JP2007247226A - Method of estimating ground displacement and method of determining ground liquefaction - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To facilitate the estimation of ground displacement and the determination of ground liquefaction based on various ground data. <P>SOLUTION: In a method of estimating the ground displacement caused by an earthquake, the ground displacement corresponding to a ground characteristic value of a stratum at an objective point with respect to arbitrary earthquake waves is calculated by using a correlation graph between the pre-calculated ground characteristic value and the ground displacement. Herein a relationship between the ground characteristic value with respect to essential earthquake waves and the ground displacement is obtained by a regression analysis based on data plotted on a graph between the ground characteristic values of a plurality of objective points and the ground displacement at the point with respect to the essential earthquake waves, and the ground displacements with respect to the arbitrary earthquake waves at a plurality of model points are obtained by using the ground data of the plotted model points that are approximated by a regression formula obtained from the regression analysis, and the regression analysis is performed again based on the obtained ground displacement and the ground characteristic values at the respective model points, to thereby calculate the correlation graph. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a ground displacement estimation method and ground liquefaction determination method, and more particularly to a method for easily estimating ground displacement due to an earthquake and determining ground liquefaction.

For the seismic evaluation of structures for underground power transmission, the horizontal displacement of the ground due to the earthquake is estimated, the presence or absence of liquefaction is judged, and if the ground liquefies, the ground due to liquefaction It is necessary to calculate the amount of settlement. And it is necessary to grasp the external force generated by the horizontal displacement of the ground, the liquefaction of the ground and the subsidence of the ground, and the strength of the structure for underground power transmission against this external force. Here, the external force can be calculated with high accuracy by software for earthquake response analysis in consideration of the dynamic nonlinearity of the soil soil (for example, see Non-Patent Document 1).
"One-dimensional ground earthquake response analysis software user manual" Chubu Electric Power Co., Inc. issued in 2002

However, the conventional earthquake response analysis software described above divides the ground into a gravel soil layer, a silt layer, a cohesive soil layer, a sandy soil layer, etc. in order from the bottom. It is necessary to measure ground data such as “wet unit volume weight”, “shear wave velocity”, “shear elastic modulus”, “strain dependence curve”. For this reason, when the structure of underground power transmission lines subject to seismic evaluation is large and extensive, it is necessary to input a huge amount of ground data at a large number of points to the above-mentioned earthquake response analysis software. Therefore, there is a problem that it takes a lot of labor and time.
Therefore, the problem to be solved by the present invention is to provide a method for easily estimating the ground displacement of the target point and determining the liquefaction of the ground from various ground characteristic values of the target point.

In order to solve the above-mentioned problem, the invention according to claim 1 is a ground displacement estimation method for calculating the influence of the ground of the target point by the occurrence of an earthquake using the ground characteristic value of the target point. Estimation of ground displacement by calculating the ground displacement corresponding to the ground property value obtained from the stratum of the target site for the seismic wave using a correlation graph between the ground property value calculated in advance and the ground displacement Is the method.
According to the first aspect of the present invention, a correlation graph between the ground characteristic value and the ground displacement is calculated in advance, and using this correlation graph, the ground characteristic value obtained from the formation of the target point with respect to an arbitrary seismic wave is obtained. By calculating the corresponding ground displacement, it can be estimated that the calculated ground displacement occurs.

