JP2813835B2 - Earthquake countermeasure construction method of underground structure installed in liquefied ground under pavement - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial application field) The present invention relates to an earthquake countermeasure method (gravel drain) for an underground structure installed in the ground which is easily liquefied during an earthquake, and is used under pavement or the like. The present invention relates to a construction method for preventing floating of an underground structure even when a drainage path cannot be secured outside the ground.

(Prior Art) In a saturated loose sandy ground, excessive pore water pressure in the ground increases due to earthquake motion, and liquefaction of the sandy ground may occur. This is because the sandy ground becomes liquid-like, and its specific gravity is much larger than that of water. In addition, underground structures such as manholes with hollow interiors may have an apparent specific gravity smaller than that of the sandy ground exhibiting the liquefaction phenomenon, which is considered to be caused by the liquefaction phenomenon at the time of the earthquake. Damage to underground structures has often occurred in past earthquakes.

Countermeasures against such problems include soil replacement, soil compaction, and groundwater level lowering methods.However, vibration does not occur during construction. There is a gravel drain construction method (first prior art) which has an advantage that it does not adversely affect the ground.

In this method, there is a common ditch that is used jointly by lifeline companies as a kind of underground structure, and the guidebook for the common ditch design (edited by the Japan Road Association, published by the first edition published in March 1986) 8, An example of this gravel drain method is shown in a cross-sectional view (see Fig. 2).

In this construction method, a gravel drain 1 is applied around the common ditch (up, down, left and right) with crushed stone 6, and a drainage path is installed with the crushed stone 6 up to a median strip 2 just above the road. As a result, groundwater is collected at the gravel drain around the common ditch and discharged onto the median strip 2, thereby quickly dissipating excess pore water pressure of the ground liquefied by the earthquake and acting on the bottom of the common ditch. It is to reduce the lift.

As a second conventional technique, there is a "method of protecting underground structures in sandy ground which is liable to liquefy" disclosed in Japanese Patent Application Laid-Open No. 1-239217. According to this technique, as shown in FIG. 3, a gravel layer 4 also serving as a paving stone is formed in a horizontal direction below a bottom plate of an underground structure 3 constructed in a sandy ground which is easily liquefied. One or a plurality of water distribution pipes 5 extending directly above the underground structure are installed, and excess pore water generated in the sandy ground is collected by a gravel layer, and then collected from the water distribution pipes 5 on the ground or in the ground. This method drains water into the middle structure.

(Problems to be Solved by the Invention) However, the first conventional technique can be applied only to a point such as below a median strip where crushed stone is exposed on the ground surface where a drainage path to the ground surface can be secured. . Even in the conventional gravel drain method where the gravel layer is buried in the ground, a drainage route is secured on the ground surface, and no consideration is given to the case where the ground surface cannot be used as a drainage route due to some restrictions on the ground surface.

Further, in the second prior art, one or a plurality of water distribution pipes extending right above through the underground structure are installed, so that the working space in the underground structure cannot be reduced, and the underground structure cannot be avoided. Disturbing the installation of goods in the structure, accidentally breaking the water distribution pipe while working in the underground structure, or causing psychological pressure due to the presence of the water distribution pipe There are even. In addition, in order to make the working space in the underground structure as large as possible, the number and diameter of water distribution pipes must be limited. Further, since a penetration hole for passing a water distribution pipe is formed at the bottom of the underground structure, if the construction is poor, water infiltrates into the underground structure from the penetration hole below the groundwater level.

The present invention has been proposed to remedy the above drawbacks, and its purpose is to provide a gravel drain drainage path that is easy to work without being influenced by external factors in order to protect underground structures from earthquakes. To provide.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a gravel drain on an underground structure whose upper part is opened like an entrance of a manhole, and a normal gravel drain is provided on the underground structure. A penetration hole is provided above the groundwater level, and one or more drainage pipes are arranged along the outer surface of the side wall of the underground structure and the upper floor slab, and the upper part of the drainage pipe is connected to the penetration hole. An object of the present invention is to provide a method for constructing an underground structure provided in a liquefied ground under a pavement for earthquake countermeasures.

(Action) In the present invention, in addition to the point of performing the gravel drain around the conventional underground structure, the crushed stone layer under the underground structure bottom plate extends along the outer wall surface 7a and the upper floor plate surface 7b of the underground structure. One or more drainage pipes are installed, a penetration hole is made to pass the drainage pipe through the underground structure at or above the normal groundwater level, and a drainage path leading into the underground structure is provided. As a result, even when a drainage path cannot be secured on the ground surface due to pavement or the like, the head inside the drainage pipe rises due to the rise in excess pore water pressure, and groundwater is quickly drained from the penetration hole into the underground structure. As a result, the excess pore water pressure generated in the liquefied ground is reduced, and the underground structure does not float.

