Transparent soil experimental device for simulating hydraulic erosion of pile foundation

Abstract

The utility model relates to the field of simulation of pile foundation hydraulic erosion, in particular to a transparent soil experimental device for simulating pile foundation hydraulic erosion, which comprises an experimental box, a sealing gate is slidably connected to one side of the top end of the experimental box, and a storage tank is arranged inside the experimental box close to the right side of the sealing gate. A CCD camera and a laser generator are driven by a moving block to move, so that when the flow field form of the horizontal section is researched, the CCD camera is matched with the laser generator to shoot from top to bottom, and when a positioning rod is embedded into a second positioning hole under the action of a tension spring and rotates on the outer wall of a stud through a threaded cylinder, the CCD camera and the laser generator can shoot from top to bottom. In this way, the CCD camera and the laser generator are fixed to the front side of the experiment box, the CCD camera and the laser generator are made to be perpendicular to the front side of the experiment box, when the form of a vertical section flow field is researched, the CCD camera and the laser generator are used for capturing pictures of transparent debris flow, in conclusion, the positions of the CCD camera and the laser generator can be conveniently adjusted according to experiment requirements, and operation of experimenters is facilitated.

Description

Technical Field

[0001] This utility model relates to the field of simulating hydraulic erosion of pile foundations, specifically a transparent soil experimental device for simulating hydraulic erosion of pile foundations. Background Technology

[0002] Transparent soil deformation visualization technology is a new model experiment technique developed in recent years. This technology can achieve non-invasive, undisturbed, transient, and visualized measurement of soil internal deformation, providing a powerful technical means to reveal the catastrophe mechanism of underground rock and soil. It integrates materials science, optoelectronic information, and digital imaging into soil mechanics, and combines transparent soil preparation technology, laser spotting technology, and image processing technology to form a cutting-edge discipline of transparent soil mechanics and deformation measurement. Transparent soil preparation technology is a method that uses the principle of refractive index matching. By adjusting the ratio of solid particles and pore fluid, their refractive indices are made equal, thereby creating a transparent soil sample. Transparent soil is usually needed when simulating hydraulic erosion of pile foundations.

[0003] However, existing transparent soil experimental devices for simulating hydraulic erosion of pile foundations generally require experimenters to manually adjust the positions of the laser generator and CCD camera when studying vertical or horizontal flow field morphology, and to install the laser generator and CCD camera on an external device. Due to the lack of a convenient mechanism for adjusting the horizontal and vertical directions of the laser generator and CCD camera, the staff has to disassemble and install the laser generator and CCD camera one by one each time they experiment with vertical and horizontal flow field morphology. This process is not convenient and is quite troublesome. Utility Model Content

[0004] This utility model aims to provide a transparent soil experimental device for simulating hydraulic erosion of pile foundations. It is mainly used to solve the technical problem that the existing technology lacks a mechanism for conveniently adjusting the horizontal and vertical directions of the laser generator and CCD camera. This means that the staff needs to disassemble and install the laser generator and CCD camera one by one each time they experiment with vertical and horizontal flow field patterns. This process is not convenient and is quite troublesome.

[0005] To solve the above-mentioned technical problems, this utility model provides the following technical solution:

[0006] A transparent soil experimental device for simulating hydraulic erosion of pile foundations includes an experimental chamber. A sealing gate is slidably connected to one side of the top of the experimental chamber. A material storage tank is set up inside the experimental chamber near the right side of the sealing gate. An experimental channel is set up inside the experimental chamber near the left side of the sealing gate. A pile foundation is installed at the bottom of the experimental chamber near the experimental channel. A force sensor is installed at the top of the experimental chamber near the left side of the pile foundation. A CCD camera is set above the experimental chamber. A laser generator is set above the experimental chamber near the right side of the CCD camera. The device also includes a lateral movement mechanism, a guide component, a longitudinal movement mechanism, an elastic locking component, and a rotating component. The lateral movement mechanism is equipped with... The guide is slidably mounted on the horizontal moving mechanism and the vertical moving mechanism is slidably mounted on the outside of the guide. The bottom of the vertical moving mechanism penetrates the inner wall of the guide. The elastic snap-fit ​​is mounted on the top of the vertical moving mechanism. The outer wall of the guide is provided with a limiting component, which consists of two parts: one part is located on the top of the guide and the other part is located on the bottom of the guide. One end of the elastic snap-fit ​​is adapted to both parts of the limiting component. The rotating component is rotatably mounted at the bottom of the vertical moving mechanism via a thread. The CCD camera and the laser generator are located on the left and right sides of the rotating component, respectively.

