Construction method of compacted grouting type anchor rod static pressure pile in collapsible loess area

Abstract

The present application relates to a kind of collapsible loess region compaction grouting formula anchor rod static pressure pile construction method, comprising the following steps: pouring has pressure pile cap and reserving pressure pile hole in the circumferential end surface of original foundation pile, install pressure pile counterforce device on pressure pile cap and press into to foundation with steel pipe pile body root by root, cement mortar tamping seal is used to the contact part of steel pipe pile top outside and ground soil body in one meter range after steel pipe pile pressure pile construction is completed, remove the pressure pile component of pressure pile counterforce device, and install jack on the counterforce frame of pressure pile counterforce device, and there is hold frame in each pressure pile hole;Through respective sealing plate, it is respectively connected with grouting pipe, and simultaneously pressure injection cement slurry to each steel pipe pile by respective high-pressure grouting pump, cement slurry is sprayed and diffused to the gap or loophole of steel pipe pile surrounding ground by jet grouting hole, and form slurry vein, so that each steel pipe pile and original foundation pile are connected into an integral cement column;The present application can improve the bearing capacity of original foundation pile.

Description

Technical Field

[0001] This invention belongs to the field of anchor static pressure pile construction technology, and particularly relates to a method for constructing anchor static pressure piles by compaction grouting in collapsible loess areas. Background Technology

[0002] Since its inception, static pressure piles have played a vital role in the reinforcement of existing building foundations and foundation replacement due to their numerous advantages, including flexible construction, good reinforcement effect, low noise, and suitability for indoor and outdoor operations, generating significant economic benefits. Consequently, more and more anchored static pressure piles are being used in the collapsible loess regions of Northwest my country. The principle is as follows: using the self-weight of the existing building as the pile driving force through anchors or counterweights, steel pipe or precast concrete piles are statically pressed into the foundation soil in sections. The static pressure piles and the foundation soil jointly bear the load of the superstructure, thereby achieving the purpose of preventing settlement and reinforcement.

[0003] In collapsible loess areas, the cross-sectional dimensions of conventional concrete anchor static pressure piles are mostly above 200mm. This presents two limitations when driving piles in loess areas: Firstly, due to the large pile cross-section, the pile driving reaction force often exceeds the ultimate bearing capacity of the pile segment, causing pile buckling and preventing the designed pile length from being reached. Secondly, when the reinforced foundation is flooded again, the surrounding soil becomes waterlogged and collapses, generating negative skin friction on the pile, leading to pile settlement and underpinning failure. Therefore, conventional anchor static pressure piles have certain limitations in reinforcing building foundations in collapsible loess areas. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a method for constructing static pressure anchor piles with compaction grouting in collapsible loess areas. By adopting this construction method, the effectiveness of anchor static pressure steel pipe pile foundation replacement after water immersion in collapsible loess areas is improved, and the soil around the pile is compacted by compaction grouting to eliminate its collapsibility and effectively reduce the additional settlement during the compaction grouting process.

[0005] The objective of this invention is achieved through the following technical solution: the construction method for compaction grouting anchor static pressure piles in collapsible loess areas includes the following steps:

[0006] S1. Excavate a construction pit in the ground around the original foundation pile that needs to be reinforced, and construct a pile cap by arranging a steel mesh around the original foundation pile. The pile cap is located below the pile cap of the original foundation pile, and a trapezoidal pile hole with a cross-section that is smaller at the top and larger at the bottom is reserved on the pile cap.

[0007] S2. Install the pile driving reaction device on the pile driving platform, and align the center of the pile driving reaction device with the core of the pile driving hole. Through the pile driving reaction device, steel pipes with grouting holes are used as the pile bodies of steel pipe piles and are driven into the foundation one by one. Adjacent steel pipe piles are joined by welding. The bottom of the first driven steel pipe pile is provided with a pile tip, and the top of the last driven steel pipe pile is welded with a sealing plate and located below the bottom surface of the pile driving platform.

[0008] S3. Two to four steel pipe piles are driven into the pile holes around the original foundation pile, and the steel pipe piles are symmetrically distributed along the core of the original foundation pile.

