Simulation of floating damage of glass steel pipeline on silt coast and reinforcement method

Abstract

This invention provides a method for simulating and reinforcing the floating failure of fiberglass reinforced plastic (FRP) pipes in silty coastal areas, belonging to the field of water intake and drainage engineering technology. It simulates the working conditions of the pipeline during construction and operation, monitors and reveals the dynamic process of pipeline floating in silt over time, and sets up effective emergency reinforcement measures. The method includes the following steps: Step 1, determining the main experimental parameters; Step 2, setting the model test scale, designing the required water tank, and forming a circulating flow; Step 3, conducting a floating failure test of the FRP pipe in silt, monitoring the dynamic process of pipeline floating in silt over time; Step 4, setting up emergency reinforcement structures for the floating FRP pipe in silt. This invention's method simulates and reveals targeted reinforcement after floating, ultimately achieving the safety and stability of FRP pipes in silty coastal areas.

Description

Technical Field

[0001] This invention belongs to the field of water intake and drainage engineering technology, and relates to water intake and drainage engineering in silty coastal areas, and particularly to simulation and reinforcement methods for the floating and damage of fiberglass pipes in silty coastal areas. Background Technology

[0002] With the development of modern science and technology, the requirements for materials in all walks of life are becoming increasingly higher, and the single material properties can no longer meet the needs of production and social development. In water intake and drainage projects on silty coasts, fiberglass pipes (RPM pipes) have a series of advantages, such as good corrosion resistance, antifouling and anti-insect properties, heat resistance, frost resistance, light weight, high strength, low friction resistance, and high conveying capacity. They are also suitable for different types of acids, alkalis, salts, and various oils, seawater, and organic solvents. Especially in seawater, cathodic protection and other anti-corrosion measures are not required, and they will not cause secondary pollution to water and other media. In addition, their relative density is only 1.8~2.1×103kg / m3, which means that their weight is only 1 / 3 of that of steel pipes or ductile iron pipes, 1 / 5 of that of cast iron pipes, and 1 / 10 of that of concrete pipes. These advantages have led to the increasing application of fiberglass pipes in water intake and drainage projects for coastal power stations and industrial discharges. When applied under favorable geological conditions, FRP pipes exhibit strong adaptability to boundaries. However, in silty coastal areas with high mud content, especially during offshore construction, the density of the FRP pipes after water injection approaches that of seawater. Under the buoyancy of the water-sand mixture, they are highly susceptible to deviation from their installation position and localized floating. If the pipes are easily fixed using piles and pipe clamps, the FRP pipes, primarily composed of resin, glass fiber, and silicone, are generally brittle and have low impact resistance. Impacts can easily lead to pipe damage or even breakage, posing significant challenges for subsequent construction. Furthermore, during the operational phase after construction, FRP pipes, in addition to bearing the static pressure of the protective soil and overlying water, will also be subjected to external wave and water flow cyclic loads. Especially during typhoon seasons with high waves, cyclic wave loads can cause the silty seabed to liquefy, causing the pipes to float and directly threatening their safety. Therefore, addressing the potential floating accidents of FRP pipes during both construction and operation in silty coastal areas, and ensuring the structural safety of the pipeline, is crucial. Summary of the Invention

[0003] The problem this invention aims to solve is to provide a method for simulating and reinforcing the floating failure of fiberglass pipelines in silty coastal areas. This method simulates the test conditions of the pipeline during the construction and operation phases, monitors the dynamic process of the pipeline's floating in silt over time, solves the problems in the background technology, and proposes an effective reinforcement method based on the measured buoyancy force, ultimately achieving the safety and stability of the pipeline in silty coastal areas.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by this invention is: a method for simulating and reinforcing the floating failure of fiberglass pipes in silty coastal areas. This method simulates the test conditions of the pipe during construction and operation, and monitors the dynamic process of pipe floating in silt over time, including the following steps:

[0005] Step 1: Determine the main test parameters, including the density and size of the fiberglass pipes; the quantity and method of placement in the trench; the cross-sectional shape of the trench excavation; the density and siltation rate of the silt in the engineering sea area; the parameters of the floating rock cover layer on the pipes; the wave elements and water flow velocity in the external cyclic load; and the design water level.

[0006] Step 2: Set the model test scale, and design the water tank required for the test according to the scale, and equip it with the corresponding functions to form a circulating flow. Set the test trench in the middle of the water tank as the test section. Make sludge and pipes according to the test scale and put them into the test section trench in sequence.

[0007] Step 3: Conduct a floating failure test on the fiberglass pipe in the silt to monitor the dynamic process of the pipe floating in the silt over time. Record the dynamic response of the pipe floating and the magnitude of the buoyancy force on the pipe by setting up monitoring equipment in the water tank in advance as the silt settling rate in the foundation trench gradually increases and the external cyclic load is continuously applied.

[0008] Step 4: Install emergency reinforcement structures for the fiberglass pipes floating in the silt and conduct tests to verify the stability of the reinforced structure.

