X-shaped pile. The pile body of the X-shaped pile includes at least one pile segment, adjacent pile segments are connected by a connecting device, and each pile segment includes a web region located in the center and four flanges spaced around the web region. Adjacent flanges are connected by an inner arc surface transition, so that the cross-section of the X-shaped pile is X-shaped as a whole.

[0006] The X-shaped piles employ two reinforcement schemes:

[0007] Reinforcement scheme 1: Several longitudinal prestressing tendons and two sets of annular stirrups are pre-embedded in the pile body. The two sets of annular stirrups are staggered, and several longitudinal prestressing tendons are arranged around the annular stirrups inside the annular stirrups. The annular stirrups are densely arranged at both ends of the X-shaped pile.

[0008] Reinforcement scheme 2: Several longitudinal prestressing tendons, one set of spiral stirrups and two sets of single-sided stirrups are pre-embedded in the pile body. The two sets of single-sided stirrups are staggered. The spiral stirrups are set in the web area. Several longitudinal prestressing tendons are set around the spiral stirrups inside the spiral stirrups. The spiral stirrups and the two sets of single-sided stirrups are densely set at both ends of the X-shaped pile.

[0009] The pile section is made of high-strength concrete with a strength grade greater than or equal to C60.

[0010] Furthermore, the central angle corresponding to the inner arc surface The range is 90°-150°.

[0011] X-shaped cross-section perimeter The calculation formula is as follows:

[0012] (1)

[0013] In the formula: The width of the major axis of the X-shaped cross-section; This refers to the wing width;

[0014] X-shaped cross-sectional area The calculation formula is as follows:

[0015] (2)

[0016] Furthermore, the connecting device adopts any one of the following: a plug-in connection structure, a circular flange connection structure, an X-shaped flange connection structure, and a tenon-and-mortise connection structure.

[0017] Furthermore, when there are two pile sections and a plug-in connection structure is used, the bottom of the top pile section and the top of the bottom pile section are respectively provided with a plug structure and a socket structure.

[0018] When there are more than two pile sections and a plug-in connection structure is used, the bottom of the top pile section is equipped with a plug structure, the top and bottom of the middle pile sections are equipped with a socket structure and a plug structure respectively, and the top of the bottom pile section is equipped with a socket structure.

[0019] The plug structure is cylindrical and located at the center of the web region, with several plug bolt holes spaced radially along the plug structure. The axis of the plug bolt holes is parallel to the central axis of two of the flanges. The outer wall of the plug structure has multiple annular grooves spaced apart, and rubber sealing rings are fitted into the grooves.

[0020] The socket structure is a cylindrical groove structure, located at the center of the web region and within the web region. The flanges, located on the outer wall of the socket structure, have a plurality of socket bolt holes spaced radially along the socket structure. The axes of the socket bolt holes are parallel to the central axes of two of the flanges.

[0021] The dimensions of the plug structure are adapted to the dimensions of the socket structure.

[0022] The number and position of the plug bolt holes correspond one-to-one with the number and position of the socket bolt holes.

[0023] During assembly, high-strength bolts are passed through the plug bolt holes and socket bolt holes to fix the two pile sections together.

[0024] Furthermore, when there are two pile sections and a circular flange connection structure is used, a circular flange is provided at the bottom of the top pile section and the top of the bottom pile section.

[0025] When there are more than two pile sections and a circular flange connection structure is used, circular flanges are provided at the bottom of the top pile section, the top and bottom of the middle pile section, and the top of the bottom pile section.

[0026] The circular flange includes a circular flange body and an annular boss I extending along the edge of the circular flange body. A cylindrical mounting groove is formed between the circular flange body and the annular boss I. The cylindrical mounting groove and the annular boss I are respectively provided with a plurality of bolt positioning holes I and boss bolt positioning holes I at intervals.

[0027] The pile segment has several pile end positioning holes spaced apart at corresponding ends. During assembly, the pile segment is embedded in the cylindrical mounting groove of the circular flange, and the pile end positioning holes of the pile segment correspond one-to-one with the bolt positioning holes I of the circular flange. High-strength bolts pass through the bolt positioning holes I and the pile end positioning holes to fix the circular flange to the end of the pile segment.

[0028] A sealing gasket is provided between the pile section and the cylindrical mounting groove.

[0029] High-strength bolts pass through the bolt positioning holes I on the two circular flanges to connect two adjacent pile sections.

[0030] Furthermore, when there are two pile sections and an X-shaped flange connection structure is used, X-shaped flanges are provided at the bottom of the top pile section and the top of the bottom pile section.

[0031] When there are more than two pile sections and an X-shaped flange connection structure is used, X-shaped flanges are provided at the bottom of the top pile section, the top and bottom of the middle pile section, and the top of the bottom pile section.

[0032] The X-shaped flange includes an X-shaped flange body and an annular boss II extending along the edge of the X-shaped flange body. An X-shaped mounting groove is formed between the X-shaped flange body and the annular boss II. The X-shaped mounting groove and the annular boss II are respectively provided with a plurality of bolt positioning holes II and boss bolt positioning holes II at intervals.

[0033] The corresponding ends of the pile section are provided with a number of pile end positioning holes at intervals.

[0034] During assembly, the pile section is embedded in the X-shaped mounting groove of the X-shaped flange, and the pile end positioning holes of the pile section correspond one-to-one with the bolt positioning holes II of the X-shaped flange. High-strength bolts pass through the bolt positioning holes II and the pile end positioning holes to fix the X-shaped flange to the end of the pile section.

[0035] A sealing gasket is provided between the pile section and the X-shaped mounting groove.

[0036] High-strength bolts pass through the bolt positioning holes II on the two X-shaped flanges to connect two adjacent pile sections.

[0037] Furthermore, when there are two pile sections and a mortise and tenon joint is used, the bottom of the top pile section and the top of the bottom pile section are respectively provided with a mortise joint and a tenon joint. When there are more than two pile sections and a mortise and tenon joint is used, the bottom of the top pile section is provided with a mortise joint, the top and bottom of the middle pile sections are respectively provided with a tenon joint and a mortise joint, and the top of the bottom pile section is provided with a tenon joint.

[0038] The mortise joint is U-shaped, and the tenon joint is U-shaped, with the two shapes fitting together. The mortise joint and the tenon joint are respectively provided with a number of bolt positioning holes III and a number of bolt positioning holes IV at intervals. The number and position of the bolt positioning holes III correspond one-to-one with the number and position of the bolt positioning holes IV.

[0039] During assembly, high-strength bolts pass through bolt positioning holes III and IV to connect adjacent pile sections, and a sealing ring is provided between the tenon joint and the mortise joint.

[0040] Furthermore, the high-strength concrete comprises cement, aggregate, admixtures, and water in a mass ratio of 1:0.2:3.5:0.3.

[0041] The cement used is silicate cement with a strength grade of 52.5 or higher. When the aggregate has alkali reactivity, low-alkali cement is used.

[0042] The aggregate includes fine aggregate and coarse aggregate. The fine aggregate is natural hard medium-coarse sand or manufactured sand with a fineness modulus of 2.5 to 3.2. The coarse aggregate is crushed stone or crushed pebbles. The rock mass compressive strength of the crushed stone is greater than 1.2 times the strength of the concrete to be mixed. The crushing index of the pebbles is less than or equal to 6%, and the maximum particle size of the crushed pebbles is less than or equal to 25 mm and less than or equal to 3 / 4 of the clear spacing of the reinforcing bars.

[0043] The admixture is made of slag powder, silica fume, or silica sand powder.

[0044] The water-cement ratio of the high-strength concrete is 0.26-0.30.

[0045] Furthermore, the prestressed longitudinal reinforcement is made of high-strength, low-relaxation steel strand or steel bars for prestressed concrete.

[0046] When the prestressed longitudinal reinforcement is high-strength, low-relaxation steel strand, the standard value of the tensile strength of the reinforcement is greater than 1860 MPa. The criterion for low relaxation is: when the initial stress is 60% of the nominal maximum force, the stress relaxation rate measured after 1000 hours is not greater than 1.0%.

[0047] When the prestressed longitudinal reinforcement is a steel bar for prestressed concrete, the standard value of the tensile strength of the reinforcement is greater than or equal to 1420 Pa and the plastic elongation strength is greater than or equal to 1280 MPa.