[0009] S4. After the steel pipe pile driving construction is completed, cement mortar is used to tamp and seal the area within one meter of the outer side of the steel pipe pile top in contact with the foundation soil. The upper end of the solidified cement mortar block after tamping and sealing is connected to the bottom surface of the driving pile cap, and the side is flush with the side wall of the sealing plate.

[0010] S5. Remove the pile driving components of the pile driving reaction device, and install jacks on the reaction frame of the pile driving reaction device. Each steel pipe pile is equipped with a reaction frame with jacks. During the grouting process of the steel pipe pile, the jacks simultaneously apply prestress to the steel pipe pile so that it has a lifting force on the pile driving cap and the original foundation pile.

[0011] S6. A support frame is placed in each of the pile driving holes. The bottom surface of the support frame abuts against the sealing plate on the steel pipe pile, and the top surface of the support frame abuts against the jack.

[0012] S7. Each of the sealing plates is connected to a grouting pipe, which passes through the pressure support frame and is connected to a high-pressure grouting pump on the ground.

[0013] S8. Cement grout is simultaneously injected into the pile body of each steel pipe pile through their respective high-pressure grouting pumps. The cement grout is sprayed through the grouting holes to spread, fill, split, and compact the soil around the pile, forming grout veins to strengthen the soil around the pile between each steel pipe pile and the original foundation pile and eliminate collapsibility.

[0014] S9. Remove the pile driving reaction device, the bearing frame and the grouting pipe, fill and seal the pile driving hole, and backfill and compact the construction pit in step S1.

[0015] The beneficial effects of this invention are as follows: compared with the existing anchor static pressure pile construction method in collapsible loess areas, it improves the suitability of anchor static pressure piles in collapsible loess areas and their effectiveness after immersion in water, solves the problem of how to efficiently compact the soil around the pile through compaction grouting, and effectively controls the additional settlement during the compaction grouting process by applying prestress to the pile top.

[0016] Preferably, during the reinforcement arrangement process, through holes are pre-reserved according to the number of steel pipe piles. These through holes form the pile driving holes during the pouring of the pile cap. The number of pile driving holes is consistent with the number of steel pipe piles, and the pile driving holes are symmetrically distributed along the core of the original foundation piles, and are consistent with the longitudinal or transverse direction of the reinforcement in the reinforcement mesh. The pre-reserved through holes ensure that the strength of the reinforcement mesh is not damaged when the pile driving holes are formed in the pile cap, greatly improving the strength of the pile cap. At the same time, the arrangement direction of the pile driving holes is limited, making the reinforcement arrangement in the reinforcement mesh more convenient and greatly improving construction efficiency.

[0017] Preferably, the center-to-center distance of the multiple symmetrically distributed steel pipe piles is 3 to 4 times the diameter of the original foundation pile; this not only ensures the strength stability of the original foundation pile after reinforcement, but also improves the convenience of construction and installation of the pile driving reaction device.

[0018] Preferably, the depth of the steel pipe pile in the foundation is greater than the depth of the original foundation pile in the foundation. When cement grout is sprayed through the grouting hole, it spreads, fills, splits, and compacts into the foundation soil around the steel pipe pile. The compaction zone formed between the cement grout sprayed from the grouting hole at the bottom of the steel pipe pile and the foundation will serve as a support platform at the bottom of the original foundation pile. In this way, the original foundation pile can improve its bearing capacity both through the overall structure formed by the grout veins formed by the steel pipe pile and through the support platform formed at the bottom of the original foundation pile, thus achieving a dual bearing effect.

[0019] Preferably, the grouting holes are provided in a plurality of form and arranged on the circumferential wall of the steel pipe pile body. The grouting holes are distributed in a quincunx pattern along the circumferential wall of the steel pipe pile body, and the spacing between adjacent grouting holes along the height direction of the steel pipe pile body is 0.5 to 0.8 m, and the diameter of the grouting holes is 2 cm. With the above structure, cement grout can be sprayed radially along the outer wall of the pile body through the grouting holes. After the grout is sprayed, an outer cement wall is formed in the gap between the outer wall of the pile body and the soil. This not only increases the effective pile diameter of the anchor static pressure pile, but also compacts the soil around the pile and eliminates subsidence.

