A method for evaluating the risk of underground disease in loess

Abstract

The present invention provides a method for evaluating the risk of underground disease bodies in loess, comprising the following steps: constructing a development level index of an internal characteristic system and an external characteristic system; establishing an initial value evaluation system for each subsystem of the internal characteristic and the external characteristic; determining the weight of each indicator in the initial value evaluation system of each subsystem of the internal characteristic and the external characteristic based on an entropy weighting method, and determining the weight of each indicator of the subsystem after correcting the weight using expert experience analysis and a hierarchical analysis method; constructing a prediction model for the development coordination level of internal and external characteristics, determining the development coordination relationship of internal and external characteristics in different areas of the area to be evaluated; establishing an evaluation standard system for the coupling coordination level of internal and external characteristics, and evaluating the risk of disease bodies in the area to be evaluated. Based on the coupling synergy theory, a coupling coordination model of the underground disease body evaluation system is established, and the risk assessment of collapsible diseases and collapse diseases can provide support for the evaluation and prevention of underground disease bodies.

Description

Technical Field

[0001] The invention relates to the technical field of disease body hazard assessment, and in particular to a method for assessing the hazard of underground disease bodies in loess. Background Art

[0002] The traditional concept holds that the geological conditions in the disaster area as the internal characteristics and the external conditions such as rainfall that induce the disaster as the external characteristics are two relatively independent systems. Taking into account the influencing factors, causes and formation mechanisms of collapsing disasters and subsidence disasters, the internal characteristics of loess in the urban area of ​​Xining and the external characteristics such as rainfall conditions are the two important factors causing loess collapsing disasters and subsidence disasters, and the internal characteristics are the background factors. Especially for the loess collapsing disasters and subsidence disasters that occur frequently in the loess areas of my country, the internal characteristics of their occurrence are the result of long-term geological action and are relatively stable, while the external characteristics determine the possibility and start time of the occurrence of collapsing disasters and subsidence disasters, and are the key triggering conditions of the disasters. When evaluating the risk of loess collapsing disasters and subsidence disasters, the stimulating effect of the external characteristics should be emphasized. The existing technology lacks the consideration of the correlation between the internal and external characteristics. For this reason, the present invention proposes a new method for evaluating the risk of underground loess diseases. Summary of the invention

[0003] In order to solve the above problems, the present invention provides a method for evaluating the hazard of underground disease bodies in loess.

[0004] To achieve the above object, the present invention provides the following technical solutions.

[0005] A method for evaluating the risk of underground disease bodies in loess comprises the following steps:

[0006] According to the geological conditions of the area to be evaluated as the evaluation index of the internal characteristic system, and the external induced conditions as the evaluation index of the external characteristic system, the development level index of the internal characteristic system and the external characteristic system are constructed respectively;

[0007] According to the evaluation indexes of the internal and external characteristic systems, an initial value evaluation system for each subsystem of the internal and external characteristic systems is established;

[0008] Based on the entropy weighting method, the weights of each indicator in the initial value evaluation system of each subsystem of internal and external characteristics are determined, and the weights of each subsystem indicator are determined after the weights are modified using expert experience analysis and hierarchical analysis method;

[0009] Based on the development level index of the internal and external characteristic systems, a prediction model of the coordination level of the development of internal and external characteristics is constructed to determine the coordination relationship between the development of internal and external characteristics in different areas of the evaluated area;

[0010] According to the prediction model of the coordination level of the development of endogenous and exogenous characteristics, a standard system for the evaluation of the coupling coordination level of endogenous and exogenous characteristics is established, and the risk of disease bodies in the evaluation area is evaluated.

[0011] Preferably, the construction of the endogenous characteristic system development level model and the exogenous characteristic system development level model comprises the following steps:

[0012] Establish a two-level evaluation index system and select the internal characteristic system evaluation index u ij , external characteristic system evaluation index v ij Evaluate the internal and external characteristic development indexes.

[0013]

[0014]

[0015] In the formula, u i 、v i (i=1,2,…,n) are the i-th item and evaluation index of the internal characteristic system and the external characteristic system respectively; u ij 、v ij (i=1, 2, ..., n, j=1, 2, ..., m) are the jth secondary index of the i-th primary index of the internal characteristic system and the external characteristic system respectively;

[0016] Each evaluation index is divided into positive index and negative index, among which u' ij 、v' ij are the ordered efficacy coefficients of the endogenous characteristic system and the exogenous characteristic system, respectively, representing the variable u ij 、v ij The contribution value to the system's effectiveness reflects the degree of satisfaction with each influencing factor in achieving the goal. The value range is [0, 1], where 1 represents the most satisfactory and 0 represents the least satisfactory.

