Distributed optical fiber deformation monitoring method for multi-stage high and steep road slope

Abstract

The invention discloses a distributed optical fiber deformation monitoring method for a multistage high and steep road slope. The distributed optical fiber deformation monitoring method comprises the following steps: step 1, establishing a distributed optical fiber deformation monitoring system; 2, data acquisition: monitoring strain parameter values and temperature change values of the strain optical fiber and temperature sensing optical fiber lines in real time through a Brillouin data acquisition instrument to obtain strain parameter values and temperature change value data of all points along the strain optical fiber and temperature sensing optical fiber lines; 3, data processing: carrying out integration and summation calculation on the strain parameter value and temperature change value data of each point along the line to obtain the strain distribution and displacement condition of a specific position; step 4, data analysis and early warning; and step 5, all monitoring data are classified and archived, and long-term storage and traceability of the monitoring data are ensured. The device can accurately measure tiny strain and displacement changes, is high in sensitivity, is suitable for detecting early slope deformation or crack propagation, and provides a scientific basis for early warning.

Description

Technical Field

[0001] The invention relates to a slope monitoring method, in particular to a distributed optical fiber deformation monitoring method for multi-level high and steep road slopes. Background Art

[0002] In the construction of modern transportation infrastructure, with the emergence of a large number of high and steep slope projects, the stability of slopes has become an important issue to ensure road safety. Although traditional slope monitoring technologies, such as strain gauges, inclinometers, total stations, and multi-point displacement meters and other electrical sensors, have been widely used in engineering practice, their limitations are becoming more and more obvious, especially for the monitoring of multi-level high and steep road slopes.

[0003] Traditional monitoring methods have the following main disadvantages: 1. Point monitoring has limited coverage: strain gauges and inclinometers can usually only monitor the stress or displacement of specific points, making it difficult to obtain comprehensive data on the entire slope and unable to reflect the overall deformation law of the slope.

[0004] 2. Poor real-time performance: manual reading or data collection through a complex wiring system is required, and real-time monitoring cannot be achieved. This may cause monitoring data to lag when the slope changes rapidly and fail to provide timely warnings.

[0005] 3. Large environmental impact: Electrical sensors are easily affected by environmental factors such as corrosion and lightning, have a short service life and high maintenance costs; in addition, this type of sensor has limited anti-interference ability under complex geological conditions, and the measurement data is easily affected by noise.

[0006] 4. Low stability and reliability: Due to the limited number of monitoring points and environmental influences, the stability and reliability of data from traditional monitoring technology are low during long-term monitoring, making it difficult to meet the safety monitoring needs of large-scale slope projects. Summary of the invention

[0007] In view of this, the present invention proposes a distributed optical fiber deformation monitoring method for multi-level high and steep road slopes, aiming to solve the defects of existing road slope monitoring methods in terms of insufficient real-time performance, coverage, data accuracy and system stability.

