JP2017110456A - Ground improvement device and ground improvement method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ground improvement device and a ground improvement method capable of efficiently executing work, by restraining influence of a negative pressure loss caused by consolidation settlement.SOLUTION: This device 2 comprises a plurality of drain materials 3, 3, etc. buried in the ground 1 and a catchment pipe 4 communicating the respective drain materials, and the catchment pipe 4 comprises a pipe body 10 communicating/connecting the respective drain materials 3, 3, etc., a nozzle 12 turning an injection port to a drain side end part 11 of the pipe body 10 and a driving fluid supply inner pipe 13 inserted into the pipe body 10 in a state of being communicated with/connected to the nozzle, and a driving fluid is supplied to the nozzle 12 via the driving fluid supply inner pipe 13 from driving fluid supply means.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a ground improvement device and a ground improvement method for causing a soft ground to settle down by applying a negative pressure to a drain material embedded in the ground.

  Conventionally, to improve soft ground, multiple drain materials are placed on the soft ground, a negative pressure is applied to each drain material, and the ground surface is evacuated to the ground while draining pore water in the soft ground to the ground. The consolidation drain method is widely used (see, for example, Patent Document 1).

  The drainage device used at that time includes a drain material such as a plastic drain buried in the ground, a water collecting pipe arranged in the horizontal direction on the ground surface where each drain material is connected and connected, and each drainage device. It has a header pipe that is connected to the end of the water pipe and a pump unit that is connected to the header pipe. The pump unit is operated and negative pressure is generated in each water collecting pipe. The interstitial water is sucked and drained to a water storage tank or the like through a water collection pipe and a header pipe.

JP 2002-242171 A

  However, in the conventional technology as described above, when the installation height of the pump unit must be higher than the ground surface of the ground to be improved due to the influence of topography or the like, or when the ground surface sinks due to consolidation, When the difference in height (water level difference) between the installation height and the water absorption point increases, the negative pressure acting on the ground decreases due to the height difference (water level difference) between the installation height of the pump unit and the water absorption point. There is a problem that the efficiency of the compacting operation is lowered.

  On the other hand, in order to prevent negative pressure drop due to such height difference, it is conceivable to embed a water tank or pump unit on the surface of the improved ground, but when embedding the upper part of the improved area, There was a problem that the water tank and pump unit could not be removed and were left in the ground.

  Furthermore, the pump unit used in the conventional method has a problem that the introduction cost and the running cost are increased because the pump unit is very expensive and has a large rated output and large power consumption.

  Therefore, in view of such conventional problems, the present invention has been made for the purpose of providing a ground improvement device and a ground improvement method capable of suppressing the influence of negative pressure loss due to consolidation settlement and the like and performing work efficiently. Is.

  The feature of the invention according to claim 1 for solving the conventional problem as described above includes a plurality of drain materials embedded in the ground, and a water collecting pipe through which the drain materials communicate, In the ground improvement device in which negative pressure is generated in the water collecting pipe and the pore water in the ground is sucked through each drain material, the water collecting pipe and / or the header pipe to which the water collecting pipe is connected are each drain. A pipe main body in which a material or a water collecting pipe is communicated, a nozzle disposed in the pipe main body with an injection port facing the drain side end of the pipe main body, and in the pipe main body in a state of being connected to the nozzle. The ground improvement device includes a driving fluid supply inner pipe inserted therethrough, and the driving fluid is supplied to the nozzle from the driving fluid supply means through the driving fluid supply inner pipe.

  According to a second aspect of the present invention, in addition to the configuration of the first aspect, an airtight sheet covering the ground surface is provided, and the water collecting pipe is disposed under the airtight sheet, and the water collecting pipe and each drain member are The upper end is in communication with the hermetic sheet.

  According to a third aspect of the present invention, in addition to the configuration of the first or second aspect, a diffuser is interposed at the drain side end of the pipe body.

  According to a fourth aspect of the present invention, in addition to the structure of any one of the first to third aspects, the water collecting pipe or the header pipe is connected in communication with a pump unit installed on the ground.

  According to a fifth aspect of the present invention, in addition to the structure of any one of the first to fourth aspects, the driving fluid supply means stores pore water in the ground sucked through the water collecting pipe or the header pipe. And a driving pump for draining water in the water storage tank, and the driving pump is connected to the driving fluid supply inner pipe.

