Small-diameter high-bearing-capacity composite pile foundation

Abstract

The application discloses a small-diameter high-bearing-capacity composite pile foundation, and relates to the technical field of pile foundation construction.The small-diameter high-bearing-capacity composite pile foundation comprises a pile hole, a steel casing, a steel pile and a grouting body, the pile hole is arranged in a foundation, the steel casing is arranged on the upper portion of the pile hole and is attached to the pile hole, the steel pile is arranged in the pile hole in a penetrating mode, the top of the steel pile is connected with a pile cap, the bottom of the steel pile is embedded into a bedrock, and the grouting body is arranged in the pile hole and the steel casing, so that the steel casing, the steel pile and the surrounding rock mass form a composite stress structure together, the small-diameter rock-embedded steel pile structure is adopted, the single-pile bearing capacity is significantly improved through the composite stress mechanism among the steel casing, the steel pile, the grouting body and the rock mass under the condition that the pile diameter is kept small, the pile foundation structure construction equipment requirement is low, the construction technology is relatively simple, the construction cost and difficulty are reduced, and the construction efficiency under the condition of narrow site is improved.

Description

Technical Field

[0001] This invention relates to the field of pile foundation construction technology, and in particular to a small-diameter, high-bearing-capacity composite pile foundation. Background Technology

[0002] In municipal bridges, urban elevated roads, underground utility tunnels, and urban building foundation engineering, due to the large engineering loads and complex foundation conditions, pile foundations are usually required to meet the requirements for bearing capacity and settlement control. Commonly used pile foundation types in existing technologies mainly include bored cast-in-place piles, large-diameter steel pipe piles, and precast concrete piles. These types of pile foundations typically increase the bearing capacity of a single pile by increasing the pile diameter or length, and are used in the form of pile group foundations to jointly bear the load of the superstructure.

[0003] However, urban construction land is usually scarce, and construction sites are restricted by surrounding roads, existing buildings and underground pipelines, which greatly limits the entry and construction of large drilling equipment. Large-diameter pile foundations usually require large construction equipment and large construction space, resulting in high construction costs and difficulties, and low construction efficiency under narrow site conditions. Summary of the Invention

[0004] This invention provides a small-diameter, high-bearing-capacity composite pile foundation to address the technical problems in existing large-diameter pile foundations, which typically require large construction equipment and a large construction space, have significant limitations on the access and construction of large drilling equipment, and result in high construction costs and difficulties, as well as low construction efficiency under narrow site conditions.

[0005] Firstly, a small-diameter, high-bearing-capacity composite pile foundation is provided, comprising: The pile hole is located in the foundation. A steel casing is provided on the upper part of the pile hole and is fitted therewith; A steel pile, wherein the steel pile is inserted through the pile hole, the top of the steel pile is connected to the pile cap, and the bottom of the steel pile is embedded in the bedrock; The grouting body is placed inside the pile hole and the steel casing, so that the steel casing and the steel pile, and the steel pile and the surrounding rock mass together form a composite stress structure.

[0006] In some embodiments, the top of the steel casing is located at the bottom of the support platform and is fixedly connected thereto, and the bottom of the steel casing is embedded in the bedrock to a predetermined depth.

[0007] In some embodiments, the steel pile is an H-shaped steel pile, and a plurality of shear bars are spaced apart on the steel pile.

[0008] In some embodiments, the pile hole, the steel casing, and the steel pile are vertical piles arranged in a vertical direction.

[0009] In some embodiments, the pile hole, the steel casing, and the steel pile are inclined piles with a preset inclination angle.

[0010] In some embodiments, the grout body is made of cement-based non-shrink grouting material.

[0011] In some embodiments, the support platform includes: A steel plate, wherein the steel plate is disposed on top of the steel pile; Multiple anchoring bars are spaced apart on the steel plate.

[0012] In some embodiments, the steel plate has multiple ventilation holes spaced apart in the middle.

[0013] In some embodiments, the bottom of the support platform is further provided with a pad layer, which is arranged around the outside of the top of the steel casing.

