Slurry flow test system for slurry feeding / discharging pipeline of slurry balance shield in soft soil stratum

Abstract

The invention provides a soft soil stratum slurry balance shield slurry feeding / discharging pipeline slurry flow test system. The system comprises a slurry circulation pipeline, monitoring equipment, a soil body cutting simulation system, a PIV-based visualization device, an analysis system and a control system. The slurry circulating pipeline comprises a slurry tank, a vortex pump and a slurry conveying pipe; the monitoring equipment comprises a plurality of sensors; the soil body cutting simulation system is used for simulating a shield excavation working condition; the visual device based on PIV is used for recording a visual flow field of slurry flowing in the slurry conveying pipe in real time; the analysis system is used for macroscopic and microscopic analysis; and the control system controls equipment power in the system. The device and the method can simulate the working conditions of most slurry balance shield slurry discharge pipelines and record macro and micro evaluation indexes in the slurry flowing process, so that the flowing property and the slag carrying capacity of slurry in the slurry feeding / discharging pipelines under different stratum conditions are explored, and the device and the method are low in cost, high in operability and high in compatibility.

Description

Technical Field

[0001] The invention belongs to the field of civil engineering. Background Art

[0002] In recent years, with the development and utilization of underground space, the construction environment of tunnel projects has gradually changed from shallow underground space to deep underground space, and from single strata to composite strata. During tunnel excavation, especially in soft soil strata, the addition of cut soil will increase the viscosity of the slurry in the slurry discharge pipe, which will cause the slurry particles to adhere to the pipe wall. In severe cases, it will cause the pipe to be blocked, causing delays in the construction period. At present, fluid flow tests are widely used in chemical engineering, mining engineering and other fields. However, the design of the test device during the flow test is closely related to the particle size, particle grading and pipe diameter in the slurry transportation process in different fields, and cannot be directly applied to the study of slurry flow properties and slag carrying capacity in the slurry inlet / discharge pipe of the slurry balance shield. Therefore, it is necessary to improve the excavation efficiency of the shield machine in actual engineering to avoid pipe blockage. Existing test systems and test methods often target large particles and non-stratum particles (such as food and chemicals), lack consideration of different particle gradations and small-size particles in soft soil strata, and are not combined with the shield excavation process. It is urgent to design a pipeline slurry flow performance and slag carrying capacity test system that considers the slurry balance shield excavation process, so as to conduct a detailed study on the behavior of soil particles in different strata in the slurry discharge pipeline before excavation, and at the same time determine the pipeline transportation speed to meet relevant scientific research needs and engineering needs. Summary of the invention

[0003] Based on the problems in the background technology, the present invention proposes a new mud flow test system for the inlet / outlet pipeline of a mud-water balance shield in soft soil, providing a low-cost, efficient and comprehensive test method for the mud flow performance and slag carrying capacity of pipelines: The present invention is achieved through the following technical solutions: A slurry flow test system for a slurry inlet / outlet pipeline of a slurry-water balance shield in soft soil, comprising: a slurry circulation pipeline, monitoring equipment, a soil cutting simulation system, a visualization device based on PIV, an analysis system and a control system; The mud circulation pipeline includes a mud tank, a vortex pump, and a mud transmission pipe, wherein: Mud tank, including tank body and stirring device, used for storage and production of mud; A mud transmission pipe, the input end and the output end of which are respectively connected to the outlet and the inlet of the mud tank; The vortex pump is connected to the mud transmission pipe, close to the outlet of the mud tank, and is used to push the mud so that the mud circulates in the mud transmission pipe; The monitoring equipment includes a plurality of sensors, which are arranged in the mud transmission pipe of the mud circulation pipeline and are connected to the analysis system signal; The soil cutting simulation system is located above the mud tank of the mud circulation pipeline, and the cut soil enters the mud tank to simulate the shield excavation working condition; The PIV-based visualization device is used to record in real time the visualized flow field of the mud flow in the mud transmission pipe of the mud circulation pipeline; The analysis system uses the data collected by the monitoring equipment for macroscopic analysis and uses the image data transmitted by the PIV-based visualization device for microscopic analysis; The control system is connected with the mud circulation pipeline and the soil cutting simulation system to realize power control.

