JP2002195993A - Liquefaction test equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquefaction test equipment allowing upward groundwater to generate excess pore water pressure in the ground for reproducing a liquefaction phenomenon. SOLUTION: An air vent pipe is connected to both halfway position of a water tube conveying water from a head tank to a nozzle plumbing and the nozzle plumbing itself. A check valve for preventing negative pressure is installed in the end section of the water tube channeling water from the head tank to the nozzle plumbing, the nozzle plumbing is covered with cotton net and mesh, and a permeable layer lined with broken stones other than fine grains is formed on the circumference of the nozzle.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the technical field of a liquefaction test apparatus for reproducing a liquefaction phenomenon by generating an excessive pore water pressure in the ground by an upward seepage flow using a large shear soil tank.

[0002]

2. Description of the Related Art Methods for reproducing liquefaction in a laboratory test include, for example, (1) a physical property test method. (2) A vibration test method using a shaking table. (3) A liquefaction test method that causes liquefaction in a water stream. Are known and implemented.

Regarding the liquefaction test method of the above (3),
For example, a method of liquefying the ground by repeatedly applying a load to soil collected from the in-situ ground has been developed, as in a liquefaction test apparatus described in Japanese Patent Application Laid-Open No. 6-18393.

[0004] However, generally, as shown in FIG. 1, the outline of the principle of the test is schematically shown in a large shear soil tank 1 using a sandy soil and a saturated soil layer (liquefied layer = about 4 m). 2 is made, and the water head difference H (= about 4 m) from the surface of the soil layer to the surface of the elevated water tank 3 is used. A liquefaction test device for generating a permeated water stream 5 is known. Liquefied ground 2
The horizontal displacement is applied to the pile head of the test pile 9 inside, and the resistance value at that time is determined. Reference numeral 10 in FIG.
It refers to the lower support layer.

[0005] Normally, an upward seepage water flow 5 is generated in the ground by the head difference H or a pressure corresponding thereto. And if you use a large shear soil tank 1,
Since a large amount of water is required to generate the permeated water flow 5, the permeated water that has overflowed to the upper surface of the saturated soil layer 2 is returned to the lower notch tank 7 using the water pipe 6, and The water is circulated back to the elevated water tank 3 by the operation of the pump 8. During the test, water is continuously supplied from the elevated water tank 3 to the saturated soil layer 2 with a constant head difference H, so that the liquefaction test can be performed with the water pressure continuously applied.

When the liquefaction test is repeatedly performed, consolidation occurs in the state of the ground 2, particularly in the sand particles around the test pile 9, which is different from the initial condition. Sending a strong stream of water to perform so-called boiling and calm down is always performed between tests.

[0007]

The above-described liquefaction test apparatus shown in FIG. 1 performs a liquefaction test using the ground 2 in the earthen tank once prepared, and then performs boiling to substantially reduce the time of preparation. It can be returned to the ground with the same initial conditions. However, if boiling is repeated many times, sand is clogged in the pipe (water pipe) and water does not flow, and there is a disadvantage that the test fails or ends abnormally. For example, when the water surface of the elevated water tank 3 is suddenly lowered, the inside of the blow-out pipe 4 is in a negative pressure state, and fine particles of sand in the earth 2 in the earth tank enter the blow-out pipe 4 (backflow), The piping may be clogged.

[0008] Further, when air is accumulated in the piping during boiling, the water pressure in the soil in the earthen tub (saturated soil layer 2) does not increase, and an upward seepage water flow may not be generated. Therefore, an object of the present invention is to provide clogging and other inconveniences (troubles) even if boiling is repeated several times.
It is an object of the present invention to provide a liquefaction test apparatus improved to have a structure that does not generate the liquefaction.

