JP2001193048A - Ground and/or water quality improvement method by injection of gaseous dissolution water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide method and management of ground improvement and water purification with regard to pore fluid of the ground, especially, the decompression of the pressure and increase of permeability resistance. SOLUTION: An air-river system dissolving the air with pressure higher than groundwater pressure is basically substituted for the groundwater under the groundwater table.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquefaction-preventing ground improvement method that focuses on pore fluid in the ground, a ground improvement method that focuses on a decrease in pressure of pore water in the ground and an increase in water permeability resistance, and a quality control method thereof. Further, the present invention relates to improvement of water quality environment such as increasing oxygen content in water quality of lakes and marshes.

[0002]

2. Description of the Related Art The main soil improvement methods for preventing liquefaction of sandy ground and the like that occur during an earthquake below groundwater level include a method for tightening and increasing the density of a ground, a method for lowering groundwater, and an excess method for generating an earthquake. There is a drain method that drains pore water pressure, a solidification method, a displacement method, etc.

In addition to the above, there is a construction method in which air is mixed into groundwater (pore water) of the ground to be liquefied or partially replaced with air. For example, JP-A-8-3975 "Method for preventing liquefaction of ground", JP-A-10-102473 "Method for preventing liquefaction of sandy ground", JP-A-10-338939 "Method for preventing liquefaction of ground during earthquake, and this method And an exhaust pipe structure using the same. Japanese Unexamined Patent Publication No. Hei 8-3975 "Soil liquefaction prevention method" discloses a method of lowering the groundwater level by pumping water, temporarily injecting air into the gaps in the ground, and then injecting water from above to mix air bubbles in the gaps to prevent groundwater. This is a method to prevent liquefaction by making it saturated.

The second Japanese Unexamined Patent Publication No. 10-102473, "Method for preventing liquefaction of sandy ground", is a method of injecting air at high pressure into the ground to cause a local fluidized state to improve the ground. The third Japanese Unexamined Patent Publication No. Hei 10-338939, "Method of preventing liquefaction of ground during earthquakes and structure of air supply / exhaust pipe using this method," aims to prevent liquefaction by blowing compressed air into the ground and mixing fine bubbles. It is assumed that.

[0005]

The liquefaction-prevention method that has been most often used in the past is a method of compacting the ground, which involves some deformation of the ground (such as settlement or horizontal movement), and that it is directly under the existing structure. It is in principle difficult to carry out improvement work without hindrance while sharing the improvement.

[0006] A drain construction method for quickly discharging excess pore water pressure generated during an earthquake to prevent liquefaction,
Deformation of the ground during construction can be suppressed, but it is theoretically impossible to improve the ground immediately below the existing structure while sharing the drain installation interval because it cannot be theoretically widened and the need for drainage ditches to be installed. Have difficulty.

On the other hand, a liquefaction-prevention method for suppressing the rise in pore water pressure during an earthquake by mixing air into groundwater (pore water) is a method of pumping groundwater, introducing air, and then pouring water from above. There are problems such as ground deformation due to drainage (subsidence) and necessity of water stoppage work. The method of blowing air into the ground to be improved is straightforward, but it tries to mix air bubbles while extruding pore water, and the injection of air lighter than the pore water involves the installation of impermeable barriers, etc. There are problems such as the necessity of construction and the difficulty of mixing homogeneous air bubbles.

When excavating the ground below the groundwater level in underground construction or the like, drainage work is required, and the magnitude of water pressure is an important design factor among pressures acting on anti-earth pressure structures (such as retaining walls). Becomes Conventionally, in most cases, the water pressure acts as an external force in a hydrostatic pressure distribution from the groundwater level. If the permeability of the ground can be reduced, the scale of drainage facilities can be reduced, and the effect of drainage works on nearby areas can be reduced.If the water pressure can be further reduced, the design of anti-earth pressure structures can be facilitated become.

In the case of land reclamation work at sea or the like, where mountain sand and the like are transported by ship and the bottom is opened at a predetermined place to release land and sand, land is created. Has never been a problem. If enough air bubbles are mixed into the pore water during land development, it will help prevent liquefaction. In order to improve the water quality of lakes and marshes, the method of injecting air has already been put into practical use, but it is not efficient because it disappears immediately on the water surface as bubbles,
The problem is to efficiently dissolve oxygen in water.

