JP2017031598A - Groundwater level lowering device for water bottom ground, volume reduction method for mud and sludge at water bottom, and recovery device and method for methane hydrate in seabed - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure a sea route and a supplied water volume, by enabling volume reduction of mud, sludge, etc. at water bottom and volume reduction of dredge soil.SOLUTION: A groundwater level lowering device is for a water bottom ground G, and includes: a strainer pipe 11 buried in the water bottom ground G and having a water permeable strainer part 12 at a bottom end; a filter 13 formed along an outer periphery of the strainer pipe 11; a drainage pump 14 installed inside the strainer pipe 11; a drain pipe 15 for discharging groundwater pumped by the drainage pump 14 above a water surface; a vacuum pump for pumping inside the strainer pipe 11 from inside the drain pipe 15, to make the groundwater inside the water bottom ground G flow into the strainer pipe 11; and a guide pipe 16 having a bottom end installed in the water bottom ground G and a top end protruding above the water surface, the guide pipe having the strainer pipe 11 inserted and guided from above the water surface.SELECTED DRAWING: Figure 1

Description

  The present invention is a device for lowering the groundwater level of the bottom of the sea such as the seabed, a method for reducing the volume of mud and sludge in the bottom using the device, a device for recovering methane hydrate in the seabed, The present invention relates to a method for recovering methane hydrate using the apparatus.

In patent document 1, the ground consolidation method is proposed.
This method embeds a groundwater level lowering device in the ground, then covers the ground surface with an airtight sheet, and then lowers the groundwater level with the groundwater level lowering device, thereby reducing the air pressure between the groundwater surface and the airtight sheet. The pressure of the difference between the atmospheric pressure and the atmospheric pressure between the groundwater surface and the airtight sheet is reduced and applied to the ground through the airtight sheet to perform the consolidation of the ground.

  In addition, most of the conventional ground improvement has been a method in which various vertical drains are placed, the pore water pressure is increased while being pressurized with planned embankment + surcharge (surplus), and subsidence is performed.

And in patent document 2, the improvement construction method of the ground is proposed.
In this construction method, the saturated groundwater is pumped up by negative pressure propagation using SWP (Super Well Point), so that only the target area is concentrated and the water level can be lowered spotwise to create an unsaturated zone. After that, using a SWP vacuum pump or vortex pump, it promotes vacuum vaporization in the range of the unsaturated zone to remove moisture, VOCs (volatile organic compounds), and vaporizable substances such as oil from the ground. And promote ground improvement and soil purification.
As described above, the basis of the conventional ground improvement method is a method of forcibly draining groundwater by vacuum suction, forming an unsaturated zone, promoting vacuum vaporization, and promoting dehydration and drying.

JP 2007-247184 A Japanese Patent No. 4114944 (Japanese Patent Laid-Open No. 2007-303095)

  However, when the conventional vacuum evaporation dehydration method and drying method are applied to, for example, the drying and dehydration of mud and sludge under the sea surface and under the water surface, the ground water in the enclosed yard on the sea and water is reduced, and dry work is reduced. When it is aimed, since the supply amount is infinite, it is difficult to form the unsaturated zone.

An object of the present invention is to reduce the volume of sludge and mud on the bottom of the water and to reduce the volume of dredged sand, and to secure a navigation channel and a supply amount of water.
Another object of the present invention is to recover methane hydrate in the seabed ground.

In order to solve the above problems, the invention described in claim 1
A strainer pipe embedded in the bottom of the ground and having a permeable strainer at the lower end;
A filter formed on the outer periphery of the strainer tube;
A drainage pump disposed in the strainer pipe;
A drain pipe for discharging the ground water sucked by the drain pump onto the water surface;
A vacuum pump that sucks the inside of the strainer pipe from the drain pipe and causes the ground water in the bottom ground to flow into the strainer pipe;
An apparatus for lowering the ground water level of a bottom bottom ground, comprising: a guide pipe that has a bottom end placed on the bottom bottom ground, a top end projects on the water surface, and a guide pipe that is inserted and guided from above the water surface.

The invention described in claim 2
It is a groundwater level lowering device for water bottom ground according to claim 1,
A waterproof cap layer is provided between the inner periphery of the lower end of the guide tube and the outer periphery of the strainer tube.

The invention according to claim 3
It is a groundwater level lowering device for water bottom ground according to claim 1 or 2,
A lower end is placed on the water bottom ground, an upper end protrudes on the water surface, and an air supply pipe that feeds pressurized air from the lower end into the water bottom ground, and an intake pipe that sucks air in the water bottom ground from the lower end. It is characterized by.

The invention according to claim 4
It is a groundwater level lowering device for water bottom ground according to any one of claims 1 to 3,
A second air supply pipe is provided outside the target area of the water bottom ground, and is placed in the water bottom ground and sends pressurized air into the water bottom ground from a lower end.