  According to a sixth aspect of the present invention, in addition to the structure of any one of the first to fifth aspects, a detachable end cap that closes an end of the tube body is provided, and the driving fluid supply is provided to the end cap. This is because the inner pipe for operation is supported in a penetrating state, and the inner pipe for supplying driving fluid can be removed from the pipe main body.

  A feature of the invention described in claim 7 is that a water collecting pipe communicating with a plurality of drain materials embedded in the ground is disposed on the ground surface, and a negative pressure is generated in the water collecting pipe. In the ground improvement method for sucking pore water in the ground and consolidating the ground surface, a pipe body in which each drain material or water collection pipe is communicated with a header pipe to which the water collection pipe and / or the water collection pipe is connected A nozzle disposed in the tube main body with an injection port facing an end drain outlet of the tube main body, a driving fluid supply inner tube that is inserted into the tube main body and supplies a driving fluid to the nozzle. And a drive fluid is supplied to the nozzle through the drive fluid supply inner pipe, and the drive fluid is ejected from the nozzle to generate a negative pressure in the water collecting pipe and / or the header pipe.

  According to an eighth aspect of the present invention, in addition to the structure of the seventh aspect, a water-permeable layer is formed in which an upper end of the drain material is connected under an airtight sheet covering the ground surface, The water collecting pipe is disposed, and the driving fluid is ejected from the nozzle to generate a negative pressure in the water collecting pipe, thereby generating a negative pressure in each drain member through the water flow layer. .

  According to a ninth aspect of the present invention, in addition to the configuration of the seventh or eighth aspect, the water collecting pipes are connected in communication with a pump unit installed on the ground, and the pump unit is operated to be loaded on the water collecting pipe. It is to apply pressure.

  A feature of the invention described in claim 10 is that, in addition to the structure of claim 9, the pump unit is operated for a predetermined time and then stopped.

  As described above, the ground improvement device according to the present invention includes a plurality of drain materials embedded in the ground and a water collecting pipe communicating with each drain material, and generates negative pressure in the water collecting pipe. In the ground improvement device that sucks pore water in the ground through each drain material, the drain pipe or the water collection pipe is connected to the header pipe to which the water collection pipe and / or the water collection pipe is connected. A pipe main body, a nozzle disposed in the pipe main body with the injection port facing the drain side end of the pipe main body, and a driving fluid supply inner pipe inserted into the pipe main body in a state of being connected to the nozzle. A drive fluid is supplied to the nozzle from the drive fluid supply means through the drive fluid supply inner tube, so that the water collection pipe or header pipe installed near the water absorption point has an ejector structure. Completion , The negative pressure in the water collecting tube or header pipe occurs, is accompanied ground surface compaction suppressing pressure loss such as a case of subsidence, it is possible to perform efficient compaction work. Further, since a water collecting pipe having an ejector structure is used, a pump unit composed of an expensive vacuum pump or the like can be omitted.

  Further, in the present invention, an airtight sheet covering the ground surface is provided, the water collecting pipe is disposed under the airtight sheet, and the water collecting pipe and the upper end portion of each drain member are communicated under the airtight sheet. Thus, a negative pressure environment can be provided on the ground surface layer portion efficiently and inexpensively.

  Furthermore, in the present invention, the inside of the water collecting pipe or the header pipe can be efficiently decompressed by interposing a diffuser at the drain side end of the pipe body.

  Furthermore, in the present invention, the water collecting pipe or the header pipe is connected to the pump unit installed on the ground, so that the installation height of the pump unit is less than the ground surface of the ground to be improved due to the influence of topography and the like. The effect of pressure loss (head loss) when it must be high or when the ground surface sinks due to consolidation and the height difference (water level difference) between the installation height of the pump unit and the water absorption point increases. Can be suppressed.

  In the present invention, the driving fluid supply means includes a water storage tank that stores pore water in the ground sucked through the water collecting pipe or the header pipe, and a driving pump that discharges water in the water storage tank. And the drive pump is connected in communication with the drive fluid supply inner pipe, so that the interstitial water in the ground pumped up can be circulated as the drive fluid.

  Furthermore, in the present invention, a detachable end cap for closing the end of the tube body is provided, and the end fluid is supported in a state where the inner tube for driving fluid supply penetrates the end cap. Since the pipe body can be removed, the inner pipe for supplying driving fluid can be reused even when embankment is constructed on the upper part.

