Underwater load pressure environment root soil complex simple shear strength determination system

Abstract

The invention relates to the technical field of geotechnical engineering and plant root mechanics, in particular to an underwater load pressure environment root-soil complex single shear strength measuring system which comprises shear boxes, a pressurizing mechanism and a drawing mechanism, the shear boxes are of a square frame structure, and the multiple shear boxes are stacked in the longitudinal direction; soil which is of a square structure and used for allowing root systems to penetrate through is arranged in the shearing box, a pressurizing plate of the pressurizing mechanism can stretch into an inner cavity of the shearing box and apply set pressure to the soil in the shearing box, and a through hole is formed in the middle of the pressurizing plate; the top end of the root system is connected with the bottom end of the drawing mechanism through a buckle; a friction force sensor is arranged on the outer wall of the root system, and a displacement sensor is arranged on the side of the shear box. According to the invention, the design of a plurality of shear boxes which can be longitudinally stacked is adopted, and friction resistance distribution data of the root system in soil layers with different depths can be synchronously obtained in one test in cooperation with the friction force sensor on the root system and the displacement sensor on the side.

Description

Technical Field

[0001] This invention relates to the fields of geotechnical engineering and plant root mechanics, and in particular to a system for measuring the single shear strength of root-soil composites under underwater pressure. Background Technology

[0002] Plant roots enhance soil stability through friction and anchoring effects, and the frictional force between individual roots and the soil is a core parameter in the design of ecological slope protection, vegetation reinforcement, and other engineering projects. Existing research has largely focused on the overall shear strength of the root system, lacking systematic testing methods for the variation of frictional force in individual roots under different burial depths and pressure conditions.

[0003] The existing technology has the following shortcomings: 1. Low pressure control precision: Traditional rigid pressurization methods are difficult to achieve uniform and adjustable soil pressure; 2. Uncontrollable burial depth: Most devices only test the overall friction of a single piece, and cannot obtain the local friction values ​​at different heights in segments; 3. Poor test repeatability: Re-sampling is required when changing the burial depth, and the root-soil contact state is difficult to reproduce.

[0004] To address the aforementioned issues, this invention proposes a system for determining the single shear strength of root-soil composites under underwater pressure. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a single shear strength measurement system for root-soil composites under underwater pressure environment. The system adopts a design of multiple longitudinally stackable shear boxes, combined with friction force sensors on the root system and displacement sensors on the sides. It can simultaneously acquire data on the distribution of frictional resistance experienced by the root system in soil layers at different depths in a single test, providing a direct means to analyze the variation law of root shear contribution along depth.

[0006] To achieve the objectives of this invention, the technical solution adopted is as follows: This invention discloses a single shear strength testing system for root-soil composites under underwater pressure, comprising a shear box, a pressurizing mechanism, and a pull-out mechanism. Several shear boxes are stacked longitudinally, with roots penetrating the center of the inner cavity of each shear box vertically. Soil is filled between the inner wall of each shear box and the root system. The soil inside adjacent shear boxes is separated by a sealing membrane. The pressurizing plate of the pressurizing mechanism can extend into the inner cavity of the shear box and apply a set pressure to the soil inside. A through hole is provided in the center of the pressurizing plate. The top of the root system is connected to the bottom of the pull-out mechanism via a snap-fit. A friction sensor is provided on the outer wall of the root system, and a displacement sensor is provided on the side of each shear box.

[0007] The pressurizing mechanism includes a pressurizing plate, a pressurizing bracket, a pressurizing motor, a pressurizing lead screw, a transmission block, and a pressurizing bearing seat. The pressurizing bracket is disposed on the side of the shearing box, and its bottom is fixed to the base plate. A mounting plate is provided on the inner top of the pressurizing bracket, and the pressurizing motor is fixed on the top of the mounting plate. The output end of the pressurizing motor passes through the middle of the mounting plate and is connected to the bottom end of the pressurizing lead screw. The bottom end of the pressurizing lead screw is fixedly connected to the inner ring of the bearing in the pressurizing bearing seat. The pressurizing bearing seat is fixed to the base plate. The transmission block has a square structure, and its top is provided with a threaded hole that matches the external thread of the pressurizing lead screw. The outer wall of the transmission block is fixedly connected to one side of the top of the pressurizing plate through a corner plate.

