CN114965954A - Shallow layer rainfall type landslide early warning method based on unsaturated soil body conductivity - Google Patents
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Abstract
The invention discloses a shallow layer rainfall type landslide early warning method based on the conductivity of an unsaturated soil body, which specifically comprises the following steps: determining a landslide range according to site investigation, determining physical and mechanical parameters of a soil body through a test, establishing a monitoring station, and uploading data of water content, conductivity, matrix suction and temperature to a monitoring cloud platform; establishing a VG model, a conductivity-water content relation model and a conductivity-matrix suction relation model according to the monitoring data; and deducing a rainfall landslide stability calculation formula based on the conductivity of the soil body, and comparing early warning indexes according to the obtained result to realize monitoring and early warning. The invention comprehensively and objectively reflects the dynamic evolution process of rainfall induced landslide from multiple dimensions such as hydrology, conductivity, temperature, mechanics, landslide mechanism and the like, reveals the relation between the water-electricity-mechanical properties of soil in the landslide, observes the occurrence mechanism of rainfall induced landslide from the angle of soil electricity, and provides a new method for monitoring and early warning of landslide.
Description
Technical Field
The invention relates to the technical field of landslide hazard early warning, in particular to a shallow layer rainfall type landslide early warning method based on the conductivity of unsaturated soil.
Background
At present, the rainfall amount monitored in real time is taken as a basic means based on a rainfall critical value and a rainfall intensity plus an early rainfall amount or a rainfall intensity plus a rainfall duration, and a landslide physical mechanical mechanism and a landslide unsaturated destruction condition are usually ignored. Many rainfall-induced shallow landslides often involve complex properties of shallow slip zone unsaturated soil, and rainfall statistics have large spatial difference, so that the rainfall index itself has large uncertainty and limitation, and the stability analysis of the rainfall landslide based on the uncertainty and limitation is difficult to meet the accuracy requirement. The failure mechanism of the shallow rainfall landslide is that the water content of the slope unsaturated soil body is increased under the infiltration action of rainfall to increase the weight of the soil body, and meanwhile, the suction force of the unsaturated soil matrix is reduced, so that the gliding force is increased and the anti-sliding force is reduced, and finally, the slope is unstable to generate the shallow landslide.
Therefore, there are several disadvantages to developing a landslide warning method based on rainfall: firstly, the method of rainfall critical value is disjointed with the mechanics mechanism of landslide destruction, and the physical meaning is unclear. The rainfall may generate flow distribution such as slope runoff and evapotranspiration, and the amount of the rainfall infiltrating into the soil body is greatly different; secondly, early rainfall occurring on the landslide is difficult to accurately count and calculate, rainfall data often deviates from actual conditions due to the reasons of station dispersion, low density, interpolation distortion and the like due to the difference of different landslide geological conditions, and results obtained by only adopting regional and empirical statistical analysis have great limitation, so that the landslide success early warning rate is not ideal; thirdly, the early warning model based on single rainfall index has single index and cannot reflect the mechanical property, the conductivity and the hydrological characteristics of the landslide soil body. In the process of landslide damage induced by rainfall, the matrix suction, the water content, the conductivity and other hydrological, mechanical and electrical parameters are changed differently, so that the physical and mechanical characteristics of deformation and damage of shallow landslide cannot be comprehensively reflected by a model without considering the indexes of landslide soil, and fine warning of landslide is difficult to achieve.
Disclosure of Invention
In view of the above, the invention aims to provide a shallow rainfall type landslide early warning method based on the conductivity of an unsaturated soil body, which aims at the technical defect that the existing landslide early warning method mostly adopts a single rainfall index, and the physical and mechanical state of landslide and the unsaturated damage of landslide are not sufficiently considered, so that the early warning is inaccurate.
