Double-row pile foundation pit supporting structure and construction method thereof

Abstract

This invention discloses a double-row pile foundation pit support structure and its construction method, belonging to the field of foundation pit engineering. It includes an existing front row of piles in the foundation pit and a rear row of piles located outside the front row. The tops of the front and rear rows of piles are respectively provided with front and rear capping beams, and the front and rear rows of piles are connected by a connecting beam between the front and rear capping beams. The rear row of piles forms an acute angle with the front row of piles in the vertical plane. The inclined rear row of piles enhances the deformation control capability and overall stability of the front row of piles. The rear row of piles is an SMW (Small Sandwich Wrap) pile structure, comprising an outer pile body formed by cement grout and an inner pile formed by structural steel. This double-row pile foundation pit support structure and its construction method, through the double-row pile design, solves the problem of insufficient deformation control capability and inadequate stability in deep foundation pit engineering, especially in deep foundation pit engineering using internal bracing, when reinforcement is required, greatly improving the stability of the foundation pit support.

Description

Technical Field

[0001] This invention relates to the field of foundation pit engineering technology, and in particular to a double-row pile foundation pit support structure and its construction method. Background Technology

[0002] In foundation pit engineering, especially deep foundation pit engineering, the stability and deformation control capability of the foundation pit support structure are directly related to project safety and construction efficiency. When internal bracing is used as the core support structure for the foundation pit, if unexpected situations occur during construction (such as sudden changes in geological conditions or abnormal loads), the deformation of the foundation pit may exceed the design allowable range. In this case, a double-row pile support structure can be added to strengthen the foundation pit support.

[0003] However, traditional vertical double-row pile support has problems: as the depth of the foundation pit increases, the lateral pressure of the soil increases significantly, the horizontal force transmission path of the vertical double-row piles is singular, and the deformation control ability of the pile top and deep soil is insufficient, making it difficult to meet the strict requirements of deep foundation pit reinforcement for deformation limits. Summary of the Invention

[0004] The purpose of this invention is to address the problem of insufficient deformation control and inadequate stability of double-row pile foundation pit support in existing deep foundation pit engineering, especially deep foundation pit engineering using internal support, when reinforcement is required. Therefore, this invention proposes a double-row pile foundation pit support structure and its construction method.

[0005] To achieve the above objectives, the present invention employs the following technology: a double-row pile foundation pit support structure and its construction method, comprising an existing front row of piles in the foundation pit and a rear row of piles located outside the front row of piles, wherein the tops of the front row of piles and the rear row of piles are respectively provided with a front row cap beam and a rear row cap beam, and the front row of piles and the rear row of piles are connected by a connecting beam between the front row cap beam and the rear row cap beam. The rear row of piles and the front row of piles form an acute angle in the vertical plane. The inclined rear row of piles enhances the deformation control capability and overall stability of the front row of piles.

[0006] As a further description of the above technical solution: the rear pile is an SMW pile structure, which includes an outer pile body formed by cement grout and an inner pile formed by steel sections.

[0007] As a further description of the above technical solution: the material of the inner pile can be Q235B or Q345B, and the surface of the inner pile is coated with a friction reducer.

[0008] As a further description of the above technical solution: the inner pile is detachably connected to it through an inclined pile connecting lug set on the rear crown beam.

[0009] As a further description of the above technical solution: the top height of the inner pile exceeds the height of the rear crown beam by more than 500 mm, and the top of the inner pile is also provided with a lifting hole for its recovery.

[0010] As a further description of the above technical solution: the included angle between the rear row of piles and the front row of piles is 15°-30°.

[0011] As a further description of the above technical solution: the front and rear crown beams are respectively provided with front connecting ears and rear connecting ears, and the two ends of the connecting beam are provided with connecting slots that mate with the two connecting ears. The connecting beam is detachably installed between the front and rear crown beams through the cooperation of the two connecting ears and connecting bolts.

