Monitoring method and system for thickness of active layer and thickness change in permafrost region

Abstract

The present invention discloses a monitoring method and system for the thickness and thickness change of the active layer in permafrost areas. The active layer thickness monitoring includes the following steps: in the warm season, a measuring tube with sealed ends and smooth inside and outside is buried underground, and the buried depth below the surface is, pure water is injected into the measuring tube, and the height of the pure water is flush with the surface, a buoy is provided in the measuring tube and floats on the liquid surface, and a vent is provided on the top of the measuring tube; when the active layer melts to the maximum depth, the buoy height is detected; when the active layer is completely frozen, the buoy height is detected; by monitoring the change of the buoy height, the difference between the highest position and the lowest position of the buoy in a freeze-thaw cycle is used to automatically calculate the thickness of the active layer, wherein. The measuring method of the present invention is simple and has high measurement accuracy.

Description

Technical Field

[0001] The present invention relates to the field of permafrost distribution and characteristic monitoring, cold region engineering design and disease protection technology, and in particular to a method and system for monitoring the thickness of an active layer in a permafrost region and the thickness change process of the active layer caused by the external environment. Background Art

[0002] Permafrost is an extremely special geological phenomenon, widely distributed in high latitudes and high altitudes. The active layer above the permafrost layer freezes and melts with seasonal temperature changes. Its thickness and changing trend have an important impact on local ecosystems, infrastructure, climate change research, etc. As the global climate warms, the thickness of the active layer in permafrost areas gradually increases. This change directly affects surface heat exchange, water cycle and local ecosystems. The thickening of the active layer will cause foundation settlement, structural deformation and even collapse of infrastructure in permafrost areas, such as roads, pipelines, buildings, etc. Accurately measuring the thickness of the active layer not only helps to assess the impact of climate change on permafrost and provide data support for environmental protection, but is also crucial to the design, construction and maintenance of infrastructure in permafrost areas.

[0003] At present, the monitoring methods of active layer thickness in permafrost areas are mainly divided into two categories: field monitoring and remote sensing monitoring. Field monitoring methods include drilling method, thermal probe method, resistance method, geological radar method (GPR), etc. However, field monitoring methods such as pit exploration, resistance, and geological radar cannot measure continuously, and can only roughly determine the thickness of the active layer in summer, and cannot determine the exact maximum melting depth. Although the thermal probe method can continuously measure the ground temperature and infer the melting depth based on the ground temperature curve, its accuracy depends on the setting density of thermocouples near the upper limit. Remote sensing monitoring methods are suitable for large-scale observations, but the accuracy is usually low. Therefore, developing a reliable, accurate, highly automated, precise data acquisition, and adaptable to harsh environments method for measuring the thickness and changes of the active layer has important practical significance and engineering prospects for permafrost surveys and infrastructure stability. Summary of the invention

[0004] The present invention is aimed at the technical defects existing in the prior art of monitoring the thickness of the active layer in permafrost areas, and aims to provide a method and a monitoring system for accurately and continuously monitoring the thickness and thickness changes of the active layer in permafrost areas.

[0005] To achieve the purpose of the present invention, the technical solution adopted is:

[0006] A method for monitoring the thickness of an active layer in a permafrost region comprises the following steps:

[0007] In the warm season, bury the measuring tube with both ends sealed and smooth inside and outside underground to a depth of , pure water is injected into the measuring tube, the height of the pure water is flush with the ground surface, a buoy is provided in the measuring tube and floats on the liquid surface, and a vent hole is provided on the top of the measuring tube;

[0008] The water below the freezing front in permafrost and active layer freezes gradually first. When the active layer melts to the maximum depth, the total volume of water ice in the measuring tube is the smallest, the liquid level is the lowest, and the height of the monitoring buoy is recorded as , is the lowest position of the buoy;

[0009] In the cold season, the active layer and permafrost freeze towards each other. When the active layer is completely frozen, the liquid in the measuring tube is completely frozen, the total volume of water ice in the measuring tube is the largest, and the height of the monitoring buoy is recorded as , is the highest position of the buoy;

[0010] By monitoring the change in the buoy height, the highest position of the buoy during a freeze-thaw cycle is used and the lowest position of the buoy The difference , calculate the active layer thickness ,in, , is the thickness of the active layer, It is the difference between the highest position and the lowest position of the buoy during a freeze-thaw cycle.

