Test system and test method for simulating soil deformation caused by pipeline leakage

Abstract

The invention discloses a test system for simulating soil deformation caused by pipeline leakage, which comprises a model box, the model box is made of a transparent glass material, the upper part of the model box is not sealed, the model box is sequentially divided into a water inlet section, a simulation section and a water outlet section along the horizontal direction, a laser range finder is arranged on the simulation section, and a strain measurement optical fiber is embedded in the simulation section; the strain measurement optical fiber is connected with the OFDR demodulator and the laser range finder, and the OFDR demodulator is used for collecting and recording test data. The invention further discloses a test method of the test system for simulating soil deformation caused by pipeline leakage. The problem that an existing simulation test system does not conform to the actual pipeline leakage condition, and the accuracy of a test result is affected is solved.

Description

Technical Field

[0001] The invention belongs to the technical field of experimental simulation equipment for water conservancy engineering equipment, and specifically relates to a test system for simulating soil deformation caused by pipeline leakage, and also relates to a test method for the test system for simulating soil deformation caused by pipeline leakage. Background Art

[0002] In water diversion and water transfer projects, a large number of water pipelines need to be buried. After long-term use, the buried water pipelines have aged and their tensile and impact strengths have decreased, which can easily lead to leakage, rupture and other problems. When a buried water pipeline leaks, water seeps through the soil pores, and the soil particles lose support, which in turn causes ground deformation and collapse accidents, which not only affects the normal use of the project, but also endangers the lives and property of surrounding residents.

[0003] In the study of monitoring technology for soil deformation around buried water pipelines, distributed fiber optic strain sensing (DFOSS) technology has the advantages of good real-time performance, distributed measurement, and little environmental impact. It can monitor the deformation of the soil layer around the pipeline for a long time, continuously, and with high precision. It has been applied in the fields of roof settlement, collapse in karst areas, slope rock and soil monitoring, stratum monitoring, and frozen soil deformation monitoring.

[0004] At present, Wei Chao et al. have conducted ground collapse model tests using distributed optical fiber monitoring methods. The results show that the optical fiber strain monitoring curve accurately reflects the deformation state of the overlying soil at different collapse stages. Cheng et al. conducted indoor model tests to explore the monitoring effect of distributed optical fiber strain sensing technology on ground subsidence caused by underground cavities under different conditions; Li et al. used optical fiber strain sensing technology to monitor pipe soil deformation and proposed an analytical model that uses optical fiber strain measurement values ​​to calculate ground subsidence. The above studies all used water bag pumping to simulate the cavity generated after the leakage of buried water pipelines, and did not simulate the process of soil deformation caused by pipeline leakage. The monitoring application of distributed optical fiber monitoring methods in the process of soil deformation caused by pipeline leakage needs further study. The existing test system for simulating soil deformation caused by pipeline leakage has a simulation method that does not match the actual pipeline leakage situation, and the optical fiber layout method is not fully considered, resulting in incomplete soil deformation monitoring results. Summary of the invention

[0005] One object of the present invention is to provide a test system for simulating soil deformation caused by pipeline leakage, thereby solving the problem that the existing simulation test system does not conform to the actual pipeline leakage situation, thus affecting the accuracy of the test results.

[0006] Another object of the present invention is to provide a test method for soil deformation caused by pipeline leakage.

[0007] A technical solution adopted by the present invention is a test system for simulating soil deformation caused by pipeline leakage, including a model box, the model box is made of transparent glass, the upper part of the model box is not sealed, the model box is divided into a water inlet section, a simulation section and a water outlet section in the horizontal direction, a laser rangefinder is arranged on the simulation section, a strain measurement optical fiber is buried inside the simulation section, the strain measurement optical fiber is connected to an OFDR demodulator, and the laser rangefinder and the OFDR demodulator are used to collect and record test data.

[0008] The present invention is also characterized in that: Partitions are vertically arranged on both sides of the model box, which divide the model box into an inlet section, a simulation section and an outlet section. The inlet section is connected to an inlet pipe, the inlet pipe is connected to an inlet pump, the outlet section is connected to an outlet pipe, the outlet pipe is connected to a water inlet of a water tank, and the inlet pipe is connected to a water outlet of the water tank.

