JPH02159561A - Estimating method of range of movement of landslide or landslip - Google Patents

Abstract

PURPOSE:To know the surface range of movement of landslide or landslip by sampling soil beforehand from the place where there is a possibility of unstable earth on a slope causing sliding movement, by subjecting the soil to a soil test and by determining the deformation characteristic of a moving lump of earth. CONSTITUTION:When a lump of earth due to landslide or landslip slides down on a slope, the distance of movement of the center of gravity thereof is proportional to an apparent coefficient of friction between the moving lump of earth and the firm ground, and the expansion of the moving lump of earth is proportional to a coefficient of horizontal earth pressure. Values of these two coefficients are determined from soil exploration and water content exploration, while a slope whereon the landslip is estimated to occur and the slope whereon the lump of earth is expected to run down are cut in a mesh of a prescribed width, and the movement of a columnar earth element in the mesh is computed numerically for each time step from the time of start of the movement to the time of stop thereof by using the inclination of the slope, the apparent coefficient of friction and the coefficient of horizontal earth pressure. Thereby the height and speed of the earth element in each mesh in each time are computed, and the range of movement of the landslide or the landslip and the depth of a pile of the earth are estimated from the height and the distribution of the earth element at the time when the speed turns zero.

Description

[Detailed Description of the Invention] <Industrial Field of Application> The present invention is applicable to the case where a landslide or landslide occurs on the slope in question.
This relates to a method for predicting the range of movement in order to predict in advance how far danger will extend and to reduce disasters through measures such as warning and evacuation during rain or land use regulations.

<Conventional technology> Conventionally, in order to predict the movement distance of a landslide or landslide, the difference in height between the position of the center of gravity of the soil mass after the movement in landslides and landslides that occurred in the past and the position of the center of gravity of the soil mass after the movement has stopped is used. and the horizontal distance between each center of gravity, and this is considered to be equivalent to the coefficient of traction during movement, and this is called the equivalent skew number, which is roughly proportional to the scale of the moving soil mass. Therefore, it is assumed that the equivalent friction coefficient obtained from the past slope with a similar scale to the slope where the landslide or cliff collapse occurs is equal to the equivalent friction coefficient of the slope. We have estimated the distance of movement of the center of gravity of a moving soil mass by replacing the motion of a collapsed soil mass with the motion of a mass point with zero volume at its center of gravity, and assuming that this mass point slides down the slope.

<Problem to be solved by the invention> The above-mentioned conventional technology does not solve the problem of landslides and landslides of similar scale in the past.
Although the uniform friction coefficient for landslides has been applied to the slope, the actual friction coefficient of the slope differs from slope to slope, and sometimes changes due to changes in moisture conditions such as rain and melting snow. Furthermore, each part of the slope where the flow is expected to flow has a different coefficient of friction due to differences in soil quality and changes in moisture conditions. Conventional technology ignores these effects, which reduces the reliability of estimates of travel distance. There was a problem.

Furthermore, in the conventional technology, the movement of the collapsed earth is approximated as the movement of a mass point with zero volume, so the planar spread of the moving earth mass cannot be estimated. However, in reality, the collapsing soil not only accumulates in a certain width in the direction of movement, but also spreads widely in the horizontal direction if it contains a large amount of water, increasing the damaged area. This method was extremely inadequate as a method for predicting the range of motion of landslides and landslides. Therefore, the present invention aims to provide a highly reliable prediction method that is free from such drawbacks.

Means for solving problems> When a landslide/cliff slides on a slope, the moving distance of its center of gravity is proportional to the apparent coefficient of friction between the moving soil mass and the immovable ground, and the spread of the moving soil mass is horizontal. Proportional to the upper pressure coefficient.

In addition to finding both values through soil and moisture surveys,
Slopes where landslides and landslides are predicted to occur and slopes where landslides are predicted to flow are cut into 11 fixed meshes, and the movement of the columnar soil elements within the meshes is measured at each time from the start of movement to the time it stops. By performing numerical calculations using the slope slope, the above-mentioned apparent friction coefficient, and horizontal soil pressure coefficient for each step, the height and velocity of the soil elements in each mesh at each time are calculated, and the velocity becomes zero. Based on the height and distribution of soil elements at the time of occurrence, the range of movement and sedimentation depth of landslides and landslides can be predicted.

