Construction method of precast pile inclination and fracture prevention composite foundation in soft soil area

Abstract

The invention provides a construction method for a precast pile inclination and fracture prevention composite foundation in a soft soil area. The construction method comprises the following steps that S1, an engineering pile super-long reinforcement cage is filled with a core; s2, powder spraying pile enclosure; s3, soil body plain concrete is replaced and filled between the powder spraying pile and the engineering pile, the engineering pile super-long reinforcement cage is adopted for core filling, and in other words, the bending resistance and the shearing resistance of the engineering pile are enhanced by lengthening the length of the filling core; and by replacing and filling plain concrete between the powder spraying pile and the engineering pile, the overall stability between the powder spraying pile and the engineering pile can be improved, and the side friction resistance of soil around the engineering pile to the engineering pile is reduced.

Description

Technical Field

[0001] The invention belongs to foundation and basic engineering, and in particular relates to a construction method of a composite foundation with prefabricated piles that are prevented from tilting and breaking in soft soil areas. Background Art

[0002] Prestressed hollow square piles are widely used in soft soil foundation reinforcement in construction projects due to their high cost-effectiveness, high bearing capacity, high pile quality, and high construction efficiency. A residential project in Wuhu's Jiangbei New District uses a composite foundation consisting of prestressed high-strength concrete hollow square piles and powder injection piles.

[0003] Conventional construction techniques typically employ a composite foundation treatment method combining precast piles and powder injection piles: First, the powder injection piles are constructed, using cement to replace and reinforce the weak soil to increase the bearing capacity of the foundation, followed by the sinking of the precast piles. Powder injection piles improve soil stiffness and strength, reduce the negative friction on the sides of the precast piles, and assist in controlling settlement. They also prevent soil displacement and prevent the piles from tilting or breaking due to lateral soil pressure. However, due to the limited operating space available for powder injection pile construction machinery, the powder injection piles often need to be arranged at intervals around the precast piles. The two methods primarily function independently, failing to form an effective synergistic system.

[0004] The project site is limited, with municipal roads to the east, west, and north, and a steel material yard to the south. A temporary concrete road, 4 to 6 meters wide, was constructed around the slope to transport materials within the site. Because the bearing strata of the temporary road and material yard consist of plain fill and silt soil, which have low bearing capacity, the high loads of heavy vehicles and material stacking on the sloped road can easily cause cracking and deformation of the slope, and even lead to instability and collapse. This can cause the sloped road to tilt and sink, leading to uplift and lateral deformation of the soil in the foundation pit, and the risk of tilting and breaking the project piles.

[0005] In light of this situation, and in conjunction with a residential project in Wuhu's Jiangbei New District, this application employs extra-long steel cages for core filling of engineering piles. Plain concrete is used to replace the gaps between the engineering piles and the powder-sprayed piles to create integrity, preventing the engineering piles from tilting, misalignment, or breaking. Therefore, the applicant, drawing on years of experience in design, development, and actual production in this relevant industry, has researched and improved existing structures and deficiencies, providing a composite foundation construction method for precast piles in soft soil areas that prevents tilting and breaking, with the goal of achieving greater practical value. Summary of the Invention

[0006] The present invention proposes a composite foundation construction method for preventing precast piles from tilting and breaking in soft soil areas, which effectively solves the problem of engineering piles being prone to tilting and breaking due to lateral soil pressure during the construction of concrete precast piles in deep and soft soil layers.

[0007] To achieve the above object, the technical solution adopted by the present invention is: A method for constructing a composite foundation with precast piles to prevent tilting and fracture in soft soil areas, characterized by comprising the following steps: S1, engineering pile extra-long steel cage core filling; S2, powder injection pile enclosure; S3. Replace the soil between the powder injection pile and the engineering pile with plain concrete.

[0008] As a preferred technical solution of the present invention: Step S1 is specifically as follows: S11. Select extra-long steel cages of appropriate length for engineering piles in different areas: The length of the super-long steel cage used to fill the core of the engineering pile is 1.5m below the top of the pile head. The length of the engineering pile in the basement area is 30m, and the length of the pile in the main building area is 45m. The anchorage length between the pile and the foundation beam in the basement area is 40d, d=22mm, and the anchorage length between the pile and the foundation beam in the main building area is 35d, d=20mm. The length of a single section of the prestressed high-strength concrete hollow square pile PHS-AB500 (310) is L≤15m. Therefore, the maximum length L of the super-long steel cage used to fill the core of the engineering pile in the basement area is h The maximum length of the super-long steel cage used for the core filling of the engineering piles in the main building area is L h 17.2m; S12. Extra-long steel cages are manufactured using segmented prefabrication, straight thread sleeves or welding connection technology; S13, after the core of the engineering pile is excavated, the extra-long steel cage can be completely placed into the pile body; S14. After the extra-long steel cage is fixed in the engineering pile, C40 micro-expansive concrete is poured into it to perform core filling construction on the extra-long steel cage.

