A displacement reference device integrated within a pile foundation

Abstract

The application discloses a displacement reference device integrated in a pile foundation, and belongs to the technical field of civil engineering monitoring. The device comprises a pre-buried guide pipe, a reference transmission rod and a friction isolation structure. The pre-buried guide pipe is fixed in the pile body and extends along the axial direction; the reference transmission rod is arranged in the guide pipe, the upper end of the reference transmission rod is exposed on the pile top as a measuring end, and the lower end of the reference transmission rod is anchored to a stable stratum below the pile end; and the friction isolation structure ensures that the guide pipe can slide vertically relative to the transmission rod without adhesion. The stable reference point is directly embedded in the pile top, the problem of no stable external reference point in a soft soil area is solved, and long-term displacement monitoring of the pile top is realized with high precision, low cost and convenience.

Description

Technical Field

[0001] This invention relates to the field of civil engineering pile foundation and monitoring technology, specifically to a reference device for long-term monitoring of the vertical displacement of pile foundations. This device is particularly suitable for complex engineering conditions such as soft soil areas, large-area fill areas, or areas without stable external reference points. It can directly integrate the displacement reference point inside the pile body, achieving high-precision, low-cost, and convenient pile top settlement monitoring. Background Technology

[0002] In civil engineering, long-term vertical deformation monitoring of pile foundations, especially test piles, is a crucial step in assessing their bearing capacity and long-term stability. Conventional monitoring methods involve finding one or more fixed benchmarks outside the pile body that are considered stable, and calculating the displacement of the pile top by measuring the relative elevation difference between the pile top and these benchmarks. The effective implementation of this method relies on two fundamental prerequisites: first, the existence of truly stable benchmarks near the test area; and second, optical visibility between the benchmarks and the measuring point at the pile top.

[0003] However, in engineering environments with large-scale ground settlement, such as soft soil areas, it is often difficult to find truly stable external reference points within a large area around the pile. To address this issue, two alternative solutions are typically employed. The first solution is to introduce a reference point from a greater distance. However, this method often suffers from poor visibility due to obstructions on site, requiring the establishment of multiple intermediate transition points, which significantly increases the accumulation of measurement errors and ultimately reduces monitoring accuracy. The second solution involves constructing reference piles that extend deep into bedrock or uncompressible stable strata around the test pile. However, to ensure sufficient rigidity and stability of the reference piles themselves, they typically need to be designed as large-diameter, deep piles, resulting in high costs, long construction periods, and poor economic efficiency and timeliness.

[0004] In summary, existing technologies suffer from several technical problems, including difficulty in finding stable external reference points, complex measurement links leading to reduced accuracy, and high costs and long construction periods associated with setting up dedicated external reference piles. Therefore, there is an urgent need for a high-precision displacement reference device that can be integrated into the pile foundation itself. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a displacement reference device integrated inside the pile foundation. This device can directly transfer a stable vertical displacement reference to the vicinity of the pile top, without relying on unstable or distant external reference points, and without the need to construct expensive dedicated external reference piles. Thus, while ensuring high-precision monitoring, it effectively reduces costs, simplifies the measurement process, and shortens the construction period.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A displacement reference device integrated inside a pile foundation includes a pre-embedded guide pipe, a reference transmission rod, and a friction isolation structure.

[0007] The pre-embedded guide pipe is fixed inside the pile body and extends along the axial direction of the pile foundation, forming an internal channel that runs from the top of the pile to the bottom of the pile or near the bottom of the pile. The guide pipe is pre-installed before the pile body is poured or driven, becoming part of the pile structure.

[0008] The reference transmission rod is inserted into the pre-embedded conduit. Its upper end forms a measuring end exposed at the top of the pile for direct elevation measurement; its lower end passes through the bottom of the pre-embedded conduit and is anchored to a stable stratum below the pile tip using anchoring measures. The stable stratum is, for example, an uncompressible layer such as bedrock or dense sand and gravel.

