JPS61294018A - Judging apparatus for liquefaction of ground - Google Patents

Abstract

PURPOSE:To precisely determine the liquefaction of the ground by using a constitution in which reaction forces produced by vibration of a vibrator and a vibrating plate is received by the reaction floor and reaction wall of a tank, and the vibration output of the vibrator is transmitted as it is to a test soil layer. CONSTITUTION:A concrete floor and four concrete side walls are integrally formed, and a tank 1 consisting of the floor as a reaction floor 2 and a side wall as reaction wall 3a is constructed. In the tank 1, two vibrating plates 4a and 4b facing each other at a given interval are erectly set between both side walls adjacent to the reaction wall 3a, and their lower ends are connected to the reaction floor 2 in a pivotally movable manner. When a vibrator 15 is operated to apply repeated horizontal vibrations to the plates 4a and 4b, the plates 4a and 4b are displaced in a rocking manner and the shearing deformation is received by a test soil layer (a) in the soil tank 5. The occurrence and degree of liquefaction are judged from measured values of a void water pressure gauge 23 and a seismometer, etc.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention is directed to determining the presence or absence of liquefaction of sandy ground that liquefies during an earthquake;
The present invention relates to a device for testing and determining the degree of liquefaction as well as the effectiveness of preventing liquefaction.

[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. In general, the grain size, density,
It is said that there is a danger in fine sandy ground saturated with water due to groundwater levels, etc.

Measures to prevent the above liquefaction include driving sand piles to increase the relative density of the sandy ground and replacing it with sand of a grain size that is difficult to liquefy, or to improve water permeability. Prevention techniques such as driving gravel piles of good quality 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. there were.

Therefore, as a device to judge the liquefaction of the ground, two pieces of liquefaction plates are installed vertically in the ground at the original location at the required interval, and an additional device is connected to these plates. A device was developed that determined the state and degree of liquefaction of the ground by applying vibrations to the ground between the two plates, and the applicant of the present invention filed a patent application (Japanese Patent Application No.
No. 8, Japanese Unexamined Patent Publication No. 178718/1982).

[Problems to be Solved by the Invention] However, since the above-mentioned judgment device is installed by setting the Joro board into the ground at its original location, it is necessary to set it up for each ground to be judged. Not,
In addition to being extremely troublesome to install, the device had to be removed and the ground had to be backfilled after the evaluation test.

In particular, although the west side of the test ground is separated from other ground by two rock plates and side plates, it is connected to other strata at the bottom, and the addition equipment is connected to a platform installed on the ground. Although it is mounted on L, there is a strong possibility that the sound itself will vibrate due to the reaction force generated when the additional device is activated, and the vibration transmission to the Joro plate (Joro force) will be attenuated, and the output of the additional device will be There was also the disadvantage that it was not possible to apply vibrations commensurate with the amount of vibration, which resulted in errors in the measured values and the inability to make accurate judgments.

In view of the above, the present invention enables a judgment test without being installed on the ground at the original location where the judgment is to be made, and also provides a part where the test soil is completely separated from other ground and receives the reaction force at the time of dew. It is an object of the present invention to provide a liquefaction determination device that can apply vibrations equivalent to the same exposure force 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 1] The determination device of the present invention which solves the above problems is constructed by integrally constructing a concrete floor and four side walls, and applying a reaction force to each of the floor and one side wall. A tank body formed as a wall is installed, and within this tank body, two plates facing each other at a required interval are erected between both side walls adjacent to the reaction wall, and the lower end is set as a reaction floor. In addition, the area surrounded by both vibration plates and the above-mentioned side walls is used as a model soil tank, and an additional device is connected to and supported by the reaction wall on this rock plate. The test soil layer in the model soil tank is vibrated through the connecting plates.

[Function] The above-mentioned device of the present invention fills a model soil tank inside a concrete tank with soil from the ground to be judged or soil corresponding to the ground, or soil whose soil conditions such as density and particle size are the same. When the additional device is operated in this state, vibrations in the horizontal direction are applied repeatedly to the two plates, and the 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, the accompanying changes in the pore water pressure of the earth and sand, the generation of excessive pore water pressure, etc., and the state of liquefaction of the test earth and sand are measured using additional equipment using various instruments such as pore water pressure gauges, seismometers, and displacement meters. The existence and extent of liquefaction in the test soil layer can be determined by reading the changes in the amplitude and frequency of the vibrations as well as the changes in relation to the changes using an appropriate recording means.

According to the present invention, however, the sliding plates that define the model soil tank are provided inside the concrete tank body and connected to the reaction floor, and the addition device is connected and supported by the reaction wall that is integrated with the reaction floor. Because of this, the reaction force at the time of dew can be supported by the reaction floor and reaction wall, and the model soil tank is completely separated from other ground by -〇- in the tank body. This allows the same vibration force produced by the vibration device to be applied 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 evaluated, or the soil conditions can be made to be the same as that of the ground.
It is possible to test and determine the state and degree of liquefaction in different grounds without having to install each site individually.

