Buried pipeline protection earth surface concrete cushion parameter design method and system based on falling rock influence

Abstract

The invention discloses a buried pipeline protection earth surface concrete cushion layer parameter design method and system based on falling rock influence. The method comprises the following steps: constructing a falling rock impact model, a buried pipeline model and a cushion layer model; collecting strain data and speed of rockfall, change of soil pressure in an undisturbed soil layer and strain of the buried pipeline model by using a data testing device; analyzing the collected data, and retaining data which does not exceed a preset safety range; a control variable method is adopted, parameters of the cushion model are changed, other model parameters are kept unchanged, and the process is stopped until all the parameters of the cushion model are analyzed; further analyzing the reserved data to obtain the relationship between the strain and the parameters of the cushion model, and completing the parameter design of the buried pipeline. The device effectively simulates the protection effect of the concrete cushion on the buried pipeline under the impact of falling rocks, is closer to actual engineering, and provides reference value for the actual engineering.

Description

Technical Field

[0001] The present invention relates to the fields of pipeline technology and disaster control technology, and in particular to a method and system for designing parameters of a surface concrete cushion layer for protecting buried pipelines based on the impact of falling rocks. Background Art

[0002] Concrete pipes have been widely used due to their low cost, ease of construction, excellent corrosion resistance and good sealing. As the main laying method of pipeline systems, buried pipelines have the advantages of relatively convenient construction and not occupying ground space, but unexpected ground impacts will seriously affect the stability and operational safety of buried pipelines.

[0003] At present, protective measures can be divided into two types: active protection and passive protection. Active protection focuses on preventing the occurrence of rockfall disasters, including supporting, sealing, and laying active protection nets for dangerous rock masses; passive protection focuses on protection after rockfall occurs, including setting up retaining walls and rock-blocking nets to intercept rockfall. Based on the display dynamics analysis method, Li Qiaozhen et al. established a three-dimensional dual nonlinear dynamic response analysis model for buried pipelines impacted by spherical falling bodies, and explored the changing laws of pipeline dynamic response with different influencing factors. Wang Dongyuan et al. studied the load reduction and energy dissipation buffering problems of shallow buried oil and gas pipelines under the impact of collapse and rockfall, and simulated the energy dissipation and vibration isolation effect of polystyrene foam cushions under different thicknesses and initial densities using the finite element dynamics software ANSYS / LS-DYNA. Wu Jianli et al. studied the impact force attenuation law of the composite structure of reinforced concrete slabs and a certain thickness of soil particle buffer layer under the action of rockfall and the failure mode of reinforced concrete slabs, and carried out a series of outdoor rockfall impact tests.

[0004] Most of the research on rockfall impact on buried pipelines focuses on treating the pipeline as a rigid structure and ignores the connection between pipelines to discuss the pipeline dynamic response, which is actually a simplification. However, in actual engineering, both spherical graphite cast iron pipelines and concrete water pipelines have flange connections or rubber ring connections. Summary of the invention

[0005] The purpose of the present invention is to provide a parameter design method and system for a surface concrete cushion layer for protecting buried pipelines based on the impact of falling rocks, which can not only realize the principle of controlling a single variable and solve the problem of the difficulty in operating the simulated rockfall impact dynamic load, but also objectively reflect the protective effect of the concrete cushion layer on the buried pipeline under the rockfall impact dynamic load, and provide a basis for the safety evaluation of buried pipeline protection.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] The parameter design method of the surface concrete cushion layer for buried pipeline protection based on the impact of falling rocks includes the following steps:

[0008] S1. Determine rockfall parameters, pipeline parameters, soil parameters and concrete cushion parameters.

[0009] S2. Construct a rockfall impact model, a buried pipeline model and a cushion model; the buried pipeline model is placed in a trench filled with original soil, the cushion model is placed above the buried pipeline model, and the rockfall impact model is placed above the cushion model.

[0010] S3. Use the data testing device to collect the strain data and velocity of the rockfall, the change of earth pressure in the original soil layer, and the strain of the buried pipeline model.