[0014] Secondly, a construction method for small-diameter, high-bearing-capacity composite pile foundations is provided, including the following steps: Step S10: Drive a steel casing into the foundation, so that the top of the steel casing passes through the overlying soil layer and extends to the top of the bedrock. Step S20: Using drilling equipment, pile holes are formed in the foundation and steel casing, and the pile holes penetrate the overlying soil layer and extend into the bedrock; Step S30: Lower the steel casing so that its bottom is embedded in the bedrock to a preset depth, so that the steel casing and the surrounding soil form a stable support structure. Step S40: Insert the steel pile into the pile hole so that the bottom of the steel pile is embedded in the bedrock to form a rock-embedded section. Step S50: The grout is injected into the pile hole and the steel casing, so that the steel casing and the steel pile, and the steel pile and the surrounding rock mass together form a composite stress structure.

[0015] The beneficial effects of the technical solution provided by this invention include: This invention provides a small-diameter, high-bearing-capacity composite pile foundation, comprising: a pile hole, a steel casing, a steel pile, and a grouting body. The pile hole is located in the foundation, the steel casing is located above and fitted to the pile hole, the steel pile is inserted through the pile hole, the top of the steel pile is connected to the pile cap, and the bottom of the steel pile is embedded in the bedrock. The grouting body is located in the pile hole and the steel casing, so that the steel casing, the steel pile, and the surrounding rock mass together form a composite force-bearing structure. By adopting a small-diameter rock-embedded steel pile structure, while maintaining a small pile diameter, the bearing capacity of a single pile is significantly improved through the composite force-bearing mechanism between the steel casing, the steel pile, the grouting body, and the rock mass. Furthermore, the steel casing, in conjunction with the grouting body, forms a stable embedded connection between the steel pile and the surrounding rock mass, which can fully utilize the lateral resistance of the rock mass and the bearing capacity of the pile end, thereby improving the overall stability of the pile foundation. Moreover, the construction equipment requirements for the pile foundation structure are relatively low, the construction process is relatively simple, reducing construction costs and difficulties, and improving construction efficiency under narrow site conditions. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the overall structure of a small-diameter, high-bearing-capacity composite pile foundation provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the pile cap structure of a vertical pile provided in an embodiment of the present invention; Figure 3 This is a side view of the pile cap of a vertical pile provided in an embodiment of the present invention; Figure 4 This is a top view of the pile cap of a vertical pile provided in an embodiment of the present invention; Figure 5 A cross-sectional view of a vertical pile provided in an embodiment of the present invention; Figure 6 This is a schematic diagram of the overall structure of the inclined pile provided in an embodiment of the present invention; Figure 7 This is a schematic diagram of the pile cap structure of the inclined pile provided in an embodiment of the present invention; Figure label: 1. Pile hole; 2. Steel casing; 3. Steel piles; 31. Shear reinforcement; 4. Grouting body; 5. Foundation; 51. Steel plate; 511. Vent hole; 52. Anchoring reinforcement; 6. Bedrock; 7. Subbase layer. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of 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, 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.

[0019] This invention provides a small-diameter, high-bearing-capacity composite pile foundation, which solves the technical problems of existing large-diameter pile foundations, which usually require large construction equipment and large construction space, and the access and construction of large drilling equipment are greatly restricted, resulting in high construction costs and difficulties, as well as low construction efficiency under narrow site conditions.

[0020] Figure 1 This is a schematic diagram of a small-diameter, high-bearing-capacity composite pile foundation structure provided by an embodiment of the present invention, including: a pile hole 1, a steel casing 2, a steel pile 3, and a grouting body 4. The pile hole 1 is located in the foundation, the steel casing 2 is located on the upper part of the pile hole 1 and fits against it, the steel pile 3 is inserted through the pile hole 1, the top of the steel pile 3 is connected to the pile cap 5, the bottom of the steel pile 3 is embedded in the bedrock 6, and the grouting body 4 is located in the pile hole 1 and the steel casing 2, so that the steel casing 2 and the steel pile 3, and the steel pile 3 and the surrounding rock mass together form a composite load-bearing structure.