In order to achieve the purpose, the invention adopts the following technical scheme: a shallow layer rainfall type landslide early warning method based on unsaturated soil body conductivity comprises the following steps:
the method comprises the following steps: determining the landslide range according to on-site geological survey, and determining physical and mechanical parameters of a landslide unsaturated soil body through a rock-soil test: wherein, the physical mechanical parameters comprise: effective internal friction angle phi 'of soil body, effective cohesive force c' of soil body and dry volume weight gamma of soil body d Selecting the position of a landslide monitoring station and formulating a monitoring scheme;
step two: building a site monitoring station, excavating a test pit, embedding a probe type volume water content meter, a conductivity meter, a thermometer and a matrix suction sensor, realizing long-term monitoring, transmitting data and synchronizing to a monitoring cloud platform;
step three: establishing a VG model of the unsaturated soil matrix suction and the volume water content according to the volume water content and the matrix suction obtained by on-site long-term monitoring, and calculating the physical characterization parameter of the VG model, namely the saturated water content theta s And residual water content theta r ；
Step four: establishing the conductivity and volume of the unsaturated soil according to the temperature, volume water content and conductivity data obtained by long-term monitoring on siteA relation model of the water content and calculating the saturated conductivity sigma according to the model s And residual conductivity σ r ；
Step five: establishing a relation model of the unsaturated soil conductivity and the substrate suction according to temperature, substrate suction and conductivity data obtained by long-term field monitoring;
step six: according to the unsaturated soil strength theory and the landslide stability analysis theory, combining a relation model of conductivity-volume water content and conductivity-matrix suction to obtain a rainfall type landslide stability calculation formula based on soil body conductivity;
step seven: and the monitoring cloud platform compares landslide early warning grading indexes according to the calculation result, and carries out monitoring and early warning on the rainfall landslide.
In a preferred embodiment, in the construction of the monitoring station in the first step and the second step, the landslide monitoring station is arranged in a landslide range, and the sensor burying depth is 50-300 cm.
In a preferred embodiment, the second step is as follows: (1) determining a landslide monitoring range according to landslide site investigation, building a landslide site monitoring station, developing monitoring station arrangement, and embedding and installing a sensor; (2) and further carrying out on-site monitoring on the volume water content, the conductivity and the matrix suction of the landslide soil body, and transmitting and uploading the monitoring data to the monitoring cloud platform in real time through wireless transmission.
In a preferred embodiment, the VG model formula in step three is:
in the formula (I), the compound is shown in the specification,
to monitor the resulting substrate suction; m and n are both VG model fitting parameters.
In a preferred embodiment, the conductivity in the fourth step and the conductivity in the fifth step are calculated by using a standard value after temperature correction, and the specific correction formula is as follows:
in the formula, σ T The conductivity value is obtained by monitoring at T temperature, sigma is a conductivity standard value after being calibrated to 25 ℃ standard temperature, T is the soil temperature obtained by monitoring, and xi is 0.0271-1 and is a temperature correction coefficient;
the model fitting formula of the relationship between the conductivity and the volume water content in the fourth step is as follows:
θ＝aσ+b
in the formula, theta is the volume water content of the soil obtained by monitoring, and a and b are fitting parameters; then the saturation conductivity σ s Residual conductivity σ r The specific calculation formula of (a) is written as:
relative conductivity σ e Is defined as:
in a preferred embodiment, the grade of landslide warning is divided according to landslide stability, and the landslide stability is divided by "landslide prevention engineering investigation Specification" (GB/T32864-2016) into: the stable state Fs is more than 1.15, the basic stable state Fs is more than 1.05 and less than or equal to 1.15, the less stable state Fs is more than 1.00 and less than or equal to 1.05, and the unstable state Fs is less than or equal to 1.00, and the landslide early warning levels correspond to four levels of safety early warning, yellow early warning, orange early warning and red early warning respectively.
In a preferred embodiment, the relational model fitting formula of the conductivity-matrix suction in the fifth step is as follows:
in the formula, e is a mathematical constant, and c, p and q are model fitting parameters.
