Photoelectric testing system and method for in-situ frozen soil ice water group identification and dynamic tracing

Abstract

The present invention discloses a photoelectric testing system and method for identifying and dynamically tracing in-situ frozen soil ice-water components, the testing system comprising a photoelectric sensor testing assembly, a data demodulation and analysis system, and a self-sufficient pulse power supply control system; the photoelectric sensor testing assembly comprises a plurality of photoelectric sensor testing units connected in series; the photoelectric sensor testing unit comprises a variable temperature ultra-weak fiber Bragg grating sensing cable and a plurality of frequency domain reflection probes, the frequency domain reflection probes corresponding to the measuring points of the variable temperature ultra-weak fiber Bragg grating sensing cable. The present invention uses ultra-weak fiber Bragg grating temperature sensing and frequency domain reflection technology, based on the pulse variable temperature and multi-phase heat dissipation principle, through the relationship between the frozen soil temperature response value and the thermal conductivity, water content, and ice content of the soil, to realize the identification of ice-water components in in-situ frozen soil and the accurate determination of water field parameters, realize the identification and dynamic tracing of frozen soil ice-water components, solve the problem of difficulty in measuring parameters due to the instability of frozen soil properties, and has the advantages of small disturbance, distribution, real-time, and automation.

Description

Technical Field

[0001] The invention relates to a device and method for measuring the moisture content and ice content of frozen soil in geotechnical engineering and geological engineering, and in particular to a photoelectric testing system and method for identifying and dynamically tracing ice-water components of in-situ frozen soil. Background Art

[0002] Frozen soil is a multiphase complex system composed of soil particles, ice, unfrozen water, and gas. Its characteristics are related to a variety of basic physical properties such as soil texture, density, and moisture content. Among them, soil temperature and soil moisture field parameters with moisture content and ice content as basic parameters are important information required for theoretical research on water-heat-mechanical coupling and engineering practice in frozen soil areas. However, due to the strong temperature sensitivity of frozen soil, the temperature, moisture content, and ice content of in-situ frozen soil are in dynamic changes under the influence of natural factors such as ambient temperature and rainfall. Therefore, the accurate measurement of these in-situ parameters is of great significance for theoretical and experimental research on frozen soil.

[0003] At present, the main methods for measuring in-situ moisture content and ice content are dielectric spectroscopy and thermal pulse probe method. Dielectric spectroscopy, including frequency domain reflectometry (FDR) and time domain reflectometry (TDR), indirectly reflects parameters by measuring the dielectric constant of the soil. TDR has the advantages of fast response and accurate measurement, but its field application is limited due to its complex circuit and expensive equipment. Compared with TDR, FDR has been widely used in moisture measurement of unsaturated soil at normal temperature due to its simple application, wide range, and fixed-point continuous measurement. However, its measurement results are easily affected by external factors such as salinity and temperature. The measurement accuracy of unfrozen water in frozen soil areas with large temperature fluctuations is reduced, and its applicability needs to be further improved.

[0004] The heat pulse probe method determines the equivalent thermal conductivity of the soil by means of its response characteristics to the heat pulse, thereby calculating the moisture content of the soil. In recent years, the active heating fiber (AHFO) technology based on distributed temperature sensing (DTS) is a new form of the heat pulse method. This method is based on the linear heat source model. Direct current is passed through the sheath or tube body of the protective optical fiber to generate heat pulses. The optical fiber is used as a distributed temperature sensor to measure the thermal response of the soil. The relevant parameters are measured by establishing the relationship between temperature changes and thermal physical parameters. It has the advantages of high sensitivity, anti-electromagnetic interference, chemical corrosion resistance, and high spatial resolution (cm level) of distributed measurement. It has great application potential in the field of geological and geotechnical engineering monitoring. However, the bottleneck of this technology is mainly that the optical cable active heating method has the problems of too long heating time, large interference to the soil moisture field, and inability to effectively realize the identification of ice and water groups under negative temperature conditions, which causes too large test errors and hinders the application of this technology.

