Method for monitoring cracking of inner-layer concrete in PCCP (prestressed concrete cylinder pipe) manufacturing process

Abstract

The invention discloses a method for monitoring cracking of inner-layer concrete in the PCCP manufacturing process, and relates to the technical field of pipeline health monitoring, and the method comprises the following steps: S1, arranging a first optical fiber sensor on a steel cylinder, fixing a second optical fiber sensor, and setting a gap between the second optical fiber sensor and the steel cylinder; s2, the steel cylinder is vertically placed, and the strain in the pipe core concrete pouring procedure and the strain in the steam curing procedure are continuously monitored; s3, pipe core concrete is demolded, a third optical fiber sensor is arranged on inner-layer concrete, and real-time strain monitoring is carried out while prestressed steel wire winding, roller shooting of a mortar protection layer and spraying of an asphalt anti-corrosion layer are carried out in the PCCP manufacturing process; and S4, the finished PCCP is transversely placed, and continuous monitoring is carried out. And S5, according to the strain distribution curve and the theoretical strain of concrete cracking, the working procedure and the position where the inner-layer concrete crack occurs are judged, the trouble of the cracking cause of the inner-layer concrete crack is effectively solved, and an effective method is provided for determining the working procedure and the position where the crack occurs.

Description

Technical Field

[0001] The present invention relates to the technical field of pipeline health monitoring, and in particular to a method for monitoring cracking of inner concrete during the PCCP manufacturing process. Background Art

[0002] Prestressed concrete cylinder pipe (PCCP) refers to a composite pressure water pipe structure with a steel cylinder embedded within a prestressed reinforced concrete pipe body. It primarily consists of prestressed steel wire, a steel cylinder, and a concrete core. PCCP is widely used in long-distance water transmission projects due to its excellent tensile strength, high strength, excellent impermeability, high sealing, strong durability, and simple and quick installation. Traditional PCCP structures are categorized as either lined or embedded, depending on the relative position of the steel cylinder within the concrete core.

[0003] Common structural damage to PCCP pipes includes cracking of the core concrete and mortar, and breakage of prestressing wires. During the production, handling, placement, and installation of PCCP pipes, cracks in the core concrete surface are common, particularly circumferential and spiral cracks in the inner concrete core. These inner concrete cracks are sometimes unavoidable and cause significant trouble for manufacturers, as their customers are generally reluctant to accept cracks in their products. Quality disputes arising from inner concrete cracks are common in actual engineering applications. Monitoring inner concrete cracks is crucial to ensure they do not expand or negatively impact pipeline safety.

[0004] At present, the cause of cracks in the inner layer of concrete during the PCCP manufacturing process is still unclear, and it is impossible to obtain the strain conditions of the manufacturing process through monitoring tests to determine the cause of the cracks and control them. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for monitoring cracking of the inner layer of concrete during the PCCP manufacturing process to solve the problems existing in the above-mentioned prior art. It can monitor the cracking of the inner layer of concrete in the prestressed steel cylinder concrete pipe manufacturing process in real time, effectively solve the problem of the cause of cracks in the inner layer of concrete, and provide an effective method for determining the process and location of cracks.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] The present invention provides a method for monitoring cracking of inner concrete during PCCP manufacturing, comprising the following steps:

[0008] S1: placing a steel cylinder horizontally on a roller frame, placing a first optical fiber sensor on the inner surface of the steel cylinder, welding a plurality of fixing members to the inner surface of the steel cylinder, fixing a second optical fiber sensor by each of the fixing members, and providing a gap between the second optical fiber sensor and the inner surface of the steel cylinder;

[0009] S2: The steel cylinder is placed upright with the PCCP socket facing upward, the pigtails of the first optical fiber sensor and the second optical fiber sensor are led out and connected to the monitoring and processing equipment on the casting platform through the first optical fiber lead, and then the pipe core concrete casting process is carried out. The strain during the pipe core concrete casting process and the steam curing process is continuously monitored by the monitoring and processing equipment;