[0009] Furthermore, in step four, the reinforcement structure is installed on the side of the construction vessel dumping the sand and gravel cover layer. According to the longitudinal length of the pipeline, two identical reinforcement structures, namely No. 1 and No. 2, are installed at the bow and stern of the construction vessel to form an "n" shaped structure. The crossbar in the middle is a freely rotating mechanical arm, and the two sides of the crossbar are designed as synchronously extending and retracting compression springs.

[0010] Furthermore, a certain pull-out force G is pre-set on the control interface of the telescopic spring. Based on the burial depth of the pipe in the silt, the telescopic spring automatically moves downward to the specified height, always maintaining a pull-out force G greater than the buoyancy force F of the pipe. A pipe clamp is installed at the head of the telescopic spring. The formula for calculating the pull-out force G is as follows:

[0011] ;

[0012] In the formula: The magnitude of the pipeline reinforcement structure, in kN / m; The scaling factor is set to 2.63; Specific weight of water, unit: kN / m³ 3 , The spacing of different emergency-type pipe clamp arrangements, in meters (m); S is the cross-sectional area of ​​the pipe, in square meters (m²). 2 .

[0013] Furthermore, the pipe clamps are inverted "U" shaped structures made of alloy materials. In the area where the pipe clamps directly contact the outer wall of the pipe, arc-shaped high-elasticity rubber is installed to form a soft connection. After the backfilling of the pipe section is completed, the reinforcement structure and the construction vessel are withdrawn at the same time, and the construction of the next pipe section continues with the construction vessel until the entire pipeline of the project is completed.

[0014] Furthermore, in step one, during the pipeline operation period, the pipeline is covered with artificial backfill stones or blocks. The backfill material can be divided into three layers from bottom to top: a crushed stone backfill layer, 0.3m above the top of the pipe, a dry-mixed concrete layer, and a stone paving layer.

[0015] Furthermore, in step three, during the construction period test, only the floating test group affected by the sediment deposition of high-sediment-content water bodies in the external seawater simulated the large amount of sediment falling and returning to the seawater in the silted coast. The steps are as follows: the pipeline is freely placed in the foundation trench. According to the sediment deposition rate of the engineering area, the prepared mud-water mixture is poured at fixed intervals. The thickness of the sediment return in the foundation trench is observed to determine when the pipeline will float. The monitoring is carried out through the initial markers set on the glass observation windows on both sides of the test water tank and the wave force acquisition system. The results are recorded and analyzed as follows: the pipeline in the silt has the fact of floating and failure. When the sediment deposition thickness in the foundation trench reaches 0.4m, the pipeline begins to float. The dynamic process of pipeline floating is divided into 4 stages, namely the initial stable stage → slow start stage → rapid floating stage → oscillation equilibrium stable stage. The time taken for the entire floating process is recorded.

[0016] Furthermore, in step three, during the construction period test, the pipeline was subjected to free siltation from high-sediment-content water bodies, superimposed with the effect of artificial backfilling during construction. The pipeline was freely placed in the trench, and experimental data were observed and recorded. The conclusion was that the pipeline floated under different mud-water mixture densities and backfilling methods. The faster the backfilling and the higher the silt density, the faster the pipeline began to float; that is, the floating on both sides of the pipeline was greater than that on a single layer. Simultaneously, the buoyancy force on the pipeline under different working conditions was measured and recorded, concluding that the force was only related to the density of the silt.

[0017] Furthermore, during the operational period, after the backfilling above the pipeline in the trench was completed, the pipeline was subjected to external wave and current cyclic load tests for several cycles. The results were observed and recorded. Under different wave heights, the pipeline did not float after being subjected to the ballast of the overlying layer. The conclusions are: a) The buoyancy force on the pipeline is directly proportional to the wave height and period, and inversely proportional to the water depth; b) The pressure distribution on the outer wall of the pipeline is greater at the top than at the bottom, and greater on the wave-facing side than on the wave-avoiding side.

[0018] Furthermore, in step three, corresponding measurement and monitoring instruments and equipment are installed, including a total force sensor for measuring the buoyancy force of the pipeline, a displacement gauge for measuring the thickness of siltation in the trench over time, sensors for measuring the external circulating load carrier height and water flow velocity, as well as a pipeline buoyancy motion measuring instrument and test video recording equipment, and monitoring of the test water level.

[0019] Compared with the prior art, the present invention has the following advantages and positive effects.

[0020] 1. The method of this invention involves designing a test tank of a specific size in the laboratory to simulate the dynamic evolution of the pipeline as it floats in silt during two phases: the construction phase when the pipeline is in the foundation trench and experiences significant siltation, and the operational phase when the fiberglass pipeline is covered by soil and subjected to external wave and water circulation loads. The changes in buoyancy force during the floating process are measured. Based on the measured buoyancy force results, an effective reinforcement method is proposed, ultimately achieving the goal of ensuring the safety and stability of the pipeline in silty coastal areas. This invention not only solves practical problems in major domestic water intake and drainage projects but also provides technical support and basic data for the widespread application of fiberglass pipelines with smooth inner walls, no secondary pollution, and reduced leakage and chlorine consumption, as people's living standards continue to improve and requirements for drinking water and environmental protection increase.