Further, the invention according to claim 2 is the ground displacement estimation method according to claim 1, wherein the ground characteristic value at each of a plurality of target points and the ground displacement at each of the target points are calculated with respect to a base seismic wave. Then, plotting on the graph with the ground characteristic value and the ground displacement as axes respectively, and from the plotted data, obtain the relationship between the ground characteristic value and the ground displacement with respect to the base seismic wave by regression analysis, and from the regression analysis From the obtained regression equation, a plurality of plotted points that are more approximated are used as model points, and ground data of the plurality of model points are extracted. Using the extracted ground data, the points at the plurality of model points are extracted. The ground displacement for an arbitrary seismic wave is obtained, and by performing a regression analysis again with the ground displacement for the obtained arbitrary seismic wave and the ground characteristic value of the model point, A method of estimating ground displacement according to claim 1, wherein the calculating the relationship graph.
According to the second aspect of the present invention, a plurality of model points that are approximated by a regression analysis formula between the ground characteristic value and the ground displacement with respect to the base seismic wave are selected, and the model points can be reduced to, for example, about 15 points. . Then, when the ground displacement for an arbitrary seismic wave is obtained from the ground data of multiple model points, and the regression analysis is performed again using the obtained ground displacement and the ground property values of the model points, the ground property values of many points are not required. become. Therefore, the correlation graph can be calculated by simply performing a regression analysis again. And the ground displacement of many points with respect to arbitrary seismic waves can be estimated using the correlation graph.

Furthermore, the invention according to claim 3 is the ground displacement estimation method according to claim 1 or 2, wherein the ground characteristic value is a natural period of the ground, and the ground displacement is a horizontal displacement. This is a characteristic ground displacement estimation method.
That is, the present inventors have found from the past earthquake data that there is a correlation between the natural period of the ground and the horizontal displacement of the ground relative to the seismic wave, and have reached the present invention. The horizontal displacement can be easily estimated from the natural period of the ground.

Furthermore, the invention according to claim 4 is the formation below the first threshold value of the ground characteristic value of the target point and the correction N value in the stratum of the target point affected by the occurrence of the earthquake. A ground liquefaction determination method that uses a thickness to calculate a ground liquefaction determination at a target point with respect to an arbitrary seismic wave, which is equal to or less than a first threshold value of the ground characteristic value of the target point and a correction N value. Evaluation is performed by comparing the points plotted from the formation thickness with the threshold graph of the liquefaction determination boundary correlated with the previously calculated ground characteristic value and the formation thickness below the first threshold value of the corrected N value. This is a ground liquefaction determination method.
That is, the present inventors have found that the presence or absence of liquefaction of the ground at the time of the earthquake depends on the characteristic value of the ground and the formation thickness below the first threshold value (for example, 10) of the correction N value, The present invention has been achieved, and a liquefaction determination boundary correlated with a ground characteristic value with respect to the arbitrary seismic wave and a formation thickness below a first threshold value of the correction N value is calculated in advance, and the liquefaction determination boundary and the liquefaction determination boundary The presence or absence of liquefaction of the ground can be determined by comparing the point plotted from the ground characteristic value of the target point and the formation thickness below the first threshold value of the correction N value.

Furthermore, in the invention according to claim 5, when it is determined that the target point is liquefied, the ground subsidence amount after liquefaction is determined by calculating the subsurface thickness below the second threshold value of the corrected N value calculated in advance and after liquefaction. It is the estimation method of the amount of ground subsidence after the liquid of the ground characterized by calculating using the correlation graph with the amount of ground subsidence.
That is, the present inventors have found that the ground subsidence amount after liquefaction is a stratum below the second threshold value (for example, 15) of the corrected N value, regardless of the difference in waveforms such as inland earthquakes and plate boundary earthquakes. It was found that there is a correlation with the thickness, and the present invention has been achieved, and a correlation graph between the layer thickness below the second threshold value of the corrected N value and the amount of ground subsidence after liquefaction was calculated in advance. Using the correlation graph, the amount of land subsidence after liquefaction at the target point can be calculated.

