A construction method and device of a stiff composite support pile

Abstract

The application provides a construction method of a stiff composite supporting pile, which comprises the following steps: forming uniaxial cement-soil mixing piles by using a mixing pile machine at the periphery of a foundation pit to form a closed water-stopping curtain; vertically pressing or implanting a prefabricated prestressed pipe pile into the center of the mixing pile by using a static pressure or vibration device before the cement soil of the mixing pile is initially cured; and forming a stiff composite force-bearing community by interfacial bonding between the prefabricated pipe pile and the outer cement-soil pile body after the cement soil is solidified. The application also discloses a construction device for realizing the method, which comprises a mixing pile machine, a static pressure pile machine and a pipe pile implantation guide frame. The application organically combines the water-stopping function of the mixing pile and the high-strength, high-rigidity and bending-resistant function of the prefabricated pipe pile to form a supporting unit which simultaneously has the water-stopping and bending-shear resisting capabilities, and the construction speed is fast and the quality is easy to control, and the application is especially suitable for small foundation pit projects in soft soil areas.

Description

Technical Field

[0001] This invention relates to the field of foundation pit support technology in geotechnical engineering, and in particular to a method and apparatus for constructing rigid composite support piles. Background Technology

[0002] In foundation pit engineering, the support structure must simultaneously meet the requirements of soil retention and water prevention. Currently, the commonly used foundation pit support methods mainly include the following: I. Combined Support Form of Piles and Water-stop Curtain: This form uses bored cast-in-place piles as foundation pit support piles, and sets a row of interlocking cement-soil mixing piles or jet grouting piles as a water-stop curtain on the outside or inside of the support piles. The bored cast-in-place piles provide bending and shear stiffness to resist earth pressure, and the water-stop curtain blocks groundwater seepage. This technology is mature and widely used, but it has obvious drawbacks: the construction process is complicated and the construction period is long, requiring the construction of the support piles and the water-stop curtain as two main processes separately; the construction of bored cast-in-place piles generates a large amount of mud discharge, causing serious environmental pollution; the mud wall forming process is complex, quality control is difficult, and common quality problems such as necking, pile breakage, and excessive sediment thickness are prone to occur; the material and machinery costs are high, and the overall cost is considerable.

[0003] II. Interlocking Pile Support: Interlocking piles involve arranging bored cast-in-place piles (cast piles) and plain concrete piles (plain piles) alternately and interlocking with each other, using the interlocking between the piles to achieve integrated soil retention and water stoppage. Interlocking piles overcome the problem of water and sand flowing through the gaps between adjacent piles in ordinary bored cast-in-place piles. However, interlocking piles still fall under the category of cast-in-place concrete piles, requiring large equipment such as full-casing drilling rigs for construction, resulting in large equipment investment and high costs. On-site concrete pouring requires a long curing time, leading to a long construction period. When constructing in soft soil areas, drilling is difficult and problems such as borehole collapse are prone to occur.

[0004] III. SMW Method (Steel-Cement-Soil Mixing Wall): The SMW method involves drilling to a certain depth on-site using a multi-axis drilling and mixing machine, while simultaneously spraying a cement-based reinforcing agent at the drill bit to repeatedly mix with the foundation soil. Overlapping construction is adopted between each construction unit, and H-beams or steel plates are inserted as stress reinforcement materials before the cement-soil mixture hardens. This method combines water-stopping and support functions into one, and has the advantages of fast construction speed, good water-stopping effect, and no mud discharge.

[0005] However, the SMW method has the following prominent problems: First, steel recycling is difficult: H-beams in the SMW method usually need to be recycled to reduce project costs, but extracting and recycling the steel is a technical challenge, with complex procedures, and may disturb the surrounding soil during extraction; if the steel is left unrecycled, the cost is high. Second, the steel section is limited: Because the H-beams need to be completely encased in the cement-soil pile to ensure water-stopping performance, this limits the width and stiffness of the H-beam pile section, thus limiting the application depth of SMW method piles, making it mainly... It is applied to the construction of shallow foundation pits in basements with two or fewer floors; third, high construction precision requirements: the SMW method has high requirements for the construction quality of mixing piles and the insertion accuracy of steel sections. If the grout ratio, mixing uniformity, pile overlap and steel section verticality are not properly controlled, problems such as leakage, deformation and insufficient local strength are likely to occur; fourth, the problem of the synergistic work between steel sections and cement-soil: the surface of H-beams is smooth and the bonding force with cement-soil is limited. Moreover, when the steel sections are recycled, a release agent needs to be coated on the surface, which further weakens the bond between the steel sections and cement-soil and affects the composite stress effect.

[0006] IV. In recent years, some engineering practices and patent documents have involved technical solutions for inserting prestressed pipe piles into cement-soil mixing piles. For example, CN102373710A discloses a method for retaining prestressed centrifugal pipe piles (square piles) in triaxial (biaxial) cement-soil mixing piles; there are also reports in engineering practice of "implanting PRC pipe piles into cement-soil mixing piles" and research on "cement-soil mixing composite piles with built-in prestressed pipes".

