CN115308387A - Soil monitoring device and method for monitoring freezing depth of frozen soil containing salt - Google Patents
Soil monitoring device and method for monitoring freezing depth of frozen soil containing salt Download PDFInfo
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Abstract
The invention relates to the technical field of soil detection, and provides a soil monitoring device and a method for monitoring freezing depth of frozen soil containing salt, wherein the device comprises: the device comprises a measuring unit, a sensor unit and a power supply unit; wherein, measuring unit's moisture meter includes neutron moisture meter and time domain reflection principle TDR moisture meter, and the neutron moisture meter is connected with first survey pipe, and TDR moisture meter is connected with the second and surveys the pipe, and the interval that first survey pipe and second surveyed the pipe is confirmed based on neutron meter moderation reaction radius, and the cover is equipped with the guard plate on the first survey pipe. The invention combines the structural characteristics of the salt-containing frozen soil, reasonably arranges the position of the measuring tube in the measuring unit, has stronger representativeness of the measured moisture, solves the problem of neutron overflow during measurement, and ensures the precision and the scientificity of the quantification of the soil moisture phase change process. Finally, a power supply unit and a sensor unit are designed to ensure automatic monitoring of soil water heat and salt elements.
Description
Technical Field
The invention relates to the technical field of soil detection, in particular to a soil monitoring device and a method for monitoring freezing depth of salt-containing frozen soil.
Background
The problem of hydrothermal salt migration of freeze-thaw soil is an important problem in agricultural hydrology research, and has important significance for efficient utilization of regional agricultural water resources and prevention and control of soil salinization and secondary salinization. The water heat salt migration of freeze-thaw soil is restricted by the soil freeze-thaw process (freezing frontal surface), and in a submerged shallow area, the water heat salt migration process of the frozen soil is more complicated due to the influence of mineralization diving. The problem of soil salinization and secondary salinization is usually accompanied in the shallow area of diving, and the existence of salinity in the soil will reduce its freezing point, and then influences the development of freezing front and finally influences the soil freeze thawing process.
The research for accurately determining the hydrothermal salt migration of the saline soil not only can provide a theoretical basis for the research on the problem of the hydrothermal solute migration of the soil in the salinized frozen soil area, but also can provide an improved thought and data verification for the development of a relevant numerical model. The soil phase transition process monitoring technology of current scheme has neutron excessive problem, can make shallow soil moisture content measured value littleer, and parameter measurement needs artifical observation every day simultaneously, and is consuming time and power and inefficiency.
Disclosure of Invention
The invention provides a soil monitoring device and a method for monitoring freezing depth of salt-containing frozen soil, which are used for solving the defects that in the prior art, freeze-thaw soil is inconvenient to monitor in situ, detection precision is low, and research on the freeze-thaw process of the salt-containing frozen soil is lacked, and realizing in-situ monitoring of hydrothermal salt elements of the freeze-thaw soil.
The invention provides a soil monitoring device, comprising:
the measuring unit is used for measuring the total water content of the soil and the liquid water content of the soil through a moisture meter;
the sensor unit is used for automatically measuring the soil temperature and the conductivity through sensors arranged at different depths and correcting the measurement result of the liquid water content of the soil of the measurement unit;
a power supply unit for supplying power to the measuring unit and the sensor unit;
the moisture meter of the measuring unit comprises a neutron moisture meter and a time domain reflection principle TDR moisture meter, the neutron moisture meter is connected with a first measuring tube, the TDR moisture meter is connected with a second measuring tube, the distance between the first measuring tube and the second measuring tube is determined based on the moderation reaction radius of the neutron meter, and a protection plate is sleeved on the first measuring tube.
According to the soil monitoring device provided by the invention, the sensor unit comprises the sensors and the data acquisition unit, the sensors are sequentially arranged on the vertical section of the soil from top to bottom, and the arrangement intervals of the sensors are gradually increased from top to bottom.
According to the soil monitoring device provided by the invention, the sensors comprise a soil hydrothermal salt sensor and a soil temperature sensor, and the horizontal positions of the soil hydrothermal salt sensor and the soil temperature sensor are not coincident.
According to the soil monitoring device provided by the invention, the first measuring pipe is made of aluminum, the second measuring pipe is made of TECANAT special plastic, and the protection plate is made of polyethylene.
According to the soil monitoring device provided by the invention, the device further comprises a groundwater monitoring well, and the sensor unit further comprises a groundwater level sensor.
According to the present invention there is provided a soil monitoring device, the device further comprising: the net fence is surrounded by the measuring unit, the sensor unit and the power supply unit, the net fence comprises an upper cover, the upper cover can be opened and closed, an access door is arranged on the net fence, and an anti-theft lock is arranged at the opening and closing end of the upper cover of the net fence.