[0009]

As a means for solving the above-mentioned problems, a liquefaction test apparatus according to the invention described in claim 1 uses a large shearing soil tank, and uses an upwardly penetrating water flow to penetrate the ground. In a liquefaction test device that reproduces liquefaction phenomena by generating excess pore water pressure, the blowout pipe laid flat in the lower part of the shear soil tank is installed at a certain height from the surface of the ground in the earthen tank A water circulation system is connected to the elevated water tank, and a water pipe for guiding the infiltration water overflowing to the ground surface is connected to the notch tank. That
A position in the middle of the water pipe that sends water from the elevated water tank to the discharge pipe, and that an air vent pipe is connected to the discharge pipe, and a reverse end for preventing negative pressure at the end of the water pipe that guides water from the elevated water tank to the discharge pipe That a stop valve is installed, the blow-out pipe is covered with a cotton net and a mesh, and a water-permeable layer in which crushed stone or the like from which fine particles are removed is formed around the blow-out port, Each feature.

According to a second aspect of the present invention, in the liquefaction test apparatus according to the first aspect, fine particles contained in the water are removed at a drain outlet of a drain pipe for guiding excess water of the elevated water tank to the notch tank. The surface of the permeable layer covered with crushed stone and the like is covered with a mesh, and a piezometer is installed in a shear soil tank.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a liquefaction test apparatus according to the first and second aspects of the present invention will be described with reference to FIGS. 1 and 2. FIG.

FIG. 2 shows an improved piping system based on the principle diagram of FIG. That is, the liquefaction test apparatus of the present invention uses the large shear soil tank 1 and generates an upward seepage water flow 5 into the saturated soil layer 2 created therein, thereby generating excess pore water pressure in the soil inside the earth tank. This is to reproduce the liquefaction phenomenon. Ground 2 in the soil tank (saturated soil layer)
Is created using in situ ground soil or experimental sandy soil.

In the case of FIG. 2, six (six systems) blow-out pipes 4 laid flatly on the lower part of the ground in the shear soil tank 1 are arranged in parallel and three-dimensionally. They are connected by a common pipe and branched into two systems. The blow-out pipe 4 is provided with blow-off ports having a diameter of about 5 mm at equal intervals in the pipe axis direction, and water supplied from the elevated water tank 3 at a constant water pressure is blown out from the blow-out ports, and the seepage water flows upward into the ground. 5
Generate.

Therefore, the water pipe 11 led from the elevated water tank 3
Is divided into two systems on the way, and the two branch pipes 12 and 12
Are connected to the headers 13 of the blow-out pipe 4 via check valves 14, respectively. The check valve 14 automatically prevents the backflow phenomenon from occurring in the water flow in the pipe when the elevated water tank 3 is suddenly lowered for calming after boiling. As a result, the inside of the blow-out pipe 4 becomes negative pressure due to the backflow phenomenon of the water, which has conventionally occurred, and fine particles of sand in the shear soil tank 1 enter the blow-out pipe 4 and the inside of the same pipe becomes clogged. It prevents accidents that would otherwise occur.

The elevated water tank 3 is installed at a fixed height (for example, a head difference of 0 to 4 m) from the surface of the ground 2 in the earthen tank.

The permeated water that has overflowed to the surface of the ground 2 in the shear tank 1 is pumped up by a pump 15, and a water pipe 6 for guiding the water is connected to a notch tank 7. The water accumulated in the notch tank 7 is pumped up by a pump 8, and a water pipe 16 for guiding the water is connected to the elevated water tank 3, thereby forming a water circulation system for sequentially circulating the water. The overflow of the elevated water tank 3 is returned to the notch tank 7 by a water pipe 20. Therefore, for the liquefaction test, a large amount of water must be continuously supplied into the shear soil tank 1. However, by configuring the water circulation system as described above, wasteful consumption of water can be avoided, and The liquefaction test can be performed stably with good quality and economically by supplying water under a constant water pressure.