[0011] S4. Analyze the data collected in step S3. If the analysis result exceeds the preset safety range, the control system automatically starts the emergency plan; otherwise, the data is retained.

[0012] S5. Use the control variable method to change the parameters of the cushion model and keep other model parameters unchanged, repeat steps S3-S4 until all parameters of the cushion model are analyzed and then stop.

[0013] S6. Further analyze the retained data to obtain the relationship between strain and cushion model parameters, and complete the parameter design of the buried pipeline.

[0014] Furthermore, in step S1, determining the test parameters includes the following:

[0015] Parameter design is carried out according to the first and second similarity theory criteria, and the geometric similarity ratio of the layout geometric dimensions is determined to be L=1. The cross-sectional dimensions and burial depth are designed according to the 1:1 of the prototype dimensions, the gravity acceleration similarity ratio Cg=1, the bulk density similarity ratio Cγ=1, and the density similarity ratio Cr=1. The similarity ratio based on the geometric similarity ratio and the bulk density similarity ratio is used to achieve full similarity of Poisson's ratio and friction angle, and the elastic modulus is designed according to the similarity ratio of the prototype soil elastic modulus being 1.

[0016] Rockfall parameters include shape, mass, angle and release height; pipeline parameters include material, diameter, wall thickness and burial depth; soil parameters include soil type, water content and compaction degree.

[0017] Furthermore, in step S2, constructing the model includes the following:

[0018] A rockfall impact model was constructed using cast-in-place concrete balls, a buried pipeline model was obtained by splicing four sections of concrete pipes through tongue-and-groove joints, and a cushion model was obtained by pouring concrete.

[0019] Use an excavator to dig a trench, place the buried pipeline model in the trench, and then use the excavator to backfill the original soil on site. When backfilling, one side of the buried pipeline model is completely filled and the other side is sloped.

[0020] Furthermore, in step S3, the collected data includes the following:

[0021] The data testing device includes strain bricks, soil pressure gauges, strain gauges and high-speed cameras.

[0022] Use a crane to lift the fallen rocks to a high altitude and keep them still. After turning on the data testing device, wait for the unhooking command to make the fallen rocks land at a fixed point.

[0023] When the rocks in the rockfall impact model fall and impact, the strain bricks fixed inside the steel cage of the rockfall impact model collect rockfall strain data, the strain gauges pasted on the inner wall of the buried pipeline model collect the dynamic strain of the pipeline, the earth pressure gauge set at a set distance from the ground just above the center line of the buried pipeline model collects the characteristics of earth pressure change, and the high-speed camera set next to the impact point records the image produced by the falling process of the rockfall after being released from high altitude, thereby obtaining the speed of the rockfall impact; wherein, the set impact point is located at the center of the concrete cushion layer.

[0024] Furthermore, the strain bricks are made by using epoxy resin.

[0025] The strain gauges include annular strain gauges and axial strain gauges. Five strain gauge monitoring sections are set on the inner wall of the buried pipeline model, namely the top, waist, and bottom positions of two sections directly below the impact point and one meter along the axis, as well as the top position of the section 3 meters to the left and right of the center impact point along the axis.

[0026] Furthermore, in step S4, data analysis includes the following:

[0027] The strain gauge is connected to the dynamic signal test and analysis system through a quarter bridge. The collected dynamic strain is plotted into a strain time history curve at the corresponding pipe section using software. The curve is used to analyze whether the strain value exceeds the limit tensile strain value corresponding to the unstable expansion of the concrete pipe crack.

[0028] The earth pressure meter is connected to the dynamic signal test and analysis system through a full bridge. The product of the collected earth pressure change characteristics and the constant coefficient K is plotted into an earth pressure time history curve, and the changing trend of the earth pressure is analyzed based on the curve.

[0029] The images acquired by the high-speed camera are input into the image analysis system, and the falling trajectory and the impact body's ground contact speed are obtained based on the height of the falling rock at different times.

[0030] The emergency plan includes suspending the test, adjusting the rockfall release parameters and rearranging the data testing equipment.

[0031] Furthermore, in step S5, the parameters of the cushion model include the thickness of the cushion and the concrete strength.

