Construction method of a precast hollow pile expanding pile and a precast hollow pile expanding pile formed thereby

Abstract

The application discloses a construction method of a prefabricated hollow pile expansion pile and a prefabricated hollow pile expansion pile formed by the method. The construction method of the prefabricated hollow pile is external, in the construction process, a spiral drilling tool is inserted into a hole cavity of the prefabricated hollow pile; in the process of spiral soil extruding drilling and sinking of the prefabricated hollow pile, a bottom end cone soil extruding part of a spiral soil extruding drill bit at the lower end of the spiral drilling tool is always extended out of the bottom end of the prefabricated hollow pile. The application fully utilizes the advantages of low carbon and high strength of the high-strength concrete prefabricated pile, improves the bearing capacity of the formed pile foundation, reduces the pile foundation cost, and reduces the adverse effects of the soil extruding negative effect. The prefabricated hollow pile expansion pile and the construction method change the overall pile type structure and the pile-soil joint formation mode, realize more energy-saving, more environmental protection, higher quality, and wider adaptation to geological conditions of the pile foundation.

Description

Technical Field

[0001] This invention belongs to the field of building pile construction, specifically relating to a construction method for precast hollow pile extension piles and the resulting precast hollow pile extension piles. Background Technology

[0002] In building pile foundations, high-strength precast concrete piles are becoming increasingly prevalent. There are two main construction methods: one is to drive the piles by static pressure or hammer driving to form foundation piles that bear the load of the building; the other is to combine them with cement-soil piles to form composite piles. The core pile of the composite pile is a high-strength precast concrete pile, and the outer pile is a cement-soil pile, forming a composite pile that is rigid inside and flexible outside. Static pressure or hammer driving piles involve complete soil displacement, which has significant negative effects and can easily lead to quality defects such as pile inclination and floating piles. This is especially true for projects with softer foundation soils, requiring longer pile lengths and resulting in excessively high pile foundation costs. At the same time, it is difficult to penetrate harder soil and rock layers for construction. While composite piles effectively solve the problem of excessive pile length in softer foundation soils, they require overall reinforcement of the foundation soil. This is usually done by jet grouting cement slurry to create cement-soil mixtures, which are then implanted into precast concrete piles. This results in a large amount of cement-soil spillage, causing environmental pollution and material waste. The resulting composite piles are end-bearing friction piles with primary side friction, which have relatively poor bearing capacity, high costs, and low efficiency. Summary of the Invention

[0003] To fully leverage the advantages of high-strength precast concrete piles—low carbon footprint and high pile strength—and improve the bearing capacity of the resulting pile foundation, reduce pile foundation costs, and mitigate the adverse effects of soil displacement, this invention proposes an extended pile for precast hollow piles and a construction method. By altering the overall pile structure and the interaction between the pile and soil, the invention achieves a more energy-efficient, environmentally friendly, higher-quality pile foundation that is adaptable to a wider range of geological conditions.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is: a construction method for precast hollow pile extension piles, which adopts an external construction method for precast hollow piles. During the construction process, the auger drill bit is inserted into the inner cavity of the precast hollow pile in a concentric manner; during the auger soil squeezing drilling and sinking of the precast hollow pile, the soil squeezing part of the bottom cone of the auger soil squeezing drill bit at the lower end of the auger drill bit is always kept protruding from the bottom end of the precast hollow pile.

[0005] Furthermore, the above-mentioned construction method for precast hollow pile extension piles includes the following steps:

[0006] 1) Preparation and Drilling

[0007] Align the precast hollow pile with the pile position; insert the auger with the soil squeezing bit into the inner cavity of the precast hollow pile to the ground surface; during the auger soil squeezing drilling and sinking of the precast hollow pile, keep the soil squeezing part of the bottom cone of the soil squeezing bit at the bottom of the auger always below the bottom of the precast hollow pile, and perform partial soil squeezing drilling on the soil within the inner cavity of the precast hollow pile at the pile position.

[0008] 2) Formation of the enlarged body

[0009] The precast hollow pile is lowered to the top elevation of the first enlarged section. The auger drill continues drilling to the bottom elevation of the first enlarged section, maintaining its rotation. The concrete pump is started to inject concrete into the auger drill's inner cavity, while simultaneously driving the drill bit's enlarged section to extend. The diameter of the circle formed by the extended enlarged section's outer edge is larger than the outer diameter or diagonal dimension of the precast hollow pile. The rotating drill bit is then raised, and the cavity formed by the soil-squeezing drilling and the auger section's spiral groove are injected until the top elevation of the first enlarged section is reached, forming an enlarged diameter concrete threaded pile segment. The enlarged section is then retracted, and the drill bit is raised and injected for at least the height of one cone-shaped soil-squeezing portion of the drill bit. The drilling and injection are stopped, and the rotating drill bit is released downwards, with the drill bit's cone-shaped soil-squeezing portion passing through... After the bottom end face of the precast hollow pile is completed, the concrete threaded pile segment is first expanded, and then the precast hollow pile is sunk. The bottom end of the precast hollow pile is expanded again with the concrete threaded pile segment. The drilling of the auger and the sinking of the precast hollow pile are maintained until the bottom elevation of the first enlarged body is reached. During this process, the soil-squeezing part of the drill bit cone is kept below the bottom end face of the precast hollow pile. By compacting the concrete threaded pile segment twice, a concrete ring-shaped body of the enlarged body is formed. At the same time, some concrete is squeezed into the soil it contacts, forming a concrete-soil mixture layer. The inner surface of the concrete ring-shaped body wraps the precast hollow pile, and the outer surface of the concrete ring-shaped body is wrapped by the compacted concrete-soil mixture layer, completing the construction of the first enlarged body. This process is repeated to form multiple enlarged bodies.