In a preferred embodiment, the landslide stability calculation method related in the sixth step is to couple the unsaturated soil strength theory and the landslide stability analysis theory, and solve the landslide stability coefficient based on a relation model of conductivity-volume water content and conductivity-matrix suction, and is specifically implemented according to the following method:
according to the unsaturated soil theory, the shear strength formula of unsaturated soil is as follows:
wherein tau is the shear strength of the soil body, (sigma) n -u a ) Is the effective stress;
according to the landslide stability analysis theory, the stability calculation formula of the infinite slope under rainfall infiltration is as follows:
in the formula, F s Is the landslide stability factor; beta is the slope of the landslide; z is the depth of the sliding surface, u w Pore water pressure;
coupling the unsaturated soil strength theory and the landslide stability analysis theory, and combining a relation model of conductivity-volume water content and conductivity-matrix suction to obtain a rainfall type landslide stability calculation formula based on soil body conductivity:
compared with the prior art, the invention has the following beneficial effects:
(1) the invention directly combines physical and mechanical parameters of soil body, utilizes the data of water content, conductivity, temperature and matrix suction monitored on site, comprehensively and objectively reflects the dynamic evolution process and development trend of rainfall induced landslide from multiple dimensions such as hydrology, conductivity, temperature, mechanics, landslide mechanism and the like.
(2) The invention establishes a relation model of soil conductivity-water content and conductivity-matrix suction, reveals the relation between water-electricity-mechanical properties of soil in the landslide, observes the occurrence mechanism of rainfall induced landslide from the angle of soil electricity, and provides a new research idea for monitoring and early warning of landslide.
(3) The method has the advantages of being more theoretical and scientific, objective in calculation result, and stronger in applicability and accuracy, providing a more comprehensive and scientific technical means, and having theoretical and practical significance for promoting landslide research progress.
Drawings
FIG. 1 is a flow chart of a method of a preferred embodiment of the present invention;
FIG. 2 is a schematic diagram of monitoring data of moisture content, conductivity, substrate suction and rainfall which are transmitted back by a construction monitoring station according to a preferred embodiment of the invention and change with time;
FIG. 3 is a model diagram of soil VG in accordance with a preferred embodiment of the present invention;
FIG. 4 is a model diagram of the relationship between the conductivity and the volumetric water content of soil according to the preferred embodiment of the present invention;
FIG. 5 is a model graph of soil conductivity versus substrate suction in accordance with a preferred embodiment of the present invention;
fig. 6 is a diagram of a process of calculating a change over time of a landslide stability factor and a corresponding achieved early warning index level according to a preferred embodiment of the present invention.
Detailed Description
The invention is further explained below with reference to the drawings and the embodiments.
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application; as used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.
A shallow layer rainfall type landslide early warning method based on unsaturated soil body conductivity comprises the following steps:
the method comprises the following steps: determining the landslide range according to on-site geological survey, and determining physical and mechanical parameters of a landslide unsaturated soil body through a rock-soil test: wherein, the physical mechanical parameters comprise: effective internal friction angle phi 'of soil body, effective cohesive force c' of soil body and dry volume weight gamma of soil body d (ii) a In the embodiment, the monitoring points and the positions are determined as early warning areas after the landslide body is surveyed on the spot, and a monitoring scheme is formulated according to the survey results on the spot.
Step two: building a site monitoring station, excavating a test pit, embedding a probe type volume water content meter, a conductivity meter, a thermometer and a matrix suction sensor, realizing long-term monitoring, and transmitting monitoring data to a monitoring cloud platform in real time through wireless transmission; the sensor buried depth related to the embodiment is generally 50 to 300cm, and the reason is that the sliding surface of the shallow rainfall type landslide mostly occurs in the soil body of 50 to 300cm, so the monitoring data of the depth has important significance for the calculation of the stability of the subsequent landslide.
