Full-scale in-situ test structure for buried pipeline and its test method

Abstract

The present invention relates to the technical field of pipeline engineering, and discloses a full-scale in-situ test structure for buried pipelines and a test method therefor. The structure includes a foundation pit, a settlement pit, a vertical loading actuator, a sealed pipeline, and a vacuum pump. The foundation pit is filled with soil; the settlement pit is formed on one side of the bottom surface of the foundation pit; a loading plate is arranged on the top surface of the settlement pit; one end of the vertical loading actuator is installed on the bottom surface of the settlement pit, and the other end thereof is connected to the loading plate; the sealed pipeline is buried in the foundation pit; and the vacuum pump is communicated with the sealed pipeline through a vacuum tube. The present invention can consider the influence of the trench size effect, the relative stiffness of the soil inside and outside the trench, and the air pressure in the pipeline on the mechanical properties and deformation response of the buried full-scale pipeline, and provide key technical indicators for the design and construction of buried pipelines.

Description

Technical Field

[0001] The present invention relates to the technical field of pipeline engineering, and in particular to a full-scale in-situ test structure for buried pipelines and a test method therefor. Background Art

[0002] As the "lifeblood of the city", underground pipelines are in disrepair and frequently damaged over the years, leading to safety accidents such as gas explosions, urban fires, and road surface collapses, as well as environmental problems such as groundwater leakage and river pollution. In order to reduce the safety accidents caused by urban underground pipelines, it is necessary to accurately select the design parameters of the ultimate state and the key construction technical indicators of the pipeline during the design stage and the construction stage. The determination of the ultimate state of the pipeline mainly depends on the measurement of the displacement and internal force values of the pipeline under the action of formation dislocation. This is because the relatively large ground displacement is irreversible, and the pipeline damage rate caused in a small area is often relatively high. Moreover, the softening of the soil around the pipeline caused by seismic waves allows the pipeline to reduce the impact of seismic waves through greater adaptive deformation. Therefore, analyzing the displacement and internal force responses of the pipeline under the action of formation dislocation is an essential part of the seismic design of the pipeline.

[0003] Before the construction of buried pipeline projects, monitoring instruments are often not arranged, resulting in the lack of on-site measured data of the deformation and internal force of buried pipelines. Therefore, the acquisition of deformation data of buried pipelines mainly relies on experimental means. At present, the commonly used experimental means for buried pipelines include indoor model box tests, centrifuge tests, and shaking table tests. Among them, the shaking table test focuses on the impact of seismic excitation on the pipeline. However, earthquake damage examples show that formation dislocation is the main cause of the failure of buried pipelines, and the above means cannot consider the influence of the trench size and the parameters of the backfill soil inside and outside the trench on the pipeline deformation. In actual projects, the design of the trench is crucial for pipeline safety. Moreover, the existing test methods often ignore the influence of the internal gas pressure of the pipeline on the pipeline performance under the action of pipe-soil coupling, resulting in an overestimation of the leakage displacement limit of the pipeline interface and a deviation in the evaluation of the pipeline sealing performance, which is not conducive to the design and construction of pressurized pipe networks. Therefore, there is an urgent need for a test structure and a test method that meet the existing requirements. Summary of the Invention

[0004] The object of the present invention is to provide a full-scale in-situ test structure for buried pipelines and a test method therefor, which has a simple and compact structure, can consider the influence of the trench size effect, the relative stiffness of the soil inside and outside the trench, and the internal gas pressure of the pipeline on the mechanical properties and deformation response of the full-scale buried pipeline, and provides key technical indicators for the design and construction of buried pipelines.

[0005] To solve the above technical problems, the present invention provides a full-scale in-situ test structure for buried pipelines, including a foundation pit, a settlement pit, a vertical loading actuator, a sealed pipeline and a vacuum pump. The foundation pit is filled with soil; the settlement pit is opened on one side of the bottom surface of the foundation pit; a loading plate is arranged on the top surface of the settlement pit; one end of the vertical loading actuator is installed on the bottom surface of the settlement pit, and the other end is connected to the loading plate; the sealed pipeline is buried in the foundation pit; the vacuum pump is communicated with the sealed pipeline through a vacuum tube.