[0021] 2. This invention simulates the phenomenon of pipelines floating and breaking in silt through seawater sediment deposition tests. Furthermore, it shows that the pipeline begins to float when the silt accumulation thickness in the trench reaches 0.4m. The research results provide a technical basis for precise control of pipeline floating nodes in the trench. The dynamic process of pipeline floating in silt can be divided into four stages: initial stabilization stage → slow start-up stage → rapid floating stage → oscillating equilibrium stabilization stage. The floating stage time is found to be between 60 and 120 minutes, providing precise time control for setting the subsequent reinforcement construction period.

[0022] 3. In the simulation process of this invention, during the construction period, the pipeline in the foundation trench was backfilled (dropped) with silt of different densities and in different ways by the simulated on-site personnel. It was determined that when the backfilling method was the same, the higher the density of the backfilled silt, the greater the buoyancy force on the pipeline wall, and the easier it was for the pipeline to float. Furthermore, it was found that the maximum buoyancy force on the pipeline was less than 60kN / m. The results can clarify the magnitude of load control for subsequent pipeline reinforcement measures.

[0023] 4. During the simulation process of this invention, the pipeline in the trench during the operation period was subjected to simulated external wave and water flow circulation loads, which determined that: ① the buoyancy force on the pipeline is directly proportional to the external wave height and period, and inversely proportional to the water depth. At the same time, it was found that the maximum buoyancy force was less than 15kN / m; ② the pressure distribution on the outer wall of the pipeline showed a pattern of greater pressure at the top than at the bottom, and greater pressure on the wave-facing side than on the wave-repelling side. This also provides accurate data for load control in subsequent reinforcement measures.

[0024] 5. Through multi-angle data detection and statistics, this invention derives an empirical formula for the buoyancy force on pipes in silt based on experimental results. This formula provides a reference for the construction and operation design of similar pipeline projects and can improve the work efficiency of designers by more than 70%. This invention not only solves practical problems in major domestic water intake and drainage projects, but also provides technical support and basic data for the promotion and application of lightweight fiberglass pipes to other fields such as drinking water transportation. It is expected to generate positive social and economic benefits in related fields. Attached Figure Description

[0025] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0026] Figure 1 The present invention provides an experimental simulation method and flowchart.

[0027] Figure 2 This is a schematic diagram of the cross-section of the foundation trench excavation and the placement of pipelines during the construction period in an embodiment of the present invention; wherein; (a) is a plan view, and (b) is an elevation view;

[0028] Figure 3 This is a schematic diagram of the installation of fiberglass pipes in the trench during the operation period in an embodiment of the present invention;

[0029] Figure 4 This is a schematic diagram of the fabrication of the test chamber and the placement of the model in an embodiment of the present invention; wherein, (a) is a plan view and (b) is an elevation view;

[0030] Figure 5 This is a schematic diagram of the pipeline rising as the thickness of the silt increases in an embodiment of the present invention; wherein, (a) is a schematic diagram simulating the silt settling in the foundation trench, (b) is a schematic diagram simulating the pipeline rising in the foundation trench, and (c) is a schematic diagram monitoring the pipeline rising process in the silt.

[0031] Figure 6 This is a schematic diagram illustrating the floating process of the glass pipe and its relationship with the buoyancy force under different backfill densities and siltation rates in an embodiment of the present invention.

[0032] Figure 7 This is a schematic diagram of the pressure distribution on the outside of the pipe at the moment of maximum buoyancy force under wave-current cyclic loading in an embodiment of the present invention.

[0033] Figure 8 This is a schematic diagram of a novel emergency pipeline reinforcement structure proposed in an embodiment of the present invention; wherein, (a) is a schematic diagram of the elevation of the novel reinforcement structure, and (b) is a schematic diagram of the plan of the novel reinforcement structure;

[0034] Figure 9 This is a schematic diagram of the verification test of the novel emergency pipeline reinforcement structure in an embodiment of the present invention.

[0035] Figure label:

[0036] 1. Fiberglass pipe; 2. Telescopic compression spring; 3. Crossbar; 5. Press control interface; 6. Pipe clamp; 7. Rubber pad. Detailed Implementation

[0037] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0038] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0039] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0040] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0041] Addressing the technical challenge of lightweight fiberglass reinforced plastic (FRP) pipes floating and breaking in silty coastal areas with high mud content, where the pipeline trenches for water intake and drainage projects are subjected to adverse factors such as large amounts of siltation during construction, artificial backfilling, and external wave and current loads during operation, this invention proposes a method for simulating and reinforcing the floating failure of FRP pipes in silty coastal areas. Specifically, it utilizes experimental simulation to model the dynamic process of pipe floating in silt, obtaining the magnitude and distribution of buoyancy forces on the pipe, and proposing effective reinforcement measures to reduce the risk of pipe floating and breaking, thus achieving the safe and stable operation of lightweight FRP pipes in silt. This technology not only solves practical problems in water supply and drainage engineering but also provides technical support and basic data for the promotion and application of lightweight FRP pipes in other fields such as drinking water transportation.

