Large-scale shear test device and method for root reinforced soil based on PIV technology

Abstract

The present invention discloses a large-scale shear test device and method for root reinforced soil based on PIV technology, which belongs to the field of geotechnical testing, and includes a test bench, an embedded combined shear box arranged on the top of the test bench, a mechanical loading mechanism for loading a sample in the embedded combined shear box, and a monitoring mechanism, wherein the monitoring mechanism includes a displacement sensor assembly and a PIV camera assembly arranged on the mechanical loading mechanism, wherein the displacement sensor assembly and the PIV camera assembly are both connected to a computer, and the PIV camera assembly is aligned with a transparent observation surface of the embedded combined shear box. The present invention adopts the above-mentioned large-scale shear test device and method for root reinforced soil based on PIV technology, and uses PIV technology (particle image velocimetry technology) to monitor the movement direction and velocity of shear zone soil particles in real time during the shear test, so as to obtain the evolution process of the shear zone of the soil under the reinforcement effect of the undisturbed plant root system, and gain an in-depth understanding of the stability and safety issues of the root reinforced soil.

Description

Technical Field

[0001] The invention relates to the field of geotechnical tests, and in particular to a large-scale shear test device and method for root reinforced soil based on PIV technology. Background Art

[0002] In recent years, due to the impact of climate warming, the intensified water cycle has led to frequent extreme weather such as typhoons and rainstorms. Environmental geological disasters such as landslides and soil erosion have become increasingly prominent, causing a large number of casualties and property losses.

[0003] The existing plant protection and restoration technology can improve the above problems. Plants can not only reduce soil erosion and improve slope stability, but also reduce net carbon dioxide emissions with their strong carbon fixation ability. They have both engineering protection and environmental beautification effects, and play a very positive role in responding to climate change and the natural disasters it causes. However, due to the complex interaction between roots and soil, the vegetation suitable for growth in different regions is also very different, resulting in the fact that its basic theory has not been well developed, and many applications are still based on experience, which limits the large-scale application of vegetation in the field of natural disaster prevention and slope protection.

[0004] The root system can be regarded as a three-dimensional reinforcement material with a prestressed effect, which can improve the shear strength of the soil. Domestic and foreign scholars have conducted a lot of research on the reinforcement and soil consolidation effect of plant roots based on factors such as soil root content and root system configuration through direct shear tests, triaxial tests, and field in-situ shear tests. Among them, the triaxial test instrument has problems such as cumbersome operation and long test cycle. The field in-situ shear test has high requirements for site selection and uniformity of soil physical and chemical properties. The direct shear test is easy to operate and has strong repeatability, but most of the existing direct shear test devices are small in size, and the boundary effect has a large influence during the shear process. At the same time, direct shear tests often use fiber or disturbed root reshaped reinforced soil to carry out the test, which cannot reflect the interaction between the root system and the soil under real conditions.

[0005] At the same time, the large-scale shear test equipment commonly used in laboratories for reinforced soil usually directly fills and compacts the overall shear box before conducting shear tests. The filling and compaction process of soil samples often wastes a lot of time, and multiple reinforced soil sample preparations cannot be carried out simultaneously, resulting in low shear efficiency. In addition, for naturally growing reinforced bodies such as plant roots, large-scale shear tests often use simulated roots instead of natural roots, which causes large soil disturbance and poor test repeatability. Summary of the invention

[0006] In order to solve the above problems, the present invention provides a large-scale shear test device and method for root reinforced soil based on PIV technology. The PIV technology (particle image velocimetry technology) is used to monitor the shear zone soil particles and velocities in real time during the shear test, so as to obtain the evolution process of the soil shear zone under the reinforcement of the undisturbed plant roots, and gain an in-depth understanding of the stability and safety issues of the root reinforced soil.

[0007] To achieve the above-mentioned objectives, the present invention provides a large-scale shear test device for root reinforced soil based on PIV technology, comprising a test bench, an embedded combined shear box arranged on the top of the test bench, a mechanical loading mechanism for loading the sample in the embedded combined shear box, and a monitoring mechanism, the monitoring mechanism comprising a displacement sensor assembly and a PIV camera assembly arranged on the mechanical loading mechanism, the displacement sensor assembly and the PIV camera assembly are both connected to a computer, and the PIV camera assembly is aligned with a transparent observation surface of the embedded combined shear box.

[0008] Preferably, the embedded combined shear box comprises an upper direct shear box and a lower direct shear box located at the bottom end of the upper direct shear box;

[0009] An inverted U-shaped fixing frame is fixed on the top of the test bench. The mechanical loading mechanism includes a lifting unit for moving the upper direct shear box upward to a set distance, a vertical loading unit for applying a vertical force to the test in the upper direct shear box, and a horizontal loading unit for applying a horizontal thrust to the lower direct shear box.

