JPH0295256A - Method of deciding liquefaction - Google Patents

Abstract

PURPOSE:To allow the direct measurement of the liquefaction rate of an object layer for decision of liquefaction by applying the P waves obtd. by a longitudinal wave (P wave) oscillator to the measuring object layer. CONSTITUTION:The ground 5 which has the possibility of causing liquefaction is bored to expose the measuring object layer 6 and thereafter, a rod 8 mounted with a P wave oscillator 9 and measuring instrument at the front end is put into a hole 7 and the various characteristics of the measuring object layer 6 are measured. The P waves of the prescribed intensity are thereafter applied to the object layer 6 for a prescribed period of time by the oscillator 9 to liquefy the object layer 6. The various characteristics of the object layer 6 before the P waves are applied thereto are measured by the measuring instrument while this state is maintained. The various characteristics of the object layer 6 before the P waves are applied by the oscillator 9 and the various characteristics of the object layer 6 after the P waves are applied are compared, by which the liquefaction rate of the object layer 6 is determined.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a liquefaction determination method for determining the liquefaction rate of a layer to be measured.

(Prior Art) When constructing a building on sandy ground, it is usually determined whether the ground will liquefy or not, and measures such as ground improvement are taken based on the result of this determination.

In this case, the following method is used to determine liquefaction of the ground.

First, as shown in Figure 6, the ground that is subject to liquefaction assessment is polled to a predetermined depth, the layer that is subject to liquefaction assessment is sampled using a sand sampler, and the soil obtained through this sampling is transported to the test site. Then, the sampled soil is placed in an experimental water tank 101 as shown in Figure 7(a) and foreshocked by a seismic device to liquefy the sampled soil, and a triaxial compression test as shown in Figure 7(b) is carried out. vessel 10
2, the liquefaction rate at that time was measured, and the liquefaction rate (degree of liquefaction) of the layer targeted for liquefaction determination was determined.

When the liquefaction rate of this layer was high, measures such as geological improvement of the ground were taken.

However, such conventional liquefaction determination methods have the following problems.

(1) - Since the liquefaction rate can only be determined for the depth at which sampling was performed, only point information can be obtained.

(2) Sampling must be done without disturbing the soil condition, so advanced techniques are required during sampling.

(3) Since the soil must be transported 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 was not conducted in situ, there is an element of estimation in the confining pressure of the vibratory triaxial test.

(5) Earthquake motion is a composite wave of many frequency components, but since tests are conducted using only specific frequency components, it is necessary to estimate the liquefaction rate during an earthquake from the test results.

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

(Objective of the Invention) The present invention has been made in view of the above circumstances, and is capable of directly measuring the liquefaction rate of a layer subject to liquefaction determination, thereby preventing the above-mentioned problems from occurring. The purpose is to provide a liquefaction determination method that can

(Summary of the invention) In order to solve the above problems, in the liquefaction determination method according to the present invention, P waves obtained by a P wave oscillator penetrated into the ground or a P wave oscillator installed on the ground are measured. It is characterized in that the liquefaction rate of the layer to be measured is measured by applying it to the layer to be measured.

(Example) First, the basic principle of the present invention will be explained with reference to FIG.

Previously, it was thought that liquefaction of sandy ground was mainly caused by transverse waves (S waves), but after repeated various experiments, it was concluded that liquefaction of sandy ground is actually caused mainly by longitudinal waves (P waves). Ta.

In other words, if sand 2 and water 3 are placed in a container 1 as shown in FIG. 1(a), and a P wave is applied to this container 1 as shown in FIG. An impact is applied to the soil particles 4, causing movement of the center of gravity and rotational movement at the same time.
As a result, each soil particle 4 behaves as if it were migrating in water, and the sand 2 and water 3 are mixed and liquefied.

On the other hand, when S waves without P waves were used under similar conditions, almost no liquefaction phenomenon occurred.

From these results, it was found that the liquefaction rate of sandy soil can be measured by the method described below.

First, as shown in Fig. 2(a), a hole is drilled in the ground 5 that is likely to liquefy to expose the measurement target layer 6, and a P-wave oscillator is placed at the tip in the hole 7 formed by this post-drilling. 9 and a rod 8 to which a measuring device is attached are inserted to measure various characteristics of the layer 6 to be measured, such as P-wave velocity, adhesive force, internal friction angle, vane rotational resistance force, penetration resistance force, and pore water pressure.

Thereafter, the P wave oscillator 9 applies P waves of a predetermined intensity to the measurement target layer 6 for a predetermined period of time to liquefy the measurement target N6.