[0042] Simulation and reinforcement methods for the floating failure of fiberglass pipelines in silty coastal areas: This study simulates the test conditions of the pipeline during construction and operation, and monitors the dynamic process of pipeline floating in silt over time. The steps include:

[0043] Step 1: Determine the main test parameters, including the density and size of the fiberglass pipe 1; the quantity and method of placement in the trench; the cross-sectional type of the trench excavation; the density and siltation rate of the silt in the engineering sea area; the parameters of the floating rock cover layer on the pipe; the wave elements (including wave height and period) and water flow velocity (including velocity magnitude and direction) in the external cyclic load; and the design water level.

[0044] Step 2: Set the model test scale, and design the water tank required for the test according to the scale, and equip it with the corresponding functions to form a circulating flow. Set the test trench in the middle of the water tank as the test section. Make sludge and pipes according to the test scale and put them into the test section trench in sequence.

[0045] Step 3: Conduct a floating failure test on the fiberglass pipe in the silt to monitor the dynamic process of the pipe floating in the silt over time. Record the dynamic response of the pipe floating and the magnitude of the buoyancy force on the pipe by setting up monitoring equipment in the water tank in advance as the silt settling rate in the foundation trench gradually increases and the external cyclic load is continuously applied.

[0046] Step 4: Install emergency reinforcement structures for the fiberglass pipes floating in the silt and conduct tests to verify the stability of the reinforced structure.

[0047] Preferably, in step four, the reinforcement structure is installed on the side of the construction vessel dumping the sand and gravel cover layer. According to the longitudinal length of the pipeline, two identical reinforcement structures, namely 1# and 2#, are installed at the bow and stern of the construction vessel to form an "n"-shaped structure. The crossbar 3 in the middle is a freely rotating mechanical arm. The two sides of the crossbar are designed as synchronously extending and retracting telescopic springs 2. A coaxial hollow cylinder is set outside the telescopic spring 2 to guide and limit the telescopic spring 2. The lower end of the telescopic spring 2 closest to the construction vessel is set on the construction vessel.

[0048] Preferably, a certain pull-out force G is pre-set on the control interface of the telescopic spring. Based on the burial depth of the pipeline in the silt, the telescopic spring automatically moves downward to the specified height, always maintaining a pull-out force G greater than the buoyancy force F of the pipeline. A pipe clamp is installed at the head of the telescopic spring. The formula for calculating the pull-out force G is as follows:

[0049] ;

[0050] In the formula: The magnitude of the pipeline reinforcement structure, in kN / m; The scaling factor is set to 2.63; Specific weight of water, unit: kN / m³ 3 , The spacing of different emergency-type pipe clamp arrangements, in meters (m); S is the cross-sectional area of ​​the pipe, in square meters (m²). 2 .

[0051] Preferably, the pipe clamp is an inverted "U" shaped structure made of alloy material. In the area where the pipe clamp directly contacts the outer wall of the pipe, an arc-shaped high-elasticity rubber is installed to form a soft connection. After the backfilling of the pipe section is completed, the reinforcement structure and the construction vessel are removed at the same time, and the construction of the next pipe section continues with the construction vessel until the entire pipeline of the project is completed.

[0052] Preferably, in step one, during the pipeline operation period, the pipeline is covered with artificial backfill stones or blocks. The backfill material can be divided into three layers from bottom to top: a crushed stone backfill layer, 0.3m above the top of the pipe, a dry-mixed concrete layer, and a stone paving layer.

[0053] Preferably, in step three, during the construction period test, only the floating test group affected by the sediment deposition of high-sediment-content water bodies in the external seawater is simulated to simulate the large amount of sediment falling and returning to the seawater in the silted coast. The steps are as follows: The pipeline is freely placed in the foundation trench. According to the sediment deposition rate of the engineering area, the prepared mud-water mixture is poured at fixed intervals. The thickness of the sediment return in the foundation trench is observed to determine when the pipeline will float. The monitoring is carried out through the initial markers set on the glass observation windows on both sides of the test water tank and the wave force acquisition system. The results are recorded and analyzed as follows: The pipeline in the silt has the fact of floating and failure. When the sediment deposition thickness in the foundation trench reaches 0.4m, the pipeline begins to float. The dynamic process of pipeline floating is divided into 4 stages, namely the initial stable stage → slow start stage → rapid floating stage → oscillation equilibrium stable stage. The time taken for the entire floating process is recorded.

[0054] Preferably, in step three, during the construction period test, the pipeline is subjected to free siltation from high-sediment-content water bodies, superimposed with the effect of artificial backfilling during construction. The pipeline is freely placed in the trench, and experimental data are observed and recorded. The conclusion is that under different mud-water mixture densities and backfilling methods, the pipeline floats. The faster the backfilling and the higher the silt density, the faster the pipeline begins to float; that is, the floating on both sides is greater than on a single layer. Simultaneously, the buoyancy force on the pipeline under different working conditions is measured and recorded, concluding that the force is only related to the silt density.