[0007] However, these existing technical solutions still have the following shortcomings: First, existing technologies mostly use triaxial or biaxial mixing piles, which are large and costly, and are not suitable for small foundation pit projects with limited space; Second, existing technologies lack precise quantitative control over the time window for implanting pipe piles into cement soil, resulting in unstable construction quality; Third, existing technologies do not quantitatively limit the matching relationship between the diameter of mixing piles and pipe piles, making it difficult to ensure that the pipe piles are completely wrapped by cement soil and that there is effective interlocking between adjacent piles; Fourth, existing technologies have not formed a systematic construction device solution and lack effective means to control the accuracy of pipe pile implantation (verticality, centering).

[0008] Therefore, there is an urgent need for a new type of support structure, construction method, and device that is simple to construct, has a short construction period, is economical, has controllable quality, and can simultaneously ensure water-stopping effect and support rigidity. Summary of the Invention

[0009] This invention provides a method for constructing rigid composite support piles, which can effectively solve the above-mentioned problems.

[0010] This invention is implemented as follows: A method for constructing rigid composite retaining piles includes: S1. Pile location layout and equipment placement: According to the design drawings, the pile locations are marked out around the foundation pit, and the mixing pile machine is moved to the designated pile location and placed in place. S2. Construction of mixing piles: Start the mixing pile machine, and the mixing drill bit rotates and sinks while spraying cement slurry to mix evenly with the foundation soil in situ until the design depth is reached to form a single-axis cement-soil mixing pile; the pile diameter of the single-axis cement-soil mixing pile is set to D1, and adjacent single-axis cement-soil mixing piles interlock with each other with an interlocking amount of not less than 200mm, and are arranged along the perimeter of the foundation pit to form a closed water-stop curtain. S3. Precast Pipe Pile Installation: Before the initial setting of the cement and soil in the uniaxial cement-soil mixing pile formed in step S2, the prestressed pipe pile is hoisted to the pile position, positioned and centered using a guide frame, and the prestressed pipe pile is vertically pressed or implanted into the center design depth of the uniaxial cement-soil mixing pile using static pressure equipment or vibration equipment; the pile diameter of the prestressed pipe pile is set to D2, and D1-D2≥300mm; S4. Complete single pile construction: Remove the construction equipment and allow the cement-soil to cure and solidify naturally. The prestressed pipe pile and the outer cement-soil pile body are bonded together at the interface to form a rigid composite support pile.

[0011] As a further improvement, in step S2, the water-cement ratio of the cement slurry is set to 0.5~1.0, and the cement admixture ratio per linear meter is set to 15%~25%.

[0012] As a further improvement, in step S3, the timing of implanting the prestressed pipe pile is set between 60 and 180 minutes after the completion of the uniaxial cement-soil mixing pile construction.

[0013] As a further improvement, in step S3, a guide frame is used to control the verticality of the prestressed pipe pile, and the verticality deviation is no greater than 1 / 200.

[0014] As a further improvement, the prestressed pipe pile is a prestressed high-strength concrete pipe pile with an outer diameter of 300mm~800mm and a wall thickness of 70mm~150mm.

[0015] As a further improvement, the pile diameter D1 of the uniaxial cement-soil mixing pile is set to 600mm~1200mm, and the pile diameter D2 of the prestressed pipe pile is set to 300mm~800mm, and D1-D2=300mm~500mm.

[0016] As a further improvement, step S5 is also included: after all the reinforced composite support piles have been constructed, the soil between the piles is excavated, and a reinforced concrete cap beam is poured on the top of the piles to connect the reinforced composite support piles into an integral load-bearing system.

[0017] A construction apparatus for implementing the aforementioned rigid composite support pile construction method includes: A mixing pile machine is used to construct the aforementioned uniaxial cement-soil mixing piles. A static pressure pile driver or a vibratory pile driver is used to press or implant the prestressed pipe pile into the center of the uniaxial cement-soil mixing pile; and A guide frame, mounted on the static pressure pile driver or vibratory pile driver, is used to control the verticality and planar position of the prestressed pipe pile; The guide frame includes a guide cylinder, a verticality adjustment device, and a horizontal positioning device. The inner diameter of the guide cylinder is adapted to the outer diameter of the prestressed pipe pile. The verticality adjustment device is used to adjust the verticality of the guide cylinder, and the horizontal positioning device is used to center the center of the guide cylinder with the center of the uniaxial cement-soil mixing pile.

[0018] As a further improvement, the guide frame also includes a laser alignment device, which is disposed at the upper end of the guide cylinder and is used to emit a laser beam to indicate that the central axis of the guide cylinder coincides with the central axis of the uniaxial cement-soil mixing pile.

