JP2012241383A - Ground improvement method and decompression container - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ground improvement method for enabling the installation of a decompression container which can be manufactured in a ground-to-be-improved region and has sufficient strength and air-tightness, and to provide the decompression container.SOLUTION: The ground improvement method includes completing a decompression container 20 in a ground by a step of driving a steel pipe 29 having an annular part 28 protruded from the inner face of the upper part, into a ground, a step of removing soil from the driven steel pipe, a step of installing a bottom plate 27 on the bottom side of the steel pipe, and a step of placing a cover body 30 through which a drain pipe 25 connected to a water pump 24 stored inside the steel pipe, a suction pipe 26 connected to a vacuum pump 23 and a vertical pipe 21 for functioning a siphon are passed, at rest in the annular part 28 of the steel pipe, and then closely attaching the cover body to the annular part of the steel pipe with negative pressure given by driving the vacuum pump for developing the suction force of the vacuum pump and the suction force of the vertical pipe due to its siphon function to suck and drain interstitial water from the ground to be improved through a vertical drain member 11 driven into the ground.

Description

  The present invention relates to a ground improvement method by vacuum consolidation and a decompression vessel usable for the ground improvement method.

  A suction device using a vacuum pump is known as a device that generates a suction force to suck and drain water. In the conventional technology, for example, after placing a vertical drain in soft ground, a method of promoting consolidation of the ground by applying a negative pressure to decompress the ground using a vacuum pump suction device. It is used (for example, Patent Documents 1 to 3). Further, as disclosed in Patent Document 4, a suction force generating device in which a vertical pipe is inserted into a decompression chamber and a gas-liquid two-phase flow is formed in the vertical pipe so as to exhibit a siphon function is disclosed by one of the present inventors and others. Proposed by the inventors.

JP 2000-328550 A JP 2001-226951 A JP 2002-138456 JP JP 2010-090696 A

  When suctioning and draining using the vacuum pump and siphon suction force together as in Patent Document 4 for the ground in the land area, in order to make the siphon function, a decompression container having a vertically long drain pipe Is required. When introducing a decompression vessel for the purpose of improving soft ground on land, it is necessary to install the decompression vessel in the ground, so the production and installation method of the decompression vessel becomes a problem. In particular, when manufacturing a decompression container locally, it is often difficult to manufacture a container having sufficient strength and airtightness. Moreover, it is necessary to make the siphon function stably because of construction conditions that tend to be mixed with air, such as airtight leakage and vaporization of dissolved gas at high negative pressure.

  The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to provide a ground improvement method and a vacuum container that can be installed in a ground improvement target area and can be installed with a vacuum container having sufficient strength and airtightness. And

  A ground improvement method for achieving the above object includes a step of placing a steel pipe having an annular portion protruding from an upper inner surface into the ground, a step of removing soil in the placed steel pipe, A lid that penetrates a step of installing a bottom plate on the bottom side, a drain pipe connected to a pumping pump housed inside the steel pipe, an intake pipe connected to a vacuum pump, and a vertical pipe that functions a siphon, respectively. The vacuum vessel is completed in the ground by the step of standing in the annular part of the steel pipe, and then the lid is brought into close contact with the annular part of the steel pipe by the negative pressure generated by driving the vacuum pump. It is characterized in that the pore water in the ground to be improved is sucked and drained through the vertical drain material placed on the ground by exerting the suction force by the pump and the suction force by the siphon function of the vertical pipe. .

  According to this ground improvement method, a decompression container can be easily completed in the ground by placing an easily available and strong steel pipe on the ground and leaving the lid on the annular portion of the steel pipe. A container body that accommodates a vertical pipe that allows the siphon to function while ensuring the airtightness of the decompression container without using attachment fixing means such as bolts and welding by closely attaching the lid to the annular portion by driving the vacuum pump Since it can be composed of a steel pipe, the decompression vessel can be easily manufactured in the ground improvement target area, and the ground improvement by vacuum consolidation can be easily performed.

  In the ground improvement method, an airtight member made of an elastic body is disposed between the lid and the annular portion, whereby the airtightness of the decompression container can be enhanced.