[0007] The working principle and beneficial effects of this utility model:

[0008] 1. Working Principle: The lateral movement of the mechanism drives the guide to move laterally, facilitating the movement of the CCD camera and laser generator to the required experimental position. The elastic locking mechanism separates the CCD camera and laser generator from the limiting component at the top of the guide, allowing the longitudinal movement mechanism to move them downwards. This enables the CCD camera and laser generator to capture images from above when studying horizontal flow profiles. Alternatively, when one end of the elastic locking mechanism is inserted into the limiting component at the bottom of the guide, the CCD camera and laser generator can be fixed to the front of the experimental chamber. The angle of the CCD camera and laser generator can be adjusted by a rotating component, allowing them to be perpendicular to the front of the experimental chamber. This is useful for capturing images of transparent debris flows when studying vertical flow profiles. In summary, the position of the CCD camera and laser generator can be easily adjusted according to experimental needs, facilitating operation by the experimenter.

[0009] 2. Beneficial effects:

[0010] (1) The motor can drive the screw to rotate, and with the guide rod, the placement ring can move laterally on the screw and guide rod, so as to facilitate the adjustment of the position of the CCD camera and the laser generator. The positioning rod separates from the first positioning hole, so that the moving block can slide from top to bottom on the outer wall of the guide rod. Thus, the moving block drives the CCD camera and the laser generator to move. Therefore, when studying the horizontal cross-sectional flow field morphology, the CCD camera and the laser generator take pictures from top to bottom. When the positioning rod is embedded into the second positioning hole by the action of the tension spring, and rotates on the outer wall of the stud by the threaded cylinder, the CCD camera and the laser generator are fixed on the front side of the experimental box, and the CCD camera and the laser generator are perpendicular to the front side of the experimental box. When studying the vertical cross-sectional flow field morphology, it is used to capture pictures of transparent mudflow. In summary, the position of the CCD camera and the laser generator can be conveniently adjusted according to the experimental requirements, which is convenient for the experimenters to operate.

[0011] Preferably, the lateral movement mechanism includes a connecting block, a motor, a screw, and a guide rod. Two sets of connecting blocks are provided, with each set of connecting blocks fixedly connected to the front and rear sides of the experimental chamber, respectively. A motor is installed on the right side of one connecting block in each set, and the motor output shaft passes through the left side of one connecting block. A screw is fixedly connected to the motor output shaft, and one end of the screw is connected to another connecting block via a bearing. A guide rod is fixedly connected between the other set of connecting blocks. Starting the motor causes the screw to rotate, which in turn causes the guide rod to move laterally on the fixed rod. This facilitates adjusting the positions of the CCD camera and laser generator on the adjustment plate, allowing the CCD camera and laser generator to be moved to the designated experimental position.

[0012] Preferably, the guide includes a placement ring, a mounting groove, and a fixing rod. The bottom of the placement ring is slidably mounted on the transverse moving mechanism. The same mounting groove is formed through one side of the outer and inner walls of the placement ring, and the fixing rod is fixedly connected inside the mounting groove. One side of the bottom of the placement ring is threadedly connected to the outer wall of the screw, and the other side is slidably connected to the outer wall of the guide rod. The fixing rod is in the shape of a discontinuous circular ring, which facilitates the movement of the placement ring on the outer walls of the screw and the guide rod when the screw rotates.

[0013] Preferably, the longitudinal moving mechanism includes a moving block, the outer wall of which is slidably connected to the inside of the guide member, the bottom of which penetrates the outer wall of the guide member and extends to the inside of the guide member, the moving block is slidably connected to the outside of the fixed rod, and the outer wall of the moving block is adapted to the inside of the mounting groove, so that the moving block can move along the outside of the fixed rod.