[0005] Therefore, how to provide an effective device and method to achieve accurate measurement of in-situ frozen soil moisture content and ice content, and provide strong support for theory and engineering practice in frozen areas, has become a technical problem that needs to be solved urgently. Summary of the invention

[0006] Purpose of the invention: In view of the shortcomings in the prior art, the present invention provides a photoelectric testing system and method for identifying and dynamically tracing the ice-water components of in-situ frozen soil, which realizes the identification and dynamic tracing of the ice-water components of frozen soil, and accurately measures the moisture content and ice content of the in-situ frozen soil, thereby realizing real-time dynamic monitoring of key parameters of the in-situ frozen soil moisture field, solving the problem of difficult parameter measurement caused by the unstable nature of frozen soil, and has the advantages of small disturbance, distribution, real-time and automation.

[0007] Technical solution: The photoelectric test system for in-situ frozen soil ice water group identification and dynamic tracing of the present invention comprises a photoelectric sensor test assembly, a data demodulation and analysis system and a self-sufficient pulse power supply control system; the photoelectric sensor test assembly comprises a plurality of photoelectric sensor test units connected in series;

[0008] The photoelectric sensing test unit comprises a variable temperature ultra-weak fiber Bragg grating sensing cable and a plurality of frequency domain reflection probes, and the frequency domain reflection probes correspond to the measuring point positions of the variable temperature ultra-weak fiber Bragg grating sensing cable.

[0009] The photoelectric sensor test unit is arranged horizontally or vertically in the in-situ frozen soil.

[0010] The data demodulation and analysis system includes a data demodulation and transmission device, a data cloud and a data storage and analysis terminal. The data demodulation and transmission device includes a high-precision optical fiber demodulation module, an FDR data interpretation module and a data transmission module; the data transmission module transmits the collected data to the data storage and analysis terminal through the data cloud.

[0011] The self-sufficient pulse power supply control system includes a wind turbine generator set, a photovoltaic power generation system and an intelligent switch.

[0012] The photoelectric testing method for in-situ frozen soil ice water component identification and dynamic tracing of the present invention comprises the following steps:

[0013] (1) Placing the photoelectric sensor test units connected in series vertically or horizontally in the in-situ frozen soil;

[0014] (2) The photoelectric sensing test assembly is connected to a data demodulation and analysis system and a self-sufficient pulse power supply control system, and the wavelength data of the in-situ frozen soil at the measuring point of the variable temperature ultra-weak fiber Bragg grating sensing cable is continuously collected through multiple frequency domain reflection probes and converted into temperature data, so as to obtain the spatial distribution of the initial temperature of the in-situ frozen soil along the depth or distance and its change over time;

[0015] (3) Determine the freeze-thaw front based on the spatial distribution and temporal changes of the initial temperature of the in-situ frozen soil, locate and track the position changes of the freeze-thaw front, and define the frozen soil and unfrozen soil areas;

[0016] (4) Turn on the self-sufficient pulse power supply control system with constant power P and time t 2 The variable temperature ultra-weak fiber Bragg grating sensing cable is heated to provide a pulse heat source for the in-situ temperature field. The data demodulation and analysis system simultaneously records the wavelength data of the variable temperature UFBG sensing cable and the initial water content data of the FDR probe. w′ , where the wavelength data collection interval is t 3 ;

[0017] (5) According to the initial temperature of the in-situ frozen soil and the error analysis results of the FDR probe, the initial moisture content data collected by the FDR probe is corrected to obtain the corrected in-situ frozen soil moisture content θ w ;

[0018] (6) The wavelength of the variable temperature ultra-weak fiber Bragg grating sensing cable is converted into temperature information to obtain the characteristic parameters of soil thermal response, thereby obtaining the equivalent thermal conductivity λ of the soil; the specific process is as follows:

[0019] The variable temperature UFBG sensing optical cable is a steady-state linear heat source. The measured temperature change ΔT of the variable temperature UFBG sensing optical cable after heating t for:

[0020]

[0021] Where t is the heating time, q is the heating power, λ is the thermal conductivity of the soil to be tested, and c is a constant related to the thermal diffusivity of the soil;

[0022] t 1 ,t 2 The temperature difference at that moment is:

[0023]

[0024] The equivalent thermal conductivity of soil λ is derived from formula (2):

[0025]

[0026] (7) Combined with the in-situ soil moisture data θ w , equivalent thermal conductivity λ and theoretical model of soil thermal conductivity λ=f(θ i ,θ w ), and the ice content of the in-situ frozen soil is obtained as θ i and the total moisture content of in-situ frozen soil θ t , where the total soil moisture content θ t =θw +θ i ; Carry out identification of in-situ frozen soil ice water components, and obtain the temporal and spatial distribution of in-situ frozen soil ice water component content through continuous and distributed monitoring. During the freezing period, water freezes into ice, the ice content in the in-situ frozen soil increases, the water content decreases, and the water in the unfrozen area migrates to the frozen area. After the ice crystals melt during the thawing period, the ice content decreases and the water content increases.