[0048] Another objective of this invention is to provide a method for fabricating pile sections based on a prestressed high-strength concrete X-shaped pile structure, comprising the following steps:

[0049] S1. Fabricate a special mold, which includes a left half mold, a right half mold, an upper end plate, and a lower end plate. The inner walls of the left and right half molds are adapted to the outer walls of the X-shaped pile, and the left and right half molds are connected by half mold connecting bolts. After the left and right half molds are installed, the upper and lower end plates are assembled to both ends of the left and right half molds by end plate bolts. The upper end plate has pre-drilled holes for prestressing tendons and grouting holes, and the lower end plate has pre-drilled holes for prestressing tendons.

[0050] S2. Tie or weld the longitudinal prestressing tendons, as well as the ring stirrups / spiral stirrups and single-sided stirrups together to form a steel cage, and hoist the steel cage into the mold and fix the steel cage with positioning pads.

[0051] S3. The longitudinal prestressing tendons are passed through the prestressing tendon holes and fixed by the wedge-type anchors set at both ends of the pile section. A pressure-bearing pad is provided between the wedge-type anchors and the upper and lower end plates.

[0052] S4. Using a through-hole jack, the longitudinal prestressing tendons are tensioned in three stages, starting with the middle of the web and then the ends of the flanges. During tensioning, the elongation of the longitudinal prestressing tendons is monitored, and the deviation between the actual elongation and the theoretical elongation is ≤ ±6%.

[0053] S5. Concrete is poured into the mold using a pumping method.

[0054] S6. After pouring, cover the top plate with plastic film. Then use steam to cure the concrete until the concrete strength reaches more than 80% of the design strength.

[0055] S7. After the concrete strength reaches the specified requirements, slowly release the tensioning equipment to release the temporary anchorage of the reinforcing bars.

[0056] S8. Remove the end plate bolts, remove the upper and lower end plates, then remove the half-mold connecting bolts, move the left and right half-molds to complete demolding. After demolding, inspect the pile section. If the inspection fails, the material is recycled and remanufactured.

[0057] The technical effects of this invention are undeniable, and its beneficial effects are as follows:

[0058] (1) Excellent bearing capacity and high material utilization: Through the X-shaped section design (opening arc angle 90°-150°), the pile-soil contact area is larger than that of a circular pile under the same concrete usage, and the pile side friction is significantly increased. Therefore, the vertical bearing capacity and pull-out force of the pile are significantly increased. With the two reinforcement schemes and prestressing configuration (tension stress 1300-1450MPa), the crack resistance moment of the pile is increased by more than 30%, which effectively reduces the number of piles and significantly reduces the total cost of foundation engineering.

[0059] (2) Stable quality and high construction efficiency: By using standardized prefabrication process in the factory, the concrete density and prestressing tension accuracy are highly controllable, and the finished product qualification rate reaches more than 98%, which effectively avoids the problem of on-site defects that are easy to occur in cast-in-place piles; the steam curing cycle of this invention is only 6-10 hours (curing to strength of more than 80%), and no curing is required on-site construction, shortening the construction period by more than 50% compared with cast-in-place piles; the newly added synchronous release step of prestressing tendons can prevent the pile body from impact cracking, further effectively ensuring the quality of finished products.

[0060] (3) Strong adaptability and wide scene coverage: Four types of pile connection (insert-type connection, flange connection, tenon and mortise connection) can be flexibly selected according to geological environment and load conditions.

[0061] (4) High-performance materials with good durability: The high-strength concrete uses 52.5 grade silicate cement, aggregates and special admixtures that conform to GB / T14685, and has a 28-day compressive strength ≥60MPa (steam curing is required to achieve early strength so that it can quickly reach the demolding strength. The 28-day strength test is conducted after steam curing, when the concrete strength still needs to develop slowly to reach the final strength. The test is conducted on the final strength), and the impermeability grade is ≥P8. The prestressing tendons are selected from high tensile strength steel strands or steel bars, combined with a sealed and corrosion-resistant connection structure, so that the service life of the pile is higher than that of traditional piles. Attached Figure Description

[0062] Figure 1 This is a three-dimensional perspective view of the X-shaped pile of the present invention;

[0063] Figure 2 These are three views of the X-shaped pile of the present invention, wherein... Figure 2 (a) is the front view. Figure 2 (b) is a side view. Figure 2 (c) is a top view;

[0064] Figure 3 This is the reinforcement diagram of the X-shaped pile of the present invention, wherein... Figure 3(a) is the reinforcement diagram for reinforcement scheme one. Figure 3 (b) is the reinforcement diagram for reinforcement scheme two;

[0065] Figure 4 This is a schematic diagram of the plug structure in a socket-type connection structure, where... Figure 4 (a) is a front view of the plug structure. Figure 4 (b) is a right view of the plug structure. Figure 4 (c) is a top view of the plug structure. Figure 4 (d) is Figure 4 (a) Sectional view of section AA;

[0066] Figure 5 This is a schematic diagram of a socket structure in a plug-in connection structure, where... Figure 5 (a) is a front view of the socket structure. Figure 5 (b) is the left view of the socket structure. Figure 5 (c) is a top view of the socket structure. Figure 5 (d) is Figure 5 (a) Sectional view of BB;

[0067] Figure 6 This is a schematic diagram of a circular flange structure, in which... Figure 6 (a) is a top view. Figure 6 (b) is Figure 6 (a) Cross-sectional view of section CC, Figure 6 (c) is Figure 6 (a) Sectional view of DD, Figure 6 (d) is the front view. Figure 6 (e) is the left view;

[0068] Figure 7 This is a schematic diagram of an X-shaped flange structure, in which... Figure 7 (a) is a top view. Figure 7 (b) is Figure 7 (a) Sectional view of EE, Figure 7 (c) is Figure 7 (a) Cross-sectional view of FF section, Figure 7 (d) is the front view. Figure 7 (e) is the left view;

[0069] Figure 8 The three-view diagram shows the arrangement of bolt holes at the pile end when connecting piles with flanges. Figure 8 (a) is the front view. Figure 8 (b) is a side view. Figure 8 (c) is a top view;

[0070] Figure 9 This is a schematic diagram of a mortise joint, in which... Figure 9 (a) is the front view. Figure 9(b) is the right view. Figure 9 (c) is a top view. Figure 9 (d) is Figure 9 (a) Cross-sectional view of GG section;

[0071] Figure 10 This is a schematic diagram of a tenon joint, in which... Figure 10 (a) is the front view. Figure 10 (b) is the left view. Figure 10 (c) is a top view. Figure 10 (d) is Figure 10 (a) Cross-sectional view of section HH, Figure 10 (e) is Figure 10 (a) Section II;

[0072] In the diagram: 1-Pile body; 2-Inner arc surface; 3-Central angle; 4-Flange; 5-Web area; 6-Longitudinal prestressing tendon; 71-Helical stirrup; 72-Single-sided stirrup; 8-Both ends of the pile; 9-Middle part of the pile; 10-Thin iron wire; 11-Circular stirrup; 12-Plug structure; 13-Socket structure; 14-Plug bolt hole; 15-Socket bolt hole; 16-Circular flange; 17-Cylindrical mounting groove; 18-X-shaped flange; 19-X-type mounting groove; 20-Bolt positioning hole I; 21-Boss bolt positioning hole I; 22-Bolt positioning hole II; 23-Boss bolt positioning hole II; 24-Pile end positioning hole; 25-Rivet joint; 26-Bolt positioning hole III; 27-Tongue joint; 28-Bolt positioning hole IV. Detailed Implementation

[0073] The present invention will be further described below with reference to embodiments, but it should not be construed that the scope of the present invention is limited to the following embodiments. Various substitutions and modifications made based on ordinary technical knowledge and common practices in the art without departing from the above-described technical concept of the present invention should be included within the scope of protection of the present invention.

[0074] Example 1:

[0075] A prestressed high-strength concrete X-shaped pile structure is provided. The pile body 1 of the X-shaped pile includes at least one pile segment. Adjacent pile segments are connected by a connecting device. Each pile segment includes a web region 5 located in the center and four flanges 4 spaced around the web region 5. Adjacent flanges 4 are connected by an inner arc surface 2, so that the cross-section of the X-shaped pile is X-shaped as a whole.

