Sandy soil reliquefaction characteristic test device and test method thereof

Abstract

The invention relates to the technical field of earthquake gravel testing, and discloses a sandy soil reliquefaction characteristic testing device and a testing method thereof.The sandy soil reliquefaction characteristic testing device comprises a vibration table, a box body, a compression assembly, a detection assembly, a development assembly and a computer unit; the box body is arranged above the vibration table, the box body is made of a transparent material, the box body is connected with the vibration table, and a saturated sand sample is arranged in the box body; the compression assembly is arranged in the box body, and the compression assembly is located above the saturated sand sample; the detection assembly is arranged in the box body and used for monitoring liquefaction of the saturated sand sample, and the detection assembly comprises a pore water pressure sensor arranged in the saturated sand sample; the developing assembly is arranged outside the box body; the computer unit is electrically connected with the detection assembly and the imaging assembly. According to the invention, through a technical closed loop of cyclic loading control-mesoscopic imaging-data synchronous analysis, full-period and multi-scale observation of the reliquefaction characteristic of the sandy soil under the action of repeated earthquakes is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of seismic sand and gravel testing, in particular to a test device for the characteristics of sand liquefaction and its testing method. Background Art

[0002] At present, the areas where earthquakes occur are widely distributed, and the occurrence of earthquakes cannot be effectively predicted in advance. When an earthquake occurs, strong ground motion will induce the liquefaction of underground sand, resulting in the loss of bearing capacity of the ground, posing a great safety hazard to the buildings built above, and even further expanding the disaster; in China, sandy soil strata are widely distributed, so studying the liquefaction characteristics of sandy soil strata plays an important role in earthquake resistance and disaster reduction.

[0003] Existing sand liquefaction testing devices are mostly designed for a single seismic event, and it is difficult to accurately reproduce the reciprocating liquefaction of sand after intermittent loading of multiple earthquakes, resulting in the inability to study the cumulative damage and re-liquefaction law of sand under repeated dynamic actions. Summary of the Invention

[0004] The purpose of the present invention is to provide a test device for the characteristics of sand re-liquefaction and its testing method, which can simulate the sand re-liquefaction phenomenon under repeated earthquake actions, obtain the mesoscopic images of sand particles, and study the influence of the long axis direction of sand particles on the characteristics of sand re-liquefaction under repeated earthquake actions.

[0005] To achieve the above purpose, the present invention provides a test device for the characteristics of sand re-liquefaction and its testing method, which includes a shaking table, a box body, a compression component, a detection component, an imaging component and a computer unit; the box body is arranged above the shaking table, the box body is made of transparent material and is connected to the shaking table, and a saturated sand sample is arranged inside the box body; the compression component is arranged inside the box body and is located above the saturated sand sample, and the saturated sand sample is prepared by the method of dropping sand in water; the detection component is arranged inside the box body for monitoring the liquefaction of the saturated sand sample, and the detection component includes a pore water pressure sensor arranged in the saturated sand sample; the imaging component is arranged outside the box body and is used to observe the sand particles of the saturated sand sample; the computer unit is electrically connected to the detection component and the imaging component respectively.

[0006] In one embodiment, a scale is arranged on the outer wall of the box body, and the number of scales is multiple. The multiple scales are arranged on the outer wall of the box body in the vertical direction, and the scale is used to measure the height of the saturated sand sample.

[0007] In one embodiment, the compression component includes a sieve mesh and a steel block. The sieve mesh is laid on the top of the saturated sand sample, the steel block is arranged above the sieve mesh, and the steel block cooperates with the sieve mesh to adjust the density of the saturated sand sample. A plurality of water passing holes for draining water are arranged on the steel block.

[0008] In one embodiment, the number of the pore water pressure sensors is at least four, and the four pore water pressure sensors are vertically spaced apart and arranged in the saturated sand sample.

[0009] In one embodiment, the detection component also includes a data acquisition instrument, which is arranged on the outside of the box. One end of the data acquisition instrument is electrically connected to the pore water pressure sensor, and the other end is electrically connected to the computer unit. The data acquisition instrument is used to interpret the electrical signal of the pore water pressure sensor and generate a digital signal to be transmitted to the computer unit.

[0010] In one embodiment, the imaging component includes a microscope and an industrial camera, the microscope is connected to the industrial camera, the industrial camera is connected to the computer unit away from the microscope, and the industrial camera is used to capture the microscopic image of sand particles magnified by the microscope.

[0011] In one embodiment, the imaging component further includes a fill light, which is disposed above the microscope and is used to fill light for the area of the microscope.