[0011] Another aspect of the present invention also includes a method for monitoring the thickness change of the active layer in the permafrost region caused by the change of the external environment, comprising the following steps:

[0012] In the warm season, bury the measuring tube with both ends sealed and smooth inside and outside underground to a depth of , pure water is injected into the measuring tube, the height of the pure water is flush with the ground surface, a buoy is provided in the measuring tube and floats on the liquid surface, and a vent hole is provided on the top of the measuring tube;

[0013] The water below the permafrost and active layer freezing fronts freezes gradually first. When the active layer melts to the maximum depth, the total volume of water ice in the measuring tube is the smallest, the liquid level reaches the lowest level of the year, and the height of the monitoring buoy is recorded as , is the lowest position of the buoy in that year;

[0014] In the cold season, the active layer is completely frozen. During the freezing and melting process of the active layer, the volume of water ice in the measuring tube changes continuously. In the next year, when the active layer melts to the maximum depth again, the liquid level reaches the lowest level of the year. The height of the monitoring buoy is recorded as , is the lowest position of the buoy in the next year. The change of active layer thickness is calculated by the difference of the lowest position of the buoy in two consecutive years. Specifically, if , then the active layer in this year is deeper than that in the previous year. ;like , then the thickness of the active layer in this year is thinner than that in the previous year. .

[0015] In the above technical solution, a scale is provided on the outer wall of the measuring tube located above the ground surface.

[0016] In the above technical solution, the material of the measuring tube is organic high-strength tempered glass, so that after the water in the measuring tube turns into ice, the increase in volume will not cause the change in the inner diameter of the measuring tube.

[0017] In the above technical solution, the diameter of the measuring tube does not exceed 5 cm, and the tube diameter is small, so as to ensure that the freezing front of the active layer and the water-ice interface in the measuring tube are kept consistent as much as possible. The diameter of the vent hole is 0.02-0.05 cm, and the vent hole is small, which can ensure that the air pressure inside and outside the measuring tube is consistent and the water in the measuring tube is not lost by evaporation. Preferably, a one-way membrane is provided on the vent hole.

[0018] In the above technical solution, the buoy is fixed to the top inner wall of the measuring tube through a freely retractable connecting part, and the connecting part is a flexible connecting part, such as a flexible rope or a freely retractable connecting rod. The buoy can move freely as the volume of water ice in the tube changes, and is always on the top of the water ice to measure the highest peak surface of the water ice.

[0019] In the above technical solution, a hole is drilled in advance on the surface, a soft material is applied to the outer wall of the measuring tube body, and the measuring tube is vertically sunk into the drilled hole, and the pores between the measuring tube and the soil are filled with non-frost heaving materials.

[0020] In the above technical solution, the height of the exposed portion of the measuring tube above the ground surface is at least 1 / 10 of the estimated active layer thickness.

[0021] In the above technical solution, the buried depth below the surface is It is 1.5~2 times the estimated active layer thickness.

[0022] In the above technical solution, the diameter of the drill hole is 6~7cm.

[0023] Another aspect of the present invention also includes a monitoring system for running the monitoring method, including a freezing front sensing unit, a data acquisition unit and a data analysis unit, wherein:

[0024] The freezing front sensing unit includes the measuring tube and the pure water inside. The data acquisition unit is used to collect the height of the buoy and transmit the corresponding electrical signal to the data analysis unit. The data analysis unit obtains the thickness of the active layer by analyzing the data of each freeze-thaw cycle monitored, or obtains the deepening or shallowing thickness of the active layer each year according to the annual data analysis of continuous monitoring.

