JP2004204573A - Method of preventing liquefaction of ground - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize an effective method of preventing liquefaction with excellent reliability obtaining sufficient liquefaction preventing effect. <P>SOLUTION: An underground water level is lowered by pumping up underground water from the ground 3 to be prevented from liquefaction, and the ground is put in an unsaturated state by injecting water 6 with a large quantity of dissolved air into the ground to recover the underground water level. The pumped-up underground water is aerated to enhance the quantity of dissolved air, and injected into the ground. Pumping of underground water from the ground and injection of water with the large quantity of dissolved air into the ground are performed at the same time. Injection of water with the large quantity of dissolved air into the ground is performed by infiltrating the water into the ground from a ground surface part. While measuring the degree of saturation of the ground, pumping of underground and injection of water with the large quantity of dissolved air are repeated until the degree of saturation reaches a prescribed set value. While monitoring the degree of saturation of the ground, pumping of the underground water and injection of water with the large quantity of dissolved air are performed based on the result to maintain the degree of saturation to the set value. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for preventing liquefaction of the ground.
[0002]
[Prior art]
As is well known, liquefaction of the ground means that the water pressure of the pore water, which exists in a saturated state between the soil particles, suddenly increases as the ground with a high moisture content is deformed by the impact and vibration caused by the earthquake. As a result, the frictional resistance between soil particles disappears, and the ground behaves like a liquid and loses its proof stress.
[0003]
In order to prevent such liquefaction, techniques such as increasing the ground strength or injecting fine particles into the ground are known, but recently, a liquefaction prevention method by pumping groundwater is also effective. It is believed that. As shown in FIG. 4, this involves surrounding a ground 3 to be prevented from liquefaction by a water blocking wall 2 provided so as to reach an impermeable layer 1 and providing a pumping well 4 inside the ground 3 from which groundwater is to be prevented. By continuously pumping groundwater to keep the groundwater level low, pore water in soil particles, which is the root cause of liquefaction, is eliminated from the ground.
[0004]
Although the above liquid prevention method by groundwater pumping is considered to be sufficiently effective, groundwater must be continuously and permanently pumped to keep the groundwater level low. However, the operation and maintenance costs required for this are enormous, and there is a concern that consolidation settlement may occur due to a drop in the groundwater level, and this is considered unrealistic at present.
[0005]
Therefore, instead of continuously pumping groundwater and keeping the groundwater level constantly low, as shown in FIG. 5, the groundwater level is temporarily lowered and the ground saturation (the volume of groundwater in the ground / the volume of the ground gap) is reduced. ), Thereby increasing the ground strength against liquefaction. According to such a method, the liquefaction prevention effect is maintained for a long time even after the groundwater level is restored. It is said that it can be obtained.
[0006]
For example, in Patent Document 1, after temporarily lowering the groundwater level, the "wet front" is gradually lowered by injecting water from the ground surface to recover the groundwater level, thereby enclosing bubbles between soil particles. There is disclosed a method of converting the ground from a saturated state to an unsaturated state to increase the strength against liquefaction.
[0007]
Also, in Patent Document 2, similarly, after temporarily lowering the groundwater level to lower the saturation, the natural rise of the saturation accompanying the natural rise of the groundwater level is monitored, and the saturation is set to a predetermined value. A method is disclosed in which re-pumping is performed intermittently so as to maintain the value.
[0008]
[Patent Document 1]
JP-A-8-3975 [Patent Document 2]
Japanese Patent Application Laid-Open No. 2002-256540
[Problems to be solved by the invention]
However, the methods disclosed in Patent Document 1 and Patent Document 2 may not be able to sufficiently reduce the degree of saturation depending on ground conditions or other conditions, or may not be able to expect a sufficient liquefaction prevention effect. The fact is that the development of an effective liquefaction prevention method with excellent reliability is being sought.
[0010]
[Means for Solving the Problems]
In view of the above circumstances, the invention of claim 1 lowers the groundwater level by pumping groundwater from the ground where liquefaction is to be prevented, and restores the groundwater level by pouring water with a large amount of dissolved air into the ground. This makes the ground into an unsaturated state.
[0011]
According to a second aspect of the present invention, in the method for preventing liquefaction of the ground according to the first aspect of the present invention, the groundwater pumped up is exploded to increase the amount of dissolved air thereinto and injected into the ground.
