Flexible compensation structure of socket joint of nodular cast iron pipe and groove backfilling method of flexible compensation structure

Abstract

The invention provides a flexible compensation structure of a ductile cast iron pipe bell and spigot joint and a groove backfilling method thereof, and relates to the technical field of rain and sewage pipeline construction, the flexible compensation structure comprises a plurality of pipe bodies connected end to end, one end of each pipe body is a spigot, and the other end of each pipe body is a bell mouth; the compensation structure comprises an installation ring, a supporting ring and a plurality of guiding pieces, the installation ring is arranged in the bell mouth, the supporting ring is movably arranged in the installation ring through a plurality of elastic pieces, the guiding pieces are arranged around the inner wall of the circumference of the bell mouth at equal intervals, and the sealing ring is arranged on the periphery of the spigot. The method has the beneficial effects that through the synergistic effect of the elastic floating structure of the mounting ring and the supporting ring embedded in the bell mouth, the elastic guiding pieces evenly distributed in the circumferential direction and the staged backfilling technology; the technical problems that traditional nodular cast iron pipe socket connection has harsh requirements for coaxiality, a sealing ring is prone to distortion and failure, differential settlement is caused, and the adaptability is poor are fundamentally solved.

Description

Technical Field

[0001] This invention relates to the field of stormwater and sewage pipeline construction technology, and in particular to a flexible compensation structure for ductile iron pipe socket joints and a trench backfilling method thereof. Background Technology

[0002] In the field of pipeline connection technology, the socket-type flexible joint is the most widely used connection method. Its typical construction process involves using a manual hoist, tensioner, or other traction tools to axially align the spigot end of the pipe to be installed with the socket end of the already laid pipe. Under mechanical traction, the spigot is slowly inserted. A circular rubber sealing ring is pre-fitted onto the outer wall of the spigot, and a seal is achieved through the compression deformation of the sealing ring against the inner cavity of the socket. This connection method offers advantages such as convenient installation and low cost, and demonstrates good sealing reliability in pipe sections with favorable geological conditions.

[0003] However, due to the small design gap between the socket and spigot, and the fact that the sealing ring is directly fitted onto the outer wall of the spigot, it is difficult to guarantee the coaxiality of the two pipes during actual construction by using a manual hoist to pull them together. When there is an angular or radial deviation between the spigot axis and the socket axis, the sealing ring is prone to uneven compression, twisting, or even rolling during its entry into the socket. This results in insufficient local sealing stress or stress concentration, significantly reducing the sealing effect and accelerating rubber aging. Once an axial offset occurs, the pipe is in a state of continuous eccentric stress, which easily forms a capillary seepage channel between the sealing ring and the inner wall of the socket. After long-term operation, this can induce joint leakage and soil erosion around the pipe, seriously threatening the structural safety and service life of the pipeline system.

[0004] Therefore, there is an urgent need to develop a socket-type flexible interface structure that can allow for initial installation deviations and ultimately ensure coaxiality through backfill consolidation. Summary of the Invention

[0005] In view of this, embodiments of the present invention provide a flexible compensation structure for the socket joint of ductile iron pipe and a trench backfilling method thereof, in order to solve the technical problem that the existing sewage pipes, when controlled by manual hoists to control the socket and spigot joint sealing, are prone to twisting of the sealing ring and reduce the sealing effect.

[0006] Embodiments of the present invention provide a flexible compensation structure for a ductile iron pipe socket joint, comprising: Multiple pipes connected end to end, one end of which is a spigot and the other end is a socket; The compensation structure includes a mounting ring, a support ring, and multiple guide members. The mounting ring is disposed within the socket, and the support ring is movably disposed within the mounting ring by multiple elastic members. The multiple guide members are equally spaced around the inner circumference of the socket. A sealing ring is disposed on the outer periphery of the socket. When the socket of one tube passes through the socket of another tube, the socket passes through the support ring and can maintain coaxiality with the tube under the elastic compression of the plurality of guide members.

[0007] Furthermore, the socket includes a tapered outward expansion section and a cylindrical guide section, and the outer wall of the mounting ring is in contact with the inner wall of the cylindrical guide section.

