A kind of subgrade settlement displacement wireless passive monitoring system and method

Abstract

This invention discloses a wireless passive monitoring system and method for roadbed settlement displacement. The method includes: S1, acquiring the calibration parameters of the wireless passive monitoring system for roadbed settlement displacement; S2, installing the wireless passive monitoring system for roadbed settlement displacement, and after installation, sending an excitation signal to a pressure-temperature dual-mode sensor via an external handheld reader / writer. The pressure-temperature dual-mode sensor measures the pressure and temperature inside the sealed air chamber and sends the data to the reader / writer, recording the pressure and temperature inside the sealed air chamber at this time; S3, when settlement displacement data needs to be collected, sending an excitation signal to the pressure-temperature dual-mode sensor via the reader / writer. The pressure-temperature dual-mode sensor simultaneously measures the current pressure and temperature inside the sealed air chamber and sends the data to the reader / writer; S4, based on the current pressure and temperature, the reader / writer performs compensation calculations according to the multi-parameter coupling error compensation displacement formula to obtain the current settlement displacement result and displays it. The monitoring method of this invention eliminates systematic errors.

Description

Technical Field

[0001] This invention belongs to the field of engineering safety monitoring, specifically relating to a wireless passive monitoring system and method for roadbed settlement and displacement. Background Technology

[0002] With the large-scale construction and operation of transportation infrastructure in my country, the long-term stability of roadbeds (including railways, subways, trams, etc.) is crucial to operational safety. Under the influence of long-term loads, groundwater changes, and geological activity, roadbeds are prone to uneven settlement and horizontal displacement. If these are not detected and addressed in a timely manner, they will seriously threaten traffic safety. Therefore, long-term, continuous, and automated monitoring of underground soil displacement is of significant engineering importance.

[0003] Currently, the main technologies used for roadbed settlement monitoring are as follows:

[0004] (1) Manual measurement method using level / total station: It has high accuracy, but requires manual on-site operation, which is inefficient and cannot achieve continuous and real-time automated monitoring. It is also greatly affected by weather and visibility conditions.

[0005] (2) Static level instrument method: It can realize automated monitoring, but it requires the laying of complex pipelines and cables, resulting in high installation and maintenance costs. It is not suitable for long distances and outdoor environments, and is easily affected by temperature.

[0006] (3) Fiber Bragg grating sensor method: high accuracy and resistance to electromagnetic interference, but it also requires laying optical cables, resulting in high system cost, complex signal demodulation equipment, and limited sensor deployment density.

[0007] (4) Traditional electronic displacement gauges / inclinometers: They usually require power supply and signal transmission cables. In harsh outdoor environments, the cables are easily damaged, and long-term reliability is challenged. In addition, battery power supply has lifespan issues.

[0008] The aforementioned monitoring technologies face challenges in power supply and cabling difficulties during long-term field monitoring. All of these technologies are active monitoring solutions that rely on batteries or cables for power supply. In underground buried environments, they have high maintenance costs and high failure rates, making it difficult to meet the engineering requirements for long-term maintenance-free operation. Summary of the Invention

[0009] To address the problems existing in the prior art, one objective of this invention is to provide a wireless passive monitoring system for roadbed settlement and displacement, and another objective of this invention is to provide a wireless passive monitoring method for roadbed settlement and displacement with error compensation function.

[0010] Therefore, the present invention adopts the following technical solution:

[0011] A passive wireless monitoring system for roadbed settlement and displacement includes a displacement-to-air pressure conversion unit, a temperature and pressure sensing unit, a wireless communication unit, an error compensation calculation unit, and a display unit, wherein:

[0012] The displacement-pressure conversion unit is used to convert the settlement displacement of the roadbed into the volume change of the sealed air chamber inside the bellows through the piston rod, thereby converting the displacement into the pressure change inside the sealed air chamber.

[0013] The temperature and pressure sensing unit is used to synchronously collect the pressure and temperature of the sealed air chamber;

[0014] The wireless communication unit is used to transmit a radio frequency signal for power supply to the temperature and pressure sensing unit, and to receive the pressure and temperature of the sealed air chamber collected by the temperature and pressure sensing unit.

[0015] The error compensation calculation unit is used to invert the relative displacement between the monitoring point and the reference point based on the pressure and temperature of the sealed air chamber.

[0016] The display unit is used to display the relative displacement obtained by the error compensation calculation unit;

[0017] The error compensation calculation unit, wireless communication unit, and display unit are integrated into one unit.