[0006] Preferably, the cross-section of the foundation pit is a trapezoidal structure.

[0007] Preferably, foam blocks are arranged on the inner wall of the settlement pit.

[0008] Preferably, the vertical loading actuator includes an end spherical hinge with a connection plate, a load sensor, an actuator body with an in-built displacement sensor, and a connection flange plate arranged from top to bottom.

[0009] Preferably, sealing flange plates are arranged at both ends of the sealed pipeline.

[0010] Preferably, a sealing ring is arranged at the connection between the sealing flange plate and the sealed pipeline.

[0011] Preferably, earth pressure cells, strain gauges and distributed optical fibers are buried in the soil, and the strain gauges and distributed optical fibers are attached to the outer wall of the sealed pipeline.

[0012] Preferably, a data acquisition unit is further included, and the data acquisition unit is electrically connected to the vertical loading actuator, the earth pressure cell, the strain gauge and the distributed optical fiber.

[0013] Preferably, a monitoring unit for monitoring the height of the soil is further included. The monitoring unit includes a reflecting prism and a total station for capturing the movement of the reflecting prism, and the reflecting prism is arranged on the top surface of the soil.

[0014] To solve the above technical problems, the present invention discloses a full-scale in-situ test method for buried pipelines, including the following steps:

[0015] S1. Select a site to dig a test foundation pit and a settlement pit, and install a vertical loading actuator and a loading plate;

[0016] S2. Connect the sealed pipeline with the vacuum pump for standby; and arrange monitoring elements on the sealed pipeline;

[0017] S3. Fill and compact the test foundation pit with soil in layers,

[0018] S4. When backfilling to the buried depth of the sealed pipeline, longitudinally excavate the buried trench along the pre-buried position of the sealed pipeline, hoist the whole sealed pipeline, gently place it into the buried trench, then continue to fill the soil into the foundation pit, embed earth pressure cells, and set up monitoring units on the top surface of the soil mass;

[0019] S5. Start the vacuum pump, apply the vacuum pressure required by the specification by adjusting the valve on the vacuum pump, and then close the valve and the vacuum pump;

[0020] S6. Through the data acquisition unit, read the initial readings of the earth pressure cells and monitoring elements before the test, and manually / computer record the data of the monitoring units; issue commands through the built-in program of the computer, start four vertical loading actuators through the control system, and gradually lower the loading plate synchronously and coordinately according to the displacement control method to achieve uneven dislocation of the formation;

[0021] S7. During the process of the gradual descent of the loading plate, collect the readings of the earth pressure cells, monitoring elements and monitoring units; record the vacuum pressure values of the vacuum gauge on the vacuum pump changing with the formation displacement;

[0022] S8. During the interval of each level of descent of the loading plate, start the vacuum pump, apply the vacuum pressure required by the specification into the pipe, then close the vacuum pump, calculate the vacuum pressure loss value and the average dissipation rate of the vacuum pressure within the specified time, and compare them with the allowable values in the specification, so as to judge the formation dislocation limit displacement corresponding to the air leakage in the pipe and reveal the degradation mechanism of the pipeline structure tightness under different formation dislocation displacements;

[0023] S9. When the formation dislocation displacement reaches the total dislocation amount set in the test, end the test, layer by layer excavate the backfill soil above the sealed pipeline, observe and photograph the actual deformation of the pipeline, and further analyze the stress characteristics and deformation response laws of the pipeline under different formation dislocation amounts according to the collected data.

