Soil body true triaxial speckle observation device and method

Abstract

The invention relates to the technical field of soil mass mechanical testing, in particular to a soil mass true triaxial speckle observation device and method. The soil body true triaxial speckle observation device comprises an observation device and a sample bin used for placing a soil body sample, the sample bin comprises a first bearing surface on the top, a second bearing surface on the left side adjacent to the first bearing surface, a third bearing surface on the rear side, a buffer surface on the right side and a visible surface on the front side, a first direction stress loading part, a second direction stress loading part and a third direction stress loading part are respectively arranged on the first bearing surface, the second bearing surface and the third bearing surface; wherein the first bearing surface is a deformable bearing surface, and sliding mechanisms are arranged at contact positions among the second bearing surface, the third bearing surface, the buffer surface and the visual surface, so that the bearing surfaces can relatively slide through the sliding mechanisms; and the observation device is used for observing the soil body sample through the visual surface. According to the invention, three-way independent loading is realized, and the problem of mutual interference of multi-way loading in a traditional loading system is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of soil mechanics testing, and particularly relates to a true triaxial speckle observation device and method for soil. Background Art

[0002] In soil mechanics research, the true triaxial test is a commonly used experimental method to reveal the deformation and failure laws of soil under complex stress conditions, which can simulate and study the mechanical response of soil under real stress states. As a non-contact full-field measurement method, the speckle observation technology can accurately obtain the full-field strain distribution on the surface of the specimen through Digital Image Correlation (DIC) technology, and a large amount of speckle field deformation data of the soil under stress action can be obtained. However, there are still significant limitations in the combination of these two experimental methods in terms of test device design and test method, which restricts the in-depth development of related research.

[0003] Although the existing true triaxial test devices can achieve three-direction independent stress loading on soil specimens, due to the limitation of structural design, there are only stress and displacement sensors, and generally lack optical observation windows, resulting in only the normal stress and normal displacement on the soil surface being measurable during the loading process. This single data acquisition method is difficult to comprehensively reflect the entire deformation process of the soil under complex stress conditions, especially when studying key issues such as localized deformation and shear band formation. In addition, the traditional true triaxial device uses a full-rigidity wrapping or rubber mold flexible wrapping method for loading, and the surfaces of the soil samples are covered by opaque interfaces, which not only cannot observe the morphological changes of the soil during the loading process in real time, but also cannot synchronously collect speckle images, restricting the application of the speckle observation technology in true triaxial tests.

[0004] When the true triaxial apparatus is loading, since it is necessary to apply three-direction stresses σ1, σ2, and σ3 to the six surfaces of the cubic specimen simultaneously, loading from three directions on the six surfaces of the cube will inevitably cause conflicts, resulting in the inability to load simultaneously in several directions. Moreover, the existing true triaxial apparatuses for soil are generally small in size (3 - 10 cm), and it is impossible to conduct full-loading experiments in three directions on soil samples with larger specimen sizes. The triaxial apparatus for cylindrical soil samples is generally called a pseudo triaxial apparatus, and only the cylindrical side and the top are loaded, which is not a strictly three-direction loading. Summary of the Invention

[0005] The purpose of the present invention is to provide a true triaxial speckle observation device for soil to solve the problem in the prior art that the observation results are inaccurate due to conflicts during the three-direction stress loading process.

[0006] To solve the above problems, the present invention proposes a true triaxial speckle observation device for soil, and the technical solution adopted is as follows:

[0007] A true triaxial speckle observation device for soil includes: an observation device and a specimen chamber for placing a soil specimen. The specimen chamber includes a first bearing surface at the top, a second bearing surface adjacent to its left side, a third bearing surface at the rear, a buffer surface on the right side, and a visible surface on the front side. A first-direction stress loading component, a second-direction stress loading component, and a third-direction stress loading component are respectively arranged on the first bearing surface, the second bearing surface, and the third bearing surface. Among them, the first bearing surface is a deformable bearing surface, and a sliding mechanism is arranged at the contact positions between the second bearing surface, the third bearing surface, the buffer surface, and the visible surface, so that they can slide relative to each other through the sliding mechanism. The observation device is used to observe the soil specimen through the visible surface.

[0008] Further, the sliding mechanism is a roller, the roller is arranged along the length direction of the contact position, and the soft structure deforms with the stress generated by the first-direction stress loading component, the second-direction stress loading component, and the third-direction stress loading component.