[0021] This invention relates to a small-diameter, high-bearing-capacity composite pile foundation, comprising: a pile hole, a steel casing, a steel pile, and a grouting body. The pile hole is located in the foundation, the steel casing is positioned above and fitted to the pile hole, the steel pile is inserted through the pile hole, the top of the steel pile is connected to the pile cap, and the bottom of the steel pile is embedded in the bedrock. The grouting body is located within the pile hole and the steel casing, forming a composite load-bearing structure with the steel casing, the steel pile, and the surrounding rock. By employing a small-diameter, rock-embedded steel pile structure, while maintaining a relatively small pile diameter, the composite load-bearing capacity and structural stability of the single pile are significantly improved through the composite load-bearing mechanism between the steel casing, the steel pile, the grouting body, and the rock mass. The steel casing, in conjunction with the grouting body, ensures the steel pile's structural integrity and structural stability. The piles and shear reinforcements form a stable embedded connection with the surrounding rock mass. The steel casing and grouting body work together to form a stable confined environment, enabling the steel piles to form a reliable embedded connection with the surrounding rock mass. This fully utilizes the lateral resistance of the rock mass and the bearing capacity of the pile ends, improving the overall stability of the pile foundation. The small-diameter high-bearing-capacity composite pile foundation of this invention requires less equipment for pile foundation construction and has a relatively simple construction process, reducing construction costs and difficulty. It also improves construction efficiency in narrow site conditions. By reducing the pile diameter and increasing the bearing capacity of a single pile, it reduces construction costs while ensuring structural safety and minimizing the impact on the surrounding environment and traffic. It is suitable for foundation engineering projects with limited construction space in urban municipal engineering.

[0022] As an optional implementation, in one embodiment of the invention, see [link to relevant documentation]. Figure 2 , Figure 3 and Figure 4 As shown, the top of the steel casing 2 is located at the bottom of the pile cap 5 and is fixedly connected to it. The bottom of the steel casing 2 is embedded in the bedrock 6 to a preset depth, and the bottom of the steel casing 2 is embedded in the bedrock 6 to 500mm. The steel casing 2 is used to prevent borehole collapse and ensure pile quality, stabilize the borehole wall structure, physically prevent soil collapse, ensure the regular shape of the pile hole 1, avoid waste of concrete or grouting materials, ensure the integrity of the pile body, and also isolate groundwater and mud. The steel casing 2 can effectively prevent upper groundwater or construction mud from entering the lower rock layer area of ​​the pile hole 1, prevent contamination of the rock surface, and ensure the bonding quality between the pile end and the bedrock. The use of the steel casing 2 in conjunction with the grouting structure enables the steel pile 3 to form a stable embedded connection with the surrounding rock mass, which can fully utilize the rock mass side resistance and pile end bearing capacity, and improve the overall stability of the pile foundation.

[0023] As an optional implementation, in one embodiment of the invention, see [link to relevant documentation]. Figure 4 and Figure 5As shown, the steel pile 3 is an H-shaped steel pile, with several shear bars 31 spaced apart on it. The flange and web structure of the H-shaped steel pile can form a better mechanical interlock with the surrounding grouting body 4. The grouting body 4 fills the space between the flanges, significantly improving the shear resistance and bond strength of the interface between the steel pile 3 and the grouting body 4, preventing relative slippage of the steel pile 3 within the grouting body 4. The H-shaped steel pile has an extremely high strength-to-weight ratio. Within the confined small-diameter pile hole 1, the H-shaped steel can provide higher sectional stiffness and bearing capacity than concrete piles of the same diameter, solving the problem of... It resolves the contradiction between small diameter and high bearing capacity; H-shaped steel piles have strong and weak axes, and when subjected to unidirectional horizontal loads, the material utilization rate can be maximized by adjusting the placement direction of the H-shaped steel; by adopting a small-diameter rock-embedded H-shaped steel pile structure, while keeping the pile diameter small, the bearing capacity of a single pile is significantly improved through the composite force mechanism between the H-shaped steel pile, the grouting body, and the rock mass, thereby reducing the number of pile foundations, reducing the pile diameter, and increasing the bearing capacity of a single pile. While ensuring structural safety, it reduces construction costs and reduces the impact on the surrounding environment and traffic, and has good engineering application value.

