Frozen soil layer real-time monitoring device and method based on microwave measurement

Abstract

The invention discloses a frozen soil layer real-time monitoring device and method based on microwave measurement, the monitoring device comprises a main control module, a power supply module and a plurality of detection modules installed on a detection rod at intervals, the detection modules are coated with a water absorption layer, at least part of the water absorption layer is in direct contact with detected soil, and the water absorption layer is in direct contact with the detected soil. A temperature sensor is installed nearby the detection module, and the main control module receives temperature measurement information of the temperature sensor, generates a control signal to control detection operation of the detection module and collects detection information in real time. Through real-time dielectric constant and temperature measurement, the current thawing and freezing state is judged in combination with the previous state of the detected soil, so that the real-time performance and the accuracy are improved, and inconvenience and complexity of manual field detection are avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of geological monitoring, and in particular relates to a real-time monitoring device and method for frozen soil layers based on microwave measurement. Background Art

[0002] Frozen soil is unstable. During the thawing process, water, heat, solutes, and mineral particles inside the soil will migrate. Frost heave, thaw settlement, salt heave, cold-freeze cracks, and thermal thaw landslides will cause damage to the construction of railways, roads, bridges, and houses. Especially in Northeast and Northwest my country, long-term monitoring of frozen soil around key infrastructure is an important task to respond to possible changes in a timely manner.

[0003] The commonly used frozen depth pipe method is a method with better measurement accuracy and is more reliable, but it is expensive and requires manual operation. In particular, remote measuring points require manual operation and measurement, which is very inconvenient and difficult to achieve real-time monitoring.

[0004] The existing capacitance method determines the thawing state by measuring the dielectric constant of the soil, which can realize real-time monitoring. However, the measurement equipment is expensive and measures the capacitance of the local soil, which is greatly affected by the local environment. For example, when there are many local rocks, the measurement results are difficult to reflect the actual situation. In essence, this method calculates the absolute dielectric constant through frequency measurement, and the frequency is easily affected by the surrounding electromagnetic interference, resulting in inaccurate measurement of the dielectric constant. Therefore, it is difficult to promote actual engineering applications.

[0005] Therefore, how to provide a high-precision, real-time measurement method or device for the thawing state of frozen soil to improve the reliability, accuracy and timeliness of frozen soil depth measurement is an urgent problem to be solved. Summary of the invention

[0006] The purpose of the present invention is to overcome the defects in the prior art and provide a real-time monitoring device and method for frozen soil layer based on microwave measurement.

[0007] To achieve the above-mentioned purpose, the present invention designs a real-time monitoring device for frozen soil layer based on microwave measurement, the monitoring device comprises a main control module, a power module and a plurality of detection modules installed at intervals on a detection rod, the detection module is coated with a water absorbing layer on the outside, at least part of the water absorbing layer is in direct contact with the soil to be measured (generally, at least part of the water absorbing layer in close contact with the sensor, i.e., the transmission line, is in direct contact with the soil to be measured), the detection module is installed with a temperature sensor nearby, the main control module is electrically connected to the power module and the detection module respectively, the temperature sensor is electrically connected to the detection module or the main control module, the main control module receives the temperature measurement information of the temperature sensor, generates a control signal to control the detection operation of the detection module and collects the detection information in real time; the detection module is installed below the ground surface along with the lower part of the detection rod; The detection module at least includes a support and a microstrip transmission line. The microstrip transmission line is installed on the outside of the support through a microstrip line substrate. The microstrip transmission line is coated with a water-absorbing layer (which can be achieved by filling water-absorbing materials). When installing the detection module, moisture-proof measures such as sealing should be taken to avoid affecting the normal operation of electronic devices.

[0008] Furthermore, the main control module includes a microcontroller and a power communication circuit, and the detection module also includes a microwave generator, a power distributor and a detection circuit; the detection circuit at least includes a phase-sensitive detector, a low-pass filter, a microcontroller and a power communication circuit and other units electrically connected in sequence; the power distributor is electrically connected to the microwave generator, the microstrip transmission line and the phase shifter, respectively, and is electrically connected to the phase-sensitive detector through the phase shifter; the microcontroller is simultaneously connected to the microwave generator and the temperature sensor, respectively controlling the generation and shutdown of the microwave signal and the signal frequency setting, and simultaneously receiving the ambient temperature information of the measuring point.

[0009] Furthermore, one end of the plurality of detection modules connected in series is electrically connected to the main control module, and specific connection signals include power supply signals (V+, G) and detection signals (RS485A, RS485B).

[0010] Furthermore, the monitoring device also includes a DTU (remote transmission unit) electrically connected to the main control module, and the power supply module includes a battery and a wind-solar combination new energy power supply module.

[0011] Furthermore, the microwave generator outputs a variable frequency signal of 200-960 MHz, and the power divider divides two signals with a 1:1 ratio and consistent phases, one of which is output to the microstrip transmission line 42 and the other is output to the phase shifter.

[0012] Furthermore, the microstrip line substrate includes non-metallic materials such as epoxy resin glass fiber board, PEEK (polyetheretherketone), polytetrafluoroethylene or polyimide to ensure that the microstrip transmission line independently transmits microwave signals; the support member includes metal materials such as steel, aluminum, copper, or rigid hard materials covered with metal materials.