[0009] Further, the true triaxial speckle observation device for soil further includes an internal loading mechanism, which includes an airbag, an air pipe, and a pneumatic controller. The airbag is installed inside the soil specimen and is arranged along the direction perpendicular to the third bearing surface. One end of the air pipe is communicated with the airbag, and the other end passes through the soil specimen and penetrates through the first bearing surface to extend out for conducting gas. The pneumatic controller is arranged on the air pipe and is used to control the magnitude of the gas pressure, and further control the magnitude of the pressure exerted on the soil specimen by the airbag.

[0010] Further, pressure dispersion components are arranged on the first bearing surface, the second bearing surface, and the third bearing surface. The pressure dispersion components include pressure dispersion plates arranged along the bearing surface and pressure support plates penetrating and connecting the pressure dispersion plates. And a central circular plate is arranged at the part of the pressure dispersion component for contacting the stress loading component.

[0011] Further, the true triaxial speckle observation device for soil further includes a loading control system. Stress sensors are arranged on the pressure dispersion components. The loading control system is used to control the loading stress of the first-direction stress loading component, the second-direction stress loading component, and the third-direction stress loading component according to the stress sensors.

[0012] Further, pressure buffer components are arranged on the first bearing surface, the second bearing surface, and the third bearing surface. The pressure buffer components include three pressure buffer plates arranged on the bearing surface. The three pressure buffer plates form a drawer-shaped structure. The pressure dispersion component is arranged inside the drawer-shaped structure, and there is a gap between them.

[0013] Further, the true triaxial soil speckle observation device further includes a bearing frame, which includes a square frame and a triangular bracket perpendicularly connected to one end thereof. The upper and lower ends of the square frame are of I-shaped structures. The upper I-shaped structure is connected to the first-direction stress loading component, and the lower I-shaped structure is connected to the bottom of the sample chamber. Along the height direction of the square frame on the triangular bracket, there is an I-shaped column, which is connected to the third-direction stress loading component. On the side of the I-shaped column away from the square frame, there is a triangular channel steel support frame.

[0014] Further, the visible surface includes a square support frame and toughened glass connected to one side surface thereof. One side edge of the square support frame connected to the buffer surface is set as a steel plate structure, and the other three side edges are all set as steel groove structures. The grooves of the steel groove structures face outward, and an L-shaped groove is installed at the lower end position of the toughened glass, and the L-shaped groove is matched with the lower end of the toughened glass.

[0015] Further, the true triaxial soil speckle observation device further includes an L-shaped bottom plate arranged at the bottom, and the L-shaped bend of the L-shaped bottom plate is matched with the L-shaped groove at the lower end position of the toughened glass.

[0016] The present invention also provides a true triaxial soil speckle observation method, which includes the following steps:

[0017] Step 1: Place the soil sample in the sample chamber;

[0018] Step 2: The first-direction stress loading component, the second-direction stress loading component, and the third-direction stress loading component simultaneously apply stresses to the first bearing surface, the second bearing surface, and the third bearing surface; meanwhile, the observation device observes the changes of the soil sample through the visible surface.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention is an improved invention. In the true triaxial soil speckle observation device of the present invention, a sliding mechanism is arranged at the contact positions between the second bearing surface, the third bearing surface, the buffer surface, and the visible surface in the true triaxial soil speckle observation device, so that they can relatively slide through the sliding mechanism, and the first bearing surface is a deformable bearing surface, so that the three-direction loading does not affect each other, avoiding hard contact collisions between the loading surfaces. By using such a "two rigid + one flexible" method to achieve three-direction independent loading, effective three-direction simultaneous loading can be realized, avoiding hard contact and collisions that may occur between the loading plates during multi-directional joint loading, thereby improving the accuracy of the cube loading experiment measurement and solving the problem of mutual interference in multi-directional loading in the traditional loading system.

[0021] Meanwhile, through the observation device and the visible surface, this application can observe the soil specimen, enabling the observation of the internal situation of the soil during the triaxial experiment and more accurate measurement. It solves the problem that the existing loading device cannot perform speckle observation under the true triaxial condition. The true triaxial speckle observation device for soil of the present invention can conduct triaxial loading experiments on soil samples of relatively large sizes, while the existing triaxial apparatuses are generally of relatively small sizes, usually only a few centimeters. This device is a new type of test device that can apply true triaxial loads to the soil specimen and simultaneously conduct optical speckle observation; it effectively integrates the stress loading and optical observation functions, providing strong experimental support for deeply revealing the deformation mechanism of the soil under complex stress conditions; and this device has a relatively low cost, a simple structure, and is easy to disassemble and replace components, thus facilitating the assembly of the soil specimen.