<Example> The present invention will be described in detail below based on the drawings. FIG. 1 shows a moving earth mass (2) moving on a sloped immovable ground (1). Regarding this moving earth mass, as shown in the figure, the X-Y coordinate is taken on the horizontal plane and the Z coordinate is taken in the vertical direction. Then, meshes are placed at equal intervals in the X direction and in the X direction. Now, consider a vertical columnar element (3) whose length extends from the immovable ground to the surface of the collapsed soil mass surrounded by meshes i and i+1 in the X direction and j and j+1 in the X direction.

FIG. 2 shows the force acting on the columnar element (3) after t8 from the occurrence of the landslide/landslide using vectors. This force is the self-weight of the earth mass W (ij, t), and the horizontal earth pressure acting in the X direction from adjacent elements: Px (ij.

t) and Px(i+1.j, t), horizontal earth pressure that also acts in the X direction: Py(i, j, t) and Py(i, j+l,
t), frictional resistance force R(i, j, t) on the bottom of the soil clod
and the vertical reaction force N(i, j.

Now, the self-weight is expressed as the slope direction component Wp(i, j, t
) and the component Wn(i, j, t) perpendicular to the slope, we get
Since Wn and N have opposite directions and the same magnitude, they cancel each other out. Therefore, the vector sum of the remaining forces causes a change in the acceleration of this clod. That is, if the mass of this clod is expressed as (i, j, t) and the acceleration is a(i, j, t), then
The following relationship holds.

a(ij, t) ・s+(i, j, t)=Wp(i, j
,t)+(Px(i,j,t)-Px(i+1.j,t
)l+(Py(i,j,t)−Py(i,j+1.t)
)+R(ij, t)------------------<1) In this equation, the force per unit surface area of the frictional resistance force R applied to the bottom of the element can be calculated by applying the concept of soil mechanics. The effective normal stress obtained by subtracting the pore water pressure (u) during the movement of the soil mass acting on the sliding surface from the force perpendicular to the slope due to the soil mass's own weight (vertical part σ), and the coefficient of friction during the motion of the soil (janφm)
It should be multiplied by . Further, this frictional resistance force can be expressed as the product of the normal stress without considering the pore water pressure by the apparent coefficient of friction (tanφa). Therefore,
(σ−u) −janφm= 6− tanφatan
φa=((σ-u)/σ)・janφ----(2>This apparent coefficient of friction (tanφa) is calculated by performing a soil test on the soil on the slope and calculating the coefficient of friction during movement (janφ餉).
It can be obtained by determining the pore water pressure (u).

Further, the horizontal earth pressure (Px, Py) is calculated by multiplying the element's own weight by the horizontal earth pressure coefficient. Furthermore, by adding the condition that the density of the moving soil mass does not change during movement, and calculating the above equation numerically, we get
The height and velocity of the columnar elements for each mesh can be calculated for each time, and the accumulation range and accumulation rate of soil addition can be determined in contrast to the case where the velocity is zero.

Figures 3 to 5 show examples in which the present invention is applied to landslides on small-scale hypothetical slopes. is a longitudinal section of
The dotted area is unstable soil (2) before it begins to move. X-Y back side 1. The mesh is cut into m meshes, and A shows the distribution of the heights of the columnar elements in each mesh at the median of 10e-. Now, in the case where the horizontal soil coefficient and j2 are 0.4 (value for sandy soil that does not contain water) from the soil test of the soil on the slope, the apparent friction coefficient is 0.7.
Let's calculate the movement range of soil expansion for two cases: case 065 and case 065.

First, the 41st interval (a) is a planar view of the sedimentation depth distribution (A,) when the apparent coefficient of friction is 0.7. Part of the landslide mass remains on the slope, Some of it is deposited on the foot of the slope. Also, l with an apparent friction coefficient of 0.5
Figure 4<b) shows the sedimentation depth distribution of the 11!1 soil increase A,). All of the moving soil masses have moved a little distance from the foot of the slope. . In other words, both figures show that the distance traveled by soil reinforcement is inversely proportional to the apparent coefficient of friction.
2, which accurately shows that it is increasing.