[0013] The detection rod material includes non-metallic materials (pipes or rods) with good thermal insulation properties such as polytetrafluoroethylene, which avoids heat conduction between detection modules, so that the temperature between each detection module can be consistent with the surrounding formation temperature and have little mutual influence.

[0014] Furthermore, the installation method of the detection module on the detection rod includes a set method with a certain distance between them, and the detection rod can adopt a segmented installation mode to avoid being too long and difficult to carry; or the detection rod includes a plurality of segmented extension tubes, and the detection module is installed between the extension tube and the detection rod and between adjacent extension tubes.

[0015] Furthermore, a protective tube is arranged outside the water absorbing layer, a water hole of 5-10 mm is arranged on the protective tube, and the protective tube comprises a metal material tube such as a stainless steel tube.

[0016] On the other hand, a real-time monitoring method for frozen soil layer based on microwave measurement, for any of the above-mentioned real-time monitoring devices for frozen soil layer based on microwave measurement or other devices capable of synchronously measuring the dielectric constant and corresponding temperature of frozen soil layer, is characterized in that the current real-time thawing state of soil is judged by jointly detecting the dielectric constant and temperature of the soil in the measuring point environment and combining the previous state of the soil (the initial state can generally be obtained by sampling and combining artificial experience); the thawing state includes a stable state or a transitional state, the stable state includes dryness, water accumulation (a state dominated by liquid water) or a frozen state, the transitional state includes water absorption, water loss, ice melting (in the process of ice melting into water) or ice formation (in the process of water forming ice) state, the above invention is collectively referred to as the thawing state of soil; the thawing state judgment method includes: When the dielectric constant is less than or equal to 5 and remains stable, and the temperature remains stable, the soil is judged to be dry; When the dielectric constant is greater than or equal to 60 and remains stable, and the temperature is greater than 0°C and remains stable, the soil is judged to be in a waterlogged state; When the dielectric constant is between 5 and 10 and remains stable, the temperature remains stable and is below 0°C or fluctuates within the range of 0±0.2°C, and the previous state of the tested soil is not dry, the soil is judged to be frozen; When the dielectric constant is in an increasing state and the temperature is greater than 0°C, and the soil under test was previously dry, waterlogged, dehydrated or absorbing water, the soil is judged to be in a water absorbing state; When the dielectric constant is greater than 5 and is in a decreasing state, and the temperature is greater than 0°C, and the soil under test was previously in a state of water accumulation, water loss or water absorption, the soil is judged to be in a water loss state; When the dielectric constant is greater than 10 and is in an increasing state, and the temperature is greater than 0°C or fluctuates within the range of 0±0.2°C, and the soil under test was previously in a melting, freezing or icing state, the soil is judged to be in a melting state; When the dielectric constant is in a decreasing state, and the temperature is less than or equal to 0°C, and the previous state of the tested soil is not dry, the soil is judged to be in a frozen state; If the above conditions cannot be met, the soil state will be determined to remain unchanged from the previous state.

[0017] Furthermore, the real-time monitoring method also includes a calibration method, by preparing water-absorbing materials with different moisture contents, burying the module therein, and waiting for 10 minutes to reach equilibrium and a stable state, and then recording the detection results as calibration values, and establishing a correspondence table between the actual measured direct detection results of the detection module and the soil state in at least a dry state, a waterlogged state, and a frozen state, as a basis for subsequently determining the soil thawing state according to the dielectric constant value.

[0018] The advantages and beneficial effects of the present invention are as follows: according to the difference in microwave transmission characteristics of soil media under different thawing states, the dielectric constant is measured, and the soil thawing state is determined in real time in combination with the ambient temperature measurement, without the need for on-site manual sampling and measurement; through the design of the water-absorbing layer, it enters a thawing state equilibrium with the surrounding soil, and the detection medium environment of the sensor is more uniform, stable, substantial and balanced, so that on-site measurements can more accurately reflect the thawing situation and avoid the influence of local environments such as gravel; the dielectric constant is combined with the temperature and the soil thawing state of the adjacent previous state. The real-time monitoring method is based on the microwave reference signal to measure the cut-off dielectric constant more accurately on the one hand, and the joint state determination is more reliable on the other hand; at the same time, the present invention also provides a synchronous moisture content calibration and detection method in the following specific embodiments, which is of greater significance for the stability analysis of the foundation of large-scale basic buildings. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a structural schematic diagram of a real-time monitoring device for frozen soil layer based on microwave measurement of the present invention; Figure 2 yes Figure 1 Schematic diagram of the detection module structure in FIG. Figure 3 It is the electrical connection schematic diagram of the detection module; Figure 4 It is a schematic diagram of the connection relationship between the main control module and the detection module; Figure 5 It is a schematic diagram of the protective tube structure.