The invention described in claim 5
Using the groundwater level lowering device for the bottom of the ground according to any one of claims 1 to 4,
On the outside of the target area of the submarine ground, construct a soil dam surrounding the target area on the bottom of the water,
Into the bottom of the water surrounded by the earth dam, the mud and sludge dripped from the water bottom outside the earth dam is thrown and deposited,
The method is characterized in that the volume of mud and sludge in the bottom of the water is reduced.

The invention described in claim 6
A method for reducing the volume of mud and sludge at the bottom of water according to claim 5,
In the water bottom ground of the target area, negative pressure is propagated by suction by the vacuum pump to reduce the pressure, and the mud and sludge deposited and deposited on the water bottom surrounded by the earth dam is consolidated and subsidized. And

The invention described in claim 7
A method for reducing the volume of mud and sludge in the bottom of water according to claim 5 or 6,
An air curtain having water-stopping property is formed in the water bottom ground outside the target region by sending pressurized air from the lower end of the second air pipe into the water bottom ground outside the target region. To do.

The invention according to claim 8 provides:
The groundwater level lowering device for water bottom ground according to claim 1 or 2,
A float carrier arranged on the sea surface and holding the upper end of the guide pipe,
The methane hydrate recovery apparatus in the seabed ground is characterized in that methane hydrate in the seabed ground is sucked from the strainer pipe by the vacuum pump and collected on the float carrier.

The invention according to claim 9 is:
Using the methane hydrate recovery device in the seabed ground according to claim 8,
In the target area of the seabed ground, a negative pressure is propagated by the vacuum pump to reduce the pressure, and the gasification of the methane hydrate in the seabed ground is promoted by promoting the gasification of the methane hydrate in the seabed ground. It features a method for recovering methane hydrate in seabed ground that recovers hydrate.

  According to the present invention, it is possible to reduce the volume of sludge and mud on the bottom of the water and to reduce the volume of dredged sand, and to secure the channel and the amount of supplied water.

  In addition, methane hydrate in the seabed can be recovered.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a construction method according to an embodiment to which the present invention is applied, and is a cross-sectional view showing an example of volume reduction and consolidation promotion of submarine mud and sludge. FIG. 9 is a cross-sectional view showing an example of the method of Embodiment 2 for promoting the evaporation under reduced pressure of the methane hydrate layer directly under the seabed.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings.
(Embodiment 1)
FIG. 1 shows an example of the volume reduction and consolidation promotion of submarine mud and sludge as a construction method according to one embodiment to which the present invention is applied. W is underwater, G is submarine ground, D is earth dam, 1 is groundwater drop Device 2 is an air supply pipe, 3 is an intake pipe, and 4 is an outer air supply pipe.

In the embodiment, in the harbor, as shown in the drawing, the seabed ground G by the sand layer has at least two pairs (or three or more pairs by the circumferentially spaced arrangement) through the sea W and at least two pairs of groundwater reduction devices 1. Is deeply buried by boring.
A plurality of air supply pipes 2 and a plurality of intake pipes 3 are buried between the two sets (or three or more sets) of groundwater lowering devices 1 at relatively shallow positions near the seabed.

Moreover, the earth dam D surrounding the object area | region of the seabed ground G is constructed in the seabed.
Further, outside the target region of the seabed ground G, outside the earth dam D, a plurality of air pipes 4 are arranged deeply in the circumferential direction at equal intervals.

The groundwater level lowering apparatus 1 includes a strainer pipe 11 that is deeply embedded in the seabed ground G, a drain pump 14 and a drain pipe 15 therein, and a vacuum pump that is disposed on the ground (not shown).
The strainer pipe 11 has a water permeable strainer portion 12 at the lower end, a filter 13 is formed on the outer periphery, and a drain pump 14 is disposed inside. The drainage pump 14 drains groundwater in the seabed G through the drainage pipe 15 to the sea.
Further, by suctioning and exhausting the inside of the strainer pipe 11 with a vacuum pump, the groundwater in the seabed ground G flows into the strainer pipe 11.

  In FIG. 1, the filter 13 is notched and the drain pump 14 and the drain pipe 15 inside the filter 13 are exposed.

That is, the groundwater level lowering device 1 is SWP, and as shown by an arrow, the inside of the strainer pipe 11 deeply embedded in the seabed ground G is sucked and exhausted by a ground vacuum pump, so that the strainer portion 12 at the lower end and the surroundings The groundwater in the seabed ground G is caused to flow into the strainer pipe 11 through the filter 13.
Then, the groundwater that has flowed in is drained to the ground through the drainage pipe 15 by being sucked by the drainage pump 14 in the strainer pipe 11.