[0008] Furthermore, each of the guide members is a bent steel plate, which is elastic, and its length direction is oriented toward the center of the socket. One end of the plurality of guide members is welded to the inner wall of the mounting ring, and the ends of the plurality of guide members away from the mounting ring are arranged to form a circle with the same inner diameter as the tube.

[0009] Furthermore, a limiting ring is provided at one end of the mounting ring, the support ring is fitted to the limiting ring, and a plurality of stops are provided on the inner wall of the mounting ring. The side of the support ring away from the limiting ring slides in contact with the plurality of stops.

[0010] Furthermore, the outer circumferential wall of the support ring is uniformly provided with a plurality of mounting seats, and each elastic element corresponds to a mounting seat that abuts against the support ring and the inner wall of the mounting ring.

[0011] Furthermore, the diameter of the through-hole in the middle of the limiting ring is larger than the outer diameter of the insertion port but smaller than the outer diameter of the support ring.

[0012] Embodiments of the present invention also provide a method for backfilling trenches in ductile iron pipe socket joints, employing a flexible compensation structure for the ductile iron pipe socket joint, characterized by comprising the following steps: S1: Insert the spigot of the pipe body into the socket with an axial deviation of ≤5°. Under the elastic guidance of the guide member, the spigot passes through the support ring. The sealing ring enters the socket with the spigot and contacts the inner wall of the pipe body to form an initial seal. At this time, the elastic member is adaptively compressed according to the eccentricity of the spigot, allowing the interface to complete the initial connection in an skewed state. S2: No lateral backfilling is performed on both sides of the interface. Instead, a medium-coarse sand pad with a thickness of H=0.5-0.8 times the pipe diameter and a compaction degree of ≥90% is laid at the bottom of the trench along the pipe axis. This allows the socket and spigot to be in a free state on the pad, where they can move slightly axially and float radially. This floating and centered state is maintained for 12-24 hours. The restoring force of the elastic element and the elastic extrusion force of the guide element work together to drive the spigot to automatically return to center until the axial deviation is ≤2mm. S3: After the joint automatically returns to its correct position, backfill medium-coarse sand symmetrically in layers on the medium-coarse sand pads on both sides of the socket and compact each layer. The compaction thickness of each layer is 200-300mm. When backfilling to the center elevation of the pipe, a lateral limit is formed. During the backfilling process, use a laser level or total station to monitor the coaxiality of the joint in real time. When a coaxiality deviation > 2mm is detected, dynamically correct the deviation by adjusting the difference in backfill height on both sides. S4: Continue backfilling medium-coarse sand in layers to 500mm above the top of the socket. During the compaction process, fill the gap between the socket and the spigot and perform a secondary seal. Then, the backfill material enters the socket to fill the gap left by the secondary sealing structure, locking the final coaxiality of the interface. At the same time, the relative position of the support ring with the inner wall of the socket is fixed under the constraint of the backfill around the perimeter. The sealing ring reaches the design compression rate of 25%±3%, ultimately achieving long-term stability of the interface sealing performance and coaxiality.

[0013] Furthermore, in step S3, the layered backfilling and compaction is carried out using a vibratory plate compactor with a compaction frequency of 60-80Hz, and the horizontal distance between the backfilling and compaction working surface on each side and the center line of the interface is always kept symmetrical.

[0014] Furthermore, the dynamic correction in step S3 specifically includes: when the coaxiality deviation is detected to be >2mm, pausing backfilling on the side of the misaligned socket and increasing the backfill height by 100-150mm on the opposite side, using the lateral thrust generated by the pressure difference between the backfill soils on both sides to correct the deviation. Symmetrical backfilling can only continue after the coaxiality deviation is ≤1.5mm following the correction. Furthermore, it also includes step S5: In the entire backfill area from 500mm above the top of the socket to the ground, the original soil is used for layered backfilling, with each layer compacted to a thickness of 300mm and a compaction degree of ≥95%. Settlement monitoring piles are installed in this area, and the coaxiality change of the interface is monitored monthly for 6 months after the backfilling is completed. If the cumulative settlement difference is >10mm, grouting is performed to reinforce the area around the socket.