[0014] Preferably, the elastic snap-fit ​​component includes a fixing block, a positioning rod, a connecting plate, and a tension spring. Two fixing blocks are provided, with one end of each fixedly connected to the left and right sides of the movable block, respectively. The same positioning rod slides through the top and bottom of each fixing block. The tops of the two positioning rods are fixedly connected to the same connecting plate. A tension spring is sleeved on the outer wall of the positioning rod, with one end fixedly connected to the bottom of the connecting plate and the other end fixedly connected to the top of the fixing block. Pulling the connecting plate upwards causes the connecting plate to separate the positioning rod from the first positioning hole, thereby releasing the restriction on the movable block. This allows the movable block to slide from top to bottom on the outer wall of the guide rod. At this time, the movable block moves the adjusting plate, which in turn moves the CCD camera and the laser generator.

[0015] Preferably, the limiting component includes a first positioning hole and a second positioning hole. There are two first positioning holes, which are formed in the placement ring. The bottom of the outer wall of the placement ring is provided with second positioning holes on both sides near the mounting groove. The two first positioning holes are respectively near the two sides of the mounting groove. The outer wall of the positioning rod is adapted to the interior of the first positioning hole and the second positioning hole. In the initial state, the positioning rod is aligned with the first positioning hole. Due to the force of the tension spring, the connecting plate moves downward, thereby causing the connecting plate to move the outer wall of the positioning rod through the fixing block downward. Then, the positioning rod is embedded in the interior of the first positioning hole, thereby limiting the position of the moving block.

[0016] Preferably, the rotating component includes an extension plate, a stud, a threaded cylinder, and an adjusting plate. Two extension plates are provided, with the top ends of both extension plates fixedly connected to the bottom end of the moving block. A stud is fixedly connected between the two extension plates, and a threaded cylinder is connected to the outside of the stud. An adjusting plate is fixedly connected to the bottom of the threaded cylinder. Pulling the adjusting plate causes the threaded cylinder to rotate on the outer wall of the stud, so that the CCD camera and the laser generator are perpendicular to the front of the experimental box. Attached Figure Description

[0017] Figure 1 This is a three-dimensional structural diagram of a transparent soil experimental device for simulating hydraulic erosion of pile foundations, which is a patent of this utility model.

[0018] Figure 2 This is a rear view of the experimental box of a transparent soil experimental device for simulating hydraulic erosion of pile foundations, as per this utility model patent.

[0019] Figure 3 This is a structural diagram of the moving block of a transparent soil experimental device for simulating hydraulic erosion of pile foundations, which is a utility model patent.

[0020] Figure 4 This is a partial placement ring structure diagram of a transparent soil experimental device for simulating hydraulic erosion of pile foundations, as per this utility model patent.

[0021] Figure 5This is a structural diagram of the rotating component of a transparent soil experimental device for simulating hydraulic erosion of pile foundations, which is part of this utility model patent.

[0022] The reference numerals in the accompanying drawings of the instruction manual include: 1. Experimental chamber; 2. Storage tank; 3. Sealing gate; 4. Experimental passage; 5. Force sensor; 6. Connecting block; 7. Motor; 8. Screw; 9. Fixing rod; 10. Placement ring; 11. Mounting groove; 12. Guide rod; 13. Moving block; 14. Fixing block; 15. Positioning rod; 16. Connecting plate; 17. Tension spring; 18. First positioning hole; 19. Second positioning hole; 20. Extension plate; 21. Stud; 22. Threaded cylinder; 23. Adjusting plate; 24. CCD camera; 25. Laser generator; 26. Pile foundation. Detailed Implementation

