CN117418535A

CN117418535A - Construction method of prefabricated hollow pile extension pile and prefabricated hollow pile extension pile formed by construction method

Info

Publication number: CN117418535A
Application number: CN202311536213.1A
Authority: CN
Inventors: 赵世范; 赵越; 鲁爽; 吴建祥; 洪学哲; 王莉莉; 刘涛; 王金来; 牛敬涵; 金寿焕; 张喜才; 刘守进
Original assignee: Individual
Current assignee: Individual
Priority date: 2023-11-17
Filing date: 2023-11-17
Publication date: 2024-01-19

Abstract

The invention discloses a construction method of a prefabricated hollow pile extension pile and the prefabricated hollow pile extension pile formed by the construction method. The construction method of the external prefabricated hollow pile is adopted, and in the construction process, a spiral drilling tool is concentrically inserted into an inner cavity of the prefabricated hollow pile; in the process of spiral soil extrusion drilling and sinking the prefabricated hollow pile, the cone soil extrusion part at the bottom end of the spiral soil extrusion drill head at the lower end of the spiral drilling tool always extends out of the bottom end of the prefabricated hollow pile. The invention fully exerts the advantages of low carbon and high pile body strength of the high-strength concrete precast pile, improves the bearing capacity of the formed pile foundation, reduces the pile foundation cost and the adverse effect of soil compaction negative effect.

Description

Construction method of prefabricated hollow pile extension pile and prefabricated hollow pile extension pile formed by construction method

Technical Field

The invention belongs to the field of construction of building piles, and particularly relates to a construction method of a prefabricated hollow pile extension pile and the prefabricated hollow pile extension pile formed by the construction method.

Background

In a building pile foundation, the occupancy of a high-strength concrete precast pile is higher and higher, and the construction method mainly comprises two types: one is to use static pressure or hammering pile sinking, and the foundation pile bears the load of the building; the other is combined with the cement soil pile to construct a composite pile, the core pile of the composite pile is a high-strength concrete precast pile, and the outer pile of the composite pile is the cement soil pile to form a combined pile with rigid inner part and flexible outer part. Static pressure or hammering pile sinking belongs to complete soil compaction, has large soil compaction negative effect, is easy to cause quality defects such as pile inclination, floating piles and the like, particularly, the engineering of softer foundation soil requires longer pile length, causes overhigh pile foundation cost, and is difficult to penetrate through harder rock soil layers for construction; the composite pile effectively solves the problem that the pile length is too long in softer foundation soil, but the foundation soil needs to be integrally reinforced, usually, spin-spray cement slurry is adopted to stir cement, then a method of implanting the concrete precast pile is adopted, so that a large amount of cement overflows, the environment is polluted, the materials are wasted, the formed composite pile is an end-bearing friction pile mainly comprising side friction, the bearing capacity of the pile is not very good, the cost is high, and the work efficiency is low.

Disclosure of Invention

In order to fully exert the advantages of low carbon and high pile body strength of the high-strength concrete precast pile, improve the bearing capacity of a formed pile foundation, reduce the cost of the pile foundation and reduce the adverse effect of soil compaction negative effect, the invention provides an extended pile of the precast hollow pile and a construction method.

In order to achieve the above purpose, the invention adopts the following technical scheme: a construction method of a prefabricated hollow pile extension pile adopts an external construction method of the prefabricated hollow pile, and in the construction process, a spiral drilling tool is concentrically inserted into an inner cavity of the prefabricated hollow pile; in the process of spiral soil extrusion drilling and sinking the prefabricated hollow pile, the cone soil extrusion part at the bottom end of the spiral soil extrusion drill head at the lower end of the spiral drilling tool always extends out of the bottom end of the prefabricated hollow pile.

Further, the construction method of the prefabricated hollow pile extension pile comprises the following steps:

1) Preparation and drilling

Aligning the prefabricated hollow pile to the pile position; concentrically inserting a spiral drilling tool with a soil squeezing drill bit into an inner cavity of the prefabricated hollow pile to the ground surface; in the process of spiral soil extrusion drilling and sinking of the prefabricated hollow pile, keeping a cone soil extrusion part at the bottom end of an earth extrusion drill head at the lower end of a spiral drilling tool below the bottom end of the prefabricated hollow pile all the time, and carrying out partial soil extrusion drilling on soil in the range of an inner hole cavity of the prefabricated hollow pile on a pile hole site;

2) Formation of enlarged body

Sinking the bottom end of the prefabricated hollow pile to the top end of the first expansion body, continuously drilling the spiral drilling tool to the top end of the first expansion body, keeping the drilling tool to rotate, starting the concrete conveying pump to press and irrigate concrete to the inner cavity of the spiral drilling tool, driving the drill bit expansion body to extend out, firstly extruding and expanding the concrete screw pile section after the outer edge of the extending expansion body forms a circular diameter larger than the outer diameter or the diagonal dimension of the outer edge of the prefabricated hollow pile, lifting and sinking the rotating drilling tool, pressing and grouting a cavity formed by the concrete drilling and a spiral groove formed by the expansion body until the top end of the first expansion body is high, forming a concrete screw pile section with an expansion diameter, withdrawing the expansion body, continuously lifting and grouting a cone extrusion part of a drill bit, stopping lifting and grouting, downwards, releasing the drilling tool with the continuous rotation, extruding the cone extrusion part of the drill bit after penetrating the bottom end of the prefabricated hollow pile, firstly extruding and expanding the concrete screw pile section, sinking the prefabricated hollow pile again, keeping the spiral expansion and the spiral pile to sink to the first expansion body, continuously extruding and expanding the cavity and the spiral pile section until the expansion hole is formed by the spiral extrusion hole cavity and the expansion body, and the expansion part of the spiral pile is formed by the top end surface of the spiral pile, and the concrete is formed by the ring-shaped expansion body, and the mixed extrusion part is formed in the top surface of the ring-shaped concrete body, and the ring-shaped concrete pile is formed, and the mixed, and the sealing surface is formed by the ring-shaped expansion is formed and the expansion part of the ring-shaped concrete body and the expansion surface is formed;

