JP3307590B2 - Ground liquefaction detection method, liquefaction detection device and system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquefaction detection method, a liquefaction detection apparatus and a system for detecting liquefaction of a ground caused by seismic motion.

[0002]

2. Description of the Related Art In the liquefaction of ground, the shear strength of sandy soil and the like decrease with an increase in pore water pressure of a sandy soil layer during an earthquake, the ground rapidly becomes unstable, and sand and fountains are formed. Or, a phenomenon in which lateral flow occurs. The liquefaction phenomenon is likely to occur in a loose sandy soil layer located deeper than the groundwater level, and is one of the factors that causes damage to lifelines and other buried pipes of buildings. Therefore, it is important to detect the occurrence of liquefaction immediately after the occurrence of an earthquake and to understand the degree of liquefaction when it occurs, in order to reduce secondary disasters.

For example, it is said that the liquefaction of the ground causes an increase in the damage rate of water pipes and gas pipes, which are lifelines. Supply must be stopped. Therefore, development of a rapid detection method of liquefaction is desired.

Conventionally, as a method of detecting such liquefaction of the ground, there is a method of installing a pore water pressure gauge directly under the ground to measure the pore water pressure.
There is a method for detecting liquefaction of the ground disclosed in Japanese Patent Application Laid-Open Publication No. HEI 10-303, 1988. In this liquefaction detection method, a hollow pipe with an opening at the tip is installed in a loose sandy soil layer where liquefaction is expected, and the flow of groundwater generated by excessive pore water pressure of the ground generated during an earthquake etc. is opened. The liquefaction is estimated by measuring the amount of rise in the water level in the hollow tube with a water pressure gauge installed in the hollow tube. As another detection method, there is a method for detecting liquefaction of the ground disclosed in Japanese Patent Application Laid-Open No. 6-17413. In this liquefaction detection method, the upper end of the above-described hollow tube is closed, a number of openings are provided on the lower side surface, and a pressure gauge for measuring air pressure is installed inside the hollow tube, for example, to raise the water level in the hollow tube. The rise of the air pressure in the hollow tube accompanying the above is measured, and the degree of liquefaction is estimated based on the sum of the rise in the water level of the hollow tube and the air pressure at the upper end. Further, as another detection method, Japanese Patent Application Laid-Open No. 7-1097
There is a method for early detection of liquefaction of ground disclosed in Japanese Patent Publication No. 25. In this liquefaction detection method, the scale and distance range and acceleration level of the earthquake that causes liquefaction are set in advance, the magnitude and distance of the earthquake are estimated from the information of the initial earthquake, and the earthquake acceleration is monitored. Based on these results, it is determined whether or not liquefaction of the ground is caused, and the liquefaction is prevented by pumping water based on the determination.

[0005]

As described above, conventionally,
Various liquefaction detection methods have been proposed. However, the method of measuring pore water pressure by installing a pore pressure gauge directly under the ground is costly due to the need for boring work when installing the pore pressure gauge. There is a problem that the gauge is apt to break down, and if it breaks down, it is necessary to perform boring work again, so that the cost is further increased.

In the liquefaction detection method disclosed in Japanese Patent Application Laid-Open No. Hei 6-10335, compared to a method of burying a pore water pressure gauge underground and directly measuring fluctuations in pore water pressure, the method for installing and repairing the apparatus is more difficult. Such cost and labor can be reduced. In addition, all the measuring electronics are on the surface of the earth, and they are easy to maintain and manage, because they have few failures, are durable, and can be easily replaced even if they fail. It has the advantage of being In addition, in the liquefaction detection method disclosed in Japanese Patent Application Laid-Open No. Hei 6-17413, in addition to the above-described advantages, it is possible to measure a wide range of pore water pressure by closing the upper end and suppressing the rise in water level. , And good reactivity. However, even in these methods, there is a problem that the boring work is still required for installing the detecting device such as the hollow tube, which is large and expensive.

Furthermore, the liquefaction detection method disclosed in Japanese Patent Application Laid-Open No. 7-109725 has the advantage that liquefaction can be detected at an early stage. However, the occurrence of liquefaction is basically based only on the seismic acceleration level. Since the presence / absence is determined, there is a problem in reliability regarding determination of occurrence of liquefaction.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a ground which can be installed at low cost and can quickly and reliably determine whether or not liquefaction has occurred. Liquefaction detection method, liquefaction detection device and system.