[0008] The pressure support is an "I"-shaped structure composed of a square support column and a wing plate. The wing plate is disposed on both sides of the front and rear walls of the square support column. Limiting plates are provided on both sides of the rear wall of the transmission block. There is a gap between the inner wall of the limiting plate and the end of the wing plate. Limiting wheels are fixed on both sides of the inner wall of the limiting plate by a fixed shaft. The outer walls of the two limiting wheels are in contact with the outer wall of the wing plate.

[0009] The buckle includes a semi-circular ring retainer, ear plates, connecting bolts, connecting nuts, and lifting rings. The semi-circular ring retainer has a semi-circular ring structure with ear plates at both ends. The middle of the ear plates has an ear plate hole for the connecting bolt to pass through. The two semi-circular ring retainers are joined together to form a ring structure. After the connecting bolt passes through the ear plate holes on the two ear plates, it is locked with the connecting nut. A semi-circular rubber pad is fixed to the inner wall of the semi-circular ring retainer. The rubber pads on both sides are joined together to form a rubber ring for clamping the root system. Several lifting rings are arranged in a ring array at the top of the two semi-circular ring retainers.

[0010] The pulling mechanism includes a pulling bracket, a crossbeam, a servo cylinder, a hanging ring, chains, and a push rod. The pulling bracket is a square frame structure disposed outside the shearing box. The crossbeam is fixed to the top of the pulling bracket. The servo cylinder is fixed to the top of the crossbeam. The bottom end of the push rod of the servo cylinder passes through the crossbeam and is connected to the hanging ring. The top ends of several chains are connected to the hanging rings. The bottom ends of the chains are provided with hooks, which are engaged with the hanging rings on the semi-circular ring retainer.

[0011] The pull-out bracket includes support rods and crossbars. The bottom end of a support rod is connected to each of the four corners of the base plate. The top ends of adjacent support rods are connected by the crossbars. The two ends of the crossbeam are connected to the middle of the crossbars on the left and right sides.

[0012] The bottom of the shear box is connected to a base. Rollers are provided on the lower left and right sides of the front and rear walls of the base. The front and rear sides of the base are provided with slide rails with an inverted "L" shaped cross section. The rollers slide in cooperation with the slide rails. End beams are connected between the ends of the slide rails on both sides. A transmission mechanism is provided between the end beams and the base.

[0013] The transmission mechanism includes a transmission screw and a transmission motor. One end of the transmission screw is fixedly connected to the inner ring of a bearing in the middle of the inner wall of the left end beam. The other end of the transmission screw passes through the middle of the right end beam and is connected to the output end of the transmission motor. The left and right ends of the base are provided with base threaded holes that match the external thread of the transmission screw.

[0014] The base plate is located on the top right side of the tabletop, and a mounting bracket is provided on the top left side of the tabletop. Several displacement sensors are evenly spaced along the vertical direction on the mounting bracket; a control console is fixed to the bottom of the tabletop.

[0015] The beneficial effects of this invention are as follows: (1) The present invention adopts a design of multiple shear boxes that can be stacked longitudinally, and with the friction force sensor set on the root system and the displacement sensor on the side, it can simultaneously acquire the distribution data of friction resistance of the root system in soil layers at different depths in one test, providing a direct means for analyzing the variation law of root shear resistance contribution along depth. (2) The present invention applies controllable vertical pressure to the soil in the shear box through a pressurization mechanism, which can highly restore the overlying soil pressure and water environment of the root system in the underwater slope under natural conditions, making the test results closer to the actual engineering situation. (3) The present invention uses a semi-circular ring with a rubber pad to clamp the root system, thus avoiding stress concentration and damage to the root system; (4) The present invention drives the base and shear box to move along the slide rail through the transmission mechanism, which facilitates flexible switching between sample loading, root threading and testing positions, and improves operation efficiency; (5) The system of the present invention integrates the functions of pressurization, pull-out, displacement and friction measurement, and is centrally controlled and data collected through the console located under the table, realizing the automation and intelligence of the testing process. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of the present invention. Figure 1 ; Figure 2 for Figure 1 A magnified view of a portion of the image; Figure 3 This is a schematic diagram of the structure of the present invention. Figure 2 ; Figure 4 for Figure 3 A magnified view of a portion of the image; Figure 5 This is the front view of the present invention; Figure 6 for Figure 5 A cross-sectional view along AA.

