JPH06317436A - Method for diagnosing stability of slope - Google Patents

Abstract

PURPOSE:To diagnose the stability of a slope or predict the left time until the slope comes to collapse by burying ground surface inclinometers in the slope and measuring the inclined angular velocity at the positions. CONSTITUTION:At the time of constructing a large cut slope 10, small steps 12 are usually formed in the middle of the slope 10 and ground surface inclinometers 14 are buried in the slope 10 by utilizing the steps 12 so as to measure the inclined angle of the slope 10. After a first-stage cut slope is constructed, an inclinometer (a) is buried in the uppermost part of the slope and the inclined angle theta of the slope is found with the lapse of time t. Then the second-stage cut slope is constructed and an inclinometer (b) is buried in a narrow horizontal section between the slopes. Although not only the measured value of the inclinometer (b) largely changes due to the cutting work, but also the output of the inclinometer (a) changes abruptly, the measured values of the inclinometers (a) and (b) approximate fixed values in a short time when the slope 10 is stable. In case the output of an inclinometer (d) is stabilized, but that of another inclinometer (e) indicates a large inclined angle after the inclined angle changes immediately after the cutting work when the cutting work is continued and the inclined angle is measured with the inclinometers (d) and (e), the left time until the slope comes to collapse can be predicted from the variation of the inclined angle.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for diagnosing the stability of a slope such as a cut slope. More specifically, a ground surface type inclinometer is embedded in the slope to measure the slope angular velocity of the slope. By doing so, the present invention relates to a method of evaluating the stability of the slope or predicting a margin time until the slope collapses.

[0002]

2. Description of the Related Art Natural ground is extremely heterogeneous and varied, and even in places where it was stable for many years before excavation of the slope, excavation work caused the slope of the cut slope to become gradually uneven over time. It becomes stable. Significant deformation or collapse of a slope means that the position and direction of the fracture surface is determined by the stress state regardless of the specific layer surface, and that some weak layer or weak surface already exists, such as a landslide, or It is said that there are new ones, and activities occur along the layer surface as the resistance decreases. The slope survey is carried out for the purpose of assessing the long-term stability of the slope, assuming the existence and spread of this fracture surface or slip surface, but it is dense enough to obtain sufficient ground information for the target slope. Surveys are rarely conducted, and the reality is that engineers are boldly estimating the experience of themselves from a small amount of information.

As a field survey for cut slopes,
There is observation of ground structure and topography. Furthermore, as a method for obtaining ground information of the target slope, there are sampling and observation of a boring core, utilization of resistivity imaging and resistivity tomography. For the observation of the boring core, after the geological column diagram was created, especially the weathering condition of the whole core sample was reconfirmed, the condition of the core that appeared when the survey site was included in the landslide moving mass, and the surface of the core was cut with a knife. The nails are sharpened with a sharp edge to scratch the core in the extension direction, the presence of a thin soft clay pinch is sensed, and the confirmed weak layer is specified in the column diagram. Resistivity tomography treats potential data measured by electrodes placed in the ground, in holes, and on the ground surface as projection data of a region with a certain spread,
This is a technique for reconstructing a cross-sectional image of the target ground. The resistivity imaging method obtains a cross-sectional image using only measured values of electrodes arranged on the ground surface. This measuring system is simpler than that of elastic waves and electromagnetic waves, and can be measured in a short time. Therefore, it is economical and has been used in various places recently as a supplement to a boring survey.

[Problems to be Solved by the Invention]

Wherever there are slopes, especially weathering, a slow downward movement of the soil mass called creep occurs. The speed is
It is considered that many factors such as slope slope, soil composition and meteorological conditions are influencing. By the way, as a landslide investigation, there is a method of digging a boring hole, inserting an underground inclinometer into the hole, and measuring the inclination at each depth to observe the position of the sliding surface and the amount of slip. The underground stress of the slope left by excavation decreases, and the slope variation due to the stress decrease can be roughly classified into the following three patterns. From the data obtained by the underground inclinometer, the slope of any pattern It is possible to determine whether or not there is fluctuation. If there is an old landslide scratch: Forward deformation under the slope, clear shear deformation in the old sliding surface area in the center, rearward deformation in the head, etc.
The deformation (displacement speed) is large below the slope and small above. In case of slope of flow bed or horizontal plate structure: Deformation in which shear strain is concentrated appears in the relatively soft part of the ground. In general, the deformation (displacement speed) is large in the lower part of the slope and becomes smaller as the distance from the slope increases. In the case of a slope with a basin and a steep slope structure: Rebound deformation due to stress release becomes noticeable, and almost all slope parts undergo forward deformation.

