Interface soil pressure sensor calibration device and working method thereof

Abstract

The application discloses an interface soil pressure sensor calibration device, which comprises a calibrator, a structure, a soil pressure sensor, a spacer and a top cover. A circle of accommodating grooves is formed in the bottom end of the cavity of the calibrator along the side wall. A spring base is installed in the accommodating groove. The spring base is fixedly connected with the spacer. There is a gap between the spacer and the side wall of the cavity. A ball is arranged in the gap. The diameter of the ball is larger than the distance between the top of the base and the side wall of the cavity. The structure is installed at the bottom end of the cavity. The soil pressure sensor is fixed in the structure. A layer of target soil sample is arranged above the structure and the soil pressure sensor. The top cover is arranged above the target soil sample. The calibrator is used as the main calibration operation to provide the circumferential and vertical constraint and support conditions. The spacer, the ball and the spring base are arranged to replace the direct contact between the calibrator and the target soil sample and other internal materials. The ball is indirectly contacted to eliminate the frictional resistance of the tangential motion, so that the problem of calibration error caused by the frictional resistance is solved.

Description

Technical Field

[0001] This invention relates to a sensor calibration device, specifically to a calibration device for an interface earth pressure sensor and its working method. Background Technology

[0002] Currently, earth pressure at the interface between a structure and the foundation soil is the most common test item in geotechnical engineering. It is mainly used to evaluate the normal earth pressure acting on the surface of underground structures and can be called "interface earth pressure." Due to the concealed nature of underground engineering, interface earth pressure testing has a certain degree of randomness and uncertainty. Therefore, it is essential to ensure the accuracy of earth pressure sensor calibration and provide reliable sensor coefficients. The principle of interface earth pressure sensor calibration is simple: first, the sensor is fixed to the surface of the structure, with the upper surface of the sensor flush with the structure; then, precise earth pressures are applied in stages, the sensor data is read, and this process is repeated multiple times to calibrate the coefficient between the sensor readings and the corresponding earth pressures.

[0003] Before leaving the factory, earth pressure sensors are typically calibrated using hydraulic pressure. However, research by Jiang Yanbin et al. in their paper "Analysis of Soil Stress Distribution in Centrifugal Model Test Piles of Composite Foundations" indicates that the calibration medium significantly affects the coefficient of the earth pressure sensor, and that soil samples should be used for calibration. Since soil is a discrete material, the external calibration pressure acting on the target soil sample within the calibrator should be flexible. Furthermore, because earth pressure sensors typically come in various sizes, primarily involving different thicknesses and diameters, ordinary calibrators cannot adapt to the interface earth pressure calibration of sensors with different sizes, thus compromising calibration accuracy.

[0004] In addition, after applying an overburden load to the calibration device, the soil inside the calibrator will be compressed to a certain extent, and the soil and the side wall of the calibrator will generate a certain frictional resistance. At this time, the pressure transmitted to the soil pressure sensor will be partially lost, which will lead to measurement errors and thus make it impossible to guarantee the calibration accuracy.

[0005] Therefore, there is an urgent need for a calibration device for interface earth pressure sensors to solve the problem that the measurement accuracy cannot be guaranteed due to the loss of transmitted pressure in existing interface earth pressure sensor calibration devices. Summary of the Invention

[0006] This invention addresses the shortcomings of existing technologies by providing an interface earth pressure sensor calibration device and its operating method. This solves the problem that existing interface earth pressure sensor calibration devices suffer from losses in transmitted pressure, leading to unreliable measurement accuracy.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A calibration device for an interface soil pressure sensor, characterized in that it comprises a calibrator, a structure, a soil pressure sensor, a partition cylinder, and a top cover. The calibrator has a cavity at its center, and a receiving groove is formed along the side wall of the cavity at its bottom end. A spring base is installed in the receiving groove, and the upper end of the spring base is fixedly connected to the lower end of the partition cylinder. The partition cylinder can slide up and down within the receiving groove. There is a gap between the partition cylinder and the side wall of the cavity, and several balls are evenly arranged in the gap. A base extends from the lower end of the partition cylinder toward the side wall of the cavity to confine the balls in the gap. The diameter of the balls is larger than the distance between the partition cylinder above the base and the side wall of the cavity. The structure is installed on a platform surrounded by the receiving groove at the bottom end of the cavity. The soil pressure sensor is fixed in the structure. A target soil sample is placed above the structure and the soil pressure sensor. A top cover is placed above the target soil sample. Both the target soil sample and the top cover are located inside the partition cylinder.