[0004] According to the above technical solution, the beneficial effects of the present invention are as follows: The present invention proposes a mud flow test system for the inlet / discharge pipe of a slurry balance shield in soft soil, which can simulate most of the working conditions of the slurry balance shield and discharge pipe, record the macro and micro evaluation indicators during the mud flow process, and thus explore the flow performance and slag carrying capacity of the slurry in the inlet / discharge pipe under different formation conditions. The system can comprehensively complete the study of the mud flow performance of the inlet / discharge pipe of a slurry balance shield in soft soil, and the test system has low cost, strong operability and high compatibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Figure 1 Schematic diagram of the structure of the mud flow test system of the mud-water balance shield inlet / discharge pipeline in the soft soil layer of the embodiment; Figure 2 It is the structural diagram of the soil cutting simulation system; Figure 3 Schematic diagram of the principle of the PIV-based visualization device.

[0006] Numbers in the figure: 1-1 acrylic straight pipe, 1-2 acrylic elbow, 1-3 flange connector, 1-4 rubber hose; 2 Mud tank; 3 Eddy current pump; 4 soil cutting simulation system, 4-1 rotating motor, 4-2 soil sample chamber, 4-3 rotating shaft, 4-4 cutting disc; 5 PIV-based visualization device, 5-1 high-speed camera, 5-2 solid-state laser, 5-3 tracer particles; 6-1 density meter, 6-2 flow meter; 7 computers, 8 frequency conversion cabinets. DETAILED DESCRIPTION

[0007] The technical solution provided by the present application will be further described below in conjunction with specific embodiments and accompanying drawings. The advantages and features of the present application will become more apparent with the following description.

[0008] like Figure 1As shown, a mud flow test system for the mud-water balance shield inlet / outlet pipeline in soft soil layer includes: a mud circulation pipeline, a monitoring device, a soil cutting simulation system 4, a visualization device based on PIV 5, an analysis system and a control system.

[0009] The mud circulation pipeline includes a mud tank 2, a vortex pump 3, and a mud transmission pipe. Among them: The mud tank comprises a tank body and a stirring device, and is used for storing and making mud; The mud transmission pipe has an input end and an output end connected to the outlet and the inlet of the mud tank respectively; The vortex pump is connected to the mud transmission pipe, close to the outlet of the mud tank, and is used to push the mud so that the mud circulates in the mud transmission pipe.

[0010] Furthermore, the stirring device comprises a stirring motor, and the stirring motor and the eddy current pump are respectively connected to the control system via cables.

[0011] Further, the mud transmission pipe includes rubber hoses 1-4 and acrylic pipes, wherein: The acrylic pipe is the main transmission pipe; The rubber hoses 1-4 are connecting pipes, which are used to connect the vortex pump 3 between the outlet of the mud tank 2 and the inlet of the acrylic pipe, and to connect the outlet of the acrylic pipe to the inlet of the mud tank 2, so as to avoid the pipe vibration caused by the vibration of the mud tank 2 and the vortex pump 3.

[0012] Specifically, the rubber hose has three sections. The first section of the rubber hose is connected between the mud tank 2 and the vortex pump 3, the second section of the rubber hose is connected between the vortex pump 3 and the acrylic pipe, and the third section of the rubber hose is connected between the acrylic pipe and the mud tank 2 to avoid the pipe vibration caused by the vibration of the mud tank and the vortex pump. Except for the third section of the rubber hose which is directly placed in the mud tank, all rubber hoses and other devices are connected with flanges. Among them, the first section of the rubber hose is used to transport the mud pumped out of the mud tank to reduce the vibration of the mud tank caused by the vibration of the vortex pump; the second section of the rubber hose transports the mud pumped out of the vortex pump to the acrylic pipe to reduce the vibration of the acrylic pipe caused by the vibration of the vortex pump; the third section of the rubber hose is used to transport the mud in the acrylic pipe to the mud tank; in this way, a closed loop of mud is formed to realize the circulation of mud.

[0013] The mud starts from the mud tank 2 and is driven by the vortex pump 3 to flow through the rubber hose connecting the mud tank and the vortex pump, the rubber hose connecting the vortex pump and the acrylic pipe, the acrylic pipe, and the rubber hose connecting the acrylic pipe and the mud tank 2 in sequence, so that the mud loop is closed and the circulation of the mud is realized.

[0014] Furthermore, the acrylic pipe includes a plurality of acrylic straight pipes 1-1 and acrylic curved pipes 1-2, which are connected to each other via flange connectors 1-3.