[0009] The friction isolation structure is installed between the embedded guide pipe and the reference transfer rod. Its function is to ensure that the embedded guide pipe can slide freely vertically with no adhesion or low friction relative to the reference transfer rod. The embedded guide pipe deforms along with the pile body, while the lower end of the reference transfer rod is anchored in stable strata, thus maintaining a relatively stable vertical position. Through the combined action of these components, the absolute position reference of the deep stable strata is transferred to the vicinity of the pile top, thereby forming a constant or nearly constant reference point relative to the stable strata at the pile top—the top of the reference transfer rod—ultimately constituting a displacement reference device integrated within the pile foundation.

[0010] As a further improvement of the present invention, the pre-embedded conduit is a hollow tube pre-set before pile construction, such as a steel pipe or a high-rigidity plastic pipe.

[0011] As a further improvement of the present invention, the friction isolation structure is implemented in ways including but not limited to the following two: the first is a lubricating layer coated on the outer surface of the reference transmission rod, such as grease or special engineering grease; the second is a spiral rib structure set on the inner wall of the pre-embedded conduit, the top of which forms line contact or point contact with the outer wall of the reference transmission rod, so that the reference transmission rod is in a multi-point contact state, thereby greatly reducing the contact area and effectively reducing the sliding friction resistance.

[0012] As a further improvement of the present invention, the device also includes a stabilizing casing. The stabilizing casing is disposed inside the pre-embedded guide pipe, forming a continuous internal channel with the pre-embedded guide pipe of the pile body, and its lower end extends and is anchored in a stable stratum below the pile bottom. The reference transmission rod is disposed inside the stabilizing casing. The stabilizing casing further enhances the lateral constraint and long-term stability of the lower part of the reference transmission rod.

[0013] As a further improvement of the present invention, when a stabilizing sleeve is provided, a spiral rib structure that makes the reference transmission rod make multi-point contact can be provided on the inner wall of the stabilizing sleeve as part of the friction isolation structure to optimize the sliding performance of the reference transmission rod in the sleeve.

[0014] As a further improvement of the present invention, the bottom of the stabilizing casing is solidified with the stabilizing stratum by injecting cement grout or other high-strength grout to form a reliable anchor.

[0015] As a further improvement of the present invention, the stabilizing casing can be a segmented steel pipe implanted by the casing drilling process to adapt to different formation depths and facilitate construction.

[0016] As a further improvement of the present invention, the lower end of the pre-embedded conduit is pre-set with a punctureable sealing structure. This sealing structure can be a low-strength concrete block, a wooden plug, or a weldable thin steel plate. After the pile body is formed, the sealing structure is punctured by working downwards from inside the conduit using equipment such as a core drill, so that the reference transfer rod or stabilizing casing can be subsequently implanted into the stable stratum below.

[0017] As a further improvement of the present invention, the lower end of the reference transmission rod is provided with an enlarged head or barb structure for enhancing anchoring, which works in conjunction with the grouting body to ensure that it is firmly bonded to the stable stratum.

[0018] The beneficial effects of this invention are as follows: 1. Built-in benchmark, eliminating the need for external reference: The displacement benchmark is directly built into the pile body being measured, fundamentally solving the problem of having no stable external benchmark available in soft soil areas.

[0019] 2. High accuracy: During measurement, the height difference between the top of the pile and the top of the built-in reference rod is read directly. The measurement chain is extremely short, avoiding the accumulation of errors caused by long-distance measurement or multiple station transfers, which significantly improves the accuracy and reliability of displacement monitoring.

[0020] 3. Low cost and short construction period: It makes full use of the depth of the test pile itself, eliminating the need for additional construction of large-scale special benchmark piles. The main materials are guide pipes and rods, resulting in significantly lower costs than traditional methods. The device can be constructed simultaneously with or after the pile foundation, without occupying critical construction time.

[0021] 4. High adaptability: Through the design of pre-embedded guide pipe and puncture-proof sealing structure, the reference transfer rod can still be easily implanted into stable strata after pile formation, which is suitable for various pile types and construction processes.

[0022] 5. Good long-term stability: The lower end of the reference transmission rod is anchored in a deep stable stratum, and is less affected by the deformation of shallow soil; the friction isolation structure ensures that the rod is not constrained when the pile settles, and can maintain its function as a stable reference at the top for a long time. Attached Figure Description

[0023] Figure 1 This is a vertical cross-sectional structural diagram of a displacement reference device integrated inside a pile foundation according to an embodiment of the present invention.

