JP2008052143A - Unit type liquefaction experimental equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide compact, portable, and maintenance-free liquefaction experimental equipment capable of reproducing a liquefaction phenomenon in a state closer to reality, capable of giving a viewer the right image before and after liquefaction, and enabling anyone to quickly and repeatedly observe the liquefaction phenomenon. <P>SOLUTION: The unit type liquefaction experimental equipment is equipped with: an experimental tank 10 having a double structure of an inner water tank 12 and an outer water tank 14 communicating with each other in the lower part; a strainer section 20 assembled to the bottom of the inner water tank; a submerged pump 28 assembled to the lower part inside the experimental tank so as to squirt water through the strainer section; and a water level regulating tank 32 which is installed outside the experimental tank so that the vertical position can be adjusted, and which communicates with the lower part of the experimental tank via a flexible communicating tube. At least the front upper part of the experimental tank is made of a transparent body, and the inner part can be seen through. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an apparatus for performing a model experiment on ground liquefaction that occurs during an earthquake. More specifically, the apparatus is unitized by incorporating a submersible pump in a double-structured experimental tank, and the liquid can be easily and quickly repeated. The present invention relates to a unit type liquefaction experiment apparatus that can observe liquefaction. This device is useful for demonstration of liquefaction phenomena in science education and disaster prevention education, for example.

  In science education and disaster prevention education, a method of demonstrating the liquefaction phenomenon is effective in explaining the ground liquefaction phenomenon that occurs during an earthquake. As a method of preparing a liquefiable ground, spray sand in the aquarium, or add water and sand to the aquarium and stir, leave it as it is to settle the sand in water, and then drain from the bottom of the aquarium. There is a way to lower the water level slightly below the sand surface level. As a result, a tightened drained sand layer is formed above the water level, and a loose liquefiable sand layer with many gaps below the water level can be formed. When vibration is applied to this, it is possible to observe a phenomenon in which sand and water are united and behave like a liquid (liquefaction). However, in these methods, in order to produce a ground that can be liquefied again after being liquefied, the sand and water in the aquarium are completely replaced, or water is poured into the aquarium and agitated. Takes time and laborious work.

  As an instrument that can more easily observe the liquefaction phenomenon, there has been proposed a ground liquefaction bottle in which water and sand and a simulated structure in the ground or on the ground are placed in a transparent sealed container (see Patent Document 1). . This is to make water and sand uniform by shaking the sealed container, and then leave it as it is to sink the sand and set a simulated object in the ground or on the ground at a predetermined position. . Here, when a vibration is applied to the closed container, the sedimentation layer of sand liquefies, and the simulated product sinks to a new balance position. Therefore, the same experiment can be performed any number of times by shaking the sealed container.

  However, in the experiment using this ground liquefaction bottle, even if the reason for liquefaction is correct, it is impossible to swing the closed container including the simulated structure of the ground and the ground. Water remains on the sand layer that has settled in the sealed container, and it is difficult to give the observer an image before and after liquefaction.

As a technique for reproducing liquefaction more realistically, there are a liquefaction test apparatus as shown in Patent Document 2, for example, in addition to a number of experimental examples using a large earth tub. However, this equipment is a large-scale and complicated installation equipment in which several water tanks are connected by piping, and even if it is useful for more accurate understanding of ground behavior in specialized laboratories, etc. It is not suitable for scientific / disaster education applications where liquefaction can be observed. This is because it is difficult to carry around for exhibitions and exhibitions, and to quickly and repeatedly demonstrate liquefaction phenomena.
JP 2001-296800 A JP 2002-195993 A

  The problem to be solved by the present invention is that the liquefaction phenomenon can be reproduced in a more realistic state, the image before and after liquefaction can be given to the observer, and it is compact and portable, maintenance-free. It is to enable anyone to observe the liquefaction phenomenon quickly and repeatedly.