[0008] To achieve the above object, the present invention adopts the following technical solutions: The distributed optical fiber deformation monitoring method for multi-level high and steep road slopes of the present invention comprises the following steps: Step 1: Establish a distributed optical fiber deformation monitoring system: Step 1.1, laying of strain optical fiber on the inner side of the road: Step 1.1.1, on the inner side of the road (the side close to the slope), select a suitable laying area to ensure that the entire slope area where deformation may occur is covered, and set the strain optical fiber laying route according to the terrain and monitoring requirements; Step 1.1.2: dig a trench with a depth of 510 cm along the set strain optical fiber laying route, and lay a 23 cm layer of fine sand at the bottom of the trench to prevent damage to the strain optical fiber; the strain optical fiber should be laid straight to avoid bending and twisting; Step 1.1.3, use steel anchors to straighten and fix the strain optical fiber at set intervals of about 2m, and finally cover the strain optical fiber with fine sand and lay a layer of clay or concrete to prevent the strain optical fiber from being exposed and damaged; Step 1.2, laying of strain optical fiber outside the road: Step 1.2.1, dig a groove with a depth of 5 to 10 cm on the outer shoulder of the road, and lay the strain optical fiber and protective material according to steps 1.1.2 to 1.1.2; Step 1.2.2, deployment of deep displacement monitoring device: Drill an installation hole at the set monitoring position, install a PVC pipe in the installation hole with a gap, and then lay the strain optical fiber downward along the outer wall of the PVC pipe, bypass the bottom of the PVC pipe, and extend upward from the outer wall on the other side to the installation hole; Step 1.3, laying of temperature-sensitive optical fiber: laying of temperature-sensitive optical fiber in parallel with strain optical fiber, real-time monitoring and adjustment of errors caused by ambient temperature through the data processing system to ensure the accuracy of monitoring data; Step 1.4, fiber splicing: Step 1.4.1, after the strain optical fiber and the temperature-sensitive optical fiber are laid, each section of the strain optical fiber and the temperature-sensitive optical fiber is connected to form a continuous sensing line, that is: use a fiber optic cutting knife to accurately cut the end face of each section of the strain optical fiber and the temperature-sensitive optical fiber to ensure that the cut surface is smooth and free of impurities to reduce the fusion loss; Step 1.4.2, use a fusion splicer to fusion splice each section of strain optical fiber and temperature-sensitive optical fiber; during fusion splicing, place both ends of each section of strain optical fiber and temperature-sensitive optical fiber in the V-groove of the fusion splicer so that their end faces are precisely aligned; after starting the fusion splicer, use electric arc heating to melt and fuse the end faces of each section of strain optical fiber and temperature-sensitive optical fiber together; after the fusion splicing is completed, check the optical fiber strength and loss at the joint to ensure that the fusion splicing quality meets the requirements; Step 1.4.3, protection and packaging: Use heat shrink tubing to protect the fiber optic connector after fusion. Put the heat shrink tubing on the fiber optic connector and heat it to make it tightly wrapped on the fiber optic connector to prevent the external environment from damaging the fusion point. At the same time, use polyurethane coating to further seal the fiber optic connector to increase the durability and stability of the fiber optic connector. Step 1.4.4, Testing and calibration of strain optical fiber and temperature sensing optical fiber lines: Line test: Use OTDR (Optical Time Domain Reflectometer) to test the integrity and loss of strain optical fiber and temperature-sensitive optical fiber lines, that is, detect any breakpoints or high-loss points in the strain optical fiber and temperature-sensitive optical fiber lines, and generate corresponding loss curves. If abnormalities are found, re-splice or repair the optical fiber; Calibration and calibration: Before monitoring data collection, the strain optical fiber and temperature-sensing optical fiber line are calibrated; first, the known strain and temperature data (factory strain parameters, on-site ambient temperature data) signals are input into the distributed optical fiber deformation monitoring system (strain optical fiber and temperature-sensing optical fiber line), and the response data of the distributed optical fiber deformation monitoring system is recorded to ensure that the distributed optical fiber deformation monitoring system can accurately reflect the actual strain and temperature changes; after the calibration is completed, the strain optical fiber and temperature-sensing optical fiber line are connected to the Brillouin data acquisition instrument (BOTDR) respectively to prepare for subsequent data collection; Step 2, data collection: Step 2.1, real-time monitoring of the strain parameter value and temperature change value of the strain optical fiber and the temperature-sensitive optical fiber line by a Brillouin data acquisition device (BOTDR); that is, using the Brillouin scattering principle, pulse light is injected into the strain optical fiber and the temperature-sensitive optical fiber line respectively by BOTDR, and the strain parameter value and temperature change value data of each point along the strain optical fiber and the temperature-sensitive optical fiber line are obtained by analyzing the frequency shift of the backscattered light; Step 2.2, the data acquisition frequency is set according to the monitoring requirements, which can be continuous acquisition or timed acquisition; all the collected monitoring data are stored in the built-in memory of the BOTDR and transmitted to the local computer through the GPIB (general purpose interface bus) or Ethernet interface; Step 3, data processing: Step 3.1, the local computer first pre-processes the received monitoring data, including abnormal data identification, denoising, and smoothing; marks high loss points or abnormal signals in strain optical fiber and temperature-sensitive optical fiber lines, and takes measures such as re-splicing, replacing damaged optical fiber, adjusting the laying path, adding relay equipment, and optimizing software algorithms to avoid interference with the overall data; Step 3.2, integrating and summing the pre-processed data to obtain strain distribution and displacement at a specific location; predicting the potential sliding surface and possible instability point of the slope by analyzing the variation trend of strain and displacement; Step 3.3, using the data collected by the temperature-sensitive optical fiber, the strain data is temperature compensated to correct the optical fiber deformation error caused by temperature change to ensure the accuracy of the monitoring results; Step 4: Data analysis and early warning: Step 4.1, using MATLAB data analysis software to analyze the displacement data processed in step 3.2 and the strain data after temperature compensation in step 3.3, identify the deformation trend and potential risks of the slope; by establishing the Brillouin scattering analysis model and the slope limit equilibrium model, predict the future deformation behavior and evaluate the stability of the current monitoring area; Step 4.2, according to the analysis results of step 4.1, set the warning threshold; when the monitoring data exceeds the preset safety range, the local computer triggers the warning signal and sends an alarm to the relevant management personnel, prompting them to take necessary safety measures to prevent the occurrence of geological disasters such as landslides; Step 5: All monitoring data are classified and archived to ensure long-term preservation and traceability of the monitoring data; that is, the original data of each monitoring, the processed analysis results and the early warning records are saved for subsequent analysis and verification; according to the monitoring cycle, monitoring reports are generated regularly; the monitoring reports include the collection of monitoring data, processing and analysis results, slope stability assessment and future monitoring recommendations, providing a scientific basis for decision makers.