[0010] 3) Formation of the bearing layer of the bottom reinforcement section

[0011] Continue sinking the precast hollow piles to the top elevation of the bearing stratum in the expanded pile bottom reinforcement section. At this point, maintain the top elevation of the precast hollow piles higher than the design top elevation of the expanded piles. Simultaneously, while the auger extrusion drilling reaches the top elevation of the bearing stratum in the expanded pile bottom reinforcement section, restart the drill bit expansion body to extend and expand the diameter. The diameter of the circle formed by the outer edge of the extended expansion body should be larger than the outer diameter or diagonal dimension of the precast hollow pile, until the bottom elevation of the bearing stratum in the expanded pile bottom reinforcement section is reached. Start the concrete pump to inject concrete, then slowly raise the rotating drill bit. The pressure concrete inside the drill bit opens the drill tip gate and is injected into the cavity formed by the expanded drilling. Under the stirring action of the rotating expansion body, it mixes with the soil remaining in the cavity. Raise the drill bit, inject concrete, and stir until the top elevation of the bearing stratum in the expanded pile bottom reinforcement section is reached. Stop raising the drill bit and injecting concrete, then release the drill bit downwards. The drill bit continues to rotate, the drill tip gate is closed, and the cone part of the drill bit squeezes the mixture of concrete and soil, expands the surrounding rock and soil walls, and further mixes the concrete and soil. The squeezing and drilling continues until the bottom elevation of the bearing layer reinforcement section of the pile bottom is reached. The concrete is pumped in again and the drill is lifted. At the same time, the rotating expansion body continues to mix the concrete and soil in the expanded diameter cavity. When the drill is lifted, pumped in, and mixed until the top elevation of the expanded bearing layer reinforcement section of the pile bottom is reached, the expansion body is retracted. The drill is lifted and pumped in for a height of 1 to 1.5m. The drilling and pumping are stopped, and the drill bit is released down 1 to 1.5m. The concrete below the drill bit closes the drill tip gate of the drill bit, and the drill bit stops moving down and rotating. The precast hollow pile is then driven down to meet the top elevation of the expanded pile. At this time, the bottom of the precast hollow pile has sunk into the bearing layer of the reinforcement section to a certain depth or penetrated it.

[0012] 4) The introduction of auger drilling tools

[0013] The auger drill bit is directly pulled out of the inner cavity of the precast hollow pile to complete the construction of an extended pile where the inner cavity of the precast hollow pile is partially filled with concrete; or

[0014] Continue drilling and pouring concrete until the top of the precast hollow pile is reached, then insert the reinforcing cage to complete the construction of the extended pile, in which the entire cavity of the precast hollow pile is filled with concrete.

[0015] Furthermore, the above-mentioned construction method for precast hollow pile extension pile includes the following steps: In step 1), when the soil squeezing drill bit performs partial soil squeezing drilling, the enlarged diameter body of the drill bit can be partially extended, and the diameter of the circle formed by its extended outer edge is not greater than the outer diameter of the precast hollow pile or the diagonal dimension of its outer edge.

[0016] Furthermore, in the above-mentioned construction method for precast hollow pile extension piles, the bottom end of the precast hollow pile may be provided with an inverted cone-shaped hollow pile tip, the internal hollow cross-section dimensions of which are the same as the cross-section of the inner cavity of the precast hollow pile.

[0017] A precast hollow pile extension pile formed according to the above-mentioned extension pile construction method includes a precast hollow pile, the outer surface of which is provided with a bottom reinforcement bearing layer and at least one enlarged body; except for the bottom reinforcement bearing layer and the enlarged body, the outer surface of the pile body is not provided with a concrete layer.

[0018] Furthermore, in the aforementioned precast hollow pile extension pile, the extension body includes a concrete ring with a radially spiral outer contour and a concrete-soil mixture layer. The concrete ring surrounds the outer surface of the precast hollow pile and is integrally formed with the precast hollow pile. The concrete-soil mixture layer wraps around the concrete ring and is integrally formed with it. The inner cavity of the precast hollow pile is filled with concrete in whole or in part. The bottom reinforcement bearing layer is set at the bottom of the precast hollow pile, and its transverse section is larger than the transverse section of the outer surface of the precast hollow pile. The bottom of the precast hollow pile enters the reinforcement bearing layer (30) to a certain depth or penetrates the thickness of the reinforcement bearing layer.

[0019] Furthermore, the aforementioned type of precast hollow pile extension pile has at least two extension bodies, which are set at any position on the precast hollow pile body, and adjacent extension bodies are connected as one unit by the precast hollow pile.

[0020] Furthermore, in the aforementioned type of precast hollow pile extension pile, the outer diameter of the bearing layer of the bottom reinforcement section is larger than the outer diameter or outer diagonal dimension of the precast hollow pile, and its vertical height is not less than 1 to 5 times the outer diameter or outer diagonal dimension of the precast hollow pile.

[0021] Furthermore, in the aforementioned type of precast hollow pile extension pile, the bearing layer of the reinforcement section encloses the bottom of the precast hollow pile; the depth of the bottom end of the precast hollow pile entering the bearing layer of the reinforcement section is 0.5 to 2 times the outer diameter or outer diagonal dimension of the precast hollow pile.

[0022] Furthermore, in the aforementioned type of precast hollow pile extension pile, the bottom end of the precast hollow pile is provided with an inverted cone-shaped hollow pile tip, which is positioned and set with the bottom end of the precast hollow pile.

[0023] The beneficial effects of this invention are:

[0024] 1. The precast hollow pile extension pile provided by the construction method of this invention has good interaction with the surrounding soil and high bearing capacity. The extension pile has high lateral resistance of the enlarged body and generates new end resistance. At the same time, the bottom bearing layer of the extension pile is compacted and strengthened to form a high-strength bearing layer mixture section. The effective working area of ​​the strengthened bottom bearing layer is larger than the cross-sectional area of ​​the precast hollow pile, thereby effectively improving the end bearing capacity of the extension pile. The soil around the pile in the part of the precast hollow pile not surrounded by the enlarged body is also in a compacted state, which is also conducive to improving the bearing capacity of the extension pile. The compressive and tensile strength of the extension pile are both improved.