[0018] The displacement-pressure conversion unit includes a piston rod, a monitoring system housing, and a metal bellows inside the housing; the temperature and pressure sensing unit is a dual-mode pressure and temperature sensor; the wireless communication unit, the error compensation calculation unit, and the display unit are integrated on the reader.

[0019] A settlement plate is pre-embedded on the roadbed to be monitored. The top of the monitoring system shell is fixedly connected to the settlement plate through a connector. The lower end of the connector is inserted into the monitoring system shell, and the contact part between the upper end of the connector and the settlement plate serves as a monitoring point.

[0020] The monitoring system housing is made of high-strength stainless steel to protect its internal structure;

[0021] The top end of the metal bellows is fixed to the bottom of the connector, forming a sealed air chamber inside, which is filled with dry inert gas.

[0022] The bottom end of the metal bellows is fixed to the piston at the top of the piston rod, and the piston and the monitoring system housing 1 can move relative to each other. The rod of the piston rod 2 passes through the bottom center of the monitoring system housing 1, and the bottom end of the rod is fixed to the stable bedrock as a reference point.

[0023] The pressure-sensing port of the pressure-temperature dual-mode sensor is inserted into the L-shaped channel inside the connector through a capillary tube and communicates with the sealed air chamber; the pressure-temperature dual-mode sensor and its antenna are installed in a special protective box on the road shoulder, and the protective box is installed on the reference pile.

[0024] When the soil of the roadbed settles, the displacement of the monitoring point relative to the benchmark point is transmitted through the piston rod, causing the metal bellows to deform, which in turn causes the air pressure in the sealed air chamber to change.

[0025] The reader / writer is handheld and is used to send excitation signals to the pressure-temperature dual-mode sensor.

[0026] The pressure-temperature dual-mode sensor operates instantaneously using the radio frequency energy in the collected excitation signal, simultaneously measuring the current pressure and temperature inside the sealed air chamber, and packaging them into the same radio frequency signal frame to send to the reader.

[0027] The error compensation calculation unit in the reader stores the calibration parameters of the wireless passive monitoring system for underground soil displacement, as well as the pressure and temperature in the sealed air chamber measured after the system is installed.

[0028] The reader calculates and displays the current settlement displacement based on the pressure and temperature inside the sealed air chamber measured after system installation, as well as the current pressure and temperature.

[0029] The reader receives the current pressure and temperature, calculates the current settlement displacement, and displays it.

[0030] A method for monitoring roadbed settlement displacement using the aforementioned wireless passive monitoring system includes the following steps:

[0031] S1, Obtain the calibration parameters of the wireless passive monitoring system for roadbed settlement displacement, including the effective cross-sectional area of ​​the metal corrugated pipe at a reference temperature of 20℃. Effective area temperature coefficient and the initial volume of the sealed air chamber ;

[0032] S2. Install the roadbed settlement and displacement wireless passive monitoring system. After the system is installed, an excitation signal is sent to the pressure-temperature dual-mode sensor via an external handheld reader. The sensor utilizes the radio frequency energy in the collected excitation signal to operate instantaneously, simultaneously measuring the pressure and temperature within the sealed chamber. These two raw data points are packaged into a single radio frequency signal frame and sent to the reader, thus recording the pressure within the sealed chamber in this initial state. and temperature ;

[0033] S3, when settlement displacement data needs to be collected, an excitation signal is sent to the pressure-temperature dual-mode sensor via an external handheld reader / writer. The pressure-temperature dual-mode sensor uses the radio frequency energy in the collected excitation signal to work instantaneously, while simultaneously measuring the current pressure in the sealed air chamber. and current temperature The data is sent to the reader / writer, and the Celsius temperature is calculated simultaneously. ;

[0034] S4, the reader calculates the current settlement displacement based on the received current pressure and temperature inside the sealed air chamber, according to the following multi-parameter coupling error compensation displacement formula, and displays the result:

[0035] ,

[0036] in, This is a nonlinear correction coefficient.

[0037] The process of constructing the multi-parameter coupled error compensation displacement formula is as follows:

[0038] Settlement displacement of roadbed The piston rod causes the metal bellows to produce the same axial displacement. This displacement directly changes the volume of the sealed air chamber. The volume-displacement formula is as follows:

[0039] ,

[0040] in, The effective cross-sectional area of ​​the metal bellows. This represents the current volume of the sealed gas chamber.

