Early identification method for shallow soil landslide

Abstract

This is an early identification method for a shallow soil landslide, belonging to the technical field of landslide prevention and control engineering. The present invention accurately determines and identifies a shallow soil landslide in a quantitative manner, improving the early identification efficiency of a landslide and helping to improve the disaster prevention effect.

Claims

1. An early identification method for a shallow soil landslide, characterized by comprising the following steps: S1, obtaining topographic digital elevation model (DEM) data of a terrain area to be identified, generating a topographic map based on the DEM data, and determining a slope area with a depressed cross section based on contour lines in the topographic map, wherein the slope area with a depressed cross section refers to an area where the contour lines bulge upward when viewed from the bottom to the top of the topographic map; then determining outer boundaries of two sides of a potential landslide mass from the beginning of straight segments or downward bulged vertices on both sides of an upward bulged vertex of each contour line in the slope area; drawing a straight line to connect the beginning of straight segments or downward bulged vertices on both sides of the upward bulged vertex of a contour line located at the bottom of the slope area, and determining the straight line as a bottom boundary of the potential landslide mass; drawing an intermediate line at an intermediate position of the potential landslide mass and perpendicular to the bottom boundary of the potential landslide mass, wherein the upward bulged vertex of each contour line in the potential landslide mass is located near the intermediate line; and determining a plurality of intermediate points on the intermediate line, with one DEM point spacing between each of two adjacent intermediate points, and one of the intermediate point being located at an intersection of the bottom boundary and the intermediate line; drawing plurality of parallel lines respectively, wherein each parallel line is perpendicular to the intermediate line and across the intermediate point to intersect the outer boundaries of the potential landslide mass, wherein the intersection points of each parallel line and the outer boundaries of the potential landslide mass 20 are determined as outer boundary points, which together with the intermediate point on the same parallel line constitute a three-point group of a plane curvature Qp of the intermediate point of the potential landslide mass; S2, calculating a slope of each intermediate point according to the position and grid data of the intermediate point in the topographic map, and finally, taking an arithmetic average of the slopes of all the intermediate points as a slope a of the potential landslide mass; assigning, according to the distribution principle of topographic DEM data, all points in each grid of the topographic map with the same values, comprising coordinates and elevation, which are obtained through the grid; S3, calculating the plane curvature Qp of each intermediate point of the potential landslide mass through a three-point method according to Formula 1 to Formula 7, and then taking an arithmetic average of the plane curvatures Qp of all of the intermediate points to obtain a plane curvature Q of the potential landslide mass; $\begin{array}{cc}\mathrm{Qp}=2\sin A/a& \mathrm{Formula}1\end{array}$ $\begin{array}{cc}A=\arccos \left[\left(b^2+c^2-a^2\right)/\left(2\mathrm{bc}\right)\right]& \mathrm{Formula}2\end{array}$
a=?{square root over ((x.sub.1?x.sub.2).sup.2+(y.sub.1?y.sub.2).sup.2)}Formula 3
b=?{square root over ((x.sub.1?x.sub.3).sup.2+(y.sub.1?y.sub.3).sup.2)}Formula 4
c=?{square root over ((x.sub.3?x.sub.2).sup.2+(y.sub.3?y.sub.2).sup.2)}Formula 5 where Qp is a plane curvature of an intermediate point of the potential landslide mass, x.sub.1, x.sub.2 and x.sub.3 are projected X coordinates of the first group of points 1, 2 and 3 in turn, x.sub.1=0, and x.sub.2 is a linear distance between points 1 and 2 and is calculated by Formula 6; x.sub.3 is a linear distance between points 1 and 3 and is calculated by Formula 7; y.sub.1, y.sub.2 and y.sub.3 are elevations of points 1, 2 and 3 respectively;
x.sub.2=?{square root over ((Xa?Xb).sup.2+(Ya?Yb).sup.2)}Formula 6
x.sub.3=?{square root over ((Xa?Xc).sup.2+(Ya?Yc).sup.2)}Formula 7 where Xa and Ya are X and Y coordinates of point 1 in turn; Xb and Yb are X and Y coordinates of point 2 in turn; Xc and Yc are X and Y coordinates of point 3 in turn; wherein the plane curvatures Qp of the intermediate points of the second group of points to the fifth group of points of the potential landslide mass are each calculated by the Formula 1 to the Formula 7; S4, calculating a topographic factor T of the potential landslide mass according to Formula 8;
T=tan ??5QFormula 8 where T is the topographic factor of the potential landslide mass, ? is the slope of the potential landslide mass, and Q is the plane curvature of the potential landslide mass; S5, performing early identification of the shallow soil landslide according to the slope ? of the potential landslide mass, the plane curvature Q of the potential landslide mass and the topographic factor T: when the slope ? of the potential landslide mass is less than 15? or more than 50?, the possibility of landslide occurrence on the potential landslide mass is identified as low; when the plane curvature Q of the potential landslide mass is more than 0, the possibility of landslide occurrence on the potential landslide mass is identified as low; when the topographic factor T is less than 0.75, the possibility of landslide occurrence on the potential landslide mass is identified as low; when the slope ? of the landslide mass is more than or equal to 15? and less than or equal to 50?, the plane curvature Q of the potential landslide mass is less than or equal to 0 and the topographic factor T is more than or equal to 0.75, the possibility of landslide occurrence on the potential landslide mass is identified as medium; and when the slope ? of the landslide mass is more than or equal to 15? and less than or equal to 50?, the plane curvature Q of the potential landslide mass is less than or equal to 0 and the topographic factor T is more than or equal to 1.0, the possibility of landslide occurrence on the potential landslide mass is identified as high.