[0017] In the attached diagram, 1 is the shearing box, 2 is the pressurizing mechanism, 3 is the pulling mechanism, 4 is the root system, 6 is the buckle, 7 is the base, 8 is the roller, 9 is the slide rail, 10 is the end beam, 11 is the transmission mechanism, 12 is the table, 13 is the mounting bracket, 14 is the control console, 15 is the displacement sensor, 21 is the pressurizing plate, 22 is the pressurizing bracket, 23 is the pressurizing motor, 24 is the pressurizing lead screw, 25 is the transmission block, 27 is the mounting plate, 28 is the base plate, 29 is the corner plate, 31 is the pulling bracket, 32 is the crossbeam, 33 is the servo cylinder, 34 is the hanging ring, 35 is the chain, 36 is the push rod, 37 is the hook, 61 is the semi-circular ring clasp, 62 is the ear plate, 63 is the connecting bolt, 65 is the lifting ring, 111 is the transmission lead screw, 112 is the transmission motor, 221 is the square support column, 222 is the wing plate, 251 is the limiting plate, 252 is the fixed shaft, 253 is the limiting wheel, 311 is the support rod, and 312 is the crossbar. Detailed Implementation

[0018] The present invention will be further described below: Please see Figure 1-6 , This invention discloses a system for determining the single shear strength of a root-soil composite under underwater pressure, comprising a shear box 1, a pressurizing mechanism 2, and a pull-out mechanism 3. The shear box 1 has a square frame structure, and several shear boxes 1 are stacked longitudinally. Roots 4 pass through the center of the inner cavity of the shear box 1 vertically. Soil is filled between the inner wall of each layer of shear box 1 and the root system 4. The soil inside adjacent shear boxes 1 is separated by a sealing membrane. The pressurizing plate 21 of the pressurizing mechanism 2 can extend into the inner cavity of the shear box 1 and apply a set pressure to the soil inside the shear box 1. The pressurizing plate 21 has a through hole in the middle. The top of the root system 4 is connected to the pull-out mechanism 3 by a buckle 6. The bottom of the mechanism 3 is connected; a friction sensor is provided on the outer wall of the root system 4, and a displacement sensor 15 is provided on the side of the shear box 1. The design of multiple shear boxes 1 that can be stacked longitudinally, together with the friction sensor on the root system 4 and the displacement sensor 15 on the side, can simultaneously obtain the distribution data of friction resistance of the root system 4 in soil layers at different depths in a single test, providing a direct means to analyze the variation law of root shear resistance contribution along depth; by applying controllable vertical pressure to the soil in the shear box 1 through the pressurization mechanism 2, the overlying soil pressure and water environment of the root system in the underwater slope under natural conditions can be highly restored, making the test results closer to the actual engineering situation.

[0019] Furthermore, the pressurizing mechanism 2 includes a pressurizing plate 21, a pressurizing bracket 22, a pressurizing motor 23, a pressurizing lead screw 24, a transmission block 25, and a pressurizing bearing seat. The pressurizing bracket 22 is disposed on the side of the shearing box 1, and the bottom of the pressurizing bracket 22 is fixed to the base plate 28. The top inner side of the pressurizing bracket 22 is provided with a mounting plate 27, and the top of the mounting plate 27 is fixed with the pressurizing motor 23. The output end of the pressurizing motor 23 passes through the middle of the mounting plate 27 and is connected to the bottom end of the pressurizing lead screw 24. The bottom end of the pressurizing lead screw 24 is fixedly connected to the inner ring of the bearing in the pressurizing bearing seat. The pressurizing bearing seat is fixed to the base plate 28. The transmission block 25 has a square structure, and its top is provided with a threaded hole that matches the external thread of the pressurizing lead screw 24. The outer wall of the transmission block 25 is fixedly connected to one side of the top of the pressurizing plate 21 through a corner plate 29.