[0027] In step (1), the optoelectronic combined sensing unit is vertically arranged in the in-situ frozen soil by means of drilling and backfilling, and the optoelectronic combined sensing unit is horizontally arranged at different depths in the in-situ frozen soil by means of trenching.

[0028] In step (3), the freeze-thaw front position is the 0°C soil temperature position, the area where the soil temperature is higher than 0°C is the unfrozen soil area, and the area where the soil temperature is lower than 0°C is the frozen soil area.

[0029] In step (5), the error analysis result of the FDR probe is determined by indoor testing, and the specific steps are as follows:

[0030] (5.1) Take samples from the monitoring site and prepare several groups of soil samples with known temperature and moisture content;

[0031] (5.2) placing an FDR probe in the soil sample and collecting the moisture content measurement results of the soil sample through the FDR probe;

[0032] (5.3) Confirm the error between the moisture content measurement results of the FDR probe at different temperatures and the known moisture content;

[0033] (5.4)Establish the relationship between error and temperature.

[0034] In step (7), the soil equivalent thermal conductivity λ in step (6) and the corrected in-situ frozen soil moisture content θ in step (5) are w Substituting into formula (4) we can get the soil ice content θ i ; The formula (4) is as follows:

[0035]

[0036] Among them, S r is the soil saturation coefficient, θ w is the soil moisture content of in-situ frozen soil, θ i is the ice content of the soil; for unsaturated soil at room temperature, θ i =0;λ w is the thermal conductivity of water, λ i is the thermal conductivity of ice, λ s is the thermal conductivity of soil particles; n is the porosity of the soil, k 2, χ, and η are coefficients related to soil particle size distribution and particle shape.

[0037] In step (7), the calculation of the ice content of the in-situ soil is based on the theoretical model of soil thermal conductivity λ = f(θ i ,θ w ), soil moisture content of in-situ frozen soil θ w The total water content of the soil is obtained by inversion. t =θ w +θ i .

[0038] Working principle: The present invention combines ultra-weak fiber Bragg grating (UFBG) temperature sensing and frequency domain reflectometry (FDR) technology, based on the principle of pulse temperature variation and multi-phase heat dissipation, and realizes the identification of ice water components in in-situ frozen soil and the accurate determination of water field parameters through the theoretical relationship between the temperature response value of frozen soil and the thermal conductivity, water content, and ice content of the soil. The photoelectric sensing component of the present invention is integrated with a variable temperature ultra-weak fiber Bragg grating sensing cable and an FDR probe, which dynamically observes the soil temperature, water content, and ice content at different locations, and combines the in-situ soil water content data θ w , equivalent thermal conductivity λ and theoretical model of soil thermal conductivity λ=f(θ i ,θ w ), and the ice content of the in-situ frozen soil is obtained as θ i and the total moisture content of in-situ frozen soil θ t , where the total soil moisture content θ t =θ w +θ i ; Identify the ice-water components of in-situ frozen soil, and obtain the spatiotemporal distribution of the content of the ice-water components of in-situ frozen soil through continuous and distributed monitoring. The spatiotemporal distribution is reflected in that during the freezing period, water freezes into ice, the ice content in the in-situ frozen soil increases and the water content decreases, the water in the unfrozen area migrates to the frozen area, and the ice content decreases and the water content increases after the ice crystals melt during the thawing period. The present invention realizes the identification and dynamic tracing of the ice-water components of frozen soil based on the photoelectric combined tracing method, which solves the problem of difficult parameter measurement caused by the unstable nature of frozen soil.

[0039] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0040] (1) The present invention uses optical fiber temperature sensing to correct the FDR moisture content measurement results, thereby improving the FDR moisture content measurement accuracy and achieving accurate measurement of the unfrozen water content of frozen soil at all temperatures.