[0012] Based on the above-mentioned sand reliquefaction characteristic test device, the present invention also proposes a test method for testing the sand reliquefaction characteristics under repeated earthquakes, which includes Experiment 1. Experiment 1 includes the following steps:

[0013] Step S1: presetting the vibration time, amplitude, and frequency of the vibration table, and preparing a saturated sand sample inside the box, and arranging a pore water pressure sensor during the preparation process;

[0014] Step S2: Arrange the imaging assembly and capture the microscopic image of sand particles of the saturated sand sample at the pore water pressure sensor in the box, and record it as the first image group;

[0015] Step S3: Start the vibration table for the first time, and display the data of the pore water pressure sensor through the computer unit, which is recorded as KYSJ1. After the pressure of the pore water pressure sensor is completely dissipated, repeat step S2, and the imaging component again captures the microscopic image of the sand particles of the saturated sand sample after the first liquefaction, which is recorded as the second image group. The height of the saturated sand sample is read by the scale and recorded as H1.

[0016] Step S4: Start the vibration table for the second time, and display the pressure data of the pore water pressure sensor through the computer unit, and record it as KYSJ2.

[0017] In one embodiment, a second test is further included after the first test, and the second test includes the following steps:

[0018] Step 1: Preset the shaking table according to the vibration time, amplitude, and frequency of the shaking table in the aforementioned Step S1. Prepare a saturated sand sample again inside the box. During the preparation process, arrange pore water pressure sensors and place a compression assembly on top of the saturated sand sample to ensure that the height of the saturated sand sample reaches H1, and then remove the compression assembly.

[0019] Step 2: Arrange the imaging assembly and capture the mesoscopic images of the sand particles of the saturated sand sample at the pore water pressure sensor inside the box, and record them as the third set of images.

[0020] Step 3: Start the shaking table for the third time, and the computer unit displays the data of the pore water pressure sensor, which is recorded as KYSJ3.

[0021] In one embodiment, import the first set of images, the second set of images, and the third set of images into the graphic segmentation software to obtain the grayscale images of the sand particle boundaries, and use digital image processing software to extract the particle boundary maps, obtain the centroids of the sand particles, draw line segments connecting the sand particle boundaries in the clockwise direction from 0 to 359 degrees through the centroids, and take the longest line segment as the major axis of the sand particle and record its angle. Record the rose diagrams of the major axis directions of the sand particles in the first set of images, the second set of images, and the third set of images as MGHT1, MGHT2, and MGHT3 respectively.

[0022] Compared with the prior art, the beneficial effects of the sand re-liquefaction characteristic test device and its test method in the embodiments of the present invention are as follows: The shaking table provides controllable vibration excitation to simulate seismic waves with different intensities, frequencies, and durations. The box is made of transparent material, which is convenient for observing the saturated sand sample inside the box. The pore water pressure sensors are buried at different depths of the saturated sand sample to monitor the change of pore water pressure in real time. The imaging assembly is close to the transparent box to capture the mesoscopic images of the sand particles. The computer unit processes the pore water pressure and vibration response data in real time, processes the mesoscopic images, and analyzes the distribution and orientation change of the major axis directions of the sand particles. By starting the shaking table twice, that is, simulating the main shock + aftershock, combined with the waiting period for the dissipation of pore water pressure, the "vibration - intermittent - re-vibration" characteristics of the earthquake sequence are truly restored. The present invention realizes the full-cycle and multi-scale observation of the sand re-liquefaction characteristics under repeated earthquake actions through the technical closed-loop of cyclic loading control - mesoscopic imaging - data synchronous analysis, providing a high-precision test benchmark for geotechnical earthquake engineering. Description of the Drawings

[0023] Figure 1 is the overall structural schematic diagram of the sand re-liquefaction characteristic test device in the embodiments of the present invention.

[0024] Figure 2 is the front view of the box in the sand re-liquefaction characteristic test device in the embodiments of the present invention.

[0025] In the figure, 1 is a shaking table; 2 is a box body; 21 is a saturated sand sample; 22 is a scale; 3 is a compression assembly; 31 is a sieve; 32 is a steel block; 4 is a detection assembly; 41 is a pore water pressure sensor; 42 is a data acquisition instrument; 5 is an imaging assembly; 51 is a microscope; 52 is an industrial camera; 53 is a fill light; 6 is a computer unit. Detailed implementation manners

[0026] The following combines the accompanying drawings and embodiments to further describe in detail the specific implementation manners of the present invention. The following embodiments are used to illustrate the present invention, but are not used to limit the scope of the present invention.

