A prefabricated micro steel pipe pile post-grouting composite foundation and a construction method thereof

Abstract

The present application belongs to the technical field of composite foundation, and discloses a prefabricated micro steel pipe pile post-grouting composite foundation and a construction method thereof. In order to solve the problem that the bearing capacity of the micro steel pipe pile composite foundation is poor due to the low strength of the core area. The present application comprises a prefabricated micro steel pipe pile implanted in a pile hole in the stratum or a prefabricated micro steel pipe pile directly implanted in the stratum. The prefabricated micro steel pipe pile comprises a seamless steel pipe, a plurality of grouting ports are formed on the circumferential wall of the seamless steel pipe, a grouting flower pipe is inserted into the seamless steel pipe, a prefabricated fine stone concrete layer is arranged between the grouting flower pipe and the seamless steel pipe, a jet flow channel for connecting the grouting hole on the grouting flower pipe and the grouting port on the seamless steel pipe is formed in the prefabricated fine stone concrete layer, and a concrete layer is poured in the grouting flower pipe, between the grouting flower pipe and the soil body of the stratum through the jet flow channel.

Description

Technical Field

[0001] This invention belongs to the field of steel pipe pile technology, specifically relating to a precast micro steel pipe pile post-grouting composite foundation and its construction method. Background Technology

[0002] Deep fill is extremely common in current construction projects, especially in hilly areas. Site leveling often involves digging mountains and filling ditches, resulting in uneven distribution of backfill thickness, messy backfill materials, and lack of compaction. After construction, the site often experiences large-scale settlement, ground delamination and cracking, and wall cracking, affecting operation.

[0003] The bearing capacity of micro steel pipe piles is generally similar to that of conventional pile foundations. However, in areas with high backfill, the compressive yield strength largely determines the bearing capacity of micro piles. Therefore, when micro steel pipe piles pass through thick layers of backfill, the buckling stability of the micro steel pipe piles must be considered, and piles with a large slenderness ratio are more prone to compressive yield failure.

[0004] Post-grouting is an auxiliary measure to address the large porosity of the surrounding fill. On the one hand, it fills the voids in the fill within the grouting influence area, forming a cemented structure layer; on the other hand, it increases the side friction resistance of the fill within the cemented layer and the influence radius, further improving the bearing capacity and stability of the micropiles.

[0005] Under vertical loads, the axial force of micro-steel pipe piles is mainly borne by the core concrete, and it gradually increases with the increase of load, with the curvature showing an upward trend. Therefore, one way to solve the buckling failure is to improve the strength of the core area of ​​the micro-steel pipe pile. Currently, there are two methods for micro-pile construction: one is to lower a seamless steel pipe after drilling, followed by grouting with cement slurry or cement mortar; the other is to form cement-soil through jet grouting, followed by inserting a seamless steel pipe. Both methods have the following problems: First, the core area strength is not high. Although pouring concrete into the core area can be considered, the small diameter of the micro-steel pipe pile makes pouring difficult, and vibration is impossible when the pile length is long. Second, the subsequent grouting is all pressure grouting at the borehole opening. Due to the overflow holes along the entire length, the pressure is high and the grouting effect is good near the grouting opening, while the grouting effect is extremely poor at the lower part farther from the opening. Therefore, this is also an important factor affecting the treatment effect. Currently, in the post-grouting process, grout is injected from the top of the grouting pipe. The grout outlet holes on the grouting pipe are distributed throughout the entire grouting pipe. Since the positions of each grout outlet hole are not the same, the amount of grout sprayed from each grout outlet hole is not uniform during the grouting process, resulting in poor grouting quality; which in turn leads to poor bearing capacity of the micro steel pipe pile composite foundation.

[0006] However, if pile foundations (such as concrete mixing piles and cast-in-place piles) are used to reinforce composite foundations to improve bearing capacity, the construction cost of pile foundations is high.

[0007] Therefore, how to improve the bearing capacity of micro steel pipe pile composite foundations under the premise of limited construction costs has always been a research direction for technicians in this field. Summary of the Invention

[0008] To address the problem of poor bearing capacity in existing micro-steel pipe pile composite foundations due to the low strength of the core area of ​​the micro-steel pipe piles, this invention provides a precast micro-steel pipe pile post-grouting composite foundation and its construction method. This method can improve the strength of the core area of ​​the steel pipe pile and the buckling stability of the steel pipe pile, thereby improving the bearing capacity of the micro-steel pipe pile composite foundation.

[0009] To solve the technical problem, the technical solution adopted by this invention is as follows:

[0010] A precast micro steel pipe pile post-grouting composite foundation is characterized by comprising precast micro steel pipe piles embedded in pile holes in the stratum or precast micro steel pipe piles directly embedded in the stratum. The precast micro steel pipe piles include seamless steel pipes, and a plurality of grouting nozzles are opened on the circumferential wall of the seamless steel pipes. A grouting perforated pipe is inserted into the seamless steel pipe. A precast fine stone concrete layer is provided between the grouting perforated pipe and the seamless steel pipe. A jetting channel is formed in the precast fine stone concrete layer to connect the grouting holes on the grouting perforated pipe and the grouting nozzles on the seamless steel pipe. Concrete layers are poured inside the grouting perforated pipe and between the grouting perforated pipe and the soil of the stratum through the jetting channel.