[0025] 2. The precast hollow pile extension pile provided by the construction method of this invention features a discontinuous high-strength extension body on the outer surface of the precast hollow pile, which changes the traditional interaction between the precast pile and the surrounding soil. In traditional precast piles, the interaction between the precast pile and the surrounding soil manifests as pile-soil frictional resistance in terms of pile body lateral resistance. However, in the precast hollow pile extension pile provided by this invention, the extension body and the surrounding soil are connected in a threaded manner in terms of pile body resistance. The annular body inside the extension body is connected to the surrounding soil through a mixed layer around the extension body. This provides strong support for the shear stress of the surrounding soil, which is the main force between the outer surface of the extension body and the surrounding soil. This interaction mode is greater than the pile-soil frictional resistance, and the extension body generates new end resistance.

[0026] 3. The precast hollow pile extension pile provided by the construction method of this invention has a small soil displacement negative effect. The extension pile is a partial soil displacement pile. During construction, a portion of the soil and rock is discharged to the ground surface through the inner cavity of the precast hollow pile using a spiral drilling tool, which reduces the horizontal displacement of the soil around the pile when the precast hollow pile is driven, thereby reducing the soil displacement negative effect.

[0027] 4. The precast hollow pile extension pile provided by the construction method of this invention is adaptable to a wide range of geological conditions. For hard interlayers such as stiff plastic cohesive soil, dense sand layer, and gravelly soil, where static pressure or hammering is not feasible, the hard interlayer is expanded by using the expansion body of the soil squeezing and enlarging drill bit. Its outer diameter is slightly smaller than that of the precast hollow pile, thus ensuring smooth pile driving while maintaining the lateral friction resistance between the pile surface and the hard interlayer soil.

[0028] 5. The precast hollow pile extension pile provided by the construction method of this invention can improve the pile body strength. The design value of static pressure or hammer-driven precast piles and cement-soil composite piles is not greater than the pile body strength of the precast pile. The inner cavity of the precast hollow pile in the extension pile can be filled with concrete during construction. This is an integrated construction function inherent in the construction method itself. The precast hollow pile after filling becomes a solid pile, and the pile body strength is enhanced. This is conducive to the full utilization of the bearing potential of the soil around the pile, thereby improving the bearing capacity of a single pile and saving energy.

[0029] 6. The precast hollow pile extension pile provided by the construction method of this invention reduces the effort required for driving the precast hollow pile and results in a high-quality extension body formation. During construction, the inverted conical hollow pile tip at the bottom of the precast hollow pile facilitates the horizontal movement of the surrounding soil during pile driving, reducing the vertical pressure on the pile. In particular, for piles penetrating the extension body, the outer conical pile tip effectively controls the displacement direction of the concrete in the extension body, which is beneficial for further squeezing and expanding the surrounding soil to form a larger diameter extension body, providing support for the high bearing capacity of the extension body after pile completion.

[0030] 7. The precast hollow pile extension pile provided by the construction method of the present invention can be designed and constructed according to the soil properties and bearing capacity requirements around the pile. It can realize the extension body at different positions of the pile body, which is conducive to optimizing the pile foundation design and achieving energy saving and low carbon emissions.

[0031] 8. The precast hollow pile extension pile provided by the construction method of the present invention uses micro-expansion concrete for the concrete grouting by lifting the auger during construction. This forms a pre-pressure on the pile end and the enlarged body, which is beneficial to improving the bearing capacity of the extension pile. The micro-expansion concrete grouting in the inner cavity of the precast hollow pile increases the bonding strength between the precast hollow pile and the grouting body in the inner cavity, thereby improving the strength of the pile body.

[0032] 9. The precast hollow pile extension pile provided by the construction method of this invention uses super-fluid concrete to reinforce the bottom bearing layer, forming a concrete-soil mixture bearing layer. This layer has high strength, good overall stability, simple construction equipment, and is easy to operate, all of which are superior to reinforcement with cement slurry. The overall strength and overall stability of the bottom bearing layer after reinforcement are also higher than those of the spherical carrier at the bottom of the rammed and expanded pile. The spherical carrier of the rammed and expanded pile consists of the influencing soil, compacted soil, and cement sand mixture from the outside to the inside. The bonding force between the influencing soil, compacted soil, and cement sand mixture is small, and the overall strength is low. In particular, the influencing soil and compacted soil will gradually reduce their supporting capacity for the pile as construction stress is released and groundwater is affected. The cement sand mixture is a dry material without water mixing and stirring, resulting in low strength and high dispersion. This leads to poor overall stability and long-term effectiveness of the spherical carrier of the rammed and expanded pile composed of the influencing soil, compacted soil, and cement sand mixture, which can easily cause excessive settlement of the building in the later stages.

[0033] 10. The precast hollow pile extension pile provided by the construction method of this invention typically consists of undisturbed soil layers and loose soil disturbed during construction in the bottom bearing layer. For extension piles where the pile bottom penetrates a certain depth into the hard rock bearing layer, the depth into the bearing layer is achieved by first enlarging the drill bit diameter, then lifting the drill and grouting concrete, followed by re-drilling and compaction, then lifting the drill and grouting concrete again, and finally driving the precast hollow pile to the designed elevation of the pile bottom. By enlarging the drill bit diameter, the designed depth into the hard rock bearing layer is achieved. Then, by lifting the drill and grouting for mixing, re-drilling and compaction for mixing, and then lifting the drill and grouting for mixing again, the adverse effects of the loose soil generated during drill bit diameter enlargement on the bearing capacity of the pile end are eliminated, while maintaining the original bearing strength of the hard rock bearing layer. This saves costs and solves the problem of difficult static pressure pile driving in hard rock layers.