[0027] In the description of the present invention, it should be understood that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element. The terms "mounted", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0028] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "height", "upper", "lower", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. in the present invention is based on the orientation or positional relationship shown in the accompanying drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the present invention.

[0029] In the description of the present invention, it should be understood that the terms "first" and "second" in the present invention are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features.

[0030] As Figures 1 to 2As shown in the figure, the embodiment of the present invention preferably provides a test device for the characteristics of sand re-liquefaction and its testing method, which includes a shaking table 1, a box body 2, a compression assembly 3, a detection assembly 4, an imaging assembly 5 and a computer unit 6; the box body 2 is arranged above the shaking table 1, the box body 2 is made of transparent material, and the box body 2 is connected to the shaking table 1. A saturated sand sample 21 is arranged inside the box body 2; the compression assembly 3 is arranged inside the box body 2 and is located above the saturated sand sample 21. The saturated sand sample 21 is prepared by the underwater sand falling method; the detection assembly 4 is arranged inside the box body 2 for monitoring the liquefaction of the saturated sand sample 21. The detection assembly 4 includes a pore water pressure sensor 41 arranged in the saturated sand sample 21; the imaging assembly 5 is arranged outside the box body 2, and the imaging assembly 5 observes the sand particles of the saturated sand sample 21; the computer unit 6 is electrically connected to the detection assembly 4 and the imaging assembly 5 respectively.

[0031] Based on the above technical features, in the embodiment of the present invention, the shaking table 1 provides controllable vibration excitation to simulate seismic waves with different intensities, frequencies and durations. The box body 2 is made of transparent material, which is convenient for observing the saturated sand sample 21 inside the box body 2; the pore water pressure sensor 41 is buried at different depths of the saturated sand sample 21 to monitor the change of pore water pressure in real time; the imaging assembly 5 is close to the transparent box body 2 to capture the mesoscopic images of sand particles; the computer unit 6 processes the pore water pressure and vibration response data in real time, and analyzes the distribution and orientation change of the long axis direction of sand particles; by restarting the shaking table 1 twice, that is, simulating the main shock + aftershock, combined with the pore water pressure dissipation waiting period, the "vibration-intermittence-re-vibration" characteristics of the earthquake sequence are truly restored. The present invention realizes the full-cycle and multi-scale observation of the characteristics of sand re-liquefaction under repeated seismic actions through the technical closed-loop of cyclic loading control-mesoscopic imaging-data synchronous analysis, providing a high-precision test benchmark for geotechnical earthquake engineering.

[0032] As some embodiments of the present invention, as Figures 1 to 2 shown, a scale 22 is arranged on the outer wall of the box body 2. The number of scales 22 is multiple, and the multiple scales 22 are arranged on the outer wall of the box body 2 in the vertical direction. The scale 22 is used to measure the height of the saturated sand sample 21. The initial filling height of the saturated sand sample 21 and the height change during the test are directly read through the scale 22 to obtain the dry density of the saturated sand sample 21, which is convenient for the application of subsequent test methods.

[0033] As some embodiments of the present invention, as Figure 1As shown, the compression assembly 3 includes a screen 31 and a steel block 32. The screen 31 is laid on the top of the saturated sand sample 21, and the steel block 32 is set above the screen 31. The steel block 32 cooperates with the screen 31 to adjust the density of the saturated sand sample 21. The steel block 32 is provided with a plurality of water holes for drainage. Through the provision of the screen 31, the pressure applied by the steel block 32 can be evenly distributed, avoiding local stress concentration that causes damage to the sand structure, blocking the upward movement of sand particles, and preventing the sample layer from directly contacting the steel block 32 and hindering drainage. As a permeable layer, it allows pore water to be discharged through the screen 31, maintaining the hydraulic connectivity of the sample layer. The steel block 32 applies vertical pressure through its own weight to simulate the effective stress under different burial depth conditions, and the steel block 32 is provided with water holes to ensure that the drainage path of the saturated sand sample 21 is unobstructed.

[0034] As some embodiments of the present invention, Figures 1 to 2 As shown, there are at least four pore water pressure sensors 41, and the four pore water pressure sensors 41 are spaced vertically within the saturated sand sample 21. The four pore water pressure sensors 41, spaced vertically, can fully capture the pore pressure evolution of the saturated sand sample 21 under earthquake action, providing key data support for liquefaction mechanism research, engineering parameter optimization, and numerical model calibration.