2. The early identification method for a shallow soil landslide according to claim 1, characterized in that in step S3, taking an arithmetic average refers to calculating a positive or negative sign of the plane curvature Qp of the intermediate point of the potential landslide mass according to Formula 9 and Formula 10;
if y.sub.2?kx.sub.2y.sub.1>0Formula 9 the plane curvature Qp of the intermediate point of the potential landslide mass is positive, indicating a bulged topography;
if y.sub.2?kx.sub.2y.sub.1<0Formula 10 the plane curvature Qp of the intermediate point of the potential landslide mass is negative, indicating a depressed topography; where k is a coefficient, calculated by Formula 11;
k=(y.sub.3y.sub.1)/x.sub.3Formula 11 then bringing the calculated positive or negative sign of the plane curvature Qp of the intermediate point of the potential landslide mass into the plane curvature Qp of the intermediate point of the potential landslide mass, and finally, performing arithmetic averaging on the plane curvatures Qp of the intermediate points of all groups of the potential landslide mass.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram of a topographic map generated based on topographic DEM data according to an embodiment of the present disclosure.

(2) FIG. 2 is a schematic diagram of a point selection for planar curvature of a potential landslide mass based on the topographic map shown in FIG. 1 according to an embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(3) An early identification method for a shallow soil landslide comprises the following steps.

(4) S1, topographic digital elevation model (DEM) data of a terrain area to be identified is obtained, a topographic map (as shown in FIG. 1) is generated based on the DEM data, and a slope area with a depressed cross section is determined based on contour lines 10 in the topographic map, where the slope area with a depressed cross section refers to an area where the contour lines 10 bulge upward when viewed from the bottom to the top of the topographic map; then outer boundaries 21 of two sides of a potential landslide mass 20 are determined from the beginning of straight segments or downward bulged vertices on both sides of an upward bulged vertex of each contour line 10 in the slope area; a straight line is drawn to connect the beginning of straight segments or downward bulged vertices on both sides of the upward bulged vertex of a contour line 10 located at the bottom of the slope area, and the straight line is determined as a bottom boundary 22 of the potential landslide mass 20; an intermediate line 31 is drawn at an intermediate position of the potential landslide mass 20 and perpendicular to the bottom boundary 22 of the potential landslide mass 20, where the upward bulged vertex of each contour line 10 in the potential landslide mass 20 is located near the intermediate line 21; as shown in FIG. 2, a plurality of intermediate points 2 are determined on the intermediate line 31, with one DEM point spacing between each of two adjacent intermediate points 2, and one of the intermediate point 2 being located at an intersection of the bottom boundary 22 and the intermediate line 31; a plurality of parallel lines I, II, III, IV, V are drawn respectively, where each parallel line is perpendicular to the intermediate line 31 and across the intermediate point 2 to intersect the outer boundaries of the potential landslide mass, where the intersection points of each parallel line and the outer boundaries of the potential landslide mass 20 are determined as outer boundary points 1 and 3; where the outer boundary points 1 and 3 together with the intermediate point 2 on the same parallel line constitute a three-point group of a plane curvature Qp of the intermediate point 2 of the potential landslide mass 20.

(5) In this embodiment, the topographic DEM data represents the topography or terrain of a topographic area in a digital format. It provides detailed information about the elevation, slope, and shape of the Earth's surface. DEM data is typically derived from various sources such as satellite imagery, LiDAR (Light Detection and Ranging) technology, or ground survey measurements. It is widely used in fields like geography, geology, environmental science, and urban planning. DEM data is crucial for analyzing and visualizing terrain features, creating accurate topographic maps, conducting hydrological modeling, and simulating landscape changes. With its precise elevation information, DEM data plays a vital role in a wide range of applications, including land management, flood risk assessment, infrastructure planning, and 3D visualization.