3) Formation of bearing layer of bottom reinforcement section

Continuously sinking the prefabricated hollow pile to the top elevation of the bearing layer of the reinforcement section at the bottom of the expansion pile, keeping the top elevation of the prefabricated hollow pile higher than the top design elevation of the expansion pile at the moment, starting the drill bit diameter-expanding body to extend out for diameter-expanding drilling when the spiral soil-squeezing drill reaches the top elevation of the bearing layer of the reinforcement section at the bottom of the expansion pile, and forming a circle with the diameter larger than the outer diameter of the prefabricated hollow pile or the diagonal dimension of the outer edge until the bottom elevation of the bearing layer of the reinforcement section at the bottom of the expansion pile is stopped; starting a concrete conveying pump to pump concrete, slowly lifting a continuously rotating drilling tool, opening a drilling tip door to pour the pressurized concrete in the inner cavity of the drilling tool into a hole cavity formed by expanding drilling, mixing the pressurized concrete with soil reserved in the hole cavity under the stirring action of a rotating expanding body, lifting, pressing and stirring to the top elevation of a supporting layer of a reinforcing section at the bottom of an expanded pile, stopping lifting and pressing the drilling tool, downwards releasing the continuously rotating drilling tool, closing the drilling tip door, extruding a mixture of the concrete and the concrete by a cone-shaped extruding part of the drilling tool, extruding and expanding surrounding rock concrete walls, further mixing the stirred concrete with the concrete, extruding and stirring to the bottom elevation of the reinforcing section at the bottom of the pile, pumping the concrete and lifting the drilling tool again, simultaneously continuously stirring the concrete in the expanding hole cavity, lifting and pressing the drilling tool, stirring to the top elevation of the reinforcing section at the bottom of the expanded pile, continuously lifting and pressing the drilling tool by 1-1.5 m, stopping lifting and pressing the drilling tool, downwards releasing the mixture of the concrete and the drilling tool by 1-1.5 m, and downwards sinking the drilling tool to the bottom elevation of the reinforcing section at the moment, closing the drilling tool or the hollow pile, and the hollow pile is stopped at the top elevation of the bottom of the reinforcing section, and the hollow pile is stopped at the top of the reinforcing section is reached, and the hollow pile is stopped, and the hollow pile is at a certain depth is reached, and the hollow pile is filled, and the hollow pile has a hollow pile and the pile has a pile;

4) Screw drilling tool

Directly lifting the spiral drilling tool out of the inner cavity of the prefabricated hollow pile to finish the construction of an extension pile by partially pouring concrete into the inner hole cavity of the prefabricated hollow pile; or (b)

And continuously lifting the drilling pressure concrete to the top of the prefabricated hollow pile, and then placing a reinforcement cage to complete the construction of the extension pile with all the concrete poured into the inner hole cavity of the prefabricated hollow pile.

Further, the construction method of the prefabricated hollow pile extension pile comprises the following steps: in the step 1), when the soil squeezing drill bit is used for partially squeezing soil and drilling, the diameter expanding body of the drill bit can partially extend out, and the diameter of a circle formed by the extending outer edge of the drill bit is not larger than the outer diameter of the prefabricated hollow pile or the diagonal dimension of the outer edge.

Furthermore, in the construction method of the prefabricated hollow pile extension pile, the bottom end of the prefabricated hollow pile can be provided with the inverted cone type hollow pile tip, and the size of the inner hollow section of the inverted cone type hollow pile tip is the same as the section of the inner cavity hole of the prefabricated hollow pile.

The prefabricated hollow pile extension pile formed according to the extension pile construction method comprises a prefabricated hollow pile, wherein a bottom reinforcement section bearing layer and at least one expansion body are arranged on the outer surface of the prefabricated hollow pile; the outer surface of the prefabricated hollow pile is not provided with a concrete layer except for a bearing layer and an expansion body of the bottom reinforcing section.

Further, the expansion body comprises a concrete annular body with a radial outer contour in a threaded shape and a concrete-soil mixing layer, wherein the concrete annular body surrounds the outer surface of the prefabricated hollow pile and is fixedly integrated with the prefabricated hollow pile, and the concrete-soil mixing layer wraps the concrete annular body and is fixedly integrated with the concrete annular body; filling all or part of the inner cavity of the prefabricated hollow pile with concrete; the bottom reinforcing section bearing layer is arranged at the bottom of the prefabricated hollow pile, the transverse section of the bottom reinforcing section bearing layer is larger than the transverse section of the outer surface of the prefabricated hollow pile, and the bottom of the prefabricated hollow pile enters the reinforcing section bearing layer (30) to a certain depth or penetrates through the thickness of the reinforcing section bearing layer.

Furthermore, the prefabricated hollow pile extension pile is provided with at least two extension bodies, the extension bodies are arranged at any position of the pile body of the prefabricated hollow pile, and two adjacent extension bodies are connected into a whole through the prefabricated hollow pile.

Furthermore, in the prefabricated hollow pile extension pile, the outer diameter of the bottom reinforcement section bearing layer is larger than the outer diameter or the outer edge diagonal dimension of the prefabricated hollow pile, and the vertical height of the bottom reinforcement section bearing layer is not smaller than 1-5 times of the outer diameter or the outer edge diagonal dimension of the prefabricated hollow pile.

Further, according to the prefabricated hollow pile extension pile, the bottom of the prefabricated hollow pile is wrapped by the reinforcing section bearing layer; the depth of the bottom end of the prefabricated hollow pile entering the bearing layer of the reinforcing section is 0.5-2 times of the outer diameter or the outer edge diagonal dimension of the prefabricated hollow pile.

Further, according to the prefabricated hollow pile extension pile, the bottom end of the prefabricated hollow pile is provided with the inverted cone type hollow pile tip and is positioned and arranged with the bottom end of the prefabricated hollow pile.

The beneficial effects of the invention are as follows:

1. the prefabricated hollow pile extension pile provided by the construction method has good interaction with surrounding soil of the pile and high bearing capacity. The side resistance of the expansion body in the expansion pile is high, a new end resistance is generated, and meanwhile, the bottom bearing layer of the expansion pile is subjected to compaction strengthening treatment to form a high-strength bearing layer mixture section, and the effective acting area of the bottom bearing layer after strengthening is larger than the cross section area of the prefabricated hollow pile, so that the end bearing capacity of the expansion pile is effectively improved; the pile surrounding soil of the part of the prefabricated hollow pile which is not surrounded by the expanding body is in a compaction state, so that the bearing capacity of the expanding pile is improved, and the compression resistance and the pulling resistance of the expanding pile are improved.

