1. A microscopic test method of a sandy soil structure is characterized in that an adopted test device comprises a counter-force mechanism (1), a static force loading mechanism (2), a model stacking mechanism (3), a data acquisition system (4) and a shooting system (5); the device comprises a counter-force mechanism (1) and a data acquisition system, wherein the counter-force mechanism (1) comprises a counter-force cross beam (6), two side slideways (7), two side lifting ropes (8) and a cross beam height adjusting controller (9), the static loading mechanism (2) comprises a motor (10), a speed reducer (11), a lifter (12) and a loading plate (13), the model stacking mechanism (3) comprises a sand and soil particle simulation material (14), a model frame (15) and a placing box (16), the data acquisition system (4) comprises a pressure sensor (17) and a data acquisition instrument (18), and the shooting system (5) comprises a square illumination plate (20) and a camera (21) capable of continuously shooting;

the reaction beam (6) comprises a beam (22) and a connecting plate (23), two ends of the beam (22) and one end of the connecting plate (23) are provided with small screw holes (24), the other end of the connecting plate (23) is provided with a large screw hole (25), the beam (22) is connected with the connecting plate (23) through the small screw holes (24), the connecting plate (23) is fixed on the model frame (15) through the large screw hole (25), and a plurality of holes (26) are formed in the beam (22);

the two-side slide ways (7) comprise slide way plates (27) and slide way blocks (28), the slide way plates (27) are fixed on the model frame (15), the slide way blocks (28) are connected with the two ends of the cross beam (22) by using super glue, and the slide way blocks (28) can move up and down in the slide way plates (27) so as to drive the cross beam (22) to adjust the up-and-down position;

the cross beam height adjusting controller (9) is fixed on the outer side wall of the model frame (15), the lifting ropes (8) on the two sides are wound on the cross beam height adjusting controller (9) through a pulley (29) on the upper part of the model frame (15), the two ends of the cross beam (22) are suspended on the lifting ropes (8) on the two sides, and the height of the cross beam (22) is changed by rotating a handle (30) of the cross beam height adjusting controller (9);

the motor (10), the speed reducer (11) and the lifter (12) are connected through a rotating shaft (31), the speed reducer (11) and the lifter (12) are fixed on the cross beam (22) through screws I (32), and the speed reducer (11) is used for changing the rotating speed of the rotating shaft (31) and further controlling the lifting speed of the lifter (12);

a lifting rod (33) in the lifter (12) penetrates through the cross beam (22) through a hole (26) formed in the cross beam (22), a flange (34) is arranged at the bottom of the lifting rod (33), the flange (34) is connected with the pressure sensor (17) through a screw II (35), the loading plate (13) is connected with the pressure sensor (17) through strong glue, and the longitudinal axes of the lifting rod (33), the pressure sensor (17) and the loading plate (13) are located at the same position;

the sandy soil particle simulation material (14) is a cylindrical aluminum bar, the length of the aluminum bar is 6-10cm, and the diameter of the aluminum bar is 0.15cm-0.6 cm;

the model frame (15) is used for piling up sandy soil particle simulation materials (14), two sides of the bottom of the model frame (15) are provided with fixing frames (36) for reinforcing the model frame (15) and ensuring the overall stability of the model, and the model frame (15) is provided with a plurality of rows of screw holes (37) for fixing connecting plates (23) at two ends of the reaction cross beam (6);

the test operation steps are as follows:

1) the motor (10), the speed reducer (11) and the lifter (12) are connected, and the lifting speed of the lifting rod (33) is adjusted to be 1mm/min through the speed reducer (11);

2) the cross beam (22) is adjusted to a height position 80cm away from the bottom of the model frame (15) through a cross beam height adjusting controller (9), and the cross beam (22) is fixed on the model frame (15) through a connecting plate (23);

3) selecting the particle grading of each sandy soil particle simulation material: selecting fractal gradation meeting the requirement that the mass fractal dimension D is 1.5 as particle gradation; the fractal gradation selection method comprises the following steps:

M(d<d_i)/M_T＝(d_i/d_max)^3-D (1)

wherein M is_TMeans the total mass of all diameter particles, d_maxMeans the diameter of the largest particle, d_iRefers to the diameter of a particle, M (d)<d_i) Means less than the diameter of the particle d_iThe sum of the particle mass of (a);

4) total mass of particles M_TThe following formula is adopted for calculation:

M_T＝ρBHL×(1-n) (2)

where ρ is the density of all particles, typically, ρ is 2700kg/m³B is the width of the foundation model, H is the height of the foundation model, L is the length of the particles, n is the porosity of the foundation model, generally taken to be 0.2;

5) calculating according to the formula (2) to obtain the total mass M of the particles in the foundation model_T＝155.5kg；

6) Selecting sand and soil particle simulation materials (14) with the diameters of 1.5mm, 2.0mm, 2.5mm, 3.0mm, 3.5mm, 4.0mm, 4.5mm, 5.0mm, 5.5mm and 6.0mm respectively, and calculating according to the formula (1) to obtain the mass of particles with each diameter as follows: 26.5kg, 10.5kg, 11.7kg, 12.7kg, 13.6kg, 14.5kg, 15.3kg, 16.1kg, 16.8kg, 17.6 kg;

7) fully mixing the selected sandy soil particle simulation materials (14) and placing the materials in a placing box (16) for later use;

8) according to the size of the test simulation, the sand and soil particle simulation material (14) placed in the placing box (16) is placed on the model frame (15), in order to ensure that the front and back surfaces of the accumulation body of the sand and soil particle simulation material (14) are flat, a flat plate (38) with the same width as that of the model frame (15) is placed on the back side of the accumulation body of the sand and soil particle simulation material (14), and when the sand and soil particle simulation material (14) is placed, the back side of the sand and soil particle simulation material (14) is contacted with the flat plate (38) by pushing the sand and soil particle simulation material (14) from the front side, so that the flatness of the front and back side surfaces of the accumulation body of the sand and soil particle simulation material (14) is ensured;

9) when the sandy soil particle simulation material (14) is placed, the soil pressure sensor (40) is placed at a position where particle pressure needs to be monitored, when the vertical particle pressure is measured, the soil pressure sensor (40) is horizontally placed, and when the horizontal particle pressure is measured, the soil pressure sensor (40) is vertically placed;

10) after the sand and soil particle simulation material (14) is stacked, the pressure sensor (17) and the loading plate (13) are installed on the lifting rod (33), the static loading mechanism (2) is started, and when the loading plate (13) is about to contact the sand and soil particle simulation material (14), the static loading mechanism (2) is closed;

11) placing a displacement sensor (39) at a corresponding position of a sand particle simulation material (14) accumulation body, connecting plug wires in the displacement sensor (39), a pressure sensor (17) and a soil pressure sensor (40) with a data acquisition instrument (18), and automatically recording the numerical value of the sensors by using the data acquisition instrument (18);

12) placing a square lighting plate (20) and a camera (21) in front of a model frame (15) to enable the camera (21) to shoot the full view of a sand particle simulation material (14) accumulation body;

13) placing the whole test model in a cuboid light-proof curtain shed (19); turning on the square illuminating plate (20) and the camera (21), carrying out interval shooting, and recording the time when the camera (21) starts shooting;

14) starting the static loading mechanism (2) to load a sand particle simulation material (14) accumulation body, and simultaneously recording the initial loading time;

15) continuously applying a vertical load to a sand particle simulation material (14) accumulation body through a static loading mechanism (2), continuously shooting at intervals by a camera (21) in the loading process, and automatically recording the numerical value of a sensor by a data acquisition instrument (18) until the test is finished;

16) closing the static loading mechanism (2), the data acquisition instrument (18) and the camera (21);

17) processing the sensor data measured by the data acquisition instrument (18) to respectively obtain a relation curve of vertical displacement and vertical stress of the sand and soil particle simulation material (14) accumulation body and particle pressure distribution in the sand and soil particle simulation material (14) accumulation body;

18) and (3) introducing the pictures shot at intervals into PIV software for processing to obtain the displacement and the speed of each particle and the speed field and the displacement field of the whole accumulation body of the sand and soil particle simulation material (14), and analyzing the displacement field to obtain the damage form of the accumulation body of the sand and soil particle simulation material (14).

