Negative friction reduction device and method of pipe pile for existing building foundation reinforcement

Abstract

The invention provides a negative friction reduction device and method for pipe piles for existing building foundation reinforcement, the negative friction reduction device comprises a pressure-bearing pile formed by connecting a plurality of pipe piles end to end, the pressure-bearing pile is sleeved with a steel sleeve, and the bottom end of the steel sleeve is connected with a steel sleeve base; the bottom of the pressure-bearing pile is connected with a linkage pile shoe used for separating the steel sleeve and the pipe pile at the soil layer boundary, the linkage pile shoe is installed in the steel sleeve base, and the bottom end of the linkage pile shoe extends out of the steel sleeve base. The top of the linkage pile shoe is connected with a grouting pipe, and the grouting pipe and the pipe pile are concentrically arranged. According to the device, the upper portion of the pipe pile and the under-consolidated soil layer are separated through the steel sleeve on the outer side, when the under-consolidated soil layer settles and deforms, generated negative friction acts on the steel sleeve, the steel sleeve moves downwards along with deformation of a soil body, and due to the fact that the steel sleeve and the pipe pile are mutually independent, the pipe pile cannot be affected by the negative friction; and the stability of installation and long-term use of the pressure-bearing pile formed by connecting a plurality of tubular piles is ensured.

Description

Technical Field

[0001] The invention belongs to the technical field of civil engineering, and particularly relates to a negative skin friction reduction device and method for pipe piles used in the foundation reinforcement of existing buildings. Background Technique

[0002] With the development and construction of cities, in some areas, due to insufficient urban construction land and lack of large-scale construction land in the surrounding areas, artificial construction sites with large areas are formed by cutting mountains and filling ditches, and development and construction are carried out when the foundation soil in the filled site is not fully consolidated. However, the uneven settlement caused by the incomplete consolidation of the backfill soil has caused cracking, tilting or even damage to some buildings in the backfill area, or during the urban development process, the foundation soil of existing buildings has settled and deformed due to large-scale groundwater extraction.

[0003] With the popularization of anchor jacked piles, the settlement and deformation of buildings can be controlled by pile pressing. However, the long-term negative skin friction exerted by the foundation soil on the bearing piles will cause the pile foundation to settle or be damaged again. In order to reduce the long-term negative skin friction exerted by the foundation soil on the bearing piles, existing methods such as asphalt coating on the pile body, casing grouting, and preloading and drainage are used to eliminate the negative skin friction of the foundation soil on the pile foundation. Then, in the actual use process, the asphalt coating on the pile body is prone to aging. During the coating or preparation process of the asphalt coating on the pile body, due to unreasonable mixing ratio and uneven coating, it is scraped off by friction during pile pressing and cannot effectively weaken the negative skin friction exerted by the foundation soil; for casing grouting, the casing needs to be first pressed into the ground, the soil in the casing is dug out, and a double-layer plastic film is laid inside the casing and then concrete is poured to form a pile. This method is cumbersome in the construction process and it is difficult to pull out the casing when constructing under existing buildings, with high construction costs and time-consuming and laborious; while the preloading and drainage method will cause the foundation soil of surrounding buildings to be affected synchronously during the construction process, resulting in settlement and damage to surrounding buildings; therefore, the existing methods have poor effects on reducing the negative skin friction borne by the bearing piles, and the construction difficulty is large, affecting the function of the bearing piles. Summary of the Invention

[0004] In order to solve the problems of poor effect in reducing the negative skin friction exerted by the existing foundation soil on the bearing piles and large construction difficulty, the invention provides a negative skin friction reduction device and method for pipe piles used in the foundation reinforcement of existing buildings, which eliminates the negative skin friction exerted by the unconsolidated foundation soil on the pipe piles due to settlement.

[0005] To achieve the above object, the invention provides the following technical solutions: The invention provides a negative skin friction reduction device for pipe piles used in the foundation reinforcement of existing buildings, including a bearing pile formed by connecting a plurality of pipe piles end to end. A steel sleeve is sleeved outside the bearing pile, and a steel sleeve base is connected to the bottom end of the steel sleeve.

[0006] The bottom of the pressure-bearing pile is connected with a linkage pile shoe for separating the steel sleeve and the pipe pile at the boundary of the soil layer. The linkage pile shoe is installed in the steel sleeve base, and the bottom end extends out of the steel sleeve base.

[0007] The top of the linkage pile shoe is connected with a grouting pipe, and the grouting pipe is arranged concentrically with the pipe pile.

[0008] Preferably, the linked pile shoe comprises a pile shoe and a lifting and retracting foot support assembly, and the lifting and retracting foot support assembly is installed on the pile shoe.

[0009] The top of the pile shoe is connected with a grouting tube cover plate, and the bottom end of the grouting pipe is connected with the upper end surface of the grouting tube cover plate.

[0010] The top of the lifting and retractable foot support assembly is connected to the bottom end of the pipe pile at the bottom position in the pressure-bearing pile. When the lifting and retractable foot support assembly is opened, the outer wall of the lifting and retractable foot support assembly is tangent to the inner wall of the steel sleeve. When the lifting and retractable foot support assembly is retracted, the pipe pile is pressed, and the lifting and retractable foot support assembly extends from the bottom of the steel sleeve, thereby realizing the separation of the steel sleeve and the pipe pile at the boundary of the soil layer.

[0011] Preferably, the pile shoe comprises a grouting barrel, one end of which is mounted on the bottom end surface of the grouting barrel cover plate, a pile shoe top plate is arranged on the outer wall of the grouting barrel, a guide member is arranged on the pile shoe top plate, and the guide member is connected to the lifting and retractable foot support assembly.

[0012] A pile shoe bottom plate is arranged on the other end of the grouting tube, and the bottom end surface of the pile shoe bottom plate is connected to the pile bottom enlarged head.

[0013] Preferably, a pile shoe side edge plate is provided between the pile shoe bottom plate and the pile shoe top plate.

[0014] Preferably, the lifting and retracting foot support assembly comprises a small foot lifting member and a plurality of tubular pile outwardly expanded feet that can be aggregated to form a ring, and the small foot lifting member is connected to the tubular pile outwardly expanded small foot.

[0015] The small foot lifting member is movably installed on the guide member, and the top of the small foot lifting member is connected with a lifting plate, and the lifting plate is connected to the pipe pile.

