Interface adjusting precast pile and using method
By setting pits and guide ribs on the outer surface of precast piles and injecting reinforcing agents or weakening agents through reserved pipes, the problems of poor economy and low bearing capacity of traditional precast piles are solved, thereby increasing the side resistance of the pile body and reducing the negative friction, making it suitable for complex geological conditions.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-02-10
- Publication Date
- 2026-04-03
AI Technical Summary
Traditional precast piles are not economical to construct, have low single pile bearing capacity, and often require pile cutting and replacement because they cannot reach the design elevation. In particular, the negative friction effect is significant under complex geological conditions.
Recesses and guide ribs are set on the outer surface of the precast pile body. Combined with a reserved pipeline system, the pile-soil interface properties are adjusted by injecting interface reinforcing agents or weakening agents to form a soil nail structure to increase lateral resistance or reduce negative friction.
It increases the lateral resistance of the pile body in the normally consolidated and overconsolidated soil regions, reduces the negative skin friction effect in underconsolidated soil and seismically subsided soil layers, improves the bearing capacity of single piles, and simplifies the construction process.
Smart Images
Figure CN121781580A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of foundation construction technology in building engineering, specifically to an interface-adjustable precast pile and its usage method. Background Technology
[0002] In the foundation construction of modern building projects, precast piles are widely used due to their advantages such as controllable quality and fast construction speed. Traditional precast piles are usually made of concrete and steel and are prefabricated in a factory. The outer surface of the pile body is mostly a smooth cylindrical or square column.
[0003] However, this smooth surface structure has gradually revealed its shortcomings in practical applications. After the pile is driven into the soil, the friction coefficient between the smooth pile body and the surrounding soil is relatively low, resulting in less lateral resistance. For single pile bearing capacity requirements of greater capacity, large-diameter and long piles are often necessary, leading to poor economic efficiency. In complex geological conditions such as underconsolidation and seismic subsidence, and in environments with large-area loading, the negative skin friction effect further reduces the actual single pile bearing capacity. Increasing the pile length is currently the main solution to address the negative skin friction effect. However, the construction of large-diameter, longer precast piles increases the technical difficulty of pile driving, requiring sophisticated equipment and often resulting in numerous pile cuts and replacements due to the inability to reach the design elevation. Summary of the Invention
[0004] To address the shortcomings of existing technologies, this invention provides an interface-adjustable precast pile and its usage method, which solves the problems of poor economic efficiency, low actual single pile bearing capacity, and the frequent need for pile cutting and replacement due to the inability to reach the design elevation of traditional precast piles.
[0005] To achieve the above objectives, the present invention provides the following technical solution: an interface-adjustable precast pile and its usage method.
[0006] In a first aspect, the present invention provides an interface-adjustable precast pile, comprising a pile body:
[0007] The pile body is made of reinforced concrete or steel, and the outer peripheral sidewall of the pile body forms the outer surface of the pile body;
[0008] The outer surface of the pile body is provided with an inwardly recessed pit and a guide rib protruding from the outer surface of the pile body;
[0009] The opening of the pit on the outer surface of the pile body forms a pit edge;
[0010] The interior of the pit has an inner surface, and the inner surface of the pit is provided with a secondary pit structure with concave and convex shapes.
[0011] The pile body is provided with a reserved pipe inside, which is arranged along the length of the pile body and communicates with the pit.
[0012] Preferably, the pit includes shallow pits and deep pits;
[0013] The shallow pit has a depth of less than 10 mm, and the ratio of the equivalent diameter of the pit edge to the depth is greater than or equal to 2. The slope of the inner sidewall of the shallow pit is less than or equal to 1.
[0014] The depth of the deep pit is greater than 10 mm, and the ratio of the equivalent diameter of the pit edge to the depth is less than 2. The slope of the inner sidewall of the deep pit is greater than or equal to 3.
[0015] Preferably, the guide rib has a bottom tip, which forms an angle of 10 to 15 degrees with the horizontal direction;
[0016] The guide ribs are arranged in the area surrounding the edge of the pit and on the outer surface of the pile body away from the edge of the pit;
[0017] The top width of the guide rib is 2mm to 3mm, and the guide rib is connected to the outer surface of the pile body by an arc transition.