[0020] Markings in the figure: 1. Main control module, 2. Power module, 3. Detection rod, 4. Detection module, 5. Water absorption layer, 6. Protection tube; 31. extension tube, 41. support, 42. microstrip transmission line, 43. microstrip line substrate, 44. threaded interface, 45. sealing ring, 61. water hole. DETAILED DESCRIPTION

[0021] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and embodiments. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0022] The capacitance method and resistance method are more common in measuring the depth of frozen soil. The principle of the capacitance method and resistance method is that when the water in the soil turns into ice crystals, the dielectric constant will change significantly, which can be used for measurement. Although the prior art has adopted a frozen soil sensor to detect the thawing state of the soil based on the dielectric constant, it is impossible to accurately identify the state of the soil based on the change in the dielectric constant alone, and thus it is impossible to accurately identify the depth of the frozen soil. Because the size of the dielectric constant before and after the soil freezes mainly depends on the amount of soil water content and the degree of freezing, it is not feasible to directly judge the freezing state of the soil by the size of the dielectric constant. Therefore, the change law of the dielectric constant of frozen soil is particularly important in frozen soil detection. Temperature detection + moisture content detection (conductive properties); optical transmittance detection; resistance detection, radar image detection.

[0023] (1) Definitions of dry soil and frozen soil (see Xu Xuezu's "Frozen Physics") Soil in its natural state is generally composed of three parts: solid, liquid and gas. If all the pores in the soil are filled with gas, it is called dry soil. Soil with a moisture content of less than 5% is dry soil; 5%-30% is moist soil; and more than 30% is wet soil.

[0024] This public definition: When the soil moisture content is less than or equal to the wilting moisture, it is called dry soil.

[0025] According to the temperature and ice content, frozen soil can be divided into five categories: Unfrozen soil (thawed soil): soil with a temperature above 0°C and without ice crystals; Cold soil: soil with a temperature below 0°C and no ice crystals (soil with low water content or high concentration of aqueous solution); Frozen soil: soil with a temperature below 0°C and containing ice crystals; Frozen soil: soil that is in the process of cooling below 0°C and where ice crystals form and grow; Thawing soil: soil that is in the process of warming below 0℃ and the ice crystals are gradually decreasing.

[0026] Frozen soil in different states has different dielectric constants due to different water content, degree of freezing, and ice crystal content. Accurately measuring the relative dielectric constant (not the absolute dielectric constant) of soil at different depths and its changing characteristics can accurately reflect the thawing state of the permafrost layer.

[0027] Embodiment 1: Based on the above understanding of frozen soil, the present invention designs a real-time monitoring device for frozen soil layer based on microwave measurement, such as Figure 1As shown, the monitoring device includes a main control module 1, a power module 2 and a plurality of detection modules 4 installed at intervals on a detection rod 3. The detection module 4 is externally coated with a water-absorbing layer 5, at least part of the water-absorbing layer 5 is in direct contact with the soil to be detected (generally, at least part of the water-absorbing layer in close contact with the sensor, i.e., the transmission line, is in direct contact with the soil to be detected), a temperature sensor is installed near the detection module, the main control module is electrically connected to the power module and the detection module respectively, the temperature sensor is electrically connected to the detection module or the main control module, the main control module receives the temperature measurement information of the temperature sensor, generates a control signal to control the detection operation of the detection module and collects the detection information in real time; the detection module is installed below the ground surface along with the lower part of the detection rod; the main control module and small modules such as batteries can be independently installed near the detection rod, or installed on the top of the detection rod or in the top cavity, and the main control module and the detection module are powered separately or jointly by a new energy power supply module, a lithium battery, etc.

[0028] like Figure 2 As shown, the detection module 4 includes a support 41 and a microstrip transmission line 42. The microstrip transmission line 42 is installed on the outside of the support through a microstrip line substrate 43. The microstrip transmission line 42 is coated with a water-absorbing layer 5 (which can be achieved by filling water-absorbing materials). When installing the detection module, moisture-proof measures such as sealing should be taken to avoid affecting the normal operation of electronic devices.

[0029] The relative dielectric constant of dry water-absorbing materials is low, generally around 3-5; if the water in the water-absorbing material is in liquid form, its dielectric constant will become higher, and the higher the water content, the higher the dielectric constant. When the water-absorbing material is saturated, the relative dielectric constant can reach about 80. When the water in the water-absorbing material is frozen in a solid state, the dielectric constant will rapidly decrease, about 6-10. Therefore, by measuring the dielectric constant and temperature through microwaves, it can be determined whether the current water-absorbing material (i.e., the soil around the detection module) is dry, accumulating water (liquid water), or frozen in a stable state, or whether it is absorbing water, losing water, melting ice (in the process of ice melting into water) or freezing (in the process of water freezing into ice) in a transitional state. The above is collectively referred to as the thawing state of the soil in the present invention.

[0030] The basic principle of microwave measurement is that due to the different external medium environments of the transmission lines, their dielectric constants are different. According to the microwave transmission principle: Wherein, c is the speed of light, ε is the mixed dielectric constant, and μ is the magnetic permeability. The magnetic permeability is 1 and can be ignored, so the transmission speed of microwaves depends on the dielectric constant of the medium. Since the reference signal of the present invention uniformly adopts the original signal of the power divider, the difference in the dielectric constant of the transmission line on the measurement side leads to different microwave transmission speeds and transmission paths. Different transmission speeds / paths lead to different phase shifts and / or amplitudes of microwave signals. Therefore, by detecting and comparing the phases and amplitudes of the two microwave signals of the measurement signal and the reference signal, and outputting different detection voltage signals, the relative change of the dielectric constant can be obtained, and the relative change of the medium concentration (thaw state when the water content is known) can be obtained through the relative change of the dielectric constant.