  Moreover, when the decompression container is installed on the soft ground by making the distance between the position of the bottom plate of the steel pipe and the lower end position of the steel pipe more than 1/2 of the diameter of the steel pipe, Even if buoyancy acting upward is applied, the stability of the decompression vessel can be secured.

  The ground improvement method for achieving the above object is that a decompression container is a decompression container that is installed in the ground and whose inside is decompressed by a vacuum pump, and a steel pipe that is placed in the ground as a container body, and the container A bottom plate provided on the bottom side of the main body, and a lid for closing the container main body, the lid body being configured to be stationary on an installation portion of the container main body, and by driving the vacuum pump The lid is brought into close contact with the portion to be installed with a negative pressure.

  According to this decompression container, the container main body that houses the vertical pipe for functioning the siphon is made of a steel pipe that is easily available and strong, and the lid body is placed on the installation part of the container main body. Since the lid is brought into close contact with the portion to be installed by driving, the lid can be manufactured in the ground improvement target area and can have sufficient strength and airtightness.

  In the decompression vessel, the steel pipe has an annular portion provided so as to protrude from an upper inner surface thereof, and the lid body is placed on the annular portion with the annular portion as the installation portion. It is preferable that an airtight member made of an elastic body is disposed between the annular portion. Thereby, the airtightness of the decompression container can be enhanced with a simple configuration.

  Moreover, the airtight member can be further improved in airtightness of the decompression container by being composed of a high-height packing that is easy to deform and a low-height packing that is difficult to deform.

  The above-described ground improvement method can be executed by installing the above-described decompression container in the ground.

  ADVANTAGE OF THE INVENTION According to this invention, the ground improvement method and pressure reduction container which can be manufactured in the ground improvement object area and can install the pressure reduction container which has sufficient intensity | strength and airtightness can be provided.

It is a figure which shows roughly the structure of the vacuum consolidation ground improvement system containing the pressure reduction container which can perform the ground improvement method by vacuum consolidation of this embodiment. It is the top view (a) which looked at the steel pipe of the decompression container of FIG. 1 from the upper part, and the top view (b) which has arrange | positioned the rubber packing to the annular part of the steel pipe. It is a flowchart for demonstrating each process S01-S12 of the ground improvement method by the vacuum consolidation of this embodiment using the vacuum consolidation ground improvement system of FIG. It is the top view (a) and principal part longitudinal cross-sectional view (b) which show another structural example of the packing of FIG.2 (b). It is a principal part longitudinal cross-sectional view which shows the structural example different from the packing of FIG. It is a figure for demonstrating the structural example which lengthened the lower end position of the steel pipe with respect to the position of the bottom plate of the steel pipe after the placement of FIG. FIG. 1A for explaining the problem when the lower end position of the steel pipe is short with respect to the position of the bottom plate of the steel pipe after placement in FIG. 1, and for explaining the effect in the case of the configuration of FIG. FIG. It is a figure for demonstrating the baseplate installed in the bottom part side of the steel pipe of FIG.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a diagram schematically showing a configuration of a vacuum consolidation ground improvement system including a decompression vessel capable of executing the ground improvement method by vacuum consolidation of the present embodiment. 2 is a top view (a) of the steel pipe of the decompression vessel of FIG. 1 as viewed from above and a top view (b) in which rubber packing is arranged on the annular portion of the steel pipe.

  As shown in FIG. 1, the vacuum consolidation ground improvement system 1 includes a vertical drain material 11 placed in a ground G to be improved, and a vacuum decompression device 10 including a decompression container 20 installed in the ground. Prepare.

  The vacuum decompression device 10 includes a vertical drain pipe 21, a horizontal drain pipe 22 connected to the upper end of the vertical drain pipe 21, a vacuum pump 23 and an intake pipe 26 as exhaust facilities, and a pumping pump 24 and drainage as drain facilities. The pipe 25 and the decompression container 20 installed in the ground are provided, and installed in the ground G1 near the ground G to be improved. The inside of the decompression container 20 is decompressed by the vacuum pump 23, so that the vacuum decompression device 10 functions as a decompression generation source.

  The decompression container 20 includes a cylindrical steel pipe 29 that constitutes the container main body and is placed in the ground G1, and a disk-shaped disk disposed on the upper side of the steel pipe 29 to close the container main body and seal the inside. A lid 30 and a bottom plate 27 disposed on the bottom side of the steel pipe 29 are provided.