[0009] To optimize the above technical solution, the specific measures also include:

[0010] Furthermore, several vertical grooves are spaced apart on the sidewall of the calibrator cavity opposite to the partition cylinder, and the balls are respectively disposed in the grooves. The maximum distance from the groove to the sidewall of the calibrator cavity is less than the diameter of the balls.

[0011] Furthermore, the spring base includes several vertically arranged springs, which are equally spaced in the receiving groove.

[0012] Furthermore, the partition cylinder is connected to the spring base, is set in the receiving groove and can slide up and down, and the horizontal height of the bottom end of the partition cylinder is lower than the horizontal height of the platform at the bottom end of the calibrator cavity.

[0013] Furthermore, it also includes a base and a dial indicator. The upper end of the calibrator is fixed with a base, and a dial indicator is fixed on the base. The probe of the dial indicator is located directly above the partition cylinder.

[0014] Furthermore, it also includes a pressure conversion device, which comprises standard sand wrapped with a latex film, the standard sand wrapped with a latex film being placed between the target soil sample and the top cover.

[0015] Furthermore, a wiring groove is provided on the upper surface of the platform at the bottom of the cavity of the calibrator, and a through vertical hole is provided at the bottom of the calibrator, with the wiring groove connected to the vertical hole.

[0016] Furthermore, the structure is made of a cementing material.

[0017] Furthermore, the top cover is a disc-shaped object with a flat bottom and a raised top surface. A groove is provided in the center of the raised top surface, and the groove is used to directly receive external forces.

[0018] A method for operating an interface earth pressure sensor calibration device includes the following steps:

[0019] (a) Using a universal testing machine, calibrate the spring coefficient K of the spring base, and then connect and install the spring base, the partition and the calibrator in sequence, and put the ball into the gap between the partition and the calibrator;

[0020] (b) Place the earth pressure sensor at the bottom of the calibrator cavity and run the earth pressure sensor data cable.

[0021] (c) Use cementitious material inside the diaphragm and pour a leveling structure of the same thickness as the soil pressure sensor.

[0022] (d) Place the target soil samples above the earth pressure sensor in sequence, level them thoroughly, place the standard sand wrapped with a layer of latex film, and then place the top cover.

[0023] (e) Place the dial indicator probe directly above the diaphragm and zero the reading;

[0024] (f) Apply external force in stages using a universal testing machine. After each stage of load is applied and the dial gauge reading stabilizes, record the settlement amount Δi and the required calibration value until the marking test is completed. The settlement amount Δi is used to deduct the influence of frictional resistance F when converting the pressure acting on the surface of the target soil sample, i.e., F=K·Δi.

[0025] The beneficial effects of this invention are:

[0026] This invention provides the main circumferential and vertical constraints and support conditions for calibration by using a calibrator. The calibrator replaces direct contact with the target soil sample and other internal materials with a partition cylinder, ball bearings, and spring base. The indirect contact via the ball bearings eliminates the frictional resistance of tangential motion, thus addressing the calibration error caused by the compression of the internal material and frictional resistance between its sidewalls after pressurization in the original calibration device. The inclusion of a target soil sample simulates the working environment of the earth pressure sensor, further ensuring calibration accuracy. Attached Figure Description

[0027] Figure 1 This is a cross-sectional view of the overall structure of an interface earth pressure sensor calibration device proposed in this invention.

[0028] Figure 2 This invention provides a calibration device for an interface earth pressure sensor. Figure 1 Schematic diagram of the cross section at point AA;

[0029] Figure 3This invention provides a calibration device for an interface earth pressure sensor. Figure 1 A cross-sectional view of section BB.