The installation of the groundwater level lowering device 1 by such SWP is performed by inserting the strainer pipe 11 from above the sea surface into the guide pipe 16 in which the lower end is driven on the seabed ground G and the upper end protrudes on the sea surface.
Then, a waterproof cap layer 17 is provided between the lower end portion of the guide tube 16 and the strainer tube 11 by filling and filling the ultra-short-lived injection material of the double tube injection method with the cement-based chemical solution from the guide tube 16. Form.

  The air supply pipe 2 is connected to a large-scale compressor installed on the ground (not shown), and feeds pressurized air into the seabed ground G as indicated by arrows.

The intake pipe 3 is connected to a blower pump installed on the ground (not shown) to dry the inside of the seabed ground G as indicated by arrows.

  A water channel is formed in the seabed ground G by air supply and intake by the intake pipe 2 and the intake pipe 3 to improve water permeability.

  Thus, in the seabed ground G in the harbor, when the groundwater is vacuum-sucked by the SWP method, negative pressure propagates into the ground and soil, that is, as shown, longitudinal waves in which the negative pressure proceeds laterally. As it propagates quickly, the pressure can be reduced in a spot while being under the seabed, and the vacuum suction effect and the vacuum evaporation are promoted.

Then, when the mud dredged in the harbor cannot be taken out of the bay due to environmental factors, the mud mud is stocked by providing a soil dam D as shown in the figure.
That is, mud and sludge dredged from above the bottom of the soil dam D are thrown into the sea floor surrounded by the soil dam D and accumulated, and the volume of the mud and sludge is reduced.

That is, although the water content of the mud deposited on the seabed surrounded by the soil dam D is large, consolidation settlement can be promoted by vacuum suction and vacuum evaporation drying of the seabed ground G below it.
That is, by sucking the vacuum pump of the groundwater level lowering device 1 by SWP, the negative pressure is propagated in the seabed ground G in the target area to reduce the pressure, so that it is thrown into the seabed surrounded by the earth dam D above it. As shown in the figure, the accumulated mud and sludge can be sequentially consolidated from the first consolidated sedimentation layer to the fourth consolidated settlement tank.

In addition, when the groundwater in the enclosed yard at sea is reduced and the purpose is dry work, the supply amount is infinite, so a second air supply pipe 4 is provided around the yard, and the pressure and pressure of the compressor Thus, as shown in the drawing, an air curtain can be formed around the second air supply pipe 4 to form an unsaturated zone, and an area with high water stopping properties can be provided.
Therefore, the cost can be reduced by reducing the number of wells of the groundwater level lowering device 1 by SWP.

The compressor pressure at that time should be within the range of water depth + air supply resistance pressure, and air blow to the sea should be minimized.
The compressor pressure is controlled by automated operation using a tank pressure sensor.

  As described above, according to the method for reducing mud and sludge on the seabed using the groundwater level lowering device 1 by SWP of the seabed ground G of the embodiment, dredged sludge and mud can be reduced on the seabed of the port. In the harbor, it is possible to secure the water supply by securing the route.

(Modification)
In the above embodiment, the object is the seabed ground, but the present invention is not limited to this, and may be a lakebed ground such as a dam lake or a waterbed ground such as a riverbed ground.

(Embodiment 2)
FIG. 2 shows an example of the reduced pressure evaporation promotion of the methane hydrate layer directly under the seabed as the construction method of the second embodiment. As in the above-described embodiment, W is in the sea, G is the seabed ground, and 1 is a groundwater reduction device using SWP. , 11 is a strainer pipe, 12 is a strainer section, 13 is a filter, 14 is a drain pump, 15 is a drain pipe, 16 is a guide pipe, 17 is a waterproof cap layer, and 5 is a float carrier.

In the second embodiment, as shown in the figure, in the offshore, the seabed ground G has at least two pairs (or more than three pairs by circumferentially spaced arrangement) at least facing each other through a deep underwater W having a water depth of about 1000 m. The groundwater lowering device 1 is deeply buried by boring.
The groundwater level lowering device 1 is SWP, and a long strainer pipe 11, a drain pipe 15 and a guide pipe 16 are used corresponding to a deep water depth.
Moreover, the drainage pump 14 arrange | positioned in the strainer pipe | tube 11 has the capability of about 600 m of heads, for example.

  In FIG. 2, the filter 13 is cut out, and the underwater portion of the strainer pipe 11 is cut away to expose the drain pump 14 and the drain pipe 15 inside thereof.

And the upper end of the guide pipe | tube 16 is fixed and hold | maintained at the float carrier 5 arrange | positioned on the sea surface.
On the float carrier 5, a gas tank or a gas pipeline is connected to the upper end of the strainer pipe 11.