[0010] Preferably, the vertical loading unit comprises a top plate fixed to the inner wall of the top end of the inverted U-shaped fixing frame and located directly above the embedded combined shear box, a loading cylinder fixed to the bottom end of the top plate, and a vertical loading head fixed to the bottom output end of the piston rod of the loading cylinder, a vertical loading plate is also fixed to the bottom end of the vertical loading head, the center of the vertical loading plate and the center of the embedded combined shear box are located on the same vertical axis, and the cross-sectional dimension of the vertical loading plate is smaller than the inner dimension of the cross-sectional dimension of the embedded combined shear box; a guide plate is also fixed to the piston rod of the loading cylinder, the guide plate is slidably connected to the bottom end of the vertical guide rod, and the top end of the vertical guide rod is fixedly connected to the top plate;

[0011] The horizontal loading unit includes a horizontal servo motor fixed on an inner wall of one side of the bottom end of the inverted U-shaped fixing frame and located on one side of the embedded combined shear box, a reducer connected to the output end of the horizontal servo motor, a horizontal lead screw connected to the output end of the reducer, a horizontal displacement nut threadedly connected to the horizontal lead screw, and a horizontal loading plate fixedly connected to one end of the horizontal displacement nut away from the horizontal lead screw, the horizontal displacement nut is also horizontally slidably connected to a horizontal guide rod fixed to the housing of the horizontal servo motor, the horizontal loading plate is aligned with one side of the lower direct shear box, and the horizontal loading plate is also fixedly connected to the inverted U-shaped fixing frame via the horizontal guide rod;

[0012] The lifting unit includes a lifting drive motor fixed on the inner wall on the other side of the bottom end of the inverted U-shaped fixing frame, a vertical lead screw connected to the top output end of the lifting drive motor via a coupling, a vertical displacement nut threadedly connected to the vertical lead screw, and a lifting panel connected to the vertical displacement nut. A lifting connecting plate is fixed to the side of the lifting panel facing the upper direct shear box embedded in the combined shear box via a suspension rod, and the lifting connecting plate is fixedly connected to the side of the upper direct shear box; vertical guide rails are fixed on the inverted U-shaped fixing frame and on both sides of the vertical lead screw, the vertical guide rails are vertically slidably connected to the lifting panel, and vertical limit blocks are fixed to the upper and lower ends of the vertical guide rails.

[0013] Preferably, the displacement sensor assembly includes four vertical displacement sensors arranged at the four corners of the top plate, a first pressure sensor arranged at the bottom end of the vertical loading plate, a horizontal displacement sensor arranged on the horizontal servo motor, and a second pressure sensor arranged on the side of the horizontal loading plate facing the lower direct shear box, wherein the four vertical displacement sensors are used to monitor the overall vertical displacement of the top surface of the sample in real time, the first pressure sensor is used to monitor the vertical loading force applied by the vertical loading unit to the top of the embedded combined shear box, the horizontal displacement sensor is used to monitor the horizontal displacement of the lower direct shear box, and the second pressure sensor is used to monitor the horizontal loading force applied by the horizontal loading unit to the side of the lower direct shear box;

[0014] The PIV camera assembly includes a tripod support frame, a fixed platform fixed on the top of the tripod support frame, and a PIV camera fixed on the top of the fixed platform. The camera head of the PIV camera faces the transparent observation surface embedded in the combined shear box, and a ring light source is fixed on the fixed platform between the camera head of the PIV camera and the embedded combined shear box.

[0015] Preferably, the bottom end of the embedded combined shear box is slidably disposed on the top end of the test bench via a bottom plate and a horizontal guide rail, and vertical limit blocks are fixed at both ends of the horizontal guide rail.

[0016] Preferably, the sample includes a soil sample and tracer particles, and the upper direct shear box and the lower direct shear box both include a semi-enclosed shear box and a baffle, the semi-enclosed shear box is a hollow box structure with openings on the top, bottom and one side, and the side opening position of the semi-enclosed shear box is fixedly connected to the baffle by screws.

[0017] Preferably, the sample includes a soil sample, a plant root system and tracer particles, the upper direct shear box and the lower direct shear box both include a semi-enclosed shear box and a plant culture box, the semi-enclosed shear box is a hollow box structure with openings on the top and bottom and one side, the plant culture box is a hollow box structure with openings on the top and bottom, and an assembly plate is provided on one side of the plant culture box facing the semi-enclosed shear box;

[0018] The plant culture box is inserted into the semi-enclosed shear box from the side opening of the semi-enclosed shear box, and both sides of the assembly plate are fixedly connected to the side opening of the semi-enclosed shear box by screws;

[0019] A monitoring hole is provided on the side of the plant culture box, and a soil moisture sensor is inserted into the monitoring hole or a sealing plate is clamped in the monitoring hole;

[0020] The bottom end of the plant culture box is in contact with the culture water permeable plate or the bottom plate.

