JP5388193B2 - Suction force generator and vacuum consolidation ground improvement method - Google Patents

Description

  The present invention relates to a suction force generation device using a siphon function and a vacuum consolidation ground improvement method using the suction force generation device.

  2. Description of the Related Art 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, a method of promoting the consolidation of the ground by placing a vertical drain in soft ground and then depressurizing the ground by applying a negative pressure using a vacuum pump suction device (vacuum) The consolidation ground improvement method) is used (for example, refer to Patent Documents 1 to 4).

JP 2001-226951 A JP 2002-138456 A JP 2003-261929 A JP 2000-328550 A

  A conventional vacuum pump suction device relies only on the capacity of the vacuum pump to perform suction. For this reason, according to the conventional suction device, the suction force which promotes compaction beyond the capability of the vacuum pump cannot be applied. For this reason, when the suction force is insufficient with the vacuum pump alone in the conventional vacuum consolidation method for soft ground, it is necessary to use loading with embankment in combination.

  In addition, regarding a suction device that uses the force of the vacuum pump and the force due to the difference in the water surface position, a method for reducing the volume of the soft bottom has been proposed for the purpose of suctioning pore water in the ground below the water surface (Patent Document). 3). In this conventional technology, since the water surface is higher than the ground where the pore water is to be sucked, the compressive force due to the water pressure acts to squeeze the pore water, and the ground to be improved is in the water. It is applicable only under the condition that the ground surface position is lower than the water level of the drainage section (decompression chamber). This conventional method does not assume that the ground to be improved is on land, and the hose guided from the top end position of the improved ground surface is coupled to the side surface of the decompression chamber.

  Under conditions that apply a large suction force, it is necessary to consider the vaporization of dissolved oxygen, etc., and the presence of gas flowing in from the airtight leak of the water pipe. By simply changing the shape of the pipe and connecting the pipe vertically from the top, the water and gas flows are separated, so the suction force according to the siphon principle does not work. That is, when the land on the ground is targeted, according to the prior art, it has not been possible to exert a suction force exceeding the capacity of the vacuum pump.

  An object of this invention is to provide the attraction | suction force generator which can generate | occur | produce the attraction | suction force according to the principle of siphon even when gas is contained in water. It is another object of the present invention to provide a vacuum consolidation ground improvement method capable of promoting vacuum consolidation in ground improvement and realizing reduction or omission of loading due to embankment and shortening of the ground improvement period.

In order to achieve the above object, the suction force generator according to the present embodiment includes a first pipe extending from the upper part toward the lower part, and a second pipe connected to the first pipe at the upper part and extending in the horizontal direction. And a difference in water level between the lower end side of the first tube and the front end side of the second tube, from the front end of the second tube toward the lower end of the first tube. A suction force generating device for applying a suction force by a siphon function to improve the ground by vacuum consolidation , wherein a diameter of the first tube is smaller than a diameter of the second tube, and the second tube And the first pipe are connected via a gradually reducing connection pipe having a diameter that gradually decreases, and air existing separately from water in the second pipe becomes bubbles in the gradually reducing connection pipe. of to generate a suction force by siphon function by flowing down as a gas-liquid two-phase flow within the tube, the lower end of the first tube A sealed chamber for storing, a vacuum pump for depressurizing the sealed chamber, and a drainage facility for draining stored water in the sealed chamber to the outside, and by depressurizing the sealed chamber by the vacuum pump, The suction force by the siphon function is added to the suction force, the stored water in the sealed chamber is drained by the drainage facility, and the lower end of the first pipe is positioned below the water level of the stored water in the sealed chamber. It is characterized by.

  According to this suction force generating device, the diameter of the first pipe extending from the upper part toward the lower part is made smaller than the diameter of the second pipe extending in the horizontal direction, and the diameters of the second pipe and the first pipe are reduced. By connecting through the gradually reducing connection pipe where the pressure gradually decreases, the air that is separated from the water in the second pipe becomes bubbles in the water in the gradually reducing connection pipe, and the gas-liquid two-phase flow in the first pipe It can flow stably and can generate a suction force by the siphon function, and can suck water containing air from the tip of the second tube and drain it from the lower end of the first tube. For this reason, even when gas is contained in water, the suction force according to the siphon principle can be stably generated.