[0032] Furthermore, in step S6, the parameter design of the buried pipeline includes the following contents:

[0033] By changing the parameters of the cushion model, the protection effect of the pipeline under different rockfall impacts can be obtained.

[0034] The ultimate tensile strain of the concrete pipe is set as the safety threshold, and the relationship between the peak tensile strain of the pipe and the thickness of the cushion layer is obtained, which is:

[0035]

[0036] Among them, ε p is the peak tensile strain, h is the thickness of the cushion layer, and A, B, and k are all correlation coefficients.

[0037] The relationship between the peak tensile strain of the pipeline and the concrete strength of the cushion layer is:

[0038]

[0039] Among them, C is the concrete strength grade.

[0040] Furthermore, the present invention also proposes a parameter design system for the surface concrete cushion layer for protecting buried pipelines based on the impact of falling rocks, including:

[0041] The data preparation module is used to determine the rockfall parameters, pipeline parameters, soil parameters and different concrete cushion parameters required for the test.

[0042] The test model construction module is used to construct a rockfall impact model, a buried pipeline model and a cushion model; the buried pipeline model is placed in a trench filled with original soil, the cushion model is placed above the buried pipeline model, and the rockfall impact model is placed above the cushion model.

[0043] The data acquisition module is used to collect the rockfall strain data and velocity in the simulated rockfall impact model, the change of soil pressure in the original soil layer and the strain of the buried pipeline model using a data testing device.

[0044] The data analysis module is used to analyze the data collected in the data acquisition module. If the analysis result exceeds the preset safety range, the control system automatically starts the emergency plan; otherwise, the data is retained.

[0045] The test module is used to change the parameters of the cushion model by using the control variable method, and keep other model parameters unchanged, and repeat the steps of data acquisition model and data analysis model until all parameters of the cushion model are analyzed and then stop.

[0046] The parameter design module is used to further analyze the retained data, obtain the relationship between strain and cushion thickness, and complete the parameter design of the buried pipeline.

[0047] Compared with the prior art, the present invention adopts the above technical solution and has the following technical effects:

[0048] 1. The present invention establishes a corresponding field test model by determining a reasonable similar scale, simplifies the analysis of the concrete cushion test prototype of the buried pipeline under rockfall impact, and realizes the adaptability to different engineering practices. By simulating the rockfall impact, pipeline burial depth, and cushion protection, the protective effect of the concrete cushion on the buried pipeline under rockfall impact is effectively simulated, which is closer to the actual project and provides reference value for the actual project.

[0049] 2. The present invention simulates the impact of falling rocks by using reinforced concrete spheres, and simulates the protective effect on buried pipelines in actual projects by changing the thickness of the concrete cushion layer. The device is simple and reliable, can accurately control the size of the dynamic load, and basically realizes the principle of experimental control of a single variable.

[0050] 3. The present invention can simulate the strain of the buried pipeline caused by falling rocks on the concrete cushion layer and the change of soil pressure of the clay layer through the measurement system, so as to provide an experimental basis and research method for further revealing the protective effect of different thicknesses of concrete cushion layers on the buried pipeline. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 It is the overall structural diagram of the present invention.

[0052] Figure 2 It is a schematic diagram of the pasting position of the strain gauge of the present invention.

[0053] Figure 3 It is a front view of the concrete cushion layer of the present invention and a schematic diagram of the position of the impact point.

[0054] Figure 4 is a curve diagram of strain and cushion thickness in an embodiment of the present invention.

[0055] Figure 5 is a graph of strain and concrete strength in an embodiment of the present invention.

