JPH0751791B2 - Basic structure of structure - Google Patents

Description

TECHNICAL FIELD The present invention relates to a basic structure of a structure in which at least a part is buried in a sand layer, and in particular, although the floating due to hydrostatic pressure does not occur, the sand layer is in a liquid state. The present invention relates to a basic structure of a structure that is suitable for use in a structure that is likely to be lifted due to aging.

"Conventional technology" In recent years, development of reclaimed land and waterfront
As the development of the area becomes active, liquefaction of sand ground becomes a problem at the time of earthquakes, and various methods for preventing the structure from rising are realized. As an example, a gravel drainage column called gravel drain is constructed in the sand ground to prevent liquefaction by draining pore water in the sand ground through the gravel drain to the drainage layer on the ground surface. There are a gravel drain method and a groundwater lowering method that lowers the groundwater level by digging a well in the sand ground and pumping groundwater from the well to prevent liquefaction near the ground surface.

[Problems to be Solved by the Invention] However, the conventional means for preventing liquefaction of sand ground has the following problems and there is room for improvement.
That is, in the gravel drain method, the drainage performance greatly varies depending on the arrangement of the drains, the intervals between the drains, etc., and it is difficult to obtain a reliable drainage effect. Further, in the groundwater reduction method, there is a problem that equipment costs and the like increase because groundwater needs to be pumped at all times.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a basic structure of a structure that does not require construction work on the ground around the structure and can take liquefaction prevention measures at low cost. .

"Means for Solving the Problem" Therefore, the present invention is to form a hollow chamber at the bottom of a structure at least a part of which is buried in a sand layer, and the hollow chamber is made of an expandable / contractible material. A bag body is provided, and a communication hole opening in the sand layer is provided in the bag body,
Furthermore, the inside of the bag body is maintained at a pressure higher than the groundwater pressure in the vicinity of the communication hole, and when the sand layer may be liquefied, the inside of the bag body is depressurized to the groundwater pressure or less. The above problem is solved by forming a basic structure of a structure to which a pressure means is attached.

[Operation] When seismic force acts on the sand layer in which the structure according to the present invention is constructed, the pressurizing means reduces the pressure in the bag to below groundwater pressure when there is a risk of liquefaction in the sand layer. As a result, groundwater in the sand layer is guided into the bag body through the communication hole, and the pore water pressure immediately below the structure is dissipated to prevent the sand layer from liquefying.

[Examples] Examples of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a basic structure of a structure which is an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a structure to which the present embodiment is applied.
The lower part is buried in the ground surface part of the sand layer S extending on the impermeable layer C. In addition, a water blocking wall W is provided in the sand layer S so as to surround the structure 1, and the lower end of the water blocking wall W reaches the impermeable layer C, so that at the time of an earthquake or the like. The structure prevents the ground water from being supplied from the sand layer S outside the water blocking wall W to the sand layer S directly below the structure 1.

In this sand layer S, for example, the groundwater level WL reaches near the ground surface as shown in FIG. 1, and the structure 1 does not rise due to hydrostatic pressure, but there is a possibility that the structure 1 may rise due to liquefaction (liquefaction). Apparent specific gravity of time = 1.9).

The bottom slab 2 of the structure 1 buried in the sand layer S is doubly constituted by a pair of slabs 3 and 3 formed at a predetermined interval in the vertical direction, and a hollow chamber 4 is provided between these slabs 3 and 3. It is said that. The hollow chamber 4 may be divided into a plurality of chambers by the partition member 5 or the like. The reference numeral 6 is a through hole 6 that is opened in the slab 3 located below, opens in the sand layer S, and communicates with the hollow chamber 4.

A hollow bag body 7 is disposed inside the hollow chamber 4. The bag body 7 is made of a flexible material such as rubber so that it can be expanded and contracted. It should be noted that the bag body 7 is expanded in the hollow chamber 4
The size is preferably such that it substantially covers the inner surface.

A communication hole 8 is formed in the bag body 7. The communication hole 8 is opened in the sand layer S by facing the through hole 6 of the slab 3. The internal pressure of the bag body 7 is increased or decreased by the pressurizing means 10 in the structure 1 based on a signal from the sensor 9 installed in the sand layer S.

Specifically, the pressurizing means 10 is provided with a control means 11 (for example, a computer), and the control means 11 determines whether or not liquefaction occurs in the sand layer S based on a signal from the sensor 9. Judgment is made, and normally, in order to maintain the pressure inside the bag body 7 higher than the water pressure of the groundwater in the vicinity of the communication hole 8, the pressurizing means 10
In addition to the above control, the pressurizing means 10 is controlled so as to reduce the internal pressure of the bag body 7 to the water pressure or less when it is determined that liquefaction may occur. The sensor 9 can be arbitrarily selected from well-known means as long as it can detect the liquefaction of the sand layer S. In this embodiment, a sensor for detecting the water pressure of groundwater is used.