  The present invention has a double structure of an inner water tank and an outer water tank, the inner water tank and the outer water tank communicate with each other at the lower part, a strainer part incorporated in the bottom of the inner water tank, and the strainer part. A submersible pump incorporated below the inside of the experimental tank so that water can be ejected through the water, and a water level that is installed so that the vertical position can be adjusted outside the experimental tank and communicates with the lower part of the experimental tank through a flexible communication pipe It is a unit type liquefaction experiment apparatus comprising an adjustment tank, and at least the front upper part of the experiment tank is made of a transparent body so that the inside can be seen through. Usually, the experimental tank is placed on a shaking table.

  Here, the horizontal cross-sectional shape of the inner water tank and the outer water tank is set to be (horizontal cross-sectional area of the inner water tank) = (horizontal cross-sectional area of the outer water tank-horizontal cross-sectional area of the inner water tank), and the water level is set in the inner water tank. It is preferable to put a measure to be measured. The strainer part is a combination of, for example, a gravel layer accommodated in the inner water tank, a mesh plate for receiving the gravel layer, etc., and a partition plate provided with a gap below it. Incorporate to be located in.

  The liquefaction experiment apparatus according to the present invention is unitized as a whole, does not require assembly by piping, etc., and operates simply by supplying power to the submersible pump, so it is compact and portable, such as a demonstration venue. Carrying in and out, and setting of the device can be performed easily. In addition, the device of the present invention is a method in which the sand is lifted and loosened by blowing water through the strainer section, and the water level is lowered to form a tight sand layer on the loose sand layer. Liquefaction can be reproduced, and an image before and after liquefaction can be given to an observer. Furthermore, in the present invention, since the experimental tank has a double structure and water is communicated between the inner water tank and the outer water tank, there is no need to drain or pour water, and maintenance is free for a long time. Anyone can quickly and repeatedly observe the liquefaction phenomenon.

  Here, if the horizontal cross-sectional shape of the inner water tank and the outer water tank is set to be (horizontal cross-sectional area of the inner water tank) = (horizontal cross-sectional area of the outer water tank-horizontal cross-sectional area of the inner water tank), By observation, changes in groundwater level can be observed, and changes in the volume of the sand layer due to liquefaction can also be observed. If a measure is attached to the inner water tank, the surface height of the sand layer and the water level of the outer water tank can be accurately measured.

  Further, the strainer portion is a combination of a gravel layer accommodated in the inner water tank, a mesh plate for receiving the gravel layer, and a partition plate provided with a gap below the gravel layer, and the discharge port of the submersible pump is the aforementioned If it is incorporated so that it is located in the gap, water can be ejected almost uniformly from the entire bottom of the inner water tank, and the sand can be rolled up, and the gravel layer (cobblestone layer) on the mesh plate exhibits a strainer function against sand. The sand can be prevented from entering the gap through the mesh plate.

  A basic configuration of a unit type liquefaction experiment apparatus according to the present invention is shown in FIG. A shows the front, and B shows the horizontal section of the experimental tank. The experimental tank 10 has a double structure of an inner water tank 12 and an outer water tank 14, and the inner water tank 12 and the outer water tank 14 communicate with each other at the lower part. The inner water tank 12 is supported in the outer water tank 14 so that the bottom thereof is located in the vicinity of the center in the vertical direction of the experimental tank. Here, the side wall of the inner water tank 12 extends downward, and the extended portion 16 reaches the bottom surface of the outer water tank 14 to support the inner water tank 12. A communication hole 18 is formed in the extended 16 portion.

  A strainer portion 20 is incorporated in the bottom of the inner water tank 12. The strainer portion 20 is composed of a combination of a gravel layer 22 accommodated in the inner water tank, a mesh plate 24 for receiving the gravel layer 22 and the like, and a partition plate 26 provided with a gap below. A submersible pump 28 is incorporated below the inner water tank 12, and a discharge port 30 of the submersible pump 28 is located in the gap so that water can be dispersed and ejected almost uniformly through the strainer section 20. It has a simple structure.