  A gas-liquid two-phase flow bubble flowing out from the lower end of the first pipe in the suction force generating apparatus includes an air backflow prevention device for preventing the bubbles from rising again and flowing back into the first pipe; The backflow of bubbles to the first tube can be prevented, and the gas-liquid two-phase flow of water and air flows stably, contributing to the maintenance of a stable siphon function.

  Further, it is preferable that the gradually reducing connecting pipe is linearly inclined and the inner diameter is gradually reduced, and the gradually reducing angle θ is 45 ° or less when an extension line extending downward from the inclined line intersects. When the taper angle θ is 45 ° or less, the loss of flow energy is reduced, and the flow becomes smooth.

  The suction force generator is preferably used in combination with a power device using a vacuum pump. Thereby, when a siphon function stops, the restart can be performed easily.

  The vacuum consolidation ground improvement method according to the present embodiment is characterized in that ground improvement by vacuum consolidation is performed on soft ground using the above-described suction force generator.

  According to this vacuum consolidation ground improvement method, the vacuum consolidation in the ground improvement can be promoted by using the suction of the siphon function by the above-described suction force generator together, and the load due to the embankment can be reduced or omitted. Therefore, it is possible to reduce the amount of materials and equipment used and shorten the work period, and the suction force increases compared with the conventional vacuum consolidation method, so the ground improvement period required for the soft ground to reach the specified strength is shortened. can do.

  In the suction force generating device, the first tube may be installed so as to extend in the vertical direction, but is not limited to the one installed in the vertical direction, and may be installed at an inclination.

  According to the suction force generator of the present invention, suction force according to the siphon principle can be stably generated even when gas is contained in water.

  According to the vacuum consolidation ground improvement method of the present invention, by using the above suction force generator together with a vacuum pump, vacuum consolidation in ground improvement can be promoted, load reduction or omission due to embankment and ground improvement period Can be shortened.

It is the figure (a) which shows schematically the structure of the attraction | suction force generator by 1st Embodiment, and a principal part enlarged view (b). It is a schematic diagram for demonstrating the flow of the water and air in the taper connection pipe | tube of the attraction | suction force generator of FIG. It is a schematic diagram for demonstrating the state which cannot implement | achieve the flow of the water and air by a siphon function. 3 and 4 are schematic diagrams for explaining another state in which the flow of water and air by the siphon function cannot be realized. It is a figure which shows the swirling gas-liquid two-phase flow (the amount of air is small on the left side and large on the right side) with an inner diameter of 30 mm (Kobe City National College of Technology Education Research Seeds (http://www.kobe-kosen.ac. jp / kyoudou / seeds / pdf / M / M_shakutui.pdf) [Study on water flow including bubbles (gas-liquid two-phase flow)]). It is a figure which shows roughly the structure of the vacuum consolidation ground improvement system which performs the vacuum consolidation ground improvement construction method by 2nd Embodiment. FIG. 6A is a diagram showing a main part for explaining the function and effect of the air backflow prevention device provided at the lower end of the vertical water pipe of FIG. 6 and FIG. 6B is a diagram for explaining a problem occurring at the lower end of the vertical water pipe. is there. It is a figure which shows roughly the structure of the vacuum consolidation ground improvement system which performs the vacuum consolidation ground improvement construction method by 3rd Embodiment. It is a figure which shows roughly the experimental apparatus used in the present Example. In Comparative Example 1, each position St. was measured under the conditions of a flow rate of 0.7 m / sec and an air mixing rate of 0%. A to St. 6 is a graph showing a change in the working negative pressure according to E with time. In Comparative Example 2, St. at the lowermost portion measured under conditions of a flow rate of 0.7 m / second and an air mixing rate of 5%. Each position St. with reference to the pressure of A. B to St. 6 is a graph showing a change in elapsed time of a pressure deviation in E. In the examples, the St. at the bottom was measured under conditions of a flow rate of 0.7 m / sec and an air mixing rate of 10%. Each position St. with reference to the pressure of A. B to St. 6 is a graph showing a change in elapsed time of a pressure deviation in E. In Comparative Example 3, the St. at the bottom was measured under the conditions of a flow rate of 0.7 m / sec and an air mixing rate of 10%. Each position St. with reference to the pressure of A. B to St. 6 is a graph showing a change in elapsed time of a pressure deviation in E. In an Example and Comparative Examples 1-3, it is a graph which shows the relationship between an air mixing rate when a flow velocity is 0.4 m / sec, and a pressure deviation. In an Example and Comparative Examples 1-3, it is a graph which shows the relationship between an air mixing rate when a flow velocity is 0.7 m / sec, and a pressure deviation. It is a figure for demonstrating the energy loss in the case of the rapid contraction pipe | tube in which the diameter of a pipe | tube reduces rapidly. FIG. 17 is a table showing the loss coefficient f _sc in the case of the sudden contraction tube in FIG. 16 in relation to the area ratio A1 / A2 before and after the rapid expansion (see “The Hydraulics Official Collection” edited by the Japan Society of Civil Engineers (1999), page 374). . In the case of a gradually reduced tube with a gradually decreasing tube diameter, it is a graph showing the relationship between the loss factor and the angle θ for each area ratio A1 / A2 (Yoshiro Iwasa, Asakura Civil Engineering Course 3, Asakura Publishing, page 268).