[0009] As a preferred technical solution of the present invention: in step S12, each section of the steel cage is provided with standoff steel bars for fixing adjacent steel cages for segmented connection.

[0010] As a preferred technical solution of the present invention: in step S13, the inner wall of the engineering pile is provided with a pile connection for stabilizing the extra-long steel cage, the bottom of the extra-long steel cage is provided with a 5mm thick steel support plate, and the bottom wall of the engineering pile is provided with welding points, and the steel support plate is welded and fixed to the main reinforcement of the bottom wall of the engineering pile through the welding points.

[0011] As a preferred technical solution of the present invention: in step S14, when performing core filling construction, the pumped concrete is poured in layers using a string of barrels, and the pouring height each time is no more than 2m.

[0012] As a preferred technical solution of the present invention: Step S2 is specifically as follows: Install protective plates around the powder injection piles to protect them.

[0013] As a preferred technical solution of the present invention: Step S3 is as follows: S31. Excavate the silty soil between the engineering piles and the surrounding powder injection piles to a depth of 500mm. Carry out circular excavation along the engineering piles. The excavation width is the clear distance between the engineering piles and the powder injection piles, and shall not be less than 1m. S32. After the over-excavation of the soil between the powder injection pile and the engineering pile is completed, a layer of solidifying desiccant is first sprinkled on the silty soil to form a solidified body on the surface of the silty soil. Then, the impermeable side of the one-way permeable geotextile is laid on the solidified body. S33, between the powder injection pile and the engineering pile, pour C20 plain concrete in layers. First, pour 200mm thick C20 plain concrete on the one-way permeable geotextile. After initial setting, pour the remaining 300mm thick C20 plain concrete. S34. After pouring is completed, a cushion layer is laid on top of the C20 plain concrete and powder injection piles. The cushion layer is located between the C20 plain concrete, powder injection piles and raft slab.

[0014] As a preferred technical solution of the present invention: in step S32, the curing desiccant is dry cement or lime.

[0015] As a preferred technical solution of the present invention: in step S33, when pouring C20 plain concrete in layers, the poured C20 plain concrete is vibrated immediately after pouring, and the curing time of the C20 plain concrete shall not be less than 7 days.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention utilizes a triple technical approach: ultra-deep core filling, powder injection pile enclosure, and plain concrete replacement, creating a composite system of "core reinforcement, lateral restraint, and circumferential support." This utilizes PHS-AB hollow square piles with a C40 slightly expansive concrete core filling extending 1.5 meters below the pile connection. This, combined with peripheral powder injection piles and an annular C20 plain concrete replacement band, effectively addresses the technical challenges of pile tilting and fracture in soft soil environments, ensuring project quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a cross-sectional view of an extra-long core-fill of a prestressed bearing pile.

[0018] Figure 2 This is a cross-sectional view of an extra-long core-filled prestressed pull-out pile; Figure 3 This is the cross-section diagram of the soil replacement between the engineering piles and the powder injection piles; Figure 4 Schematic diagram of soil reinforcement between engineering piles.

[0019] List of reference numerals: 1. Foundation beam; 2. Cross reinforcement; 3. C40 slightly expansive concrete; 4. Pile joints; 5. Welding points; 6. Steel support plate; 7. Powder injection piles; 8. Cushion layer; 9. C20 plain concrete; 10. Muddy soil; 11. Raft slab. DETAILED DESCRIPTION

[0020] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments: like Figure 1-4 As shown, the present invention proposes a method for constructing a composite foundation with precast piles to prevent tilting and fracture in soft soil areas, comprising the following steps: S1. Engineering piles with extra-long steel cage core filling The details are as follows: S11. Select extra-long steel cages of appropriate length for engineering piles in different areas: The length of the extra-long steel cage used to fill the engineering pile core is 1.5m below the top of the pile head. The length of the engineering pile in the basement area is 30m, and the length of the pile in the main building area is 45m. The anchorage length between the pile in the basement area and foundation beam 1 is 40d, d=22mm, and the anchorage length between the pile in the main building area and foundation beam 1 is 35d, d=20mm. The length of a single section of the prestressed high-strength concrete hollow square pile PHS-AB500 is ≤15m. Therefore, the maximum length Lh of the extra-long steel cage used to fill the engineering pile core in the basement area is 17.38m, and the maximum length Lh of the extra-long steel cage used to fill the engineering pile core in the main building area is 17.2m. S12. Extra-long steel cages are manufactured using segmented prefabrication, straight thread sleeves or welding connection technology; S13, after the core of the engineering pile is excavated, the extra-long steel cage can be completely placed into the pile body; S14. After the extra-long steel cage is fixed in the engineering pile, C40 slightly expansive concrete is poured into it to perform core filling construction on the extra-long steel cage.