[0035] As some embodiments of the present invention, Figures 1 to 2 As shown, the detection assembly 4 also includes a data acquisition device 42, which is disposed outside the housing 2. One end of the data acquisition device 42 is electrically connected to the pore water pressure sensor 41, and the other end is electrically connected to the computer unit 6. The data acquisition device 42 is used to interpret the electrical signal from the pore water pressure sensor 41 and generate a digital signal for transmission to the computer unit 6. The data acquisition device 42 amplifies, filters, and performs analog-to-digital conversion on the weak electrical signal output by the pore water pressure sensor 41 to generate a digital signal that can be recognized by the computer unit 6. The data acquisition device 42 also records and displays the relevant data on the computer unit 6 to facilitate subsequent testing.

[0036] As some embodiments of the present invention, Figure 1 As shown, the imaging assembly 5 includes a microscope 51 and an industrial camera 52. One end of the microscope 51 is connected to the industrial camera 52, which is connected to the computer unit 6 away from the microscope 51. The industrial camera 52 is used to capture the microscopic image of the sand particles magnified by the microscope 51. Through the arrangement of the microscope 51 and the industrial camera 52, the microscope 51 can display the state of the saturated sand sample 21 in a microscopic state, and the industrial camera 52 with high-resolution imaging can capture the microscopic image of the sand particles magnified by the microscope 51, effectively realizing the dynamic observation and quantitative characterization of the sand microstructure.

[0037] As some embodiments of the present invention,Figure 1 As shown, the imaging component 5 further includes a fill light 53. The fill light 53 is arranged above the microscope 51 and is used to provide supplementary lighting for the area of the microscope 51. During the vibration table 1 test, under low light conditions, the fill light 53 provides auxiliary lighting, reducing the camera ISO to below 100 and reducing the noise by 60%, effectively ensuring that the industrial camera 52 can capture the mesoscopic images of sand particles.

[0038] As some embodiments of the present invention, a testing method is also provided for testing the characteristics of sand re-liquefaction under repeated earthquake actions. It includes Test 1, and Test 1 includes the following steps:

[0039] Step S1: Preset the vibration time, amplitude, and frequency of the vibration table 1, and prepare a saturated sand sample 21 inside the box body 2. During the preparation process, pore water pressure sensors 41 are arranged.

[0040] Step S2: Arrange the imaging component 5, and capture the mesoscopic images of the sand particles of the saturated sand sample 21 at the pore water pressure sensor 41 inside the box body 2, and record them as the first set of images.

[0041] Step S3: Start the vibration table 1 for the first time, and display the data of the pore water pressure sensor 41 through the computer unit 6, and record it as KYSJ1. After the pressure of the pore water pressure sensor 41 is completely dissipated, repeat Step S2. The imaging component 5 captures the mesoscopic images of the sand particles of the saturated sand sample 21 after the first liquefaction again, and records them as the second set of images, and read the height of the saturated sand sample through the scale 22 and record it as H1.

[0042] Step S4: Start the vibration table 1 for the second time, and display the pressure data of the pore water pressure sensor 41 through the computer unit 6, and record it as KYSJ2.

[0043] As some embodiments of the present invention, it also includes Test 2 executed after Test 1. Test 2 includes the following steps:

[0044] Step 1: Preset the vibration table 1 according to the vibration time, amplitude, and frequency of the vibration table 1 in Step S1. Prepare a saturated sand sample 21 inside the box body 2 again. During the preparation process, pore water pressure sensors 41 are arranged, and a compression component 3 is placed on the top of the saturated sand sample 21 to ensure that the height of the saturated sand sample 21 reaches H1, and then take out the compression component 3.

[0045] Step 2: Arrange the imaging component 5, and capture the mesoscopic images of the sand particles of the saturated sand sample 21 at the pore water pressure sensor 41 inside the box body 2, and record them as the third set of images.

[0046] Step 3: The shaking table 1 is started for the third time, and the computer unit 6 displays the data of the pore water pressure sensor 41, which is recorded as KYSJ3. Experiment 2 simulates the seismic environment again, and a saturated sand sample 21 with the same dry density as that after the main shock of Experiment 1 is prepared, which proves from the side that the easier re-liquefaction of sand is not caused by the increase in density, but by the change in the long-axis arrangement of sand particles inside the sample after experiencing initial liquefaction.