[0024] Figure 2 This is a cross-sectional view of a displacement reference device integrated inside a pile foundation according to an embodiment of the present invention.

[0025] Figure 3 This is a friction isolation structure, namely, the arrangement of spiral ribs.

[0026] Figure label: 1. Pile body; 2. Embedded guide pipe; 3. Reference transmission rod; 31. Measuring end; 32. Expanding head; 4. Friction isolation structure, i.e., spiral rib; 5. Stabilizing casing; 6. Sealing structure; 7. Grouting body; 8. Stabilizing stratum; 9. Soil layer at pile tip. Detailed Implementation

[0027] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. Example

[0028] like Figure 1 As shown, this embodiment provides a displacement reference device integrated inside the pile foundation, which is applied to the long-term settlement monitoring of a cast-in-place pile, namely the pile body (1).

[0029] Before the pile body (1) is poured, a steel pipe is used as a pre-embedded guide pipe (2), which is vertically tied and fixed to the inside or center of the reinforcing cage to ensure that its axis is roughly parallel to the pile foundation axis. The length of the pre-embedded guide pipe (2) is slightly shorter than the designed pile length, with its top end reserved about 20cm to 50cm above the future pile top design elevation, and its bottom end located near the pile bottom design elevation. At the bottom end of the pre-embedded guide pipe (2), a low-strength concrete block is pre-sealed as a sealing structure (6).

[0030] After the concrete of the pile body (1) has reached a certain strength, a small core drilling machine is used to drill downward from the top of the pre-embedded guide pipe (2), drill through the bottom sealing structure (6), and continue to drill downward, passing through the possible weak soil layer below the pile bottom, i.e. the pile tip soil layer (9), until it enters a certain depth of stable bedrock or dense sand and gravel layer, i.e. stable stratum (8).

[0031] Subsequently, using a casing drilling process, segmented steel pipes were lowered from the pre-embedded guide pipe (2) as stabilizing casings (5) to a predetermined depth in the stable stratum (8). The stabilizing casing (5) isolates the soil layer below the pile bottom and forms a continuous internal channel with the pre-embedded guide pipe (2) inside the pile. After the stabilizing casing (5) is in place, pressure grouting is performed through its inner cavity into the gap between the bottom and the stable stratum (8) to form a solid grout body (7), anchoring the lower end of the stabilizing casing (5) in the stable stratum (8).

[0032] Then, a high-rigidity metal rod (3) is placed inside the stabilizing casing (5) as a reference transfer rod. The reference transfer rod (3) can be made of plain round steel bars, precision rolled threaded steel bars, steel pipes, or seamless steel pipes. Its length must ensure that its lower end can be inserted into the grouting body (7), and the upper measuring end (31) protrudes a certain length from the top of the pre-embedded conduit (2) for measurement. An enlarged head (32) can be pre-welded to the lower end of the reference transfer rod (3) to enhance the anchoring force in the grouting body (7). Before lowering the reference transfer rod (3), lubricating grease can be evenly applied to its surface as a preliminary friction isolation structure.

[0033] like Figure 3 As shown, in this embodiment, the inner wall of the stabilizing casing (5) is pre-processed with continuous spiral ribs (4). When the reference transfer rod (3) is inserted, its outer wall only contacts the top protrusion of the spiral ribs (4), forming a multi-point line contact. This constitutes the main friction isolation structure. Together with the lubricating grease pre-coated on the rod body, it ensures that when the pile body (1) settles, the pre-embedded guide pipe (2) can slide freely relative to the reference transfer rod (3), while the reference transfer rod (3) remains basically unchanged in its vertical position because its lower end is anchored to the stable stratum (8).

[0034] During monitoring, a level or total station is used to periodically measure the height difference between the measuring point on the top of the pile and the top measuring end (31) of the reference transfer rod (3). The change in this height difference directly reflects the absolute vertical displacement of the pile top relative to the deep stable stratum (8), i.e., the settlement. Example

[0035] The main difference between this embodiment and embodiment 1 is that the special stabilizing sleeve (5) is omitted, and a simpler structure is adopted.