[0019] A type of rigid composite retaining pile, comprising: An outer cement-soil pile body is formed by in-situ mixing of a single-axis cement-soil mixing pile, and is cylindrical in shape. The diameter of the outer cement-soil pile body is set as D1. A prestressed pipe pile is coaxially arranged at the center of the outer cement-soil pile body and is wrapped with cement and soil along the entire length of the outer cement-soil pile body. The diameter of the prestressed pipe pile is set to D2, and D1-D2≥300mm. The outer cement-soil pile body and the prestressed pipe pile are bonded together as one unit through the interfacial bonding effect during the cement-soil curing process. Several of the aforementioned rigid composite support piles are arranged around the perimeter of the foundation pit. The outer cement-soil pile bodies of adjacent rigid composite support piles interlock with each other, with an interlocking amount of not less than 200mm, forming a closed retaining structure that simultaneously has water-stopping and soil-retaining functions.

[0020] The beneficial effects of this invention are: 1) Functional Integration and Multifunctional Pile: By innovatively combining the water-stopping function of uniaxial cement-soil mixing piles with the high-strength support function of prestressed pipe piles, a three-in-one rigid composite support unit of "water-stopping, soil retention, and bending resistance" is formed. The cement-soil piles interlock to form a continuous water-stopping curtain, and the prestressed pipe piles provide strong bending and shear stiffness. The two work together through interface bonding, which greatly simplifies the foundation pit support system. Compared with the traditional separate arrangement of "pile rows and water-stopping curtains", the integrated design of this invention significantly reduces the number of structural units and construction procedures.

[0021] 2) Fast construction speed and significantly shortened construction period: The core component of this invention is the prestressed pipe pile, which is a factory-prefabricated product with stable quality and timely supply; on-site construction only requires two main processes: mixing and implantation, and the construction of a single pile can be completed within a few hours, avoiding the long concrete curing time of bored piles (usually requiring 28 days) and the recycling process of H-beams in the SMW method; construction efficiency is greatly improved and the construction period is significantly shortened; according to calculations, compared with the traditional pile and water-stop curtain schemes, the construction period of this invention can be shortened by 40% to 60%.

[0022] 3) Quality is easily guaranteed: Prestressed pipe piles are factory-produced, with stable quality and high strength, and do not have the quality problems that may occur in cast-in-place piles, such as necking, pile breakage, sediment, honeycomb pitting; and the construction process is controllable, the water-cement ratio and cement admixture ratio of the mixing pile can be precisely controlled; the timing of pipe pile implantation, verticality, and centering accuracy can all be effectively guaranteed through guide frames and construction parameters; the interface bonding quality between cement and soil and pipe pile is reliable, avoiding the problem of weakened bonding force due to the need to apply release agent when recycling steel in the SMW method.

[0023] 4) Good economic benefits: This invention eliminates the need for separate construction of water-stop curtain and bored piles, reducing material usage and machinery operating costs; prestressed pipe piles are standardized prefabricated products with transparent pricing and stable supply; site occupation is reduced, and temporary facility costs are lowered; the overall cost can be reduced by 20% to 35% compared to the traditional "pile and water-stop curtain" scheme; compared to the SMW method, this invention does not require the steel recycling process, avoiding equipment investment and construction period occupation for steel recycling, and the permanent retention of pipe piles eliminates the need to consider recycling issues.

[0024] 5) Environmental protection and energy saving, green construction: There is no mud discharge during the construction process of this invention, which avoids the mud pollution problem of bored pile construction; the cement and soil mixing is in-situ mixing, and there is no waste soil transportation; the prestressed pipe piles are prefabricated products, and there is no concrete pouring loss on site; the entire construction process has low noise and low vibration (during static pressure construction), and has little impact on the surrounding environment, which is in line with the concept of green construction and sustainable development.

[0025] 6) Strong applicability and high flexibility: By adjusting the diameter (D1) of the mixing pile, the cement admixture ratio, the water-cement ratio, and the specifications (diameter, wall thickness, reinforcement) of the prestressed pipe pile, this invention can flexibly adapt to the foundation pit support needs of different excavation depths (3m~10m) and different geological conditions (clay, silt, sand, soft soil); the single-axis mixing pile equipment is lightweight and is especially suitable for small foundation pit projects in densely populated urban areas where the site is limited and large equipment cannot enter.

[0026] 7) High construction precision: This invention uses a guide frame and laser centering device to precisely control the implantation process of the pipe pile. The verticality deviation is no more than 1 / 200, and the planar position deviation can be controlled within the allowable range of the specification, ensuring the construction quality of the composite pile. The precise positioning of the pipe pile ensures the coaxiality of the pipe pile and the outer cement-soil pile body, thereby ensuring the overall stress performance of the composite pile. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0028] Figure 1 This is a plan view of the rigid composite support system according to an embodiment of the present invention.

[0029] Figure 2 This is a longitudinal cross-sectional schematic diagram of the rigid composite support pile structure according to an embodiment of the present invention.

[0030] Figure 3 This is a schematic cross-sectional view of the rigid composite support pile structure according to an embodiment of the present invention.

[0031] Figure 4 This is a schematic diagram of the construction device structure according to an embodiment of the present invention.

[0032] In the picture: 1. Cement-soil pile body; 2. Prestressed pipe pile; 3. Interlocking area; 4. Crown beam; 5. Core cavity of prestressed pipe pile; 6. Soil outside the foundation pit; 7. Finished surface of foundation pit excavation; 8. Static pressure pile driver; 9. Mixing pile driver. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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 a part of the embodiments of the present invention, not all of them. 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. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to represent selected embodiments of the invention. 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.