[0011] In some embodiments, the jet channel is arranged in a downward-sloping direction.

[0012] In some embodiments, the seamless steel pipe is provided with spherical or hemispherical protrusions on its periphery, with one protrusion corresponding to each grouting nozzle, and the protrusions are located at the lower edge of the grouting nozzle.

[0013] In some embodiments, spiral reinforcements embedded in the precast fine stone concrete layer are provided at both ends of the periphery of the grouting pipe near the seamless steel pipe.

[0014] In some embodiments, the pile hole extends into the bearing layer in the stratum, and the length of the precast micro steel pipe pile is adapted to the depth of the pile hole.

[0015] This invention also provides a construction method for a precast micro steel pipe pile post-grouting composite foundation, comprising the following steps:

[0016] (1) Prefabricated micro steel pipe piles are prepared in advance;

[0017] (2) Drill pile holes in the stratum according to the design location and insert precast micro steel pipe piles into the pile holes, or directly press precast micro steel pipe piles into the stratum according to the design location;

[0018] (3) Insert the post-grouting device into the grouting pipe of the precast micro steel pipe pile, connect the post-grouting device with the external grouting pipe and perform grouting; when grouting into the grouting pipe, the post-grouting device first fills the space in the grouting pipe below the post-grouting device with grout, and then injects grout into each grouting port within the height range of the grouting pipe corresponding to the post-grouting device; along the grouting pipe from bottom to top, grout is injected in a cyclic manner until the top of the grouting pipe is grouted, thus completing the grouting operation; after the post-grouting operation is completed, remove the post-grouting device;

[0019] (4) After the grout injected by the grouting device reaches the design strength, a mattress layer is constructed on the surface of the stratum.

[0020] In some embodiments, the post-grouting device includes an upper float plug and a lower float plug, which are connected together by a second pipe and have a gap. Both the upper and lower float plugs are equipped with air bladders that can seal against the grouting perforation pipe after the grout is filled. The upper float plug is connected to a first pipe for injecting grout, and the lower float plug is connected to a third pipe. The grout can enter the interior of the upper float plug and fill the air bladder, the interior of the lower float plug and the space between the air bladder and the lower float plug through the first, second and third pipes. The grout can also enter the grouting perforation pipe below the lower float plug.

[0021] In some embodiments, both the upper and lower floats include an upper cover plate and a lower cover plate, with a gap between them; an airbag connects the upper and lower cover plates, and both the upper and lower cover plates have through holes. These through holes are located closer to the outer edges of the upper and lower cover plates than the connection points between the airbag and the airbag, and the airbag can cover the through holes when filled with slurry, while exposing the through holes when the airbag is not fully filled with slurry. A sealed cavity is formed between the upper float and the airbag. A first pipe is connected to the upper cover plate of the upper float and communicates with the cavity of the upper float. The first pipe is used to connect to the grouting pipe. The upper end of the second pipe is fixedly connected to the upper cover plate of the upper float. The lower end of the second pipe passes through the lower cover plate of the upper float and the upper cover plate of the lower float in sequence and is then fixedly connected to the lower cover plate of the lower float. A third pipe is connected to the upper cover plate of the lower float and communicates with the cavity of the lower float. Several through holes are opened on the circumferential wall at the bottom of the second pipe located in the cavity of the upper and lower floats.

[0022] In some embodiments, the lower cover plate of the lower float plug has a discharge channel, a spring is installed at the bottom of the discharge channel, a piston is installed at the top of the spring and is sealed to the discharge channel, a feed channel is opened at the top of the piston, a through channel is opened inside the piston and communicates with the feed channel, and an outlet is provided on the lower cover plate of the lower float plug that can communicate with or disconnect from the through channel.

[0023] In some embodiments, the upper surface of the lower cover plate of the upper and lower floats is a spherical or hemispherical surface, and the second channel is connected to the middle of the arc groove.

[0024] In some embodiments, a counterweight is provided around the periphery of the first pipe extending from the upper cover of the upper float plug.

[0025] In some embodiments, the number of the third pipes is 1, 2, 3 or 4. When the number of the third pipes is 2, 3 or 4, the third pipes are evenly distributed on the upper cover of the lower float plug.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The precast micro-steel pipe pile post-grouting composite foundation of the present invention, through its structural design of seamless steel pipes, grouting perforated pipes, and a precast fine aggregate concrete layer poured between them, significantly improves the strength and bending resistance of the core area of ​​the micro-steel pipe piles under the reinforcement of the grouting perforated pipes and the precast fine aggregate concrete layer. This enhances the durability, buckling stability, and reliability of the micro-steel pipe piles, thereby increasing the bearing capacity of the composite foundation. Furthermore, compared to using pile foundations to reinforce the strata (mainly soft strata), this invention significantly reduces construction costs and time. This is because the micro-steel pipe piles are precast, and the amount of grout poured is reduced compared to pile foundations, thus shortening the construction period. Additionally, when dealing with silty soil strata, the invention allows for direct injection of precast micro-steel pipe piles (i.e., eliminating the need to drill pile holes in the strata), further shortening the construction period.

