JPH035528A - Base structure of structure - Google Patents

Abstract

PURPOSE:To form a structure that stands liquefaction effect of a sand layer at the time of earthquake when constructing is executed on the sand layer by surrounding a construction with a cut-off wall linked to an impermeable layer, and by covering the bottom surface and the side surface of the construction with a ballast that works as a discharge layer. CONSTITUTION:To a sand layer S in the vicinity of a construction 1, a cut-off wall 2 is buried so as to surround the construction, and for its lower end to reach an impermeable layer C. In constructing the construction 1, by backfilling up to the ground surface with a ballast so as to cover the bottom surface and the side surface of the construction 1 in the cut-off wall 2, a discharge layer D is formed. When an appropriate impermeable layer does not exist, by chemical feeding, the ground is improved so as to link to the lower end of the cut-off wall 2, as an impermeable layer C'. Even when liquefaction of the sand layer S occurs at the time of earthquake, hydrostatic excess pressure is eliminated due to the existence of the discharge layer D extended in a wide region, whereby the construction 1 can be protected against bad effect.

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, in the groundwater reduction method, since it is necessary to constantly pump up groundwater, permanent facilities such as drainage pumps are indispensable, and there are problems such as increased equipment costs.

This invention was made in view of the above-mentioned circumstances, and provides a structure that does not require permanent facilities such as a drainage pump, and can prevent structures from floating due to liquefaction of sandy ground by providing a reliable drainage effect. Its purpose is to provide the basic structure of things.

"Means for Solving the Problem" Therefore, the invention according to the first claim of the present invention is directed to a foundation structure of a structure which is at least partially buried in a sand layer on an impermeable layer. A water-stop wall is provided in the sand layer to surround the area where the water-stop wall is to be constructed, and the lower end of this water-stop wall extends to the impermeable layer, and the upper part of the sand layer surrounded by the water cut-off wall is , by providing a drainage layer made of gravel or the like to cover the bottom and side surfaces of the structure,
We are trying to solve the above problem.

Further, the invention according to the second claim is a foundation structure of a structure in which at least a part of the structure is buried in a sand layer, in which a water-stop wall is placed in the sand layer so as to surround a place where the structure is to be constructed. The lower part of the sand layer surrounded by this water-stop wall is made into an impermeable layer by injecting a chemical solution, etc., and a drainage layer made of gravel or the like is provided above it to cover the bottom and side surfaces of the structure. .

"Function" When the foundation structure of the structure of this invention is susceptible to liquefaction of the sand layer due to seismic force, etc., the water cutoff wall restrains the deformation of the sand, thereby preventing the sand layer immediately below the structure from becoming liquefied. liquefaction is less likely to occur. In addition, even if liquefaction occurs in the sand layer directly beneath the structure, the pore water in the sand layer will be drained to the drainage layer, and the excess water pressure will be immediately dissipated by this drainage layer.
No harmful lifting occurs. Rather, the slight uplift has the effect of reducing excess water pressure in the sand layer, so
Not harmful to structures.

"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 a first embodiment of the present invention. In FIG. 1, the symbol l is a structure to which this embodiment is applied, and this structure 1 is located on the ground surface of a sand layer S extending on an impermeable layer C. is buried. In this sand layer S, for example, the groundwater level WL reaches close to the ground surface as shown in Figure 1,
The ground does not lift due to hydrostatic pressure, but there is a risk of lifting due to liquefaction (apparent specific gravity = approximately 1.9
).

A water cutoff wall 2 is constructed in the sand layer S near the structure 1 so as to surround the structure 1, and the lower end of the water cutoff wall 2 reaches the impermeable layer C.

The members forming this water stop wall 2 and its structure are arbitrary.
It may be appropriately selected from well-known and commonly used means.

Further, the shape of the water stop wall 2 in a plan view is also arbitrary, and may be appropriately determined depending on the planar shape of the structure 1, such as circular or rectangular.

A drainage layer made of gravel or the like is formed above the sand layer S surrounded by the water-stop wall 2, and this drainage layer covers the bottom and side surfaces of the underground portion of the structure 1. Also,
In order to improve the permeability of this drainage layer, perforated pipes (with tips protruding above the ground) are installed in the drainage layer.
(Illustrated paths) are inserted as appropriate.

The method for constructing the foundation structure of a structure with the above configuration is arbitrary and does not require an equivalent special construction method, but
An example is shown below.

First, when constructing the underground part of the structure 1, a water stop wall 2 is constructed within the sand layer S so as to surround the structure 1, and its lower end reaches the impermeable layer C.

The method for constructing this water-stop wall 2 is also arbitrary, and well-known and conventional construction methods such as underground continuous wall construction, fill cement wall construction, cast-in-place wall construction, and sheet pile construction can be suitably used.

After the construction of the water stop wall 2 is completed, the sand layer S surrounded by the water stop wall 2 is excavated from the ground surface to a depth where a drainage layer is to be formed. Next, while backfilling this excavated part with gravel etc., the underground part of structure 1 is constructed one by one.
Finally, a drainage layer is formed to cover the bottom and side surfaces of the underground portion of the structure 1.

Therefore, if seismic force or the like acts on the foundation structure of a structure with such a configuration and the sand layer S is likely to liquefy, the water cutoff wall 2 will prevent the deformation of the sand in the area surrounded by it. By restraining, liquefaction of the sand layer S directly under the structure 1 becomes difficult to occur. Furthermore, since the lower end of the water-stopping wall 2 reaches the impermeable layer C, the sand layer S outside the water-stopping wall 2 does not have an adverse effect on the structure 1. Furthermore, if structure 1
Even if liquefaction occurs in the sand layer S immediately below, the pore water in the sand layer S will be drained to the drainage layer, and the excess water pressure will be immediately dissipated by this drainage layer, causing collapse of the structure l. Such harmful lifting does not occur. Rather, the slight uplift has the effect of reducing the excess water pressure in the sand layer S, so it is not harmful to the structure 1.