[0009] Preferably, in step 1.2.2, a groove is radially provided on the lower end surface of the PVC tube, and the bottom of the groove is an arc-shaped surface; after the laid strain optical fiber is passed downward along the outer wall of the PVC tube around the groove, a mounting hole is extended upward along the outer wall of the other side of the PVC tube; the bottom of the groove is an arc-shaped surface structure, the purpose of which is to ensure that the strain optical fiber passing around the groove has a certain curvature to avoid breakage.

[0010] The advantages of the present invention are mainly reflected in the following aspects: (1) Continuous distributed monitoring: Continuous monitoring of the entire optical fiber line is achieved, no longer limited to a single monitoring point. This means that the strain and displacement data of the entire slope can be obtained, thereby more accurately assessing the overall stability of the slope.

[0011] (2) Real-time data acquisition: Real-time data acquisition and transmission are realized. Through the Brillouin scattering principle, the strain and temperature data of each point on the optical fiber can be quickly obtained, providing timely and reliable basic data for slope stability analysis.

[0012] (3) High anti-interference ability: Optical fiber itself has strong anti-electromagnetic interference ability and is not affected by factors such as lightning and corrosion in the environment. Therefore, under harsh geological and climatic conditions, optical fiber monitoring technology can still operate stably and reliably.

[0013] (4) Long life and low maintenance: Due to its material properties, optical fiber is corrosion-resistant and has a long life. It does not require frequent maintenance like electrical sensors, which greatly reduces the cost of long-term monitoring.

[0014] (5) High precision and sensitivity: It can accurately measure tiny strain and displacement changes with high sensitivity, which is suitable for detecting early slope deformation or crack expansion, providing a scientific basis for early warning. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of the layout of the distributed optical fiber deformation monitoring system of the present invention.

[0016] Figure 2 It is a schematic diagram of the strain optical fiber of the present invention, after passing through the card slot downward along the outer wall of the PVC tube, and then extending upward along the outer wall of the other side of the PVC tube to form a mounting hole. DETAILED DESCRIPTION

[0017] The following is a detailed description of an embodiment of the present invention in conjunction with the accompanying drawings. This embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation method and a specific operation process are given, but the protection scope of the present invention is not limited to the following embodiment.

[0018] It should be noted that, in the description of the present invention, relational terms such as “first” and “second” are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations.