[0022] The sliding mechanism is a roller, and the roller is arranged along the length direction of the contact position. This simple structure enables sufficient lubrication even when the loading surface undergoes relative dislocation; moreover, the first bearing surface is a soft structure, and the soft structure deforms with the stresses generated by the first-direction stress loading component, the second-direction stress loading component, and the third-direction stress loading component, avoiding hard-contact collisions between the loading surfaces.

[0023] The true triaxial speckle observation device for soil further includes an internal loading mechanism, which includes an airbag, an air pipe, and a pneumatic controller. The airbag is installed inside the soil specimen and arranged along the direction perpendicular to the third bearing surface; one end of the air pipe is connected to the airbag, and the other end passes through the soil specimen and extends through the first bearing surface for conducting gas; the pneumatic controller is arranged on the air pipe for controlling the magnitude of the gas pressure, and thus controlling the magnitude of the pressure exerted by the airbag on the soil specimen. This structure applies pressure to the soil specimen by inflating the airbag; meanwhile, the three loading surfaces apply pressure to the three surfaces of the soil specimen. At this time, the soil can be restored to the state simulating before the tunnel excavation. When simulating the tunnel excavation, the gas pressure of the airbag is slowly reduced to simulate the unloading process of the soil around the tunnel during the tunnel excavation.

[0024] Pressure dispersion components are arranged on the first bearing surface, the second bearing surface, and the third bearing surface. The pressure dispersion components include pressure dispersion plates arranged along the bearing surface and pressure support plates connecting the pressure dispersion plates through. Moreover, a central circular plate is arranged at the part of the pressure dispersion component for contacting the stress loading component. This structure enables the pressures of the first-direction stress loading component, the second-direction stress loading component, and the third-direction stress loading component to be dispersed on the entire pressure dispersion component, preventing concentration at one place and avoiding the phenomenon of uneven loading stress.

[0025] The true triaxial soil speckle observation device further includes a loading control system. A stress sensor is provided on the pressure dispersion component. The loading control system is used to control the loading stress of the first-direction stress loading component, the second-direction stress loading component, and the third-direction stress loading component according to the stress sensor. This structure facilitates real-time tracking of the stress magnitudes received by the first bearing surface, the second bearing surface, and the third bearing surface and making adjustments.

[0026] Pressure buffer components are provided on the first bearing surface, the second bearing surface, and the third bearing surface. The pressure buffer component includes three pressure buffer plates provided on the bearing surface. The three pressure buffer plates form a drawer-shaped structure. The pressure dispersion component is arranged inside the drawer-shaped structure, and there is a gap between them. This structure can prevent the first bearing surface, the second bearing surface, and the third bearing surface from generating large local deformations under the action of the pressure buffer plates.

[0027] The true triaxial soil speckle observation device further includes a bearing frame. The bearing frame includes a square frame and a triangular bracket vertically connected to one end of it. The upper and lower ends of the square frame are of I-shaped structures. Its upper I-shaped structure is connected to the first-direction stress loading component, and its lower I-shaped structure is connected to the bottom of the specimen chamber. Along the direction of the square frame, I-shaped columns are provided on the triangular bracket, which are connected to the third-direction stress loading component. On the side of the I-shaped column away from the square frame, a triangular channel steel support frame is provided. This structure can reduce the weight of the frame itself and has a large bearing capacity. At the same time, a triangular channel steel support frame is provided on the side of the I-shaped column away from the square frame, which is beneficial to preventing the I-shaped column from deforming under the reaction force of the stress loading component.

[0028] The visible surface includes a square support frame and toughened glass connected to one of its side surfaces. One side edge of the square support frame connected to the buffer surface is set as a steel plate structure, and the other three side edges are all set as steel groove structures. The grooves of the steel groove structures face outward, and an L-shaped groove is installed at the lower end position of the toughened glass, which cooperates with the lower end of the toughened glass. This structure is beneficial to cleaning air dust and broken soil generated during the experiment.