[0056] Figure numerals: 1-rockfall impact model, 2-cushion model, 3-clay layer, 4-concrete pipe, 5-earth pressure gauge, 6-strain gauge, 7-impact point. DETAILED DESCRIPTION

[0057] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0058] To achieve the above purpose, the present invention proposes a parameter design method for the surface concrete cushion layer of buried pipeline protection based on the influence of rockfall. The model test site selected a field experimental base of a university located in Jiangxia District, Wuhan City as the test site. Small balls were used to simulate rockfall. The soil layer of the site was drilled and sampled and sent to a professional testing company for geotechnical testing. The specific steps are as follows:

[0059] S1. Test preparation stage: According to the actual engineering situation and research purpose, determine the rockfall parameters, pipeline parameters, soil parameters and different concrete cushion parameters required for the test; the specific contents are:

[0060] Parameter design is carried out according to the first and second similarity theory criteria, and the geometric similarity ratio of the layout geometric dimensions is determined to be L=1. The model test adopts a large-scale field test; the design is carried out according to the cross-sectional dimensions and burial depth at 1:1 of the prototype dimensions, the gravity acceleration similarity ratio Cg=1, the bulk density similarity ratio Cγ=1, the density similarity ratio Cr=1, and the similarity ratio based on the geometric similarity ratio and the bulk density similarity ratio to achieve full similarity of Poisson's ratio and friction angle, and the elastic modulus is designed according to the similarity ratio of the prototype soil elastic modulus of 1.

[0061] Rockfall parameters include shape, mass, angle and release height; pipeline parameters include material, diameter, wall thickness and burial depth; soil parameters include soil type, water content and compaction degree.

[0062] S2. Make a field test model: construct a rockfall impact model 1, a buried pipeline model and a cushion model 2; the buried pipeline model is placed in a trench filled with undisturbed soil, the cushion model 2 is placed above the buried pipeline model, and the rockfall impact model 1 is placed above the cushion model 2; Figure 1 The specific contents are as follows:

[0063] A rockfall impact model 1 is constructed using cast-in-place concrete balls. On the premise of sufficient investigation and inspection, in order to ensure that the obtained model test results are consistent with the engineering conditions of the subway tunnel, four sections of finished concrete pipes 4 that have been cast by the manufacturer are spliced ​​through tongue-and-groove joints to ensure that the pipes conform to general water pipes, thereby obtaining a buried pipe model. The concrete pipes 4 are connected with flexible interfaces. The cushion model 2 is obtained by concrete pouring.

[0064] Use an excavator to dig a trench, do not pressurize the inside of the pipe, backfill the bottom of the pipe, and compact the pipe cover layer by layer. The compaction degree meets the requirements of the water supply and drainage pipeline construction and acceptance standards. The constraints at both ends of the pipe can be regarded as the same as the actual buried pipe. Place the buried pipe model in the trench, and then use an excavator to backfill with the original soil on site. When backfilling, the density of the backfill soil must be ensured to ensure that the soil covering the tunnel is in close contact with the tunnel and the compaction degree is stable, which is convenient for subsequent patching; when backfilling, one side of the buried pipe model is completely buried, and the other side is sloped to facilitate the subsequent deployment of strain gauges6.

[0065] The inner diameter of the finished concrete pipe 4 is 1500 mm, the outer diameter is 1800 mm, and the length is 2000 mm; the depth of the groove is 3.8 m, the length is 9 m, and the width is 2 m; the size of the concrete is 200 cm*200 cm*10 cm.

[0066] The reinforced concrete ball is reinforced with 3 M8 stirrups and 2 M8 longitudinal bars. The steel grade is level one. The sphere is cast with C30 concrete. The diameter of the cast reinforced concrete ball is 340mm and the mass is approximately 50kg.

[0067] The pipe wall thickness is 150mm and the total weight of the pipe is 1943kg, of which 1865kg is concrete and 55.36kg is steel.

[0068] S3, loading test model: using a crane to lift the rock in the rockfall impact model 1, and suspend the rock above the buried pipeline model, the crane unhooks the rock and lets it fall freely; using a data testing device to collect rockfall strain data, impulse and velocity, changes in soil pressure in the original soil layer, and strain of the buried pipeline model in the simulated rockfall impact model 1; the specific contents are as follows:

[0069] The data testing device includes a strain brick, an earth pressure gauge 5, a strain gauge 6 and a high-speed camera. The strain brick is made of epoxy resin.

[0070] like Figure 2 As shown, the strain gauge 6 includes annular strain gauges and axial strain gauges, and 5 strain monitoring sections are set on the inner wall of the buried pipeline model, namely the top, waist, and bottom positions of two sections just below the impact point and one meter along the axis, and the top position of the section 3 meters to the left and right of the center impact point along the axis.