[0041] (2) The present invention realizes the identification of ice and water components of in-situ frozen soil through variable temperature ultra-weak fiber Bragg grating sensing cable and frequency domain reflectometry FDR technology, as well as photoelectric sensing test components, thus solving the problem of being unable to obtain in-situ parameters of frozen soil. It has the advantages of small disturbance, distribution, real-time and automation.

[0042] (3) The present invention realizes high-resolution, densely distributed measurement of in-situ frozen soil moisture field parameters by horizontally or vertically arranging photoelectric sensor components.

[0043] (4) The present invention realizes dynamic monitoring of frozen soil moisture and tracing of moisture migration through continuous measurement of frozen soil moisture field parameters.

[0044] (5) The present invention provides short-term strong pulses through variable temperature sensing optical cables, which causes little disturbance to the soil and solves the problem of difficulty in measuring parameters due to unstable soil properties.

[0045] (6) The present invention is economical and safe, easy to operate, highly automated, highly anti-interference and has reliable accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a schematic diagram of the structure of the photoelectric testing system for in-situ frozen soil ice water component identification and dynamic tracing of the present invention;

[0047] Figure 2 It is a distribution curve diagram of the unfrozen water content, ice content and total water content of the in-situ frozen soil along the depth in an embodiment of the present invention. DETAILED DESCRIPTION

[0048] like Figure 1 As shown, the photoelectric testing system for identifying and dynamically tracing in-situ frozen soil ice water components of the present invention comprises a photoelectric sensor testing assembly, a high-precision data demodulation and analysis system 5, and a self-sufficient pulse power supply control system 9. The photoelectric sensor testing assembly comprises a plurality of photoelectric sensor testing units connected in series, and the photoelectric sensor testing units are arranged in the in-situ frozen soil in a horizontal or vertical manner.

[0049] The photoelectric sensing test unit includes a variable temperature ultra-weak fiber Bragg grating (UFBG) sensing cable 3 and a plurality of frequency domain reflection FDR probes 4, wherein the frequency domain reflection probes 4 correspond to the measuring point positions of the variable temperature ultra-weak fiber Bragg grating sensing cable 3, thereby dynamically and continuously observing the soil temperature, moisture content, and ice content at different depths.

[0050] In this embodiment, the photoelectric sensor test assembly includes a first photoelectric sensor unit 1 and a second photoelectric sensor unit 2, wherein the first photoelectric sensor unit 1 is vertically arranged in the in-situ frozen soil, and the second photoelectric sensor unit 2 is horizontally arranged in the in-situ frozen soil. The first photoelectric sensor unit 1 and the second photoelectric sensor unit 2 are connected in series via a lead 11.

[0051] The high-precision data demodulation and analysis system 5 includes a data demodulation transmission device 8, a data cloud 6 and a data storage and analysis terminal 7. The data demodulation transmission device 8 includes a high-precision optical fiber demodulation module, an FDR data interpretation module and a data transmission module. The data transmission module uses GPRS or 4G mode to upload the collected data to the data cloud 6 and finally transmit it to the data storage and analysis terminal 7. The self-sufficient pulse power supply control system 9 includes a wind turbine generator set, a photovoltaic power generation system and an intelligent switch to provide power support and unattended pulse heating control for the system. The data demodulation transmission device 8 is connected to the self-sufficient pulse power supply control system 9 through a wire 10.

[0052] The photoelectric test system for in-situ frozen soil ice water group identification and dynamic tracing of this embodiment is deployed in a loess tableland area in the Loess Plateau in northwestern China. The temperature in this area is relatively low in winter, with the lowest temperature reaching -26°C, and seasonal frozen soil develops. The in-situ monitoring time of this embodiment is from January 8 to February 15, 2022.

[0053] The photoelectric testing method for in-situ frozen soil ice water component identification and dynamic tracing of the present invention comprises the following steps:

[0054] (1) The photoelectric sensor test assembly is arranged vertically or horizontally in the in-situ frozen soil 12 to be tested; the specific process is: the first photoelectric sensor test unit 1 is vertically installed in the frozen soil to be tested by using the buried method of drilling backfill, and the second photoelectric sensor test unit 2 is horizontally laid at different depths of the frozen soil to be tested by using the trench excavation method; the backfill material uses the in-situ soil, and the coupling between the in-situ soil and the sensor assembly is ensured.