[0034] 11. The construction method provided by this invention has no mud overflow, no noise, no vibration, less soil discharge, and good environmental performance. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the structure of a precast hollow pile extension pile according to the present invention.

[0036] Figure 2 This is a schematic diagram of the structure of a precast hollow pile extension pile according to the present invention.

[0037] Figure 3 yes Figure 2 AA sectional view.

[0038] Figure 4 This is a schematic diagram of the drill bit with the enlarged body extended and the drill tip gate open in a auger drill bit.

[0039] Figure 5 This is a schematic diagram of the drill bit expansion body retracted and the drill tip gate open in a spiral drilling tool.

[0040] Figure 6 This is a schematic diagram of the drill bit retracting and the drill tip gate closed in a spiral drilling tool.

[0041] Figure 7 This is a schematic diagram of the drill bit with the enlarged body extended and the drill tip gate closed in a auger drill bit.

[0042] Figure 8 This is a schematic diagram of the construction status.

[0043] Figure 9 This is a schematic diagram of construction status two.

[0044] Figure 10 This is a schematic diagram of the third construction phase.

[0045] Figure 11 This is a schematic diagram of the fourth construction phase. Detailed Implementation

[0046] Example 1: A precast hollow pile extension pile and its construction method

[0047] I. A structure of a precast hollow pile extension pile

[0048] like Figure 1 , Figure 2 and Figure 3 As shown, a precast hollow pile extension pile includes a precast hollow pile (10), at least one extension body (20), and a bottom reinforcement bearing layer (30).

[0049] In the precast hollow pile extension pile, the outer surface of the precast hollow pile (10) is not provided with a concrete layer except for the bottom reinforcement section bearing layer (30) and the enlarged body (20).

[0050] The inner cavity of the precast hollow pile (10) is filled with concrete (11) in whole or in part. Preferably, in this embodiment, the bottom end of the precast hollow pile (10) is equipped with a precast inverted conical hollow pile tip (12). Preferably, the precast hollow pile (10) is any one of the following: precast concrete pile, precast steel pile, precast steel-concrete composite pile, precast pile made from renewable and biodegradable raw materials, precast pile made from biomimetic low-carbon building materials, or precast pile made from industrial slag as building material, and its cross-sectional shape is a hollow circle or a hollow polygon. Preferably, in this embodiment, as an example, the precast hollow pile (10) is a precast concrete pile. Preferably, the precast inverted conical hollow pile tip (12) can be a high-strength precast concrete component or a steel component.

[0051] The enlarged body (20) surrounds a portion of the outer surface of the precast hollow pile (10) and is integrally formed with the precast hollow pile. Preferably, in this embodiment, the enlarged body (20) includes a concrete ring (21) with a radially spiral outer contour and a concrete-soil mixture layer (22). The concrete ring (21) surrounds the outer surface of the precast hollow pile (10) and is integrally formed with the precast hollow pile (10). The concrete-soil mixture layer (22) is disposed outside the concrete ring (21) and is integrally formed with the concrete ring (21). The enlarged body undergoes at least two compaction processes. When the extended pile is subjected to vertical ultimate pressure and displacement occurs, the slip fracture failure interface between the pile and the soil occurs at the interface between the outer side of the radial mixture layer of the enlarged body and the surrounding soil. The force between them is a stress state dominated by the shear strength of the surrounding soil.

[0052] like Figure 1 As shown, as an example, a precast hollow pile extension pile includes an enlarged body (20).

[0053] like Figure 2 As shown, as an example, the precast hollow pile extension pile includes two extension bodies (20), which are connected together by a precast hollow pile (10).

[0054] Of course, more than two enlarged bodies (20) can be set according to actual needs, such as three, four or five. The enlarged bodies (20) can be set at any position on the pile body of the precast hollow pile (10), and two adjacent enlarged bodies (20) are connected as one unit by the precast hollow pile (10).

[0055] The reinforcing bearing layer (30) is located at the bottom of the precast hollow pile (10), and the bottom of the precast hollow pile (10) is wrapped by or penetrates the bottom reinforcing bearing layer (30). Preferably, in this embodiment, the bottom reinforcing bearing layer (30) wraps the bottom of the precast hollow pile (10), and the outer diameter of the bottom reinforcing bearing layer (30) is larger than the outer diameter or outer diagonal dimension of the precast hollow pile (10), and its vertical height is not less than 1 to 5 times the outer diameter or outer diagonal dimension of the precast hollow pile (10). The depth to which the bottom end of the precast hollow pile (10) enters the bottom reinforcing bearing layer (30) is 0.5 to 2 times the outer diameter or outer diagonal dimension of the precast hollow pile (10). Preferably, part or all of the bottom reinforcing bearing layer (30) is a compacted concrete-soil mixture.

[0056] The concrete used in the expanded body, the bearing layer of the bottom reinforcement section, and the inner cavity of the precast hollow pile is superfluid micro-expansion concrete.

[0057] II. Construction Methods for Precast Hollow Pile Spread Piles

[0058] The construction method of externally mounted precast hollow piles is adopted. During the construction process, the auger drill bit (40) is inserted into the inner cavity of the precast hollow pile (10) concentrically. During the auger soil squeezing drilling and sinking of the precast hollow pile (10), the soil squeezing part of the bottom cone of the auger soil squeezing drill bit at the lower end of the auger drill bit (40) is always kept protruding from the bottom end of the precast hollow pile (10). The method is as follows:

[0059] The combined equipment and working status of static pressure pile driving device and pressure grouting pile device are as follows: Figures 4-7 The auger drill bit (40) shown.