[0025] In the above technical solution, the data acquisition unit includes a capacitive, pressure or ultrasonic sensor installed on the upper part of the measuring tube to monitor the position of the buoy.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The measurement principle of the present invention is to utilize the freezing and thawing characteristics of the soil and the water at the corresponding depth in the measuring tube caused by the temperature change of the active layer, and to estimate the maximum thawing depth of the permafrost surface by measuring the volume change difference of a fixed mass of water in the vertical measuring tube in the active layer during the freezing and thawing process. The measurement method reduces manual intervention, ensures continuous data collection, and greatly improves monitoring accuracy and data timeliness;

[0028] 2. The diameter of the measuring tube of the present invention is relatively small, which can ensure that the freezing and thawing front of the active layer soil is consistent with the water ice front in the measuring tube. The monitoring device is simple, the construction is simple, and it is convenient for commercial promotion and application;

[0029] 3. The application of the present invention to monitor the thickness and changes of the permafrost layer will help to determine the health status of the ecosystem in the permafrost area, provide a scientific basis for ecological protection and restoration, analyze the impact of permafrost changes on the global climate system, support the improvement and prediction of climate models, provide risk warnings for the stability of cold-region projects, and help make decisions on project maintenance and transformation. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is the position of the freezing front and the change of water ice volume in the measuring tube during the freezing and melting process of the active layer.

[0031] Figure 2 It is the change of the buoy position during the freeze-thaw cycle of the active layer.

[0032] Figure 3 It is the seasonal change of permafrost ground temperature.

[0033] Figure 4 It is the characteristic of the minimum liquid level change during the thickening of the active layer.

[0034] Figure 5 It is the characteristic of the lowest liquid level change during the thinning of the active layer.

[0035] In the figure, ① is the initial state of the liquid level in the glass tube after installation in the warm season, ② is the gradual freezing state of water below the freezing front of permafrost and active layer, ③ is the distribution state of water ice in the measuring tube when the active layer melts to the maximum depth, ④ is the freezing state of the active layer from the surface and permafrost in the cold season, and ⑤ is the complete freezing state of the active layer;

[0036] 1- measuring tube, 2- pure water, 3- scale, 4- float, 5- frozen ice, 6- vent.

[0037] Figure 2 , Figure 4 and Figure 5 According to the heat transfer theory, COMSOL finite element software was used to establish a frozen ground temperature calculation model, and the position change of the buoy in the measuring tube was calculated under the conditions of climate change, where the horizontal axis is time and the vertical axis is the change of the buoy position. DETAILED DESCRIPTION

[0038] The present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0039] Example 1

[0040] A method for monitoring the thickness of an active layer in a permafrost region comprises the following steps:

[0041] like Figure 1 As shown in ① (the initial state of the liquid level in the glass tube after installation in the warm season), in the warm season, the measuring tube 1 with both ends sealed is buried underground, and the buried depth below the surface is The measuring tube 1 is made of organic high-strength tempered glass material. The measuring tube 1 made of tempered glass has high strength to ensure that the measuring tube 1 has no radial deformation when the water in the tube freezes. The measuring tube 1 is polished smooth inside and outside to ensure that the volume of the water in the tube can expand freely upward after freezing when the active layer freezes, and there is no freezing force between the active layer soil outside the tube and the measuring tube 1.

[0042] The measuring tube 1 is installed as follows: a deep hole with a diameter of 6-7 cm is drilled in advance on the surface. The depth of the hole is 1.5-2 times the estimated thickness of the active layer and is the same as the length of the buried part of the measuring tube 1. The measuring tube 1 is vertically sunk into the borehole, and a soft substance (such as vaseline) is applied around the outer wall of the measuring tube 1. The pores between the outer wall of the measuring tube 1 and the soil are filled with non-frost heaving materials.

[0043] The height of the exposed part of the measuring tube 1 above the surface is at least 1 / 10 of the estimated active layer thickness and has a scale 3, the buried depth below the surface is 1.5 to 2 times the estimated active layer thickness, and the diameter of the measuring tube 1 does not exceed 5 cm.

[0044] After the measuring tube 1 is installed, pure water 2 is injected into the measuring tube 1, and its height is flush with the ground surface. A buoy 4 is provided in the measuring tube 1 to float on the liquid surface. The buoy 4 is fixed to the top inner wall of the measuring tube 1 through a freely retractable connection part. The connection part is a flexible connection part, such as a flexible rope or a freely retractable connection rod. The buoy 4 can move freely with the change of the volume of water ice in the tube, and is always on the top of the water ice to measure the highest peak of the water ice. There is a tiny vent 6 at the top of the measuring tube 1, and the diameter of the vent 6 is 0.05 cm, which ensures that the air above the inside of the measuring tube 1 can freely enter and exit from the vent 6 as the temperature changes, and there is no atmospheric pressure difference inside and outside the measuring tube 1.