[0055] (2) The first photoelectric sensing test unit 1 and the second photoelectric sensing test unit 2 are connected to a high-precision data demodulation and analysis system 5 and a self-sufficient pulse power supply control system 9, and the wavelength data of the variable temperature ultra-weak fiber Bragg grating (UFBG) sensing cable 3 in the in-situ frozen soil are continuously collected and converted into temperature information, so as to obtain the spatial distribution of the initial temperature of the in-situ frozen soil along the depth or distance and its change over time, wherein the collection time interval of the wavelength data is t 1 The time is determined according to the specific monitoring situation. In this embodiment, the shortest interval time is set to 10s.

[0056] (3) The freeze-thaw front is determined based on the spatial distribution of the initial temperature of the in-situ frozen soil and its temporal changes, and the position changes of the freeze-thaw front are located and tracked, while the frozen soil and unfrozen soil areas are defined. The freeze-thaw front is located at the position where the soil temperature is 0°C, the area with a soil temperature above 0°C is the unfrozen soil area, and the area with a soil temperature below 0°C is the frozen soil area.

[0057] (4) Turn on the self-sufficient pulse power supply control system 9, with constant power P and time t 2The variable temperature ultra-weak fiber Bragg grating sensing cable UFBG 3 is heated to provide a pulse heat source for the in-situ temperature field. The high-precision data demodulation and analysis system simultaneously records the wavelength data of the variable temperature ultra-weak fiber Bragg grating sensing cable UFBG 3 and the initial water content data of the FDR probe 4. w′ , where the wavelength data collection interval is t 3 The time interval is determined according to the specific monitoring situation, and the shortest time interval is set to 10 seconds.

[0058] The pulse heat source is controlled by a strong constant power P and a short time t 2 Provide short-term strong pulses to reduce the disturbance to the in-situ soil and improve the measurement accuracy. In this embodiment, P = 13W / m, time t 2 =100s.

[0059] (5) According to the initial temperature of the in-situ frozen soil 12 and the error analysis result of the FDR probe 4, the initial moisture content data collected by the FDR probe 4 is corrected to obtain the corrected moisture content θ of the in-situ frozen soil 12. w .

[0060] The error of the FDR probe is related to the soil temperature during operation, which is determined by indoor calibration tests. In-situ monitoring further determines the field measurement error and corrects the error based on the temperature and the correlation between the error and temperature obtained by indoor calibration.

[0061] The error analysis result of the FDR probe 4 is determined by indoor tests, and the specific steps are as follows:

[0062] (1) Sampling from the corresponding locations of the monitoring site and preparing ten groups of soil samples with known temperature and moisture content;

[0063] (2) placing an FDR probe in the soil sample and collecting the moisture content measurement results of the FDR probe;

[0064] (3) Confirm the error between the moisture content measurement results of the FDR probe and the known moisture content at different temperatures;

[0065] (4) Establish the relationship between error and temperature.

[0066] (6) Convert the wavelength data of the variable temperature ultra-weak fiber Bragg grating sensing cable 3 into temperature information to obtain the soil thermal response characteristic parameter, thereby obtaining the soil equivalent thermal conductivity λ. The soil thermal response characteristic parameter refers to the temperature change value within the corresponding time after pulse heating. The specific process of this step (6) is:

[0067] The variable temperature UFBG sensing optical cable is a steady-state linear heat source. The measured temperature change ΔT of the variable temperature UFBG sensing optical cable after heating t for:

[0068]

[0069] Where t is the heating time, q is the heating power, λ is the thermal conductivity of the soil to be tested, and c is a constant related to the thermal diffusivity of the soil;

[0070] t 1 ,t 2 The temperature difference at that moment is:

[0071]

[0072] The equivalent thermal conductivity of soil λ is derived from formula (2):

[0073]

[0074] (7) Combined with the moisture content of the in-situ soil θ w , equivalent thermal conductivity λ and theoretical model of soil thermal conductivity λ=f(θ i ,θ w ), and λ and θ w Substituting into formula (4), by solving the equation, we can obtain the ice content θ of the in-situ soil: i , total moisture contentθ t , to achieve the identification of in-situ frozen soil ice water components, and obtain the spatiotemporal distribution of the in-situ frozen soil ice water component content through continuous and distributed monitoring. The spatiotemporal distribution is that during the freezing period, water freezes into ice, the ice content in the in-situ frozen soil increases and the water content decreases, the water in the unfrozen area migrates to the frozen area, and the ice content decreases and the water content increases after the ice crystals melt during the thawing period.