[0030] Figure reference numerals: 1-1, Earth pressure sensor; 2-1, Calibrator; 2-2, Gauge base; 2-3, Receiving groove; 3-1, Structure; 3-2, Cable tray; 3-3, Vertical hole; 3-4, Data cable; 4-1, Target soil sample; 4-2, Standard sand; 4-3, Latex membrane; 5-1, Divider; 5-2, Ball bearing; 5-3, Spring base; 5-4, Dial gauge; 6, Top cover. Implementation

[0031] The invention will now be described in further detail with reference to the accompanying drawings.

[0032] As attached Figure 1 and attached Figure 3 As shown, an interface earth pressure sensor calibration device according to an embodiment of the present invention includes a calibrator 2-1, a structure 3-1, an earth pressure sensor 1-1, a partition cylinder 5-1, and a top cover 6. The calibrator 2-1 has a cavity at its center. A receiving groove 2-3 is formed along the side wall of the cavity at its bottom end. A spring base 5-3 is installed in the receiving groove 2-3. The upper end of the spring base 5-3 is fixedly connected to the lower end of the partition cylinder 5-1. The partition cylinder 5-1 can slide up and down in the receiving groove 2-3. There is a gap between the partition cylinder 5-1 and the side wall of the cavity. Several ball bearings 5-2 are evenly arranged in the gap. The lower end of the partition cylinder 5-1 moves towards the side wall of the cavity. An extension includes a base for confining the ball 5-2 within a gap. The diameter of the ball 5-2 is larger than the distance between the partition cylinder 5-1 above the base and the side wall of the cavity. This ensures that the ball 5-2 can effectively eliminate the frictional resistance between the partition cylinder 5-1 and the calibrator 2-1 during use. The structure 3-1 is mounted on a platform at the bottom of the cavity surrounded by the receiving groove 2-3. The earth pressure sensor 1-1 is fixed in the structure 3-1. A target soil sample 4-1 is placed above the structure 3-1 and the earth pressure sensor 1-1. A top cover 6 is placed above the target soil sample 4-1. Both the target soil sample 4-1 and the top cover 6 are located inside the partition cylinder 5-1.

[0033] Therefore, the calibrator 2-1 provides the main circumferential and vertical constraints and support conditions for the calibration operation. The calibrator 2-1, ball bearings 5-2, and spring base 5-3 replace the direct contact between the calibrator 2-1 and the internal materials of the target soil sample 4-1, and the indirect contact through the ball bearings 5-2 eliminates the frictional resistance of tangential motion. This eliminates the calibration error caused by the compression of the internal materials and the frictional resistance between the internal materials and the sidewalls of the original calibration device after pressurization. The target soil sample 4-1 simulates a scenario consistent with the working environment of the soil pressure sensor 1-1, further ensuring calibration accuracy. In this embodiment, a gap may exist between the structure 3-1 and the calibrator 5-1 during actual use to minimize friction between them and further ensure calibration accuracy.

[0034] In another embodiment, several vertical grooves are spaced apart on the sidewalls of the partition cylinder 5-1 and the cavity of the calibrator 2-1. The balls 5-2 are respectively disposed in the grooves. The maximum distance from the groove to the sidewall of the cavity of the calibrator 2-1 is less than the diameter of the balls 5-2. In this way, the balls 5-2 are evenly distributed on the periphery of the partition cylinder 5-1 and in uniform contact with the sidewall of the cavity of the calibrator 2-1, thereby ensuring the elimination of frictional resistance.

[0035] In another embodiment, the spring base 5-3 includes several vertically arranged springs, which are equally spaced in the receiving groove 2-3; thereby ensuring the overall movement effect of the partition cylinder 5-1 during use and ensuring the stability and reliability of the device.