[0024] The present invention has the following beneficial effects:

[0025] 1. The structure of the present invention is simple and compact. By setting up a foundation pit and reasonably arranging settlement pits in the foundation pit to simulate the formation dislocation effect, and using a vacuum pump to monitor the tightness of the sealed pipeline, it can fully simulate the test environment of the pipeline under the formation dislocation effect, and provide guarantee for the accuracy of the pipeline test data;

[0026] 2. The present invention takes into account the influence of the trench size effect, the relative stiffness of the soil inside and outside the trench, and the air pressure in the pipe on the mechanical properties and deformation response of the buried full-scale pipeline, obtains the pipeline displacement and internal force response results more in line with the actual working conditions, reveals the degradation mechanism of the pipeline structure tightness, and provides key technical indicators for the design and construction of buried pipelines. Description of the Drawings

[0027] Figure 1It is a schematic structural diagram of the full-scale in-situ test structure of the buried pipeline provided by the embodiment of the present invention;

[0028] Figure 2 It is a schematic cross-sectional structure diagram of the full-scale in-situ test structure of the buried pipeline provided by the embodiment of the present invention;

[0029] Figure 3 It is a schematic structural diagram of the vertical loading actuator provided by the embodiment of the present invention;

[0030] Figure 4 It is a flow block diagram provided by the embodiment of the present invention.

[0031] Reference numerals: 1, foundation pit; 11, first backfill area; 12, second backfill area; 2, settlement pit; 21, loading plate; 22, foam block; 3, vertical loading actuator; 31, end spherical hinge; 32, load sensor; 33, actuator body; 34, connecting flange; 4, sealed pipeline; 41, sealed flange plate; 42, fixture; 5, vacuum pump; 51, vacuum tube; 52, vacuum gauge; 6, earth pressure cell; 7, reflecting prism; 8, total station; 9, soil body. Detailed implementation manners

[0032] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the protection scope of the present application.

[0033] In the description of the present application, it should be understood that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be understood as a limitation to the present application.

[0034] In the description of the present application, it should be noted that unless otherwise clearly defined and limited, the terms "installed", "connected", "connected" 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 directly connected, or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific situations.

[0035] SeeFigure 1 and Figure 2 In a preferred embodiment of the present invention, a full-scale in-situ test structure for buried pipelines is provided, including a foundation pit 1, a settlement pit 2, a vertical loading actuator 3, a sealed pipeline 4, and a vacuum pump 5. The foundation pit 1 is filled with soil mass 9; the settlement pit 2 is opened on one side of the bottom surface of the foundation pit 1; a loading plate 21 is arranged on the top surface of the settlement pit 2; one end of the vertical loading actuator 3 is installed on the bottom surface of the settlement pit 2, and the other end is connected to the loading plate 21; the sealed pipeline 4 is buried in the foundation pit 1; the vacuum pump 5 is communicated with the sealed pipeline 4 through a vacuum tube 51.

[0036] Specifically, a vacuum gauge 52 is arranged on the vacuum pump 5.

[0037] As a preferred solution, the cross-section of the foundation pit 1 is a trapezoidal structure.

[0038] As a preferred solution, foam blocks 22 are arranged on the inner wall of the settlement pit 2. Specifically, arranging the foam blocks 22 on the inner wall of the settlement pit 2 can ensure the smooth descent of the loading plate 21 while preventing the soil mass 9 particles from falling into the settlement pit 2 through the gaps of the loading plate 21.

[0039] See Figure 3 , as a preferred solution, the vertical loading actuator 3 includes an end ball joint 31 with a connecting disc, a load sensor 32, an actuator body 33 with an in-built displacement sensor, and a connecting flange 34 arranged from top to bottom.

[0040] As a preferred solution, sealing flange plates 41 are arranged at both ends of the sealed pipeline 4. Specifically, using the sealing flange plates 41 to seal both ends of the sealed pipeline 4 ensures the sealing performance of the sealed pipeline 4 and also facilitates the overall assembly and disassembly.