[0023] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0024] Please see Figures 1-5As shown, a transparent soil experimental device for simulating hydraulic erosion of pile foundations includes an experimental chamber 1. A sealing gate 3 is slidably connected to one side of the top of the experimental chamber 1. A storage tank 2 is set inside the experimental chamber 1 near the right side of the sealing gate 3. An experimental channel 4 is set inside the experimental chamber 1 near the left side of the sealing gate 3. A pile foundation 26 is installed at the bottom inside the experimental chamber 1 near the experimental channel 4. A force sensor 5 is installed at the top of the experimental chamber 1 near the left side of the pile foundation 26. A CCD camera 24 is set above the experimental chamber 1. A laser generator is set above the experimental chamber 1 near the right side of the CCD camera 24. 25, also includes a lateral moving mechanism, a guide component, a longitudinal moving mechanism, an elastic locking component, and a rotating component. The lateral moving mechanism is located on the bottom outer side of the experimental chamber 1. The lateral moving mechanism includes a connecting block 6, a motor 7, a screw 8, and a fixing rod 9. There are two sets of connecting blocks 6. The inner sides of each set of connecting blocks 6 are fixedly connected to the front and rear sides of the experimental chamber 1, respectively. In one set, a motor 7 is installed on the right side of one connecting block 6, and the output shaft of the motor 7 passes through the left side of one connecting block 6. The output shaft of the motor 7 is fixedly connected to the screw 8. One end of the screw 8 is connected to another connecting block 6 through a bearing. The other set of connecting blocks... A fixed rod 9 is fixedly connected between blocks 6. A guide member is slidably mounted on the transverse moving mechanism. The guide member includes a placement ring 10, a mounting groove 11, and a guide rod 12. The bottom of the placement ring 10 is slidably mounted on the transverse moving mechanism. The same mounting groove 11 is opened through one side of the outer and inner walls of the placement ring 10. The guide rod 12 is fixedly connected inside the mounting groove 11. When the motor 7 is started, the motor 7 drives the screw 8 to rotate, thereby the screw 8 drives the placement ring 10 to move laterally on the fixed rod 9. This facilitates the adjustment of the CCD camera 24 and the laser generator 2 on the adjustment plate 23. Position 5 facilitates the movement of the CCD camera 24 and laser generator 25 to the designated experimental position. In addition, pulling the connecting plate 16 upward causes the connecting plate 16 to separate the positioning rod 15 from the first positioning hole 18, thereby releasing the restriction on the moving block 13. This allows the moving block 13 to slide from top to bottom on the outer wall of the guide rod 12. At this time, the moving block 13 drives the adjusting plate 23 to move, and the adjusting plate 23 drives the CCD camera 24 and laser generator 25 to move. Therefore, when studying the horizontal cross-sectional flow field morphology, the CCD camera 24, in conjunction with the laser generator 25, takes pictures from top to bottom.

[0025] The longitudinal moving mechanism is slidably disposed on the outside of the guide member, and its bottom penetrates the inner wall of the guide member. An elastic locking member is disposed on the top of the longitudinal moving mechanism. The longitudinal moving mechanism includes a moving block 13, the outer wall of which is slidably connected to the inside of the guide member. The bottom of the moving block 13 penetrates the outer wall of the guide member and extends to the inner side of the guide member. The elastic locking member includes a fixing block 14, a positioning rod 15, a connecting plate 16, and a tension spring 17. Two fixing blocks 14 are provided, with one end of each fixedly connected to the left and right sides of the moving block 13, respectively. The top and bottom ends of the fixing blocks 14 are slidably connected to the same positioning rod 15. The two positioning rods 15... A connecting plate 16 is fixedly connected to the top end. A tension spring 17 is sleeved on the outer wall of the positioning rod 15. One end of the tension spring 17 is fixedly connected to the bottom end of the connecting plate 16, and the other end is fixedly connected to the top end of the fixing block 14. A limiting member is provided on the outer wall of the guide member, and the limiting member is provided in two parts. One part of the limiting member is located at the top of the guide member, and the other part of the limiting member is located at the bottom of the guide member. The limiting member includes a first positioning hole 18 and a second positioning hole 19. There are two first positioning holes 18, which are opened in the placement ring 10. The bottom of the outer wall of the placement ring 10 near the mounting groove 11 on both sides is provided with a second positioning hole 19. 18 are located near the two sides of the mounting groove 11. One end of each elastic snap-fit ​​component is adapted to the two limiting components. The rotating component is rotatably mounted at the bottom of the longitudinal moving mechanism via a thread. The rotating component includes an extension plate 20, a stud 21, a threaded cylinder 22, and an adjusting plate 23. There are two extension plates 20. The top ends of both extension plates 20 are fixedly connected to the bottom end of the moving block 13. A stud 21 is fixedly connected between the two extension plates 20. A threaded cylinder 22 is connected to the outside of the stud 21. An adjusting plate 23 is fixedly connected to the bottom of the threaded cylinder 22. The CCD camera 24 and the laser generator 25 are respectively located on the left and right sides of the rotating component. When the moving block 13 moves... When the positioning rod 15 moves to align with the second positioning hole 19, the positioning rod 15 is embedded into the second positioning hole 19 under the force of the tension spring 17, and pulls the adjusting plate 23, causing the adjusting plate 23 to drive the threaded cylinder 22 to rotate on the outer wall of the stud 21, thereby fixing the CCD camera 24 and the laser generator 25 on the front side of the experimental box 1, and making the CCD camera 24 and the laser generator 25 perpendicular to the front side of the experimental box 1, so as to capture transparent debris flow photos when studying the vertical cross-sectional flow field morphology. In this way, the position of the CCD camera 24 and the laser generator 25 can be conveniently adjusted according to the experimental needs, making it convenient for the experimenters to operate.

