CN113405903B - Sand soil structure microscopic test method - Google Patents
Sand soil structure microscopic test method Download PDFInfo
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- CN113405903B CN113405903B CN202110547750.0A CN202110547750A CN113405903B CN 113405903 B CN113405903 B CN 113405903B CN 202110547750 A CN202110547750 A CN 202110547750A CN 113405903 B CN113405903 B CN 113405903B
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- 239000002689 soil Substances 0.000 title claims abstract description 66
- 239000004576 sand Substances 0.000 title claims abstract description 60
- 238000010998 test method Methods 0.000 title claims abstract description 11
- 239000002245 particle Substances 0.000 claims abstract description 127
- 238000004088 simulation Methods 0.000 claims abstract description 77
- 239000000463 material Substances 0.000 claims abstract description 73
- 230000007246 mechanism Effects 0.000 claims abstract description 43
- 238000012360 testing method Methods 0.000 claims abstract description 30
- 238000006073 displacement reaction Methods 0.000 claims abstract description 25
- 230000003068 static effect Effects 0.000 claims abstract description 23
- 239000003638 chemical reducing agent Substances 0.000 claims abstract description 20
- 230000006378 damage Effects 0.000 claims abstract description 6
- 238000009825 accumulation Methods 0.000 claims description 11
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 10
- 229910052782 aluminium Inorganic materials 0.000 claims description 10
- 238000005286 illumination Methods 0.000 claims description 7
- 238000000034 method Methods 0.000 claims description 7
- 238000012545 processing Methods 0.000 claims description 7
- 239000003292 glue Substances 0.000 claims description 6
- 239000000203 mixture Substances 0.000 claims description 5
- 238000004364 calculation method Methods 0.000 claims description 4
- 230000008569 process Effects 0.000 claims description 3
- 230000003014 reinforcing effect Effects 0.000 claims description 3
- 238000010187 selection method Methods 0.000 claims description 3
- 230000008859 change Effects 0.000 abstract description 2
- 238000006243 chemical reaction Methods 0.000 description 4
- 238000010586 diagram Methods 0.000 description 4
- 238000004458 analytical method Methods 0.000 description 3
- 230000008878 coupling Effects 0.000 description 2
- 238000010168 coupling process Methods 0.000 description 2
- 238000005859 coupling reaction Methods 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 238000011160 research Methods 0.000 description 2
- 230000004927 fusion Effects 0.000 description 1
- 239000008187 granular material Substances 0.000 description 1
- 230000005484 gravity Effects 0.000 description 1
- 238000010191 image analysis Methods 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
- 230000000007 visual effect Effects 0.000 description 1
- 238000012800 visualization Methods 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/02—Details
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/02—Details
- G01N3/06—Special adaptations of indicating or recording means
- G01N3/068—Special adaptations of indicating or recording means with optical indicating or recording means
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0014—Type of force applied
- G01N2203/0016—Tensile or compressive
- G01N2203/0019—Compressive
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/02—Details not specific for a particular testing method
- G01N2203/06—Indicating or recording means; Sensing means
- G01N2203/0641—Indicating or recording means; Sensing means using optical, X-ray, ultraviolet, infrared or similar detectors
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/02—Details not specific for a particular testing method
- G01N2203/06—Indicating or recording means; Sensing means
- G01N2203/067—Parameter measured for estimating the property
- G01N2203/0676—Force, weight, load, energy, speed or acceleration
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/02—Details not specific for a particular testing method
- G01N2203/06—Indicating or recording means; Sensing means
- G01N2203/067—Parameter measured for estimating the property
- G01N2203/0682—Spatial dimension, e.g. length, area, angle
Abstract
The invention relates to a sandy soil structure microscopic test method, which belongs to the technical field of geotechnical engineering, and has the IPC classification number of E02D33/00. The test device adopted by the test method comprises a counter force mechanism, a static force loading mechanism, a model stacking mechanism, a data acquisition system and a shooting system; the counter-force mechanism comprises a counter-force cross beam and a cross beam height adjustment controller, the static loading mechanism comprises a speed reducer, a lifter and a loading plate, the model stacking mechanism comprises sand and soil particle simulation materials and a model frame, and the data acquisition system comprises a pressure sensor and a data acquisition instrument. The test method can intuitively observe the change of the internal particles of the structure, test the displacement of the internal particles of the sandy soil structure at each moment, further determine the movement rule of the internal particles and the damage mechanism of the sandy soil structure, and has low requirements on operators.