[0012] A construction method for a double-row pile foundation pit support structure based on any one of the above-mentioned methods includes the following steps: S1. Rear pile construction: Set up guide frames or positioning clips to accurately control the inclination angle of the rear piles within 15°–30°, ensuring that the pile position deviation and verticality meet the design and specification requirements. Mix cement slurry according to the design mix ratio, control the sinking and lifting speed of the mixing pile machine, and ensure that the cement slurry and soil are mixed evenly. The repeated mixing length at the bottom of the pile is not less than 1m. After cleaning and drying the surface of the inner pile, apply friction-reducing agent evenly. Insert the piles by relying on the self-weight of the steel or by using static pressure equipment and vibratory hammer. After the inner piles are in place, correct the inclination angle and temporarily fix them. S2. Front row pile top surface treatment: Clean and roughen the top of the wall to the solid aggregate, rinse and keep dry, set the positioning steel bars and the embedded parts of the front row connecting ears on the top surface, and build a formwork support system. S3. Construction of the front cap beam: Before pouring concrete, check the axis, elevation and reinforcement protective layer, strengthen vibration and curing, ensure reliable connection with the top of the front piles, and fix the front connecting ears at the same time and check their position accuracy. S4. Rear cap beam construction: tie steel bars, support formwork and install embedded parts, set embedded parts / connecting ear plates inside the rear cap beam for connection with the inner piles and connecting beams and verify them, pour concrete and cure, and form a rigid connection in the rear row. S5. Construction of connecting beams: The connecting beams are manufactured in the factory according to the design requirements, and connecting slots that fit the front and rear connecting ears are opened at both ends. After the connecting beams are transported to the construction site, they are hoisted into place so that the connecting slots fit precisely with the front and rear connecting ears. The connecting beams are fastened to the front and rear connecting ears with connecting bolts to form a detachable connection. The elevation, axis and deflection of the connecting beams are re-measured to ensure that the front piles, front cap beams, connecting beams, rear cap beams and rear piles form an integral portal frame structure.

[0013] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: 1. The obliquely arranged rear piles can effectively withstand the horizontal tensile force transmitted by the top cap beam, thereby reducing the displacement of the pile top; 2. Since the spacing between the front and rear rows of piles increases with depth, the obliquely arranged rear row of piles can reduce the displacement of deeper layers to a certain extent. 3. The foundation pit support structure extensively utilizes prefabricated steel structures, which can effectively reduce construction time and, after completion, can be recycled, significantly reducing project costs. Attached Figure Description

[0014] Figure 1 A schematic diagram of the overall structure provided according to an embodiment of the present invention is shown; Figure 2 A front view provided according to an embodiment of the present invention is shown; Figure 3 A schematic diagram of the installation structure of the connecting beam provided according to an embodiment of the present invention is shown; Figure 4 A schematic diagram of the installation structure of the rear beam provided according to an embodiment of the present invention is shown; Figure 5 A schematic diagram of the structure of the rear beam provided according to an embodiment of the present invention is shown.

[0015] Legend: 1. Front row piles; 2. Front row cap beam; 21. Front row connecting lugs; 3. Rear row cap beam; 31. Rear row connecting lugs; 32. Inclined pile connecting lugs; 4. Connecting beam; 41. Connecting slot; 42. Connecting bolts; 5. Rear row piles; 51. Outer pile body; 52. Inner pile; 53. Lifting hole. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] Reference Figures 1-5 This embodiment provides a double-row pile foundation pit support structure and its construction method, including an existing front row of piles 1 in the foundation pit and a rear row of piles 5 located outside the front row of piles 1. The tops of the front row of piles 1 and the rear row of piles 5 are respectively provided with a front row capping beam 2 and a rear row capping beam 3, and the front row of piles 1 and the rear row of piles 5 are connected by a connecting beam 4 between the front row capping beam 2 and the rear row capping beam 3. The rear row of piles 5 is an SMW pile structure, which includes an outer pile body 51 formed by cement grout and an inner pile 52 formed by steel sections.

[0018] In this invention, the existing front row of piles 1 in the foundation pit is a diaphragm wall. The construction of the rear row of piles 5 is carried out first: the pile position is determined by measurement and layout, the guide frame is set to accurately control the inclination angle of the rear row of piles 5, the three-axis mixing pile hole is completed and the cement slurry is poured according to the preset parameters to form the outer pile body 51 of the rear row of piles 5. Then the inner pile 52 is inserted to the design position with the help of static pressure. After the rear row of piles 5 is formed and fixed firmly, the front row of cap beams 2 and the rear row of cap beams 3 are fixed at the top of the front row of piles 1 and the rear row of piles 5 by binding, bolt fixing, welding and other methods. After the front row of cap beams 2 and the rear row of cap beams 3 are cured to the standard, the connecting beam 4 is hoisted into place, the elevation, axis and deflection are re-measured, and the high-strength bolts are tightened and finally tightened to form the portal frame as a whole.