[0009] A loess layer, a sand cushion layer, a water pipeline, a strain measurement optical fiber, and a loess layer are laid in sequence from bottom to top at the bottom of the simulation section. The loess layer at the bottom is used as the foundation loess, and the loess layer at the top is used as the overlying loess. Through holes are opened at relative positions on the two partitions, and the water pipeline passes through the through holes on the partitions and is sealed with glass glue to stop water. One end of the water pipeline passes through the through holes and extends into the water inlet section, and the other end extends into the water outlet section. An inlet valve is set on the side where the water pipeline extends into the water inlet section, and an outlet valve is set on the side where the water pipeline extends into the water outlet section; a slide rail is horizontally set on the top of the model box, and a fixed bracket is slidably connected to the slide rail. A laser rangefinder is set on the fixed bracket. The strain measurement optical fiber and the laser rangefinder are arranged in the soil around the water pipeline to monitor the entire process of soil deformation caused by pipeline leakage.

[0010] The loess thickness of the bottom loess layer is 40cm, which is filled in layers. Each layer is 10cm thick after compaction. Before the next layer of soil is backfilled, the surface of the soil is roughened. The thickness of the overlying loess layer at the top is filled to the corresponding thickness according to different test conditions.

[0011] The sand cushion layer is 5cm thick and is filled after the foundation loess is completed.

[0012] The water supply pipeline uses a PVC pipe with an outer diameter of 9 cm, which is placed on a sand cushion layer. The neutral plane axis of the water supply pipeline is 49.5 cm away from the bottom plate of the model box. The water supply pipeline is covered with loess backfill in multiple layers. The first layer is 6 cm thick after compaction, and each subsequent layer is 3 cm thick after compaction. Before the next layer of soil is backfilled, the soil surface is roughened.

[0013] When laying out the strain measurement optical fiber in the simulation section, the pre-buried method is adopted, and it is laid out in two layers above and below the water pipeline. The upper layer is the surface deformation measurement optical fiber, and the lower layer is the soil deformation measurement optical fiber under the pipeline.

[0014] The buried depth of the optical fiber for measuring surface deformation is always 3 cm. The optical fiber for measuring soil deformation under the pipeline is buried in the foundation loess, 30 cm away from the bottom plate of the model box, and is arranged in an "S" shape. The middle measuring section of the "S" shape is located directly above or below the axis of the water pipeline. The other two sections of the "S" shape are on both sides of the middle measuring section, with a spacing of 10 cm. The optical fiber turning radius is 20 cm, and the distance from the optical fiber to the glass wall is 10 cm. Two measuring sections of strain measurement optical fiber are arranged around the water pipeline to locate the leakage position of the water pipeline. When monitoring surface deformation, the surface deformation monitoring optical fiber effectively monitors the underlying cavity formation process caused by leakage of buried water pipelines; when measuring the deformation of the soil under the pipeline, the soil deformation measurement optical fiber under the pipeline identifies the infiltration direction of water after leakage of the buried water pipeline.

[0015] An adjusting baffle is vertically clamped in the water outlet section, and the adjusting baffle is located 50 cm behind the water outlet end of the water delivery pipeline. Both baffles and the adjusting baffle are made of acrylic plates with a thickness of 1 cm.

[0016] Another technical solution adopted by the present invention is a test method for soil deformation caused by pipeline leakage, which adopts a test system simulating soil deformation caused by pipeline leakage, and is specifically implemented according to the following steps: Step 1: The outlet section starts to store water, and stops storing water when the water level reaches the bottom of the water delivery pipe, and the outlet valve is always in an open state; Step 2: The water inlet section starts to store water. When the water inlet section reaches the set water level, the water inlet valve is opened, and water is passed through the water pipeline. At the same time, the water passing time is taken as the starting time, and the water passing time is recorded; Step 3: Turn on the laser rangefinder and set the monitoring time interval to 1 minute, that is, the strain measurement optical fiber collects data every 1 minute, and the laser rangefinder measures the distance every 1 minute; Step 4: Observe the transparent glass wall of the simulation section and end the test when the distance between the soil wetting range and the bottom plate of the model box is 10 cm.

[0017] Step 5: Draw the strain curve and ground settlement curve during the test.

[0018] The beneficial effects of the present invention are: when the present invention uses distributed optical fiber to monitor soil deformation, the coupling relationship between the optical fiber and the soil, and the use of DOFSS technology has good applicability in monitoring ground collapse deformation caused by leakage of buried water pipelines, providing a new idea for the early identification of such geological disasters. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the structure of the test system for simulating soil deformation caused by pipeline leakage according to the present invention; Figure 2It is a structural schematic diagram of the water inlet tank section of the present invention; Figure 3 It is a structural diagram of the water outlet box section of the present invention; Figure 4 It is a schematic diagram of the arrangement of the strain measurement optical fiber of the present invention.