[0021] In step S12, each section of the steel cage is provided with stand-off steel bars for fixing adjacent steel cages for segmented connection.

[0022] In step S13, the inner wall of the engineering pile is provided with a pile connection 4 for stabilizing the extra-long steel cage, the bottom of the extra-long steel cage is provided with a 5 mm thick steel support plate 6, and the bottom wall of the engineering pile is provided with a welding point 5, through which the steel support plate 6 is welded and fixed to the main reinforcement of the bottom wall of the engineering pile.

[0023] In step S14, during the core filling construction, the pumped concrete is poured in layers using a string of barrels, with each pouring height not exceeding 2m to ensure the density of the concrete.

[0024] When the engineering piles are filled with extra-long steel cages, the filling depth is extended to 1.5m below the pile head, which strengthens the bending and shear resistance of the upper part of the engineering pile, enhances the integrity of the pile top, reduces stress concentration at the joint, and effectively reduces the risk of engineering pile fracture.

[0025] S2, powder injection pile 7 enclosure A guard plate is installed around the powder injection pile 7 to protect it.

[0026] S3, replace the soil between the powder injection pile 7 and the engineering pile with plain concrete The details are as follows: S31, over-excavate the silt soil 10 between the engineering pile and the surrounding powder injection pile 7 to a depth of 500 mm, and excavate in a circular manner along the engineering pile body. The excavation width is the net distance between the engineering pile and the powder injection pile 7, and is not less than 1 m; Since the soil between the powder injection pile 7 and the engineering pile is silty clay, the soil moisture content is relatively high. In addition to bound water, it contains a large amount of free water. The entire soil layer is saturated and plastic, prone to collapse and difficult to consolidate. Therefore, the application uses a solidification layer and a one-way permeable geotextile to cooperate with each other to effectively solve this problem.

[0027] After the over-excavation of the soil between the powder injection pile 7 and the engineering pile is completed, a layer of curing desiccant is first sprinkled on the silt soil 10 body to form a solidified body of a certain strength on the surface of the silt soil 10 body, and then the impermeable side of the one-way permeable geotextile is laid on the solidified body to ensure that the replacement concrete does not penetrate into the silt soil 10; S33, the plain concrete replacement construction between the powder injection pile 7 and the engineering pile is layered pouring of C20 plain concrete, first pouring 200mm thick C20 plain concrete on the one-way permeable geotextile, and then pouring the remaining 300mm thick C20 plain concrete after initial setting; S34, after pouring is completed, a cushion layer 8 is laid on top of the C20 plain concrete and the powder injection piles 7, and the cushion layer 8 is located between the C20 plain concrete, the powder injection piles 7 and the raft 11.

[0028] In step S32, the curing desiccant is dry cement or lime.

[0029] In step S33, when pouring C20 plain concrete in layers, the poured C20 plain concrete is vibrated immediately after pouring, and the curing time of the C20 plain concrete shall not be less than 7 days.

[0030] The plain concrete replacement between the powder injection pile 7 and the engineering pile is to replace the silt soil 10 between the powder injection pile 7 and the engineering pile with plain concrete, which can effectively form a composite foundation with the powder injection pile 7 and the engineering pile.

[0031] This application adopts an extra-long steel cage filling for engineering piles, that is, by lengthening the filling length, the bending and shear resistance of the engineering piles are enhanced; The plain concrete replacement between the powder injection pile 7 and the engineering pile can improve the overall stability between the powder injection pile 7 and the engineering pile, and reduce the lateral friction resistance of the soil around the engineering pile.

[0032] The above description is merely a preferred embodiment of the present invention and does not constitute any other form of limitation to the present invention. Any modification or equivalent variation based on the technical essence of the present invention shall still fall within the scope of protection claimed by the present invention.

