JPH03187415A - Foundation structure of structure - Google Patents

Abstract

PURPOSE:To prevent the liquefaction of a sand layer by providing an open/close valve opened to the sand layer on the bottom surface of a structure, which has been built on the sand layer, for communicating the sand layer with an empty chamber provided in the bottom part of the structure, so that the gap haydraulic pressure directly beneath the structure can be dispersed. CONSTITUTION:In the bottom part of a structure 1 at least a part of which has been embedded in a sand layer S, an empty chamber 4 is formed, and on the bottom surface of the structure 1, an open/close value 6 which is opened to the sand layer S and is communicated with the empty chamber 4 is provided. When there is the possibility that an earthquake force is exerted to the sand layer S on which the structure 1 is built for liquefying the sand layer S, the open/close valve 6 is opened by a control means 8, so that the water in the inside of the sand layer S can be introduced into the empty chamber 4 through the open/close valve 6. Thus, it is unnecessary to operate a pump 10 always, and the gap hydraulic pressure directly beneath the structure 1 can be dispersed for restraining the liquefaction of the sand layer S.

Description

Detailed Description of the Invention "Field of Industrial Application" This invention relates to the foundation structure of a structure that is at least partially buried in a sand layer. The present invention relates to a basic structure of a structure that is suitable for use in a structure that is likely to lift up due to oxidation.

“Conventional technology” In recent years, the development of reclaimed land and the development of waterfront
As development in these areas becomes more active, liquefaction of sandy ground during earthquakes has become a problem, and various methods have been developed to prevent structures from rising due to this. -For example, by constructing pillars made of gravel called gravel drains in sandy ground, liquefaction can be prevented by draining pore water in the sandy ground into the drainage layer on the ground surface through the gravel drains during earthquakes, etc. There are gravel drain construction methods, which lower the groundwater level by digging wells in sandy ground, and pumping up groundwater from these wells, thereby preventing liquefaction near the ground surface.

``Problems to be Solved by the Invention'' However, the conventional means for preventing liquefaction of sandy ground has the following problems, and there is room for improvement.

That is, in the gravel drain construction method, the drainage performance varies greatly depending on the arrangement of drains, their spacing, etc., and it is difficult to obtain a reliable drainage effect. In addition, the groundwater reduction method has problems such as increased equipment costs because it is necessary to constantly pump up groundwater.

This invention has been made in view of the above-mentioned circumstances, and aims to provide a foundation structure for a structure that does not require construction work on the ground around the structure and can take measures to prevent liquefaction at low cost. .

"Means for Solving the Problems" Therefore, the present invention forms a hollow chamber at the bottom of a structure that is at least partially buried in a sand layer, and has an opening in the sand layer at the bottom of the structure. An on-off valve communicating with the hollow chamber is provided, and the on-off valve is provided with a control means for opening the on-off valve when there is a risk of liquefaction in the sand layer. , is trying to solve the above problem.

"Operation" When an earthquake force acts on the sand layer on which the structure according to the present invention is constructed, and there is a risk of liquefaction in the sand layer, the control means controls the on-off valve to open the on-off valve. As a result, groundwater within the sand layer is guided into the hollow chamber through the on-off valve, pore water pressure directly under the structure is dissipated, and liquefaction of the sand layer is suppressed.

"Embodiments" Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing the basic structure of a structure that is an embodiment of the present invention. In FIG. 1, the reference numeral 1 indicates a structure to which this embodiment is applied, and this structure 1
The lower part of the sand layer S is buried in the ground surface part of the sand layer S that extends on the impermeable layer C. In addition, a water cutoff wall W is provided in this sand layer S so as to surround the structure 1, and the lower end of this water cutoff wall W extends to the impermeable layer C, thereby preventing water damage during an earthquake. The structure prevents groundwater from being supplied from the sand layer S located outside the water-stop wall W to the sand layer S directly below the structure 1.

In this sand layer S, for example, the groundwater level WL reaches close to the ground surface as shown in Fig. 1, and the structure 1 does not rise due to hydrostatic pressure, but the ground is likely to rise due to liquefaction (liquefaction Apparent specific gravity of time = approximately 1.
9).

The bottom plate 2 of the structure l buried in the sand layer S is constructed in double form by a pair of slabs 3.3 formed at a predetermined interval in the vertical direction, and a hollow chamber 4 is formed between these slabs 3.3. It is said that Note that this hollow chamber 4 may be divided into a plurality of chambers by a partition member 5 or the like.

Further, the slab 3 located below is provided with an on-off valve 6 that opens into the sand layer S and communicates with the hollow chamber 4 . The opening/closing operation of the opening/closing valve 6 is controlled by a control means (for example, a computer) 8 within the structure 1 based on a signal from a sensor 7 installed in the sand layer S.

