JPH01239217A - Method for protecting underground structure in sand base liable to be liquefied - Google Patents

Abstract

PURPOSE:To discharge water in gaps so as to prevent liquefaction by constructing an underground structure on a gravel layer of a specified thickness in constructing it in a sand base liable to be liquefied, and communicating the layer and the ground surface with a drain pipe. CONSTITUTION:A gravel layer 16 is formed in a specified thickness in a sand base 12 liable to be liquefied. Next, a bottom plate 14 of an underground structure 10 is constructed on the layer 16, and further side walls and upper plate 20 are provided on the bottom plate to construct the structure 10. At least one drain pipe 22a is vertically installed at a catch-basin 26 on or under the ground. As a result, even if water pressure of gaps increase due to earthquake force applied to the base 12, the water of the gaps are speedily discharged through drain pipes 22a-22c, thereby it is possible to prevent the water pressure of the gaps from rising and the underground structure from floating up.

Description

Detailed Description of the Invention (Industrial Application Field) This invention relates to a method for protecting underground structures in sandy ground that is prone to liquefaction, and in particular, when an underground structure rises, it prevents sand from forming beneath the structure. Concerning construction methods to prevent the outflow of water.

(Prior art) Underground structures with hollow interiors, such as underground tunnels, have a small apparent specific gravity. Therefore, when such underground structures are constructed in sandy ground, excess energy generated in the ground during an earthquake can be avoided. In past earthquakes, sandy ground liquefies due to increased pore water pressure, causing these underground structures to float up.

Countermeasures against such problems include ground improvement, gravel drains, and groundwater level lowering methods, but these are not often adopted due to site constraints and long-term maintenance issues.

Therefore, it is conceivable to apply, for example, a liquefaction prevention structure as disclosed in Japanese Patent Application Laid-Open No. 58-127823 to this type of underground structure.

However, there are problems in applying the structure disclosed in this publication to the protection of underground structures as described below.

(Problems to be Solved by the Invention) In other words, in the liquefaction prevention structure of the above-mentioned publication, gravel is placed around the outer periphery of the permeable concrete columns in the foundation ground that supports the structural remains.
A predetermined number of drain columns with permeable walls made of fine stone, slag, or other materials are installed to prevent excessive pore water pressure from rising. There was a problem in that pouring was not only difficult but also expensive.

Furthermore, in a structure in which a drain column is provided below an underground structure, there is a problem in that when the ground liquefies, the pressure of water rising in the drain column causes the underground structure to float up.

This invention was made in view of these conventional problems, and its purpose is to provide an easy-to-implement and economical construction method for sandy ground that is prone to liquefaction, which can prevent underground structures from floating up. The objective is to provide a protection method for underground structures.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a method for installing gravel that also serves as paving stones in the horizontal direction below the bottom slab of an underground structure constructed in sandy ground that is prone to liquefaction. At the same time as forming a layer, one or more drainage pipes were installed extending directly above the gravel layer through the underground structure, and excess pore water generated in the sandy ground was collected by the gravel layer. After that, the water is drained from the drain pipe onto the ground or into an underground structure.

(Function) According to the protection method with the above configuration, when seismic force acts on the sandy ground and it liquefies and the pore water pressure increases, the excess pore water is collected in the gravel layer and then inside the underground structure. Since water is quickly drained above ground or into the underground structure from the drainage pipe extending directly above the structure, floating of the structure due to an increase in pore water pressure in the ground surrounding the structure is effectively prevented.

(Embodiments) Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows an embodiment of the method for protecting underground structures in sandy ground that is prone to liquefaction according to the present invention.

The underground structure 10 shown in the figure is built on sandy ground 1 that is easily liquefied.
It is located at a predetermined depth within 2, and is made of concrete and has a hollow shape similar to an underground tunnel.

In the construction of the protection method, before constructing the underground structure 10, a gravel layer 16 having a predetermined thickness is formed below the bottom slab 14 of the structure 10.

The gravel layer 16 uses gravel having a predetermined size, and is spread in a size corresponding to the area of the bottom slab 14 to be constructed.

This gravel layer 16 can also serve as paving stone work carried out during normal construction.

Once the gravel layer 16 is formed in this way, the bottom slab 14 is constructed above it, and the side walls 18 and the top slab 20 are constructed on the bottom slab 14, so that the underground structure 10 is constructed.

Then, during or after construction of the structure 10, the gravel layer 1
One or more drain pipes 22a extending directly above from 6
-c is installed.

In this embodiment, three hollow vibe-shaped drain pipes 22a-
A drainage pipe 22a on the left side in the figure has one end located in the gravel layer 16 and the other end extending to the ground.

The drain pipe 22b installed in the center has one end in the gravel layer 16, and the other end opens into a manhole 24 extending from the upper plate 18 of the underground structure 10 to the ground.

For example, if the height of this opening is set higher than the groundwater level in steady state, groundwater will not flow in through this opening.

Furthermore, one end of the right drainage pipe 22c is located in the gravel layer 16, and the other end opens into a drainage mass 26 provided on the ground.

Now, in the protection method configured as above, sand ground 1
When seismic force acts on 2 and the pore water pressure increases, excess pore water is collected in the gravel layer 16 and then drained from the drain pipe 22 a = c that extends directly above through the inside of the underground structure 10 to the ground. Alternatively, since the water is quickly drained into the underground structure 10, an increase in pore water pressure and liquefaction around the structure 10 is suppressed, and floating of the structure 10 is effectively prevented.

(Effects of the Invention) As explained above in the embodiments, according to the method for protecting underground structures in sandy ground that is prone to liquefaction according to the present invention, paving stones are installed in the horizontal direction below the bottom slab of the underground structure. In addition to forming a gravel layer that also serves as a gravel layer, one or more drainage pipes are installed that extend directly above the gravel layer through the underground structure, and excess pore water generated in the sandy ground is drained from the gravel layer. After the water is collected, it is drained from the drain pipe onto the ground or into the underground structure, so the increase in uplift pressure caused by the increase in pore water pressure is alleviated and eliminated, and the lifting of the underground structure is prevented. Ru.

Furthermore, when draining water into an underground structure, this increases the apparent specific gravity of the structure, further increasing the floating prevention effect.

Furthermore, the protection method is easy to install, as it simply involves forming a gravel layer that also serves as paving stone beneath the bottom slab of the underground structure, and installing one or more drainage pipes extending directly above this gravel layer. This can be done economically and is economically advantageous.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of the method of the present invention.

Claims (1)

[Claims] A gravel layer that also serves as paving stone is formed horizontally below the bottom slab of an underground structure built in sandy ground that is prone to liquefaction, and extends directly above the gravel layer through the inside of the underground structure. One or more drainage pipes are installed, excess pore water generated in the sandy ground is collected in the gravel layer, and then drained from the drainage pipe onto the ground or into an underground structure. A protection method for underground structures in sandy ground that is prone to liquefaction.