Soil body freezing state monitoring system and method

Abstract

The invention discloses a soil body freezing state monitoring system and method, and relates to the field of geotechnical engineering monitoring, and the system comprises a piezoelectric sensor which is arranged in a to-be-monitored soil body and is used for converting the pressure generated by the to-be-monitored soil body on the surface of the piezoelectric sensor into an original electric signal; the state monitoring device is used for obtaining soil body freezing state characteristics according to the original electric signals; the soil body freezing state characteristics comprise soil body frost heaving stress and soil body elasticity modulus. The integrated soil body freezing state monitoring system is built based on the piezoelectric sensor, and frozen soil characteristics and strength characters in the soil body construction period and the operation and maintenance period can be timely and effectively analyzed.

Description

Technical Field

[0001] The present application relates to the field of geotechnical engineering monitoring, and in particular to a soil freezing state monitoring system and method. Background Art

[0002] In sections of road with special frozen ground, the construction of newly excavated earthen cutting slopes disrupts the initial stress and thermal equilibrium of the natural soil. After long freeze-thaw cycles, spring snowmelt, rainfall infiltration, and groundwater migration, the internal soil strength of the slopes significantly decreases, weakening their anti-slip capabilities. Frozen soil degradation causes uneven settlement of the roadbed soil. Simultaneously, under the coupled stress fields of the slope's own weight, snow accumulation, and soil frost heave and thaw collapse, slope engineering disasters such as collapse, fluidized landslides, and avalanches frequently occur. Numerous studies have shown that strength damage caused by freeze-thaw cycles in cold-region soils plays a key role in the development and evolution of slip zones. It is essential to identify and monitor the frozen state of soils using cold-region soil freezing state identification technology to ensure the safety and effectiveness of projects.

[0003] Currently, methods for determining soil freezing status can be categorized into local and regional methods. Local methods primarily involve sampling for indoor testing and in-situ measurements, such as drying, resistivity, and nuclear magnetic resonance (NMR). Regional methods employ macroscopic methods, such as ground penetrating radar (GPR) and remote sensing imaging, to comprehensively assess and determine the freezing status of the entire soil. Factors influencing stability under freeze-thaw cycles should fully reflect the dynamic evolution of multiple factors within the soil, including temperature, moisture, and stress. However, the interactions between these factors are complex and difficult to comprehensively consider. In the long-term monitoring of soil strength and freezing characteristics in cold regions under extreme environments, existing observation technologies often lack sufficient temporal and spatial resolution, resulting in inadequate identification of the continuity and dynamics of soil state changes. Therefore, a low-cost, fast-response, and highly accurate soil freezing status monitoring system and method is needed, enabling continuous, remote, and long-term monitoring. Summary of the Invention

[0004] The purpose of this application is to provide a soil freezing state monitoring system and method, to build an integrated soil freezing state monitoring system based on piezoelectric sensors, and to timely and effectively analyze the frozen soil characteristics and strength properties during the construction and operation and maintenance periods.

[0005] To achieve the above objectives, this application provides the following solutions:

[0006] In a first aspect, the present application provides a soil freezing state monitoring system, comprising:

[0007] A piezoelectric sensor is arranged inside the soil to be monitored and is used to convert the pressure generated by the soil to be monitored on the surface of the piezoelectric sensor into an original electrical signal;

[0008] The state monitoring device is used to obtain soil freezing state characteristics based on the original electrical signal; the soil freezing state characteristics include soil frost heave stress and soil elastic modulus.

[0009] In a second aspect, the present application provides a method for monitoring the freezing state of soil, comprising:

[0010] The piezoelectric sensor is used to convert the pressure generated by the soil to be monitored on the surface of the piezoelectric sensor into an original electrical signal;

[0011] A state monitoring device is used to obtain soil freezing state characteristics based on the original electrical signal; the soil freezing state characteristics include soil frost heave stress, soil frost heave stress distribution and soil elastic modulus.