  After the steel pipe 29 is driven into the ground to remove the soil in the steel pipe 29, the bottom plate 27 is constructed by installing a solidified body such as concrete on the bottom side of the steel pipe 29. Thereby, the intensity | strength and water stop of the bottom part of the pressure reduction container 20 are securable.

  As shown in FIGS. 1 and 2A, an annular portion 28 that is formed in an annular shape is provided on the inner surface of the upper portion of the steel pipe 29 so as to protrude in the radial direction from the inner peripheral surface. The lid body 30 is placed on the annular portion 28 as an installation portion of the lid body 30. That is, the vertical drain pipe 21, drain pipe 25, and intake pipe 26 are attached to the lid body 30, and in this state, the lid body 30 is placed on the annular portion 28 on the upper inner surface of the steel pipe 29. Placed. In this case, the lid body 30 has a structure in which mounting and fixing means such as bolts and welding are omitted with respect to the annular portion 28 of the steel pipe 29 and is simply placed.

  As described above, since a strong steel pipe is used as the container body of the decompression container 20, the strength of the container body can be secured, and the steel pipe is relatively easy to obtain. Suitable for.

  Further, the lid 30 is placed in the annular portion 28 of the steel pipe 29, and the lid 30 is brought into close contact with the annular portion 28 by the negative pressure action when the vacuum pump 23 is driven. Kept. Thus, since the process of welding and bolt fixation is unnecessary for installation of the lid body 30, the decompression container 20 can be easily manufactured on site.

  Further, as shown in FIG. 2B, by placing a packing (O-ring) 31 made of elastic rubber as an airtight member between the lid 30 and the annular portion 28 of the steel pipe 29, the lid 30 And the airtightness between the annular portion 28 can be enhanced.

  The vertical drain material 11 in FIG. 1 is placed in the soft ground G in order to suck the pore water in the soft ground G to be improved. The air-impermeable portion 12 connected to the upper end of the vertical drain material 11 is located on the groundwater level surface H0. The upper end of the air-impermeable portion 12 is connected to the horizontal drain pipe 22 of the vacuum decompression device 10 on the ground surface S.

  In addition, the vertical drain material 11 can be made into the structure disclosed by patent document 2, 3, for example with the air-impermeable part 12 etc. by having multiple pieces poured in the soft ground G as needed.

  The interstitial water sucked in the direction a in the soft ground G by the vertical drain material 11 flows in the direction b through the horizontal drain pipe 22 and the vertical drain pipe 21 and is drained from the lower end 21a of the vertical drain pipe 21, and the bottom of the decompression vessel 20 However, the stored water flows through the drain pipe 25 in the direction c by the pump 24 and is drained to the outside.

  Next, each step S01 to S12 of the ground improvement method by vacuum consolidation of the present embodiment using the vacuum consolidation ground improvement system of FIG. 1 will be described with reference to the flowchart of FIG.

  First, the annular portion 28 of FIG. 2A is provided on the upper surface of the inner surface of the steel pipe 29 (S01). The steel pipe 29 is preferably a steel pipe having a diameter of about 800 mm to 1000 mm, and general-purpose products for civil engineering and construction such as steel pipe piles (SKK400, 490) and steel pipe sheet piles (SKY400, SKY490) can be used.

  Next, the steel pipe 29 is driven into the ground G1 by, for example, about 4 m by driving the steel pipe 29 into the ground near the ground to be improved by a vibro hammer or the like (S02). Thereafter, the soil in the steel pipe 29 is excavated and removed by an auger or a hammer grab (S03). Thereby, the decompression space 20a is formed in the steel pipe 29 driven in the ground. The excavated earth and sand will be temporarily placed near the construction site in order to refill it after the ground improvement work. Further, the excavated earth and sand may be used as a preload load.

  Next, a solidified body made of concrete or the like is constructed on the bottom side of the steel pipe 29 and the bottom plate 27 is installed (S04). Thereby, the intensity | strength of the bottom face of the pressure reduction container 20 is ensured. Next, the pump 24 to which the drain pipe 25 is connected is housed in the bottom of the steel pipe 29 (S05).