[0018] Preferably, the guide ribs arranged in the periphery of the edge of the recess include at least one of vertical guide ribs, inclined guide ribs, and semi-enclosed guide ribs;
[0019] The guide ribs arranged on the outer surface of the pile body away from the edge of the pit include straight guide ribs or curved guide ribs.
[0020] The bottom tip of the guide rib points in the direction of pile driving or in the opposite direction to the pile driving direction.
[0021] Preferably, when the pile body corresponds to the area of normally consolidated soil and overconsolidated soil layer, the shallow pit is provided on the outer surface of the pile body, and a guide rib with the bottom tip pointing in the direction of pile driving is provided at the edge of the shallow pit, which is used to guide the soil on the side of the pile into the shallow pit.
[0022] When the pile body corresponds to the area of underconsolidated soil and collapsible soil layer, the deep pit-shaped depression is provided on the outer surface of the pile body, and a semi-enclosed guide rib is provided at the edge of the deep pit-shaped depression to guide the soil on the pile side away from the deep pit-shaped depression.
[0023] Preferably, the reserved pipeline is divided into a first pipeline group and a second pipeline group, and the first pipeline group and the second pipeline group are not connected to each other inside the pile body;
[0024] The first pipeline group is used to connect the depressions located in the regions of normally consolidated soil and overconsolidated soil layers, and the second pipeline group is used to connect the depressions located in the regions of underconsolidated soil and subsidence soil layers.
[0025] Preferably, the connection method between the reserved pipe and the recess includes a sequential series connection method and a reverse series connection method;
[0026] The sequential connection method is that the reserved pipes are connected to the pits one by one from the top of the pile downwards;
[0027] The reverse-sequence connection method involves reserving a pipe that extends from the top of the pile area to below the lowest recess that needs to be connected, and then connects it to the recess one by one upwards.
[0028] Preferably, the concave-convex secondary pit is constructed as a geometric structure in which the inner surface of the pit is further recessed and protruded.
[0029] The depth of the depression and the height of the protrusion in the concave-convex secondary pit structure are less than one-third of the equivalent diameter of the pit edge.
[0030] A second aspect of the present invention provides a method for using interface-adjustable precast piles, including methods for increasing the side resistance of the pile and for reducing the negative skin friction of the pile, wherein increasing the side resistance of the pile includes the following steps:
[0031] Shallow pit-shaped recesses and guide ribs pointing in the direction of pile driving are set on the outer surface of the pile body;
[0032] During the pile driving process, the guide ribs are used to guide and press the soil on the side of the pile into the shallow pit and compact it, so that the soil on the side of the pile combines with the concave and convex secondary pit structure to form a soil nail.
[0033] After the pile driving is completed, an interface reinforcing agent is injected into the shallow pit through a reserved pipe to solidify the soil nail and form a reinforced soil nail.
[0034] The ultimate lateral resistance of the pile body in each soil layer after improvement is determined according to the following principle: the sum of the areas enclosed by the projections of the edges of all pits on the outer surface of the pile body within the range of the enhanced pile segment and the shear strength of the current soil layer, plus the product of the total area of the outer surface of the enhanced pile segment minus the sum of the areas enclosed by the projections and the ultimate lateral resistance of the original corresponding soil layer, and the sum of the two is divided by the total area of the outer surface of the enhanced pile segment.
[0035] Preferably, the method for reducing negative skin friction of the pile includes the following steps:
[0036] Deep pit-shaped recesses and semi-enclosed guide ribs are set on the outer surface of the pile body;
[0037] During the pile driving process, the semi-enclosed guide ribs are used to guide the soil on the pile side away from the deep pit, forming a detached cavity in the deep pit.
[0038] After the pile driving is completed, an interface weakening agent is injected into the deep pit through a reserved pipe;
[0039] The ultimate negative skin friction of the pile body in each soil layer after reduction is determined according to the following principle: the sum of the areas enclosed by the projections of the edges of all pits on the outer surface of the pile body within the reduced pile section, the product of the original ultimate negative skin friction of the pile body and the adjustment coefficient, plus the product of the total area of the outer surface of the pile body of the reduced pile section minus the sum of the areas enclosed by the projections and the ultimate negative skin friction of the pile body of the original corresponding soil layer, and the sum of the two is divided by the total area of the outer surface of the pile body of the reduced pile section.