[0041] As a preferred solution, a sealing ring is arranged at the connection between the sealing flange plate 41 and the sealed pipeline 4. And clamps 42 are arranged at both ends of the sealed pipeline 4. Specifically, using the sealing ring can further ensure the airtightness of the sealed pipeline 4, and using the clamps 42 can make the installation of the sealed pipeline 4 more convenient and stable.

[0042] As a preferred solution, earth pressure cells 6, strain gauges, and distributed optical fibers are buried in the soil mass 9, and the strain gauges and distributed optical fibers are attached to the outer wall of the sealed pipeline 4. Specifically, using the earth pressure cells 6 can monitor the pressure in the soil mass 9, and the strain gauges and distributed optical fibers can monitor the deformation and other states of the pipeline.

[0043] As a preferred solution, it further includes a data acquisition unit, which is electrically connected to the vertical loading actuator 3, the earth pressure cell 6, the strain gauge and the distributed optical fiber. Specifically, the data acquisition unit is used to collect each monitoring data, improving the convenience and accuracy of the test.

[0044] As a preferred solution, it further includes a monitoring unit for monitoring the height of the soil mass 9. The monitoring unit includes a reflecting prism 7 and a total station 8 for capturing the movement of the reflecting prism 7. The reflecting prism 7 is arranged on the top surface of the soil mass 9. Specifically, the monitoring unit can be used to monitor the height of the soil mass 9, so as to quantify the settlement of the soil mass 9.

[0045] See Figure 4 , a full-scale in-situ test method for buried pipelines according to a preferred embodiment of the present invention includes the following steps:

[0046] S1. Select a site to dig a test foundation pit 1 and a settlement pit 2, and reinforce the base of the settlement pit 2. Foam blocks 22 are arranged on the inner wall of the settlement pit 2. Four vertical loading actuators 3 are bolted to the base of the settlement pit 2, and their wires are externally connected to a control system. The loading plate 21 is bolted to the four vertical loading actuators 3. The loading plate 21 is leveled as a whole by the vertical loading actuator 3 and is at the same height as the bottom surface of the foundation pit 1.

[0047] S2. The sealing flange plate 41 is adhesively connected to the two ends of the pipeline through a strong sealant. The clamp 42 is fixed to the pipeline end through bolts to further ensure the sealing performance of the adhesive connection between the sealing flange plate 41 and the pipeline end, avoiding the leakage of the initial air pressure in the pipeline and interfering with the test results. The left end of the pipeline is connected to the vacuum pump 5 through the vacuum tube 51. According to the test purpose, strain gauges and distributed optical fiber monitoring elements are pasted on the pipeline surface. When the monitoring elements are pasted on the inner wall of the pipeline, holes can be drilled in the sealing flange plate 41 at the right end of the pipeline to lead out the wires of the monitoring elements. Start the vacuum pump 5 and adjust the valve to conduct a trial air extraction on the pipeline to verify whether the pipeline is well sealed before the test.

[0048] S3. According to the requirements of the buried pipeline construction specification, the soil mass 9 is backfilled and compacted in layers. The backfill area is divided into a first backfill area 11 and a second backfill area 12. The compaction degree of the soil mass 9 in the first backfill area 11 is the same as that of the original soil. The second backfill area 12 is a pipe trench, and the size of the pipe trench and the compaction degree of the soil mass 9 meet the specification requirements. During the test, different bottom widths of the pipe trench and the compaction degree of the soil mass 9 inside and outside the pipe trench can be further set to study the influence of the bottom width of the pipe trench and the relative stiffness of the soil mass 9 inside and outside the pipe trench on the mechanical properties of the pipeline.