[0041] The change in volume of the sealed gas chamber causes a change in internal pressure. According to the ideal gas law:

[0042] ,

[0043] Effective cross-sectional area of ​​the temperature-compensated metal bellows 1 for:

[0044] ,

[0045] Nonlinear stroke compensation is performed on the effective cross-sectional area of ​​the temperature-compensated metal bellows 1, and a nonlinear correction coefficient is set. The effective cross-sectional area after nonlinear stroke compensation is obtained. for:

[0046] ,

[0047] ,

[0048] Effective cross-sectional area Substituting into the ideal gas law, we obtain the gas law after temperature compensation and nonlinear stroke compensation:

[0049] ,

[0050] For a sealed, metered gas, the above gas equation of state is modified by introducing a gas compressibility factor. The modified gas equation of state is as follows:

[0051] ,

[0052] in, , Let be the gas compressibility factor under the initial and current conditions, respectively. Within the temperature and pressure range for engineering applications, the gas compressibility factor can be approximated as:

[0053] ,

[0054] in, The second virial coefficient, Volume is the molar volume;

[0055] Therefore, the displacement formula for multi-parameter coupling error compensation is obtained as follows:

[0056] ,

[0057] The expanded form of the multi-parameter coupling error compensation displacement formula is as follows:

[0058] .

[0059] The method for obtaining the current value of the nonlinear correction coefficient is as follows:

[0060] Calibration is performed at certain intervals across the full range of the metal bellows to obtain the theoretical values ​​of the nonlinear correction coefficients at each calibration point. The values ​​for the nonlinear correction coefficients between calibration points are then considered. The theoretical values ​​of the corresponding nonlinear correction coefficients are calculated using cubic spline interpolation; the values ​​of the nonlinear correction coefficients are solved using a successive approximation iterative method.

[0061] make The initial estimated settlement displacement values ​​are obtained as follows:

[0062] ,

[0063] according to The theoretical value of the nonlinear correction coefficient obtained from the calibration results or cubic spline interpolation results. Used to update the effective cross-sectional area and settlement displacement:

[0064] ,

[0065] Repeat the above process until convergence. The estimated values ​​of the effective cross-sectional area and settlement displacement of the stainless steel corrugated pipe obtained in each update are:

[0066] ,

[0067] The condition for convergence is: , To be the convergence threshold, take m;

[0068] Save the theoretical values ​​of the nonlinear correction coefficients at convergence as the current nonlinear correction coefficients. The value of .

[0069] The full range of the metal bellows is 0 to 20 mm, and the interval is 2 mm.

[0070] Compared with the prior art, the present invention has the following beneficial effects:

[0071] 1. The monitoring system of the present invention has a very simple mechanical structure. It adopts a direct drive method of bellows and piston rod, which directly converts displacement into volume change, reducing the number of conversion stages and error sources. The structure is simple and reliable, and the bellows structure is compact, which is convenient for large-scale network deployment.

[0072] 2. The sensors in the monitoring system of the present invention do not require battery power; they obtain energy through radio frequency excitation, and their service life is limited only by device aging.

[0073] 3. The monitoring method of this invention establishes a complete compensation chain for bellows effective area temperature correction, nonlinear stroke compensation, and gas non-ideality correction, fundamentally eliminating systematic errors such as temperature drift, large stroke nonlinearity, and gas deviation. Experiments show that, under an environment with a temperature difference of 30℃, this method can reduce the measurement error from... mm converges to Within mm. The aforementioned accuracy improvement is guaranteed by the iterative convergence characteristics of nonlinear stroke compensation, and the sensor hardware only needs to meet conventional engineering-grade machining accuracy.

[0074] 4. The multi-parameter error compensation displacement formula in the monitoring method of the present invention contains a temperature ratio term, which eliminates the temperature drift pressure increment caused by Charles's law in the sealed gas chamber from the physical principle level of the ideal gas law, without the need for additional temperature compensation steps.

[0075] 5. In the monitoring method of the present invention, apart from the real-time measured air pressure and temperature, all other required parameters can be obtained through factory calibration. Attached Figure Description

[0076] Figure 1 This is a schematic diagram of the structure of the wireless passive monitoring system for roadbed settlement and displacement in an embodiment of the present invention.

[0077] In the diagram: 1. Metal bellows; 2. Piston rod; 3. Sealed air chamber; 4. Pressure and temperature dual-mode sensor; 5. Capillary tube; 6. Benchmark pile; 7. Roadbed; 8. Settlement plate; 9. Reader; 10. Monitoring system housing; 11. Connector. Detailed Implementation

[0078] The technical solution of the invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. Obviously, the following embodiments are only some embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0079] This invention provides a wireless passive monitoring system for roadbed settlement and displacement, installed in a measuring hole in the roadbed to be measured. It measures the relative displacement between a reference point fixed in stable bedrock or a geologically stable area and a monitoring point in the soil to be measured. The system includes a displacement-to-pressure conversion unit, a temperature and pressure sensing unit, a wireless communication unit, an error compensation calculation unit, and a display unit.