[0071] A crane is used to lift the fallen rocks to a height of 30m above the buried pipeline model and leave them still. After turning on various collection instruments, the test personnel evacuate to a safe location and wait for the unhooking command to make the fallen rocks fall at a fixed point. The fixed-point landing can accurately control the landing point of each fallen rock.

[0072] When the rockfall in the rockfall impact model 1 falls and impacts, the strain bricks fixed inside the steel cage of the rockfall impact model 1 collect rockfall strain data, the strain gauge 6 pasted on the inner wall of the buried pipeline model collects the dynamic strain of the pipeline, and the soil pressure gauge 5 set at 2.0m and 3.8m above the ground surface just above the center line of the buried pipeline model collects soil pressure change characteristics. The high-speed camera set next to the impact point records the image produced by the falling process of the rockfall after being released from high altitude, and then obtains the speed of the rockfall impact, providing key data support for the subsequent impact force and impulse calculation; among them, in order to simulate the most dangerous situation of the buried tongue-and-groove concrete pipe 4 being impacted by rockfall, the impact point 7 is set at the center of the concrete cushion layer, such as Figure 3 shown.

[0073] In this embodiment, a Phantom high-speed camera is placed 10m away from the impact point, and the trajectory and falling speed are calculated with the domestic Qianyanlang image analysis software. The length of the strain gauge 6 is 80mm and the resistance is 120Ω. The model of the dynamic signal test and analysis system is DH5956. When analyzing the data of the strain gauge 6, the measurement accuracy of the dynamic signal test and analysis system is 10 microstrain, and the sampling rate is 2000Hz for each channel; when analyzing the data of the soil pressure gauge 5 at a depth of 2.0 meters, the range of the dynamic signal test and analysis system is 0.5MPa, and when analyzing the data of the soil pressure gauge 5 at a depth of 3.8 meters, the range of the dynamic signal test and analysis system is 0.2MPa.

[0074] The falling height of the rock is h = 30 meters, and the bottoming speed is v = 24.5m / s.

[0075] S4, model test and data recording: Analyze the data collected in step S3. If the analysis results exceed the preset safety range or the instrument data is inaccurate due to improper arrangement of monitoring equipment, the control system automatically starts the emergency plan to ensure the safety of the test and the reliability of the data; otherwise, the data is retained; the specific contents are as follows:

[0076] The strain gauge 6 is connected to the dynamic signal test and analysis system through a quarter bridge, and the collected dynamic strain is plotted into a strain time history curve at the corresponding pipeline section using software, and the strain value is analyzed based on the curve to see whether it exceeds the ultimate tensile strain value corresponding to the unstable expansion of the crack in the reinforced concrete pipeline 4 used in the test.

[0077] The earth pressure meter 5 is connected to the dynamic signal test and analysis system through a full bridge. The product of the collected earth pressure change characteristics and the constant coefficient K is plotted into an earth pressure time-history curve, and the change law of earth pressure is analyzed based on the curve. The earth pressure not only has a direct impact on the structural integrity of the pipeline, but also affects the deformation, displacement and possible failure mode of the pipeline under impact load.

[0078] The images acquired by the high-speed camera are input into the image analysis system, and the falling trajectory and the impact body's ground contact speed are obtained based on the height of the falling rock at different times;

[0079] The emergency plan includes suspending the test, adjusting the rockfall release parameters and rearranging the data testing equipment.

[0080] S5. Using the control variable method, change the cushion thickness and concrete strength of cushion model 2, and keep other model parameters unchanged, repeat steps S3-S4 until all parameters of cushion model 2 are tested. The parameters of cushion model 2 include cushion thickness and concrete strength.

[0081] In this embodiment, the pipeline parameters are kept unchanged, the pipeline burial depth is 2.0m, the rockfall impact energy is 100kJ, the concrete strength of the cushion layer is C30, the thickness of the cushion layer is changed to 10cm, 15cm, 20cm, 25cm, and 30cm, and the soil pressure and the strain of the buried pipeline are recorded under different concrete cushion layer thicknesses.