[0020] Furthermore, the pressure support 22 is an "I"-shaped structure composed of a square support column 221 and a wing plate 222. The wing plate 222 is disposed on both sides of the front and rear walls of the square support column 221. Limiting plates 251 are provided on both sides of the rear wall of the transmission block 25. A gap is provided between the inner wall of the limiting plate 251 and the end of the wing plate 222. Limiting wheels 253 are fixed on both sides of the inner wall of the limiting plate 251 through a fixed shaft 252. The outer walls of the two limiting wheels 253 are in contact with the outer walls of the wing plate 222. The limiting wheels 253 limit the wing plate 222 on the "I"-shaped pressure support 22, thereby playing a guiding role and ensuring the smooth and accurate vertical movement of the pressure plate 21, preventing bias pressure.

[0021] Furthermore, the buckle 6 includes a semi-circular ring retainer 61, ear plates 62, connecting bolts 63, connecting nuts, and lifting rings 65. The semi-circular ring retainer 61 has a semi-circular ring structure with ear plates 62 at both ends. The middle of the ear plates 62 has an ear plate hole for the connecting bolts 63 to pass through. The two semi-circular ring retainers 61 on both sides are joined to form an annular structure. After the connecting bolts 63 pass through the ear plate holes on the two ear plates 62, they are locked to the connecting nuts. The inner wall of the semi-circular ring retainer 61 is fixed with a semi-circular rubber pad. The rubber pads on both sides are joined to form a rubber ring for clamping the root system 4. The top of the two semi-circular ring retainers 61 is arranged in a ring with several lifting rings 65. By clamping the root system 4 with the semi-circular ring retainer 61 with rubber pads, stress concentration damage to the root system is avoided.

[0022] Furthermore, the pulling mechanism 3 includes a pulling bracket 31, a crossbeam 32, a servo cylinder 33, a hanging ring 34, chains 35, and a push rod 36. The pulling bracket 31 is a square frame structure disposed outside the shearing box 1. The crossbeam 32 is fixed to the top of the pulling bracket 31. The servo cylinder 33 is fixed to the top of the crossbeam 32. The bottom end of the push rod 36 of the servo cylinder 33 passes through the crossbeam 32 and is connected to the hanging ring 34. The top ends of several chains 35 are connected to the hanging rings 34. The bottom end of each chain 35 is provided with a hook 37. The hook 37 is hooked to the hanging ring 65 on the semi-circular ring 61. The connection between the hanging rings 65 and the chains 35 at multiple points ensures the uniform transmission and centering of the pulling force. The root system 4 is pulled by the servo cylinder 33, and the pulling speed can be set to ensure that the pulling speed is consistent during the measurement process.

[0023] Furthermore, the pull-out bracket 31 includes support rods 311 and crossbars 312. The bottom end of a support rod 311 is connected to each of the four corners of the base plate 28. The top ends of adjacent support rods 311 are connected by the crossbars 312. The two ends of the crossbeam 32 are connected to the middle of the crossbars 312 on the left and right sides for easy observation.

[0024] Furthermore, the bottom of the shearing box 1 at the bottom is connected to a base 7. Rollers 8 are provided on the lower left and right sides of the front and rear walls of the base 7. The front and rear sides of the base 7 are provided with slide rails 9 with an inverted "L" shape cross-section. The rollers 8 slide in cooperation with the slide rails 9. An end beam 10 is connected between the ends of the two slide rails 9. A transmission mechanism 11 is provided between the end beam 10 and the base 7. The transmission mechanism 11 includes a transmission screw 111 and a transmission motor 112. One end of the transmission screw 111 is fixedly connected to the inner ring of the bearing in the middle of the inner wall of the left end beam 10. The other end of the transmission screw 111 passes through the middle of the right end beam 10 and is connected to the output end of the transmission motor 112. The middle of the left and right ends of the base 7 is provided with a base thread hole that matches the external thread of the transmission screw 111. The transmission mechanism 11 drives the base 7 and the shearing box 1 as a whole to move along the slide rails 9, which facilitates flexible switching between sample loading, root threading and testing positions, and improves operating efficiency.

[0025] Furthermore, the base plate 28 is located on the top right side of the tabletop 12, and the top left side of the tabletop 12 is provided with a mounting bracket 13. Several displacement sensors 15 are equally spaced along the vertical direction on the mounting bracket 13. The bottom of the tabletop 12 is fixed with a control console 14. The system integrates functions of pressurization, pull-out, displacement and friction force measurement, and performs centralized control and data acquisition through the control console 14 located under the tabletop 12, realizing the automation and intelligence of the testing process.