[0055] During the preferred operational period, after the backfilling above the pipeline in the trench is completed, the pipeline is subjected to external wave and current cyclic load tests. The results are observed and recorded. Under different wave heights, the pipeline does not float after being subjected to the ballast of the overlying layer. The conclusions are: a) The buoyancy force on the pipeline is directly proportional to the wave height and period, and inversely proportional to the water depth; b) The pressure distribution on the outer wall of the pipeline is greater at the top than at the bottom, and greater on the wave-facing side than on the wave-avoiding side.

[0056] Preferably, in step three, corresponding measuring and monitoring instruments and equipment are installed, including a total force sensor for measuring the buoyancy force of the pipeline, a displacement gauge for measuring the thickness of siltation in the trench over time, sensors for measuring the external circulating load carrier height and water flow velocity, as well as a pipeline buoyancy motion measuring instrument and test video recording equipment, and monitoring of the test water level.

[0057] Example:

[0058] Step 1: Determine the main test parameters: ① The density of the fiberglass pipe is 1.8~2.1×103kg / m3, the length of each section is 12m, and the inner diameter is... m, wall thickness 7.25mm; ② The cross-sectional shape of the foundation trench excavation is as follows: the bottom elevation of the foundation trench is -8.54m, the top mud surface elevation is -3.0m, the bottom width of the foundation trench is 12.0m, the two sides are sloped with a slope of 1:2, a single A pipe is placed in the foundation trench, and in the comparative test group, two pipes A and B are placed side by side, with a distance of 2.0m between the outer walls of the two pipes; see the cross-section of the pipe and the foundation trench excavation. Figure 2 ③ Parameters during project implementation, namely, the density of silt in the project area during the construction period. ×103kg / m3, and comparative test group ×103kg / m3; the natural sediment settling rate in seawater is 0.2m / month; during pipeline operation, the pipeline is covered with artificial backfill of rubble or blocks. The backfill material can be divided into three layers from bottom to top: a 40~60mm crushed stone backfill layer (0.3m above the top of the pipe), a 0.3m thick dry-mixed concrete layer, and a 1m thick 250~300kg rubble facing layer. See details. Figure 3 ④ External cyclic load parameters, i.e. wave elements, where wave height H = 0.6m, 0.8m, 1.0m, 1.2m, 1.4m, period T = 4.5s, 5.4s, 6.3s, 7.2s, 8.0s, and water flow velocity v = 0.5m / s and 1.0m / s; ⑤ Design water level d parameter, taken as 1.4m, 1.8m, 2.2m, 2.6m above the mud surface.

[0059] Step Two: Preparation of Experimental Facilities. Based on the basic parameters from Step One, the scale of the simulated model experiment is determined to be 1:20. Using this scale, a rectangular test water tank is designed with dimensions of length × width × height = 68m × 1.0m × 1.0m. A wave generator, a motor-servo-driven push-plate absorption wave generator, is installed on one side of the tank. Its wave generation capacity is: maximum wave depth 1.0m, wave height 0~35cm, and period 0.5~5.0s. A flow-generating device is designed at the other end to create circulating flow with a maximum velocity of 2.0m / s. A test trench is excavated 32m away from the wave generator location as the test section. The layout of the test water tank and test model is shown in [details omitted]. Figure 4 Based on the experimental scale, the silt and pipes were constructed: ① A soil mixer was used to prepare the silt and pipes with the appropriate density. ×103kg / m3, ① Two types of sludge (sludge-water mixture) with a density of ×103kg / m³; ② Based on the size and density of the fiberglass pipe, fabricate a model of the pipe, and then place the completed pipe and sludge sequentially into the test section trench, see... Figure 4 .

[0060] Step 3: Calibration and pre-test debugging of measurement and monitoring equipment. After the model is completed in Step 2, the corresponding measurement and monitoring instruments and equipment are installed, including a total force sensor to measure the buoyancy force of the pipeline, a displacement gauge to measure the thickness of siltation in the trench over time, sensors to measure the external circulating load carrier height and water flow velocity, as well as a pipeline buoyancy motion measuring instrument and test video recording equipment, and monitoring of the test water level.

[0061] Step 4: Conducting the floating and destructive test of the fiberglass pipe in the silt. ① Construction period test: During this period, the pipe is freely placed in the foundation trench and is only affected by the siltation of the high-sediment-content seawater in the external environment. To simulate the large amount of siltation and backfilling in the seawater of the silted coast, and based on the siltation rate of 0.2m / month in the project area, a 1500ml container was used on the model, and a prepared mud-water mixture was poured in every 3 minutes. See details below. Figure 5 (a) Observe the thickness of the silt backfill in the trench at which the pipeline will float. This is monitored by the initial markers set on the glass observation windows on both sides of the test water tank and the wave force acquisition system. See details below. Figure 5 (b) and (c), the monitoring equipment recorded the results, showing that as the silt deposition rate increased, the pipeline in the silt gradually experienced a floating failure event. This indicates that the experiment verified the fact that pipelines in silt can float and fail. Furthermore, it was found that when the silt deposition thickness in the trench reaches 0.4m, the pipeline begins to float. The dynamic process of pipeline floating can be divided into four stages: initial stabilization stage → slow start-up stage → rapid floating stage → oscillating equilibrium stabilization stage. The entire floating process took between 60 and 120 minutes, providing precise time control for the subsequent implementation of reinforcement measures.

