JP3374224B2 - Ground liquefaction prevention method - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for preventing liquefaction of ground.

[0002]

2. Description of the Related Art As is well known, liquefaction of ground is the hydraulic pressure of pore water existing in a saturated state between soil particles when the ground with a high water content is deformed by shock and vibration due to an earthquake. Is a sudden rise and the frictional resistance between soil particles disappears. As a result, the ground behaves like a liquid and loses its proof stress.

In order to prevent such liquefaction, various ground improvement methods have been conventionally practiced. However, all of them are difficult in terms of construction cost and construction period. For example, liquefaction prevention as shown in FIG. Methods are being considered. This is intended to suppress liquefaction by lowering the water content of the ground and eliminating interstitial water between soil particles. The ground 2 immediately below the building 1 reaches the impermeable soil layer 3 Surrounded by wall 4,
By pumping water from the well 5 provided inside it, the groundwater level in the water blocking wall 4 is lowered and the state is maintained.

[0004]

The method shown in FIG. 5 is effective as long as the groundwater level is maintained at a low level, but even if the water blocking wall 4 is provided, groundwater constantly flows from the surrounding area. In order to keep the groundwater level in the water cutoff wall 4 low, it is necessary to continuously and permanently pump up groundwater, which significantly increases the operating costs and maintenance costs. It was unavoidable to break.

The present invention has been made in view of the above circumstances and an object thereof is to provide an effective method capable of preventing liquefaction of the ground.

[0006]

According to the present invention, the ground in the target area for which liquefaction is to be prevented is surrounded by a water stop wall, and groundwater is pumped from there to lower the groundwater level .
Gradually water poured from the surface of the ground in the elephant area
By infiltrating it, it has almost reached the original groundwater level.
By condensing water and enclosing air between soil particles, the ground in the target area is converted into an unsaturated state in which air bubbles are mixed in the interstitial water between the soil particles. In this case, it is preferable to observe the degree of unsaturation of the ground that has been converted to an unsaturated state, and based on the result, pump up groundwater and inject water from the ground surface to maintain the degree of unsaturation.

[0007]

As described above, the liquefaction of the ground is due to the sudden increase in the water pressure of the pore water existing in a saturated state between soil particles during an earthquake. In the state in which the air bubbles are present, that is, in the unsaturated state, the presence of the bubbles alleviates the rapid increase in the pore water pressure and makes it difficult for liquefaction to occur. Therefore, in order to convert the ground in a saturated state into an unsaturated state, the present invention lowers the groundwater level and once eliminates the interstitial water between soil particles, and then reinjects water from the surface of the soil to condense water to form bubbles. The interstitial water mixed with is filled between the soil particles.

In this case, by performing the condensate upward from the lower part of the ground (that is, gradually raising the water level), the air between the soil particles is discharged upward without resistance as the water level rises. As a result, air is unlikely to remain in the pore water, and therefore the unsaturated state cannot be effectively achieved. On the other hand, as in the present invention, by pouring water from the surface of the ground to condense it downward from the upper part of the ground (that is, gradually lowering the so-called “wetting front”), air between soil particles is discharged. It becomes difficult to be treated, and it is confined between the soil particles as it is and mixed in the pore water, so that the unsaturated state is effectively realized.

Further, in the present invention, by maintaining the water level after the condensate equal to the initial groundwater level, the water pressure of the ground in the target area and the groundwater pressure of the ground around it are balanced, and therefore the ground in the target area is balanced. There is no constant inflow of groundwater from the surroundings, as in the case of maintaining the groundwater level at a level sufficiently lower than the surroundings. Therefore, according to the present invention, the unsaturated state of the ground in the target area is naturally maintained for a long period of time, and it is not necessary to continuously continuously pump water.

[0010]

Embodiments of the method of the present invention will be described below with reference to the drawings. 1 to 3 show an embodiment in which the method of the present invention is applied to a building 1 (see FIG. 3) when the ground 2 immediately below the building 1 is used as a target area.

First, as shown in FIG. 1, the ground 2 in the target area for which liquefaction is to be prevented is surrounded by a water blocking wall 4 which reaches the impermeable soil layer 3, and a little above the impermeable soil layer 3 inside thereof. A well 5 reaching up to is provided. Then, the groundwater is pumped up by the well 5 to lower the groundwater level. In addition, in the ground where the impermeable soil layer 3 does not exist, it is advisable to artificially form the impermeable soil layer beforehand by ground improvement or the like.

Next, as shown in FIG. 2, a water permeable layer 7 is formed by laying, for example, a crushed stone layer or a water permeable mat on the excavated surface inside the water blocking wall 4, and the water permeable layer 7 is formed from the water injection pipe 8. Water is injected from the surface of the ground 2 through As a result, the injected water gradually permeates into the ground 2. In other words, the so-called "wetting front" will gradually decline. At this time, the pumping by the well 5 may be stopped, but if necessary, the pumping may be continued as it is. However, care should be taken not to directly pour water into the deep part of the ground 2 through the well 5.

"Wet front" at the lowered groundwater level
When the time reaches, the water injection is stopped and the pumping by the well 5 is also stopped. As a result, the ground 2 is reconstituted to almost the original groundwater level, that is, the groundwater level outside the water blocking wall 4. Therefore, the building 1 is constructed on the ground 2. In addition, the water injection from the water injection pipe 8 to the ground 2 through the permeable layer 7
It may be after the construction of the building 1.