[0040] This invention provides an interface-adjustable precast pile and its usage method. It has the following beneficial effects:
[0041] 1. This invention, by setting a gently sloping shallow pit on the outer surface of the pile, can effectively utilize the lateral pressure effect of the soil on the pile side during the pile driving process, press the soil on the pile side into the pit and compact it, and form a stable soil nail structure by using the concave and convex secondary structure, so that the pile-soil interface changes from the traditional planar friction to a mechanical interlocking mode with higher shear strength, thereby improving the pile side resistance in the normally consolidated soil and over-consolidated soil areas.
[0042] 2. This invention sets up a gently sloping shallow pit and matching guide ribs on the outer surface of the pile body. For relatively hard soil layers such as dense and hard plastic, while utilizing the lateral pressure effect of the soil on the pile side during the pile driving process, the guide ribs work together to forcibly guide the soil on the pile side into the pit for compaction. The concave and convex secondary structure forms a stable soil nail structure, which changes the pile-soil interface from the traditional planar friction to a mechanical interlocking mode with higher shear strength, thereby improving the pile side resistance in the areas of normally consolidated soil and overconsolidated soil.
[0043] 3. This invention achieves physical isolation and guidance of soil flow along the pile by setting steep-slope deep pits and diversion-type guide ribs on the outer surface of the pile. The guide ribs push the soil away from the pit opening, and together with the steep pit walls, prevent soil backfilling, forming a detached cavity within the pit. This reduces the substantial contact area between the pile and the soil along the pile, effectively reducing the negative skin friction effect caused by settlement of underconsolidated soil or seismically subsided soil layers, and ensuring the effective bearing capacity of a single pile.
[0044] 4. This invention utilizes a pipeline system pre-installed inside the pile and connected to the pit to establish a secondary control mechanism for the pile-soil interface performance. By injecting cement-based reinforcing agents or oil-based weakening agents through the pipeline, the soil nail strength can be specifically strengthened or a lubricating layer can be constructed, further expanding the adjustment range of lateral resistance and negative friction. At the same time, the pipeline system also serves as a channel for monitoring cables, allowing sensors to be installed without slotting the pile body, providing non-destructive and convenient implementation conditions for performance monitoring of the pile foundation throughout its entire life cycle. Attached Figure Description
[0045] Figure 1 This is a schematic diagram of the pile driving process according to the present invention;
[0046] Figure 2 This is a schematic diagram of the staggered arrangement of the recesses in this invention;
[0047] Figure 3 This is a schematic diagram of the rectangular arrangement of the recesses in this invention;
[0048] Figure 4 This is a schematic diagram of the guide rib arrangement in the shallow pit-type depression area of the present invention.
[0049] Figure 5 This is a schematic cross-sectional view of the guide rib arrangement in the edge area of the shallow pit type depression of the present invention.
[0050] Figure 6 This is a top view of the steep slope deep pit type concave pit of the present invention;
[0051] Figure 7 This is a schematic cross-sectional view of the steep slope deep pit type concave pit of the present invention;
[0052] Figure 8 This is a schematic diagram of the vertical guide rib of the present invention;
[0053] Figure 9 This is a schematic diagram of the inclined guide rib of the present invention;
[0054] Figure 10 This is a schematic diagram of the semi-enclosed guide rib of the present invention;
[0055] Figure 11 This is a schematic diagram of the straight guide rib of the present invention;
[0056] Figure 12 This is a schematic diagram of the curved guide rib of the present invention;
[0057] Figure 13 This is a schematic diagram of the steep slope deep pit type recess and the arrangement of guide ribs in the edge area of the recess according to the present invention.
[0058] Figure 14 This is a schematic diagram of soil nails formed in a shallow, gentle-slope pit according to the present invention.
