Land subsidence evaluation and early warning management method

Abstract

The application discloses a kind of ground subsidence evaluation and early warning management and control method, comprising the following steps: S1, determine evaluation factor, establish ground subsidence safety hazard evaluation index system;S2, weight calculation is carried out to each evaluation factor in evaluation index system, and evaluation factor is graded and standardized;S3, find out the geological condition of research area, collect research area data, use three-dimensional visual transparent model to reveal the geological stratum hazard distribution of disaster body;S4, the ground subsidence of research area is evaluated by software, and the degree of its risk and partition are obtained;S5, according to the evaluation result and the evaluation factor in index system, the geological hazard key area of research area is monitored and early warned, and control measures are proposed simultaneously.The application constructs ground subsidence evaluation index system.Through analyzing the geological environmental characteristics of research area, the hidden stratum of research area is disclosed using three-dimensional model, and then the risk evaluation is realized using Arcgis software.

Description

Technical Field

[0001] This invention relates to the field of geological information evaluation technology, and in particular to a method for evaluating and controlling ground subsidence. Background Technology

[0002] Urban geological safety is the foundation of ecological civilization construction. In recent years, with the continuous acceleration of urbanization, people have disrupted the original natural balance due to a lack of systematic and comprehensive geological safety awareness while modifying the original natural environment. This has triggered various geological disasters such as landslides, debris flows, collapses, ground subsidence, karst subsidence, and soil liquefaction. As urbanization continues to accelerate, the geological safety problems faced by cities are becoming increasingly prominent, and methods for assessing and controlling urban geological safety hazards are urgently needed. Ground subsidence is a geological phenomenon in which the ground elevation decreases regionally due to soil compression under the influence of natural conditions and human activities. The hazards of ground subsidence include:

[0003] (1) Failure of measurement benchmarks: Ground subsidence can cause urban ground leveling points to fail. Ground leveling points are the main basis for urban planning and construction. Failure of benchmarks can affect and interfere with certain tasks.

[0004] (2) Foundation settlement leads to frequent ground cracks. Uneven ground settlement may harm bridges and roads, causing crack development, pier sinking, and bridge deck cracking. In addition, the foundations of civil buildings will also experience a certain degree of settlement, affecting the housing safety of residents.

[0005] (3) The safety of urban pipe networks is threatened. There are a large number of underground pipe networks in the city. When the ground subsides, a series of uneven stresses will be generated on the underground pipe networks, causing them to bend, deform, crack, or even break, which will hinder industrial production and affect the normal life of urban residents.

[0006] (4) Well pipe rising and ground subsidence may cause well pipes on deep bedrock to rise and be exposed to the ground, shortening their service life, aggravating pipeline corrosion, and in severe cases, may cause them to break, resulting in serious damage.

[0007] (5) Building tilting: There are a large number of buildings in the city. If the ground settles unevenly, the upper buildings will tilt. If the tilt is too large or too fast, the buildings will collapse, thereby causing damage and loss to the life and property of people inside and around the buildings.

[0008] Currently, for foreign scholars, accurately classifying the hazard levels of evaluation indicators and results has become a key challenge for further exploration. In China, previous geological hazard assessments have involved varying selections of evaluation factors, lacking a systematic framework and complete system. Furthermore, the quantification of evaluation indicators and hazard classification still require further discussion. Therefore, the following problems exist:

[0009] (1) Although most geological disaster-causing bodies have their corresponding evaluation index systems, there is still a lack of a systematic urban geological safety risk evaluation index system.

[0010] (2) In previous evaluations, the classification and value of indicator factors still need to be explored;

[0011] (3) There is a relative lack of visualization of potential geological hazards in urban soil layers;

[0012] (4) The methods for monitoring and early warning of urban geological safety are relatively simple. Summary of the Invention

[0013] To address the problems of existing technologies, the present invention aims to provide a method for land subsidence evaluation and early warning control. It employs the analytic hierarchy process (AHP) combined with expert scoring to obtain the weights of each evaluation factor, ensuring the integrity of the indicator system. The evaluation indicator system is constructed by considering the geological environment, inducing factors, and historical subsidence conditions. Software is then used for analysis and evaluation, and for monitoring and early warning of key areas with potential hazards. The specific details are as follows:

[0014] A method for land subsidence assessment and early warning control includes the following steps:

[0015] S1. Determine the evaluation factors and establish a ground subsidence safety hazard evaluation index system;

[0016] S2. Calculate the weights of each evaluation factor in the evaluation index system, and classify and standardize the evaluation factors.

[0017] S3. Investigate the geological conditions of the study area, collect data from the study area, and use a three-dimensional visual transparent model to reveal the distribution of geological and soil layer hazards of the disaster-causing body;

[0018] S4. Use software to assess the risk of ground subsidence in the study area, and determine its risk level and zoning.

[0019] S5. Based on the evaluation results and the evaluation factors in the indicator system, monitor and issue early warnings for key areas of geological hazards in the study area, and propose control measures.

[0020] Furthermore, the evaluation index system in step S1 is constructed using the analytic hierarchy process (AHP) and expert scoring method. The AHP decomposes the system into a target layer, a quasi-measurement layer, and a scheme layer. The target layer is the ground settlement hazard evaluation index system. The quasi-measurement layer includes geological environment, inducing factors, and historical disaster conditions. The geological environment scheme layer includes the cumulative thickness of soft soil, compression coefficient, cumulative thickness of aquifer, and groundwater depth. The inducing factors scheme layer includes groundwater extraction intensity and the load of the superstructure. The historical disaster conditions scheme layer includes cumulative settlement, settlement rate, and building tilt.

[0021] Furthermore, in step S2, when calculating the weights, a pairwise comparison judgment matrix is ​​constructed using expert scoring by setting up a matrix. The weights of each indicator are calculated and their consistency is checked. If the consistency check fails, the matrix is ​​adjusted again until the consistency check passes. Specifically, this includes the following steps:

[0022] S2.1. Based on the actual situation, the types of geological disasters, and their specific influencing factors, select easily obtainable and quantifiable indicators, and combine them into a set:

[0023] X = {X1, X2, X3, X4, X5}

[0024] S2.2 From the established indicator system, various evaluation indicator factors at the same level are selected based on different perspectives and degrees of importance to construct a discriminant construction matrix as shown in formula (2.3), which mainly represents the relative importance between the various indicators:

[0025]

[0026] In the formula: R ij —This indicates the relative importance of element i to element j under certain conditions. The relative importance of the indicator is determined by quantifying the indicator through expert scoring.