According to the first aspect of the present invention, the ground displacement of the target point can be easily estimated from various ground characteristic values of the target point for any seismic wave.
Furthermore, according to the invention described in claim 2, in addition to the effect of the invention described in claim 1, it is possible to estimate the ground displacement at a number of the target points by a simpler method than the invention described in claim 1.
Furthermore, according to the invention described in claim 3, in addition to the effect of the invention described in claim 1 or 2, estimation of the horizontal displacement of the ground accompanying the seismic wave is facilitated.
Furthermore, according to invention of Claim 4, the liquefaction of the ground by an earthquake wave can be determined easily.
Furthermore, according to the invention of Claim 5, the amount of ground subsidence after liquefaction can be estimated easily.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
Fig. 1 shows the seismic wave of an inland direct earthquake, Fig. 2 shows the seismic wave of a plate boundary type earthquake, Fig. 3 shows the relationship between the natural period of the ground and the horizontal displacement due to earthquake motion, and Fig. 4 shows the characteristic of the ground at the model site. Fig. 5 shows the relationship between the period and horizontal displacement, the formation thickness with a correction N value of 10 or less, and the liquefaction index PL. Fig. 5 shows the theory of the relationship between the natural period of the ground and the formation thickness with a correction N value of 10 or less and the liquefaction index PL. FIG. 6 shows the relationship between the formation thickness of the corrected N value 15 and the amount of subsidence. Further, FIG. 7 shows empirical data on the relationship between the natural period of the ground, the formation thickness with a corrected N value of 10 or less, and the liquefaction index PL, and FIG. 8 shows the formation thickness with a corrected N value of 15 or less and the subsidence amount after liquefaction. FIG. 9 shows an example of the horizontal displacement of the ground and the deformation state of the underground power transmission structure, and FIG. 10 shows an example of the deformation state of the underground power transmission structure due to the ground subsidence.

(Ground displacement estimation method)
In the ground displacement estimation method that calculates the influence of the ground at the target point by the occurrence of an earthquake using the ground characteristic value of the target point, the ground characteristics obtained from the stratum of the target point for any seismic wave The ground displacement corresponding to the value is calculated using a correlation graph between the ground property value calculated in advance and the ground displacement.
Here, the “ground characteristic value” is a natural period of the ground shown in FIG. 3, for example. The “ground displacement” is, for example, a horizontal displacement (see FIG. 9) and a vertical displacement. The “correlation graph” is, for example, the correlation graph shown in FIG.

Specifically, first, with respect to the base seismic wave, the ground characteristic value at each of a plurality of target points and the ground displacement at each target point are plotted on a graph with the ground characteristic value and the ground displacement as axes. Then, from the plotted data, the relationship between the ground characteristic value and the ground displacement with respect to the base seismic wave is obtained by regression analysis using the least square method.
Here, the “basic seismic wave” is, for example, the seismic wave of the inland earthquake shown in FIG. 1 or the seismic wave of the plate boundary type earthquake shown in FIG. Here, 1 gal = 0.01 m / s ² . The “regression equation” is, for example, in FIG. 3, where x is the natural period Tg (s) of the ground on the horizontal axis and y is the horizontal displacement δmax (cm) on the vertical axis. 39.267x + 1.6232
It is. In the plate boundary earthquake shown in Fig. 3, y = 6.2804x + 4.4335
It is.

Then, from the regression equation obtained from the regression analysis, among the plotted points, a plurality of plotted points that are more approximate to the regression equation are used as model points, and the ground data of the plurality of model points is obtained. Extract.
Here, the “model points” are, for example, 15 points shown in FIG. Note that the correction N value (equivalent N value) on the vertical axis in FIG.
Na = {170 N / (σ _v +70)} × C ₁ + C ₂
It is. N represents an N value. Here, the N value refers to the number of drops until the ground is recessed 30 cm when a predetermined ball is dropped from the predetermined height onto the ground. In addition, N value becomes large, so that the ground becomes hard. Further, the sigma _v (to remove the influence of the pressure, as active on No圧100KN / m ² corresponds to N values, to calculate the inherent strength soil.) Effective on No圧it is.
If the fine particle content is FC,
For 0% ≦ FC <10%, C ₁ = 1 and C ₂ = 0.
For 10% ≦ FC <60%, C ₁ = (FC + 40) / 50,
A _{C 2 = (FC-10)} / 18.
For FC ≧ 60%, C ₁ = FC / 20-1 and C ₂ = (FC-10) / 18.
In addition, “the ground data of plotted points that are more approximate” is model ground data, and this ground data is data of each layer from the lower layer to the upper layer constituting the ground. These are the bottom depth of the stratum, “wet unit volume weight”, “shear wave velocity”, “shear elastic modulus”, “strain dependence curve” and the like.
Then, using the ground data, the conventional seismic response analysis software obtains the ground displacement for any seismic wave at the plurality of model points, and the regression is performed again based on the found ground displacement and the ground property values of the model points. By performing the analysis, the correlation graph (for example, shown in the lower diagram of FIG. 4) is calculated.