[0080] The displacement-pressure conversion unit is used to convert the settlement displacement of the roadbed into the volume change of the sealed air chamber inside the bellows through the piston rod, thereby converting the displacement into the pressure change inside the sealed air chamber.

[0081] The temperature and pressure sensing unit is used to synchronously collect the pressure and temperature of the sealed air chamber;

[0082] The wireless communication unit is used to transmit a radio frequency signal for power supply to the temperature and pressure sensing unit, and to receive the pressure and temperature of the sealed air chamber collected by the temperature and pressure sensing unit.

[0083] The error compensation calculation unit is used to invert the relative displacement between the monitoring point and the reference point based on the pressure and temperature of the sealed air chamber.

[0084] The display unit is used to display the relative displacement obtained by the error compensation calculation unit;

[0085] The error compensation calculation unit, wireless communication unit, and display unit are integrated into one unit.

[0086] Example 1

[0087] like Figure 1As shown, this embodiment provides a wireless passive monitoring system for roadbed settlement displacement, including a displacement-to-pressure conversion unit, a temperature and pressure sensing unit, a wireless communication unit, an error compensation calculation unit, and a display unit. The displacement-to-pressure conversion unit includes a piston rod 2, a monitoring system housing 10, and a metal bellows 1 inside the housing. The temperature and pressure sensing unit is a pressure-temperature dual-mode sensor 4. The wireless communication unit, the error compensation calculation unit, and the display unit are integrated on a reader 9.

[0088] A settlement plate 8 is pre-embedded on the roadbed 7 to be monitored. The top of the monitoring system housing 10 is fixedly connected to the settlement plate 8 through a connector 11. The lower end of the connector 11 is inserted into the monitoring system housing 10, and the contact part between the upper end of the connector 11 and the settlement plate 8 serves as a monitoring point.

[0089] The outer casing 1 of the monitoring system is made of high-strength stainless steel to protect its internal structure.

[0090] The top end of the metal bellows 1 is fixed to the bottom of the connector 11, forming a sealed gas chamber 3 inside, which is filled with dry inert gas, which is nitrogen in this embodiment. The bottom end of the metal bellows 1 is fixed to the piston at the top of the piston rod 2, and the piston and the monitoring system housing 1 can move relative to each other. The rod of the piston rod 2 extends from the bottom center of the monitoring system housing 1, and the bottom end of the rod is fixed to a stable bedrock as a reference point.

[0091] The pressure-temperature dual-mode sensor 4 and its antenna are housed in a dedicated protective box on the road shoulder. The protective box is installed on the reference pile 6 to prevent direct crushing by construction machinery. The pressure-sensing port of the pressure-temperature dual-mode sensor 4 is connected to the sealed gas chamber 3 via a stainless steel capillary tube 5 inserted into an L-shaped channel within the connector 11. The volume of the capillary tube 5 is much smaller than the volume of the sealed gas chamber 3, and the gas thermal balance is mainly determined by the sealed gas chamber 3.

[0092] When the soil of the roadbed 7 settles, the displacement of the monitoring point relative to the benchmark point is transmitted through the piston rod 2, causing the metal bellows 1 to deform, which in turn causes the air pressure in the sealed air chamber 3 to change.

[0093] The reader 9 is handheld and is used to send excitation signals to the pressure-temperature dual-mode sensor 4. The pressure-temperature dual-mode sensor 4 operates instantaneously using the radio frequency energy in the collected excitation signal, simultaneously measuring the current pressure and temperature inside the sealed air chamber 3, and packaging these two raw data into the same radio frequency signal frame before sending it to the reader 9. The error compensation calculation unit in the reader 9 stores the calibration parameters of the underground soil displacement wireless passive monitoring system, as well as the pressure and temperature inside the sealed air chamber 3 measured after system installation. The reader 9 calculates and displays the current settlement displacement based on the pressure and temperature inside the sealed air chamber 3 measured after system installation, as well as the current pressure and temperature.

[0094] The reader 9 receives the current pressure and temperature, calculates the current settlement displacement, and displays it.