[0020] Preferably, the sealing plate is provided with threaded mounting holes, through which the grouting head of the grouting pipe is connected and sealed; this allows the grouting pipe to be connected to the sealing plate, resulting in better grouting effect and less grout leakage.

[0021] Preferably, the bottom surface of the support frame is provided with a through hole for inserting the grouting pipe, and the through hole corresponds to the threaded mounting hole. The top surface of the support frame is higher than the top surface of the pile cap. This allows the grouting pipe to be inserted into the sealing plate through the support frame, and the support frame and the sealing plate can be tightly fitted. At the same time, the top surface of the support frame is higher than the top surface of the pile cap, which facilitates the arrangement and insertion of the grouting pipe.

[0022] Preferably, the pressure holding frame includes an upper pressure plate and a lower pressure plate, and four support rods are installed between the upper pressure plate and the lower pressure plate, with the four support rods located at the four corners of the pressure holding frame respectively; the above structure makes the pressure holding frame more evenly stressed. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the static pressure pile device for compaction grouting anchor bolts of the present invention.

[0024] Figure 2 yes Figure 1 A magnified structural diagram at point A.

[0025] The labels in the attached diagram are as follows: 1. Pile driving reaction device; 2. Steel pipe pile; 3. Original foundation pile; 4. Pile driving cap; 5. Support frame; 6. Grouting pipe; 7. High-pressure grouting pump; 8. Cement mortar block; 9. Grout vein; 10. Construction pit; 11. Jack; 12. Reaction frame; 13. Compaction zone; 21. Grouting hole; 22. Pile tip; 23. Sealing plate; 24. Steel pipe pile body; 41. Pile driving hole; 51. Through hole; 52. Upper pressure plate; 53. Lower pressure plate; 54. Support rod; 61. Grouting head. Detailed Implementation

[0026] The following will be combined with the appendix Figure 1 , 2 The present invention will be described in detail below: The construction method of the present invention includes the following steps:

[0027] S1. A construction pit 10 is dug down the ground around the original foundation pile 3 that needs to be reinforced, and a steel mesh with longitudinally and transversely arranged steel bars is connected to the circumferential end face of the original foundation pile 3. A pile cap 4 is poured on the steel mesh. The pile cap 4 is located below the pile cap of the original foundation pile 3, and a trapezoidal pile hole 41 with a cross section that is smaller at the top and larger at the bottom is reserved on the pile cap 4. By setting a steel mesh with longitudinally and transversely arranged steel bars, the bearing capacity of the cast pile cap 4 is better during the construction process. The steel mesh is connected to the side wall of the original foundation pile 3, so that when the pile cap 4 applies prestress to the steel pipe pile 2 through the jacks on the reaction frame, the lifting force of the pile cap 4 and the original foundation pile 3 is better and more stable, further preventing additional settlement caused by grouting in the foundation of the steel pipe pile body 24.

[0028] S2. Install the pile driving reaction device 1 on the pile driving cap 4, and align the center of the pile driving reaction device 1 with the core of the pile driving hole 41. Through the pile driving reaction device 1, the steel pipe with grouting hole 21 is used as the pile body 24 of the steel pipe pile and is driven into the foundation one by one. Adjacent steel pipe pile bodies 24 are joined by welding. The bottom of the first driven steel pipe pile body 24 is provided with a pile tip 22 and abuts against the bearing soil layer in the foundation. The top of the last driven steel pipe pile body 24 is welded with a sealing plate 23 and is located below the bottom surface of the pile driving cap 4. The steel pipe is a steel pipe with a diameter of A165mm and a wall thickness of not less than 5mm. The steel pipe is divided into sections of 1.5m. In the limited space, it is more convenient to drive the anchor static pressure pile into the foundation. Moreover, the stability after the pile is joined by welding the splice strip is better.

[0029] S3. Two to four steel pipe piles 2 are driven into the pile hole 41 around the original foundation pile 3, and the steel pipe piles 2 are symmetrically distributed along the pile core of the original foundation pile 3. Two to four steel pipe piles 2 are set. Since the original foundation pile 3 is generally cylindrical or square, two to four can be set according to the construction design requirements. It is preferred to set two or four. If three are set, under the same strength, the reinforcement arrangement of the steel mesh will be very complicated, which will greatly increase the construction difficulty and construction cost. However, if two or four are set, since the reinforcement of the steel mesh is usually arranged in a crisscross pattern, the through hole for inserting the steel pipe pile 2 can be reserved in advance, so that the reinforcement does not need to be cut when setting the pile hole 41 on the pile cap 4. The construction is very convenient and the cost can be greatly reduced.