[0045] like Figure 1 As shown in ②, the water below the freezing front of permafrost and active layer gradually freezes to form ice. Figure 1 As shown in ③ (the distribution of water ice in measuring tube 1 when the active layer melts to the maximum depth (upper limit of permafrost)), when the active layer melts to the maximum depth, the total volume of water ice in measuring tube 1 is the smallest, the liquid level is the lowest, and the height of monitoring buoy 4 is recorded as , is the lowest position of buoy 4, h u is the distance between buoy 4 and the upper limit of frozen ground when the active layer melts to the maximum depth;

[0046] In the cold season, Figure 1 As shown in ④ (the cold season active layer freezes towards the surface and permafrost), the active layer freezes towards the surface and permafrost, as shown in Figure 1 As shown in ⑤ (the active layer is completely frozen), when the active layer is completely frozen, the liquid in the measuring tube 1 is completely frozen, the total volume of water ice in the measuring tube 1 is the largest, and the height of the monitoring buoy 4 is recorded as , The highest position of buoy 4;

[0047] Calculate the highest position of buoy 4 during a freeze-thaw cycle and buoy 4 lowest position The difference , , The difference between the highest position of buoy 4 and the lowest position of buoy 4 during a freeze-thaw cycle;

[0048] Calculate the active layer thickness , is the thickness of the active layer.

[0049] The position change of buoy 4 during the freeze-thaw cycle is as follows: Figure 2 shown.

[0050] The measuring principle of the present invention is as follows:

[0051] The volume of water after freezing is 10 / 9 of that before freezing, that is, the volume increases by 1 / 9, and the volume decreases by 1 / 10 after the ice melts, and the mass remains unchanged. The present invention utilizes the volume change characteristics of the water-ice phase change, measures the change in the height of the liquid / solid surface in the measuring tube 1 during the freezing and melting periods, and estimates the thickness of the active layer. The measurement process only considers the volume change during the freezing and melting of water and ice, and does not consider the change in the surface position during the temperature change, and does not consider the volume change of water and ice due to temperature change. When the measuring tube 1 is sunk into the borehole and installed, pure water 2 is injected into the measuring tube 1 until the liquid level in the tube is flush with the surface. During the freezing and thawing of the active layer, the pure water 2 in the measuring tube 1 freezes and melts according to the temperature of the soil around the measuring tube 1. When the temperature of the soil outside the measuring tube 1 is lower than 0°C, the pure water 2 at the corresponding position in the measuring tube 1 begins to freeze, the volume increases, and the total volume of water ice in the measuring tube 1 increases, thereby pushing the buoy 4 to move upward. During the melting period, when the soil temperature outside the measuring tube 1 is higher than 0°C, the frozen ice 5 at the corresponding position in the measuring tube 1 begins to melt and its volume decreases. The total volume of water ice in the measuring tube 1 decreases, the liquid level decreases, and the buoy 4 moves downward. The position of the buoy 4 is monitored during its movement to monitor the position change of the liquid level or ice surface. Figure 3 As shown, the temperature distribution and freezing and melting state of the water in the measuring tube 1 are basically consistent with the soil on the side of the tube, which proves that the water ice distribution in the measuring tube 1 can truly reflect the changes in the freezing front of the active layer.

[0052] According to the liquid level change process and the depth of the buried measuring tube 1, the thickness of the active layer can be calculated. The principle is as follows:

[0053] According to the fact that the volume increase of water after freezing is 1 / 9 of the original volume of water, we can know that:

[0054] (1);

[0055] According to the fact that ice loses 1 / 10 of its volume after melting, Figure 1 In ③, after the frozen ice 5 in the measuring tube 1 is completely melted, the liquid level is equal to the buried depth below the ground surface. , it can be seen that (the freeze-thaw cycle process is as follows Figure 2 shown):

[0056] (2);

[0057] Substituting formula (1) into formula (2) yields

[0058] ;