[0012] According to the specific embodiments provided in this application, this application discloses the following technical effects:

[0013] The present application provides a soil freezing state monitoring system and method. An integrated soil freezing state monitoring system is built based on piezoelectric sensors, which can timely and effectively analyze the frozen soil characteristics and strength properties during the construction and operation and maintenance periods, improve the spatiotemporal resolution of soil freezing observation technology, and achieve outstanding results in the field of geotechnical engineering monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0015] Figure 1 A schematic diagram of the functional modules of a soil freezing state monitoring system provided in one embodiment of the present application;

[0016] Figure 2 A schematic diagram of the structure of a piezoelectric sensor provided in one embodiment of the present application;

[0017] Figure 3 A schematic diagram of the structure of a multi-strand shielded cable electrically connected to a piezoelectric sensor provided in one embodiment of the present application;

[0018] Figure 4 A schematic diagram of the overall structure of a soil freezing state monitoring system provided in one embodiment of the present application;

[0019] Figure 5A schematic diagram of the arrangement of the piezoelectric sensor in frozen soil according to an embodiment of the present application;

[0020] Figure 6 A schematic flow chart of a soil freezing state monitoring method provided in one embodiment of the present application;

[0021] Figure 7 A schematic diagram of the overall framework of a soil freezing state monitoring method provided in one embodiment of the present application;

[0022] Figure 8 This is an intentional illustration of the relationship between the impedance of the piezoelectric sensor and the frost heave stress of the soil provided in one embodiment of the present application.

[0023] Figure 1: 101-piezoelectric sensor, 102-condition monitoring device, 201-piezoelectric ceramic, 202-high-strength epoxy resin filled protective layer, 203-multi-strand shielded cable, 301-unit conductor group, 302-electromagnetic shielding layer, 303-external package, 401-impedance measurement module, 4011-waveform generator, 4012 sampling unit, 4013-signal processing unit, 402-data processing module, 403-main control module, 404-wireless transmission module, 405-power supply module, 501-inclinometer casing, 502-sand. DETAILED DESCRIPTION

[0024] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0025] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0026] In an exemplary embodiment, Figure 1 As shown, a soil freezing state monitoring system is provided, comprising a piezoelectric sensor 101 and a state monitoring device 102. The piezoelectric sensor 101 is disposed within the soil to be monitored and is configured to convert the pressure generated by the soil on the surface of the piezoelectric sensor 101 into a raw electrical signal. The state monitoring device 102 is configured to obtain soil freezing state characteristics based on the raw electrical signal. These soil freezing state characteristics include soil frost heave stress and soil elastic modulus.

[0027] In an exemplary embodiment, Figure 2As shown, the piezoelectric sensor 101 is a circular structure with a diameter of 24mm and a material thickness controlled at 2mm to 5mm. The material of the piezoelectric ceramic 201 is PZT-5H, and the electrical polarization direction is thickness polarization. The piezoelectric sensor 101 uses a high-strength epoxy resin filled protective layer 202 to prevent the sensor from being corroded by water, moisture and salt. Among them, the material of the high-strength epoxy resin filled protective layer 202 is polymethyl methacrylate, which can isolate the conductive current in the soil and effectively alleviate the problem of crosstalk of the collected signal. The piezoelectric sensor 101 also includes positive and negative connectors connected to the status monitoring device 102, and is electrically connected using a multi-strand shielded cable 203. Among them, as Figure 3 As shown, the structure of the multi-strand shielded cable 203 from the inside out is a unit conductor group 301, an electromagnetic shielding layer 302 and an outer package 303. The electromagnetic shielding layer 302 is a metal film layer, and the outer package 303 is made of polyethylene.

[0028] In an exemplary embodiment, Figure 4 As shown, the condition monitoring device 102 includes an impedance measurement module 401 and a data processing module 402. The impedance measurement module 401 is connected to the piezoelectric sensor 101 and is configured to obtain an impedance signal from the piezoelectric sensor 101 based on the raw electrical signal. The data processing module 402 is configured to obtain the soil frost heave stress and soil elastic modulus based on the impedance signal. In this embodiment, the impedance measurement module 401 is an AE5891 high-precision impedance measurement chip.