[0075] Among them, the theoretical model of soil thermal conductivity λ=f(θ i ,θ w ) is determined by soil type and composition and is selected according to different soil properties. The theoretical model of soil thermal conductivity λ=f(θ i ,θ w ) moisture content θ w 、Ice contentθ i is its unknown quantity, and other parameters are obtained through field tests and indoor geotechnical foundation tests. The thermal conductivity λ of the in-situ frozen soil in this embodiment is applicable to and the Konrad model:

[0076]

[0077] Among them, S r is the soil saturation coefficient, θ w is the moisture content of in-situ frozen soil, θ i is the ice content of the soil; for unsaturated soil at room temperature, θ i=0;λ w is the thermal conductivity of water, λ i is the thermal conductivity of ice, λ s is the thermal conductivity of soil particles; n is the porosity of the soil, k 2 , χ, and η are empirical coefficients related to soil particle size distribution and particle shape.

[0078] Among them, the ice content of the in-situ soil is θ i The calculation of and Konrad model, moisture content θ w The total moisture content of the in-situ soil is obtained by inversion: t =θ w +θ i .

[0079] The specific process of step (7) is to convert the soil equivalent thermal conductivity λ in step (6) and the corrected moisture content θ of the in-situ frozen soil 12 in step (5) into w Substituting into formula (4) we can get the soil ice content θ i .

[0080] Figure 2 In the data, the content of ice water components reflects the entire freezing and thawing process of in-situ frozen soil and the law of water migration inside the soil. Figure 2 It can be seen that during the winter freezing period (January 8-January 22, 2022), the water in the in-situ soil froze into ice, the water content decreased, the ice content increased, and the total water content at a depth of 60 cm increased. This is due to the migration of water during the freezing process, and the migrated water gathered at the freezing front (near the depth of 60 cm); during the melting period (February 10-February 15, 2022), the ice crystals melted, and the data in the figure reflected the phenomenon that the ice content of the in-situ soil decreased and the water content increased. Moreover, since the water content increased after freezing and the water migrated to the deep, the total water content showed a downward trend.