[0015] Furthermore, the eddy current pump 3 is fixed on the ground to avoid excessive vibration.

[0016] The monitoring equipment includes a plurality of sensors, which are arranged in the mud transmission pipe of the mud circulation pipeline and are connected with the analysis system signal.

[0017] Furthermore, the sensors include a density meter 6-1, a flow meter 6-2, and the like.

[0018] The data monitored by the monitoring equipment sensor is transmitted to the analysis system via a 4-20mA signal for data recording and macroscopic evaluation of mud flow properties and slag carrying capacity.

[0019] The monitoring equipment can be installed in the observation section selected according to the needs.

[0020] In the embodiment of the present invention, the densitometer is arranged on the acrylic pipe near the end of the mud circulation pipe.

[0021] Usually, the flow meter is placed at the test inlet of the slurry to measure the flow rate. The test inlet refers to the position where the slurry flow pattern develops to a certain extent and can continue to develop after passing through this position, which is convenient for subsequent more extensive and in-depth research (such as setting numerical simulation parameters according to the flow rate of the test inlet, etc.). In the embodiment of the present invention, the test inlet is the connection between the acrylic straight pipe and the acrylic elbow near the end of the mud circulation pipeline.

[0022] The soil cutting simulation system 4 comprises a rotating motor 4-1, a soil sample chamber 4-2 and a cutting disc 4-4. Figure 2 As shown, the upper end of the mud tank 1-5 is open, and the soil cutting simulation system 4 is located above the mud tank 1-5 as a whole, wherein: The soil sample bin 4-2 is fixed separately and used to store soil samples to simulate the cut strata, and has openings at the upper and lower ends; The rotating motor 4-1 is located above the soil sample chamber 4-2, and the rotating shaft 4-3 of the rotating motor 4-1 passes through the openings at the upper and lower ends of the soil sample chamber 4-2 and is connected to the cutting disc 4-4 below the soil sample chamber 4-2. When cutting, the cutting disc 4-4 is driven upward and rotated by the rotating motor 4-1 to cut the soil in the soil sample chamber 4-2, and the soil naturally falls to the mud tank 1-5 after cutting. The rotating motor 4 - 1 is connected to a control system via a cable, and the control system controls the start and stop and the speed of the rotating motor.

[0023] In order to better simulate the actual excavation process of the shield machine, the rotation speed of the 4-1 cutting disc 4-4 driven by the rotary motor is controlled to match the advancement speed / penetration of the shield machine. Before the test, the cutting speed of the cutting disc is calibrated through a pre-test so that the soil cutting speed during the test matches the slag discharge speed converted from the advancement speed / penetration. During the test, according to the corresponding geological conditions, different soil samples are configured with particle grading, cohesion, and internal friction angle as calibration parameters, and the simulation of stratum cutting and soil input are carried out to be close to the actual situation during the excavation process.

[0024] The PIV-based visualization device 5 records the visualized flow field of the mud flow in the mud transmission pipe of the mud circulation pipeline in real time, and includes a high-speed camera 5-1, a solid laser 5-2 and tracer particles 5-3, such as Figure 3 As shown. Wherein: the tracer particles 5-3 are distributed in the fluid in the pipeline, that is, the mud in the mud circulation pipeline; the solid laser 5-2 is arranged above the acrylic pipe in the mud transmission pipeline of the mud circulation pipeline, and the emitted laser is perpendicular to the plane where the acrylic pipe and the high-speed camera 5-1 are located, and is used to irradiate the tracer particles 5-3 in the mud in the acrylic pipe; the high-speed camera 5-1 is used to record the image data of the tracer particle distribution at different times. The image data recorded by the visualization device based on PIV is transmitted to the analysis system through the USB interface, so that the analysis system can record data and conduct microscopic evaluation of mud flow performance and slag carrying capacity.

[0025] By means of scattered light of tracer particles with good tracking properties uniformly distributed in the fluid, the positions of multiple particles in a certain area of ​​the fluid are continuously recorded, and the displacement vector of each particle within the time interval between two exposures is calculated, thereby obtaining the velocity vector field of the area. During the test, solid laser 5-2 is used to irradiate tracer particles 5-3 dispersed in the mud slurry in advance, and the distribution of tracer particles at different times is recorded by high-speed camera 5-1, so that the velocity distribution of liquid phase and particle phase can be obtained, and the concentration distribution of particle phase can be reflected to a certain extent. If it is observed that the particles move in the pipeline in the form of jumping or sliding, and the particle distribution basically shows a trend of sparse top and dense bottom, it means that the flow rate of the mud is moderate; if the particles move in the pipeline in the form of jumping or sliding, and the particle distribution is relatively uniform, it means that the mud flow rate is too fast; if the particles move slowly in the pipeline, it means that the mud will block the pipeline over time, and the flow rate should be increased.