[0026] Test procedure: First, several shear boxes 1 are stacked vertically on the base 7. Then, the root system 4 passes through the middle of the shear box 1. Soil is filled between the root system 4 and the shear box 1 in layers. Each layer of soil is separated by a sealing film. The bottom shear box 1 is fixed on the base 7, and the top of the root system 4 extends out of the top soil to prepare a root-soil composite sample.

[0027] Subsequently, the entire shear box assembly is moved to the test position (directly below the pulling mechanism) via the transmission mechanism 11. By controlling the pressure motor 23, the pressure plate 21 is extended into the top shear box 1, and the top of the root system 4 passes through the through hole in the middle of the pressure plate 21. The buckle 6 is installed at the designated position at the top of the root system and connected to the chain 35 of the pulling mechanism 3.

[0028] By controlling the pressurizing motor 23, the pressurizing plate 21 applies a set vertical pressure to the lower soil layer to simulate the overburden load. The servo electric cylinder 33 is activated to lift the root system 4 upwards at a constant rate. During this process, relative shear occurs between the root system 4 and each soil layer. Friction sensors attached to the root system 4 (which can be miniature strain sensors applied to the root surface) record the changes in frictional resistance at each depth in real time. Simultaneously, the drive motor 111 is activated, applying a rightward force to the base 7 through the transmission mechanism 11. Due to the pressure applied to the top of the soil by the top pressurizing plate 21, different shear forces are generated between each soil layer and the root system 4, resulting in different lateral displacements in the shear boxes 1 of each layer. The displacement sensor 15 (mounted on the mounting bracket 13 on the left side of the table, with the measuring point aligned with the detection point on the outer wall of the shear box 1) monitors the soil displacement or the relative lateral displacement of each shear box 1. All sensor data and control commands for the motor and electric cylinder are processed and recorded by the control console 14.

[0029] By analyzing data such as pull-out force-displacement curves and friction force distribution at various depths, the single shear strength parameters of the root-soil composite under different underwater load conditions can be calculated. The local friction coefficient μ = friction force / (pressure × root surface area) of each segment can be calculated, and the relationship curve of "burial depth-confining pressure-friction force" can be established to analyze the variation law of friction force with burial depth and confining pressure. This can be used to correct the empirical parameter of "friction attenuation along burial depth" in the root reinforcement model.

[0030] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent modifications made based on the content of the present invention specification and drawings, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A system for determining the single shear strength of a root-soil composite under underwater pressure, characterized in that: It includes a shear box (1), a pressurizing mechanism (2), and a pulling mechanism (3). Several shearing boxes (1) are stacked longitudinally, and the root system (4) passes through the middle of the inner cavity of the shearing box (1) in a vertical direction. Soil is filled between the inner wall of each layer of shearing box (1) and the root system (4). The soil inside adjacent shearing boxes (1) is separated by a sealing film. The pressure plate (21) of the pressure mechanism (2) can extend into the inner cavity of the top shearing box (1) and apply a set pressure to the soil inside the shearing box (1). The pressure plate (21) has a through hole in the middle. The top of the root system (4) is connected to the bottom of the pulling mechanism (3) by a buckle (6); a friction sensor is provided on the outer wall of the root system (4), and a displacement sensor (15) is provided on the side of the shear box (1).

2. The underwater load-bearing environment root-soil composite single shear strength testing system according to claim 1, characterized in that: The pressurizing mechanism (2) includes a pressurizing plate (21), a pressurizing bracket (22), a pressurizing motor (23), a pressurizing lead screw (24), a transmission block (25), and a pressurizing bearing seat. The pressurizing bracket (22) is located on the side of the shear box (1). The bottom of the pressurizing bracket (22) is fixed to the base plate (28). The top inner side of the pressurizing bracket (22) is provided with a mounting plate (27). The top of the mounting plate (27) is fixed with the pressurizing motor (23). The output end passes through the middle of the mounting plate (27) and is connected to the bottom end of the pressure screw (24). The bottom end of the pressure screw (24) is fixedly connected to the inner ring of the bearing of the pressure bearing seat. The pressure bearing seat is fixed on the base plate (28). The transmission block (25) has a square structure and its top is provided with a threaded hole that matches the external thread of the pressure screw (24). The outer wall of the transmission block (25) is fixedly connected to the top side of the pressure plate (21) through the corner plate (29).

