Method for evaluating evolutionary state of permafrost based on single-hole ground temperature

Abstract

The invention discloses a permafrost evolution state evaluation method based on single-hole ground temperature, and the method is characterized in that the method comprises the following steps: 1, collecting single-hole ground temperature data; 2, effective negative temperature is determined, 3, space-time integration is conducted on the effective negative temperature, and space-time negative accumulated temperature is obtained; 4, selecting a reference year, and calculating the space-time negative accumulated temperature of the reference year; 5, calculating the space-time negative accumulated temperature of the target year, and calculating a frozen soil state index; and 6, judging the evolutionary or degenerative state of the frozen soil according to the frozen soil state index. According to the evolutionary state evaluation method for the permafrost based on the single-hole ground temperature, the original space curve of the ground temperature changing along with depth and time is converted into the integral quantity value capable of representing the thermal state characteristics of the permafrost, so that ground temperature data can be effectively integrated, and the integrity and reliability of the data are improved; and quantitative evaluation of the evolutionary trend of the permafrost can be realized, and the method can be widely applied to cold region environments and engineering practices under different regions and conditions.

Description

Technical Field

[0001] This invention relates to the field of permafrost monitoring technology, specifically a method for assessing the evolution status of permafrost based on single-hole ground temperature. Background Technology

[0002] In recent years, permafrost in some regions has experienced a certain degree of degradation, manifested by rising ground temperatures, deepening of the active layer, and upward shift of the lower permafrost limit. However, permafrost in other areas has shown a certain degree of evolution under specific environmental conditions. The state of permafrost is crucial to the safe operation of foundation engineering projects. Therefore, accurately and comprehensively assessing permafrost and understanding its evolution / degradation state, i.e., the state of permafrost evolution, is of paramount importance for engineering design, operation and maintenance, and resource development and protection in cold regions.

[0003] Currently, monitoring of permafrost conditions mainly relies on ground temperature monitoring. Traditional methods typically involve setting up multiple temperature measurement wells in the permafrost area to periodically or continuously measure ground temperature data at different depths. These data can reflect the temperature change trend of permafrost, thus providing basic information for the assessment of permafrost conditions.

[0004] Existing technologies have many shortcomings in assessing the evolution of permafrost, such as: 1. Traditional ground temperature monitoring methods suffer from uneven spatial distribution of data. Data from local areas cannot accurately reflect the overall state of permafrost, and the measurement frequency is low, making it impossible to capture rapid changes in permafrost over a short period of time, especially during freeze-thaw cycles. 2. Existing methods are mostly qualitative descriptions and lack quantitative assessment indicators for changes in permafrost conditions, making them difficult to use directly for engineering decision-making; 3. Existing technologies have poor adaptability to different regions and conditions, making them difficult to apply widely in complex and variable cold environments; Therefore, this invention provides a method for assessing the evolution status of permafrost based on single-hole geothermal temperature to solve the problems mentioned above. Summary of the Invention

[0005] The purpose of this invention is to provide a method for assessing the evolution of permafrost based on single-hole geothermal data. This method addresses the problem of uneven spatial distribution of data in traditional geothermal monitoring methods mentioned in the background, where data from local areas cannot accurately reflect the overall permafrost state. Furthermore, the low measurement frequency makes it difficult to capture rapid changes in permafrost over short periods, especially during freeze-thaw cycles. These methods primarily rely on qualitative descriptions and lack quantitative assessment indicators for changes in permafrost state, making them unsuitable for direct engineering decision-making. They also exhibit poor adaptability to different regions and conditions, hindering their widespread application in complex and variable cold environments.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for assessing the evolution state of permafrost based on single-hole geothermal data, comprising the following steps: Step 1: Collect geothermal data from a single borehole, wherein the geothermal data is a function of depth and time; Step 2: Determine the effective negative temperature, which is the difference between the ground temperature (below the freezing temperature of the soil) and the freezing temperature. Step 3: Perform spatiotemporal integration on the effective negative temperature to obtain the spatiotemporal negative accumulated temperature; Step 4: Select a reference year and calculate the spatiotemporal negative accumulated temperature for the reference year; Step 5: Calculate the spatiotemporal negative accumulated temperature for the target year and calculate the permafrost state index; Step 6: Determine the evolution or degradation of permafrost based on the permafrost state index, and determine the state of permafrost evolution.

[0007] Preferably, the formula for calculating the effective negative temperature is: ; in, The freezing temperature of the soil. It refers to the ground temperature.