[0028] In summary, the precast micro steel pipe pile post-grouting composite foundation provided by this invention has the characteristics of low construction cost and high bearing capacity.

[0029] The downward-sloping jet channel design of the precast micro-steel pipe piles in this invention, compared to the horizontally opened design of existing technologies, allows for increased impact force on the soil when the grout is ejected from the inclined jet channel, due to the pressure of the grout itself and the clamping effect of gravity. Compared to existing structures, under the same grout pressure, this invention exerts a greater impact force on the soil, increases the compressive strength on the soil sidewalls, and results in a larger outer diameter concrete layer, thereby further improving the bearing capacity of the composite foundation.

[0030] This invention features a protrusion at the lower edge of the grouting nozzle. When the stratum is silty soil, the precast micro steel pipe pile can be directly pressed into the silty soil. The protruding structure design can prevent the soil from clogging the grouting nozzle, solving the problem of easy clogging of the grouting hole when directly pressing the grouting pipe in the prior art. This ensures the smooth flow of each grouting nozzle and improves the quality of subsequent grouting.

[0031] In the operation of the post-grouting device of the present invention, the upper and lower float plugs are first placed at appropriate positions on the grouting perforation pipe, such that the grouting hole of the grouting perforation pipe to be grouted is located between the upper and lower float plugs. Then, grout is injected into the first pipe. The grout enters the cavity of the upper float plug along the first pipe, and then enters the second pipe through the through hole and into the cavity of the lower float plug. The grout in the cavity of the lower float plug first passes through the discharge channel, the piston feed channel, and the piston through channel, and then is ejected through the spray outlet of the lower float plug to fill the grouting perforation pipe below the lower float plug (at this time, the piston through channel is connected to the spray outlet of the lower float plug), thereby filling the lower float plug. The grouting pipe below the lower float plug is filled to prevent voids from forming. After the grouting pipe below the lower float plug is filled, as the grout pressure increases, the piston inside the lower cover plate of the lower float plug gradually slides down under the grout pressure, thus disconnecting the through channel from the nozzle. This allows the grout to fill the air bladder of the lower float plug, causing the air bladder to expand and make close contact with the inner wall of the grouting pipe. At the same time, the counterweight stabilizes the entire device inside the grouting pipe. As more and more grout is injected, it flows out from the third pipe and fills the gap between the upper and lower float plugs. Then, the grout is injected into the formation through the grouting holes on the grouting pipe. After the grouting of the grouting pipe section is completed, grouting is stopped, and the entire device (i.e., the upper and lower floating plugs) is slowly lifted upwards. As the grout pressure inside the upper and lower floating plugs decreases, the piston inside the lower cover of the lower floating plug moves upwards, causing the through channel on the piston to reconnect with the spray outlet of the lower cover, thereby filling the space below the lower floating plug with grout. That is, when the upper and lower floating plugs are lifted upwards, the grout will automatically fill the space that the upper and lower floating plugs have moved out of. This cycle is repeated to complete the grouting of the entire grouting pipe. During use, the piston inside the lower cover of the lower float plug automatically adjusts according to changes in slurry pressure, allowing the nozzle inside the lower cover to be disconnected from or connected to the through channel. When the upper and lower float plugs move upward together, they automatically fill the area below the lower float plug with slurry. On one hand, the slurry fills the interior of the grouting pipe below the lower float plug, ensuring that the slurry sprayed from the grouting hole of the grouting pipe forms a unified whole with the slurry inside the grouting pipe, greatly improving the integrity of the subsequent grouting and enhancing the grouting quality. On the other hand, it avoids the negative pressure formed at the lower end of the lower float plug when the upper and lower float plugs are moved, preventing grouting cracks caused by backflow of slurry sprayed through the grouting hole under negative pressure, further improving the molding quality.

[0032] Furthermore, during use, the grout first fills the grouting pipe below the lower float plug through the first, second, and third pipes, then fills the air bladder of the lower float plug, and finally fills the air bladder of the upper float plug. This allows air between the upper and lower float plugs to be discharged through the through hole, preventing voids in the grout due to air retention and improving the quality of grouting. As mentioned in the background section of this application, in the prior art, the sealing effect of the grouting plug prevents complete air release, leading to voids in the solidified grout. This invention avoids voids caused by air retention (incomplete air release), further improving the quality of subsequent grouting. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the precast micro steel pipe pile post-grouting composite foundation of the present invention;

[0034] Figure 2 for Figure 1 A schematic diagram of the cross-sectional structure at point AA;

[0035] Figure 3 This is a schematic diagram of the prefabricated micro steel pipe pile of the present invention;

[0036] Figure 4 This is a schematic diagram of the structure of the present invention when post-grouting is performed on grouting pipes or steel pipes;

[0037] Figure 5 for Figure 4 A partial enlarged view of point A in the middle. In this view, the through channel on the piston is disconnected from the nozzle on the lower cover.