[0062] ② During the construction period, the pipeline is freely placed in the foundation trench. At this time, it is not only affected by the free deposition of sediment from the high-sediment-content water body, but also by the artificial backfilling of sediment during construction to accelerate the progress, resulting in several floating tests. Under different mud-water mixture densities and backfilling methods, the following tests were conducted: Figure 6 As can be seen from the stress on the pipeline, the pipeline also exhibits a floating phenomenon. The faster the backfilling and the higher the density of the silt, the faster the pipeline begins to float; that is, the floating on both sides of the pipeline is greater than that on a single layer. Table 1 shows the buoyancy forces on the pipeline under different working conditions. The results in the table show that the stress is only related to the density of the silt. The maximum buoyancy forces measured are all less than 60 kN / m. These results can clarify the magnitude of the load control for subsequent pipeline reinforcement measures.

[0063] Table 1 Comparison of stress results for FRP pipes with different densities and backfilling methods

[0064]

[0065] ③ During the operational period, after the backfilling was completed above the pipeline in the foundation trench, the test group was subjected to external wave current cyclic load only. Under different wave heights, the test observed that the pipeline did not float after being subjected to the ballast of the overlying layer, which was verified by the engineering site example. The stress results of the pipeline at this time are shown in Table 2, and the distribution of pressure on the pipe wall is shown in Table 3. Figure 7 The results from the graphs and tables show that: a) the buoyancy force on the pipeline is directly proportional to the wave height and period, and inversely proportional to the water depth, and the maximum buoyancy force is less than 15 kN / m; b) the pressure distribution on the outer wall of the pipeline shows a pattern of greater force at the top than at the bottom, and greater force on the wave-facing side than on the wave-repelling side, which provides precise control of the load for subsequent reinforcement measures.

[0066] To further verify the possibility of pipeline buoyancy, the test results of the pipeline buoyancy force were obtained, and a force balance analysis was performed on the pipeline, that is, the buoyancy force was verified by the pipeline's own weight plus the weight of the covering layer. The design gives the weight of the FRP pipe as 1.8t / m, so the underwater weight is 0.8t / m. The weight of the backfill boulders (note: the underwater density of the boulders is taken as 7.0kN / m3, and the boulders in the trench are oriented towards the ballast pipeline) is 39.32t / m. The maximum buoyancy force on the pipeline under different test groups was 1.5~3.0t / m, which is less than the sum of the underwater weight of the FRP pipe and the backfill boulders, 40.12t / m. Therefore, it can be concluded that the pipeline can remain stable under the protection of the backfill boulders, which is consistent with the test results.

[0067] Table 2 Results of maximum wave force on the pipeline under different wave heights

[0068]

[0069] Step 5: Based on the magnitude and distribution of the buoyancy force on the pipeline obtained in Step 4, and in response to the floating of FRP pipelines in silt during the construction period, (1) a new emergency measure to reinforce the structure is proposed, see Figure 8As shown in the figure: ① The entire reinforcement structure can be directly installed on the side of the construction vessel dumping the sand and gravel cover layer. This allows for simultaneous construction and pipeline safety, saving costs and accelerating the construction progress. The entire reinforcement structure implementation process is as follows: First, according to the longitudinal length of the pipeline, two identical reinforcement structure devices (i.e., 1# and 2#, see the figure markings) are installed at the bow and stern of the construction vessel. The entire reinforcement structure device resembles an "n" shape, with the middle crossbar being a freely rotating mechanical arm. The two sides of the crossbar are designed as telescopic compression springs 2 that can extend and retract synchronously. For the telescopic compression springs 2 installed on the side of the vessel, in order to resist the buoyancy force F of the pipeline in the silt, a certain pull-out force G needs to be set in advance on the pressure control interface 5 of the telescopic compression spring. The magnitude of the pull-out force is calculated based on the pipeline length L placed during construction and the test measurement results. That is, the maximum buoyancy force on the pipeline is 60kN / m, so the pull-out force G is calculated. The formula is G=L*60kN / m. After setting the G value, the telescopic spring 2 will automatically move downward to the specified height according to the burial depth of the pipeline in the silt, always keeping the pull-out force G greater than the buoyancy force F of the pipeline, thus ensuring the stability of the pipeline; ② For installation on the pipeline side, an inverted "U"-shaped alloy pipe clamp 6 is set at the head of its spring, with a width of 1.0m along the longitudinal direction of the pipeline. The height design of the "U" shape can cover 2 / 3 of the pipeline's outer diameter. At the same time, since lightweight fiberglass pipes are brittle, a 20cm thick arc-shaped high-elasticity rubber pad 7 is set in the area where the pipe clamp 6 directly contacts the outer wall of the pipeline to form a soft connection, thereby further maintaining the safety and stability of the pipeline. ③ After the backfilling of the pipeline section is completed, that is, when the ballast weight of the backfill soil meets the requirements for pipeline stability, the new reinforcement structure and the construction vessel are withdrawn simultaneously, and the construction of the next pipeline section continues with the construction vessel until the entire pipeline project is completed.