[0076] The X-shaped piles employ two reinforcement schemes:

[0077] Reinforcement scheme 1: Several longitudinal prestressed tendons 6 and two sets of annular stirrups 11 are pre-embedded in the pile body 1. The two sets of annular stirrups 11 are staggered. Several longitudinal prestressed tendons 6 are arranged around the annular stirrups 11 inside the annular stirrups 11, and the annular stirrups 11 are densely arranged at both ends of the X-shaped pile.

[0078] The first reinforcement scheme is suitable for building pile foundations in low-intensity seismic zones and auxiliary pile foundations that bear pressure loads.

[0079] Reinforcement scheme 2: Several longitudinal prestressing tendons 6, a set of spiral stirrups 71 and two sets of single-sided stirrups 72 are pre-embedded in the pile body 1. The two sets of single-sided stirrups 72 are staggered. The spiral stirrups 71 are set in the web area 5. Several longitudinal prestressing tendons 6 are set around the spiral stirrups 71 inside the spiral stirrups 71. The spiral stirrups 71 and the two sets of single-sided stirrups 72 are densely set at both ends of the X-shaped pile.

[0080] The second reinforcement scheme is applicable to earthquake-fortified areas, and is suitable for pile foundations that can withstand large horizontal loads and bending moments, as well as high-rise building foundations that require high structural ductility.

[0081] The pile section is made of high-strength concrete with a strength grade greater than or equal to C60.

[0082] Example 2:

[0083] The main structure of this embodiment is the same as that of Embodiment 1. Furthermore, the central angle corresponding to the inner arc surface 2 is... The range of 3 is 90°-150°.

[0084] X-shaped cross-section perimeter The calculation formula is as follows:

[0085] (1)

[0086] In the formula: The width of the major axis of the X-shaped cross-section; This refers to the wing width;

[0087] X-shaped cross-sectional area The calculation formula is as follows:

[0088] (2)

[0089] Example 3:

[0090] The main structure of this embodiment is the same as any one of embodiments 1 to 2. Furthermore, the connecting device adopts any one of the following: a plug-in connection structure, a circular flange connection structure, an X-shaped flange connection structure, and a tenon and mortise connection structure.

[0091] The following table is a comprehensive selection recommendation table:

[0092]

[0093] Example 4:

[0094] The main structure of this embodiment is the same as any one of embodiments 1 to 3. Furthermore, when there are two pile sections and a plug-in connection structure is adopted, the bottom of the top pile section and the top of the bottom pile section are respectively provided with a plug structure 12 and a socket structure 13.

[0095] When there are more than two pile sections and a plug-in connection structure is adopted, the bottom of the top pile section is provided with a plug structure 12, the top and bottom of the middle pile section are provided with a socket structure 13 and a plug structure 12 respectively, and the top of the bottom pile section is provided with a socket structure 13.

[0096] The plug structure 12 is a cylindrical structure, located at the center of the web region 5, and has a plurality of plug bolt holes 14 spaced radially along the plug structure 12. The axis of the plug bolt holes 14 is parallel to the central axis of two of the flanges 4. The outer wall of the plug structure 12 has a plurality of annular grooves spaced apart, and rubber sealing rings are fitted in the grooves.

[0097] The socket structure 13 is a cylindrical groove structure, located at the center of the web region 5 and inside the web region 5. The flange 4, located on the outer wall of the socket structure 13, has a plurality of socket bolt holes 15 spaced radially along the socket structure 13. The axis of each socket bolt hole 15 is parallel to the central axis of two of the flanges 4.

[0098] The dimensions of the plug structure 12 are adapted to the dimensions of the socket structure 13. The number and position of the plug bolt holes 14 correspond one-to-one with the number and position of the socket bolt holes 15.

[0099] During assembly, high-strength bolts pass through the plug bolt hole 14 and the socket bolt hole 15 to fix the two pile sections together.

[0100] Example 5:

[0101] The main structure of this embodiment is the same as any one of embodiments 1 to 4. Furthermore, when there are two pile sections and a circular flange connection structure is used, a circular flange 16 is provided at the bottom of the top pile section and the top of the bottom pile section. When there are more than two pile sections and a circular flange connection structure is used, a circular flange 16 is provided at the bottom of the top pile section, the top and bottom of the middle pile section, and the top of the bottom pile section.

[0102] The circular flange 16 includes a circular flange body and an annular boss I extending along the edge of the circular flange body. A cylindrical mounting groove 17 is formed between the circular flange body and the annular boss I. The cylindrical mounting groove 17 and the annular boss I are respectively provided with a plurality of bolt positioning holes I20 and boss bolt positioning holes I21 at intervals.

[0103] The corresponding ends of the pile sections are provided with a plurality of pile end positioning holes 24 at intervals. During assembly, the pile sections are embedded in the cylindrical mounting grooves 17 of the circular flanges 16, and the pile end positioning holes 24 of the pile sections correspond one-to-one with the bolt positioning holes I20 of the circular flanges 16. High-strength bolts pass through the bolt positioning holes I20 and the pile end positioning holes 24 to fix the circular flanges 16 to the ends of the pile sections. A sealing gasket is provided between the pile sections and the cylindrical mounting grooves 17. High-strength bolts pass through the boss bolt positioning holes I21 of the two circular flanges 16 to connect two adjacent pile sections.

[0104] Example 6:

[0105] The main structure of this embodiment is the same as any one of embodiments 1 to 5. Furthermore, when there are two pile sections and an X-shaped flange connection structure is used, an X-shaped flange 18 is provided at the bottom of the top pile section and at the top of the bottom pile section.

[0106] When there are more than two pile sections and an X-shaped flange connection structure is used, X-shaped flanges 18 are provided at the bottom of the top pile section, the top and bottom of the middle pile section, and the top of the bottom pile section.

[0107] The X-shaped flange 18 includes an X-shaped flange body and an annular boss II extending along the edge of the X-shaped flange body. An X-shaped mounting groove 19 is formed between the X-shaped flange body and the annular boss II. The X-shaped mounting groove 19 and the annular boss II are respectively provided with a plurality of bolt positioning holes II22 and boss bolt positioning holes II23 at intervals.

[0108] The corresponding ends of the pile section are provided with a number of pile end positioning holes 24 at intervals.

[0109] During assembly, the pile section is embedded in the X-shaped mounting groove 19 of the X-shaped flange 18, and the pile end positioning hole 24 of the pile section corresponds one-to-one with the bolt positioning hole II22 of the X-shaped flange 18. High-strength bolts pass through the bolt positioning hole II22 and the pile end positioning hole 24 to fix the X-shaped flange 18 to the end of the pile section. A sealing gasket is provided between the pile section and the X-shaped mounting groove 19. High-strength bolts pass through the boss bolt positioning holes II23 of the two X-shaped flanges 18 to connect two adjacent pile sections.

[0110] Example 7:

[0111] The main structure of this embodiment is the same as any one of embodiments 1 to 6. Furthermore, when there are two pile sections and a mortise and tenon connection structure is adopted, the bottom of the top pile section and the top of the bottom pile section are respectively provided with a mortise joint 25 and a tenon joint 27.

[0112] When there are more than two pile sections and a mortise and tenon connection structure is used, the bottom of the top pile section is provided with a mortise joint 25, the top and bottom of the middle pile section are provided with a mortise joint 27 and a mortise joint 25 respectively, and the top of the bottom pile section is provided with a mortise joint 27.

[0113] The mortise joint 25 is U-shaped, and the tenon joint 27 is U-shaped, with their shapes fitting together. The mortise joint 25 and the tenon joint 27 are respectively provided with a number of bolt positioning holes III26 and a number of bolt positioning holes IV28 at intervals. The number and position of the bolt positioning holes III26 correspond one-to-one with the number and position of the bolt positioning holes IV28.

[0114] During assembly, high-strength bolts pass through bolt positioning holes III26 and IV28 to connect adjacent pile sections, and a sealing ring is provided between the tenon joint 27 and the mortise joint 25.

[0115] Example 8:

[0116] The main structure of this embodiment is the same as any one of embodiments 1 to 7. Furthermore, the high-strength concrete includes cement, aggregate, admixture and water in a mass ratio of 1:0.2:3.5:0.3.