2. The sand structure mesoscopic test model as recited in claim 1, wherein said data acquisition system (4) further comprises a displacement sensor (39) and a soil pressure sensor (40).

Background

In geotechnical engineering, when structural stability of foundations, side slopes, retaining walls, embankments and the like constructed by granular materials such as sand (sand) and soil is researched, indoor model tests are usually required to be developed, wherein three-dimensional model tests are a main means for researching the structural stability of the geotechnical materials, however, the three-dimensional model tests are used for researching macroscopic expression forms of the geotechnical structures, the motion rules of granules in the structures cannot be known from a microscopic level, and the operation is complicated in most cases and certain labor force is required.

The patent CN201010182628 'contact surface shear test visualization device for interaction of soil and structure' only can realize visualization observation of a shear zone of the soil and the structure, and cannot carry out all-round observation on geotechnical engineering structures such as foundations, side slopes, retaining walls, embankments and the like.

In the prior patent CN201010142417, "a geotechnical model test system and a refinement test method based on macro and mesomechanics", refinement analysis of a test model can be realized only by means of simultaneously integrating geotechnical model tests, special mesoscopic image analysis techniques, complex continuous-discrete coupling numerical simulation and the like, and the test method has the disadvantages of various contents, complex operation and high requirements on testers. Since only a few qualified and advanced persons can master continuous-discrete coupling numerical simulation, the method has high requirements on test operation and analysts.

Disclosure of Invention

Therefore, the invention aims to provide a sand structure microscopic test method which is simple and quick to operate, and the technical solution of the invention is as follows:

a microscopic test method for a sandy soil structure is characterized in that an adopted test device comprises a counter-force mechanism, a static loading mechanism, a model stacking mechanism, a data acquisition system and a shooting system; the counter-force mechanism comprises a counter-force cross beam, two side slideways, two side lifting ropes and a cross beam height adjustment controller, the static loading mechanism comprises a motor, a speed reducer, a lifter and a loading plate, the model stacking mechanism comprises a sand particle simulation material, a model frame and a placing box, the data acquisition system comprises a pressure sensor and a data acquisition instrument, and the shooting system comprises a square illumination plate and a camera capable of continuously shooting.

The reaction beam comprises a beam and a connecting plate, wherein small screw holes are formed in the two ends of the beam and one end of the connecting plate, a large screw hole is formed in the other end of the connecting plate, the beam passes through the small screw holes and the connecting plate, the connecting plate is fixed on the model frame through the large screw holes, and a plurality of holes are formed in the beam.

The two-side slide comprises a slide plate and slide blocks, the slide plate is fixed on the model frame, the slide blocks are connected with two ends of the cross beam by using strong glue, and the slide blocks can move up and down in the slide plate so as to drive the cross beam to adjust the upper position and the lower position.

The cross beam height adjusting controller is fixed on the outer side wall of the model frame, the lifting ropes on the two sides are wound on the cross beam height adjusting controller through a pulley on the upper portion of the model frame, the two ends of the cross beam are suspended on the lifting ropes on the two sides, and the height of the cross beam is changed by rotating a handle of the cross beam height adjusting controller.

The motor, the speed reducer and the elevator are connected through the rotating shaft, the speed reducer and the elevator are fixed on the cross beam through the screws I, and the speed reducer is used for changing the rotating speed of the rotating shaft and further controlling the lifting speed of the elevator.

A lifting rod in the lifter penetrates through the cross beam through a hole formed in the cross beam, a flange is arranged at the bottom of the lifting rod and connected with a pressure sensor through a screw II, a loading plate is connected with the pressure sensor through strong glue, and the longitudinal axes of the lifting rod, the pressure sensor and the loading plate are located at the same position.

The sandy soil particle simulation material is a cylindrical aluminum bar, the length of the aluminum bar is 6-10cm, and the diameter of the aluminum bar is 0.15-0.6 cm.