According to the present invention there is provided a soil monitoring device, the device further comprising: and the communication unit is used for transmitting the data acquired by the sensor unit and the transmission measurement unit to a cloud end or other terminals.
The invention also provides a frozen depth monitoring method of the frozen soil containing salt, which comprises the following steps:
sampling the salt-containing frozen soil, and determining the total salt content and the dominant ions of the salt-containing frozen soil;
collecting the total water content and the conductivity of the soil containing the frozen soil and the soil temperature of different sections through the soil monitoring device;
determining equivalent freezing points of the salt-containing frozen soil based on the total soil moisture content, the conductivity, the total salt content and the dominant ions of the salt-containing frozen soil;
and determining the freezing depth of the frozen soil containing salt based on the equivalent freezing point of the frozen soil containing salt and the soil temperatures of different sections.
According to the freezing depth monitoring method for the frozen soil containing salt provided by the invention, the saline water equivalent freezing point is determined based on the total soil moisture content, the conductivity, the total salt content and the dominant ions of the frozen soil containing salt, and the method comprises the following steps:
determining the average pore water volume of the soil based on the total water content and the profile depth of the soil with different profiles of the frozen soil containing salt;
determining the molar concentration of the leading ions based on the average pore water volume, conductivity, total salt content and leading ions of the soil;
and determining the equivalent freezing point of the frozen soil containing salt based on the molar concentration of the dominant ions, the freezing point reduction constant of water, the ion number and the valence dominant ions of the solute.
According to the frozen depth monitoring method for the frozen soil containing salt provided by the invention, the step of determining the frozen depth of the frozen soil containing salt based on the equivalent freezing point of the frozen soil containing salt and the soil temperatures of different sections comprises the following steps:
drawing a temperature contour map based on the soil temperatures of the different sections;
extracting a temperature contour line of an equivalent freezing point of salt-containing frozen soil based on the temperature contour line graph, and interpolating the temperature contour line of the equivalent freezing point of the salt-containing frozen soil;
and determining the freezing depth of the frozen soil containing salt based on the interpolated temperature contour line of the equivalent freezing point of the frozen soil containing salt.
According to the soil monitoring device provided by the invention, the positions of the measuring tubes of the neutron moisture meter and the TDR moisture meter are reasonably arranged, so that the measured moisture is more representative, and the measurement precision of the total moisture content of the soil and the liquid moisture content of the soil is improved. Meanwhile, a protective plate is sleeved on the neutron moisture meter measuring tube, so that neutron overflow in shallow soil during measurement is prevented, and the precision and the scientificity of quantification of the phase change process of soil moisture are ensured. The sensor unit is additionally arranged, so that not only can the soil temperature and the conductivity of different depths be automatically monitored, but also the liquid water content of the soil can be automatically monitored, and the checking and effective supplement of the result of the liquid water content of the soil measured by the measuring unit can be realized.
Drawings
In order to more clearly illustrate the technical solutions of the present invention or the prior art, the drawings needed for the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and those skilled in the art can also obtain other drawings according to the drawings without creative efforts.
FIG. 1 is a schematic diagram of a soil monitoring device according to the present invention;
FIG. 2 is a schematic view of the underground deployment of a soil monitoring device provided by the present invention;
FIG. 3 is a front view of a soil monitoring device provided by the present invention;
FIG. 4 is a left side view of a soil monitoring device provided by the present invention
FIG. 5 is a top view of a soil monitoring device provided by the present invention;
FIG. 6 is a schematic view of a net pen configuration of a soil monitoring device provided by the present invention;
FIG. 7 is a schematic flow chart of a frozen depth monitoring method for frozen soil containing salt provided by the invention;
FIG. 8 is an isotherm of the equivalent freezing point of low-salinity soil and an isotherm at 0 ℃ according to the present invention;
FIG. 9 is the equivalent freezing point isotherm and 0 ℃ isotherm of high-salinity soil provided by the present invention.
Reference numerals:
1: a first measuring tube; 2: a second measuring tube; 3: a temperature sensor; 4: a hydrothermal salt sensor; 5: an underground water monitoring well; 6: a solar power supply and storage device; 7: a solar panel; 8: a net enclosure; 9: an upper cover; 10: an access door; 11: an anti-theft lock;
a: the distance from the equivalent point to the first measuring tube; b: the distance from the first measuring tube to the second measuring tube; c: the distance from the equivalent point to the second measuring tube; d: soil profile excavation baseline
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings, and it is obvious that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without inventive step based on the embodiments of the present invention, are within the scope of protection of the present invention.