[0029] The true triaxial soil speckle observation device further includes an L-shaped bottom plate provided at the bottom. The L-shaped bend of the L-shaped bottom plate cooperates with the L-shaped groove at the lower end position of the toughened glass. This structure jointly maintains the tightness of the specimen chamber. Description of the Drawings

[0030] Figure 1 is the rear view of the structure of the true triaxial soil speckle observation device of the present invention;

[0031] Figure 2 is the front view of the structure of the true triaxial soil speckle observation device of the present invention;

[0032] Figure 3 is the schematic diagram of the front view structure disassembly of the true triaxial soil speckle observation device of the present invention;

[0033] Figure 4 is the schematic diagram of the stress-free loading of the true triaxial soil speckle observation device of the present invention;

[0034] Figure 5 is the schematic diagram of the stress loading in the true triaxial soil speckle observation device of the present invention;

[0035] Figure 6 is the front view of the overall structure with a frame of the true triaxial soil speckle observation device of the present invention;

[0036] Figure 7 is the rear view of the overall structure with a frame of the true triaxial soil speckle observation device of the present invention;

[0037] Figure 8 is the schematic diagram of the structure of the frame in the true triaxial soil speckle observation device of the present invention;

[0038] Figure 9 is the schematic diagram of the structure of the internal loading mechanism in the true triaxial soil speckle observation device of the present invention;

[0039] Figure 10 is the installation schematic diagram of the internal loading mechanism in the true triaxial soil speckle observation device of the present invention;

[0040] Figure 11 is the schematic diagram of the loading mode of the true triaxial soil speckle observation device of the present invention;

[0041] In the figure, 1. bearing frame, 11. I-shaped column, 12. frame cross beam, 13. frame column, 14. lifting lug, 15. universal wheel, 16. short I-shaped steel column, 17. angle steel, 18. threaded rod, 2. specimen chamber, 21. loading upper cover, 22. soft wood block, 23. third bearing surface, 24. buffer surface, 25. second bearing surface, 26. L-shaped bottom plate, 261. bull's-eye pulley, 27. pressure dispersion component, 271. pressure dispersion plate, 272. pressure support plate, 28. roller, 29. observation window, 291. toughened glass, 292. L-shaped groove, 3. hydraulic jack, 4. gasket, 5. stress sensor, 6. soil specimen, 7. airbag, 8. air pipe, 9. pressure gauge. Detailed implementation mode

[0042] To enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0043] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and do not necessarily need to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances so that the embodiments of the present invention described here can be implemented in an order other than those illustrated or described here. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0044] Specific Embodiment 1 of the True Triaxial Speckle Observation Device for Soil Body of the Present Invention:

[0045] In this embodiment, as Figure 1 , 2 , 3, and 4 show, the true triaxial speckle observation device for soil body includes: an observation device and a specimen chamber 2 for placing a soil specimen 6. The specimen chamber 2 includes a first bearing surface at the top, a second bearing surface 25 adjacent to its left side, a third bearing surface 23 at the rear side, a buffer surface 24 on the right side, and a visible surface on the front side. A first-direction stress loading component, a second-direction stress loading component, and a third-direction stress loading component are respectively arranged on the first bearing surface, the second bearing surface 25, and the third bearing surface 23; wherein, the first bearing surface is a deformable bearing surface, and a sliding mechanism is arranged at the contact positions between the second bearing surface 25, the third bearing surface 23, the buffer surface 24, and the visible surface, so that they can slide relative to each other through the sliding mechanism; the observation device is used to observe the soil specimen 6 through the visible surface. Among them, the first-direction stress loading component, the second-direction stress loading component, and the third-direction stress loading component are all hydraulic jacks 3. The sliding mechanism is a roller 28, and the roller 28 is arranged along the length direction of the contact position. The first bearing surface is a soft body structure, that is, a soft wood block 22, and the soft body structure deforms with the stress generated by the first-direction stress loading component, the second-direction stress loading component, and the third-direction stress loading component. The observation device is a high-speed camera.

[0046] When the first-direction stress loading component, the second-direction stress loading component, and the third-direction stress loading component on the specimen chamber 2 are not loaded, the soil specimen 6 does not move, and the specimen chamber 2 remains unchanged. During use, the soil specimen 6 is placed in the specimen chamber 2, and then the second bearing surface 25, the third bearing surface 23, the buffer surface 24, and the visible surface are built close to the side wall of the soil specimen 6 to facilitate subsequent stress loading. Then, a soft wood block 22 is placed on the soil specimen 6, and the loading upper cover 21 is covered on the soft wood block 22.