[0070] (2) Model tests were conducted to verify the effectiveness of the proposed reinforced structure. To verify the effectiveness of the proposed reinforced structure, corresponding physical model tests were conducted. Specifically, in a test water tank, pipe clamps with a pre-set G-value were used to restrict the pipes in the foundation trench. The stability under continuous action of siltation and external cyclic loads was tested. The model test results are shown in [link to test]. Figure 9 The verification test results show that, regardless of whether the pipeline is in a free state during construction or in operation, the glass pipeline in the silt can remain stable under the continuous long-term action of external siltation and cyclic load, with the help of the newly proposed emergency reinforcement structure.

[0071] (3) An empirical formula for calculating the pull-out force G of the new reinforcement structure was derived. In order to prevent pipeline rupture caused by uneven longitudinal stress due to pipeline floating, a certain number of pull-out piles need to be designed in the longitudinal direction of the pipeline. The pull-out force on piles with different spacing depends on the buoyancy force on the pipeline and the resultant force of its own weight and the water in the pipeline. However, it is often difficult to determine the value of the buoyancy force. According to the results of this test, the buoyancy force can be taken as the maximum value of the buoyancy force when the pipeline reaches dynamic equilibrium during the construction period and the overall buoyancy force under wave action. For the convenience of engineering use, based on the above buoyancy test results, the empirical formula for the pull-out pile force is derived as follows:

[0072] ;

[0073] In the formula: Pipeline reinforcement structure amplitude (kN / m); This is a proportionality coefficient, calculated from the experimental data to be 2.63; The spacing (m) for different emergency-type pipe clamp arrangements, and S is the cross-sectional area of ​​the pipe (m²). 2 ).

[0074] Based on the derived empirical formula, in engineering, when the distance L between two adjacent emergency-type pipe clamps and the cross-sectional area S of the pipe are known, they can be substituted into the above empirical formula to obtain the value of the pipe reinforcement structure G. After inputting G into the telescopic spring control interface, the pipe reinforcement function can be realized. Therefore, this result not only ensures the safety of the pipe, but also directly improves the work efficiency of designers by 70%.

[0075] In summary, this invention, through a simulated floating test of lightweight FRP pipes in silt, reveals the fact that pipes in silt can float and break. It further clarifies the starting point for floating when the silt thickness reaches 0.4m, the floating time within 120 minutes, and the maximum buoyancy force during the floating process within 60kN / m. The test results can provide technical support for precise control of floating events in lightweight FRP pipes. Simultaneously, a novel emergency reinforcement measure and method are proposed, and an empirical calculation formula for the pull-out resistance G of the new reinforcement structure is derived. Model tests verify its significant effectiveness. This measure ensures the stability and safety of the pipe in silt while improving the work efficiency of designers. Therefore, this invention not only solves the practical problem of pipe floating in silty coastal areas during water intake and drainage projects but also provides technical support for the promotion and application of lightweight FRP pipes in other fields. It is expected to generate positive social and economic benefits in related fields.

[0076] Although the preferred embodiments of the patent have been described above in conjunction with the accompanying drawings, this patent is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this patent without departing from the spirit and scope of the claims, and these all fall within the scope of protection of this patent.

Claims

1. A simulation and reinforcement method for the floating failure of fiberglass pipes in silty coastal areas, simulating the test conditions of the pipeline during construction and operation, and monitoring the dynamic process of pipeline floating in silt over time, characterized by: Includes the following steps, Step 1: Determine the main test parameters, including the density and size of the fiberglass pipes; the quantity and method of placement in the trench; the cross-sectional shape of the trench excavation; the density and siltation rate of the silt in the engineering sea area; the parameters of the floating rock cover layer on the pipes; the wave elements and water flow velocity in the external cyclic load; and the design water level. Step 2: Set the model test scale, and design the water tank required for the test according to the scale, and equip it with the corresponding functions to form a circulating flow. Set the test trench in the middle of the water tank as the test section. Make sludge and pipes according to the test scale and put them into the test section trench in sequence. Step 3: Conduct a floating failure test on the fiberglass pipe in the silt to monitor the dynamic process of the pipe floating in the silt over time. Record the dynamic response of the pipe floating and the magnitude of the buoyancy force on the pipe by setting up monitoring equipment in the water tank in advance as the silt settling rate in the foundation trench gradually increases and the external cyclic load is continuously applied. Step 4: Install an emergency reinforcement structure for the fiberglass pipes floating in the silt and conduct testing to verify the stability of the reinforced structure. The reinforcement structure is installed on the side of the vessel and includes a crossbar. Both sides of the crossbar are designed with synchronously extending and retracting compression springs. The lower end of the compression spring closest to the vessel is mounted on the construction vessel, and the lower end of the other compression spring is fitted with a pipe clamp. A certain pull-out force G is pre-set on the control interface of the compression springs. Based on the burial depth of the pipe in the silt, the compression springs automatically move downwards to the designated height, always maintaining a pull-out force G greater than the buoyancy force F of the pipe. The formula for calculating the pull-out force G is as follows: ； In the formula: The magnitude of the pipeline reinforcement structure, in kN / m; The scaling factor is set to 2.63; Specific weight of water, unit: kN / m³ 3 , The spacing of different emergency-type pipe clamp arrangements, in meters (m); S is the cross-sectional area of ​​the pipe, in square meters (m²). 2 .