[0026] The analysis system is deployed in the computer 6, and includes a data receiving module, a macro analysis module and a micro analysis module. The data receiving module receives the sensor signal, converts the received sensor signal into corresponding physical quantities, and stores them in the computer. The physical quantities include density signal and flow rate signal, which are transmitted to the macro analysis module; the data receiving module obtains the image data recorded by the PIV-based visualization device through the USB interface and transmits it to the micro analysis module.

[0027] The data receiving module also receives the geometric and physical parameters of the slurry and pipeline input in advance by the researchers, including static macroscopic indicators such as pipeline diameter, particle grading, particle density, initial slurry concentration (i.e., initial particle volume fraction), for use by the macroscopic analysis module and the microscopic analysis module.

[0028] The macro analysis module performs a macro evaluation of the mud flow performance and slag carrying capacity based on the obtained physical quantities and the static macro indicators such as pipeline diameter, particle gradation, particle density, and initial slurry concentration (i.e., initial particle volume fraction) input in advance. The specific steps are as follows: Step 1.1: According to the physical quantities and static macroscopic indicators monitored by the monitoring equipment, the formation particle properties, pipeline diameter, and particle volume fraction are obtained, and the slurry flow rate calculation formula is selected when the slurry is in a critical state of heterogeneous flow and about to form a sedimentary bed: (1) Formula (1) is applicable to pipe diameter: D ≤100mm, particle size is less than 2.5mm, particle volume fraction ≤50%; (2) Formula (2) is applicable to pipe diameter: 50mm≤D≤500mm and particle size less than 5.25mm.

[0029] in, is the critical flow velocity; is the measured particle volume fraction; is the average particle size; is the acceleration due to gravity; is the pipe diameter; is the specific gravity of particles to water; Drag coefficient; is the final settling velocity of the particles, that is, the velocity of the particles settling freely at a uniform speed in water, which can be determined by preliminary tests or calculated by Stokes' formula: ,in is the particle density, is the water density.

[0030] Step 1.2: Select the corresponding formula in 1.1 according to the geometric and physical parameters of the slurry and the pipeline to calculate the critical flow rate of the slurry. The slurry density and slurry flow rate have been measured, and the geometric and physical parameters of the pipeline and particles are known. The measured particle volume fraction can be obtained from the slurry density and the geometric and physical parameters of the particles.

[0031] Step 1.3: According to the critical flow rate of the slurry obtained in step 1.2; The actual flow rate By calculating the relative error, we can get the corresponding macroscopic evaluation index of mud flow performance: If the index is greater than 0 and less than 10%, it means that the mud is in a non-settling state, and the flow rate is not too high, the mud has good flow performance and strong slag carrying capacity; if the index is less than 0 and greater than -10%, it means that the flow rate is in a reasonable range, the mud has good flow performance and strong slag carrying capacity, but there is a small probability of sedimentation risk.

[0032] Furthermore, if there are other research needs, corresponding sensors such as pressure gauges, concentration meters, etc. can be installed in the mud transmission pipe.