[0020] In the figure, 1. water inlet section, 2. simulation section, 3. water outlet section, 4. water inlet pump, 5. water tank, 6. water inlet pipe, 7. OFDR demodulator, 8. water inlet valve, 9. partition, 10. strain measurement optical fiber, 11. water pipeline, 12. sand cushion layer, 13. loess layer, 14. laser rangefinder, 15. adjustment partition, 16. water outlet valve, 17. water outlet pipe. DETAILED DESCRIPTION

[0021] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0022] Example 1 The test system of the present invention simulates soil deformation caused by pipeline leakage, and its structure is as follows: Figure 1 As shown, the test system comprises a model box, which is made of transparent glass. The upper part of the model box is not sealed. The model box is divided into a water inlet section 1, a simulation section 2 and a water outlet section 3 in the horizontal direction. A laser rangefinder 14 is arranged on the simulation section 2. A strain measurement optical fiber 10 is buried in the soil inside the simulation section 2. The strain measurement optical fiber 10 is connected to an OFDR demodulator 7. The simulation section 2 is the core part of the entire test system and is used to simulate the buried water pipeline and the soil around the pipeline so as to measure the ground settlement. The laser rangefinder 14 and the OFDR demodulator 7 are used to collect and record the test data. The test data draws a data process line or image data, and real-time distributed monitoring is performed on the soil deformation caused by pipeline leakage.

[0023] Example 2 On the basis of Example 1, Figure 2 and Figure 3 As shown, partitions 9 are vertically arranged on both sides of the model box, and the partitions serve to separate the water inlet section 1, the simulation section 2 and the water outlet section 3. The two sides of the simulation section 2 are divided into the water inlet section 1 and the water outlet section 3 by the partition 9. The water inlet section 1 is connected to the water inlet pipe 6, the water inlet pipe 6 is connected to the water inlet pump 4, and the end of the water inlet pipe 6 is connected to the water tank 5. The flow rate pumped into the water inlet section 1 is adjusted by the water inlet pump 4, and the water head in the water inlet section 1 is stabilized by adjusting the water inlet pump 4. The water outlet section 3 is connected to the water outlet pipe 17, the water outlet pipe 17 is connected to the water inlet of the water tank 5, and the water inlet pipe 6 is connected to the water outlet of the water tank 5.

[0024] The bottom of the simulation section 2 is laid with loess layer 13, sand cushion layer 12, water pipeline 11, strain measurement optical fiber 10, and loess layer 13 from bottom to top. The loess layer 13 at the bottom is used as foundation loess, and the loess layer 13 at the top is used as overlying loess. Through holes are provided at relative positions on the two partitions 9. The water pipeline 11 passes through the through holes on the partitions 9 and is sealed with glass glue to stop water. One end of the water pipeline 11 passes through the through holes and extends into the water inlet section 1, and the other end extends into the water outlet section 3. The water pipeline 11 is extended into the water inlet section 1. The side where the water pipeline 11 extends into the water inlet section 1 is provided with a water inlet valve 8, and the side where the water pipeline 11 extends into the water outlet section 3 is provided with a water outlet valve 16. A slide rail is horizontally arranged on the top of the model box, and a fixed bracket is slidably connected to the slide rail. A laser rangefinder 14 is arranged on the fixed bracket to measure the surface settlement of the soil under different working conditions. The entire process of soil deformation caused by pipeline leakage is monitored by arranging a strain measurement optical fiber 10 and a laser rangefinder 14 in the soil around the water pipeline 11.

[0025] Example 3 On the basis of Example 2, the loess layer 13 at the bottom is 40 cm thick and is filled in 4 layers. Each layer is 10 cm thick after compaction. Before the next layer of soil is backfilled, the surface of the soil is roughened. The loess covering the loess layer 13 at the top is filled to a corresponding thickness according to different test conditions.

[0026] The sand cushion layer 12 is 5 cm thick and is filled after the foundation loess is completed. The loess on top of the sand cushion layer is continued to be backfilled. The thickness can be filled to the corresponding thickness according to different test conditions.