[0016] A pressure ring is arranged between the lifting plate and the outer enlarged foot of the pipe pile.

[0017] The outer enlarged foot of the pipe pile is installed on the top plate of the pile shoe, and a limiting member is arranged between the top plate of the pile shoe and the outer enlarged foot of the pipe pile; The inner wall of the enlarged outer foot of the pipe pile is connected to the large-foot lifting member, and the large-foot lifting member is installed on the guiding member.

[0018] Preferably, the small-foot lifting member includes a small-foot lifting block. An active lifting plate is arranged at the bottom of the small-foot lifting block. The active lifting plate is slidably installed on the guiding member, and the top of the small-foot lifting block is connected to the lifting plate. A chute is arranged on the end face of the small-foot lifting block opposite to the bearing ring. A slider is slidably installed in the chute. A small-foot parallel link is hinged to the slider, and the end of the small-foot parallel link far from the slider is hinged to the enlarged outer small foot of the pipe pile.

[0019] Preferably, the large-foot lifting member includes a large-foot lifting block. A passive lifting plate is arranged on the large-foot lifting block. The large-foot lifting block and the passive lifting plate are slidably installed on the guiding member, and the passive lifting plate is located above the active lifting plate. One end of a large-foot parallel link is hinged to the end face of the large-foot lifting block opposite to the enlarged outer foot of the pipe pile, and the other end of the large-foot parallel link is hinged to the inner side wall of the enlarged outer foot of the pipe pile.

[0020] Preferably, the guiding member includes a plurality of lifting plate fixing rods, a plurality of small-foot lifting block fixing rods and a plurality of large-foot lifting block fixing rods. One ends of the plurality of lifting plate fixing rods, the plurality of small-foot lifting block fixing rods and the plurality of large-foot lifting block fixing rods are all fixed on the pile shoe top plate; and the small-foot lifting block fixing rods and the large-foot lifting block fixing rods are arranged at intervals circumferentially around the grouting cylinder, and the lifting plate fixing rods are arranged between the small-foot lifting block fixing rods and the large-foot lifting block fixing rods. The small-foot lifting block is slidably installed on the small-foot lifting block fixing rod, and the large-foot lifting block is slidably installed on the large-foot lifting block fixing rod. The passive lifting plate and the active lifting plate are slidably installed on the lifting plate fixing rod.

[0021] Preferably, an annular guiding assembly is arranged between the steel sleeve and the pipe pile; the annular guiding assembly includes a pipe pile centering ring. The outer wall of the pipe pile centering ring is fixedly connected to the inside of the steel sleeve, and steel balls are rotatably installed on the inner wall of the pipe pile centering ring. The outer walls of the steel balls are tangent to the outer wall of the pipe pile.

[0022] The present invention provides a method for reducing negative skin friction of a pipe pile for reinforcing the foundation of an existing building. By applying the above-mentioned device for reducing negative skin friction of a pipe pile for reinforcing the foundation of an existing building, the method includes the following steps: Excavate a circular groove at the pressing position with a depth higher than that of the lifting and retractable foot support assembly. Place the steel sleeve base on the ground at the circular groove, install the linkage pile shoe in the steel sleeve base and expand it, connect the steel sleeve to the steel sleeve base, and connect the pipe pile and the grouting pipe to the top of the linkage pile shoe; Apply synchronous pressure to the top of the pipe pile through a pressurizing device. When the depth of the steel sleeve pressed into the soil layer reaches the predetermined depth, lift the pipe pile to cause the linkage pile shoe to contract, and then apply pressure to the top of the pipe pile again so that the bottom end of the pipe pile at the bottom of the bearing pile reaches the predetermined position in the soil layer.

[0023] Compared with the prior art, the present invention has the following beneficial technical effects: The present invention provides a negative skin friction reduction device for pipe piles used in the foundation reinforcement of existing buildings. During the pile pressing process, the device uses a linkage pile shoe to press the steel sleeve and the pipe pile into the soil layer together. Compared with the traditional construction process of first pressing the sleeve to remove soil and then pressing the pile, the soil removal process inside the steel sleeve is reduced, and the generation of construction waste is reduced. At the same time, by using the steel sleeve outside the pipe pile, when the pipe pile is pressed down in the under-compacted soil layer, it is separated from the under-consolidated soil layer. Therefore, when the under-consolidated soil layer undergoes settlement deformation, the generated negative skin friction acts on the steel sleeve, and the steel sleeve will displace downward following the deformation of the soil. Since the steel sleeve and the pipe pile are independent of each other, the pipe pile will not be affected by the negative skin friction, ensuring the installation and long-term use stability of the bearing pile formed by connecting multiple pipe piles.

[0024] Furthermore, during the use of the device, when the steel sleeve reaches the predetermined position, the steel sleeve and the pipe pile are separated by lifting and retracting the foot support assembly, which does not affect the continued construction of the pipe pile, reduces the construction difficulty, and lowers the construction cost. Description of the Drawings