[0038] Figure 6 This is a schematic diagram showing the state when the through channel on the piston of the present invention is connected to the nozzle on the lower cover.

[0039] Figure 7 This is a schematic diagram of the connection state between the airbag and the upper and lower cover of the present invention. In this schematic diagram, the airbag is in an uninflated state, thus exposing the through hole.

[0040] The markings in the diagram are as follows: 01, stratum; 101, weak layer; 102, bearing layer; 02, grouting pipe; 03, grouting hole; 04, grouting pipe; 05, seamless steel pipe; 06, precast fine stone concrete layer; 07, grouting nozzle; 08, jetting channel; 09, concrete layer; 010, mattress layer; 011, foundation; 012, spiral reinforcement; 013, protrusion; 1, upper floating plug; 11, upper cover; 111, through hole; 112, mounting block; 12, airbag; 13, lower cover; 131, discharge channel; 132, piston; 133, feed channel; 134, through channel; 135, spray outlet; 136, spring; 2, lower floating plug; 3, first pipe; 4, second pipe; 41, through hole; 5, third pipe; 6, counterweight. Detailed Implementation

[0041] The present invention will be further described below with reference to embodiments. These embodiments are merely some, not all, of the embodiments of the present invention. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the protection scope of the present invention.

[0042] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. The terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, unless otherwise explicitly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention in conjunction with the specific circumstances.

[0043] Combined with appendix Figure 1 To be continued Figure 3The precast micro steel pipe pile post-grouting composite foundation of the present invention includes precast micro steel pipe piles implanted in pile holes in stratum 01 or precast micro steel pipe piles directly implanted in stratum 01. The precast micro steel pipe pile includes a seamless steel pipe 05. A plurality of grouting nozzles 07 are opened on the circumferential wall of the seamless steel pipe 05. A grouting perforated pipe 02 is inserted into the seamless steel pipe 05. A precast fine stone concrete layer 06 is provided between the grouting perforated pipe 02 and the seamless steel pipe 05. A jetting channel 08 is formed in the precast fine stone concrete layer 06 for connecting the grouting holes 03 on the grouting perforated pipe 02 and the grouting nozzles 07 on the seamless steel pipe 05. A concrete layer 09 is poured inside the grouting perforated pipe 02 and between the grouting perforated pipe 02 and the soil of stratum 01 through the jetting channel 08.

[0044] The precast micro-steel pipe pile post-grouting composite foundation of the present invention, through its structural design of seamless steel pipes, grouting perforated pipes, and a precast fine aggregate concrete layer poured between them, significantly improves the strength and bending resistance of the core area of ​​the micro-steel pipe piles under the reinforcement of the grouting perforated pipes and the precast fine aggregate concrete layer. This enhances the durability, buckling stability, and reliability of the micro-steel pipe piles, thereby increasing the bearing capacity of the composite foundation. Furthermore, compared to using pile foundations to reinforce the strata (mainly soft strata), this invention significantly reduces construction costs and time. This is because the micro-steel pipe piles are precast, and the amount of grout poured is reduced compared to pile foundations, thus shortening the construction period. Additionally, when dealing with silty soil strata, the invention allows for direct injection of precast micro-steel pipe piles (i.e., eliminating the need to drill pile holes in the strata), further shortening the construction period.

[0045] In summary, the precast micro steel pipe pile post-grouting composite foundation provided by this invention has the characteristics of low construction cost and high bearing capacity.

[0046] In the implementation of this invention, whether the precast micro steel pipe pile is installed in the stratum 01 by constructing a pile hole and then inserting it, or the precast micro steel pipe pile is directly inserted into the stratum 01 by pressing, the precast micro steel pipe pile should pass through the weak layer 101 in the stratum 01 and extend into the bearing layer 102 of the stratum 01.

[0047] Combined with appendix Figure 1 and attached Figure 2 Preferably, one end of the grouting perforated pipe 02 extends out of the seamless steel pipe 05, thereby facilitating grouting through the grouting perforated pipe. After grouting is completed through the grouting perforated pipe 02, the grouting perforated pipe 02 extending out of the seamless steel pipe 05 extends into the mattress layer 010. This invention, by extending the grouting perforated pipe 02 with the seamless steel pipe 05 extending into the mattress layer 010, can further improve the bearing capacity of the entire composite foundation.