[Example] In the figure, (1) is a tank body mainly in the shape of a rectangle or the like, in which the floor and the side walls around the four circumferences are integrally made of concrete 1- with reinforced steel, etc., and the floor and one side wall are respectively It is configured as a reaction floor (2) and a reaction wall (3a) having a sufficient thickness larger than the others, and the upper end (3a') of the reaction wall (3a) is configured upward from the side wall of the sacrum. It's getting expensive.

This tank body (1) is usually buried so that the upper ends of the four side walls are exposed at the ground surface, but in some cases, only the lower part can be buried, or it can be installed on the ground. It is desirable to ensure that it remains immobile during dew by driving piles into the underlying ground.

(4a) and (4b) are reaction walls (3) inside the tank body (1).
a) refers to two horizontal board beams that are erected between the two side walls (3b) and (311) in the cross direction so as to face each other at a required interval in the cross direction, and the lower end is the reaction force. floor (2
), and the area surrounded by both vibration plates (4a) (4b) and both side walls (3b) (3b) corresponds to the ground to be tested. It is configured as a model earthen tank (5) filled with earth and sand.

The above-mentioned Nyoro plates (4a) and (4b) are mainly composed of plate bodies (6a and 6b) formed by connecting steel plates, H-beams, etc., and one side of the plates, that is, the opposite side from the opposing surfaces. Consists of type steel such as H-shaped steel and other steel materials. Support columns (7a) (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). ing. As shown in FIG. 3, the pivotable connecting structure includes connecting plates (8) suspended from the lower ends of the support columns (7a) (7b), which are connected to the reaction floor (2) at required intervals. It loosely fits between the upright connecting plates (9) and (9), and is connected by passing a pin (10) through these connecting plates (8) and (9). (4a)
(4b) can swing in a direction perpendicular to the plate surface using the pin (10) as a fulcrum.

Further, both the vibration plates (4aH4b) are plate bodies (6a) (6
b) The upper ends of the support columns (7a) and (7b) protruding upward are connected to each other by a connecting girder (11) with pin connecting means, etc.
The two are connected to each other via the connecting girder (11) so that they both swing in synchronization in a linked manner.

(12)(13)L;L Indicates the connecting portion such as the pin connecting means of the above-mentioned [j tie girder (11) g support fj column (7a) (7b) g.

A cross beam (14) is installed between the support columns (7a) (7a) on the side plate (4a) on the side of the reaction wall (3a), and a hydraulic The output side end of the fitting ff1 (15) such as an actuator is connected via a joint part (16) such as a pin connection or a universal joint, and the vibrating device (15) is connected to the fitting plate (4a) (4b). On the other hand, it is possible to apply vibration in a direction perpendicular to the plate surface.

In particular, the vibration device (15) has a support portion (17) whose base on the opposite side to the output side is embedded and fixed in the reaction wall (3a).
) is connected and supported via a joint part (18) such as a universal joint similar to the above, and the reaction force generated during its operation is transferred to the reaction wall (
3a).

The above-mentioned vibration exciter (15) is attached to the Nyoro plates (4a) (4b) via the crossbeam (14), that is, to the model earthen tank (5) between them.
It is configured to be able to apply repeated shear deformation to the test soil layer (a) at vibrations and frequencies corresponding to seismic waves, and it is desirable to use high-speed reciprocating motion using hydraulic pressure as the power source, for example. Normal displacement is several cm
~ Set to several tens of centimeters.

Moreover, between the above-mentioned vibration absorbing plates (4a) (4b) and the reaction wall (3a) and the side wall (3C) opposite thereto, at least the maximum rocking displacement of the upper part of the shock absorbing plate (4a) (4b), respectively. It is configured as a side gutter (19) (20) with a larger width, allowing the rocking displacement of the rock plate (4aH4b) and storing water seeping out from the test soil layer (a). ing. This gutter (19) (2
0) may be filled with a viscous liquid such as bentonite.

In the case of the illustrated embodiment, there is a reaction wall (
A side groove (19) inscribed in 3a) and between the side plate (4a)
), the water tank (21) is provided so that the water tank (21) exists, and the side gutter (1
9) Water overflowing from (20) flows into the inlet (22) and is stored. Therefore, the tank body (1
), each side wall (38H3b) (3C) is a Joro plate (4aH
The upper surface of the water tank (21) is formed slightly lower than the plates (6a) and (6b), while the upper surface of the water tank (21) is formed to be slightly higher than the plates (6a) and (6b) which are the main bodies of the water storage tank 4b). Instead of the water tank described above, a drainage bit may be provided on 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 and horizontal displacement gauge, (2
6) is a horizontal displacement gauge, and (27) is a wall earth pressure gauge, and each of these closures is connected to a recorder, etc. (28) is a pit for wiring and piping of various instruments, which is connected to the negative side of the tank body (1).