[0025] Figure 1 It is a construction schematic diagram of a negative skin friction reduction device for pipe piles used in the foundation reinforcement of existing buildings provided by the present invention; Figure 2 It is a partial sectional view of a negative skin friction reduction device for pipe piles used in the foundation reinforcement of existing buildings provided by the present invention; Figure 3 It is one of the partial sectional views during the lifting process of the lifting and retracting foot support mechanism in a negative skin friction reduction device for pipe piles used in the foundation reinforcement of existing buildings provided by the present invention; Figure 4 It is the second partial sectional view during the lifting process of the lifting and retracting foot support mechanism in a negative skin friction reduction device for pipe piles used in the foundation reinforcement of existing buildings provided by the present invention; Figure 5The third partial sectional view of the lifting and contracting foot support mechanism in the negative skin friction reduction device for the foundation reinforcement of existing buildings provided by the present invention during the lifting process; Figure 6 The fourth partial sectional view of the lifting and contracting foot support mechanism in the negative skin friction reduction device for the foundation reinforcement of existing buildings provided by the present invention during the lifting process; Figure 7 The partial sectional view of the steel sleeve after reaching the soil layer boundary in the negative skin friction reduction device for the foundation reinforcement of existing buildings provided by the present invention; Figure 8 The partial sectional view of the steel sleeve in the negative skin friction reduction device for the foundation reinforcement of existing buildings provided by the present invention; Figure 9 The partial sectional view of the steel sleeve base in the negative skin friction reduction device for the foundation reinforcement of existing buildings provided by the present invention; Figure 10 The structural schematic diagram of the lifting and contracting foot support mechanism in the negative skin friction reduction device for the foundation reinforcement of existing buildings provided by the present invention; Figure 11 The structural schematic diagram of the pile shoe in the negative skin friction reduction device for the foundation reinforcement of existing buildings provided by the present invention; Figure 12 The partial sectional view of the connection of the small foot lifting block, bearing ring and lifting plate in the negative skin friction reduction device for the foundation reinforcement of existing buildings provided by the present invention; Figure 13 The structural schematic diagram of the small foot lifting block in the negative skin friction reduction device for the foundation reinforcement of existing buildings provided by the present invention; Figure 14 The structural schematic diagram of the large foot lifting block in the negative skin friction reduction device for the foundation reinforcement of existing buildings provided by the present invention; Figure 15 The structural schematic diagram of the externally expanded small foot of the pipe pile in the negative skin friction reduction device for the foundation reinforcement of existing buildings provided by the present invention; Figure 16 The first structural schematic diagram of the externally expanded large foot of the pipe pile in the negative skin friction reduction device for the foundation reinforcement of existing buildings provided by the present invention; Figure 17 The second structural schematic diagram of the externally expanded large foot of the pipe pile in the negative skin friction reduction device for the foundation reinforcement of existing buildings provided by the present invention; In the accompanying drawings: 1. Gantry; 2. Positioning base; 3. Anchor rod; 4. Reaction beam; 5. Loading beam; 6. Jack; 7. Steel sleeve; 7-1. Pipe pile centering ring; 7-2. Steel ball; 7-3. Steel sleeve base; 7-4. Pile channel; 8. Pipe pile; 8-1. Welding plate at pile end; 8-2. Pipe pile hole; 9. Pile shoe; 9-1. Pile shoe top plate; 9-2. Pile shoe bottom plate; 9-3. Pile shoe side rib plate; 9-4. Grouting cylinder; 9-5. Grout outlet hole; 9-6. Big foot chute; 9-7. Fixed rod of big foot lifting block; 9-8. Fixed rod of small foot lifting block; 9-9. Fixed rod of lifting plate; 10. Pile bottom enlarged head; 11. Outer enlarged foot of pipe pile; 11-1. Outer small foot groove of pipe pile; 11-2. Big foot parallel hinge support; 11-3. Big foot slider; 12. Outer small foot of pipe pile; 12-1. Small foot protrusion; 12-2. Small foot parallel support; 13. Big foot lifting member; 13-1. Fixed hole of big foot lifting block; 13-2. Big foot lifting block parallel hinge support; 13-3. Passive lifting plate; 13-4. Serial hole of passive lifting plate; 13-5. Big foot lifting block; 14. Small foot lifting member; 14-1. Fixed hole of small foot lifting block; 14-2. Active lifting plate; 14-3. Serial hole of active lifting plate; 14-4. Slider; 14-5. Chute; 14-6. Small foot lifting block parallel hinge support; 14-7. Small foot lifting block; 15. Lifting plate; 16. Bearing ring; 17. Grouting cylinder cover plate; 18. Grouting pipe; 19. Big foot parallel connecting rod; 20. Small foot parallel connecting rod; 21. Lifting and retractable foot support mechanism; 22. Pin. Detailed implementation manners

[0026] In the following text, only some exemplary embodiments are simply described. As those skilled in the art can recognize, the described embodiments can be modified in various different ways without departing from the spirit or scope of the present invention. Therefore, the accompanying drawings and the description are considered to be exemplary in nature rather than restrictive.

[0027] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention.

[0028] In addition, the terms "first" and "second" are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "a plurality of" means two or more unless otherwise specifically defined.

[0029] In the present invention, unless otherwise clearly specified and defined, terms such as "installed", "connected", "joined", "fixed", etc. should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or integrated; it may be a mechanical connection, an electrical connection, or a communication connection; it may be directly connected, or indirectly connected through an intermediate medium, and it may be the internal communication of two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0030] In the present invention, unless otherwise clearly specified and defined, the first feature being "on" or "under" the second feature may include the first and second features being in direct contact, or may include the first and second features not being in direct contact but being in contact through additional features therebetween. Moreover, the first feature being "above", "over" and "on top of" the second feature includes the first feature being directly above and obliquely above the second feature, or merely indicating that the first feature has a higher horizontal height than the second feature. The first feature being "under", "beneath" and "underneath" the second feature includes the first feature being directly below and obliquely below the second feature, or merely indicating that the first feature has a lower horizontal height than the second feature.

[0031] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0032] The present invention provides a negative skin friction reduction device for pipe piles used in the foundation reinforcement of existing buildings, as Figures 1 to 17As shown in the figure, it includes a bearing pile formed by connecting multiple pipe piles 8 end to end. Among them, the length of a single pipe pile 8 is 1000 mm, the outer diameter of the pipe pile 8 is 500 mm, and a pile-end welding plate 8-1 is provided at the end of the pipe pile 8. A pipe pile hole 8-2 is arranged along the circumferential direction at the central position of the pipe pile 8, and the diameter of the pipe pile hole 8-2 is 200 mm. A steel sleeve 7 is sleeved outside the bearing pile. A steel sleeve base 7-3 is connected to the bottom end of the steel sleeve 7. The steel sleeve 7 is a hollow steel pipe with an inner diameter 3 cm larger than the diameter of the pipe pile. The steel sleeve 7 is provided with multiple sections, and the length of each section is 1000 mm. The length of the special part in the steel sleeve 7 is 800 mm, and the thickness of the steel sleeve 7 is 2 cm. A linkage pile shoe for separating the steel sleeve 7 and the pipe pile 8 at the soil layer boundary is connected to the bottom of the bearing pile. The linkage pile shoe is installed in the steel sleeve base 7-3, and the bottom end extends outside the steel sleeve base 7-3; the top of the linkage pile shoe is connected with a grouting pipe 18. The length of a single grouting pipe 18 is 1000 mm, and the length of the special part is 800 mm. The grouting pipe 18 is installed in the pipe pile hole 8-2 inside the pipe pile 8 and is concentric with the pipe pile 8, and the top of the grouting pipe 18 is slightly lower than the top of the bearing pile. This device separates the pipe pile 8 and the unconsolidated foundation soil layer by arranging the steel sleeve 7 outside the bearing pile, and a linkage pile shoe is arranged at the bottom position of the pipe pile 8 inside the steel sleeve 7. When the linkage pile shoe expands, its edge is tangent to the inner wall of the steel sleeve 7.