[0008] Preferably, the formula for calculating the spatiotemporal negative accumulated temperature is as follows: ; The lower limit of integration is generally the depth of the temperature measuring hole, or the burial depth range of key concern, expressed as... The maximum score is generally the surface level. If the permafrost in the active layer melts, the upper limit of the integral needs to be re-determined through interpolation.

[0009] Preferably, the interpolation method for the upper limit of integration is as follows: When m and m One adjacent temperature measurement point meets the following conditions: ; The upper limit of linear interpolation can be expressed as: .

[0010] Preferably, the formula for calculating the permafrost state index is: η ; in The spatiotemporal negative accumulated temperature of the base year, The spatiotemporal negative accumulated temperature is the target year. If n is greater than 100%, it indicates that the permafrost is in an evolving state; otherwise, it indicates that the permafrost is degrading.

[0011] Preferably, the Considering the influence of air temperature fluctuations on ground temperature, a fluctuation range can be set in practical applications. If η For the evolution of permafrost, if η This indicates permafrost degradation, meaning the permafrost has undergone evolution; otherwise, it indicates permafrost stability.

[0012] Preferably, the method for numerically solving the spatiotemporal negative accumulated temperature includes: ① Integrate along the depth direction, assuming that the temperature measuring hole has not reached the lower limit of the frost, determine the lower limit of integration as the lower position of a single hole, and the upper limit of integration as the corresponding burial depth z value; ②If the assessment scope is the entire permafrost layer, then the lower limit of the permafrost layer needs to be determined by referring to the method for determining the upper limit of the integration; ③ Considering that single-well geothermal measurements often involve sensors with non-equidistant spacing, the integral value of the effective negative temperature of a single well along the depth direction at time k is expressed as: ; Where n represents the number of discrete temperature measurement points, divided into n-1 trapezoidal intervals, and numerical integration is performed using the trapezoidal rule.

[0013] Preferably, the integration along the depth direction is performed in addition to the integration along the time direction. The total time integration duration is 1 year, with a total of h time points. If the time intervals are uniformly set, then: ; Select a base year, calculate the spatiotemporal integral value of the i-th year and obtain the permafrost state index.

[0014] Compared with existing technologies, the beneficial effects of this invention are as follows: This method for assessing the evolution status of permafrost based on single-hole geothermal data, by introducing a spatiotemporal integration method, transforms the original spatial curve of geothermal variation with depth and time into an integral value that can characterize the thermal state of permafrost. This not only effectively integrates geothermal data and improves the integrity and reliability of the data, but also enables a quantitative assessment of the evolution trend of permafrost, providing a scientific basis for cold region engineering design, operation and maintenance, resource development and protection, and other fields. Furthermore, the method is simple to operate, highly adaptable, and has low computational cost, making it widely applicable to cold region environments and engineering practices under different conditions.

[0015] 1. By integrating the effective negative temperature along the depth direction, the ground temperature changes at different depths can be comprehensively considered, avoiding evaluation errors caused by the non-uniformity of local temperature measurement data. By integrating the effective negative temperature along the time direction, the temperature changes of permafrost at different time scales can be captured, including rapid changes during freeze-thaw cycles, thereby improving the accuracy and reliability of the evaluation results and ensuring uniform spatial distribution and measurement frequency. 2. By calculating the ratio of the spatiotemporal negative accumulated temperature of the target year to the spatiotemporal negative accumulated temperature of the base year, the Frost State Index (FSI) is obtained, which provides a clear quantitative indicator for the assessment of the Frost State and can be directly used for engineering decision-making. Considering the influence of air temperature fluctuations on ground temperature, the fluctuation range is also introduced, which further improves the stability and reliability of the assessment results. 3. Permafrost condition assessment can be performed using single-hole geothermal data. The operation is relatively simple, requiring no complex equipment or a large number of input parameters, which lowers the application threshold. At the same time, by introducing spatiotemporal integration and permafrost condition index, it can adapt to cold environments under different regions and conditions, and has wide applicability. It can provide reliable assessment results in high-latitude, high-altitude areas or in complex freeze-thaw cycles. 4. By converting geothermal data into integral values, complex numerical models and a large number of input parameters are avoided, simplifying the calculation process and significantly reducing computational costs. This enables rapid and efficient assessment of permafrost conditions and is suitable for large-scale regional applications. Attached Figure Description

[0016] Figure 1 This is a graph showing the change in ground temperature with depth according to the present invention; Figure 2 This is a geothermal curve for the baseline year of permafrost assessment in this invention; Figure 3 This is a graph showing the change in the frozen soil state index according to the present invention. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] Please see Figures 1-3 This invention provides a technical solution: a method for assessing the evolution status of permafrost based on single-hole geothermal data. Formula for calculating effective negative temperature: ; in, The freezing temperature of the soil. Ground temperature; As a preferred technical solution of the present invention, the calculation formula for effective negative temperature is clarified. As a key parameter in the evaluation method, it is used to determine the degree to which the ground temperature is lower than the freezing temperature, which is directly related to the thermal state of the permafrost and provides basic data for subsequent spatiotemporal integration.