[0034] In the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0035] Reference Figures 1-4 As shown, a rigid composite retaining pile includes an outer cement-soil pile body 1 and a prestressed pipe pile 2, which are combined. Multiple rigid composite retaining piles are arranged around the perimeter of the foundation pit. The outer cement-soil pile bodies 1 of adjacent piles interlock with each other through interlocking areas 3, with an interlocking amount of not less than 200mm, forming a continuous and closed water-stop curtain around the perimeter of the foundation pit.

[0036] like Figure 2 and Figure 3 As shown, the prestressed pipe pile 2 is coaxially positioned at the center of the cement-soil-encased pile body 1, and is completely encased in cement-soil along the entire length of the cement-soil-encased pile body 1. The diameter of the cement-soil-encased pile body 1 is D1, and the diameter of the prestressed pipe pile 2 is D2. The two satisfy the relationship that D1-D2≥300mm, to ensure that the prestressed pipe pile 2 is completely encased in cement-soil, and at the same time, to ensure that there is sufficient interlocking between adjacent cement-soil-encased pile bodies 1 to achieve the purpose of water stoppage.

[0037] The cement-soil encased pile 1 is formed by in-situ mixing and solidification of cement and foundation soil. It has a low permeability coefficient, typically on the order of 10⁻⁶ to 10⁻⁷ cm / s, effectively blocking groundwater. The prestressed pipe pile 2 is a prestressed high-strength concrete pipe pile, also known as a PHC pipe pile, possessing high bending and shear strength, and is the main load-bearing component. The cement-soil encased pile 1 and the prestressed pipe pile 2 are firmly bonded together through interfacial chemical action and mechanical interlocking during the cement-soil solidification process, forming a unified whole that works synergistically. Its overall bending stiffness is far greater than that of a single mixing pile of the same diameter, and also greater than that of an SMW method pile with the same steel consumption.

[0038] The present invention provides a method for constructing a rigid composite retaining pile, comprising the following steps: Step S1, Pile location layout and equipment placement: Clear and level the construction site, removing underground obstacles. Based on the design drawings, use a total station or GPS surveying equipment to locate and lay out the pile positions, determining the plane coordinates and elevation of each pile location. The accuracy of the pile location layout should meet the specifications, with a deviation not exceeding 20mm. Organize the mixing pile machine 9 and the static pressure pile machine 8 or vibratory pile machine to enter and position themselves in sequence. For work conditions with narrow sites, walking or tracked pile frames can be used for easy movement and positioning.

[0039] Step S2, Construction of mixing piles: Start the mixing pile machine 9. The mixing drill bit rotates and sinks while simultaneously spraying cement slurry, performing in-situ forced mixing with the foundation soil. The sinking speed is controlled at 0.5~1.0 m / min, and the lifting speed is controlled at 0.8~1.2 m / min to ensure uniform mixing. The spraying pressure is controlled at 0.5~1.0 MPa to ensure the cement slurry is evenly distributed across the entire cross-section of the mixing pile. After the mixing drill bit sinks to the design elevation, continuous spraying and mixing at the pile bottom for at least 30 seconds ensures the quality of the pile bottom. Then, while lifting, spraying and mixing continues until the pile top reaches the design elevation, forming a single-axis cement-soil mixing pile.

[0040] Furthermore, the cement slurry is prepared as follows: using P.O42.5 grade ordinary Portland cement, with a water-cement ratio controlled at 0.5~1.0, and a cement admixture ratio of 15%~25% per linear meter. Preferably, the water-cement ratio is controlled at 0.6~0.8, and the cement admixture ratio is 18%~22% per linear meter, which can improve the performance of the cement slurry. Moreover, it can be appropriately adjusted according to the soil properties: in soft soil areas, the cement admixture ratio can be appropriately increased to 22%~25%; in sandy soil areas, it can be appropriately reduced to 15%~18%. Appropriate admixtures can be added to improve the cement-soil properties; these admixtures can be early-strength agents or water-reducing agents.

[0041] The pile diameter D1 of a single-axis cement-soil mixing pile is determined according to design requirements, ranging from 600mm to 1200mm. The interlocking amount between adjacent mixing piles should not be less than 200mm to ensure the continuity of the cutoff wall. For foundation pits with a depth not exceeding 6m, D1 can be 800mm; for foundation pits with a depth of 6m to 10m, D1 can be 1000mm to 1200mm.

[0042] Step S3, Precast Pipe Pile Installation: Prestressed pipe piles 2 are inserted before the initial setting of the cement-soil mixture in the uniaxial cement-soil mixing pile formed in step S2. The insertion time is between 60 and 180 minutes after the completion of the mixing pile construction. Determining this time window is of significant technical importance, as detailed below: Premature implantation (<60 minutes): The cement-soil is still in a fluid state, its initial setting is incomplete, and its strength has not yet been formed. Implanting prestressed pipe piles at this time makes it difficult to position the pipe piles, making it hard to ensure verticality and centering accuracy. At the same time, due to the large buoyancy of the cement-soil, the pipe piles are prone to "floating pile" phenomenon, that is, the pipe piles float in the cement-soil and cannot reach the design elevation, or they bounce back due to buoyancy after reaching the design elevation, which seriously affects the quality of pile formation.