[0033] The microscopic analysis module separates the particle phase from the fluid phase and calculates the particle concentration distribution according to the image data transmitted by the PIV-based visualization device through image noise reduction, image enhancement and image threshold segmentation. The specific steps are as follows: Step 2.1: Remove the noise points in the image caused by photoelectric interference during the shooting process through filtering to enhance the contrast of the image; Step 2.2: Separate the particle phase from the fluid phase in the image by image threshold segmentation technology for subsequent concentration calculation; Step 2.3: Referring to the grid division technology in computational fluid dynamics, the image is divided into rectangular grids, and the boundary layer (i.e., the area near the bottom, within about 0.2 times the pipe diameter) is grid-encrypted; Step 2.4: Traverse all grids, calculate the concentration of different grids according to the results of step 2.2, and obtain the concentration distribution of particles; Step 2.5: If the ratio of the concentration distribution of particles in the boundary layer (i.e., within about 0.2 times the pipe diameter near the bottom of the pipeline) calculated in step 2.4 to the initial concentration of the slurry from the data receiving module is greater than 2, and the concentration distribution of particles in the entire pipeline shows an obvious trend of decreasing at the top and increasing at the bottom along the height, it means that the mud flow rate is too low, the flow performance is poor, and the slag carrying capacity is weak; if the ratio of the concentration distribution of particles in the boundary layer area calculated in step 2.4 to the initial concentration of the slurry from the data receiving module is less than 2, and the concentration distribution of particles in the entire pipeline shows an obvious trend of decreasing at the top and increasing at the bottom along the height, it means that the mud flow rate is moderate, the flow performance is good, and the slag carrying capacity is good; if the concentration distribution of particles in the entire pipeline calculated in step 2.4 is relatively uniform along the height and close to 1, it means that the flow rate is too fast, the flow performance is excessive, and the slag carrying capacity is too strong.

[0034] The control system includes a frequency conversion cabinet 8 and a computer 7. The frequency conversion cabinet includes a power converter, a power switch, and a start / pause button. The power converter converts the 220V standard voltage into a 380V voltage suitable for motor equipment, providing a stable and reliable power supply. The power switch controls the power supply to ensure safety. The motor equipment includes an eddy current pump 3, a stirring motor in a mud tank, and a rotating motor 4-1, which are connected to the frequency conversion cabinet 8 through a cable and are controlled separately by their respective controllers under normal circumstances. The start / pause button can start / pause the motor with one button, which can cope with emergencies during the test and ensure the safety of the test. The frequency conversion cabinet can be directly connected to a computer, and programming can be performed using programming software to set the power of the eddy current pump 3 and the rotating motor 4-1 in the soil cutting simulation system.

[0035] The mud flow test system for the slurry inlet / discharge pipe of the soft soil slurry balance shield described above can simulate the working conditions in various slurry discharge pipes, including single strata and composite strata, by configuring soil samples with different particle gradations, different geometries and physical properties according to geological survey reports; the flow velocity of the slurry in the test system can be changed by changing the power of the vortex pump, and the movement state and distribution of particles in the pipe at different flow velocities can be observed through a transparent mud circulation pipeline and a PIV-based visualization device.

[0036] When conducting the test on the slurry flow test system for the slurry inlet / outlet pipe of the slurry balance shield in the soft soil layer, the specific operation steps are as follows: Step 1: Install and debug the mud flow test system of the slurry inlet / outlet pipe of the slurry balance shield in soft soil.

[0037] according to Figure 1 Install the test system. Specifically: The installation location of the monitoring equipment is determined according to the monitoring variable requirements. A density meter 6-1 is provided on the acrylic straight pipe near the mud tank inlet, and a flow meter 6-2 is provided at the connection between the acrylic straight pipe and the acrylic elbow near the mud tank inlet.

[0038] The high-speed camera 5-1 and the acrylic pipe it records are located at the same height, the laser emitted by the solid laser 5-2 is perpendicular to the plane where the pipe and the high-speed camera 5-1 are located, and the laser plane contains the central axis of the acrylic pipe section.

[0039] Before the test, the rotation speed of the rotary motor 4-1 in the soil cutting simulation system 4 is calibrated by the model similarity ratio, so that the speed of the cutting disc 4-4 cutting the soil matches the corresponding excavation conditions. And according to the geological survey report, soil samples are prepared in the soil sample bin 4-2 according to the particle distribution, cohesion and internal friction angle of the soil.

[0040] Step 2: Add clean water of the mass required for the test into the mud tank 2, turn on the stirring motor therein, and then add the required mass of bentonite particles to prepare the mud.

[0041] Step 3: Make mud and fill the pipe with mud. Specifically, after the bentonite particles are stirred evenly, add the tracer particles 5-3 and continue to stir evenly; then, open the outlet valve in the mud tank 2, turn on the vortex pump 3, and gradually increase the power of the vortex pump through the computer so that the data shown by the flow meter is the maximum flow rate of 4m / s under the test condition, so as to avoid the bentonite particles from settling prematurely due to too low flow rate; keep the mud flowing for 3-5 cycles, remove the air in the pipe, and make the mud fill the pipe.