[0026] As can be seen from the above, the specific implementation of this utility model is as follows: In the initial state, the positioning rod 15 is aligned with the first positioning hole 18. Due to the force of the tension spring 17, the connecting plate 16 moves downward, thereby the connecting plate 16 drives the outer wall of the positioning rod 15 to move downward through the fixing block 14, and then the positioning rod 15 is embedded in the first positioning hole 18, thereby restricting the position of the moving block 13. The motor 7 is started, so that the motor 7 drives the screw 8 to rotate, thereby the screw 8 drives the placement ring 10 to move laterally on the fixing rod 9, so as to facilitate the adjustment of the position of the CCD camera 24 and the laser generator 25 on the adjusting plate 23, and facilitate the movement of the CCD camera 24 and the laser generator 25 to the designated experimental position. During the experiment, the transparent soil is located inside the storage tank 2. Then, the sealing gate 3 is pulled upward, so that when the sealing gate 3 releases the restriction on the transparent soil, the transparent soil flows from the storage tank 2 into the experimental channel 4. When the transparent soil impacts the pile foundation body 26, the impact data is measured through the force sensor 5. In addition, the connecting plate 16 is pulled upward, so that the connecting plate 15 moves downward through the fixing block 14, thereby restricting the position of the CCD camera 24 and the laser generator 25 to the designated experimental position. 6. The positioning rod 15 is separated from the first positioning hole 18, thereby releasing the restriction on the moving block 13, allowing the moving block 13 to slide from top to bottom on the outer wall of the guide rod 12. At this time, the moving block 13 drives the adjusting plate 23 to move, and the adjusting plate 23 drives the CCD camera 24 and the laser generator 25 to move. Thus, when studying the horizontal profile flow field morphology, the CCD camera 24, in conjunction with the laser generator 25, takes pictures from top to bottom. When the moving block 13 drives the positioning rod 15 to align with the second positioning hole 19, the positioning rod 15 is held in place by the tension spring 17. Under the action of force, it is embedded into the second positioning hole 19, and the adjustment plate 23 is pulled, so that the adjustment plate 23 drives the threaded cylinder 22 to rotate on the outer wall of the stud 21, thereby fixing the CCD camera 24 and the laser generator 25 on the front side of the experimental box 1, and making the CCD camera 24 and the laser generator 25 perpendicular to the front side of the experimental box 1, so as to capture transparent debris flow photos when studying the vertical cross-sectional flow field morphology. In this way, the position of the CCD camera 24 and the laser generator 25 can be conveniently adjusted according to the experimental needs, making it convenient for the experimental personnel to operate.