[0015] The beneficial effects of the technical solution provided by the embodiments of the present invention are as follows: The flexible compensation structure of the ductile iron pipe socket joint and its groove backfilling method of the present invention, through the synergistic effect of the elastic floating structure of the socket embedded installation ring and support ring, the circumferentially distributed elastic guide, and the staged backfilling process, fundamentally solves the technical problems of the traditional ductile iron pipe socket connection, such as the stringent requirements for coaxiality, the easy twisting and failure of the sealing ring, and the poor adaptability to uneven settlement. First, when the socket is inserted, axial deviation is allowed. The elastic deformation of the guide generates radial guiding force, which forces the socket to adjust adaptively towards the socket axis. Under the action of the elastic element, the support ring floats and compensates according to the eccentricity of the socket, so that the compression of each part of the sealing ring is uniform, avoiding the problem of uneven compression, twisting and rolling of the sealing ring due to axial deviation in the traditional structure, which reduces the sealing effect. Secondly, by laying a medium-coarse sand pad at the bottom of the trench to allow the interface to float freely and remain stationary, the restoring force of the elastic element and the elastic squeezing force of the guide element work together to drive the spigot to automatically return to center, so that the axial deviation gradually decreases. Installation can be achieved without manual precise alignment, which significantly improves the structural safety, sealing durability and adaptability of the pipeline system to soft soil foundations. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the flexible compensation structure of the ductile iron pipe socket joint and its trench backfilling method according to the present invention. Figure 2 This is an exploded view of the flexible compensation structure of the ductile iron pipe socket joint and its trench backfilling method according to the present invention.

[0017] In the diagram: 1. Pipe body; 101. Spigot; 102. Socket; 2. Mounting ring; 3. Limiting ring; 4. Support ring; 5. Stop; 6. Mounting seat; 7. Elastic element; 8. Guide element; 9. Sealing ring. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described below with reference to the accompanying drawings. The following description presents a preferred embodiment of the various possible embodiments of the present invention, intended to provide a basic understanding of the invention, but not intended to identify key or decisive elements of the invention or to limit the scope of protection sought.

[0019] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values.

[0020] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and equipment should be considered part of the specification.

[0021] It should be noted that similar labels and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be discussed further in subsequent figures. Also, it should be understood that, for ease of description, the dimensions of the various parts shown in the figures are not drawn to actual scale.

[0022] In the description of this invention, it should be noted that the circuits, electronic components and modules involved in this invention are all prior art, which can be fully implemented by those skilled in the art, and need not be elaborated upon. The content protected by this invention does not involve improvements to the internal structure and method.

[0023] It should be further noted that, unless otherwise explicitly specified and limited, the terms "installation" and "connection" 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; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0024] Please refer to Figures 1 to 2 The present invention provides a flexible compensation structure for the socket joint of ductile iron pipe and a method for backfilling the trench thereon, comprising a pipe body 1, a compensation structure and a sealing ring 9.

[0025] In this embodiment, the pipe body 1 is made of centrifugal ductile iron. One end of each pipe body 1 is a spigot 101 and the other end is a socket 102. The socket 102 is machined to form a two-section structure: the inlet side is a tapered outward expansion section; the remaining part connected to the tapered outward expansion section is a cylindrical guide section. The connection between the tapered outward expansion section and the cylindrical guide section is a rounded transition to avoid stress concentration.

[0026] In this embodiment, the compensation structure consists of a mounting ring 2, a support ring 4, an elastic element 7, and a guide element 8. The mounting ring 2 and the cylindrical guide section of the socket 102 are fitted with a clearance fit. Epoxy resin adhesive is applied between the outer wall of the mounting ring 2 and the inner wall of the socket 102. Two trapezoidal sealing grooves are formed on the outer circumferential surface of the mounting ring 2, and O-rings are embedded in the grooves to achieve a static seal between the mounting ring 2 and the socket 102. The inlet end of the mounting ring 2 (the end near the tapered expansion section) is fixedly connected to the end flange of the socket 102 by stainless steel hexagonal head screws, with the screws evenly distributed along the circumferential direction.