[0033] As Figure 8 and Figure 9 shown in the figure, the height of the steel sleeve base 7-3 is 10 cm. The diameter of the outer wall of the steel sleeve base 7-3 is the same as the diameter of the outer wall of the steel sleeve 7. A pipe pile channel 7-4 with a diameter of 505 mm is arranged on the bottom end surface of the steel sleeve base 7-3, so that an annular steel plate ring is formed at the bottom end position inside the steel sleeve base 7-3. An annular guiding component is arranged at every 4 m along the length direction of the steel sleeve 7. The inner side of the annular guiding component is attached to the outer wall of the pipe pile 8. The annular guiding component includes a pipe pile centering ring 7-1, and the pipe pile centering ring 7-1 is welded to the inner wall of the steel sleeve 7. The vertical section of the pipe pile centering ring 7-1 is an isosceles trapezoid with a height of 2.5 cm. Mounting holes are arranged on the inner side wall of the pipe pile centering ring 7-1, and steel balls 7-2 are rotatably installed in the mounting holes, and part of the steel balls 7-2 is exposed outside the pipe pile centering ring 7-1 and is attached to the outer wall of the pipe pile 8; after the pipe pile 8 is separated from the steel sleeve 7 through the annular guiding component, the pipe pile 8 can stably move vertically in the steel sleeve 7, reducing the friction between the pipe pile 8 and the steel sleeve 7 and ensuring the coaxiality of the pipe pile 8 and the steel sleeve 7.

[0034] As Figures 2 to 17As shown in the figure, the linkage pile shoe includes a pile shoe 9. A grouting cylinder cover plate 17 is connected to the top end of the pile shoe 9, and the bottom end of a grouting pipe 18 is installed on the grouting cylinder cover plate 17. A lifting and retractable foot support assembly 21 is movably connected to the pile shoe 9. The top of the lifting and retractable foot support assembly 21 is connected to the pile end welding plate 8-1 of the pipe pile 8 at the bottom position in the bearing pile. When the lifting and retractable foot support assembly 21 is expanded, the outer wall of the lifting and retractable foot support assembly 21 is tangent to the inner wall of the steel sleeve 7. When the lifting and retractable foot support assembly 21 is retracted, the outer contour dimension of the lifting and retractable foot support assembly 21 is the same as the outer diameter of the pipe pile 8. Then, the pipe pile 8 is pressed, and the lifting and retractable foot support assembly 21 extends from the bottom of the steel sleeve 7, realizing the separation of the steel sleeve 7 and the pipe pile 8 at the soil layer boundary.

[0035] As Figures 10 to 17 shown in the figure, the pile shoe 9 includes a grouting cylinder 9-4. One end of the grouting cylinder 9-4 is installed on the bottom end face of the grouting cylinder cover plate 17. The outer diameter of the grouting cylinder 9-4 does not exceed 100 mm. The outer wall diameter of the grouting cylinder 9-4 is smaller than the outer wall diameter of the grouting cylinder cover plate 17. The grouting cylinder 9-4 is connected to the grouting cylinder cover plate 17 by threads, and a slurry guiding hole is provided on the grouting cylinder cover plate 17 to connect the grouting pipe 18 and the grouting cylinder 9-4 through the slurry guiding hole. A pile shoe top plate 9-1 is provided on the outer wall of the grouting cylinder 9-4. The outer diameter of the pile shoe top plate 9-1 is the same as the outer diameter of the pipe pile 8. The thickness of the pile shoe top plate 9-1 is the same as the thickness of the annular steel plate ring. A guiding member is provided on the pile shoe top plate 9-1, and the guiding member is connected to the lifting and retractable foot support assembly 21. A pile shoe bottom plate 9-2 is provided at the other end of the grouting cylinder 9-4. The pile shoe bottom plate 9-2 is arranged parallel to the pile shoe top plate 9-1, and the outer wall diameter of the pile shoe top plate 9-1 is larger than the outer wall diameter of the pile shoe bottom plate 9-2. A plurality of pile shoe side rib plates 9-3 are provided between the pile shoe bottom plate 9-2 and the pile shoe top plate 9-1. The plurality of pile shoe side rib plates 9-3 are arranged at equal intervals circumferentially around the grouting cylinder 9-4. One end of a pile shoe side rib plate 9-3 is attached to the grouting cylinder 9-4. The top edge of the pile shoe side rib plate 9-3 is aligned with the edge of the pile shoe top plate 9-1, and the bottom edge of the pile shoe side rib plate 9-3 is aligned with the edge of the pile shoe bottom plate 9-2. A slurry outlet hole 9-5 is provided at the position between two adjacent pile shoe side rib plates 9-3 on the outer wall of the grouting cylinder 9-4. The outer wall diameter of the pile shoe bottom plate 9-2 is larger than the outer wall diameter of the grouting cylinder 9-4 to prevent the slurry outlet hole 9-5 from being blocked by foundation soil during the pile pressing process. The diameter of the slurry outlet hole 9-5 is 2 cm.

[0036] As Figures 10 to 17As shown, the lifting and contracting type foot support assembly 21 includes a small foot lifting member 14 and a plurality of pipe pile outer expanding feet 11 that can aggregate to form a circular ring. A pipe pile outer expanding small foot 12 is connected to the small foot lifting member 14; the small foot lifting member 14 is movably installed on the guiding member, and the pipe pile outer expanding small foot 12 is located between two adjacent pipe pile outer expanding feet 11. A lifting plate 15 is connected to the top of the small foot lifting member 14. The lifting plate 15 is arranged parallel to the pile shoe top plate 9-1, and the lifting plate 15 is welded to the pipe pile 8; a pressure-bearing ring 16 is arranged on the bottom end face of the lifting plate 15, and the outer diameter of the pressure-bearing ring 16 is the same as the outer diameter of the pipe pile 8; the lifting plate 15 is connected to the pile end welding plate 8-1 arranged at the top end of the pipe pile 8; the pipe pile outer expanding feet 11 are installed on the pile shoe top plate 9-1, and a limiting member is arranged between the pile shoe top plate 9-1 and the pipe pile outer expanding feet 11; a large foot lifting member 13 is connected to the inner wall of the pipe pile outer expanding feet 11. After the steel sleeve 7 reaches a predetermined position, the pipe pile 8 is pulled upward along the axial direction of the steel sleeve 7, so that the small foot lifting member moves on the guiding member. At the same time, during the rising process of the small foot lifting member, the large foot lifting member 13 is driven to move upward, and the pipe pile outer expanding feet 11 are pulled towards the grouting cylinder 9-4 and contracted into a circular ring. After applying pressure to the pipe pile 8 again, the lifting and contracting type foot support assembly 21 extends out from the pipe pile channel 7-4 on the bottom end face of the steel sleeve base 7-3 and continues to penetrate into the soil layer.