(6) As shown in FIG. 1, from the bottom to the top of the topographic map, the elevation of the contour lines 10 gradually increases. The sliding direction of the potential landslide mass 20 is along a direction from the top to the bottom of the intermediate line 31. The potential landslide mass 20 refers to a slope where landslides may occur.

(7) S2, a slope of each intermediate point 2 is calculated according to the position and grid data of the intermediate point 2 in the topographic map, and finally, an arithmetic average of the slopes of all the intermediate points 2 is taken as a slope a of the potential landslide mass 20; according to the distribution principle of topographic DEM data, all points in each grid of the topographic map are assigned with the same values, including coordinates and elevation, which are obtained through the grid.

(8) In the embodiment, the slope refers to a gradient in the sliding direction of potential landslide mass 20. A ratio of the height difference and horizontal displacement of two adjacent intermediate points 2 on the intermediate line 31, is the tangent of a slope of the hillside between these two intermediate points 2. The slope of each intermediate point can be calculated with specific software tools, such as ArcGis, which is a comprehensive geographic information system (GIS) software developed by Esri, a leading provider of GIS solutions. It is widely used in various industries for analyzing, managing, and visualizing geographic data.

(9) S3, the plane curvature Qp of each intermediate point 2 of the potential landslide mass 20 is calculated through a three-point method according to Formula 1 to Formula 7, and then an arithmetic average of the plane curvatures Qp of all of the intermediate points 2 is taken to obtain a plane curvature Q of the potential landslide mass 20.

(10) $\begin{array}{cc}\mathrm{Qp}=2\sin A/a& \mathrm{Formula}1\end{array}$$\begin{array}{cc}A=\arccos \left[\left(b^2+c^2-a^2\right)/\left(2\mathrm{bc}\right)\right]& \mathrm{Formula}2\end{array}$$\begin{array}{cc}a=\sqrt{{\left(x_1-x_2\right)}^2+{\left(y_1-y_2\right)}^2}& \mathrm{Formula}3\end{array}$$\begin{array}{cc}b=\sqrt{{\left(x_1-x_3\right)}^2+{\left(y_1-y_3\right)}^2}& \mathrm{Formula}4\end{array}$$\begin{array}{cc}c=\sqrt{{\left(x_3-x_2\right)}^2+{\left(y_3-y_2\right)}^2}& \mathrm{Formula}5\end{array}$

(11) Where Qp is a plane curvature of an intermediate point 2 of the potential landslide mass 20, x.sub.1, x.sub.2 and x.sub.3 are projected X coordinates of the first group of points 1, 2 and 3 in turn, x.sub.1=0, and x.sub.2 is a linear distance between points 1 and 2 and is calculated by Formula 6; x.sub.3 is a linear distance between points 1 and 3 and is calculated by Formula 7; y.sub.1, y.sub.2 and y.sub.3 are elevations of points 1, 2 and 3 respectively.

(12) $\begin{array}{cc}{x}_2=\sqrt{{\left(Xa-Xb\right)}^2+{\left(Ya-Yb\right)}^2}& \mathrm{Formula}6\end{array}$$\begin{array}{cc}{x}_3=\sqrt{{\left(Xa-Xc\right)}^2+{\left(Ya-Yc\right)}^2}& \mathrm{Formula}7\end{array}$

(13) Where Xa and Ya are X and Y coordinates of point 1 in turn; Xb and Yb are X and Y coordinates of point 2 in turn; Xc and Yc are X and Y coordinates of point 3 in turn.

(14) The plane curvatures Qp of the intermediate points 2 of the second group of points to the fifth group of points of the potential landslide mass are each calculated by Formula 1 to Formula 7.

(15) S4, a topographic factor T of the potential landslide mass is calculated according to Formula 8.
T=tan ??5QFormula 8

(16) Where T is the topographic factor of the potential landslide mass, ? is the slope of the potential landslide mass, and Q is the plane curvature of the potential landslide mass.