[0048] Combined with appendix Figure 2To improve the uniformity of post-grouting, three grouting channels 09 are connected at the same height position of the grouting pipe 02. That is to say, there are 3 grouting holes 03 on the grouting pipe 02 at the same height position, and each grouting hole 03 corresponds to one grouting channel 09. Correspondingly, there are also 3 grouting nozzles 07 at the same height position.

[0049] In some embodiments, the jetting channel 08 is arranged in a downwardly inclined direction. The downwardly inclined arrangement described in this invention refers to the jetting channel 08 being arranged downwardly when the precast micro-steel pipe pile is implanted into the stratum 01. Compared to the horizontally opened method used in the prior art, the downwardly inclined design of the jetting channel on the precast micro-steel pipe pile of this invention increases the impact force on the soil in the stratum when the grout is ejected from the inclined jetting channel, under the pressure of the grout itself and the clamping effect of gravity. Compared to the structure of the prior art, under the same grout pressure, this invention exerts a greater impact force on the soil, improves the squeezing capacity of the soil sidewalls, and results in a larger outer diameter of the formed concrete layer, thereby further improving the bearing capacity of the composite foundation.

[0050] In some embodiments, the seamless steel pipe 05 is provided with a spherical or hemispherical protrusion 013 on its periphery. Each grouting port 07 is provided with a corresponding protrusion 013, and the protrusion 013 is located at the lower edge of the grouting port 07. The lower edge mentioned in this invention refers only to the location of the protrusion 013 at the lower edge of the grouting port 07 when the precast micro-steel pipe pile is implanted into the stratum 01 (i.e., when the precast micro-steel pipe pile is in a vertical state). By providing a protrusion at the lower edge of the grouting port, this invention allows the precast micro-steel pipe pile to be directly pressed into the silty soil when the stratum is silty. The protrusion's structural design prevents soil from clogging the grouting port, solving the problem of easy clogging of the grouting holes when directly pressing in the grouting pipe in the prior art, thereby ensuring smooth grouting at each grouting port and improving the quality of subsequent grouting.

[0051] In some embodiments, spiral reinforcement bars 012, embedded in the precast fine stone concrete layer 06, are provided at both ends of the grouting pipe 02 near the seamless steel pipe 05. By providing the spiral reinforcement bars 012, the strength at both ends of the precast micro steel pipe pile can be improved, which helps to prevent damage to the precast micro steel pipe pile when it is driven into the stratum.

[0052] The buckling stability of micro steel pipe piles (columns) is mainly determined by calculating the compressive bearing capacity of micro steel pipe piles in accordance with the "Technical Specification for Concrete-Concrete Structural Structures" (CECS28:2012). Those skilled in the art can calculate and design according to this "Technical Specification for Concrete-Concrete Structural Structures" (CECS28:2012), and will not be elaborated upon here.

[0053] This invention also provides a construction method for a precast micro steel pipe pile post-grouting composite foundation, comprising the following steps:

[0054] (1) Pre-prepared precast micro steel pipe piles; wherein, for the pre-preparation of precast micro steel pipe piles, firstly, a grouting nozzle 07 is opened on the seamless steel pipe 05, then a grouting pipe 02 with a grouting hole 03 is inserted into the seamless steel pipe, and the grouting nozzle 07 and the grouting hole 03 are aligned with each other, then the jetting channel 08 is set up and the grouting hole 03, the jetting channel 08, and the inside of the grouting pipe are sealed, and finally fine stone concrete is injected and solidified.

[0055] In practical implementation, the jetting channel 08 can be pre-reserved (i.e., the jetting channel 08 is formed by pre-embedded molds when pouring fine aggregate concrete); or it can be formed by connecting a pipe to the outside of the grouting pipe and communicating with the grouting port 03, with the pipe itself forming the jetting channel 08. Those skilled in the art can manufacture based on the structure of this invention, and will not elaborate further here.

[0056] (2) Piling holes are opened in the stratum according to the design location and precast micro steel pipe piles are inserted into the pile holes, or precast micro steel pipe piles are directly pressed into the stratum according to the design location; that is to say, different implantation methods are used for different strata. For example, when dealing with silty soil, precast micro steel pipe piles can be directly pressed into stratum 01 by pressing. When dealing with other strata, common hole-forming methods for soft strata in building construction can be used, such as jet grouting, down-the-hole hammer drilling, etc. Those skilled in the art can understand and comprehend these methods, so they will not be elaborated here.

[0057] (3) Insert the post-grouting device into the grouting pipe 02 of the precast micro steel pipe pile, connect the post-grouting device with the external grouting pipe 04 and perform grouting; when grouting into the grouting pipe 02, the post-grouting device first fills the space in the grouting pipe 02 below the post-grouting device with grout, and then injects grout into each grouting port within the height range of the grouting pipe corresponding to the post-grouting device; along the grouting pipe from bottom to top, grout is injected in sequence until the top of the grouting pipe is grouted and the grouting operation is completed; after the post-grouting operation is completed, the post-grouting device is removed; that is to say, since the post-grouting device itself has a certain height (i.e. can occupy a certain depth of the grouting pipe 02), when grouting the grouting pipe 02 with the post-grouting device, the grouting is carried out in sequence from bottom to top.