[0027] The support ring 4 is an annular component made of PTFE (polytetrafluoroethylene) modified and reinforced material, and a radial floating gap is formed between its outer wall and the inner wall of the mounting ring 2. Multiple mounting seats 6 are welded on the outer circumference of the support ring 4 for mounting the elastic element 7.

[0028] Furthermore, the elastic element 7 is a cylindrical helical compression spring. One end of the elastic element 7 is embedded in the blind hole of the mounting base 6 and fixed with epoxy resin, while the other end abuts against a pre-set spring seat hole on the inner wall of the mounting ring 2. Multiple elastic elements are evenly distributed along the circumference of the support ring 4, forming a multi-point elastic support system, which allows the support ring 4 to float relative to the mounting ring 2 in the radial direction, while always being subjected to a radial restoring force pointing towards the axis.

[0029] To mitigate the repeated floating caused by the elastic element 7, six guide elements 8 are provided, formed by stamping and bending spring steel plates. The root of the guide element 8 is a straight section, which is fixedly connected to the inner wall of the inlet end of the mounting ring 2 by welding. The main body of the guide element 8 is a bent section, and the free end of the guide element 8 (the end away from the mounting ring 2) is an arc surface. The virtual circle formed by the free ends of the six guide elements 8 is tangent to the outer circumference of the insertion port 101 after insertion or maintains a gap of 0.5-1.0 mm.

[0030] The guide 8 plays an elastic guiding role during the insertion of the socket 101. Its root welded structure provides sufficient rigid support, while the bent section allows elastic deformation. When the socket 101 is eccentric, the guide 8 is compressed to generate an elastic restoring force pointing towards the axis, forcing the socket 101 to move towards the center position.

[0031] Furthermore, the limiting ring 3 is an annular boss integrally cast with the mounting ring 2, with the same outer diameter as the mounting ring 2. The limiting ring 3 is located at the outlet end of the mounting ring 2 and is used to axially limit the support ring 4. One end face of the support ring 4 is fitted to the end face of the limiting ring 3. At least three stops 5, made of stainless steel, are welded to the inner wall of the mounting ring 2 and are evenly distributed along the circumference. The end face of the stops 5 slides in contact with the other end face of the support ring 4, allowing the support ring 4 to make radial micro-movements between the stops 5 and the limiting ring 3 to accommodate axial impacts during installation. The diameter of the through-hole in the middle of the limiting ring 3 is larger than the outer diameter of the insertion port 101 but smaller than the outer diameter of the support ring 4. Therefore, the inner diameter of the limiting ring 3 is smaller than the outer diameter of the support ring 4, which can prevent the support ring 4 from axially dislodging. At the same time, it is larger than the outer diameter of the insertion port 101, allowing the insertion port 101 to pass through smoothly.

[0032] The sealing ring 9 is made of ethylene propylene diene monomer (EPDM) rubber and is stretched and fitted into the sealing groove of the socket 101. After installation, the inner diameter of the sealing ring 9 is interference-fitted with the bottom diameter of the sealing groove of the socket 101 to prevent the sealing ring 9 from slipping or falling off during the insertion process.

[0033] When the spigot 101 passes through the support ring 4, the outer surface of the sealing ring 9 makes interference contact with the inner surface of the support ring 4. As the spigot 101 is fully inserted into the socket 102, the sealing ring 9 enters the cylindrical guide section of the socket 102 and forms a radial seal with the inner surface of the socket 102, ensuring sealing reliability.

[0034] This embodiment provides a trench backfilling method that is compatible with the above-mentioned flexible compensation structure. By using a phased backfilling process, the adaptive characteristics of the compensation structure are fully utilized to ultimately achieve the technical goals of interface coaxiality ≤2mm and sealing ring compression rate 25%±3%.