  A water level adjusting tank 32 is provided outside the experimental tank 10. The water level adjustment tank 32 communicates with the lower part of the experimental tank 10 through a flexible communication pipe 34. For example, the water level adjustment tank 32 can be attached to and detached from the outer surface of the experimental tank 10 with a hook-and-loop fastener (not shown) or the like, thereby adjusting the vertical position.

  Here, as shown in FIG. 1B, the horizontal cross-sectional shapes of the inner water tank 12 and the outer water tank 14 are both square, and (horizontal cross-sectional area of the inner water tank) S1 = (horizontal cross-sectional area of the outer water tank-inner water tank) The dimensions are set so as to satisfy the relationship of (horizontal sectional area) S2. That is, the horizontal cross-sectional area of the inner water tank 12 is equal to the area of a square frame-like portion (shown by hatching) between the outer water tank 14 and the inner water tank 12. The horizontal cross section of the inner water tank and the outer water tank may be an arbitrary polygon such as a rectangle, or may be a circle.

  The mesh plate 24 in the inner water tank 12 is a plate-like body having a large number of small holes, on which a heavy and large cobblestone layer (gravel layer 22) is placed. A light and fine sand layer 36 is accommodated. The gravel layer 22 has a thickness capable of exhibiting a strainer function, and the sand layer 36 has a thickness necessary for the liquefaction experiment. Accordingly, the mesh plate 24 has a structure that can withstand the weight of the gravel layer 22 and the sand layer 36.

  In addition, a necessary amount of water (an amount in which the water level is above the gravel layer 22) is injected into the experiment tank 10 in advance. Here, at least the front upper side of the experimental tank 10 (the inner water tank 12 and the outer water tank 14) is made of a transparent body, and the inside (the sand layer in the inner water tank 12, the water level in the outer water tank 14, etc.) can be seen through from the outside. The water used may be tap water or the like, but it is desirable to add a surfactant or the like. As a result, it is possible to prevent algae and the like from growing on the wall surface of the water tank without replacing the water for a relatively long period of time, eliminating the need for cleaning the water tank, and realizing maintenance-free operation.

  Such an experimental tank is usually placed on the vibration table 40. Here, the vibration table 40 is configured such that a soft rubber plate 46 (or a soft resin plate or the like) is sandwiched between an upper plate 42 and a lower plate 44 so that horizontal vibration is possible, and a lever 48 is erected on one side. The simple configuration is such that the shaking table 40 vibrates by swinging the lever 48. Of course, the vibration table may be a table with wheels attached to the lower surface. Instead of a manual method, a method of exciting with a motor or the like may be used.

  Next, the operation of this apparatus will be described with reference to FIG. Prior to the experiment, make sure that water has been added to a predetermined water level. The water level is set to be above the gravel layer surface.

  As shown in FIG. 2A, the submersible pump 28 is operated, and the sand is suspended in the water by the water supplied by the submersible pump 28. Discharged water from the submersible pump 28 passes through the strainer unit 20 and is ejected almost uniformly from the entire bottom surface of the inner water tank 12. The lower part of the inner water tank 12 is a gravel layer 22, which does not squirt (does not move) by water supply, rolls up the sand layer 36 above it, and floats the sand in water. Water overflows from the upper edge of the inner water tank 12 and flows out to the outer water tank 14. The flow of water is indicated by arrows. By making the inner water tank 12 sufficiently deep with respect to the sand layer 36, the sand rolled up by the jetted water does not rise up to the water surface but can float on the way. If it does in this way, sand will not mix in the water which overflows from the upper edge of the inner side water tank 12, but it can discharge only water. The submersible pump 28 is continuously operated to maintain this state for about 5 to 10 seconds.