[0037] As Figure 11 and Figure 17 shown, the limiting member includes a large foot slider 11-3 arranged on the bottom end face of the pipe pile outer expanding feet 11, and a large foot sliding groove 9-6 is arranged on the top end face of the pile shoe top plate 9-1. The large foot slider 11-3 is slidably installed in the large foot sliding groove 9-6. Through the cooperation of the large foot slider 11-3 and the large foot sliding groove 9-6, the pipe pile outer expanding feet 11 move radially along the top of the pile shoe top plate 9-1 above the pile shoe top plate 9-1.

[0038] As Figures 10 to 17As shown, the small-foot lifting member 14 includes a small-foot lifting block 14-7. The small-foot lifting block 14-7 is in the shape of a cuboid. At the position of the bottom end of the small-foot lifting block 14-7, two active lifting plates 14-2 are symmetrically arranged. The active lifting plates 14-2 are slidably installed on the guiding members. Through the guiding members, the small-foot lifting block 14-7 moves axially along the grouting cylinder 9-4 above the pile shoe top plate 9-1. The top of the small-foot lifting block 14-7 is connected to a lifting plate 15. On the end face of the small-foot lifting block 14-7 opposite to the pressure-bearing ring 16, a chute 14-5 is arranged axially along the pipe pile 8. A slider 14-4 is slidably installed in the chute 14-5. On the end face of the slider 14-4 opposite to the pipe pile 8, two small-foot lifting block parallel hinge supports 14-6 with a longer upper part and a shorter lower part are arranged. One end of a small-foot parallel link 20 is hinged to each small-foot lifting block parallel hinge support 14-6. The other end of the small-foot parallel link 20 is hinged to a pipe pile outward-expanding small foot 12. The pipe pile outward-expanding small foot 12 is movably installed between two adjacent pipe pile outward-expanding large feet 11. The pipe pile outward-expanding small foot 12 is in the shape of a cube. A small-foot protrusion 12-1 is arranged on the bottom end face of the pipe pile outward-expanding small foot 12. On the inner end face of the pipe pile outward-expanding small foot 12, a small-foot parallel hinge support 12-2 with a shorter upper part and a longer lower part is arranged. The small-foot parallel hinge support 12-2 is hinged to the other end of the small-foot parallel link 20. Among them, the maximum rotation angle at the hinge joints of the small-foot parallel link 20 with the small-foot parallel hinge support 12-2 and the small-foot lifting block parallel hinge support 14-6 is 90°. At the same time, a pipe pile outward-expanding small-foot groove 11-1 is arranged on the upper end face of the pipe pile outward-expanding large foot 11. When the lifting and retractable foot support assembly 21 retracts, the small-foot protrusion 12-1 is clamped in the pipe pile outward-expanding small-foot groove 11-1 to limit two adjacent pipe pile outward-expanding large feet 11.

[0039] As Figures 10 to 17 shown, the large-foot lifting member 13 includes a large-foot lifting block 13-5. After the large-foot lifting block 13-5 is installed on the guiding members, at the position near the top end of the large-foot lifting block 13-5, two passive lifting plates 13-3 are symmetrically arranged. The large-foot lifting block 13-5 and the passive lifting plates 13-3 are slidably installed on the guiding members. The passive lifting plates 13-3 are located above the active lifting plates 14-2. On the end face of the large-foot lifting block 13-5 opposite to the pipe pile outward-expanding large foot 11, two large-foot lifting block parallel hinge supports 13-2 with a longer upper part and a shorter lower part are arranged. One end of a large-foot parallel link 19 is hinged to the outer end of the large-foot lifting block parallel hinge support 13-2. The other end of the large-foot parallel link 19 is hinged to the inner side wall of the pipe pile outward-expanding large foot 11. That is, at the center of the inner end wall of the pipe pile outward-expanding large foot 11, two large-foot parallel hinge supports 11-2 with a shorter upper part and a longer lower part are arranged. The large-foot parallel hinge supports 11-2 are hinged to the other end of the large-foot parallel link 19.

[0040] As Figures 10 to 17As shown in the figure, the guiding member includes a plurality of lifting plate fixing rods 9-9, a plurality of small-foot lifting block fixing rods 9-8, and a plurality of large-foot lifting block fixing rods 9-7. In this embodiment, three lifting plate fixing rods 9-9, three small-foot lifting block fixing rods 9-8, and a plurality of large-foot lifting block fixing rods 9-7 are provided; one ends of the three lifting plate fixing rods 9-9, the three small-foot lifting block fixing rods 9-8, and the plurality of large-foot lifting block fixing rods 9-7 are all fixed on the pile shoe top plate 9-1; and the small-foot lifting block fixing rods 9-8 and the large-foot lifting block fixing rods 9-7 are circumferentially arranged at intervals around the grouting cylinder 9-4, and the lifting plate fixing rods 9-9 are arranged between the small-foot lifting block fixing rods 9-8 and the large-foot lifting block fixing rods 9-7; a small-foot lifting block fixing hole 14-1 is vertically provided at the center position on the top end surface of the small-foot lifting block 14-7, the bottom end of the small-foot lifting block fixing hole 14-1 penetrates through the bottom end surface of the small-foot lifting block 14-7, and the small-foot lifting block fixing rod 9-8 is inserted into the small-foot lifting block fixing hole 14-1, so that the small-foot lifting block 14-7 is slidably mounted on the small-foot lifting block fixing rod 9-8; a large-foot lifting block fixing hole 13-1 is vertically provided at the center position on the top end surface of the large-foot lifting block 13-5, the bottom end of the large-foot lifting block fixing hole 13-1 penetrates through the bottom end surface of the large-foot lifting block 13-5, and the large-foot lifting block fixing rod 9-7 is inserted into the large-foot lifting block fixing hole 13-1, so that the large-foot lifting block 13-5 is slidably mounted on the large-foot lifting block fixing rod 9-7; a passive lifting plate connecting hole 13-4 is provided on the top end surface of the passive lifting plate 13-3, and an active lifting plate connecting hole 14-3 is provided on the top end surface of the active lifting plate 14-2. The lifting plate fixing rod 9-9 sequentially passes through the active lifting plate connecting hole 14-3 and the passive lifting plate connecting hole 13-4 from bottom to top, so that the passive lifting plate 13-3 and the active lifting plate 14-2 are slidably mounted on the lifting plate fixing rod 9-9, to prevent the small-foot lifting block 14-7 and the large-foot lifting block 13-5 from rotating when the small-foot lifting block 14-7 and the large-foot lifting block 13-5 move along the axial direction of the grouting cylinder 9-4, resulting in the inability of the active lifting plate 14-2 to drive the large-foot lifting block 13-5 to move upward during the lifting process.