2. The discontinuous high-strength expansion body is arranged on the outer surface of the prefabricated hollow pile, so that the action mode between the traditional prefabricated pile and the surrounding soil of the pile is changed. The prefabricated hollow pile expansion pile provided by the invention has the advantages that on the pile body resistance, the expansion body and the pile surrounding soil are combined in a threaded fit manner, the annular body in the expansion body is combined with the pile surrounding soil through the mixing layer at the periphery of the expansion body, and a powerful support is provided for the action between the outer side surface of the expansion body and the pile surrounding soil to be mainly represented as the shearing stress of the pile surrounding soil, and the combination action mode is larger than the friction resistance between the pile and the soil, and meanwhile, the expansion body generates new end resistance.

3. The prefabricated hollow pile extension pile provided by the construction method has small soil squeezing negative effect. The extension pile belongs to a part of soil-squeezing pile, and during construction, part of rock soil is discharged to the ground surface by utilizing the spiral drilling tool through the inner hole cavity of the prefabricated hollow pile, so that the horizontal displacement of the soil around the pile during sinking of the prefabricated hollow pile is reduced, and the soil-squeezing negative effect is reduced.

4. The prefabricated hollow pile extension pile provided by the construction method disclosed by the invention is wide in adaptability to geological conditions. For the stratum which cannot be constructed by static pressure or hammering of hard interlayer such as hard plastic cohesive soil, dense sand layers and gravel soil, the diameter of the hard interlayer is expanded by the diameter expanding body of the soil extrusion diameter expanding drill bit while the prefabricated hollow pile is sunk, the outer diameter of the hard interlayer is slightly smaller than the outer diameter of the prefabricated hollow pile, and the pile sinking is smoothly realized on the premise of ensuring the side friction between the surface of the pile body and the hard interlayer soil.

5. The pile body strength of the prefabricated hollow pile extension pile provided by the construction method can be improved. The design value of the static pressure or hammering precast pile and the cement soil composite pile is not greater than the pile body strength of the precast pile, the inner hole cavity of the precast hollow pile in the extension pile can be filled with concrete in a pressing mode during construction, the integral construction function of the construction method is achieved, the filled precast hollow pile is changed into a solid pile, the pile body strength of the foundation pile is enhanced, full play of the bearing potential of soil around the pile is facilitated, the bearing capacity of the single pile is improved, and the energy is saved.

6. The prefabricated hollow pile extension pile provided by the construction method disclosed by the invention is labor-saving in sinking the prefabricated hollow pile and good in formation quality. During construction, the prefabricated hollow pile bottom is provided with the reverse cone-shaped hollow pile tip, so that the horizontal movement of the pile surrounding soil is facilitated during pile sinking, the vertical pile sinking pressure is reduced, and particularly, the pile sinking of the expanding body is penetrated, the outer cone-shaped pile tip effectively controls the displacement direction of concrete in the expanding body, is beneficial to further squeezing and expanding the pile surrounding soil, forms a large-diameter expanding body, and provides support for the expanding body with high bearing capacity after pile forming.

7. The prefabricated hollow pile extension pile provided by the construction method can be designed and constructed according to the property of the surrounding soil of the pile and the bearing capacity requirement at the position of the pile body, can realize the extension bodies at different positions of the pile body, is beneficial to optimizing the pile foundation design, and realizes energy conservation and low carbon.

8. The precast hollow pile extension pile provided by the construction method is characterized in that the concrete filled by the lifting screw drilling tool is micro-expansion concrete in construction, and the pre-pressure is formed at the pile end and the expansion body, so that the improvement of the bearing capacity of the extension pile is facilitated, the micro-expansion concrete is filled into the inner hole cavity of the precast hollow pile, the bonding strength of the precast hollow pile and the inner hole cavity filling body is improved, and the pile body strength is improved.

9. The prefabricated hollow pile extension pile provided by the construction method adopts the superfluid concrete for reinforcement of the bottom bearing layer to form the mixture bearing layer of the concrete and the soil, and has the advantages of high strength, good overall stability, simple construction equipment, convenient operation and the like, and is superior to the reinforcement with cement slurry participation; the overall strength and the overall stability of the reinforced bottom bearing layer are higher than those of the bottom spherical carrier of the rammed pile, the spherical carrier of the rammed pile sequentially comprises an impact soil body, a compaction soil body and a cement sand mixture from outside to inside, the impact soil body, the compaction soil body and the cement sand mixture have small bonding force, the overall strength is low, particularly the impact soil body and the compaction soil body can gradually reduce the supporting capacity of the pile along with the release of construction stress and the influence of groundwater, the cement sand mixture is a dry matter, no water is mixed and stirred, the strength is low, the dispersibility is high, the overall stability of the rammed pile spherical carrier formed by the impact soil body, the compaction soil body and the cement sand mixture is poor, the long-acting performance is poor, and the later sedimentation of a building is easy to cause.

10. The soil quality of the bottom bearing layer of the prefabricated hollow pile extension pile provided by the construction method is generally composed of an undisturbed soil layer and construction disturbed virtual soil, for the extension pile with the pile bottom end entering the hard rock soil bearing layer to a certain depth, the pile bottom end entering the depth of the bearing layer is expanded by adopting a pre-drill bit, then drilling and grouting concrete, re-compaction drilling, drilling and grouting concrete, and finally sinking the prefabricated hollow pile to the designed elevation of the pile bottom. The design depth of the pile bottom end which can enter the hard rock-soil bearing layer is realized through the diameter expansion of the drill bit, and then the adverse effect of the virtual soil generated during the diameter expansion of the drill bit on the pile end bearing capacity is eliminated through the pressure-filling stirring by lifting the drill bit, the compaction drilling stirring by repeating the compaction drilling stirring by lifting the drill bit, meanwhile, the supporting strength of the original hard rock-soil bearing layer is maintained, the cost is saved, and the problem of difficult static pressure pile sinking of the hard rock-soil layer is also solved.