Description
Technical Field
The invention relates to an indoor model test method for geotechnical engineering, in particular to a microscopic test method for a sandy soil structure, which belongs to the technical field of geotechnical engineering, and has IPC classification number of E02D33/00.
Background
When researching structural stability of a foundation, a side slope, a retaining wall, a embankment and the like constructed by granular materials such as sand (sand) soil and the like in geotechnical engineering, an indoor model test is usually required to be carried out, wherein the three-dimensional model test is a main means for researching the structural stability of the geotechnical structure, however, the three-dimensional model test researches a macroscopic expression form of the geotechnical structure, the movement rule of particles in the structure cannot be known from a microscopic level, and in most cases, the operation is complicated and a certain labor force is required.
The prior patent CN201010182628 'contact surface shear test visualization device of soil and structure interaction' only can realize the visual observation of soil and structure shear bands, and cannot perform omnibearing observation on geotechnical engineering structures such as foundations, slopes, retaining walls, embankments and the like.
The prior patent CN201010142417 'geotechnical model test system and method based on macro-micro mechanics' can realize the fine analysis of the test model by means of simultaneous fusion of geotechnical model test, special micro image analysis technology, complex continuous-discrete coupling numerical simulation and the like, and has the advantages of various contents, complex operation and higher requirements on testers. Since only a few quality advanced personnel can master the continuous-discrete coupling numerical simulation, the method has high requirements on test operation and analysis personnel.
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 scheme of the invention is as follows:
the 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 slide ways, 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 sand and soil particle simulation materials, a model frame and a placement box, the data acquisition system comprises a pressure sensor and a data acquisition instrument, and the shooting system comprises a square lighting plate and a camera capable of continuously shooting.
The counter-force crossbeam includes crossbeam and connecting plate, and the both ends of crossbeam and the one end of connecting plate are equipped with little screw hole, and the other end of connecting plate is equipped with big screw hole, and the crossbeam passes through little screw hole is connected with the connecting plate, and the connecting plate passes through big screw hole to be fixed on the model frame, sets up a plurality of holes in the crossbeam.
The two-side slide way comprises a slide way plate and slide way blocks, the slide way plate is fixed on the model frame, the slide way blocks are connected with two ends of the cross beam through strong glue, and the slide way blocks can move up and down in the slide way plate, so that the cross beam is driven to adjust the upper and lower positions.
The beam height adjusting controller is fixed on the outer side wall of the model frame, the lifting ropes on two sides are wound on the beam height adjusting controller through pulleys on the upper part of the model frame, two ends of the beam are suspended on the lifting ropes on two sides, and the height of the beam is changed by rotating a handle of the beam height adjusting controller.
The motor, the speed reducer and the lifter are connected through a rotating shaft, the speed reducer and the lifter are fixed on the cross beam through screws I, and the speed reducer is used for changing the rotating speed of the rotating shaft, so that the lifting speed of the lifter can be controlled.
The lifter in the lifter passes the crossbeam through the hole that sets up in the crossbeam, and the lifter bottom has the flange, and the flange passes through screw II with pressure sensor to be connected, and the loading board passes through powerful glue and is connected with pressure sensor, and the longitudinal axis of lifter, pressure sensor and loading board is in same position.
The sand 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 sand and soil particle simulation materials, fixing frames are arranged on two sides of the bottom of the model frame and used for reinforcing the model frame, the overall stability of the model is guaranteed, and a plurality of rows of screw holes are formed in the model frame and used for fixing connecting plates at two ends of the counter-force beam.
The test operation steps are as follows:
1) The motor, the speed reducer and the lifter are connected, and the lifting speed of the lifting rod is adjusted to be 1mm/min through the speed reducer;
2) The beam is adjusted to a height position 80cm away from the bottom of the model frame through a beam height adjustment controller, and is fixed on the model frame through a connecting plate;
3) The grain composition of each sand grain simulation material is selected: fractal grading meeting the requirement of the mass fractal dimension D of 1.5 is selected as the grain grading. The fractal grading selection method comprises the following steps:
M(d<d i )/M T ＝(d i /d max ) 3-D (1)
wherein M is T Refers to the total mass of all diameter particles, d max Refers to the diameter of the largest particle, d i Refers to the diameter of a particle, M (d<d i ) Refers to particles smaller than diameter d i Particle mass and of (c) are described.