[0060] A spiral section is installed on the static pressure pile driver platform for soil displacement and grouting construction, including a column tower, power head, spiral drill bit, concrete pouring device, winch, control system, etc. The side of the column tower is equipped with a pair of vertical guide rails for installing and fixing the power head. The guide rails are always perpendicular to the static pressure pile driver platform. The power head slides with the column tower's rails and is controlled by a winch and wire rope to move up and down along the column tower's rails. The output end of the power head is connected to the top of the auger drill bit. The auger drill bit consists of an auger drill rod and an auger soil squeezing drill bit, and has a concrete grouting pipe inside. The bottom end of the auger soil squeezing drill bit is a conical soil squeezing part, and it is equipped with a hydraulically controlled, extendable and retractable expansion body device. The maximum opening angle of the drill bit tip gate is β, where β = 40°. The bottom end of the column tower is set to a movable connection with the static pressure pile driver platform, which can move within a certain range. It is hydraulically controlled and has two lockable positions: one is a position that keeps the center of the auger drill bit coincident with the center of the pile when the static pressure pile driver is driving the pile; the other is a position that keeps the power head and auger drill bit from interfering with the static pressure pile driver's hoisting of the precast pile into the inner hole of the pile holder.

[0061] 1. Preparation and Drilling

[0062] Using the pile driving device of a static pressure pile driver, straighten and lower the precast hollow pile (10) with pile tip (12).

[0063] Using a spiral soil squeezing and grouting pile construction device, the spiral drill bit (40) is inserted into the inner cavity of the precast hollow pile (10) in a concentric manner.

[0064] Align the precast hollow pile (10) with the pile tip (12) with the pile position, such as Figure 8 (a)

[0065] Insert the auger into the inner cavity of the precast hollow pile (10) concentrically until it reaches the ground surface, as follows: Figure 8 (b)

[0066] First, start the power head to drive the auger to rotate and move downward in the drilling direction. Then, start the static pressure pile driver to sink the precast hollow pile. During the auger soil squeezing drilling and sinking of the precast hollow pile (10), keep the soil squeezing part of the bottom cone of the auger soil squeezing drill bit at the bottom of the auger always below the pile tip (12). Figure 8 (c) and (d) in the middle.

[0067] In this step, if the precast hollow pile is driven through a hard interlayer (such as hard plastic cohesive soil, dense sand, gravelly soil, strongly weathered rock, etc.), the enlarged body in the auger soil squeezing drill bit can be partially extended. The circle formed by the maximum outer edge of the extended enlarged body should not be larger than the outer circle or side length of the precast hollow pile. When the auger drill bit is lowered, the diameter is enlarged to form a hole, reducing the pressure required for static pressure pile driving through the hard interlayer, thus completing the pile driving through the hard interlayer.

[0068] 2. Formation of the enlarged body (20)

[0069] Sink the precast hollow pile (10) to the top elevation of the first enlarged body (20), then stop sinking the precast hollow pile (10). Figure 9(e) The auger continues drilling until the bottom cone of the auger bit reaches the elevation of the first enlarged section. The drill bit is kept rotating, and the concrete pump is started to inject concrete into the auger's inner cavity. Simultaneously, the drill bit's enlarged section extends, with the diameter of the circle formed by the extended enlarged section being larger than the outer diameter or diagonal dimension of the precast hollow pile. The rotating auger is then lifted, and the extended enlarged section squeezes the soil wall to form a stepped spiral groove. The concrete in the auger's inner cavity opens the drill tip, filling the pile hole formed by the soil displacement drilling and the spiral groove formed by the enlarged section. With the drilling and grouting matched, the drilling continues, the enlarged section squeezes the soil wall to form a spiral groove, and the grouting forms a spiral-shaped concrete ring with a threaded outer contour, until the top elevation of the first enlarged section is reached. The enlarged section is then retracted, and the drilling and grouting continue for at least one cone cone of the drill bit's soil displacement height. Drilling and grouting are then stopped, and the drill bit is released downwards. As the drill bit continues to rotate, the drill tip gate, under the upward pressure of the concrete below, rotates to close the concrete pouring channel, preventing the concrete poured into the pile hole from flowing back into the drill bit's inner cavity. The rotating drill bit's cone-shaped soil-displacing part drills to compact the concrete. The compressed concrete threaded pile segment radially compresses the surrounding soil cavity, expanding it, and a small amount of concrete is squeezed into the surrounding soil. Simultaneously, after the soil-displacing part of the drill bit's cone exposes the inverted cone-shaped precast pile tip at the bottom of the precast hollow pile, the static pressure pile driver is restarted to drive the precast hollow pile. The inverted cone-shaped pile tip at the bottom of the precast hollow pile again radially compresses the concrete of the threaded pile segment, further expanding the surrounding rock and soil cavity, and a small amount of concrete is squeezed into the surrounding soil again. During the drilling process of the drill bit compressing the concrete to expand the diameter and the pile driving process of compressing the concrete to expand the diameter, the soil-displacing part of the drill bit is always kept below the pile tip. The pile is driven until the bottom elevation of the first enlarged body is reached, completing the construction of the first enlarged body. Figure 9 (e), (f), (g). Continue spiral drilling and pile driving, keeping the cone-shaped soil-displacing part of the drill bit always below the pile tip. Drive the pile to the top elevation of the second enlarged body of the extended pile, stop driving the pile, and repeat the construction process of the first enlarged body to achieve the formation of the second enlarged body. In this way, multiple enlarged bodies can be formed.