[0059] Figure 15 This is a schematic diagram of the detachment cavity formed in the steep slope deep pit type depression of the present invention;
[0060] Figure 16 This is a schematic diagram of the reverse-order series connection of the reserved pipe and the pit in this invention;
[0061] Figure 17 This is a schematic diagram of the sequential connection of the reserved pipe and the recess in this invention;
[0062] Figure 18 This is a schematic diagram showing the arrangement of guide ribs (non-pit edge) to guide the soil on the pile side away from the pit when the pit is arranged in a rectangular pattern according to the present invention.
[0063] Figure 19 This is a schematic diagram showing the arrangement of guide ribs on the non-pit edges to guide the soil on the pile side away from the pits when the pits are arranged in an alternating pattern according to the present invention.
[0064] Figure 20 This is a schematic diagram of the reinforced soil nail formed in the shallow pit of the present invention.
[0065] Among them, 1. Pile body; 2. Outer surface of pile body; 3. Recess; 4. Edge of recess; 5. Inner surface of recess; 6. Reserved pipe; 7. Concave-convex secondary pit structure; 8. Inner side wall of pit; 9. Guide rib; 10. Soil nail; 11. Soil on pile side; 12. Reinforced soil nail; 13. Detachable cavity; 901. Vertical guide rib; 902. Inclined guide rib; 903. Semi-enclosed guide rib; 904. Straight guide rib; 905. Curved guide rib. Detailed Implementation
[0066] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0067] Please see the appendix Figure 1 -Appendix Figure 3This invention provides an interface-adjustable precast pile and its usage method, including a pile body 1. The pile body 1 is made of reinforced concrete or steel, and its cross-sectional shape can be a solid circle, a solid rectangle, a hollow ring, a hollow rectangle, or an irregular shape, depending on design requirements. The outer peripheral sidewalls of the pile body 1 constitute the outer surface 2 of the pile body, and the outer surface 2 integrates structural features for actively adjusting the mechanical properties of the pile-soil interface. Specifically, the outer surface 2 has inwardly recessed pits 3 and protruding guide ribs 9 distributed in an organized manner along the axial and circumferential directions. The openings of the pits 3 at the outer surface 2 define the pit edges 4, and the shape of the pit edges 4 can be circular, elliptical, rectangular, polygonal, or a combination of arcs and straight lines. The internal space of the pits 3 is defined by the inner surface 5 of the pits. To enhance the mechanical interlocking ability inside the pits 3, the inner surface 5 of the pits further integrates concave-convex secondary pit structures 7. The interior of the pile body 1 is provided with a reserved pipe 6, which is arranged along the length of the pile body 1 and has a branch channel that connects to the pit 3.
[0068] See attached document Figure 4 -Appendix Figure 7 Based on their geometric characteristics and functional definitions, the pits 3 are divided into shallow pits and deep pits. Shallow pits are mainly arranged in the pile body area corresponding to normally consolidated or over-consolidated soil, and their depth is set to less than 10mm. To ensure that the soil can easily enter and compact, the ratio of the equivalent diameter to the depth of the pit edge 4 of the shallow pit is designed to be greater than or equal to 2, and the slope of its inner sidewall 8 is gentle, with a value less than or equal to 1. As a specific embodiment, the depth of the shallow pit can be set to 8mm, the sidewall slope to be 0.8, and the projected area enclosed by the pit edge 4 is approximately 1200mm². 2 Deep-pit-type depressions are mainly arranged in the pile body area corresponding to under-consolidated soil or seismically collapsed soil, with a depth greater than 10mm. To prevent soil from entering and maintain the internal cavity, the ratio of the equivalent diameter to the depth of the depression edge 4 is less than 2, and the inner sidewall 8 is steep with a slope greater than or equal to 3. As a specific embodiment, the depth of the deep-pit-type depression can be set to 20mm, the sidewall slope to be 4, and the projected area enclosed by the depression edge 4 is approximately 250mm². 2 .
[0069] See attached document Figure 14 -Appendix Figure 15 The concave-convex secondary pit structure 7 is a micro-geometric structure directly formed on the inner surface 5 of the pit, and its form includes cones, frustums, cylinders, or spheres. The depth of the depressions or the height of the protrusions of these microstructures are controlled within one-third of the equivalent diameter of the pit edge 4. For example, a conical secondary structure with a depth of 3 mm is formed on the inner surface 5 of the pit. The function of this structure is to increase the specific surface area inside the pit 3, so that it can provide multi-directional mechanical interlocking force when the external medium is filled into the pit 3.