[0082] Keeping the pipeline parameters unchanged, the buried depth of the pipeline is 2.0m, the rockfall impact energy is 100kJ, the thickness of the cushion layer is 0.1m, and the concrete strength of the cushion layer is changed to C20, C25, C30, C35, and C40. The soil pressure and the strain of the buried pipeline are recorded under different concrete strengths.

[0083] S6. Test summary and feedback: Further analyze the retained data to obtain the relationship between strain and cushion model 2 parameters, and complete the parameter design of the buried pipeline. The specific contents are:

[0084] By changing the parameters of cushion model 2, the protection effect of the pipeline under different rockfall impacts can be obtained.

[0085] Taking the ultimate tensile strain of prestressed (self-stressed) concrete pipe 4 specified in GB50268-2008 Water Supply and Drainage Pipeline Engineering Construction Acceptance Code as the safety threshold, the relationship between the peak tensile strain of the pipe and the cushion thickness is obtained, which is:

[0086]

[0087] Among them, ε p is the peak tensile strain, h is the thickness of the cushion layer, and A, B, and k are all correlation coefficients.

[0088] The relationship between the peak tensile strain of the pipeline and the concrete strength of the cushion layer is:

[0089]

[0090] Among them, C is the concrete strength grade.

[0091] S7. Evaluate the effectiveness and accuracy of the test system and methods, propose improvement measures and optimization suggestions for the problems found in the test, and provide reference for the next test or actual engineering application. At the same time, organize the test data and results into a report to facilitate subsequent research and communication.

[0092] In this embodiment, the corresponding strain-to-cushion thickness curve and strain-to-cushion concrete strength curve are plotted based on the acquired data. Figure 4 As shown in the figure, the peak strain of the pipeline increases with the thickness of the concrete cushion layer, showing a nonlinear decreasing trend. When the cushion layer thickness is 30 cm, the peak tensile strain of the pipeline can be reduced by 27.91% compared with the cushion layer thickness of 10 cm. Figure 5 As shown in the figure, the peak strain of the pipeline also shows a nonlinear decreasing trend with the increase of the cushion concrete strength. When the cushion concrete strength is C40, the peak strain of the pipeline can be reduced by 19.65% compared with the concrete strength of C20.

[0093] The method provided by the present invention can provide guidance for the protection setting of buried tongue-and-groove concrete pipes. The provided example gives the specific parameter design process and conclusion of the concrete cushion layer, achieves the expected goal, and can effectively solve the research problem.

[0094] In order to ensure the accuracy of the experiment, a lot of materials and equipment were used in this experiment. Subsequent research can be based on this experiment and use numerical simulation software to build a model to complete further research.

[0095] The present invention can simplify the analysis of the concrete cushion test prototype of the buried pipeline under rockfall impact by determining a reasonable similarity scale to establish a corresponding field test model, thereby achieving adaptability to different engineering practices. By simulating rockfall impact, pipeline burial depth, and cushion protection, the protective effect of the concrete cushion on the buried pipeline under rockfall impact is effectively simulated, which is closer to the actual project and provides reference value for the actual project.

[0096] The impact of falling rocks is simulated by reinforced concrete spheres, and the protective effect of buried pipelines in actual projects is simulated by changing the thickness of the concrete cushion layer. The device is simple and has a certain degree of reliability. It can accurately control the size of the dynamic load and can basically realize the principle of experimental control of a single variable.

[0097] The measurement system can simulate the strain of fallen rocks on the concrete cushion layer on the buried pipeline and the change of soil pressure in the clay layer, providing experimental basis and research methods for further revealing the protective effect of different thicknesses of concrete cushion layers on buried pipelines.

[0098] In the absence of conflict, the above embodiments and features in the embodiments may be combined with each other.

[0099] The embodiment of the present invention also proposes a parameter design system for the surface concrete cushion layer of the buried pipeline protection based on the impact of falling rocks, including a data preparation module, a test model construction module, a data acquisition module, a data analysis module, a test module, a parameter design module and a computer program that can be run on a processor. It should be noted that each module in the above system corresponds to the specific steps of the method provided in the embodiment of the present invention, and has the functional modules and beneficial effects corresponding to the execution method. For technical details not described in detail in this embodiment, please refer to the method provided in the embodiment of the present invention.