[0027] The water delivery pipeline 11 is a PVC pipe with an outer diameter of 9 cm, which is placed on the sand cushion layer 12. The neutral plane axis center of the water delivery pipeline 11 is 49.5 cm away from the bottom plate of the model box.

[0028] The water pipeline 11 is backfilled with loess in multiple layers. The first layer is 6 cm thick after compaction, and each subsequent layer is 3 cm thick after compaction. Before the next layer of soil is backfilled, the soil surface is roughened.

[0029] like Figure 4As shown, when the strain measurement optical fiber 10 is laid in the simulation section 2, it is pre-buried and laid in two layers in the water pipeline 11, the upper layer is the surface deformation measurement optical fiber, and the lower layer is the pipeline lower soil deformation measurement optical fiber. According to the changes in different test conditions, the distance between the surface deformation measurement optical fiber and the bottom plate of the model box is adjusted, but the buried depth of the surface deformation measurement optical fiber is always 3cm. The pipeline lower soil deformation measurement optical fiber is buried in the foundation loess, 30cm away from the bottom plate of the model box, and they are all arranged in an "S" shape. The middle measurement section of the "S" shape is located directly above or directly below the axis of the water pipeline 11. The other two sections of the "S" shape are on both sides of the middle measurement section, with a spacing of 10cm, a fiber turning radius of 20cm, and a distance of 10cm from the fiber to the glass wall. Two measurement sections of strain measurement optical fiber 10 are arranged around the water pipeline 11, and both locate the leakage position of the water pipeline 11.

[0030] When monitoring ground deformation, the ground deformation monitoring optical fiber effectively monitors the formation process of the underlying cavity caused by the leakage of the buried water pipeline. When measuring the deformation of the soil under the pipeline, the soil deformation measurement optical fiber under the pipeline can identify the infiltration direction of water after the leakage of the buried water pipeline.

[0031] The water outlet section 3 is used to collect water and sediment discharged from the water pipeline 11. The adjusting baffle 15 is vertically clamped in the water outlet section 3. The adjusting baffle 15 is located 50 cm behind the water outlet end of the water pipeline 11. The height of the adjusting baffle 15 is adjusted according to different working conditions so that the water head height in the water outlet section 3 is the same as that in the water inlet section 1, and the water pipeline 11 is always in a full flow and constant pressure state.

[0032] The two partitions 9 and the adjustment partition 15 are both made of acrylic plates with a thickness of 1 cm.

[0033] The buried water pipeline in the long-distance water diversion project and the water pipeline 11 in the simulation section 2 are made using a length ratio of 1:34.

[0034] The test method of the test system for simulating soil deformation caused by pipeline leakage of the present invention adopts the test system for simulating soil deformation caused by pipeline leakage, and is specifically implemented according to the following steps: Step 1: The outlet section 3 starts to store water, and stops storing water when the water level reaches the bottom of the water delivery pipe 11, and the outlet valve 16 is always in an open state; Step 2, the water inlet section 1 starts to store water. When the water inlet section 1 reaches the set water level, the water inlet valve 8 is opened, and the water delivery pipeline 11 is passed through. At the same time, the water passing time is taken as the starting time, and the water passing time is recorded; Step 3, turn on the laser rangefinder 14, and set the monitoring time interval to 1 minute, that is, the strain measurement optical fiber 10 collects data once every 1 minute, and the laser rangefinder 14 measures the distance once every 1 minute; Step 4: Observe the transparent glass wall of simulation section 2 and end the test when the distance between the soil wetting range and the bottom plate of the model box is 10 cm.

[0035] Step 5: Draw the strain curve and ground settlement curve during the test.

[0036] Example 4 On the basis of Example 3, the lengths of the surface deformation monitoring optical fiber and the pipe lower soil deformation monitoring optical fiber in the test are both 26.5m, wherein 2.5m is the position where the strain measurement optical fiber 10 enters the simulation section 2, and 25.65m is the position where the strain measurement optical fiber 10 leaves the simulation section 2. The test does not consider the influence of groundwater, rainfall and other external loads. Only the influence of factors such as the leakage position, leakage size, flow velocity in the pipe and the buried depth of the pipe of the water pipeline is simulated in the test. By changing these different test variables, the simulation of different working conditions is achieved.