[0017] When u ij 、v ij When it is a positive indicator:

[0018]

[0019]

[0020] When u ij 、v ij When it is a negative indicator:

[0021]

[0022]

[0023] In the formula, The maximum contribution value of the jth secondary evaluation index of the i-th primary evaluation index to the system for the internal characteristic system and the external characteristic system respectively; The minimum efficacy contribution value of the jth secondary evaluation index of the i-th primary evaluation index of the internal characteristic system and the external characteristic system to the system respectively;

[0024] According to the ordered efficacy coefficients of the internal characteristic system and the external characteristic system, the internal characteristic system development level index UU and the external characteristic system development level index UV are used to evaluate the development level of the internal characteristic system and the external characteristic system respectively:

[0025]

[0026]

[0027] in,

[0028] λ i is the weight of the first-level indicator of item i, μ j is the weight of the j-th secondary indicator.

[0029] Preferably, the secondary index is calculated by using the entropy weighting method to calculate the index weights of each subsystem, and then the weights are corrected by expert experience analysis and hierarchical analysis to determine the weights of each subsystem index μ j .

[0030] Preferably, the geological conditions as the primary evaluation index of the internal characteristic system include: topography, stratum lithology, hydrogeological conditions and geological structure; the geological conditions as the secondary evaluation index of the internal characteristic system include: terrace type, relative position of disease, loess zoning, thickness, degree of wetting, permeability, internal friction angle, cohesion, groundwater burial position and earthquake fault;

[0031] The external induced conditions as the first-level evaluation indicators of the external characteristic system include: rainfall conditions, water collection conditions, leakage conditions, road surface load and underground voids; the external induced conditions as the second-level evaluation indicators of the external characteristic system include: average monthly rainfall, concentrated rainfall, local topography, structural layer type, surface water discharge, road surface cracks, underground pipeline leakage, underground structure of rainwater wells, green belt irrigation, urban road load, thickness of silt covering voids and water seepage, and air-raid shelters.

[0032] Preferably, the construction of the prediction model for the coordination level of the development of endogenous characteristics and exogenous characteristics comprises the following steps:

[0033] Establish a coupling degree model for the interaction between internal and external characteristics:

[0034]

[0035] Construct system coupling coordination function:

[0036] D=(CI·CEI) 1 / 2

[0037] T=α·UU+β·UV

[0038] Where: D is the system coupling coordination degree, T is the comprehensive coordination index of internal and external characteristics, reflecting the overall synergistic effect of the risk assessment system of underground disease bodies in loess; α and β are the unknown coefficients of contribution of the internal and external characteristics system.

[0039] Preferably, the contribution coefficients of the intrinsic characteristic system and the exogenous characteristic system are respectively: α=0.4, β=0.6.

[0040] Preferably, the establishment of a standard system for evaluating the coupling coordination level of endogenous characteristics and exogenous characteristics, and conducting a disease risk assessment on the area to be assessed, comprises the following steps:

[0041] According to the calculation result of the system coupling coordination degree D, the coordination level of the internal and external characteristics is divided into five levels, forming a system coupling coordination degree D index grading evaluation standard system for evaluation.

[0042] Beneficial effects of the present invention:

[0043] The present invention proposes a method for evaluating the risk of underground disease bodies in loess. In the underground disease body evaluation system, there are multiple correlations between the internal and external characteristics and related influencing factors, which promote and restrict each other and are coupled together into a complex, multi-level system. Based on the coupling synergy theory, the present invention establishes a coupling coordination model for the underground disease body evaluation system, and the risk assessment of collapsible diseases and collapse diseases can provide support for the evaluation and prevention of underground disease bodies, and can systematically, comprehensively and objectively evaluate risks. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a flow chart of the evaluation method of an embodiment of the present invention. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0046] Example 1

[0047] A method for evaluating the risk of underground disease bodies in loess according to the present invention is as follows: Figure 1 As shown,

[0048] The invention is further illustrated by taking the prediction of underground loess disease bodies occurring in the Nanshan Courtyard Community of the Mineral Resources Department at No. 17, Nanshan Road, Chengzhong District, Xining City, the east side road of Xiangtang Road, Chengdong District, and the old residential community at No. 5, Nanxiao Street, Chengdong District as examples.

[0049] S1: Based on the geological conditions of the area to be evaluated as the evaluation index of the endogenous characteristic system and the external induced conditions as the evaluation index of the exogenous characteristic system, the development level index of the endogenous characteristic system and the exogenous characteristic system are constructed respectively:

[0050] Establish a two-level evaluation index system, select the internal characteristic system evaluation index uij and the external characteristic system evaluation index v ij Evaluate the internal and external characteristic development indexes.

[0051]

[0052]

[0053] In the formula, u i 、v i (i=1,2,…,n) are the i-th item and evaluation index of the internal characteristic system and the external characteristic system respectively; u ij 、v ij (i=1, 2, ..., n, j=1, 2, ..., m) are the jth secondary index of the i-th primary index of the internal characteristic system and the external characteristic system respectively;

[0054] The evaluation indexes of loess collapsibility and collapse in Xining urban area are shown in Table 1 and Table 2 respectively.