[0009]

According to a first aspect of the present invention, there is provided a method for detecting liquefaction of a ground, comprising detecting a seismic wave generated by the occurrence of a seismic motion, determining a natural period of the vibration of the seismic wave, and detecting a displacement of the ground. If both the natural period and the displacement are equal to or larger than a predetermined threshold, it is determined that the liquefaction phenomenon has occurred in the ground.

In this method for detecting liquefaction of the ground, when a seismic wave is detected, a natural period of the vibration of the seismic wave is obtained, and a displacement of the ground is detected. It is determined that the liquefaction phenomenon occurred on the ground.

The liquefaction detection device for ground according to claim 2 is
A seismic wave detecting means for detecting a seismic wave, a natural period detecting means for detecting a natural period of a vibration of the seismic wave detected by the seismic wave detecting means, a ground displacement detecting means for detecting a ground displacement, and a natural period detecting means It is determined whether the detected natural period and the ground displacement detected by the ground displacement detecting means are each equal to or greater than a predetermined threshold. If both the natural period and the ground displacement are equal to or greater than the threshold, a liquefaction phenomenon occurs in the ground. Liquefaction determining means for determining that the liquefaction has been performed.

In this ground liquefaction detection device, the seismic wave is detected by the seismic wave detecting means, the natural period of the vibration of the seismic wave detected by the natural period detecting means, and the ground displacement caused by the earthquake detected by the ground displacement detecting means. Are respectively equal to or greater than predetermined threshold values, the liquefaction determining means determines that the liquefaction phenomenon has occurred in the ground.

According to a third aspect of the present invention, there is provided an apparatus for detecting liquefaction of a ground,
3. The apparatus according to claim 2, further comprising: a maximum acceleration detecting means for detecting a maximum acceleration based on the seismic wave; and an SI value calculating means for calculating an SI value based on the seismic wave. And whether the maximum acceleration and the SI value are each equal to or greater than a predetermined threshold in addition to the ground displacement and the ground displacement. Is determined to have occurred.

According to a fourth aspect of the present invention, there is provided an apparatus for detecting liquefaction of a ground,
The method according to claim 2 or 3, wherein the natural period of the seismic wave is estimated based on a time interval (zero crossing time) at which the seismic waveform crosses the base line.

The liquefaction detection device for ground according to claim 5 is
The method according to any one of claims 2 to 4, wherein the displacement of the ground is estimated based on the maximum acceleration and the SI value.

The liquefaction detection device for ground according to claim 6 is
The apparatus according to any one of claims 2 to 5, further comprising an alarm unit that issues an alarm when the liquefaction determining unit determines that a liquefaction phenomenon has occurred.

A liquefaction detection system for a ground according to a seventh aspect is a liquefaction detection system for a ground for intensively monitoring the occurrence of liquefaction at a plurality of liquefaction detection points. A seismic wave detecting means for detecting a seismic wave at a point, a natural period detecting means for detecting a natural period of vibration of the seismic wave detected by the seismic wave detecting means, and a ground displacement detecting means for detecting a displacement of the ground at each liquefaction detecting point And, at each liquefaction detection point, it is determined whether the natural period detected by the natural period detecting means and the ground displacement detected by the ground displacement detecting means are respectively equal to or more than a predetermined threshold, and the natural period and the ground displacement are determined. Liquefaction determining means for determining that a liquefaction phenomenon has occurred in the ground when both are greater than or equal to a threshold value, and liquefaction determining means for each of a plurality of liquefaction detection points Communication means for transmitting the result of determination by the communication means, and monitoring means for monitoring the liquefaction occurrence status at a plurality of liquefaction detection points based on the determination result of each liquefaction detection point transmitted by the communication means. is there.