[0027] For example, R ij =1 indicates factor X i With X j Equally important;

[0028] For example, R ij =3 indicates factor X i Compared to X j Slightly important;

[0029] For example, R ij =5 indicates factor X i Compared to X j Quite important;

[0030] For example, R ij =7 indicates factor X i Compared to Xj Much more important;

[0031] For example, R ij =9 indicates factor X i Comparison is extremely important;

[0032] For example, R ij =2,4,6,8 represent the intermediate values ​​of adjacent judgments 1 to 3, 3 to 5, 5 to 7, and 7 to 9, respectively;

[0033] The reciprocal of X i With X j Comparison, X j Compared to X i The degree of importance;

[0034] S2.3 Calculate the importance ranking and weights. Through the judgment matrix, calculate the eigenvector corresponding to the largest eigenvalue of T, and normalize it to obtain the weights of the indicator factors. Finally, sort them according to the relative weights of each indicator factor to obtain the main factors, general factors and minor factors. The factor weight calculation formula is shown in (2.4) below:

[0035]

[0036] S2.4 Consistency test of evaluation index weights: Since the expert scoring method is subjective, in order to make the results more effective, the eigenvectors obtained by the constructed judgment matrix need to be tested for consistency and randomness. The formula is as follows (2.5):

[0037] CR = CI / RI (2.5)

[0038] In the formula: CR is the random consistency ratio of the judgment matrix; CI is the consistency index of the judgment matrix; its calculation formula is shown in Figure 2.6 below:

[0039]

[0040] In the formula: λmax is the maximum feature, and its calculation formula is shown in (2.7) below:

[0041]

[0042] In the formula: (TA)i represents the i-th element of vector TA, and its expression is as shown in (2.8):

[0043]

[0044] In the formula: m — is the order of the judgment matrix; RI is the average random consistency index of the judgment matrix, obtained from a large number of experiments. For low-order judgment matrices, RI can be selected according to the following correspondence:

[0045] In order m, 1 to 11 correspond to RI values ​​of 0.00, 0.00, 0.58, 0.90, 1.12, 1.24, 1.32, 1.41, 1.45, 1.49, and 1.51, respectively. If CR ≤ 0.1, the consistency test is considered to have passed, indicating that the weight allocation is reasonable. Otherwise, the judgment matrix needs to be readjusted until CR ≤ 0.1.

[0046] Furthermore, the weight calculation results are as follows:

[0047] In the criterion layer, the weights for geological environment, inducing factors, and historical disasters are 0.2793, 0.2585, and 0.0867, respectively; in the scheme layer, the cumulative thickness of soft soil, compression coefficient, cumulative thickness of aquifer, groundwater depth, groundwater extraction intensity, superstructure load, cumulative settlement, settlement rate, and building tilt are 0.1037, 0.2041, 0.0680, 0.0527, 0.3673, 0.0612, 0.0613, 0.0205, and 0.0612, respectively.

[0048] Furthermore, geological environment, inducing factors, and historical disasters were selected as primary indicators for this ground subsidence risk assessment; nine factors were selected as secondary indicators: cumulative soft soil thickness, compression coefficient, cumulative aquifer thickness, groundwater level depth, groundwater extraction intensity, superstructure load, cumulative settlement, settlement rate, and building tilt degree. In step S4, based on PS-InSAR technology, the inverse distance weighted interpolation method and reclassification tool in ArcGIS software were used to draw corresponding images of the secondary indicators to evaluate the ground subsidence risk; when drawing the images using the reclassification tool, the classification standards in the table of risk classification and value standards for urban geological safety risk assessment index factors were used.

[0049] Furthermore, for the secondary indicators, the analytic hierarchy process (AHP) combined with the comprehensive index method, along with the weights calculated in S2, was used. The grid calculation tool in ArcGIS software was then used to overlay different evaluation factors in the study area according to the model in formula (4.1). Finally, the hazard assessment zoning map and zoning attribute table for the ground subsidence of the study area were obtained. The formula (4.1) is shown below:

[0050]

[0051] In the formula: n = 9, which is the number of secondary indicators for the assessment of ground subsidence risk;

[0052] R: Comprehensive index for assessing ground subsidence risk;

[0053] M: The scale value of the ground subsidence risk assessment index;

[0054] Wi is the weight value of the i-th evaluation factor.

[0055] Furthermore, based on the hazard assessment results obtained in step S4, areas with significant potential for ground subsidence within the study area were selected as monitoring point deployment areas. Groundwater level drawdown, cumulative subsidence, and building tilt were used as monitoring parameters. Specifically, when the cumulative subsidence is less than 50mm, the risk is low, and no warning is required; when the cumulative subsidence reaches 50mm to 100mm, a yellow warning is issued, indicating a moderate risk; when the cumulative subsidence is between 100mm and 150mm, an orange warning is issued, indicating a relatively high risk; and when the cumulative subsidence reaches 150mm or more, a red warning is issued, indicating a very high risk. In other words, when the groundwater level drawdown is less than (62.04-3.15h') / 50m, the risk is low, and no warning is required; when the groundwater level drawdown reaches (62.04-3.15h') / 50m to (62.04-3.15h') / 50m, the risk is high, and no warning is required. A yellow alert is issued when the groundwater level drawdown is between (62.04-3.15h') / 100m and (62.04-3.15h') / 150m, indicating a moderate risk. An orange alert is issued when the groundwater level drawdown is between (62.04-3.15h') / 100m and (62.04-3.15h') / 150m, indicating a high risk. A red alert is issued when the groundwater level drawdown is 62.04-3.15h') / 150m or higher, indicating a high risk. When the building tilt is less than 0.0002°, the risk is low and no warning is needed. A yellow alert is issued when the building tilt is between 0.0002° and 0.00025°, indicating a moderate risk. An orange alert is issued when the building tilt is between 0.00025° and 0.00225°, indicating a relatively high risk. A red alert is issued when the building tilt is 0.00225° or higher, indicating a high risk.

[0056] Furthermore, the method for calculating the groundwater level drawdown is as follows:

[0057] y = -3.15x 2 +62.047x-152.22(5.1)

[0058] In the formula, x represents the depth of the groundwater level; y represents the cumulative settlement.

[0059] Let h1 be the groundwater level at time t1, and h2 be the groundwater level at time t2, where h2 > h1. Substitute h1 and h2 into the above...

[0060] After subtracting from Equation 5.1, the groundwater drawdown H at a certain location in the study area from time t1 to time t2 can be derived as follows:

[0061]

[0062] In the formula, H represents the drawdown of the groundwater level from time t1 to time t2. When a = 0, H is taken as 0m.

[0063] h1: Indicates the depth of the groundwater level at time t1;

[0064] h2: indicates the depth of the groundwater level at time t2;

[0065] a: represents the cumulative settlement from time t1 to time t2;

[0066] h': represents the sum of the groundwater level at time t1 (h1) and the groundwater level at time t2 (h2), i.e., h' = h1 + h2.

[0067] Furthermore, the control measures in step S5 include avoidance measures, engineering protection, monitoring measures, and the establishment of a community-based prevention system; wherein the avoidance measures include using areas with medium or high risk and no buildings on the ground for the construction of parks and green spaces; for areas with medium or high risk and buildings, measures should be taken to monitor them in real time, and relocation measures should be taken when the situation is serious; the engineering protection includes strictly controlling the extraction and use of groundwater, and artificial groundwater recharge and artificial backfilling can be used when necessary.