[0019] As a preferred technical solution of the present invention, the formula for calculating the spatiotemporal negative accumulated temperature is as follows: ; The lower limit of integration is generally the depth of the temperature measuring hole, or the burial depth range of key concern, expressed as... The maximum score is generally the surface level. If the permafrost in the active layer melts, the upper limit of the integral needs to be re-determined through interpolation. Ground temperature data can be converted into integral values ​​that reflect the thermal state of permafrost, thereby enabling a quantitative assessment of the permafrost condition.

[0020] As a preferred embodiment of the present invention, the interpolation method for the upper limit of integration is as follows: When m and m One adjacent temperature measurement point meets the following conditions: ; The upper limit of linear interpolation can be expressed as: .

[0021] This paper solves the problem of determining the upper limit of integration when permafrost thaws within the active layer. The upper limit of integration is determined by linear interpolation, ensuring the accuracy and applicability of the evaluation method under permafrost thawing conditions. As a preferred embodiment of the present invention, the formula for calculating the frozen soil state index is as follows: η ; in The spatiotemporal negative accumulated temperature of the base year, The spatiotemporal negative accumulated temperature for the target year is n. If n is greater than 100%, it indicates that the permafrost is in an evolving state; otherwise, it indicates that the permafrost is degrading. By calculating the permafrost state index, a quantitative indicator is provided to determine the evolution state of permafrost, which can be directly used for engineering decision-making and provide a scientific basis for engineering design and operation and maintenance in permafrost areas.

[0022] As a preferred technical solution of the present invention Considering the influence of air temperature fluctuations on ground temperature, a fluctuation range can be set in practical applications. If η For the evolution of permafrost, if η If it indicates permafrost degradation, otherwise it indicates permafrost stability; Considering the influence of air temperature fluctuations on ground temperature, the concept of fluctuation range is introduced, which makes the assessment of permafrost conditions more stable and reliable, and improves the adaptability of the assessment method to environmental changes.

[0023] As a preferred technical solution of the present invention, the method for numerically solving the spatiotemporal negative accumulated temperature includes: ① Integrate along the depth direction, assuming that the temperature measuring hole has not reached the lower limit of the frost, determine the lower limit of integration as the lower position of a single hole, and the upper limit of integration as the corresponding burial depth z value; ②If the assessment scope is the entire permafrost layer, then the lower limit of the permafrost layer needs to be determined by referring to the method for determining the upper limit of the integration; ③ Considering that single-well geothermal measurements often involve sensors with non-equidistant spacing, the integral value of the effective negative temperature of a single well along the depth direction at time k is expressed as: ; Where n represents the number of discrete temperature measurement points, divided into n-1 trapezoidal intervals, and numerical integration is performed using the trapezoidal rule. The numerical solution method for spatiotemporal negative accumulated temperature, including integration along the depth and time directions, and numerical integration using the trapezoidal rule, improves the accuracy and efficiency of the calculation.

[0024] As a preferred embodiment of the present invention, integration is performed along the depth direction and then along the time direction. The total duration of the time integration is one year, with a total of h time points. If the time intervals are uniformly set, then: ; Select a base year, calculate the spatiotemporal integral value of the i-th year and obtain the permafrost state index; This ensures the integrity of the spatiotemporal negative accumulated temperature calculation, enabling the assessment method to cover the entire permafrost layer and providing comprehensive information on permafrost conditions.

[0025] Step 1: Collect geothermal data from a single borehole ① Select a representative temperature measurement well in a permafrost region; ② Install ground temperature sensors, arranged along the depth direction, with a temperature measuring hole depth of 5.0m and a temperature measuring interval of 0.2m, for a total of 26 temperature measuring points; ③ Set the sampling interval to 5 days and continuously collect ground temperature data.

[0026] Step 2: Determine the effective negative temperature ① Set the soil freezing temperature

[0027] ② For the ground temperature at each temperature measurement point ,calculate .

[0028] Step 3: Calculate the negative spacetime temperature using spacetime integration. ① Integrate the effective negative temperature in space and time to obtain the space-time negative accumulated temperature S; ②If the permafrost within the active layer thaws, the upper limit of integration is determined using linear interpolation. .