である。なお、Ｈ_ｉは第ｉ層の厚さ（ｍ）であり、Ｖ_ｓｉは第ｉ層のせん断弾性波速度（ｍ／ｓ）である。
なお、粘性土では、Ｖ_ｓｉ＝１００×Ｎ_ｉ ^{（１／３）} （１≦Ｎ_ｉ≦２５）
砂質土では、Ｖ_ｓｉ＝８０×Ｎ_ｉ ^{（１／３）} （１≦Ｎ_ｉ≦５０）
となる。 Further, “the natural period Tg of the ground” is shown in, for example, FIGS. 3, 4, and 5. In particular,

It is. Note that H _i is the thickness (m) of the i-th layer, and V _si is the shear elastic wave velocity (m / s) of the i-th layer.
In viscous soil, V _si = 100 × N _i ^(1/3) (1 ≦ N _i ≦ 25)
In sandy soil, V _si = 80 × N _i ^(1/3) (1 ≦ N _i ≦ 50)
It becomes.

Further, the “horizontal displacement δmax” is shown in FIG. 9, for example, and is shown on the vertical axis in FIG. 3 and FIG.
In FIG. 9, a pipe line 4 joined to a manhole 3 buried in the ground 2 at a joint point 5 is shown. Reference numeral 4 a denotes a central axis of the pipe 4. There is a possibility that the pipeline 4 may be broken at the maximum bending portions 4b and 4c in the horizontal direction of the pipeline 4 due to the horizontal displacement δmax of the underground 2. Further, the ground spring 7 in the horizontal direction of the underground 2 is shown on both sides of the pipeline 4. The ground spring 7 indicates the elasticity of the ground when an external force due to the horizontal displacement of the ground acts on the pipe 4.

ここで、ＦＬは液状化に対する抵抗率であり、ｘは土層厚（ｍ）である。
０＜ＰＬ≦５では液状化の危険度は低く、５＜ＰＬ≦１５では液状化の危険度が高くなり、さらに、ＰＬ＞１５では液状化の危険度が極めて高いことになる。 (Method of judging liquefaction of ground)
Furthermore, the ground liquefaction determination method according to the present invention is the ground layer having a ground characteristic value of the target point and a correction N value of 10 or less in the base layer of the target point due to the occurrence of an earthquake. In the ground liquefaction judgment method calculated using the thickness, plot the ground liquefaction judgment at the target point for any seismic wave from the ground characteristic value of the target point and the stratum thickness with a correction N value of 10 or less. This is evaluated by comparing the ground characteristic value calculated in advance with the threshold graph of the liquefaction determination boundary correlated with the formation thickness of the correction N value of 10 or less.
Here, the “threshold graph of the liquefaction determination boundary” is the threshold straight line (PL = 5 discriminant line) shown in FIG. 4 and FIG.
FIG. 5 shows the risk of liquefaction using the liquefaction index PL. PL is an index of the degree of liquefaction below 20 m and is calculated as follows.

Here, FL is the resistivity against liquefaction, and x is the soil layer thickness (m).
When 0 <PL ≦ 5, the risk of liquefaction is low. When 5 <PL ≦ 15, the risk of liquefaction is high, and when PL> 15, the risk of liquefaction is extremely high.