A soil monitoring device according to an embodiment of the present invention is described below with reference to fig. 1 to 6, including:
the measuring unit 101 is used for measuring the total water content of the soil and the liquid water content of the soil through a moisture meter;
the sensor unit 102 is used for automatically measuring the soil temperature and the conductivity through sensors arranged at different depths and correcting the measurement result of the liquid water content of the soil of the measurement unit;
a power supply unit 103 for supplying power to the measurement unit and the sensor unit;
wherein, measuring unit's moisture meter includes neutron moisture meter and time domain reflection principle (TDR) moisture meter, and the neutron moisture meter is connected with first survey pipe, and TDR moisture meter is connected with the second survey pipe, and the interval of first survey pipe and second survey pipe is confirmed based on neutron meter moderation reaction radius, and the cover is equipped with the guard plate on the first survey pipe.
For the measurement unit 101, it should be noted that in the embodiment of the present invention, a Trime-TDR moisture meter is used as the TDR moisture meter. In the prior art, for the measurement of a neutron moisture meter and a Trime-TDR, a common-cavity common-emission method or a different-cavity common-emission method can be adopted. When the co-cavity co-emission method is adopted, the neutron moisture meter and the Trime-TDR share one measuring tube, and because the shared measuring tube is generally made of special organic plastic materials such as TECANAT materials and contains hydrogen elements, fast neutrons emitted by the neutron meter can be decelerated when meeting hydrogen atoms and are detected by the instrument after the moderation reaction, the counting measured value of the neutron meter is larger. Therefore, the same cavity common emission method cannot be adopted to obtain accurate total soil moisture content and liquid soil moisture content.
When the heterocavity co-emission method is adopted, although the neutron moisture meter and the Trime-TDR can solve the problems by arranging different measuring tubes, if the positions of the measuring tubes still influence the representativeness of the moisture phase change measurement, the representativeness is poor. In addition, the problem that the measured value of the water content of the shallow soil is small due to neutron overflow when the neutron moisture meter measures the total water content of the shallow soil cannot be solved.
Therefore, in the embodiment of the invention, the neutron moisture meter and the TDR moisture meter are respectively connected with the first measuring tube and the second measuring tube, the interval between the first measuring tube and the second measuring tube is set according to the moderation reaction radius of the neutron moisture meter to improve the representativeness of the moisture phase change measurement, and the protective plate is sleeved on the first measuring tube of the neutron moisture meter to solve the problem that neutrons overflow in shallow soil during the measurement of the neutron moisture meter.
In addition, the measuring unit 101 may determine the dynamic change of the liquid water-ice composition in the soil by measuring the total water content of the soil (neutron instrument) and the liquid water content of the soil (TDR/HydraProbe) to indirectly obtain the ice content of the soil.
For the sensor unit 102, it should be noted that the sensor unit 102 includes various sensors, which can be used to measure physical quantities such as soil temperature, electrical conductivity, and soil liquid water content. Different from the measurement unit 101, the sensor unit 102 does not need manual intervention, not only realizes automatic monitoring and synchronous acquisition of soil water heat salt elements, but also can use data obtained by automatic monitoring to carry out proofreading, verification and effective supplement on data measured by the measurement unit 101, and ensures the accuracy of data acquisition.
For the power supply unit 103, it should be noted that the power supply unit 103 includes two systems of solar power supply and storage and dc power supply, which are mutually designed for backup and redundancy, and can provide energy support for unattended automatic monitoring. Specifically, the power supply unit 103 includes a 30W solar panel, a solar charging controller and a storage battery.
According to the soil monitoring device disclosed by the embodiment of the invention, the measuring unit, the sensor unit and the power supply unit are designed by analyzing the characteristics of the frozen soil containing salt, the total water content and the liquid water content of the soil can be accurately obtained through manual measurement, the defect of low time resolution of the measuring unit can be compensated through the sensor unit, and the accurately obtained liquid water content of the soil can be checked and compensated through automatically acquired parameters. In addition, the sensor unit can also be combined with the characteristics of the frozen soil containing salt to set sensors or probes at different depths, so that the real-time monitoring on the temperature and the conductivity of the soil is realized, and the reliable guarantee is provided for the follow-up research based on hydrothermal salt parameters.
In at least one embodiment of the invention, the sensor unit comprises sensors and a data acquisition unit, the sensors are sequentially arranged on the vertical section of the soil from top to bottom, and the arrangement intervals of the sensors are gradually increased from top to bottom.
It should be noted that, in the traditional method, the direct method for measuring the freezing depth of the soil mainly utilizes physical penetration soil monitoring (artificial exploration), usually utilizes a soil sampler to fetch soil to sense penetration resistance and observe the form of a soil sample to determine the freezing depth, is suitable for the detection of melting depth in wet soil, low water content materials and gravel stratum, and is very difficult to detect the freezing surface of a low water content soil medium in the gravel stratum; it is also very difficult to determine the location of the freezing front when detecting an unfrozen layer from the penetration of the frozen layer, the measurement results are greatly influenced by the subjective judgment of testers, and the method is time-consuming, labor-consuming and destructive.