[0029] In an exemplary embodiment, Figure 4 As shown, the impedance measurement module 401 includes a waveform generator 4011, a sampling unit 4012 and a signal processing unit 4013. The waveform generator 4011 is used to control the piezoelectric sensor 101 to perform resonant motion. The sampling unit 4012 is used to convert the original electrical signal into a digital signal. The signal processing unit 4013 is used to perform discrete Fourier transform processing on the digital signal to obtain an impedance signal. In this embodiment, the waveform generator 4011 can emit a sinusoidal excitation signal of 0.015Hz-200kHz to cause the piezoelectric sensor 101 to generate high-frequency resonant motion, thereby obtaining changes in the physical properties of frozen soil. The signal processing unit 4013 is used to obtain the real and imaginary values ​​of the impedance signal, that is, the modulus and phase of the impedance of the piezoelectric sensor 101.

[0030] In an exemplary embodiment, Figure 4As shown, the condition monitoring device 102 also includes a main control module 403. The main control module 403 is connected to the impedance measurement module 401 and is used to set multiple excitation frequencies and multiple sampling frequencies for the impedance measurement module 401. The main control module 403 can configure basic parameters of the impedance measurement module 401, such as the excitation frequency, excitation voltage, and sampling frequency, and finally transmit the impedance signal back.

[0031] In an exemplary embodiment, Figure 4 As shown, the status monitoring device 102 also includes a wireless transmission module 404 and a power supply module 405. The wireless transmission module 404 is connected to the impedance measurement module 401 and is used to transmit the impedance signal to the gateway and send it to the data processing module 402. The power supply module 405 is used to provide long-term and stable power supply to the impedance measurement module 401 and the wireless transmission module 404. In this embodiment, the wireless transmission module 404 uses a 4G DTU to build a wireless communication network. The wireless transmission module 404 has working and sleep modes, and the main control module 403 can adjust the working mode of the wireless transmission module 404 according to the requirements of seasonal monitoring frequency in high-latitude permafrost areas.

[0032] In an exemplary embodiment, the number of piezoelectric sensors is greater than 1, and the state monitoring device 102 is further configured to obtain the soil frost heave stress distribution based on the original electrical signals of all piezoelectric sensors. Figure 5 As shown, the piezoelectric sensors 101 are arranged along the depth of the soil and evenly bonded to the sidewalls of the inclinometer casing 501. Taking a soil depth of 1.2m as an example, the piezoelectric sensors are bonded to the sidewalls of the inclinometer casing 501, spaced 20cm apart. The inclinometer casing 501 is then buried to the specified depth using a drilled hole method. Finally, the inclinometer casing 501 is backfilled in sections with sand 502 until the remaining space around the inclinometer casing 501 is completely filled.

[0033] In another exemplary embodiment, Figure 6 As shown, a soil freezing state monitoring method is provided, including the following steps 601 and 602.

[0034] Step 601: Use a piezoelectric sensor to convert the pressure generated by the soil to be monitored on the surface of the piezoelectric sensor into an original electrical signal.

[0035] Step 602: Using a state monitoring device, obtain soil freezing state characteristics based on the original electrical signal. The soil freezing state characteristics include soil frost heave stress, soil frost heave stress distribution, and soil elastic modulus.

[0036] In an exemplary embodiment, the original electrical signal is the original impedance value of the piezoelectric sensor. Before step 602, the soil freezing state monitoring method further includes correcting the original impedance value using an impedance calibration coefficient.

[0037] In this embodiment, before using the piezoelectric sensor 101 to monitor the frozen soil state, the sensor impedance signal needs to be calibrated to improve the measurement accuracy of the impedance data. In the calibration experiment, the impedance calibration coefficient of the piezoelectric sensor is calculated by dividing the average impedance of all piezoelectric sensors by the impedance value of a particular piezoelectric sensor. The calculation formula for the impedance signal calibration coefficient of different sensors is as follows:

[0038]

[0039] Among them, X i is the impedance calibration coefficient of the i-th piezoelectric sensor, Z i is the impedance value of the i-th piezoelectric sensor measured in the calibration experiment, and n is the number of piezoelectric sensors in the calibration experiment.