(Estimation method of land subsidence)
When it is determined that the target site is liquefied, the subsidence amount after liquefaction is further calculated using a correlation graph between the subsidence thickness after the correction N value of 15 or less calculated in advance and the subsidence amount after liquefaction. Calculate. Specifically, the correlation graph is shown in FIG. In FIG. 6, where x is the value on the horizontal axis and y is the value on the vertical axis, y = 3.1414x + 10.642 corresponds to the plotted data of land subsidence after liquefaction during an inland earthquake Y = 2.7993x + 11.726 shows the correlation graph corresponding to each plotted data of land subsidence amount after liquefaction at the time of plate boundary type earthquake, and both correlation graphs become close values ing.
FIG. 10 corresponds to FIG. 9 and shows the amount of ground subsidence. In FIG. 10, the pipelines 4 of the ground 1 and the underground 2 are sinking as indicated by a two-dot chain line. Note that the ground spring 6 in the vertical direction is shown. In this case, there is a risk of damage at the joint 5.

According to the ground displacement estimation method, the ground liquefaction determination method, and the ground subsidence estimation method having the above-described configuration, the following effects are obtained.
A correlation graph between the ground characteristic value and the ground displacement for any seismic wave is calculated in advance, and the ground displacement corresponding to the ground characteristic value obtained from the stratum at the target point for this arbitrary seismic wave is calculated using this correlation graph. It can be estimated that the calculated ground displacement occurs.

Furthermore, it is possible to select a plurality of model points that are approximated by a regression analysis formula between the ground characteristic value and the ground displacement with respect to the base seismic wave, and to set the number of model points to about 15, for example. Then, when the ground displacement for an arbitrary seismic wave is obtained from the ground data of multiple model points, and the regression analysis is performed again using the obtained ground displacement and the ground property values of the model points, the ground property values of many points are not required. become. Therefore, the correlation graph can be calculated by simply performing a regression analysis again. And the ground displacement of many points with respect to arbitrary seismic waves can be estimated using the correlation graph.
In addition, since a plurality of model points can be set to about fifteen, when the regression analysis is performed again with respect to an arbitrary seismic wave, data of ground characteristic values at many points becomes unnecessary. For this reason, the regression analysis can be easily performed again.

Since the horizontal displacement of the ground due to seismic waves can be predicted with the natural period of the ground, as in the above embodiment, the natural period of the ground is used as the ground characteristic value, and the ground displacement is set as the horizontal displacement. This makes it easy to estimate the ground displacement.
Note that the present invention is not limited to the above-described embodiment, and may be any combination as long as a correlation is recognized between the ground characteristic value and the ground displacement, and may be a combination other than the natural period of the ground and the horizontal displacement. .

Liquefaction of the ground depends on the characteristic value of the ground and the thickness of the corrected N value of 10 or less. Therefore, the liquefaction judgment correlates with the ground characteristic value for the arbitrary seismic wave and the thickness of the corrected N value of 10 or less. Calculating the boundary in advance and comparing the liquefaction determination boundary with the point plotted from the ground characteristic value of the target point and the layer thickness of the correction N value of 10 or less to determine liquefaction of the ground it can.
FIG. 7 shows the result of verifying the above “determination method of ground liquefaction” by ground liquefaction caused by the Hyogo-ken Nanbu Earthquake. In FIG. 7, the above “determination method of ground liquefaction” is correct in all 8 points of “with liquefaction” out of 10 points actually measured, and correct in 1 of 2 points of “no liquefaction”. As a result.

The subsidence after liquefaction correlates with the formation thickness of corrected N value of 15 or less regardless of the difference in waveforms such as inland earthquakes and plate boundary earthquakes. The correlation graph of the subsidence thickness after the liquefaction and the subsidence amount after the liquefaction N value of 15 or less and the subsidence amount after liquefaction are calculated in advance. The quantity can be calculated.
FIG. 8 shows the result of verifying the above-mentioned “correlation graph of the layer thickness with a corrected N value of 15 or less and the amount of ground subsidence after liquefaction” by actual measurement in Kobe City.