[0117] The cement used is silicate cement with a strength grade of 52.5 or higher. When the aggregate has alkali reactivity, low-alkali cement is used.

[0118] The aggregate includes fine aggregate and coarse aggregate. The fine aggregate is natural hard medium-coarse sand or manufactured sand with a fineness modulus of 2.5 to 3.2. The coarse aggregate is crushed stone or crushed pebbles. The rock mass compressive strength of the crushed stone is greater than 1.2 times the strength of the concrete to be mixed. The crushing index of the pebbles is less than or equal to 6%, and the maximum particle size of the crushed pebbles is less than or equal to 25 mm and less than or equal to 3 / 4 of the clear spacing of the reinforcing bars.

[0119] The admixture is made of slag powder, silica fume, or silica sand powder.

[0120] The water-cement ratio of the high-strength concrete is 0.26-0.30.

[0121] Example 9:

[0122] The main structure of this embodiment is the same as any one of embodiments 1 to 8. Furthermore, the prestressed longitudinal steel bar 6 is made of high-strength low-relaxation steel strand or steel bar for prestressed concrete.

[0123] When the prestressed longitudinal steel bar 6 is a high-strength, low-relaxation steel strand, the standard value of the tensile strength of the steel bar is greater than 1860 MPa. The criterion for low relaxation is: when the initial stress is 60% of the nominal maximum force, the stress relaxation rate measured after 1000 hours is not greater than 1.0%.

[0124] When the prestressed longitudinal steel bar 6 is a steel bar for prestressed concrete, the standard value of the tensile strength of the steel bar is greater than or equal to 1420 Pa and the plastic elongation strength is greater than or equal to 1280 MPa.

[0125] Example 10:

[0126] A method for fabricating pile sections based on the prestressed high-strength concrete X-shaped pile structure described in any one of Examples 1 to 9 includes the following steps:

[0127] S1. Fabricate a special mold, which includes a left half mold, a right half mold, an upper end plate, and a lower end plate; the inner walls of the left half mold and the right half mold are adapted to the outer wall of the X-shaped pile, and the left and right half molds are connected by half mold connecting bolts; after the left and right half molds are installed, the upper and lower end plates are assembled at both ends of the left and right half molds by end plate bolts; the upper end plate is reserved with prestressing tendon holes and grouting holes, and the lower end plate is reserved with prestressing tendon holes;

[0128] S2. Tie or weld the longitudinal prestressed tendons 6, the annular stirrups 11 / spiral stirrups 71 and the single-sided stirrups 72 together to form a steel cage, and hoist the steel cage into the mold and fix the steel cage with positioning pads.

[0129] S3. Pass the longitudinal prestressing tendon 6 through the prestressing tendon hole and fix it through the wedge-type anchors set at both ends of the pile section; a pressure-bearing pad is provided between the wedge-type anchor and the upper and lower end plates;

[0130] S4. Using a through-hole jack, the longitudinal prestressing tendon 6 is tensioned in three stages in the order of "first the middle of the web, then the end of the flange". During the tensioning process, the elongation value of the longitudinal prestressing tendon 6 is monitored, and the deviation between the actual elongation value and the theoretical elongation value is ≤ ±6%.

[0131] S5. Concrete is poured into the mold using a pumping method;

[0132] S6. After the pouring is completed, cover the upper end plate with plastic film; and use steam to cure the concrete until the concrete strength reaches more than 80% of the design strength.

[0133] S7. After the concrete strength reaches the specified requirements, slowly release the tensioning equipment to release the temporary anchorage of the reinforcing bars;

[0134] S8. Remove the end plate bolts, remove the upper and lower end plates, then remove the half-mold connecting bolts, move the left and right half-molds to complete the demolding; after demolding is completed, inspect the pile section. If the inspection fails, the material is recycled and remade.

[0135] Example 11:

[0136] The main structure of this embodiment is the same as any one of embodiments 1 to 10. Furthermore, this invention aims to solve three core problems existing in the prior art: First, traditional circular concrete piles have a small pile-soil contact area with the same material usage, resulting in insufficient vertical bearing capacity and pull-out resistance, and low material utilization. Second, traditional cast-in-place concrete piles are greatly affected by the site environment, easily exhibiting density defects and cracks, and have a long curing period (7-14 days), leading to low construction efficiency. Third, existing pile connection methods have poor adaptability, making it difficult to meet the engineering requirements of complex geological environments (such as high water levels and narrow spaces) and diverse load conditions (such as high stiffness and high integrity). This invention provides a "high-efficiency, high-strength, economical, and versatile" prestressed high-strength concrete X-shaped pile by optimizing the pile cross-sectional structure, innovating reinforcement schemes, standardizing prefabrication processes, and using multiple types of connection structures. This pile is suitable for complex engineering scenarios such as foundations, slope protection, and retaining structures.

[0137] To achieve the above objectives, the present invention adopts the following technical solution, the core content of which includes three parts: the structural construction of prestressed high-strength concrete X-shaped piles, the manufacturing method, and the splicing method, as detailed below:

[0138] I. Structural Construction of Prestressed High-Strength Concrete X-Shaped Piles

[0139] The structure includes the pile body (1), and its core technical features are as follows:

[0140] 1. Cross-sectional shape design:

[0141] The cross-section of the pile body 1 is symmetrical X-shaped, and it is integrally formed by four identical flanges 4 and web area 5.

[0142] The opening angle of the X-shaped cross-section is 90°-150°, and the four flanges 4 extend from the central web region 5 outwards. The major axis width of the X-shaped cross-section is several times the flange width. Its cross-sectional perimeter and area are calculated according to the following formulas:

[0143] Cross-sectional perimeter:

[0144] (1)

[0145] Cross-sectional area:

[0146] (2)

[0147] With this cross-sectional design, the pile-soil contact area is increased by 20%-30% compared to a circular pile, under the same concrete usage, significantly improving the pile side friction resistance.

[0148] 2. Reinforcement scheme:

[0149] The pile body 1 adopts two selectable reinforcement schemes to adapt to different load requirements.

[0150] The first reinforcement scheme is as follows: two sets of annular stirrups 11 are used in conjunction with longitudinal prestressed tendons 6. The annular stirrups 11 are connected to the upper and lower and left and right flanges respectively, and the longitudinal prestressed tendons 6 are evenly distributed along the long side of the annular stirrups 11.

[0151] The second reinforcement scheme is as follows: a set of spiral stirrups 71 and two sets of single-sided stirrups 72 are used together, and the longitudinal prestressed tendons 6 are evenly distributed along the spiral stirrups 71.

[0152] The spiral stirrups 7 and the annular stirrups 11 are densely arranged at both ends 8 of the pile body, and the density in the middle part 9 of the pile body is lower than that at both ends, to ensure the shear and crack resistance of the pile end (the stress concentration area); the longitudinal prestressed tendons 6 and the stirrups are tied and fixed with thin iron wires 10 to avoid displacement during the pouring process.

[0153] 3. Materials and Prestressing Configuration:

[0154] The pile body 1 is made of high-strength concrete with a strength grade of not less than C60, the concrete water-cement ratio is 0.26-0.30, and the 28-day compressive strength is ≥60MPa; in the high-strength concrete, the cement is selected as silicate cement with a strength grade of not less than 52.5 (low-alkali cement is used when the aggregate has alkali reactivity).

[0155] The fine aggregate is clean, natural, hard, medium-coarse sand or manufactured sand (fineness modulus 2.5-3.2), and the coarse aggregate is crushed stone or broken pebbles (rock compressive strength > 1.2 times concrete strength, crushing index ≤ 6%, maximum particle size ≤ 25mm and ≤ 3 / 4 of the net spacing of reinforcing bars, in accordance with GB / T14685). The admixtures should preferably be slag powder, silica fume, silica sand powder or admixtures for steam-cured concrete products.

[0156] The number of longitudinal prestressing tendons 6 is 10-16, and they can be high-strength low-relaxation steel strands (tensile strength standard value > 1860MPa) or prestressed concrete steel bars (complying with the requirements of GB / T5223.3 for low-relaxation spiral groove steel bars, tensile strength standard value ≥ 1420MPa, and specified plastic elongation strength ≥ 1280MPa).