[0058] (4) After the grout injected by the grouting device reaches the design strength, the mattress layer 010 is constructed on the surface of the stratum 01. After the mattress layer 010 is constructed, the foundation 011 can be constructed on top of the mattress layer 010.

[0059] This invention uses a post-grouting device to perform post-grouting on precast micro steel pipe piles, which improves the uniformity and quality of grouting compared to existing post-grouting methods.

[0060] Combined with appendix Figure 4 To be continued Figure 7 The post-grouting device of the present invention includes an upper float plug 1 and a lower float plug 2, which are connected together by a second pipe 4 and have a gap. Both the upper float plug 1 and the lower float plug 2 are equipped with airbags 12 that can seal and contact the grouting perforation pipe 02 after being filled with grout. The upper float plug 1 is connected to a first pipe 3 for injecting grout, wherein the first pipe 3 is used to connect to a grouting pipe 04, and grout is injected into the first pipe 3 through the grouting pipe 04. The lower float plug 2 is connected to a third pipe 5, and the grout can enter the interior of the upper float plug 1 and fill the interior of the airbags 12 and the lower float plug 3 through the first pipe 3, the second pipe 4 and the third pipe 5, and fill the space between the airbags 12 and the upper float plug 1 and the lower float plug 2. The grout can also enter the grouting perforation pipe below the lower float plug. That is to say, after the grout enters through the first pipe 3, it can fill the air bladder of the upper float plug 1, the air bladder of the lower float plug 2, and the gap between the upper float plug 1 and the lower float plug 2; thereby filling the grouting perforated pipe 02 located between the upper float plug and the lower float plug, and spraying the grout into the stratum 01 through the grouting hole 03 on the grouting perforated pipe 02, thereby impacting and squeezing the stratum 01. After the grout solidifies, the stratum 01 and the grouting perforated pipe 02 form a whole through concrete, thus completing the grouting reinforcement operation.

[0061] In some embodiments, both the upper float 1 and the lower float 2 include an upper cover plate 11 and a lower cover plate 13, with a gap between the upper cover plate 11 and the lower cover plate 13; an airbag 12 is connected between the upper cover plate 11 and the lower cover plate 13, and both the upper cover plate 11 and the lower cover plate 13 have through holes 111. The through holes 111 are closer to the outer edges of the upper cover plate 11 and the lower cover plate 13 than the connection position between the airbag 12 and the upper cover plate 11 and the lower cover plate 13, and the airbag 12 can cover the through holes 111 when it is filled with slurry, and can expose the through holes 111 when the airbag 12 is not filled with slurry; the upper cover plate 11. A sealed cavity is formed between the lower cover plate 13 and the airbag 12. A first pipe 3 is connected to the upper cover plate 11 of the upper float plug 1, passing through the upper cover plate 11 and communicating with the cavity of the upper float plug 1. The first pipe 3 is used to connect with the grouting pipe 04. The upper end of the second pipe 4 is fixedly connected to the upper cover plate 11 of the upper float plug 1. The lower end of the second pipe 4 passes through the lower cover plate 13 of the upper float plug 2 and the upper cover plate 11 of the lower float plug 2 in sequence, and then is fixedly connected to the lower cover plate 13 of the lower float plug 2. A third pipe 5 is connected to the upper cover plate 11 of the lower float plug 2, passing through the upper cover plate 11 and communicating with the cavity of the lower float plug 2. Several through holes 41 are opened on the circumferential wall at the bottom of the second pipe 5 located in the cavity of the upper float plug 1 and the lower float plug 2.

[0062] Combined with appendix Figure 7 The lower end of the upper cover plate 11 and the upper end of the lower cover plate 13 are provided with grooves, and mounting blocks 112 are provided in the grooves. The upper and lower edges of the airbag 12 are respectively clamped in the grooves and fixed by the mounting blocks. The mounting blocks 112 are then fixedly connected to the upper cover plate or the lower cover plate 13 by fastening bolts, so that the upper and lower edges of the airbag 12 are respectively mounted on the upper cover plate and the lower cover plate.

[0063] Since the airbag needs to be in close contact with the circumferential wall of the grouting pipe 02, preferably, the groove is an annular groove, and the mounting block 112 is annular. During use, when the grout pressure reaches a certain level, the grout fills the cavities inside the upper and lower float plugs, causing the airbag to expand and seal tightly against the inner wall of the grouting pipe 02, thus sealing the grout within the space between the upper and lower float plugs. This allows grouting to be injected into the grouting holes 03 of the grouting pipe 02, reinforcing the stratum 01.

[0064] Once the grouting pipe 02 in a certain area (length) is poured, the injection of grout into the grouting pipe 04 is stopped. As the grout pressure decreases, the airbag 12 gradually separates from the inner wall of the grouting pipe 02, making it easier to lift the entire device and move it along the inside of the grouting pipe.