[0035] S1: Initial Insertion Step Using a hand-operated hoist as the traction tool, the spigot 101 of the pipe body 1 to be installed is aligned with the socket 102 of the already installed pipe body 1. Precise alignment is not required from the operator; an angle of ≤5° between the axis of the spigot 101 and the axis of the socket 102 is allowed. Under the traction force of the hoist, the spigot 101 slowly enters the socket 102, first contacting the guide member 8. The guide member 8 undergoes elastic deformation under force, applying a radial guiding force to the spigot 101, forcing it to move towards the axis of the socket 102. As the spigot 101 continues to advance, it drives the sealing ring 9 through the support ring 4. The outer surface of the sealing ring 9 contacts and compresses the inner surface of the support ring 4. Because the support ring 4 is floatingly supported by the elastic member 7, when the spigot 101 is eccentric, the support ring 4 can adaptively adjust its position, making the compression of all parts of the sealing ring 9 more uniform, avoiding the twisting phenomenon of the sealing ring in traditional structures. When the spigot 101 is inserted to the designed depth, traction is stopped, completing the initial connection. At this time, the interface is in a skewed but sealed state. The compression of the elastic element 7 is adaptively adjusted according to the eccentricity. The compression of some springs increases by 5-8mm, and the corresponding spring force increases by 42.5-68N.

[0036] S2: Floating centering and stationary step After the initial connection is completed, backfilling on the pipe side is strictly prohibited immediately. A medium-coarse sand cushion layer 10 is manually laid at the bottom of the trench along the pipe axis. The cushion material has a particle size of 2-5mm and a mud content of ≤3%. The thickness of the cushion layer 10 is H = 0.5-0.8 times the pipe diameter; in this embodiment, H = 400mm (0.67 times the DN600 pipe diameter). The compaction degree of the cushion layer 10 is controlled to ≥90%, using a plate vibrator for compaction at a frequency of 60-80Hz and a walking speed of 0.5-1.0m / min. After the cushion layer 10 is laid, the socket 102 and spigot 101 in the interface area are in a free state on the cushion layer 10, allowing for axial slight movement and radial floating. At this time, the interface does not contact any rigid object and only bears its own weight and the elastic support of the cushion layer 10.

[0037] Maintain this floating alignment state for 12-24 hours. The settling time is determined based on the ambient temperature: 12 hours when the ambient temperature is ≥20℃; and 24 hours when the ambient temperature is <20℃. During the settling period, the restoring force of the elastic element 7 continuously acts on the support ring 4, driving the support ring 4 to move towards the axis of the socket 102; simultaneously, the elastic compressive force of the guide element 8 acts on the outer wall of the socket 101, forcing the socket 101 to return to its upright position. The combined effect of these two forces gradually reduces the interface axis deviation from the initial ≤5° to ≤2mm.

[0038] S3: Layered Backfilling and Dynamic Correction Steps After the interface automatically returns to its correct position, lateral backfilling begins. Medium-coarse sand is symmetrically backfilled in layers on the medium-coarse sand pads 10 on both sides of the socket 102, with each layer being 200-300mm thick. A vibratory plate compactor is used to compact each layer at a frequency of 60-80Hz. When the backfill reaches the pipe center elevation (i.e., 300mm below the top of the pipe), the backfill material contacts the outer wall of the pipe body 1, forming preliminary lateral restraint and limiting further radial displacement of the interface.

[0039] During backfilling, the coaxiality of the joints is monitored in real time using a laser level or total station. Monitoring is conducted once per layer of backfill, with monitoring points set at both ends of the socket 102 and the middle of the spigot 101. When a coaxiality deviation > 2mm is detected, dynamic correction measures are immediately initiated: backfilling is suspended on the side of the socket 102 that is deviating, and the backfill height is increased by 100-150mm on the opposite side, utilizing the lateral thrust generated by the pressure difference between the backfill soil on both sides to correct the deviation. Symmetrical backfilling can only continue when the coaxiality deviation is ≤ 1.5mm after correction. This dynamic correction process can be repeated 2-3 times until the coaxiality meets the design requirements.