[0029] Step 4: Calculate the frozen soil state index ① Select a reference year and calculate the spatiotemporal negative accumulated temperature for the reference year. ; ② Calculate the spatiotemporal negative accumulated temperature for the target year. ; ③ Calculate the frozen soil state index η; ④ Determine the state of frozen soil based on η.

[0030] This is how to use the method for assessing the evolution status of permafrost based on single-hole geothermal temperature.

[0031] All standard parts used in this invention can be purchased from the market, and irregular parts can be customized according to the description and drawings. The specific connection methods of each part adopt conventional methods such as bolts, rivets, and welding that are mature in the prior art. The machinery, parts and equipment adopt conventional models in the prior art, and the circuit connection adopts conventional connection methods in the prior art, which will not be described in detail here. The contents not described in detail in this specification belong to the prior art known to those skilled in the art.

[0032] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for assessing the evolution state of permafrost based on single-pore geothermal data, characterized in that, Includes the following steps: Step 1: Collect geothermal data from a single borehole, wherein the geothermal data is a function of depth and time; Step 2: Determine the effective negative temperature, which is the difference between the ground temperature (below the freezing temperature of the soil) and the freezing temperature. Step 3: Perform spatiotemporal integration on the effective negative temperature to obtain the spatiotemporal negative accumulated temperature; Step 4: Select a reference year and calculate the spatiotemporal negative accumulated temperature for the reference year; Step 5: Calculate the spatiotemporal negative accumulated temperature for the target year and calculate the permafrost state index; Step 6: Determine the evolution or degradation of permafrost based on the permafrost state index, and determine the state of permafrost evolution.

2. The method for assessing the evolution state of permafrost based on single-hole geothermal temperature according to claim 1, characterized in that: The formula for calculating the effective negative temperature is as follows: ； in, The freezing temperature of the soil. It refers to the ground temperature.

3. The method for assessing the evolution state of permafrost based on single-hole geothermal temperature according to claim 1, characterized in that: The formula for calculating the spatiotemporal negative accumulated temperature is as follows: ； The lower limit of integration is generally the depth of the temperature measuring hole, or the burial depth range of key concern, expressed as... The maximum score is generally the surface level. If the permafrost in the active layer melts, the upper limit of the integral needs to be re-determined through interpolation.

4. The method for assessing the evolution state of permafrost based on single-hole geothermal temperature according to claim 3, characterized in that: The interpolation method for the upper limit of integration is as follows: When m and m One adjacent temperature measurement point meets the following conditions: ; The upper limit of linear interpolation can be expressed as: 。 5. The method for assessing the evolution state of permafrost based on single-hole geothermal temperature according to claim 1, characterized in that: The formula for calculating the frozen soil state index is as follows: or ; in The spatiotemporal negative accumulated temperature of the base year, The spatiotemporal negative accumulated temperature is the target year. If n is greater than 100%, it indicates that the permafrost is in an evolving state; otherwise, it indicates that the permafrost is degrading.

6. The method for assessing the evolution state of permafrost based on single-hole geothermal temperature according to claim 5, characterized in that: The Considering the influence of air temperature fluctuations on ground temperature, a fluctuation range can be set in practical applications. If η For the evolution of permafrost, if η If it indicates permafrost degradation, otherwise it indicates permafrost stability.

7. The method for assessing the evolution state of permafrost based on single-well geothermal temperature according to claim 1, characterized in that: The method for numerically solving the spatiotemporal negative accumulated temperature includes: ① Integrate along the depth direction, assuming that the temperature measuring hole has not reached the lower limit of the frost, determine the lower limit of integration as the lower position of a single hole, and the upper limit of integration as the corresponding burial depth z value; ②If the assessment scope is the entire permafrost layer, then the lower limit of the permafrost layer needs to be determined by referring to the method for determining the upper limit of the integration; ③ Considering that single-well geothermal measurements often involve sensors with non-equidistant spacing, the integral value of the effective negative temperature of a single well along the depth direction at time k is expressed as: ； Where n represents the number of discrete temperature measurement points, divided into n-1 trapezoidal intervals, and numerical integration is performed using the trapezoidal rule.

8. The method for assessing the evolution state of permafrost based on single-hole geothermal temperature according to claim 7, characterized in that: The integration along the depth direction is followed by integration along the time direction. The total time integration duration is 1 year, with a total of h time points. If the time intervals are uniformly set, then: ； Select a base year, calculate the spatiotemporal integral value of the i-th year and obtain the permafrost state index.

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