The control means 11 constantly monitors the fluctuation of groundwater pressure due to the tide, calculates the pressure gradient, that is, the time increment of the water pressure,
When it reaches a certain level or above, it is judged that the sand layer S may be liquefied, and the pressure means for depressurizing the inside of the bag body 7 is reached.
Control 10 That is, the water pressure of groundwater during an earthquake is equal to the hydrostatic pressure during normal times plus the pore water pressure between particles, and the rate of increase is greater than that during normal times. Liquefaction is detected. When measuring the pressure gradient, it is considered possible to measure the pressure increment of groundwater for 5 to 10 seconds with sufficient accuracy.

Further, the bag body 7 has a drain pipe 12 having one end opened inside.
Is provided, the other end of the drain pipe 12 is located above the ground, and a drain pump 13 is provided in the middle of the drain pipe 12.

The reference numeral 14 designates a gravel layer (water collecting layer) G which is laid evenly below the bottom slab 2 and leveled and which also serves as paving masonry.

Therefore, since the inside of the bag body 7 is normally maintained at a pressure higher than the groundwater pressure in the vicinity of the communication hole 8, groundwater does not enter the inside of the bag body 7 through the communication hole 8, but seismic force is applied to the sand layer S. When acting, the pore water pressure between particles in the sand layer S rises, and the sensor 9 detects this and the control means 11 controls the pressurizing means 10 to reduce the pressure inside the bag body 7. After that, when the pore water pressure further rises, the pressure inside the bag body 7 is reduced from the water pressure of the ground water. Therefore, after the ground water is collected by the gravel layer G, it enters the bag body 7 through the through hole 8. guided by,
Pore water pressure immediately below the structure 1 is dissipated and liquefaction is suppressed. After the earthquake ends, the groundwater stored in the bag body 7 may be discharged to the ground via the drain pipe 12 by operating the drain pump 13.

Therefore, according to this embodiment, it is possible to prevent liquefaction from occurring in the sand layer S around the structure 1 without performing any construction work on the ground around the structure 1 unlike the conventional gravel drain method. Therefore, liquefaction prevention measures can be taken easily and inexpensively. Further, the drainage pump 13 need only be operated when the groundwater is stored in the bag body 7, and it is not necessary to constantly operate the pump as in the conventional groundwater reduction method. Anti-aging measures can be realized. Moreover, since the inside of the bag body 7 is normally closed and the infiltration of groundwater into the bag body 7 due to hydrostatic pressure is blocked, the bag body 7 is in a dry state.
The structure will not be adversely affected by corrosion or the like. Furthermore, by controlling the internal pressure of the bag body 7,
Since the intrusion of groundwater into the inside and the cutoff thereof are controlled, the structure is simpler and maintenance is easier than in the case where a valve mechanism or the like is provided in the communication hole 8, for example.

The details of the basic structure of the structure of the present invention are not limited to those in the above-described embodiment, and various modifications are possible. As an example, groundwater can be introduced into the hollow chamber 4 by opening the on-off valve 6 a predetermined time after detecting a seismic wave of a predetermined level or higher using the sensor 7 as a seismometer.

[Advantages of the Invention] As described in detail above, according to the present invention, a hollow chamber is formed at the bottom of a structure at least a part of which is embedded in a sand layer, and a material capable of expanding and contracting in this hollow chamber. While disposing a hollow bag body formed in, the bag body is provided with a communication hole opening in the sand layer, further, in the bag body, the inside of the bag to a pressure higher than the groundwater pressure in the vicinity of the communication hole. Since the basic structure of the structure was constructed so as to maintain the sand layer and pressurize the inside of the bag to reduce the pressure below the groundwater pressure when there is a risk of liquefaction, the conventional gravel drain Liquefaction can be prevented from occurring in the sand layer around this structure without performing any construction work on the ground around the structure as in the construction method, and liquefaction prevention measures can be taken easily and inexpensively. . Further, since the groundwater is not always stored in the bag body, it is not necessary to constantly operate the pump as in the conventional groundwater lowering construction method, and also from this aspect, inexpensive liquefaction prevention measures can be realized.

[Brief description of drawings]

1 and 2 are views showing a basic structure of a structure which is an embodiment of the present invention. FIG. 1 is a cross-sectional view showing the entire structure, and FIG. 2 is an enlarged view of the vicinity of a hollow chamber. It is the sectional view shown. S ... sand layer, 1 ... structure, 2 ... bottom plate, 3 ... slab, 4 ... hollow chamber, 7 ... bag, 8 ... communication hole, 9 ...
Sensor, 10 ... pressurizing means, 11 ... control means, 12 ... drain pipe, 13 ... drain pump.

Claims (1)

[Claims] 1. A hollow chamber is formed at the bottom of a structure at least a part of which is buried in a sand layer, and the hollow chamber is expanded and expanded.
A hollow bag body made of a contractible material is provided, and the bag body is provided with a communication hole that opens into the sand layer. The basic structure of the structure, which is maintained at a pressure higher than the groundwater pressure near the hole, and is provided with a pressurizing means for depressurizing the inside of the bag body to the groundwater pressure or less when there is a risk of liquefaction in the sand layer. .