[0024] In addition, the shear reinforcement 31 is welded to the two side flanges of the steel pile 3, and is mainly set in the rock-embedded section of the steel pile 3 and the connection area with the pile cap 5. The shear reinforcement 31 is not set in the overlying soil section. The shear reinforcement 31 extends laterally into the grouting body 4 to enhance the interfacial interlocking and shear force transmission capacity between the steel pile 3 and the grouting body 4. During the stress process, the shear reinforcement 31 effectively improves the shear connection between the steel pile 3 and the grouting body 4 through mechanical interlocking and interfacial bonding with the grouting body 4. Yes, it can prevent the steel pile 3 from slipping relative to each other during the stress process; at the same time, the shear reinforcement 31 will more evenly transfer the axial load and horizontal shear force borne by the steel pile 3 to the surrounding grouting body 4 and rock mass, thereby enhancing the cooperative stress-bearing capacity between the pile body and the rock mass, improving the side resistance efficiency of the rock-embedded section, and significantly improving the interface shear resistance performance. Since the rock-embedded section is the main stress-bearing area, setting the shear reinforcement 31 can significantly improve the interface shear resistance performance. However, the soil-covered section mainly relies on the side friction of the soil, and its interface shear resistance requirements are lower, so the shear reinforcement 31 is not set.

[0025] As an optional implementation, in one embodiment of the invention, see [link to relevant documentation]. Figure 1 , Figure 2 and Figure 3As shown, the pile hole 1, the steel casing 2, and the steel pile 3 are vertical piles arranged in the vertical direction. The pile hole 1, the steel casing 2, and the steel pile 3 can be set as vertical piles according to the stress conditions of the project. They are used to bear vertical loads, withstand the vertical pressure (gravity) or pull force transmitted from the superstructure, and also to transfer the load to the bearing layer. The load is transferred to the deep bedrock through the friction of the pile body and the resistance of the pile end. This improves the ability of the small-diameter high-bearing-capacity composite pile foundation of the present invention to resist horizontal loads and overturning moments, and enhances its adaptability.

[0026] As an optional implementation, in one embodiment of the invention, see [link to relevant documentation]. Figure 6 and Figure 7 As shown, the pile hole 1, the steel casing 2, and the steel pile 3 are inclined piles with a preset inclination angle. Depending on the stress conditions of the project, the pile hole 1, the steel casing 2, and the steel pile 3 can be configured as inclined piles with a preset inclination angle to resist horizontal loads. They can effectively distribute the horizontal forces (such as wind loads, seismic forces, water flow impact forces, vehicle braking forces, etc.) acting on the pile cap 5 or the superstructure through the axial pressure or tension of the pile foundation, reducing the simple dependence of the pile foundation on the lateral resistance of the soil. They are also used to resist overturning moments. When subjected to large bending moments, the inclined pile arrangement can increase the equivalent moment of inertia of the pile foundation group, improve the overall overturning stability of the foundation, and optimize the stress system. The pile arrangement is no longer limited to the vertical direction; the pile position can be adjusted according to the principal stress direction, allowing for more full utilization of the strength of the pile material and avoiding uneven stress distribution. When an inclined pile arrangement is used, the ability of the foundation structure to resist horizontal loads and overturning moments can be effectively improved, making it suitable for engineering structures such as bridges and viaducts subjected to large horizontal forces.

[0027] As an optional implementation, in one embodiment of the invention, see [link to relevant documentation]. Figure 1 and Figure 5 As shown, the grouting body 4 is made of cement-based non-shrink grouting material. The grouting body 4 serves as a load transfer medium and composite structural binder, uniformly transferring the load borne by the steel pile 3 to the surrounding rock mass (lateral resistance) and the bedrock at the pile end (end resistance), binding all components into a whole. This allows the steel pile 3, the grouting body 4, and the surrounding rock mass to form a composite structure, enabling them to deform collaboratively and share the load, thus achieving a composite load-bearing system. The grouting body 4 also serves as an anti-corrosion protective layer. The alkaline environment provided by the cement-based material can form a passivation film on the surface of the steel pile 3, preventing the steel pile 3 from directly contacting groundwater or corrosive soil, thereby improving durability. The cement-based non-shrink grouting material can eliminate contact gaps, ensuring close contact between the surface of the steel pile 3 and the grouting body 4, and between the grouting body 4 and the borehole wall, avoiding stress concentration. This ensures composite load-bearing, ensuring that the steel pile 3 and the rock mass can deform synchronously, fully utilizing the rigidity of the composite pile foundation.