[0055] Table 1 Evaluation indexes of loess collapsible diseases in Xining urban area

[0056]

[0057]

[0058] Table 2 Evaluation indexes of loess subsidence diseases in Xining urban area

[0059]

[0060]

[0061] Each evaluation index is divided into positive index and negative index, where u' ij 、v' ij are the ordered efficacy coefficients of the endogenous characteristic system and the exogenous characteristic system, respectively, representing the variable u ij、v ij The contribution value to the system's effectiveness reflects the degree of satisfaction with each influencing factor in achieving the goal. The value range is [0, 1], where 1 represents the most satisfactory and 0 represents the least satisfactory.

[0062] When u ij 、v ij When it is a positive indicator:

[0063]

[0064]

[0065] When u ij 、v ij When it is a negative indicator:

[0066]

[0067]

[0068] In the formula, The maximum contribution value of the jth secondary evaluation index of the i-th primary evaluation index to the system for the internal characteristic system and the external characteristic system respectively; The minimum efficacy contribution value of the jth secondary evaluation index of the i-th primary evaluation index of the internal characteristic system and the external characteristic system to the system respectively;

[0069] According to the ordered efficacy coefficients of the internal characteristic system and the external characteristic system, the internal characteristic system development level index UU and the external characteristic system development level index UV are used to evaluate the development level of the internal characteristic system and the external characteristic system respectively:

[0070]

[0071]

[0072] in,

[0073] λ i is the weight of the first-level indicator of item i, μ j is the weight of the j-th secondary indicator.

[0074] The secondary indicators are calculated by using the entropy weighting method to calculate the weights of each subsystem, and then the weights are modified by expert experience analysis and hierarchical analysis to determine the weights of each subsystem indicator μ j .

[0075] S2: Based on the evaluation indicators of the internal characteristic system and the external characteristic system, an initial value evaluation system for each subsystem of the internal characteristic and the external characteristic is established.

[0076] S3: Based on the entropy weighting method, the weights of each indicator in the initial value evaluation system of each subsystem of internal and external characteristics are determined, and the weights of each subsystem indicator are determined after the weights are corrected using expert experience analysis and hierarchical analysis method: The risk evaluation index systems of loess collapsible diseases and collapse diseases in Xining City are shown in Table 3 and Table 4 respectively:

[0077] Table 3 Evaluation index system of loess collapsible diseases in Xining urban area

[0078]

[0079]

[0080] Table 4 Evaluation index system of loess subsidence diseases in Xining urban area

[0081]

[0082]

[0083] S4: Based on the development level index of the internal and external characteristic systems, a prediction model for the coordination level of the development of internal and external characteristics is constructed to determine the coordination relationship between the development of internal and external characteristics in different areas of the evaluated area:

[0084] Establish a coupling degree model for the interaction between internal and external characteristics:

[0085]

[0086] Construct system coupling coordination function:

[0087] D=(CI·CEI) 1 / 2

[0088] T=α·UU+β·UV

[0089] In the formula: D is the system coupling coordination degree, T is the comprehensive coordination index of internal and external characteristics, reflecting the overall synergistic effect of the loess underground disease body hazard assessment system; α and β are the undetermined coefficients of the contribution of the internal and external characteristics system. This evaluation of the hazard of loess collapsible diseases and collapse-type diseases based on the coupling synergy theory comprehensively considers the influencing factors, causes and formation mechanisms of the occurrence of collapsible disasters and collapse-type disasters. The internal characteristics of loess in the urban area of ​​Xining and the external characteristics such as rainfall conditions are the two important factors causing loess collapsible disasters and collapse-type disasters, and the internal characteristics are background factors. Especially for the loess collapsible disasters and collapse-type disasters that occur more frequently in the loess areas of my country, the internal characteristics of their occurrence are the result of long-term geological action and are relatively stable, while the external characteristics determine the possibility and start time of the occurrence of collapsible disasters and collapse-type disasters, and are the key triggering conditions of the disasters. When evaluating the hazard of loess collapsible disasters and collapse-type disasters, the stimulating effect of external characteristics should be emphasized. Therefore, the contribution coefficients of the internal characteristic system and the external characteristic system are α=0.4 and β=0.6 respectively.

[0090] S5: Develop a coordination level prediction model based on the internal and external characteristics, establish a standard system for evaluating the coupling coordination level of internal and external characteristics, and conduct a disease risk assessment on the assessment area.

[0091] According to the calculation result of the system coupling coordination degree D, the coordination level of the internal and external characteristics is divided into five levels, forming a system coupling coordination degree D index grading evaluation standard system for evaluation.

[0092] T is the comprehensive coordination index of internal and external characteristics, reflecting the overall synergy of the total system. According to the calculation results of the D index, the coupling coordination value of the system is between [0, 1]. The ground settlement of collapsible loess will be controlled by multiple internal characteristic index factors such as topography, soil thickness, collapsibility coefficient, permeability, and soil shear strength. In addition, it will be affected by multiple external characteristic index factors such as rainfall conditions, leakage conditions, water catchment conditions, and underground cavities. Therefore, it is necessary to accurately judge its hazards and further analyze the possibility of causing accidents. There is no fixed pattern for the classification of the grade interval of the coupling coordination model. You can choose equal interval, quantile, geometric interval, standard deviation, and natural point discontinuity classification. Since the geometric interval method is a compromise of the other methods, it can ensure that the sum of squares of each type of elements is minimized and the range and value domain of each type of elements are consistent. Therefore, according to the calculation results and actual work experience, the geometric interval method is used to divide the types and grades of coupling coordination. According to the actual work experience and related research results in the references, the coupling coordination type and risk degree of the collapsible loess collapsible disease assessment system and the collapse disease assessment system are divided into five types respectively based on the degree of coupling coordination (see Tables 5 and 6).