[0021] Preferably, when the soil sample is gravel soil, the tracer particles are white ceramic particles or reinforced soil sample materials;

[0022] When the soil sample is silt or clay, the tracer particles are white quartz sand of 20-80 mesh.

[0023] Preferably, the upper semi-enclosed shear box and the lower semi-enclosed shear box are fixedly connected by screws and ear plates in sequence;

[0024] A water-permeable plate is arranged at the top end of the embedded combined shear box, or a water-blocking plate is arranged at the bottom end of the embedded combined shear box.

[0025] The method of the large-scale shear test device for root reinforced soil based on PIV technology comprises the following steps:

[0026] S1. Sample acquisition and loading:

[0027] When the sample includes a soil sample and tracer particles, the sample acquisition steps are as follows: first, the soil sample and the tracer particles are mixed to obtain the sample, and then two baffles are respectively fixed to the opening ends of the upper semi-enclosed shear box and the lower semi-enclosed shear box to form an embedded combined shear box, and finally the sample is pressed into the embedded combined shear box in layers until it is filled;

[0028] When the sample includes a soil sample, a plant root system and tracer particles, the sample acquisition steps are as follows: first, the soil sample and the tracer particles are mixed, and pressed into a plant culture box in layers until they are flush with the top of the plant culture box, plant seeds are sown, and then soil is covered on the top of the plant seeds, and then a soil moisture sensor is inserted into the soil in the plant culture box, and culture is carried out until the plant roots contact the culture permeable plate and the soil moisture content collected by the soil moisture sensor reaches a set value, the soil moisture sensor is pulled out and the sealing plate is inserted into the monitoring hole, and at the same time, the above-ground plants are cut off and leveled, and the plant culture box is inserted into the semi-enclosed shear box, and the upper plant culture box and the upper semi-enclosed shear box, as well as the lower plant culture box and the lower semi-enclosed shear box are respectively fixed with screws to form an embedded combined shear box;

[0029] S2. Shear test:

[0030] First, turn on the annular light source and the PIV camera. Under the monitoring of the PIV camera, use the lifting unit to drive the upper direct shear box to move upward to the set shear zone height. Then use the vertical loading unit to apply a vertical load to the top of the upper direct shear box. After a set time, use the horizontal loading unit to apply a horizontal load to the lower direct shear box. In this process, use the displacement sensor assembly to collect the overall vertical displacement, vertical loading force, horizontal displacement and horizontal loading force of the sample respectively.

[0031] S3. Experimental analysis:

[0032] The shear stress-horizontal displacement curve and the vertical strain-horizontal displacement curve are plotted using the Origin drawing software based on the overall vertical displacement, vertical loading force, horizontal displacement and horizontal loading force of the specimen obtained in step S2, and the PIV camera is used to perform PIV processing on the acquired images to obtain the evolution process.

[0033] The present invention has the following beneficial effects:

[0034] 1. PIV technology (particle image velocimetry) is used to monitor the shear zone soil particles and velocity in real time during the shear test, which can obtain the evolution process of the soil shear zone under the reinforcement of the undisturbed plant roots, and gain an in-depth understanding of the stability and safety of the root-reinforced soil, solving the problem that existing instruments and equipment cannot effectively study the sliding deformation of plant roots in the soil and their true reinforcement effect;

[0035] 2. It can carry out large-scale shear tests on root-soil complexes or other types of reinforced soils with a length, width and height of 30 cm. That is, the soil shear size is large, which reduces the boundary effect in traditional conventional shear tests, so that the shear strength of soils with different textures can be measured and the reinforcement effect of different reinforcement materials can be obtained more accurately.

[0036] 3. The culture box and the shear box are embedded and filled as a whole, which reduces the disturbance to the soil and roots during the traditional sampling and sample filling process, and can more truly reflect the reinforcement effect of the roots on the soil, thereby effectively measuring the reinforcement effect of the roots under natural growth conditions. At the same time, it makes the shear test operation more convenient and efficient, and the sample is less likely to be damaged during the filling process, thereby improving the repeatability of large-scale shear tests;

[0037] 4. The transparent side wall of the direct shear box makes the PIV technology have a wider visual range, which can effectively analyze the displacement and deformation of soil particles in a larger sample range;

[0038] 5. The use of four vertical displacement sensors can effectively obtain the overall displacement changes of the top surface of the specimen, thereby accurately reflecting the shear expansion phenomenon of the test. At the same time, the use of horizontal displacement sensors can more accurately reflect the displacement of the soil on the side where the PIV technology is applied, thereby more effectively analyzing the movement of the soil particles on that side.