The model frame is used for piling sandy soil particle simulation materials, and the bottom both sides of model frame are equipped with the mount for consolidate the model frame, guarantee the overall stability of model, are equipped with multirow screw hole on the model frame, are used for the connecting plate at fixed reaction beam both ends.

The test operation steps are as follows:

1) connecting a motor, a speed reducer and a lifter, and adjusting the lifting speed of a lifting rod to be 1mm/min through the speed reducer;

2) adjusting the cross beam to a height position 80cm away from the bottom of the model frame through a cross beam height adjusting controller, and fixing the cross beam on the model frame through a connecting plate;

3) selecting the particle grading of each sandy soil particle simulation material: and selecting fractal gradation meeting the requirement that the mass fractal dimension D is 1.5 as particle gradation. The fractal gradation selection method comprises the following steps:

M(d<d_i)/M_T＝(d_i/d_max)^3-D (1)

wherein M is_TMeans the total mass of all diameter particles, d_maxMeans the diameter of the largest particle, d_iRefers to the diameter of a particle, M (d)<d_i) Means less than the diameter of the particle d_iThe sum of the particle mass.

4) Total mass of particles M_TThe following formula is adopted for calculation:

M_T＝ρBHL×(1-n) (2)

where ρ is the density of all particles, typically, ρ is 2700kg/m³B is the width of the foundation model, H is the height of the foundation model, L is the length of the particles, n is the porosity of the foundation model, generally taken to be 0.2;

5) calculating according to the formula (2) to obtain the total mass M of the particles in the foundation model_T＝155.5kg；

6) Selecting sand and soil particle simulation materials with the diameters of 1.5mm, 2.0mm, 2.5mm, 3.0mm, 3.5mm, 4.0mm, 4.5mm, 5.0mm, 5.5mm and 6.0mm respectively, and calculating according to a formula (1) to obtain the mass of particles with each diameter as follows: 26.5kg, 10.5kg, 11.7kg, 12.7kg, 13.6kg, 14.5kg, 15.3kg, 16.1kg, 16.8kg, 17.6 kg;

7) fully mixing the selected sandy soil particle simulation materials, and placing the materials in a placing box for later use;

8) according to the size of the test simulation, the sandy soil particle simulation material placed in the placing box is placed on the model frame, in order to ensure that the front surface and the back surface of the sandy soil particle simulation material stacking body are flat, a flat plate with the same width as the model frame is placed on the back side of the sandy soil particle simulation material stacking body, and when the sandy soil particle simulation material is placed, the back side of the sandy soil particle simulation material is contacted with the flat plate by pushing the sandy soil particle simulation material from the front side, so that the flatness of the front side surface and the back side surface of the sandy soil particle simulation material stacking body is ensured;

9) when the sandy soil particle simulation material is placed, a soil pressure sensor is placed at a position where particle pressure needs to be monitored, when the vertical particle pressure is measured, the soil pressure sensor is horizontally placed, and when the horizontal particle pressure is measured, the soil pressure sensor is vertically placed;

10) after the sand and soil particle simulation material is stacked, the pressure sensor and the loading plate are installed on the lifting rod, the static force loading mechanism is started, and when the loading plate is about to contact the sand and soil particle simulation material, the static force loading mechanism is closed;

11) placing a displacement sensor at a corresponding position of a sand particle simulation material accumulation body, connecting plug wires in the displacement sensor, the pressure sensor and the soil pressure sensor with a data acquisition instrument, and automatically recording the numerical value of the sensor by using the data acquisition instrument;

12) placing the square illumination plate and the camera in front of the model frame to enable the camera to shoot the complete picture of the sandy soil particle simulation material stack;

13) placing the whole test model in a cuboid light-proof curtain shed; opening the square illuminating plate and the camera, carrying out interval shooting, and recording the time for starting shooting by the camera;

14) starting a static loading mechanism to load a sand particle simulation material accumulation body, and simultaneously recording the initial loading time;

15) continuously applying a vertical load to the sandy soil particle simulation material stacking body through the static loading mechanism, continuously shooting at intervals by the camera in the loading process, and automatically recording the numerical value of the sensor by the data acquisition instrument until the test is finished;