[0019] Compared to traditional vertical double-row pile support, the rear piles 5 and the front piles 1 of this foundation pit support structure form an acute angle in the vertical plane. Specifically, the angle between the rear piles 5 and the front piles 1 is 15°-30°. The inclined rear piles 5 enhance the deformation control capability and overall stability of the front piles 1. Due to the inclined rear piles 5, the distance between the front and rear piles increases with the depth of the foundation pit, which can form effective support in the deep soil and constrain deep lateral deformation, thereby greatly improving the stability of the foundation pit support.

[0020] It should be noted that, in order to facilitate the construction of the rear pile 5 and improve its strength, the inner pile 52 is made of Q235B or Q345B material, and the surface of the inner pile 52 is coated with a friction reducer. The inner pile 52 needs to be inserted into the core of the already formed outer pile body 51. After applying the friction reducer, the friction between the steel surface and the cement soil can be significantly reduced, allowing the inner pile 52 to be inserted more smoothly to the design position by its own weight or with the assistance of static pressure / vibratory hammer, avoiding difficulties in insertion, pile tilting or deformation due to excessive resistance.

[0021] Furthermore, the top height of the inner pile 52 exceeds the height of the rear crown beam 3 by more than 500 mm, and a lifting hole 53 for its recovery is also provided at the top of the inner pile 52. The top of the inner pile 52 extends beyond the rear crown beam 3, providing sufficient operating space and connection length for the connection node, ensuring that the length of the weld and the bolt anchoring depth of the connection between the inner pile 52 and the embedded parts of the rear crown beam 3 meet the stress requirements; Lifting hooks or slings can be directly hung through the lifting hole 53. With the friction-reducing agent coated on the surface of the inner pile 52, the inner pile 52 can be quickly pulled out from the cement-soil pile body, avoiding damage to the pile body or surrounding structure in traditional recycling methods, greatly improving recycling efficiency, thereby reducing recycling costs and realizing material reuse.

[0022] To facilitate the installation of the connecting beam 4 and the rear piles 5, the inner piles 52 are detachably connected to the rear cap beam 3 via inclined pile connecting lugs 32. The front cap beam 2 and the rear cap beam 3 are respectively equipped with front connecting lugs 21 and rear connecting lugs 31. Connecting slots 41 that mate with the two connecting lugs are provided at both ends of the connecting beam 4. The connecting beam 4 is detachably installed between the front cap beam 2 and the rear cap beam 3 through the engagement of the two connecting lugs and connecting bolts 42. This detachable design allows for the non-destructive recycling and reuse of the inner piles 52 and the connecting beam 4, simplifying the construction process, shortening the work cycle, and reducing the risk of damage to the existing structure.

[0023] A construction method for a double-row pile foundation pit support structure includes the following steps: S1. Rear pile construction: Set up guide frames or positioning clips to precisely control the inclination angle of the rear pile 5 within 15°–30°, ensuring that the pile position deviation and verticality meet the design and specification requirements. Mix cement slurry according to the design mix ratio, control the sinking and lifting speed of the mixing pile machine, and ensure that the cement slurry and soil are mixed evenly. The repeated mixing length at the bottom of the pile is not less than 1m. After cleaning and drying the surface of the inner pile 52, apply friction reducing agent evenly. Insert the pile by relying on the self-weight of the steel section or with the assistance of static pressure equipment and vibratory hammer. After the inner pile is in place, correct the inclination angle and temporarily fix it. S2, Top surface treatment of front row pile 1: Clean the top of the wall, roughen it to the solid aggregate, rinse and keep it dry, set the positioning steel bars and the embedded parts of the front row connecting ears 21 on the top surface, and build a formwork support system. S3, Construction of front row cap beam 2: Before concrete pouring, check the axis, elevation and steel reinforcement protective layer, strengthen vibration and curing, ensure reliable connection with the top of front row pile 1, and simultaneously fix the front row connecting ear 21 and check its position accuracy. S4, Rear Crown Beam 3 Construction: Binding steel bars, setting up formwork and installing embedded parts, setting embedded parts / connecting ear plates inside the rear crown beam 3 for connection with the inner pile 52 and connecting beam 4 and verifying them, pouring concrete and curing, forming a rigid connection in the rear row; S5. Construction of Connecting Beam 4: The connecting beam 4 is manufactured in the factory according to the design requirements, and connecting slots 41 that are compatible with the front connecting lugs 21 and the rear connecting lugs 31 are opened at both ends of the beam. After the connecting beam 4 is transported to the construction site, it is hoisted into place so that the connecting slots 41 are precisely fitted with the front and rear connecting lugs. The connecting beam 4 is fastened to the front and rear connecting lugs by connecting bolts 42 to form a detachable connection. The elevation, axis and deflection of the connecting beam 4 are re-measured to ensure that the front pile 1, the front cap beam 2, the connecting beam 4, the rear cap beam 3 and the rear pile 5 form a portal frame integral structure.