[0027] The above descriptions are merely embodiments of this utility model, and common knowledge regarding specific structures and characteristics is not elaborated upon here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of this utility model, and these should also be considered within the scope of protection of this utility model. These modifications will not affect the effectiveness of the implementation of this utility model or the practicality of the patent. The scope of protection claimed in this application shall be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A transparent soil experimental device for simulating hydraulic erosion of pile foundations, characterized in that, The test chamber includes an experimental chamber (1), a sealing gate (3) is slidably connected to one side of the top of the test chamber (1), a storage tank (2) is set up on the right side of the test chamber (1) near the sealing gate (3), an experimental channel (4) is set up on the left side of the test chamber (1) near the sealing gate (3), a pile foundation (26) is installed at the bottom of the test chamber (1) near the experimental channel (4), a force sensor (5) is installed on the left side of the top of the test chamber (1) near the pile foundation (26), a CCD camera (24) is set up above the test chamber (1), and a laser generator (25) is set up on the right side of the top of the test chamber (1) near the CCD camera (24). It also includes a lateral movement mechanism, a guide, a longitudinal movement mechanism, and a guide component. The elastic snap-fit ​​and rotating parts, the lateral moving mechanism is set at the bottom outside of the experimental box (1), the guide is slidably set on the lateral moving mechanism, the longitudinal moving mechanism is slidably set on the outside of the guide, and the bottom of the longitudinal moving mechanism penetrates the inner wall of the guide, the elastic snap-fit ​​is set at the top of the longitudinal moving mechanism, the outer wall of the guide is provided with a limiting part, and the limiting part is set in two parts, one part of the limiting part is set at the top of the guide, and the other part of the limiting part is set at the bottom of the guide, one end of the elastic snap-fit ​​is adapted to both parts of the limiting part, the rotating part is rotatably set at the bottom of the longitudinal moving mechanism through the thread, and the CCD camera (24) and the laser generator (25) are respectively set on the left and right sides of the rotating part.

2. The transparent soil experimental device for simulating hydraulic erosion of pile foundations according to claim 1, characterized in that: The lateral movement mechanism includes a connecting block (6), a motor (7), a screw (8), and a fixing rod (9). There are two sets of connecting blocks (6). The inner side of each set of connecting blocks (6) is fixedly connected to the front and rear sides of the experimental box (1), respectively. A motor (7) is installed on the right side of one of the connecting blocks (6) in one set, and the output shaft of the motor (7) passes through the left side of one connecting block (6). The output shaft of the motor (7) is fixedly connected to the screw (8). One end of the screw (8) is connected to another connecting block (6) through a bearing. A fixing rod (9) is fixedly connected between the other set of connecting blocks (6).

3. The transparent soil experimental device for simulating hydraulic erosion of pile foundations according to claim 1, characterized in that: The guide includes a placement ring (10), a mounting groove (11), and a guide rod (12). The bottom of the placement ring (10) is slidably mounted on the transverse moving mechanism. The same mounting groove (11) is opened through one side of the outer wall and the inner wall of the placement ring (10). The guide rod (12) is fixedly connected inside the mounting groove (11).

4. The transparent soil experimental device for simulating hydraulic erosion of pile foundations according to claim 1, characterized in that: The longitudinal moving mechanism includes a moving block (13), the outer wall of which is slidably connected to the inside of the guide, and the bottom of the moving block (13) penetrates the outer wall of the guide and extends to the inside of the guide.

5. The transparent soil experimental device for simulating hydraulic erosion of pile foundations according to claim 4, characterized in that: The elastic snap-fit ​​component includes a fixing block (14), a positioning rod (15), a connecting plate (16), and a tension spring (17). There are two fixing blocks (14), one end of which is fixedly connected to the left and right sides of the moving block (13). The top and bottom ends of the fixing blocks (14) are slidably connected to the same positioning rod (15). The top ends of the two positioning rods (15) are fixedly connected to the same connecting plate (16). The outer wall of the positioning rod (15) is fitted with a tension spring (17). One end of the tension spring (17) is fixedly connected to the bottom end of the connecting plate (16), and the other end is fixedly connected to the top end of the fixing block (14).

6. The transparent soil experimental device for simulating hydraulic erosion of pile foundations according to claim 3, characterized in that: The limiting component includes a first positioning hole (18) and a second positioning hole (19). There are two first positioning holes (18), which are opened on the placement ring (10). The bottom of the outer wall of the placement ring (10) is provided with second positioning holes (19) on both sides near the mounting groove (11). The two first positioning holes (18) are respectively close to both sides of the mounting groove (11).

7. The transparent soil experimental device for simulating hydraulic erosion of pile foundations according to claim 4, characterized in that: The rotating component includes an extension plate (20), a stud (21), a threaded cylinder (22), and an adjusting plate (23). There are two extension plates (20), and the top ends of the two extension plates (20) are fixedly connected to the bottom end of the moving block (13). A stud (21) is fixedly connected between the two extension plates (20). A threaded cylinder (22) is connected to the outside of the stud (21). An adjusting plate (23) is fixedly connected to the bottom of the threaded cylinder (22).

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