[0039] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a schematic diagram of the overall structure of the large-scale shear test device for root reinforced soil based on PIV technology of the present invention;

[0041] Figure 2 It is a schematic diagram of the lifting unit structure of the large-scale shear test device for root reinforced soil based on PIV technology of the present invention;

[0042] Figure 3 It is a schematic diagram of the vertical loading unit structure of the large-scale shear test device for root reinforced soil based on PIV technology of the present invention;

[0043] Figure 4 It is a schematic diagram of the structure of the horizontal loading unit of the large-scale shear test device for root reinforced soil based on the PIV technology of the present invention;

[0044] Figure 5 It is a schematic diagram of the structure of the PIV camera assembly of the large-scale shear test device for root reinforced soil based on the PIV technology of the present invention;

[0045] Figure 6 It is a schematic diagram of the plant culture box structure of the large-scale shear test device for root reinforced soil based on PIV technology of the present invention;

[0046] Figure 7 This is a schematic diagram of the assembly of a semi-enclosed shear box and a baffle of a large-scale shear test device for root reinforced soil based on PIV technology of the present invention.

[0047] Among them: 1. Test bench; 11. Inverted U-shaped fixing frame; 2. Vertical loading unit; 21. Vertical guide rod; 22. Vertical loading head; 23. Loading cylinder; 24. Vertical loading plate; 25. Top plate; 3. Lifting unit; 31. Lifting drive motor; 32. Vertical lead screw; 33. Lifting panel; 34. Vertical guide rail; 35. Vertical limit block; 36. Suspension rod; 37. Lifting connecting plate; 4. Horizontal loading unit; 41. Horizontal servo motor; 42. Horizontal lead screw; 43. Horizontal displacement nut; 44. Horizontal loading plate; 45. Horizontal guide rod; 5. Monitoring mechanism; 51. Horizontal displacement sensor; 52. Vertical displacement sensor; 53. Ring light source; 54. PIV camera; 55. Triangle support frame; 6. Semi-enclosed shear box; 61. Ear plate; 7. Plant culture box; 71. Assembly plate; 72. Sealing plate; 73. Soil moisture sensor; 8. Horizontal guide rail; 9. Culture permeable plate; 10. Baffle. DETAILED DESCRIPTION

[0048] In order to make the purpose, technical scheme and advantages disclosed in the embodiments of the present invention clearer, the embodiments of the present invention are further described in detail in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the embodiments of the present invention and are not intended to limit the embodiments of the present invention. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application. Examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions.

[0049] It should be noted that the terms "include", "have" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or server comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products or devices.

[0050] Like reference numerals and letters denote similar items in the following drawings, and thus, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0051] In the description of the present invention, it should be noted that the terms "upper", "lower", "inside", "outside", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings, or are directions or positional relationships in which the product of the invention is usually placed when in use. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as a limitation on the present invention.

[0052] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "setting", "installation" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0053] PIV technology (Particle Image Velocimetry) is an advanced technology for measuring fluid velocity fields. It has been increasingly widely used in geotechnical tests in recent years. This technology measures the velocity field by tracking the movement of particles. It has the advantages of non-contact, full-field measurement, and high precision. It is particularly suitable for studying complex particle movement phenomena. Therefore, PIV technology is used in large-scale shear tests of root-reinforced soil to monitor the changes in the velocity field of soil particles during stress, deformation, and destruction, to explore the influence of the reinforcement of the roots of naturally growing plants on the soil shear zone, and to reveal the deformation mechanism and destruction process of root-reinforced soil. This is of great significance for predicting the stability of the soil and evaluating the safety of the project.

[0054] Based on the above analysis, the present invention is designed as follows: Figure 1-Figure 7 As shown, the large-scale shear test device for root reinforced soil based on PIV technology described in the present invention includes a test bench 1, an embedded combined shear box arranged on the top of the test bench 1, a mechanical loading mechanism for loading the sample embedded in the combined shear box, and a monitoring mechanism 5. The monitoring mechanism 5 includes a displacement sensor assembly and a PIV camera assembly arranged on the mechanical loading mechanism. The displacement sensor assembly and the PIV camera assembly are both connected to a computer, and the PIV camera assembly is aligned with a transparent observation surface of the embedded combined shear box.

[0055] Among them, the embedded combined shear box includes an upper direct shear box and a lower direct shear box located at the bottom of the upper direct shear box; an inverted U-shaped fixing frame 11 is fixed to the top of the test bench 1, and the mechanical loading mechanism includes a lifting unit 3 for moving the upper direct shear box upward to a set distance, a vertical loading unit 2 for applying a vertical force to the test in the upper direct shear box, and a horizontal loading unit 4 for applying a horizontal thrust to the lower direct shear box.