[0010]

Means for Solving the Problems Sand having relatively good water permeability,
By mixing fine bubbles in the pore water of the gravel ground,
The solution to the first problem of the present invention is to prevent the generation of excess pore water larger than the hydrostatic pressure generated during an earthquake by compressing and collapsing bubbles to prevent liquefaction. In this case, the homogeneity of the ground to be improved after the improvement, no additional work such as impermeable walls, etc. are required, and the work can be performed outside the scope of the improvement work, so that the work can be performed while sharing the ground. To solve this problem, a drain well is provided on one side outside the construction area, and air-dissolved water is injected from the injection well on the opposite side.

The present invention also prevents liquefaction by releasing air and sediment into water to create land by mixing air bubbles into pore water of the formed ground.
Below that, air-dissolved water or compressed air is released downward from the conduit, sediment is rapidly settled, and it is deposited in water mixed with air bubbles, so that the ground that contains air bubbles in the gaps is denser than the natural sedimentation method. The goal is to solve the problem by creating.

According to the present invention, similarly to the above-mentioned two means, by injecting air-dissolved high-pressure water and generating bubbles by releasing the pressure, the water permeability can be reduced and the pore water pressure can be reduced.

Further, the present invention provides a method in which air-dissolved high-pressure water is ejected from the vicinity of the bottom of a lake or the like to replace air with substantially saturated water, and excess saturated air is discharged as air bubbles. Means. With this method, it is also possible to homogenize the water quality after improvement by stirring by jetting high-pressure water.

It is feared that the amount of air bubbles mixed in the pore water in the ground may partly disappear for a long period of time due to the flow of groundwater and other causes. Therefore, it is necessary to monitor the bubble mixing ratio (saturation degree), and a method of measuring and managing the compression wave (P wave) velocity, the specific resistance, and the like at the original position with high accuracy is required.

[0015]

[Function] As a result of various experiments in the room, the liquefaction strength is surely increased when the saturation is lowered by mixing bubbles in the pore water, and the relationship between the saturation of the ground gap and the compression wave velocity is the saturation. It has been proved that the compression wave velocity decreases as the air pressure decreases (the air content rate increases) (Reference example: 1999 Geotechnical Society Symposium Evaluation of liquefaction resistance of unsaturated sand using P-wave velocity Yellow et al. ). In addition, it has been experimentally proved that the permeability decreases when the degree of saturation decreases due to the incorporation of air into the voids in the ground (air content in the pore water) (Reference example: 1996 Geotechnical Society Symposium Unsaturated sandy material) Enomoto et al.) As described above, the principle has already been proved, but by dissolving gas such as air in water at a pressure higher than the in-situ water pressure and then injecting it, fine bubbles, water quality mixed with air, pore fluid It became possible to change to. As a result, it is possible to solve the above-described problems including an increase in liquefaction strength.

It has already been confirmed that the specific resistance increases as the degree of saturation decreases (reference example: 1996 Geotechnical Society, Analysis of current state of water permeability evaluation in unsaturated ground). By using this principle, it is possible to manage the degree of achievement of the purpose.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A device for generating air-dissolved high-pressure water has already been put to practical use. For example, Nikuni swirl pump material: Using a swirl turbine pump, a mixture of hardly soluble liquids or a mixture of liquid and gas is melted and discharged to a tank, etc., and is used for separating waste liquid or for a milky bath. .

FIG. 1 shows a demonstration model for increasing the liquefaction strength by injecting air-dissolved high-pressure water into the liquefaction prevention ground and replacing it with natural groundwater to generate fine bubbles in the gaps between the grounds. This is an overview. The building structure (1) is directly supported on the first stratum (2) on the foundation, and the second stratum (3)
Is a saturated sand layer with moderate confinement and the groundwater level (5) is near the bottom of the building foundation. The third formation (4) consists of strong ground. A drainage pipe (1
0) and a drainage strainer pipe (11) connected to the lower surface of the second formation connected to the lower part, and pumped up by a drainage pump (6), temporarily stored in a tank (7), and connected via a connecting hose (8). hand,
The pressure of the output water is adjusted by the air-dissolved high-pressure water generator (9), and water is injected from the head of a water injection pipe (12) penetrating the first formation. High-pressure water is injected from the water injection strainer pipe (13) reaching the lower end of the second formation connected to the lower end of the water injection pipe.