[0070] See attached document Figure 8 -Appendix Figure 13 and appendix Figure 18 -Appendix Figure 20 The black arrows indicate the direction of soil movement. The guide rib 9 is a key component controlling the flow of soil 11 along the pile. It has a pointed tip at its bottom, forming an angle of 10 to 15 degrees with the horizontal direction. Its top width is 2 to 3 mm, protruding approximately 3 mm above the outer surface 2 of the pile body, and it is connected to the outer surface 2 of the pile body via an arc transition. The arrangement strategy of the guide rib 9 directly determines the pile-soil contact state. In the periphery of the pit edge 4, vertical guide ribs 901, inclined guide ribs 902, or semi-enclosed guide ribs 903 are arranged. Vertical guide ribs 901 and inclined guide ribs 902 are mainly used to guide the soil flow into the pit 3; while semi-enclosed guide ribs 903 surround the front end of the pit edge 4 in a U-shape or V-shape, used to push the soil flow away from the pit 3. In the area away from the pit edge 4, straight guide ribs 904 or curved guide ribs 905 are arranged to macroscopically construct a continuous soil flow channel.
[0071] See attached document Figure 16 and attached Figure 17 The reserved pipes 6 are physically isolated within the pile body 1 into a first pipe group and a second pipe group, which are not interconnected. The first pipe group is specifically used to connect shallow pits located in the drag-increasing area, and the second pipe group is specifically used to connect deep pits located in the drag-reducing area. Connection methods include sequential series and reverse series. Sequential series involves connecting the pipes to the pits 3 one by one from top to bottom, suitable for fluid injection with low flow resistance. Reverse series involves the pipes first reaching the bottom of the lowest pit 3, and then connecting them one by one from bottom to top. This method utilizes the fluid's own weight and jacking pressure, suitable for injecting high-viscosity slurry and effectively expelling accumulated air from the pipes. The reserved pipes 6 can be fabricated using pre-embedded PVC pipes, metal pipes, or through a drilling process.
[0072] The application method and working principle of this invention are divided into two aspects based on the soil properties: increasing the side resistance of the pile and reducing the negative skin friction of the pile.
[0073] When pile 1 corresponds to the regions of normally consolidated and overconsolidated soil layers, the aim is to increase the lateral resistance of the pile. A shallow pit is created on the outer surface 2 of the pile in this region, and a vertical guide rib 901 or an inclined guide rib 902 with its bottom tip pointing in the direction of pile driving is placed at the edge 4 of the pit. During pile driving, the guide rib 9 forcibly guides the cut soil 11 from the pile side into the shallow pit. Due to the gentle slope of the inner sidewall 8 of the pit, the soil can smoothly slide in and be compacted under high pressure, encasing the concave-convex secondary pit structure 7, forming a physically stable soil nail 10. After pile driving is completed, cement grout and other interface reinforcing agents are injected into the pit 3 through the first pipeline group in a reverse-series series manner. The reinforcing agent penetrates the pores of the soil nail 10 and undergoes a hydration reaction, solidifying to form a high-strength reinforced soil nail 12.
[0074] At this point, the ultimate side resistance of the improved pile is calculated according to the formula:
[0075] ;
[0076] in, For the first pile side Layering soil to increase the ultimate lateral resistance of the pile body in the subsequent pile segment; For the first pile side Layering soil to increase the ultimate lateral resistance of the pile body in the preceding pile section; For the first pile side Shear strength of the soil layer; For the first pile side The soil layer is the sum of the areas enclosed by the projections of the edges 4 of all pits 4 on the outer surface 2 of the pile body within the reinforced pile segment. For the first pile side The soil layer enhances the surface area of the outer surface 2 of the pile body of the pile segment.
[0077] This formula shows that as the density of the shallow pit coverage increases, the lateral resistance of the pile will depend more on the shear strength of the soil itself. This effectively overcomes the friction limitations of traditional smooth pile bodies.