Therefore, the existing methods for collecting the soil temperature often adopt indirect methods, such as a frozen soil device method, a 0 ℃ isotherm method, a conductivity detection method and a ground penetrating radar method. Other than ground penetrating radar methods, these methods only provide data measurements of specific points throughout the landscape and hysteresis effects may occur during periods of rapid temperature change. The freezers, ground penetrating radar method are generally considered to be time consuming, labor intensive and inefficient methods. The 0 ℃ isotherm method is a common method for indirectly detecting the freezing depth, and the method is characterized in that a plurality of temperature sensors (thermistors/thermocouples and the like) are arranged at a specific depth in a vertical soil profile, the 0 ℃ isotherm obtained by linearly interpolating the soil temperature is taken as the upper boundary and the lower boundary of the freezing depth, and after the temperature sensors are connected with a data acquisition device, the method can realize automatic and continuous freezing depth monitoring in a specific time period. However, the method needs to be provided with equipment such as a temperature sensor in advance, and is not suitable for large-scale monitoring of the soil freezing depth. In addition, the existence of soil salt can cause the reduction of the freezing point of the soil, and the estimation of the freezing depth of the saline soil by the method can cause errors. It is assumed that the temperature gradient between adjacent soil temperature sensors is linear, which also introduces some errors, and the accuracy of which remains questionable.
In order to deal with the characteristic that the existence of soil salinity in the saline frozen soil can lead to the reduction of soil freezing point, the sensor units can be arranged vertically and densely, and the method is suitable for large-range monitoring of soil freezing depth. In the surface soil interval, i.e. 0-10 cm, the sensors need to be arranged in an encrypted manner, so the first interval is generally 2-3 cm, and the setting depth of the corresponding sensors is, for example: 0cm, 2cm, 5cm, 8cm and 10cm from the ground; then, in the interval of 0 to 1.5m, the arrangement interval is generally 10cm and set at equal intervals, and below 1.5m, the arrangement interval is generally 20cm and set at equal intervals.
According to the soil monitoring device provided by the embodiment of the invention, the sensors with different depths are arranged underground, so that the sensing acquisition range is expanded, different distances are set for the sensors with different depths of soil, and the waste of resources caused by equidistant acquisition is avoided.
In at least one embodiment of the invention, the sensors include a soil hydrothermal salt sensor and a soil temperature sensor, the soil hydrothermal salt sensor and the soil temperature sensor being positioned at horizontal positions that do not coincide.
It should be noted that in the embodiment of the present invention, the soil hydrothermal salt sensor is a Steven Hydra Probe soil moisture sensor, and is used for automatically monitoring the unfrozen water content, temperature and conductivity of the soil, and is arranged at an equal interval of 20cm on a 0-2m vertical section of the soil, so as to prevent the influence of water flow blockage and section preferential flow on the measurement, and the sensor is installed while the sensor is horizontally staggered. The soil temperature sensor is selected to collect soil with the temperature range of minus 40 ℃ to 80 ℃, the soil is arranged at intervals of 10cm, and the surface soil of 0cm to 10cm is arranged in a closed manner.
In addition, it should be noted that because the hydrothermal salt sensor has high manufacturing cost, a soil temperature sensor is further arranged on the basis of the hydrothermal salt sensor, and the vertical sections of the soil of the hydrothermal salt sensor and the soil are not overlapped, so that one sensor can measure each required depth, and the cost is reduced to the greatest extent on the basis of ensuring the measurement accuracy.
In at least one embodiment of the present invention, the first measuring tube is made of aluminum, the second measuring tube is made of a tecnat plastic, and the protection plate is made of polyethylene.
It should be noted that, in the embodiment of the present invention, the first measuring tube is made of aluminum, specifically, the first measuring tube is made of aluminum with a length of 2.3m and has a bottom sealing bottom, and 50cm is reserved on the ground to prevent the autumn watering from flowing backwards. The second survey pipe is provided with two, sets up two because TDR survey soil liquid water receives the variability influence of soil property great, consequently, the system error that the repeated survey pipe that sets up can reduce the survey, and is specific, and the second survey pipe is the long special plastics of TECANAT of 3m, and ground reservation 0.5m prevents that the autumn watering from flowing backward.
As shown in the top view of the soil monitoring device in FIG. 5, the position of the measuring tube is reasonably arranged according to the neutron instrument moderation reaction radius formula to be as close as possible, so that the measured moisture is more representative. Before measurement, a polyethylene plate is sleeved on the neutron moisture meter to prevent neutrons in shallow soil from overflowing during measurement, and the precision and the scientificity of quantification of the phase change process of soil moisture are ensured.