When air is accumulated in the piping (water pipe) system when the soil 2 in the earth tank is boiled, the water pressure in the ground 2 does not increase and the upward seepage water flow 5 does not occur. As a countermeasure, an air vent pipe 17 is connected to a position as high as possible above the water pipe 11, and an air vent ball valve 17 a is installed in the pipe 17. 17b is a water pressure gauge. An air vent pipe 18 is also connected to the center of the blow-off pipe 4, and an air vent ball valve 18a is provided in the middle thereof. Each of the air vent pipes 1
7 and 18 are connected to the notch tank 7. Therefore, the problem that air accumulates in each pipe (water pipe) system has been solved.

The excess water in the shear tank 1 is supplied to the notch tank 7
A strainer 21 for removing fine particles contained in the water is provided at a drain of the water pipe 6 leading to the water. In the elevated water tank 3 and the notch tank 7, underwater weirs 3a and 3b or 7a, which also serve as a sedimentation tank and regulate a certain water level, are installed.

The outlet of the outlet pipe 4 is covered with a cotton net and a mesh, although not shown in detail. Further, a water permeable layer 30 laid with crushed stones or the like from which fine particles have been removed is formed around the surface, and the surface of the water permeable layer 30, that is, the boundary position with the saturated soil layer 2 is covered with a mesh 31. This is to prevent the inconvenience of the crushed stone floating into the ground during boiling.

Although not shown in detail,
Piezometers are provided in the shear soil tank 1 at predetermined intervals in the vertical direction (or at a predetermined height) so that changes in excess pore water pressure distribution in the soil 2 in the earth tank can be visually confirmed in real time. There are multiple installations.

[0021]

The liquefaction test apparatus according to the first and second aspects of the present invention has the above-described structure, so that there is no need to worry about troubles such as clogging of the blow-out pipe, even if boiling is performed many times. This makes it possible to repeatedly and stably perform a high-quality liquefaction test, thereby contributing to more accurate understanding of the ground behavior.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the principle of a liquefaction test apparatus.

FIG. 2 is a piping diagram of a liquefaction test apparatus improved according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Large shearing tank 5 Upward seepage water flow 2 Ground in a tank 4 Blow-out piping 3 Elevated water tank 6 Water pipe 11 Water pipe 7 Notch tank 8 Pump 17 Air release pipe 18 Air release pipe 14 Check valve 30 Permeable layer 31 Mesh 20 Drain pipe 21 strainer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Junji Hamada 1-5-1, Otsuka, Inzai City, Chiba Prefecture Inside the Research Institute of Takenaka Corporation (72) Inventor Eisaku Kawai 1-5-1, Otsuka, Inzai City, Chiba Prefecture Inside Takenaka Corporation Technical Research Institute (72) Inventor Kazuto Takahashi 1-5-1, Otsuka, Inzai-shi, Chiba Prefecture F-term inside Technical Research Center Takenaka Corporation 2D043 AA09 BA10

Claims (2)

[Claims] 1. A liquefaction test apparatus for reproducing a liquefaction phenomenon by generating excessive pore water pressure in the ground by upward seepage water flow using a large shear soil tank. Is connected to an elevated water tank installed at a certain height from the surface of the ground in the earthen tank, and a water pipe that guides the seepage water overflowing to the ground surface is connected to the notch tank, A water circulation system that returns water in the notch tank to the elevated water tank by a pump is configured, an intermediate position of a water pipe that sends water from the elevated water tank to a blowing pipe, and an air vent pipe connected to the blowing pipe. That a check valve for preventing negative pressure is installed at the end of the water pipe that guides water from the elevated water tank to the blow-off pipe, and that the blow-out pipe is covered with a cotton net and a mesh, and around the blow-out port. To Is a liquefaction test apparatus characterized in that a permeable layer formed by laying crushed stone or the like from which fine particles have been removed is formed. 2. A strainer for removing fine particles contained in water is installed at a drain of a drain pipe for guiding surplus water in an elevated water tank to a notch tank, and a surface of a permeable layer covered with crushed stones is meshed. The liquefaction test apparatus according to claim 1, wherein the liquefaction test apparatus is covered with a piezometer installed in a shear soil tank.