JPH039248B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention not only tests and determines the presence or absence of liquefaction of sandy ground that liquefies during an earthquake, but also the degree of liquefaction, as well as the prevention effect of technology to prevent liquefaction. Concerning testing and judgment equipment.

[Prior Art] There are already many known cases in which sandy ground liquefies during an earthquake and loses its supporting capacity, resulting in buildings sinking and collapsing. The cause of the liquefaction mentioned above is that the pore water pressure of sandy ground saturated with water increases rapidly due to repeated shear deformation during earthquakes, and as a result, excessive pore water pressure is generated and the sandy ground loses its supporting capacity. Generally, it is said that there is a danger in fine sandy ground saturated with water, depending on the grain size, density, groundwater level, etc. of the sandy ground.

Measures to prevent the above liquefaction include driving sand piles to increase the relative density of the sandy ground and replacing it with sand with a grain size that is difficult to liquefy, or to prevent water permeability from occurring. Prevention techniques such as driving high-quality gravel piles to dissipate excess pore water pressure, which is the main cause of liquefaction, have been implemented; The reality is that liquefaction countermeasures are being taken in extremely uncertain conditions, as they have not been implemented based on the evaluation of how effective the prevention technology will be in the event of an earthquake. It was hot.

Therefore, as a device to determine the liquefaction of the ground,
Two vibration plates are installed vertically in the ground at the original location to be determined at a required interval, and a vibration device is connected to this to apply vibrations to the ground between the plates through the vibration plates. As a result, a device was developed to determine the state and degree of liquefaction of the ground, and the applicant of the present invention filed a patent application (Japanese Patent Application No. 57-61508, Japanese Patent Application Laid-Open No. 1983-1989).
No. 178718).

[Problems to be Solved by the Invention] However, in the above-mentioned determination device, the vibration plate is set up in the ground at the original location, so it is necessary to set up the vibration plate in each ground where the determination test is to be performed. However, the installation work was extremely complicated, and after the evaluation test, the equipment had to be removed and the ground had to be backfilled.

In particular, although the four sides of the test ground were separated from other ground by two vibration plates and side plates, the bottom part was connected to other strata, and the vibration device was installed on the ground. Although it is mounted on a table, there is a high possibility that the table itself will vibrate due to the reaction force generated when the vibration device is activated, and the vibration transmission (seismic force) to the vibration plate will be attenuated. Another drawback was that it was not possible to apply vibrations commensurate with the output of the vibration exciter, which resulted in errors in the measured values and the inability to make precise judgments.

In view of the above, the present invention enables judgment tests without being installed on the ground at the original location where the judgment is to be made, and at the same time, the test soil is completely separated from other ground and the part that receives the reaction force at the time of an earthquake is placed. The object of the present invention is to provide a liquefaction determination device that can apply vibrations equivalent to the vibration output to test soil and make accurate determinations, and can also accurately determine the degree of effectiveness of liquefaction prevention technology. .

[Means for solving the problems] The determination device of the present invention that solves the above problems has the following features:
A tank body is installed in which a floor and four surrounding side walls are integrally constructed of concrete, and each of the floor and one side wall is formed as a reaction wall. Two vibration plates are erected facing each other at a required interval, and their lower ends are pivotally connected to the reaction floor. tank and pear,
A vibration device connected and supported by a reaction wall is connected to this vibration plate, and vibrations are applied to the test soil layer in the model soil tank via the vibration plate.

[Function] The device of the present invention described above fills a model soil tank inside a concrete tank with soil from the ground to be judged or soil corresponding to the ground, that is, soil whose soil conditions such as density and particle size are the same. Then, when the vibration device is operated in this state, horizontal vibrations are applied repeatedly to the two vibration plates, and the vibration plates are oscillated about the joint with the reaction floor as a fulcrum. As a result, the test soil layer in the model soil tank between both vibration plates vibrates, causing shear deformation in the test soil layer. Therefore, we used various instruments such as pore water pressure gauges, seismometers, and displacement meters to monitor changes such as rapid increases in soil pore water pressure, excessive pore water pressure, and liquefaction of the test soil. By reading the changes in the amplitude and frequency of the vibration applied by the device and the changes in relation to the changes using an appropriate recording means, it is possible to determine the presence or absence of liquefaction in the test soil layer and the degree of liquefaction.