In this ground liquefaction detection system, when a seismic wave is detected at each liquefaction detection point by the seismic wave detecting means, the natural period detecting means detects the natural period of the vibration of this seismic wave and the ground displacement detects each liquefaction. The displacement of the ground at the detection point is respectively detected, and when both the natural period and the ground displacement are equal to or more than the threshold value, the liquefaction determining means determines that the liquefaction phenomenon has occurred in the ground.
The liquefaction determining means determines whether or not liquefaction has occurred at each of the plurality of liquefaction detection points, and the result is transmitted by the communication means. Be monitored.

The liquefaction detection system according to the eighth aspect of the present invention is the ground liquefaction detection system according to the seventh aspect, further comprising: a maximum acceleration detecting means for detecting a maximum acceleration based on a seismic wave at each liquefaction detection point; Liquefaction determining means determines whether the maximum acceleration and the SI value are each equal to or greater than a predetermined threshold value in addition to the natural period and the ground displacement, and When the ground displacement, the maximum acceleration, and the SI value are all equal to or larger than the threshold value, it is determined that the liquefaction phenomenon has occurred in the ground.

A liquefaction detection system according to a ninth aspect of the present invention is the ground liquefaction detection system according to the seventh or eighth aspect, wherein a plurality of liquefaction detection points are provided in a gas supply area in which a number of gas pipes are buried. is there.

A liquefaction detection system for a ground according to a tenth aspect of the present invention is the liquefaction detection system for a ground according to the ninth aspect, further comprising: The shutoff instruction is given to the gas pipe in consideration of the burial condition.

[0022]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a block diagram showing a functional configuration of a ground liquefaction detecting apparatus 100 according to an embodiment of the present invention. Note that the method for detecting liquefaction of the ground according to the present invention is embodied in the operation of the liquefaction detection device 100, and a description thereof will be omitted.

The liquefaction detection device 100 includes a seismic wave detection sensor 101 and a liquefaction determination unit 102. The seismic wave detection sensor 101 includes a seismic wave detecting unit 10 for detecting a seismic wave, a maximum acceleration detecting unit 12 for detecting a maximum acceleration (A _max ) based on the seismic wave detected by the seismic wave detecting unit 10, and a detection by the seismic wave detecting unit 10. And an SI value calculating means 13 for calculating an SI value (SI) based on the obtained seismic wave. The liquefaction determination unit 102
The apparatus includes a natural period detecting means 11 for detecting a natural period (T) of vibration of a seismic wave detected by the seismic wave detecting means 10, and a ground displacement detecting means 14 for detecting a ground displacement (D).

The liquefaction determining section 102 further includes a liquefaction determining means 15. The liquefaction determining means 15 includes a natural period T detected by the natural period detecting means 11, a ground displacement D detected by the ground displacement detecting means 14, a maximum acceleration A _max detected by the maximum acceleration detecting means 12, and an SI value. It is determined whether the SI values calculated by the calculating means 13 are larger than predetermined thresholds (T ₀ , D ₀ , A ₀ , SI ₀ ), respectively, and the natural period T, the ground displacement D, and the maximum acceleration A
If both the _max and SI values are larger than the respective threshold values, it is determined that a liquefaction phenomenon has occurred in the ground. In ground displacement detecting means 14, a displacement D of the ground may be detected directly by a displacement sensor, but as described later, TOWHATA et al using the maximum acceleration A _max and SI values. (Soils A
ND FOUNDATIONS, Vol. 36, 29-44, 1996) can be used to obtain a simple configuration.

FIG. 2 shows the liquefaction detection device 100 shown in FIG.
1 shows a configuration example in which a ground liquefaction detection system provided with a gas supply line is applied to a gas supply line.

This gas supply line is connected to a gas production plant 30
0 to supply gas to a home 500, a factory 501, and the like in each area, and a governor station 400 and a liquefaction detection device 10 for adjusting the gas pressure on the way.
0 is provided. The liquefaction detection device 100 is connected to a central monitoring room 200 via a communication network. Monitoring room 2
Liquefaction detection devices in other areas are similarly connected to 00, and monitor the presence or absence of liquefaction based on information from each area to shut off gas supply. Monitoring room 2
00 corresponds to the monitoring means of the present invention.