[0019] In the description of the present invention, unless otherwise clearly specified and limited, the terms "connected" and "connection" that may appear should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be the internal communication of two components. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0020] like Figure 1 As shown, the distributed optical fiber deformation monitoring method for multi-level high and steep road slopes of the present invention comprises the following steps: Step 1: Establish a distributed optical fiber deformation monitoring system: Step 1.1, laying of strain optical fiber on the inner side of the road: Step 1.1.1, on the inner side of the road (the side close to the slope), select a suitable laying area to ensure that the entire slope area where deformation may occur is covered, and set the strain optical fiber laying route according to the terrain and monitoring requirements; Step 1.1.2: dig a trench with a depth of 510 cm along the set strain optical fiber laying route, and lay a 23 cm layer of fine sand at the bottom of the trench to prevent damage to the strain optical fiber; the strain optical fiber should be laid straight to avoid bending and twisting; Step 1.1.3, use steel anchors to straighten and fix the strain optical fiber every 2 meters or so, and finally cover the strain optical fiber with fine sand and lay a layer of clay or concrete to prevent the strain optical fiber from being exposed and damaged; Step 1.2, laying of strain optical fiber outside the road: Step 1.2.1, dig a groove with a depth of 5 to 10 cm on the outer shoulder of the road, and lay the strain optical fiber and protective material according to steps 1.1.2 to 1.1.2; Through the dual-path redundant design of laying strain optical fiber inside and outside the road, when one strain optical fiber is damaged, the other strain optical fiber can still work normally, ensuring the continuity and stability of monitoring; greatly improving the reliability and fault resistance of the system; Step 1.2.2, deployment of deep displacement monitoring device: like Figure 2 As shown, a mounting hole is drilled at a set monitoring position, a PVC pipe 1 is installed in the mounting hole with a gap, a slot 2 is radially provided on the lower end surface of the PVC pipe 1, and the bottom of the slot 2 is an arc-shaped surface; then, the strain optical fiber 3 is laid downward along the outer wall of the PVC pipe 1 and bypasses the slot 2, and then extends upward along the outer wall of the other side of the PVC pipe 1 to form the mounting hole, and finally, the strain optical fiber 3 is fixed on the outer wall of the PVC pipe 1, and fine sand 4 or a concrete layer is filled in the gap between the outer wall of the PVC pipe 1 and the mounting hole; the bottom of the slot 2 is an arc-shaped surface, the purpose of which is to ensure that the strain optical fiber 3 bypassing the slot 2 has a certain curvature to avoid breaking; By combining strain optical fiber with deep displacement monitoring device, it is possible to monitor the deep deformation of the slope, further enhance the detection capability of potential slip surface and ensure the comprehensiveness of monitoring data.

[0021] Step 1.3, laying of temperature-sensitive optical fiber: Lay the temperature-sensitive optical fiber in parallel with the strain optical fiber, and use the data processing system to monitor and adjust the errors caused by the ambient temperature in real time; compensate the data by real-time monitoring of temperature changes, eliminate the interference of temperature on strain measurement, and ensure the accuracy of the monitoring data.