[0010] S3: Demolding the core concrete, placing a third optical fiber sensor on the sidewall of the inner layer of the core concrete away from the steel cylinder, suspending the monitoring and processing equipment inside the core concrete, and connecting the first and second optical fiber sensors to the monitoring and processing equipment via a first optical fiber lead, and connecting the third optical fiber sensor to the monitoring and processing equipment via a second optical fiber lead. Then, during the PCCP manufacturing process, while performing the prestressed steel wire winding, roller-spraying the mortar protective layer, and spraying the asphalt anti-corrosion layer, the monitoring and processing equipment performs real-time strain monitoring.

[0011] S4: After the asphalt anti-corrosion layer spraying process is completed, the finished PCCP is placed horizontally and continuously monitored by the monitoring and processing equipment.

[0012] S5: Determine the process and location of the inner concrete cracks by comparing the strain distribution curve measured by the monitoring and processing equipment with the theoretical strain of concrete cracking.

[0013] Preferably, in step S1, the first optical fiber sensor is a carbon fiber composite-based optical cable, the layout path of the carbon fiber composite-based optical cable on the steel cylinder is polished and cleaned, and the cleaning width of the layout path is not less than 10 cm, the first optical fiber sensor is preliminarily fixed with a magnet and spray paint, and carbon fiber impregnation glue is brushed on the entire carbon fiber composite-based optical cable 1 to 2 times to allow the carbon fiber impregnation glue to penetrate into the entire carbon fiber composite-based optical cable to fix the carbon fiber composite-based optical cable to the steel cylinder.

[0014] Preferably, in step S1, the second optical fiber sensor is a high-transmission tight-sheathed strain sensing optical cable, the fixing part is a fixing clip, the fixing clip is welded and fixed to the inner surface of the steel cylinder, the width of the fixing clip is not less than 3 cm, the length of the fixing clip is not less than 10 cm, the fixing clip is bent to fix the high-transmission tight-sheathed strain sensing optical cable, and the distance between the high-transmission tight-sheathed strain sensing optical cable and the inner surface of the steel cylinder is not less than 3 cm, each of the fixing clips is arranged along the extension direction of the high-transmission tight-sheathed strain sensing optical cable, and the number of the fixing clips is not less than 2.

[0015] Preferably, in step S2, one end of a lead protection air tube of not less than 2 m is fixed at the socket position of the PCCP, and the pigtails of the carbon fiber composite-based optical cable and the high-transmission tight-sheathed strain sensing optical cable pass through the lead protection air tube and are connected to the monitoring and processing equipment placed on the casting platform through the first optical fiber lead.

[0016] Preferably, in step S2, the monitoring and processing equipment is turned on to obtain the light intensity signals of the carbon fiber composite-based optical cable and the high-transmission tight-sheathed strain sensing optical cable, and the effective monitoring areas of the carbon fiber composite-based optical cable and the high-transmission tight-sheathed strain sensing optical cable in the axial direction of the steel cylinder are calibrated by bending and changing the light intensity.

[0017] Preferably, in step S2, when the core concrete pouring process is carried out, the lead protection air pipe is protected by a tool to prevent the lead protection air pipe from being damaged by thrown sand and gravel.

[0018] Preferably, in step S3, the third optical fiber sensor is a glass fiber composite-based optical cable. After the core concrete is demoulded, it is hoisted to the scaffolding position, and the glass fiber composite-based optical cable is preliminarily fixed to the side wall of the inner layer of concrete of the core concrete using spray paint, and then epoxy resin glue is applied along the glass fiber composite-based optical cable to tightly bond the glass fiber composite-based optical cable to the side wall of the inner layer of concrete of the core concrete.