In this gas supply line, high-pressure gas produced in a gas production plant 300 is usually supplied to a gas tank 301.
Shut-off valve 302a
After the pressure is adjusted by a governor (gas pressure regulator) 302 having the gas pressure, the gas passes through a high-pressure conduit 303 and is sent to a governor station 400 installed at each of the gas supply areas, for example, at 3600 locations. Governor station 400
Has a governor 401 and an emergency shutoff valve 402,
The gas sent to the governor station 400 is governor 4
After the pressure is adjusted to the medium pressure by the pressure controller 01, the pressure is adjusted to the low pressure by the governor 104 having the shut-off valve 104a which passes through the medium pressure conduit 403 and is shut off in an emergency included in the liquefaction detection device 100. It passes through the conduit 105 and is supplied to each home 500, factory 501, and the like.

The liquefaction detection device 100 is installed between the governor station 400 and the line between each home 500 and factory 501 and the like.
In addition to the liquefaction determination unit 102 and the governor 104, an alarm notification unit 103 is included. Note that the alarm notification unit 103 corresponds to the alarm unit of the present invention.

The seismic wave detection sensor 1 according to the present embodiment
Reference numeral 01 denotes an SI (Spectrum Intensity) sensor, which can store and output an earthquake waveform on the ground surface and measure acceleration due to an earthquake (maximum acceleration A _max ). The SI value obtained by the SI sensor is a numerical value of the degree of vibration of a general building due to an earthquake, and is an average value in a specific natural frequency range obtained by performing a response analysis with the acceleration of the earthquake as an input. It is. Specifically, the SI value can be obtained by the following equation (1), and it is known from past observation results that the correlation with the seismic intensity and the presence or absence of earthquake damage is higher than the maximum acceleration. . Note that the SI sensor includes a semiconductor acceleration sensor of a capacitance type, a piezoresistive type, a piezoelectric type, or the like.

[0031]

(Equation 1)

As described above, the seismic wave detecting means 10,
The maximum acceleration detecting means 12 and the SI value calculating means 13 can be realized by the seismic wave detecting sensor 101, respectively.

The liquefaction determination unit 102 obtains a natural period T and a ground displacement D of the earthquake waveform based on the output (earthquake waveform, maximum acceleration _Amax and SI value) of the seismic wave detection sensor 101, and obtains these natural periods T , Ground displacement D, maximum acceleration A _max and SI value are all threshold values (T ₀ , D ₀ , A ₀ , S
I ₀ ) is determined, and if both are greater than the threshold value, it is determined that the liquefaction phenomenon has occurred in the ground on which the liquefaction detection device 100 is installed, and the monitoring room is connected via the communication network. The liquefaction generation signal 1021 is transmitted to the control unit 200. The liquefaction determination unit 102 is specifically constituted by a microcomputer, and a ROM (not shown)
The program operates as described later by executing a program stored in an ad only memory or the like.
That is, the liquefaction determination unit 102 implements the natural period detection unit 11, the ground displacement detection unit 14, and the liquefaction determination unit 15, respectively.

Incidentally, one of the features of the seismic wave when the liquefaction phenomenon occurs is that the period of the wave is long. Therefore, in the present embodiment, as the natural period T, a zero-cross period estimated based on a time interval (zero-cross time) at which the earthquake waveform crosses the base line Z as shown in FIG. 3 is used. Here, the time required for the seismic wave crossing the base line Z to further cross the base line Z twice is defined as one zero-cross cycle.

Another characteristic of the seismic wave when the liquefaction phenomenon occurs is that the displacement is large despite the acceleration waveform, and the waveform is similar to a sine curve. The above-mentioned TOWHATA et al. Shows that when the earthquake waveform is similar to a sine curve, the maximum value _Dmax of the ground displacement D can be approximately calculated by the following equation 2. In the present embodiment, the maximum acceleration A output by the seismic wave detection sensor 101
_The ground displacement D is calculated from this approximate expression (Expression 2) using the _max and SI values.

[0036]

D _max = 2 × (SI) ² / A _max (2)

Since the seismic wave detection sensor 101 always outputs the maximum acceleration A _max and the SI value, the method of calculating the ground displacement D using the equation 1 is a method suitable for the present system. Accordingly, it is not necessary to directly measure the displacement of the unstable ground where the long-period noise of the seismic wave is enlarged and the displacement can be calculated easily and accurately.