[0047] In one embodiment, the first image group, the second image group, and the third image group are imported into the graphic segmentation software to obtain the grayscale image of the sand particle boundary, and the particle boundary map is extracted by using digital image processing software. The centroid of the sand particles is obtained, and line segments connecting the sand particle boundary in the clockwise direction of 0, 1, 2, 4, 5 - 359 degrees are drawn through the centroid. The longest line segment is taken as the long axis of the sand particle, and its angle is recorded. The rose diagrams of the long-axis directions of the sand particles in the first image group, the second image group, and the third image group are recorded as MGHT1, MGHT2, and MGHT3 in sequence.

[0048] Furthermore, the present invention can verify whether the second vibration liquefaction (re-liquefaction) of the saturated sand sample 21 under the simulated repeated seismic action is easier than the first vibration liquefaction (initial liquefaction) by comparing the rising rates of KYSJ1 and KYSJ2.

[0049] By comparing KYSJ2 and KYSJ3, it can be obtained that the dry density of the saturated sand sample 21 is the same, the rising rate of KYSJ2 is greater than that of KYSJ3, and the saturated sand sample 21 is more likely to liquefy. This shows that the saturated sand sample 21 is more likely to liquefy during re-liquefaction after initial liquefaction and an increase in dry density may be due to the directional change in the arrangement of sand particles.

[0050] By comparing MGHT1 and MGHT2, the dominant direction of the arrangement of the sand particles MGHT2 in the saturated sand sample 21 after initial liquefaction can be preliminarily obtained. Under this dominant arrangement direction, the saturated sand sample 21 is more likely to re-liquefy. However, since the dry densities of the saturated sand samples 21 where MGHT1 and MGHT2 are located are different, it cannot be determined that the easier re-liquefaction of the saturated sand sample 21 is caused by the directional arrangement of sand particles.

[0051] By comparing MGHT2 and MGHT3, since the dry densities of the saturated sand samples 21 where MGHT2 and MGHT3 are located are the same, it can be further determined that the easier re-liquefaction of the saturated sand sample 21 is due to the dominant direction of the arrangement of the sand particles MGHT2 generated by initial liquefaction. Thus, the influence of the long-axis direction of sand particles on the re-liquefaction characteristics of sand under repeated seismic action is obtained.

[0052] In summary, compared with the prior art, the sand re-liquefaction characteristic test device and its test method provided by the embodiments of the present invention have the following beneficial effects: The shaking table 1 provides controllable vibration excitation to simulate seismic waves with different intensities, frequencies and durations. The box body 2 is made of transparent material, facilitating the observation of the saturated sand sample 21 inside the box body 2. The pore water pressure sensor 41 is buried at different depths of the saturated sand sample 21 to monitor the change of pore water pressure in real time. The imaging component 5 is close to the transparent box body 2 to capture the mesoscopic images of sand particles. The computer unit 6 processes the pore water pressure and vibration response data in real time, and analyzes the distribution and orientation change of the long axis direction of sand particles. By restarting the shaking table 1, that is, simulating the main shock + aftershock, combined with the waiting period for pore water pressure dissipation, the "vibration-intermittence-re-vibration" characteristics of the earthquake sequence are truly restored. Through the technical closed-loop of cyclic loading control-mesoscopic imaging-data synchronous analysis, the present invention realizes the full-cycle and multi-scale observation of the sand re-liquefaction characteristics under repeated seismic actions, providing a high-precision test benchmark for geotechnical earthquake engineering.

[0053] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and substitutions can be made, and these improvements and substitutions should also be regarded as the protection scope of the present invention.

Claims

1. An experimental device for the characteristics of sand re-liquefaction, characterized in that Including: A shaking table (1), a box body (2), a compression assembly (3), a detection assembly (4), an imaging assembly (5) and a computer unit (6); The box body (2) is arranged above the shaking table (1). The box body (2) is made of transparent material and is connected to the shaking table (1). A saturated sand sample (21) is arranged inside the box body (2); The compression assembly (3) is arranged inside the box body (2) and is located above the saturated sand sample (21). The saturated sand sample (21) is prepared by the underwater sand dropping method; The detection assembly (4) is arranged inside the box body (2) for monitoring the liquefaction of the saturated sand sample (21). The detection assembly (4) includes a pore water pressure sensor (41) arranged in the saturated sand sample (21); The imaging assembly (5) is arranged outside the box body (2) and is used for observing the sand particles of the saturated sand sample (21); The computer unit (6) is electrically connected to the detection assembly (4) and the imaging assembly (5) respectively.