Therefore, in this embodiment, the water stop wall 2 surrounding the structure 1 suppresses the liquefaction of the sand layer S directly below the structure 1, and the bottom and side surfaces of the underground part of the structure 1 are protected from gravel, etc. Since it is covered with a drainage layer, if structure 1
Even if liquefaction occurs in the sand layer S immediately below, the existence of a drainage layer that spreads over a wide area allows the excess water pressure in the sand layer S to be quickly dissipated, resulting in more reliable drainage compared to the conventional gravel drain method. An effective drainage layer can be constructed. Further, unlike the conventional groundwater lowering method described above, permanent facilities such as a drainage pump are not required, and equipment costs, maintenance costs, etc. are almost unnecessary. Furthermore, in order to construct the underground part of the structure 1, the water-stop wall 2 is required in any case for excavating the underground part, so this is suitable because it can be used to prevent liquefaction of the sand layer S. be. Moreover, the water-stopping wall 2 only has to function to block the temporary increase in water pressure in the sand layer S surrounded by it during an earthquake, and there is no need to expect a complete water-stopping effect, which simplifies its construction. It is also possible to convert

Next, FIG. 2 is a diagram showing the basic structure of a structure that is a second embodiment of the present invention. In addition, in the following explanation,
Components that are the same as those in the first embodiment are given the same reference numerals, and their explanations will be omitted.

The difference between the basic structure of the structure of this embodiment and the first embodiment is that the lower end of the water-stopping wall 2 does not reach the impermeable layer C. Instead, the lower layer of the sand layer S in the portion surrounded by the water-stop wall 2 is ground-improved by a chemical injection method to form an impermeable layer C'. Furthermore, in this embodiment, perforated vibrators 3, .

The method of constructing the basic structure of a structure with such a configuration is
The construction method is the same as that in the first embodiment. however,
After constructing the water stop wall 2, it is necessary to dig the sand layer S surrounded by the water stop wall 2 to the depth of the drainage layer, and then inject a chemical solution into the sand layer S to improve the ground. This chemical injection can be carried out using the equipment used in the well-known and commonly used chemical injection method. be done.

Therefore, when seismic force or the like acts on the foundation structure of a structure with such a configuration, and the sand layer S is likely to liquefy, the water cutoff wall 2 is used to prevent this, as in the first embodiment. By restraining the deformation of the sand in the area surrounded by the structure 1, liquefaction of the sand layer S directly under the structure 1 becomes less likely to occur. In addition, since the sand layer S directly under the structure 1 has been improved to become an impermeable layer C', the sand layer S below the impermeable layer C' is
has no adverse effect on Furthermore, even if liquefaction occurs in the sand layer S directly below the structure 1, the pore water in the sand layer S will be drained to the drainage layer, and the excess water pressure will be immediately dissipated by the drainage layer D. There will be no harmful uplift that could cause the collapse of the building.

Therefore, this embodiment can also provide the same effects as those of the first embodiment.

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. - As an example, each of the above embodiments was applied to the foundation structure of the structure 1, but it is also suitably applicable to civil engineering structures such as bridge piers and bank protection.

"Effects of the Invention" As explained in detail above, according to the present invention, the water-stop wall surrounding the structure can suppress the liquefaction of the sand layer directly under the structure, and the bottom and side surfaces of the underground part of the structure can be prevented from liquefying. is covered with a drainage layer made of gravel, etc., so even if liquefaction of the sand layer occurs directly beneath the structure, the presence of the drainage layer that spreads over a wide area will quickly dissipate excess water pressure in the sand layer, ensuring It is possible to construct a drainage layer that has a good drainage effect. In addition, there is no need for permanent facilities such as drainage pumps,
Equipment costs, maintenance costs, etc. are almost unnecessary. Furthermore, in order to construct an underground part of a structure, a water-stop wall is required for excavating the underground part, so this is suitable because it can be used to prevent liquefaction of the sand layer. In addition, the water-stop wall only has to function to block the temporary increase in water pressure during an earthquake in the sand layer that surrounds it. It is also possible to do so.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the basic structure of a structure according to a first embodiment of the invention, and FIG. 2 is a cross-sectional view showing the basic structure of a structure according to a second embodiment of the invention. c, c'... Impermeable layer, D... Drainage layer, S... Sand layer, 1... Structure, 2...
・Water stop wall.

Claims (2)

[Claims] (1) A foundation structure for a structure that is at least partially buried in a sand layer on an impermeable layer, and a water-stop wall is provided in the sand layer to surround the area where the structure is to be constructed. ,
The lower end of this water cutoff wall extends to the impermeable layer, and a drainage layer made of gravel or the like is provided above the sand layer surrounded by the water cutoff wall to cover the bottom and side surfaces of the structure. A basic structure of a structure characterized by being provided with. (2) A foundation structure for a structure that is at least partially buried in a sand layer, in which a water-stop wall is provided in the sand layer to surround the area where the structure is to be constructed, and this water-stop wall The lower part of the surrounded sand layer is made into an impermeable layer by injecting a chemical solution, etc., and the upper part thereof is provided with a drainage layer made of gravel or the like so as to cover the bottom and side surfaces of the structure. The basic structure of the structure.