[0095] In this embodiment, the method for wireless passive monitoring of roadbed settlement displacement using the above system includes the following steps:

[0096] S1, Obtain the calibration parameters of the wireless passive monitoring system for roadbed settlement displacement, the calibration parameters including:

[0097] The inner diameter of the metal bellows 1 is 30mm, and the wall thickness is 0.3mm (stainless steel).

[0098] The effective cross-sectional area of ​​metal bellows 1 at a reference temperature of 20°C: m (Right now )

[0099] Effective area temperature coefficient: / ℃

[0100] Initial volume of sealed air chamber 3: m (i.e., 50 cm) )

[0101] All calibration parameters were obtained from factory calibration.

[0102] S2. Install the roadbed settlement and displacement wireless passive monitoring system. After the system is installed, the external handheld reader 9 sends an excitation signal to the pressure-temperature dual-mode sensor 4. The pressure-temperature dual-mode sensor 4 uses the radio frequency energy in the collected excitation signal to work instantaneously, simultaneously measuring the pressure and temperature inside the sealed air chamber 3, and packaging them into the same radio frequency signal frame to send to the reader 9, thereby recording the pressure inside the sealed air chamber 3 in the initial state. Pa, and temperature K ( ℃).

[0103] S3, when settlement displacement data needs to be collected, an excitation signal is sent to the pressure-temperature dual-mode sensor 4 via the external handheld reader 9. The pressure-temperature dual-mode sensor 4 uses the radio frequency energy in the collected excitation signal to work instantaneously, simultaneously measuring the current pressure and temperature inside the sealed gas chamber 3 and sending it to the reader 9. The Celsius temperature is also calculated simultaneously. .

[0104] In this embodiment, the current temperature inside the sealed gas chamber 3 is measured by the pressure-temperature dual-mode sensor 4: K ( ℃); Current pressure: Pa.

[0105] S4, the reader 9 calculates the current settlement displacement result based on the received current pressure and temperature in the sealed air chamber 3 using a multi-parameter coupling error compensation displacement formula, and displays it.

[0106] The derivation process of the multi-parameter coupling error compensation displacement formula is as follows:

[0107] When the roadbed settles, the monitoring points move with the roadbed soil, and the settlement displacement... (Unit: m, compression is positive) The piston rod 2 causes the metal bellows 1 to produce the same axial displacement. This displacement directly changes the volume of the sealed air chamber 3. The volume-displacement formula is as follows:

[0108] ,

[0109] in, The effective cross-sectional area of ​​metal bellows 1 (unit: m²) ), This is the current volume of the sealed air chamber 3.

[0110] The change in volume of the sealed chamber 3 causes a change in internal pressure. According to the ideal gas law:

[0111] ,

[0112] Current pressure of sealed chamber 3 It is simultaneously affected by two factors: piston rod displacement (i.e., volume change) and ambient temperature change.

[0113] Temperature compensation is applied to the effective cross-sectional area of ​​the metal bellows 1 to eliminate the influence of temperature on the effective area of ​​the bellows. Specifically:

[0114] The effective cross-sectional area of ​​the metal bellows 1 depends on its geometry and the elastic modulus of its material. The elastic modulus of the material of the metal bellows 1 (typically stainless steel or beryllium bronze) changes with temperature, causing a shift in the effective cross-sectional area. The effective cross-sectional area of ​​the metal bellows 1 after temperature compensation... for:

[0115] .

[0116] In this embodiment:

[0117] .

[0118] Nonlinear stroke compensation is performed on the effective cross-sectional area of ​​the temperature-compensated metal bellows 1, specifically as follows:

[0119] Within a small stroke range, the effective cross-sectional area of ​​the metal bellows 1 can be considered constant, but when the settlement displacement... When the area is large, the geometric configuration of the metal bellows 1 changes significantly, and the effective cross-sectional area is no longer constant, thus requiring the setting of a nonlinear correction coefficient. The effective cross-sectional area after nonlinear stroke compensation is obtained. for:

[0120] ,

[0121] ,

[0122] Effective cross-sectional area Substituting into the ideal gas law, we obtain the gas law after temperature compensation and nonlinear stroke compensation:

[0123] .

[0124] Under high pressure or low temperature conditions, the gas inside sealed chamber 3 deviates from ideal gas behavior. For a sealed, metered gas, a gas compressibility factor is introduced to correct the above gas equation of state. The corrected gas equation of state is as follows:

[0125] ,

[0126] in, , Let be the gas compressibility factor under the initial and current conditions, respectively. Within the temperature and pressure range for engineering applications, the gas compressibility factor can be approximated as:

[0127] ,

[0128] in, The second virial coefficient, The volume is the molar volume.