3. The underwater load-bearing environment root-soil composite single shear strength testing system according to claim 2, characterized in that: The pressure support (22) is an "I" shaped structure composed of a square support column (221) and a wing plate (222). The wing plate (222) is located on both sides of the front and rear walls of the square support column (221). The transmission block (25) has a limiting plate (251) on both sides of the rear wall. There is a gap between the inner wall of the limiting plate (251) and the end of the wing plate (222). The inner walls of the limiting plate (251) are fixed with limiting wheels (253) by a fixed shaft (252). The outer walls of the two limiting wheels (253) are in contact with the outer wall of the wing plate (222).

4. The underwater load-bearing environment root-soil composite single shear strength testing system according to claim 3, characterized in that: The buckle (6) includes a semi-circular ring buckle (61), ear plates (62), connecting bolts (63), connecting nuts, and lifting rings (65). The semi-circular ring buckle (61) has a semi-circular ring structure with ear plates (62) at both ends. The middle of the ear plates (62) has an ear plate hole for the connecting bolts (63) to pass through. The two semi-circular ring buckles (61) on both sides are joined together to form a ring structure. After the connecting bolts (63) pass through the ear plate holes on the two ear plates (62), they are locked together with the connecting nuts. The inner wall of the semi-circular ring buckle (61) is fixed with a semi-circular rubber pad. The rubber pads on both sides are joined together to form a rubber ring for clamping the root system (4). The top of the two semi-circular ring buckles (61) has a number of lifting rings (65) arranged in a ring.

5. The underwater load-bearing environment root-soil composite single shear strength testing system according to claim 4, characterized in that: The pulling mechanism (3) includes a pulling bracket (31), a crossbeam (32), a servo cylinder (33), a hanging ring (34), a chain (35), and a push rod (36). The pulling bracket (31) is a square frame structure set outside the shear box (1). The crossbeam (32) is fixed to the top of the pulling bracket (31). The servo cylinder (33) is fixed to the top of the crossbeam (32). The bottom end of the push rod (36) of the servo cylinder (33) passes through the crossbeam (32) and is connected to the hanging ring (34). The top ends of several chains (35) are connected to the hanging ring (34). The bottom end of the chain (35) is provided with a hook (37). The hook (37) is hooked to the hanging ring (65) on the semi-circular ring clasp (61).

6. The underwater load-bearing environment root-soil composite single shear strength testing system according to claim 5, characterized in that: The pull-out bracket (31) includes a support rod (311) and a crossbar (312). The bottom of the base plate (28) is connected to the bottom of a support rod (311) at each of the four corners. The tops of adjacent support rods (311) are connected by the crossbar (312). The two ends of the crossbeam (32) are connected to the middle of the crossbars (312) on the left and right sides.

7. The underwater load-bearing environment root-soil composite single shear strength testing system according to claim 6, characterized in that: The bottom of the shear box (1) at the bottom is connected to a base (7). Rollers (8) are provided on the left and right sides below the front and rear walls of the base (7). The front and rear sides of the base (7) are provided with slide rails (9) with an inverted "L" shape in cross section. The rollers (8) slide in cooperation with the slide rails (9). An end beam (10) is connected between the ends of the two slide rails (9). A transmission mechanism (11) is provided between the end beam (10) and the base (7).

8. The underwater load-bearing environment root-soil composite single shear strength testing system according to claim 7, characterized in that: The transmission mechanism (11) includes a transmission screw (111) and a transmission motor (112). One end of the transmission screw (111) is fixedly connected to the inner ring of the bearing in the middle of the inner wall of the left end beam (10). The other end of the transmission screw (111) passes through the middle of the right end beam (10) and is connected to the output end of the transmission motor (112). The left and right ends of the base (7) are provided with base thread holes that match the external thread of the transmission screw (111).

9. The underwater load-bearing environment root-soil composite single shear strength testing system according to claim 8, characterized in that: The base plate (28) is located on the top right side of the tabletop (12), and the top left side of the tabletop (12) is provided with a mounting bracket (13). Several displacement sensors (15) are equally spaced along the vertical direction on the mounting bracket (13); a control console (14) is fixed at the bottom of the tabletop (12).

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