Step three: establishing a VG model of the unsaturated soil matrix suction and the volume water content according to the volume water content and the matrix suction obtained by long-term field monitoring, and calculating the physical characterization parameter saturated water content theta of the VG model s And residual water content theta r (ii) a The VG model formula is:
in the formula (I), the compound is shown in the specification,
to monitor the resulting substrate suction; m and n are both VG model fitting parameters;
step four: according to the temperature, the volume water content and the conductivity data obtained by long-term monitoring on site, a relational model of the unsaturated soil conductivity and the volume water content is established, and the fitting formula of the relational model is as follows:
θ＝aσ+b
in the formula, theta is the volume water content of the soil obtained by monitoring, and a and b are fitting parameters;
calculating the saturated conductivity sigma according to the model s And residual conductivity σ r Is then σ s And σ r The specific calculation of (a) can be written as:
relative conductivity σ e The calculation formula defined is:
step five: according to the temperature, the substrate suction and the conductivity data obtained by on-site long-term monitoring, a relational model of the unsaturated soil conductivity and the substrate suction is established, and the fitting formula of the relational model is as follows:
in the formula, e is a mathematical constant, and c, p and q are model fitting parameters.
Step six: and obtaining a rainfall type landslide stability calculation formula based on the soil body conductivity by combining a relation model of conductivity-volume water content and conductivity-matrix suction according to a non-saturated soil strength theory and a landslide stability analysis theory.
The core of the method is to couple the unsaturated soil theory, the soil electricity theory and the landslide stability analysis theory, solve the stability coefficient of the landslide unsaturated soil through the volume water content, the conductivity, the temperature and the matrix suction of the soil layer depth at different moments monitored on site, not only can early warn rainfall landslide according to results to solve the actual problem of landslide disaster prevention and reduction, but also can reveal the physical process and the mechanical mechanism of deformation and damage of the rainfall-excited shallow landslide under the unsaturated condition, and further lay a foundation for promoting the landslide theory.
The landslide stability solving process provided by the invention is described in detail below, and according to the unsaturated soil theory, the shear strength formula of unsaturated soil is as follows:
wherein tau is the shear strength of the soil body, (sigma) n -u a ) Is the effective stress;
according to the landslide stability analysis theory, the stability calculation formula of the infinite slope under rainfall infiltration is as follows:
in the formula, F s Is the landslide stability factor; beta is the slope of the side slope; z is the depth of the sliding surface, u w Pore water pressure;
coupling the unsaturated soil strength theory and the landslide stability analysis theory, and combining a relation model of conductivity-volume water content and conductivity-matrix suction to obtain a rainfall type landslide stability calculation formula based on soil body conductivity:
step seven: according to the calculated landslide stability coefficient calculated in real time, the early warning grading index (table 1) of the shallow rainfall landslide provided by the invention is compared to determine whether to send out early warning of corresponding grade or not, and an early warning result is issued.
According to the landslide stability state division standard specified in landslide prevention and control engineering investigation Specification (GB/T32864-2016), the landslide early warning and forecasting index is divided into 4 grades, see Table 1. According to the regulation of the specification, the landslide stability state is divided into 4 levels through the stability coefficient of the landslide.
TABLE 1 early warning and grading index for shallow rainfall type landslide
| Coefficient of stability | Steady state | Early warning index | Deformation condition |
| Fs>1.15 | Steady state | Safety precaution | The landslide is in a stable state |
| 1.05<Fs≤1.15 | Basic steady state | Yellow early warning | The landslide is in a creeping extrusion state |
| 1.00<Fs≤1.05 | Under stable state | Orange early warning | The landslide is in a creep deformation state |
| Fs≤1.00 | Unstable state | Red early warning | Slide on a landslide |
The technical idea of the invention is as follows: the method is characterized in that the formation process and the mechanical mechanism of shallow landslide of unsaturated soil under rainfall condition are used as theoretical basis, hydrology and electricity theory are combined, the conductivity of the unsaturated soil of the shallow landslide at different moments is connected with the stability coefficient of the landslide, and the stable state and the early warning index of the shallow landslide are judged by using a conventional method of landslide stability analysis.