[0019] Preferably, step S3 also includes clearing the concrete on the surface of the punching hole corresponding to the reserved position of the steel ring at the PCCP socket position and the wood chips blocking the inside, inserting a bolt, tying a steel wire rope on the inner side of the bolt, hanging the hanging frame in the steel wire rope, and placing the monitoring and processing equipment in the hanging frame. The monitoring and processing equipment is provided with multiple channels, and multiple optical fiber leads can be connected to the carbon fiber composite-based optical cable, the high-transmission tight-sheathed strain sensing optical cable and the glass fiber composite-based optical cable at the same time, connecting the monitoring and processing equipment to the glass fiber composite-based optical cable, obtaining the light intensity signal of the glass fiber composite-based optical cable, and calibrating the effective monitoring area of ​​the glass fiber composite-based optical cable in the axial direction of the steel cylinder by bending to change the light intensity.

[0020] Preferably, in step 3, after waiting for the core pipe concrete to reach 70% of the design strength, the monitoring and processing equipment is turned on to continuously monitor the lifting process of the core pipe concrete; after the core pipe concrete is lifted to the wire winding machine, the lower part of the hanging basket is fixed to the wire winding turntable with wire to overcome the rotation during the wire winding process; the processes of prestressed steel wire winding, roller-sprayed mortar protective layer and sprayed asphalt anti-corrosion layer are continuously monitored while they are being constructed.

[0021] Preferably, the monitoring and processing equipment includes a monitoring data acquisition device, a control computer and a mobile power supply. The theoretical strain for the appearance of microcracks in the concrete cracking process is 207.6 με, and the theoretical strain for the appearance of visible cracks in the concrete cracking process is 1522.6 με.

[0022] Compared with the prior art, the present invention has achieved the following technical effects:

[0023] The purpose of the present invention is to provide a monitoring method for cracking of the inner layer of concrete during the PCCP manufacturing process. This monitoring method realizes real-time monitoring of the cracking of the inner layer of concrete during the PCCP manufacturing process by arranging different optical fiber sensors at different stages, utilizing specific installation and fixing methods, and combining monitoring data acquisition equipment. This helps to solve the problem of the cause of cracks in the inner layer of concrete and is beneficial to the control and prevention of cracks. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0025] Figure 1 A schematic flow chart of a method for monitoring cracking of inner concrete during PCCP manufacturing provided by the present invention;

[0026] Figure 2 A schematic diagram of the arrangement of a carbon fiber composite-based optical cable and a high-transmission tight-sheathed strain-sensing optical cable on the inner surface of a steel cylinder in the method for monitoring cracking of inner concrete during PCCP manufacturing provided by the present invention;

[0027] Figure 3 A schematic diagram of the structure of the arrangement of the glass fiber composite-based optical cable on the inner surface of the inner layer of concrete of the core concrete in the method for monitoring cracking of the inner layer of concrete during the PCCP manufacturing process provided by the present invention;

[0028] Figure 4 A schematic diagram of a method for fixing a high-transmission tight-buffered optical cable embedded in inner concrete in a method for monitoring cracking of inner concrete during PCCP manufacturing provided by the present invention;

[0029] Figure 5 A schematic diagram of a method for fixing a monitoring and processing device during the pouring of core concrete in a method for monitoring cracking of inner concrete during PCCP manufacturing provided by the present invention;

[0030] Figure 6A schematic diagram of a method for fixing monitoring and processing equipment during the construction process of the prestressed steel wire winding process in the method for monitoring cracking of the inner layer concrete during the PCCP manufacturing process provided by the present invention;

[0031] Figure 7 A schematic diagram of a method for fixing the middle hanging frame in the method for monitoring cracking of inner concrete during PCCP manufacturing provided by the present invention;

[0032] Figure 8 A schematic diagram of the placement of monitoring and processing equipment during monitoring of finished PCCP in the method for monitoring cracking of the inner layer of concrete during the PCCP manufacturing process provided by the present invention;

[0033] Figure 9 This is a diagram showing monitoring results during the construction process of the prestressed steel wire winding process in Example 1;