[0040] In an exemplary embodiment, the above step 602 may be replaced by the following steps 701 and 702. In which:

[0041] Step 701: Using an impedance measurement module, obtain an impedance signal of the piezoelectric sensor according to the original electrical signal.

[0042] Step 702: Using a data processing module, obtain the soil frost heave stress and soil elastic modulus according to the impedance signal.

[0043] In an exemplary embodiment, the above step 702 can be replaced by the following steps 7021 to 7023. In which:

[0044] Step 7021: Using a data processing module, the soil frost heave stress and the coupled electromechanical impedance between the piezoelectric sensor and the soil to be monitored are obtained according to the impedance signal.

[0045] Step 7022: Obtain the spring stiffness of the soil to be monitored based on the coupled electromechanical impedance.

[0046] Step 7023: Obtain the elastic modulus of the soil according to the spring stiffness.

[0047] In an exemplary embodiment, the number of the piezoelectric sensors is greater than 1. The soil freezing state monitoring method further includes obtaining a soil frost heave stress distribution based on original electrical signals from all the piezoelectric sensors.

[0048] In an exemplary embodiment, Figure 7As shown, the method for monitoring the frozen state of soil includes: obtaining the soil frost heave stress and the coupled electromechanical impedance of the piezoelectric sensor and the monitored soil based on the impedance signal. According to the soil frost heave stress, combined with the specific embedding points of multiple piezoelectric sensors in the monitored soil, the soil frost heave stress distribution is obtained. According to the coupled electromechanical impedance of the piezoelectric sensor and the monitored soil, the equivalent mass of the monitored soil is obtained. According to the equivalent mass of the monitored soil, combined with the coupled electromechanical impedance of the piezoelectric sensor and the monitored soil, the spring stiffness of the monitored soil is obtained. According to the spring stiffness of the monitored soil, the elastic modulus of the soil is obtained.

[0049] Specifically, the soil frost heave stress is obtained by the following formula:

[0050] σ=|Z| / S.

[0051] Where σ is the soil frost heave stress, |Z| is the measured impedance of the piezoelectric sensor, and S is the stress sensitivity coefficient of the piezoelectric sensor. S is determined through piezoelectric sensor impedance and dynamic stress calibration tests.

[0052] In this embodiment, the relationship between the piezoelectric sensor impedance and the soil frost heave stress is as follows: Figure 8 shown.

[0053] The coupled electromechanical impedance between the piezoelectric sensor and the soil to be monitored is obtained by the following formula:

[0054]

[0055] Among them, Z eq is the coupled electromechanical impedance between the piezoelectric sensor and the soil to be monitored, Z a is the mechanical impedance of the piezoelectric sensor, d 33 is the strain voltage constant of the piezoelectric sensor at zero electric field strength, is the complex Young's modulus of the piezoelectric ceramic at zero electric field strength, ε T 33 is the dielectric constant of the piezoelectric sensor at zero electric field strength, j is the imaginary unit, δ is the dielectric loss coefficient of the piezoelectric sensor, ω is the resonant frequency of the piezoelectric sensor, S a is the cross-sectional area of ​​the piezoelectric sensor, h a is the thickness of the piezoelectric sensor.

[0056] The equivalent mass of the soil to be monitored is obtained by the following formula:

[0057]

[0058] B=jωZ eq +ω 2 m i -jωc i -k i.

[0059] Among them, m s is the equivalent mass of the soil to be monitored, c i is the damping of the piezoelectric sensor, k i is the contact stiffness of the piezoelectric sensor, c s is the damping of the soil structure, k s is the contact stiffness of the soil structure, ξ c is the ratio of the piezoelectric sensor damping to the contact damping, ξ k is the ratio of the stiffness of the piezoelectric sensor to the contact stiffness, B is the simplified calculation term for the equivalent mass of the soil, m i is the equivalent mass of the piezoelectric sensor.

[0060] The spring stiffness of the soil to be monitored is obtained by the following formula:

[0061]

[0062] Among them, K s is the spring stiffness of the soil to be monitored.