[0031] Considering that the microstrip transmission line is directly in contact with the soil to be tested, on the one hand, the detection module may be damaged during drilling and installation; on the other hand, the soil at the detection position may not be uniform, that is, the surface medium of the microstrip transmission line may not be uniform, which will make it difficult for the dielectric constant measurement to reflect the actual thawing situation; thirdly, the change in thawing state will cause relative displacement between the surrounding soil and the microstrip transmission line, thereby affecting the consistency and stability of the measurement. Therefore, in this embodiment, a uniform water-absorbing layer is set near the detection module, and the water-absorbing material of the water-absorbing layer normally absorbs the moisture of the surrounding soil. After forming a balance, it can not only accurately characterize the actual thawing state of the soil, but also ensure reliable and stable contact between the water-absorbing layer and the microstrip transmission line, so as to achieve accurate measurement of the microstrip transmission line. It only requires some balancing time, which is not a problem for the needs of this field. The material of the water-absorbing layer includes soil at the detection point, water-absorbing resin or water-absorbing sponge, etc.

[0032] Since the dielectric constant affects the phase change of the microwave signal on the microstrip transmission line, the dielectric constant of the water-absorbing material around the detection module can be obtained through the phase difference signal output by the main control module (which sends out microwave signals and detects phase changes through a phase-sensitive detector). The current state of the soil around the detection module can be determined through the change in the dielectric constant and the change in temperature.

[0033] When working, the water-absorbing material on the surface of the microstrip transmission line absorbs water from the surrounding soil and can lock the water to a large extent until it reaches equilibrium with the soil; when the moisture in the surrounding soil decreases, the moisture in the water-absorbing material will precipitate and eventually reach equilibrium with the soil moisture; and the thawing state of the water-absorbing material will also be consistent with the surrounding soil. Therefore, by detecting the change in the dielectric constant of the water-absorbing material and combining it with temperature measurement, the thawing state of the measured soil can be comprehensively judged based on the causal relationship between the changes in different states, so as to timely learn about soil changes and respond to possible impacts on infrastructure.

[0034] Preferably, Figure 3As shown, the main control module 1 includes a microcontroller and a power communication circuit (not shown in the main control module figure), and the detection module also includes a microwave generator, a power divider and a detection circuit; the detection circuit at least includes a phase-sensitive detector, a low-pass filter, a microcontroller and a power communication circuit and other units electrically connected in sequence; the power divider is electrically connected to the microwave generator, the microstrip transmission line and the phase shifter, respectively, and is electrically connected to the phase-sensitive detector through the phase shifter; the microcontroller is connected to the microwave generator and the temperature sensor at the same time, respectively controls the generation and shutdown of the microwave signal and the signal frequency setting, and receives the ambient temperature information of the measuring point at the same time.

[0035] The dielectric constant of the water-absorbing material near the detection module will affect the phase change of the microwave signal on the microstrip transmission line. The dielectric constant of the water-absorbing material around the detection module can be obtained through the phase difference signal output by the phase-sensitive detector. The current state of the surrounding soil can be determined by the change in dielectric constant and temperature. The circuit of each detection module is the same. The microwave signal generator generates a microwave signal of fixed frequency and transmits it to the power divider; the power divider outputs two microwave signals with the same power and phase, among which the out1 signal of the power divider is output to the metal microstrip transmission line and then to the in1 end of the phase-sensitive detector through the metal microstrip transmission line; the out2 signal of the power divider is output to the phase shifter, and the output of the phase shifter is connected to the in2 end of the phase-sensitive detector. The output of the phase-sensitive detector is connected to the input of the low-pass filter, and the output of the low-pass filter is connected to the AD port of the microcontroller.

[0036] In this embodiment, the main control module controls each detection module in turn to perform detection sampling, and the soil thawing and freezing conditions at different underground locations can be obtained. In essence, each detection module is designed to work independently, that is, each detection module is equipped with an independent power distributor, microwave generator, phase-sensitive detector, low-pass filter, microcontroller, power communication circuit and other units, which can be detected independently, while the main control module mainly retains the control, data acquisition and external communication functions, that is, the main control module and the detection module are designed with microcontrollers respectively, and information is exchanged through the communication circuit. The detection module of this design can work independently, and the main control module and the detection module are convenient to connect, but the detection module function circuit is repeated. .

[0037] In fact, the main control module and the detection module can share the microcontroller of the main control module. In this case, the communication interface needs to be adapted, and the control logic of a single main control module needs to adapt to actual detection requirements.

[0038] In addition, in principle, the detection module only needs a microstrip transmission line, that is to say, other circuit units including microwave generators, power dividers and detection circuits can be designed on the main control module, that is, all detection modules share circuit units such as microwave transmission and reception detection. However, this design has high requirements for the implementation of microwave transmission circuit design, because the transmission requirements of high-frequency signals and low-frequency signals are different, and there are multiple microwave transmission channels on a monitoring device. The hardware is complex, the cost is high, the debugging is difficult, and the circuit performance is greatly affected by the environment. Therefore, this design is rarely used in engineering.