However, in the present invention, the vibration plate that defines the model soil tank is provided inside the concrete tank body and is connected to the reaction floor, and the vibration device is connected and supported to the reaction wall that is integrated with the reaction floor. Because of this, the reaction force at the time of the earthquake can be received and supported by the reaction floor and reaction wall, and the model soil tank can be completely separated from other ground by the tank body. , it is possible to apply the same vibration output from the vibration device to the test soil through the vibration plate, and it is not affected by other ground.

In addition, since a model soil tank is installed inside the concrete tank body, the soil inside this tank can be replaced with the soil of the ground to be judged, or by making the conditions the same as the ground, the soil can be built up for each ground individually. It is possible to test the liquefaction status and degree of different ground without installing it.

[Example] In the figure, 1 is a tank body mainly having a square shape such as a rectangle, in which a floor and four side walls are integrally made of reinforced concrete, etc. The reaction wall 3a has a reaction floor 2 and a reaction wall 3a having a thickness of 1,000,000,000 yen, and the upper end 3a' of the reaction wall 3a extends upward and is higher than the other side walls. This tank body 1 is usually buried so that the upper ends of the four side walls are exposed at the ground surface.
In some cases, it can be carried out with only the lower part buried or installed on the ground. In either case, it is necessary to ensure that it remains immobile during an earthquake by driving piles into the underlying ground, etc. It is desirable to do so.

Reference numerals 4a and 4b refer to two additional plates erected inside the tank body 1 between both side walls 3b, 3b in a direction crossing the reaction wall 3a so as to face each other at a required interval in the direction crossing the reaction wall 3a. It is a shaking plate, and the lower end is a reaction force floor 2
A model in which the area surrounded by both vibration plates 4a, 4b and both side walls 3b, 3b is filled with earth and sand corresponding to the ground to be tested. It is configured as a soil tank 5. The vibration plates 4a, 4b are mainly plate bodies 6a, 6b formed by connecting steel plates, H-beams, etc.
H on one side, that is, on the opposite side of each other.
Support column 7 made of shaped steel such as shaped steel or other steel materials, etc.
a, 7b are integrally installed by welding or other means, and the lower ends of the support columns 7a, 7b are pivotally connected to and supported by the reaction floor 2. As shown in FIG. 3, the pivotable connecting structure includes a connecting plate 8 vertically provided at the lower ends of the support columns 7a and 7b, and a connecting plate 9 vertically provided at a required interval from the reaction force plate 2. , 9, and are connected to each other by passing a pin 10 through these connecting plates 8, 9, and 9, and the vibration plates 4a and 4b are perpendicular to the plate surface with the pin 10 as a fulcrum. It is designed to be able to swing in any direction. In addition, both the vibration plates 4a and 4b have a plate body 6.
The upper ends of support columns 7a and 7b that protrude upward from a and 6b are connected by a connecting girder 11, each having a pin connecting means, etc., and both swing in synchronization in a link manner via the connecting girder 11. It is set up to do so. 12 and 13 are the connecting girder 11 and the support column 7
a, 7b and connecting parts such as pin connecting means are shown.

A cross beam 14 is installed between the support columns 7a, 7a of the vibration plate 4a on the side of the reaction wall 3a, and a vibration device 15 such as a hydraulic actuator is installed in the center of the cross beam 14. The output side end portions are connected via a joint portion 16 such as a pin connection or a universal joint, and the vibration device 15 can apply vibrations to the vibration plates 4a and 4b in a direction perpendicular to their plate surfaces. ing. In particular, the vibration exciter 15 has its base opposite to the output side connected to and supported by a support portion 17 embedded and fixed in the reaction wall 3a via a joint portion 18 such as a universal joint similar to the above, It is provided so that the reaction force generated during its operation is received and supported by the reaction wall 3a.