16) closing the static loading mechanism, the data acquisition instrument and the camera;

17) processing the sensor data measured by the data acquisition instrument to respectively obtain a relation curve of vertical displacement and vertical stress of the sand and soil particle simulation material accumulation body and particle pressure distribution in the sand and soil particle simulation material accumulation body;

18) and (3) introducing the pictures shot at intervals into PIV software for processing to obtain the displacement and the speed of each particle and the speed field and the displacement field of the whole sandy soil particle simulation material accumulation body, and analyzing the displacement field to obtain the damage form of the sandy soil particle simulation material accumulation body.

Further, the data acquisition system also comprises a displacement sensor and a soil pressure sensor.

According to the microscopic test method for the sand-soil structure, provided by the invention, the change of the particles in the structure can be visually observed without combining a numerical simulation means, the displacement of the particles in the sand-soil structure at each moment can be tested, the motion rule of the particles in the sand-soil structure and the damage mechanism of the sand-soil structure are further determined, and meanwhile, the macroscopic mechanical expression of a model can be obtained, so that reference is provided for the calculation and analysis of the structures such as loose particle foundations, side slopes, retaining walls, embankments and the like of sand and soil; the method is combined with the existing image processing technology PIV program, the displacement and the speed of each particle in the structure and the speed field, the displacement field and the damage form of the whole structure can be analyzed, the operation is simple and rapid, and the requirement on operators is low.

Drawings

FIG. 1 is a schematic view of a test apparatus used in the present invention;

FIG. 2 is a schematic view of a reaction beam of the present invention;

FIG. 3 is a schematic view of a two-sided skid of the present invention;

FIG. 4 is a schematic view of a lifter of the present invention;

FIG. 5 is a schematic view of a beam height adjustment control according to the present invention;

FIG. 6 is a schematic view of a sandy soil particle simulation material according to the present invention;

FIG. 7 is a schematic view of a data acquisition system of the present invention;

FIG. 8 is a schematic view of a model stand according to the present invention;

FIG. 9 is a schematic view of the holding box of the present invention;

FIG. 10 is a schematic view of the curtain shed of the present invention.

In the figure, 1, a reaction force mechanism; 2. a static loading mechanism; 3. a data acquisition system; 4. a model stacking mechanism; 5. a shooting system; 6. a counter-force beam; 7. two side slideways; 8. lifting ropes at two sides; 9. a beam height adjustment controller; 10. an electric motor; 11. a speed reducer; 12. an elevator; 13. a loading plate; 14. a sandy soil particle simulation material; 15. a model frame; 16. placing a box; 17. a pressure sensor; 18. a data acquisition instrument; 19. a curtain cloth shed; 20. a square lighting panel; 21. a camera; 22. a cross beam; 23. a connecting plate; 24. a small screw hole; 25. a large screw hole; 26. a hole; 27. a slide plate; 28. a slide way block; 29. a pulley; 30. a handle; 31. a rotating shaft; 32. a screw I; 33. a lifting rod; 34. a flange; 35. a screw II; 36. a fixed mount; 37. a screw hole; 38. a flat plate; 39. a displacement sensor; 40. a soil pressure sensor.

Detailed Description

The present invention is described in detail below with reference to the accompanying drawings.

A microscopic test method for a sandy soil structure adopts a test device which comprises a counter-force mechanism 1, a static force loading mechanism 2, a model stacking mechanism 3, a data acquisition system 4 and a shooting system 5; the counter-force mechanism 1 comprises a counter-force cross beam 6, two side slideways 7, two side lifting ropes 8 and a cross beam height adjusting controller 9, the static force loading mechanism 2 comprises a motor 10, a speed reducer 11, a lifter 12 and a loading plate 13, the model stacking mechanism 3 comprises a sand and soil particle simulation material 14, a model frame 15 and a placing box 16, the data acquisition system 4 comprises a pressure sensor 17 and a data acquisition instrument 18, and the shooting system 5 comprises a square illumination plate 20 and a camera 21 capable of continuously shooting.