According to the technical idea, the basic technical principle of the landslide early warning method is as follows: and in the first step, determining basic data such as physical and mechanical parameters of a landslide monitoring area and a landslide soil body according to geological survey, and building monitoring sites of volume water content, conductivity, temperature and matrix suction. On the basis, establishing a VG model by utilizing the moisture content and the matrix suction data returned by the monitoring station in the third step to obtain the saturated moisture content and the residual moisture content of the field soil; in the fourth step, the water content, the conductivity and the temperature data returned by the monitoring station are utilized, the conductivity is subjected to temperature correction, a conductivity-water content relation model is established with the water content, and the saturated conductivity, the residual conductivity and the relative conductivity of the soil are calculated according to the model; establishing a conductivity-matrix suction relation model by using the matrix suction and conductivity data transmitted back by the monitoring station in the fifth step; and step six, combining the stability calculation method based on unsaturated soil provided by the invention, and calculating the real-time stability of the landslide according to the conductivity data returned in real time. And step seven, establishing early warning grading indexes according to a landslide stability analysis method specified by the specification, judging and evaluating the stability of the landslide in the early warning area according to whether the comparison calculation value reaches an early warning value, and thus realizing landslide forecast early warning, as shown in fig. 1. The method is adopted to forecast and early warn the shallow landslide in the rainfall process, the current indirect indexes such as effective early rainfall or rainfall critical value based on statistics are comprehensively replaced by indexes of multiple dimensions such as hydrology, conductance, temperature, mechanics and landslide mechanism to represent the real-time soil body mechanics condition and stability of a landslide area along with the change of time and rainfall conditions, the landslide stability is calculated through the soil body conductivity to judge whether the landslide soil body is close to or achieves instability damage, the relation of soil in the landslide between water-electricity-mechanical properties is disclosed, and compared with the rainfall index method, the method has higher reliability, accuracy and comprehensiveness.
The early warning method provided by the invention is mainly suitable for forecasting and early warning for inducing unsaturated soil shallow landslide under the action of rainfall, and is exemplified as follows:
by using the method provided by the embodiment, the example analysis of the shallow rainfall type landslide early warning method based on the conductivity of the unsaturated soil body is carried out on the rock-pocket village landslide in the plum area of Sanming city.
The landform of the rock pocket village landslide belongs to a medium-low mountain land feature unit, the slope of the whole landform is steep upward and slow downward, the slope of the whole landform is about 30-40 degrees, a large amount of slope soil is lost, the plane is in a round-chair shape, the coverage rate of slope vegetation is high, the superficial layer is residual cohesive soil, the underlying completely weathered granite is deep by about 2m, and the landslide is a typical rainfall induced landslide.
The method comprises the following steps: the method comprises the following steps of surveying the rock pocket village landslide area in the plum train area of Sanming city on the spot, collecting landslide residual cohesive soil samples, and carrying out indoor soil mechanics experiments to test physical and mechanical parameters of soil (see table 2 in detail):
table 2 values of physical and mechanical parameters of rock pocket village landslide soil
| (symbol) | Description of the parameters | Test value |
| c′ | Effective cohesive force of soil body; (unit: kPa) | 14.8 |
| φ′ | Effective internal friction angle of soil body; (Unit:degree) | 20.1 |
| γ d | Dry volume weight of soil body; (Unit: kN/m3) | 13.7 |
| β | A landslide slope; (Unit:degree) | 35 |
| Z | The depth of the soil body; | 2 |
step two: the method is adopted to further monitor and early warn the rock pocket village landslide, in the embodiment, on the basis of acquiring physical and mechanical parameters of the soil body by adopting an experiment for residual cohesive soil in the early warning area, a monitoring station is further built in the early warning area, and the water content, the conductivity, the matrix suction, the temperature and the rainfall of the landslide are monitored in real time. The probes of the sensors are arranged on the soil body of the landslide slope, and the buried depth of the sensors is 200 cm. The data acquisition interval is 1h, the monitoring data acquired by the real-time monitoring station is uploaded to a monitoring cloud platform of Fuzhou university-Haixi institute through wireless transmission, and the field monitoring data of 2021.3.6-2022.3.6 in one year is shown in FIG. 2.