[0030] S4. After the steel pipe pile 2 is driven, cement mortar is used to tamp and seal the area within one meter of the outer side of the steel pipe pile 2 where it contacts the foundation soil. The upper end of the solidified cement mortar block 8 after tamping and sealing is connected to the bottom surface of the pile cap 4, and the side is flush with the side wall of the sealing plate 23. By pouring cement mortar block 8, the cement mortar sprayed from the grouting hole 21 will not flow back to the bottom of the pile cap 4, but will surge back up through the pile driving hole 41, which is more conducive to grouting.

[0031] S5. Remove the pile driving components of the pile driving reaction device 1, and install jacks 11 on the reaction frame 12 of the pile driving reaction device 1. Each steel pipe pile 2 is equipped with a reaction frame 12 with jacks 11. During the grouting process of the steel pipe pile 2, the jacks 11 of each pile 2 simultaneously apply prestress to the steel pipe pile 2 so that it has a lifting force on the pile driving cap 4 and the original foundation pile 3; to prevent additional settlement of the foundation due to grouting in the steel pipe.

[0032] S6. A support frame 5 is placed in each pile hole 41. The bottom surface of the support frame 5 abuts against the sealing plate 23 on the steel pipe pile 2, and the top surface of the support frame 5 abuts against the jack 11.

[0033] S7. Each of the sealing plates 23 is connected to a grouting pipe 6, which passes through the pressure support frame 5 and is connected to the high-pressure grouting pump 7 on the ground.

[0034] S8. Cement grout is simultaneously injected into the pile body 24 of each steel pipe pile by their respective high-pressure grouting pumps 7. The cement grout is sprayed and diffused into the foundation around the steel pipe pile 2 through the grouting holes 21, forming grout veins 9 to connect each steel pipe pile 2 with the original foundation pile 3 into a whole cement column. The soil around the pile is reinforced and collapsibility is eliminated. The cement grout mix ratio is: cement: water: water glass = 1:0.6:0.03, and the grouting pressure is controlled at 0.2~0.6 MPa.

[0035] S9. Remove the pile reaction device 1, the support frame 5 and the grouting pipe 6, fill and seal the pile hole 41, and bury the construction pit 10 from step S1.

[0036] Compared with traditional static pressure steel pipe piles, although the construction process involves additional steps such as sealing the pile top, installing the reaction frame, and pressure grouting, it offers the following advantages:

[0037] 1) Increase pile diameter and compact the soil around the pile. The injected cement grout forms an inner cement pile inside the steel pipe pile body. The injected cement grout is sprayed radially along the outer wall of the steel pipe pile through the grouting hole. After the grout is sprayed, an outer cement pile is formed in the gap between the outer wall of the steel pipe pile and the soil. This not only increases the pile diameter of the steel pipe pile, but also compacts the soil around the pile.

[0038] 2) Improve the effectiveness of anchor-mounted static pressure steel pipe pile reinforcement in collapsible loess areas after water immersion. Through compaction grouting, the bearing capacity of the pile foundation is improved, the physical and mechanical properties of the soil around the pile are improved, and the collapsibility of the soil around the pile is eliminated, thereby solving the problem of pile foundation failure caused by negative skin friction.

[0039] 3) Effectively reduce additional settlement during compaction grouting. Since cement grout is simultaneously injected into the steel pipe pile body under pressure, additional settlement will occur in the foundation before the grout solidifies. Therefore, a reaction frame is installed before grouting, and prestress is applied to the steel pipe pile simultaneously using its respective jacks, giving it a lifting force on the pile cap and the original foundation piles. This allows the steel pipe pile to undergo compaction grouting under load support. During the grouting process, prestress is continuously applied to the pile foundation, effectively preventing additional settlement caused by grouting.