  Next, the lid body 30 through which the drain pipe 25, the intake pipe 26, and the vertical drain pipe 21 are passed is placed on the annular portion 28 (S06). In this case, the lid 30 is not attached to the steel pipe 29 by bolting or welding. The lid 30 is preferably made of a steel plate or a PC (precast concrete) plate, and is manufactured in a factory. In addition, as a method of standing the lid 30, there is a method of hanging a hanging wire on a hook attached to the lid 30 and standing still while lowering the wire.

  At the time of the above-described step S06, the rubber packing 31 of FIG. 2 (b) is bonded in advance to the lower region of the lid 30 corresponding to the annular portion 28, so that the handling at the time of arranging the packing 31 at the site is possible. This facilitates the maintenance of the packing 31. In addition, if a packing is installed together in the annular portion 28 of the steel pipe 29, the water stoppage is improved. The packing 31 can be made of a rubber material, but may be replaced with silicon or the like.

  While the decompression vessel 20 is completed as described above (S07), the vertical drain material 11 is placed in the soft ground G to be improved as shown in FIG. To cast. And the horizontal drain pipe 22 extended from the pressure reduction container 20 is connected to the front-end | tip of the impermeable part 12 via a connection part (illustration omitted) etc. (S08).

Next, the vacuum pump 23 is driven (S09), and the inside of the decompression vessel 20 is depressurized, whereby a high negative pressure of about −70 to 85 kN / m ² acts on the lid 30. The annular portion 28 of the steel pipe 29 comes into close contact (S10), and the airtightness in the decompression vessel 20 is ensured.

  Next, the suction force by the vacuum pump 23 and the suction force by the siphon function of the vertical drain pipe 21 are exhibited and used together (S11), and the pore water in the soft ground G is sucked and drained (S12), thereby vacuum consolidation. To improve the ground. The drained water is stored at the bottom of the decompression vessel 20 and discharged from the drain pipe 25 to the outside by the pumping pump 24.

  In the vacuum consolidation ground improvement system 1 of FIG. 1, in addition to the suction force by depressurizing the decompression space 20a in the decompression vessel 20 with the vacuum pump 23 of the vacuum decompression device 10, the ground water level surface H0 and the water level surface in the decompression vessel 20 The suction force by the siphon function due to the water level difference ΔH (= H0−H1) from H1 is generated, and the soft ground G is consolidated by sucking the pore water in the soft ground G by these suction forces. This vacuum compaction can be performed with a larger suction force as much as the suction force due to the water level difference ΔH is applied, compared with the case where suction is performed only by the vacuum pump 23. The water level difference ΔH when the water level surface H1 in the decompression vessel 20 does not reach the lower end 21a of the vertical drain pipe 21 is the difference between the ground water level surface H0 and the lower end 21a.

  According to the conventional vacuum consolidation ground improvement method, when the suction force is insufficient with only the vacuum pump, loading with embankment is used together, but the suction force that is the natural force due to the siphon function as in this embodiment By using together, loading by embankment can be reduced or omitted, so it can be expected to save materials and equipment and shorten the work period. In addition, since the suction force is increased as compared with the conventional construction method, the ground improvement period required for the soft ground to reach a predetermined strength can be shortened.

In the present embodiment, when the negative pressure by the vacuum pump 23 is lowered to about -50kN / m ² is also, in order to exhibit the least -80kN / m ² about effects a negative pressure in the vertical drain member 11, to function siphon The vertical length of the vertical drain pipe is preferably at least about 3 m.

  As described above, the decompression container 20 accommodates a vertically long vertical drain pipe 21 in order to exert a siphon function, but the container main body that accommodates the vertical drain pipe 21 is made of a steel pipe. The decompression vessel 20 can be easily manufactured locally. For this reason, the influence which it has on the construction period of ground improvement is small.

  In addition, the decompression container 20 is required to have a structure that maintains airtightness. However, according to the present embodiment, the container body of the decompression container 20 is composed of the steel pipe 29, and the lid 30 is attached to the annular portion 28 of the steel pipe 29. The lid 30 is brought into close contact with the annular portion 28 by a negative pressure action when the vacuum pump 23 is driven, and the airtightness inside the decompression vessel 20 can be maintained. Therefore, when the lid 30 is installed, the steps such as welding and bolt fixing for maintaining the internal airtightness are unnecessary, and the decompression vessel 20 can be easily manufactured on site.