[0065] Preferably, the upper cover 11 of the upper float plug 1 is provided with a lifting lug, which is used to tie the traction rope, and the traction rope drives the entire device to move up and down in the grouting pipe 02.

[0066] Combined with appendix Figure 5 and attached Figure 6 In some embodiments, the lower cover plate 13 of the lower float plug 2 has a discharge channel 131. A spring 136 is installed at the bottom of the discharge channel 131, and a piston 132 that seals against the discharge channel 131 is installed at the top of the spring 136. A feed channel 133 is provided at the top of the piston 132, and a through channel 134 communicating with the feed channel 133 is provided inside the piston 132. The lower cover plate 13 of the lower float plug 2 is provided with a spray outlet 135 that can communicate with or disconnect from the through channel 134. Specifically, when the slurry pressure is low, the through channel 134 on the piston 132 communicates with the spray outlet 135 on the lower cover, while when the slurry pressure is high, the through channel 134 on the piston 132 disconnects from the spray outlet 135 on the lower cover.

[0067] In some embodiments, the upper side surface of the lower cover plate 13 of the upper float 1 and the lower float 2 is a spherical or hemispherical surface, and the second channel 4 is connected to the middle of the arc groove.

[0068] In some embodiments, a counterweight 6 is provided around the periphery of the first pipe extending from the upper cover 11 of the float plug 1. The counterweight is used to maintain the stability of the entire device, together with a filled airbag to prevent the entire device from floating under the action of high-pressure slurry.

[0069] In some embodiments, the number of the third pipes 5 is 1, 2, 3, or 4. When the number of the third pipes is 2, 3, or 4, the third pipes 5 are evenly distributed on the upper cover of the lower float plug. Since the grouting holes 03 on the grouting perforated pipe 02 are evenly distributed, in order to make the grouting of the grouting holes 03 at the same height position on the grouting perforated pipe 02 more uniform, the number of the third pipes is the same as the number of grouting holes 03 at the same height position on the grouting perforated pipe 02, so as to make the grouting of the grouting holes 03 at the same height position on the grouting perforated pipe 02 more uniform.

[0070] In the operation of the post-grouting device of the present invention, the upper and lower float plugs are first placed at appropriate positions on the grouting perforation pipe, such that the grouting hole of the grouting perforation pipe to be grouted is located between the upper and lower float plugs. Then, grout is injected into the first pipe. The grout enters the cavity of the upper float plug along the first pipe, and then enters the second pipe through the through hole and into the cavity of the lower float plug. The grout in the cavity of the lower float plug first passes through the discharge channel, the piston feed channel, and the piston through channel, and then is ejected through the spray outlet of the lower float plug to fill the grouting perforation pipe below the lower float plug (at this time, the piston through channel is connected to the spray outlet of the lower float plug), thereby filling the lower float plug. The grouting pipe below the lower float plug is filled to prevent voids from forming. After the grouting pipe below the lower float plug is filled, as the grout pressure increases, the piston inside the lower cover plate of the lower float plug gradually slides down under the grout pressure, thus disconnecting the through channel from the nozzle. This allows the grout to fill the air bladder of the lower float plug, causing the air bladder to expand and make close contact with the inner wall of the grouting pipe. At the same time, the counterweight stabilizes the entire device inside the grouting pipe. As more and more grout is injected, it flows out from the third pipe and fills the gap between the upper and lower float plugs. Then, the grout is injected into the formation through the grouting holes on the grouting pipe. After the grouting of the grouting pipe section is completed, grouting is stopped, and the entire device (i.e., the upper and lower floating plugs) is slowly lifted upwards. As the grout pressure inside the upper and lower floating plugs decreases, the piston inside the lower cover of the lower floating plug moves upwards, causing the through channel on the piston to reconnect with the spray outlet of the lower cover, thereby filling the space below the lower floating plug with grout. That is, when the upper and lower floating plugs are lifted upwards, the grout will automatically fill the space that the upper and lower floating plugs have moved out of. This cycle is repeated to complete the grouting of the entire grouting pipe. During use, the piston inside the lower cover of the lower float plug automatically adjusts according to changes in slurry pressure, allowing the nozzle inside the lower cover to be disconnected from or connected to the through channel. When the upper and lower float plugs move upward together, they automatically fill the area below the lower float plug with slurry. On one hand, the slurry fills the interior of the grouting pipe below the lower float plug, ensuring that the slurry sprayed from the grouting hole of the grouting pipe forms a unified whole with the slurry inside the grouting pipe, greatly improving the integrity of the subsequent grouting and enhancing the grouting quality. On the other hand, it avoids the negative pressure formed at the lower end of the lower float plug when the upper and lower float plugs are moved, preventing grouting cracks caused by backflow of slurry sprayed through the grouting hole under negative pressure, further improving the molding quality.