[0068] The present invention has the following advantages over the prior art:

[0069] This invention integrates relevant industry standards and specifications to construct an index system for urban geological safety hazard assessment, particularly for land subsidence. It also classifies and standardizes the hazard levels of each assessment factor. Next, using a hierarchical analysis combined with expert scoring, the index weights of various disaster-causing bodies are obtained. Based on this, by analyzing the geological environmental characteristics of the study area, a three-dimensional model is used to reveal the hidden strata. Then, ArcGIS software is used to perform a hazard assessment, yielding accurate results. Finally, monitoring, early warning, and control methods are proposed for the aforementioned disaster-causing bodies. Attached Figure Description

[0070] Figure 1 This is a flowchart of the chromatography method described in an embodiment of the present invention;

[0071] Figure 2 This is a schematic diagram of the ground subsidence risk assessment index system described in an embodiment of the present invention;

[0072] Figure 3 This is a weighted bar chart of the secondary indicators for land subsidence risk assessment as described in an embodiment of the present invention.

[0073] Figure 4This is a distribution map of cumulative variables in the study area described in this embodiment of the invention;

[0074] Figure 5 This is a distribution map of the annual average deformation rate in the study area described in this embodiment of the invention;

[0075] Figure 6 This is a map showing the distribution of soft soil thickness in the study area described in this embodiment of the invention.

[0076] Figure 7 This is a classification diagram of the soft soil thickness in the study area described in this embodiment of the invention;

[0077] Figure 8 This is a distribution map of the compressibility coefficient of soft soil in the study area described in this embodiment of the invention;

[0078] Figure 9 This is a classification diagram of the compressibility coefficient of soft soil in the study area described in this embodiment of the invention;

[0079] Figure 10 This is a plan view showing the cumulative thickness distribution of the aquifer in the study area described in this embodiment of the invention.

[0080] Figure 11 This is a classification map of the cumulative thickness of the aquifer in the study area described in this embodiment of the invention;

[0081] Figure 12 This is a map showing the distribution of groundwater depth in the study area described in this embodiment of the invention.

[0082] Figure 13 This is a classification map of groundwater depth in the study area described in this embodiment of the invention;

[0083] Figure 14 This is a distribution map of groundwater extraction intensity in the study area described in this embodiment of the invention.

[0084] Figure 15 This is a risk classification map of groundwater extraction intensity in the study area described in this embodiment of the invention;

[0085] Figure 16 This is a load hazard classification diagram of the superstructure in the study area described in this embodiment of the invention;

[0086] Figure 17 This is a distribution map of the cumulative settlement in the study area described in this embodiment of the invention;

[0087] Figure 18 This is a risk classification map of cumulative settlement in the study area described in this embodiment of the invention;

[0088] Figure 19 This is a hazard classification map of the settlement rate in the study area described in this embodiment of the invention;

[0089] Figure 20This is a zoning map of the study area for assessing the risk of ground subsidence, as described in this embodiment of the invention. Detailed Implementation

[0090] In order to make the technical means, creative features and objectives of the present invention easy to understand, the technical solution of the invention will be further explained below with reference to one embodiment and specific implementation method of the ground subsidence evaluation and early warning control method provided by the present invention.

[0091] like Figure 1-20 As shown, specific embodiments of the invention are given below:

[0092] A method for land subsidence assessment and early warning control includes the following steps:

[0093] S1. Determine evaluation factors and establish a land settlement safety hazard evaluation index system. The evaluation index system is constructed using the analytic hierarchy process (AHP) and expert scoring. The AHP mainly decomposes a complex system into target, criterion, and scheme layers. By setting up a matrix, the expert scoring method is used to construct pairwise comparison judgment matrices, calculate the weights of each index, and verify their consistency. When the consistency test fails, the matrix is ​​adjusted until the consistency test passes, thereby reducing errors caused by subjective factors. The specific steps of the method are as follows: Figure 1 As shown.

[0094] The analytic hierarchy process (AHP) decomposes the system into a target layer, a quasi-measurement layer, and a scheme layer. The target layer is the ground settlement hazard assessment index system. The quasi-measurement layer includes the geological environment, inducing factors, and historical disaster information. The geological environment scheme layer includes the cumulative thickness of soft soil, compressibility coefficient, cumulative thickness of aquifer, and groundwater level depth. The inducing factors scheme layer includes the intensity of groundwater extraction and the load of the superstructure. The historical disaster information scheme layer includes the cumulative settlement, settlement rate, and building tilt.

[0095] (1) Geological Environment: Soft soil has a high porosity and high compression modulus, making it the most prone to settlement in land subsidence. However, the settlement amount is also affected by the cumulative thickness of soft soil. Generally speaking, land subsidence is positively correlated with the cumulative thickness of soft soil; therefore, the cumulative thickness of soft soil is listed as one of the evaluation indicators. According to the "Specification for Land Subsidence Investigation and Monitoring" (DZT0283-2015), the cumulative thickness of soft soil in the land subsidence hazard assessment is standardized in terms of hazard classification and value, as shown in Table 2.22:

[0096]

[0097] The high void ratio and compressibility of soft soil are often contributing factors to ground settlement. To quantitatively describe these characteristics, the compressibility coefficient was selected as one of the indicators for assessing the risk of ground settlement. Based on relevant industry standards and literature, the compressibility coefficient was standardized in terms of risk classification and value, as shown in Table 2.23 below.

[0098] Table 2.23 Classification of Compression Coefficient Index

[0099]

[0100] In geology, the saturated layer below the aeration layer of soil is called an aquifer. Groundwater has a significant impact on land subsidence, and the cumulative thickness of an aquifer reflects the groundwater reserves to some extent; therefore, it can be used as one of the indicators for assessing land subsidence risk. Based on relevant standards and literature, the cumulative thickness of aquifers has been standardized in terms of risk classification and value, as shown in Table 2.24 below:

[0101] Table 2.24 Classification of Cumulative Aquifer Thickness Index

[0102]

[0103] Generally speaking, in areas with shallow groundwater levels, the soil particles are less consolidated and dense, making them more prone to ground subsidence under the compression of tall buildings. Conversely, in areas with deep groundwater levels, the soil particles are more consolidated and dense, making ground subsidence less likely under the compression of tall buildings. Therefore, groundwater level depth should be considered as one of the indicators for assessing the risk of ground subsidence.

[0104] Referring to the quantitative standards for groundwater level in the "Code for Geological Investigation of Urban and Rural Planning" (CJJ 57—2012), the groundwater level depth index in the land subsidence risk assessment is standardized for risk classification and value taking according to Table 2.25 below:

[0105] Table 2.25 Classification of Groundwater Depth Indicators

[0106]

[0107] (2) Inducing factors: Based on relevant literature, regional experience and expert opinions, the groundwater level mining intensity index in the risk assessment of ground subsidence and karst collapse is standardized for risk classification and value taking according to Table 2.26 below.