[0049] S4. When backfilling to the pipeline burial depth, longitudinally excavate the burial trench along the pre-buried position of the pipeline, hoist the whole pipeline, gently place it into the burial trench, lead out the wires of the strain gauges and distributed optical fiber monitoring elements and connect them to the data acquisition unit; in accordance with step S3, continue to backfill the soil body 9 above the pipeline. When backfilling to the burial depth of the earth pressure cell 6, bury the earth pressure cells 6 at regular intervals on both sides of the soil layer dislocation surface, lead out the wires of the earth pressure cells 6 and connect them to the data acquisition unit; continue to backfill to the ground surface, and arrange the reflection prisms 7 at intervals on both sides of the soil layer dislocation surface. Capture the movement of the reflection prisms 7 through the total station 8 to observe the settlement displacement of the surface of the soil body 9.

[0050] S5. Start the vacuum pump 5, apply the vacuum pressure required by the specification by adjusting the valve on the vacuum pump 5, and then close the valve and the vacuum pump 5.

[0051] S6. Through the data acquisition unit, read the initial readings of the earth pressure cells 6, strain gauges, and distributed optical fiber monitoring elements before the test, and manually / computer record the initial elevation of the prism. Send commands through the built-in program of the computer, start the four vertical loading actuators 3 through the control system, and synchronously and coordinately lower the loading plate 21 step by step in accordance with the displacement control method to achieve uneven dislocation of the stratum; if the test process is divided into 20 levels, 10 mm for each level, the total stratum dislocation amount is 200 mm.

[0052] S7. During the process of the gradual descent of the loading plate 21, collect the readings of the earth pressure cells 6, monitoring elements, and monitoring units; record the vacuum pressure values of the vacuum gauge 52 on the vacuum pump 5 changing with the stratum displacement.

[0053] S8. During the interval of the descent of each level of the loading plate 21, start the vacuum pump 5, apply the vacuum pressure required by the specification, such as 28 kPa, into the pipe, and then close the vacuum pump 5. Calculate the vacuum pressure loss value and the average vacuum pressure dissipation rate within the specified time. When the calculated value exceeds the allowable value of the specification, such as when the vacuum pressure loss value reaches 6.9 kPa and the average vacuum pressure dissipation rate is 0.82 kPa / s, it is considered that the pipeline seal is damaged, so as to judge the limited displacement of the stratum dislocation corresponding to the air leakage in the pipe and reveal the degradation mechanism of the pipeline structure seal tightness under different stratum dislocation displacements.

[0054] S9. When the stratum dislocation displacement reaches the total dislocation amount set in the test, such as 200 mm, end the test, layer by layer excavate the backfill soil body 9 above the sealed pipeline 4, observe and photograph the actual deformation of the pipeline, and further analyze the stress characteristics and deformation response laws of the pipeline under different stratum dislocation amounts according to the collected data.

[0055] It should be noted that the monitoring elements are strain gauges and distributed optical fibers.

[0056] In summary, the preferred embodiment of the present invention provides a full-scale in-situ test structure for buried pipelines and its test method. Compared with the prior art:

[0057] 1. The structure of the present invention is simple and compact. By setting the foundation pit 1 and reasonably arranging the settlement pits in the foundation pit 1 to simulate the formation dislocation effect, and using a vacuum pump 5 to monitor the sealing performance of the sealed pipeline 4, it can fully simulate the test environment of the pipeline under the formation dislocation effect, providing guarantee for the accuracy of the pipeline test data;

[0058] 2. The present invention takes into account the influence of the trench size effect, the relative stiffness of the soil inside and outside the trench 9, and the internal air pressure of the pipe on the mechanical properties and deformation response of the buried full-scale pipeline, obtains the pipeline displacement and internal force response results that are more in line with the actual working conditions, reveals the degradation mechanism of the pipeline structure sealing performance, and provides key technical indicators for the design and construction of buried pipelines.

[0059] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and substitutions can be made, and these improvements and substitutions should also be regarded as the protection scope of the present invention.