  In the ground improvement method according to the present invention, as described above, a water collecting pipe communicating with a plurality of drain materials embedded in the ground is disposed on the ground surface, and negative pressure is generated in the water collecting pipe. In the ground improvement method in which pore water in the ground is sucked through the drain material and the ground surface is consolidated and settled, each drain material or water collection pipe is connected to the header pipe to which the water collection pipe and / or the water collection pipe is connected. A pipe body, a nozzle disposed in the pipe body with an injection port facing an end drain outlet of the pipe body, and a driving fluid supply that is inserted into the pipe body and supplies a driving fluid to the nozzle An inner pipe, supplying the driving fluid to the nozzle through the inner pipe for driving fluid supply, ejecting the driving fluid from the nozzle, and generating a negative pressure in the water collecting pipe and / or the header pipe , Water absorption point The water collection pipe or header pipe installed nearby forms an ejector structure, and negative pressure is generated in the water collection pipe or header pipe, so even if the ground surface sinks due to consolidation, etc., pressure loss is suppressed. In addition, the consolidation operation can be performed efficiently.

  Further, in the present invention, a water flow layer in which an upper end of the drain material is connected is formed under an airtight sheet covering the ground surface, the water collecting pipe is disposed in the water flow layer, and a driving fluid is supplied from the nozzle. By generating a negative pressure in the water collecting pipe, a negative pressure is generated in each drain material through the water-passing layer, and an improvement work is performed under a favorable negative pressure environment in the ground surface layer portion. It can be performed.

  In the present invention, each of the water collecting pipes is connected to a pump unit installed on the ground, and the pump unit is operated to apply a negative pressure to the water collecting pipe, thereby ejecting the pump unit and each water collecting pipe. It is possible to work efficiently due to a synergistic effect with the effect, and to suppress the effect of pressure loss (head loss) when the height difference (water level difference) between the installation height of the pump unit and the water absorption point increases. it can.

  Furthermore, in the present invention, by operating the pump unit for a certain period of time and then stopping it, it is possible to minimize the use of a pump unit having a large rated output and a large amount of electric power used, thereby reducing running costs. Can do.

It is a top view which shows the outline of the usage condition of the ground improvement apparatus which concerns on this invention. It is a longitudinal cross-sectional view same as the above. FIG. 2 is a cross-sectional view showing a water collecting pipe in FIG. It is sectional drawing which shows another example of a water collection pipe | tube. (A) is a longitudinal cross-sectional view which shows the outline of another example of the usage condition of the ground improvement apparatus which concerns on this invention, (b) is the same top view. It is a top view which shows the outline of another example of the usage condition of the ground improvement apparatus which concerns on this invention. It is a longitudinal cross-sectional view which shows the outline of another example of the usage condition of the ground improvement apparatus which concerns on this invention.

  Next, an embodiment of the ground improvement device according to the present invention will be described based on the embodiment shown in FIGS. In the figure, reference numeral 1 denotes a ground made of soft ground or the like, and reference numeral 2 denotes a ground improvement device used for the ground improvement method for the ground.

  As shown in FIG. 1 and FIG. 2, the ground improvement device 2 communicates with a plurality of drain materials 3, 3... Embedded in the ground 1 in the vertical direction, and the drain materials 3, 3. .., And one end of each of the water collecting pipes 4, 4... Is connected to the pump unit 6 installed on the ground via the header pipe 5 to absorb water. The pore water is drained into the water storage tank 7.

  Although the aspect of the pump unit 6 is not particularly limited, for example, the pump unit 6 may be configured by a commonly used vacuum pump or drain pump, and includes two types of pumps, a vacuum pump and a drain pump, and a header. A structure in which air inside the tank communicated with the pipe 5 is discharged by a vacuum pump to reduce the pressure, and water pumped up in the tank is discharged to the water tank 7 by a drain pump may be used.

  For example, a plastic board drain is used as the drain material 3, 3..., Although not particularly illustrated, both sides of the core material having a corrugated cross section are covered with a water-permeable coating material such as a nonwoven fabric. The inside and outside of 3 ... are in communication with the inflow of earth and sand prevented. The drain members 3, 3... Are not limited to plastic board drains. For example, chemical drains or paper drains made of a synthetic resin fiber porous material may be used.

  The upper ends of the drain members 3, 3... Are connected to water flow hoses 9 through impermeable connection caps 8, and the other ends of the water flow hoses 9 are connected to the water collecting pipes 4, 4. It is connected.