[0108] Table 2.26 Classification of Groundwater Extraction Intensity Indicators

[0109]

[0110] Therefore, the load of the superstructure should be included as one of the indicators for assessing the risk of ground settlement. According to the "General Code for Design of Civil Buildings" (GB 50352—2005) and the "Engineering Geology Handbook" (Fifth Edition), following the principle of the most dangerous scenario, the load of a single-story building is taken as 20 kPa (usually 15–20 kPa). However, the grading and quantification of the superstructure load index can be indirectly reflected by the number of building stories. Therefore, the superstructure load index in the assessment of ground settlement risk can be standardized for hazard classification and value taking according to Table 2.27 below.

[0111] Table 2.27 Classification of Load Indicators for Superstructure

[0112]

[0113] (3) Historical Disaster Status; This paper summarizes the cumulative settlement and settlement rate of ground subsidence into the historical disaster status, which represents the settlement status that occurred before this. According to the scale level classification of the "Technical Requirements for Design of Ground Subsidence Prevention Engineering" (Trial) and the allowable value of foundation deformation of buildings in the "Code for Design of Building Foundation" (GB50007-2011), combined with expert opinions, and in accordance with the principle of the most dangerous, the two indicators of cumulative settlement and settlement rate under the historical disaster status in the risk assessment of urban ground subsidence are standardized in terms of risk classification and value selection, as shown in Table 2.28.

[0114] Table 2.28 Classification of Ground Subsidence Scale Indicators

[0115]

[0116] Ground subsidence can cause buildings to tilt to some extent. Considering that the current building tilt is caused by past ground subsidence, this article also includes the building tilt degree in the historical disaster situation of ground subsidence.

[0117] According to the overall tilt of multi-story and high-rise buildings in the "Code for Design of Building Foundations" (GB5007-20), and in conjunction with expert opinions and relevant references, the overall tilt of multi-story and high-rise buildings is divided into four levels: large, relatively large, medium and small, as shown in Table 2.29. Then, the building tilt index in the ground settlement risk assessment is further standardized in terms of risk classification and value, as shown in Table 2.30.

[0118] Table 2.29 Overall Inclination of Multi-story and High-rise Buildings

[0119]

[0120] Table 2.30 Classification of Building Tilting Degree Indicators

[0121]

[0122] Indicator system such as Figure 2 As shown, the hazard classification and value standards of each factor under the hazard assessment index system are summarized in Table 2.46:

[0123]

[0124] S2. Calculate the weights of each evaluation factor in the evaluation index system, and classify and standardize the evaluation factors. When calculating the weights, construct a pairwise comparison judgment matrix using expert scoring by setting up a matrix, calculate the weights of each indicator, and check their consistency. If the consistency check fails, adjust the matrix again until the consistency check passes. Specifically, this includes the following steps:

[0125] S2.1. Based on the actual situation, the types of geological disasters, and their specific influencing factors, select easily obtainable and quantifiable indicators, and combine them into a set:

[0126] X = {X1, X2, X3, X4, X5}

[0127] S2.2 From the established indicator system, various evaluation indicator factors at the same level are selected based on different perspectives and degrees of importance to construct a discriminant construction matrix as shown in formula (2.3), which mainly represents the relative importance between the various indicators:

[0128]

[0129] In the formula: R ij —This indicates the relative importance of element i to element j under certain conditions. The relative importance of the indicator is determined by quantifying the indicator through expert scoring.

[0130] For example, R ij =1 indicates factor X i With X j Equally important;

[0131] For example, R ij =3 indicates factor X i Compared to X j Slightly important;

[0132] For example, R ij =5 indicates factor X i Compared to X j Quite important;

[0133] For example, R ij =7 indicates factor X i Compared to X j Much more important;

[0134] For example, R ij =9 indicates factor X i Comparison is extremely important;

[0135] For example, R ij =2,4,6,8 represent the intermediate values ​​of adjacent judgments 1 to 3, 3 to 5, 5 to 7, and 7 to 9, respectively;

[0136] The reciprocal of X i With X j Comparison, X j Compared to X i The degree of importance;

[0137] S2.3 Calculate the importance ranking and weights. Through the judgment matrix, calculate the eigenvector corresponding to the largest eigenvalue of T, and normalize it to obtain the weights of the indicator factors. Finally, sort them according to the relative weights of each indicator factor to obtain the main factors, general factors and minor factors. The factor weight calculation formula is shown in (2.4) below:

[0138]

[0139] S2.4 Consistency test of evaluation index weights: Since the expert scoring method is subjective, in order to make the results more effective, the eigenvectors obtained by the constructed judgment matrix need to be tested for consistency and randomness. The formula is as follows (2.5):

[0140] CR = CI / RI (2.5)

[0141] In the formula: CR is the random consistency ratio of the judgment matrix; CI is the consistency index of the judgment matrix; its calculation formula is shown in Figure 2.6 below:

[0142]

[0143] In the formula: λmax is the maximum feature, and its calculation formula is shown in (2.7) below:

[0144]

[0145] In the formula: (TA)i represents the i-th element of vector TA, and its expression is as shown in (2.8):

[0146]

[0147] In the formula: m — is the order of the judgment matrix; RI is the average random consistency index of the judgment matrix, obtained from a large number of experiments. For low-order judgment matrices, RI can be selected according to the following correspondence:

[0148] In order m, 1 to 11 correspond to RI values ​​of 0.00, 0.00, 0.58, 0.90, 1.12, 1.24, 1.32, 1.41, 1.45, 1.49, and 1.51, respectively. If CR ≤ 0.1, the consistency test is considered to have passed, indicating that the weight allocation is reasonable. Otherwise, the judgment matrix needs to be readjusted until CR ≤ 0.1.

[0149] Using the yaahp auxiliary software, the hierarchical analysis model was first constructed. Next, expert scoring was used to input the judgment matrix data. Then, weights were calculated and consistency checks were performed until CR ≤ 0.1. Finally, the weight calculation results of the indicator factors for each disaster-causing entity were visually displayed in a chart.

[0150] (1) Calculation results of criterion layer weights; Ground subsidence risk assessment: λ max =3.0000; CR≤0.1; the random consistency test passed, indicating that the weight values ​​are reasonable, see Table 2.64:

[0151] Table 2.64 Calculation Results of Criterion Layer Weights for Ground Settlement Risk Assessment Index System

[0152]

[0153] (2) Calculation results of scheme layer weights; Geological environment: λ max =4.2542; CR = 0.0952 ≤ 0.1; the random consistency test passed, indicating that the weight values ​​are reasonable, see Table 2.65:

[0154] Table 2.65 Calculation Results of Geological Environment Scheme Layer Weights

[0155]

[0156] Triggering factors: λ max =2.0000; CR = 0.0000 ≤ 0.1; The random consistency test passed, indicating that the weight values ​​are reasonable, see Table 2.66:

[0157] Table 2.66 Results of Calculation of Layer Weights for Inducing Factor Schemes

[0158]

[0159] Historical subsidence status: λ max =3.000; CR = 0.0000 ≤ 0.1; The random consistency test passed, indicating that the weight values ​​are reasonable, see Table 2.67:

[0160] Table 2.67 Calculation Results of Layer Weights for Historical Settlement Scheme

[0161]

[0162] (3) Summary of weight calculation results; Based on the weight calculation results, the weights of the ground settlement index are summarized in Table 2.68. At the same time, the weights of the index factors at the scheme level are compared, such as... Figure 3 As shown:

[0163] Table 2.68 Summary of Calculation Results of Weights for Ground Settlement Risk Assessment Indicators

[0164]

[0165] Based on the ArcGIS software platform's hazard zoning module, the hazard level intervals for the single-factor and comprehensive evaluations in the geological safety assessment of the study area were classified using the equal interval method, as shown in Table 2.81:

[0166] Table 2.81 Hazard Level Range Classification

[0167]

[0168] S3. Investigate the geological conditions of the study area, collect data from the study area, and use a three-dimensional visual transparent model to reveal the distribution of geological and soil layer hazards of the disaster-causing body.