Claims

1. A test method for a full-scale in-situ test structure of buried pipelines, characterized in that: The full-scale in-situ test structure of the buried pipeline includes: A foundation pit, wherein the foundation pit is filled with soil; A sinkhole, the sinkhole is opened on one side of the bottom surface of the foundation pit; a loading plate is arranged on the top surface of the sinkhole; A vertical loading actuator, one end of which is mounted on the bottom surface of the sinkhole and the other end of which is connected to the loading plate; A sealed pipeline, wherein the sealed pipeline is buried in the foundation pit; A vacuum pump, the vacuum pump being connected to the sealed pipeline through a vacuum pipe; The cross section of the foundation pit is a trapezoidal structure; A foam block is provided on the inner wall of the sinkhole; A soil pressure box, a strain gauge and a distributed optical fiber are buried in the soil body, and the strain gauge and the distributed optical fiber are attached to the outer wall of the sealed pipe; It also includes a data acquisition unit and a monitoring unit for monitoring the height of the soil; The test method comprises the following steps: S1. Select a site to dig a test foundation pit and a sinking pit, and install a vertical loading actuator and a loading plate; S2. Connect the sealed pipe to the vacuum pump for standby use; and arrange monitoring elements on the sealed pipe; S3, fill the test foundation pit with soil in layers and compact it; S4. When backfilling to the buried depth of the sealed pipe, dig a buried trench longitudinally along the pre-buried position of the sealed pipe, hoist the sealed pipe as a whole, gently put it into the buried trench, and then continue to fill the foundation pit, bury the earth pressure box and set the monitoring unit on the top surface of the soil; S5. Start the vacuum pump, apply the vacuum pressure required by the specification by adjusting the valve on the vacuum pump, and close the valve and vacuum pump; S6. The initial readings of the earth pressure box and the monitoring element before the test are read through the data acquisition unit, and the monitoring unit data is recorded manually or automatically by the computer; the computer embedded program issues a command to start the four vertical loading actuators through the control system, and the loading plates are synchronously and coordinatedly lowered step by step according to the displacement control method to achieve uneven displacement of the stratum; S7. During the step-by-step descent of the loading plate, the readings of the soil pressure box, the monitoring element and the monitoring unit are collected; and the vacuum pressure value of the vacuum gauge on the vacuum pump that changes with the displacement of the formation is recorded; S8. In the gap between each loading plate, start the vacuum pump to apply the vacuum pressure required by the specification to the pipe, then turn off the vacuum pump, calculate the vacuum pressure loss value and the average vacuum pressure dissipation rate within the specified time, and compare them with the allowable value of the specification, so as to determine the corresponding formation displacement limit when the gas pressure leaks in the pipe and reveal the degradation mechanism of the pipeline structure sealing under different formation displacements; S9. When the displacement of the stratum reaches the total displacement of the test setting, the test is terminated, the upper part of the sealed pipeline is excavated layer by layer and the soil is backfilled, the actual deformation of the pipeline is observed and photographed, and the stress characteristics and deformation response laws of the pipeline under different stratum displacements are further analyzed based on the collected data.

2. The test method of the full-scale in-situ test structure of the buried pipeline according to claim 1, characterized in that The vertical loading actuator includes an end ball joint with a connecting plate, a load sensor, an actuator body with a built-in displacement sensor and a connecting flange arranged from top to bottom.

3. The test method of the full-scale in-situ test structure for buried pipelines according to claim 1, characterized in that: Sealing flange plates are arranged at both ends of the sealing pipeline.

4. The test method of the full-scale in-situ test structure of the buried pipeline according to claim 3, characterized in that: A sealing ring is arranged at the connection between the sealing flange plate and the sealing pipeline.

5. The test method of the full-scale in-situ test structure of the buried pipeline according to claim 1, characterized in that: The data acquisition unit is electrically connected to the vertical loading actuator, earth pressure cell, strain gauge and distributed optical fiber.

6. The test method of the full-scale in-situ test structure of the buried pipeline according to claim 1, characterized in that The monitoring unit includes a reflecting prism and a total station for capturing the movement of the reflecting prism, and the reflecting prism is disposed on the top surface of the soil mass.

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