Specifically, the control means 8 determines whether liquefaction occurs in the sand layer S based on the signal from the sensor 7, and opens the on-off valve 6 when it is determined that there is a risk of liquefaction. Control as much as possible. The sensor 7 can be arbitrarily selected from known means as long as it can detect liquefaction of the sand layer S, but in this embodiment, a sensor that detects the water pressure of groundwater is used.

The control means 8 constantly monitors water pressure fluctuations in groundwater due to tides, calculates the pressure gradient, that is, the time increment of water pressure,
When this reaches a certain level or more, it is determined that there is a risk of liquefaction in the sand layer S, and control is performed to open the on-off valve 6. In other words, the water pressure of groundwater during an earthquake is the sum of the static water pressure in normal times and the pore water pressure between particles, and the rate of increase is greater than that in normal times. This is to detect liquefaction.

In addition, when measuring the pressure gradient, it is considered that sufficiently accurate measurement is possible by measuring the pressure increment of groundwater over 5 to 10 seconds.

On the other hand, except when there is a risk of liquefaction of the sand layer S, the control means 8 controls the on-off valve 6 to close it.

Further, the structure 1 is provided with a drain pipe 9 whose one end opens into the hollow chamber 4, and the other end of the drain pipe 9 reaches above the ground. A pump 10 is provided.

In addition, the code|symbol 11 is a gravel layer (water collection layer) G which also serves as the paving stone surface spread substantially horizontally below the bottom slab 2.

Therefore, the sand layer S on which the structure 1 with such a configuration is constructed
When an earthquake force acts on the sand layer S, the pore water pressure between particles in the sand layer S increases, the sensor 7 detects this, and the control means 8 controls the on-off valve 6 to open. After that, when the pore water pressure increases further, groundwater is collected by the gravel layer G and guided into the hollow chamber 4 through the on-off valve 6, and the pore water pressure immediately below the structure 1 is dissipated, causing liquefaction. is suppressed. After the earthquake ends, the control means 8 controls the on-off valve 6.
is in a closed state, and as a result, the groundwater stored in the hollow chamber 4 is drained into the drain pipe 9 by operating the drain pump 10.
It can be discharged to the ground via.

Therefore, according to this embodiment, the formation of waves in the sand layer ~S around the structure 1 can be suppressed without performing any construction work on the ground around the structure 1 as in the conventional gravel drain construction method. Therefore, liquefaction prevention measures can be taken easily and inexpensively. Moreover, the drainage pump 10 is
It is only necessary to operate the pump when groundwater is stored in the hollow chamber 4, and there is no need to constantly operate the pump as in the conventional groundwater reduction method, so from this point of view as well, it is possible to realize an inexpensive liquefaction prevention measure. can. Moreover, the on-off valve 6 is normally in a closed state, and the intrusion of groundwater into the hollow chamber 4 due to hydrostatic pressure is blocked and the inside of the hollow chamber 4 is in a dry state, so that the structure may be damaged due to corrosion etc. There will be no negative impact on

Note that the details of the basic structure of the structure of the present invention are not limited to the above embodiments, and various modifications are possible. - For example, it is also possible to introduce groundwater into the hollow chamber 4 by opening the on-off valve 6 after a predetermined time after detecting seismic waves of a predetermined level or higher using the sensor 7 as a seismometer.

"Effects of the Invention" As explained in detail above, according to the present invention, a hollow chamber is formed at the bottom of a structure at least partially buried in a sand layer, and the sand layer is formed at the bottom of the structure. The foundation of a structure is provided with an on-off valve that opens inside and communicates with the hollow chamber, and a control means is attached to this on-off valve to open the on-off valve when there is a risk of liquefaction in the sand layer. Since this structure has been constructed, liquefaction can be prevented from occurring in the sand layer around the structure without any construction work being done on the ground around the structure as in the conventional gravel drain construction method, which is simple and inexpensive. It is possible to take measures to prevent liquefaction. Moreover, since the structure is not such that groundwater is always stored in the hollow chamber, there is no need to constantly operate a pump as in the conventional groundwater lowering method, and from this point of view as well, it is possible to realize an inexpensive measure to prevent liquefaction.

[Brief explanation of drawings]

Figures 1 and 2 are diagrams showing the basic structure of a structure that is an embodiment of the present invention, with Figure 1 being a sectional view showing the overall configuration, and Figure 2 being an enlarged view of the vicinity of the hollow chamber. FIG. S...Sand layer, 1...Structure, 2...
... Bottom plate, 3 ... Slab, 4 ... Hollow chamber, 6 ... Opening/closing valve, 7 ... Sensor,
8... Control means, 9... Drain pipe, 1o
・・・・・・Drain pump.

Claims (1)

[Claims] A hollow chamber is formed at the bottom of the structure that is at least partially buried in the sand layer, and an on-off valve that opens into the sand layer and communicates with the hollow chamber is provided at the bottom of the structure. The on-off valve is also provided with a control means for opening the on-off valve when there is a risk of liquefaction in the sand layer.