When the natural period T and the ground displacement D of the seismic wave are obtained, the liquefaction determining unit 102 sets the natural period T, the ground displacement D, the maximum acceleration A _max and the SI value to threshold values (T ₀ , D ₀ , A). ₀ , SI ₀ ). This determination is first sufficient maximum acceleration A _0, for example 1 to liquefaction occurs in loose sandy soil layer
00 gal (= cm / s ² ), and similarly, an SI value SI ₀ sufficient to cause the liquefaction phenomenon is set to, for example, 20 ki.
ne (= cm / s) and the detected maximum acceleration A
A seismic wave in which both _max and the calculated SI value are larger than the set thresholds (A ₀ , SI ₀ ) is extracted. Next, among the extracted seismic waves, the natural period T indicating a characteristic behavior in the seismic wave when the liquefaction phenomenon occurs as described above, and a large value when the liquefaction phenomenon generally occurs, Those for which the indicated ground displacement D is equal to or more than the set threshold value (T ₀ , D ₀ ) are further extracted. The threshold value T ₀ of the natural period T is, for example, 2.0 seconds, and the threshold value D ₀ of the ground displacement D is, for example, 10 cm. In this way, the detected specific period T, the maximum acceleration A _max and the calculated ground displacement D, SI values are all the threshold (T _0,
At a detection point where a seismic wave larger than A ₀ , D ₀ , SI ₀ ) is extracted, it is determined that a liquefaction phenomenon has occurred on the ground.

The alarm notification unit 103 includes a liquefaction determination unit 102
When it is determined that the liquefaction phenomenon has occurred in the ground in (1), an alarm (for example, lighting or blinking of a display lamp, a buzzer alarm) is issued in response to an alarm signal output from the liquefaction determination unit 102.

When the liquefaction determining unit 102 determines that a liquefaction phenomenon has occurred in the ground, the monitoring room 200
Liquefaction occurrence signal 10 output from liquefaction determination unit 102
In response to 21, an emergency shutoff instruction is output to both or one of the governor 302 and the emergency shutoff valve 402. The output destination of the emergency shutoff instruction is determined in consideration of the burial status of the gas pipe at the liquefaction detection point to which the liquefaction detection device 100 belongs.

Next, the operation of the ground liquefaction detection apparatus 100 and the liquefaction detection system having the above-described configurations will be described with reference to FIG. 4 and FIGS.

[0042] First, determine seismic waves are detected by the seismic sensor 101 (step S100), the liquefaction judging unit 102, SI value calculated by the seismic wave detection sensor 101 whether the threshold SI ₀ or greater than (step S101), is greater than the threshold value SI _0; (step S101 Y), followed by seismic sensors 101
Maximum acceleration A _max output from determines whether the threshold A ₀ is larger than (step S102). If the maximum acceleration A _max is greater than the threshold A ₀ (step S1
02; Y), it is determined whether or not the natural period T obtained by the liquefaction determination unit 102 is larger than the threshold value T ₀ (step S103), and if it is larger than the threshold value T ₀ (step S103; Y). further displacement D of the ground obtained using equation 1 to determine whether the threshold D ₀ is greater than the liquefaction determining unit 102 (step S104).

If the displacement D of the ground is larger than the threshold value D ₀ (step S104; Y), the liquefaction determination unit 102
Determines that liquefaction has occurred on the ground (step S
105), outputs a liquefaction generation signal 1021 to the central monitoring room 200 and outputs an alarm signal to the alarm notification unit 103 (step S106). At the same time, by outputting an emergency shutoff instruction to the governor 104, the governor 10
The fourth shutoff valve 104a is driven to shut off the gas flow path after the governor 104.

In the monitoring room 200, the liquefaction generation signal 1021
And outputs an emergency shutoff instruction to both or one of the governor 302 of the gas manufacturing plant 300 and / or the emergency shutoff valve 402 of the governor station 400. Thereby, both or one of the shutoff valve 302a and the emergency shutoff valve 402 of the governor 302 is driven, and the gas flow path is shut off.