[0056] Specifically, the vertical loading unit 2 includes a top plate 25 fixed to the inner wall of the top end of the inverted U-shaped fixing frame 11 and located directly above the embedded combined shear box, a loading cylinder 23 fixed to the bottom end of the top plate 25, and a vertical loading head 22 fixed to the bottom output end of the piston rod of the loading cylinder 23. A vertical loading plate 24 is also fixed to the bottom end of the vertical loading head 22. The center of the vertical loading plate 24 and the center of the embedded combined shear box are located on the same vertical axis, and the cross-sectional size of the vertical loading plate 24 is smaller than the cross-sectional size of the embedded combined shear box. A guide plate is also fixed to the piston rod of the loading cylinder 23. The guide plate is slidably connected to the bottom end of the vertical guide rod 21, and the top end of the vertical guide rod 21 is fixedly connected to the top plate 25. In this embodiment, the air source input range of the loading cylinder 23 is 0Mpa-0.8Mpa, the maximum force that can be applied is 30KN, the pressure range is 0Kpa-300Kpa (cross-section 300×300mm), the applied force accuracy is 1Kpa, and the maximum stroke is 0mm-50mm. The vertical loading unit 2 is used to achieve: the loading cylinder 23 drives the vertical loading plate 24 to reciprocate up and down through the piston rod and the vertical loading head 22, and in the process of moving downward, it extends into the top of the embedded combined shear box to apply a vertical loading force to the sample;

[0057] The horizontal loading unit 4 includes a horizontal servo motor 41 fixed on the inner wall of one side of the bottom end of the inverted U-shaped fixing frame 11 and located on one side of the embedded combined shear box, a reducer connected to the output end of the horizontal servo motor 41, a horizontal lead screw 42 connected to the output end of the reducer, a horizontal displacement nut 43 threadedly connected to the horizontal lead screw 42, and a horizontal loading plate 44 fixedly connected to one end of the horizontal displacement nut 43 away from the horizontal lead screw 42. The horizontal displacement nut 43 is also horizontally slidably connected to a horizontal guide rod 45 fixed on the housing of the horizontal servo motor 41. In this embodiment, the horizontal guide rod 45 is fixed on an outer sheath coaxially arranged with the rotating shaft of the horizontal servo motor 41, and the horizontal loading plate 44 is aligned with one side of the lower direct shear box; the above-mentioned horizontal loading unit 4 is implemented: the horizontal servo motor 41 drives the horizontal lead screw 42 to rotate through the reducer, and drives the horizontal displacement nut 43 to move horizontally along the horizontal lead screw 42 under the cooperation of the thread, thereby driving the horizontal loading plate 44 to move horizontally back and forth, and applying a horizontal loading force to the lower direct shear box during the movement. In this embodiment, the maximum thrust that the horizontal loading unit 4 can apply is 50KN, and the corresponding horizontal driving stroke is 60mm, the displacement accuracy is 0.01mm, and the loading speed range is 0.1mm / min-20mm / min. In the test, the displacement of the sample cross-sectional size 20% strain is taken as the shear termination displacement;

[0058] The lifting unit 3 includes a lifting drive motor 31 fixed on the inner wall of the other side of the bottom end of the inverted U-shaped fixed frame 11, a vertical lead screw 32 connected to the top output end of the lifting drive motor 31 through a coupling, a vertical displacement nut threadedly connected to the vertical lead screw 32, and a lifting panel 33 connected to the vertical displacement nut. The lifting panel 33 is fixed with a lifting connection plate 37 on one side facing the upper layer direct shear box embedded in the combined shear box through a suspension rod 36, and the lifting connection plate 37 is fixedly connected to the side of the upper layer direct shear box; vertical guide rails 34 are fixed on both sides of the inverted U-shaped fixed frame 11 and located on the vertical lead screw 32. The vertical guide rails 34 are vertically slidably connected to the lifting panel 33, and vertical limit blocks 35 are fixed at both ends of the vertical guide rails 34. The lifting unit 3 is realized by: the lifting drive motor 31 drives the vertical lead screw 32 to rotate, and at this time, the vertical displacement nut is driven to move along the vertical lead screw 32 under the action of the thread, thereby driving the upper layer direct shear box to move up and down through the lifting connection plate 37.

[0059] The displacement sensor assembly includes four vertical displacement sensors 52 arranged at the four corners of the top plate 25, a first pressure sensor arranged at the bottom end of the vertical loading plate 24, a horizontal displacement sensor 51 arranged on the horizontal servo motor 41 and a second pressure sensor arranged on the side of the horizontal loading plate 44 facing the lower direct shear box, wherein the four vertical displacement sensors 52 are used to monitor the overall vertical displacement of the top surface of the sample in real time, the first pressure sensor is used to monitor the vertical loading force applied by the vertical loading unit 2 to the top of the embedded combined shear box, the horizontal displacement sensor 51 is used to monitor the horizontal displacement of the lower direct shear box, and the second pressure sensor is used to monitor the horizontal loading force applied by the horizontal loading unit 4 to the side of the lower direct shear box; the PIV camera assembly includes a tripod support frame 55, a fixed platform fixed to the top of the tripod support frame 55, and a PIV camera 54 fixed to the top of the fixed platform, the camera of the PIV camera 54 faces the transparent observation surface of the embedded combined shear box, and a ring light source 53 is fixed on the fixed platform between the camera of the PIV camera 54 and the embedded combined shear box.