[0022] Step 1.4, fiber splicing: Step 1.4.1, after the strain optical fiber and the temperature-sensitive optical fiber are laid, each section of the strain optical fiber and the temperature-sensitive optical fiber is connected to form a continuous sensing line, that is: use a fiber optic cutting knife to accurately cut the end face of each section of the strain optical fiber and the temperature-sensitive optical fiber to ensure that the cut surface is smooth and free of impurities to reduce the fusion loss; Step 1.4.2, use a fusion splicer to fusion splice each section of strain optical fiber and temperature-sensitive optical fiber; during fusion splicing, place both ends of each section of strain optical fiber and temperature-sensitive optical fiber in the V-groove of the fusion splicer so that their end faces are precisely aligned; after starting the fusion splicer, use electric arc heating to melt and fuse the end faces of each section of strain optical fiber and temperature-sensitive optical fiber together; after the fusion splicing is completed, check the optical fiber strength and loss at the joint to ensure that the fusion splicing quality meets the requirements; Step 1.4.3, protection and packaging: Use heat shrink tubing to protect the fiber optic connector after fusion. Put the heat shrink tubing on the fiber optic connector and heat it to make it tightly wrapped on the fiber optic connector to prevent the external environment from damaging the fusion point. At the same time, use polyurethane coating to further seal the fiber optic connector to increase the durability and stability of the fiber optic connector. Step 1.4.4, Testing and calibration of strain optical fiber and temperature sensing optical fiber lines: Line test: Use OTDR (Optical Time Domain Reflectometer) to test the integrity and loss of strain optical fiber and temperature-sensitive optical fiber lines, that is, detect any breakpoints or high-loss points in the strain optical fiber and temperature-sensitive optical fiber lines, and generate corresponding loss curves. If abnormalities are found, re-splice or repair the optical fiber; Calibration and calibration: Before monitoring data collection, the strain optical fiber and temperature-sensing optical fiber lines are calibrated; first, the known strain and temperature data (factory strain parameters, on-site ambient temperature) signals are input into the distributed optical fiber deformation monitoring system (strain optical fiber and temperature-sensing optical fiber lines), and the response data of the distributed optical fiber deformation monitoring system is recorded to ensure that the distributed optical fiber deformation monitoring system can accurately reflect the actual strain and temperature changes; after the calibration is completed, the strain optical fiber and temperature-sensing optical fiber lines are connected to the Brillouin data acquisition instrument (BOTDR) respectively to prepare for subsequent data collection; Step 2, data collection: Step 2.1, real-time monitoring of the strain parameter value and temperature change value of the strain optical fiber and the temperature-sensitive optical fiber line by a Brillouin data acquisition device (BOTDR); that is, using the Brillouin scattering principle, pulse light is injected into the strain optical fiber and the temperature-sensitive optical fiber line respectively by BOTDR, and the strain parameter value and temperature change value data of each point along the strain optical fiber and the temperature-sensitive optical fiber line are obtained by analyzing the frequency shift of the backscattered light; Step 2.2, the data acquisition frequency is set according to the monitoring requirements, which can be continuous acquisition or timed acquisition; all the collected monitoring data are stored in the built-in memory of the BOTDR and transmitted to the local computer through the GPIB (general purpose interface bus) or Ethernet interface; Step 3, data processing: Step 3.1, the local computer first pre-processes the received monitoring data, including abnormal data identification, denoising, and smoothing; marks high loss points or abnormal signals in strain optical fiber and temperature-sensitive optical fiber lines, and takes measures such as re-splicing, replacing damaged optical fibers, adjusting laying paths, adding relay equipment, and optimizing software algorithms to avoid interference with the overall data; Step 3.2, integrating and summing the pre-processed data to obtain strain distribution and displacement at a specific location; predicting the potential sliding surface and possible instability point of the slope by analyzing the variation trend of strain and displacement; Step 3.3, using the data collected by the temperature-sensitive optical fiber, the strain data is temperature compensated to correct the optical fiber deformation error caused by temperature change to ensure the accuracy of the monitoring results; Step 4: Data analysis and early warning: Step 4.1, using MATLAB data analysis software to analyze the displacement data processed in step 3.2 and the strain after temperature compensation in step 3.3, identify the deformation trend and potential risks of the slope; by establishing the Brillouin scattering analysis model and the slope limit equilibrium model, predict the future deformation behavior and evaluate the stability of the current monitoring area; Step 4.2, according to the analysis results of step 4.1, set the warning threshold; when the monitoring data exceeds the preset safety range, the local computer triggers the warning signal and sends an alarm to the relevant management personnel, prompting them to take necessary safety measures to prevent the occurrence of geological disasters such as landslides; Step 5: All monitoring data are classified and archived to ensure long-term preservation and traceability of the monitoring data; that is, the original data of each monitoring, the processed analysis results and the early warning records are saved for subsequent analysis and verification; according to the monitoring cycle, monitoring reports are generated regularly; the monitoring reports include the collection of monitoring data, processing and analysis results, slope stability assessment and future monitoring recommendations, providing a scientific basis for decision makers.

