Ground improvement methods

Abstract

To further dewater and dry the ground targeted for ground improvement in a short amount of time and with complete effectiveness. [Solution] A construction method for improving the ground 1 by causing cavitation in the water present in the gaps between soil particles, thereby causing the water to implode and generating shock waves, and removing water from the gaps between countless soil particles. Multiple first pipes 11 are installed at intervals in the ground 1, and multiple second pipes 12 for intake and supply are installed between the multiple first pipes 11. Water and air from the ground are sucked in from each of the first pipes 11, respectively, to lower the groundwater level and create an unsaturated zone in the ground. Air from the unsaturated zone is sucked in from the multiple second pipes 12 to create a negative pressure zone in the ground, and then nitrogen gas is sent into the negative pressure zone from the multiple second pipes 12 to cause cavitation in the water present in the gaps between soil particles.

Description

Technical Field

[0006] , , ,

[0005] , , ,

[0001] The present invention relates to a ground improvement method.

Background Art

[0002] According to the ground improvement method (SWP (registered trademark) method) in Patent Document 1, by pumping up saturated groundwater by negative pressure propagation, a spot reduction in the water level can be achieved, creating an unsaturated zone. Thereafter, using the vacuum pump or vortex pump of SWP, vacuum vaporization is promoted within the range of the unsaturated zone to remove moisture, and vaporizable substances such as VOCs (volatile organic compounds) and oil from the ground, and ground improvement and soil purification are advanced.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, like the conventional methods including Patent Document 1, there was a problem that only by forcibly draining groundwater by vacuum suction to form an unsaturated zone and promoting vacuum vaporization, it took a long time to dehydrate and dry the ground.

[0005] The present invention has been made in view of the above circumstances, and the problem is to dehydrate and dry the ground targeted for ground improvement more quickly and reliably.

Means for Solving the Problems

[0006] To solve the above problems, the invention described in claim 1 is a ground improvement method that improves the ground by causing cavitation in the water present in the gaps between countless soil particles, thereby causing the water to implode and generating shock waves, and removing the water from the gaps between countless soil particles, Multiple first pipes are installed at intervals in the ground exposed to the atmosphere, and multiple second pipes for intake and supply are installed between these multiple first pipes. By drawing in groundwater and air from each of the aforementioned first pipes through the lower strainer, the groundwater level is lowered, and an unsaturated zone is formed in the ground between the multiple aforementioned first pipes. The method is characterized by drawing in air from the unsaturated zone through the plurality of second pipes to create a negative pressure zone in the ground between the plurality of first pipes, and then sending nitrogen gas into the negative pressure zone from the plurality of second pipes to cause cavitation in the water present in the gaps between soil particles.

[0007] The invention described in claim 2 relates to the ground improvement method described in claim 1, The method is characterized by repeatedly performing the steps of forming a negative pressure zone and, after forming the negative pressure zone, sending nitrogen gas from the plurality of second pipes to cause cavitation in the water present in the gaps between soil particles.

[0008] The invention described in claim 3 is, in the invention described in claim 2, The method is characterized by trapping nitrogen gas in soil particles by supplying the aforementioned nitrogen gas. [Effects of the Invention]

[0009] According to the present invention, the ground targeted for ground improvement can be dewatered and dried even more quickly and reliably. [Brief explanation of the drawing]

[0010] [Figure 1]This diagram illustrates the procedure in the ground improvement method according to the present invention. [Figure 2] This diagram illustrates the procedure in the ground improvement method according to the present invention. [Figure 3] This diagram illustrates the procedure in the ground improvement method according to the present invention. [Figure 4] This diagram illustrates the procedure in the ground improvement method according to the present invention. [Figure 5] This diagram illustrates the procedure in the ground improvement method according to the present invention. [Modes for carrying out the invention]

[0011] Embodiments of the present invention will be described below with reference to the drawings. However, the embodiments described below are subject to various technically preferred limitations for carrying out the present invention, but the technical scope of the present invention is not limited to the following embodiments and illustrated examples.

[0012] In this embodiment, reference numeral 1 denotes the ground that was subjected to ground improvement. Before improvement, this ground 1 is considered to be soft ground containing a large amount of groundwater. The ground 1 comprises a lower sand layer 1a and an upper cohesive soil layer 1b. The ground is also open to the atmosphere. Reference numeral 2 denotes a large well, and multiple large wells 2 are formed in the ground 1 at predetermined intervals from each other.