[0129] For nitrogen, .

[0130] In this embodiment, , (The deviation is negligible under normal pressure).

[0131] Therefore, the displacement formula for multi-parameter coupling error compensation is obtained as follows:

[0132] ,

[0133] The expanded form of the multi-parameter coupling error compensation displacement formula is as follows:

[0134] .

[0135] Among them, the nonlinear correction coefficient The value is obtained through iterative solution, as follows:

[0136] Calibration was performed at 2mm intervals across the full range of the metal bellows 1 (0 to 20mm) to obtain the theoretical values ​​of the nonlinear correction coefficients at each calibration point. For the intervals between calibration points... The theoretical values ​​of the corresponding nonlinear correction coefficients are calculated using cubic spline interpolation. Cubic spline interpolation ensures the continuity of compensation between calibration points; the effective resolution of the system is determined by the sensor's pressure measurement accuracy, not by the calibration interval itself.

[0137] In this embodiment, the stainless steel corrugated pipe 1 has an inner diameter of 30 mm and a wall thickness of 0.3 mm. The calibration results of the theoretical values ​​of the nonlinear correction coefficients at its calibration points are shown in Table 1.

[0138] Table 1

[0139]

[0140] because rely ,and Dependence (including) This constitutes an implicit equation, which is solved using a successive approximation iterative method:

[0141] make The initial estimated settlement displacement values ​​are obtained as follows:

[0142] ,

[0143] according to The theoretical value of the nonlinear correction coefficient obtained from the calibration results or cubic spline interpolation results. Used to update the effective cross-sectional area and settlement displacement:

[0144] ,

[0145] Repeat the above process until convergence. The estimated values ​​of the effective cross-sectional area and settlement displacement of the stainless steel corrugated pipe obtained in each update are:

[0146] ,

[0147] The condition for convergence is: , To be the convergence threshold, take m.

[0148] When convergence is achieved, the theoretical values ​​of the nonlinear correction coefficients are saved as the current nonlinear correction coefficients. The value of .

[0149] because For small quantities (calibration data shows) The iterations typically converge within 2-3 steps.

[0150] In this embodiment:

[0151] ,

[0152] From the calibration table, we can find Iterative convergence.

[0153] Therefore, at this time, the settlement displacement is... Since the displacement was close to zero, the roadbed soil did not experience any settlement.

[0154] If temperature compensation is not performed, and judgment is made solely based on pressure changes... Pa, calculated under the isothermal assumption

[0155] .

[0156] Calculations without temperature compensation could lead to a misjudgment of settlement, which would be inconsistent with the actual situation.

[0157] Therefore, it can be seen that the error caused by temperature drift is effectively eliminated after compensation by the method of the present invention.

[0158] Example 2

[0159] In this embodiment, the same wireless passive monitoring system for roadbed settlement and displacement as in Embodiment 1 is used.

[0160] In this embodiment, the method of the present invention is used to perform wireless passive monitoring of roadbed settlement displacement in winter conditions, including the following steps:

[0161] S1. Obtain the calibration parameters of the wireless passive monitoring system for roadbed settlement displacement. In this embodiment, the calibration parameters are the same as those in Embodiment 1.

[0162] S2. Install the roadbed settlement and displacement wireless passive monitoring system. After the system is installed, the external handheld reader 9 sends an excitation signal to the pressure-temperature dual-mode sensor 4. The pressure-temperature dual-mode sensor 4 uses the radio frequency energy in the collected excitation signal to work instantaneously, simultaneously measuring the pressure and temperature inside the sealed air chamber 3. It then packages these two raw data points into the same radio frequency signal frame and sends it to the reader 9, thereby recording the pressure inside the sealed air chamber 3 in this initial state. Pa, and temperature K ( ℃).

[0163] S3, when settlement displacement data needs to be collected, an excitation signal is sent to the pressure-temperature dual-mode sensor 4 via the external handheld reader 9. The pressure-temperature dual-mode sensor 4 uses the radio frequency energy in the collected excitation signal to work instantaneously, simultaneously measuring the current pressure and temperature inside the sealed gas chamber 3 and sending it to the reader 9. The Celsius temperature is also calculated simultaneously. .

[0164] In this embodiment, the current temperature inside the sealed gas chamber 3 is measured by the pressure-temperature dual-mode sensor 4: K ( ℃); Current pressure: Pa.