[0037] Leakage position and size: According to the test design, holes are drilled at corresponding positions of the water pipe 11, and drill bits of different sizes are used to drill holes on the surface of the PVC water pipe to control the size of the leakage. The actual damaged opening of the water pipe 11 is often a circular hole. In this test, the first circular hole is located at the waist of the pipe, 92.5 cm away from the water inlet end of the pipe, and the hole size is 6 mm; the other five circular holes are all located at the top of the water pipe 11, and the second circular hole is set 85 cm to the left of the first circular hole on the waist of the pipe. The spacing between the second circular hole and the sixth circular hole is 85 cm, and the hole sizes are 2 mm, 4 mm, 6 mm, 8 mm and 10 mm respectively. Finally, the seventh circular hole is located at the bottom of the pipe, 92.5 cm away from the water outlet end of the pipe, and the hole size is 6 mm. The tests are carried out in sequence according to the hole number. During the test, except for the leakage hole opened under the corresponding working conditions, the other holes are sealed with rubber plugs.

[0038] Flow rate in pipe: By changing the water level in the water tank, different heads are provided to achieve the purpose of changing the flow rate in the pipe. In actual projects, the flow rate in the pipe is generally 0.5~3.0m / s, which is scaled according to the flow rate scale to 0.171m / s, 0.257m / s, 0.343m / s, 0.429m / s and 0.514m / s, and the head of the water inlet tank section is calibrated according to the flow rate in the pipe.

[0039] Pipeline burial depth: The pipeline burial depth is changed by changing the thickness of the soil above the pipeline. In actual projects, the pipeline burial depth is 2m~6m, and the burial depth is set to 6cm, 9cm, 12cm, 15cm and 18cm. The proposed test conditions are shown in Table 1: Table 1 shows the test conditions.

[0040] The deformation of the surface soil in this test is divided into two types, namely, collapse with only holes and collapse without holes. The collapse without holes occurred in working conditions 2-5, working conditions 3-1 and working conditions 4-1. These working conditions are deep buried pipes, low flow rate in pipes and small leakage size. The deformation of the surface soil during the test is similar. Taking working condition 2-5 as an example, when the leakage hole is located at the top of the pipe, the pipe is buried at a depth of 18cm, the flow rate in the pipe is 0.257m / s, and the opening size is 6mm, no holes are generated in the surface soil during the test. At about the 11th minute, the surface soil is wet and accompanied by the generation of small axial cracks. Due to the deep buried pipe, there is no pipe burst phenomenon, and no water flow appears in the surface soil. As the test progresses, a circular settlement pit centered on the leakage point appears.

[0041] The collapse of the surface soil with holes also manifests itself in two phenomena, namely, the sudden appearance of holes and collapse of the surface soil and the first small-scale wet collapse of the surface soil followed by the formation of holes and collapse. The former occurs in working conditions 1-1 and 1-3, while the latter occurs in other remaining working conditions. The sudden appearance of holes and collapse of the surface soil Taking working condition 1-1 as an example, when the leakage hole is located at the waist of the pipe, the buried depth of the pipe is 12 cm, the flow rate in the pipe is 0.257 m / s, and the opening size is 6 mm, as the water flow in the pipe is continuously discharged, the soil around the leakage hole is continuously eroded, causing elliptical annular cracks to appear in the upper surface soil, and it collapses instantly at 3 minutes and 30 seconds, and a hole similar to an ellipse appears, indicating that when the buried water pipeline leaks, a cavity will indeed appear near the leakage hole. As the test progresses, the annular cracks will expand outward with the hole as the center, and the hole will continue to expand. Due to the water absorption and capillary action of the soil, water will flow after the surface soil collapses. When the water fills the hole, the soil around the hole collapses further, and a larger annular crack appears on the surface soil. The surface soil first collapses in a small range, then forms a hole and collapses. Taking working condition 1-2 as an example, when the leakage hole is located at the top of the pipe, the pipeline is buried at a depth of 12cm, the flow rate in the pipe is 0.257m / s, and the opening size is 6mm, cracks do not appear instantly and collapse to produce holes, but annular cracks appear at 6 minutes and 30 seconds, and the surface soil collapses, but no water flow occurs. As the test progresses, a leakage channel is formed inside the soil above the leakage hole, and the water flows continuously flush the soil along the leakage channel, causing a large number of loose soil particles to accumulate below the surface, and eventually a pipe burst occurs. The leakage channel expands and forms holes, and water flows on the surface soil. After the water flow appears, the soil around the hole collapses further, just like the situation where a hole suddenly appears and collapses in the surface soil.