[0012]
According to a third aspect of the present invention, in the method for preventing liquefaction of the ground according to the first or second aspect, pumping of groundwater from the ground and injection of water having a large amount of dissolved air into the ground are simultaneously performed. .
[0013]
According to a fourth aspect of the present invention, in the method for preventing liquefaction of the ground according to the first, second, or third aspect of the present invention, water having a large amount of dissolved air is injected into the ground from the surface to penetrate into the ground. Features.
[0014]
According to a fifth aspect of the present invention, in the method for preventing liquefaction of the ground according to the first, second, third or fourth aspect, pumping and dissolving groundwater until the saturation reaches a predetermined set value while measuring the saturation of the ground. It is characterized by repeatedly injecting water with a large amount of air.
[0015]
According to a sixth aspect of the present invention, there is provided the ground liquefaction prevention method according to the first, second, third, fourth or fifth aspect of the invention, wherein the groundwater pumping and the dissolved air amount are monitored based on the result while monitoring the ground saturation. It is characterized in that the saturation level is maintained at a set value by injecting a large amount of water.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
One embodiment of the present invention will be described with reference to FIG. In the present embodiment, a well 5 for pumping and water injection is provided inside the water blocking wall 2, and groundwater is pumped from the well 5 to temporarily lower the groundwater level in the ground 3. As described above, water is injected from the surface of the ground to the ground through the well 5 to restore the groundwater level. Here, water 6 having a larger amount of dissolved air than usual is used as the water to be injected.
[0017]
After the groundwater is pumped and the groundwater level is temporarily lowered as described above, the groundwater is replaced with water having a large amount of dissolved air by injecting water 6 having a large amount of dissolved air to restore the groundwater level. This converts the saturated ground to an unsaturated state, thereby increasing the strength of the ground 3 against liquefaction and preventing liquefaction for a long period of time.
[0018]
In particular, according to the above-described method, the groundwater level is restored by injecting water 6 having a large amount of dissolved air instead of simple water. As compared with the case where the groundwater level rises naturally as shown in, the air can be positively and surely sent into the soil particles, and the saturation can be sufficiently and surely reduced. The reliability can be improved in comparison.
[0019]
As for the water 6 with a large amount of dissolved air to be injected into the ground, the groundwater pumped to lower the groundwater level is temporarily stored, and explosive (aeration) is performed on the water to reduce the amount of the dissolved air. It is possible to obtain easily and inexpensively by increasing, and it is reasonable to increase the amount of dissolved air and circulate the pumped groundwater. In such a case, only a water tank and a blower for the explosion may be used as equipment for the explosion, or the pumped groundwater may be supplied to the well 5, exploded in the well 5, and then injected into the ground 3. In any case, no significant equipment and operating costs are required.
[0020]
FIG. 2 shows another embodiment of the present invention. The pumping well 4 and the injection well 7 are provided independently, and groundwater is pumped from the pumping well 4 and, at the same time, water 6 with a large amount of dissolved air is injected into the ground 3 from the injection well 7. According to this, it is possible to more quickly perform an operation of replacing groundwater with water 6 having a large amount of dissolved air to convert the ground into an unsaturated state.
[0021]
FIG. 3 shows still another embodiment of the present invention. This is similar to the above-described embodiment in that the groundwater level is lowered by pumping water from the pumping well 4, but water from the water 6 having a large amount of dissolved air is injected into the ground through the water injection pipe 8 laid on the surface. This is done by letting them go. According to this, similarly to the method shown in Patent Document 1, the “wetting front” gradually decreases, so that the air in the soil particles in addition to the air contained in the water 6 itself having a large amount of dissolved air in large amounts. Can be contained as soil bubbles in the soil particles without falling out, so that the degree of saturation of the ground 3 can be further reduced.
[0022]
The embodiments of the present invention have been described above. However, it goes without saying that the present invention is not limited to the above embodiments, and appropriate modifications and applications can be made according to the ground conditions and other various conditions.
[0023]
For example, when the ground 3 cannot be sufficiently converted into an unsaturated state only by once pumping and water injection according to the method of each of the above embodiments, while measuring the saturation of the ground 3, the pumping is performed until the desired saturation is obtained. Water injection may be repeated.