[0093] Table 5 Coupling coordination types and risk classification of collapsible loess disease assessment system

[0094]

[0095] Table 6 Coupling coordination types and hazard classification of collapse loess collapse disease assessment system

[0096]

[0097]

[0098] In this embodiment:

[0099] The invention is further illustrated by taking the prediction of underground loess disease bodies occurring in the Nanshan Courtyard Community of the Mineral Resources Department at No. 17, Nanshan Road, Chengzhong District, Xining City, the road on the east side of Xiangtang Road, Chengdong District, and the old residential community at No. 5, Nanxiao Street, Chengdong District as examples. The following examples are only used to illustrate the invention but not to limit the invention.

[0100] By analyzing the topography, lithology and other geological conditions of the study area as endogenous characteristics, and rainfall conditions, leakage and other external induced conditions as exogenous characteristics, the development levels of the endogenous characteristic system and the exogenous characteristic system are evaluated respectively. In view of the complex nonlinear coupling relationship between the internal and external characteristics of collapsible diseases, the following comprehensive index evaluation system is constructed: (1) The establishment of the first-level index, with topography, stratum lithology, geological structure, and hydrogeological conditions as the first-level indicators of the internal characteristic subsystem; at the same time, rainfall conditions, water collection conditions, leakage conditions, and pavement structure are used as the first-level indicators of the external characteristic subsystem; (2) The second-level indicators of loess collapsible diseases in Xining City are based on the principles of representativeness, scientificity, and systematicity, referring to national standards such as "Building Code for Collapsible Loess Areas", "Geotechnical Engineering Survey Code", "Geological Survey Code for Water Conservancy and Hydropower Engineering", and the existing evaluation index system. 11 internal characteristic subsystems and 10 external characteristic subsystems are selected as second-level indicators; (3) The second-level indicators of loess collapse diseases in Xining City refer to the above principles and specifications to select 11 internal characteristic subsystems and 12 external characteristic subsystems as second-level indicators.

[0101] (1) Nanshan Garden of Geology and Mineral Resources

[0102] Taking the Dikuang Tingyuan as an example, a coupled coordinated hazard assessment was conducted. Based on the data provided by the Qinghai Hydrogeological Engineering Geological and Environmental Geological Survey Institute and existing literature, from the perspective of internal characteristics, the Dikuang Tingyuan community is located at the rear edge of the IV-level terrace of the Huangshui River, in the Q3 distribution area of ​​collapsible loess, and the thickness of the silt is relatively large, about 16.4m. The initial values ​​of the given topography, loess zoning, and thickness evaluation indexes are 0.75, 0.8, and 0.91, respectively. For the shear strength of the soil, from the physical and mechanical properties of the collapsible loess in Xining City, the internal friction angle of 20.2° and the cohesion of 17.4kPa were selected as the initial values ​​of the internal friction angle and cohesion index evaluation index of the soil, respectively. For the degree of collapse in the study area, the collapse coefficient is a good standard to measure its collapse degree. According to the data provided by the Institute of Water Conservancy, the collapse degree in the area is moderate collapse, and the permeability level is moderately permeable. Therefore, the initial value of the collapse degree evaluation index is given as 0.75, and the initial value of the permeability evaluation index is selected as 0.333. The groundwater depth of the Dikuang Tingyuan is about 21m, located below the silt layer, and there is no permeable layer such as gravel layer. Therefore, the initial value of the groundwater level buried position index is given as 1. Considering that the distance from the location of the study area to the fault structure is less than 300m, and the earthquake intensity at the location is set to 7 degrees, the initial values ​​of the fault evaluation index and the earthquake evaluation index are selected as 1 and 0.4 respectively.