[0100] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for designing parameters of surface concrete cushion for buried pipeline protection based on rockfall, characterized in that: include: S1. Determine rockfall parameters, pipeline parameters, soil parameters and concrete cushion parameters; S2, constructing a rockfall impact model (1), a buried pipeline model and a cushion model (2); the buried pipeline model is placed in a trench filled with original soil, the cushion model (2) is placed above the buried pipeline model, and the rockfall impact model (1) is placed above the cushion model (2); S3, using a data testing device to collect strain data and velocity when the rock falls, changes in earth pressure in the original soil layer, and strain of the buried pipeline model; S4, analyzing the data collected in step S3, if the analysis result exceeds the preset safety range, the control system automatically starts the emergency plan; otherwise, the data is retained; S5, using the control variable method, changing the parameters of the cushion model (2), and keeping other model parameters unchanged, repeating steps S3-S4 until all parameters of the cushion model (2) are analyzed and then stopping; S6. Further analyze the retained data to obtain the relationship between the strain and the parameters of the cushion model (2), and complete the parameter design of the buried pipeline.

2. The method for designing parameters of the surface concrete cushion layer for protecting buried pipelines based on the impact of falling rocks according to claim 1 is characterized in that: In step S1, determining the test parameters includes the following: According to the first and second similarity theory criteria, parameter design is performed to determine the geometric similarity ratio of the layout geometric dimensions as L=1, and the cross-sectional dimensions and burial depth are designed according to the 1:1 of the prototype dimensions, the gravity acceleration similarity ratio Cg=1, the bulk density similarity ratio Cγ=1, and the density similarity ratio Cr=1; the similarity ratio based on the geometric similarity ratio and the bulk density similarity ratio is used to achieve full similarity of Poisson's ratio and friction angle, and the elastic modulus is designed according to the similarity ratio of the prototype soil elastic modulus as 1; Rockfall parameters include shape, mass, angle and release height; pipeline parameters include material, diameter, wall thickness and burial depth; soil parameters include soil type, water content and compaction degree.

3. The method for designing parameters of the surface concrete cushion layer for protecting buried pipelines based on the impact of falling rocks according to claim 1 is characterized in that: In step S2, building the model includes the following: A rockfall impact model (1) is constructed by using cast-in-place concrete balls, a buried pipeline model is obtained by splicing four sections of concrete pipes (4) through tongue-and-groove joints, and a cushion model (2) is obtained by pouring concrete; Use an excavator to dig a trench, place the buried pipeline model in the trench, and then use the excavator to backfill the original soil on site. When backfilling, one side of the buried pipeline model is completely filled and the other side is sloped.

4. The method for designing parameters of the surface concrete cushion layer for protecting buried pipelines based on the impact of falling rocks according to claim 3 is characterized in that: The diameter of the concrete ball is 340 mm and the mass is 50 kg; the inner diameter of the concrete pipe (4) is 1500 mm, the outer diameter is 1800 mm and the length is 2000 mm; the depth of the groove is 3.8 m, the length is 9 m and the width is 2 m; the size of the concrete is 200 cm*200 cm*10 cm.

5. The method for designing parameters of the surface concrete cushion layer for protecting buried pipelines based on the impact of falling rocks according to claim 1 is characterized in that: In step S3, the collected data includes the following: The data testing device includes a strain brick, an earth pressure gauge (5), a strain gauge (6) and a high-speed camera; Using a crane to lift the rock in the rockfall impact model (1), and suspending the rock above the buried pipeline model and leaving it still, after turning on the data testing device, waiting for the unhooking command, and allowing the rockfall to land at a fixed point; When the rockfall in the rockfall impact model (1) falls and impacts, the strain bricks fixed inside the steel cage of the rockfall impact model (1) collect rockfall strain data, the strain gauge (6) attached to the inner wall of the buried pipeline model collects the dynamic strain of the pipeline, the soil pressure gauge (5) arranged at a set distance from the ground surface just above the center line of the buried pipeline model collects soil pressure change characteristics, and the high-speed camera arranged next to the impact point records the image generated by the falling process of the rockfall after being released from high altitude, thereby obtaining the speed of the rockfall impact; wherein, the impact point (7) is set to be located at the center of the concrete cushion layer.