According to the above method, the ground 2 inside the water blocking wall 4 is converted from a saturated state to an unsaturated state and becomes difficult to liquefy, and the building 1 can be reliably supported even during an earthquake. Become. That is, according to the above method, the ground 2
By lowering the groundwater level, the interstitial water that existed in a saturated state between the soil particles is once removed, and then by pouring water from the ground surface again to condense it, the interstitial water that contains air bubbles is generated between the soil particles. The presence of such bubbles alleviates a sudden increase in pore water pressure during an earthquake and effectively prevents liquefaction of the ground 2.

When condensing water is performed from the bottom of the ground 2 upward (that is, the water level is gradually raised),
As the water level rises, the air between the soil particles is discharged upward without resistance, so it is difficult for air to remain in the pore water,
Therefore, the unsaturated state cannot be effectively achieved. On the other hand, by pouring water from the ground surface and gradually lowering the "wetting front" as described above, the air between the soil particles is confined as it is and is mixed in the pore water. , The unsaturated state is effectively realized.

Further, if the water level after the condensate is largely changed from the original groundwater level, a large groundwater pressure difference occurs between the ground 2 in the target area and the ground around it, so that the water blocking wall 4 should be provided. Even if it is, groundwater constantly flows in from the surroundings (when the water level of the ground 2 in the target area is made sufficiently lower than the groundwater level of the surrounding ground) or outflow (the ground 2 in the target area).
However, it is inevitable that the water level of the ground will be higher than the groundwater level of the surrounding ground. However, by making the water level after condensing equal to the initial groundwater level as described above, And the groundwater pressure of the ground around it are balanced, so that the inflow or outflow of groundwater due to the water pressure difference between the ground 2 and the ground around it does not occur. Therefore, in the method of the present embodiment, the unsaturated state of the ground 2 is naturally maintained for a long period of time, and
Unlike the method shown in FIG. 5, there is no need to continuously pump the groundwater at all, which is a significant advantage in terms of operating costs.

As described above, according to the above method, the unsaturated state of the ground 2 in the target area can be naturally maintained for a long period of time, but if necessary, as in the other embodiment shown in FIG. Even if the degree of unsaturation of the ground 2 that has been converted to an unsaturated state is observed, and groundwater is pumped from the ground 2 and water is injected from the surface based on the results, the degree of unsaturation can be positively maintained. good.

That is, as shown in FIG. 4, a measurement hole 9 is provided in the ground 2, and the degree of unsaturation of the ground 2 is appropriately measured by the control device 10 through the measurement hole 9 to exceed the allowable limit. When it deteriorates (that is, when the unsaturated state returns to the saturated state, or is returning to the saturated state, etc.), the control device 10 operates the water pump in the well 5 to lower the groundwater level and then water injection. It is made to go and condense, and the ground 2 is made into an unsaturated state again by it. By doing so, even when the degree of unsaturation of the ground 2 deteriorates for some reason, it can be automatically and quickly reconverted to an unsaturated state, and reliability as a liquefaction prevention measure can be improved. Can be further improved.

[0019]

As described above, according to the present invention, after the groundwater level of the ground in the target area is lowered , the ground is applied to the entire ground.
To gradually infiltrate the water injected from the surface
Rehydrated to almost the original groundwater level and
Air is trapped between the particles to keep the ground in the target area between the soil particles.
Since it is designed to convert into the unsaturated state in which air bubbles are mixed in the pore water, the ground in the target area can be easily converted to the unsaturated state and the unsaturated state can be maintained for a long time by itself. Therefore, liquefaction can be effectively prevented. Moreover, if the degree of unsaturation of the ground that has been converted to an unsaturated state is observed and then groundwater is pumped up and water is injected from the surface based on the results, the degree of unsaturation of the ground will deteriorate for some reason. Even in such a case, the unsaturated state can be automatically and rapidly reconverted, and the reliability as a liquefaction prevention measure can be further improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a state in which the groundwater level of the ground in a target region is lowered in the liquefaction prevention method which is an embodiment of the present invention.

FIG. 2 is a diagram showing a state where water is poured from the ground surface onto the ground in the target area in the same method.

FIG. 3 is a diagram showing a state in which the ground in the target region is condensed and maintained in an unsaturated state in the same method.

FIG. 4 is a diagram showing a liquefaction prevention method which is another embodiment of the present invention.

FIG. 5 is a diagram showing an example of a liquefaction prevention method that has been conventionally studied.

[Explanation of symbols]

2 ground (ground of target area) 3 impermeable soil layers 4 water stop wall 5 wells 7 permeable layer 8 water injection pipes 9 measuring holes 10 Control device.

Front page continuation (72) Inventor Shinya Nishio 1-3-2 Shibaura, Minato-ku, Tokyo Within Shimizu Construction Co., Ltd. (56) Reference JP-A 61-60919 (JP, A) JP-A-3-43515 (JP, A) JP-A-3-5514 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) E02D 3/10 102 E02D 3/00 101

Claims (2)

(57) [Claims] 1. The ground in the target area where liquefaction is to be prevented is surrounded by a water stop wall, and groundwater is pumped from there to lower the groundwater level, and then the ground in the target area is entirely covered.
By gradually infiltrating water injected from the surface of the
And condensate to almost the original groundwater level and soil particles.
A method for preventing liquefaction of ground, comprising enclosing air between the ground and converting the ground in the target area into an unsaturated state in which air bubbles are mixed in pore water between soil particles. 2. The method according to claim 1, wherein the degree of unsaturation of the ground that has been converted into an unsaturated state is observed, and based on the result, groundwater is pumped and water is injected from the surface to determine the degree of unsaturation. A method for preventing liquefaction of ground, which is characterized by maintaining it.