Step three: and selecting the volume water content and the matrix suction according to the returned monitoring data, carrying out daily average on the data, and carrying out VG model fitting on the data by using MATLAB software, wherein as shown in FIG. 3, the saturated water content of the on-site soil is 0.4569, and the residual water content is 0.2245.
Step four: and selecting volume water content, conductivity and temperature data according to the returned monitoring data, and establishing a conductivity-water content relation model according to the method provided by the invention after all the conductivity data are subjected to temperature correction, as shown in figure 4.
Step five: according to the returned monitoring data, the conductivity and the substrate suction are selected, and according to the method provided by the invention, a conductivity-substrate suction relation model is established, as shown in fig. 5.
Step six: according to the method for calculating the stability of the unsaturated soil, provided by the invention, a formula for calculating the stability of the rainfall induced landslide based on the conductivity of the soil body is obtained by combining a conductivity-water content and conductivity-matrix suction relation model, and the stability of the landslide is calculated according to the conductivity data monitored in real time.
Step seven: according to the calculated landslide stability coefficient, as shown in fig. 6, the monitoring cloud platform establishes an early warning grading index according to a landslide stability analysis method specified by a standard, and judges and evaluates the stability of landslides in an early warning area according to whether a comparison calculation value reaches an early warning value or not. From the monitoring data of 2021.3.6-2022.3.6 in one year, when a strong rainfall event occurs on the rocky village landslide at 2021.12.24, the rainfall reaches 338.4mm within 5 accumulated days, the volume water content and the conductivity are constantly increased, the substrate suction is correspondingly reduced, and on the 2 nd day (2021.12.30) after the strong rainfall stops, the landslide stability coefficient is reduced to 1.15, and the cloud platform gives an orange early warning; at 2022.1.10, the landslide stability factor is reduced to 1.05, the landslide reaches an under-stable state, and the cloud platform sends out a yellow early warning.
Claims (8)
1. A shallow layer rainfall type landslide early warning method based on unsaturated soil body conductivity is characterized by comprising the following steps:
the method comprises the following steps: determining a landslide range according to on-site geological investigation, and determining physical and mechanical parameters of a landslide unsaturated soil body through a rock-soil test: wherein, the physical mechanical parameters comprise: effective internal friction angle phi' of soil, effective cohesive force c of soil and dry volume weight gamma of soil d Selecting the position of a landslide monitoring station and formulating a monitoring scheme;
step two: building a site monitoring station, excavating a test pit, embedding a probe type volume water content meter, a conductivity meter, a thermometer and a matrix suction sensor, realizing long-term monitoring, transmitting data and synchronizing to a monitoring cloud platform;
step three: establishing a VG model of the unsaturated soil matrix suction and the volume water content according to the volume water content and the matrix suction obtained by long-term field monitoring, and calculating the physical characterization parameter saturated water content theta of the VG model s And residual water content theta r ；
Step four: establishing a relation model of the unsaturated soil conductivity and the volume water content according to temperature, volume water content and conductivity data obtained by long-term monitoring on site, and calculating the saturated conductivity sigma according to the model s And residual conductivity σ r ；
Step five: establishing a relation model of the unsaturated soil conductivity and the substrate suction according to temperature, substrate suction and conductivity data obtained by long-term field monitoring;
step six: according to the unsaturated soil strength theory and the landslide stability analysis theory, combining a relation model of conductivity-volume water content and conductivity-matrix suction to obtain a rainfall type landslide stability calculation formula based on soil body conductivity;
step seven: and the monitoring cloud platform compares landslide early warning grading indexes according to the calculation result, and carries out monitoring and early warning on the rainfall landslide.