[0070] 3. Formation of the bearing layer (30) of the bottom reinforcement section

[0071] Keep the cone soil-squeezing part of the drill bit below the pile tip, continue the spiral soil-squeezing drilling and lower the precast hollow pile (10) until reaching the top elevation of the bearing stratum (30) of the bottom reinforcement section, at this time keep the top height of the precast hollow pile higher than the designed top elevation of the expanded pile; restart the extension of the drill bit reamer, the diameter of the circle formed by the extended reamer after diameter expansion is larger than the outer diameter or the outer edge diagonal dimension of the precast hollow pile, the continuously rotating and downward-moving drilling tool drives the reamer to perform diameter expansion drilling, part of the soil cut down by rotation is conveyed from bottom to top along the spiral drilling tool, and the rest remains in the diameter-expanded cavity, perform soil-squeezing diameter expansion drilling until reaching the bottom elevation of the bearing stratum (30) of the bottom reinforcement section, start the concrete delivery pump to pressure-grout concrete, then slowly lift the continuously rotating drilling tool, the pressurized concrete in the inner cavity of the drilling tool opens the drill tip door and is poured into the cavity formed by drilling and diameter expansion, under the stirring action of the rotating reamer, the concrete mixes with the soil remaining in the cavity, perform drilling lifting, pressure grouting and stirring until reaching the top elevation of the bearing stratum (30) of the bottom reinforcement section, stop drilling lifting and pressure grouting, then release the continuously rotating drilling tool downward, the drill tip door closes the concrete grouting passage port of the drilling tool under the action of the concrete-soil mixture below, the cone soil-squeezing part of the drill bit squeezes the concrete-soil mixture to squeeze and expand the surrounding rock-soil wall, the reamer stirs the concrete and soil for further mixing, perform extrusion drilling and stirring until reaching the bottom elevation of the reinforcement section of the bearing stratum, perform pump pressure grouting of concrete and drill lifting again, pour concrete into the cavity formed by compaction drilling, meanwhile the rotating reamer continues to stir and mix the concrete and soil in the diameter-expanded cavity, when the operations of drill lifting, pressure grouting and stirring reach the top elevation of the reinforcement section of the bearing stratum, retract the reamer, continue drill lifting and pressure grouting for a height of 1 to 1.5m, stop drill lifting and pressure grouting, release the drilling tool downward by a height of 1 to 1.5m, the concrete below the drill bit closes the drill tip door of the drill bit, stop the downward movement and rotation of the drilling tool, then start the static pressure pile sinking device to lower the precast hollow pile until the top elevation of the expanded pile is met, during the pile sinking process, the bearing stratum (30) of the bottom reinforcement section is formed at the bottom of the precast hollow pile, Figure 10 in (h), (i), (j), (k), (l), (m). The concrete for drill lifting and pressure grouting is micro-expansive concrete.

[0072] 4. Extraction of the spiral drilling tool

[0073] If the spiral drilling tool is directly extracted from the inner cavity of the precast hollow pile to complete the construction of an expanded pile with part of the inner cavity of the precast hollow pile filled with concrete, as shown Figure 11 in (n), (o), (q).

[0074] If the drill lifting and pressure grouting of concrete is continued until the top height of the precast hollow pile is reached, then a reinforcement cage is placed to complete the construction of an expanded pile with the entire inner cavity of the precast hollow pile filled with concrete, as shown Figure 11 in (p). The concrete for drill lifting and pressure grouting is micro-expansive concrete.

[0075] In this step, for a bearing layer of hard rock and soil at the bottom, and where the bottom of the extended pile penetrates to a certain depth into the bearing layer: Static pressure is applied to drive the pile to the top of the hard rock and soil bearing layer, maintaining the top height of the precast hollow pile higher than the design elevation of the extended pile. The drill bit is then activated to extend the enlarging body. The diameter of the circle formed by the enlarging body is larger than the outer diameter or diagonal dimension of the outer edge of the precast hollow pile. The rotating and downward-moving drill bit drives the enlarging body to perform enlarging drilling. Part of the soil cut off by the rotation is transported upwards along the auger, and... Part of the concrete remains in the enlarged borehole cavity. The enlarged borehole drilling depth exceeds the designed depth of the bearing stratum by 100-500mm. First, start the concrete pump to inject concrete, then slowly raise the rotating drill bit. The pressure concrete inside the drill bit opens the drill tip gate and is poured into the borehole cavity formed by the enlarged borehole. Under the stirring action of the rotating enlarged body, it mixes with the soil remaining in the borehole cavity. Raise the drill, inject, and stir until the top elevation of the bearing stratum is reached. Stop raising the drill and injecting, then release the rotating drill bit downward. The drill tip gate closes the concrete injection channel under the action of the concrete and soil mixture below. The cone part of the drill bit squeezes the concrete and soil mixture and the surrounding rock and soil walls. The enlarged body further mixes the concrete and soil. Squeeze and stir until the first drilling depth of the bearing stratum is reached. Pump concrete again and raise the drill to inject concrete into the cavity formed by the compaction drilling. At the same time, the rotating enlarged body continues to stir the concrete and soil in the enlarged borehole cavity. Raise the drill, inject, and stir. When the bearing stratum reaches its maximum height, retract the enlarged diameter body, continue drilling and grouting to a height of 1-1.5m, then stop drilling and grouting. Lower the drill string 1-1.5m, allowing the concrete below the drill bit to close the drill tip gate. Stop the drill string from moving downwards and rotating. Then, start the static pressure pile driving device to drive the precast hollow pile into the designed depth of the hard soil-rock bearing stratum, ensuring the top elevation of the extended pile is reached. During the pile driving process, the bottom of the precast hollow pile enters the designed depth of the bearing stratum and compacts the mixture of bottom concrete and soil. Figure 11 (q).