[0024]
Further, after the ground is brought into an unsaturated state by the method of each of the above embodiments, the saturation of the ground 3 is monitored, and when the saturation deteriorates, pumping and water injection are performed again to maintain the saturation at the set value. Good.
[0025]
In each of the above embodiments, the water blocking wall 2 is provided so as to surround the ground 3 to be prevented from being liquefied, and the inside thereof is replaced with the water 6 having a large amount of dissolved air. It is not necessary to provide the water stop wall 2 depending on the condition of the ground 3 or in a case where liquefaction prevention is performed over a wide range.
[0026]
【The invention's effect】
According to the invention of claim 1, groundwater is pumped from the ground where liquefaction is to be prevented to lower the groundwater level, and water with a large amount of dissolved air is injected into the ground to restore the groundwater level. Since it is in a saturated state, it is possible to reliably increase the strength of the ground against liquefaction and prevent the liquefaction for a long time.
[0027]
According to the second aspect of the present invention, since the groundwater that has been pumped up is exploded to increase the amount of dissolved air and injected into the ground, water having a large amount of dissolved air to be injected into the ground can be obtained easily and inexpensively. Recycling groundwater is reasonable.
[0028]
According to the invention of claim 3, since groundwater is pumped from the ground and water with a large amount of dissolved air is simultaneously injected into the ground, groundwater is replaced with water with a large amount of dissolved air to convert the ground into an unsaturated state. Work can be performed quickly.
[0029]
According to the invention of claim 4, water is injected into the ground with a large amount of dissolved air by infiltrating the ground from the surface portion, so that air in the soil particles in addition to air contained in a large amount in the water to be injected is removed. Without getting out to the atmosphere, it is contained as bubbles in the soil particles, and the degree of saturation can be further reduced.
[0030]
According to the fifth aspect of the present invention, while measuring the ground saturation, the pumping of groundwater and the injection of water with a large amount of dissolved air are repeatedly performed until the saturation reaches a predetermined set value, so that the saturation is reliably reduced. be able to.
[0031]
According to the invention of claim 6, since the saturation is maintained at a set value by pumping groundwater and injecting water having a large amount of dissolved air based on the result while monitoring the saturation of the ground, the saturation is deteriorated. In such a case, the unsaturated state can be quickly returned to, and the reliability as a countermeasure against liquefaction can be further improved.
[Brief description of the drawings]
FIG. 1 is an explanatory view showing one embodiment of a liquefaction prevention method of the present invention.
FIG. 2 is an explanatory diagram showing another embodiment of the present invention.
FIG. 3 is an explanatory view showing still another embodiment of the present invention.
FIG. 4 is an explanatory view showing an example of a conventional liquefaction prevention method.
FIG. 5 is an explanatory view showing another example of the conventional liquefaction prevention method.
[Explanation of symbols]
1 impermeable layer 2 water stop wall 3 ground (ground to prevent liquefaction)
4 Pumping well 5 Well 6 Water (water with a large amount of dissolved air)
7 Water well 8 Water pipe

Claims (6)

Pumping groundwater from the ground to prevent liquefaction to lower the groundwater level and pouring water with a large amount of dissolved air into the ground to restore the groundwater level makes the ground unsaturated. The method of preventing liquefaction of the ground. 2. The method for preventing liquefaction of ground according to claim 1, wherein the groundwater that has been pumped up is detonated to increase the amount of dissolved air and injected into the ground. The method for preventing liquefaction of ground according to claim 1 or 2, wherein pumping of groundwater from the ground and injection of water having a large amount of dissolved air into the ground are performed simultaneously. 4. The method for preventing liquefaction of ground according to claim 1, 2, or 3, wherein the water having a large amount of dissolved air is injected into the ground from the surface portion of the ground. The groundwater pumping and the injection of water with a large amount of dissolved air are repeatedly performed until the saturation reaches a predetermined set value while measuring the saturation of the ground. Ground liquefaction prevention method. The method according to claim 1, wherein while monitoring the degree of saturation of the ground, pumping of groundwater and injecting water having a large amount of dissolved air are performed based on the result to maintain the degree of saturation at a set value. The method for preventing liquefaction of the ground according to 4 or 5.

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