[0078] When pile 1 corresponds to the area of underconsolidated soil and seismically collapsed soil, the aim is to reduce the negative skin friction of the pile. A deep pit-shaped depression is set on the outer surface 2 of the pile in this area, and a semi-enclosed guide rib 903 is configured at the edge 4 of the depression. The semi-enclosed guide rib 903 is located on the soil-facing side of the depression 3, acting as a diversion baffle, forcibly pushing the soil 11 flowing through the pile side to both sides, causing it to deviate from the opening of the deep pit-shaped depression. Due to the large depth of the deep pit-shaped depression and the steep inner sidewall 8, the displaced cohesive soil cannot be backfilled into the pit in a short time, thus forming a detached cavity 13 inside the depression 3 that is not filled by soil. After pile driving is completed, an interface weakening agent such as oil-based grease and water-based wax emulsion is injected into the depression 3 in a sequential series through a second pipeline group to fill the detached cavity 13 and penetrate into the surrounding soil interface.
[0079] At this point, the reduced ultimate negative skin friction of the pile is calculated according to the formula:
[0080] ;
[0081] in, For the first pile side Layered soil reduces the ultimate negative skin friction of the pile body in the subsequent pile segment; For the first pile side Layer of soil to reduce the ultimate negative skin friction of the pile body in the preceding pile section; For the first pile side The adjustment coefficient for the ultimate negative skin friction of the soil layer ranges from 0.1 to 0.3.
[0082] The calculation logic shows that by maximizing the area ratio of deep pits in the negative friction-sensitive region, and combining a weakening agent to adjust the coefficient... Maintaining the load at a low level can reduce the downward load caused by soil settlement in this section. In summary, this invention achieves precise and proactive control over the distribution of pile side resistance under complex geological conditions.
Claims
1. A precast pile with interface adjustment, characterized in that, Including pile body (1): The pile body (1) is made of reinforced concrete or steel, and the outer peripheral sidewall of the pile body (1) forms the outer surface (2) of the pile body. The outer surface (2) of the pile body is provided with an inwardly recessed pit (3) and a guide rib (9) protruding from the outer surface (2) of the pile body. The pit (3) has an opening at the outer surface (2) of the pile body with a pit edge (4). The interior of the pit (3) has an inner surface (5), and the inner surface (5) of the pit is provided with a concave-convex secondary pit structure (7). The pile body (1) is provided with a reserved pipe (6) inside. The reserved pipe (6) is arranged along the length direction of the pile body (1) and is connected to the pit (3).
2. The interface-adjustable precast pile according to claim 1, characterized in that, The pit (3) includes shallow pits and deep pits; The shallow pit has a depth of less than 10 mm, and the ratio of the equivalent diameter of the pit edge (4) to the depth is greater than or equal to 2, and the slope of the inner sidewall (8) of the shallow pit is less than or equal to 1. The depth of the deep pit is greater than 10 mm, and the ratio of the equivalent diameter of the pit edge (4) to the depth is less than 2, and the slope of the inner sidewall (8) of the deep pit is greater than or equal to 3.
3. The interface-adjustable precast pile according to claim 1, characterized in that, The guide rib (9) has a bottom tip, which forms an angle of 10 to 15 degrees with the horizontal direction; The guide rib (9) is arranged in the area surrounding the edge (4) of the pit and on the outer surface (2) of the pile body away from the edge (4); The top width of the guide rib (9) is 2mm to 3mm, and the guide rib (9) is connected to the outer surface (2) of the pile body by an arc transition.
4. The interface-adjustable precast pile according to claim 3, characterized in that, The guide ribs (9) arranged in the periphery of the edge (4) of the recess include at least one of vertical guide ribs (901), inclined guide ribs (902) and semi-enclosed guide ribs (903); The guide ribs (9) arranged on the outer surface (2) of the pile body away from the edge (4) of the pit include straight guide ribs (904) or curved guide ribs (905). The bottom tip of the guide rib (9) points to the pile driving direction of the pile body (1), or points to the opposite direction of the pile driving direction.