11. The construction method provided by the invention has the advantages of no slurry overflow, no noise or vibration, less soil discharge and good environmental protection.

Drawings

Fig. 1 is a schematic structural view of a prefabricated hollow pile extension pile according to the present invention.

Fig. 2 is a schematic structural view of an expanded pile of the prefabricated hollow pile according to the present invention.

Fig. 3 is a cross-sectional view A-A of fig. 2.

Fig. 4 is a schematic view showing a state in which a bit expansion body is extended and a bit door is opened in the screw drilling tool.

Fig. 5 is a schematic view showing a state in which a bit expansion body is retracted and a bit door is opened in the screw drill.

Fig. 6 is a schematic view showing a state in which a drill bit expanding body is retracted and a drill tip gate is closed in the screw drilling tool.

Fig. 7 is a schematic view showing a state in which a bit expansion body is extended and a bit door is closed in the screw drilling tool.

Fig. 8 is a schematic view of a construction state.

Fig. 9 is a schematic diagram of a construction state two.

Fig. 10 is a three schematic views of the construction state.

Fig. 11 is a schematic view of the construction state four.

Detailed Description

Embodiment of prefabricated hollow pile extension pile and construction method

1. Structure of prefabricated hollow pile extension pile

As shown in fig. 1, 2 and 3, a prefabricated hollow pile extension pile comprises a prefabricated hollow pile (10), at least one enlarged body (20), and a bottom reinforcement section bearing layer (30).

In the prefabricated hollow pile extension pile, the outer surface of the prefabricated hollow pile (10) is not provided with a concrete layer except for a bottom reinforcing section bearing layer (30) and an expansion body (20).

The inner cavity of the prefabricated hollow pile (10) is fully or partially filled with concrete (11). Preferably, in the present embodiment, the bottom end of the prefabricated hollow pile (10) is provided with a prefabricated back taper type hollow pile tip (12). Preferably, the prefabricated hollow pile (10) is any one of a concrete prefabricated pile, a steel member prefabricated pile, a steel pipe concrete prefabricated pile, a prefabricated pile produced by renewable degradable raw materials, a prefabricated pile produced by bionic low-carbon building materials and a prefabricated pile produced by industrial slag serving as a building material, and the cross section of the prefabricated hollow pile is hollow round or hollow polygonal. Preferably, in the present embodiment, the precast hollow pile (10) is a concrete precast pile as an exemplary illustration. Preferably, the prefabricated back taper hollow pile tip (12) can be a high strength concrete prefabricated member or a steel member.

The enlarged body (20) surrounds part of the outer surface of the prefabricated hollow pile (10) and is fixed with the prefabricated hollow pile into an integral structure. Preferably, in the embodiment, the expanding body (20) comprises a concrete annular body (21) with a radial outer contour in a threaded shape and a concrete-soil mixing layer (22), the concrete annular body (21) surrounds the outer surface of the prefabricated hollow pile (10) and is fixedly integrated with the prefabricated hollow pile (10), and the concrete-soil mixing layer (22) is arranged outside the concrete annular body (21) and is fixedly integrated with the concrete annular body (21). The enlarged body is compacted at least twice. When the expansion pile is displaced by vertical limiting pressure, a slip crack failure interface between pile and soil occurs on a joint surface between the outer side of the radial mixed layer of the expansion body and surrounding soil, and acting force between the expansion pile and the surrounding soil is in a stress state mainly based on the shear strength of the surrounding soil.

As shown in fig. 1, as an exemplary illustration, the precast hollow pile extension pile includes an enlarged body (20).

As shown in fig. 2, as an exemplary illustration, the prefabricated hollow pile extension pile includes two enlarged bodies (20), and the two enlarged bodies (20) are connected together by the prefabricated hollow pile (10).

Of course, more than 2 enlarged bodies (20) can be arranged according to actual needs, such as three, four or five. The expansion bodies (20) can be arranged at any position of the pile body of the prefabricated hollow pile (10), and two adjacent expansion bodies (20) are connected into a whole through the prefabricated hollow pile (10).

The reinforcing section bearing layer (30) is arranged at the bottom of the prefabricated hollow pile (10), and the bottom of the prefabricated hollow pile (10) is wrapped by the bottom reinforcing section bearing layer (30) or penetrates through the reinforcing section bearing layer (30). Preferably, in the embodiment, the bottom reinforcement section bearing layer (30) wraps the bottom of the prefabricated hollow pile (10), the outer diameter of the bottom reinforcement section bearing layer (30) is larger than the outer diameter or the outer edge diagonal dimension of the prefabricated hollow pile (10), and the vertical height of the bottom reinforcement section bearing layer is not smaller than 1-5 times the outer diameter or the outer edge diagonal dimension of the prefabricated hollow pile (10). The depth of the bottom end of the prefabricated hollow pile (10) into the bearing layer (30) of the bottom reinforcement section is 0.5-2 times of the outer diameter or the outer edge diagonal dimension of the prefabricated hollow pile (10). Preferably, part or all of the bottom reinforcement section bearing layer (30) is a mixed reinforcement of concrete and soil in a compacted state.

The expansion body in the expansion pile, the bearing layer of the bottom reinforcement section and the concrete used for prefabricating the inner cavity of the hollow pile are ultra-fluid micro-expansion concrete.

2. Construction method of prefabricated hollow pile extension pile

The construction method of the external prefabricated hollow pile is adopted, and in the construction process, a spiral drilling tool (40) is concentrically inserted into an inner hole cavity of the prefabricated hollow pile (10); in the process of spiral soil extrusion drilling and sinking of the prefabricated hollow pile (10), the cone soil extrusion part at the bottom end of the spiral soil extrusion drill head at the lower end of the spiral drilling tool (40) is always kept to extend out of the bottom end of the prefabricated hollow pile (10), and the method is as follows:

a combined device of a static pressure pile sinking device and a pressure pile filling device is adopted, and a spiral drilling tool (40) with the working state shown in fig. 4-7 is adopted.