[0034] Figure 1: 1. Carbon fiber composite-based optical cable; 2. High-transmission tight-jacketed strain-sensing optical cable; 3. Fixing clip; 4. Steel cylinder; 5. First optical fiber lead; 6. Lead protection air tube; 7. Glass fiber composite-based optical cable; 8. Second optical fiber lead; 9. Inner concrete layer; 10. Outer concrete layer; 11. Socket steel ring; 12. Punching hole; 13. Bolt; 14. Steel wire rope; 15. Hanging frame; 16. Iron wire; 18. Monitoring data acquisition equipment; 19. Control computer. DETAILED DESCRIPTION

[0035] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0036] The purpose of the present invention is to provide a method for monitoring cracking of the inner layer of concrete during the PCCP manufacturing process to solve the problems existing in the above-mentioned prior art. It can monitor the cracking of the inner layer of concrete in the prestressed steel cylinder concrete pipe manufacturing process in real time, effectively solve the problem of the cause of cracks in the inner layer of concrete, and provide an effective method for determining the process and location of cracks.

[0037] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0038] The present invention provides a method for monitoring cracking of inner concrete during PCCP manufacturing process, such as Figures 1 to 9 As shown, the following steps are included:

[0039] S1: Place steel cylinder 4 horizontally on a roller frame, deploy a first fiber optic sensor on the inner surface of steel cylinder 4, weld multiple fixtures to the inner surface of steel cylinder 4, and secure a second fiber optic sensor with each fixture, creating a gap between the second fiber optic sensor and the inner surface of steel cylinder 4. By deploying different fiber optic sensors on the inner surface of steel cylinder 4, the first fiber optic sensor monitors the strain at the interface between inner concrete layer 9 and steel cylinder 4, while the second fiber optic sensor monitors the strain within inner concrete layer 9. The placement of the fixtures ensures the stability of the second fiber optic sensor and allows it to be placed within inner concrete layer 9 after the core concrete is poured, providing a basis for accurate monitoring.

[0040] S2: The steel cylinder 4 is placed upright with the PCCP socket facing upward. The pigtails of the first and second optical fiber sensors are led out and connected to the monitoring and processing equipment on the casting platform through the first optical fiber lead 5. Then, the pipe core concrete pouring process is carried out, including pouring concrete on the inner side of the steel cylinder 4 to form an inner concrete layer 9 and pouring concrete on the outer side of the steel cylinder 4 to form an outer concrete layer 10. The strain during the pipe core concrete pouring process and the steam curing process is continuously monitored by the monitoring and processing equipment. The steel cylinder 4 is placed upright and connected to the monitoring and processing equipment, which realizes real-time monitoring of the pipe core concrete pouring and steam curing processes, and can timely detect strain changes, providing a basis for subsequent construction adjustments.

[0041] S3: The core concrete is demoulded, and a third optical fiber sensor is arranged on the side wall of the inner layer of concrete 9 of the core concrete away from the steel cylinder 4. The monitoring and processing equipment is suspended on the inner side of the core concrete, and the first optical fiber sensor and the second optical fiber sensor are connected to the monitoring and processing equipment through a first optical fiber lead 5, and the third optical fiber sensor is connected to the monitoring and processing equipment through a second optical fiber lead 8. Then, during the PCCP manufacturing process, the prestressed steel wire winding, roller-sprayed mortar protective layer, and asphalt anti-corrosion layer spraying processes are carried out while the monitoring and processing equipment is used to monitor the strain in real time. The third optical fiber sensor is added at different construction stages and real-time monitoring is performed, which fully covers the PCCP manufacturing process, can timely detect strain changes in each process, and provide strong support for quality control.

[0042] S4: After the asphalt anti-corrosion layer spraying process is completed, the finished PCCP is placed horizontally and continuously monitored by the monitoring and processing equipment. Monitoring is continued during the finished product stage to ensure the quality stability of the PCCP and to promptly detect possible later strain changes.