In order to conduct a liquefaction determination test using the above-mentioned device of the present invention, both vibration plates (4
Fill the model soil tank (5) between a) and (4b) with the soil of the ground to be judged, or fill the test soil with soil conditions that approximately correspond to the ground, such as density, particle size, and moisture content. etc. should be made the same as the ground described above. In this way, the additional device (15)
When activated, horizontal vibrations are applied repeatedly to both vibration plates (4a) and (4b), and both vibration plates (4a and 4b) swing around 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, causing excessive pore water pressure and causing the test soil layer (a) to become liquid. to become At this time, using a pore water pressure gauge (23), seismometer (accelerometer), various displacement meters, etc. installed in the soil layer, the changes in the amplitude and frequency of the vibration given by the addition device are read by a recording means, and at the same time By reading changes such as increases in pore water pressure and generation of excess pore water pressure in relation to the changes in vibration,
This is to determine the presence or absence of liquefaction and its degree.

However, during the above test, the reaction force accompanying the vibration of the addition device (15) is supported by the reaction wall (3a), so the output vibration of the addition device (15) is directly transmitted to the mounting plate (4a) ( 4
b) A reaction force bed (2) to which the lower ends of the reaction force transmitted and generated due to the rocking of the sliding plates (4a) and (4b) are connected.
The receiver is supported by the tank body (
Since it is separated from the external ground by 1), it is not affected by other strata, and the output vibration from the additional device (15) can be directly applied to the test soil layer (a), allowing precise and accurate testing. Able to make judgments.

In addition, as shown in Figures 4 and 5, the test soil layer (a
) Technology to prevent liquefaction inside, for example, by driving one or both of gravel piles (b) or sand piles at required intervals,
If a test similar to the above is performed, it will be possible to test and determine the extent to which the applied liquefaction prevention technology exhibits a prevention effect in response to changes in vibration, or whether or not it is possible to prevent liquefaction from occurring. can do.

Furthermore, as shown in Figures 6 and 7, a model soil tank (
5) A cylindrical pile (30) and/or a knotted pile (31) are driven as foundation piles to support the structure in the test soil layer (a), and a predetermined load (W) is applied to the pile head. )
By carrying out a test similar to the above with the foundation piles (30) and (31) loaded with The effectiveness of liquefaction prevention technology can be understood more accurately by comparing with the above.

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

Furthermore, at the time of dew in the above judgment test, the reaction wall (3a)
Friction occurs due to the deformation and movement of the earth and sand at the contact surfaces between the adjacent both side walls (3bH3b) and the test earth and sand layer (a). To remove this effect, both side walls (3b) (3b)
It is desirable to apply a slippery paint, plating, etc. to the inner surface. 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 technologies, we compared the prevention effects of each technology. At the same time, it is 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 to the vibration device and the rock plate is supported by the reaction floor and the reaction wall, and the vibration output from the vibration device is directly transmitted to the test soil layer. Moreover, the test can be performed while isolated from the ground by the tank body, and the test soil layer in the model soil tank between both vibration plates is not affected by other strata such as vibration propagation due to reaction force. Therefore, very precise test results can be obtained and accurate judgments can be made of the degree of liquefaction and the degree of effectiveness of prevention techniques.

In addition, since the tank body isolates the ground from other ground, tests can be performed by filling the model soil tank with earth and sand with the same soil conditions as the ground on which the structure will be constructed. There is no need to install it, 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, and FIG. 3 is an enlarged side view of the pin connection structure.
FIG. 4 is a longitudinal sectional view showing another embodiment, FIG. 5 is a plan view of the same as above, FIG. 6 is a longitudinal sectional view showing still another embodiment, and FIG.
The figure is a plan view of the same as above. (1)...tank body, (2)...reaction floor, (3a)...
・Reaction wall, (3b) (3b) (3c)...Side wall, (4
a) (4b)--Nyoro board, (5)...Model earthen tank, (
7a) (7b) Support column, (15) Vibration device, (a) Test soil layer. Patent applicant: Takechi Kogyo Co., Ltd. Procedural Amendment (October 1, 1985 1, case description 1985 Patent Application No. 134825 3, person making the amendment Takechi Kogyo Co., Ltd. Representative: Sada Yabuuchi Man 4, agent

Claims (1)

[Claims] 1. A specimen is installed in which a floor and four side walls are constructed integrally with concrete, and the floor and one side wall are formed as a reaction floor and a reaction wall, respectively. 2 facing each other at the required interval between adjacent both side walls
Two vibration plates are erected, the lower ends of which are pivotally connected to the reaction floor, and the area surrounded by both vibration plates and the above-mentioned both side walls is used as a model soil tank. Liquefaction of the ground characterized in that a vibration device is connected to and supported by a reaction wall, and vibration is applied to a test soil layer in a model soil tank via the vibration plate. Judgment device.