4) Total mass M of particles T The following formula is used for calculation:
M T ＝ρBHL×(1-n)(2)
where ρ refers to the density of all particles, typically ρ=2700 kg/m 3 B is the width of the foundation model, H is the height of the foundation model, L is the length of the particles, and n is the porosity of the foundation model, typically taken to be 0.2;
5) Calculating according to formula (2) to obtain total mass M of particles in foundation model T ＝155.5kg；
6) The sand 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 are selected, and the mass of the particles with each diameter is calculated according to a formula (1): 26.5kg, 10.5kg, 11.7kg, 12.7kg, 13.6kg, 14.5kg, 15.3kg, 16.1kg, 16.8kg, 17.6kg;
7) Fully mixing the selected sand particle simulation materials, and placing the mixture in a placing box for standby;
8) According to the size of the test simulation, placing the sand-soil particle simulation materials placed in the placement box on a model frame, placing a flat plate with the same width as the model frame on the rear side of the sand-soil particle simulation material stacking body in order to ensure the front and rear surfaces of the sand-soil particle simulation material stacking body, and pushing the sand-soil particle simulation materials from the front side to enable the rear side of the sand-soil particle simulation materials to contact the flat plate when placing the sand-soil particle simulation materials, so that the flatness of the front and rear side surfaces of the sand-soil particle simulation material stacking body is ensured;
9) When the sand soil particle simulation material is placed, placing a soil pressure sensor at a position where particle pressure needs to be monitored, horizontally placing the soil pressure sensor when vertical particle pressure is measured, and vertically placing the soil pressure sensor when horizontal particle pressure is measured;
10 After stacking the sand particle simulation materials, installing the pressure sensor on the lifting rod together with the loading plate, starting the static loading mechanism, and closing the static loading mechanism when the loading plate is about to contact the sand particle simulation materials;
11 Placing the displacement sensor at the corresponding position of the sand and soil 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 lighting plate and the camera in front of the model frame, so that the camera can shoot the overall view of the sand and soil particle simulation material accumulation body;
13 Placing the whole test model in a cuboid light-proof curtain shed; opening a square lighting plate and a camera, performing interval shooting, and recording shooting starting time of the camera;
14 A static loading mechanism is started to load the sand particle simulation material accumulation body, and the initial loading time is recorded;
15 Continuously applying vertical load to the sand particle simulation material accumulation body through a static loading mechanism, continuously shooting at intervals by a camera in the loading process, and automatically recording the numerical value of a sensor by a 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 particle simulation material accumulation body and particle pressure distribution in the sand particle simulation material accumulation body;
18 The pictures shot at intervals are imported into PIV software for processing, so that the displacement and the speed of each particle and the speed field and the displacement field of the whole sand particle simulation material accumulation body are obtained, and meanwhile, the displacement field is analyzed to obtain the damage form of the sand 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 sandy soil structure, provided by the invention, the change of the particles in the structure can be intuitively observed without combining a numerical simulation means, the displacement of the particles in the sandy soil structure at each moment can be tested, and further, the movement rule of the particles in the sandy soil structure and the damage mechanism of the sandy soil structure are clarified, and meanwhile, the macroscopic mechanical performance of a model can be obtained, so that references are provided for the calculation and analysis of the structures such as the foundation, the side slope, the retaining wall, the embankment and the like of the particulate body such as sandy soil; the PIV program combining the existing image processing technology can also analyze the displacement and the speed of each particle in the structure, and the speed field, the displacement field and the destruction form of the whole structure, and has simple and quick operation and low requirement on operators.
Drawings
FIG. 1 is a schematic diagram of a test apparatus employed 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 slide of the present invention;
FIG. 4 is a schematic view of a lifter according to the present invention;
FIG. 5 is a schematic diagram of a beam height adjustment controller according to the present invention;
FIG. 6 is a schematic view of a sand grain simulation material of the present invention;
FIG. 7 is a schematic diagram of a data acquisition system according to the present invention;
FIG. 8 is a schematic diagram of a mold frame of the present invention;
FIG. 9 is a schematic view of a placement box of the present invention;
fig. 10 is a schematic view of a curtain booth according to the present invention.