[0036] The installation of the pre-embedded conduit (2) and the puncture of the sealing structure (6) are the same as in embodiment (1). After puncturing the sealing structure (6) and drilling to the stable stratum (8), the reference transfer rod (3) with a thick grease coating on its surface is directly lowered into the pre-embedded conduit (2), and its lower end is anchored in the stable stratum (8) by grouting. The inner wall of the pre-embedded conduit (2) can be smooth, mainly relying on grease to reduce friction; or spiral ribs can be machined on the inner wall during factory prefabrication to further reduce the contact area. This scheme is suitable for situations where the lateral stability requirements of the reference transfer rod (3) are not high or the stratum conditions such as the pile bottom penetrating into rock are relatively good. Example

[0037] This embodiment is applied to precast piles. During the fabrication of precast piles, the pre-embedded guide pipe (2) is pre-fixed in the core of the pile body, and its lower end is sealed by welding a thin steel plate. After the pile is driven, the thin steel plate at the lower end is pierced through the inside of the guide pipe, and then a reference transfer rod or a stabilizing casing is implanted and anchored. The steps are similar to those in embodiment (1) or (2).

[0038] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A displacement reference device integrated inside a pile foundation, characterized in that, The device includes a pre-embedded guide pipe and a reference transmission rod. The pre-embedded guide pipe is fixed inside the pile body and extends along its axial direction, forming an internal channel from the pile top to the pile bottom. The reference transmission rod passes through the pre-embedded guide pipe, with its upper end forming a measuring end exposed at the pile top and its lower end passing through the bottom end of the pre-embedded guide pipe and anchored to a stable stratum below the pile end. A friction isolation structure is provided between the pre-embedded guide pipe and the reference transmission rod to allow the pre-embedded guide pipe to slide vertically relative to the reference transmission rod without adhesion. The pre-embedded guide pipe, the reference transmission rod, and the friction isolation structure together form a displacement reference device relative to a stable stratum.

2. The displacement reference device integrated inside a pile foundation according to claim 1, characterized in that: The pre-embedded guide pipe is a hollow pipe that is pre-set before the pile body is poured or driven in.

3. The displacement reference device integrated inside a pile foundation according to claim 1, characterized in that: The friction isolation structure is either a lubricating layer coated on the surface of the reference transmission rod, or a spiral rib structure disposed on the inner wall of the pre-embedded conduit, which makes the reference transmission rod have multiple points of contact, with the top of the spiral rib contacting the outer wall of the reference transmission rod.

4. The displacement reference device integrated inside a pile foundation according to claim 1, characterized in that, It also includes a stabilizing casing, which is installed inside the pre-embedded conduit, with its lower end extending and anchored in the stable stratum, forming a continuous internal channel with the pre-embedded conduit of the pile body, and the reference transmission rod is installed inside the stabilizing casing.

5. A displacement reference device integrated inside a pile foundation according to claim 4, characterized in that: The inner wall of the stabilizing sleeve is provided with a spiral rib structure that makes the reference transmission rod make multi-point contact, and the top of the spiral rib contacts the outer wall of the reference transmission rod.

6. A displacement reference device integrated inside a pile foundation according to claim 4, characterized in that, The bottom of the stabilizing casing is fixed to the stabilizing stratum by grouting.

7. A displacement reference device integrated inside a pile foundation according to claim 4, characterized in that, The stabilizing casing is a segmented steel pipe implanted through a casing drilling process.

8. A displacement reference device integrated inside a pile foundation according to claim 1, characterized in that, The lower end of the pre-embedded channel pipe is pre-set with a puncture-proof sealing structure.

9. A displacement reference device integrated inside a pile foundation according to claim 7, characterized in that, The sealing structure is a low-strength concrete block, a wooden plug, or a weldable thin steel plate.

10. A displacement reference device integrated inside a pile foundation according to claim 1, wherein the lower end of the reference transmission rod is provided with an enlarged diameter head or barbs for enhancing anchorage.

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