  In addition, each drain member 3, 3... Is embedded in the upper end portion (cap portion) from the ground surface of the ground 1 to a desired depth, so that the surface layer portion of the ground 1 forms an airtight seal layer. A pressure difference is preferably generated inside and outside of 3.

  As shown in FIG. 3, the water collecting pipes 4, 4... Are installed on the ground surface 1 a of the improvement target ground so as to be horizontal and parallel to each other, and the drain materials 3, 3. The pipe body 10, the nozzle 12 disposed in the pipe body 10 with the injection port 12 a facing the drain side end 11 of the pipe body 10, and the nozzle body 12 being connected to the nozzle 12, were inserted into the pipe body 10. The driving fluid supply inner pipe 13 is provided, and the driving fluid is supplied from the driving fluid supply means to the nozzle 12 through the driving fluid supply inner pipe 13 at a high pressure.

  The pipe main body 10 is formed in a long cylindrical shape, and includes a plurality of connecting portions 10a, 10a... To which the water hose 9 is connected and connected at intervals in the cylinder axis direction. ) Is connected to the header pipe 5 via a flexible connecting hose 14, and the other end is closed by an end cap 15 to keep the airtightness inside. In this embodiment, the drain side end 11 is formed by connecting a short pipe having the same diameter to the end of the pipe body 10, but the drain side end 11 may be integrated with the pipe body 10.

  The driving fluid supply inner tube 13 is formed in a long cylindrical shape having a smaller tube diameter than that of the tube main body 10, and one end is connected to the driving fluid supply means via a flexible connecting hose 17, and the other end is connected to the other end. The nozzle 12 is connected in a coaxial arrangement.

  The nozzle side end portion of the driving fluid supply inner pipe 13 is supported so as to be insertable / removable by a mounting holder 16 protruding from the inner peripheral portion of the pipe body 10, and the discharge port 12 a of the nozzle 12 and the drain side end portion 11 are supported. The center is held in a continuous state in the tube axis direction.

  Therefore, the driving fluid supply inner tube 13 is supported such that the distal end portion is supported on the inner peripheral surface of the tube body 10 via the attachment holder 16 and the proximal end side penetrates the end cap 15 through the insertion hole 15a. The tube body 10 is disposed at the approximate center and forms a double tube structure with the tube body 10.

As shown in FIG. 1, for example, the driving fluid supply means includes a driving pump 18 composed of a submersible pump installed in the water storage tank 7, a distribution pipe 19 installed on the opposite side of the header pipe 5, and a driving pump. A water supply pipe 20 connecting the pump 18 and the distribution pipe 19 is provided, and the interstitial water in the ground stored in the water storage tank 7 through the water supply pipe 20 is used as the drive fluid supply inner pipe 13 of each of the water collecting pipes 4, 4. The nozzle 12 is supplied with water as a driving fluid at high pressure.
Next, the ground improvement method using this apparatus will be described.

  In this construction method, first, the operation of the pump unit 6 is started, a negative pressure is applied to the pipe body 10 of each of the water collecting pipes 4, 4. Thus, the pore water in the ground is absorbed through the drain materials 3, 3... To promote consolidation, and the pumped-up pore water in the ground is stored in the water tank 7.

  At the same time, the supply of water as the drive fluid is started from the drive fluid supply means to the drive fluid supply inner pipes 13 of the water collecting pipes 4, 4..., And the water is discharged from the nozzle 12 to the drain side of the pipe body 10. Injected as a high-pressure jet stream toward the end 11.

  Thereby, the surrounding water is caught in the water flow of the jetted water, and the negative pressure acts on the upstream side of the drain side end portion 11, that is, in the pipe main body 10 due to the ejector effect. 3. The inside is decompressed.

  Therefore, in the pipe body 10, the negative pressure by the pump unit 6 and the negative pressure by the ejector effect of the water collecting pipes 4, 4... Act simultaneously. The pressure is reduced, consolidation is promoted, and the pumped water is stored in the water tank 7.

  Further, the water stored in the water storage tank 7 is supplied to the driving fluid supply inner pipe 13 of the water collecting pipes 4, 4... As a driving fluid by the driving pump 18, and the water storage tank 7 and the water collecting pipes 4, 4. Cycle between ..

  When consolidation is promoted in this way, the ground surface of the improvement target ground 1 sinks, the height difference (water level difference) between the installation height of the pump unit 6 and the water absorption point increases, and the pumping amount by the pump unit 6 increases. descend.