[0042] During data processing, since the test time for each working condition is different, in order to reflect the law of soil deformation during the test, the data are analyzed in appropriate time periods, and the relative position of the cross section where each leakage point is located and the optical fiber measurement section in the length direction is measured and located to obtain the measurement results.

[0043] The strain values ​​obtained by the distributed optical fiber strain monitoring section on the soil surface after pipeline leakage under different working conditions are somewhat different, but basically show similar distribution patterns. When the working condition 1-2 test was carried out, that is, the leakage hole was located at the top of the pipe, the pipeline was buried at a depth of 12 cm, the flow rate in the pipe was 0.257 m / s, and the opening size was 6 mm, because the opening position was facing upward, at 10 minutes, the strain value of the soil directly above the pipeline leakage position was the largest, while the strain values ​​on both sides were relatively small, and the affected area was about 1 m long and 0.28 m wide. After 20 minutes, the strain values ​​of the soil on both sides began to increase, and the strain value of the soil directly above the pipeline leakage position began to decrease. The reason for the decrease was the pipe surge that occurred at 15 minutes of the test. When the leakage channel was formed, part of the optical fiber in the leakage channel would be emptied, causing the strain value to decrease. After 50 minutes, the water flow on the surface soil had contacted the glass walls on both sides of the model box and began to spread to both sides, causing the strain values ​​of the soil on both sides to begin to decrease.

[0044] The monitoring results of the surface deformation monitoring optical fiber show that the optical fiber locates the position of pipeline leakage. In the deformation area of ​​the soil, the strain optical fiber measurement value will change significantly. Most of the results obtained by the optical fiber show a "saddle" shape with high ends and a depression in the middle. The optical fiber monitoring data shows that after the underground water pipeline leaks, a cavity will be formed inside the soil under the erosion of the water flow. When the buried water pipeline leaks, it will cause the settlement of the surface soil. When the pipeline opening is upward, the ground settlement develops similarly. In addition, considering that the maximum and minimum ground settlement values ​​occur under different water flow rates in the pipeline, this experiment is to analyze the development of ground settlement under different positions of the leakage hole and different water flow rates in the pipeline. When the leakage hole is located at the waist of the pipe, the position where the maximum displacement of the surface soil occurs is 0.15m, and the maximum settlement is 5.3cm. When the seepage hole is located at the top of the pipe, the maximum displacement of the surface soil is at 0.2m, the maximum settlement is 8.9cm, and the settlement curve roughly conforms to the normal distribution. When the seepage hole is located at the bottom of the pipe, the maximum displacement of the surface soil is at 0.25m, and the maximum settlement is 4.1cm. The settlement of the surface soil corresponds to the test phenomenon. When the seepage hole is located at the bottom of the pipe, the settlement of the soil on the upper side of the pipe is small due to the existence of the pipe. When the seepage hole is located at the top of the pipe, due to the erosion of the water flow and the leakage of soil particles into the pipe, the largest settlement of the surface soil is located above the opening. When the flow rate in the pipe is changed, the position where the maximum settlement of the surface soil remains unchanged, still at 0.2m. The settlement value of the soil surface is basically triangularly distributed. With the increase of the flow rate in the pipe, the maximum settlement of the surface soil is: 1.2cm, 8.9cm, 9.8cm, 10.5cm, 11.1cm. When the flow rate in the pipe is low, there will be no holes in the surface soil, so the settlement is small. As the flow rate in the pipe increases, the water flow will more easily break open the soil above the pipe, forming a funnel-shaped defect area, which further increases the settlement.

[0045] The ground collapse deformation during the leakage of the buried water pipeline was monitored by changing the position of the pipeline leakage port, the pipeline burial depth, the water flow rate in the pipeline and the size of the pipeline leakage port. At the same time, the optical fiber monitoring results during the collapse process were used. The test method of the test system for simulating soil deformation caused by pipeline leakage was used. The deformation of the surface soil was divided into three categories, namely, collapse without holes, sudden holes and collapse, and small-scale wet collapse of the surface soil before holes and collapse. When the pipeline is buried deeper, the flow rate in the pipe is lower or the leakage size is smaller, collapse without holes will occur. In terms of the ground collapse mode, the ground collapse caused by the leakage of the buried pipeline is a sudden ground collapse.