On the other hand, when the obtained SI value is smaller than the threshold value SI ₀ (step S101; N), when the maximum acceleration A _max is smaller than the threshold value A ₀ (step S1).
02; N), when the natural period T is less than the threshold value T ₀ (step S103; N), or when the obtained ground displacement D is less than the threshold value D ₀ (step S10).
4; N), in any case, the liquefaction determination unit 1
In No. 02, it is determined that no liquefaction phenomenon has occurred on the ground (step S107).

Next, the zero-cross period T, the ground displacement D, the maximum acceleration A _max and the SI value are calculated by analyzing the seismic waveform recorded when the earthquake occurred in the past, and the ground level according to the present embodiment is calculated. The result applied to the liquefaction detection system described above will be described.

FIG. 5 shows the relationship between the zero-cross period and the displacement obtained from the seismic waveforms of various places recorded during the past earthquake. The zero-cross cycle was obtained from the seismic waveform, and the maximum zero-cross cycle within 10 seconds after the maximum acceleration was recorded was used. The displacement is calculated from the maximum acceleration and the SI value using the above equation (2).
Was calculated. In the figure, those indicated by rectangular marks are T
> 2.0 sec, D> 10 cm, A _max > 100 gal, S
The one that satisfies the four parameters of I> 20 kinetics, that is, the one that is determined by the liquefaction determining unit 102 to have a liquefaction phenomenon. Those indicated by triangular marks are those where A _max > 100 gal, SI> 20 kinetics, and T _z <2.0 seconds or D <10 cm, that is, the liquefaction phenomenon occurs in the liquefaction determination unit 102. It is determined that they have not been done. In addition, those indicated by diamond marks are A _max <100 gal or SI
<20 kinetics, that is, it is determined that no liquefaction phenomenon has occurred.

Among these seismic motions, all of the seismic waveforms recorded at the points where liquefaction actually occurred could be determined to have liquefaction. In addition, there is almost no erroneous determination that liquefaction has occurred based on the seismic waveform recorded at a point where liquefaction did not occur, and liquefaction phenomena caused by past earthquakes can be detected with almost 100% accuracy. It could be judged. When the liquefaction detection system is actually driven, if the gas pipe is cut off due to erroneous determination, a considerable amount of time is required for the subsequent recovery work, but it can be said that there is almost no such danger in the present system.

From the simulation results based on the past earthquake waveform, the natural period T and the ground displacement D
In most cases, the liquefaction of the ground occurs for the earthquakes exceeding the thresholds. In addition to the natural period T and the ground displacement D, in addition to the earthquakes exceeding the thresholds for both the maximum acceleration A _max and the SI value, almost all the earthquakes are almost equal. It was found that 100% liquefaction occurred.

As described above, the system for detecting liquefaction of the ground according to the present embodiment determines whether or not liquefaction of the ground has occurred using only the seismic waveform of the ground surface. It is only necessary to install the seismic wave detection sensor 101 on the ground surface at the detection point, and all other electronic devices for calculation and the like are present on the ground surface. Therefore, the system becomes inexpensive as compared with a system in which measuring devices are buried underground. In addition, since it can be easily installed, more seismic wave detection sensors 101 can be installed, and a high-density liquefaction detection network can be realized to grasp the state of liquefaction occurrence in a two-dimensional manner. is there. Further, this system can be configured in a system including only a general seismometer capable of measuring the acceleration for the presence or absence of liquefaction. Therefore, a special device for directly observing the liquefaction phenomenon is not required, and it can be realized at low cost.

In the present embodiment, the natural period T is set to the zero-cross period and the displacement D of the ground is obtained by an approximate expression, so that the calculation speed is remarkably improved. Therefore,
When the liquefaction phenomenon of the ground occurs, the liquefaction determination unit 102
, It is possible to detect more quickly, and to take a subsequent countermeasure quickly.

Further, in the present embodiment, the natural period T, the ground displacement D, the maximum acceleration A _max and the SI value are used as parameters for determining whether or not liquefaction has occurred. A highly reliable determination result can be obtained.