6. The method for designing parameters of the surface concrete cushion layer for protecting buried pipelines based on the impact of falling rocks according to claim 5 is characterized in that: Using epoxy resin to make strain bricks; The strain gauge (6) includes an annular strain gauge and an axial strain gauge. Five strain gauge monitoring sections are arranged on the inner wall of the buried pipeline model, namely, the top, waist and bottom positions of two sections just below the impact point and one meter along the axis, and the top position of the section 3 meters to the left and right of the impact point along the axis.

7. The method for designing parameters of the surface concrete cushion layer for protecting buried pipelines based on the impact of falling rocks according to claim 5 is characterized in that: In step S4, data analysis includes the following: The earth pressure meter (5) is connected to the dynamic signal test and analysis system through the full bridge, and the product of the collected earth pressure change characteristics and the constant coefficient K is plotted into an earth pressure time history curve graph, and the change trend of the earth pressure is analyzed based on the curve graph; The strain gauge (6) is connected to a dynamic signal test and analysis system through a quarter bridge, and the collected dynamic strain is plotted into a strain time history curve diagram at the corresponding pipe section by software, and the strain value is analyzed based on the curve diagram to determine whether it exceeds the limit tensile strain value corresponding to the unstable expansion of the crack in the concrete pipe (4); The images acquired by the high-speed camera are input into the image analysis system, and the falling trajectory and the impact body's ground contact speed are obtained based on the height of the falling rock at different times; The emergency plan includes suspending the test, adjusting the rockfall release parameters and rearranging the data testing equipment.

8. The method for designing parameters of the surface concrete cushion layer for protecting buried pipelines based on the impact of falling rocks according to claim 1 is characterized in that: In step S5, the parameters of the cushion model (2) include the thickness of the cushion and the concrete strength.

9. The method for designing parameters of the surface concrete cushion layer for protecting buried pipelines based on the impact of falling rocks according to claim 8 is characterized in that: In step S6, the parameter design of the buried pipeline includes the following contents: By changing the parameters of the cushion model (2), the protection effect of the pipeline under different rockfall impacts is obtained; The ultimate tensile strain of the concrete pipe (4) is set as the safety threshold, and the relationship between the peak tensile strain of the pipe and the cushion thickness is obtained, which is: Among them, ε p is the peak tensile strain, h is the thickness of the cushion layer, and A, B, and k are all correlation coefficients; The relationship between the peak tensile strain of the pipeline and the concrete strength of the cushion layer is: Among them, C is the concrete strength grade.

10. A system applied to the method for designing parameters of surface concrete cushion for buried pipeline protection based on rockfall impact as claimed in claim 1, characterized in that: include: Data preparation module, used to determine the rockfall parameters, pipeline parameters, soil parameters and different concrete cushion parameters required for the test; The test model construction module is used to construct a rockfall impact model, a buried pipeline model and a cushion model; the buried pipeline model is placed in a trench filled with undisturbed soil, the cushion model is placed above the buried pipeline model, and the rockfall impact model is placed above the cushion model; A data acquisition module, used to collect rockfall strain data and velocity in a simulated rockfall impact model, changes in soil pressure in an original soil layer, and strain of a buried pipeline model using a data testing device; The data analysis module is used to analyze the data collected by the data acquisition module. If the analysis result exceeds the preset safety range, the control system automatically starts the emergency plan; otherwise, the data is retained; The test module is used to change the parameters of the cushion model by using the control variable method, and keep other model parameters unchanged, and repeat the steps of data acquisition model and data analysis model until all parameters of the cushion model are analyzed and then stop; The parameter design module is used to further analyze the retained data, obtain the relationship between strain and cushion thickness, and complete the parameter design of the buried pipeline.

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