[0157] The longitudinal prestressing tendons 6 are arranged along the spiral stirrups 71 or the annular stirrups 11, and both ends are fixed to the pile end by the wedge-type anchors. The tension control stress is 1300-1450MPa, so that the pile body is pre-stressed and the concrete cracking is suppressed.

[0158] II. Fabrication Method of Prestressed High-Strength Concrete X-Shaped Piles

[0159] The manufacturing method includes the following steps to achieve standardized prefabrication and ensure stable finished product quality:

[0160] S1: Special mold making. The mold is made of Q235 steel and consists of two half molds and upper and lower end plates. The inner wall of the half mold is processed according to the cross-sectional shape of the X-shaped pile. The half molds are connected by bolts with a spacing of 300-500mm. The end plates are reserved with prestressing tendon holes and grouting holes. Rollers are provided at the bottom of the mold (for easy demolding). Mold precision control ensures that the cross-sectional dimensions of the pile meet the requirements.

[0161] S2: Fabrication and installation of the reinforcing cage. The reinforcing cage consists of longitudinal reinforcing bars 29 and spiral stirrups 71 / circumferential stirrups 11. The longitudinal reinforcing bars 29 are HRB400 threaded steel bars, and the spiral stirrups 71 / circumferential stirrups 11 are HPB300 plain round steel bars. The longitudinal reinforcing bars 29 and the stirrups are connected by binding or welding with thin iron wire. The reinforcing cage is hoisted into the mold, maintaining a 50-70mm protective layer distance from the inner wall of the mold, and fixed with positioning pads (to prevent displacement during pouring).

[0162] S3: Installation and tensioning of prestressed tendons. Pass the prestressed steel strands (or bars) through the pre-drilled holes in the end plate, and install wedge-type anchors at both ends. Place a 16-20mm thick bearing pad between the anchors and the end plate. Use a through-hole jack to tension in three stages, starting with the middle of the web and then the ends of the flanges: First stage tensioning to 20% of the control stress and holding for 2 minutes; second stage tensioning to 60% of the control stress and holding for 2 minutes; third stage tensioning to 100% of the control stress and holding for 5 minutes before anchoring. Monitor the elongation of the steel strands during tensioning; the deviation between the actual elongation and the theoretical elongation should be ≤±6%.

[0163] S4: Concrete pouring. High-strength concrete is poured using a pump. During pouring, an immersion vibrator with a frequency of 2000-2500 r / min is used for compaction. The vibration point spacing is 300-400 mm, and each point is vibrated for 20-30 seconds until the concrete surface is smooth and free of air bubbles (to ensure compaction). After pouring, the top of the pile is covered with a plastic film (to prevent moisture evaporation).

[0164] S5: Concrete curing, using steam curing, with a heating rate ≤25℃ / h. After heating to 50-70℃, it enters the constant temperature stage (constant temperature for 6-10h), and then cools down at a rate ≤20℃ / h until the temperature difference between the mold and the environment is ≤20℃; curing is carried out until the concrete strength reaches more than 80% of the design strength (ensuring that the pile strength meets the requirements of subsequent processes).

[0165] S6: Prestressing tendon release. The prestressing tendon release is to slowly release the tensioning equipment after the concrete strength reaches the specified requirements, thereby releasing the temporary anchorage of the steel bars. The release process must be slow and synchronous (to prevent impact stress on the pile body that could lead to cracking). The rebound force generated by the retraction of the steel bars is transferred to the concrete through the bond force between the steel bars and the concrete, so that the pile body concrete obtains prestress.

[0166] S7: Demolding and inspection. First, remove the end plate bolts, then loosen the half-mold connecting bolts, and move the half-mold through the rollers at the bottom of the mold to complete the demolding. The inspection items include: no obvious cracks, honeycomb, or pitting on the appearance (local defect area ≤0.02m², depth ≤5mm), dimensional deviations meet the design requirements, and mechanical properties meet the standards (such as vertical compressive strength and crack resistance).

[0167] III. Splicing Methods of Prestressed High-Strength Concrete X-Shaped Piles

[0168] This invention designs three pile splicing methods to adapt to different engineering scenarios, ensuring that the strength of the connection node is not lower than that of the pile body, as detailed below:

[0169] 1. Plug-in connection structure: used to connect adjacent X-shaped piles. The lower end of the upper pile is equipped with a plug structure 12 (length 300-500mm, cross-sectional dimension 10-15mm smaller than the pile body), and the upper end of the lower pile is equipped with a socket structure 13 (depth matched with plug length).

[0170] Both the plug structure 12 and the socket structure 13 have two bolt holes side by side, with the openings of the bolt holes facing the central axis of the X-shaped pile flange (to ensure symmetrical force distribution).

[0171] The mating surfaces of the plug and socket are provided with two circular cross-section rubber sealing rings (embedded in the annular groove on the outer wall of the plug to improve sealing and leak-proof performance).

[0172] 2. Flange connection structure: The flange connection structure includes a circular flange connection structure and an X-shaped flange connection structure.

[0173] The circular flange connection structure includes a circular steel flange, high-strength bolts, and a sealing gasket. The flange is made of Q345 steel (15-25mm thick) and has 8-16 evenly spaced bolt holes with a diameter of 18-24mm. The sealing gasket is made of nitrile rubber (3-5mm thick) and has through holes corresponding to the bolt holes on its surface. During connection, two circular flanges 16 with circular grooves are first connected to the upper and lower X-shaped piles through the pre-drilled pile end positioning holes 24. Then, the upper and lower piles are connected and fixed using high-strength bolts through the pre-drilled boss bolt positioning holes I 21. After connection, the gap between the flange mating surfaces is ≤0.3mm (ensuring rigidity and sealing).

[0174] The X-shaped flange connection structure includes an X-shaped steel flange, high-strength bolts, and a sealing gasket. The X-shaped flange is made of Q345 steel (15-25mm thick) and has 8-16 evenly spaced bolt holes with a diameter of 18-24mm. The sealing gasket is made of nitrile rubber (3-5mm thick) and has through holes corresponding to the bolt holes on its surface. During connection, two X-shaped flanges 18 with X-shaped grooves are first connected to the upper and lower X-shaped pile sections through the pre-drilled pile end positioning holes 24. Then, the upper and lower pile sections are connected and fixed using high-strength bolts through the pre-drilled boss bolt positioning holes II23. After connection, the gap between the flange mating surfaces is ≤0.3mm (adapting to the X-shaped pile cross-section for more uniform stress distribution).

[0175] 3. Mortise and tenon connection structure: In the mortise and tenon connection structure, the pile end of one pile is a concave structure and the pile top of the other pile is a convex structure. The convex structure and the concave structure fit together tightly (to ensure integrity); the mortise and tenon structure of the connection part of the two piles has reserved positioning holes. After the mortise and tenon fit together, bolts are used to fix it through the positioning holes (to improve the reliability of the connection and is suitable for scenarios with high requirements for integrity).

[0176] Example 12:

[0177] The main structure of this embodiment is the same as any one of embodiments 1 to 11, and further,

[0178] 1. Project Background: A multi-story to mid-rise residential project has a foundation of cohesive soil or silty clay soil with a certain groundwater level. The foundation needs to meet the basic requirements of the residential foundation for the vertical bearing capacity, pull-out performance and seepage prevention of the piles, and the construction period needs to be adapted to the overall project schedule.

[0179] 2. Pile body parameter design

[0180] Cross-sectional shape: The pile body adopts a symmetrical X-shaped cross-section, which is formed by four identical flanges and the central core area. The opening angle of the X-shaped cross-section is selected within the range of 90°-150° to adapt to the stress requirements of the project. The dimensions of the flanges and the core area are designed according to the principle of "ensuring that the pile-soil contact area is better than that of traditional circular piles". The ratio of the major axis width to the flange width meets the requirements for cross-sectional stress optimization.

[0181] Material selection: The pile body uses high-strength concrete with a strength grade of not less than C60. The cement used is silicate cement of grade not less than 52.5 (low-alkali cement is used if the aggregate is alkali-reactive). The fine aggregate is clean medium-coarse sand or manufactured sand (fineness modulus 2.5-3.2). The coarse aggregate is crushed stone or crushed pebbles (crushing index and maximum particle size comply with GB / T14685). The admixtures are slag powder, silica fume and other types suitable for the performance of high-strength concrete. The water-cement ratio is controlled at 0.26-0.30 to ensure that the 28-day compressive strength meets the standard.