In the figure, 1, a reaction force mechanism; 2. a static loading mechanism; 3. a model stacking mechanism; 4. a data acquisition system; 5. a shooting system; 6. a reaction beam; 7. two side slideways; 8. hanging ropes at two sides; 9. a beam height adjustment controller; 10. a motor; 11. a speed reducer; 12. a lifter; 13. a loading plate; 14. sand grain simulation material; 15. a model frame; 16. placing a box; 17. a pressure sensor; 18. a data acquisition instrument; 19. curtain shed; 20. a square illumination plate; 21. a camera; 22. a cross beam; 23. a connecting plate; 24. a small screw hole; 25. large screw holes; 26. a hole; 27. a slideway plate; 28. a slideway 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 fixing frame; 37. screw holes; 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.
The test device comprises a counter force mechanism 1, a static 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 slide ways 7, two side lifting ropes 8 and a cross beam height adjustment controller 9, the static loading mechanism 2 comprises a motor 10, a speed reducer 11, an elevator 12 and a loading plate 13, the model stacking mechanism 3 comprises sand and soil particle simulation materials 14, a model frame 15 and a placement 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 small screw holes 24 are formed in two ends of the beam 22 and one end of the connecting plate 23, large screw holes 25 are formed in the other end of the connecting plate 23, 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 holes 25, and a plurality of holes 26 are formed in the beam 22.
The slideway 7 comprises a slideway plate 27 and slideway blocks 28, wherein the slideway blocks 28 are arranged in the middle of the slideway plate 27, the slideway plate 27 is fixed on the model frame 15, the slideway blocks 28 are connected with two ends of the cross beam 22 by adopting strong glue, and the slideway blocks 28 can move up and down on the slideway plate 27 so as to drive the cross beam 22 to adjust the up and down positions.
The beam height adjusting controller 9 is fixed on the outer side wall of the model frame 15, the two side lifting ropes 8 are wound on the beam height adjusting controller 9 through pulleys 29 on the upper portion of the model frame 15, two ends of the beam 22 are suspended on the two side lifting ropes 8, and the height of the beam 22 can be changed by rotating handles 30 of the 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 a screw 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 lifter 12.
The lifting rod 33 in the lifter 12 passes through the beam 22 through the hole 26 arranged in the beam 22, the bottom of the lifting rod 33 is provided with a flange 34, 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 lifting rod 33, the pressure sensor 17 and the longitudinal axis of the loading plate 13 are positioned at the same position.
The sand particle simulation material 14 is a cylindrical aluminum rod, the length of the aluminum rod is 6-10cm, and the diameter (namely the particle size) is 0.15cm-0.6cm. The specific gravity of the aluminum bar material is close to that of the soil, so that the application selects the aluminum bar as the sand particle simulation material for research. The placing box 16 is open and placed on one side of the model frame 15, and is used for placing the sand and soil particle simulation material 14 before the test starts and after the test ends.
The model frame 15 is used for piling up sand and soil particle simulation materials 14, fixing frames 36 are arranged on two sides of the bottom of the model frame 15 and used for reinforcing the model frame 15, the overall stability of the model is guaranteed, and a plurality of rows of screw holes 37 are formed in the model frame 15 and used for fixing connecting plates 23 at two ends of the counter-force cross beam 6.
In the test, a square illumination plate 20 and a camera 21 capable of continuously photographing are placed in front of the model frame 15 for observing the movement law of the sand and soil particle simulation material 14 during the test, and then the whole model device is placed in a cuboid light-proof curtain shed 19.
The implementation method of the sand structure microscopic test method provided by the invention is specifically described below by taking a foundation model as an example. The foundation 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 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 beam 22 is adjusted to a height position 80cm away from the bottom of the model frame 15 by a beam height adjustment controller 9, and the beam 22 is fixed on the model frame 15 by a connecting plate 23;
3) The particle grading of each sand particle simulation material (namely, the mass of each particle size) is selected, and when no special requirement is imposed on the particle grading, the fractal grading meeting the mass fractal dimension D of 1.5 is selected as the particle grading. The fractal grading selection method comprises the following steps:
M(d<d i )/M T ＝(d i /d max ) 3-D (1)
wherein M is T Refers to the total mass of all diameter particles, d max Refers to the diameter of the largest particle, d i Refers to the diameter of a particle, M (d<d i ) Refers to particles smaller than diameter d i Particle mass and of (c) are described.