[0040] S4: Final Locking and Sealing Steps Continue backfilling with medium-coarse sand in layers up to 500mm above the top of the socket 102. During the backfilling and compaction process, polyurethane sealant is used to seal the circumferential gap between the socket 102 and the spigot 101 for secondary sealing to prevent groundwater infiltration. Backfilling continues, and the backfill material, under compaction, enters the gap between the socket 102 and the spigot 101, filling the small gaps between the support ring 4, the limiting ring 3, and the stop block 5, thus locking the final coaxiality of the interface. At this point, the relative position of the support ring 4 to the inner wall of the socket 102 is completely fixed under the constraint of the surrounding backfill, the compression of the elastic element 7 stabilizes near the pre-compression value, and the compression rate of the sealing ring 9 reaches the design value of 25% ± 3%, achieving long-term stability in the interface sealing performance and coaxiality.

[0041] S5: Long-term monitoring and maintenance procedures In the entire backfill area from 500mm above the top of the socket 102 to the ground, undisturbed soil is used for layered backfilling, with each layer compacted to a thickness of 300mm and a compaction degree of ≥95%. Within this area, settlement monitoring piles are installed 1m away from the end face of the socket 102. The monitoring piles are made of φ20mm stainless steel pipes, with the top extending 100mm above the ground and equipped with protective covers.

[0042] Within 6 months after backfilling, the coaxiality of the joint should be observed monthly using a total station or level with an accuracy of ±1mm. If the cumulative settlement difference exceeds 10mm, it indicates abnormal settlement of the foundation. In this case, grouting reinforcement should be carried out around socket 102. The grouting material is cement-water glass double-liquid grout, with a grouting pressure of 0.2-0.3MPa. Three grouting holes are evenly distributed around socket 102, with a depth of 500mm below the bottom of the pipe. After grouting reinforcement, the coaxiality of the joint can be restored to ≤2mm, effectively extending the service life of the pipeline.

[0043] In this document, the directional terms such as front, back, top, and bottom are defined based on the location of the components in the accompanying drawings and their relative positions to each other, solely for the purpose of clarity and convenience in expressing the technical solution. It should be understood that these are relative concepts and can vary depending on the method of use and placement; the use of directional terms should not limit the scope of protection claimed in this application.

[0044] Where there is no conflict, the above embodiments and features described herein can be combined with each other.

[0045] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A flexible compensation structure for a ductile iron pipe socket joint, characterized in that, include: Multiple pipe bodies (1) connected end to end, one end of which is a spigot (101) and the other end is a socket (102). The compensation structure includes a mounting ring (2), a support ring (4) and a plurality of guide members (8). The mounting ring (2) is disposed inside the socket (102). The support ring (4) is movably disposed inside the mounting ring (2) by a plurality of elastic members (7). The plurality of guide members (8) are equally spaced around the inner circumference of the socket (102). A sealing ring (9) is disposed on the outer periphery of the socket (101). When the socket (101) of one tube (1) passes through the socket (102) of another tube (1), the socket (101) passes through the support ring (4) and can maintain coaxiality with the tube (1) under the elastic compression of the plurality of guides (8).

2. The flexible compensation structure for the ductile iron pipe socket joint as described in claim 1, characterized in that: The socket (102) includes a tapered outward expansion section and a cylindrical guide section, and the outer wall of the mounting ring (2) is in contact with the inner wall of the cylindrical guide section.

3. The flexible compensation structure for the ductile iron pipe socket as described in claim 1, characterized in that: Each of the guide members (8) is a bent steel plate, which is elastic, and is oriented along the length of the socket (102) axis. One end of the multiple guide members (8) is welded to the inner wall of the mounting ring (2). The ends of the multiple guide members (8) away from the mounting ring (2) are arranged to form a circle with the same inner diameter as the tube body (1).

4. The flexible compensation structure for the ductile iron pipe socket as described in claim 1, characterized in that: One end of the mounting ring (2) is provided with a limiting ring (3), the support ring (4) is attached to the limiting ring (3), and a plurality of blocks (5) are provided on the inner wall of the mounting ring (2). The side of the support ring (4) away from the limiting ring (3) slides in contact with the plurality of blocks (5).