[0024] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A double-row pile foundation pit support structure characterized by, The foundation includes the existing front piles (1) in the foundation pit and the rear piles (5) located outside the front piles (1). The tops of the front piles (1) and the rear piles (5) are respectively provided with front cap beams (2) and rear cap beams (3), and the front piles (1) and the rear piles (5) are connected by a connecting beam (4) between the front cap beams (2) and the rear cap beams (3). The rear piles (5) and the front piles (1) form an acute angle on the vertical plane. The deformation control capability and overall stability of the front piles (1) are improved by the inclined rear piles (5).

2. A double-row pile foundation pit support structure according to claim 1, characterized in that, The rear pile (5) is an SMW pile structure, which includes an outer pile body (51) formed by cement grout and an inner pile (52) formed by steel sections.

3. A double-row pile foundation pit support structure according to claim 2, characterized in that, The material of the inner pile (52) can be Q235B or Q345B, and the surface of the inner pile (52) is coated with a friction reducer.

4. A double-row pile foundation pit support structure according to claim 3, characterized in that, The inner pile (52) is detachably connected to the inclined pile connecting lug (32) set on the rear crown beam (3).

5. A double-row pile foundation pit support structure according to claim 4, characterized in that, The top height of the inner pile (52) exceeds the height of the rear crown beam (3) by more than 500 mm, and the top of the inner pile (52) is also provided with a lifting hole (53) for its recovery.

6. The double-row pile foundation pit support structure according to claim 1, characterized in that, The angle between the rear pile (5) and the front pile (1) is 15°-30°.

7. The double-row pile foundation pit support structure according to claim 1, characterized in that, The front row crown beam (2) and the rear row crown beam (3) are respectively provided with front row connecting ears (21) and rear row connecting ears (31). The two ends of the connecting beam (4) are provided with connecting slots (41) that cooperate with the two connecting ears. The connecting beam (4) is detachably installed between the front row crown beam (2) and the rear row crown beam (3) through the cooperation of the two connecting ears and the connecting bolts (42).

8. A construction method for a double-row pile foundation pit support structure according to any one of claims 1-7, characterized in that, Includes the following steps: S1. Rear pile construction: Set up guide frames or positioning cards to accurately control the inclination angle of the rear pile (5) at 15°–30°, ensuring that the pile position deviation and verticality meet the design and specification requirements. Mix cement slurry according to the design mix ratio, control the sinking speed and lifting speed of the mixing pile machine, and ensure that the cement slurry and soil are mixed evenly. The repeated mixing length at the bottom of the pile is not less than 1m. After cleaning and drying the surface of the inner pile (52), apply friction reducing agent evenly. Insert the inner pile by relying on the self-weight of the steel section or by using static pressure equipment and vibratory hammer. After the inner pile is in place, correct the inclination angle and temporarily fix it. S2, Front row pile (1) Top surface treatment: Clean the top of the wall, roughen it to solid aggregate, rinse and keep it dry, set the positioning steel bars and the embedded parts of the front row connecting ears (21) on the top surface, and build a formwork support system; S3, Construction of front row cap beam (2): Before concrete pouring, check the axis, elevation and steel reinforcement protective layer, strengthen vibration and curing, ensure reliable connection with the top of the front row pile (1), fix the front row connecting ear (21) at the same time and check its position accuracy; S4, Rear Crown Beam (3) Construction: Tie steel bars, support formwork and install embedded parts, set embedded parts / connecting ear plates inside the rear crown beam (3) for connection with the inner pile (52) and connecting beam (4) and check them, pour concrete and cure, and form a rigid connection in the rear row; S5. Construction of connecting beam (4): The connecting beam (4) is manufactured in the factory according to the design requirements, and connecting slots (41) are opened at both ends to match the front connecting ears (21) and the rear connecting ears (31). The connecting beam (4) is transported to the construction site and hoisted into place so that the connecting slots (41) fit precisely with the front and rear connecting ears. The connecting beam (4) is fastened to the front and rear connecting ears by connecting bolts (42) to form a detachable connection. The elevation, axis and deflection of the connecting beam (4) are re-measured to ensure that the front pile (1), the front crown beam (2), the connecting beam (4), the rear crown beam (3) and the rear pile (5) form a portal frame overall structure.

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