  When the operation of the submersible pump 28 is stopped and the water supply is stopped, as shown in FIG. 2B, the water in the inner water tank 12 flows backward to the outer water tank 14, and the water level in the inner water tank 12 gradually decreases. That is, the water in the inner water tank 12 is discharged through the strainer portion 20 arranged at the bottom. At this time, the sand floating in water settles down from a heavy thing and accumulates on a gravel layer, and the sand layer which liquefies is produced | generated. Since the sand remains on the gravel layer 22, only water flows backward in the submersible pump 28 and further flows out to the outer water tank 14. This flow of water continues until the water level in the inner water tank 12 is balanced with the water level in the outer water tank 14, and is maintained in that state.

  As shown in C of FIG. 2, the water level in the experimental tank 10 is adjusted so that the water level is positioned about 1 cm below the surface of the sand layer 36 in the inner water tank 12. The adjustment of the water level can be easily performed by raising and lowering the position of the water level adjustment tank 32 installed outside. As a result, the sand layer 36a is drained and tightened above the water level, and a loose sand layer is automatically formed below the water level.

  Therefore, if the building model 50 is placed on the sand layer 36a having a tight surface, preparation for the liquefaction experiment is completed (see D in FIG. 2). The shaking table 40 is shaken by the lever 48 to give vibration to the experimental tank 10 placed thereon. If the lever is gently rocked left and right, liquefaction does not occur at that stage. When the lever is shaken gradually, liquefaction can be observed at a certain point. The state of liquefaction of the sand layer can be observed from the outside of the transparent experimental tank 10. Differences in model behavior when liquefaction occurs can be observed by shallowing or deepening the piles of the building model or placing a manhole model.

  The surface height and water level of the sand layer are stored in the stage before liquefaction (the state shown in FIG. 2D). And the surface height and water level of the sand layer after completion | finish of liquefaction are read. Although not shown, if a measure is attached to the inner water tank, the surface height and water level of the sand layer can be easily read. As a result, changes in volume and groundwater level due to liquefaction of the sand layer can be observed. If the relationship of (horizontal cross-sectional area of the inner aquarium) = (horizontal cross-sectional area of the outer aquarium-horizontal cross-sectional area of the inner aquarium) is satisfied, the water level in the inner aquarium can be directly measured by observing the amount of water level change in the outer aquarium. It is because it can ask for.

  In this liquefaction experiment apparatus, anyone can generate a sand layer that can be liquefied easily and quickly only by turning the submersible pump 28 on and off, and repeated experiments can be performed. If the vertical position of the water level adjustment tank 32 is changed, the water level (groundwater level) in the sand layer is changed, so that it is possible to observe the difficulty of liquefaction depending on the groundwater level.

  A specific structural example of the experimental tank used in the present invention is shown in FIG. The experimental tank 60 is made of a transparent acrylic resin and has a double structure of a rectangular inner cylinder 62 and an outer cylinder 64. The outer cylinder 64 constitutes an outer water tank with a bottom and a lid. The inner cylinder 62 is provided with a partition plate 66 in the middle, and an upper portion thereof serves as an inner water tank. Here, the horizontal cross-sectional shapes of the inner cylinder 62 and the outer cylinder 64 are set so that (horizontal cross-sectional area of the inner water tank) = (horizontal cross-sectional area of the outer water tank-horizontal cross-sectional area of the inner water tank). The experimental tank is prepared by a method such as adhesion by incorporating a reinforcing plate inside as required. The outer cylinder can be produced, for example, with a size of about a dozen cm on a side and a height of about 20 to 30 cm.

  A mesh plate 68 is provided above the partition plate 66 at an interval, and the mesh plate 68 supports the gravel layer 22 and the sand layer 36 thereon. A submersible pump 28 is incorporated below the inner cylinder 62, and its discharge port 30 is positioned in the space between the mesh plate 68 and the partition plate 66. An overflow hole 70 is opened near the upper end of the inner cylinder 62, and a communication hole 72 is opened near the lower end (several centimeters above the bottom of the outer water tank). Further, an air vent hole 74 is provided immediately below the partition plate of the inner cylinder 62. This air vent hole 74 functions to vent the air below the inner cylinder 62 when water is first injected so that the experimental tank is filled with water. In addition, a measure 76 for measuring the water level is attached to the upper part of the inner cylinder (the inner water tank portion).