The reaction beam 6 comprises a beam 22 and a connecting plate 23, wherein two ends of the beam 22 and one end of the connecting plate 23 are provided with small screw holes 24, the other end of the connecting plate 23 is provided with a large screw hole 25, the beam 22 passes through the small screw holes 24 to be connected with the connecting plate 23, the connecting plate 23 is fixed on the model frame 15 through the large screw holes 25, and a plurality of holes 26 are formed in the beam 22.

The slide 7 comprises a slide plate 27 and a slide block 28, the slide block 28 is arranged in the middle of the slide plate 27, the slide plate 27 is fixed on the model frame 15, the slide block 28 is connected with two ends of the cross beam 22 by using strong glue, and the slide block 28 can move up and down on the slide plate 27 so as to drive the cross beam 22 to adjust the up-and-down position.

The beam height adjusting controller 9 is fixed on the outer side wall of the model frame 15, the lifting ropes 8 on both sides are wound on the beam height adjusting controller 9 through the pulleys 29 on the model frame 15, both ends of the beam 22 are suspended on the lifting ropes 8 on both sides, and the height of the beam 22 can be changed by rotating the handle 30 of the beam height adjusting controller 9.

The motor 10, the speed reducer 11 and the elevator 12 are connected through a rotating shaft 31, the speed reducer 11 and the elevator 12 are fixed on the cross beam 22 through screws I32, and the speed reducer 11 is used for changing the rotating speed of the rotating shaft 31 so as to control the lifting speed of the elevator 12.

A lifting rod 33 in the lifter 12 penetrates through the cross beam 22 through a hole 26 arranged in the cross beam 22, a flange 34 is arranged at the bottom of the lifting rod 33, the flange 34 is connected with the pressure sensor 17 through a screw II 35, the loading plate 13 is connected with the pressure sensor 17 through super glue, and the longitudinal axes of the lifting rod 33, the pressure sensor 17 and the loading plate 13 are in the same position.

(explanation: the screw I and the screw II in the present application do not represent the type of the screw, but are used differently depending on the position of the two screws.)

The sandy soil particle simulation material 14 is a cylindrical aluminum bar, the length of the aluminum bar is 6-10cm, and the diameter (namely the particle diameter) is 0.15cm-0.6 cm. The specific gravity of the aluminum bar material is close to that of soil, so the aluminum bar is selected as a sandy soil particle simulation material for research. The placing box 16 is opened and placed on one side of the model frame 15 for placing the sand grain simulation material 14 before the start of the test and after the end of the test.

The model frame 15 is used for piling up sandy soil particle simulation materials 14, two sides of the bottom of the model frame 15 are provided with fixing frames 36 for reinforcing the model frame 15 and ensuring the overall stability of the model, and the model frame 15 is provided with a plurality of rows of screw holes 37 for fixing the connecting plates 23 at two ends of the counter-force beam 6.

During the test, the square lighting plate 22 and the camera 21 capable of continuously shooting are placed in front of the model frame 15 for observing the movement law of the sandy soil particle simulation material 14 in the test process, and then the whole model device is placed in a cuboid opaque curtain shed 19.

The following is a concrete description of the implementation method of the sand structure microscopic test method proposed by the present invention, taking a foundation model as an example.

The ground model was 120cm wide and 60cm high, as shown in FIG. 1. The specific test steps are as follows:

1) the motor 10, the speed reducer 11 and the elevator 12 are connected, and the lifting speed of the lifting rod 33 is adjusted to be 1mm/min through the speed reducer 11;

2) the beam 22 is adjusted to a height position 80cm away from the bottom of the model frame 15 through the beam height adjusting controller 9, and the beam 22 is fixed on the model frame 15 through the connecting plate 23;

3) the particle grading of each sandy soil particle simulation material is selected (namely, the mass of particles with each particle size is selected), and when no special requirement is made on the particle grading, the fractal grading which meets the requirement that the mass fractal dimension D is 1.5 is selected as the particle grading. The fractal gradation selection method comprises the following steps:

M(d<d_i)/M_T＝(d_i/d_max)^3-D (1)

wherein M is_TMeans the total mass of all diameter particles, d_maxMeans the diameter of the largest particle, d_iRefers to the diameter of a particle, M (d)<d_i) Means less than the diameter of the particle d_iThe sum of the particle mass.