[0042] The mud starts from the mud tank 2, and under the drive of the vortex pump 3, passes through the rubber hose 1-4 connecting the mud tank and the vortex pump, and the rubber hose 1-4 connecting the vortex pump and the acrylic pipe, and then reaches the acrylic pipe formed by the acrylic straight pipe 1-1 and the acrylic curved pipe 1-2, and then returns to the mud tank 2 through the rubber hose 1-4 connecting the acrylic pipe and the mud tank, completing a circulation flow.

[0043] Step 4: Turn on the recording function of all sensors in the monitoring equipment; adjust the solid laser 5-2 so that the laser irradiates vertically into the plane where the acrylic pipe and the high-speed camera are located, and the incident plane contains the axis of the acrylic pipe. The tracer particles 5-3 are evenly distributed in the mud, move with the mud, and reflect light after being irradiated by the solid laser 5-2. Turn on the high-speed camera 5-1 in the PIV-based visualization device 5 to start recording the flow field.

[0044] Step 5: Test the critical flow rate of the slurry. Specifically, according to the design working conditions, the power of the vortex pump 3 is changed by the frequency converter in the control system, and the flow rate is observed by the flow meter. The flow rate is reduced with a tolerance of 0.2 m / s until the bentonite particles begin to settle in the high-speed camera 5-1. The flow rate at this time is the non-silting flow rate of the mud. Each time the flow rate is reduced, the mud should be kept flowing for at least 5 cycles.

[0045] Step 6: Maintain the flow rate at which bentonite particles begin to settle, control the rotating motor 4-1 in the soil cutting simulation system 4 to the pre-test calibrated power, so that the cutting disc 4-4 cuts the soil at a specified speed to form soil samples in the sample bin 4-2, and the cut soil samples naturally fall into the mud tank 2.

[0046] Step 7: Test the critical flow rate of the soil-containing slurry. Specifically, keep the flow rate constant, and increase the power of the vortex pump when a static bed of particles appears at the bottom of the pipeline, so that the flow rate gradually increases with a tolerance of 0.2m / s until the static bed of particles disappears. The flow rate at this time is the non-silting flow rate of the soil-containing slurry. Each increase in the flow rate should maintain at least 5 cycles of slurry flow; various indicators of the soil-containing slurry at different flow rates are transmitted to the computer by the monitoring equipment and the PIV-based visualization device 5, and the flow performance and slag carrying capacity of the soil-containing slurry at different flow rates are evaluated according to the analysis system.

[0047] Step 8: Shut down all motor equipment and monitoring instruments, and discharge and clean the waste pulp.

[0048] The test was repeated by replacing slurry and soft soil samples with different concentrations to simulate the flowability and slag carrying capacity of the slurry in the inlet / outlet pipes of the slurry balance shield in soft soil when excavating in different strata with different slurry concentrations.

[0049] The above description is only a description of the preferred embodiments of the present application, and is not intended to limit the scope of the present application. Any changes or modifications made by any person skilled in the art based on the above disclosed technical contents shall be deemed as equivalent effective embodiments and shall fall within the scope of protection of the technical solution of the present application.

Claims

1. A slurry flow test system for the slurry inlet / outlet pipeline of a slurry balance shield in soft soil, characterized in that: include: Mud circulation pipeline, monitoring equipment, soil cutting simulation system (4), PIV-based visualization device (5), analysis system and control system; The mud circulation pipeline comprises a mud tank (2), a vortex pump (3), and a mud transmission pipe, wherein: A mud tank (2), comprising a tank body and a stirring device, and used for storing and making mud; A mud transmission pipe, the input end and the output end of which are respectively connected to the outlet and the inlet of the mud tank; A vortex pump (3) is connected to the mud transmission pipe and is close to the outlet of the mud tank (2) and is used to push the mud so that the mud circulates in the mud transmission pipe; The monitoring equipment includes a plurality of sensors, which are arranged in the mud transmission pipe of the mud circulation pipeline and are connected to the analysis system signal; The soil cutting simulation system (4) is located above the mud tank (2) of the mud circulation pipeline, and the cut soil enters the mud tank (2) to simulate the shield excavation working condition; The PIV-based visualization device (5) is used to record in real time the visualized flow field of the mud flow in the mud transmission pipe of the mud circulation pipeline; The analysis system uses the data collected by the monitoring equipment for macroscopic analysis and uses the image data transmitted by the PIV-based visualization device for microscopic analysis; The control system is connected with the mud circulation pipeline and the soil cutting simulation system to realize power control.