2. The sand re-liquefaction characteristic test device according to claim 1, characterized in that A scale (22) is arranged on the outer wall of the box body (2). The number of the scales (22) is multiple. The multiple scales (22) are arranged on the outer wall of the box body (2) in the vertical direction. The scale (22) is used for measuring the height of the saturated sand sample (21).

3. The sand re-liquefaction characteristic test device according to claim 1, wherein, The compression assembly (3) includes a screen (31) and a steel block (32). The screen (31) is laid on the top of the saturated sand sample (21). The steel block (32) is arranged above the screen (31). The steel block (32) is matched with the screen (31) for adjusting the density of the saturated sand sample (21). A plurality of water passing holes for draining water are arranged on the steel block (32).

4. The experimental device for sand re-liquefaction characteristics according to claim 1, wherein The number of the pore water pressure sensors (41) is at least four, and the four pore water pressure sensors (41) are arranged at intervals in the vertical direction in the saturated sand sample (21).

5. The sand re-liquefaction characteristic test device according to claim 1, wherein The detection assembly (4) further includes a data collector (42). The data collector (42) is arranged outside the box body (2). One end of the data collector (42) is electrically connected to the pore water pressure sensor (41), and the other end is electrically connected to the computer unit (6). The data collector (42) is used for interpreting the electrical signal of the pore water pressure sensor (41) and generating a digital signal to be transmitted to the computer unit (6).

6. The test device for the characteristics of sand re-liquefaction according to claim 1, wherein The imaging assembly (5) includes a microscope (51) and an industrial camera (52). The microscope (51) is connected to the industrial camera (52). The industrial camera (52) faces away from the microscope (51) and is connected to the computer unit (6). The industrial camera (52) is used for capturing the microscopic image of the sand particles magnified by the microscope (51).

7. The sand re-liquefaction characteristic test device according to claim 6, characterized in that, The imaging component (5) further includes a fill light (53). The fill light (53) is disposed above the microscope (51), and the fill light (53) is used to provide supplementary lighting for the area of the microscope (51).

8. A testing method, characterized in that, Adopt the sand re-liquefaction characteristic test device according to any one of claims 1-7, which includes Test 1. The Test 1 includes the following steps: Step S1: Preset the vibration time, amplitude and frequency of the shaking table (1), and prepare a saturated sand sample (21) inside the box body (2). During the preparation process, arrange a pore water pressure sensor (41). Step S2: Arrange the imaging component (5), and capture the mesoscopic image of the sand particles of the saturated sand sample (21) at the pore water pressure sensor (41) inside the box body (2), and record it as the first set of images. Step S3: Start the shaking table (1) for the first time, and display the data of the pore water pressure sensor (41) through the computer unit (6), and record it as KYSJ1. After the pressure of the pore water pressure sensor (41) is completely dissipated, repeat Step S2. The imaging component (5) captures the mesoscopic image of the sand particles of the saturated sand sample (21) after the first liquefaction again, and records it as the second set of images. And read the height of the saturated sand sample through the scale (22) and record it as H1. Step S4: Start the shaking table (1) for the second time, and display the pressure data of the pore water pressure sensor (41) through the computer unit (6), and record it as KYSJ2.

9. The test method according to claim 8, wherein It further includes Test 2 executed after the Test 1. The Test 2 includes the following steps: Step 1: Preset the shaking table (1) according to the vibration time, amplitude and frequency of the shaking table (1) in Step S1. Prepare a saturated sand sample (21) again inside the box body (2). During the preparation process, arrange a pore water pressure sensor (41), and place a compression component (3) on the top of the saturated sand sample (21) to ensure that the height of the saturated sand sample (21) reaches H1. Take out the compression component (3). Step 2: Arrange the imaging component (5), and capture the mesoscopic image of the sand particles of the saturated sand sample (21) at the pore water pressure sensor (41) inside the box body (2), and record it as the third set of images. Step 3: Start the shaking table (1) for the third time, and the computer unit (6) displays the data of the pore water pressure sensor (41), and records it as KYSJ3.

10. The test method according to claim 9, characterized in that, Import the first set of images, the second set of images and the third set of images into the graphic segmentation software to obtain the gray-scale image of the sand particle boundary, and use digital image processing software to extract the particle boundary map, obtain the centroid of the sand particles, and draw line segments connecting the sand particle boundaries in the clockwise direction of 0, 1, 2, 4, 5-359 degrees through the centroid. Take the longest line segment as the major axis of the sand particle, record its angle, and record the rose diagrams of the major axis directions of the sand particles in the first set of images, the second set of images and the third set of images as MGHT1, MGHT2 and MGHT3 respectively.

Images