[0043] Late implantation (>180 minutes): The cement-soil has begun to set and has developed a certain structural strength. Implanting the pipe pile at this time will significantly increase the pile driving resistance, making pile driving difficult and increasing the equipment load. It may also damage the already set cement-soil structure, affecting the water-stopping performance and integrity of the cement-soil, and may even prevent the pipe pile from being driven to the designed depth.

[0044] The 60-180 minute time window: During this period, the cement-soil mixture is in a thixotropic state before initial setting. It possesses a certain degree of fluidity and plasticity, facilitating the smooth sinking of the pipe pile; at the same time, it has begun to develop a certain structural strength and thixotropy, providing sufficient lateral restraint to prevent the pipe pile from shifting or floating, while ensuring that no significant displacement occurs after the pipe pile is positioned. Precise control of this time window is crucial for achieving high-quality composite bonding between the pipe pile and the cement-soil mixture.

[0045] Specifically, the prestressed concrete pipe pile 2 is hoisted to the pile location. In this embodiment, the prestressed concrete pipe pile 2 is a PHC pipe pile with an outer diameter D2 of 300mm~800mm and a wall thickness of 70mm~150mm. A static pressure pile driver 8 with a guide frame, or a vibratory pile driver, is used to hoist the pipe pile 2 into the guide cylinder. The center of the guide cylinder is aligned with the center of the uniaxial cement-soil mixing pile using a horizontal positioning device to ensure that the two are coaxial. The verticality of the guide cylinder is adjusted using a verticality adjustment device, and monitored using a two-way level or electronic inclinometer to ensure that the verticality deviation is not greater than 1 / 200.

[0046] Start the static pressure pile driver 8 and slowly and continuously press the pipe pile 2 into the center of the single-axis cement-soil mixing pile at a uniform speed. Control the pressing speed at 0.3~0.8 m / min to avoid excessive disturbance to the cement-soil mixture or pipe pile displacement due to excessive speed. During the pressing process, continuously monitor the verticality and planar position of the pipe pile, and promptly adjust any deviations using the guide frame. After the pipe pile is pressed to the design elevation, maintain the static pressure load for 3~5 minutes to ensure the pipe pile remains stable and does not sink or float.

[0047] For situations where pile splicing is required, such as when the length of the pipe pile is insufficient, splicing can be carried out by welding or mechanical connection. After splicing, the pile can be driven into the design elevation.

[0048] Step S4: Complete the single pile construction: Remove the static pressure pile driver 8 and guide frame, allowing the pile body to cure naturally. During the curing process, the cement-soil continuously solidifies, forming a strong interface bond with the surface of the pipe pile 2. The curing time is determined based on the temperature and type of cement, generally not less than 7 days. After the cement-soil has completely solidified, the prestressed pipe pile 2 and the outer cement-soil pile body 1 form a rigid composite support pile.

[0049] Step S5: Forming a complete support system: Repeat steps S1 to S4 according to the designed spacing to complete the construction of all rigid composite support piles. In this embodiment, the designed spacing is generally set to 1.2 to 2.0 times D1. The interval between the construction of adjacent piles should be controlled to be completed before the initial setting of the cement-soil of the preceding pile to ensure effective interlocking between adjacent piles. If the interval is too long for any reason, resulting in cold joints on the interlocking surface, remedial measures such as additional piles or grouting should be taken.

[0050] After all composite piles are constructed, excavate the soil between the piles to the bottom elevation of the capping beam, remove any laitance at the pile tops (if any), and expose the pile heads of the prestressed concrete pipe piles 2. Tie reinforcing bars at the pile tops, erect formwork, and pour reinforced concrete capping beam 4. The concrete strength grade should not be lower than C30, connecting all the reinforced composite support piles into an integral load-bearing system. The cross-sectional dimensions of capping beam 4 are generally set to 0.5m × 0.8m ~ 0.8m × 1.2m, specifically determined based on stress calculations.

[0051] Furthermore, key construction parameters need to be strictly controlled, as follows: Water-cement ratio control: The water-cement ratio is a key parameter affecting the strength and waterproofing performance of cement-soil. If the water-cement ratio is too low (<0.5), the cement grout has poor fluidity, uneven mixing, and large dispersion in cement-soil strength; if the water-cement ratio is too high (>1.0), the cement-soil strength decreases, and the waterproofing performance deteriorates. This invention controls the water-cement ratio within the range of 0.5~1.0, preferably 0.6~0.8, balancing the fluidity of the cement grout and the strength of the cement-soil.

[0052] Control of cement admixture ratio: The cement admixture ratio directly affects the strength and permeability coefficient of cement-soil. When the admixture ratio is too low (<15%), the cement-soil strength is insufficient, the permeability coefficient is too high, and the water-stopping effect is difficult to guarantee; when the admixture ratio is too high (>25%), the cost increases, the heat of hydration increases, and shrinkage cracks may occur. This invention controls the cement admixture ratio per linear meter at 15%~25%, which can be adjusted within the range according to the soil properties and the depth of the foundation pit.