[0047] As Figure 5 shown, when the first-direction stress loading component, the second-direction stress loading component, and the third-direction stress loading component are loaded simultaneously, the second bearing surface 25 is loaded by the second-direction stress loading component, pushing the soil specimen 6 to deform. At this time, under the action of the second bearing surface 25, the third bearing surface 23 slides to the right along the soil surface through the sliding mechanism, and the third bearing surface 23 does not squeeze the soil specimen 6, and the second bearing surface 25 and the third bearing surface 23 do not interfere with each other; at the same time, the third bearing surface 23 is loaded by the third-direction stress loading component, pushing the soil specimen 6 to deform. At this time, the loading borne by the second bearing surface 25 remains stationary, and the buffer surface 24 slides downward along the soil surface through the sliding mechanism under the action of the third bearing surface 23, and the buffer surface 24 does not squeeze the soil specimen 6, and the second bearing surface 25 and the third bearing surface 23 do not interfere with each other; the first bearing surface is loaded by the first-direction stress loading component, and the loading stress is downward. At this time, the first bearing surface will be affected by the directional loads of the second-direction stress loading component and the third-direction stress loading component and produce compressive deformation. Therefore, the second bearing surface 25 and the third bearing surface 23 will not have hard contact and collision effects with the first bearing surface.

[0048] Specific embodiment 2 of the true triaxial speckle observation device for soil body of the present invention:

[0049] Based on the above technical concept of the present invention, or on the basis of the specific embodiments of the present invention introduced above, another embodiment is provided below.

[0050] In this embodiment, as Figure 9 and Figure 10 shown, the true triaxial speckle observation device for soil body further includes an internal loading mechanism. The internal loading mechanism includes an airbag 7, an air pipe 8, and a pneumatic controller. The airbag 7 is installed inside the soil specimen 6 and is arranged along the direction perpendicular to the third bearing surface 23; one end of the air pipe 8 is communicated with the airbag 7, and the other end passes through the soil specimen 6 and extends out through the first bearing surface for conducting gas; the pneumatic controller is arranged on the air pipe 8 for controlling the size of the gas pressure and thus controlling the size of the pressure exerted by the airbag 7 on the soil specimen 6. Among them, the pneumatic controller is a pressure gauge 9.

[0051] Specifically, a circular hole is provided inside the soil specimen 6 in a direction perpendicular to the third bearing surface 23. The airbag 7 is installed in the circular hole, and one end of the airbag 7 communicates with one end of the air pipe 8. A through hole is provided in the soil specimen 6 in a direction perpendicular to the first bearing surface, and a perforation corresponding to the through hole is provided on the first bearing surface. The air pipe 8 extends out from the first bearing surface through the through hole and the perforation; the other end of the air pipe 8 is connected to an air pump, and the air pump is used to inflate the airbag 7 through the air pipe 8. When inflating, the airbag exerts pressure radially outward along the cylindrical hole. A pressure gauge 9 is provided at one end of the air pipe 8 close to the air pump, and the magnitude of the pressure exerted by the airbag 9 on the soil specimen 6 can be controlled according to the reading of the pressure gauge 9.

[0052] Specific Embodiment 3 of the True Triaxial Speckle Observation Device for Soil of the Present Invention:

[0053] Based on the above technical concept of the present invention, or on the basis of the specific embodiments of the present invention introduced above, another embodiment is provided below.

[0054] In this embodiment, as Figure 5 shown, pressure dispersion components 27 are provided on the first bearing surface, the second bearing surface 25, and the third bearing surface 23. The pressure dispersion component 27 includes pressure dispersion plates 271 arranged along the bearing surface and pressure support plates 272 that penetrate and connect the pressure dispersion plates 271, and a central circular plate is provided at the part of the pressure dispersion component 27 for contacting the stress loading component. Among them, the pressure dispersion component 27 on the first bearing surface is provided on the loading upper cover 21, and the pressure dispersion plate 271 is a ribbed plate, which is beneficial to dispersing the pressure of the hydraulic jack 3 on the entire pressure dispersion plate 271 and preventing it from concentrating at one place. At the same time, pressure buffering components are provided on the first bearing surface, the second bearing surface 25, and the third bearing surface 23. The pressure buffering component includes three pressure buffering plates provided on the bearing surface. The three pressure buffering plates form a drawer-shaped structure. The pressure dispersion component 27 is arranged inside the drawer-shaped structure, and there is a gap between the two.