[0023] Finally, it should be emphasized that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions recorded in the aforementioned embodiments without creative work, or replace some of the technical features therein with equivalents. Therefore, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A distributed optical fiber deformation monitoring method for multi-level high and steep road slopes. Features: The steps include: Step 1: Establish a distributed optical fiber deformation monitoring system: Step 1.1, laying of strain optical fiber on the inner side of the road: Step 1.1.1, setting the strain optical fiber laying route in the laying area on the inner side of the road close to the slope; Step 1.1.2, digging a groove along the set strain optical fiber laying line, laying a fine sand layer at the bottom of the groove, and laying the strain optical fiber straight in the groove to maintain; Step 1.1.3, use steel anchors to straighten and fix the strain optical fiber at set intervals, and finally cover the strain optical fiber with fine sand and lay a clay or concrete layer; Step 1.2, laying of strain optical fiber outside the road: Step 1.2.1, dig a groove on the outer shoulder of the road, and lay the strain optical fiber and protective material according to steps 1.1.2 to 1.1.2; Step 1.2.2, deployment of deep displacement monitoring device: Drill an installation hole at the set monitoring position, install a PVC pipe in the installation hole with a gap, and then lay the strain optical fiber downward along the outer wall of the PVC pipe, bypass the bottom of the PVC pipe, and extend upward from the outer wall on the other side to the installation hole; Step 1.3, laying of temperature-sensitive optical fiber: laying of temperature-sensitive optical fiber in parallel with strain optical fiber, real-time monitoring and adjustment of errors caused by ambient temperature through the data processing system to ensure the accuracy of monitoring data; Step 1.4, fiber splicing: Step 1.4.1, after the strain optical fiber and the temperature sensing optical fiber are laid, each section of the strain optical fiber and the temperature sensing optical fiber is connected to form a continuous sensing line; Step 1.4.2, using a fusion splicer to fusion splice each section of the strain optical fiber and the temperature sensitive optical fiber; Step 1.4.3, protection and packaging: Use heat shrink tubing to protect the fiber optic connector after fusion; Step 1.4.4, Testing and calibration of strain optical fiber and temperature sensing optical fiber lines: Line testing: Use OTDR to test the integrity and loss of strain fiber and temperature-sensitive fiber lines; Calibration and calibration: Before monitoring data collection, the strain optical fiber and temperature sensing optical fiber lines are calibrated; first, the known strain and temperature signals are input into the distributed optical fiber deformation monitoring system, and the response data of the distributed optical fiber deformation monitoring system is recorded. After the calibration is completed, the strain optical fiber and temperature sensing optical fiber lines are connected to the Brillouin data acquisition instrument respectively; Step 2, data collection: Step 2.1, real-time monitoring of the strain parameter value and temperature change value of the strain optical fiber and the temperature sensing optical fiber line by a Brillouin data acquisition instrument, and obtaining the strain parameter value and temperature change value data of each point along the strain optical fiber and the temperature sensing optical fiber line; Step 2.2, the data collection frequency is set according to the monitoring requirements, and all the collected monitoring data are stored in the built-in memory of the BOTDR and transmitted to the local computer; Step 3, data processing: Step 3.1, the local computer first pre-processes the received monitoring data, including abnormal data identification, denoising, and smoothing; marks high loss points or abnormal signals in strain optical fiber and temperature-sensitive optical fiber lines, and takes measures such as re-splicing, replacing damaged optical fiber, adjusting the laying path, adding relay equipment, and optimizing software algorithms to avoid interference with the overall data; Step 3.2, integrating and summing the pre-processed data to obtain the strain distribution and displacement of a specific position; Step 3.3, using the data collected by the temperature-sensitive optical fiber, temperature compensation is performed on the strain data to correct the optical fiber deformation error caused by temperature change; Step 4: Data analysis and early warning: Step 4.1, using MATLAB data analysis software to analyze the displacement data processed in step 3.2 and the strain data after temperature compensation in step 3.3, to identify the deformation trend and potential risks of the slope; By establishing the Brillouin scattering analysis model and the slope limit equilibrium model, the future deformation behavior is predicted and the stability of the current monitoring area is evaluated; Step 4.2, according to the analysis results of step 4.1, set the warning threshold; when the monitoring data exceeds the preset safety range, the local computer triggers the warning signal and sends an alarm to the relevant management personnel, prompting them to take necessary safety measures; Step 5: Classify and archive all monitoring data to ensure long-term preservation and traceability of monitoring data.

2. According to claim 1, the distributed optical fiber deformation monitoring method for multi-level high and steep road slopes, Features: The lower end surface of the PVC pipe is provided with a groove in the radial direction, and the bottom of the groove is an arc surface.

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