[0013] Multiple first pipes 11 made of SWP are installed in the ground 1 at predetermined intervals from each other. Specifically, a first pipe 11 is installed in each of the multiple large wells 2. Furthermore, each of the multiple large wells 2 is equipped with a third pipe 13 along with the first pipe 11.

[0014] The first pipe body 11 has a water pump 11e connected to an inner pipe 11c which is connected to a water pump 11b installed at the bottom of the strainer 11a below it, via an on-off valve 11d, and a suction pipe 21a which is connected to a vacuum pump 21 installed on the ground. In the large well 2, water and air in the ground are sucked through the strainer 11a by the pumping pump 11b and the vacuum pump 21.

[0015] Here, the SWP is explained as follows. SWP is a construction method that performs forced drainage while maintaining a vacuum inside the well by making the strainer part a double pipe structure (special separate screen). The special separate screen has a double pipe structure of an inner cylinder pipe and a wound wire strainer. The groundwater flowing in from the wound wire strainer is separated into air and water between the double pipes and flows into the well through the ventilation holes at the bottom. By applying a negative pressure inside the double pipes with a vacuum pump, continuous vacuum drainage is made possible. According to this SWP, a vacuum effect can be exerted at a large depth by the special separate screen and propagated over a wide range to perform forced drainage.

[0016] As shown in FIG. 3 and the like, the third pipe body 13 is arranged along the periphery of the first pipe body 11 in a plurality of large wells 2. On the ground, a vortex blower 22 (that is, an air intake device) is connected via an intake pipe 22a. This vortex blower 22 sucks only gas.

[0017] Also, as shown in FIGS. 2 to 5, a plurality of second pipe bodies 12 are embedded in the ground so as to be located between (inside) a plurality of first pipe bodies 11. There are cases where a plurality of second pipe bodies 12 are connected to the vortex blower 22 via an intake pipe 22a on the ground and cases where a large compressor 23 (that is, an air supply device) is connected via an air supply pipe 23a. When the vortex blower 22 is connected (see FIG. 3), the plurality of second pipe bodies 12 are used for intake, and when the large compressor 23 is connected (see FIGS. 2 and 4), they are used for the supply of air or nitrogen gas. The plurality of second pipe bodies 12 include a fixed second pipe body 12a fixedly embedded and installed in the ground 1, and a movable second pipe body 12b held by a boring machine (see FIG. 5) and slid upward and pulled up by about 0.5 m at a time.

[0018] Furthermore, as shown in FIG. 5, a fourth pipe body 14 is embedded in the ground so as to be located between (inside) the plurality of first pipe bodies 11 in the ground 1. The embedding of the fourth pipe body 14 is performed by a large-diameter boring machine 24. The large-diameter boring machine 24 is movable, and the fourth pipe body 14 held by the large-diameter boring machine 24 can change the embedding location. Since the fourth pipe body 14 is a pipe body, it not only has openings at the top and bottom, but also has a plurality of through holes formed in the cylinder wall. Also, on the ground, a large compressor 23 is connected to the fourth pipe body 14 via an air supply pipe 23a. That is, the fourth pipe body 14 can supply air or nitrogen gas not only from its lower end but also from the middle part thereof.

[0019] Also, in the present embodiment, as shown in FIGS. 4 and 5, an overlying load by a fill 3 (also referred to as a planned fill) is loaded on the ground 1. The fill 3 is loaded on the ground 1 as an overlying load when the groundwater level drops and the interstitial water between soil particles is replaced with nitrogen gas. Due to this overlying load, the soil particle skeleton is compressed and settlement is promoted, increasing the ground strength. Although the consolidation of the ground 1 can be promoted only by the fill 3, as shown in FIG. 5, the overlying load may be loaded by construction machines such as a vibrating roller 25 or a bulldozer to promote the consolidation of the ground 1.

[0020] Hereinafter, the ground improvement method will be described in more detail.