[0053] The control requirement for the pile diameter difference, D1-D2 ≥ 300mm, is technically significant for the following reasons: Firstly, it ensures that the prestressed pipe pile 2 is completely encased in cement-soil, providing sufficient contact area between the pipe pile and the cement-soil to guarantee bond strength. Secondly, it ensures sufficient interlocking between adjacent cement-soil-encased pile bodies 1. In this embodiment, the interlocking amount is equal to D1 minus the pile spacing, which is typically set to D1 minus 200mm~300mm to achieve reliable water-stopping effect. Thirdly, it provides sufficient operating space for pipe pile implantation, preventing contact with adjacent already constructed pile bodies during implantation. Preferably, D1-D2 = 300mm~500mm.

[0054] Timing of implantation: Implantation should be controlled between 60 and 180 minutes after the completion of the mixing pile construction. In actual construction, adjustments should be made according to factors such as temperature, cement type, and admixture type: when the temperature is high, the cement-soil initial setting is fast, and the implantation time can be appropriately shortened (e.g., 60-120 minutes); when the temperature is low, the implantation time can be appropriately extended (e.g., 120-180 minutes). The implantation timing can be accurately determined by testing the penetration resistance of the cement-soil through on-site sampling. In other embodiments, the precise determination of the implantation timing by testing the penetration resistance of the cement-soil through on-site sampling specifically includes: After the construction of the uniaxial cement-soil mixing pile is completed, a miniature static cone penetration test (Mini-CPT) is inserted along the central axis of the mixing pile to a predetermined depth below the pile top to measure the cone tip resistance q of the cement-soil mixture. c ; The measurement was repeated at predetermined time intervals to obtain the curve of the cone tip resistance changing over time; When the cone tip resistance q c The threshold range of 0.3MPa to 1.5MPa is reached, and the ratio of sidewall friction to cone tip resistance f is... s / q c When the value is in the range of 0.02~0.10, the cement-soil is determined to be in a thixotropic state, and a pipe pile implantation command is issued. s / q c Friction ratio is used to distinguish between "true thixotropy" (structural strength derived from cement hydration) and "false thixotropy" (temporary hardening caused only by water seepage) in cement-soil.

[0055] The main parameters of the miniature static cone penetrometer are as follows, as shown in Table 1.

[0056] Table 1 shows the parameters of the miniature static cone penetration test probe:

[0057] As a further improvement, since the cement admixture ratio and compaction degree differ at different depths of the cement-soil pile (the pile bottom is usually higher than the pile body), a depth correction is introduced: ; Where, λ h For depth correction factor: 0.3~5m below the pile top: λ h =1.0; 5~10m: λ h =0.85 0.90 (The cement-soil at the bottom of the pile is usually denser). 10m:λ h =0.80.

[0058] The relationship between the penetration resistance threshold and ambient temperature is established as follows: ; in: =0.3~1.5MPa (reference temperature 20℃); T is the actual measured temperature of the cement-soil (℃); α=0.015 0.025 / ℃ (temperature coefficient, determined by calibration test), which is the cone tip resistance. You can first perform depth correction and then temperature correction to obtain the final result.

[0059] like Figure 4 As shown, a construction device for implementing the aforementioned rigid composite support pile construction method according to the present invention includes a mixing pile machine 9, a static pressure pile machine 8, and a guide frame.

[0060] The mixing pile machine 9 is a single-shaft mixing pile machine, which includes a pile frame, a power head, a mixing drill rod, and a mixing drill bit. The pile frame can use a walking or tracked chassis for easy movement within the site. The power head provides rotational and pressurizing power, and the mixing drill rod is a hollow rod with an internal cement slurry delivery channel. The mixing drill bit is equipped with a slurry injection nozzle to evenly inject cement slurry into the soil during the mixing process.

[0061] The static pressure pile driver 8 includes a pile frame, a static pressure device, and a clamping device. The pile frame can adopt the same chassis form as the mixing pile driver 9. The static pressure device uses a hydraulic system to provide static pressure to press the pipe pile 2 into the soil. The clamping device is used to clamp the pipe pile 2, ensuring that the pressing force is evenly transmitted to the pipe pile.

[0062] The guide frame is mounted on the static pressure pile driver 8 and includes a guide cylinder, a verticality adjustment device, a horizontal positioning device, and a laser centering device.

[0063] The guide cylinder is a cylindrical structure, and its inner diameter is adapted to the outer diameter of the prestressed pipe pile 2. In this embodiment, the inner diameter of the guide cylinder can be slightly larger than the outer diameter of the prestressed pipe pile 2 by 2 to 5 mm to restrain the horizontal displacement of the pipe pile 2 during the pressing process. The height of the guide cylinder is not less than 1.5 m to ensure sufficient guiding length.