[0165] S4, the reader 9 calculates the current soil displacement result based on the received current pressure and temperature in the sealed air chamber 3 using a multi-parameter coupling error compensation displacement formula, and displays the result.

[0166] The multi-parameter coupling error compensation displacement formula is as follows:

[0167] ,

[0168] The expanded form of the multi-parameter coupling error compensation displacement formula is as follows:

[0169] .

[0170] In this embodiment, , .

[0171] .

[0172] The values ​​of the pre-nonlinear correction coefficients are calculated through iterative solutions:

[0173] In this embodiment:

[0174] ,

[0175] Interpolation values ​​from the calibration table: ,

[0176] ,

[0177] ,

[0178] mm ,convergence.

[0179] Thus, the actual settlement displacement was found to be 7.78 mm.

[0180] If temperature compensation is not performed, use directly Pa is calculated based on the isothermal assumption:

[0181] ,

[0182] Without temperature compensation, the settlement displacement result had an error of 22% compared to the actual result.

[0183] Therefore, it can be seen that after compensation by the method of the present invention, the effects of temperature drift and nonlinear error are eliminated.

Claims

1. A wireless passive monitoring system for subgrade settlement displacement, characterized in that, It includes a displacement-to-pressure conversion unit, a temperature and pressure sensing unit, a wireless communication unit, an error compensation calculation unit, and a display unit, wherein: The displacement-pressure conversion unit is used to convert the settlement displacement of the roadbed into the volume change of the sealed air chamber inside the bellows through the piston rod, thereby converting the displacement into the pressure change inside the sealed air chamber. The temperature and pressure sensing unit is used to synchronously collect the pressure and temperature of the sealed air chamber; The wireless communication unit is used to transmit a radio frequency signal for power supply to the temperature and pressure sensing unit, and to receive the pressure and temperature of the sealed air chamber collected by the temperature and pressure sensing unit. The error compensation calculation unit is used to invert the relative displacement between the monitoring point and the reference point based on the pressure and temperature of the sealed air chamber. The display unit is used to display the relative displacement obtained by the error compensation calculation unit; The error compensation calculation unit, wireless communication unit, and display unit are integrated into one unit.

2. The wireless passive monitoring system for roadbed settlement and displacement according to claim 1, characterized in that: The displacement-pressure conversion unit includes a piston rod, a monitoring system housing, and a metal bellows inside the housing; the temperature and pressure sensing unit is a dual-mode pressure and temperature sensor; the wireless communication unit, the error compensation calculation unit, and the display unit are integrated on the reader.

3. The wireless passive monitoring system for roadbed settlement and displacement according to claim 2, characterized in that: A settlement plate is pre-embedded on the roadbed to be monitored. The top of the monitoring system shell is fixedly connected to the settlement plate through a connector. The lower end of the connector is inserted into the monitoring system shell, and the contact part between the upper end of the connector and the settlement plate serves as the monitoring point. The monitoring system housing is made of high-strength stainless steel to protect its internal structure; The top end of the metal bellows is fixed to the bottom of the connector, forming a sealed air chamber inside, which is filled with dry inert gas. The bottom end of the metal bellows is fixed to the piston at the top of the piston rod, and the piston and the monitoring system housing 1 can move relative to each other. The rod of the piston rod 2 passes through the bottom center of the monitoring system housing 1, and the bottom end of the rod is fixed to the stable bedrock as a reference point.

4. The wireless passive monitoring system for roadbed settlement and displacement according to claim 3, characterized in that: The pressure-sensing port of the pressure-temperature dual-mode sensor is inserted into the L-shaped channel inside the connector through a capillary tube and communicates with the sealed air chamber; the pressure-temperature dual-mode sensor and its antenna are installed in a special protective box on the road shoulder, and the protective box is installed on the reference pile.

5. The wireless passive monitoring system for roadbed settlement and displacement according to claim 4, characterized in that: When the soil of the roadbed settles, the displacement of the monitoring point relative to the benchmark point is transmitted through the piston rod, causing the metal bellows to deform, which in turn causes the air pressure in the sealed air chamber to change.

6. The wireless passive monitoring system for roadbed settlement and displacement according to claim 5, characterized in that: The reader / writer is handheld and is used to send excitation signals to the pressure-temperature dual-mode sensor. The pressure-temperature dual-mode sensor operates instantaneously using the radio frequency energy in the collected excitation signal, simultaneously measuring the current pressure and temperature inside the sealed air chamber, and packaging them into the same radio frequency signal frame to send to the reader. The error compensation calculation unit in the reader stores the calibration parameters of the wireless passive monitoring system for underground soil displacement, as well as the pressure and temperature in the sealed air chamber measured after the system is installed. The reader calculates and displays the current settlement displacement based on the pressure and temperature inside the sealed air chamber measured after system installation, as well as the current pressure and temperature. The reader receives the current pressure and temperature, calculates the current settlement displacement, and displays it.