[0182] Reinforcement and prestressing configuration: Any reinforcement scheme (circular stirrups + longitudinal prestressing tendons or spiral stirrups + single-sided stirrups) can be selected. The stirrups are densely arranged at both ends of the pile (in areas of concentrated stress) and arranged at a conventional density in the middle. The number of longitudinal prestressing tendons is 10-16, using high-strength low-relaxation steel strands or prestressed concrete steel bars (both conforming to the corresponding material standards), and evenly distributed along the stirrups. The two ends of the prestressing tendons are fixed by wedge-type anchors and tensioned according to the design control stress of 1300-1450MPa.

[0183] 3. Manufacturing and Implementation Process

[0184] S1: Special mold making, using Q235 steel to make the left and right half molds and the upper and lower end plates. The inner wall of the half mold is processed according to the design X-shaped cross section to ensure the accuracy of the cross section shape. The half molds are connected by bolts. The end plates are reserved with prestressing tendon holes and grouting holes. Rollers are provided at the bottom of the mold for easy demolding. Reinforcing ribs are provided at corresponding positions on the web plate to ensure the rigidity of the mold.

[0185] S2: Fabrication and installation of the reinforcing cage. Fabricate the reinforcing cage according to the design requirements. The longitudinal reinforcing bars and stirrups are connected by binding or welding with thin iron wire to ensure the overall rigidity of the reinforcing cage. Hoist the reinforcing cage into the mold and fix it with positioning pads to ensure that the thickness of the protective layer between the reinforcing cage and the inner wall of the mold meets the design requirements (generally 50-70mm).

[0186] S3: Installation and tensioning of prestressed tendons. Pass the prestressed tendons through the pre-drilled holes in the end plate, and install wedge-type anchors and bearing pads at both ends. Use a through-hole jack to tension in three stages in the order of "first the middle of the web, then the end of the flange". After each stage of tensioning reaches the corresponding control stress ratio, hold the load to stabilize. Monitor the elongation value of the prestressed tendons during the tensioning process to ensure that the deviation between the actual elongation value and the theoretical elongation value is within ±6%. After meeting the standard, anchor the tendons.

[0187] S4: Concrete pouring. High-strength concrete is poured using a pump. During the pouring process, an immersion vibrator is used to compact the concrete until the surface is smooth and free of air bubbles, ensuring density. After pouring, the pile top is covered in time to prevent moisture evaporation from affecting the strength.

[0188] S5: Concrete curing adopts steam curing process, and the heating rate, constant temperature and cooling rate are controlled in accordance with the concrete curing specifications. The concrete is cured until the strength reaches more than 80% of the design strength to avoid strength loss caused by improper curing.

[0189] S6: Release the prestressed tendons. After the concrete strength reaches the standard, slowly release the tensioning equipment and release the temporary anchorage. The release process must be carried out synchronously and smoothly to prevent the pile body from cracking due to impact stress, so that the pile concrete can obtain the design prestress through the retraction of the steel bars.

[0190] S7: Demolding and inspection. Remove the end plate and half-mold bolts in sequence, and move the half-mold through the rollers at the bottom of the mold to complete the demolding. Inspect the appearance of the pile (no obvious cracks, honeycomb, pitting or other defects), dimensional deviations (meeting design and specification requirements), and mechanical properties (sampling test of bearing capacity and crack resistance meets the standards).

[0191] 4. Implementation of pile splicing method

[0192] The lower end of the upper pile section is equipped with a plug structure, and the upper end of the lower pile section is equipped with a socket structure. The length of the plug is adapted to the depth of the socket, and the cross-sectional dimension of the plug is slightly smaller than that of the pile body. Bolt holes are opened at corresponding positions (the holes are directly opposite the central axis of the X-shaped pile flange). Multiple rubber sealing rings are provided on the mating surface of the plug and socket to ensure anti-seepage performance.

[0193] On-site connection steps: a. Clean impurities from the plug and socket surfaces and check the integrity of the sealing rings; b. Hoist the upper section of the pile, adjust the verticality to meet engineering requirements, and slowly insert the plug into the socket to the designed depth; c. Align the bolt holes, fix with high-strength bolts, and tighten the bolts in a symmetrical order; d. Check the sealing performance of the connection parts to ensure no leakage (suitable for groundwater level scenarios).

[0194] 5. Engineering Application Results

[0195] Pile bearing capacity: On-site testing showed that the vertical bearing capacity and pull-out performance of the piles met the design requirements for residential foundations; Construction efficiency: Factory prefabrication avoids defects in on-site casting, has a short curing period, and the on-site construction progress meets the overall project plan; Adaptability: The sealed design of the plug-in connection effectively copes with the impact of groundwater level and meets the long-term durability requirements of residential foundations; Economic benefits: Prestressed high-strength concrete X-shaped piles significantly reduce the amount of concrete used under the same bearing capacity requirements, while the pile quality is better than that of cast-in-place piles, resulting in significant economic benefits.

[0196] Example 13:

[0197] The main structure of this embodiment is the same as any one of embodiments 1 to 11. Furthermore, this embodiment provides an implementation plan for prestressed high-strength concrete X-shaped pile groups to meet the needs of wind power pile foundation engineering. It focuses on the core technical logic and key operation steps, without involving unspecified specific values. Personnel in the relevant technical field can adjust the adaptation parameters according to the actual working conditions of the wind power project (such as wind turbine model, geological conditions, and load requirements) to ensure that the solution can be implemented repeatedly.

[0198] 1. Project Background

[0199] A certain onshore wind power project has medium to large-capacity wind turbines that need to withstand vertical loads (the weight of the turbine, tower, and foundation), horizontal loads (long-term wind loads and instantaneous strong wind loads), and cyclic alternating loads. Furthermore, the site has an alternating distribution of soft soil and sand layers, placing high demands on the pile foundation's bearing capacity, lateral displacement resistance, durability, and the synergistic force-bearing effect of the pile group. Traditional circular pile groups suffer from insufficient resistance to horizontal loads and low material utilization. Therefore, the prestressed high-strength concrete X-shaped pile group of this invention is adopted as the wind turbine foundation pile foundation.

[0200] 2. Parameter Design of Prestressed High-Strength Concrete X-Shaped Piles

[0201] Based on the aforementioned structural features of this invention, an X-shaped pile unit is designed according to the stress characteristics of wind power pile foundations. The core design logic is as follows:

[0202] Cross-sectional design: The cross-section of the pile body adopts a symmetrical X shape, and the arc angle is selected according to the horizontal load resistance requirements of the wind turbine pile foundation (prioritizing the angle range of horizontal force transmission). The size ratio between the flange and the central core area is determined according to the principle of "improving the pile side friction resistance and enhancing shear resistance"—the flange length must ensure the effective contact area with the stratum to resist the cyclic horizontal load during wind turbine operation; the stiffness of the core area must be adapted to the vertical load transmission requirements.

[0203] Material and Concrete Selection: The pile body uses high-strength concrete with a strength grade of not less than C60. The concrete mix design focuses on "crack resistance and durability" - low-alkali cement is selected (to avoid alkali-aggregate reaction and to meet the long-term service requirements of wind power). Admixtures are selected to improve the performance of cyclic load resistance. The concrete water-cement ratio is controlled within a reasonable range that is suitable for high strength and crack resistance, ensuring that the pile body is not prone to cracking under cyclic load.

[0204] Reinforcement and prestressing configuration: The reinforcement scheme adopted in this invention is suitable for "cyclic load and horizontal load" (preferably the scheme of combining ring stirrups and longitudinal prestressing tendons, or the scheme of spiral stirrups with denser design). The stirrups are densely arranged at the upper and lower ends of the pile body (the section connecting the pile group and the pile cap, and the section where the pile end is embedded in stable stratum) to enhance shear resistance and fatigue resistance. The longitudinal prestressing tendons are selected from high-strength, low-relaxation types (steel strands or steel bars). The tension control stress is determined according to the principle of "offsetting part of the tensile stress generated by the cyclic load". Both ends are fixed by wedge-type anchors to ensure the long-term stability of the prestressing stress of the pile body.