[0103] From the perspective of external factors, the study area is located at No. 17, Nanshan Road, Chengzhong District, Xining City. Therefore, the rainfall in the area refers to the nearest rain gauge station to the study area: Xining Station. The initial value of the annual rainfall index is the multi-year average precipitation of 380.1 mm. August, when loess collapsible and subsidence disasters are more frequent in Xining City, is selected as the initial value of the monthly rainfall evaluation index. From the acquisition of meteorological data, the maximum rainstorm of 29.8 mm in 2017, which is the closest to the disaster time in the study area, is selected as the initial value of the concentrated rainfall evaluation index. The water source of the study area mainly comes from rainfall, and other extremely small amounts of external water sources have little impact on the study area. Therefore, the impact of rainwater on the study area is mainly considered, and the initial value of the external water source evaluation index is positioned at 0. The local terrain of the study area is relatively flat, and there are a few cracks in the concrete pavement structure. The upper fill is not completely compacted and compacted. The structure is loose, uneven, and not dense, which provides more convenient water collection conditions for rainwater to penetrate into the soil. In addition, there is a large area of ​​green belts near the study area, which provides good water collection and leakage conditions for rainwater and irrigation water. Therefore, the initial value of the local terrain index is set at 0.5, and the initial values ​​of the pavement structure layer type and pavement damage evaluation index are both 0.3. Combined with the irrigation volume of the green belt in the study area, the initial value of the given index is 0.333. The location with the largest collapse depth in the study area occurs in the irrigation water leakage area of ​​the green belt and around the drainage grate. In addition, the community was built earlier, and the underground water supply and drainage pipelines may be damaged. There is also the possibility that the structure under the drainage grate is damaged and cracks may form, which also creates infiltration conditions for surface water to penetrate into the soil. Considering that the rainwater well structure inside the community is mostly concrete, the initial values ​​of the underground pipeline leakage and drainage well leakage evaluation indicators are given as 0.15 and 0.2 respectively. For the location where the collapse disaster occurs, it is on the internal lane of the community and is an urban branch road, so the initial value of the road load index is set at 0.5.

[0104] The stability and safety of the road base will also show a decreasing trend with the increase of water seepage. The greater the water seepage, the higher the danger. In severe cases, it will cause the road to collapse. The safety of the road is also related to the thickness of the silt layer overlying the cavity. For underground cavities of the same size, the thinner the thickness of the silt layer overlying the cavity, the higher the danger. However, when the thickness of the overlying soil layer is large enough, under general infiltration conditions, the increase in water seepage has little effect on the soil at the top of the cavity. The thickness of the loess layer in the study area is large, which is consistent with the situation that the thickness of the silt layer is greater than 15m. Combined with the water seepage in the study area, the initial value of the silt thickness index over the cavity is given as 0.1. Considering that there is no record of air-raid shelters near the study area, the leakage of groundwater from the infiltration point in the community to the air-raid shelter can be basically ignored, so the initial values ​​of the evaluation indicators of the air-raid shelters are given as 0.

[0105] (2) Road east of Xiangtang Road

[0106] Taking the road on the east side of Xiangtang Road as an example, a coupled coordinated hazard assessment was conducted. Based on the data provided by the Qinghai Hydrogeological Engineering Geological and Environmental Geological Survey Institute and existing literature, Xiangtang Road is located at the rear edge of the IV-level terrace of the Huangshui River. The thickness of the silt is relatively large, about 17m, and the loess distribution area is located in Q3. The initial values ​​of the given topography, loess zoning, and thickness evaluation indexes are 0.75, 0.8, and 0.93, respectively. For the shear strength of the soil, the changes in the internal friction angle and cohesion of the silt are negatively correlated with the change trend of the ground settlement. As the internal friction angle and cohesion of the soil increase, the road settlement gradually decreases. From the physical and mechanical properties of the collapsible loess in Xining City, the internal friction angle of 20.2° and the cohesion of 17.4kPa were selected as the initial values ​​of the evaluation indexes of the internal friction angle and cohesion index of the soil, respectively. According to the data provided by the Institute of Water Conservancy, the area is moderately subsident and moderately permeable, so the initial value of the evaluation index for the degree of subsidence is 0.75, and the initial value of the evaluation index for permeability is 0.333. Considering that the location of the study area is more than 1200m away from the fault structure, it means that the fault has little impact on the occurrence of disasters in the study area, but the earthquake intensity at the location of the study area is 7 degrees, so the initial values ​​of the fault evaluation index and the initial values ​​of the earthquake evaluation index are selected as 0 and 0.4 respectively.