5. The interface-adjustable precast pile according to claim 2, characterized in that, When the pile body (1) corresponds to the area of normal consolidated soil and overconsolidated soil layer, the shallow pit is provided on the outer surface (2) of the pile body, and a guide rib (9) with the bottom tip pointing to the direction of pile driving is provided at the edge (4) of the shallow pit, which is used to guide the soil (11) on the side of the pile into the shallow pit. When the pile body (1) corresponds to the area of underconsolidated soil and collapsible soil layer, the deep pit type depression is provided on the outer surface (2) of the pile body, and a semi-enclosed guide rib (903) is provided at the edge (4) of the deep pit type depression to guide the soil (11) on the side of the pile away from the deep pit type depression.
6. The interface-adjustable precast pile according to claim 1, characterized in that, The reserved pipe (6) is divided into a first pipe group and a second pipe group, and the first pipe group and the second pipe group are not connected to each other inside the pile body (1); The first pipeline group is used to connect the pit (3) located in the area of normal consolidated soil and overconsolidated soil layer, and the second pipeline group is used to connect the pit (3) located in the area of underconsolidated soil and subsidence soil layer.
7. The interface-adjustable precast pile according to claim 6, characterized in that, The connection between the reserved pipe (6) and the recess (3) includes a sequential series connection and a reverse series connection. The sequential connection method is that the reserved pipe (6) is connected to the pit (3) one by one from the top of the pile area downwards; The reverse serial connection method is to extend the reserved pipe (6) from the top of the pile area to the bottom of the pit (3) that needs to be connected, and then connect it to the pit (3) one by one upwards.
8. The interface-adjustable precast pile according to claim 1, characterized in that, The concave-convex secondary pit structure (7) is a geometric structure that is recessed and protruded again on the inner surface (5) of the pit; The depth of the depression and the height of the protrusion of the concave-convex secondary pit structure (7) are less than one-third of the equivalent diameter of the pit edge (4).
9. A method of using an interface-adjustable precast pile according to any one of claims 1-8, characterized in that, This includes methods for increasing the side resistance of the pile and methods for reducing the negative skin friction of the pile. The method for increasing the side resistance of the pile includes the following steps: Shallow pit-shaped recesses and guide ribs (9) pointing in the direction of pile driving are provided on the outer surface (2) of the pile body (1). During the pile driving process, the guide rib (9) is used to guide and press the soil (11) on the pile side into the shallow pit and compact it, so that the soil (11) on the pile side and the concave-convex secondary pit structure (7) are combined to form soil nails (10). After the pile driving is completed, an interface reinforcing agent is injected into the shallow pit through the reserved pipe (6) to solidify the soil nail (10) and form a reinforced soil nail (12). The ultimate lateral resistance of the pile body in each soil layer after improvement is determined according to the following principle: the sum of the areas enclosed by the projections of all pit edges (4) of the corresponding soil layers within the enhanced pile segment onto the outer surface (2) of the pile body, multiplied by the shear strength of the current soil layer, plus the product of the area of the total area of the outer surface (2) of the enhanced pile segment minus the sum of the areas enclosed by the projections and the ultimate lateral resistance of the original corresponding soil layer, and the sum of the two is divided by the total area of the outer surface (2) of the enhanced pile segment.
10. The method of using an interface-adjustable precast pile according to claim 9, characterized in that, The method for reducing negative skin friction of the pile includes the following steps: A deep pit and a semi-enclosed guide rib (903) are provided on the outer surface (2) of the pile body (1). During the pile driving process, the semi-enclosed guide rib (903) is used to guide the soil (11) on the pile side away from the deep pit, forming a detached cavity (13) in the deep pit. After the pile driving is completed, an interface weakening agent is injected into the deep pit through the reserved pipe (6); The ultimate negative skin friction of each soil layer after reduction is determined according to the following principle: the sum of the areas enclosed by the projections of the edges (4) of all corresponding soil layers within the reduced pile section onto the outer surface (2) of the pile body, the product of the original ultimate negative skin friction and the adjustment coefficient, plus the product of the total area of the outer surface (2) of the reduced pile section minus the sum of the areas enclosed by the projections and the ultimate negative skin friction of the original corresponding soil layer, and the sum of the two is divided by the total area of the outer surface (2) of the reduced pile section.