Next, when the moving soil mass contains a large amount of water and the Kinoshita soil pressure coefficient is 0.8, the apparent friction coefficient is (
Figure 5 (a) shows the muscle accumulation depth distribution (A,') obtained when the value is 0.6, which is between a) and (b), and compares it with Figure 4 above. It is clear that it is widely spread. In addition, in the steeply sloped part of the second part (area where
As in a), the apparent coefficient of friction is 0.6, but in the gently sloping part at the bottom of the slope (area where Deposition depth distribution (A2) calculated for the case where the apparent coefficient of friction is reduced to 0.25, in which case it flows far and spreads widely. In other words, if a landslide occurs after a long period of rain or when a snow melter contains a large amount of water, it is predicted that an extremely wide area will be exposed to danger.

The result of applying the present invention to this hypothetical landslide C on a pure slope corresponds well to the state of landslides that actually occur7.
If the present invention is used, even if a landslide of the same shape and scale occurs on the same slope, the range of motion can be adjusted with high precision depending on the soil characteristics and water content of the slope. This shows that it is possible to predict.

On the other hand, for reference, the equivalent *friction coefficient obtained from a past landslide of the same scale is 0.5, which shows the case where the conventional technology is applied to the same landslide i1 in Figure 3. ), then
It is estimated that the mass point of soil expansion moves from the initial center of gravity (po) in Figure 3 to point (P,). However, in this case, it is not only impossible to estimate the difference in the slipperiness caused by changes in the moisture content of the slope, and also the difference in the deformation and softness caused by changes in the moisture content of the bars, but also the two-dimensional estimation of the landslide risk range. is difficult.

Next, an example will be described in which the present invention is applied to a landslide caused by an excessive amount.

During the Western Nagano Prefecture Earthquake of 1981, a large landslide occurred in a part of Mt. Owa17, and the increased soil flowed into the Denjo River and the Nuri River.
It then flowed further downstream into the Otaki River main river, blocking the Otaki River with sediment approximately 40 meters thick. The volume of the collapse was 35,000,000 i, and the distance traveled was approximately 10 km, causing a major disaster.1. Ta. We will examine how accurately the range of motion of this large landslide could be measured by applying the present invention.

Figure 6 is a topographical map showing the Miyake landslide (B,) and its flow/sediment range (B1).

The analysis range is approximately 10 km (right side of the figure) and approximately 3 km (F side of the figure), and this range is cut into meshes every 200 m.
The mesh number L7 is shown in the figure with length 50 (left side of the figure) and width 15 (bottom side of the figure).

Some of the collapsed sand ran aground on the opposite bank of the Denjo River (Ll), but most of it flowed down the Denkami River, and some of it climbed over the ridge (■1.) at the point where the river made a sharp curve. 4. It flowed into the muddy river. It then merged at the confluence of the Denjo River and the Miguri River, and then flowed down to the Otaki River, where about 40 pieces of water were deposited and blocked the river. Since most of the sediment that flowed into the Otaki River stopped at the narrowed part (L) called the Gaki no throat, the present invention was applied to this area as the analysis range. The steps for its implementation are as follows.

First, in this case, the depth distribution of unstable sediment was read from a topographic map drawn from aerial photographs before and after the collapse occurred. The depth of each category is determined in the case of small-scale slope failures by driving an iron rod into the soil and a penetration test to determine the depth of unstable soil, and in the case of large-scale failures, it is determined by boring surveys and elastic wave exploration. In places where these cannot be carried out, the depth of the bedrock inside the slope is estimated from the running and inclination of the outcrops of bedrock found on the banks at both ends of the slope.Secondly, the shape of the slope on which the earth and sand flows depends on the topography. I read it from the diagram.