[0046] Distributed fiber optic sensing technology effectively monitors the strain distribution of soil during the collapse process and can locate the location of pipeline leakage. In the deformation area of ​​the soil, the strain fiber optic measurement value will change significantly. The fiber optic monitoring value can predict the maximum settlement location and effectively identify the collapse displacement impact area and determine the location of ground collapse development.

[0047] The strain values ​​measured by the optical fiber for monitoring surface deformation are mainly tensile strains, and most of the results show a "saddle" shape with high ends and a depression in the middle. This law is not only consistent with other studies, but also further studies the variation law of the optical fiber strain peak under different leakage sizes, flow rates, burial depths and leakage locations. That is, the smaller the leakage size, the smaller the flow rate in the pipe, the shallower the buried depth of the pipeline, and the leakage location is at the top of the pipe, the more obvious the peak value.

[0048] Most of the results obtained by the optical fiber for monitoring the deformation of the soil under the pipeline show a single-peak distribution, and the strain peak is basically consistent with the leakage location.

[0049] By comparing the monitoring results of different measurement sections, it is recommended to preferentially arrange the optical fiber above the pipeline in order to more effectively identify the location of ground collapse development.

[0050] The direction of seepage can be effectively determined based on the order of the moments when the strain measurement values ​​of the buried optical fiber show obvious changes. This method provides a new technical means for early identification of leakage.

[0051] The test method of the test system for simulating soil deformation caused by pipeline leakage of the present invention is adopted, and the optical fiber measured strain monitoring data accurately reflects the temporal and spatial variation law of the strain field of the soil around the pipe during the collapse process, and the development position of the ground collapse caused by the pipeline leakage is determined by analyzing the monitoring data; the pipeline leakage makes the spatial distribution of the soil strain above the pipeline roughly in the shape of a "saddle", and the spatial distribution of the soil strain below the pipeline is mostly in a single-peak distribution, and the position where the strain peak appears is basically consistent with the pipeline leakage position; the peak value of the soil strain above the pipeline is more obvious when the leakage size is smaller, the flow velocity in the pipe is smaller, and the leakage position is located at the top of the pipe, and the peak value is less obvious when the pipeline is buried deeper; the monitoring optical fiber at the bottom of the pipeline can judge the direction of water seepage in the soil according to the time when the monitoring values ​​of different measuring sections show obvious changes; the monitoring value of the monitoring optical fiber at the top of the pipeline is mainly manifested as tensile strain, and the unique "saddle" shape distribution makes it easier to identify the development position of the ground collapse.

Claims

1. The test system for simulating soil deformation caused by pipeline leakage is characterized by: The invention comprises a model box, the model box is made of transparent glass, the upper part of the model box is not sealed, and the model box is divided into a water inlet section (1), a simulation section (2) and a water outlet section (3) in sequence in the horizontal direction. A laser rangefinder (14) is arranged on the simulation section (2), a strain measurement optical fiber (10) is buried inside the simulation section (2), and the strain measurement optical fiber (10) is connected to an OFDR demodulator (7). The laser rangefinder (14) and the OFDR demodulator (7) are used to collect and record test data.

2. The test system for simulating soil deformation caused by pipeline leakage according to claim 1 is characterized in that: Partitions (9) are vertically arranged on both sides of the model box, and the partitions (9) divide the model box into a water inlet section (1), a simulation section (2) and a water outlet section (3). The water inlet section (1) is connected to a water inlet pipe (6), the water inlet pipe (6) is connected to a water inlet pump (4), the water outlet section (3) is connected to a water outlet pipe (17), the water outlet pipe (17) is connected to a water inlet of a water tank (5), and the water inlet pipe (6) is connected to a water outlet of the water tank (5).

3. The test system for simulating soil deformation caused by pipeline leakage according to claim 2 is characterized in that: The bottom of the simulation section (2) is laid with a loess layer (13), a sand cushion layer (12), a water pipeline (11), a strain measurement optical fiber (10), and a loess layer (13) in order from bottom to top. The loess layer (13) at the bottom is used as the foundation loess, and the loess layer (13) at the top is used as the overlying loess. Through holes are provided at relative positions on the two partitions (9). The water pipeline (11) passes through the through hole on the partition (9) and is sealed with glass glue to stop water. One end of the water pipeline (11) passes through the through hole and extends into the water inlet section. (1), and the other end extends into the water outlet section (3); a water inlet valve (8) is arranged on the side of the water delivery pipe (11) extending into the water inlet section (1), and a water outlet valve (16) is arranged on the side of the water delivery pipe (11) extending into the water outlet section (3); a slide rail is horizontally arranged on the top of the model box, a fixed bracket is slidably connected to the slide rail, and a laser rangefinder (14) is arranged on the fixed bracket. The whole process of soil deformation caused by pipeline leakage is monitored by arranging a strain measurement optical fiber (10) and a laser rangefinder (14) in the soil around the water delivery pipe (11).