[0060] The bottom end of the embedded combined shear box is slidably arranged on the top end of the test bench 1 through the bottom plate and the horizontal guide rail 8. Both ends of the horizontal guide rail 8 are fixed with vertical limit blocks 35 to facilitate the adjustment of the position of the embedded combined shear box.

[0061] The sample includes a soil sample and tracer particles, that is, conventional reinforced soil. The upper direct shear box and the lower direct shear box both include a semi-enclosed shear box 6 and a baffle 10. The semi-enclosed shear box 6 is a hollow box structure with openings on the top, bottom and one side, that is, a concave structure, and the side opening position of the semi-enclosed shear box 6 is fixedly connected to the baffle 10 by screws.

[0062] Alternatively, the sample includes a soil sample, a plant root system and tracer particles, that is, reinforced soil containing a plant root system, and the upper direct shear box and the lower direct shear box both include a semi-enclosed shear box 6 and a plant culture box 7, the semi-enclosed shear box 6 is a hollow box structure with openings on the top, bottom and one side, the plant culture box 7 is a hollow box structure with openings on the top and bottom, and an assembly plate 71 is provided on the side of the plant culture box 7 facing the semi-enclosed shear box 6; the plant culture box 7 is inserted into the interior of the semi-enclosed shear box 6 from the side opening side of the semi-enclosed shear box 6, and both sides of the assembly plate 71 are fixedly connected to the side opening position of the semi-enclosed shear box 6 by screws; a monitoring hole is opened on the side of the plant culture box 7, and a soil moisture sensor 73 is inserted into the monitoring hole or a sealing plate 72 is clamped in the monitoring hole; the bottom end of the plant culture box 7 is in contact with the culture permeable plate 9 or the bottom plate.

[0063] When the soil sample is gravel soil, the tracer particles are white ceramic particles or reinforced soil sample materials; when the soil sample is silt or clay, the tracer particles are white quartz sand with a mesh size of 20-80.

[0064] The upper semi-enclosed shear box 6 and the lower semi-enclosed shear box 6 are fixedly connected in sequence by screws and ear plates 61, so that when conducting conventional reinforced soil experiments, the upper semi-enclosed shear box 6 and the lower semi-enclosed shear box 6 can be fixed by screws to facilitate loading of samples, and the screws can be removed after loading to facilitate experiments; a permeable plate is provided at the top end of the embedded combined shear box, or a water-blocking plate is provided at the bottom end of the embedded combined shear box.

[0065] In this embodiment, the semi-enclosed shear box 6 is made of an opaque metal material with one side open, and the plant culture box 7 is made of a transparent acrylic material, so that after the plant culture box 7 is inserted from the open side of the semi-enclosed shear box 6, the insertion side of the plant culture box 7 is aligned with the PIV camera assembly.

[0066] The method of the large-scale shear test device for root reinforced soil based on PIV technology comprises the following steps:

[0067] S1. Sample acquisition and loading:

[0068] When the sample includes a soil sample and tracer particles, the sample acquisition steps are as follows: first, the soil sample and the tracer particles are mixed to obtain the sample, and then two baffles 10 are respectively fixed to the opening ends of the upper semi-enclosed shear box 6 and the lower semi-enclosed shear box 6 to form an embedded combined shear box, and finally the sample is pressed into the embedded combined shear box in layers until it is filled;

[0069] When the sample includes soil sample, plant root system and tracer particles, the sample acquisition steps are as follows: first, the soil sample and the tracer particles are mixed, and layered and pressed (scrape the hair between layers and compact the soil sample) into the plant culture box until it is flush with the top of the plant culture box, plant seeds are sown, and then soil is covered on the top of the plant seeds, and then the soil moisture sensor 73 is inserted into the soil in the plant culture box 7, and cultivated (watering is performed regularly during the cultivation process, and the distribution of the plant roots in the plant culture box 7 is observed) until the plant roots contact the culture permeable plate 9 and the soil moisture content collected by the soil moisture sensor 73 reaches the set value. In this embodiment, when the plant roots grow naturally to contact the culture permeable plate 9, the cultivation can be ended, the soil moisture sensor 73 is pulled out and the sealing plate 72 is inserted into the monitoring hole, and at the same time, the above-ground plants are cut off and leveled, and the plant culture box 7 is inserted into the semi-enclosed shear box 6, and the upper plant culture box 7 and the upper semi-enclosed shear box 6, as well as the lower plant culture box 7 and the lower semi-enclosed shear box 6 are respectively fixed with screws to form an embedded combined shear box;

[0070] S2. Shear test:

[0071] First, the annular light source 53 and the PIV camera 54 are turned on. Under the monitoring of the PIV camera 54, the upper direct shear box is driven to move upward to the set shear zone height by the lifting unit 3, and then the vertical loading unit 2 is used to apply a vertical load to the top of the upper direct shear box. After a set time, the horizontal loading unit 4 is used to apply a horizontal load to the lower direct shear box. In this process, the displacement sensor assembly is used to collect the overall vertical displacement, vertical loading force, horizontal displacement and horizontal loading force of the sample respectively;

[0072] S3. Experimental analysis:

[0073] The shear stress-horizontal displacement curve and the vertical strain-horizontal displacement curve are plotted using the Origin drawing software based on the overall vertical displacement, vertical loading force, horizontal displacement and horizontal loading force of the sample obtained in step S2, and the PIV camera 54 is used to perform PIV processing on the collected image to obtain the evolution process (in this embodiment, the image is processed using the Pivlab program developed based on Matlab using the PIV technology to trace the movement direction and speed of the soil particles, thereby obtaining the evolution process), which facilitates the subsequent analysis of the influence of plant roots, fibers and other reinforcements on the movement and displacement of the soil body, the range of the shear band, the displacement of the shear band and the evolution characteristics.

[0074] Therefore, the present invention adopts the above-mentioned large-scale shear test device and method for root reinforced soil based on PIV technology, and uses PIV technology (particle image velocimetry technology) to monitor the shear zone soil particles and velocity in real time during the shear test, so as to obtain the evolution process of the soil shear zone under the reinforcement effect of the undisturbed plant roots, and gain an in-depth understanding of the stability and safety issues of the root reinforced soil.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A large-scale shear test device for root reinforced soil based on PIV technology, characterized by: It includes a test bench, an embedded combined shear box arranged on the top of the test bench, a mechanical loading mechanism for loading a sample in the embedded combined shear box, and a monitoring mechanism, wherein the monitoring mechanism includes a displacement sensor assembly and a PIV camera assembly arranged on the mechanical loading mechanism, wherein the displacement sensor assembly and the PIV camera assembly are both connected to a computer, and the PIV camera assembly is aligned with a transparent observation surface of the embedded combined shear box; The embedded combined shear box comprises an upper direct shear box and a lower direct shear box located at the bottom end of the upper direct shear box; An inverted U-shaped fixing frame is fixed on the top of the test bench, and the mechanical loading mechanism includes a lifting unit for moving the upper direct shear box upward to a set distance, a vertical loading unit for applying a vertical force to the test in the upper direct shear box, and a horizontal loading unit for applying a horizontal thrust to the lower direct shear box; The sample includes a soil sample, a plant root system and tracer particles. The upper direct shear box and the lower direct shear box both include a semi-enclosed shear box and a plant culture box. The semi-enclosed shear box is a hollow box structure with openings on the top, bottom and one side. The plant culture box is a hollow box structure with openings on the top and bottom, and an assembly plate is provided on one side of the plant culture box facing the semi-enclosed shear box. The plant culture box is inserted into the semi-enclosed shear box from the side opening of the semi-enclosed shear box, and both sides of the assembly plate are fixedly connected to the side opening of the semi-enclosed shear box by screws; A monitoring hole is provided on the side of the plant culture box, and a soil moisture sensor is inserted into the monitoring hole or a sealing plate is clamped in the monitoring hole; The bottom end of the plant culture box is in contact with the culture permeable plate or the bottom plate; The method of the large-scale shear test device for root reinforced soil based on PIV technology comprises the following steps: S1. Sample acquisition and loading: First, the soil sample and the tracer particles are mixed, and the soil sample and the tracer particles are pressed into the plant culture box in layers until they are flush with the top of the plant culture box, and the plant seeds are sown, and then the soil is covered on the top of the plant seeds, and then the soil moisture sensor is inserted into the soil in the plant culture box, and the soil is cultivated until the plant root system contacts the culture permeable plate and the soil moisture content collected by the soil moisture sensor reaches the set value, and then the soil moisture sensor is pulled out and the sealing plate is inserted into the monitoring hole, and at the same time, the above-ground plants are cut off and leveled, and the plant culture box is inserted into the semi-enclosed shear box, and the upper plant culture box and the upper semi-enclosed shear box, as well as the lower plant culture box and the lower semi-enclosed shear box are respectively fixed with screws to form an embedded combined shear box; S2. Shear test: First, turn on the annular light source and the PIV camera. Under the monitoring of the PIV camera, use the lifting unit to drive the upper direct shear box to move upward to the set shear zone height. Then use the vertical loading unit to apply a vertical load to the top of the upper direct shear box. After a set time, use the horizontal loading unit to apply a horizontal load to the lower direct shear box. In this process, use the displacement sensor assembly to collect the overall vertical displacement, vertical loading force, horizontal displacement and horizontal loading force of the sample respectively. S3. Experimental analysis: The shear stress-horizontal displacement curve and the vertical strain-horizontal displacement curve are plotted using the Origin drawing software based on the overall vertical displacement, vertical loading force, horizontal displacement and horizontal loading force of the specimen obtained in step S2, and the PIV camera is used to perform PIV processing on the acquired images to obtain the evolution process.