[0055] In this embodiment, as Figure 6 、 7As shown in Figures 7 and 8, the true triaxial soil speckle observation device further includes a load-bearing frame 1. The load-bearing frame 1 includes a square frame and a triangular bracket perpendicularly connected to one end thereof. The upper and lower ends of the square frame are of I-shaped structures, that is, the I-shaped structures at both ends are frame crossbeams 12, and the structures on the left and right sides are frame columns 13. The upper I-shaped structure is connected to the first-direction stress loading component, and the lower I-shaped structure is connected to the bottom of the specimen chamber 2. There is an I-shaped column 11 arranged along the direction of the square frame on the triangular bracket, which is connected to the third-direction stress loading component. On the side of the I-shaped column 11 away from the square frame, there is a triangular channel steel support frame. Among them, the load-bearing frame 1 is a large-scale loading frame, made of high-strength alloy steel material, with a maximum bearing capacity of more than 10 tons. The bottom of the load-bearing frame 1 is equipped with universal wheels 15 for easy movement and convenient movement in a limited space; lifting lugs 14 are configured at the upper end to achieve the rapid movement and hoisting of the equipment.

[0056] At the top of the frame crossbeam 12 at the upper end of the load-bearing frame 1, there are multiple angle steels 17. Multiple threaded rods 18 are connected to the multiple angle steels 17. The multiple threaded rods 18 are arranged perpendicular to the frame crossbeam 12, and an I-shaped steel short column 16 is installed between the multiple threaded rods 18. One end of the I-shaped steel short column 16 is connected to the hydraulic jack 3, and a gasket 4 is arranged at the connection. The function of the gasket 4 is to flexibly adjust the distance between the hydraulic jack 3 and the I-shaped steel short column 16 because the extension distance of the hydraulic jack 3 is limited. The number of gaskets 4 can be flexibly adjusted to make the contact dense.

[0057] Three hydraulic jacks 3 can be installed on three sides of the load-bearing frame 1 to provide independent support reactions for the three stress loading directions and ensure the stability and accuracy of the loading process, mainly because the bottom of the hydraulic jack 3 needs sufficient support. Specifically, the first hydraulic jack 3 is installed above the first bearing surface. One end thereof abuts on one end of the I-shaped steel short column 16, and the other end contacts the pressure dispersion component 27 on the first bearing surface. When the hydraulic jack 3 extends, it should accurately abut on the central circular plate of the pressure dispersion component 27, so that the initial axis position of the hydraulic jack 3 coincides with the central position of the surface of the soil specimen 6, so that the initial state is a uniform loading state. The second hydraulic jack 3 is installed on the outer side of the second bearing surface 25. One end thereof is connected to the corresponding I-shaped column 11, and the other end contacts the pressure dispersion component 27 on the second bearing surface 25; the third hydraulic jack 3 is installed on the outer side of the third bearing surface 23. One end thereof is connected to the side end of the load-bearing frame 1, and the other end contacts the pressure dispersion component 27 on the third bearing surface 23.

[0058] Among them, the visible surface includes a square support frame and a toughened glass 291 connected to one side thereof, which forms an observation window 29. One side edge of the square support frame connected to the buffer surface 24 is set as a steel plate structure, and the other three side edges are all set as steel channel structures. The groove of the steel channel structure faces outward, and an L-shaped groove 292 is installed at the lower end position of the toughened glass 291, and the L-shaped groove 292 cooperates with the lower end of the toughened glass 291. The toughened glass 291 can be used to observe the change of the soil sample 6 during the loading process, and can also provide a glass transparent window for speckle photography, so that the high-speed camera can capture clear images of speckle displacement changes. Combining with the high-precision DIC (Digital Image Correlation) algorithm, the whole process record of the speckle displacement of the soil sample can be realized.

[0059] Here, the toughened glass 291 serves as the observation window 29. Since the observation window 29 part will bear a great force from the direction of the third-direction stress loading component, the glass of the observation window 29 must be made of toughened glass 291. The steel channel structure is a channel steel. Due to the cross-section stress characteristics of the channel steel, the web of the channel steel must face the stress direction, and the groove of the channel steel faces outward, which is beneficial to cleaning air dust and the broken soil generated by the experiment. The L-shaped groove 292 is an angle steel. Since steel and glass are two different hard substances, flexible glass glue is used to bond the toughened glass 291 to the square support frame. At the same time, angle steel is used to support the toughened glass 291 at the lower part to prevent the slow deformation and failure of the flexible glass glue.