[0107] From the perspective of external factors, the study area is located on Xiangtang Road in Chengdong District and the road east of the south gate of Shengyuan Phase III. The rainfall in the area refers to the nearest rain gauge station to the study area: Xining Station. The initial value of the annual rainfall index is the multi-year average precipitation of 380.1 mm. August, when loess collapsible and subsidence disasters are more frequent in Xining City, is selected as the initial value of the monthly rainfall evaluation index. From the acquisition of meteorological data, the maximum rainstorm of 29.8 mm in 2017, which is the closest to the disaster time in the study area, is selected as the initial value of the concentrated rainfall evaluation index. In addition to atmospheric rainfall, the water source of the Xiangtang Road study area also has 6 rainwater pipes and 1 small box culvert on the small ridge behind the settlement area of ​​the study area. The distribution area of ​​ground settlement corresponds to the location of the rainwater pipe and the small box culvert. Therefore, external surface drainage such as rainwater pipes is also an important influencing factor for the occurrence of disasters. The initial value of the external water discharge evaluation index is 0.75. The most serious settlement of the disease point of Xiangtang Road extends to the periphery around a sunken rain grate as the center. The local terrain with concave terrain provides extremely good water collection conditions for the occurrence of wet collapse disasters. In addition, the road structure is a concrete pavement with many cracks on the pavement. Under good water collection conditions, it creates more convenient conditions for water to penetrate into the soil. Therefore, the initial values ​​of the local terrain condition evaluation index, the pavement structure layer type evaluation index, and the pavement damage evaluation index are given as 1, 0.3, and 0.6 respectively. The settlement of the study area extends to the periphery around a sunken rain grate and drainage well. Most of the nearby building types are early buildings. It is very likely that the structures under the rain grate and drainage well have been damaged and cracked. The rainwater drainage pipe under the rain grate may also be damaged. This provides convenient infiltration conditions for surface water to penetrate into the soil. In addition, the leakage of old underground rainwater pipelines will continue to aggravate the infiltration of surface water into the soil. Therefore, the pipeline type evaluation index and the rainwater well aging evaluation index are given as 0.3 and 0.5 respectively. Considering that Xiangtang Road is a secondary urban road and there are trees planted on the sidewalks, there will be a situation where the soil is not covered by a structural layer and the soil is directly exposed on the surface. Therefore, atmospheric rainfall and surface water drainage will directly infiltrate into the soil. Considering that the exposed area of ​​the soil in the green belt is not large and Xiangtang Road is a secondary urban road, the initial values ​​of the green belt irrigation water leakage evaluation index and the road load evaluation index are given as 0.167 and 0.65 respectively. The stability and safety of the road base are related to the seepage volume and the thickness of the overlying layer of the void. The greater the seepage volume, the higher the danger. For underground voids of the same size, the thinner the thickness of the overlying silt layer, the higher the danger. The thickness of the loess layer in the study area is relatively large, which is consistent with the situation that the thickness of the silt layer is greater than 15m. Combined with the seepage volume in the study area, the initial value of the overlying silt thickness index of the void is given as 0.1.Considering that there is no record of air-raid shelters near the study area, the leakage of groundwater from the infiltration points in the community to the air-raid shelters can be basically ignored, so the initial values ​​of the evaluation indicators of the air-raid shelters are given as 0.

[0108] (3) No. 5, Nanxiao Street

[0109] Taking No. 5 Courtyard of Nanxiao Street as an example, a coupled coordinated hazard assessment was conducted. According to the data provided by the Qinghai Hydrogeological Engineering Geological and Environmental Geological Survey Institute and existing literature, No. 5 Courtyard of Nanxiao Street is located at the rear edge of the second-level terrace of Huangshui River, in the collapsible loess zone. The thickness of the loess layer at the diseased point is not large, about 5m. The initial values ​​of the given topography, loess zoning, and thickness evaluation index are 0.25, 1, and 0.5, respectively. For the shear strength of the soil, the changes in the internal friction angle and cohesion of the silt are negatively correlated with the change trend of the ground settlement. As the internal friction angle and cohesion of the soil increase, the road settlement gradually decreases. From the physical and mechanical properties of the collapsible loess in Xining City, the internal friction angle of 20.2° and the cohesion of 17.4kPa are selected as the initial values ​​of the evaluation index of the internal friction angle and cohesion index of the soil, respectively. The degree of collapsibility in the area is medium, and the permeability grade is medium permeable. Therefore, the initial value of the evaluation index of the degree of collapsibility is given as 0.75, and the initial value of the evaluation index of the permeability is selected as 0.333. Since the groundwater in the study area is buried deep in the gravel layer, considering the good permeability of the gravel layer, the initial value of the evaluation index of the groundwater burial position is selected as 0. The disaster point is located less than 300m away from the fault structure, and the earthquake intensity at the location is set to 7 degrees. The initial values ​​of the fault evaluation index and the earthquake evaluation index are selected as 1 and 0.4 respectively.