[0169] The collected information includes meteorological and hydrological data, topography, stratigraphy and lithology, hydrogeological conditions, geological structure, and seismic activity, in order to study the characteristics of land subsidence development in the region.

[0170] (1) Selection of data source

[0171] Fifteen Sentine-1A images, taken between October 26, 2019 and December 26, 2021, in interferometric Wid swath (IW) imaging mode, were used. These images were in the C-band and had a resolution of 14m, as shown in Table 3.3. Additionally, the DEM elevation data in this paper were derived from SRTM1 data, with an accuracy of 30m.

[0172] Table 3.3 Sentinel-1A dataset information for the study area

[0173]

[0174] (2) Data processing

[0175] The above uses Sentinel-1A to acquire 15 images. Here, the image with the code 20191026 is first selected and matched with the other images for interferometric pairing. Then, differential interferometry is performed. After generating the interferogram through differential calculation, the flat phase is removed using the DEM elevation data obtained from SRTM1. The next step is to obtain the deformation rate and residual topography through deformation inversion. Then, the final deformation rate is inverted based on atmospheric phase estimation. Finally, geocoding is performed to transform the image coordinate system from the radar coordinate system to the geographic coordinate system. Figure 4 and Figure 5 These are the cumulative deformation map and the annual average deformation rate map of the ground subsidence in the study area from October 26, 2019 to December 26, 2021, obtained by processing PS-InSAR technology.

[0176] (3) Characteristics of ground subsidence development in the study area

[0177] pass Figure 4 and Figure 5 It can be seen that most of the surface deformation areas in the study area can be effectively monitored. Only a small number of areas have surface deformation and deformation rate that cannot be monitored. This is because these areas have lakes, forests, etc., and their coherence is low, making it impossible to obtain accurate surface deformation and deformation rate data, thus creating a monitoring blind spot. Numerically, the cumulative deformation range in the study area is 0–76 mm, and the annual average deformation is 0–68 mm / a. Spatially, monitoring in the urban area is almost complete, and the coherence is good. The cumulative deformation in most areas is 38–47 mm, and the deformation rate is 29–34 mm / a. A monitoring blind spot appears near area F, mainly because there are water bodies in this area, which have low coherence and affect the acquisition of monitoring data.

[0178] (4) Analysis of soil layers with potential geological hazards in the study area

[0179] Soft soil is the most significant soil layer causing land subsidence, and the organic soil in the study area is classified as soft soil. Using extensive geological data, including drilling and geophysical data, the soft soil layer was identified through EVS software modeling. (Combined with the above...) Figure 4 and Figure 5 The settlement characteristics reveal that areas with soft soil may pose a relatively high risk, while settlement in other areas may be influenced by the thickness of the aquifer or other related factors. Therefore, based on the ground settlement characteristics and potential geological hazards, a comprehensive risk assessment of ground settlement in the study area should be conducted.

[0180] S4. Use software to assess the risk of ground subsidence in the study area and determine its risk level and zoning.

[0181] The specific steps are as follows:

[0182] S4.1 First, determine the evaluation units and then divide the evaluation units into grids;

[0183] S4.2 Secondly, based on the actual data of the study area, the evaluation factors of the disaster-causing bodies were vectorized and normalized respectively. For some evaluation factors, the inverse distance weighted interpolation method and Kriging interpolation method in ArcGIS software were used for analysis.

[0184] S4.3 Next, the calculated weights are assigned to each evaluation factor, and the ArcGIS spatial analysis function is used to perform spatial overlay analysis on each evaluation index. The comprehensive risk index is calculated based on the discriminant of the hazard assessment of the disaster-causing body.

[0185] S4.4 Finally, the comprehensive risk index evaluation results are reclassified and assigned different colors to obtain the risk evaluation zoning map of each disaster-causing body.

[0186] Geological environment, inducing factors, and historical disasters were selected as primary indicators for this ground subsidence risk assessment. Nine factors were selected as secondary indicators: cumulative soft soil thickness, compressibility coefficient, cumulative aquifer thickness, groundwater level depth, groundwater extraction intensity, superstructure load, cumulative settlement, settlement rate, and building tilt degree. In step S4, PS-InSAR technology was used, along with the inverse distance weighted interpolation method and reclassification tool in ArcGIS software, to plot the corresponding images of the secondary indicators and evaluate the ground subsidence risk. The reclassification tool was used to plot the images according to the classification standards in the table of urban geological safety risk assessment index factor risk classification and value standards.

[0187] (1) Cumulative thickness of soft soil

[0188] Using detailed borehole data from the study area, the distribution of soft soil thickness was plotted using the inverse distance weighted interpolation method in ArcGIS software, as shown in the figure. Figure 6 As shown in the distribution map, soft soil is relatively scarce in the area, mainly distributed around point D, with a maximum thickness of 5.1m. A small amount is distributed northwest of point A, with a maximum thickness of 2.1m. Using ArcGIS reclassification, the soft soil thickness in the study area was divided into four categories according to the standards in Table 2.46: low risk (<10m), medium risk (10–20m), relatively high risk (20–30m), and high risk (>30m). Figure 7 The soft soil thickness classification shows that the soft soil thickness in the study area is <10m, therefore, the risk level is low.

[0189] (2) Compression coefficient

[0190] The compressibility coefficient of soil has a significant impact on the amount of compression. Generally speaking, a larger compressibility coefficient results in a larger amount of compression, and vice versa. Using borehole data from the study area and the inverse distance weighted interpolation method in ArcGIS software, a clear and intuitive distribution map of the compressibility coefficient of soft soil was created, as shown below. Figure 8 As shown. Simultaneously, according to the classification criteria in Table 2.46 of Chapter 2, the hazard classification is performed using the "Reclassification" tool in ArcGIS, such as... Figure 9 As shown in the figure, the soil north of point D has a high compressibility coefficient, but its area is not large; the southwest and northeast of the study area have a low risk level.