[0060] The true triaxial soil speckle observation device further includes an L-shaped bottom plate 26 arranged at the bottom, and the L-shaped bend of the L-shaped bottom plate 26 cooperates with the L-shaped groove 292 at the lower end position of the toughened glass 291. Here, the drawer-shaped structure on the second bearing surface 25 is connected to the L-shaped bottom plate 26 through a bull's-eye pulley 261. Therefore, the gap size between the pressure dispersion component 27 and the drawer-shaped structure and the height of the bull's-eye pulley 261 should be coordinated. Neither can the height of the bull's-eye pulley 261 be too short, affecting the free sliding of the bearing surface, nor can the height of the bull's-eye pulley 261 be too high, resulting in a gap between the lower part of the second bearing surface 25 and the L-shaped bottom plate 26, causing the soil to leak from this place during loading.

[0061] Specific embodiment 4 of the true triaxial soil speckle observation device of the present invention:

[0062] Based on the above technical concept of the present invention, or on the basis of the specific embodiments of the present invention introduced above, another embodiment is provided below.

[0063] In this embodiment, as Figure 7As shown, the soil true triaxial speckle observation device also includes a loading control system. A stress sensor 5 is provided on the pressure dispersion component 27. The loading control system is used to control the loading stress of the first direction stress loading component, the second direction stress loading component and the third direction stress loading component according to the stress sensor 5.

[0064] Specifically, such as Figure 11 As shown, the loading mode can be selected. The loading pressure of the three hydraulic jacks 3 is controlled by the loading control system, and the total circuit of the hydraulic jacks 3 is controlled by a switch. When the switch is turned on, the entire control system starts to work. The loading control system can quantitatively set the load size in a certain direction, and then select the automatic gear. When the load display is greater than the load setting, the pressure output will automatically decrease. When the load display is less than the load setting, the pressure output will automatically increase, thereby ensuring the stability of the set load pressure value. You can also switch to manual gear to manually control the output pressure size. When you need to increase the load, press the jog button to increase, and when you need to reduce the load, press the jog button to decrease.

[0065] Specifically, the top of the hydraulic jack 3 is directly connected to the stress sensor 5. The three hydraulic jacks 3 correspond to three bearing surfaces, respectively, and can independently load the three bearing surfaces. A high-speed camera is used to shoot the visible surface, and the shooting requires synchronous high-speed continuous frame shooting. When pressure is applied to the surface of the soil sample 6, the soil sample 6 undergoes various deformations, and the speckle pattern sprayed on the soil surface will also change. These are all captured by the high-speed camera and processed to obtain displacement data. At the same time, the stress sensor 5 will also record the pressure load data. Here, the principle of speckle measurement of soil surface displacement is used to perform true triaxial speckle observation of the soil.

[0066] The principle of speckle pattern measurement of soil surface displacement is as follows: the first frame of the speckle image captured has no displacement, and the program needs to record the position of each point. Assume that the initial position of a point is (x0, y0), and after displacement, the position of the point changes to (x1, y1), and then changes to (x2, y2), (x3, y3)... (x n ,y n ), then by calculating:

[0067]

[0068] In this way, the total displacement of each point can be calculated. The distributed displacement of each step of the point can be calculated by the following formula:

[0069]

[0070] Finally, the displacement tracked and calculated for each point is summarized to form a displacement cloud image.

[0071] Specific Embodiment 1 of the True Triaxial Speckle Observation Method for Soil Mass of the Present Invention:

[0072] The present invention also provides a true triaxial speckle observation method for soil mass. Based on the above-mentioned true triaxial speckle observation device for soil mass, it includes the following steps:

[0073] Step 1: Place the soil sample 6 in the sample chamber 2;

[0074] Step 2: The first-direction stress loading component, the second-direction stress loading component, and the third-direction stress loading component simultaneously apply stress to the first bearing surface, the second bearing surface 25, and the third bearing surface 23; meanwhile, the observation device observes the changes of the soil sample 6 through the visible surface.

[0075] As mentioned above, it is only the preferred embodiment of the present invention and is not used to limit the present invention. The patent protection scope of the present invention is subject to the claims. Any equivalent structural changes made by using the description and drawings of the present invention should, by the same token, be included in the protection scope of the present invention.

Claims

1. A true triaxial speckle observation device for soil mass, characterized in that, Comprising: An observation device and a specimen chamber (2) for placing a soil specimen (6). The specimen chamber (2) includes a first bearing surface at the top, a second bearing surface (25) adjacent to its left side, a third bearing surface (23) at the rear side, a buffer surface (24) at the right side, and a visible surface at the front side. A first-direction stress loading component, a second-direction stress loading component, and a third-direction stress loading component are respectively provided on the first bearing surface, the second bearing surface (25), and the third bearing surface (23); wherein, the first bearing surface is a deformable bearing surface, and a sliding mechanism is provided at the contact positions between the second bearing surface (25), the third bearing surface (23), the buffer surface (24), and the visible surface, such that they can slide relative to each other through the sliding mechanism; the observation device is used to observe the soil specimen (6) through the visible surface.