4) Total mass M of particles T The following formula is used for calculation:
M T ＝ρBHL×(1-n)(2)
where ρ refers to the density of all particles, typically ρ=2700 kg/m 3 B is the width of the foundation model, H is the height of the foundation model, L is the length of the particles, and n is the porosity of the foundation model, typically taken to be 0.2;
5) Calculating according to formula (2) to obtain the total mass of particles in the foundation modelQuantity M T ＝155.5kg；
5) Calculating according to formula (2) to obtain total mass M of particles in foundation model T ＝155.5kg；
6) The sand 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 are selected, and the mass of the particles with each diameter is calculated according to a formula (1): 26.5kg, 10.5kg, 11.7kg, 12.7kg, 13.6kg, 14.5kg, 15.3kg, 16.1kg, 16.8kg, 17.6kg;
7) Fully mixing the particles in the selected sand particle simulation material 14 and placing the mixture in a placing box 16 for standby;
8) According to the size of the foundation model, placing the sand-soil particle simulation material 14 placed in the placing box 16 on the model frame 15, placing a flat plate 38 with the same width as the model 15 on the rear side of the pile of the sand-soil particle simulation material 14 in order to ensure the front and rear surfaces of the pile of the sand-soil particle simulation material 14 to be flat, and pushing the sand-soil particle simulation material 14 from the front side when placing the sand-soil particle simulation material 14, so that the rear side of the sand-soil particle simulation material 14 contacts the flat plate 38, thereby ensuring the flatness of the front and rear surfaces of the pile of the sand-soil particle simulation material 14;
9) When the sand and 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 piled up, the pressure sensor 17 is installed on the lifting rod together with the loading plate 13, the static loading mechanism 2 is started, and when the loading plate 13 is about to be contacted with the sand and soil particle simulation material 14, the switch is closed;
11 Placing the displacement sensor 39 at a 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 sensor by using the data acquisition instrument 18;
12 Placing the square illumination plate 20 and the camera 21 in front of the model frame 15 so that the camera 21 can take a full view of the model;
13 Placing the whole test model in a cuboid light-proof curtain shed 19; the square illumination plate 20 and the camera 21 are turned on to perform interval shooting, and the shooting start time of the camera 21 is recorded;
14 A static loading mechanism 2 is started to load the foundation model, and the initial loading time is recorded;
15 Vertical load is applied to the sand particle simulation material through the static loading mechanism 2, the camera 21 is adopted to continuously carry out interval shooting in the loading process, and meanwhile, the data acquisition instrument 18 continuously and automatically records the numerical value of the sensor 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 foundation of the sand-soil particle simulation material and the pressure distribution of the sand-soil particle simulation material particles in the foundation;
18 The pictures shot at intervals are imported into PIV software for processing, so that the displacement and the speed of each particle, the speed field and the displacement field of the whole structure are obtained, and meanwhile, the displacement field is analyzed to obtain the damage form of the foundation.
Claims (2)
1. The sand structure microscopic test method is characterized in that the 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 counter-force mechanism (1) comprises a counter-force cross beam (6), two side slide ways (7), two side lifting ropes (8) and a cross beam height adjustment 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 sand and soil particle simulation materials (14), a model frame (15) and a placement 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 counter-force beam (6) comprises a beam (22) and a connecting plate (23), wherein small screw holes (24) are formed in two ends of the beam (22) and one end of the connecting plate (23), large screw holes (25) are formed in the other end of the connecting plate (23), 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 holes (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 two ends of the cross beam (22) through strong glue, and the slide way blocks (28) can move up and down in the slide way plates (27), so that the cross beam (22) is driven to adjust the up and down positions;
the beam height adjusting controller (9) is fixed on the outer side wall of the model frame (15), the lifting ropes (8) on two sides are wound on the beam height adjusting controller (9) through pulleys (29) on the upper part of the model frame (15), two ends of the beam (22) are suspended on the lifting ropes (8) on two sides, and the height of the beam (22) is changed by rotating handles (30) of the 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 a screw I (32), 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 lifter (12);
the 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 positioned at the same position;
the sand 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 0.15-0.6 cm;