In order to find the apparent coefficient of friction between the moving soil mass and the immobile soil mass, we found that the movable mass of soil moved forward while gouging the marsh deposits, and that it was a volcanic deposit of almost the same quality as the landslide slope and the theory of the soil mass flowing down. Therefore, as a representative point, samples were taken from point L4) in Figure 6 and tested. FIG. 7 shows the friction angle during motion using a ring shear tester, which was 34.7 degrees, and the friction coefficient (janφ-) was 0.69.

In addition, when the moving soil mass that has flowed down rests on the wetland deposits, pore water pressure is generated in terms of physical deposits, but the ratio of the generated pore water pressure to the vertical stress loaded by the mobile soil mass (pore water pressure coefficient Figure 8 shows Bd) obtained by a triaxial test.As shown in Figure 0, the pore water pressure coefficient varies depending on the degree of saturation.
It varies between ~1.0. From the ratio of test conditions and test results, when the sample was submerged in water for a sufficiently long time, the Bd value was 0.9, and when it was submerged in water for a short time, it was 0.6, indicating that it was sufficiently wet. It was found that when there was no flooding, the value was around 0.2. From this, the water content state of the slope soil layer is
Since it had rained a lot before the landslide, Bd[0,2,
Also, from the landslide occurrence area to the source of the Denjo River (L,)
Since surface water appears only during heavy rains on the slopes at concave points where surface water tends to accumulate, the pore water pressure coefficient is 0.6 when the water is flooded for a short period of time. There is always a sufficient amount of water below the confluence point (L6), so the Bd value when flooded for a sufficiently long time is 0.9, and
The intermediate theory (point position, ~Lm) was estimated to have an intermediate Bd value of 0.8.

The coefficient of friction during motion (Lanφ
-) and the pore water pressure coefficient (Bd) and another pore water pressure coefficient Ad related to the volume change that occurs when soil undergoes shear deformation: (0.2 by constant volume shear test of the same sample
5), the apparent coefficient of friction between the moving soil mass and the immovable ground is calculated based on the relationship in equation (2). ,
), points within the law (Ls to L,), and point combs,
) to the downstream logic are respectively 0.
It became 5.0.25.0, 12.0.08.

Furthermore, the horizontal earth pressure coefficient, which represents the deformation characteristics of a moving soil mass, is determined by the ratio of change in how much horizontal earth pressure is generated when vertical earth pressure is applied to this sample. Regarding the moisture content of the moving soil mass, we considered that the overall average corresponds to a state in which the sample was almost halfway filled with water, because the slope of Mt. Mitake is subject to landslides and water from the mountain stream gradually enters the soil mass. A horizontal earth pressure coefficient of 0.6 was used.

Figure 9 shows the results obtained by numerical analysis using soil constants estimated based on soil tests of samples taken from these sites and field observations.

First, FIG. 9(a) shows the accumulation depth of unstable earth and sand before the start of the landslide movement, divided into nine levels 1 to 9 as shown in Table F, from 0 to 1401. Figure 9 (b) shows the soil being moved and starting to climb over the ridge from the Denjo River to the Muddy River. Figure 9(c) shows the area where the clod is progressing further downstream from the confluence of the Denjo River and the Muddy River. Figure 9(d) shows the area where the movement of soil expansion has stopped, and it can be seen that the soil has accumulated to a thickness of over 40 meters, blocking the Otaki River. The predicted range of motion of the landslide mass matches the actual range of motion shown in Figure 6 (B), and the sediment depth of 40 cm in the Otaki River also matches the actual phenomenon.

An example of the present invention regarding the movement of a large landslide on Mt.tJg is as follows:
The movement of a landslide mass flowing down a complex topography with intricate slopes and valleys was predicted very accurately, demonstrating that the present invention provides a method for predicting a high range of movement of a landslide. ing.

The movement of small-scale earth clods on steep slopes adjacent to human residences on Miyako's vehicles is carried out by Kawasujiredo Kano A2, but the two are essentially the same!
). If a clod of earth moves over a long distance and at high speed τ within the soil, it will result in a debris flow, but the present invention is applicable V +
There is Hm-c. It seems that the method for determining the C5 constant is different, or that the avalanche motion prediction C= can also be used.