[0110] Considering the external characteristics, the disease point of No. 5 courtyard of Nanxiao Street is located in an old residential area in the eastern part of the city. The rainfall in the area refers to the nearest rain gauge station to the study area: Xining Station. The initial value of the annual rainfall index is the multi-year average precipitation of 380.1 mm. The monthly rainfall of 77.6 mm in August, when loess collapsible and subsidence disasters are more frequent in Xining City, is selected as the initial value of the monthly rainfall evaluation index. From the acquisition of meteorological data, the maximum rainstorm of 29.8 mm in 2017, which is the closest to the disaster time in the study area, is selected as the initial value of the concentrated rainfall evaluation index. The diseases in No. 5 courtyard of Nanxiao Street mostly occur in the season of abundant rainfall from July to August. The occurrence of diseases is highly correlated with the infiltration of concentrated rainfall. In addition, the rainwater pipes around the disease points are directly discharged on the surface. Some damaged rainwater pipes are directly discharged from 2-3 m above the surface, but the water source of the disease points is mainly rainfall infiltration. The overall terrain in the No. 5 courtyard of Nanxiao Street is relatively flat, the pavement structure layer is a concrete structure, and there are many rainwater drainage wells in the community, which is more favorable for water to gather into the drainage wells. Therefore, the initial values ​​of the local terrain evaluation index, the initial values ​​of the pavement structure layer type evaluation index, and the initial values ​​of the external water discharge evaluation index are selected as 0.5, 0.3, and 0.75, respectively. Considering that there are many road damages in the community and many locations of concrete patching on the road surface, it can be judged that the road surface cracks are more serious, which provides convenient conditions for surface water to directly infiltrate the soil. There are a large number of rainwater drainage wells and sewage wells in the community. When the well covers are opened, it is found that the underground structure is a brick structure. Rainfall and surface water can penetrate into the soil through the cracks of the brick structure. Therefore, the initial values ​​of the underground pipeline leakage, pavement damage, and drainage well leakage evaluation index are given as 0.6, 0.6, and 0.65, respectively. The stability and safety of the road base will also show a decreasing trend with the increase of water seepage. The greater the water seepage, the higher the danger. In severe cases, it will cause road collapse. The stability and safety of the road base are related to the amount of water seepage and the thickness of the layer covering the void. The greater the water seepage, the higher the danger. For underground voids of the same size, the thinner the thickness of the overlying silt layer, the higher the danger. The thickness of the loess layer in the study area is not large, which is consistent with the situation when the thickness of the silt layer is 5m. The initial value of the silt thickness index overlying the void is given as 0.77. Because there is a gravel layer below the silt layer, the groundwater is shallow, and the burial depth of the nearby air-raid shelter is not large and the distance from the disaster point is far, the possible hydraulic gradient is small. Therefore, it is difficult for groundwater to leak from the infiltration point in the community to the air-raid shelter and hollow out the soil on the seepage path. Groundwater is more likely to infiltrate downward into the gravel layer. Considering that the disease is mainly distributed along the direction of the sewage pipe, it is highly correlated with the sewage pipe. The sewage pipe joint is damaged. During the infiltration process of the infiltrating water body, part of the water body enters the sewage pipe and hollows out the soil around the sewage pipe. In view of the above situation, the initial values ​​of the thickness index of the silt covering the cavity and the evaluation index of the air-raid shelter are given as 0.77 and 0 respectively.

[0111] Through the calculation of the D index of loess collapsible and subsidence diseases in Nanshan Courtyard, Xiangtang Road, and No. 5 Courtyard of Nanxiao Street in Xining City, it was found that the predicted values ​​were consistent with the on-site conditions. See Table 7 and Table 8.

[0112] Table 7 Evaluation results of the coordination level of internal and external factors of loess collapsible disease in No. 5 courtyard of Nanshan Courtyard, Xiangtang Road and Nanxiao Street, Xining City:

[0113]

[0114] According to the results of coupling coordination and hazard classification, it is concluded that the coupling coordination of loess collapsible diseases in the study areas of Nanshan Courtyard of Mineral Resources and Nanxiao Street No. 5 is moderately coupled, and the coupling coordination of loess collapsible diseases in the study area of ​​Xiangtang Road is highly coupled, and the occurrence of collapsible diseases should be monitored and prevented. The results show that the mutual promotion, coordinated evolution and weight of influencing factors between subsystems in the study areas of Nanshan Courtyard of Mineral Resources and Nanxiao Street No. 5 are moderate, but the coordination degree is acceptable, which may cause small-scale collapsible settlement in the loess area and cause ground subsidence. The interaction between subsystems in the study area of ​​Xiangtang Road is large, the system evolution is strong, the weight of influencing factors is large, the coupling coordination degree is high, and the probability of medium-scale collapsible disasters in the loess area is high, forcing ground subsidence. This is consistent with the actual situation. Therefore, the risk of loess collapsible diseases in the study area with high coupling and coordination is higher, and the risk of loess collapsible diseases in the study area with low coupling and coordination is lower. The risk of loess collapsible diseases in the study area shows good consistency with the coupling and coordination degree.

[0115] Table 8 Evaluation results of the coordination level of internal and external factors of loess collapse disease in Nanshan Courtyard, Xiangtang Road and No. 5 Nanxiao Street, Xining City:

[0116]

[0117]

[0118] According to the results of coupling coordination and hazard classification, it is concluded that the coupling coordination of loess collapse-type diseases in the study areas of Nanshan Courtyard and Xiangtang Road of the Mineral Resources Bureau is moderately coupled, and the coupling coordination of loess collapse-type diseases in the study area of ​​No. 5 Courtyard of Nanxiao Street is highly coupled. The occurrence of collapse-type diseases should be monitored and prevented. The results show that the mutual promotion, coordinated evolution and weight of influencing factors between subsystems in the study areas of Nanshan Courtyard and Xiangtang Road of the Mineral Resources Bureau are moderate, but the degree of coordination is acceptable, which may cause the formation of underground cavities in the loess area and cause ground collapse. The interaction between subsystems in the study area of ​​No. 5 Courtyard of Nanxiao Street is large, the system evolution is strong, the weight of influencing factors is large, and the coupling coordination is high. Small or medium-sized cavities may form underground, causing small and medium-sized collapse-type disasters in the loess area. This is consistent with the actual situation. Therefore, the risk of loess collapse diseases in the study area with high coupling and coordination is higher, and the risk of loess collapse diseases in the study area with low coupling and coordination is lower. The risk of loess collapse diseases in the study area shows good consistency with the coupling and coordination degree.