However, in the method using the underground inclinometer, it is necessary to excavate a boring hole and install the underground inclinometer, and to measure at each depth. Therefore, the installation cost is high and the measurement work is complicated. Therefore, it is economically difficult to observe at many points. Moreover, this method cannot be applied to slope failures where there are no sliding surfaces. In addition, it has been customary to install a ground surface type inclinometer on the slope to measure the inclination angle, but the use of the measured value was merely used to judge whether the slope moved. In fact, the use of inclinometers was very limited.

As a method of measuring the movement of the landslide soil mass, there is a method in which a wire is stretched between both soil masses that sandwich the generated crack and the change in the length of the wire is measured. However, in this method, the wire cannot be stretched unless the landslide condition becomes remarkable enough to cause a crack on the ground surface,
It cannot be used for slope stability diagnosis.

The object of the present invention is to provide long-term stability of any slope (including not only cut slopes but also slopes in natural terrain) and slope changes by using simple and inexpensive equipment. It is to provide a method of diagnosing the stability of a slope without relying only on the experience and intuition of a slope survey engineer, by predicting whether or not the slope can be secured, and the margin time until the collapse.

[0008]

The inventor of the present invention has found that the amount of change in the inclination angle of the slope is closely related to the stability of the slope (whether or not the slope can secure long-term stability and the margin time until the collapse). That is, the present invention has been completed by focusing on that. The present invention embeds a ground surface type inclinometer on a slope, measures the inclination angular velocity at that position, and utilizes the fact that the inclination angular velocity and the margin time until the collapse are in inverse proportion, It is a method of diagnosing slope stability and predicting the margin time until failure or failure. Here, as the ground surface type inclinometer, a format that can measure two horizontal components is used, and it is buried in the horizontal part of the small step of the cut slope to a depth of about 50 to 70 cm from the surface of the earth, and the angular velocity in the maximum tilt direction is thereby obtained. It is desirable to ask.

[0009]

[Function] Natural ground is extremely inhomogeneous and rich in variation, and the cut slope becomes gradually unstable with the passage of time due to the downward movement of the soil mass due to the creep phenomenon. When the slope angular velocity of the slope is measured, when the slope is stable, there is little fluctuation in the slope angle, but the amount of change in the slope angle increases as the instability increases, and eventually the slope collapses or landslides occur. Leading to. In this way, the stability of the slope and the amount of change in the inclination angle of the slope are closely related, and this is not limited to the cut slope and the natural slope. Therefore, in the present invention, by actively using the measurement value of the ground surface type inclinometer,
The slope stability is diagnosed. Therefore, even in the stratum where the landslide surface is not clear, quantitative diagnosis can be performed without relying only on the experience and intuition of the slope survey engineer.

By the way, the shear strain in the slip region can be obtained from the horizontal displacement amount and the measurement interval obtained by the underground inclinometer, and the moving velocity of the landslide block can be obtained from the shear strain rate and the measurement interval. However, when evaluating from the moving speed of the slope, the thickness of the shear region of the target slope must always be considered. This is because the movement speed of the ground surface becomes different when the thickness of the main fluctuation portion (shear zone) changes even if the shear strain rate is the same.