[0071] Furthermore, during use, the grout first fills the grouting pipe below the lower float plug through the first, second, and third pipes, then fills the air bladder of the lower float plug, and finally fills the air bladder of the upper float plug. This allows air between the upper and lower float plugs to be discharged through the through hole, preventing voids in the grout due to air retention and improving the quality of grouting. As mentioned in the background section of this application, in the prior art, the sealing effect of the grouting plug prevents complete air release, leading to voids in the solidified grout. This invention avoids voids caused by air retention (incomplete air release), further improving the quality and precision of subsequent grouting.

Claims

1. A construction method for a precast micro-steel pipe pile post-grouting composite foundation, characterized in that, Includes the following steps: (1) Prefabricated micro steel pipe piles are prepared in advance; the prefabricated micro steel pipe piles include seamless steel pipes, and a number of grouting holes are opened on the circumferential wall of the seamless steel pipes. A grouting flower pipe is inserted into the seamless steel pipes, and a prefabricated fine stone concrete layer is provided between the grouting flower pipes and the seamless steel pipes. A jetting channel for connecting the grouting holes on the grouting flower pipes and the grouting holes on the seamless steel pipes is formed in the prefabricated fine stone concrete layer. (2) Drill pile holes in the stratum according to the design location and insert precast micro steel pipe piles into the pile holes, or directly press precast micro steel pipe piles into the stratum according to the design location; (3) Insert the post-grouting device into the grouting pipe of the precast micro steel pipe pile, connect the post-grouting device with the external grouting pipe and perform grouting; when grouting into the grouting pipe, the post-grouting device first fills the space in the grouting pipe below the post-grouting device with grout, and then injects grout into each grouting port within the height range of the grouting pipe corresponding to the post-grouting device; along the grouting pipe from bottom to top, grout is injected in a cyclic manner until the top of the grouting pipe is grouted, thus completing the grouting operation; Remove the post-grouting device after the post-grouting operation is completed; (4) After the grout injected by the post-grouting device reaches the design strength, a mattress layer is constructed on the surface of the stratum; The post-grouting device includes an upper float plug and a lower float plug, each comprising an upper cover plate and a lower cover plate, with a gap between them. An air bladder connects the upper and lower cover plates. Both the upper and lower cover plates have through holes, which are located closer to the outer edges of the upper and lower cover plates than the connection points between the air bladder and the grout. When the air bladder is filled with grout, it can cover the through hole; when the air bladder is not filled with grout, the through hole is exposed. A sealed cavity is formed between the cover plate, the lower cover plate, and the airbag. A first pipe is connected to the upper cover plate of the upper float plug, passing through the upper cover plate and communicating with the cavity of the upper float plug. The first pipe is used to connect to the grouting pipe. The upper end of the second pipe is fixedly connected to the upper cover plate of the upper float plug, and the lower end of the second pipe passes through the lower cover plate of the upper float plug and the upper cover plate of the lower float plug in sequence, and is then fixedly connected to the lower cover plate of the lower float plug. A third pipe is connected to the upper cover plate of the lower float plug, passing through the upper cover plate of the lower float plug and communicating with the cavity of the lower float plug. The second pipe located inside the cavities of the upper and lower floats has several through holes on its bottom circumferential wall; the lower cover plate of the lower float has a discharge channel, the bottom of the discharge channel is equipped with a spring, the top of the spring is equipped with a piston that seals with the discharge channel, the top of the piston has a feed channel, and the piston has a through channel that communicates with the feed channel; the lower cover plate of the lower float has an outlet that can communicate with or disconnect from the through channel. Slurry is injected into the first pipe. The slurry enters the cavity of the upper float plug along the first pipe, and then enters the second pipe through the through hole and enters the cavity of the lower float plug. The slurry in the cavity of the lower float plug is sprayed out through the discharge channel and the spray outlet of the lower float plug to fill the grouting pipe below the lower float plug. After the grouting pipe below the lower float plug is filled, as the pressure of the grout increases, the discharge channel and the spray outlet of the lower float plug are disconnected. The injected grout fills the air bladder of the lower float plug. As more and more grout is injected, the grout flows out from the third pipe and fills the space between the upper and lower float plugs.

2. The construction method of the precast micro-steel pipe pile post-grouting composite foundation according to claim 1, characterized in that, The jetting channel is set at a gradually downward angle along the vertical direction of the pile hole.

3. The construction method for precast micro-steel pipe pile post-grouting composite foundation according to claim 1, characterized in that, The seamless steel pipe is provided with spherical or hemispherical protrusions on its outer periphery, and each grouting nozzle is provided with a corresponding protrusion, and the protrusions are located at the lower edge of the grouting nozzle.

4. The construction method of the precast micro-steel pipe pile post-grouting composite foundation according to claim 1, characterized in that, The outer periphery of the grouting pipe is provided with spiral reinforcements embedded in the precast fine stone concrete layer at both ends near the seamless steel pipe.

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