Claims

1. A method for constructing a composite foundation with precast piles to prevent tilting and fracture in soft soil areas, characterized in that: The steps include: S1, engineering pile extra-long steel cage core filling; S2, powder injection pile (7) enclosure; S3. Replace the soil between the powder injection pile (7) and the engineering pile with plain concrete.

2. The method for constructing a composite foundation with anti-tilting and anti-fracture precast piles in soft soil areas according to claim 1, characterized in that: Step S1 is specifically as follows: S11. Select extra-long steel cages of appropriate length for engineering piles in different areas: The length of the super-long steel cage used for filling the core of the engineering pile is 1.5m below the top of the pile head of the pile body. The length of the engineering pile in the basement area is 30m, and the length of the pile in the main building area is 45m. The anchorage length between the pile in the basement area and the foundation beam (1) is 40d, d=22mm, and the anchorage length between the pile in the main building area and the foundation beam (1) is 35d, d=20mm. The length of a single section of the prestressed high-strength concrete hollow square pile PHS-AB500 is L≤15m. Therefore, the maximum length Lh of the super-long steel cage used for filling the core of the engineering pile in the basement area is 17.38m, and the maximum length Lh of the super-long steel cage used for filling the core of the engineering pile in the main building area is 17.2m. S12. Extra-long steel cages are manufactured using segmented prefabrication, straight thread sleeves or welding connection technology; S13, after the core of the engineering pile is excavated, the extra-long steel cage can be completely placed into the pile body; S14. After the extra-long steel cage is fixed in the engineering pile, C40 micro-expansive concrete (3) is poured into it to perform core filling construction on the extra-long steel cage.

3. The method for constructing a composite foundation with anti-tilting and anti-fracture precast piles in soft soil areas according to claim 2, characterized in that: In step S12, each section of the steel cage is provided with stand-off steel bars for fixing adjacent steel cages for segmented connection.

4. The method for constructing a composite foundation with anti-tilting and anti-fracture precast piles in soft soil areas according to claim 2, characterized in that: In step S13, a connection point (4) for stabilizing the extra-long steel cage is provided on the inner wall of the engineering pile, a 5 mm thick steel support plate (6) is provided at the bottom of the extra-long steel cage, and a welding point (5) is provided on the bottom wall of the engineering pile, and the steel support plate (6) is welded and fixed to the main reinforcement of the bottom wall of the engineering pile through the welding point (5).

5. The method for constructing a composite foundation with anti-tilting and anti-fracture precast piles in soft soil areas according to claim 2, characterized in that: In step S14, during the core filling construction, the pumped concrete is poured in layers using a series of barrels, and the pouring height each time is no more than 2m.

6. The method for constructing a composite foundation with anti-tilting and anti-fracture precast piles in soft soil areas according to claim 1, characterized in that: Step S2 is specifically as follows: A guard plate is provided between the powder injection pile (7) and the muddy soil (10) to protect them.

7. The method for constructing a composite foundation with precast piles to prevent tilting and fracture in soft soil areas according to claim 1, characterized in that: Step S3 is as follows: S31, over-excavating the silty soil (10) between the engineering pile and the surrounding powder injection pile (7) to a depth of 500 mm, and excavating in a circular manner along the engineering pile body, with the excavation width being the net distance between the engineering pile and the powder injection pile (7), and not less than 1 m; S32, after the soil between the powder injection pile (7) and the engineering pile is over-excavated, a layer of solidifying desiccant is first sprinkled on the silt soil (10) to form a solidified body on the surface of the silt soil (10), and then the impermeable side of the one-way permeable geotextile is laid on the solidified body; S33, the plain concrete replacement construction between the powder injection pile (7) and the engineering pile is carried out by pouring C20 plain concrete (9) in layers, first pouring 200mm thick C20 plain concrete (9) on the one-way permeable geotextile, and then pouring the remaining 300mm thick C20 plain concrete (9) after initial setting; S34, after pouring is completed, a cushion layer (8) is laid above the C20 plain concrete (9) and the powder injection pile (7), and the cushion layer (8) is located between the C20 plain concrete (9), the powder injection pile (7) and the raft (11).

8. The method for constructing a composite foundation with precast piles to prevent tilting and fracture in soft soil areas according to claim 7, characterized in that: In step S32, the curing desiccant is dry cement or lime.

9. The method for constructing a composite foundation with precast piles to prevent tilting and fracture in soft soil areas according to claim 7, characterized in that: In step S33, when pouring the C20 plain concrete (9) in layers, the poured C20 plain concrete (9) is vibrated immediately after pouring, and the curing time of the C20 plain concrete (9) shall not be less than 7 days.

Images