[0036] In another embodiment, the partition cylinder 5-1 is connected to the spring base 5-3, is disposed within the receiving groove 2-3, and can slide up and down. The horizontal height of the bottom end of the partition cylinder 5-1 is lower than the horizontal height of the platform at the bottom end of the cavity of the calibrator 2-1. In this way, the receiving groove 2-3 can constrain the sliding stability of the partition cylinder 5-1, while ensuring that the partition cylinder 5-1 can fully replace the calibrator 2-1 to contact the internal materials such as the target soil sample 4-1, thereby truly reflecting the elimination of frictional resistance.

[0037] In another embodiment, a base 2-2 and a dial indicator 5-4 are also included. The base 2-2 is fixed to the upper end of the calibrator 2-1, and the dial indicator 5-4 is fixed to the base 2-2. The probe of the dial indicator 5-4 is located directly above the partition cylinder 5-1. Thus, by setting the dial indicator 5-4, the amount of sinking of the partition cylinder 5-1 after the external force is applied during the test can be read in real time, which is the compression of the spring base 5-3. This allows for the calculation of the frictional resistance of the external force on the calibrator 2-1, providing the measurement parameters required for the test.

[0038] In another embodiment, a pressure conversion device is also included. This device comprises standard sand 4-2 wrapped with a latex film 4-3, positioned between the target soil sample 4-1 and the top cover 6. The standard sand 4-2 is medium sand with uniform particle size and poor gradation. Wrapped with a latex film 4-3, it forms a complete unit, capable of converting the rigid load transmitted from the top cover 6 into a flexible load acting on the upper surface of the target soil sample 4-1, thus acting as a flexible transition layer. In this embodiment, the thickness of the standard sand 4-2 can be 10 mm. In this embodiment, a latex film 4-3 can also be placed above the structure 3-1 and the soil pressure sensor 1-1.

[0039] As attached Figure 2 As shown, in another embodiment, a wiring groove 3-2 is provided on the upper surface of the platform at the bottom of the cavity of the calibrator 2-1, and a through vertical hole 3-3 is provided at the bottom of the calibrator 2-1. The wiring groove 3-2 is connected to the vertical hole 3-3. Thus, by setting the wiring groove 3-2 and the vertical hole 3-3, it is convenient for the earth pressure sensor 1-1 to extend out of the calibrator 2-1 to connect to external detection equipment, etc.

[0040] In another embodiment, structure 3-1 is made of a cementitious material. This allows for quick and easy fixation of different types of earth pressure sensors 1-1, i.e., those with varying thicknesses and diameters. Furthermore, it facilitates leveling before the cementitious material is applied, ensuring calibration accuracy. Specifically, by arranging cementitious material of the same thickness around the earth pressure sensor 1-1, making it flush with the upper surface of the earth pressure sensor 1-1, standard interface earth pressure sensor operating conditions are provided.

[0041] In another embodiment, the top cover 6 is a disc-shaped structure with a flat bottom and a raised upper surface. A groove is provided in the center of the raised upper surface, which is used to directly receive external forces. In this way, the load can be applied evenly downwards through the top cover 6. In this embodiment, the maximum diameter of the bottom of the top cover 6 is 1.0 mm smaller than the inner diameter of the partition cylinder 5-1.

[0042] A method for operating an interface earth pressure sensor calibration device includes the following steps:

[0043] Using a universal testing machine, the spring coefficient K of the spring base 5-3 is calibrated. Then, the spring base 5-3, the partition 5-1 and the calibrator 2-1 are connected and installed in sequence, and the ball bearing 5-2 is placed in the gap between the partition 5-1 and the calibrator 2-1.

[0044] b. Place the earth pressure sensor 1-1 at the bottom of the cavity of the calibrator 2-1, and route the data cable 3-4 of the earth pressure sensor 1-1 through the cable tray 3-2 and the vertical hole 3-3.