  On the other hand, each of the water collecting pipes 4, 4... Constituting the ejector structure is installed on the ground surface 1a in the improved ground area where the subsidence is settled. Even if the height difference (water level difference) between the upper surface of the field and the water collection pipes 4, 4 ... increases, the supply pressure rises due to the water level difference, so there is little effect, and each water collection pipe 4, 4 ... The negative pressure due to the ejector structure acts stably in the tube body 10.

  Therefore, even if the pressure loss (head loss) due to the subsidence of the ground surface increases and the pumping efficiency by the pump unit 6 decreases, the loss is compensated by the ejector effect of each of the water collecting pipes 4, 4. Can be promoted.

  The pump unit 6 is operated for a certain period of time, and after the height difference (water level difference) between the installation height of the pump unit 6 and the water absorption point is increased, the pumping amount by the pump unit 6 is reduced to the reference amount. The pump unit 6 having a large rated output and a large power consumption can be kept to a minimum, and the running cost can be reduced.

  Further, in the ground improvement method of the present application, the pump unit 6 is operated and stopped according to the observed value while observing the increase / decrease in the pumping amount and the increase / decrease in the negative pressure in the collecting pipes 4, 4. It may be.

  Next, if necessary, the earth is filled on the ground surface 1a of the ground to be improved, and consolidation is further promoted by the load pressure of the earth.

  Finally, the nozzle 12 and the driving fluid supply inner pipe 13 are extracted and removed together with the end cap 15 from the end portion of the pipe body 10, and the operation is completed.

  In the above-described embodiment, the example in which the pump unit 6 is used has been described. However, depending on the situation, the pump unit 6 is not used, and the compaction is performed only by the negative pressure due to the ejector effect of each of the water collecting pipes 4, 4. You may make it perform work.

  In this case, the introduction cost of the pump unit 6 composed of an expensive vacuum pump or the like is not necessary, and the running cost can be reduced.

  In addition, the aspect of the water collection pipe | tube 4 is not limited to the above-mentioned Example, As shown in FIG. 4, a diffuser is interposed in the waste_water | drain side edge part 11 of the pipe | tube main body 10, and the nozzle 12 is installed according to the position. May be.

  The diffuser that forms the drain side end 11 is formed in a duct shape that includes a reduced diameter portion 11a that is smaller than the inner diameter of the pipe body 10 and tapered portions 11b and 11c that are respectively formed on the upstream and downstream sides of the reduced diameter portion 11a. The upstream side is connected to the pipe body 10 and the downstream side is connected to the header pipe 5 via a flexible connecting hose 14.

  Then, since the flow rate of the jetted water is increased by the diffuser 11, the pressure is reduced due to the venturi effect, and the surrounding water is entrained in the depressurized water flow, and the upstream side of the diffuser 11, that is, in the pipe body 10. Negative pressure is applied.

  Further, in the above-described embodiment, the example in which the vertical drain is used for the drain materials 3, 3... Has been described. However, as shown in FIG. can do. In addition, the same code | symbol is attached | subjected to the structure similar to the above-mentioned Example, and description is abbreviate | omitted.

  Further, in the above-described embodiment, the example in which each of the water collecting pipes 4, 4... Is provided with an ejector structure has been described. However, as shown in FIG. The pipe 23 may be provided with an ejector structure, and both the water collecting pipes 22, 22... And the header pipe 23 may be provided with an ejector structure. In addition, the same code | symbol is attached | subjected to the same structure and description is abbreviate | omitted.

  Furthermore, as shown in FIG. 7, the ground improvement device 30 of the present invention is arranged under the airtight sheet 31 covering the surface of the ground 1 and the airtight sheet 31, and the upper ends of the drain members 32, 32. The water collecting pipe 4 is disposed under the airtight sheet 31, and the water collecting pipe 4 and the drain members 32, 32. It is possible to communicate with each other. In addition, the same code | symbol is attached | subjected to the structure similar to the above-mentioned Example, and description is abbreviate | omitted.

  In this embodiment, the pipe body 10 of the water collecting pipe 4 is provided with a plurality of communication holes 34, 34... Communicating with the inside and outside of the pipe body 10 at intervals in the cylinder axis direction. The communication hole 34 includes a filter and has air permeability and water permeability, but prevents foreign matters such as sand from entering the pipe body 10.