[0063] The elastic modulus of soil is obtained by the following formula:

[0064]

[0065] Among them, E s is the elastic modulus of soil, L is the length of frozen soil spring, and A is the cross-sectional area of ​​frozen soil spring.

[0066] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, stored data, displayed data, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties, and the collection, use and processing of relevant data must comply with relevant regulations.

[0067] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0068] This document uses specific examples to illustrate the principles and implementation methods of this application. The description of the above examples is only intended to help understand the method and core concept of this application. At the same time, for those skilled in the art, based on the concept of this application, there may be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A soil freezing state monitoring system, characterized in that: The soil freezing state monitoring system includes: A piezoelectric sensor is arranged inside the soil to be monitored and is used to convert the pressure generated by the soil to be monitored on the surface of the piezoelectric sensor into an original electrical signal; The state monitoring device is used to obtain soil freezing state characteristics based on the original electrical signal; the soil freezing state characteristics include soil frost heave stress and soil elastic modulus.

2. The soil freezing state monitoring system according to claim 1, characterized in that: The condition monitoring device comprises: an impedance measurement module, connected to the piezoelectric sensor, and configured to obtain an impedance signal of the piezoelectric sensor based on the original electrical signal; A data processing module is used to obtain the soil frost heave stress and the soil elastic modulus according to the impedance signal.

3. The soil freezing state monitoring system according to claim 2, characterized in that: The impedance measurement module includes: a waveform generator for controlling the piezoelectric sensor to perform resonant motion; A sampling unit, configured to convert the original electrical signal into a digital signal; A signal processing unit is used to perform discrete Fourier transform processing on the digital signal to obtain the impedance signal.

4. The soil freezing state monitoring system according to claim 3, characterized in that: The state monitoring device further includes a main control module, which is connected to the impedance measurement module and is used to set multiple excitation frequencies and multiple sampling frequencies for the impedance measurement module.

5. The soil freezing state monitoring system according to claim 1, characterized in that: The number of the piezoelectric sensors is greater than 1; The state monitoring device is also used to obtain the frost heave stress distribution of the soil based on the original electrical signals of all piezoelectric sensors.

6. A soil freezing state monitoring method, applied to the soil freezing state monitoring device according to any one of claims 1 to 5, characterized in that: The soil freezing state monitoring method comprises: The piezoelectric sensor is used to convert the pressure generated by the soil to be monitored on the surface of the piezoelectric sensor into an original electrical signal; A state monitoring device is used to obtain soil freezing state characteristics based on the original electrical signal; the soil freezing state characteristics include soil frost heave stress, soil frost heave stress distribution and soil elastic modulus.

7. The soil freezing state monitoring method according to claim 6, characterized in that: The original electrical signal is the original impedance value of the piezoelectric sensor; Before obtaining the soil freezing state characteristics according to the original electrical signal using a state monitoring device, the soil freezing state monitoring method further includes correcting the original impedance value using an impedance calibration coefficient.

8. The soil freezing state monitoring method according to claim 6, characterized in that: A state monitoring device is used to obtain soil freezing state characteristics based on the original electrical signal, specifically including: Using an impedance measurement module to obtain an impedance signal of the piezoelectric sensor according to the original electrical signal; A data processing module is used to obtain the soil frost heave stress and the soil elastic modulus according to the impedance signal.

9. The soil freezing state monitoring method according to claim 8, characterized in that: Using a data processing module, the soil frost heave stress and the soil elastic modulus are obtained according to the impedance signal, specifically including: Using a data processing module, according to the impedance signal, the soil frost heave stress and the coupled electromechanical impedance between the piezoelectric sensor and the soil to be monitored are obtained; Obtaining the spring stiffness of the soil to be monitored according to the coupled electromechanical impedance; The soil elastic modulus is obtained according to the spring stiffness.

10. The soil freezing state monitoring method according to claim 6, characterized in that: The number of the piezoelectric sensors is greater than 1; The soil freezing state monitoring method further includes obtaining soil frost heave stress distribution based on original electrical signals of all piezoelectric sensors.

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