(17) S5, early identification of the shallow soil landslide is performed according to the slope ? of the potential landslide mass, the plane curvature Q of the potential landslide mass and the topographic factor T:

(18) When the slope a of the potential landslide mass is less than 15? or more than 50?, the possibility of landslide occurrence on the potential landslide mass is identified as low;

(19) When the plane curvature Q of the potential landslide mass is more than 0, the possibility of landslide occurrence on the potential landslide mass is identified as low;

(20) When the topographic factor T is less than 0.75, the possibility of landslide occurrence on the potential landslide mass is identified as low;

(21) When the slope ? of the potential landslide mass is more than or equal to 15? and less than or equal to 50?, the plane curvature Q of the potential landslide mass is less than or equal to 0, and the topographic factor T is more than or equal to 0.75 and less than 1.0, the possibility of landslide occurrence on the potential landslide mass is identified as medium;

(22) When the slope ? of the potential landslide mass is more than or equal to 15? and less than or equal to 50?, the plane curvature Q of the potential landslide mass is less than or equal to 0, and the topographic factor T is more than or equal to 1.0, the possibility of landslide occurrence on the potential landslide mass is identified as high.

(23) The topographic factor T can be used to identify the possibility of landslide occurrence on a potential landslide mass only when a slope condition and a cross-sectional non-bulged condition are present, and the greater the T value, the higher the possibility of future landslide occurrence on the potential landslide mass; otherwise, the smaller the T value, the lower the possibility of future landslide occurrence on the potential landslide mass. Accurately determining and identifying a shallow soil landslide in a quantitative manner improves the early identification efficiency of the landslide, and the early identification of the landslide is intuitive and clear, which is conducive to improving the effect of disaster prevention.

(24) In this embodiment, a three-point method is used to calculate the plane curvature of the potential landslide mass, so that the calculated plane curvature is more in line with the actual plane curvature of the potential landslide mass, and the calculation result is more accurate and reasonable, thus making the identification of the possibility of landslide occurrence on the potential landslide mass more accurate.

(25) In addition, the range (boundaries) of the potential landslide mass is determined by means of DEM topographic data and the contour lines in the topographic map, and important DEM points and each group of data points (two outer boundary points 1 and 3 together with one intermediate point 2 on the same parallel line constitute a group of data points) are determined within this range. According to each group of data points, the slope a of the potential landslide mass and the plane curvature Qp of each intermediate point of the potential landslide mass are calculated; then the topographic factor T of the potential landslide mass is calculated; finally, the shallow soil landslide is identified according to the slope ? of the potential landslide mass, the plane curvature Qp of each intermediate point of the potential landslide mass, and the topographic factor T; internal mechanism research is conducted on the possibility of landslide occurrence on the potential landslide mass based on topographic factors, which completely integrates the slope and cross-sectional topographic conditions of the potential landslide mass, comprehensively considers the role of topographic factors, and reflects the mutual relation and importance of various influence factors; where T, tan(a) and Q are all dimensionless parameters and can be used under various shallow soil landslide conditions, which greatly improves the applicability of disaster prevention.

(26) In an embodiment, in step S3, taking an arithmetic average refers to that a positive or negative sign of the plane curvature Qp of the intermediate point of the potential landslide mass is calculated according to Formula 9 and Formula 10;
If y.sub.2?kx.sub.2?y.sub.1>0Formula 9

(27) The plane curvature Qp of the intermediate point of the potential landslide mass is positive, indicating a bulged topography;
If y.sub.2?kx.sub.2?y.sub.1<0Formula 10

(28) The plane curvature Qp of the intermediate point of the potential landslide mass is negative, indicating a depressed topography;

(29) Where k is a coefficient, calculated by Formula 11;
k=(y.sub.3?y.sub.1)/x.sub.3Formula 11

(30) Then the calculated positive or negative sign of the plane curvature Qp of the intermediate point of the potential landslide mass is brought into the plane curvature Qp of the intermediate point of the potential landslide mass, and finally, arithmetic averaging is performed on the plane curvatures Qp of the intermediate points of all groups of the potential landslide mass.

(31) The plane curvature of a potential landslide mass is calculated by a three-point method, which avoids errors caused by DEM data intervals and landslide scale differences. The conventional default method calculates the plane curvature of a potential landslide mass by means of a specific DEM point, as well as 8 points in upper (1), lower (1), left (1), right (1) and oblique direction (4), totaling 9 points, and the calculated plane curvature is related to the grid scale and range where the 9 points are located. However, if the scale of the potential landslide mass is quite different from the grid scale of this DEM, the plane curvature cannot reflect the plane curvature of the potential landslide mass; if the scale of the potential landslide mass is much larger than the grid scale of the DEM, the calculated plane curvature is a part of the plane curvature of the potential landslide mass, and even if multiple plane curvatures on the potential landslide mass are averaged, it cannot represent the depressed or bulged characteristics of the whole potential landslide mass; if the scale of the potential landslide mass is much smaller than the grid scale of the DEM, the calculated plane curvature is a plane curvature in an area outside the outer boundary of the potential landslide mass, and cannot represent the depressed or bulged characteristics of the whole potential landslide mass. The present invention overcomes the conventional curvature calculation problems by organically combining the three-point method, and the calculated plane curvature can reflect the true depressed or bulged characteristics of the potential landslide mass, which is conducive to improving the early identification accuracy of the shallow soil landslide.