5. The flexible compensation structure for the ductile iron pipe socket as described in claim 1, characterized in that: The outer circumferential wall of the support ring (4) is uniformly provided with a plurality of mounting seats (6), and each elastic element (7) corresponds to a mounting seat (6) and abuts against the inner wall of the support ring (4) and the mounting ring (2).

6. The flexible compensation structure for the ductile iron pipe socket as described in claim 4, characterized in that: The diameter of the central through-hole of the limiting ring (3) is larger than the outer diameter of the insertion port (101) but smaller than the outer diameter of the support ring (4).

7. A method for backfilling trenches for ductile iron pipe socket joints, employing the flexible compensation structure for ductile iron pipe socket joints as described in claims 1-6, characterized in that... Includes the following steps: S1: Insert the socket (101) of the pipe body (1) into the socket (102) with an axial deviation of ≤5°. Under the elastic guidance of the guide (8), the socket (101) passes through the support ring (4). The sealing ring (9) enters the socket (102) along with the socket (101) and contacts the inner wall of the pipe body (1) to form an initial seal. At this time, the elastic element (7) adaptively compresses according to the eccentricity of the socket (101), allowing the interface to complete the initial connection in an skewed state. S2: No lateral backfilling is performed on both sides of the interface. Instead, a medium-coarse sand pad with a thickness of H=0.5-0.8 times the pipe diameter and a compaction degree of ≥90% is laid at the bottom of the trench along the pipe axis. This allows the socket (102) and the spigot (101) to be in a free state on the pad that can move slightly axially and float radially. This floating and centered state is kept still for 12-24 hours. The restoring force of the elastic element (7) and the elastic extrusion force of the guide element (8) work together to drive the spigot (101) to automatically return to center until the axial deviation is ≤2mm. S3: After the interface automatically returns to its correct position, backfill medium-coarse sand symmetrically in layers on both sides of the socket (102) and compact it layer by layer. The compaction thickness of each layer is 200-300mm. When backfilling to the center elevation of the pipe, a lateral limit is formed. During the backfilling process, use a laser level or total station to monitor the coaxiality of the interface in real time. When the coaxiality deviation is detected to be >2mm, the deviation is dynamically corrected by adjusting the backfill height difference on both sides. S4: Continue backfilling medium and coarse sand in layers to 500mm above the top of the socket (102). During the compaction process, fill the gap between the socket (102) and the spigot (101) and perform secondary sealing. Then, the backfill material enters the socket (102) to fill the gap left by the secondary sealing structure, locking the final coaxiality of the interface. At the same time, the relative position of the support ring (4) to the inner wall of the socket (102) is fixed under the constraint of the backfill around the perimeter. The sealing ring (9) reaches the design compression rate of 25%±3%, and finally achieves long-term stability of the interface sealing performance and coaxiality.

8. The trench backfilling method for the socket joint of ductile iron pipe as described in claim 7, characterized in that, In step S3, the layered backfilling and compaction is carried out using a vibratory plate compactor with a compaction frequency of 60-80Hz, and the horizontal distance between the backfilling and compaction working surface on each side and the center line of the interface is always kept symmetrical.

9. The trench backfilling method for the socket joint of ductile iron pipe as described in claim 7, characterized in that, The dynamic correction in step S3 specifically includes: when the coaxiality deviation is detected to be >2mm, backfilling is suspended on the side of the socket (102) that is deviated, and the backfilling height is increased by 100-150mm on the opposite side. The lateral thrust generated by the difference in backfill soil pressure on both sides is used to correct the deviation. After the deviation is corrected, the coaxiality deviation is ≤1.5mm before symmetrical backfilling can continue.

10. The trench backfilling method for the socket joint of ductile iron pipe as described in claim 7, characterized in that, The method also includes step S5: In the entire backfill area from 500mm above the top of the socket (102) to the ground, the original soil is used for layered backfilling, with each layer compacted to a thickness of 300mm and a compaction degree of ≥95%. Settlement monitoring piles are installed in this area, and the coaxiality of the interface is monitored monthly for 6 months after the backfilling is completed. If the cumulative settlement difference is >10mm, grouting is performed around the socket (102) for reinforcement.

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