7. A method of monitoring according to the roadbed settlement displacement wireless passive monitoring system of claim 6, characterized in that, Includes the following steps: S1, Obtain the calibration parameters of the wireless passive monitoring system for roadbed settlement displacement, including the effective cross-sectional area of ​​the metal corrugated pipe at a reference temperature of 20℃. Effective area temperature coefficient and the initial volume of the sealed air chamber ; S2. Install the roadbed settlement and displacement wireless passive monitoring system. After the system is installed, an excitation signal is sent to the pressure-temperature dual-mode sensor via an external handheld reader. The sensor utilizes the radio frequency energy in the collected excitation signal to operate instantaneously, simultaneously measuring the pressure and temperature within the sealed chamber. These two raw data points are packaged into a single radio frequency signal frame and sent to the reader, thus recording the pressure within the sealed chamber in this initial state. and temperature ; S3, when settlement displacement data needs to be collected, an excitation signal is sent to the pressure-temperature dual-mode sensor via an external handheld reader / writer. The pressure-temperature dual-mode sensor uses the radio frequency energy in the collected excitation signal to work instantaneously, while simultaneously measuring the current pressure in the sealed air chamber. and current temperature The data is sent to the reader / writer, and the Celsius temperature is calculated simultaneously. ; S4, the reader calculates the current settlement displacement based on the received current pressure and temperature inside the sealed air chamber, according to the following multi-parameter coupling error compensation displacement formula, and displays the result: ， in, This is a nonlinear correction coefficient.

8. The method according to claim 7, characterized in that, The process of constructing the multi-parameter coupled error compensation displacement formula is as follows: Settlement displacement of roadbed The piston rod causes the metal bellows to produce the same axial displacement. This displacement directly changes the volume of the sealed air chamber. The volume-displacement formula is as follows: ， in, The effective cross-sectional area of ​​the metal bellows. This represents the current volume of the sealed gas chamber. The change in volume of the sealed gas chamber causes a change in internal pressure. According to the ideal gas law: ， Effective cross-sectional area of ​​the temperature-compensated metal bellows 1 for: ， Nonlinear stroke compensation is performed on the effective cross-sectional area of ​​the temperature-compensated metal bellows 1, and a nonlinear correction coefficient is set. The effective cross-sectional area after nonlinear stroke compensation is obtained. for: ， ， Effective cross-sectional area Substituting into the ideal gas law, we obtain the gas law after temperature compensation and nonlinear stroke compensation: ， For a sealed, metered gas, the above gas equation of state is modified by introducing a gas compressibility factor. The modified gas equation of state is as follows: ， in, , Let be the gas compressibility factor under the initial and current conditions, respectively. Within the temperature and pressure range for engineering applications, the gas compressibility factor can be approximated as: ， in, The second virial coefficient, Volume is the molar volume; Therefore, the displacement formula for multi-parameter coupling error compensation is obtained as follows: ， The expanded form of the multi-parameter coupling error compensation displacement formula is as follows: 。 9. The method according to claim 8, characterized in that, The method for obtaining the current value of the nonlinear correction coefficient is as follows: Calibration is performed at certain intervals across the full range of the metal bellows to obtain the theoretical values ​​of the nonlinear correction coefficients at each calibration point. The values ​​for the nonlinear correction coefficients between calibration points are then considered. The theoretical values ​​of the corresponding nonlinear correction coefficients are calculated using cubic spline interpolation. The values ​​of the nonlinear correction coefficients are obtained by successive approximation iterative method: make The initial estimated settlement displacement values ​​are obtained as follows: ， according to The theoretical value of the nonlinear correction coefficient obtained from the calibration results or cubic spline interpolation results. Used to update the effective cross-sectional area and settlement displacement: ， Repeat the above process until convergence. The estimated values ​​of the effective cross-sectional area and settlement displacement of the stainless steel corrugated pipe obtained in each update are: ， The condition for convergence is: , To be the convergence threshold, take m; Save the theoretical values ​​of the nonlinear correction coefficients at convergence as the current nonlinear correction coefficients. The value of .

10. The method according to claim 9, characterized in that: The full range of the metal bellows is 0 to 20 mm, and the interval is 2 mm.

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