[0059] Example 2

[0060] Climate warming will directly affect the active layer (the seasonally frozen and thawed surface soil above the permafrost zone) in permafrost areas, triggering a series of ecological and engineering problems. As the temperature rises, the active layer thaws deeper in the summer and becomes thicker year by year. The melted water seeps into the lower layer and changes the moisture content of the permafrost. This change in humidity will accelerate the degradation of permafrost. The increase in the thickness of the active layer will also lead to increased soil carbon release, changes in plant and animal habitats, and changes in wetland ecosystems. For engineering structures, the melting of the active layer reduces the bearing capacity of the soil, causing ground subsidence, posing a major threat to infrastructure in permafrost areas, such as roads, bridges, pipelines, and buildings. The thawing of permafrost will also increase the incidence of disasters such as landslides and ground cracks, especially in areas with large slopes. Monitoring changes in the active layer is crucial in studying climate warming, protecting ecosystems, ensuring engineering safety, and supporting community adaptive management.

[0061] This embodiment provides a method for monitoring the deepening of active layers in permafrost areas, comprising the following steps:

[0062] The steps for burying the measuring tube 1 are the same as those in Example 1 and will not be repeated here;

[0063] The water below the freezing front of permafrost and active layer gradually freezes. When the active layer melts to the maximum depth, the total volume of water ice in measuring tube 1 is the smallest, the liquid level reaches the lowest level of the year, and the height of monitoring buoy 4 is recorded as , It is the lowest position of buoy 4 in that year;

[0064] In the cold season, the active layer is completely frozen. In the next year, when the active layer melts to the maximum depth, the liquid level reaches the lowest level of the year. The height of the monitoring buoy 4 is recorded as , This is the lowest position of buoy 4 in the next year. , the thickness change of the active layer is calculated by the lowest position of buoy 4 in two consecutive years. The thickness of the active layer in this year is deeper than that in the previous year. .

[0065] This embodiment can well monitor the change of active layer thickness under climate warming conditions. Figure 4 As shown in Figure 1, as the permafrost below the upper limit of the active layer gradually melts, the annual minimum height of the liquid surface gradually decreases. Nine times the difference in the minimum liquid surface between two consecutive years is the deepening thickness of the active layer in the two consecutive years.

[0066] Example 3

[0067] In contrast to Example 2, when the upper limit of the active layer gradually moves upward, the annual minimum height of the liquid level gradually increases.

[0068] In this embodiment, a method for monitoring the thinning of the active layer in permafrost areas is provided. The steps for burying the measuring tube 1 are the same as those in Embodiment 1 and will not be described in detail herein.

[0069] The water below the freezing front of permafrost and active layer gradually freezes. When the active layer melts to the maximum depth, the total volume of water ice in measuring tube 1 is the smallest, the liquid level reaches the lowest level of the year, and the height of monitoring buoy 4 is recorded as , It is the lowest position of buoy 4 in that year;

[0070] In the cold season, the active layer is completely frozen. In the next year, when the active layer melts to the maximum depth, the liquid level reaches the lowest level of the year. The height of the monitoring buoy 4 is recorded as , This is the lowest position of buoy 4 in the next year. The active layer in this year is thinner than that in the previous year. .like Figure 5 As shown in the figure, 10 times the difference in the lowest liquid level between two consecutive years is the thinning thickness of the active layer in the two consecutive years.

[0071] Example 4

[0072] A monitoring system for running the monitoring method described in any one of Examples 1-3, comprising a freezing front sensing unit, a data acquisition unit and a data analysis unit. The freezing front sensing unit comprises a measuring tube 1 and pure water 2 inside. The pure water 2 is kept frozen or melted by the temperature of the soil around the tube. The data acquisition unit comprises a buoy sensor installed on the upper part of the measuring tube 1. The buoy sensor can be a capacitive, pressure or ultrasonic sensor, and outputs a corresponding electrical signal or digital signal according to the change in liquid height. The data acquisition unit collects the height of the buoy 4 and transmits the corresponding electrical signal to the data analysis unit. The data analysis unit comprises a communication module and a control center. The unit can obtain the thickness of the active layer by analyzing the data of each freeze-thaw cycle monitored, or obtain the deepening or shallowing thickness of the active layer each year according to the annual data monitored.