From the relatively long-term data of landslide movement records around the world, the data of the report of Skempton (1969) summarizing the movement speed of the ground surface before landslide was borrowed and Extra time T _R and moving speed V
When the relationship of is plotted, it becomes like FIG. Although each point varies, it is roughly approximated by the following linear equation. _{T R · V = 20 ... (} 1) However, T _R: spare time until the sliding (day) V: movement speed (cm / day) This equation (1), when the mobile speed increases monotonically, landslides It is considered to be the most suitable for predicting the sliding down time. As described above, the moving speed of the ground surface increases as the thickness of the main fluctuation portion (shear zone) increases, even if the shear strain speed is the same. Considering the relationship between the thickness D of the main fluctuation part obtained by the recent underground inclinometer measurement, the moving speed of the ground surface, and the margin time until sliding down, the constant (= 20) is roughly D = 10
It is estimated to be a constant corresponding to 0 cm. It is said that the collapse of rock slopes is faster and more dangerous than general landslides. It is sandwiched between hard rocks and is thin (for example, D =
In the case of a 5 cm) shear band, the constant in equation (1) is 1.0.
In this way, when the risk of landslide is to be evaluated from the moving speed, it is important to evaluate the thickness of the shear zone which is responsible for the fluctuation.

Therefore, in the present invention, the stability of the slope is evaluated from the inclination angular velocity measured on the ground surface. In the case of the forward deformation, it is not possible to set a clearer sliding surface. Considering the forward deformation as a stack of small shear deformations, the tilt angular velocity dθ / d
When t is displayed in units of radian / day, in a region where the inclination angular velocity is small, the value becomes the same as the moving velocity when the measurement interval D = 1 cm. In that case, the constant on the right side of the equation (1) is 0.2. _{T R · dθ / dt = T} R · V = 0.2 ... (2)

By the way, based on the laboratory test results of Ishimoto and Iida (1936) using a clay vane shearing device, the shearing angular velocity of the clay part sandwiched between the vane and the inner wall of the outer cylindrical tube (equivalent to dθ / dt here) 2) and the failure margin time T _R are plotted on a logarithmic scale, the point group of the experimental results approximates to the following equation as shown in FIG. _{T R · dθ / dt = 0.3} ... (3) However, T _R: spare time to slide down (= destruction margin time)
(Sun) dθ / dt: Inclination angular velocity (= shearing angular velocity) (radian /
Despite the different method and process derived, it can be considered that equations (2) and (3) are almost the same. This result will be verified from the following actual slope dynamic observation results and slope condition evidence. Roadside slope variation on a coastal road in Wight, England. Stable with steady fluctuations. Angular velocity of forward slope variation of the ground at an excavation depth of 50 to 170 m on an open-pit slope of the Santa Barbara mine in Italy. This slope collapsed at an excavation depth of 205 m. The measured value is when there is some margin until collapse. Tilt angular velocity of the slip-shear zone on the slope of the landslide block, which is currently active on the California coast of the United States. Inclination angular velocities of shear bands on the sliding surface of a landslide that has nearly two days left to slide in Niigata Prefecture.
It can be seen that the relationship between the slope stability evaluation and the inclination angular velocity is relatively harmonious, and is an index of slope stability. In other words, by measuring the inclination angular velocity on the surface of the slope, it becomes possible to predict the stability of the slope, that is, the margin time until the collapse.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 3 shows an embodiment for carrying out the slope stability diagnosis method according to the present invention. This is a stability diagnosis in the process (AD) of constructing a cut slope. When constructing a large cut slope, a small step 12 is usually formed in the middle of the slope 10. Therefore, the ground surface type inclinometer 14 is buried using the small steps 12. Then, the angle of the slope is measured. As shown in FIG. 3A, first, a cut slope of the first stage is constructed, and an inclinometer a is embedded in the uppermost stage to obtain the inclination angle θ with respect to the passage of time t. Immediately after construction, the ground is unstable, and the change in inclination angle due to rebound is large,
Eventually it becomes smaller. This shows that the cut slope is stable. As shown in FIG. 3B, a second-stage cut slope is then constructed, and an inclinometer b is embedded in the small horizontal section between them. Due to this cutting work, the value measured by the inclinometer b (inclination angle) changes significantly, and the inclinometer a at the top stage
The output also changes suddenly. However, if the stability of the slope is maintained, they will eventually approach a certain value. The same applies to C in FIG. From these facts, it can be seen that the cut slope on the upper stage is stable. Therefore, when performing the construction on the lower stage, the inclinometer used for the measurement on the upper stage may be moved and used. Furthermore, when cutting work is performed as shown in D of FIG. 3 and the angle is measured by the inclinometers d and e, the output of the inclinometer d becomes stable after a large angle change immediately after the construction, whereas It is assumed that the output of the inclinometer e may show a gradually increasing inclination angle. In that case, it is highly likely that the slope will go to collapse, and it is possible to predict the margin time until the collapse from the amount of change in the inclination angle. Therefore, from this predicted data, it is possible to take measures to stabilize the slope.