[0040] 4) Improved the overall integrity of the foundation and the bearing capacity of the pile foundation. Cement grout is sprayed through the grouting holes to spread, fill, split, and compact the soil around the piles, forming grout veins that reinforce the soil around each steel pipe pile and the original foundation piles and eliminate collapsibility, thereby improving the integrity of the foundation and the bearing capacity of the pile foundation.

[0041] During the reinforcement arrangement process, through holes are reserved according to the number of steel pipe piles 2. These through holes form pile driving holes 41 during the pouring of the pile driving cap 4. The number of pile driving holes 41 is consistent with the number of steel pipe piles 2, and the pile driving holes 41 are symmetrically distributed along the core of the original foundation piles 3, and are consistent with the longitudinal or transverse direction of the reinforcement on the reinforcement mesh.

[0042] The center-to-center distance between the two symmetrically distributed steel pipe piles 2 is 3 to 4 times the diameter of the original foundation pile 3.

[0043] The depth of the steel pipe pile 2 in the foundation is greater than the depth of the original foundation pile 3 in the foundation. The cement grout is sprayed through the grouting hole 21 to diffuse, fill, split and compact the foundation around the steel pipe pile 2. The compaction zone 13 formed between the cement grout sprayed through the grouting hole 21 at the bottom of the steel pipe pile 2 and the foundation will serve as the support platform at the bottom of the original foundation pile 3.

[0044] Several grouting holes 21 are provided and set on the circumferential wall of the steel pipe pile body 24. The grouting holes 21 are distributed in a plum blossom pattern along the circumferential wall of the steel pipe pile body 24. The spacing between adjacent grouting holes 21 along the height direction of the steel pipe pile body 24 is 0.5 to 0.8 m, and the diameter of the grouting hole 21 is 2 cm.

[0045] The sealing plate 23 is provided with threaded mounting holes, which are connected to and sealed to the grouting head 61 of the grouting pipe 6.

[0046] The bottom surface of the support frame 5 is provided with a through hole 51 for inserting the grouting pipe 6, and the through hole 51 corresponds to the threaded mounting hole. The top surface of the support frame 5 is higher than the top surface of the pile cap 4.

[0047] The pressure frame 5 includes an upper pressure plate 52 and a lower pressure plate 53. Four support rods 54 are installed between the upper pressure plate 52 and the lower pressure plate 53. The four support rods 54 are located at the four corners of the pressure frame 5.

[0048] This invention is not limited to the above-described embodiments. Any changes made to its shape, grouting method, or material composition, as long as the structural design provided by this invention is a variation of this invention, should be considered within the scope of protection of this invention.