[0041] The present invention provides a method for reducing negative skin friction of pipe piles for strengthening existing building foundations. By applying the above-mentioned device for reducing negative skin friction of pipe piles for strengthening existing building foundations, the method includes the following steps: Excavate a circular groove at the pressing position with a depth higher than that of the lifting and retractable foot support assembly 21. Place the steel sleeve base 7-3 on the ground at the circular groove, install the linkage pile shoe in the steel sleeve base 7-3 and expand it, connect the steel sleeve 7 to the steel sleeve base 7-3, and connect a pipe pile 8 and a grouting pipe 18 to the top of the linkage pile shoe. Synchronously apply pressure to the top of the pipe pile 8 through a pressurizing device. After the depth of the pressure soil layer of the steel sleeve 7 reaches the predetermined depth, lift the pipe pile 8 to cause the linkage pile shoe to contract, and then apply pressure to the top of the pipe pile 8 so that the bottom end of the pipe pile 8 at the bottom of the bearing pile reaches the predetermined position in the soil layer.

[0042] Specifically, in step 1, prefabricate a pipe pile 8 with a length of 1000 mm, a steel sleeve 7 with the same length as a single-section pipe pile 8, and a grouting pipe 18. For the grouting pipe 18 and the steel sleeve 7, prepare a part of special components with a length of about 800 mm according to the number of pile pressing.

[0043] In step 2, assemble the steel sleeve base 7-3, the lifting and contracting type foot support mechanism 21, and the pile shoe 9. After leveling the site, assemble the gantry 1 at the predetermined pile pressing position. After fixing the gantry 1 with the anchor rod 3, place the steel sleeve base 7-3 on the ground. Excavate a circular groove on the ground according to the inner diameter of the steel sleeve base 7-3 to ensure that the groove can cover the components below the pile shoe top plate 9-1. Place the assembled lifting and contracting type foot support mechanism 21 inside the steel sleeve base 7-3. After ensuring the fitting of the pile channel 7-4 of the steel sleeve base 7-3 and the pile shoe top plate 9-1, use a steel rope to sling the lifting plate 15 around the gantry 1. Stop lifting when the outer expanding small foot 12 of the pipe pile is lifted. Pull open the outer expanding large foot 11 of the pipe pile so that its edge contacts the inner wall of the steel sleeve 7. Then slowly lower the lifting plate 15. After the bearing ring 16 contacts the outer expanding large foot 11 of the pipe pile, push the outer expanding small foot 12 of the pipe pile outward from the hole in the middle of the lifting plate 15 until the slider 14-4 is at the lowermost end of the sliding groove 14-5. Install the grouting cylinder cover plate 17 on the grouting cylinder 9-5. Vertically lift a section of the pipe pile 8 and place it inside the special component of the steel sleeve 7 with a length of 800 mm. Slowly lower the pipe pile 8 until the pile end welding plate 8-1 coincides with the lifting plate 15. After welding the pile end welding plate 8-1 and the lifting plate 15, lower the special component of the steel sleeve 7 with a length of 800 mm and dock it with the steel sleeve base 7-3. After docking, weld the special component of the steel sleeve 7 and the steel sleeve base 7-3. Wait for the welding joint to cool according to the regulations, and the cooling time shall not be less than 15 minutes. Pile pressing work shall not be carried out before the cooling is completed; Step 3, pile pressing: pull out the pins 22 on both sides of the load beam 5 and make it fall to the top of the pile 8. Adjust the height of the reaction beam 4 according to the height of the jack 6 to ensure that the jack 6 can be placed between the load beam 5 and the reaction beam 4. Use the pins 22 to fix the two sides of the reaction beam 4. Place the jack 6 in the middle of the top of the load beam 5, start the jack 6, and press the pile 8 downward. When the jack 6 reaches the maximum stroke, release the pressure. After the jack 6 retracts, pull out the pin 22 of the reaction beam 4 and move it downward. Move it to the vicinity of the top of the jack 6 and fix it again with the pin 22. Start the jack 6 to press the pile 8 downward until the top of the steel sleeve 7 is about 50 cm from the ground. Stop pile pressing, remove the jack 6, and lift the load beam 5 and the reaction beam 4 to a high place and fix them with the pin 22.