  Thus, in the offshore deep seabed G, the groundwater is vacuum-sucked by the SWP method, and as shown in the figure, the negative pressure is quickly propagated as a longitudinal wave that travels in the horizontal direction, while being deep under the seabed. The pressure can be reduced in a spot manner, and the vacuum suction effect and vacuum vaporization are promoted.

Then, due to the vacuum suction effect and the promotion of vacuum vaporization, methane hydrate in the seabed ground G can be sucked from the strainer pipe 11 by a vacuum pump and recovered from the upper end to the gas tank or gas pipeline on the float carrier 5.
That is, the negative pressure is propagated in the target area of the seabed ground G by the suction of a vacuum pump to reduce the pressure, and the gasification of the methane hydrate in the seabed ground G is promoted by evaporating gasification of the methane hydrate in the seabed ground. Hydrate can be collected in the float carrier 5.

  As described above, according to the methane hydrate recovery apparatus and method using the groundwater level lowering device 1 by SWP in the seabed ground G of the second embodiment, the methane hydrate layer in the seabed ground G is promoted to be evaporated under reduced pressure. Hydrate can be recovered.

(Other variations)
In each of the embodiments described above, the shape, dimensions, and the like of each part are arbitrary, and it is a matter of course that specific detailed structures can be appropriately changed.

W Underwater (underwater)
G Submarine ground (submarine ground)
D Drainage dam 1 Groundwater level lowering device 11 Strainer pipe 12 Strainer section 13 Filter 14 Drain pump 15 Drain pipe 16 Guide pipe 17 Waterproof cap layer 2 Air supply pipe 3 Intake pipe 4 Second air supply pipe 5 Float carrier

Claims (9)

A strainer pipe embedded in the bottom of the ground and having a permeable strainer at the lower end;
A filter formed on the outer periphery of the strainer tube;
A drainage pump disposed in the strainer pipe;
A drain pipe for discharging the ground water sucked by the drain pump onto the water surface;
A vacuum pump that sucks the inside of the strainer pipe from the inside of the drain pipe and causes the groundwater in the water bottom ground to flow into the strainer pipe;
An apparatus for lowering the groundwater level of a submerged ground, comprising: a guide pipe in which a lower end is placed on the submerged ground, an upper end projects on the water surface, and a guide pipe is inserted and guided from above the water surface.   The groundwater level lowering device for a water bottom ground according to claim 1, further comprising a waterproof cap layer filled between an inner periphery of a lower end portion of the guide tube and an outer periphery of the strainer tube.   A lower end is placed on the water bottom ground, an upper end protrudes on the water surface, and an air supply pipe that feeds pressurized air from the lower end into the water bottom ground, and an intake pipe that sucks air in the water bottom ground from the lower end. The groundwater level lowering device for water bottom ground according to claim 1 or 2.   4. The air supply pipe according to claim 1, further comprising: a second air supply pipe that is placed in the water bottom ground outside the target area of the water bottom ground and feeds pressure air into the water bottom ground from a lower end. 5. The groundwater level lowering device for water bottom ground as described in the paragraph. Using the groundwater level lowering device for the bottom of the ground according to any one of claims 1 to 4,
On the outside of the target area of the submarine ground, construct a soil dam surrounding the target area on the bottom of the water,
Into the bottom of the water surrounded by the earth dam, the mud and sludge dripped from the water bottom outside the earth dam is thrown and deposited,
A method for reducing the volume of mud and sludge at the bottom of the water, wherein the volume of mud and sludge is reduced.   In the water bottom ground of the target area, negative pressure is propagated by suction by the vacuum pump to reduce the pressure, and the mud and sludge deposited and deposited on the water bottom surrounded by the earth dam is consolidated and subsidized. The method for reducing the volume of mud and sludge in the bottom of water according to claim 5.   An air curtain having water-stopping property is formed in the water bottom ground outside the target region by sending pressurized air from the lower end of the second air pipe into the water bottom ground outside the target region. The method for reducing the volume of mud and sludge in the bottom of the water according to claim 5 or 6. The groundwater level lowering device for water bottom ground according to claim 1 or 2,
A float carrier arranged on the sea surface and holding the upper end of the guide pipe,
An apparatus for recovering methane hydrate in submarine ground, wherein methane hydrate in submarine ground is sucked from the strainer pipe by the vacuum pump and collected on the float carrier. Using the methane hydrate recovery device in the seabed ground according to claim 8,
In the target area of the seabed ground, a negative pressure is propagated by the vacuum pump to reduce the pressure, and the gasification of the methane hydrate in the seabed ground is promoted by promoting the gasification of the methane hydrate in the seabed ground. A method for recovering methane hydrate in submarine ground, characterized by recovering hydrate.

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