the model frame (15) is used for piling sand and soil particle simulation materials (14), fixed frames (36) are arranged on two sides of the bottom of the model frame (15) and used for reinforcing the model frame (15), the overall stability of the model is guaranteed, a plurality of rows of screw holes (37) are formed in the model frame (15) and used for fixing connecting plates (23) at two ends of the counter-force cross beam (6);
the test operation steps are as follows:
1) a motor (10), a speed reducer (11) and a lifter (12) are connected, and the lifting speed of a 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 adjustment controller (9), and the cross beam (22) is fixed on the model frame (15) through a connecting plate (23);
3) The grain composition of each sand grain simulation material is selected: selecting fractal grading meeting the requirement of the quality fractal dimension D of 1.5 as particle grading; the fractal grading selection method comprises the following steps:
M(d<d i )/M T ＝(d i /d max ) 3-D (1)
wherein M is T Refers to the total mass of all diameter particles, d max Refers to the diameter of the largest particle, d i Refers to the diameter of a particle, M (d<d i ) Refers to particles smaller than diameter d i Particle mass sum of (2);
4) Total mass M of particles T The following formula is used for calculation:
M T ＝ρBHL×(1-n) (2)
where ρ refers to the density of all particles, typically ρ=2700 kg/m 3 B is the width of the foundation model, H is the height of the foundation model, L is the length of the particles, and n is the porosity of the foundation model, typically taken to be 0.2;
5) Calculating according to formula (2) to obtain total mass M of particles in foundation model T ＝155.5kg；
6) The sand 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 are selected, and the mass of the particles with each diameter is calculated according to a formula (1): 26.5kg, 10.5kg, 11.7kg, 12.7kg, 13.6kg, 14.5kg, 15.3kg, 16.1kg, 16.8kg, 17.6kg;
7) Fully mixing the selected sand particle simulation materials (14) and placing the mixture in a placing box (16) for standby;
8) According to the size of test simulation, placing the sand particle simulation materials (14) placed in the placement box (16) on a model frame (15), and placing a flat plate (38) with the same width as the model frame (15) on the rear side of the sand particle simulation materials (14) in order to ensure the front and rear surfaces of the sand particle simulation materials (14) to be flat, and pushing the sand particle simulation materials (14) from the front side when placing the sand particle simulation materials (14), so that the rear side of the sand particle simulation materials (14) contacts the flat plate (38), thereby ensuring the flatness of the front and rear side surfaces of the sand particle simulation materials (14) to be flat;
9) When the sand and soil particle simulation material (14) is placed, placing a soil pressure sensor (40) at a position where particle pressure needs to be monitored, when vertical particle pressure is measured, placing the soil pressure sensor (40) horizontally, and when horizontal particle pressure is measured, placing the soil pressure sensor (40) vertically;
10 After stacking the sand grain simulation materials (14), installing a pressure sensor (17) on a lifting rod (33) together with a loading plate (13), starting a static loading mechanism (2), and closing the static loading mechanism (2) when the loading plate (13) is about to contact the sand grain simulation materials (14);
11 Placing a displacement sensor (39) at a corresponding position of a sand and soil 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 sensor 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 whole view of the sand and soil particle simulation material (14) accumulation body;
13 Placing the whole test model in a cuboid light-proof curtain shed (19); opening the square illumination plate (20) and the camera (21), performing interval shooting, and recording the shooting starting time of the camera (21);
14 Starting a static loading mechanism (2) to load the sand particle simulation material (14) stacking body, and recording the initial loading time;
15 Continuously applying vertical load to the sand and soil particle simulation material (14) accumulation body through the static loading mechanism (2), continuously shooting at intervals by the camera (21) in the loading process, and automatically recording the numerical value of the sensor by the 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 sensor data measured by a data acquisition instrument (18) to respectively obtain a relation curve of vertical displacement and vertical stress of a sand particle simulation material (14) stacking body and particle pressure distribution in the sand particle simulation material (14) stacking body;
18 The pictures taken at intervals are imported into PIV software for processing, so that the displacement and the speed of each particle and the speed field and the displacement field of the whole sand particle simulation material (14) stacking body are obtained, and meanwhile, the displacement field is analyzed to obtain the damage form of the sand particle simulation material (14) stacking body.
2. A sand structure microscopic examination method according to claim 1, characterized in that the data acquisition system (4) further comprises a displacement sensor (39) and a soil pressure sensor (40).
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