[0205] 3. X-shaped pile manufacturing process

[0206] The manufacturing method described above, when implemented according to the present invention, focuses on the "quality stability and durability" requirements of wind power pile foundations, as detailed below:

[0207] S1: Special mold preparation. The mold is processed according to the cross-sectional shape of the X-shaped pile. High-strength steel is selected as the material to ensure rigidity (to avoid cross-sectional deformation during prefabrication, which would affect the consistency of the stress of the pile group). The mold end plate is reserved with prestressing tendon holes and grouting holes. The hole arrangement must ensure that the prestressing tendons are evenly distributed along the cross-section. The bottom of the mold is equipped with a movable structure to facilitate demolding and transportation during batch prefabrication of wind power projects.

[0208] S2: Fabrication and installation of the reinforcing cage. The reinforcing cage consists of longitudinal reinforcing bars and stirrups. The connection method (tying or welding) is determined according to the requirements of "ensuring node strength and fatigue resistance". The reinforcing cage is fixed by positioning pads during installation to ensure that the protective layer thickness is uniform with the inner wall of the mold. The protective layer thickness must be suitable for the possible corrosive environment of the wind power site to avoid the corrosion of the reinforcing bars affecting durability.

[0209] S3: Installation and tensioning of prestressed tendons. After the prestressed tendons pass through the reserved holes in the end plates, anchorages and bearing pads are installed at both ends. Tensioning is carried out in three stages. After each stage is tensioned to the corresponding stress ratio, the load is held to stabilize. During the tensioning process, the elongation value of the prestressed tendons is monitored to ensure that the deviation between the actual elongation value and the theoretical elongation value is within the allowable range of the specification, so as to avoid uneven stress on the pile body due to improper tensioning (affecting the collaborative performance of the pile group).

[0210] S4: Concrete pouring and curing. Concrete is poured using a pumping method. During the pouring process, it is vibrated until the surface is covered with slurry and free of air bubbles to ensure the pile body is dense (avoiding cracking under cyclic load due to insufficient density). Steam curing is used to control the heating, constant temperature, and cooling rate. The concrete is cured until the strength reaches more than 80% of the design strength to ensure that the early strength of the pile body meets the requirements for transportation and pile driving.

[0211] S5: Demolding and Inspection. Demolding should be carried out in the order of "avoiding damage to the pile body". First, remove the end plate bolts and then loosen the half-formwork connection. The key points of inspection include: no obvious cracks or honeycomb in appearance (to avoid potential durability problems), dimensional deviations that meet the requirements of uniform stress distribution of the pile group, and sampling tests of mechanical properties (crack resistance and shear resistance) that meet the standards.

[0212] 4. Arrangement and connection of prestressed high-strength concrete X-shaped pile groups

[0213] Pile group layout: Based on the requirement of uniform stress distribution of the wind turbine foundation, the X-shaped pile group adopts a "centrally symmetrical layout" (such as circular or regular polygonal layout) to ensure that the vertical load of the wind turbine is evenly distributed to each pile, and the horizontal load is resisted by the pile group in a coordinated manner; the pile spacing is determined according to the principle of "avoiding the soil compaction effect between piles and ensuring the overall rigidity of the pile group", while adapting to the size of the wind turbine pier and the site space conditions.

[0214] Connection between pile group and pile cap: The connection method of "pre-embedded steel bar + grouting" is adopted - the top of the X-shaped pile has a pre-reserved steel bar that extends into the inside of the wind turbine pile cap; a grouting layer is set at the contact part between the pile top and the pile cap, and the grouting material is selected as a high-strength non-shrink type to ensure the rigid connection between the pile and the pile cap, so that the pile group and the pile cap form an integral force system (adapting to the overall anti-lateral displacement requirements under wind power load).

[0215] 5. Engineering Application Results

[0216] Bearing capacity suitability: The overall vertical bearing capacity, horizontal bearing capacity, and cyclic load resistance of the pile group meet the load requirements of medium and large wind turbines, with no obvious deformation or cracks in the pile body; Good stress coordination: The X-shaped cross-section increases the side friction of the piles, and the symmetrical arrangement of the pile group and the rigid connection with the pile cap ensure uniform load transfer and avoid stress concentration on individual piles; Strong construction adaptability: The factory-prefabricated X-shaped piles have stable quality, and the on-site pile driving and splicing operations are suitable for wind power site conditions, with construction efficiency superior to traditional circular pile groups; Durability meets standards: High-strength concrete and prestressed configuration can resist environmental erosion and cyclic loads during long-term wind power service, meeting the long-term use requirements of wind turbine foundations; High economic benefits and environmental protection: Compared with traditional cast-in-place circular piles, prestressed high-strength concrete X-shaped piles can reduce concrete usage and significantly improve material utilization.

[0217] This embodiment does not rely on specific numerical values, but only describes the implementation path of X-shaped pile groups in wind power pile foundations through core technical logic and steps. Those skilled in the art can adjust the parameters according to actual wind power project and repeat the implementation, fully demonstrating the practicality and adaptability of the present invention.

Claims

1. A structural design for a prestressed high-strength concrete X-shaped pile, characterized in that: The pile body (1) of the X-shaped pile includes at least one pile segment. Adjacent pile segments are connected by a connecting device. Each pile segment includes a web area (5) located in the center and four flanges (4) spaced around the web area (5). Adjacent flanges (4) are connected by an inner arc surface (2) so that the cross section of the X-shaped pile is X-shaped as a whole. The X-shaped piles employ two reinforcement schemes: Reinforcement scheme 1: Several longitudinal prestressed tendons (6) and two sets of annular stirrups (11) are pre-embedded in the pile body (1). The two sets of annular stirrups (11) are staggered. Several longitudinal prestressed tendons (6) are arranged around the annular stirrups (11) inside the annular stirrups (11). The annular stirrups (11) are densely arranged at both ends of the X-shaped pile. Reinforcement scheme 2: Several longitudinal prestressed tendons (6), a set of spiral stirrups (71) and two sets of single-sided stirrups (72) are pre-embedded in the pile body (1). The two sets of single-sided stirrups (72) are staggered. The spiral stirrups (71) are set in the web area (5). Several longitudinal prestressed tendons (6) are set around the spiral stirrups (71) inside the spiral stirrups (71). The spiral stirrups (71) and the two sets of single-sided stirrups (72) are densely set at both ends of the X-shaped pile. The pile section is made of high-strength concrete with a strength grade greater than or equal to C60.

2. The structural design of a prestressed high-strength concrete X-shaped pile according to claim 1, characterized in that: The range of the central angle θ(3) corresponding to the inner arc surface (2) is 90°-150°; The formula for calculating the perimeter u of the X-shaped cross-section is as follows: In the formula: a is the major axis width of the X-shaped cross-section; b is the flange width; X-shaped cross-sectional area A ps The calculation formula is as follows:

3. The structural design of a prestressed high-strength concrete X-shaped pile according to claim 1, characterized in that: The connecting device adopts any one of the following: plug-in connection structure, circular flange connection structure, X-shaped flange connection structure, and tenon and mortise connection structure.

4. The structural design of a prestressed high-strength concrete X-shaped pile according to claim 3, characterized in that: When there are two pile sections and a plug-in connection structure is adopted, the bottom of the top pile section and the top of the bottom pile section are respectively provided with the plug structure (12) and the socket structure (13); When there are more than two pile sections and a plug-in connection structure is adopted, the bottom of the top pile section is provided with a plug structure (12), the top and bottom of the middle pile section are provided with a socket structure (13) and a plug structure (12) respectively, and the top of the bottom pile section is provided with a socket structure (13). The plug structure (12) is a cylindrical structure, located at the center of the web area (5), and has a plurality of plug bolt holes (14) spaced radially along the plug structure (12); the axis of the plug bolt holes (14) is parallel to the central axis of two of the flanges (4); the outer side wall of the plug structure (12) is provided with a plurality of annular grooves spaced apart, and rubber sealing rings are fitted in the grooves; The socket structure (13) is a cylindrical groove structure, which is located in the center of the web area (5) and inside the web area (5); the flange (4) is located on the outer wall of the socket structure (13), and a plurality of socket bolt holes (15) are provided at radial intervals along the socket structure (13); the axis of the socket bolt holes (15) is parallel to the central axis of two of the flanges (4); The dimensions of the plug structure (12) are adapted to the dimensions of the socket structure (13); The number and position of the plug bolt holes (14) correspond one-to-one with the number and position of the socket bolt holes (15); During assembly, high-strength bolts are passed through the plug bolt hole (14) and the socket bolt hole (15) to fix the two pile sections together.