The above vibration device 15 applies vibrations and frequencies corresponding to seismic waves, that is, repeated shear deformation, to the vibration plates 4a and 4b through the cross beam 14, that is, to the test soil layer a in the model soil tank 5 between them. It is preferable to use high-speed reciprocating motion using hydraulic pressure as the power source, for example.
The amount of displacement is usually set to several centimeters to several tens of centimeters.

Furthermore, between the vibration vibration plates 4a, 4b and the reaction wall 3a and the side wall 3c facing the reaction wall 3a, side grooves 19, 20 each have a width larger than the maximum rocking displacement of the upper part of the vibration vibration plates 4a, 4b. It is configured to allow rocking displacement of the vibration plates 4a and 4b and to store water seeping out from the test soil layer a. This gutter 19,
In some cases, the inside of the container 20 is filled with a viscous liquid such as benantonite.

In the case of the implementation order shown in the figure, there is a gutter 19 inscribed in the reaction wall 3a and between the vibration plate 4a and the tank body 1.
A water storage tank 21 is provided so that the side gutter 1
Water overflowing from ports 9 and 20 flows in from an inlet 22 and is stored therein. Therefore, each side wall 3a, 3b, 3c of the tank body 1 is a vibration plate 4a, 4b.
The upper surface of the water tank 21 is formed slightly higher than the main bodies of the plates 6a and 6b, and the upper surface of the water tank 21 is
It is formed slightly lower than a and 6b. Instead of the water tank described above, a drainage pit may be provided in a part of the side wall to drain water overflowing from the side gutter to the outside of the tank body.

In the figure, 23 is a pore water pressure gauge, 24 is an underground displacement gauge installed on the reaction floor 2, 25 is a vertical-horizontal displacement gauge, 26 is a horizontal displacement gauge, and 27 is a wall soil pressure gauge, and each of these instruments is a recorder. etc. 28 is the tank body 1
This is a pit for wiring and piping for various instruments that are connected to one side of the pipe.

In order to conduct a liquefaction determination test using the apparatus of the present invention, as illustrated in FIGS. or the filled test soil is kept under soil conditions that approximately correspond to the ground, i.e., the density, particle size, moisture content, etc., are the same as those of the ground. When the vibration device 15 operates in this manner, vibrations in the horizontal direction are applied repeatedly to both vibration plates 4a and 4b, and both vibration plates 4a and 4b are oscillated about the joint with the reaction floor 2 as a fulcrum. The test soil layer a in the model soil tank 5 undergoes shear deformation, and as a result, the soil pore water pressure rapidly increases, resulting in excessive pore water pressure and liquefaction of the test soil layer a. At this time, a pore water pressure gauge 23 installed in the soil layer, a seismometer (accelerometer),
Using various displacement meters, the changes in the amplitude and frequency of the vibrations applied by the vibration device are read by recording means, and at the same time, changes such as the increase in pore water pressure and generation of excess pore water pressure are also measured in relation to the changes in the vibrations. The presence or absence of liquefaction and the degree of liquefaction can be determined by reading it.

However, during the above test, the reaction force accompanying the vibration of the vibration device 15 is supported by the reaction wall 3a, so the output vibration of the vibration device 15 is directly transferred to the vibration plate 4.
a, 4b, and the reaction force generated as a result of the rocking of the vibration plates 4a, 4b is also supported by the reaction force floor 2, the lower end of which is connected to the test soil layer a.
Since it is separated from the external ground by the tank body 1, it is not affected by other strata, and the output vibration from the vibration device 15 can be directly applied to the test soil layer a, allowing precise and accurate test judgments. I can do it.