[0064] The verticality adjustment device is located between the guide cylinder and the pile frame. It uses a hydraulic cylinder or screw adjustment mechanism to adjust the verticality of the guide cylinder from two orthogonal directions. The verticality adjustment device is equipped with an electronic inclinometer or bubble level to display the tilt angle of the guide cylinder in real time.

[0065] The horizontal positioning device is used to align the center of the guide cylinder with the center of the uniaxial cement-soil mixing pile. Laser ranging or mechanical alignment can be used to ensure an alignment accuracy within ±10mm.

[0066] The laser alignment device is located at the upper end of the guide cylinder and includes a laser emitter and a target. The laser emitter emits a laser beam along the central axis of the guide cylinder, illuminating the target at the center of the mixing pile. The operator can adjust the position of the guide cylinder according to the deviation between the laser spot and the center of the target to achieve precise alignment.

[0067] The method and apparatus of this invention are applicable to common geological formations such as clay, silt, sand, and soft soil. Specifically, by adjusting the following parameters, they can be flexibly adapted to different engineering needs: Excavation depth adaptability: For shallow foundation pits of 3m to 6m, smaller diameter mixing piles and pipe piles can be used; specifically, the D1 of the mixing piles is set between 600mm and 800mm, and the D2 of the pipe piles is set between 300mm and 500mm. For medium-deep foundation pits of 6m to 10m, larger diameter mixing piles and pipe piles can be used, i.e., the D1 of the mixing piles is set between 1000mm and 1200mm, and the D2 of the pipe piles is set between 500mm and 800mm.

[0068] Geological adaptability: In soft soil strata, the cement admixture ratio can be appropriately increased and the water-cement ratio reduced to improve the strength of cement-soil mixtures; specifically, the cement admixture ratio is set at 22%~25%, and the water-cement ratio is set at 0.5~0.6. In sandy soil strata, the cement admixture ratio can be appropriately reduced and the water-cement ratio increased to improve the fluidity of cement paste; specifically, the cement admixture ratio is set at 15%~18%, and the water-cement ratio is set at 0.8~1.0.

[0069] Pipe pile specification adaptability: Different specifications of PHC pipe piles can be selected according to stress calculations, including different reinforcement types such as type A, type AB, and type B, as well as pipe piles with different wall thicknesses. In this embodiment, the wall thickness of the pipe pile is set between 70mm and 150mm.

[0070] Furthermore, key points of quality control should include pile location control, verticality control, cement admixture control, implantation timing control, interlocking quality control, and maintenance control.

[0071] Specifically, the pile position control is to ensure that the deviation of the pile position layout is no more than 20mm, and the pile position should be checked regularly during the construction process.

[0072] Specifically, verticality control employs guide frames and bidirectional monitoring to ensure that the verticality deviation of the pipe piles is no greater than 1 / 200, and the verticality deviation of the mixing piles is also no greater than 1 / 200.

[0073] Specifically, the cement admixture is controlled by precisely controlling the amount of cement slurry injected through a flow meter and a weighing system to ensure that the cement admixture ratio per linear meter is within the set range.

[0074] Specifically, the timing of implantation should be strictly controlled within a time window of 60 to 180 minutes. Timing equipment should be provided on site, and the timing should start from the completion of the mixing pile construction.

[0075] Specifically, the quality control of the interlocking surface involves ensuring that the interval between the construction of adjacent piles is before the initial setting of the cement and soil of the preceding pile, so as to guarantee that the interlocking surface is fresh and free of cold joints. If the interval exceeds the specified time, remedial measures such as high-pressure grouting should be taken on the interlocking surface.

[0076] Specifically, vibration and disturbance should be avoided during the curing period of cement-soil under maintenance control, and the curing time should not be less than 7 days.

[0077] To verify the technical effect of the present invention, a comparative test was conducted in a small foundation pit project in a soft soil area. The excavation depth of this small foundation pit project was 5.5m, and the area of ​​the foundation pit was about 1200m².

[0078] In this embodiment, the relevant parameters of the rigid composite retaining pile constructed using the present invention are set as follows: D1=800mm, D2=500mm, D1-D2=300mm, water-cement ratio 0.65, cement admixture ratio 20%, and implantation time 120 minutes. A comparison is made with the traditional "drilled cast-in-place pile (φ600mm) and double-row mixing pile water-stop curtain" scheme used in adjacent sections: Construction period: The present invention can complete the construction of all 86 support piles in 5 days, while the traditional method takes 14 days, which shortens the construction period by about 64%.

[0079] Material consumption: The concrete consumption of the present invention (pipe piles only) is about 185m³, while the concrete consumption of the traditional solution (cast piles + mixing piles) is about 420m³, resulting in a material saving of about 56%.

[0080] Water-stopping effect: After the foundation pit was excavated, no obvious leakage points were found in the section of the present invention, and the water-stopping effect was good; the section of the traditional solution had two minor leakage points that required grouting treatment.

[0081] Support deformation: The horizontal displacement monitoring value of the pile top is 12~18mm in the present invention scheme and 15~22mm in the traditional scheme. The present invention scheme has a better deformation control effect.