[0039] The microcontroller outputs a control signal to control the microwave signal frequency and / or the generation and shutdown of the microwave signal of the microwave generator. The function of the phase shifter is to adjust the output of the phase-sensitive detector to the most appropriate range, so that the microcontroller can perform detection and processing. Each module has a temperature sensor to detect the temperature of the current environment. The detection modules are generally connected by non-heat-conducting extension tubes, so the temperature can reflect the temperature of each formation.

[0040] Preferably, Figure 4 As shown, after a plurality of detection modules are connected in series, one end is electrically connected to the main control module. The specific connection signals include power supply signals (V+, G) and detection signals (RS485A, RS485B). The number of detection modules in the present invention is between 1 and 16. The upper limit of the number is mainly set to consider the performance of the serial communication interface and the signal quality requirements. The specific number also needs to consider the soil quality of the measuring point, the foundation requirements of the building, the maximum burial depth and other requirements; Figure 4 From a structural point of view, the main control module and each detection module are connected in series, but from a circuit principle point of view, the main control module and each detection module are connected in parallel; although in principle it is also possible to structurally realize a parallel connection between the main control module and each detection module, the wiring and interface are complex and it is rarely used in actual projects.

[0041] Preferably, the monitoring device also includes a DTU (remote transmission device) electrically connected to the main control module, and the power module includes a battery and a wind-solar combination new energy power supply module. Wind power generation and solar panels during the day power the system while also charging the lithium battery. When the new energy supply is insufficient, the lithium battery is directly used for power supply. The new energy module can also use an independent wind power generation module or solar power generation module. The main control module is connected to the DTU remote transmission device through TX and RX communication signals, and transmits the detection data to the remote server and / or centralized monitoring system.

[0042] Preferably, the microwave generator outputs a variable frequency signal of 200-960 MHz, and the power divider divides two signals in a 1:1 ratio with consistent phases, one of which is output to the microstrip transmission line 42 and the other is output to the phase shifter.

[0043] In principle, it is not necessary for the two paths of power and phase to be consistent, nor is it necessary for the conductor length, shape, and material of the two transmission lines to be consistent, or for the substrates on both sides to be completely consistent. For inconsistent situations, it is only necessary to calibrate the value relationship in advance, but the implementation is more cumbersome. The design of this embodiment to be consistent is more convenient and simple for measurement and calculation processing, which is also a reasonable choice in actual engineering applications.

[0044] Preferably, the microstrip line substrate 43 includes non-metallic materials such as epoxy resin glass fiber board, PEEK (polyetheretherketone), polytetrafluoroethylene or polyimide to ensure that the microstrip transmission line independently transmits microwave signals; the support member 41 includes metal materials such as steel, aluminum, copper, or rigid hard materials covered with metal materials to ensure that the microstrip transmission line is measured under a temperature environment basically the same as the surrounding soil. The metal shell also has a common grounding function to provide better protection for the circuit, so it is necessary to do a good job of insulation between the microstrip transmission line and the metal shell; the transmission line includes copper wire, silver wire, etc.; the water-absorbing material includes soil at the detection point, water-absorbing resin, water-absorbing sponge, etc.

[0045] The detection rod material includes non-metallic materials (pipes or rods) with good thermal insulation properties such as polytetrafluoroethylene, which avoids heat conduction between detection modules, so that the temperature between each detection module can be consistent with the surrounding formation temperature and have little mutual influence.

[0046] Preferably, the detection rod includes a plurality of extension tubes 31 connected in sections, and a detection module 4 is installed between the extension tube and the detection rod and between adjacent extension tubes. When connected in sections, a sealing ring 45 is provided at the connection end of the detection module to ensure that the internal detection circuit is not affected by the external environment (such as water); the specific interval of the set or the length of the extension tube is set according to the monitoring requirements of the actual measurement point.

[0047] The detection rod, support member (corresponding to the detection module) and the extension tube (including the segmented detection rod) that may be used later include a cylindrical or cylindrical component, or a cylindrical or cylindrical component covered with a metal shell. The detection rod is covered with the metal shell to increase strength and facilitate installation, but the metal shell is discontinuous, especially not in direct contact with the metal shell of the detection module, and is separated by a heat-insulating or non-heat-conducting material; the installation methods include set-fitting, mounting, screw connection, etc. For example, for the cylindrical component, the support member can be set-fitted or partially mounted on the detection rod or the extension tube, and a corresponding mounting slot is set at the corresponding mounting position on the detection rod, and the upper and lower ends of the support member are respectively provided with mounting interfaces with the detection rod or the extension tube, such as a buckle or a fixing screw hole, etc.; or the support member (corresponding to the detection module) is connected in sections between the detection rod and the extension tube and the adjacent extension tube, and the upper and lower connecting ports of the detection rod and the extension tube and the upper and lower ends of the support member are respectively provided with mutually connected mounting interfaces, such as a threaded interface 44 and / or a screw hole interface.