2. The large-scale shear test device for root reinforced soil based on PIV technology according to claim 1 is characterized in that: The vertical loading unit includes a top plate fixed to the inner wall of the top end of the inverted U-shaped fixing frame and located directly above the embedded combined shear box, a loading cylinder fixed to the bottom end of the top plate, and a vertical loading head fixed to the bottom output end of the piston rod of the loading cylinder. A vertical loading plate is also fixed to the bottom end of the vertical loading head. The center of the vertical loading plate and the center of the embedded combined shear box are located on the same vertical axis, and the cross-sectional dimension of the vertical loading plate is smaller than the inner dimension of the cross-sectional dimension of the embedded combined shear box. A guide plate is also fixed to the piston rod of the loading cylinder. The guide plate is slidably connected to the bottom end of the vertical guide rod, and the top end of the vertical guide rod is fixedly connected to the top plate. The horizontal loading unit includes a horizontal servo motor fixed on an inner wall of one side of the bottom end of the inverted U-shaped fixing frame and located on one side of the embedded combined shear box, a reducer connected to the output end of the horizontal servo motor, a horizontal lead screw connected to the output end of the reducer, a horizontal displacement nut threadedly connected to the horizontal lead screw, and a horizontal loading plate fixedly connected to one end of the horizontal displacement nut away from the horizontal lead screw, the horizontal displacement nut is also horizontally slidably connected to a horizontal guide rod fixed to the housing of the horizontal servo motor, the horizontal loading plate is aligned with one side of the lower direct shear box, and the horizontal loading plate is also fixedly connected to the inverted U-shaped fixing frame via the horizontal guide rod; The lifting unit includes a lifting drive motor fixed on the inner wall on the other side of the bottom end of the inverted U-shaped fixing frame, a vertical lead screw connected to the top output end of the lifting drive motor via a coupling, a vertical displacement nut threadedly connected to the vertical lead screw, and a lifting panel connected to the vertical displacement nut. A lifting connecting plate is fixed to the side of the lifting panel facing the upper direct shear box embedded in the combined shear box via a suspension rod, and the lifting connecting plate is fixedly connected to the side of the upper direct shear box; vertical guide rails are fixed on the inverted U-shaped fixing frame and on both sides of the vertical lead screw, the vertical guide rails are vertically slidably connected to the lifting panel, and vertical limit blocks are fixed to the upper and lower ends of the vertical guide rails.

3. The large-scale shear test device for root reinforced soil based on PIV technology according to claim 2 is characterized by: The displacement sensor assembly includes four vertical displacement sensors arranged at the four corners of the top plate, a first pressure sensor arranged at the bottom end of the vertical loading plate, a horizontal displacement sensor arranged on the horizontal servo motor, and a second pressure sensor arranged on the side of the horizontal loading plate facing the lower direct shear box, wherein the four vertical displacement sensors are used to monitor the overall vertical displacement of the top surface of the sample in real time, the first pressure sensor is used to monitor the vertical loading force applied by the vertical loading unit to the top of the embedded combined shear box, the horizontal displacement sensor is used to monitor the horizontal displacement of the lower direct shear box, and the second pressure sensor is used to monitor the horizontal loading force applied by the horizontal loading unit to the side of the lower direct shear box; The PIV camera assembly includes a tripod support frame, a fixed platform fixed on the top of the tripod support frame, and a PIV camera fixed on the top of the fixed platform. The camera head of the PIV camera faces the transparent observation surface embedded in the combined shear box, and a ring light source is fixed on the fixed platform between the camera head of the PIV camera and the embedded combined shear box.

4. The large-scale shear test device for root reinforced soil based on PIV technology according to claim 3 is characterized by: The bottom end of the embedded combined shear box is slidably arranged on the top end of the test bench through a bottom plate and a horizontal guide rail, and vertical limit blocks are fixed at both ends of the horizontal guide rail.

5. The large-scale shear test device for root reinforced soil based on PIV technology according to claim 4 is characterized in that: When the soil sample is gravel soil, the tracer particles are white ceramic particles or reinforced soil sample materials; When the soil sample is silt or clay, the tracer particles are white quartz sand of 20-80 mesh.

6. The large-scale shear test device for root reinforced soil based on PIV technology according to claim 5 is characterized by: The upper semi-enclosed shear box and the lower semi-enclosed shear box are fixedly connected by screws and ear plates in sequence; A water-permeable plate is arranged at the top end of the embedded combined shear box, or a water-blocking plate is arranged at the bottom end of the embedded combined shear box.

Images