4) Total mass of particles M_TThe following formula is adopted for calculation:

M_T＝ρBHL×(1-n) (2)

where ρ is the density of all particles, typically, ρ is 2700kg/m³B is the width of the foundation model, H is the height of the foundation model, L is the length of the particles, n is the porosity of the foundation model, generally taken to be 0.2;

5) calculating according to the formula (2) to obtain the total mass M of the particles in the foundation model_T＝155.5kg；

5) Calculating according to the formula (2) to obtain the total mass M of the particles in the foundation model_T＝155.5kg；

6) Selecting sand and soil particle simulation materials 14 with the diameters of 1.5mm, 2.0mm, 2.5mm, 3.0mm, 3.5mm, 4.0mm, 4.5mm, 5.0mm, 5.5mm and 6.0mm respectively, and calculating according to a formula (1) to obtain the mass of particles with each diameter as follows: 26.5kg, 10.5kg, 11.7kg, 12.7kg, 13.6kg, 14.5kg, 15.3kg, 16.1kg, 16.8kg, 17.6 kg;

7) fully mixing the particles in the selected sandy soil particle simulation material 14, and placing the mixture in a placing box 16 for later use;

8) placing the sand-soil particle simulation material 14 placed in the placing box 16 on a model frame 15 according to the size of a foundation model, placing a flat plate 38 with the same width as the model 15 on the rear side of the sand-soil particle simulation material 14 accumulation body in order to ensure that the front and rear surfaces of the sand-soil particle simulation material 14 accumulation body are flat, and when placing the sand-soil particle simulation material 14, pushing the sand-soil particle simulation material 14 from the front side to enable the rear side of the sand-soil particle simulation material 14 to contact the flat plate 38 so as to ensure the flatness of the front and rear side surfaces of the sand-soil particle simulation material 14 accumulation body;

9) when the sandy soil particle simulation material 14 is placed, the soil pressure sensor 40 is placed at a position where the particle pressure needs to be monitored, when the soil pressure sensor 40 is placed horizontally, the vertical particle pressure is measured, and when the soil pressure sensor is placed vertically, the horizontal particle pressure is measured;

10) after the foundation model is stacked, the pressure sensor 17 and the loading plate 13 are installed on the lifting rod, the static loading mechanism 2 is started, and when the loading plate 13 is about to contact the sandy soil particle simulation material 14, the switch is closed;

11) placing the displacement sensor 39 at the corresponding position of the foundation model, connecting plug wires in the displacement sensor 39, the pressure sensor 17 and the soil pressure sensor 40 with the data acquisition instrument 18, and automatically recording the numerical value of the sensors by using the data acquisition instrument 18;

12) placing the square lighting plate 20 and the camera 21 in front of the model frame 15, so that the camera 21 can shoot the full view of the model;

13) placing the whole test model in a cuboid light-proof curtain shed 19; turning on the square illumination board 20 and the camera 21, carrying out interval shooting, and recording the time when the camera 21 starts shooting;

14) starting the static loading mechanism 2 to load the foundation model, and simultaneously recording the initial loading time;

15) applying a vertical load to the sandy soil particle simulation material through the static loading mechanism 2, continuously carrying out interval shooting by using the camera 21 in the loading process, and simultaneously, continuously and automatically recording the numerical value of the sensor by using the data acquisition instrument 18 until the test is finished;

16) after the test is finished, the static loading mechanism 2, the data acquisition instrument 18 and the camera 21 are closed;

17) processing the sensor data measured by the data acquisition instrument 18 to respectively obtain a relation curve of vertical displacement and vertical stress of the sand particle simulation material foundation and the pressure distribution of the sand particle simulation material particles in the foundation;

18) and (3) introducing the pictures shot at intervals into PIV software for processing to obtain the displacement and the speed of each particle and the speed field and the displacement field of the whole structure, and analyzing the displacement field to obtain the damage form of the foundation.