2. A slurry flow test system for slurry inlet / outlet pipes of a slurry balance shield in soft soil as claimed in claim 1, characterized in that: In the mud circulation pipeline, the stirring device includes a stirring motor, and the stirring motor and the vortex pump are respectively connected to a control system through cables.

3. A slurry flow test system for slurry inlet / outlet pipes of a slurry balance shield in soft soil as claimed in claim 1, characterized in that: In the mud circulation pipeline, the mud transmission pipe includes a rubber hose (1-4) and an acrylic pipe, wherein: The acrylic pipe is the main transmission pipe; The rubber hose (1-4) is a connecting pipe, which is used to connect the vortex pump (3) between the outlet of the mud tank (2) and the inlet of the acrylic pipe, and to connect the outlet of the acrylic pipe to the inlet of the mud tank (2), so as to avoid vibration of the pipe caused by vibration of the mud tank (2) and the vortex pump (3).

4. A slurry flow test system for slurry inlet / outlet pipes of a slurry balance shield in soft soil as claimed in claim 1, characterized in that: The monitoring equipment: The sensor comprises a density meter (6-1) and a flow meter (6-2).

5. A slurry flow test system for slurry inlet / outlet pipes of a slurry balance shield in soft soil as claimed in claim 1, characterized in that: The soil cutting simulation system (4) comprises a rotating motor (4-1), a soil sample chamber (4-2) and a cutting disc (4-4); the upper end of the mud tank (1-5) is open, and the soil cutting simulation system 4 is located above the mud tank (1-5), wherein: The soil sample bin (4-2) is fixed separately and used to store soil samples to simulate the cut strata, and has openings at both the upper and lower ends; The rotating motor (4-1) is located above the soil sample chamber (4-2); the rotating shaft (4-3) of the rotating motor (4-1) passes through the openings at the upper and lower ends of the soil sample chamber (4-2) and is connected to the cutting disc (4-4) below the soil sample chamber (4-2); during cutting, the cutting disc (4-4) is driven upward and rotated by the rotating motor (4-1) to cut the soil in the soil sample chamber (4-2); after the soil is cut, it naturally falls into the mud tank (1-5); The rotating motor (4-1) is connected to a control system via a cable, and the control system controls the start and stop and the speed of the rotating motor.

6. A slurry flow test system for slurry inlet / outlet pipes of a slurry balance shield in soft soil as claimed in claim 3, characterized in that: The PIV-based visualization device (5) comprises a high-speed camera (5-1), a solid laser (5-2) and tracer particles (5-3), wherein: The tracer particles (5-3) are distributed in the mud in the mud circulation pipeline; The solid laser (5-2) is arranged above the acrylic pipe in the mud transmission pipe of the mud circulation pipeline, and the emitted laser is perpendicular to the plane where the acrylic pipe and the high-speed camera (5-1) are located, and is used to irradiate the tracer particles (5-3) in the mud in the acrylic pipe; The high-speed camera (5-1) is used to record image data of tracer particle distribution at different times; The image data recorded by the PIV-based visualization device is transmitted to the analysis system through a USB interface for the analysis system to perform data recording and microscopic evaluation of mud flow properties and slag carrying capacity.

7. A slurry flow test system for slurry inlet / outlet pipes of a slurry balance shield in soft soil as claimed in claim 1, characterized in that: The analysis system comprises a data receiving module, a macro analysis module and a micro analysis module, wherein: The data receiving module receives the sensor signal, converts the received sensor signal into corresponding physical quantities, and stores them in the computer. The physical quantities include density signal and flow rate signal, and are transmitted to the macro analysis module. The data receiving module also obtains the image data recorded by the PIV-based visualization device through the USB interface, and transmits it to the micro analysis module. The data receiving module also receives static macro indicators input in advance by the test personnel for use by the macro analysis module and the micro analysis module. The static macro indicators include but are not limited to pipeline diameter, particle grading, particle density, and initial slurry concentration. The initial slurry concentration is the initial particle volume fraction. The macro analysis module performs macro evaluation of mud flow performance and slag carrying capacity based on the obtained physical quantities and static macro indicators input in advance; The microscopic analysis module separates the particle phase from the fluid phase through image noise reduction, image enhancement and image threshold segmentation according to the image data transmitted by the PIV-based visualization device, calculates the particle concentration distribution, and performs a microscopic evaluation of the mud flow performance and slag carrying capacity.