  In the improvement method using the ground improvement device 30, when the pump unit 6 is operated, the driving fluid is ejected from the nozzle 12 and a negative pressure is generated in the water collecting pipe 4, the ground surface is covered with the airtight sheet 31. Therefore, a negative pressure acts on the water-permeable layer 33, and the negative pressure is transmitted to the drain members 32, 32.

  In the embodiment of FIG. 6, the case where the water flow layer 33 is provided has been described. However, the water flow layer 33 is not provided, and the water collection pipe 4 is disposed between the airtight sheet 31 and the ground surface. 4, the upper end of the drain material may be connected under the airtight sheet 31 via the water hose 15 or the like.

1 ground (soft ground)
2 Ground improvement device 3 Drain material 4 Water collecting pipe 5 Header pipe 6 Pump unit 7 Water storage tank 8 Connection cap 9 Water flow hose 10 Pipe body 11 Drain side end 12 Nozzle 13 Driving fluid supply inner pipe 14 Connection hose 15 End cap 16 Mounting fixture 17 Connection hose 18 Drive pump 19 Distribution pipe 20 Water supply pipe 21 Horizontal drain 22 Water collection pipe 30 Ground improvement device 31 Airtight sheet 32 Drain material 33 Water flow layer 34 Communication hole

Claims (10)

A plurality of drain materials embedded in the ground, and a water collecting pipe communicating with each drain material, generating negative pressure in the water collecting pipe, and sucking pore water in the ground through each drain material In the ground improvement device that
The water collecting pipe and / or the header pipe to which the water collecting pipe is connected are arranged in the pipe main body with the drain material or the water collecting pipe communicating with each other and the outlet side facing the drain side of the pipe main body. A drive fluid supply inner pipe inserted into the pipe body in a state of being connected in communication with the nozzle,
A ground improvement device characterized in that a driving fluid is supplied from the driving fluid supply means to the nozzle through the driving fluid supply inner pipe. An airtight sheet covering the ground surface is provided,
The ground improvement device according to claim 1, wherein the water collecting pipe is disposed under the airtight sheet, and the water collecting pipe and the upper end portion of each drain member are communicated under the airtight sheet.   The ground improvement device according to claim 1 or 2, wherein a diffuser is interposed at a drain side end of the pipe body.   The ground improvement device according to any one of claims 1 to 3, wherein the water collecting pipe or the header pipe is connected in communication with a pump unit installed on the ground.   The driving fluid supply means includes a water storage tank for storing pore water in the ground sucked through the water collecting pipe or the header pipe, and a driving pump for draining water in the water storage tank. The ground improvement device according to any one of claims 1 to 4, wherein is connected to the inner pipe for supplying the driving fluid.   A removable end cap for closing the end of the tube main body is provided, and the end fluid is supported in a state where the inner tube for driving fluid supply penetrates the end cap, so that the inner tube for supplying driving fluid can be removed from the tube main body. The ground improvement device according to any one of claims 1 to 5. A water collecting pipe communicating with a plurality of drain materials embedded in the ground is arranged on the surface, a negative pressure is generated in the water collecting pipe, and pore water in the ground is sucked through each drain material, and the ground surface In the ground improvement method to consolidate
The header pipe to which the water collecting pipe and / or the water collecting pipe is connected includes a pipe main body in which the drain material or the water collecting pipe is communicated, and an injection port directed to an end drain outlet of the pipe main body. A nozzle disposed in the pipe body, and a driving fluid supply inner pipe that is inserted into the pipe body and supplies a driving fluid to the nozzle,
A ground improvement method characterized in that a driving fluid is supplied to the nozzle through the inner pipe for driving fluid supply, and the driving fluid is ejected from the nozzle to generate a negative pressure in the water collecting pipe and / or the header pipe. . Forming a water-permeable layer connected to an upper end of the drain material under an airtight sheet covering the ground surface, and arranging the water collecting pipe in the water-permeable layer,
The ground improvement method according to claim 7, wherein a negative pressure is generated in each drain member through the water flow layer by injecting a driving fluid from the nozzle and generating a negative pressure in the water collecting pipe.   The ground improvement construction method according to claim 7 or 8, wherein the water collecting pipes are connected in communication with a pump unit installed on the ground, and the pump unit is operated to apply a negative pressure to the water collecting pipe.   The ground improvement construction method according to claim 9, wherein the pump unit is operated for a predetermined time and then stopped.

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