In other words, in order to reduce the excess pore water pressure in the ground liquefied by the earthquake and prevent the underground structures from floating, the groundwater is collected by the gravel drain of the above-mentioned earthquake countermeasure method, It has the function of discharging the water into the underground structure through the penetration hole through the drainage pipe.

(Example) Next, an example of the present invention will be described. It should be noted that the embodiments are merely examples, and it is needless to say that various changes or improvements can be made without departing from the spirit of the present invention.

FIG. 1 shows an embodiment of a method for implementing an earthquake countermeasure construction method for an underground structure in a liquefiable ground under a pavement according to the present invention.

In the figure, 6 is a crushed stone layer, 7 is an underground structure, 8 is a drain pipe, 9 is a penetration hole, 10 is a pavement, 11 is a drain hole, and 12 is sand.

The underground structure 7 shown in the figure is located at a predetermined depth of the ground that is easily liquefied, has a hollow inside like a manhole, and is formed of reinforced concrete. Before the construction of the underground structure, the construction method of the earthquake countermeasures method is to install a filter layer on the side wall and bottom surface of the excavation pit to prevent sand from flowing into the crushed stone layer, 6 is formed. After constructing the underground structure 7 on the basis of the crushed stone layer, the surroundings of the underground structure are backfilled with crushed stone to form a drainage layer of crushed stone that is more permeable than sandy ground that is easily liquefied. These crushed stone layers can serve both as a paving stone work and a backfilling work performed during normal construction. During or after the construction of the underground structure, one or more drainage pipes 8 are installed from the crushed stone layer under the underground structure bottom plate along the side wall surface 7a and the upper floor plate surface 7b of the underground structure. Above the normal underground water level,
And a drainage path leading into the underground structure is provided. The holes in the underground structure are located so that underground water pressure does not allow underground water to flow into the underground structure.

Now, with the earthquake countermeasure method constructed as described above, even if liquefaction occurs in the ground due to the earthquake and the excess pore water pressure rises, the groundwater is collected into the crushed stone layer by the action of increasing the excess pore water pressure. The drainage pipe is drained into the underground structure, so that the rise in excess pore water pressure around the underground structure is reduced,
The lifting of the underground structure is prevented.

(Effects of the Invention) As described above, according to the method of the present invention for implementing an earthquake countermeasure construction method for an underground structure provided in the ground which is liable to liquefy during an earthquake under a pavement, the excessive When the pore water pressure rises, the groundwater in the surrounding sandy ground is collected in the crushed stone layer formed below the underground structure and around the side wall, and the underground water is drained by the head of excess pore water pressure. By draining into the underground structure from the penetration hole opened in the underground structure through the through hole, the rise of the excess pore water pressure is reduced, and the underground structure is prevented from floating. In addition, when the underground water flows into the underground structure, the apparent specific gravity of the underground structure increases, so that the floating prevention effect further increases.

In addition, since there is no water distribution pipe installed in the underground structure,
There is no decrease in the working space in the underground structure, there is no need to limit the number and diameter of water distribution pipes, and penetration holes can be opened above the normal groundwater level. There are advantages such as that there is no risk of water entering the middle structure.

In addition, this method replaces materials for foundation works and backfill works for underground structures with crushed stone,
Only the process of providing drainage pipes and drilling penetration holes in underground structures is easier and more economical than other methods such as installing drainage pipes under roads. become. In addition, there is an advantage that economical earthquake countermeasures can be performed irrespective of external factors such as a road structure such that a drainage path cannot be secured under a pavement.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of the construction method of the present invention, and FIGS. 2 and 3 show a conventional example. 6: Crushed stone layer 7: Underground structure 8: Drain pipe 9: Penetration hole 10: Pavement 11: Drain hole 12: Sand

Claims (1)

(57) [Claims] An underground structure having an upper portion opened like an entrance of a manhole is provided with a gravel drain, a penetration hole is provided above the underground structure above a normal groundwater level, and the underground structure is provided. One or more drainage pipes are arranged along the outer surface of the side wall of the object and the upper floor slab, and the upper part of the drainage pipe is connected to the penetration hole, provided in the liquefied ground under pavement. Earthquake countermeasures construction method for underground structures.