2. The method for simulating and reinforcing the floating failure of fiberglass pipes on silty coasts according to claim 1, characterized in that: In step four, the reinforcement structure is installed on the side of the construction vessel dumping the sand and gravel cover layer. According to the longitudinal length of the pipeline, two identical reinforcement structures, namely No. 1 and No. 2, are installed at the bow and stern of the construction vessel to form an "n" shaped structure, with the crossbar in the middle being a freely rotating mechanical arm.

3. The method for simulating and reinforcing the floating failure of fiberglass pipes on silty coastlines according to claim 1, characterized in that: The pipe clamp has an inverted "U" shaped structure and is made of alloy material. In the area where the pipe clamp directly contacts the outer wall of the pipe, an arc-shaped high-elasticity rubber is installed to form a soft connection. After the backfilling of the pipe section is completed, the reinforcement structure and the construction vessel are removed at the same time, and the construction of the next pipe section continues with the construction vessel until the entire pipeline project is completed.

4. The method for simulating and reinforcing the floating failure of fiberglass pipes on silty coastlines according to claim 1, characterized in that: In step one, during the pipeline operation period, the pipeline is covered with artificial backfill stones or blocks. The backfill material can be divided into three layers from bottom to top: a crushed stone backfill layer, which is 0.3m higher than the top of the pipe, a dry-mixed concrete layer, and a stone paving layer.

5. The method for simulating and reinforcing the floating failure of fiberglass pipes on silty coasts according to claim 1, characterized in that: In step three, during the construction period test, only the floating test group affected by the sediment deposition of high-sediment-content water in the external seawater was conducted to simulate the large amount of sediment deposition and backfilling in the seawater of the silted coast. The steps are as follows: The pipeline is freely placed in the foundation trench. According to the sediment deposition rate of the project area, the prepared mud-water mixture is poured at fixed intervals. The thickness of the sediment backfilling in the foundation trench is observed to determine when the pipeline will float. The monitoring is carried out through the initial markers set on the glass observation windows on both sides of the test water tank and the wave force acquisition system. The results are recorded and analyzed as follows: The pipeline in the silt has the fact of floating failure. When the sediment deposition thickness in the foundation trench reaches 0.4m, the pipeline begins to float. The dynamic process of pipeline floating is divided into 4 stages: initial stabilization stage → slow start stage → rapid floating stage → oscillation equilibrium stabilization stage. The time taken for the entire floating process is recorded.

6. The method for simulating and reinforcing the floating failure of fiberglass pipes on silty coasts according to claim 1, characterized in that: In step three, during the construction period test, the pipeline was subjected to free siltation by high-sediment-content water bodies, superimposed with the effect of artificial backfilling during construction. The pipeline was freely placed in the foundation trench, and the experimental data were observed and recorded. The conclusion was that the pipeline floated under different mud-water mixture densities and backfilling methods. The faster the backfilling and the higher the density of the silt, the faster the pipeline floated. That is, the pipeline floated on both sides more than on a single layer. At the same time, the buoyancy force on the pipeline under different working conditions was measured and the values ​​were recorded. The conclusion was that the force was only related to the density of the silt.

7. The method for simulating and reinforcing the floating failure of fiberglass pipes on silty coasts according to claim 1, characterized in that: During the operation period, after the backfilling above the pipeline in the foundation trench was completed, the pipeline was subjected to external wave and current cyclic load test group. The results were observed and recorded. Under different wave heights, the pipeline did not float after being subjected to the ballast of the overlying layer. The conclusions are: a) The buoyancy force on the pipeline is directly proportional to the wave height and period, and inversely proportional to the water depth; b) The pressure distribution on the outer wall of the pipeline is greater at the top than at the bottom, and greater on the wave-facing side than on the wave-repelling side.

8. The method for simulating and reinforcing the floating failure of fiberglass pipes on silty coasts according to claim 1, characterized in that: In step three, the corresponding measurement and monitoring instruments and equipment are installed, including a total force sensor for measuring the buoyancy force of the pipeline, a displacement gauge for measuring the thickness of siltation in the trench over time, sensors for measuring the external circulating load carrier height and water flow velocity, as well as a pipeline buoyancy motion measuring instrument and test video recording equipment, and monitoring of the test water level.

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