[0028] As an optional implementation, in one embodiment of the invention, see [link to relevant documentation]. Figure 2 , Figure 3 and Figure 4 As shown, the pile cap 5 includes a steel plate 51 and multiple anchoring bars 52. The steel plate 51 is located on top of the steel pile 3, and the multiple anchoring bars 52 are spaced apart on the steel plate 51. The steel pile 3 is connected to the steel plate 51 through the multiple anchoring bars 52, and the entire structure is cast to form the overall load-bearing structure of the pile cap 5, so that the load of the superstructure can be reliably transferred to the pile foundation system. The mechanical path is: the pile cap 5 to the multiple anchoring bars 52, the multiple anchoring bars 52 to the steel plate 51, and the steel plate 51 to the steel pile 3. The superstructure load acts on the concrete pile cap 5, and the force is transferred to the multiple anchoring bars 52 through the bond force between the concrete and the multiple anchoring bars 52. The multiple anchoring bars 52 are connected to the steel plate 51 and transfer the tensile or compressive force to the steel plate 51. The steel plate 51 is connected to the top of the steel pile 3 and distributes the load evenly to the web and flange of the steel pile 3.

[0029] As an optional implementation, in one embodiment of the invention, see [link to relevant documentation]. Figure 2 , Figure 3 and Figure 4 As shown, the steel plate 51 has multiple ventilation holes 511 spaced apart in the middle. The ventilation holes 511 are used for venting and depressurization. During the concrete pouring process of the foundation, the ventilation holes 511 prevent the formation of a closed space between the bottom of the steel plate 51 and the top surface of the steel pile 3. The ventilation holes 511 allow the air in the closed space to be discharged, avoiding the formation of air pockets. The ventilation holes 511 are also used to ensure compactness, allowing the concrete slurry to flow through the holes, ensuring that the concrete below and around the steel plate 51 is filled densely, and eliminating voids or honeycomb defects.

[0030] As an optional implementation, in one embodiment of the invention, see [link to relevant documentation]. Figure 1 and Figure 2 As shown, a cushion layer 7 is also provided at the bottom of the foundation 5. The cushion layer 7 is arranged around the outside of the top of the steel casing 2. The cushion layer 7 can effectively prevent underground capillary water from rising and directly contacting the bottom of the foundation 5 and the connection node of the steel pile 3. Together with the concrete covering of the foundation 5, it forms a double anti-corrosion barrier. The cushion layer 7 is also used for leveling and isolation, uniform force transmission, and protection of reinforcing bars. It provides a flat base for the concrete pouring of the foundation 5, isolates the concrete of the foundation 5 from the soil below, prevents the soil from absorbing water from the concrete or mixing in impurities, and helps to transfer the load of the foundation 5 more evenly to the soil below or the pile top area, reducing stress concentration, preventing the bottom reinforcing bars of the foundation 5 from directly contacting the soil and corroding, and ensuring the thickness of the protective layer.

[0031] This invention also provides a construction method for small-diameter, high-bearing-capacity composite pile foundations, comprising the following steps: Step S10: Drive steel casing 2 into the foundation so that the top of the steel casing 2 passes through the overlying soil layer and extends to the top of the bedrock 6. Step S20: Using drilling equipment, pile holes 1 are formed in the foundation and steel casing 2. The pile holes 1 penetrate the overlying soil layer and extend into the bedrock 6. Step S30: Sink the steel casing 2 so that its bottom is embedded in the bedrock 6 to a preset depth, so that the steel casing 2 and the surrounding soil form a stable support structure; Step S40: Insert the steel pile 3 into the pile hole 1, so that the bottom of the steel pile 3 is embedded in the bedrock 6 to form a rock-embedded section. In step S50, the grout 4 is injected into the pile hole 1 and the steel casing 2, so that the steel casing 2 and the steel pile 3, and the steel pile 3 and the surrounding rock mass together form a composite stress structure.