5. The structural design of a prestressed high-strength concrete X-shaped pile according to claim 3, characterized in that: When there are two pile sections and a circular flange connection structure is used, a circular flange (16) is provided at the bottom of the top pile section and the top of the bottom pile section. When there are more than two pile sections and a circular flange connection structure is used, a circular flange (16) is provided at the bottom of the top pile section, the top and bottom of the middle pile section, and the top of the bottom pile section. The circular flange (16) includes a circular flange body and an annular boss I extending along the edge of the circular flange body. A cylindrical mounting groove (17) is sandwiched between the circular flange body and the annular boss I. The cylindrical mounting groove (17) and the annular boss I are respectively provided with a plurality of bolt positioning holes I (20) and boss bolt positioning holes I (21). The corresponding ends of the pile section are provided with a number of pile end positioning holes (24) at intervals; during assembly, the pile section is embedded in the cylindrical mounting groove (17) of the circular flange (16), and the pile end positioning holes (24) of the pile section correspond one-to-one with the bolt positioning holes I (20) of the circular flange (16); high-strength bolts pass through the bolt positioning holes I (20) and the pile end positioning holes (24) to fix the circular flange (16) to the end of the pile section; A sealing gasket is provided between the pile section and the cylindrical mounting groove (17); High-strength bolts pass through the bolt positioning holes I (21) of the two circular flanges (16) to connect two adjacent pile sections.

6. The structural design of a prestressed high-strength concrete X-shaped pile according to claim 3, characterized in that: When there are two pile sections and an X-shaped flange connection structure is used, an X-shaped flange (18) is provided at the bottom of the top pile section and at the top of the bottom pile section. When there are more than two pile sections and an X-shaped flange connection structure is used, X-shaped flanges (18) are provided at the bottom of the top pile section, the top and bottom of the middle pile section, and the top of the bottom pile section. The X-shaped flange (18) includes an X-shaped flange body and an annular boss II extending along the edge of the X-shaped flange body. An X-shaped mounting groove (19) is sandwiched between the X-shaped flange body and the annular boss II. The X-shaped mounting groove (19) and the annular boss II are respectively provided with a plurality of bolt positioning holes II (22) and boss bolt positioning holes II (23). The corresponding ends of the pile section are provided with a number of pile end positioning holes (24) at intervals; During assembly, the pile section is embedded in the X-shaped mounting groove (19) of the X-shaped flange (18), and the pile end positioning hole (24) of the pile section corresponds one-to-one with the bolt positioning hole II (22) of the X-shaped flange (18); high-strength bolts pass through the bolt positioning hole II (22) and the pile end positioning hole (24) to fix the X-shaped flange (18) to the end of the pile section; A sealing gasket is provided between the pile section and the X-shaped mounting groove (19); High-strength bolts pass through the boss bolt positioning holes II (23) of the two X-shaped flanges (18) to connect the two adjacent pile sections.

7. The structural design of a prestressed high-strength concrete X-shaped pile according to claim 3, characterized in that: When there are two pile sections and a mortise and tenon connection structure is used, the bottom of the top pile section and the top of the bottom pile section are respectively provided with the mortise joint (25) and the tenon joint (27); when there are more than two pile sections and a mortise and tenon connection structure is used, the bottom of the top pile section is provided with the mortise joint (25), the top and bottom of the middle pile section are respectively provided with the tenon joint (27) and the mortise joint (25), and the top of the bottom pile section is provided with the tenon joint (27). The mortise joint (25) is U-shaped and the tenon joint (27) is U-shaped. The two shapes fit together, and the mortise joint (25) and the tenon joint (27) are respectively provided with a number of bolt positioning holes III (26) and a number of bolt positioning holes IV (28); the number and position of the bolt positioning holes III (26) and the number and position of the bolt positioning holes IV (28) correspond one-to-one. During assembly, high-strength bolts pass through bolt positioning holes III (26) and IV (28) to connect adjacent pile sections, and a sealing ring is provided between the tenon joint (27) and the mortise joint (25).

8. The structural design of a prestressed high-strength concrete X-shaped pile according to claim 1, characterized in that: The high-strength concrete comprises cement, aggregate, admixtures, and water in a mass ratio of 1:0.2:3.5:0.

3. The cement used is silicate cement with a strength grade of 52.5 or higher. When the aggregate has alkali reactivity, low-alkali cement is used. The aggregate includes fine aggregate and coarse aggregate; the fine aggregate is natural hard medium-coarse sand or manufactured sand with a fineness modulus of 2.5 to 3.2; the coarse aggregate is crushed stone or crushed pebbles, the rock mass compressive strength of the crushed stone is greater than 1.2 times the strength of the concrete to be mixed, the crushing index of the pebbles is less than or equal to 6%, and the maximum particle size of the crushed pebbles is less than or equal to 25 mm and less than or equal to 3 / 4 of the clear spacing of the reinforcing bars; The admixture is made of slag powder, silica fume or silica sand powder; The water-cement ratio of the high-strength concrete is 0.26-0.

30.

9. The structural design of a prestressed high-strength concrete X-shaped pile according to claim 1, characterized in that: The prestressed longitudinal reinforcement (6) is made of high-strength low-relaxation steel strand or steel bar for prestressed concrete; When the prestressed longitudinal steel bar (6) is a high-strength low-relaxation steel strand, the standard value of the tensile strength of the steel bar is greater than 1860 MPa; the criterion for low relaxation is: when the initial stress is 60% of the nominal maximum force, the stress relaxation rate measured after 1000 hours is not greater than 1.0%; When the prestressed longitudinal steel bar (6) is a steel bar for prestressed concrete, the standard value of the tensile strength of the steel bar is greater than or equal to 1420 Pa and the plastic elongation strength is greater than or equal to 1280 MPa.

10. A method for fabricating pile sections based on the structural construction of prestressed high-strength concrete X-shaped piles according to any one of claims 1 to 9, characterized in that, Includes the following steps: S1. Fabricate a special mold, which includes a left half mold, a right half mold, an upper end plate, and a lower end plate; the inner walls of the left half mold and the right half mold are adapted to the outer wall of the X-shaped pile, and the left and right half molds are connected by half mold connecting bolts; after the left and right half molds are installed, the upper and lower end plates are assembled at both ends of the left and right half molds by end plate bolts; the upper end plate is reserved with prestressing tendon holes and grouting holes, and the lower end plate is reserved with prestressing tendon holes; S2. Tie or weld the longitudinal prestressed tendons (6), as well as the ring stirrups (11) / spiral stirrups (71) and single-sided stirrups (72) together to form a steel cage, and hoist the steel cage into the mold and fix the steel cage by positioning pads. S3. Pass the longitudinal prestressing tendon (6) through the prestressing tendon hole and fix it through the wedge-type anchors set at both ends of the pile section; the wedge-type anchors are provided with pressure bearing pads between the upper and lower end plates; S4. Using a through-hole jack, the longitudinal prestressing tendons (6) are tensioned in three stages in the order of "first the middle of the web, then the end of the flange". During the tensioning process, the elongation value of the longitudinal prestressing tendons (6) is monitored. The actual elongation value deviates from the theoretical elongation value by ≤±6%. S5. Concrete is poured into the mold using a pumping method; S6. After the pouring is completed, cover the upper end plate with plastic film; and use steam to cure the concrete until the concrete strength reaches more than 80% of the design strength. S7. After the concrete strength reaches the specified requirements, slowly release the tensioning equipment to release the temporary anchorage of the reinforcing bars; S8. Remove the end plate bolts, remove the upper and lower end plates, then remove the half-mold connecting bolts, move the left and right half-molds to complete the demolding; after demolding is completed, inspect the pile section. If the inspection fails, the material is recycled and remade.

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