Specifically, the positions of the measuring tubes are limited, and one of the two positions is that all the measuring tubes cannot be located in backfill formed by the excavated soil section installation instrument (namely, the soil section excavation base line d), namely, the measuring tubes are installed in undisturbed soil. The location of the measuring tube in the backfill soil will make the measured value larger under the action of the soil preferential flow. Secondly, the measured positions of the two second measuring tubes (namely TDR measuring tubes) can be equivalently regarded as the liquid water content of the soil at the middle point of the connecting line of the two second measuring tubes, the middle point of the connecting line of the two second measuring tubes is an equivalent point, the distance a between the equivalent point and the total soil water content measuring tube (first measuring tube) is 700mm, the distance b between the equivalent point and the second measuring tube is 800mm, and the distance c between the first measuring tube and the second measuring tube which is closer to the first measuring tube is 600mm. The distance can meet the requirement of the neutron instrument for measuring the water moderation reaction radius, and the neutron instrument measuring tube can be ensured to be outside the soil profile excavation base line.
In at least one embodiment of the invention, the apparatus further comprises a groundwater monitoring well, and the sensor unit further comprises a groundwater level sensor.
Specifically, the underground water monitoring well adopts a phi 15cm PVC pipe which is exposed to the earth surface by 30cm, a double-layer nylon filter screen reverse filtering layer is arranged on a bottom perforated pipe, and the perforated pipe at the bottom of the underground water monitoring well is used for perforating and permeating water, so that sand or soil is prevented from entering the well through the perforated pipe and water only enters the well through the perforated pipe, and the reverse filtering effect is achieved. The underground water level sensor has the resolution of 2mm and the measuring range of 0-10m.
In at least one embodiment of the invention, the apparatus further comprises: the net fence is arranged around the measuring unit, the sensor unit and the power supply unit, the net fence comprises an upper cover and an upper cover, the upper cover can be opened and closed, an access door is arranged on the net fence, and an anti-theft lock is arranged at the opening and closing end of the access door and the upper cover of the net fence.
Specifically, the net rail is iron in this embodiment, and the size is 2.0mL 1.8mW 1.0mH, the long basis of bottom welding 30cm, and net rail skeleton adopts 4 cm's of side length galvanized square iron pipe welding to form, and four facades increase an iron pipe improvement intensity respectively, and the net rail upper cover can 180 open and shut and supply the tester to enter the net rail and carry out manual determination neutron moisture meter neutron count and TDR moisture meter, and net rail left side facade sets up the access door, and access door and net rail upper cover open and shut end set up the pickproof lock.
It should be noted that the device of the embodiment of the invention has certain theft prevention, all the equipment is integrated in the theft prevention metal net rack, the installation and maintenance are easy, and the metal net rack is provided with a foundation, so that the settlement caused by soil collapse and slurry return in the melting period can be prevented, and the device also has the theft prevention. The access door that the net rail set up is convenient for open the door and get into maintenance equipment, and test device is small, instrument and equipment arranges scientific compactness reasonable, and furthest reduces the obstacle of agricultural machine operation of entering into the field.
In at least one embodiment of the invention, the apparatus further comprises: and the communication unit is used for transmitting the data acquired by the sensor unit and the transmission measurement unit to a cloud terminal or other terminals.
It should be noted that the terminal may be a handheld PDA, a display screen, a computer, or another terminal, and after the collected data is sent to the cloud or another terminal, the collected data may be subjected to subsequent processing as needed. The communication unit comprises GPRS and Bluetooth transmission, and realizes automatic monitoring, synchronous acquisition, GPRS transmission and cloud storage of hot water and salt elements of farmland soil in the submerged shallow-buried area. Meanwhile, the device provided by the embodiment of the invention is provided with a GPS chip (independent power supply), can realize real-time tracking and positioning, and can send real-time early warning to a user mailbox when the position changes.
As shown in fig. 3 to 6, the soil monitoring device of the embodiment of the present invention includes: neutron moisture meter and TRIME-TDR moisture meter and respectively corresponding first survey pipe 1 and second survey pipe 2, temperature sensor 3, hydrothermal salt sensor 4, groundwater monitoring well 5, solar energy supply power storage device 6, net rail 8 and data acquisition system. The solar panel 7 is connected to the solar power supply and storage device 6, and can provide a solar power and dc power supply system. The net fence 8 is provided with an upper cover 9, an access door 10 and an anti-theft lock 11. The temperature sensor 3 is a vertically distributed multi-channel temperature sensor, the hydrothermal salt sensor 4 is a multi-channel soil hydrothermal salt sensor, and the underground water monitoring well 5 is also connected with an underground water level sensor.
The soil monitoring device in the embodiment of the invention not only can monitor soil hydrothermal salt elements through the soil hydrothermal salt element monitoring system, but also can prevent burglary and protect the monitored environment through the net fence.