The device for constructing the soil squeezing and pile grouting of the spiral part is arranged on the static pressure pile machine platform and comprises a column tower, a power head, a spiral drilling tool, a concrete pouring device, a winch, a control system and the like. The side of the column tower is provided with a pair of vertical guide rails for installing and fixing a power head, the guide rails are always vertical to a static pressure pile driver platform, the power head is in sliding fit with a track of the column tower, a winch and a steel wire rope are utilized to control the power head to move up and down along the track of the column tower, the output end of the power head is connected with the top end of a spiral drilling tool, the spiral drilling tool consists of a spiral drill rod and a spiral soil extrusion drill bit, a concrete filling pipe is arranged in the spiral drilling tool, the bottom end part of the spiral soil extrusion drill bit is a cone soil extrusion part, an extendable and retractable expanding body device controlled by hydraulic pressure is arranged, and the maximum opening angle of a drill tip door of the drill bit is beta, and beta=40 degrees; the bottom end of the column tower is movably connected with the static pile machine platform in a certain range, and is controlled by hydraulic pressure, and two fixable locking stations are arranged: the first is to keep the center of the spiral drilling tool coincident with the pile center when the static pile driver is driven; and secondly, the station for hoisting the precast pile into the inner hole of the pile holder by the static pile machine is not influenced by the power head and the spiral drilling tool.

1. Preparation and drilling

A pile sinking device of a static pile machine is used for straightening and lowering a prefabricated hollow pile (10) with a pile tip (12).

A spiral drilling tool (40) is concentrically inserted into an inner hole cavity of a prefabricated hollow pile (10) through a spiral soil squeezing and pile filling construction device.

The prefabricated hollow pile (10) with the pile tip (12) is aligned to the pile position as shown in fig. 8 (a).

The screw drill is concentrically inserted into the inner cavity of the prefabricated hollow pile (10) to the ground surface as shown in fig. 8 (b).

The power head is started to drive the spiral drilling tool to rotate and move downwards in the drilling direction, then the static pressure pile machine is started to sink the prefabricated hollow pile, and in the process of spiral soil squeezing drilling and sinking the prefabricated hollow pile (10), the cone soil squeezing part at the bottom end of the spiral soil squeezing drilling head at the lower end of the spiral drilling tool is kept below the pile tip (12) all the time, as shown in (c) and (d) of fig. 8.

In this step, if the sinking prefabricated hollow pile passes through the hard interlayer (such as hard plastic cohesive soil, compact sand, broken stone, strong weathered rock, etc.), the diameter-enlarging body in the spiral soil-squeezing drill bit can partially extend, the circle formed by the maximum outer edge of the diameter-enlarging body after extending is kept not larger than the outer circle or side length of the prefabricated hollow pile, the diameter-enlarging hole is formed when the spiral drill is drilled down, the pressure required by the static pressure sinking pile passing through the hard interlayer is reduced, and the sinking pile passing through the hard interlayer is completed.

2. Formation of an enlarged body (20)

Sinking the prefabricated hollow pile (10) to the top elevation of the first enlarged body (20), and stopping sinking the prefabricated hollow pile (10), as shown in (e) of fig. 9. The spiral drilling tool continues drilling until the cone soil squeezing part at the bottom end of the spiral soil squeezing drill bit reaches the bottom elevation of the first expansion body, the drilling tool is kept rotating, the concrete conveying pump is started to press and irrigate concrete into the inner cavity of the spiral drilling tool to the inner cavity of the drill bit, meanwhile, the drill bit expansion body is driven to extend out, the diameter of a circle formed by extending out expansion body expansion is larger than the outer diameter or the outer edge diagonal dimension of the prefabricated hollow pile, the continuously rotating spiral drilling tool is lifted again, the extending expansion body extrudes the rock hole wall to form a ladder-shaped spiral groove, the concrete in the inner cavity of the spiral drilling tool presses and opens a drill tip door, the pile hole formed by filling the soil squeezing drill and the spiral groove formed by the expansion body are kept, under the condition that the lifting drill and the expansion body extrudes the rock hole wall to form the spiral groove, the compression irrigation is formed into a concrete ring body with the outer contour of a screw thread shape under the condition that the lifting drill and the compression irrigation is matched with the lifting drill and the expansion body until the top elevation of the first expansion body is reached, retrieving the expanding body, continuing to drill and press the height value of a cone soil squeezing part of the drill bit, stopping drilling and pressing the drill bit, releasing the continuously rotating drilling tool downwards, rotating the drilling tip door to close the drilling tool concrete pouring passage opening under the upward action of the pressure concrete below, limiting the concrete poured into the pile hole to flow back into the inner cavity of the drilling tool, drilling the rotating drill bit cone soil squeezing part for compaction concrete, radially squeezing the extruded concrete threaded pile section to expand the surrounding soil cavity, extruding a small amount of concrete into the surrounding soil, simultaneously starting the static pile pressing machine after the drill bit cone soil squeezing part exposes the back taper type precast pile tip at the bottom end of the precast hollow pile, sinking the precast hollow pile, radially squeezing the concrete expanding diameter of the back taper type pile tip at the bottom end of the precast hollow pile again, further squeezing the surrounding rock soil cavity, and a small amount of concrete is extruded into the surrounding soil again, and in the process of drilling tool extrusion concrete expanding drilling and pile sinking extrusion concrete expanding, the cone soil extruding part of the drill bit is always kept below the pile tip, and pile sinking is carried out until the elevation of the bottom of the first expansion body is reached, so that the construction of the first expansion body is completed, as shown in (e), (f) and (g) in fig. 9. And continuing spiral soil extrusion drilling and pile sinking, keeping the cone soil extrusion part of the drill bit below the pile tip all the time, pile sinking to the top elevation of the second expansion body of the expansion pile, stopping pile sinking, repeating the construction process of the first expansion body, forming the second expansion body, and so on, and forming a plurality of expansion bodies.