[0048] The transmission line of this embodiment adopts a silver wire with a diameter of 1.5mm and a length of 30mm, the substrate is polytetrafluoroethylene, the detection rod adopts a polytetrafluoroethylene tube, the support shell is made of stainless steel, the interior is hard plastic, a cable channel is set in the middle, and the two ends are made of metal materials, which is convenient for setting threaded interfaces. The detection rod is designed in sections, and the detection modules are set on the sectioned detection rods at a certain distance. The main control module is installed inside the top of the detection rod. The detection module is buried deep underground with the detection rod body. Four detection modules are set on the detection rod, among which the first detection module is 2m below the surface, and the subsequent detection modules are sequentially spaced 2m apart; after the detection rod and the detection module are completely connected and installed, the outer layer is wrapped with a water-absorbing sponge as a water-absorbing layer, and a detection module is placed on the detection rod. Insert it into the hole that has been drilled. The outer diameter after wrapping the water-absorbing sponge should be slightly larger than the diameter of the hole to ensure the close contact between the water-absorbing sponge and the soil around the hole. After underground installation, the upper surface part of the hole should be sealed with insulation material or soil of sufficient thickness to reduce the direct impact of surface air temperature on the detection rod; the temperature sensor is installed on the same side of the microstrip transmission line on the substrate, close to the microstrip transmission line but not in contact with it (of course, it can also be installed in other positions such as the water-absorbing layer to facilitate sensing the corresponding ambient temperature of the detection module); the power module is equipped with a solar panel and a lithium battery pack at the same time, which are installed near the monitoring point; the center frequency of the microwave generator is 330 MHz (common center frequencies also include 500 MHz, 750 MHz, etc.), and the bandwidth is 1 MHz.

[0049] Embodiment 2: The difference from Example 1 is that Figure 1 and Figure 5 As shown, in this embodiment, a protective tube 6 is arranged outside the water absorption layer, and a water hole 61 of 2 to 10 mm is arranged on the protective tube. The protective tube includes a metal material tube such as a stainless steel tube, or a hard non-metallic material; the protective tube can be designed in sections, specifically matching the length of the detection rod, the detection module or the extension section; it can also be designed as Figure 1The detection rod shown is entirely covered with a water-absorbing layer and a protective tube. The protective tube of this embodiment is made of stainless steel, and a segmented design scheme that matches the installation connection is adopted, that is, each section of the detection rod, the detection module and the extension tube are independently provided with a protective tube, and the stainless steel materials of the protection tubes between the segments are not in direct contact to reduce the heat conduction effect of the upper and lower layers. The gap inside the protective tube is filled with a water-absorbing layer material, and the water-absorbing layer can be connected together in sections, such as soil-type water-absorbing materials filled on site, or can be separated from each section, such as soil-type water-absorbing materials filled in advance. In fact, the material of the protective tube can also be preferably a hard plastic that is not easy to age, but the thickness and strength must be moderate. It is also possible to choose a protective tube with a stainless steel shell with a length shorter than the segment length and a hard plastic embedded in it, so that it is convenient to achieve heat insulation of the upper and lower layers while ensuring the installation strength; if a stainless steel tube that is connected from top to bottom is used, it may have a slightly greater impact on the original temperature gradient of the upper and lower layers. Example 1 is equivalent to the outer side of the detection module being covered with a water-absorbing layer, so there will be higher requirements for the water-absorbing layer material to facilitate installation.

[0050] Embodiment 3: The difference from Example 1 is that the transmission line and substrate of this embodiment are formed by etching a copper-clad laminate, wherein the microstrip transmission line has a width of 2 mm and a length of 30 mm, the substrate is the base plate of the copper-clad laminate, and the support member 41 is a hard plastic cylindrical structure.

[0051] Embodiment 4: The difference from Embodiment 1 is that the power module described in this embodiment further includes a wind power generation module.

[0052] Embodiment 5: The difference from Example 1 is that the detection rod of this embodiment includes a plurality of segmented extension tubes 31, and detection modules 4 are installed between the extension tubes and the detection rod and between adjacent extension tubes, that is, a segmented connection scheme is adopted to avoid being too long and difficult to carry.