Claims

1. A method for constructing static pressure piles using compaction grouting anchors in collapsible loess areas, characterized in that: The construction method includes the following steps: S1. A construction pit (10) is dug down the ground around the original foundation pile (3) that needs to be reinforced, and a steel mesh with longitudinal and transverse steel bars is connected to the circumferential end face of the original foundation pile (3), and a pile cap (4) is poured on the steel mesh. The pile cap (4) is located below the pile cap of the original foundation pile (3), and a trapezoidal pile hole (41) with a cross section that is smaller at the top and larger at the bottom is reserved on the pile cap (4). S2. Install the pile driving reaction device (1) on the pile driving pile cap (4), and align the center of the pile driving reaction device (1) with the core of the pile driving hole (41). Through the pile driving reaction device (1), the steel pipe with grouting hole (21) is used as the pile body (24) of the steel pipe pile and is driven into the foundation one by one. The adjacent pile bodies (24) of the steel pipe pile are connected by welding the splice. The bottom of the first pile body (24) of the driven steel pipe pile is provided with a pile tip (22) and abuts against the bearing soil layer in the foundation. The top of the last pile body (24) of the driven steel pipe pile is welded with a sealing plate (23) and is located below the bottom surface of the pile driving pile cap (4). S3. Two to four steel pipe piles (2) are driven into the pile hole (41) around the original foundation pile (3), and the steel pipe piles (2) are symmetrically distributed along the pile core of the original foundation pile (3). S4. After the steel pipe pile (2) is driven, cement mortar is used to tamp and seal the area within one meter of the outer side of the pile top of the steel pipe pile (2) in contact with the foundation soil. The upper end of the solidified cement mortar block (8) after tamping and sealing is connected to the bottom surface of the pile cap (4), and the side is flush with the side wall of the sealing plate (23). S5. Remove the pile driving components of the pile driving reaction device (1) and install jacks (11) on the reaction frame (12) of the pile driving reaction device (1). Each steel pipe pile (2) is equipped with a reaction frame (12) with jacks (11). During the grouting process of the steel pipe pile (2), the jacks (11) of each pile simultaneously apply prestress to the steel pipe pile (2) so that it has a lifting force on the pile driving cap (4) and the original foundation pile (3). S6. A support frame (5) is placed in each of the pile holes (41). The bottom surface of the support frame (5) abuts against the sealing plate (23) on the steel pipe pile (2), and the top surface of the support frame (5) abuts against the jack (11). S7. Each of the sealing plates (23) is connected to a grouting pipe (6), which passes through the pressure support frame (5) and is connected to a high-pressure grouting pump (7) on the ground. S8. Cement grout is injected into the pile body (24) of each steel pipe pile simultaneously by their respective high-pressure grouting pumps (7). The cement grout is sprayed and diffused into the foundation around the steel pipe pile (2) through the grouting hole (21) and forms grout veins (9) to strengthen the soil around the pile between each steel pipe pile (2) and the original foundation pile (3) and eliminate collapsibility. S9. Remove the pile reaction device (1), the support frame (5) and the grouting pipe (6), and fill and seal the pile hole (41), and bury the construction pit (10) in step S1. During the reinforcement arrangement process, the steel mesh reserves through holes according to the number of steel pipe piles (2). These through holes form the pile driving holes (41) during the pouring of the pile driving cap (4). The number of pile driving holes (41) is consistent with the number of steel pipe piles (2), and the pile driving holes (41) are symmetrically distributed along the core of the original foundation pile (3) and are consistent with the longitudinal or transverse direction of the reinforcement on the steel mesh.

2. The method for constructing compaction grouting anchor static pressure piles in collapsible loess areas according to claim 1, characterized in that: The center distance between the two symmetrically distributed steel pipe piles (2) is 3 to 4 times the diameter of the original foundation pile (3).

3. The method for constructing compaction grouting anchor static pressure piles in collapsible loess areas according to claim 1, characterized in that: The depth of the steel pipe pile (2) in the foundation is greater than the depth of the original foundation pile (3) in the foundation. When the cement grout is sprayed and diffused into the foundation around the steel pipe pile (2) through the grouting hole (21), the compaction zone (13) formed between the cement grout sprayed and diffused by the grouting hole (21) at the bottom of the steel pipe pile (2) and the foundation will serve as the support platform at the bottom of the original foundation pile (3).

4. The method for constructing compaction grouting anchor static pressure piles in collapsible loess areas according to claim 1, characterized in that: The grouting holes (21) are provided in a plurality of manner and are arranged on the circumferential wall of the steel pipe pile body (24). The grouting holes (21) are distributed in a plum blossom pattern along the circumferential wall of the steel pipe pile body (24). The spacing between adjacent grouting holes (21) along the height direction of the steel pipe pile body (24) is 0.5 to 0.8 m, and the diameter of the grouting holes (21) is 2 cm.

5. The method for constructing compaction grouting anchor static pressure piles in collapsible loess areas according to claim 1, characterized in that: The sealing plate (23) is provided with a threaded mounting hole, which is connected to and sealed to the grouting head (61) of the grouting pipe (6) through the threaded mounting hole.

6. The construction method for compaction grouting anchor static pressure piles in collapsible loess areas according to claim 5, characterized in that: The bottom surface of the pressure support frame (5) is provided with a through hole (51) for inserting the grouting pipe (6), and the through hole (51) corresponds to the threaded mounting hole. The top surface of the pressure support frame (5) is higher than the top surface of the pile cap (4).

7. The method for constructing compaction grouting anchor static pressure piles in collapsible loess areas according to claim 1, characterized in that: The pressure frame (5) includes an upper pressure plate (52) and a lower pressure plate (53). Four support rods (54) are installed between the upper pressure plate (52) and the lower pressure plate (53). The four support rods (54) are located at the four corners of the pressure frame (5).

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