2. The shallow rainfall type landslide early warning method based on the conductivity of unsaturated soil according to claim 1, wherein in the monitoring station construction in the first step and the second step, a landslide monitoring station is arranged in a landslide range, and the sensor burying depth is 50-300 cm.
3. The shallow rainfall type landslide early warning method based on the conductivity of unsaturated soil according to claim 1, wherein the second step is as follows: (1) determining a landslide monitoring range according to landslide site investigation, building a landslide site monitoring station, arranging the monitoring station, and embedding and installing a sensor; (2) and further carrying out on-site monitoring on the volume water content, the conductivity and the matrix suction of the landslide soil body, and transmitting and uploading the monitoring data to the monitoring cloud platform in real time through wireless transmission.
4. The shallow rainfall type landslide early warning method based on unsaturated soil conductivity according to claim 1, wherein a VG model formula in the third step is as follows:
in the formula (I), the compound is shown in the specification,
to monitor the resulting substrate suction; m and n are both VG model fitting parameters.
5. The shallow rainfall type landslide early warning method based on the conductivity of unsaturated soil according to claim 1, wherein the conductivity in the fourth step and the fifth step is calculated by adopting a standard value after temperature correction, and a specific correction formula is as follows:
in the formula, σ T The conductivity value is obtained by monitoring at the temperature T, sigma is a conductivity standard value after the standard temperature of 25 ℃ is calibrated, T is the soil temperature obtained by monitoring, and xi is 0.0271-1, and is a temperature correction coefficient;
the model fitting formula of the relationship between the conductivity and the volume water content in the fourth step is as follows:
θ＝aσ+b
in the formula, theta is the volume water content of the soil obtained by monitoring, and a and b are fitting parameters; then the saturation conductivity σ s Residual conductivity σ r The specific calculation formula of (a) is written as:
relative conductivity σ e Is defined as:
6. the shallow rainfall type landslide early warning method based on the conductivity of the unsaturated soil as claimed in claim 1, wherein the landslide early warning grading index in the seventh step is divided according to landslide stability state, and the landslide stability state is divided by landslide prevention engineering investigation Specification (GB/T32864-2016): the stable state Fs is more than 1.15, the basic stable state Fs is more than 1.05 and less than or equal to 1.15, the less stable state Fs is more than 1.00 and less than or equal to 1.05, and the unstable state Fs is less than or equal to 1.00, and the landslide early warning levels correspond to four levels of safety early warning, yellow early warning, orange early warning and red early warning respectively.
7. The shallow rainfall type landslide early warning method based on the conductivity of unsaturated soil according to claim 1, wherein in the fifth step, a relational model fitting formula of conductivity-matrix suction is as follows:
in the formula, e is a mathematical constant, and c, p and q are model fitting parameters.
8. The shallow rainfall type landslide early warning method based on the electrical conductivity of the unsaturated soil mass as claimed in claim 1, wherein the landslide stability calculation method involved in the sixth step is a method of coupling the unsaturated soil strength theory and the landslide stability analysis theory, solving the landslide stability coefficient based on the relationship model of the electrical conductivity-the volume water content and the electrical conductivity-the matrix suction force, and is implemented specifically according to the following method:
according to the unsaturated soil theory, the shear strength formula of unsaturated soil is as follows:
wherein tau is the shear strength of the soil body, (sigma) n -u a ) Is the effective stress;
according to the landslide stability analysis theory, the stability calculation formula of the infinite slope under rainfall infiltration is as follows:
in the formula, F s Is the landslide stability factor; beta is the slope of the landslide; z is the depth of the sliding surface, u w Pore water pressure;
the method comprises the following steps of coupling an unsaturated soil strength theory and a landslide stability analysis theory, and combining a relation model of conductivity-volume water content and conductivity-matrix suction to obtain a rainfall landslide stability calculation formula based on soil conductivity:
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