[0044] Step 4, pile connection: insert a section of grouting pipe 18 with a length of 800mm into the pile hole 8-2 in the pile 8 and tighten it with the grouting tube cover 17, put a section of the pile 8 in the steel sleeve 7 and lift it vertically, slowly lower the pile 8 until the pile end welding plates 8-1 of the upper and lower piles 8 overlap, after welding the pile end welding plates 8-1 of the two piles 8, then lower the steel sleeve 7 and dock with the special parts of the steel sleeve 7, weld the steel sleeve 7 and the special parts of the steel sleeve 7 after docking, wait for the welding to cool down, press the newly welded pile 8 and steel sleeve 7 down, and weld the pile centering ring 7-1 inside the steel sleeve 7 every 4m; Step 5, repeat step 4 until the steel sleeve 7 passes through the unconsolidated soil layer, and stop pile pressing; Step 6. Retract the external enlarged feet 11 and external small enlarged feet 12 of the pipe pile by pulling out the pile, that is, slowly lift the pipe pile 8 with a steel wire rope. At this time, the pipe pile 8 will drive the lifting plate 15 to move upward, and the small foot lifting block 14-7 welded to the lifting plate 15 will move upward with the lifting plate 15. At this time, the external small enlarged foot 12 of the pipe pile will gradually slide inward during the upward movement of the small foot lifting block 14-7. When the small foot parallel link 20 is completely vertical, the external small enlarged foot 12 of the pipe pile will move upward with the small foot lifting block 14-7. When the small foot lifting block 14-7 continues to move upward, the active lifting plate 14-2 will drive the passive lifting plate 13-3 to move upward. At this time, the large foot lifting block 13-5 will move upward, thereby driving the external enlarged feet 11 of the pipe pile to move inward. When the large foot parallel link 19 is completely vertical, the external enlarged feet 11 of the pipe pile come into contact with each other. At this time, stop lifting the pipe pile 8 and change to slow lowering. Since the large foot parallel link 19 is completely vertical at this time, the external enlarged feet 11 of the pipe pile will not be subjected to an outward force, and the large foot lifting block 13-5 will be suspended in the air by the large foot parallel link 19 and will not continue to move downward. The external small enlarged feet 12 and the small foot lifting block 14-7 of the pipe pile will continue to move downward with the pipe pile 8. During the downward movement of the external small enlarged feet 12 of the pipe pile, the small foot protrusion 12-1 will fall into the external small enlarged foot groove 11-1 of the pipe pile. At this time, the external small enlarged feet 12 of the pipe pile will stop moving, and the small foot parallel link 20 will also stop moving. The small foot parallel link 20 is connected to the slider 14-5 through the small foot lifting block parallel hinge support 14-6. The slider 14-5 will move upward relative to the chute 14-4 during the continued downward movement of the small foot lifting block 14-7 until the small foot lifting block 14-7 falls back to the pile shoe top plate 9-1. At this time, the pressure ring 15 also falls on the top of the external enlarged feet 11 of the pipe pile, and the lowering ends. Among them, before pulling out the pile, the height of pulling out the pile can be calculated in advance according to the height of the lifting and retracting foot support mechanism 21 to ensure that the pile shoe 9 will not be pulled out during operation; when pulling out the pile, the pin 22 can be inserted into the holes on both sides of the force-bearing beam 5 to fix the force-bearing beam 5, pull out the pins 22 on both sides of the reaction beam 4, wind the steel wire rope around the reaction beam 4, and use the jack 6 to lift the reaction beam 4, then the pipe pile can be pulled upward by the steel wire rope; Step 7. Continue to press down the pipe pile 8. At this time, both the external small enlarged feet 12 and the external enlarged feet 11 of the pipe pile are retracted within the circle of the cross-section of the pipe pile 8. When the upper jack 6 applies a downward force again, the pipe pile 8 will move downward while the steel sleeve 7 will remain stationary. When the upper end of the uppermost pipe pile 8 is pressed close to the steel sleeve 7, stop pile pressing, remove the jack 6, and lift the force-bearing beam 5 and the reaction beam 4 to a high position and fix them with the pin 22. Tighten the thread of a new grouting pipe 18 with the grouting pipe 18 inside the pipe pile 8, then lift another pipe pile 8 so that the bottom pile end welding plate 8-1 coincides with the top pile end welding plate 8-1 of the already pressed pipe pile 8. After welding the pile end welding plates 8-1 of the two pipe piles 8, wait for the welding joint to cool. After the welding joint has cooled, continue to press down the pile.

[0045] Step 8: Repeat Step 7, continue to press down the pipe pile 8 until the pile shoe 9 is pressed to a predetermined depth. Connect the grouting pipe 18 to the cement pump and grout below the pile shoe 9 to form an enlarged pile tip 10. After the pile tip grouting is completed, inject cement slurry into the center of the pipe pile 8 and fill the gap between the pipe pile 8 and the steel sleeve 7 with a flexible material. The flexible material is a powdery filling material that will not be cemented by water, such as foaming glue or rubber debris, or a low-strength fluid plastic filling material after consolidation. It can fill the gap between the pipe pile and the steel sleeve without cementing them together.

[0046] Step 9: Pull out the anchor rod 3, disassemble the gantry 1, process the exposed pile head of the pipe pile 8 and the steel sleeve 7, move the removed pile pressing equipment to the next pile pressing point, and press the pile again until the pile pressing work in the site is completed.

[0047] The above shows and describes the basic principles, main features and advantages of the present invention. For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present invention. Any reference signs in the claims should not be regarded as limiting the claimed rights.

[0048] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art. The above content is only to illustrate the technical idea of the present invention and cannot be used to limit the protection scope of the present invention. Any modification made on the basis of the technical solution according to the technical idea proposed by the present invention falls within the protection scope of the claims of the present invention.

Claims

1. A negative skin friction reduction device for pipe piles used in the foundation reinforcement of existing buildings, characterized in that, It includes a bearing pile formed by connecting multiple pipe piles (8) end to end. A steel sleeve (7) is sleeved outside the bearing pile, and a steel sleeve base (7-3) is connected to the bottom end of the steel sleeve (7). A linkage pile shoe for separating the steel sleeve (7) from the pipe pile (8) at the soil layer boundary is connected to the bottom of the bearing pile. The linkage pile shoe is installed in the steel sleeve base (7-3), and its bottom end extends outside the steel sleeve base (7-3). A grouting pipe (18) is connected to the top of the linkage pile shoe, and the grouting pipe (18) is concentrically arranged with the pipe pile (8).

2. The negative skin friction reduction device for pipe piles used in the foundation reinforcement of existing buildings according to claim 1, wherein, The linkage pile shoe includes a pile shoe (9) and a lifting and contracting type foot support assembly (21), and the lifting and contracting type foot support assembly (21) is installed on the pile shoe (9). A grouting cylinder cover plate (17) is connected to the top of the pile shoe (9), and the bottom end of the grouting pipe (18) is connected to the upper end face of the grouting cylinder cover plate (17). The top of the lifting and contracting type foot support assembly (21) is connected to the bottom end of the pipe pile (8) at the bottom position in the bearing pile. When the lifting and contracting type foot support assembly (21) expands, the outer wall of the lifting and contracting type foot support assembly (21) is tangent to the inner wall of the steel sleeve (7). When the lifting and contracting type foot support assembly (21) contracts, it presses the pipe pile (8), and the lifting and contracting type foot support assembly (21) extends out from the bottom of the steel sleeve (7) to realize the separation of the steel sleeve (7) from the pipe pile (8) at the soil layer boundary.