[0053] Embodiment 6: A real-time monitoring method for frozen soil layer based on microwave measurement, for any of the above-mentioned real-time monitoring devices for frozen soil layer based on microwave measurement or other devices capable of synchronously measuring the dielectric constant and corresponding temperature of frozen soil layer, characterized in that the current real-time thawing state of soil is judged by jointly detecting the dielectric constant and temperature of the soil in the measuring point environment and combining the previous state of the soil (the initial state can generally be obtained by sampling and combining artificial experience); the thawing state includes a stable state or a transitional state, the stable state includes dryness, water accumulation (a state dominated by liquid water) or a frozen state, the transitional state includes water absorption, water loss, ice melting (in the process of ice melting into water) or ice formation (in the process of water forming ice) state, the above are collectively referred to as the thawing state of soil in the present invention; the thawing state judgment method includes: When the dielectric constant (calculated by phase difference voltage in this embodiment, the same below) is less than or equal to 5 (low dielectric constant) and remains stable (for example, for more than 6 hours, the meaning of maintaining stability is similar below), and the temperature remains stable (the range of change does not exceed ±0.2°C), the soil is determined to be dry; When the dielectric constant is greater than or equal to 60 (high dielectric constant) and remains stable, and the temperature is greater than 0°C and remains stable, the soil is judged to be in a waterlogged state; When the dielectric constant is between 5 and 10 (slightly higher than the dielectric constant in the dry state) and remains stable, the temperature remains stable and is below 0°C or fluctuates within the range of 0±0.2°C, and the previous state of the tested soil is not dry, the soil is judged to be frozen; When the dielectric constant is in an increasing state (or slowly increasing, generally lasting for more than 1 hour), and the temperature is greater than 0°C, and the soil being tested was previously dry, waterlogged, dehydrated or absorbing water, the soil is judged to be in a water absorbing state; When the dielectric constant is greater than 5 (higher than the dielectric constant in the dry state) and is in a decreasing state (or slowly decreasing, generally lasting for more than 1 hour), and the temperature is greater than 0°C, and the soil under test was previously in a state of water accumulation, water loss or water absorption, the soil is judged to be in a state of water loss; When the dielectric constant is greater than 10 and is in an increasing state (generally lasting for more than 1 hour), and the temperature is greater than 0℃ or fluctuates within the range of 0±0.2℃, and the soil under test was previously in a melting, freezing or icing state, the soil is judged to be in a melting state; when it changes from a melting state to a water absorption state (melting is completed), in addition to the above conditions, the temperature must be greater than 0℃ for more than 1 hour, and there must be a turning point in the dielectric constant increasing curve where the increasing rate increases, that is, in addition to the ice melting and water increase, there is also external water. In fact, there is no need to strictly distinguish these states; when it changes from a melting state to a dehydration state, it must meet the conditions that the dielectric constant changes from increasing to decreasing or the curve has a turning point where the increasing rate decreases, and the temperature is greater than 0℃ for more than 1 hour; when it changes from a melting state to a water accumulation state, it only needs to meet the water accumulation state judgment conditions; if water is absorbed during the melting process, it is still considered to be a melting state; if water is lost during the melting process, the dielectric constant increases slowly or there is no obvious increase within 20.

[0054] When the dielectric constant is in a decreasing state, and the temperature is less than or equal to 0°C, and the previous state of the tested soil is not dry, the soil is judged to be in a frozen state; If the above conditions cannot be met, the soil state will be determined to remain unchanged from the previous state.

[0055] Embodiment 7: The difference from Example 6 is that the real-time monitoring method described in this embodiment also includes a calibration method, that is, factory calibration is performed on the detection module of the monitoring device, by preparing water-absorbing materials with different moisture contents, burying the module therein, and changing the ambient temperature of the test material when necessary, and basically reaching equilibrium and being basically stable after 10 minutes, and then recording the detection result (converting the phase difference voltage into the dielectric constant) as the calibration value, and establishing a corresponding relationship table between the actual measured direct detection results of the detection module and the soil state under at least a dry state (moisture content close to 0%), a water-accumulated state (containing saturated water, if the saturated water state is almost impossible to appear at the measured location, the highest moisture content that can appear can be used as a standard for setting and calibration, and this state can replace the water-accumulated state, strictly speaking, it should be the highest moisture content state) and a frozen state (containing saturated water frozen), as a basis for subsequently determining the soil thawing state according to the dielectric constant value, such as correcting the dielectric constant boundary value and / or temperature boundary value for state change determination in the judgment method, the present invention will only perform the above three state calibrations and refer to them as simple state calibration.

[0056] Ideally, the dielectric constant values ​​under different states such as water absorption, water loss, ice melting, and ice formation should also be calibrated, as well as the dielectric constant values ​​under water accumulation, freezing, and ice melting states at different moisture contents and temperatures. A corresponding relationship table of moisture content, soil state, dielectric constant, and temperature should be established for model interpolation to solve the soil state and moisture content under any direct detection result. After considering the moisture content and temperature, the determination of the soil thawing state will be more accurate, and it will also be more conducive to the analysis of the stability of the building foundation. The present invention calls this calibration full-state calibration, so that the soil state including moisture content information can be better obtained (that is, the soil moisture content can be measured synchronously), but the calibration workload is large. For batch products, generally only a limited number of full-state calibrations are required to confirm the consistency and change rules, and other products only need to perform simple state calibrations.

[0057] It should be noted that the saturated moisture content of soils of different soil types varies greatly. Ideally, the soil at the measured point is used as the water-absorbing layer material, so that more reliable moisture content data can be obtained after calibration.

[0058] The above are only some of the more systematic and comprehensive embodiments of the real-time monitoring device and method of frozen soil layer based on microwave measurement of the present invention. In fact, there can be many preferred schemes, such as the installation method or structure of the detection rod and the detection module, the different division of labor between the main control module and the detection module in the circuit function module, the composition of the power supply module, the layout of the main control module, the state judgment method ignoring individual unimportant state judgments, the combination scheme of different states in the calibration method, etc., all of which are within the scope of protection of the present invention and are not listed one by one here.