[0045] c. Apply cementitious material into the cavity 5-1 and cast a leveling structure 3-1 of the same thickness as the earth pressure sensor 1-1. At this time, the structure 3-1 wraps around and fixes the earth pressure sensor 1-1. At the same time, by utilizing the characteristics of the cementitious material, the method of casting the leveling interface afterward can meet the requirements of the calibration working surface of the interface pressure sensor, making it easy to make the upper surface of the earth pressure sensor 1-1 flush with the structure 3-1, thereby ensuring calibration accuracy. It can also meet the requirements of the earth pressure sensor's output cable. During casting, a layer of latex film 4-3 can be laid on top to form a flush structure 3-1.

[0046] d. Place the target soil sample 4-1 above the soil pressure sensor 1-1 in sequence, level it thoroughly, place the standard sand 4-2 wrapped with a layer of latex film 4-3, and then place the top cover 6.

[0047] e. Place the probe of dial indicator 5-4 directly above the partition cylinder 5-1 and zero the reading;

[0048] The external force is applied in stages using equipment such as a universal testing machine. After each stage of load is applied and the dial gauge reading stabilizes, the settlement amount Δi and the required calibration value are recorded until the marking test is completed. The settlement amount Δi is used to deduct the influence of frictional resistance F when converting the pressure acting on the surface of the target soil sample 4-1, i.e., F=K·Δi. The magnitude and stages of the external force on the top cover 6 can be converted according to the range of the calibrated earth pressure sensor 1-1, which is a routine operation.

[0049] In a specific implementation of the device of the present invention, the calibrator 2-1 can be a hollow cylinder with a height of 100~150mm and a wall thickness of 10~30mm. The diameter of the wiring groove 3-2 and the vertical hole 3-3 opened on it can both be 5mm. The calibrator 2-1 can be made of metal material to provide sufficient rigidity and prevent deformation that would affect the calibration results when pressure is applied. The partition cylinder 5-1 is a stainless steel ring with a wall thickness of 6-10mm corresponding to the cylindrical calibrator 2-1. The receiving groove 2-3 is an annular shape, and the spring base 5-3 is an annular shape. The maximum diameter of the bottom of the top cover 6 can be 1.0mm smaller than the inner diameter of the partition cylinder. The thickness of the standard sand 4-2 wrapped with a layer of latex film 4-3 can be 10mm.

[0050] This invention uses a standard sand 4-2 wrapped with a latex film 4-3 as a pressure conversion device to form a transition layer, which can convert the rigid load applied to the top cover 6 into a flexible load acting on the top of the target soil sample 4-1. It can be used with common pressure equipment such as a compression consolidation apparatus, an unconfined compression apparatus, and a universal tensile and compressive testing machine for calibration, making it more applicable. Using the target soil sample 4-1 to calibrate the soil pressure sensor 1-1 is more in line with the working environment of the soil pressure sensor 1-1, increasing the calibration accuracy. By setting up a cementitious material for leveling, the working surface of the soil pressure sensor 1-1 can be easily leveled, meeting the calibration conditions of the interface soil pressure. By setting up a friction reduction device with a partition cylinder 5-1 and a ball bearing 5-2 in conjunction with the side wall of the calibrator 2-1 cavity, the friction error during the calibration process can be reduced to the maximum extent.

[0051] It should be noted that the terms such as "upper", "lower", "left", "right", "front", and "back" used in the invention are only for clarity of description and are not intended to limit the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0052] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A calibration device for an interface earth pressure sensor, characterized in that: The device includes a calibrator (2-1), a structure (3-1), an earth pressure sensor (1-1), a diaphragm (5-1), and a top cover (6). The calibrator (2-1) has a cavity at its center. A receiving groove (2-3) is formed along the side wall of the cavity at its bottom end. A spring base (5-3) is installed inside the receiving groove (2-3). The upper end of the spring base (5-3) is fixedly connected to the lower end of the diaphragm (5-1). The diaphragm (5-1) can slide up and down within the receiving groove (2-3). There is a gap between the diaphragm (5-1) and the side wall of the cavity. Several ball bearings (5-2) are evenly arranged in the gap. A base extends from the lower end toward the side wall of the cavity to confine the ball (5-2) in the gap. The diameter of the ball (5-2) is larger than the distance between the partition cylinder (5-1) above the base and the side wall of the cavity. The structure (3-1) is installed on a platform surrounded by a receiving groove (2-3) at the bottom of the cavity. An earth pressure sensor (1-1) is fixed in the structure (3-1). A target soil sample (4-1) is provided above the structure (3-1) and the earth pressure sensor (1-1). A top cover (6) is provided above the target soil sample (4-1). The target soil sample (4-1) and the top cover (6) are both located inside the partition cylinder (5-1).