  As described above, a steel pipe is used for the container body in order to facilitate on-site production of the decompression container 20 and ensure the strength. However, even if the diameter of the steel pipe available locally is somewhat large, the outer portion of the annular portion 28 is outside the steel pipe. By adjusting the diameter and the inner diameter, the decompression container 20 can be easily manufactured on-site, and the lid body 30 having a constant diameter need only be prepared. In addition, since the lid 30 is not fixed to the steel pipe by welding or the like, if there is a failure such as a pump in the decompression vessel during a long period of ground improvement, the lid can be easily removed and the pump replaced. Etc. are easy to deal with.

  The decompression vessel 20 is a field production type and is dismantled after the construction is completed. That is, when construction is not performed, only the lid 30 placed on the steel pipe 29, the pump 24, the vertical drain pipe 21, the intake pipe 26, and the drain pipe 25 connected to the pump 24 are stored and managed. Just keep it. It is not necessary to store the steel pipe 29 having a large volume as well as the container body of the decompression container 20, and management is easy.

  Next, a preferred embodiment in the configuration of FIGS. 1 and 2 will be described with reference to FIGS.

  FIG. 4 is a top view (a) and a vertical cross-sectional view (b) of an essential part showing another configuration example of the packing of FIG. 2 (b). FIG. 5 is a longitudinal sectional view of a main part showing another configuration example of the packing of FIG.

  In the example of FIGS. 4A and 4B, the airtight member disposed in the annular portion 28 of the steel pipe 29 is constituted by two types of packing. That is, the hermetic member of the present example is composed of a high hardness rubber packing 32 having a low height and a high hardness rubber packing 33 having a low height. The rubber packing 32 is made of, for example, a low hardness rubber material having a hardness of about 10 degrees or less, and the rubber packing 33 is made of, for example, a high hardness rubber material having a hardness of about 70 degrees or more. The height of the rubber packing 32 is higher than that of the rubber packing 32.

The airtight member between the lid 30 and the annular portion 28 is not affected by a strong compressive force, mainly a weak compressive force due to its own weight until the inside of the decompression vessel 20 is depressurized to some extent. However, since the airtight member arranged in the annular portion 28 of the steel pipe 29 is composed of the soft and hard rubber packings 32 and 33 as described above, the low-hardness rubber packing 32 can be obtained. It can be deformed even under a weak compressive force to increase the airtightness, and by arranging a rubber packing 33 having a hardness higher than that of the rubber packing 32 together, the theoretical maximum negative pressure of -100 kN in the decompression vessel 20 chamber. Even under a condition in which a strong compressive force is applied so that the negative pressure increases up to / m ^2, the compression failure of the rubber packing 32 with low hardness can be prevented.

  The hardness of the rubber material is measured by a durometer in accordance with the provisions of “Hardness test method for vulcanized rubber and thermoplastic rubber” (JIS K6253). For example, a hardness of 10 degrees is displayed as A10, and a hardness of 70 degrees is displayed as A70.

  Since it is necessary to first deform the low-hardness rubber packing 32 in the process of pressure reduction in the vacuum container 20, the low-hardness rubber packing 32 is more than the high-hardness rubber packing 33 as shown in FIG. Also use a high height. The high-hardness rubber packing 33 is deformed after the low-hardness rubber packing 32 is deformed and becomes the same height as the rubber packing 33. However, the degree of deformation is lower than that of the rubber packing 32, and the rubber packing 33 is deformed. While being able to prevent excessive compression of 32, it contributes to the improvement of airtightness and can further improve airtightness.

  In addition, although the cross-sectional shape of the rubber packings 32 and 33 may be a rectangular shape, a circular shape or an oval shape may be sufficient. 4 (a) and 4 (b), the rubber packing 32 is located on the inner peripheral side of the annular portion 28 relative to the rubber packing 33, but may be positioned on the outer peripheral side.