In addition, as shown in Figures 4 and 5, techniques to prevent liquefaction, such as gravel piles b or sand piles, or both, are driven at required intervals inside the test soil layer a. If similar tests are conducted, it will be possible to test and determine to what extent the applied liquefaction prevention technology exhibits a prevention effect in response to changes in vibration, or whether or not it can prevent the occurrence of liquefaction. Can be done.

Furthermore, as shown in FIGS. 6 and 7, cylindrical piles 30 and/or knotted piles 31 are driven into the test soil layer a in the model soil tank 5 as foundation piles to support the structure. By carrying out a test similar to the above with a predetermined load W on the pile head, it is possible to know the effects of vibration and liquefaction on the foundation piles 30 and 31 during an earthquake. By comparing the results with the other test results mentioned above, the effectiveness of the liquefaction prevention technology can be understood more accurately.

In addition to testing separately for each ground to be used as described above, it is also possible to conduct the above test by dividing the test soil layer in one model soil tank.

Furthermore, during the earthquake in the above determination test, friction occurs due to deformation of the earth and sand at the contact surfaces between the test earth and sand layer a and the reaction wall 3a and the adjacent side walls 3b, 3b. In order to eliminate this effect, both side walls 3
It is desirable to apply a slippery paint, plating, etc. to the inner surfaces of b and 3b. Furthermore, the influence of friction can be removed by disposing a slidable plate on the side wall surface.

[Effects of the Invention] As described above, according to the liquefaction determination device of the present invention, it is possible to determine at what level of vibration (frequency, amplitude) sandy ground that is likely to liquefy during an earthquake will liquefy, and By shaking and comparing the ground treated with liquefaction prevention technology and the treated ground, and by shaking the ground treated with different liquefaction prevention technology, we compared the prevention effects of each technology. It is also possible to determine the most suitable prevention technology for the ground.

In particular, in the case of the present invention, the reaction force caused by the vibration imparted by the vibration exciter and the vibration plate is supported by the reaction floor and the reaction wall, and the vibration output from the vibration vibration apparatus is directly applied to the test soil layer. Moreover, it can be tested while being isolated from the ground by the tank body, and the test soil layer in the model soil tank between both vibration plates can prevent the vibration propagation of other strata due to reaction force. unaffected and therefore very precise test results are obtained, allowing accurate determination of the degree of liquefaction and the degree of effectiveness of prevention techniques.

In addition, by separating the ground from other ground by the tank body, tests can be performed by filling the model soil tank with soil of the same soil conditions as the ground on which the structure will be constructed, so each ground can be tested by installing a judgment device. There is no need for upright installation, and there is no need to backfill the construction ground of the structure after the judgment test, which can significantly reduce the amount of effort required for the judgment test, making it extremely economical.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal sectional view showing one embodiment of the present invention, Fig. 2 is a plan view of the same as above, Fig. 3 is an enlarged side view of the pin connection structure portion, and Fig. 4 is a longitudinal sectional view showing another embodiment. 5 is a plan view of the same as above, FIG. 6 is a longitudinal sectional view showing still another embodiment, and FIG. 7 is a plan view of the same. 1...tank body, 2...reaction floor, 3a...reaction wall,
3b, 3b, 3c...Side wall, 4a, 4b...Shake plate, 5...Model earthen tank, 7a, 7b...Support column, 1
5... Vibration device, a... Test soil layer.

Claims (1)

[Claims] 1. A tank body is installed in which a floor and four side walls are constructed integrally with concrete, and the floor and one side wall are respectively formed as a reaction floor and a reaction wall, and inside this tank body there is a wall corresponding to the reaction wall. Two vibration plates facing each other at a required interval are erected between adjacent both side walls, the lower ends of which are pivotally connected to the reaction floor, and the vibration plate is surrounded by both vibration plates and the above-mentioned side walls. This part was used as a model soil tank, and a vibration device connected and supported by the reaction wall was connected to this vibration plate to apply vibrations to the test soil layer in the model soil tank through the vibration plate. A ground liquefaction determination device characterized in that the ground liquefaction determination device is configured to give