[0076] III. Bearing and Service Principles of Precast Hollow Piles and Spread Piles

[0077] 1. Bearing principle of spread piles

[0078] The enlarged body in the extended pile is formed by two compressions of cast-in-place concrete threaded pile segments. It consists of an inner concrete ring and an outer concrete-soil mixed layer, with a radial outer contour that is threaded. After solidification, the inner ring is firmly integrated with the precast hollow pile, and the outer mixed layer is firmly integrated with the inner ring. The soil surrounding the enlarged pile is in a compacted state. The sides of the enlarged pile are spiral-shaped and tightly bonded to the surrounding soil. This is a spiral-embedded bond formed by the external spiral of the enlarged pile through the mixed layer and the surrounding soil. When the extended pile is subjected to vertical ultimate pressure and displacement occurs, the slippage failure interface between the enlarged pile and the surrounding soil occurs on the outer contour surface of the enlarged pile, that is, on the outer contour surface of the mixed layer of the enlarged pile. The concrete component on the slippage failure interface is very small and dispersed, mainly consisting of the compacted surrounding soil component. As a result, the side resistance of the enlarged pile is reflected as the shear strength of the soil, which is greater than the frictional resistance between the concrete pile and the soil. Generally, the shear strength of the soil is 1.4 to 2.0 times that of the frictional resistance between the concrete pile and the soil; it is also greater than the side resistance of the spiral pile. Because the spiral failure interface of the spiral pile has the outer diameter spiral surface of the concrete thread teeth and occupies a certain proportion of the slippage interface area, there is frictional resistance between the concrete pile and the soil. Therefore, the side resistance of the spiral pile cannot be calculated entirely based on the shear strength of the soil around the pile. The outer diameter of the enlarged body is larger than the outer diameter or diagonal dimension of the precast hollow pile. The soil at its lower end is formed by two compaction processes: the soil squeezing part of the drill bit cone and the pile tip. The enlarged body generates new end resistance. Multiple independent enlarged bodies in the spread pile are connected into one piece by precast hollow piles. The high-strength enlarged body has a large end face and good end resistance, which improves the end bearing capacity of the spread pile. As a foundation pile, the spread pile solves the problem that precast piles cannot have high-strength enlarged bodies installed in the pile body. The bearing stratum at the bottom of the extended pile is compacted and reinforced, resulting in high strength and good overall stability. The thickness of the reinforcement layer is determined based on the hardness of the underlying soil. When the underlying soil is soft, the thickness of the bearing stratum at the bottom of the extended pile is usually not less than 3 times the outer diameter or diagonal dimension of the precast hollow pile. When there is no soft soil layer, the thickness of the bearing stratum at the bottom of the pile is usually 1 to 2 times the outer diameter or diagonal dimension of the precast hollow pile, which is beneficial to improving end bearing capacity. When the bearing stratum is hard rock and soil, the original bearing stratum at the bottom of the pile does not need to be reinforced. The depth of the pile bottom into the bearing stratum needs to be achieved by enlarging the diameter, and concrete is poured in. This serves two purposes: first, to remove the adverse effects of the enlarged loose soil on the bearing capacity; and second, to increase the bonding force between the pile bottom and the original bearing stratum, which helps to improve the end resistance and pull-out resistance of the pile.

[0079] 2. The working principle of the spread pile

[0080] The position and number of the enlarged body in a spread pile are not fixed and can be selected according to the properties of the surrounding soil and the bearing capacity requirements. The construction method of spread piles can meet the requirements of various spread pile structure types, achieving optimized design. Since the design value of the pile's bearing capacity cannot exceed the pile strength, when the supporting force of the foundation soil on the spread pile is greater than the strength of the precast hollow pile, in order not to waste the bearing resources of the foundation soil, the strength of the pile body is increased by grouting concrete into the cavity of the precast hollow pile to form a solid pile, thereby increasing the design value of the spread pile's bearing capacity.