Specifically, as shown in fig. 2, the soil hydrothermal salt element monitoring system includes: the device comprises a CNC503DR neutron moisture meter and a standard measuring tube thereof; the device comprises a TRIME-PICO-IPH type TDR moisture meter and two standard measuring tubes; the method comprises the following steps that a Steven Hydra Probe soil moisture sensor automatically monitors the unfrozen water content, temperature and conductivity of soil, and the vertical sections of 0-2m of soil are respectively arranged at equal intervals of 20 cm; the soil temperature sensors which are vertically and densely arranged are arranged at intervals of 10cm, the surface soil of 0-10 cm is arranged in a closed manner, and the surface soil is taken as 0cm, 2cm, 5cm, 8cm and 10cm; the underground water monitoring well and the underground water level sensor have the resolution of 2mm and the measuring range of 0-10m.
Based on the device, the research on the hydrothermal salt migration of the freeze-thaw soil can be carried out, and because the conventional research method for the hydrothermal salt migration of the freeze-thaw soil ignores the structural change of a soil framework and the influence of the structural change on the hydrothermal kinetic parameters of the soil caused by pore water phase change in the freezing process of the freeze soil, the simulation precision is influenced definitely. Particularly in saline soil, the reduction of the freezing point of the soil by salinity brings more uncertainty to the freezing and thawing process of the soil.
The existing method is based on the assumption that the temperature gradient between adjacent temperature sensors is linear, and is suitable for non-salinized frozen soil. The existence of salt can cause the freezing point to be reduced, so the salinized frozen soil is not suitable. Meanwhile, manual observation is needed every day, time and labor are consumed, efficiency is low, and the method is not suitable for salinized frozen soil. Therefore, the embodiment of the invention also discloses a method for monitoring the freezing depth of the frozen soil containing salt after the parameters are collected by using the device. The method for monitoring the freezing depth of the frozen soil containing salt provided by the invention is described below.
As shown in fig. 7, an embodiment of the present invention discloses a method for monitoring frozen depth of frozen soil containing salt, including:
701, sampling the saline frozen soil, and determining the total salt content and the dominant ions of the saline frozen soil;
703, determining equivalent freezing points of the salt-containing frozen soil based on the total water content, the conductivity, the total salt content and the dominant ions of the salt-containing frozen soil;
and step 704, determining the freezing depth of the frozen soil containing salt based on the equivalent freezing point of the frozen soil containing salt and the soil temperature of different sections.
In step 701, it should be noted that, when salt-containing frozen soil is sampled, the soil monitoring device needs to be arranged in a submerged shallow-buried seasonal frozen soil area, the automatic monitoring sensor needs to be arranged on the inner side of a soil profile excavation baseline, in order to reduce the influence of the soil profile backfill preferential flow on the experimental result, the backfill needs to be compacted as much as possible, and the installation and debugging of the device need to be carried out before water storage, irrigation and soil freezing in winter. In the freeze thawing period, the total salt content of the soil needs to be measured by manually collecting soil samples every 1-2 weeks, the soil samples are collected by an impact power sampler within the range of 1m from the net rack on the extension lines of the central positions of the four outer vertical surfaces of the net enclosure, one sample is collected every 10cm, and the collected soil samples are taken back to a laboratory to measure the total salt content and the leading ions.
In step 702, it should be noted that the total water content of the soil in the freeze-thaw period is manually determined by a neutron moisture meter, the determination period is the same as the soil sample collection, the step length of the determination depth is 10cm, and the average value is obtained by three determinations in each depth. In addition, the conductivity can also be determined manually to verify the results of the device measurements.
In addition, it should be noted that in the embodiment of the present invention, the soil freezing point in the freezing depth range is assumed to be determined by the salt content in the 1m soil layer, and meanwhile, uncertainty of the freezing depth development caused by water and salt migration and uneven one-dimensional vertical distribution of water and salt is not considered. It is also assumed that soil salt exists in soil pore water in the freeze-thaw stage and does not change in phase state with temperature change.
According to the method for monitoring the freezing depth of the frozen soil containing salt, the freezing depth dynamic change of the salinized frozen soil area is represented by replacing an equivalent freezing point isotherm with a 0 ℃ isotherm, and the influence of salt on the reduction of the freezing point of the soil is considered. Meanwhile, the influence of the dynamic change of the underground water buried depth of the diving shallow buried area on the soil freezing depth is also considered, the lower freezing depth limit is further corrected, and the prediction precision is improved.
In at least one embodiment of the invention, determining the saline water equivalent freezing point based on the total water content, the conductivity, the total salt content and the dominant ions of the soil containing the saline soil comprises:
determining the average pore water volume of the soil based on the total water content and the profile depth of the soil with different profiles of the salt-containing frozen soil;
determining the molar concentration of the leading ions based on the average pore water volume, the conductivity, the total salt content and the leading ions of the soil;
and determining the equivalent freezing point of the frozen soil containing salt based on the molar concentration of the dominant ions, the freezing point reduction constant of water, the ion number and the valence dominant ions of the solute.