[0191] (3) Cumulative thickness of aquifer

[0192] Based on the detailed borehole data collected in the study area, the cumulative thickness distribution of aquifers in the study area was visually plotted using the inverse distance weighted interpolation method in ArcGIS software, as shown below. Figure 10 As shown in the figure, the cumulative aquifer thickness is relatively thin in most areas, with only a few areas having a deeper cumulative aquifer thickness, ranging from 0 to 18 m. The relatively thicker aquifers are mainly distributed southeast of point B, point H, and the southern part of the study area. Using ArcGIS reclassification, the cumulative aquifer thickness in the study area is divided into four categories according to the classification criteria in Table 2.46: low risk (<5 m), medium risk (5–10 m), relatively high risk (10–15 m), and high risk (>15 m), as follows: Figure 11 As shown, they account for 53.1008%, 36.3277%, 9.8279%, and 0.7436% of the study area, respectively, with an area of ​​22.7531 km². 2 15.5648km 2 4.2108km 2 0.3186km 2 .

[0193] (4) Groundwater level depth

[0194] Detailed borehole data of groundwater level depth were obtained within the study area. Using the inverse distance weighting method in ArcGIS software, the distribution of groundwater level depth was visually plotted as a plan view, as shown below. Figure 12 As shown in the diagram, the groundwater level distribution map reveals that most areas have low groundwater levels, while a few areas have high groundwater levels. The minimum depth is 0m, and the maximum depth is 8.2m. Using ArcGIS reclassification, the groundwater level depth in the study area is classified into four categories according to hazard level: high hazard (<1m), relatively high hazard (1-3m), moderate hazard (3-6m), and low hazard (>6m), as follows: Figure 13As shown, they account for 27.6036%, 66.4548%, 5.2653%, and 0.6763% of the study area, respectively, with areas of 11.8269 km². 2 28.4729km 2 2.2560km 2 0.2898km 2 .

[0195] (5) Groundwater extraction intensity

[0196] Groundwater extraction intensity directly affects groundwater level changes and indirectly influences land subsidence. Generally speaking, with a fixed recharge intensity, the greater the groundwater extraction intensity, the faster the water level drops. When the water level drops, the pores in soil particles that were originally filled with water are compressed, eventually leading to land subsidence. Therefore, groundwater extraction intensity is used as one of the indicators for assessing the risk of land subsidence.

[0197] Within the study area, groundwater extraction is mainly concentrated on agricultural irrigation from the Quaternary loose strata's unconfined water table and drainage during building foundation excavation. This results in a distribution of groundwater extraction intensity that is weaker in the west and stronger in the east. Figure 14 As shown. Figure 14 According to the grading criteria in Table 2.46, the following is obtained: Figure 15 The hazard classification of groundwater extraction intensity shown indicates that groundwater extraction in the area exists at only three levels: high risk, medium risk, and low risk. The high-risk areas are mainly distributed near points B, D, H, G, and E; the low-risk areas are mainly in the northeast of point A and the southwest of the study area; the remaining areas are of medium risk.

[0198] (6) Load of the superstructure

[0199] Looking at the entire study area, high-rise buildings are relatively few, with most buildings not exceeding six stories, thus resulting in relatively low load-bearing capacity. High-rise and large buildings are mainly distributed in the northeast of point B, the northeast of point D, and the southeast of point H. These areas have a high concentration of high-rise buildings, resulting in high ground bearing capacity and therefore greater risk, as follows: Figure 16 As shown.

[0200] (7) Cumulative ground subsidence

[0201] Ground subsidence distribution obtained based on PS-InSAR technology and ArcGIS software is as follows: Figure 17As shown in the figure, the cumulative settlement in the study area is between 0 and 76 mm. There are some blank areas in the figure because these areas contain water bodies, woodlands, etc., which have low coherence and cannot be interpreted. Regardless of the amount of settlement, these areas have a very low impact on people and buildings, so they can be classified as low-risk areas.

[0202] Will Figure 17 According to the grading criteria in Table 2.46, the following is obtained: Figure 18 The cumulative settlement hazard classification shown in the figure indicates that most areas of the study area have a low cumulative settlement hazard, while areas with moderate hazard are scattered, mainly concentrated near points B, D, and H.

[0203] (8) Settling rate

[0204] The ground subsidence distribution in the study area obtained based on PS-InSAR technology and ArcGIS software is as follows: Figure 19 As shown in the figure, the ground subsidence rate in most areas is between 35 mm / a and 50 mm / a, with only a few areas experiencing subsidence greater than 50 mm / a. The most dangerous areas are mainly located south of point H.

[0205] (9) Building tilt

[0206] Ground subsidence can cause building tilting to some extent, and building tilting can indirectly reflect ground subsidence. Therefore, building tilt can be used as one of the indicators for assessing ground subsidence risk. During the field investigation in the study area, no building tilting caused by ground subsidence was found. Therefore, the building tilt index in the ground subsidence risk assessment can be generalized to 0, with a risk level of low.

[0207] For the secondary indicators, the analytic hierarchy process (AHP) combined with the comprehensive index method, along with the weights calculated in S2, was used. The grid calculation tool in ArcGIS software was then used to overlay different evaluation factors in the study area according to the model in formula (4.1). Finally, the hazard assessment zoning map and zoning attribute table for the ground subsidence of the study area were obtained. The formula (4.1) is shown below:

[0208]

[0209] In the formula: n = 9, which is the number of secondary indicators for the assessment of ground subsidence risk;

[0210] R: Comprehensive index for assessing ground subsidence risk;

[0211] M: The scale value of the ground subsidence risk assessment index;

[0212] Wi is the weight value of the i-th evaluation factor.

[0213] Finally, a zoning map and zoning attribute table for the risk assessment of ground subsidence in the study area were obtained, and the distribution is as follows: Figure 20 As shown in Table 4.1.

[0214] Table 4.1 Attribute Table of Each Zone in the Study Area for Ground Subsidence Risk Assessment

[0215]

[0216] (1) Low risk

[0217] pass Figure 20 As shown in Table 4.1, the area with low risk of ground subsidence in the study area is approximately 0.8082 km². 2 The area affected by groundwater subsidence accounts for approximately 1.8863%, mainly distributed in parts northeast of point A and parts southwest of the study area. These areas have low groundwater extraction intensity, limited cumulative soft soil thickness, low superstructure load, and relatively minor other factors. Considering the combined effects of all indicators, the risk of ground subsidence in this area is low.

[0218] (2) Moderate risk

[0219] pass Figure 20 As shown in Table 4.1, the area with a moderate risk of land subsidence in the study area is approximately 20.5635 km². 2 Approximately 47.9947% of the area is characterized by subsidence, primarily distributed along the concave section of the "G-E-B" line, excluding parts northeast of point A and parts southwest of the study area. Scattered subsidence also exists in the eastern part of the "B-D-H" line. These areas have relatively thin soft soil, low soil compressibility, small cumulative aquifer thickness, low groundwater extraction intensity, and numerous and old superstructures. The soil has reached a consolidation state under long-term compression from the superstructure loads. Considering all factors, the ground subsidence risk level in this area is classified as moderate.

[0220] (3) High risk

[0221] pass Figure 20 As shown in Table 4.1, the area with a relatively high risk of ground subsidence in the study area is approximately 21.3982 km². 2 This accounts for approximately 49.9429%, mainly distributed in the concave areas along the line from point G to point E to point B. The water table in this area is relatively shallow, and the intensity of groundwater extraction from the Quaternary loose strata is relatively high. Taking into account these two major factors and other factors affecting land subsidence, the land subsidence risk level in this area is considered high.