Next, while maintaining this state, various characteristics of the layer 6 are measured using the measuring device.

The liquefaction rate of the measurement target M6 is determined by comparing the characteristics of the measurement target layer 6 before applying the P wave with the P wave oscillator 9 and the characteristics of the measurement target N6 after applying the P wave. You can ask for it.

Furthermore, the above-mentioned method is an example, for example, as shown in FIG.
), a P-wave oscillator 9 and a measuring device such as a penetration measuring device are attached to the upper end of a rod 8, and the P-waves obtained by the P-wave oscillator 9 are transmitted to the tip side using the rod 8 as a transmission system. Alternatively, the P wave may be transmitted to the layer 6 to be measured.

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

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

The liquefaction rate measuring device shown in this figure includes a measuring device main body 10 installed on the ground side and a sonde 11 inserted into a hole formed by poling.

The measuring instrument main body 10 generates a power supply voltage of a predetermined voltage from an external power supply. a source circuit 12; an oscillation circuit 13 that operates with the power supply voltage generated by the power supply circuit 12 to generate a white noise signal; and an oscillation circuit 13 that operates with the power supply voltage generated by the power supply circuit 12 and outputs from the oscillation circuit 13. The white noise signal amplified by the amplifier circuit 14 is supplied to the sonde section 11 via the cabtire cable 15.

The sonde section 11 is equipped with a P-wave oscillator 16, and when a white noise signal is supplied through the cabtyre cable 15, it generates a P-wave and sends it to the measurement object #18 that the sonde section 11 is in contact with. Gives P waves.

Then, using this liquefaction rate measuring device, P is measured at layer 18.
The liquefaction rate of the layer to be measured can be determined by measuring and comparing the characteristics before applying the wave with the characteristics after applying the P wave 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 given the same reference numerals.

The liquefaction rate measuring device shown in this figure is different from the one shown in FIG. While the oscillator 16 applies P waves to the measurement target N118, the ground property measuring device 17 measures various properties of the measurement target layer 18 in real time, and the measurement results are displayed on the ground property display 18. .

This makes it possible to directly measure various characteristics of the measurement object #18 while applying P waves to the measurement object layer 18, and to know the liquefaction rate of the measurement object layer 18 based on the measurement results.

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 given the same reference numerals.

The liquefaction rate detection device shown in this figure is different from the one shown in FIG. A P-wave transmission device 20 such as a rod and a ground property measuring device 17 are placed in the ground, and the P-waves obtained by the two oscillators 16 are transmitted to the measurement target layer 18 via the P-wave transmission device 20 while measuring the ground properties. The various characteristics of the measurement target layer 18 obtained by the measuring device 17 are displayed on the ground characteristics display device 1q.

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

Further, in each of the embodiments described above, the P waves are generated using the P wave oscillator 16, but the P waves 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 the layer to be determined for liquefaction can be directly measured, so that the following effects can be obtained.

(1) Since various characteristics of the layer to be measured can be measured by applying P waves while performing polling, the ground characteristics of the polled area can be determined as a line.

(2) Since there is no need to sample soil, advanced technology is not required.

(3) Since the liquefaction rate is measured at the polled location, there is no risk that the soil to be measured will be disturbed during the measurement.

(4) Since the test is conducted in-situ, there are no estimated factors involved in the confining pressure, as is the case with vibrating three-wheel tests.

(5) Since white noise can be used, measurement results close to the liquefaction rate at the time of an earthquake can be obtained.

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

[Brief explanation of the drawing]

FIGS. 1(a) and 1(b) are schematic diagrams for explaining the basic principle of the liquefaction determination method according to the present invention, and FIG. 2(a),
(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 carrying out the liquefaction determination method according to the present invention. A block diagram, FIG. 4 is a block diagram showing another example of a liquefaction rate measuring device used when implementing the liquefaction determination method according to the present invention, and FIG. 5 is a block diagram when implementing the liquefaction determination method according to the present invention. FIG. 6 is a block diagram showing another example of a liquefaction rate measuring device used for the conventional liquefaction determination method. FIG. 7(a) is a flowchart for explaining an example of a conventional liquefaction determination method.
, (b) are schematic diagrams for explaining determination test examples of conventional liquefaction determination methods. 5...Underground (ground), 6...Measurement target layer, 7...
Hole, 9...P wave oscillator.

Claims (1)

[Claims] (1) A method for determining liquefaction, characterized in that the liquefaction rate of the layer to be measured is measured by applying P-wave vibrations to the layer to be measured using a P-wave oscillator.