[0119] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for evaluating the risk of underground disease bodies in loess, characterized in that: The following steps are involved: According to the geological conditions of the area to be evaluated as the evaluation index of the internal characteristic system, and the external induced conditions as the evaluation index of the external characteristic system, the development level index of the internal characteristic system and the external characteristic system are constructed respectively; According to the evaluation indexes of the internal and external characteristic systems, an initial value evaluation system for each subsystem of the internal and external characteristic systems is established; Based on the entropy weighting method, the weights of each indicator in the initial value evaluation system of each subsystem of internal and external characteristics are determined, and the weights of each subsystem indicator are determined after the weights are modified using expert experience analysis and hierarchical analysis method; Based on the development level index of the internal and external characteristic systems, a prediction model of the coordination level of the development of internal and external characteristics is constructed to determine the coordination relationship between the development of internal and external characteristics in different areas of the evaluated area; According to the development of the coordination level prediction model of the internal and external characteristics, the evaluation standard system of the coupling coordination level of the internal and external characteristics is established to evaluate the risk of the diseased bodies in the evaluation area; The establishment of the initial value evaluation system of each subsystem of the internal and external characteristics comprises the following steps: Establish a two-level evaluation index system and select the internal characteristic system evaluation index u ij , external characteristic system evaluation index v ij Evaluate the internal and external characteristic development indexes. In the formula, u i 、v i (i=1,2,…,n) are the i-th item and evaluation index of the internal characteristic system and the external characteristic system respectively; u ij 、v ij (i=1, 2, ..., n, j=1, 2, ..., m) are the jth secondary index of the i-th primary index of the internal characteristic system and the external characteristic system respectively; Each evaluation index is divided into positive index and negative index, where u' ij 、v' ij are the ordered efficacy coefficients of the endogenous characteristic system and the exogenous characteristic system, respectively, representing the variable u ij 、v ij The contribution value to the system's effectiveness reflects the degree of satisfaction with each influencing factor in achieving the goal. The value range is [0, 1], where 1 represents the most satisfactory and 0 represents the least satisfactory. When u ij 、v ij When it is a positive indicator: When u ij 、v ij When it is a negative indicator: In the formula, The maximum contribution value of the jth secondary evaluation index of the i-th primary evaluation index to the system for the internal characteristic system and the external characteristic system respectively; The minimum efficacy contribution value of the jth secondary evaluation index of the i-th primary evaluation index of the internal characteristic system and the external characteristic system to the system respectively; According to the ordered efficacy coefficients of the internal characteristic system and the external characteristic system, the internal characteristic system development level index UU and the external characteristic system development level index UV are used to evaluate the development level of the internal characteristic system and the external characteristic system respectively: in, λ i is the weight of the first-level indicator of item i, μ j is the weight of the j-th secondary indicator; The method of constructing a prediction model for the coordination level of development of endogenous characteristics and exogenous characteristics comprises the following steps: Establish a coupling degree model for the interaction between internal and external characteristics: Construct system coupling coordination function: D=(CI·CEI) 1 / 2 T=α·UU+β·UV Where: D is the system coupling coordination degree, T is the comprehensive coordination index of internal and external characteristics, reflecting the overall synergistic effect of the risk assessment system of underground disease bodies in loess; α and β are the unknown coefficients of contribution of the internal and external characteristics system.

2. The method for evaluating the risk of underground diseases in loess according to claim 1, characterized in that: The secondary indicators are proposed by using the entropy weighting method to calculate the weight of each subsystem, and then the weight is modified by expert experience analysis and hierarchical analysis method to determine the weight of each subsystem indicator μ j .

3. The method for evaluating the risk of underground diseases in loess according to claim 1, characterized in that: The geological conditions as the first-level evaluation index of the internal characteristic system include: topography, stratum lithology, hydrogeological conditions and geological structure; the geological conditions as the second-level evaluation index of the internal characteristic system include: terrace type, relative position of disease, loess division, thickness, degree of wetting, permeability, internal friction angle, cohesion, groundwater burial position and earthquake fault; The external induced conditions as the first-level evaluation indicators of the external characteristic system include: rainfall conditions, water collection conditions, leakage conditions, road surface load and underground voids; the external induced conditions as the second-level evaluation indicators of the external characteristic system include: average monthly rainfall, concentrated rainfall, local topography, structural layer type, surface water discharge, road surface cracks, underground pipeline leakage, underground structure of rainwater wells, green belt irrigation, urban road load, thickness of silt covering voids and water seepage, and air-raid shelters.

4. The method for evaluating the risk of underground diseases in loess according to claim 1, characterized in that: The contribution coefficients of the endogenous characteristic system and the exogenous characteristic system are respectively: α=0.4, β=0.

6.

5. The method for evaluating the risk of underground diseases in loess according to claim 1, characterized in that: The establishment of the evaluation standard system for the coupling coordination level of the internal and external characteristics and the evaluation of the risk of the diseased body in the evaluation area include the following steps: According to the calculation result of the system coupling coordination degree D, the coordination level of the internal and external characteristics is divided into five levels, forming a system coupling coordination degree D index grading evaluation standard system for evaluation.

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