<Effects of the Invention> Landslides 7F disasters caused by river lanes occur during earthquakes, typhoons, rainy seasons, or snow melting, causing great damage.

Efforts have been made to prevent these slope failures [l:Surouni 5]. Efforts have been made so far to prevent the occurrence of collapses, but there are countless areas at risk of landslides and river curvature, and all of these It is almost economically impossible to carry out preventive work. In order to prevent and eliminate disasters caused by slides and river channels, it is necessary to not only directly prevent such disasters, but also to measure the f'-measure of 1.5, and the danger zone is a residential area. It is necessary to publicize or administratively regulate land use so that buildings, schools, hospitals, etc. are not used during rainfall. Warning and evacuation of ・g-
Kaname de chiru. Part 12. Therefore, it is important to know in advance whether the (-) range is dangerous (V).

j, Y end technique (it is estimated that the movement of the sujiko is 1. by the movement of the point.) The coefficient of friction is 1.
::Since the equivalent friction coefficient, l2j, obtained by back calculation from the movement of landslides and river stripes of the same scale that occurred, could only be determined, There is also a problem.) By the present invention, the range of motion of a landslide (1v collapse) can be known in terms of area. - It became possible to collect the friction coefficient, which is the basis of the distance of movement, and the water 3171 pressure coefficient, which is the basis of the degree of dispersion of lumps, from the field 1-1. The coffin is determined by the above soil test. Until 2 and 1 became n1 capabilities, and technology for predicting dangerous areas due to landslides and river lanes was dramatically improved, dangerous areas were defined as 1 on the map. 4: It was difficult to draw a line using Not only must it be possible to confirm the degree of risk and prepare for disasters in advance, but it must also be possible to gain the support of residents regarding land use regulations, warnings, and evacuations in order to prevent disasters. Person in charge of disaster prevention administration: There are some very effective inventions that can greatly contribute to the prevention of disasters.

[Brief explanation of the drawing]

Fig. 1 shows a schematic diagram of the moving target and the columnar elements therein. Fig. 2 shows the force applied to the columnar elements.
Figure (a) shows a horizontal Tonosho coefficient of 04 and an apparent friction coefficient of 0.
Figure 4 (b) is the sedimentation depth distribution map when the upper pressure coefficient of water is 0.4 and the apparent friction coefficient is 0.5. Figure 5 ( a) has a horizontal upper pressure coefficient of 0.8 and an apparent friction coefficient of 0. Deposition depth distribution IM in case of f3, Fig. 5 (1))
Figure 6 is the topographic map and range of movement of the Great Mibata landslide. , taken from the sediments for transmission: Ring shear test of the sample J,
Measuring the coefficient of friction during motion〉i! Conclusion υ, 81M is the relationship between the degree of saturation and pore water pressure coefficient t3d obtained from the triaxial pressure 12+ test for the same sample, and Figure 9 (&) is the j of the t-stable sediment before the movement of the 1fl Hatake landslide.
Q product depth division, Figure 0 (b) is fjl! , against large landslides l1. Figure 9 (c) shows the result of applying the present invention to the 1-slide landslide (sediment distribution at the beginning of the movement). Depth distribution of sediment) Figure 9(d) shows the bundling to which the present invention is applied for the tn Hatake landslide (depth distribution of sediment after cessation of 3' girding). ]... Immobile ground , 2...Movement l-mass 3...Columnar element, N...Vertical reaction force Px, Py...Horizontal earth pressure, R...R friction resistance force W...Self weight

Claims (1)

[Claims] 1. Test the soil sampled in advance from a site where there is a risk of sliding movement of unstable soil on a slope to determine the deformation characteristics of the moving soil mass, and also calculate the coefficient of friction between the moving soil mass and the immovable ground. The shape of the slope where sediment is expected to flow down is determined using topographic maps or surveys, and the depth distribution of unstable sediment before collapse is determined by boring, penetration tests, elastic wave tests, etc., and these four elements are calculated under certain conditions. A method for predicting the range of motion of landslides and landslides, which is characterized by using numerical analysis to predict in terms of how far and how far the soil mass of a landslide or landslide will flow and how much it will spread.