[0021] First, as shown in Figure 1, multiple first pipes 11 are used to spot depressurize the groundwater in the upper cohesive soil layer 1b and the lower sand layer 1a of the ground 1 by negative pressure propagation. In other words, by pumping saturated groundwater using multiple first pipes 11 by negative pressure propagation, it is possible to concentrate the water level reduction (from the natural water level OWL to the drywork water level DWL) mainly in the target area, and to form an unsaturated zone. When pumping by negative pressure propagation in this way, unlike gravity drainage, well loss is minimized and the water level is reduced efficiently. Also, since it is not necessary to reduce the water level over a wide area, it is possible to reduce the water level efficiently with a small amount of pumping.

[0022] Next, as shown in Figure 2, a large amount of water and a large compressor 23 are used to pump water and air into the ground 1. After that, the air and water are removed by vacuum suction, and then clay, colloids, and heavy metals are removed before the water is pumped up, creating negative pressure in the ground 1. Repeat this process several times (for example, about three times). By using the first pipe 11 and the second pipe 12, water and air are drawn in through the first pipe 11, and air is pumped in through the second pipe 12, thereby reducing well losses. In addition, a movable second pipe 12b is used to create a uniform water channel (water passage) underground. By creating a vein-like water channel, the permeability coefficient (k) is improved macroscopically.

[0023] Next, as shown in Figure 3, air is drawn in through the second pipe 12 and third pipe 13 connected to the vortex blower 22, creating a vacuum (negative pressure) on the top of the sand layer 1a and the cohesive soil layer 1b. This lowers the boiling point of water, causing the pore water to expand approximately 1700 times as water vapor, which is then drawn out to the surface and discharged, drying the ground 1.

[0024] Next, as shown in Figure 4, nitrogen gas is pumped into the sand layer 1a by a large compressor 23, and the cohesive soil of the cohesive soil layer 1b is compressed by the uplift pressure (U) indicated by the upward arrow U in Figure 4, and then the ground 1 is compressed and settled by negative pressure suction. In other words, since the ground 1, which has been hollowed out by vacuum vaporization, will not settle much on its own, nitrogen gas is sent to the top of the sand layer 1a by a large compressor 23, generating an uplift pressure (U) due to the gas pressure. Furthermore, the cohesive soil layer 1b is compressed evenly and directly by the movable second pipe 12b. Subsequently, the entire structure is subjected to vacuum vaporization, thereby inducing compressive settlement of the ground 1 due to atmospheric pressure and the superimposed load of the embankment 3.

[0025] By supplying nitrogen gas from multiple second pipes 12 to the negative pressure zone (the top of the sand layer 1a and the cohesive soil layer 1b), cavitation can be induced in the water (pore water) present in the pores between soil particles. Furthermore, by supplying nitrogen gas from the fourth pipe 14, which is embedded by the large-diameter boring machine 24, even more cavitation can be induced.

[0026] When the earth is placed in a vacuum, the boiling point of water decreases, causing it to boil and turn into steam at a lower temperature. At this time, if pressurized nitrogen gas is introduced from the outside, bubble collapse, or cavitation, occurs. Here, "cavitation" refers to the phenomenon in which bubbles collapse immediately after implosion, generating a shock wave (see arrow Sw) outward. In the case of water, this shock wave is equivalent to a pressure of 1,000 to 10,000 atmospheres per micron, and can cause erosion even in metals.

[0027] Within the soil particles that make up the ground, there are voids that allow air, gas, and water to enter. Such a structure (soil particle skeleton) is called a single-grain structure, honeycomb structure, or cottony structure. By removing moisture from the voids between soil particles, liquefaction and landslides can be prevented. In this embodiment, cavitation can be induced during the process to further enhance the effect of vacuum suction. In particular, wood drying experiments showed that introducing nitrogen gas reduced the introduction time by 1 / 4 compared to introducing air. Furthermore, the shock waves exert a compaction effect on the ground, making it possible to strengthen the ground as well. Furthermore, the water vapor cavity subsequently implodes due to water pressure and soil pressure, generating a large impact. In this embodiment, the entire underground area is under negative pressure, and water vapor can be recovered to the surface by the vortex blower 22. After a period of time, if nitrogen gas is then introduced into the ground, this implosion will begin, creating an impact on the ground. In other words, by creating a vacuum in the ground 1 using the vacuum pump 21 and the vortex blower 22, and maintaining that state while supplying nitrogen gas with the large compressor 23, cavitation is induced, effectively drying out the ground 1 and improving the ground. Furthermore, wood experiments have confirmed that using nitrogen gas can reduce drying time by another quarter of the sag compared to using air. It is preferable to repeat the supply of nitrogen gas multiple times.