It should be noted that, since the equivalent freezing point of the salt water is lower than that of pure water and is in direct proportion to the molar concentration of the salt, the equivalent freezing point of the salt-containing frozen soil is determined as shown in formula 1:
in the formula: t is m The freezing point (. Degree.C.) of brine, 1.86 the freezing point lowering constant (. Degree.C/(mol/L)) of water, C the molar concentration (mol/L) of salt, N m Is the ion number and Z is the valence dominant ion of the solute. In this embodiment, the dominant ion is chloride.
In particular, the method comprises the following steps of,
wherein n is solution Amount of substance (mol) of soil salt in unit volume of soil, V w Is the average pore water volume (cm) of the soil under a specific soil volume 3 /cm 3 )。
Wherein, V wi Is the ith layerTotal water content (cm) of soil in soil profile 3 /cm 3 )，h i The section depth is measured for the total water content of the i-th layer soil.
In at least one embodiment of the present invention, step 702 further collects the liquid water content of the soil through a soil monitoring device, determines the ice content of the soil according to the total water content of the soil and the liquid water content of the soil, and implements monitoring of the soil phase change process, i.e., monitoring the dynamic change of the liquid water-ice composition in the soil.
Specifically, the relationship among the components in the soil phase change process is shown as formula 2:
θ T ＝0.917θ I +θ L formula 2
Wherein, theta T The total water content of the soil (VWC,%), theta I Is the soil ice content (VWC,%), theta L The soil liquid water content (VWC,%), and the ice density relative to water density of 0.917.
In at least one embodiment of the invention, determining the freezing depth of the saline frozen soil based on the equivalent freezing point of the saline frozen soil and the soil temperature of different profiles comprises:
drawing a temperature contour map based on the soil temperatures of different sections;
extracting a temperature contour line of the salt-containing frozen soil equivalent freezing point based on the temperature contour map, and interpolating the temperature contour line of the salt-containing frozen soil equivalent freezing point;
and determining the freezing depth of the salt-containing frozen soil based on the interpolated temperature contour line of the equivalent freezing point of the salt-containing frozen soil.
It should be noted that temperature contour maps are drawn according to soil temperature profile data as shown in fig. 8 and 9, and then temperature contour lines of 0 ℃ isotherms and salt-containing frozen soil equivalent freezing points are extracted. And interpolating the temperature contour line of the salt-containing frozen soil equivalent freezing point, wherein the obtained temperature contour line of the salt-containing frozen soil equivalent freezing point can be subjected to equal time step length dispersion, and a daily freezing depth dynamic process line can be finally obtained after interpolation. The daily freezing depth dynamic process line replaces a soil 0 ℃ isotherm to represent the freezing depth of the salt-containing soil, so that the freezing depth of the salt-containing frozen soil is monitored.
In addition, it should be noted that when the salt content of the soil exceeds a certain limit, the influence of the decrease of the freezing point of the soil on the freezing and thawing process of the soil is not negligible, as shown in fig. 8-9, the maximum freezing depth of the high-salt soil exceeds 140cm if the minimum point of the 0 ℃ isotherm is used, and the minimum point of the equivalent freezing point isotherm is 104cm if the minimum point of the 0 ℃ isotherm is used; the maximum freezing depth of the low-salinity soil is 75.1cm if the maximum freezing depth is quantified by the lowest point of an isotherm at 0 ℃, and is 73.4cm if the maximum freezing depth is quantified by an isotherm at an equivalent freezing point, so that the difference between the maximum freezing depth and the isotherm is huge. Therefore, the soil freezing depth monitoring method provided by the embodiment has an important significance for improving the quantification precision of the salt-containing soil freezing and thawing process. Therefore, the freezing process of the saline soil is obtained by quantifying the equivalent freezing point isotherm, the basic characteristic of bidirectional thawing of single freezing of soil in the seasonal frozen soil area is still met, the result conforms to the rationality, and the fine quantification of the process can be realized. Since the total salt content of non-salinated soils is very low, the level of freezing point reduction is very low for soils such that the soil freezing point isotherm is very close to the soil 0 ℃ isotherm. The freezing depth monitoring method disclosed by the embodiment is not only suitable for salt-containing soil, but also suitable for precise quantification of the freezing and thawing process of non-salinized soil.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (10)
1. A soil monitoring device, comprising:
the measuring unit is used for measuring the total water content of the soil and the liquid water content of the soil through a moisture meter;
the sensor unit is used for automatically measuring the soil temperature and the conductivity through sensors arranged at different depths and correcting the measurement result of the liquid soil moisture content of the measurement unit;
a power supply unit for supplying power to the measuring unit and the sensor unit;
the moisture meter of the measuring unit comprises a neutron moisture meter and a time domain reflection principle TDR moisture meter, the neutron moisture meter is connected with a first measuring tube, the TDR moisture meter is connected with a second measuring tube, the distance between the first measuring tube and the second measuring tube is determined based on the moderation reaction radius of the neutron meter, and a protection plate is sleeved on the first measuring tube.