[0082] Overall cost: The overall cost of the present invention is about 68% of that of the traditional solution, saving about 32%.

[0083] The above comparative verification shows that the present invention has significant advantages in terms of construction period, materials, water-stopping effect, deformation control and cost.

[0084] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for constructing rigid composite retaining piles, characterized in that, include: S1. Pile location layout and equipment placement: According to the design drawings, the pile locations are marked out around the foundation pit, and the mixing pile machine is moved to the designated pile location and placed in place. S2. Construction of mixing piles: Start the mixing pile machine, and the mixing drill bit rotates and sinks while spraying cement slurry to mix evenly with the foundation soil in situ until the design depth is reached to form a single-axis cement-soil mixing pile; the pile diameter of the single-axis cement-soil mixing pile is set to D1, and adjacent single-axis cement-soil mixing piles interlock with each other with an interlocking amount of not less than 200mm, and are arranged along the perimeter of the foundation pit to form a closed water-stop curtain. S3. Precast Pipe Pile Installation: Before the initial setting of the cement and soil in the uniaxial cement-soil mixing pile formed in step S2, the prestressed pipe pile is hoisted to the pile position, positioned and centered using a guide frame, and the prestressed pipe pile is vertically pressed or implanted into the center design depth of the uniaxial cement-soil mixing pile using static pressure equipment or vibration equipment; the pile diameter of the prestressed pipe pile is set to D2, and D1-D2≥300mm; S4. Complete single pile construction: Remove the construction equipment and allow the cement-soil to cure and solidify naturally. The prestressed pipe pile and the outer cement-soil pile body are bonded together at the interface to form a rigid composite support pile.

2. The construction method for rigid composite retaining piles according to claim 1, characterized in that, In step S2, the water-cement ratio of the cement slurry is set to 0.5~1.0, and the cement admixture ratio per linear meter is set to 15%~25%.

3. The construction method for rigid composite retaining piles according to claim 1, characterized in that, In step S3, the timing of implanting the prestressed pipe pile is set between 60 and 180 minutes after the completion of the uniaxial cement-soil mixing pile construction.

4. The construction method for rigid composite retaining piles according to claim 1, characterized in that, In step S3, a guide frame is used to control the verticality of the prestressed pipe pile, and the verticality deviation is not greater than 1 / 200.

5. The construction method for rigid composite retaining piles according to claim 1, characterized in that, The prestressed pipe pile is a prestressed high-strength concrete pipe pile with an outer diameter of 300mm~800mm and a wall thickness of 70mm~150mm.

6. The construction method for rigid composite retaining piles according to claim 1, characterized in that, The diameter D1 of the uniaxial cement-soil mixing pile is set to 600mm~1200mm, and the diameter D2 of the prestressed pipe pile is set to 300mm~800mm, and D1-D2=300mm~500mm.

7. The construction method for rigid composite retaining piles according to claim 1, characterized in that, It also includes step S5, after all the rigid composite support piles have been constructed, excavating the soil between the piles, pouring a reinforced concrete cap beam on the top of the piles, and connecting the rigid composite support piles into an integral load-bearing system.

8. A construction apparatus for implementing the rigid composite retaining pile construction method as described in any one of claims 1-7, characterized in that, include: A mixing pile machine is used to construct the aforementioned uniaxial cement-soil mixing piles. A static pressure pile driver or a vibratory pile driver is used to press or implant the prestressed pipe pile into the center of the uniaxial cement-soil mixing pile; as well as A guide frame, mounted on the static pressure pile driver or vibratory pile driver, is used to control the verticality and planar position of the prestressed pipe pile; The guide frame includes a guide cylinder, a verticality adjustment device, and a horizontal positioning device. The inner diameter of the guide cylinder is adapted to the outer diameter of the prestressed pipe pile. The verticality adjustment device is used to adjust the verticality of the guide cylinder, and the horizontal positioning device is used to center the center of the guide cylinder with the center of the uniaxial cement-soil mixing pile.

9. The construction device according to claim 8, characterized in that, The guide frame also includes a laser alignment device, which is located at the upper end of the guide cylinder and is used to emit a laser beam to indicate that the central axis of the guide cylinder coincides with the central axis of the uniaxial cement-soil mixing pile.

10. A type of rigid composite retaining pile, characterized in that, include: An outer cement-soil pile body is formed by in-situ mixing of a single-axis cement-soil mixing pile, and is cylindrical in shape. The diameter of the outer cement-soil pile body is set as D1. A prestressed pipe pile is coaxially arranged at the center of the outer cement-soil pile body and is wrapped with cement and soil along the entire length of the outer cement-soil pile body. The diameter of the prestressed pipe pile is set to D2, and D1-D2≥300mm. The outer cement-soil pile body and the prestressed pipe pile are bonded together as one unit through the interfacial bonding effect during the cement-soil curing process. Several of the aforementioned rigid composite support piles are arranged around the perimeter of the foundation pit. The outer cement-soil pile bodies of adjacent rigid composite support piles interlock with each other, with an interlocking amount of not less than 200mm, forming a closed retaining structure that simultaneously has water-stopping and soil-retaining functions.

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