  Although only the experimental tank is shown in FIG. 3, in the case of use, as in FIG. 1, a water level adjustment tank is connected via a flexible communication pipe, and the water level adjustment tank is attached so that the vertical position can be freely adjusted and detached. At the same time, the experimental tank is placed on the shaking table. The inner water tank contains a gravel layer and a sand layer and injects a required amount of water. Water should contain an appropriate amount of a surfactant so as not to contaminate the water tank wall surface, and water may be injected from below the experimental tank through the flexible communication pipe.

  Since the procedure of the liquefaction experiment using this experimental tank may be the same as that in the case of FIG. 2, description thereof will be omitted.

  The liquefaction experiment apparatus according to the present invention can be variously developed. This device can create a sand layer that can be liquefied basically only by the on / off operation of the submersible pump, and the water can be kept in the experimental tank, so that it can be automated. For example, if a building model lift mechanism is attached by a motor, the building model is lifted and held, the submersible pump is turned on, water is spun up to roll up the sand, the submersible pump is turned off, the sand floating in the water is allowed to settle, and the sand layer The building model is lowered and installed on the sand layer. These series of operations can be performed by a rotary switch switching by an observer, or can be performed fully automatically.

  Although the above description is a case where one liquefaction experimental apparatus is used alone, a plurality of apparatuses can be connected and used. Multiple test tanks are juxtaposed. Although it may be placed on a common shaking table, when each experimental bath is placed on a separate shaking table, the shaking table may be connected by a connecting member. In this way, it is possible to vibrate a plurality of experimental tanks under the same conditions. Therefore, it is possible to comparatively observe changes in liquefaction behavior according to differences in groundwater levels, changes in ease of falling (difficulty) according to differences in pile lengths of building models, and the like.

Explanatory drawing which shows the basic composition of the unit type | mold liquefaction experiment apparatus which concerns on this invention. Explanatory drawing of the use state. The longitudinal cross-sectional view which shows one Example of the experimental tank used by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Experimental tank 12 Inner water tank 14 Outer water tank 20 Strainer part 22 Gravel layer 24 Mesh board 26 Partition board 28 Submersible pump 32 Water level adjustment tank 36 Sand layer 40 Shaking table

Claims (4)

  It has a double structure of an inner water tank and an outer water tank, and the inner water tank and the outer water tank communicate with each other at the lower part, a strainer part incorporated in the bottom of the inner water tank, and water through the strainer part. A submersible pump incorporated below the inside of the experimental tank so that it can be ejected, and a water level adjusting tank that is installed outside the experimental tank so that the vertical position can be adjusted and communicates with the lower part of the experimental tank through a flexible communication pipe. A unit type liquefaction experiment apparatus characterized in that at least the front upper part of the experiment tank is made of a transparent body and can be seen through.   The horizontal cross-sectional shape of the inner water tank and the outer water tank is set so that (horizontal cross-sectional area of the inner water tank) = (horizontal cross-sectional area of the outer water tank-horizontal cross-sectional area of the inner water tank) and measures the water level in the inner water tank. The unit type liquefaction experiment apparatus according to claim 1, wherein is attached.   The strainer part is a combination of a gravel layer accommodated in the inner water tank, a mesh plate for receiving the gravel layer, etc., and a partition plate provided with a gap below it. The unit-type liquefaction experiment apparatus according to claim 1 or 2, which is located in the position. The unit type liquefaction experiment apparatus according to any one of claims 1 to 3, wherein the experimental tank is placed on a vibration table.

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