Although the present invention has been described with reference to the embodiment, the present invention is not limited to the above embodiment, and various modifications can be made. For example, in the above-described embodiment, it is determined that liquefaction has occurred when all of the four parameters of the natural period T, the ground displacement D, the maximum acceleration _Amax, and the SI value are equal to or larger than the threshold. Even if it is determined that liquefaction has occurred when the two parameters of the cycle T and the ground displacement D are both equal to or greater than the threshold value, the determination can be made with fair accuracy.

In the above embodiment, the presence or absence of liquefaction is determined by using a predetermined one-period seismic waveform. However, parameters required in real time (natural period T,
The displacement D of the ground, the maximum acceleration _Amax, and the SI value) may be calculated, and the determination may be made continuously in real time.

[0055]

As described above, according to the method for detecting liquefaction of the ground according to the first aspect or the apparatus for detecting liquefaction of the ground according to any one of the second to sixth aspects, an earthquake causes The natural period of the vibration of the generated seismic wave and the displacement of the ground at the detection point are detected, and it is determined that the liquefaction phenomenon has occurred when the natural period and the ground displacement are equal to or greater than a predetermined threshold, so that it is simple and quick. This has the effect that the liquefaction of the ground can be detected.

In particular, according to the liquefaction detection apparatus for a ground according to any one of claims 3 to 6, the maximum acceleration is detected based on the seismic wave and the SI value is calculated to determine the natural period and the ground. Since it is determined that the liquefaction phenomenon has occurred when all of the four parameters of the displacement, the maximum acceleration, and the SI value are equal to or larger than the threshold value, it is possible to obtain a highly reliable determination result.

According to the liquefaction detection system for a ground according to any one of claims 7 to 10, the natural period of the vibration of the seismic wave from the seismic wave detected at each liquefaction detection point and each detection In addition to detecting the displacement of the ground at the point and determining that the liquefaction phenomenon has occurred when the natural period and the ground displacement are equal to or greater than a predetermined threshold, and transmitting the determination result to the monitoring means, With such a configuration, it is possible to easily monitor the state of liquefaction occurrence at a plurality of detection points, take quick response measures, and produce an effect that an inexpensive system can be constructed.

In particular, according to the liquefaction detection system for a ground according to any one of claims 8 to 10, further, the maximum acceleration and the SI value are obtained from the seismic wave detected at each liquefaction detection point. When all of the four parameters of the natural period, the ground displacement, the maximum acceleration, and the SI value are equal to or more than the threshold value, it is determined that the liquefaction phenomenon has occurred. This has the effect that response measures can be taken. In addition, this liquefaction detection system can be configured as a system consisting only of a general seismometer capable of measuring the acceleration of the presence or absence of liquefaction, so a special device for directly observing the liquefaction phenomenon is required. Without this, there is an effect that it can be realized at low cost.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a functional configuration of a liquefaction detection device according to an embodiment of the present invention.

FIG. 2 is a schematic diagram illustrating a configuration of a liquefaction detection system including the liquefaction detection device illustrated in FIG.

FIG. 3 is a waveform diagram for explaining a natural period of vibration of a seismic wave generated by the occurrence of an earthquake.

FIG. 4 is a flowchart illustrating the operation of the liquefaction detection system shown in FIG. 2;

FIG. 5 is a characteristic diagram for describing the reliability of the liquefaction detection system shown in FIG.

[Explanation of symbols]

10 ... seismic wave detecting means, 11 ... natural period detecting means, 12
... Maximum acceleration detection means, 13 ... SI value calculation means, 14 ...
Ground change detecting means, 15: liquefaction determining means, 100: liquefaction detecting device, 101: seismic wave detection sensor, 102: liquefaction determining section, 103: warning notification section (warning means), 200
... Monitoring room (monitoring means)

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takashi Yanada 2-12-19 Shibuya, Shibuya-ku, Tokyo Inside Yamatake Honeywell Co., Ltd. (72) Inventor Hiroyuki Furukawa 2-12-19 Shibuya, Shibuya-ku, Tokyo Yamatake Honeywell Co., Ltd. (72) Inventor Hikaru Takubo 2-12-19 Shibuya, Shibuya-ku, Tokyo Yamatake Honeywell Co., Ltd. (56) References JP-A-8-75865 (JP, A) JP-A-7-109725 (JP) , A) JP-A-10-123258 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01V 1/00 G01D 21/00 E02D 1/02