[0028] Furthermore, cavitation is induced to improve the ground 1, and at the same time, a superimposed load is applied using a vibratory roller 25 to promote consolidation of the ground 1 and increase its strength. Afterward, the suction by the vacuum pump 21 is stopped to restore the groundwater, but even after the groundwater is restored, the ground 1 remains compressed and does not become soft ground.

[0029] According to this embodiment, by sucking in water and air from the ground through the lower strainer 11a from each first pipe 11, the groundwater level is lowered, forming an unsaturated zone in the ground between the multiple first pipes 11. By sucking in the air from the unsaturated zone through the multiple second pipes 12, a negative pressure zone is formed in the ground between the multiple first pipes 11. Then, by sending nitrogen gas from the multiple second pipes 12 into the negative pressure zone, cavitation CVT is caused in the water present in the gaps between soil particles. This applies an impact force due to cavitation, drawing water out from the gaps between soil particles, and allowing the ground 1 to be dewatered and dried quickly and reliably. Furthermore, the impact force due to cavitation exerts a compaction effect on the ground 1, making it possible to strengthen the ground 1 as well.

[0030] Furthermore, since the process of forming a negative pressure zone and the process of sending nitrogen gas from multiple second pipes 12 after the formation of the negative pressure zone to cause cavitation in the water present in the gaps between soil particles are repeated, the dewatering and drying of the ground 1 can be performed more quickly and reliably.

[0031] Furthermore, by sending nitrogen gas from multiple second pipes 12 after creating a negative pressure zone, the nitrogen gas is trapped in the soil particles. Once the nitrogen gas is trapped, even if the groundwater level is restored, most of the nitrogen gas remains, permanently trapping and stabilizing the soil. Moreover, during earthquakes, the trapped nitrogen gas prevents excessive pore water pressure, making it an effective measure against liquefaction.

[0032] (modified version) The ground improvement method described above for ground 1 is not only effective in improving soft ground, but also in preventing liquefaction of ground 1, preventing landslides on mountain slopes, and contributing to soil purification.

[0033] Furthermore, in the above embodiment, nitrogen gas was introduced into the ground 1 during the and cohesive soil compression process, but it may also be introduced after the ground negative pressure process and before the cohesive soil compression process. [Explanation of Symbols]

[0034] 1 ground 1a sand layer 1b Clay layer 2. Large well 3. Embankment 11 First tube 11a Strainer 11b Water pump 11c inner tube 11d Shut-off valve 11e Water pumping pipe 12. Second section 12a Fixed second tube 12b Movable second tube 13. Third section 14. Fourth Instrument 21 Vacuum pump 21a Suction tube 22 Vortex Blower 22a Intake pipe 23 Large compressors 23a Air supply tube 24 Large-diameter boring machines 25 Vibration Roller

Claims

1. A ground improvement method that improves the ground by causing cavitation in the water present in the gaps between countless soil particles, thereby imploding the water and generating shock waves, and removing the water from the gaps between the countless soil particles, Multiple first pipes are installed at intervals in the ground exposed to the atmosphere, and multiple second pipes for intake and supply are installed between these multiple first pipes. By drawing in groundwater and air from each of the aforementioned first pipes through the lower strainer, the groundwater level is lowered, and an unsaturated zone is formed in the ground between the multiple aforementioned first pipes. A ground improvement method characterized by drawing in air from the unsaturated zone through the plurality of second pipes to form a negative pressure zone in the ground between the plurality of first pipes, and then sending nitrogen gas into the negative pressure zone from the plurality of second pipes to cause cavitation in the water present in the gaps between soil particles.

2. The ground improvement method according to claim 1, characterized by repeatedly performing the steps of forming a negative pressure zone and, after forming the negative pressure zone, sending nitrogen gas from the plurality of second pipes to cause cavitation in the water present in the gaps between soil particles.

3. The ground improvement method according to claim 2, characterized in that nitrogen gas is trapped in soil particles by supplying the aforementioned nitrogen gas.

Images