(32) The present invention is described below with a specific example.

(33) Sinan County and Yinjiang County are located in the northwest of Guizhou Province. In July 2014, the two counties suffered from rare continuous heavy rainfalls, which induced some shallow soil landslides. As shown in Table 1, landslides occurred at 11 of the 26 potential landslide masses in July 2014.

(34) Table 1 shows the topographic parameters and early identification of 26 potential landslide masses investigated in Sinan County and Yinjiang County of Guizhou Province.

(35) TABLE-US-00001 TABLE 1 Possibility Whether a Serial of landslide landslide number ? tan (?) Q T occurrence occurs 1 31.5 0.613 ?0.0377 0.802 Medium Yes 2 20.9 0.381 ?0.0398 0.580 Low No 3 28.9 0.552 ?0.0325 0.715 Low No 4 28.8 0.550 ?0.0405 0.753 Medium No 5 40.0 0.838 ?0.00263 0.851 Medium Yes 6 50.0 1.190 ?0.0002 1.191 High Yes 7 31.1 0.603 ?0.0298 0.752 Medium No 8 22.0 0.405 ?0.0208 0.509 Low No 9 20.0 0.364 ?0.0227 0.478 Low No 10 23.5 0.435 ?0.0287 0.579 Low No 11 34.1 0.676 ?0.0183 0.767 Medium Yes 12 48.3 1.124 ?0.0331 1.29 High Yes 13 40.1 0.842 ?0.00015 0.843 Medium Yes 14 43.2 0.939 ?0.0309 1.094 High Yes 15 39.3 0.818 ?0.0310 0.973 Medium Yes 16 42.3 0.910 ?0.0008 0.914 Medium Yes 17 39.2 0.816 0.0011 0.811 Low No 18 30.3 0.484 ?0.0368 0.768 Medium No 19 19.6 0.356 ?0.0242 0.477 Low No 20 41.5 0.885 ?0.0267 1.02 High Yes 21 24.9 0.464 ?0.0341 0.635 Low No 22 31.5 0.613 ?0.0302 0.764 Medium No 23 27.4 0.518 ?0.0414 0.725 Low No 24 45.6 1.02 ?0.0424 1.232 High Yes 25 24.4 0.454 ?0.0424 0.666 Low No 26 37.7 0.773 ?0.0375 0.961 Medium No

(36) Identification method: when the slope a of the potential landslide mass is less than 15? or more than 50?, the possibility of landslide occurrence on the potential landslide mass is identified as low;

(37) When the plane curvature Q of the potential landslide mass is more than 0, the possibility of landslide occurrence on the potential landslide mass is low;

(38) When the topographic factor T is less than 0.75, the possibility of landslide occurrence on the potential landslide mass is identified as low;

(39) When the slope ? of the potential landslide mass is more than or equal to 15? and less than or equal to 50?, the plane curvature Q of the potential landslide mass is less than or equal to 0, and the topographic factor T is more than or equal to 0.75 and less than 1.0, the possibility of landslide occurrence on the potential landslide mass is identified as medium;

(40) When the slope a of the potential landslide mass is more than or equal to 15? and less than or equal to 50?, the plane curvature Q of the potential landslide mass is less than or equal to 0, and the topographic factor T is more than or equal to 1.0, the possibility of landslide occurrence on the potential landslide mass is identified as high.

(41) From Table 1, the calculation results of the slope ? of the potential landslide mass, the plane curvature Q of the potential landslide mass and the value of the topographic factor T show that, among the 26 potential landslide masses, 5 potential landslide masses were identified as having high possibilities of landslide occurrence, 11 potential landslide masses were identified as having medium possibilities of landslide occurrence, and 10 potential landslide masses were identified as having low possibilities of landslide occurrence.

(42) With reference to actual situations, landslides occurred in July 2014 on all the 5 potential landslide masses identified as having high possibilities of landslide occurrence; landslides occurred in July 2014 6 of the 11 potential landslide masses identified as having medium possibilities of landslide occurrence, and landslides did not occur on the remaining 5 potential landslide masses; and no landslide occurred in July 2014 on all the 10 potential landslide masses identified as having low possibilities of landslide occurrence.

(43) The above indicates that the method of the present invention has high accuracy in early identification of shallow soil landslides.