In the above embodiment, the correction N value has a first threshold value of 10 and a second threshold value of 15. However, the present invention is not limited to this, but by appropriately selecting the first threshold value and the second threshold value. It is possible to determine whether the ground is liquefied and to estimate the amount of ground subsidence after liquefaction.
Moreover, since the said invention can assume the damage at the time of an earthquake, it is possible to evaluate the earthquake resistance of each installation in a maintenance location. And based on the obtained evaluation results, it becomes possible to prioritize equipment inspection and repair in the event of an earthquake.
Furthermore, the present invention can be applied not only to the electric power industry in which pipes are buried in the ground, but also to other embedders (gas, tap water, sewage, communication business).

It is a graph which shows the seismic wave of an inland direct type earthquake. It is a graph which shows the seismic wave of a plate boundary type earthquake. It is a graph which shows the relationship between the natural period of a ground and the horizontal displacement by an earthquake motion. It is a graph which shows the relationship between the natural period of the ground of a model point, horizontal displacement, the formation thickness of correction | amendment N value 10 or less, and the liquefaction index PL. It is a graph which shows the theoretical value of the relationship between the natural period of a ground, the formation thickness of correction | amendment N value 10 or less, and the liquefaction index PL. It is a graph which shows the relationship between the formation thickness of correction | amendment N value 15, and subsidence. It is a graph which shows the verification data of the relationship between the natural period of the ground, the formation thickness of correction | amendment N value 10 or less, and the liquefaction index PL. It is a graph which shows the relationship between formation thickness of correction | amendment N value 15 or less, and the amount of settlement after liquefaction. It is explanatory drawing which shows the example of the horizontal displacement of a ground, and the deformation | transformation state of a structure. It is explanatory drawing which shows the example of the deformation | transformation state of the structure by the subsidence of the ground.

Explanation of symbols

Tg Natural period of ground δmax Horizontal displacement PL Liquefaction index

Claims (5)

In the ground displacement estimation method for calculating the influence of the ground at the target point by the occurrence of an earthquake using the ground characteristic value of the target point,
The ground displacement corresponding to the ground characteristic value obtained from the stratum of the target point for any seismic wave is calculated using a correlation graph between the ground characteristic value calculated in advance and the ground displacement. Estimation method. A method for estimating ground displacement according to claim 1,
For the base seismic wave, plot the ground characteristic value at each target point and the ground displacement at each target point on a graph with the ground characteristic value and the ground displacement as axes, respectively. The relationship between the ground characteristic value and the ground displacement for the base seismic wave is obtained by regression analysis,
From the regression equation obtained from the regression analysis, a plurality of plotted points that are more approximated are used as model points, and ground data of the plurality of model points is extracted.
Using the extracted ground data, the ground displacement for any seismic wave at the plurality of model points is determined,
The ground displacement estimation method according to claim 1, wherein the correlation graph is calculated by performing a regression analysis again based on the ground displacement with respect to the arbitrary seismic wave and the ground characteristic value of the model point. A ground displacement estimation method according to claim 1 or 2,
The ground displacement estimation method, wherein the ground characteristic value is a natural period of the ground, and the ground displacement is a horizontal displacement. The influence of the ground on the target point due to the occurrence of the earthquake is calculated using the ground characteristic value of the target point and the layer thickness below the first threshold value of the correction N value in the stratum of the target point. A determination method,
The ground liquefaction determination at the target point for any seismic wave is plotted from the ground characteristic value of the target point and the layer thickness below the first threshold value of the correction N value, and the ground characteristic value calculated in advance And a threshold graph of a liquefaction determination boundary correlated with a formation thickness below the first threshold value of the correction N value. When it is determined that the target site will be liquefied, use the correlation graph between the subsidence amount after liquefaction and the subsidence amount after liquefaction, and the subsidence amount after the liquefaction. A method for estimating the amount of ground subsidence after liquefaction of the ground, characterized in that it is calculated.

Images