2. The true triaxial soil speckle observation device according to claim 1, wherein The sliding mechanism is a roller (28), and the roller is arranged along the length direction of the contact position; and the first bearing surface is a soft structure, and the soft structure deforms with the stresses generated by the first-direction stress loading component, the second-direction stress loading component, and the third-direction stress loading component.

3. The true triaxial soil speckle observation device according to claim 1, wherein, The true triaxial soil speckle observation device further includes an internal loading mechanism, and the internal loading mechanism includes an airbag (7), an air pipe (8), and a pneumatic controller. The airbag (7) is installed inside the soil specimen (6) and is arranged along the direction perpendicular to the third bearing surface (23); one end of the air pipe (8) is communicated with the airbag (7), and the other end passes through the soil specimen (6) and extends out through the first bearing surface for conducting gas; the pneumatic controller is arranged on the air pipe (8) and is used to control the magnitude of the gas pressure, and further control the magnitude of the pressure exerted by the airbag (7) on the soil specimen (6).

4. The true triaxial soil speckle observation device according to claim 1, characterized in that, Pressure dispersion components (27) are provided on the first bearing surface, the second bearing surface (25), and the third bearing surface (23). The pressure dispersion components (27) include pressure dispersion plates (271) arranged along the bearing surface and pressure support plates (272) penetrating and connecting the pressure dispersion plates (271), and a central circular plate is provided at the part of the pressure dispersion component (27) for contacting the stress loading component.

5. The true triaxial soil speckle observation device according to claim 4, characterized in that The true triaxial soil speckle observation device further includes a loading control system. Stress sensors (5) are provided on the pressure dispersion components (27), and the loading control system is used to control the loading stresses of the first-direction stress loading component, the second-direction stress loading component, and the third-direction stress loading component according to the stress sensors (5).

6. The true triaxial soil speckle observation device according to claim 4, characterized in that Pressure buffer components are provided on the first bearing surface, the second bearing surface (25), and the third bearing surface (23). The pressure buffer components include three pressure buffer plates provided on the bearing surface, and the three pressure buffer plates form a drawer-shaped structure. The pressure dispersion component is arranged inside the drawer-shaped structure, and there is a gap between them.

7. The true triaxial soil speckle observation device according to claim 1, characterized in that The true triaxial soil speckle observation device further includes a bearing frame (1). The bearing frame (1) includes a square frame and a triangular bracket vertically connected to one end thereof. The upper and lower ends of the square frame are of I-shaped structures. The upper I-shaped structure is connected to the first-direction stress loading component, and the lower I-shaped structure is connected to the bottom of the specimen chamber (2). An I-shaped column (11) is arranged on the triangular bracket along the height direction of the square frame and is connected to the third-direction stress loading component. A triangular channel steel support frame is arranged on the side of the I-shaped column (11) away from the square frame.

8. The true triaxial soil speckle observation device according to claim 1, characterized in that The visible surface includes a square support frame and a toughened glass (291) connected to one side surface thereof. One side edge of the square support frame connected to the buffer surface (24) is set as a steel plate structure, and the other three side edges are all set as steel channel structures. The grooves of the steel channel structures face outward, and an L-shaped groove (292) is installed at the lower end position of the toughened glass (291), and the L-shaped groove (292) is matched with the lower end of the toughened glass (291).

9. The true triaxial soil speckle observation device according to claim 8, characterized in that The true triaxial soil speckle observation device further includes an L-shaped bottom plate (26) arranged at the bottom. The L-shaped bending part of the L-shaped bottom plate (26) is matched with the L-shaped groove (292) at the lower end position of the toughened glass (291).

10. A true triaxial speckle observation method for soil mass, characterized in that Based on the true triaxial soil speckle observation device according to any one of claims 1-9, the following steps are included: Step 1: Place the soil specimen (6) in the specimen chamber (2); Step 2: The first-direction stress loading component, the second-direction stress loading component, and the third-direction stress loading component simultaneously apply stresses to the first bearing surface, the second bearing surface (25), and the third bearing surface (23); Meanwhile, the observation device observes the changes of the soil specimen (6) through the visible surface.

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