2. The interface earth pressure sensor calibration device according to claim 1, characterized in that: The partition cylinder (5-1) and the calibrator (2-1) cavity have several vertical grooves spaced apart on their opposite sidewalls. The balls (5-2) are respectively disposed in the grooves. The maximum distance from the groove to the sidewall of the calibrator (2-1) cavity is less than the diameter of the balls (5-2).

3. The interface earth pressure sensor calibration device according to claim 1, characterized in that: The spring base (5-3) includes several vertically arranged springs, which are equally spaced in the receiving groove (2-3).

4. The interface earth pressure sensor calibration device according to claim 1, characterized in that: The partition cylinder (5-1) is connected to the spring base (5-3) and is set in the receiving groove (2-3) and can slide up and down. The horizontal height of the bottom end of the partition cylinder (5-1) is lower than the horizontal height of the platform at the bottom end of the cavity of the calibrator (2-1).

5. The interface earth pressure sensor calibration device according to claim 1, characterized in that: It also includes a base (2-2) and a dial indicator (5-4). The base (2-2) is fixed to the upper end of the calibrator (2-1), and the dial indicator (5-4) is fixed on the base (2-2). The probe of the dial indicator (5-4) is located directly above the partition cylinder (5-1).

6. The interface earth pressure sensor calibration device according to claim 1, characterized in that: It also includes a pressure conversion device, which includes standard sand (4-2) wrapped with a latex film (4-3), and the standard sand (4-2) wrapped with a latex film (4-3) is placed between the target soil sample (4-1) and the top cover (6).

7. The interface earth pressure sensor calibration device according to claim 1, characterized in that: The calibrator (2-1) has a wiring groove (3-2) on the upper surface of the platform at the bottom of the cavity, and a through vertical hole (3-3) at the bottom of the calibrator (2-1). The wiring groove (3-2) is connected to the vertical hole (3-3).

8. The interface earth pressure sensor calibration device according to claim 1, characterized in that: The structure (3-1) is made of cementitious material.

9. The interface earth pressure sensor calibration device according to claim 1, characterized in that: The top cover (6) is a disc with a flat bottom and a raised top surface. A groove is provided in the center of the raised top surface, which is used to directly receive external forces.

10. A method for operating an interface earth pressure sensor calibration device, comprising the following steps: (a) Using a universal testing machine, calibrate the spring coefficient K of the spring base (5-3), and then connect and install the spring base (5-3), the partition (5-1) and the calibrator (2-1) in sequence, and put the ball (5-2) into the gap between the partition (5-1) and the calibrator (2-1); (b) Place the earth pressure sensor (1-1) at the bottom of the cavity of the calibrator (2-1) and run the data cable (3-4) of the earth pressure sensor (1-1) in a cable arrangement; (c) Apply cementitious material into the cavity (5-1) and pour a leveling structure (3-1) of the same thickness as the earth pressure sensor (1-1). (d) Place the target soil sample (4-1) above the soil pressure sensor (1-1) in sequence, level it thoroughly, place the standard sand (4-2) wrapped with a layer of latex film (4-3), and then place the top cover (6). (e) Place the probe of the dial indicator (5-4) directly above the partition cylinder (5-1) and zero the reading; (f) Apply external force in stages using a universal testing machine. After each stage of load is applied and the dial gauge reading stabilizes, record the settlement amount Δi and the required calibration value until the marking test is completed. The settlement amount Δi is used to deduct the influence of frictional resistance F when converting the pressure acting on the surface of the target soil sample (4-1), i.e., F=K·Δi.

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