Claims

1. A photoelectric testing method for in-situ frozen soil ice water component identification and dynamic tracing, characterized by: A photoelectric testing system for in-situ frozen soil ice water group identification and dynamic tracing is used, the photoelectric testing system for in-situ frozen soil ice water group identification and dynamic tracing comprising a photoelectric sensor testing component, a data demodulation and analysis system (5) and a self-sufficient pulse power supply control system (9); the photoelectric sensor testing component comprises a plurality of photoelectric sensor testing units connected in series; The photoelectric sensing test unit comprises a variable temperature ultra-weak optical fiber Bragg grating sensing cable (3) and a plurality of frequency domain reflection probes (4), wherein the frequency domain reflection probes (4) correspond to the measuring points of the variable temperature ultra-weak optical fiber Bragg grating sensing cable (3); The test method comprises the following steps: (1) vertically or horizontally arranging the photoelectric sensor test units connected in series in the in-situ frozen soil (12); (2) connecting the photoelectric sensing test assembly to a data demodulation and analysis system (5) and a self-sufficient pulse power supply control system (9), continuously collecting wavelength data in the in-situ frozen soil at the measuring point of the variable temperature ultra-weak fiber Bragg grating sensing cable (3) through a plurality of frequency domain reflection probes (4) and converting the data into temperature data, thereby obtaining the spatial distribution of the initial temperature of the in-situ frozen soil along the depth or distance and its change over time; (3) Determine the freeze-thaw front based on the spatial distribution and temporal changes of the initial temperature of the in-situ frozen soil, locate and track the position changes of the freeze-thaw front, and define the frozen soil and unfrozen soil areas; (4) The self-sufficient pulse power supply control system (9) is turned on to heat the variable temperature ultra-weak fiber Bragg grating sensing cable (3) at a constant power P and time t2 to provide a pulse heat source for the in-situ temperature field. The data demodulation and analysis system (5) simultaneously records the wavelength data of the variable temperature UFBG sensing cable (3) and the initial water content data θ of the FDR probe (4). w′ ; (5) According to the initial temperature of the in-situ frozen soil (12) and the error analysis result of the FDR probe (4), the initial moisture content data collected by the FDR probe (4) is corrected to obtain the corrected moisture content θ of the in-situ frozen soil (12) w ; (6) The wavelength of the variable temperature ultra-weak fiber Bragg grating sensing cable (3) is converted into temperature information to obtain the characteristic parameters of soil thermal response, thereby obtaining the soil equivalent thermal conductivity λ; the specific process is as follows: The variable temperature UFBG sensing optical cable is a steady-state linear heat source. The measured temperature change ΔT of the variable temperature UFBG sensing optical cable after heating t for: Where t is the heating time, q is the heating power, λ is the thermal conductivity of the soil to be tested, and c is a constant related to the thermal diffusivity of the soil; The temperature difference between t1 and t2 is: The equivalent thermal conductivity of soil λ is derived from formula (2): (7) Combined with the in-situ soil moisture data θ w , equivalent thermal conductivity λ and theoretical model of soil thermal conductivity λ=f(θ i ,θ w ), and the ice content of the in-situ frozen soil is obtained as θ i and the total moisture content of in-situ frozen soil θ t , where the total soil moisture content θ t =θ w +θ i , to realize the identification of in-situ frozen soil ice-water components and obtain the spatiotemporal distribution of the in-situ frozen soil ice-water component content.

2. The photoelectric testing method for in-situ frozen soil ice water component identification and dynamic tracing according to claim 1 is characterized by: In step (1), the optoelectronic combined sensing unit is vertically arranged in the in-situ frozen soil by means of drilling and backfilling, and the optoelectronic combined sensing unit is horizontally arranged at different depths in the in-situ frozen soil by means of trenching.

3. The photoelectric testing method for in-situ frozen soil ice water component identification and dynamic tracing according to claim 1 is characterized by: In step (3), the freeze-thaw front position is the 0°C soil temperature position, the area where the soil temperature is higher than 0°C is the unfrozen soil area, and the area where the soil temperature is lower than 0°C is the frozen soil area.

4. The photoelectric testing method for in-situ frozen soil ice water component identification and dynamic tracing according to claim 1 is characterized by: In step (5), the error analysis result of the FDR probe (4) is determined by indoor testing, and the specific steps are as follows: (5.1) Take samples from the monitoring site and prepare several groups of soil samples with known temperature and moisture content; (5.2) placing an FDR probe (4) in the soil sample, and collecting a moisture content measurement result of the soil sample through the FDR probe (4); (5.3) Confirm the error between the moisture content measurement results of the FDR probe at different temperatures and the known moisture content; (5.4) Establish the relationship between the error and temperature.

5. The photoelectric testing method for in-situ frozen soil ice water component identification and dynamic tracing according to claim 1 is characterized by: In step (7), the soil equivalent thermal conductivity λ in step (6) and the water content θ of the corrected in-situ frozen soil (12) in step (5) are w Substituting into formula (4) we can get the soil ice content θ i ; The formula (4) is as follows: Among them, S r is the soil saturation coefficient, θ w is the soil moisture content of in-situ frozen soil, θ i is the ice content of the soil; for unsaturated soil at room temperature, θ i =0;λ w is the thermal conductivity of water, λ i is the thermal conductivity of ice, λ s is the thermal conductivity of soil particles; n is the porosity of soil, and k2, χ, and η are empirical coefficients related to soil particle size distribution and particle shape.

6. The photoelectric testing method for in-situ frozen soil ice water component identification and dynamic tracing according to claim 1 is characterized by: In step (7), the calculation of the ice content of the in-situ soil is based on the theoretical model of soil thermal conductivity λ=f(θ i ,θ w ), soil moisture content of in-situ frozen soil θ w The total moisture content of the soil is obtained by inversion. t =θ w +θ i .

Images