[0032] By employing a small-diameter rock-socketed steel pile structure, while maintaining a relatively small pile diameter, the composite force mechanism between the steel casing, steel pile, grouting body, and rock mass significantly improves the single pile bearing capacity and structural stability. The steel casing, in conjunction with the grouting body, creates a stable embedded connection between the steel pile, shear reinforcement, and the surrounding rock mass. The combined action of the steel casing and grouting body forms a stable constraint environment, ensuring a reliable embedded connection between the steel pile and the surrounding rock mass. This fully utilizes the lateral resistance of the rock mass and the bearing capacity of the pile tip, improving the overall stability of the pile foundation. The small-diameter, high-bearing-capacity composite pile foundation of this invention requires less sophisticated construction equipment and employs a relatively simple construction process, reducing construction costs and difficulty, and improving construction efficiency in confined spaces. By reducing the pile diameter and increasing the single pile bearing capacity, it ensures structural safety while reducing construction costs and minimizing the impact on the surrounding environment and traffic. It is suitable for foundation engineering projects in urban municipal engineering where construction space is limited.

[0033] In the description of this invention, it should be noted that the terms "upper," "lower," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Unless otherwise expressly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication between two elements. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0034] It should be noted that in this invention, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0035] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features of the invention herein.

Claims

1. A small-diameter, high-bearing-capacity composite pile foundation, characterized in that, include: Pile hole (1), wherein the pile hole (1) is located in the foundation; A steel casing (2) is provided on the upper part of the pile hole (1) and fits therewith; A steel pile (3) is installed through the pile hole (1), the top of the steel pile (3) is connected to the pile cap (5), and the bottom of the steel pile (3) is embedded in the bedrock (6); Grouting body (4), the grouting body (4) is provided in the pile hole (1) and the steel casing (2), so that the steel casing (2) and the steel pile (3), and the steel pile (3) and the surrounding rock mass together form a composite stress structure.

2. The small-diameter high-bearing-capacity composite pile foundation according to claim 1, characterized in that: The top of the steel casing (2) is located at the bottom of the support platform (5) and is fixedly connected thereto. The bottom of the steel casing (2) is embedded in the bedrock (6) to a preset depth.

3. The small-diameter high-bearing-capacity composite pile foundation according to claim 1, characterized in that: The steel pile (3) is an H-shaped steel pile, and a number of shear bars (31) are spaced apart on the steel pile (3).

4. The small-diameter high-bearing-capacity composite pile foundation according to claim 1, characterized in that: The pile hole (1), the steel casing (2), and the steel pile (3) are vertical piles set in the vertical direction.

5. The small-diameter high-bearing-capacity composite pile foundation according to claim 1, characterized in that: The pile hole (1), the steel casing (2), and the steel pile (3) are inclined piles with a preset inclination angle.

6. The small-diameter high-bearing-capacity composite pile foundation according to claim 1, characterized in that: The grouting body (4) is made of cement-based non-shrink grouting material.

7. The small-diameter high-bearing-capacity composite pile foundation according to claim 1, characterized in that, The foundation (5) includes: A steel plate (51) is disposed on top of the steel pile (3); Multiple anchoring bars (52) are spaced apart on the steel plate (51).

8. The small-diameter high-bearing-capacity composite pile foundation according to claim 7, characterized in that: The steel plate (51) has multiple ventilation holes (511) spaced apart in the middle.

9. The small-diameter high-bearing-capacity composite pile foundation according to claim 1, characterized in that: The bottom of the support platform (5) is also provided with a pad (7), which is arranged around the outside of the top of the steel casing (2).

10. A construction method using the small-diameter, high-bearing-capacity composite pile foundation as described in claim 1, characterized in that, Includes the following steps: Step S10: Drive a steel casing (2) into the foundation so that the top of the steel casing (2) passes through the overlying soil layer and extends to the top of the bedrock (6); Step S20: Using drilling equipment, pile holes (1) are formed in the foundation and steel casing (2). The pile holes (1) penetrate the overlying soil layer and extend into the bedrock (6). Step S30: Sink the steel casing (2) so that its bottom is embedded in the bedrock (6) to a preset depth, so that the steel casing (2) and the surrounding soil form a stable support structure; Step S40: Insert the steel pile (3) into the pile hole (1) so that the bottom of the steel pile (3) is embedded in the bedrock (6) to form a rock-embedded section; Step S50: Inject the grout (4) into the pile hole (1) and the steel casing (2) so that the steel casing (2) and the steel pile (3), and the steel pile (3) and the surrounding rock mass together form a composite stress structure.

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