Claims

1. A construction method for precast hollow pile extension piles, characterized in that, The structure of the precast pile extension pile is as follows: the outer surface of the precast hollow pile (10) is provided with a bottom reinforcement bearing layer (30) and at least one extension body (20); except for the bottom reinforcement bearing layer (30) and the extension body (20), the outer surface of the precast hollow pile (10) is in direct contact with the surrounding soil; the extension body (20) includes a concrete ring (21) with a radially spiral outer contour and a concrete-soil mixture layer (22), the concrete ring (21) surrounds the outer surface of the precast hollow pile (10) and is integrally formed with the precast hollow pile (10), the concrete-soil mixture layer (22) It is formed when a concrete ring (21) is formed by two compaction of the concrete threaded pile segments, and some concrete is squeezed into the soil around the threaded pile segments in contact with it. The concrete-soil mixture layer (22) wraps the concrete ring (21) and is solidified into an integral structure with it. The bottom reinforcement bearing layer (30) is set at the bottom of the precast hollow pile (10), and its transverse section is larger than the transverse section of the outer surface of the precast hollow pile. The bottom of the precast hollow pile (10) enters the reinforcement bearing layer (30) to a certain depth or penetrates the thickness of the reinforcement bearing layer (30). The side resistance of the enlarged body (20) is reflected in the shear strength of the surrounding soil. The construction method for precast pile spread piles includes the following steps: 1) Preparation and Drilling Align the precast hollow pile (10) with the pile position; insert the spiral drill bit (40) with the soil squeezing bit into the inner cavity of the precast hollow pile (10) to the ground surface in a centered manner; during the spiral soil squeezing drilling and sinking of the precast hollow pile (10), keep the soil squeezing part of the bottom cone of the soil squeezing bit at the bottom of the spiral drill bit always below the bottom of the precast hollow pile (10) and perform partial soil squeezing drilling on the soil within the inner cavity of the precast hollow pile at the pile position; for hard interlayers such as hard plastic cohesive soil, dense sand, and gravelly soil, the enlarged diameter body of the drill bit can be partially extended, and the diameter of the circle formed by its extended outer edge is not greater than the outer diameter of the precast hollow pile or the diagonal dimension of its outer edge; 2) Formation of the enlarged body (20) The precast hollow pile (10) is lowered to the top elevation of the first enlarged body (20). The auger drill (40) continues drilling to the bottom elevation of the first enlarged body. The drill is kept rotating, and the concrete pump is started to inject concrete into the inner cavity of the auger drill. At the same time, the drill bit enlarged body is driven to extend. The diameter of the circle formed by the outer edge of the extended enlarged body is larger than the outer diameter or the diagonal dimension of the outer edge of the precast hollow pile (10). The rotating drill is then lifted, and the cavity formed by the soil squeezing and drilling and the spiral groove formed by the enlarged body are injected until the top elevation of the first enlarged body is reached, forming a concrete threaded pile section with an enlarged diameter. The enlarged body is then retracted, and the drill is lifted and injected for at least the height of the soil squeezing part of the drill bit cone. The drill is then lifted and injected, and the drill is released downwards. The soil squeezing part of the drill bit cone passes through the bottom end face of the precast hollow pile (10) and first squeezes out the soil. Expand the concrete threaded pile segment, then sink the precast hollow pile (10), and squeeze the concrete threaded pile segment again at the bottom of the precast hollow pile (10). Keep the auger drill (40) drilling and the precast hollow pile (10) sinking to the bottom elevation of the first enlarged body. During this process, keep the soil squeezing part of the drill bit cone below the bottom surface of the precast hollow pile (10). Through the two compaction of the concrete threaded pile segment, a concrete ring (21) of the enlarged body is formed. At the same time, some concrete will be squeezed into the soil it contacts, forming a concrete-soil mixture layer (22). The inner surface of the concrete ring (21) wraps the precast hollow pile (10), and the outer surface of the concrete ring (21) is wrapped by the compacted concrete-soil mixture layer (22), completing the construction of the first enlarged body. This process is repeated to achieve the formation of multiple enlarged bodies. 3) Formation of the bearing layer (30) of the bottom reinforcement section Continue to sink the precast hollow pile (10) to the top elevation of the bearing layer (30) of the extended pile bottom reinforcement section. At this time, keep the top elevation of the precast hollow pile higher than the top design elevation of the extended pile. At the same time, when the spiral soil squeezing drilling reaches the top elevation of the bearing layer (30) of the extended pile bottom reinforcement section, start the drill bit expansion body again to expand the diameter. The diameter of the circle formed by the outer edge of the extended expansion body is larger than the outer diameter or the diagonal dimension of the outer edge of the precast hollow pile until the bottom elevation of the bearing layer (30) of the extended pile bottom reinforcement section is reached. Start the concrete delivery pump to pressurize concrete, and then slowly lift the rotating drill bit. The pressure concrete in the inner cavity of the drill bit opens the drill tip door and is poured into the cavity formed by the expansion drilling. Under the stirring action of the rotating expansion body, it is mixed with the soil remaining in the cavity. Lift the drill, pressurize, and stir until the top elevation of the bearing layer (30) of the extended pile bottom reinforcement section is reached. Stop lifting the drill and Pressurize, then release the rotating drill bit downwards, close the drill tip door, the cone of the drill bit squeezes the soil-squeezing part of the concrete and soil mixture, squeezes and expands the surrounding rock and soil wall, and mixes the concrete and soil further. Pressurize and drill, mix until the bottom elevation of the bearing layer reinforcement section of the pile bottom stops, pump and pressurize concrete again and lift the drill, while the rotating expansion body continues to mix the concrete and soil in the expanded diameter cavity. Lift the drill, pressurize, and mix until the top elevation of the bearing layer reinforcement section of the expanded pile bottom is reached, then retract the expansion body, continue to lift the drill and pressurize to a height of 1-1.5m, stop lifting the drill and pressurizing, and release the drill bit downwards 1-1.5m. The concrete below the drill bit closes the drill tip door of the drill bit, stops the drill bit from moving down and rotating, and then sinks the precast hollow pile to meet the top elevation of the expanded pile. At this time, the bottom of the precast hollow pile sinks into the bearing layer (30) of the reinforcement section to a certain depth or penetrates it. 4) The introduction of auger drilling tools The auger drill bit is directly pulled out of the inner cavity of the precast hollow pile to complete the construction of an extended pile where the inner cavity of the precast hollow pile is partially filled with concrete; or the drill bit is pulled out and concrete is poured until the top of the precast hollow pile is reached, and then a steel cage is placed in to complete the construction of an extended pile where the inner cavity of the precast hollow pile is completely filled with concrete.

2. The construction method for a precast hollow pile extension pile according to claim 1, characterized in that, The bottom end of the precast hollow pile may be provided with an inverted cone-shaped hollow pile tip (12), the internal hollow cross-section size of which is the same as the cross-section of the inner cavity of the precast hollow pile.

3. The construction method for a precast hollow pile extension pile according to claim 1, characterized in that, The inner cavity of the precast hollow pile (10) is filled with concrete (11) in whole or in part; the bottom reinforcement bearing layer (30) is set at the bottom of the precast hollow pile (10), and its transverse section is larger than the transverse section of the outer surface of the precast hollow pile. The bottom of the precast hollow pile (10) enters the reinforcement bearing layer (30) to a certain depth or penetrates the thickness of the reinforcement bearing layer (30).

4. The construction method for a precast hollow pile extension pile according to claim 1, characterized in that, There are at least two enlarged bodies (20), which are set at any position on the pile body of the precast hollow pile (10), and the two adjacent enlarged bodies (20) are connected as one unit by the precast hollow pile (10).

5. The construction method for a precast hollow pile extension pile according to claim 1, characterized in that, The outer diameter of the bearing layer (30) of the bottom reinforcement section is greater than the outer diameter or outer diagonal dimension of the precast hollow pile (10), and its vertical height is not less than 1 to 5 times the outer diameter or outer diagonal dimension of the precast hollow pile (10).

6. The construction method for a precast hollow pile extension pile according to claim 1, characterized in that, The reinforcing bearing layer (30) wraps around the bottom of the precast hollow pile (10); the bottom of the precast hollow pile (10) enters the reinforcing bearing layer (30) to a depth of 0.5 to 2 times the outer diameter or outer diagonal dimension of the precast hollow pile (10).

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