3. The negative skin friction reduction device for pipe piles used in the foundation reinforcement of existing buildings according to claim 2, characterized in that, The pile shoe (9) includes a grouting cylinder (9-4). One end of the grouting cylinder (9-4) is installed on the bottom end face of the grouting cylinder cover plate (17). A pile shoe top plate (9-1) is arranged on the outer wall of the grouting cylinder (9-4), and a guiding member is arranged on the pile shoe top plate (9-1), and the guiding member is connected to the lifting and contracting type foot support assembly (21). A pile shoe bottom plate (9-2) is arranged at the other end of the grouting cylinder (9-4), and the bottom end face of the pile shoe bottom plate (9-2) is connected to the pile bottom enlargement head (10).

4. The negative skin friction reduction device for pipe piles used in the foundation reinforcement of existing buildings according to claim 3, characterized in that, A pile shoe side rib plate (9-3) is arranged between the pile shoe bottom plate (9-2) and the pile shoe top plate (9-1).

5. The negative skin friction reduction device for pipe piles used in the foundation reinforcement of existing buildings according to claim 3, characterized in that, The lifting and contracting type foot support assembly (21) includes a small foot lifting member (14) and a plurality of pipe pile outer expanding feet (11) that can aggregate to form a ring. A pipe pile outer expanding small foot (12) is connected to the small foot lifting member (14). The small foot lifting member (14) is movably installed on the guiding member. A lifting plate (15) is connected to the top of the small foot lifting member (14), and the lifting plate (15) is connected to the pipe pile (8). A pressure bearing ring (16) is arranged between the lifting plate (15) and the pipe pile outer expanding feet (11). The pipe pile outer expanding feet (11) are installed on the pile shoe top plate (9-1), and a limiting member is arranged between the pile shoe top plate (9-1) and the pipe pile outer expanding feet (11). A large foot lifting member (13) is connected to the pipe pile outer expanding feet (11), and the large foot lifting member (13) is installed on the guiding member.

6. The negative skin friction reduction device for pipe piles used in the foundation reinforcement of existing buildings according to claim 5, characterized in that, The small-foot lifting member (14) includes a small-foot lifting block (14-7). An active lifting plate (14-2) is provided at the bottom of the small-foot lifting block (14-7). The active lifting plate (14-2) is slidably mounted on a guiding member. The top of the small-foot lifting block (14-7) is connected to the lifting plate (15). A chute (14-5) is provided on the end face of the small-foot lifting block (14-7) opposite to the pressure-bearing ring (16). A slider (14-4) is slidably mounted in the chute (14-5). A small-foot parallel link (20) is hinged to the slider (14-4). The end of the small-foot parallel link (20) far from the slider (14-4) is hinged to the external-expanded small foot (12) of the pipe pile.

7. The negative skin friction reduction device for pipe piles used in the foundation reinforcement of existing buildings according to claim 6, characterized in that, The large-foot lifting member (13) includes a large-foot lifting block (13-5). A passive lifting plate (13-3) is provided on the large-foot lifting block (13-5). The large-foot lifting block (13-5) and the passive lifting plate (13-3) are slidably mounted on the guiding member, and the passive lifting plate (13-3) is located above the active lifting plate (14-2). One end of a large-foot parallel link (19) is hinged to the end face of the large-foot lifting block (13-5) opposite to the external-expanded large foot (11) of the pipe pile. The other end of the large-foot parallel link (19) is hinged to the inner side wall of the external-expanded large foot (11) of the pipe pile.

8. The negative skin friction reduction device for pipe piles used in the foundation reinforcement of existing buildings according to claim 7, characterized in that, The guiding member includes a plurality of lifting plate fixing rods (9-9), a plurality of small-foot lifting block fixing rods (9-8), and a plurality of large-foot lifting block fixing rods (9-7). One ends of the plurality of lifting plate fixing rods (9-9), the plurality of small-foot lifting block fixing rods (9-8), and the plurality of large-foot lifting block fixing rods (9-7) are all fixed to the pile shoe top plate (9-1). The small-foot lifting block fixing rods (9-8) and the large-foot lifting block fixing rods (9-7) are circumferentially arranged at intervals around the grouting cylinder (9-4). The lifting plate fixing rods (9-9) are arranged between the small-foot lifting block fixing rods (9-8) and the large-foot lifting block fixing rods (9-7). The small-foot lifting block (14-7) is slidably mounted on the small-foot lifting block fixing rod (9-8). The large-foot lifting block (13-5) is slidably mounted on the large-foot lifting block fixing rod (9-7). The passive lifting plate (13-3) and the active lifting plate (14-2) are slidably mounted on the lifting plate fixing rod (9-9).

9. A negative skin friction reduction device for pipe piles used in the foundation reinforcement of existing buildings according to claim 1, characterized in that, An annular guiding assembly is provided between the steel sleeve (7) and the pipe pile (8). The annular guiding assembly includes a pipe pile centering ring (7-1). The outer wall of the pipe pile centering ring (7-1) is fixedly connected to the inside of the steel sleeve (7). Steel balls (7-2) are rotatably mounted on the inner wall of the pipe pile centering ring (7-1). The outer walls of the steel balls (7-2) are tangent to the outer wall of the pipe pile (8).

10. A method for reducing negative skin friction of pipe piles for reinforcing the foundation of existing buildings, which applies the device for reducing negative skin friction of pipe piles for reinforcing the foundation of existing buildings according to any one of claims 1 to 9, characterized in that, Including the following steps: Excavate a circular groove at the pressing position with a depth higher than that of the lifting and retractable foot support assembly (21). Place the steel sleeve base (7-3) on the ground at the circular groove, install the linkage pile shoe in the steel sleeve base (7-3) and expand it, connect the steel sleeve (7) to the steel sleeve base (7-3), and connect the pipe pile (8) and the grouting pipe (18) to the top of the linkage pile shoe; Apply pressure synchronously at the top of the pipe pile (8) through a pressurizing device. After the depth of the steel sleeve (7) pressed into the soil layer reaches the predetermined depth, lift the pipe pile (8) to cause the linkage pile shoe to contract, and then apply pressure at the top of the pipe pile (8) to make the bottom end of the pipe pile (8) at the bottom of the bearing pile reach the predetermined position in the soil layer.

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