Natural groundwater is drained strainer pipes (1
It flows from the second stratum below and outside the building toward 1). On the other hand, air-dissolved high-pressure water also flows out of the building from the water injection strainer (13), but the natural water pressure drops due to drainage from the drainage strainer installed on the opposite side of the building, so more air-dissolved water is released. In the gap in the second formation immediately below the building, the natural water is replaced by air-dissolved water, and fine bubbles are generated in a steady state where the pressure is reduced to the natural water pressure. Arrows shown in the figure indicate natural groundwater flowing in from the building exterior side (14), groundwater flowing in directly under the building (15), dissolved air dissolved water outside the building (17), and dissolved air dissolved directly below the building (16).

In a state in which the natural pore water immediately below the building is replaced by air-dissolved water, air-dissolved high-pressure water is also injected from the drainage pipe (10) to generate fine bubbles also in the gap in the second formation around the building. This makes it possible to improve the ground immediately below the building and the surrounding ground.

In FIG. 1, a water injection strainer pipe (13) is installed, for example, in a staggered manner, and air-dissolved high-pressure water is injected to form a bubble zone into a wall, thereby increasing water permeability by one digit. It is possible to reduce the amount of drainage by applying to excavation work and the like, and to reduce the external force acting on the anti-earth pressure structure. In this construction method, it is necessary to create a group of substantially continuous bubbles in the ground gap.Therefore, when the injection water pressure is increased to a higher value and returned to the hydrostatic pressure, the amount of supersaturated air should be increased to generate more bubbles. I do.

FIG. 2 shows the distribution of pore water pressure of the model shown in FIG. 1. The distribution of hydrostatic pressure before drainage / water injection (18, natural pore water pressure distribution) shows a drop after drainage assuming a steady state after drainage. At the time of the water pressure distribution (19), if water is injected at the output gauge pressure (20) of the air-dissolved high-pressure water generator (9), the water pressure distribution at the time of water injection becomes (21), and the difference between the hydrostatic pressure and the water injection pressure is obtained. Both the pressure (23) and the pressure difference (22) between the post-drain water pressure and the water injection pressure are substantially the same in the depth direction, and water is injected at this water pressure difference.

The above water pressure distribution varies depending on the permeability of ground, drainage and water injection amount, elapsed time, and the like. However, the water is injected at substantially the same differential pressure, and as the distance from the water injection strainer pipe increases, the water pressure distribution increases. The water pressure decreases, and the supersaturated air becomes fine bubbles according to the reduced water pressure. When the drainage / water injection is stopped, the water pressure distribution becomes static, and the space near the water injection strainer is also filled with fine bubbles.

FIG. 3 shows a verification model of a construction method in which landfill is performed in a state where compressed air or high-pressure water in which air is dissolved is injected into water to form aerated water during a landfill operation by discharging earth and sand into water. Things. In the vicinity of the tip of the injection hose (25) suspended from a carrier, etc., there is a water injection port and a weight / injection port (26) to resist the injection reaction force, and this tip extends to near the ground surface (30). It descends and discharges the earth and sand from the carrier (24) or the like while injecting the compressed air or the high pressure water dissolved in the air downward. The injection hose is wound up on a ship,
Ensure that the tip is always near the top of the new landfill.

The released sediment (29) settles while entraining the rising air bubbles (28), and near the upper part of the new landfill, the sedimentation was promoted by the downward jet flow (27) from the injection port, and the hydrostatic pressure was increased. At this point, it becomes possible to create a denser landfill bed with interstitial fluid mixed with fine bubbles.

FIG. 4 shows that in order to improve the quality of water in lakes and marshes, air dissolved high pressure water is discharged into water to optimize the amount of dissolved oxygen.
It relates to a verification model of a construction method aimed at homogenizing water quality. In lakes and marshes where the water quality is deteriorating, stratification progresses, and the shallow warm surface layer (31) and the cold bottom layer (3
2) The bottom layer becomes anoxic. In order to eliminate such a situation, a water injection hose is laid on the ground equivalent to the lake bottom, or a water injection / suction hose (33) is installed so that cold water in the bottom layer can be guided near the lake surface and heated at ambient temperature to further increase efficiency. Lay two hoses.

An elastic (expandable when tension is applied) discharge hose (34) is connected to a plurality of locations of the hose. At the upper end of the discharge hose, there is a float / spray nozzle (35), so that the direction and amount of spray can be set. A suction hose water inlet (36) is attached near the base of the discharge hose. The suction hose is connected to the bottom of the water receiving pool (38) installed on the lake surface, the deep cold water stored in this water receiving pool is warmed, sucked by the air dissolving high pressure water generator (9), and melts the air under high pressure The water is then fed into the water injection hose, and is sprayed from the injection nozzle of the discharge hose to agitate the lake water, forming fine bubbles (37) and rising while floating in the water.