3. Formation of a bottom reinforcing section bearing layer (30)

The cone soil squeezing part of the drill bit is kept below the pile tip, the spiral soil squeezing drilling and sinking of the prefabricated hollow pile (10) are continued until the top of the bearing layer (30) of the bottom reinforcing section is stopped, and at the moment, the top of the prefabricated hollow pile is kept higher than the top design elevation of the extension pile; starting the drill bit expanding body to extend again, enabling the diameter of a circle formed by extending the diameter of the extending expanding body to be larger than the outer diameter or the diagonal dimension of the outer edge of the prefabricated hollow pile, continuously rotating and downwards moving the drilling tool to drive the expanding body to perform expanding drilling, conveying part of the soil body which is cut by rotation from bottom to top along the spiral drilling tool, and remaining part of the soil body in the expanded hole cavity, extruding the soil to expand drilling to the bottom elevation of the bottom reinforcement section bearing layer (30), starting the concrete conveying pump to fill concrete, slowly lifting the continuously rotating drilling tool, opening the tip gate of the pressure concrete in the inner cavity of the drilling tool, pouring the pressure concrete into the hole cavity formed by drilling expansion, mixing the pressure concrete with the soil body which is reserved in the hole cavity under the stirring action of the rotating expanding body, lifting the drilling tool, pressing and stirring the soil body to the top elevation of the bottom reinforcement section bearing layer (30), stopping lifting the drilling tool and pressing the drilling tool, and downwards releasing the continuously rotating drilling tool, closing the drilling tool concrete pouring channel opening under the action of the concrete and soil mixture, extruding the mixture of the concrete and the soil by the cone extruding part of the drill bit, extruding and expanding the surrounding rock soil wall, stirring the concrete and the soil by the diameter expanding body, further mixing, extruding, drilling and stirring until the bottom elevation of the reinforcing section of the bearing layer is stopped, pumping and pouring the concrete and lifting the drill again, pouring the concrete into the cavity formed by extruding and densely drilling, simultaneously continuously stirring the concrete in the cavity with the diameter expanding body, mixing the drill lifting, pressing and stirring until the top elevation of the reinforcing section of the bearing layer, withdrawing the diameter expanding body, continuously lifting and pressing the drill by 1-1.5 m, stopping lifting and pressing the drill, downwards releasing the height value of the drill tool by 1-1.5 m, closing the drilling tool, stopping the downward movement and rotation of the drill bit, and starting the static pressure pile sinking device to sink the prefabricated hollow pile, satisfying the pile top elevation of the extension pile, and forming a bottom reinforcement section bearing layer (30) at the bottom of the prefabricated hollow pile in the pile sinking process, wherein (h), (i), (j), (k), (l) and (m) are shown in fig. 10. The concrete of the drill bit pressure filling is micro-expansion concrete.

4. Screw drilling tool

If the spiral drilling tool is directly lifted out of the inner cavity of the prefabricated hollow pile, the construction of the extension pile with the concrete poured into the inner hole cavity of the prefabricated hollow pile is completed, as shown in (n), (o) and (q) in fig. 11.

If the drilling pressure concrete filling is continued until the prefabricated hollow pile is lifted, then a reinforcement cage is placed in the prefabricated hollow pile, and the construction of the extension pile with all concrete filled into the inner hole cavity of the prefabricated hollow pile is completed, as shown in (p) of fig. 11. The concrete of the drill bit pressure filling is micro-expansion concrete.

In the step, the bottom bearing layer is a hard rock soil layer, and the bottom end of the extension pile enters the bearing layer to a certain depth: static pressure pile sinking is stopped at the bearing layer of hard rock soil, the top of the prefabricated hollow pile is kept higher than the top design elevation of the extension pile, the diameter-enlarging body of the drill bit is started to extend, the diameter of a circle formed by diameter enlargement of the diameter-enlarging body is larger than the outer diameter or the diagonal dimension of the outer edge of the prefabricated hollow pile, the drill bit which continuously rotates and moves downwards drives the diameter-enlarging body to perform diameter-enlarging drilling, part of the soil body which is cut in rotation is conveyed from bottom to top along a spiral drilling tool, part of the soil body which is cut down remains in the hole cavity with the enlarged diameter, the diameter-enlarging drilling depth exceeds the design depth value of the bottom of the extension pile into the bearing layer by 100-500 mm, the concrete conveying pump is started firstly, then the continuously rotating drilling tool is slowly lifted, the pressure concrete in the cavity of the drilling tool is opened, the drilling tip door is poured into the hole cavity formed by the diameter-enlarging body, the soil body which remains in the hole cavity is mixed under the stirring action of the rotating diameter-enlarging body, the drilling tool is lifted, the drilling tool is pressed and stirred to the bearing layer top elevation, stopping lifting and pressing the drill, then downwards releasing the continuously rotating drilling tool, closing the drilling tool concrete pouring channel opening by the drill tip door under the action of the concrete and soil mixture, extruding the concrete and soil mixture by the cone soil extruding part of the drilling tool, extruding surrounding rock soil wall, further mixing the concrete and soil body by the diameter expanding body, extruding and drilling, stirring to the depth of the first drilling bearing layer, pumping and pouring the concrete and lifting the drill again, pouring the concrete into the hole cavity formed by the compaction and drilling, simultaneously continuously stirring the concrete in the hole cavity with the diameter expanding body, mixing the concrete and the concrete, lifting, pressing and pouring, recovering the diameter expanding body, continuously lifting and pressing the drill with the height of 1-1.5 m, stopping lifting and pressing the drill, downwards releasing the drilling tool with the height of 1-1.5 m, closing the drill tip door of the drilling tool under the drilling tool, stopping the downward moving and rotating the drilling tool, and then starting the static pressure pile sinking device to sink the prefabricated hollow pile downwards to enter the design depth of the rigid rock-soil bearing layer and meet the pile top elevation of the extension pile, and in the pile sinking process, the bottom of the prefabricated hollow pile enters the design depth of the bearing layer and compacts the mixture of the bottom concrete and the rock-soil, as shown in fig. 11 (q).