[0222] (4) High risk

[0223] pass Figure 20 As shown in Table 4.1, relative to the entire study area, the northeast side of point D has the greatest risk of ground subsidence, with an area of ​​approximately 0.07545 km². 2 The area accounts for approximately 0.1761% of the total. This region has a larger cumulative thickness of soft soil compared to other areas, a shallower groundwater level, a higher soil compressibility coefficient, and greater groundwater extraction intensity. Furthermore, the area is subject to heavy loads from the superstructure. Considering all these factors, the risk of ground subsidence in this region is high.

[0224] S5. Based on the evaluation results and evaluation factors in the indicator system, monitor and issue early warnings for key areas with geological hazards in the study area, and propose control measures. Based on the hazard assessment results obtained in step S4, select areas with high ground subsidence risks within the study area as monitoring point deployment areas.

[0225] The monitoring parameters are groundwater level drawdown, cumulative settlement, and building tilt. Specifically, when the cumulative settlement is less than 50mm, the risk is low and no warning is needed; when the cumulative settlement is between 50mm and 100mm, a yellow warning is issued, indicating a moderate risk; when the cumulative settlement is between 100mm and 150mm, an orange warning is issued, indicating a relatively high risk; and when the cumulative settlement is 150mm or more, a red warning is issued, indicating a very high risk. In other words, when the groundwater level drawdown is less than (62.04-3.15h') / 50m, the risk is low and no warning is needed; when the groundwater level drawdown is between (62.04-3.15h') / 50m and (62.04-3.15h') / 100m, a yellow warning is issued, indicating a moderate risk. When the groundwater level drawdown reaches between (62.04-3.15h') / 100m and (62.04-3.15h') / 150m, an orange alert is issued, indicating a relatively high risk. When the ground subsidence drawdown reaches (62.04-3.15h') / 150m or more, a red alert is issued, indicating a high risk. When the building tilt is less than 0.0002°, the risk is low and no warning is needed. When the building tilt is between 0.0002° and 0.00025°, a yellow alert is issued, indicating a moderate risk. When the building tilt is between 0.00025° and 0.00225°, an orange alert is issued, indicating a relatively high risk. When the building tilt is 0.00225° or more, a red alert is issued, indicating a very high risk.

[0226] The method for calculating the groundwater level drawdown is as follows:

[0227] y = -3.15x 2+62.047x-152.22(5.1)

[0228] In the formula, x represents the depth of the groundwater level; y represents the cumulative settlement.

[0229] Let h1 be the groundwater level at time t1, and h2 be the groundwater level at time t2, where h2 > h1. Substitute h1 and h2 into the above...

[0230] After subtracting from Equation 5.1, the groundwater drawdown H at a certain location in the study area from time t1 to time t2 can be derived as follows:

[0231]

[0232] In the formula, H represents the drawdown of the groundwater level from time t1 to time t2. When a = 0, H is taken as 0m.

[0233] h1: Indicates the depth of the groundwater level at time t1;

[0234] h2: indicates the depth of the groundwater level at time t2;

[0235] a: represents the cumulative settlement from time t1 to time t2;

[0236] h': represents the sum of the groundwater level at time t1 (h1) and the groundwater level at time t2 (h2), i.e., h' = h1 + h2.

[0237] According to the standard, the cumulative settlement amounts a1=0, a2=50, a3=100, and a4=150 for different risk levels are substituted into Equation 5.2 above to obtain the groundwater level drawdown warning thresholds for different risk levels as shown in Table 5.1 below.

[0238] Table 5.1 Land Subsidence Risk Early Warning Threshold Table

[0239]

[0240] The control measures in step S5 include avoidance measures, engineering protection, monitoring measures, and the establishment of a community-based prevention system. The avoidance measures include using medium- or high-risk areas without buildings on the ground for the construction of parks and green spaces. For areas with moderate or high risk and buildings, measures should be taken to monitor them in real time, and relocation measures should be taken when the situation is serious. The engineering protection measures include strictly controlling the extraction and use of groundwater, and artificial groundwater recharge and artificial backfilling can be used when necessary.

[0241] It should be understood that the specific embodiments described above are merely illustrative or explanatory of the principles of the present invention and do not constitute a limitation thereof. Therefore, any modifications, equivalent substitutions, improvements, etc., made without departing from the spirit and scope of the present invention should be included within the protection scope of the present invention. The appended claims are intended to cover all variations and modifications falling within the scope and boundaries of the appended claims, or equivalent forms of such scope and boundaries.

Claims

1. A method for evaluating and controlling ground subsidence, characterized in that, Includes the following steps: S1. Determine the evaluation factors and establish a ground subsidence safety hazard evaluation index system; S2. Calculate the weights of each evaluation factor in the evaluation index system, and classify and standardize the evaluation factors. S3. Investigate the geological conditions of the study area, collect data from the study area, and use a three-dimensional visual transparent model to reveal the distribution of geological and soil layer hazards of the disaster-causing body; S4. Use software to assess the risk of ground subsidence in the study area, and determine its risk level and zoning. S5. Based on the evaluation results and the evaluation factors in the indicator system, monitor and issue early warnings for key areas of geological hazards in the study area, and propose control measures.

2. The method for land subsidence assessment and early warning control as described in claim 1, characterized in that: The evaluation index system described in step S1 is constructed using the Analytic Hierarchy Process (AHP) and expert scoring. The AHP decomposes the system into a target layer, a quasi-measurement layer, and a scheme layer. The target layer is the land subsidence risk evaluation index system. The quasi-measurement layer includes geological environment, inducing factors, and historical disaster information. The geological environment scheme layer includes the cumulative thickness of soft soil, compressibility coefficient, cumulative thickness of aquifer, and groundwater level depth. The inducing factors scheme layer includes groundwater extraction intensity and the load of superstructures. The historical disaster situation plan includes the cumulative settlement, settlement rate, and building tilt.

3. The method for land subsidence assessment and early warning control as described in claim 2, characterized in that: In step S2, when calculating the weights, a pairwise comparison judgment matrix is ​​constructed using the expert scoring method by setting up a matrix. The weights of each indicator are calculated and their consistency is checked. If the consistency check fails, the matrix is ​​adjusted again until the consistency check passes. Specifically, the steps are as follows: S2.

1. Based on the actual situation, the types of geological disasters, and their specific influencing factors, select easily obtainable and quantifiable indicators, and combine them into a set: X = {X1, X2, X3, X4, X5} S2.2 From the established indicator system, various evaluation indicator factors at the same level are selected based on different perspectives and degrees of importance to construct a discriminant construction matrix as shown in formula (2.3), which mainly represents the relative importance between the various indicators: In the formula: R ij —This indicates the relative importance of element i to element j under certain conditions. The relative importance of the indicator is determined by quantifying the indicator through expert scoring. For example, R ij =1 indicates factor X i With X j Equally important; For example, R ij =3 indicates factor X i Compared to X j Slightly important; For example, R ij =5 indicates factor X i Compared to X j Quite important; For example, R ij =7 indicates factor X i Compared to X j Much more important; For example, R ij =9 indicates factor X i Comparison is extremely important; For example, R ij =2,4,6,8 represent the intermediate values ​​of adjacent judgments 1 to 3, 3 to 5, 5 to 7, and 7 to 9, respectively; The reciprocal of X i With X j Comparison, X j Compared to X i The degree of importance; S2.3 Calculate the importance ranking and weights. Through the judgment matrix, calculate the eigenvector corresponding to the largest eigenvalue of T, and normalize it to obtain the weights of the indicator factors. Finally, sort them according to the relative weights of each indicator factor to obtain the main factors, general factors and minor factors. The factor weight calculation formula is shown in (2.4) below: S2.4 Consistency test of evaluation index weights: Since the expert scoring method is subjective, in order to make the results more effective, the eigenvectors obtained by the constructed judgment matrix need to be tested for consistency and randomness. The formula is as follows (2.5): CR = CI / RI (2.5) Where: CR is the random consistency ratio of the judgment matrix; CI is the consistency index of the judgment matrix; its calculation formula is shown in 2.6 below: In the formula: λmax is the maximum feature, and its calculation formula is shown in (2.7) below: In the formula: (TA)i represents the i-th element of vector TA, and its expression is as shown in (2.8): In the formula: m — is the order of the judgment matrix; RI is the average random consistency index of the judgment matrix, obtained from a large number of experiments. For low-order judgment matrices, RI can be selected according to the following correspondence: In order m, 1 to 11 correspond to RI values ​​of 0.00, 0.00, 0.58, 0.90, 1.12, 1.24, 1.32, 1.41, 1.45, 1.49, and 1.51, respectively. If CR ≤ 0.1, the consistency test is considered to have passed, indicating that the weight allocation is reasonable. Otherwise, the judgment matrix needs to be readjusted until CR ≤ 0.

1.

4. The method for land subsidence assessment and early warning control as described in claim 3, characterized in that, The weight calculation results are as follows: In the criterion layer, the weights for geological environment, inducing factors, and historical disasters are 0.2793, 0.2585, and 0.0867, respectively; in the scheme layer, the cumulative thickness of soft soil, compression coefficient, cumulative thickness of aquifer, groundwater depth, groundwater extraction intensity, superstructure load, cumulative settlement, settlement rate, and building tilt are 0.1037, 0.2041, 0.0680, 0.0527, 0.3673, 0.0612, 0.0613, 0.0205, and 0.0612, respectively.

5. The method for land subsidence assessment and early warning control as described in claim 1, characterized in that: Geological environment, inducing factors, and historical disasters were selected as primary indicators for this ground subsidence risk assessment. Nine factors were selected as secondary indicators: cumulative soft soil thickness, compressibility coefficient, cumulative aquifer thickness, groundwater level depth, groundwater extraction intensity, superstructure load, cumulative settlement, settlement rate, and building tilt degree. In step S4, PS-InSAR technology was used, along with the inverse distance weighted interpolation method and reclassification tool in ArcGIS software, to plot the corresponding images of the secondary indicators and evaluate the ground subsidence risk. When using the reclassification tool to draw diagrams, the classification criteria in the table of risk classification and value standards for urban geological safety risk assessment index factors are used.

6. The method for land subsidence assessment and early warning control as described in claim 5, characterized in that: For the secondary indicators, the analytic hierarchy process (AHP) combined with the comprehensive index method, along with the weights calculated in S2, was used. The grid calculation tool in ArcGIS software was then used to overlay different evaluation factors in the study area according to the model in formula (4.1). Finally, the hazard assessment zoning map and zoning attribute table for the ground subsidence of the study area were obtained. The formula (4.1) is shown below: In the formula: n = 9, which is the number of secondary indicators for the assessment of ground subsidence risk; R: Comprehensive index for assessing ground subsidence risk; M: The scale value of the ground subsidence risk assessment index; Wi is the weight value of the i-th evaluation factor.

7. The method for land subsidence assessment and early warning control as described in claim 5, characterized in that: Based on the risk assessment results obtained in step S4, areas with high ground subsidence risk in the study area are selected as monitoring point deployment areas; groundwater level drawdown, cumulative subsidence, and building tilt are used as monitoring parameters; that is, when the cumulative subsidence is less than 50mm, the risk is low and there is no need to issue an early warning. A yellow alert is issued when the cumulative settlement is between 50mm and 100mm, indicating a moderate risk; an orange alert is issued when the cumulative settlement is between 100mm and 150mm, indicating a relatively high risk; and a red alert is issued when the cumulative settlement reaches 150mm or more, indicating a very high risk. In other words, when the groundwater level drawdown is less than (62.04-3.15h') / 50m, the risk is low, and no warning is needed; when the groundwater level drawdown reaches (62.04-3.15h') / 50m to (6... A yellow alert is issued when the groundwater level drawdown is between (62.04-3.15h') / 100m, indicating a moderate risk. An orange alert is issued when the drawdown reaches between (62.04-3.15h') / 100m and (62.04-3.15h') / 150m, indicating a high risk. A red alert is issued when the groundwater level drawdown reaches (62.04-3.15h') / 150m or higher, indicating a high risk. When the building tilt is less than 0.0002°, the risk is low, and no warning is required. A yellow alert is issued when the building's tilt is between 0.0002° and 0.00025°, indicating a moderate risk. An orange alert is issued when the building's tilt is between 0.00025° and 0.00225°, indicating a relatively high risk. A red alert is issued when the building's tilt is 0.00225° or higher, indicating a very high risk.

8. The method for land subsidence assessment and early warning control as described in claim 7, characterized in that: The method for calculating the groundwater level drawdown is as follows: y=-3.15x 2 +62.047x-152.22(5.1) In the formula, x represents the depth of the groundwater level; y represents the cumulative settlement. Let the groundwater level at time t1 be h1, and the groundwater level at time t2 be h2, where h2 > h1. Substituting h1 and h2 into Equation 5.1 above and subtracting them, we can derive the groundwater level drawdown H at a certain location in the study area from time t1 to time t2 as follows: In the formula, H represents the drawdown of the groundwater level from time t1 to time t2. When a = 0, H is taken as 0m. h1: Indicates the depth of the groundwater level at time t1; h2: indicates the depth of the groundwater level at time t2; a: represents the cumulative settlement from time t1 to time t2; h': represents the sum of the groundwater level at time t1 (h1) and the groundwater level at time t2 (h2), i.e., h' = h1 + h2.

9. The method for land subsidence assessment and early warning control as described in claim 1, characterized in that: The control measures in step S5 include avoidance measures, engineering protection, monitoring measures, and the establishment of a community-based prevention system. The avoidance measures include using medium- or high-risk areas without buildings on the ground for the construction of parks and green spaces. For areas with moderate or high risk and buildings, measures should be taken to monitor them in real time, and relocation measures should be taken when the situation is serious. The engineering protection measures include strictly controlling the extraction and use of groundwater, and artificial groundwater recharge and artificial backfilling can be used when necessary.

Images