  Further, as shown in FIG. 5, a hollow rubber packing 34 may be used instead of the low hardness rubber packing 32 of FIG. 4B, and the height of the hollow rubber packing 34 is higher than that of the rubber packing 33. To do. In this case, the packing 34 may be made of a rubber material having the same hardness as the rubber packing 33, and the hollow rubber packing 34 is more easily deformed than the solid rubber packing 33.

  FIG. 6 is a view for explaining a configuration example in which the lower end position of the steel pipe is lengthened with respect to the position of the bottom plate of the steel pipe after the placement shown in FIG. FIG. 7 is a diagram for explaining a problem when the lower end position of the steel pipe is short with respect to the position of the bottom plate of the steel pipe after the placement of FIG. It is figure (b) for demonstrating.

  As described above, by placing the steel pipe 29 and installing the bottom plate 27, the decompression space 20a can be secured. However, as shown in FIG. 6, the installation position of the bottom plate 27 and the lower end position 29a of the steel pipe 29 are provided. It is preferable that the length h between the lower surface position 27a of the bottom plate 27 and the lower end position 29a of the steel pipe 29 is equal to or greater than ½ of the diameter d of the steel pipe 29. That is, assuming that the length h is the penetration length, the penetration ratio of the steel pipe 29 (rooting length h / steel pipe diameter d) is set to 1/2 or more. The steel pipe 29 is driven and the bottom plate 27 is installed so as to obtain such a penetration ratio.

  As shown in FIG. 7 (a), when the penetration ratio of the steel pipe 29 is small (the length h between the lower surface position 27a of the bottom plate 27 and the lower end position 29a of the steel pipe 29 is short) and the ground G1 is soft, The upwardly acting buoyancy F acts on the decompression container 20 having the space 20a therein, and thus the decompression container 20 may be lifted, and the stability of the decompression container 20 is impaired. 7 is increased (the length h between the lower surface position 27a of the bottom plate 27 and the lower end position 29a of the steel pipe 29 is long), the steel pipe 29 extends in a skirt shape as shown in FIG. And since the inside is sealed, the suction force F1 works and it can resist the movement of the steel pipe 29 by the peripheral friction force F2. That is, even if buoyancy F acts on the decompression container 20 when the ground G1 is soft, the decompression container 20 is unlikely to rise, and the decompression container 20 is stabilized. In addition, it is conceivable to install a cylindrical decompression container manufactured in advance so as to be brought into the field and buried in the ground, but the stability of the decompression container 20 is higher than in such a case.

  In addition, Hiroyuki Yamazaki et al., References (Hiroyuki Yamazaki, Yoshiyuki Morikawa, Futatsuka Koike, Masakazu Deno, Takeshi Yazawa (2003): Basic experiments on suction structures, Report from the Port and Airport Research Institute, Vol.42 As shown in No. 1), a load is applied to the suction substructure under conditions where the penetration ratio represented by the penetration length / steel pipe diameter is 0.0, 1/4, 1/2, 1/1. Experiments have been conducted to investigate the relationship of displacement. As a result of the experiments, it is shown that the larger the penetration ratio, the smaller the displacement and the inclination angle with respect to the load, and the higher the stability against external force.

  FIG. 8 is a view for explaining a bottom plate installed on the bottom side of the steel pipe of FIG. 1. As described above, the bottom plate 27 installed on the bottom side of the steel pipe 29 in FIG. 1 is formed of a solidified body such as concrete, but the decompression space 20a in the decompression vessel 20 is decompressed as shown in FIG. Then, an upward force F3 acts on the bottom plate 27 due to the negative pressure, and there is a risk of heaving destruction and water leakage leakage in the bottom plate 27. In order to prevent such heaving destruction and water leakage leakage, a solidified body ( The thickness of the bottom plate 27) is preferably about 0.5 m. In addition, it is desirable to provide a tenon or the like on the inner surface of the steel pipe 29 at a position where the concrete of the bottom plate 27 and the inner surface of the steel pipe 29 are in contact with each other.

  As described above, the modes for carrying out the present invention have been described. However, the present invention is not limited to these, and various modifications can be made within the scope of the technical idea of the present invention. For example, in FIG. 1, the bottom plate 27 is not installed on the bottom side after the steel pipe 29 is cast, but a steel pipe in which the bottom plate 27 is previously installed at a predetermined position is prepared in advance to ensure airtightness and strength on the bottom side. You may do it. Moreover, although the cylindrical thing was used as a steel pipe, it is not limited to this, You may use a rectangular tube-shaped thing.