3. Bearing and using principle of prefabricated hollow pile extension pile

1. Bearing principle of extension pile

The expansion body in the expansion pile is formed by extruding the cast-in-place concrete threaded pile section twice and is composed of an inner concrete annular body and a peripheral concrete-soil mixed layer, and the radial outer contour of the expansion body is in a threaded shape. After solidification, the inner annular body and the prefabricated hollow pile are firmly integrated, and the peripheral mixed layer and the inner annular body are firmly integrated. The surrounding soil of the expansion body is in a compaction state, the side surface of the expansion body is in a thread shape and is in compaction combination with the surrounding soil, the annular external thread of the expansion body is in embedded combination with the surrounding soil through a mixed layer, when the expansion pile is displaced by vertical limiting pressure, a slip crack damage interface between the expansion body and the surrounding soil occurs on the outer profile surface of the expansion body, namely, the outer profile surface of the mixed layer of the expansion body, and the slip crack damage interface has few concrete components and is distributed discretely, mainly comprises the surrounding soil components in the compaction state, so that the side resistance of the expansion body is represented as the shearing resistance of the soil and is larger than the friction resistance between the concrete pile and the soil; in general, the shear strength of the soil is 1.4 to 2.0 times of the friction resistance between the concrete piles and the soil; the side resistance of the screw pile is larger than that of the screw pile, and the screw pile does not accord with the calculation of the side resistance according to the shearing strength of the surrounding soil of the pile completely because the slip crack damage interface of the screw pile is provided with the screw surface with the outer diameter of the concrete screw thread and occupies a certain slip crack interface area ratio, and the friction resistance between the concrete pile and the soil exists. The outer diameter of the expansion body is larger than the outer diameter or diagonal dimension of the prefabricated hollow pile, the soil at the lower end of the expansion body is formed by twice compaction of the soil compaction part of the drill bit cone and the pile tip, and the expansion body can generate new end resistance. The expansion bodies of the single sections in the expansion pile are integrated by penetrating the prefabricated hollow pile, the end face of the expansion body with high strength is large, the end resistance is good, the end bearing capacity of the expansion pile is improved, and the expansion pile is used as a foundation pile, so that the problem that the pile body of the prefabricated pile cannot be provided with the expansion body with high strength is solved. The reinforcement thickness of the bearing layer is determined according to the hardness of the soil of the lower lying layer, when the lower lying layer is a soft soil layer, the thickness of the bearing layer of the reinforcement treatment of the bottom end of the extension pile is usually not less than 3 times of the outer diameter or the diagonal dimension of the outer edge of the prefabricated hollow pile, and when the lower lying layer is not provided with the soft soil layer, the thickness of the bearing layer of the reinforcement treatment of the bottom end of the pile is usually 1-2 times of the outer diameter or the diagonal dimension of the outer edge of the prefabricated hollow pile, thereby being beneficial to the improvement of end bearing; when the bearing layer is a hard rock soil layer, the original bearing layer at the bottom end of the pile does not need reinforcement treatment, the depth of the pile bottom entering the bearing layer is realized by expanding the diameter, and meanwhile, concrete is pressed and poured.

2. Use principle of extension pile

The positions and the number of the expansion bodies in the pile body are not fixed, the expansion pile can be selected and designed according to the requirements of the surrounding soil property and the bearing capacity of the pile, and the construction method of the expansion pile can meet the pile forming requirements of various expansion pile structures and realize the optimal design. Because the bearing capacity design value of the pile cannot be larger than the pile body strength, when the bearing capacity of foundation soil to the extension pile is larger than the pile body strength of the prefabricated hollow pile, in order to not waste bearing resources of the foundation soil, the pile body strength is improved by a method of pressing and pouring concrete into an inner hole cavity of the prefabricated hollow pile to form a solid pile, so that the bearing capacity design value of the extension pile is improved.

Claims

1. The construction method of the prefabricated hollow pile extension pile is characterized in that an external construction method of the prefabricated hollow pile is adopted, and in the construction process, a spiral drilling tool (40) is concentrically inserted into an inner hole cavity of the prefabricated hollow pile (10); in the process of spiral soil extrusion drilling and sinking the prefabricated hollow pile (10), the cone soil extrusion part at the bottom end of the spiral soil extrusion drill head at the lower end of the spiral drilling tool (40) always extends out of the bottom end of the prefabricated hollow pile (10).

2. A method of constructing a precast hollow pile extension pile according to claim 1, comprising the steps of:

1) Preparation and drilling

Aligning the prefabricated hollow pile (10) to the pile position; inserting a spiral drilling tool (40) with a soil squeezing drill bit concentrically into an inner cavity of the prefabricated hollow pile (10) to the ground surface; in the process of spiral soil extrusion drilling and sinking of the prefabricated hollow pile (10), keeping a cone soil extrusion part at the bottom end of an earth extrusion drill bit at the lower end of a spiral drilling tool below the bottom end of the prefabricated hollow pile (10) all the time, and carrying out partial soil extrusion drilling on soil in the range of an inner hole cavity of the prefabricated hollow pile on a pile hole site;

2) Formation of an enlarged body (20)

Sinking the bottom end of the prefabricated hollow pile (10) to the top end of the first expansion body (20), continuously drilling the spiral drilling tool (40) to the bottom end of the first expansion body, keeping the drilling tool rotating, starting the concrete conveying pump to press and fill concrete into the cavity of the spiral drilling tool, driving the diameter-expanding body of the drill bit to extend, forming a circular diameter larger than the outer diameter or the diagonal dimension of the outer edge of the prefabricated hollow pile (10) by the outer edge of the extending diameter-expanding body, lifting the rotating drilling tool, pressing and filling the cavity formed by the soil-squeezing drilling and the spiral groove formed by the diameter-expanding body until the top end of the first expansion body is raised, forming a concrete screw pile section with the expanded diameter, recovering the diameter-expanding body, continuously lifting and pressing the drill bit to be not less than the height value of a cone soil-squeezing part of the drill bit, stopping lifting and pressing and filling, then downward releasing the continuously rotating drilling tool, after the bit cone soil squeezing part passes through the bottom end face of the prefabricated hollow pile (10), firstly squeezing and expanding the concrete screw pile section, then sinking the prefabricated hollow pile (10), squeezing and expanding the concrete screw pile section again at the bottom end of the prefabricated hollow pile (10), keeping the screw drilling tool (40) to drill and the prefabricated hollow pile (10) sinking to the first expansion body bottom elevation, in the process, keeping the bit cone soil squeezing part always below the bottom end face of the prefabricated hollow pile (10), forming a concrete ring-shaped body (21) of the expansion body by squeezing and compacting the concrete screw pile section twice, simultaneously, squeezing part of concrete into the soil contacted with the concrete ring-shaped body to form a concrete-concrete mixing layer (22), wrapping the prefabricated hollow pile (10) on the inner surface of the concrete ring-shaped body (21), the outer surface of the concrete annular body (21) is wrapped by a compacted concrete-soil mixed layer (22), the construction of a first expansion body is completed, and the like, so that the formation of a plurality of expansion bodies is realized;