4. The test system for simulating soil deformation caused by pipeline leakage according to claim 3 is characterized in that: The loess layer (13) at the bottom is 40 cm thick and is filled in (4) layers. Each layer is 10 cm thick after compaction. Before the next layer of soil is backfilled, the surface of the soil is roughened. The thickness of the loess overlying the loess layer (13) at the top is filled to a corresponding thickness according to different test conditions.

5. The test system for simulating soil deformation caused by pipeline leakage according to claim 4 is characterized in that: The sand cushion layer (12) is 5 cm thick and is filled after the foundation loess is filled.

6. The test system for simulating soil deformation caused by pipeline leakage according to claim 5 is characterized in that: The water pipeline (11) is a PVC pipe with an outer diameter of (9) cm, which is placed on the sand cushion layer (12). The neutral plane axis of the water pipeline (11) is 49.5 cm away from the bottom plate of the model box. The water pipeline (11) is backfilled with loess in multiple layers. The first layer is 6 cm thick after compaction, and each subsequent layer is 3 cm thick after compaction. Before the next layer of soil is backfilled, the soil surface is roughened.

7. The test system for simulating soil deformation caused by pipeline leakage according to claim 6 is characterized in that: When the strain measurement optical fiber (10) is laid in the simulation section (2), it is pre-buried and laid in two layers above and below the water pipeline (11), the upper layer being the optical fiber for measuring the deformation of the surface, and the lower layer being the optical fiber for measuring the deformation of the soil below the pipeline.

8. The test system for simulating soil deformation caused by pipeline leakage according to claim 7 is characterized in that: The buried depth of the optical fiber for measuring the surface deformation is always 3 cm. The optical fiber for measuring the deformation of the soil below the pipeline is buried in the foundation loess, 30 cm away from the bottom plate of the model box, and is arranged in an "S" shape. The middle measuring section of the "S" shape is located directly above or directly below the axis of the water pipeline (11), and the other two sections of the "S" shape are located on both sides of the middle measuring section, with a spacing of 10 cm. The optical fiber turning radius is 20 cm, and the distance from the optical fiber to the glass wall is 10 cm. Two measuring sections of strain measurement optical fiber (10) are arranged around the water pipeline (11), and both are used to locate the leakage position of the water pipeline (11); When monitoring surface deformation, the surface deformation monitoring optical fiber effectively monitors the underlying cavity formation process caused by leakage of buried water pipelines; when measuring the deformation of the soil under the pipeline, the soil deformation measurement optical fiber under the pipeline identifies the infiltration direction of water after leakage of the buried water pipeline.

9. The test system for simulating soil deformation caused by pipeline leakage according to claim 8, characterized in that: The water outlet section (3) is vertically connected with an adjusting baffle (15), which is located 50 cm behind the water outlet end of the water delivery pipe (11). The two baffles (9) and the adjusting baffle (15) are both made of acrylic plates with a thickness of 1 cm.

10. A test method for soil deformation caused by pipeline leakage, using the test system for simulating soil deformation caused by pipeline leakage as claimed in claim 9, specifically implemented in the following steps: Step 1: The water outlet section (3) starts to store water, and stops storing water when the water level reaches the bottom of the water delivery pipe (11), and the water outlet valve (16) is always in an open state; Step 2, the water inlet section (1) starts to store water. When the water inlet section (1) reaches a set water level, the water inlet valve (8) is opened, and water is passed through the water delivery pipeline (11). At the same time, the water passing time is taken as the starting time, and the water passing time is recorded; Step 3, turning on the laser rangefinder (14), and setting the monitoring time interval to 1 minute, that is, the strain measurement optical fiber (10) performs data collection every 1 minute, and the laser rangefinder (14) performs distance measurement every 1 minute; Step 4, observe the transparent glass wall of the simulation section (2), and end the test when the distance between the soil wetting range and the bottom plate of the model box is 10 cm; Step 5: Draw the strain curve and ground settlement curve during the test.

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