[0073] The above is only a preferred embodiment of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for monitoring the thickness of active layer in permafrost areas, characterized in that: The following steps are involved: In the warm season, bury the measuring tube with both ends sealed and smooth inside and outside underground to a depth of , pure water is injected into the measuring tube, the height of the pure water is flush with the ground surface, a buoy is provided in the measuring tube and floats on the liquid surface, the buoy is fixed to the top inner wall of the measuring tube through a freely retractable connection part, a vent is provided on the top of the measuring tube, and a scale is provided on the outer wall of the measuring tube above the ground surface, and the material of the measuring tube is organic high-strength tempered glass; The water below the freezing front in permafrost and active layer freezes gradually first. When the active layer melts to the maximum depth, the total volume of water ice in the measuring tube is the smallest, the liquid level is the lowest, and the height of the monitoring buoy is recorded as , is the lowest position of the buoy; In the cold season, the active layer and permafrost freeze towards each other. When the active layer is completely frozen, the liquid in the measuring tube is completely frozen, the total volume of water ice in the measuring tube is the largest, and the height of the monitoring buoy is recorded as , is the highest position of the buoy; By monitoring the change in the buoy height, the highest position of the buoy during a freeze-thaw cycle is used and the lowest position of the buoy The difference , calculate the active layer thickness ,in, , is the thickness of the active layer, It is the difference between the highest position and the lowest position of the buoy during a freeze-thaw cycle.

2. A method for monitoring the thickness change of active layer in permafrost area, characterized in that: The steps include: In the warm season, bury the measuring tube with both ends sealed and smooth inside and outside underground to a depth of , pure water is injected into the measuring tube, the height of the pure water is flush with the ground surface, a buoy is provided in the measuring tube and floats on the liquid surface, the buoy is fixed to the top inner wall of the measuring tube through a freely retractable connection part, a vent is provided on the top of the measuring tube, and a scale is provided on the outer wall of the measuring tube above the ground surface, and the material of the measuring tube is organic high-strength tempered glass; The water below the permafrost and active layer freezing fronts freezes gradually first. When the active layer melts to the maximum depth, the total volume of water ice in the measuring tube is the smallest, the liquid level reaches the lowest level of the year, and the height of the monitoring buoy is recorded as , is the lowest position of the buoy in that year; In the cold season, the active layer is completely frozen. During the freezing and melting process of the active layer, the volume of water ice in the measuring tube changes continuously. In the next year, when the active layer melts to the maximum depth again, the liquid level reaches the lowest level of the year. The height of the monitoring buoy is recorded as , is the lowest position of the buoy in the next year. The change of active layer thickness is calculated by the difference of the lowest position of the buoy in two consecutive years. Specifically, if , then the active layer in this year is deeper than that in the previous year. ;like , then the thickness of the active layer in this year is thinner than that in the previous year. .

3. The monitoring method according to claim 1 or 2, characterized in that: The diameter of the measuring tube does not exceed 5 cm, and the diameter of the vent hole is 0.02-0.05 cm.

4. The monitoring method according to claim 1 or 2, characterized in that: Drill a hole on the surface in advance, apply soft material on the outer wall of the measuring tube, sink it vertically into the hole, and fill the pores between the measuring tube and the soil with non-frost heaving materials.

5. The monitoring method according to claim 4, characterized in that: The drilling diameter is 6~7cm.

6. The monitoring method according to claim 1 or 2, characterized in that: The height of the exposed part of the measuring tube above the ground surface is at least 1 / 10 of the estimated active layer thickness, and the buried depth below the ground surface is It is 1.5~2 times the estimated active layer thickness.

7. A monitoring system for running the monitoring method according to claim 1 or 2, characterized in that: It includes a freezing front sensing unit, a data acquisition unit and a data analysis unit, wherein: The freezing front sensing unit includes the measuring tube and the pure water inside. The data acquisition unit is used to collect the height of the buoy and transmit the corresponding electrical signal to the data analysis unit. The data analysis unit obtains the thickness of the active layer by analyzing the data of each freeze-thaw cycle monitored, or obtains the deepening or shallowing thickness of the active layer each year according to the annual data analysis of continuous monitoring.

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