2. The soil monitoring device of claim 1, wherein the sensor unit comprises a sensor and a data collector, the sensor is sequentially arranged on a vertical section of the soil from top to bottom, and the arrangement distance of the sensor is gradually increased from top to bottom.
3. The soil monitoring device of claim 2, wherein the sensors include a soil hydrothermal salt sensor and a soil temperature sensor, the soil hydrothermal salt sensor and the soil temperature sensor being disposed at horizontal positions that do not coincide.
4. The soil monitoring device of claim 1, wherein the first measuring tube is made of aluminum, the second measuring tube is made of TECANAT special plastic, and the protection plate is made of polyethylene.
5. A soil monitoring device as claimed in claim 1, wherein the device further comprises a groundwater monitoring well, the sensor unit further comprising a groundwater level sensor.
6. A soil monitoring device as claimed in claim 1, wherein the device further comprises: the net fence is surrounded by the measuring unit, the sensor unit and the power supply unit, the net fence comprises an upper cover, the upper cover can be opened and closed, an access door is arranged on the net fence, and an anti-theft lock is arranged at the opening and closing end of the upper cover of the net fence.
7. The soil monitoring device of claim 1, further comprising: and the communication unit is used for transmitting the data acquired by the sensor unit and the transmission measurement unit to a cloud end or other terminals.
8. A method for monitoring freezing depth of frozen soil containing salt is characterized by comprising the following steps:
sampling the salt-containing frozen soil, and determining the total salt content and the dominant ions of the salt-containing frozen soil;
collecting the total water content, conductivity and soil temperature of different sections of the soil containing the frozen soil through the soil monitoring device of any one of claims 1 to 7;
determining equivalent freezing points of the salt-containing frozen soil based on the total soil moisture content, the conductivity, the total salt content and the dominant ions of the salt-containing frozen soil;
and determining the freezing depth of the frozen soil containing salt based on the equivalent freezing point of the frozen soil containing salt and the soil temperatures of different sections.
9. The method for monitoring freezing depth of frozen soil containing salt according to claim 8, wherein the determining the salt water equivalent freezing point based on the total water content, the conductivity, the total salt content and the dominant ions of the soil containing salt comprises:
determining the average pore water volume of the soil based on the total water content and the profile depth of the soil with different profiles of the frozen soil containing salt;
determining the molar concentration of the dominant ions based on the average pore water volume, the conductivity, the total salt content and the dominant ions of the soil;
and determining the equivalent freezing point of the frozen soil containing salt based on the molar concentration of the dominant ions, the freezing point reduction constant of water, the ion number and the valence dominant ions of the solute.
10. The method of claim 8, wherein said determining the freezing depth of said frozen saline soil based on said equivalent freezing point of said frozen saline soil and said different profile soil temperatures comprises:
drawing a temperature contour map based on the soil temperatures of the different sections;
extracting a temperature contour line of a salt-containing frozen soil equivalent freezing point based on a temperature contour map, and interpolating the temperature contour line of the salt-containing frozen soil equivalent freezing point;
and determining the freezing depth of the saline frozen soil based on the interpolated temperature contour line of the equivalent freezing point of the saline frozen soil.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115950900A (en) * | 2023-02-13 | 2023-04-11 | 中国科学院西北生态环境资源研究院 | Frozen water and unfrozen water splitting method based on cosmic ray neutron technology |
| CN116660323A (en) * | 2023-07-24 | 2023-08-29 | 四川省科源工程技术测试中心有限责任公司 | Agricultural farmland saline-alkali degree sampling detection device and method |
| CN117233353A (en) * | 2023-08-25 | 2023-12-15 | 浙江大学 | Detection device and detection method |
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115950900A (en) * | 2023-02-13 | 2023-04-11 | 中国科学院西北生态环境资源研究院 | Frozen water and unfrozen water splitting method based on cosmic ray neutron technology |
| CN116660323A (en) * | 2023-07-24 | 2023-08-29 | 四川省科源工程技术测试中心有限责任公司 | Agricultural farmland saline-alkali degree sampling detection device and method |
| CN116660323B (en) * | 2023-07-24 | 2023-11-14 | 四川省科源工程技术测试中心有限责任公司 | Agricultural farmland saline-alkali degree sampling detection device and method |
| CN117233353A (en) * | 2023-08-25 | 2023-12-15 | 浙江大学 | Detection device and detection method |
| CN117233353B (en) * | 2023-08-25 | 2024-02-27 | 浙江大学 | Frozen soil detection equipment and frozen soil detection method |
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