Claims (10)

(57) [Claims] 1. A method for detecting a seismic wave generated by the occurrence of a seismic motion, determining a natural period of the vibration of the seismic wave, and detecting a displacement of the ground. A method for detecting liquefaction of the ground, wherein it is determined that a liquefaction phenomenon has occurred. 2. A seismic wave detecting means for detecting a seismic wave, a natural period detecting means for detecting a natural period of a vibration of the seismic wave detected by the seismic wave detecting means, a ground displacement detecting means for detecting a displacement of the ground, It is determined whether the natural period detected by the natural period detecting means and the ground displacement detected by the ground displacement detecting means are each equal to or more than a predetermined threshold, and when both the natural period and the ground displacement are equal to or more than the threshold, A liquefaction detection device for a ground, comprising: liquefaction determination means for determining that a liquefaction phenomenon has occurred in the ground. 3. A liquefaction determining unit further comprising: a maximum acceleration detecting unit detecting a maximum acceleration based on the seismic wave; and an SI value calculating unit calculating an SI value based on the seismic wave. In addition to the displacement, it is determined whether the maximum acceleration and the SI value are each equal to or greater than a predetermined threshold, and if the natural period, the ground displacement, the maximum acceleration and the SI value are all equal to or greater than the threshold, a liquefaction phenomenon occurs on the ground. The liquefaction detection device for ground according to claim 2, wherein it is determined that the liquefaction has occurred. 4. The apparatus for detecting liquefaction of a ground according to claim 2, wherein the natural period of the seismic wave is estimated based on a time interval (zero crossing time) at which the seismic waveform crosses the base line. 5. The method according to claim 5, wherein the displacement of the ground is determined by a maximum acceleration and SI.
The liquefaction detection device for ground according to any one of claims 2 to 4, wherein the estimation is performed based on the value. 6. The apparatus according to claim 2, further comprising an alarm unit that issues an alarm when the liquefaction determining unit determines that a liquefaction phenomenon has occurred. The liquefaction detection device for ground described in the above. 7. A ground liquefaction detection system for intensively monitoring the occurrence of liquefaction at a plurality of liquefaction detection points, wherein seismic wave detection means for detecting seismic waves at each liquefaction detection point; Natural period detecting means for detecting the natural period of the vibration of the seismic wave detected by the seismic wave detecting means, ground displacement detecting means for detecting the displacement of the ground at each liquefaction detection point, and the natural period at each liquefaction detection point It is determined whether the natural period detected by the detecting means and the ground displacement detected by the ground displacement detecting means are each equal to or larger than a predetermined threshold, and when the natural period and the ground displacement are both equal to or larger than the threshold, the ground is determined. Liquefaction determining means for determining that a liquefaction phenomenon has occurred, and transmitting a determination result by the liquefaction determining means for each of a plurality of liquefaction detection points. Liquefaction of the ground, comprising: monitoring means for monitoring the liquefaction occurrence status at a plurality of liquefaction detection points based on the determination result of each liquefaction detection point transmitted by the communication means. Detection system. 8. A maximum acceleration detecting means for detecting a maximum acceleration based on a seismic wave at each liquefaction detection point, and an SI value calculating means for calculating an SI value based on the seismic wave,
The liquefaction determining means determines whether the maximum acceleration and the SI value are each equal to or greater than a predetermined threshold value, in addition to the natural period and the ground displacement, and determines that the natural period, the ground displacement, the maximum acceleration and the SI value are both equal to or greater than the threshold value. 8. When it is, it is determined that a liquefaction phenomenon has occurred in the ground.
The liquefaction detection system for the ground according to the above. 9. The ground liquefaction detection system according to claim 7, wherein a plurality of liquefaction detection points are provided in a gas supply area in which a number of gas pipes are buried. 10. The method according to claim 10, wherein when the occurrence of the liquefaction phenomenon is confirmed by the monitoring means, a shutoff instruction is given to the gas pipe in consideration of the buried state of the gas pipe at the liquefaction detection point. The ground liquefaction detection system according to claim 9, characterized in that: