JP2742798B2 - Liquefaction determination method and determination device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a liquefaction determination method for determining a liquefaction rate of a measurement target layer.

(Prior Art) When a building or the like is formed on a sandy ground, it is usually determined whether or not the ground is liquefied, and measures such as ground improvement are performed based on the determination result.

In this case, the following method is employed as a method for determining liquefaction of the ground.

First, as shown in FIG. 6, the ground to be subjected to liquefaction is drilled to a predetermined depth, a layer to be subjected to liquefaction is sampled by a sand sampler, etc., and the soil obtained by this sampling is transported to a test site. Then, this is put into an experimental water tank 101 as shown in FIG. 7 (a) and shaken by a shaker to liquefy the sampled soil, or triaxial compression as shown in FIG. 7 (b). Tester 102
And the liquefaction rate at that time was measured to determine the liquefaction rate (degree of liquefaction) of the layer to be subjected to liquefaction determination.

When the liquefaction rate of this layer is high, measures such as improving the geological condition of the ground have been taken.

However, such a conventional liquefaction determination method has the following problems.

(1) Since the liquefaction rate can be determined only for the sampled depth, only the information as points can be obtained.

(2) Since sampling must be performed so as not to disturb the state of the soil, a high level of technology is required at the time of sampling.

(3) Since soil must be carried from the sampling location to the test site, there is a strong possibility that the soil will be disturbed during this time.

(4) Since the test is not performed in situ, the sealing pressure of the vibration triaxial test includes an estimated factor.

(5) Earthquake motion is a composite wave of many frequency components. However, at the time of testing, only a specific frequency component is used for testing, so it is necessary to estimate the liquefaction rate during an earthquake from the test results.

(6) It takes too much time from the time of boring until the result of determination of the liquefaction rate is obtained.

(Object of the Invention) The present invention has been made in view of the above circumstances,
It is an object of the present invention to provide a liquefaction determination method and a liquefaction determination device that can directly measure the liquefaction rate of a layer to be liquefaction determination, thereby preventing the above-described problem from occurring.

(Summary of the Invention) In order to solve the above-mentioned problems, in the liquefaction determination method according to the present invention, a P disposed in a measurement target layer in the ground is used.
A method for determining liquefaction of the ground by applying a P-wave vibration to a layer to be measured by a wave oscillator and measuring a liquefaction rate of the layer to be measured, wherein a liquefaction step of liquefying the layer to be measured by the P-wave oscillator, A measurement step of measuring at least one of various characteristics such as a P-wave propagation velocity of the measurement target layer, or a vane rotation resistance, a cone insertion resistance, and pore water pressure, and a measurement result obtained by the measurement step. A determination step of determining a liquefaction rate by comparing with a measured value of the measurement target layer before liquefaction.

Further, the liquefaction determination device of the present invention provides a liquefaction of the ground for measuring a liquefaction rate of the measurement target layer by applying a P-wave vibration to the measurement target layer by a P-wave oscillator arranged in the measurement target layer in the ground. A determination device, wherein the P-wave oscillator for liquefying the measurement target layer and at least one of various characteristics such as a P-wave propagation velocity of the measurement target layer, or vane rotation resistance, cone insertion resistance, and pore water pressure. A measuring device that measures one, and a determination device that determines the liquefaction rate by comparing the measurement result obtained by the measuring device with the measured value of the measurement target layer before liquefaction. .

Embodiment First, the basic principle of the present invention will be described with reference to FIG.

Conventionally, liquefaction of sandy ground was thought to be mainly caused by shear waves (S-waves), but after repeating various experiments, it was concluded that it was actually caused mainly by longitudinal waves (P-waves). Was.

That is, as shown in FIG.
Water 3 is added to the container 1 as shown in FIG.
When a wave is applied, impact is applied to each of the soil particles 4 constituting the sand 2, so that the movement of the position of the center of gravity and the rotational movement occur simultaneously, thereby causing the soil particles 4 to behave as if they migrate in water. The sand 2 and the water 3 mix and liquefy.

On the other hand, when the S wave without the P wave was used under the same conditions, the liquefaction phenomenon hardly occurred.

From these results, it was found that the liquefaction rate of the sand ground could be measured by the method described below.

First, as shown in FIG. 2 (a), the ground 5 which may be liquefied is drilled to expose the measurement target layer 6, and then a P-wave oscillator is inserted into a hole 7 formed by the drilling. 9 and a measuring device (for example, a P-wave propagation velocity meter, a vanesen breaking tester,
Rod 8 with cone penetration tester, pore water pressure gauge)
, And a pressure calculated based on the data obtained at the time of drilling is applied to the bottom of the hole, and various characteristics of the measurement target layer 6, for example, P
Measure the initial values of wave velocity, adhesive strength, internal friction angle, vane rotation resistance, penetration resistance, pore water pressure, etc.

Thereafter, a P-wave of a predetermined intensity is applied to the measurement target layer 6 by the P-wave oscillator 9 for a predetermined time to liquefy the measurement target layer 6.

Next, while maintaining this state, various characteristics of the measurement target layer 6 are measured again by the measuring device.

Then, by comparing various characteristics of the measurement target layer 6 before applying the P wave by the P wave oscillator 9 and various characteristics of the measurement target layer 6 after applying the P wave, the liquefaction of the measurement target layer 6 is performed. Rate can be determined.

The above-described method is merely an example. For example, as shown in FIG. 2 (b), a rod 8 having a P-wave oscillator 9 attached to the upper end thereof and a measuring instrument such as a penetration measuring instrument is used. The P-wave obtained by the oscillator 9 may be transmitted to the distal end side using the rod 8 as a transmission system to give the P-wave to the measurement target layer 6.

Next, an example of a liquefaction rate measuring device based on the above-described liquefaction measurement principle will be described.

FIG. 3 is a block diagram showing an example of an apparatus for electrically realizing the above-described liquefaction measuring method.

The liquefaction measuring device shown in this figure includes a measuring device main body 10 installed on the ground surface side and a sonde unit 11 penetrating into a hole formed by boring.

The measuring instrument body 10 includes a power supply circuit 12 that generates a power supply voltage of a predetermined voltage from an external power supply, an oscillation circuit 13 that operates by the power supply voltage generated by the power supply circuit 12 to generate a white noise signal, Amplifying circuit 14 that operates with the power supply voltage generated by the power supply circuit 12 and amplifies the white noise signal output from the oscillation circuit 13 .The white noise signal amplified by the amplification circuit 14 is It is supplied to the sonde unit 11 via the cable 15.

The sonde unit 11 includes a P-wave oscillator 16, and generates a P-wave when a white noise signal is supplied via the cabtire cable 15 to the measurement target layer 18 with which the sonde unit 11 is in contact. Give a P wave.

Then, the liquefaction rate measuring device adds P
The liquefaction rate of the layer to be measured can be known by comparing various characteristics before applying the wave with various characteristics after applying the P wave by using various measuring instruments.

FIG. 4 is a block diagram showing an example of another liquefaction rate measuring device. In this figure, the same parts as those in FIG. 3 are denoted by the same reference numerals.

The difference of the liquefaction rate measuring apparatus shown in this figure from that shown in FIG. 3 is that a ground characteristic measuring device 17 is provided in the sound section 11 and a ground characteristic display 19 is provided in the measuring device main body 10 to provide the P wave While applying a P wave to the layer 18 to be measured by the oscillator 16, various characteristics of the layer 18 to be measured are measured in real time by the ground characteristic measuring device 17, and the measurement results are displayed on the ground characteristic
18 is displayed.

Accordingly, various characteristics of the measurement target layer 18 can be directly measured while applying the P wave to the measurement target layer 18, and the liquefaction rate of the measurement target layer 18 can be known based on the measurement result.

FIG. 5 is a block diagram showing an example of another liquefaction rate measuring device. In this figure, the same parts as those in FIG. 3 are denoted by the same reference numerals.

The difference between the liquefaction rate measuring device shown in FIG. 3 and that shown in FIG. 3 is that the measuring device main body 10, the P oscillator 16,
A ground characteristic display device 19 is arranged, and a P-wave transmission device 20 such as a rod and a ground characteristic measuring device 17 are disposed in the ground, and the P-wave obtained by the P oscillator 16 is transmitted to the P-wave transmission device 20.
Through the ground layer 18
Various characteristics of the measurement target layer 18 obtained by 17 are displayed on the ground characteristic display device 19.

Even with such a configuration, the liquefaction rate of the measurement target layer 18 can be known.

Further, in each of the embodiments described above, the P-wave is generated using the P-wave oscillator 16, but the P-wave may be generated using a vibration device using a hydraulic device, a motor, or the like.

(Effects of the Invention) As described above, according to the present invention, the liquefaction rate of a layer to be subjected to liquefaction determination can be directly measured, and the following effects can be obtained.

(1) Since various characteristics of the measurement target layer can be measured by giving a P wave while performing boring, the ground characteristics of the boring portion can be obtained as a line.

(2) Since there is no need to sample soil, no advanced technology is required.

(3) Since the liquefaction rate is measured at the place where the boring is performed, there is no possibility that the soil to be measured is disturbed during the measurement.

(4) Since the test is performed in-situ, there is no estimation factor in the sealing pressure unlike the vibration triaxial test.

(5) Since white noise can be used, a measurement result close to the liquefaction rate during an earthquake can be obtained.

(6) Since the liquefaction rate of the layer to be measured can be measured while performing boring, a determination result of the liquefaction rate can be obtained in real time.

[Brief description of the drawings]

1 (a) and 1 (b) are schematic diagrams for explaining the basic principle of the liquefaction determination method according to the present invention, and FIGS.
(B) is a schematic diagram for explaining a specific example of the liquefaction determination method according to the present invention, and FIG. 3 shows an example of a liquefaction rate measuring device used when performing the liquefaction determination method according to the present invention. FIG. 4 is a block diagram showing another example of the liquefaction rate measuring device used when performing the liquefaction determination method according to the present invention, and FIG. 5 is a diagram illustrating the case where the liquefaction determination method according to the present invention is performed. FIG. 6 is a block diagram showing another example of the liquefaction rate measuring device used in the present invention, FIG. 6 is a flowchart for explaining an example of a conventional liquefaction determination method, and FIGS. It is a schematic diagram for demonstrating the determination test example of a liquefaction determination method. 5: Underground (ground), 6: Measurement target layer, 7: Hole, 9
…… P-wave oscillator.

Claims (2)

(57) [Claims] 1. A method for determining liquefaction of a ground, comprising: applying a P-wave oscillation to a layer to be measured by a P-wave oscillator disposed in a layer to be measured in the ground to measure a liquefaction rate of the layer to be measured. A liquefaction step of liquefying the measurement target layer by the P-wave oscillator; and at least one of various characteristics such as a P-wave propagation velocity of the measurement target layer or vane rotation resistance, cone insertion resistance, and pore water pressure. Liquefaction characterized by comprising: a measurement step of measuring the measurement result obtained by the measurement step, and a determination step of determining a liquefaction rate by comparing the measurement result of the measurement target layer before liquefaction. Judgment method. 2. A soil liquefaction determination device for measuring the liquefaction rate of the measurement target layer by applying P-wave vibration to the measurement target layer by a P-wave oscillator disposed in the measurement target layer in the ground, The P-wave oscillator for liquefying the measurement target layer; and a measurement for measuring at least one of various characteristics such as a P-wave propagation velocity of the measurement target layer or vane rotation resistance, cone fitting resistance, and pore water pressure. A liquefaction determination device comprising: a device; and a determination device that determines a liquefaction rate by comparing a measurement result obtained by the measurement device with a measurement value of a measurement target layer before liquefaction.