A composite foundation of variable-spacing rigid piles for improving embankment stability

Abstract

The present invention discloses a variable spacing rigid pile composite foundation for improving the stability of the embankment. The distance from the foot of the embankment slope to the shoulder is L. The arrangement area of ​​all rigid piles is the area covered by the embankment, which is divided into the arrangement area of ​​the large spacing piles on the inside and the arrangement area of ​​the small spacing piles on the outside; the small spacing rigid piles use rigid piles with a certain ductility and a small spacing without pile caps, and the large spacing rigid piles use rigid piles with a large spacing and pile caps. The present invention solves the engineering problem that the outer pile body of the rigid pile composite foundation is prone to brittle fracture under a large bending moment, which causes the inner pile body to brittle fracture in turn, thereby causing the embankment to become unstable and the bearing capacity to be greatly reduced. The large spacing inner piles with pile caps can greatly reduce the cost on the basis of effectively controlling the settlement and uneven settlement. The present invention is simple to construct, has a good total settlement control effect, can greatly improve the stability of the embankment, has high safety, strong applicability, and good economy.

Description

Technical Field

[0001] The invention relates to a civil construction foundation, in particular to a variable-spacing rigid pile composite foundation. Background Art

[0002] In recent years, with the rapid development of high-speed railways and other construction projects in my country, higher requirements have been put forward for the construction speed and settlement control of embankments. In coastal areas of my country, the upper soil is mostly saturated soft clay, with low shear resistance and poor drainage capacity, so embankments are prone to instability and damage. In order to meet the requirements of rapid construction and settlement control, rigid pile composite foundations have been more and more widely used. Rigid piles include CFG piles, plain concrete piles, reinforced concrete piles, PCC piles and other pile types. They have the advantages of high bonding strength, strong bearing capacity, good settlement control effect, and fast construction speed. They are widely used in engineering, but their cost is high, and the material properties are very different from traditional vertical reinforcements. There have been many engineering accidents in which embankments have become unstable due to bending damage of rigid piles. How to reasonably use rigid piles to reinforce embankments in engineering, improve the stability of embankments and effectively control costs has become an urgent problem to be solved.

[0003] During the construction and use of the embankment, as the embankment continues to rise and the load on the upper part of the embankment continues to increase, the stress on each pile also increases significantly. However, there are large differences in the stress on the piles at different positions. The inner piles mainly bear vertical axial forces, which can effectively control the settlement of the embankment. The outer piles bear relatively small axial forces, but are subject to large horizontal loads on the soil, so they bear large bending moments. Under the combined action of large bending moments and small axial forces, the outer piles first approach their ultimate tensile strength, while the bearing capacity of the inner piles is not fully utilized at this time. If the outer piles undergo brittle bending failure due to the tensile strength reaching the ultimate tensile strength, after they fail, due to stress release, the internal force in the piles decreases rapidly, and the restraining effect on the soil is rapidly weakened. The soil moves and interacts with the adjacent inner piles, resulting in increased stress on the inner piles and subsequent brittle bending failure. This cycle repeats, and each pile undergoes continuous bending failure from the outside to the inside, ultimately leading to the instability of the embankment and causing huge casualties and property losses. At the same time, the pile spacing has a significant impact on the horizontal force of the pile body. However, most of the existing composite foundation design methods adopt equal-spacing piles based on the deformation and bearing capacity verification results. Even in a few non-equal-spacing pile projects, they all adopt a composite foundation form with small inner pile spacing and large outer pile spacing for the purpose of controlling settlement. From the perspective of pile bending moment, there is no non-equal-spacing embankment design method for the purpose of improving embankment stability.

[0004] In summary, how to make the outer and inner piles play their respective roles when constructing the composite foundation, improve the ability of the embankment to resist continuous damage, and control the embankment settlement and uneven settlement on the basis of controlling costs has become an urgent problem to be solved. Summary of the invention

[0005] In view of the defects existing in the prior art, the present invention provides a variable-spacing rigid pile composite foundation for improving the stability of the embankment, which solves the engineering problem that the outer pile body of the traditional equally-spaced rigid pile composite foundation is prone to brittle fracture under large bending moments, thereby causing the inner pile body to successively undergo brittle fractures, and further leading to the instability of the embankment and a significant reduction in bearing capacity. At the same time, it solves the problems of poor uneven settlement control effect when the inner pile spacing is large, and significantly increased cost and waste of resources when the spacing is small.

[0006] In order to solve the above technical problems, the present invention proposes a variable-spacing rigid pile composite foundation for improving the stability of an embankment, comprising an embankment arranged on a reinforced soil body, wherein a plurality of rigid piles are arranged in a row and column matrix in the reinforced soil body, the embankment comprises an embankment top surface and embankment slopes on both sides of the embankment top surface, and the distance from the toe of the embankment slope to the shoulder of the embankment slope on the cross section of the embankment is L, and the arrangement area of ​​all rigid piles is the area covered by the embankment; the arrangement area of ​​all rigid piles is divided into an arrangement area of ​​large-spacing piles and an arrangement area of ​​small-spacing piles; the arrangement area of ​​the small-spacing piles extends from the toe of the embankment slopes on both sides to the center line of the embankment cross-sectional width to 2L. The area occupied by the second rigid piles is the area occupied by the second rigid piles; the remaining area is the area occupied by the large-spacing piles; the rigid piles in the area occupied by the large-spacing piles are recorded as first rigid piles, and the rigid piles in the area occupied by the small-spacing piles are recorded as second rigid piles. The tops of the first rigid piles are provided with rectangular or circular pile caps. The pile diameter of the first rigid piles is D=0.3-0.8m, the pile spacing is A=2-3m, and the diameter or side length of the pile cap is ≥3D; the pile diameter of the second rigid piles is D, and the pile spacing of the second rigid piles is 1 / 2A to 2 / 3A. When the embankment filling height H≥5m and the slope angle β≥27°, the pile spacing of the second rigid piles takes a smaller value within the above value range, otherwise it takes a larger value.

[0007] Within the above range of values, the specific values ​​of the pile diameter, pile spacing and pile cap of the first rigid pile are determined by verification and calculation based on the bearing capacity and deformation requirements of composite foundation in the Technical Specifications for Building Foundation Treatment with standard number JGJ 79-2012.

[0008] Furthermore, the first rigid pile and the second rigid pile are of the same type, which are any one of reinforced concrete piles, pipe piles with non-prestressed tendons, and prestressed pipe piles. Alternatively, the first rigid pile is any one of CFG piles, plain concrete piles, reinforced concrete piles, and pipe piles, and the second rigid pile is any one of reinforced concrete piles, pipe piles with non-prestressed tendons, and prestressed pipe piles.

[0009] The tops of all the rigid piles are flush with the upper surface of the reinforced soil, and a cushion layer with a thickness of 15 to 30 cm is laid on the reinforced soil.

[0010] The lower part of the reinforced soil body is an embedding layer soil body with an embedding effect, and the depth of all rigid piles inserted into the embedding layer soil body is ≥2D.

[0011] Compared with the prior art, the present invention has the following beneficial effects:

[0012] The composite foundation of the present invention solves the problem that the outer pile body of the traditional equally spaced rigid pile composite foundation is subjected to a large horizontal action of the soil body, and then bears a large bending moment, causing the pile body to bend and fail, resulting in brittle fracture of the inner pile body in turn, causing the embankment to be unstable and the bearing capacity to be greatly reduced. At the same time, it solves the problem that the cost is high and uneconomical when the embankment treatment adopts a small-spacing pile composite foundation, and the problem that the uneven settlement at the center of the embankment is large when a large-spacing pile arrangement method is adopted, and the pile body cannot fully play its role. Since the outer piles in the composite foundation of the present invention are rigid piles with a certain ductility, and the spacing is small, the pile-soil interaction can be reduced from the source, the horizontal load on the pile body is reduced, and the bending of the pile body is reduced, and the occurrence of brittle bending failure can be effectively resisted. In addition, the outer pile body is not provided with a pile cap, which can appropriately increase the settlement of the soil at the foot of the slope, thereby reducing the uneven settlement of the embankment, and at the same time reducing the horizontal load on the pile top, further reducing the bending moment of the pile body, and preventing the occurrence of bending failure. The inner pile body adopts rigid piles with large spacing, which can control costs while ensuring the stability of the embankment. At the same time, a pile cap is arranged on the upper part of the inner pile body to improve the stress sharing ratio of the inner pile body, ensuring the bearing capacity of the embankment while effectively controlling the total settlement and uneven settlement of the embankment. The outer pile body of the present invention can adopt reinforced concrete piles with certain ductility, pipe piles containing non-prestressed tendons or prestressed pipe piles, which can form plastic hinges when the pile body reaches the limit bending moment, prevent the occurrence of brittle bending failure, and improve the safety of the embankment; the inner pile body adopts rigid piles, which do not require ductility, and can give full play to the advantages of large rigidity of rigid piles, further saving costs on the basis of ensuring stability.

[0013] The composite foundation of the present invention has the advantages of simple construction, high safety, strong applicability and good economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a vertical cross-sectional view of the composite foundation of the present invention;

[0015] Figure 2 It is a plan view of the composite foundation of the present invention;

[0016] In the figure:

[0017] 1-Embankment, 2-Reinforced soil, 3-Rigid piles, 4-Arrangement area of ​​large-spacing piles, 5-Arrangement area of ​​small-spacing piles, 6-Pile cap. DETAILED DESCRIPTION

[0018] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but the following embodiments are by no means intended to limit the present invention in any way.

[0019] like Figure 1 and Figure 2 As shown, a variable-spacing rigid pile composite foundation for improving the stability of an embankment proposed by the present invention comprises an embankment 1 arranged on a reinforced soil body 2, wherein a plurality of rigid piles 3 are arranged in a row and column matrix in the reinforced soil body 2, the embankment 1 comprises an embankment top surface and embankment slopes on both sides of the embankment top surface, and on the cross section of the embankment 1, the distance from the toe of the embankment slope to the shoulder of the embankment slope is L, and the arrangement area of ​​all the rigid piles 3 is the area covered by the embankment 1.

[0020] The arrangement area of ​​all rigid piles 3 is divided into an inner arrangement area 4 for large-pitch piles and an outer arrangement area 5 for small-pitch piles; the arrangement area 5 for small-pitch piles is an area extending from the toe of the embankment slopes on both sides to the center line of the embankment cross-sectional width to 2L; the remaining arrangement area is the arrangement area 4 for large-pitch piles.

[0021] The rigid piles 3 in the arrangement area 4 of the large-spacing piles are recorded as first rigid piles, and the rigid piles in the arrangement area 5 of the small-spacing piles are recorded as second rigid piles; the first rigid piles are rigid piles with a large pile spacing and pile caps are provided, and the second rigid piles are rigid piles with a small pile spacing and a certain ductility and are not provided with pile caps.

[0022] The first rigid pile can be a reinforced concrete pile, a pipe pile with non-prestressed tendons, a prestressed pipe pile, or a rigid pile with a certain ductility, such as a reinforced concrete pile, a pipe pile with non-prestressed tendons, or a brittle and ductile rigid pile such as a CFG pile, a plain concrete pile, a PPC pipe pile, etc. The specific selection can be determined according to the site conditions, etc. The pile diameter of the first rigid pile is D=0.3-0.8m, and the pile spacing is A=2-3m. The specific values ​​are calculated according to the composite foundation bearing capacity and deformation calculation method in the "Technical Specification for Building Foundation Treatment" (JGJ 79-2012), and the design requirements are calculated. Under the condition of meeting the requirements of the specification, a larger value can be taken accordingly. The pile top of the first rigid pile is provided with a rectangular or circular pile cap 6, and the diameter or side length of the pile cap 6 is ≥3D, thereby increasing the vertical load area of ​​the pile body under the condition of large pile spacing, increasing the pile-soil stress ratio, increasing the pile body axial force, and thus increasing the bending bearing capacity, which can reduce the number of piles on the basis of meeting the safety and normal use of the composite foundation, thereby greatly saving costs.

[0023] The second rigid piles are reinforced concrete piles, pipe piles with non-prestressed tendons or prestressed pipe piles, etc., which have certain ductility. When the bending moment reaches the limit bending moment, the pile body will not be brittlely bent and damaged, but a plastic hinge will be formed, which ensures the bending bearing capacity of the pile body and maintains the stability of the embankment. At the same time, the outer small-spacing piles are not provided with pile caps, which can effectively reduce the horizontal interaction of the soil at the pile top position, and further reduce the bending moment of the pile body. The pile diameter of the second rigid piles in this area is the same as the pile diameter of the first rigid piles in the arrangement area 4 of the large-spacing piles, and the pile spacing is 1 / 2-2 / 3 of the pile spacing of the first rigid piles. When the embankment filling height is large, such as H≥5m, the slope is steep, such as the slope angle β≥27°, and the drainage conditions of the reinforced soil are poor and the strength is low, the pile spacing of the second rigid piles takes a small value within the above range, otherwise it takes a large value. The smaller pile spacing can greatly reduce the bending moment of the pile body without changing the properties of the pile body, reduce the possibility of bending damage of the pile body, and improve the stability of the embankment.

[0024] The variable-spacing composite foundation of the present invention is significantly different from the commonly used composite foundation of equally-spaced piles, and is essentially different from the existing composite foundation densification area. The existing composite foundation densification only densifies the center position of the embankment for the purpose of settlement control, which is of no help in improving the stability of the composite foundation. The larger pile spacing on both sides increases the possibility of bending and damage of the pile body. The variable-spacing composite foundation adjusts the bending moment of the pile body by adjusting the pile spacing, thereby improving the stability of the embankment. The method only changes the pile spacing and has fewer requirements on the pile body type, thereby reducing the construction difficulty and improving the operability in the project.

[0025] The tops of all rigid piles 3 are flush with the upper surface of the reinforced soil 2, and a 15-30 cm thick cushion layer is laid on the reinforced soil 2. If the reinforced soil 2 is under a relatively hard soil layer, all rigid piles 3 should be inserted into the embedded soil layer with an embedded depth of not less than 2 times the pile diameter, that is, ≥2D. The upper cushion layer can improve the integrity of the composite foundation, make the piles with different pile spacings work in coordination, and ensure that the embedded depth of the piles can improve the bending and anti-sliding bearing capacity of the piles, and prevent the piles from overturning and causing the embankment to become unstable.

[0026] Although the present invention has been described above in conjunction with the accompanying drawings, the present invention is not limited to the above-mentioned specific embodiments, which are merely illustrative rather than restrictive. Under the guidance of the present invention, ordinary technicians in this field can make many modifications without departing from the purpose of the present invention, all of which are within the protection of the present invention.

Claims

1. A variable spacing rigid pile composite foundation for improving the stability of an embankment, comprising an embankment (1) arranged on a reinforced soil body (2), wherein a plurality of rigid piles (3) are arranged in a row and column matrix in the reinforced soil body (2), wherein the embankment (1) comprises an embankment top surface and embankment side slopes on both sides of the embankment top surface, wherein the distance from the slope foot of the embankment side slope to the slope shoulder of the embankment side slope on the cross section of the embankment (1) is L, and the arrangement area of ​​all the rigid piles (3) is the area covered by the embankment (1); characterized in that: The arrangement area of ​​all rigid piles (3) is divided into an arrangement area (4) of large-pitch piles and an arrangement area (5) of small-pitch piles; the arrangement area (5) of small-pitch piles is an area extending from the toe of the embankment slopes on both sides to the center line of the embankment cross-sectional width to 2L; the remaining arrangement area is the arrangement area (4) of large-pitch piles; The rigid piles (3) in the arrangement area (4) of the large-pile spacing piles are recorded as first rigid piles, and the rigid piles in the arrangement area (5) of the small-pile spacing piles are recorded as second rigid piles. The tops of the first rigid piles are provided with rectangular or circular pile caps (6). The pile diameter of the first rigid piles is D=0.3-0.8m, the pile spacing is A=2-3m, and the diameter or side length of the pile cap (6) is ≥3D. The pile diameter of the second rigid pile is D, the pile spacing of the second rigid pile is 1 / 2A to 2 / 3A, when the embankment filling height H≥5m and the slope angle β≥27˚, the pile spacing of the second rigid pile takes a smaller value within the above value range, otherwise takes a larger value, the second rigid pile is not provided with a pile cap, the lower part of the reinforced soil (2) is an embedding layer soil with an embedding effect, the depth of the rigid pile (3) inserted into the embedding layer soil is ≥2D, the pile top of the rigid pile (3) is flush with the upper surface of the reinforced soil (2), and a cushion layer with a thickness of 15 to 30 cm is laid on the reinforced soil (2).

2. The variable spacing rigid pile composite foundation according to claim 1 is characterized by: The specific values ​​of the pile diameter, pile spacing and pile cap of the first rigid pile are determined by verification and calculation based on the bearing capacity and deformation requirements of composite foundation in the Technical Specification for Building Foundation Treatment with standard number JGJ 79-2012.

3. The variable spacing rigid pile composite foundation according to claim 1, characterized in that: The first rigid pile and the second rigid pile are of the same pile type, which are any one of a reinforced concrete pile, a pipe pile containing non-prestressed tendons, and a prestressed pipe pile.

4. The variable spacing rigid pile composite foundation according to claim 1, characterized in that: The first rigid pile is any one of a CFG pile, a plain concrete pile, a reinforced concrete pile and a pipe pile, and the second rigid pile is any one of a reinforced concrete pile, a pipe pile containing non-prestressed tendons and a prestressed pipe pile.

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