Claims

1. A real-time monitoring device for frozen soil layer based on microwave measurement, characterized in that: The monitoring device comprises a main control module (1), a power module (2) and a plurality of detection modules (4) installed at intervals on a detection rod (3); the detection module (4) is externally coated with a water absorbing layer (5), at least a portion of the water absorbing layer (5) is in direct contact with the soil to be detected; a temperature sensor is installed near the detection module; the main control module is electrically connected to the power module and the detection module respectively; the temperature sensor is electrically connected to the detection module or the main control module; the main control module receives temperature measurement information from the temperature sensor, generates a control signal to control the detection operation of the detection module and collects detection information in real time; the detection module is installed below the ground surface along with the lower part of the detection rod; The detection module (4) comprises at least a support member (41) and a microstrip transmission line (42); the microstrip transmission line (42) is installed on the outside of the support member via a microstrip line substrate (43); and the microstrip transmission line (42) is coated with a water absorbing layer (5) on its periphery.

2. The real-time monitoring device for frozen soil layer based on microwave measurement according to claim 1 is characterized in that: The main control module (1) comprises a microcontroller and a power communication circuit, and the detection module further comprises a microwave generator, a power distributor and a detection circuit; the detection circuit at least comprises a phase-sensitive detector, a low-pass filter, a microcontroller and a power communication circuit unit which are electrically connected in sequence; the power distributor is electrically connected to the microwave generator, the microstrip transmission line and the phase shifter respectively, and is electrically connected to the phase-sensitive detector via the phase shifter; the microcontroller is simultaneously connected to the microwave generator and the temperature sensor.

3. The real-time monitoring device for frozen soil layer based on microwave measurement according to claim 1 is characterized in that: One end of the plurality of detection modules connected in series is electrically connected to the main control module, and specific connection signals include a power supply signal and a detection signal.

4. The real-time monitoring device for frozen soil layer based on microwave measurement according to claim 1 is characterized in that: The monitoring device also includes a DTU electrically connected to the main control module, and the power supply module includes a battery and a new energy power supply module.

5. The real-time monitoring device for frozen soil layer based on microwave measurement according to claim 1 is characterized in that: The microwave generator outputs a variable frequency signal of 200-960 MHz, and the power divider divides two signals of 1:1 with consistent phases, one of which is output to the microstrip transmission line and the other is output to the phase shifter.

6. The real-time monitoring device for frozen soil layer based on microwave measurement according to claim 1 is characterized in that: The microstrip line substrate (43) comprises epoxy resin glass fiber board, PEEK, polytetrafluoroethylene or polyimide non-metallic material; the support member (41) comprises a metal material, or a rigid hard material covered with a metal material; and the detection rod material comprises a non-metallic material.

7. The real-time monitoring device for frozen soil layer based on microwave measurement according to claim 1 is characterized in that: The detection module may be installed on the detection rod in a manner including being installed at a certain distance, the detection rod being installed in sections to avoid being too long and difficult to carry; or the detection rod may include a plurality of extension tubes (31) connected in sections, and the detection module (4) may be installed between the extension tube and the detection rod, and between adjacent extension tubes.

8. The real-time monitoring device for frozen soil layer based on microwave measurement according to claim 1 is characterized in that: A protective tube (6) is arranged outside the water absorbing layer, and a water hole (61) is arranged on the protective tube.

9. A real-time monitoring method for frozen soil layer based on microwave measurement, characterized in that: By jointly detecting the dielectric constant and temperature of the soil in the measuring point environment and combining the previous state of the soil, the current real-time thawing state of the soil is judged; the thawing state includes a stable state or a transitional state, the stable state includes a dry, water-accumulated or frozen state, and the transitional state includes a water absorption, water loss, ice melting or ice formation state; the thawing state judgment method includes: When the dielectric constant is less than or equal to 5 and remains stable, and the temperature remains stable, the soil is judged to be dry; When the dielectric constant is greater than or equal to 60 and remains stable, and the temperature is greater than 0°C and remains stable, the soil is judged to be in a waterlogged state; When the dielectric constant is between 5 and 10 and remains stable, the temperature remains stable and is below 0°C or fluctuates within the range of 0±0.2°C, and the previous state of the tested soil is not dry, the soil is judged to be frozen; When the dielectric constant is in an increasing state and the temperature is greater than 0°C, and the soil under test was previously dry, waterlogged, dehydrated or absorbing water, the soil is judged to be in a water absorbing state; When the dielectric constant is greater than 5 and in a decreasing state, and the temperature is greater than 0°C, and the soil under test was previously in a state of water accumulation, water loss or water absorption, the soil is judged to be in a state of water loss; When the dielectric constant is greater than 10 and is in an increasing state, and the temperature is greater than 0°C or fluctuates within the range of 0±0.2°C, and the soil under test was previously in a melting, freezing or icing state, the soil is judged to be in a melting state; When the dielectric constant is in a decreasing state, and the temperature is less than or equal to 0°C, and the previous state of the tested soil is not dry, the soil is judged to be in a frozen state; If the above conditions cannot be met, the soil state will be determined to remain unchanged from the previous state.

10. A real-time monitoring method for frozen soil layer based on microwave measurement according to claim 9, characterized in that: The real-time monitoring method also includes a calibration method, by preparing water-absorbing materials with different water contents and burying the modules therein, After 10 minutes of equilibrium and stability, the test results are recorded as calibration values, and a corresponding relationship table between the direct test results of the detection module and the soil state is established, which serves as a basis for determining the soil thawing state according to the dielectric constant value.

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