[0043] S5: By comparing the strain distribution curve measured by the monitoring and processing equipment with the theoretical strain of concrete cracking, the process and location of the cracks in the inner layer of concrete 9 are determined. By comparing with the theoretical strain, the process and location of the cracks can be accurately determined, providing a scientific basis for the prevention and control of cracks.

[0044] In a preferred embodiment, in step S1, the first optical fiber sensor is a carbon fiber composite-based optical cable 1, and the layout path of the carbon fiber composite-based optical cable 1 on the steel cylinder 4 is polished and cleaned, and the cleaning width of the layout path is not less than 10 cm. The first optical fiber sensor is preliminarily fixed with a magnet and spray paint, and carbon fiber impregnation glue is brushed on the entire carbon fiber composite-based optical cable 1 1 to 2 times to allow the carbon fiber impregnation glue to penetrate into the entire carbon fiber composite-based optical cable 1 to fix the carbon fiber composite-based optical cable 1 to the steel cylinder 4. The cleaning width is not less than 10 cm to ensure that the installation base of the carbon fiber composite-based optical cable 1 is flat. The preliminary fixation of the magnet and spray paint and the use of the carbon fiber impregnation glue ensure that the optical cable is firmly combined with the steel cylinder 4, thereby improving the stability of monitoring.

[0045] In a preferred embodiment, in step S1, the second optical fiber sensor is a high-transmission tight-sheathed strain sensing optical cable 2, and the fixing part is a fixing clip 3. The fixing clip 3 is welded and fixed to the inner surface of the steel cylinder 4. The width of the fixing clip 3 is not less than 3 cm, and the length of the fixing clip 3 is not less than 10 cm. The fixing clip 3 is bent with pliers to fix the top and bottom of the high-transmission tight-sheathed strain sensing optical cable 2, and the distance between the high-transmission tight-sheathed strain sensing optical cable 2 and the inner surface of the steel cylinder 4 is not less than 3 cm. Each fixing clip 3 is arranged along the extending direction of the high-transmission tight-sheathed strain sensing optical cable 2, and the number of fixing clips 3 is not less than 2. The fixing clips 3 of a specific size ensure stable fixation of the high-transmission tight-sheathed strain sensing optical cable 2. The provision of multiple fixing clips 3 further improves the reliability of the fixation, ensuring that there is a gap between the high-transmission tight-sheathed strain sensing optical cable 2 and the inner surface of the steel cylinder 4 and it is not easy to shift during construction.

[0046] In a preferred embodiment, in step S2, one end of a lead protection air tube 6, no less than 2 meters long, is secured to the PCCP socket. The fiber pigtails of the carbon fiber composite-based optical cable 1 and the high-transmission tight-jacketed strain sensing optical cable 2 are passed through the lead protection air tube 6 and connected to the monitoring and processing equipment placed on the casting platform via the first optical fiber lead 5. The first optical fiber lead 5 is secured to the casting platform railing using hand-tearable tape. The lead protection air tube 6 protects the fiber pigtail of the optical fiber sensor, preventing damage during construction. The hand-tearable tape securing the optical fiber lead prevents disturbances from factors such as wind, ensuring stable signal transmission.

[0047] In a preferred embodiment, in step S2, the monitoring and processing equipment is turned on to obtain the light intensity signals of the carbon fiber composite-based optical cable 1 and the high-transmission tight-sheathed strain sensing optical cable 2, and the effective monitoring areas of the carbon fiber composite-based optical cable 1 and the high-transmission tight-sheathed strain sensing optical cable 2 in the axial direction of the steel cylinder 4 are calibrated by bending to change the light intensity. Position calibration through light intensity signals improves the accuracy of monitoring, clarifies the effective monitoring area, and helps to analyze the strain situation more accurately.

[0048] In a preferred embodiment, in step S2, when the core concrete pouring process is carried out, the lead protection air tube 6 is protected by tools such as iron plates to prevent the lead protection air tube 6 from being damaged by thrown sand and gravel. The lead protection air tube 6 is protected during the concrete pouring process to ensure the normal operation of the optical fiber sensor and avoid affecting the monitoring effect due to damage by sand and gravel.

[0049] In a preferred embodiment, in step S3, the third optical fiber sensor is a glass fiber composite-based optical cable 7. After the core concrete is demolded, it is hoisted to the scaffolding position, and the glass fiber composite-based optical cable 7 is preliminarily fixed to the side wall of the inner layer of concrete 9 of the core concrete using spray paint. Then, epoxy resin glue is applied along the glass fiber composite-based optical cable 7 to tightly bond the glass fiber composite-based optical cable 7 to the side wall of the inner layer of concrete 9 of the core concrete. The use of preliminarily fixing with spray paint and epoxy resin glue ensures that the glass fiber composite-based optical cable 7 is tightly bonded to the inner layer of concrete 9, thereby improving the accuracy and reliability of monitoring.

[0050] In a preferred embodiment, step S3 also includes clearing concrete and wood chips from the surface corresponding to the punched hole 12 reserved on the PCCP socket steel ring 11, inserting a bolt 13, tying a steel wire rope 14 to the inside of the bolt 13, and suspending a hanging frame 15 within the steel wire rope 14. A monitoring and processing device is placed within the hanging frame 15. The monitoring and processing device is equipped with multiple channels, allowing multiple optical fiber leads to be connected to the carbon fiber composite-based optical cable 1, the high-transmission tight-jacketed strain sensing optical cable 2, and the glass fiber composite-based optical cable 7. The monitoring and processing device is connected to the glass fiber composite-based optical cable 7 to obtain the light intensity signal of the glass fiber composite-based optical cable 7. The effective monitoring area of ​​the glass fiber composite-based optical cable 7 along the axis of the steel cylinder 4 is calibrated by bending the light intensity. The monitoring and processing device is installed using a specific suspension method, facilitating real-time monitoring during construction. The monitoring and processing device with multiple channels can simultaneously connect different optical fiber sensors, improving monitoring efficiency and comprehensiveness. Position calibration further enhances monitoring accuracy.

[0051] In a preferred embodiment, in step 3, after the core concrete reaches 70% of its design strength, the monitoring and processing equipment is turned on to continuously monitor the hoisting process of the core concrete. After the core concrete is hoisted to the wire winding machine, the lower portion of the hanging basket is fixed to the wire winding turntable with wire 16 to overcome the rotation during the wire winding process. The prestressed steel wire winding, roller-sprayed mortar protective layer, and sprayed asphalt anti-corrosion layer construction processes are all continuously monitored simultaneously, and the timing of monitoring is selected based on the concrete strength to ensure the effectiveness of the monitoring. The wire 16 fixes the hanging basket to overcome the rotation during the wire winding process, ensuring the stability of the monitoring equipment, realizing continuous monitoring of multiple processes, and timely understanding of the strain situation.

[0052] In a preferred embodiment, the carbon fiber composite-based optical cable 1 and the high-transmission tight-sheathed strain sensing optical cable 2 are led out from the top of the tube, the length of the first optical fiber lead 5 is not less than 5m, the lead of the glass fiber composite-based optical cable 7 is always in the tube, and the length of the second optical fiber lead 8 farthest from the hanging frame 15 is not less than 4m. The lead length settings of different optical fiber sensors meet the monitoring needs in actual construction and ensure the stability and reliability of signal transmission.

[0053] In a preferred embodiment, the monitoring and processing equipment includes a monitoring data acquisition device 18, a control computer and a mobile power supply. The theoretical strains for the appearance of microcracks during concrete cracking are 207.6 με, and the theoretical strains for the appearance of visible cracks during concrete cracking are 1522.6 με. The theoretical strains for concrete cracking are clarified, providing a standard for judging the crack situation. The combination of the monitoring data acquisition device 18, the control computer 19 and the mobile power supply ensures the efficiency and convenience of monitoring.

[0054] Example 1:

[0055] Taking a PCCP with a length of 5m and an inner diameter of 3.4m as an example, the distributed sensors were installed and the whole process was monitored according to the previous steps. The strain distribution curves of different manufacturing processes were obtained. Step S5 was executed, and the results were as follows: Figure 9 As shown in the figure, the circumferential crack appeared at a position 0.2m away from the socket end and occurred after the prestressed steel wire winding process was constructed.

[0056] The present invention uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only intended to help understand the method and core concept of the present invention. At the same time, those skilled in the art will find that the specific implementation methods and application scopes may vary based on the concept of the present invention. In summary, the contents of this specification should not be construed as limiting the present invention.

Claims

1. A method for monitoring cracking of inner concrete during PCCP manufacturing, characterized in that: The following steps are involved: S1: placing a steel cylinder horizontally on a roller frame, arranging a first optical fiber sensor on the inner surface of the steel cylinder, welding a plurality of fixing members on the inner surface of the steel cylinder, fixing the second optical fiber sensor by each of the fixing members and providing a gap between the second optical fiber sensor and the inner surface of the steel cylinder; S2: The steel cylinder is placed upright with the PCCP socket facing upward, the pigtails of the first optical fiber sensor and the second optical fiber sensor are led out and connected to the monitoring and processing equipment on the casting platform through the first optical fiber lead, and then the pipe core concrete casting process is carried out, and the strain during the pipe core concrete casting process and the steam curing process is continuously monitored by the monitoring and processing equipment; S3: Demolding the core concrete, placing a third optical fiber sensor on the side wall of the inner layer of the core concrete away from the steel cylinder, suspending the monitoring and processing equipment on the inner side of the core concrete, and connecting the first optical fiber sensor and the second optical fiber sensor to the monitoring and processing equipment through a first optical fiber lead, connecting the third optical fiber sensor to the monitoring and processing equipment through a second optical fiber lead, and then performing real-time monitoring of strain through the monitoring and processing equipment while performing the prestressed steel wire winding, roller-sprayed mortar protective layer and sprayed asphalt anti-corrosion layer processes in the PCCP manufacturing process; S4: After the asphalt anti-corrosion layer spraying process is completed, the finished PCCP is placed horizontally and continuously monitored by monitoring and processing equipment. S5: By comparing the strain distribution curve measured by the monitoring and processing equipment with the theoretical strain of concrete cracking, the process and location of the inner concrete cracks are determined.

2. The method for monitoring cracking of inner concrete during the PCCP manufacturing process according to claim 1, characterized in that: In step S1, the first optical fiber sensor is a carbon fiber composite-based optical cable, the laying path of the carbon fiber composite-based optical cable on the steel cylinder is polished and cleaned, and the cleaning width of the laying path is not less than 10 cm, the first optical fiber sensor is preliminarily fixed with a magnet and spray paint, and the carbon fiber impregnation glue is brushed on the entire carbon fiber composite-based optical cable 1 to 2 times to allow the carbon fiber impregnation glue to penetrate into the entire carbon fiber composite-based optical cable to fix the carbon fiber composite-based optical cable to the steel cylinder.

3. The method for monitoring cracking of inner concrete during the PCCP manufacturing process according to claim 2, characterized in that: In step S1, the second optical fiber sensor is a high-transmission tight sheath strain sensing optical cable, and the fixing part is a fixing clip, which is welded and fixed to the inner surface of the steel cylinder, the width of the fixing clip is not less than 3 cm, and the length of the fixing clip is not less than 10 cm. The fixing clip is bent to fix the high-transmission tight sheath strain sensing optical cable, and the distance between the high-transmission tight sheath strain sensing optical cable and the inner surface of the steel cylinder is not less than 3 cm. Each fixing clip is arranged along the extension direction of the high-transmission tight sheath strain sensing optical cable, and the number of the fixing clips is not less than 2.

4. The method for monitoring cracking of inner concrete during the PCCP manufacturing process according to claim 3, characterized in that: In step S2, one end of a lead protection air tube of no less than 2 m is fixed at the socket position of the PCCP, and the pigtails of the carbon fiber composite-based optical cable and the high-transmission tight sheathed strain sensing optical cable pass through the lead protection air tube and are connected to the monitoring and processing equipment placed on the casting platform through the first optical fiber lead.

5. The method for monitoring cracking of inner concrete during the PCCP manufacturing process according to claim 4, characterized in that: In step S2, the monitoring and processing equipment is turned on to obtain the light intensity signals of the carbon fiber composite-based optical cable and the high-transmission tight sheath strain sensing optical cable, and the effective monitoring areas of the carbon fiber composite-based optical cable and the high-transmission tight sheath strain sensing optical cable in the axial direction of the steel cylinder are calibrated by bending and changing the light intensity.

6. The method for monitoring cracking of inner concrete during the PCCP manufacturing process according to claim 5, characterized in that: In step S2, when the core concrete pouring process is being carried out, the lead protection air pipe is protected by a tool to prevent the lead protection air pipe from being damaged by thrown sand and gravel.

7. The method for monitoring cracking of inner concrete during the PCCP manufacturing process according to claim 6, characterized in that: In step S3, the third optical fiber sensor is a glass fiber composite-based optical cable. After the core concrete is demoulded, it is hoisted to the scaffolding position, and the glass fiber composite-based optical cable is preliminarily fixed to the side wall of the inner layer of concrete of the core concrete by spray paint, and then epoxy resin glue is applied along the glass fiber composite-based optical cable to make the glass fiber composite-based optical cable tightly bonded to the side wall of the inner layer of concrete of the core concrete.

8. The method for monitoring cracking of inner concrete during the PCCP manufacturing process according to claim 7, characterized in that: Step S3 also includes clearing the concrete on the surface of the punching hole corresponding to the reserved position of the steel ring at the PCCP socket position and the wood chips blocking the inside, inserting a bolt, tying a steel wire rope on the inner side of the bolt, hanging a hanging frame in the steel wire rope, placing the monitoring and processing equipment in the hanging frame, and providing a plurality of channels for connecting a plurality of optical fiber leads to the carbon fiber composite-based optical cable, the high-transmission tight-sheathed strain sensing optical cable and the glass fiber composite-based optical cable at the same time, connecting the monitoring and processing equipment to the glass fiber composite-based optical cable, acquiring the light intensity signal of the glass fiber composite-based optical cable, and calibrating the position of the effective monitoring area of ​​the glass fiber composite-based optical cable in the axial direction of the steel cylinder by bending and changing the light intensity.

9. The method for monitoring cracking of inner concrete during the PCCP manufacturing process according to claim 8, characterized in that: In step 3, after the core concrete reaches 70% of the design strength, the monitoring and processing equipment is turned on to continuously monitor the lifting process of the core concrete; After the pipe core concrete is hoisted to the wire winding machine, the lower part of the hanging basket is fixed on the wire winding turntable with wire to overcome the rotation during the wire winding process; the processes of prestressed steel wire winding, roller spraying mortar protective layer and spraying asphalt anti-corrosion layer are continuously monitored while being constructed.

10. The method for monitoring cracking of inner concrete during PCCP manufacturing process according to claim 1, characterized in that: The monitoring and processing equipment includes a monitoring data acquisition device, a control computer and a mobile power supply. The theoretical strains for the appearance of micro cracks in the concrete cracking process are 207.6με, and the theoretical strains for the appearance of visible cracks in the concrete cracking process are 1522.6μ.

Images