8. A slurry flow test system for slurry inlet / outlet pipes of a slurry balance shield in soft soil as claimed in claim 7, characterized in that: The specific steps of the macro analysis module for macro evaluation of mud flow performance and slag carrying capacity include: Step 1.1: According to the physical quantities and static macroscopic indicators monitored by the monitoring equipment, the formation particle properties, pipeline diameter, and particle volume fraction are obtained, and the slurry flow rate calculation formula is selected when the slurry is in a critical state of heterogeneous flow and about to form a sedimentary bed: （1） Formula (1) is applicable to pipe diameter: D ≤100mm, particle size is less than 2.5mm, particle volume fraction ≤50%; （2） Formula (2) is applicable to pipe diameter: 50mm≤D≤500mm, particle size is less than 5.25mm; in, is the critical flow velocity; is the measured particle volume fraction; is the average particle size; is the acceleration due to gravity; is the pipe diameter; is the specific gravity of particles to water; Drag coefficient; is the final settling velocity of the particle, that is, the velocity of the particle when it settles freely at a uniform speed in water, which is determined by preliminary tests or calculated by Stokes' formula: ,in is the particle density, is the water density; Step 1.2: Select the corresponding formula in 1.1 according to the geometric and physical parameters of the slurry and the pipeline to calculate the critical velocity of the slurry, where the slurry density and slurry velocity have been measured, the geometric and physical parameters of the pipeline and the particles are known, and the measured particle volume fraction is obtained from the slurry density and the geometric and physical parameters of the particles; Step 1.3: According to the critical flow rate of the slurry obtained in step 1.2; The actual flow rate The relative error is calculated to obtain the corresponding macroscopic evaluation index of mud flow performance: If the index is greater than 0 and less than 10%, it means that the mud is in a non-settling state, and the flow rate is not too high, the mud has good flow performance and strong slag carrying capacity; if the index is less than 0 and greater than -10%, it means that the flow rate is in a reasonable range, the mud has good flow performance and strong slag carrying capacity, but there is a small probability of sedimentation risk.

9. A slurry flow test system for slurry inlet / outlet pipes of a slurry balance shield in soft soil as claimed in claim 7, characterized in that: The specific steps of the microscopic analysis module for microscopic evaluation of mud flow performance and slag carrying capacity include: Step 2.1: Remove the noise points in the image caused by photoelectric interference during the shooting process through filtering to enhance the contrast of the image; Step 2.2: Separate the particle phase from the fluid phase in the image by image threshold segmentation technology for subsequent concentration calculation; Step 2.3: Referring to the grid division technology in computational fluid dynamics, the image is divided into rectangular grids, and the boundary layer grid is encrypted; Step 2.4: Traverse all grids, calculate the concentration of different grids according to the results of step 2.2, and obtain the concentration distribution of particles; Step 2.5: If the ratio of the concentration distribution of particles in the boundary layer area calculated in step 2.4 to the initial concentration of the slurry from the data receiving module is greater than 2, and the concentration distribution of particles in the entire pipeline shows an obvious trend of decreasing at the top and increasing at the bottom along the height, it means that the mud flow rate is too low, the flow performance is poor, and the slag carrying capacity is weak; if the ratio of the concentration distribution of particles in the boundary layer area calculated in step 2.4 to the initial concentration of the slurry from the data receiving module is less than 2, and the concentration distribution of particles in the entire pipeline shows an obvious trend of decreasing at the top and increasing at the bottom along the height, it means that the mud flow rate is moderate, the flow performance is good, and the slag carrying capacity is good; if the concentration distribution of particles in the entire pipeline calculated in step 2.4 is relatively uniform along the height and close to 1, it means that the flow rate is too fast, the flow performance is excessive, and the slag carrying capacity is too strong.

10. A slurry flow test system for slurry inlet / outlet pipes of a slurry balance shield in soft soil as claimed in claim 5, characterized in that: The control system comprises a frequency conversion cabinet (7) and a computer (6), wherein: The frequency conversion cabinet (7) is connected to the computer (6) and is programmed using programming software to set the power of the vortex pump (3) in the mud circulation pipeline and the rotating motor (4-1) in the soil cutting simulation system.

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