As shown in FIG. 4, the ground surface type inclinometer 14 has a format in which two horizontal components can be measured.
It is preferable to embed it at a depth of about 70 cm so that the angular velocity in the maximum inclination direction is obtained. If the long-term stability of the slope is to be determined, it is sufficient to have a resolution of several tens of seconds. It is installed at a position of 50 to 70 cm in the ground so that it is less likely to be affected by weather and environmental conditions such as wind, vibration of trees and temperature change due to the wind.
The measurement result is stored in the recording device 16, or the result of the recording device is data-transmitted by a wireless transmitter.

The slope fluctuation serves as an index indicating the degree of instability of the slope when a weak layer exists in the deep layer, and an index indicating the degree of instability of the slope when extruded from the side of the slope. . Furthermore, the tilt variation is closely related to the collapse associated with the top ring. And the ground surface type inclinometer,
Since it is not necessary to use a fixed point as a reference, and it is the most economical and inexpensive, it is easy to install and can be installed at many points, which is extremely preferable. However, since this ground-based inclinometer is sensitive to temperature and weather (such as wind), it is necessary to bury it as described above so as not to be affected by them. Further, it is preferable to install on the horizontal surface of the small step of the slope so that it is not affected by the creep of the surface layer of the slope as much as possible, or to form a horizontal part and install it on the horizontal part when there is no small step. When installing the inclinometer on the ground, it is necessary to be careful not to disturb the ground.

[0017]

As described above, according to the present invention, a ground surface type inclinometer is embedded in a slope, the inclination angular velocity at that position is measured, and the inclination angular velocity and the margin time until collapse are inversely proportional. It is a method of diagnosing the stability of slopes that predicts the stability of the slopes or the margin time until the collapse, using simple and inexpensive equipment. The stability can be diagnosed not only on the surface but also on the slope in natural terrain), and moreover, the margin time until the collapse can be predicted. In particular, since the device is simple, it is possible to observe at many points, and there is little part that depends only on the experience and intuition of the slope survey engineer, and the reliability can be improved because the data can be grasped quantitatively.

Since the present invention can be applied especially to a terrain where the landslide surface is not clear, it is a very excellent method in that scientific ground stabilization diagnosis can be performed even in a place where prediction was uncertain in the past. .

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a moving speed of a landslide mass and a margin time until the sliding.

FIG. 2 is a diagram showing a relationship between an inclination angular velocity and a margin time until failure.

FIG. 3 is an explanatory diagram of a stable management method of a cut slope using a ground surface type inclinometer.

FIG. 4 is an explanatory view showing the installation situation of a ground surface type inclinometer.

[Explanation of symbols]

 10 Slope 12 Small Stage 14 Ground Surface Inclinometer 16 Recording Device

Claims (2)

[Claims] 1. A ground surface type inclinometer is embedded on a slope, the tilt angular velocity at that position is measured, and the fact that the tilt angular velocity and the margin time until collapse are in inverse proportion to each other is utilized. A method for diagnosing the stability of a slope, comprising evaluating the stability of the slope or predicting a margin time until the slope collapses. 2. A ground surface type inclinometer is a type capable of measuring two horizontal components and is buried in a horizontal portion of a small step of a cut slope at a depth of about 50 to 70 cm from the ground surface, whereby the maximum slope is obtained. The method of claim 1, wherein the angular velocity in the direction is determined.