When the injection pressure is increased, the discharge hose (34) is extended by the resistance of the injection nozzle portion so that water can be sprayed at a shallow portion. Can be planned.

In this method, air is dissolved in water, but in addition to air, nutrients and the like necessary for animals and plants and neutralizing agents for environmental degradation are dissolved and injected into a lake, river, or river.
It is possible to improve the environment of seawater, farms, etc.

[0030]

According to the present invention, saturated water in which air is dissolved is injected under a higher pressure than the in-situ water pressure to improve the water quality, and when the in-situ hydrostatic pressure is reached, a fluid having fine bubbles is formed,
Since bubbles cannot move freely due to the skeleton of soil particles,
Since a highly compressible gap fluid containing air bubbles can be obtained, the liquefaction resistance can be efficiently increased.

By increasing the content of bubbles in the gaps in this method, the water permeability of the ground can be reduced and the water pressure can be reduced. Also, in the process of landfilling with granular sediment, it is possible to increase the liquefaction strength as described above by mixing bubbles in pore water, and to check the reliability of these methods for compression wave velocity and ground It can be seen that the specific resistance can be obtained.

The water quality of lakes and marshes can be effectively improved by a similar method, and the water quality can be positively converted into a favorable environment to promote the growth of animals and plants.

[0033]

[Brief description of the drawings]

Fig. 1 shows an outline of a demonstration model that increases the liquefaction strength by injecting air-dissolved high-pressure water into the liquefaction prevention ground and replacing it with natural groundwater to generate fine bubbles in the gaps between the grounds. It is a thing.

FIG. 2 shows a distribution of pore water pressure in the model of FIG. 1;

FIG. 3 relates to a verification model of a construction method in which landfill is performed in a state in which compressed air or high-pressure water in which air is dissolved is injected into water to form an aerated water during landfill work by discharging earth and sand into water. .

FIG. 4 relates to a verification model of a construction method for discharging dissolved high-pressure water into water to optimize the amount of dissolved oxygen and to homogenize the water quality in order to improve the water quality of lakes and the like.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Building structure 2 1st formation 3 2nd formation 4 3rd formation 5 Groundwater level 6 Drain pump 7 Tank 8 Connecting hose 9 Air dissolving high-pressure water generator 10 Drainage pipe 11 Drainage strainer pipe 12 Water injection pipe 13 Water injection strainer pipe 14 Inflow Natural groundwater 15 Groundwater inflow directly below the building 16 Dissolved air dissolved water directly below the building 17 Dissolved air dissolved water outside the building 18 Hydrostatic pressure distribution 19 Decreased water pressure distribution after drainage 20 Output gauge pressure 21 Water pressure distribution during water injection 22 Difference between water pressure after injection and injection pressure Pressure 23 Differential pressure between hydrostatic pressure and injection pressure 24 Lead transported 25 Injection hose 26 Weight / injection port 27 Injection flow 28 Upward air bubble 29 Ejected sand 30 Ground surface 31 Surface layer 32 Bottom layer 33 Water injection / suction hose 34 Discharge hose 35 Floating / spray Nozzle 36 Water inlet 37 Bubble 38 Water receiving pool

Claims (5)

[Claims] 1. A method in which water in which air is dissolved at a pressure higher than the groundwater pressure is injected into the ground under the groundwater to replace the groundwater, and the water pressure is reduced to a hydrostatic pressure, and the dissolved air becomes supersaturated and becomes fine. A liquefaction-prevention method characterized in that the volume compression ratio of the void fluid is reduced by generating fine bubbles. 2. The method of discharging earth and sand into water and reclaiming the land.
A ground improvement method characterized by injecting compressed air or high-pressure water in which air is dissolved into water, and performing landfilling in the state of aerated water. 3. A ground improvement method comprising repeating the steps of claim 1 to increase the flow resistance of groundwater and lower the water pressure by forming continuous air bubbles in the void fluid. 4. In order to improve the quality of water in lakes and marshes, water dissolved in air is discharged at a pressure higher than the water pressure of lakes and marshes, whereby the amount of dissolved oxygen is optimized and the water quality is homogenized by stirring. Water quality improvement method. 5. The method according to claim 1, wherein the degree of saturation of the ground is controlled by measuring compressional wave velocity or specific resistance in order to measure the volume content of gas in the interstitial fluid. Construction management method characterized by doing.