3) Formation of a bottom reinforcing section bearing layer (30)

Continuously sinking the prefabricated hollow pile (10) to the top mark height of the support layer (30) of the reinforcement section of the bottom of the expansion pile, keeping the top height of the prefabricated hollow pile higher than the top design elevation of the expansion pile at the moment, simultaneously starting the drill bit expanding body to extend out for expanding drilling when the spiral soil squeezing drilling is carried out to the top elevation of the support layer (30) of the reinforcement section of the bottom of the expansion pile, and forming a circle with the diameter larger than the outer diameter or the diagonal dimension of the outer edge of the prefabricated hollow pile until the bottom elevation of the support layer (30) of the reinforcement section of the bottom of the expansion pile is stopped; starting a concrete conveying pump to pump concrete, slowly lifting a continuously rotating drilling tool, opening a drilling tip door to pour the pressurized concrete in the inner cavity of the drilling tool into a hole cavity formed by expanding drilling, under the stirring action of a rotating expanding body, mixing the pressurized concrete with soil reserved in the hole cavity, lifting the drilling tool, pressing the drilling tool, stirring the pressurized concrete to the top elevation of a supporting layer (30) of a reinforcing section of the expanded pile bottom, stopping lifting the drilling tool and pressing the drilling tool, downwards releasing the continuously rotating drilling tool, closing the drilling tip door, extruding a mixture of the concrete and the concrete by a cone extruding part of the drilling tool, extruding and expanding surrounding rock wall, further mixing the stirred concrete and the concrete, extruding and stirring the stirred concrete to the bottom elevation of the reinforcing section of the supporting layer of the pile bottom, pumping concrete and lifting the drill again, simultaneously continuously stirring the concrete and the soil in the hole with the diameter expanded by the rotating diameter expanded body, lifting the drill, pressing the drill, stirring until the top of the reinforcing section of the bearing layer at the bottom of the expanded pile is high, withdrawing the diameter expanded body, continuously lifting the drill and pressing the drill to the height of 1-1.5 m, stopping lifting the drill and pressing the drill, downwards releasing the drilling tool for 1-1.5 m, closing the drill point door of the drilling bit by the concrete below the drilling bit, stopping the downward movement and rotation of the drilling tool, sinking the prefabricated hollow pile again, and meeting the requirement of pile top elevation stop of the expanded pile, wherein the bottom of the prefabricated hollow pile is sunk into the bearing layer (30) of the reinforcing section for a certain depth or penetration at the moment;

4) Screw drilling tool

3. A method of constructing a precast hollow pile extension pile according to claim 2, comprising the steps of: in the step 1), when the soil squeezing drill bit is used for partially squeezing soil and drilling, the diameter expanding body of the drill bit can partially extend out, and the diameter of a circle formed by the extending outer edge of the drill bit is not larger than the outer diameter of the prefabricated hollow pile or the diagonal dimension of the outer edge.

4. A method of constructing a precast hollow pile extension pile according to claim 2, wherein the precast hollow pile bottom end is provided with a back taper type hollow pile tip (12) having an internal hollow section of the same size as the section of the bore of the precast hollow pile.

5. A prefabricated hollow pile extension pile formed according to the extension pile construction method of claim 2 or 3 or 4, comprising a prefabricated hollow pile (10), characterized in that the outer surface of the prefabricated hollow pile (10) is provided with a bottom reinforcement section bearing layer (30) and at least one enlarged body (20); the outer surface of the prefabricated hollow pile (10) is not provided with a concrete layer except for a bottom reinforcing section bearing layer (30) and an expansion body (20).

6. A precast hollow pile extension pile according to claim 5, characterized in that the extension body (20) comprises a concrete ring body (21) with a radial outer contour in a screw thread shape and a concrete-concrete mixing layer (22), the concrete ring body (21) surrounding the outer surface of the precast hollow pile (10) and being fastened to the precast hollow pile (10) in an integral structure, the concrete-concrete mixing layer (22) surrounding the concrete ring body (21) and being fastened to it in an integral structure; the inner cavity of the prefabricated hollow pile (10) is fully or partially filled with concrete (11); the bottom reinforcing section bearing layer (30) is arranged at the bottom of the prefabricated hollow pile (10), the transverse section of the bottom reinforcing section bearing layer is larger than that of the outer surface of the prefabricated hollow pile, and the bottom of the prefabricated hollow pile (10) enters the reinforcing section bearing layer (30) to a certain depth or penetrates through the thickness of the reinforcing section bearing layer (30).

7. A precast hollow pile extension pile according to claim 6, characterized in that at least two enlarged bodies (20) are provided, the enlarged bodies (20) being arranged at any position of the pile body of the precast hollow pile (10), adjacent two enlarged bodies (20) being connected together by the precast hollow pile (10).

8. A precast hollow pile extension pile according to claim 6, characterized in that the outer diameter of the bottom reinforcing section bearing layer (30) is larger than the outer diameter or outer edge diagonal dimension of the precast hollow pile (10), and the vertical height thereof is not smaller than 1 to 5 times the outer diameter or outer edge diagonal dimension of the precast hollow pile (10).

9. A prefabricated hollow pile extension pile according to claim 6, characterised in that the reinforcement section bearing layer (30) wraps the bottom of the prefabricated hollow pile (10); the depth of the bottom end of the prefabricated hollow pile (10) into the bearing layer (30) of the reinforcing section is 0.5-2 times the outer diameter or the outer edge diagonal dimension of the prefabricated hollow pile (10).

10. The expansion pile of the prefabricated hollow pile according to claim 6, wherein the bottom end of the prefabricated hollow pile (10) is provided with a back taper type hollow pile tip (12) and is positioned with the bottom end of the prefabricated hollow pile (10).