  Further, in order to further improve the airtightness in the decompression container 20 in FIG. 1, a weight is placed on the lid 30 or the upper portion of the lid 30 is covered with a viscous soil slurry or the like. May be.

  Further, whether or not the siphon is functioning in the vertical drain pipe 21 can be determined by whether or not a gas-liquid two-phase flow is formed in the pipe 21, but without depending on the measuring device. The vertical drain pipe 21 may be made of a transparent material, and the lid may be made of a transparent material so that the formation state of the gas-liquid two-phase flow can be observed and judged from the outside.

  In addition, after the water drained from the decompression vessel 20 through the drain pipe 25 is stored in the water tank, the water is returned to the drain path before reaching the vertical drain pipe 21 to increase the flow rate of water in the vertical drain pipe 21. By reducing the air mixing rate and reducing the size of the bubbles, the siphon can function stably even when air is mixed.

  Moreover, the ground improvement method of the present invention can be applied not only to the land ground but also to the water bottom ground by installing the top end and the lid of the steel pipe above the water surface.

  In addition, the decompression container of the present invention can obtain the suction force by the vacuum pump and the suction force by the siphon function, but the ground improvement by vacuum consolidation only by the suction force by the vacuum pump without using the siphon function. Of course, it can also be applied to the case of performing.

  According to the ground improvement method and the decompression container of the present invention, a decompression container that can be manufactured in the ground improvement target area and has sufficient strength and airtightness can be installed in the ground. Ground improvement by vacuum compaction combined with force can be done at low cost and with a shorter construction period.

DESCRIPTION OF SYMBOLS 1 Vacuum consolidation ground improvement system 10 Vacuum decompression device 11 Vertical drain material 20 Depressurization container 20a Decompression space 21 Vertical drain pipe (vertical pipe) 23 Vacuum pump 24 Lift pump 25 Drain pipe 26 Intake pipe 27 Bottom plate 28 Ring part (installed part) 29 Steel pipe 30 Lid 31, 32, 33 Rubber packing (airtight member) G Ground, soft ground ΔH Water level difference

Claims (7)

Placing a steel pipe having an annular portion protruding from the upper inner surface into the ground;
Removing the soil in the cast steel pipe;
Installing a bottom plate on the bottom side of the steel pipe;
The lid which penetrated the drainage pipe connected with the pumping pump housed in the steel pipe, the intake pipe connected to the vacuum pump, and the vertical pipe for functioning the siphon is placed in the annular portion of the steel pipe. And complete the decompression vessel in the ground by the process,
Next, the lid is brought into close contact with the annular portion of the steel pipe by negative pressure generated by driving the vacuum pump,
The suction water by the vacuum pump and the suction force by the siphon function of the vertical pipe are exerted to suck and drain the pore water in the ground to be improved through the vertical drain material placed on the ground. The ground improvement method.   The ground improvement method of Claim 1 which arrange | positions the airtight member which consists of an elastic body between the said cover body and the said annular part.   The ground improvement method according to claim 1 or 2, wherein a distance between a position of a bottom plate of the steel pipe and a lower end position of the steel pipe is not less than ½ of a diameter of the steel pipe. A decompression vessel that is installed in the ground and whose inside is decompressed by a vacuum pump,
A steel pipe placed in the ground as a container body;
A bottom plate provided on the bottom side of the container body;
A lid for closing the container body,
The lid body has a structure that is placed on an installation portion of the container body,
A decompression container, wherein the lid is brought into close contact with the portion to be installed by a negative pressure generated by driving the vacuum pump. The steel pipe has an annular portion provided so as to protrude from the upper inner surface thereof,
The lid is placed on the annular part with the annular part as the installation part,
The decompression container according to claim 4, wherein an airtight member made of an elastic body is disposed between the lid and the annular portion.   The decompression container according to claim 5, wherein the airtight member includes a high-height easily deformable packing and a low-height deformable packing.   The ground improvement method according to any one of claims 1 to 3, wherein the decompression container according to any one of claims 4 to 6 is installed in the ground.

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