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

<First Embodiment>
FIG. 1A is a diagram schematically illustrating a configuration of a suction force generator according to the first embodiment, and FIG. FIG. 2 is a schematic diagram for explaining the flow of water and air in the gradually reducing connection pipe of the suction force generator of FIG. 3 and 4 are schematic views for explaining a state in which the flow of water and air by the siphon function cannot be realized. In addition, the vertical direction of FIGS. 1-4 is a vertical direction, and a horizontal direction is a horizontal direction.

  The suction force generator of FIG. 1A is a vertical pipe 1 that is a first pipe extending in the vertical direction from the upper part toward the lower part, and a horizontal pipe that is a second pipe extending in the horizontal direction above the vertical pipe 1. The pipe 2 and the taper connecting pipe 3 disposed on the vertical pipe 1 and connected to the horizontal pipe 2 are provided. The vertical pipe 1 and the horizontal pipe 2 are formed of a cylindrical pipe. The inner diameter of the vertical pipe 1 is smaller than the inner diameter of the horizontal pipe 2, and the cross sectional area of the vertical pipe 1 is smaller than the cross sectional area of the horizontal pipe 2.

  The gradually reducing connection pipe 3 is configured such that the inner diameter thereof gradually decreases toward the lower side on the upper side of FIGS. The upper pipe 3a is connected to the horizontal pipe 2 on the upper side, and is connected to the vertical pipe 1 having an inner diameter smaller than that of the upper pipe 3a on the lower side. As shown in FIG. 1B, the gradually reducing connecting pipe 3 has an inner surface linearly inclined and an inner diameter gradually decreasing, and extension lines 1a and 1b extending downward from the inclined line intersect to form an included angle (angle θ). The angle (gradual reduction angle) θ is preferably 45 ° or less (θ ≦ 45 °).

  As shown in FIGS. 1 (a) and 1 (b), the suction force generator of this embodiment determines the diameter of the vertical tube 1 to be smaller than that of the horizontal tube 2, and the inner diameter gradually contracts at a contraction angle θ of 45 ° or less. By connecting the horizontal pipe 2 and the vertical pipe 1 having a small diameter by using the gradually reducing connecting pipe 3 having a structure, a gas-liquid two-phase flow in which water and gas are mixed in the vertical pipe 1 is stably formed. , Make the siphon work.

  As shown in FIG. 1 (a), when the lower end 1a of the vertical pipe 1 is in water, the vertical pipe 1 has a siphon function due to the water level difference ΔH between the drainage surface and the water surface on the tip 2a side of the horizontal pipe 2. When a suction force is generated on the lower end 1a side, water flows in the direction f indicated by the broken line. When the drainage surface of FIG. 1 does not reach the lower end 1a of the vertical pipe 1, the siphon function caused by the water level difference between the lower end 1a of the vertical pipe 1 and the water surface on the front end 2a side of the horizontal pipe 2 causes vertical A suction force is generated on the lower end 1 a side of the tube 1.

Next, the principle of the suction force generator of this embodiment will be described. The bubble rising speed ν _a due to buoyancy can be evaluated by the following equation (1) based on the balance between buoyancy and drag.

ν _a = [8 gr _a / (3C _D )] ^0.5 (1)

Here, r _a is the radius of the bubble, the size of the bubble can be a half of the pipe diameter at the maximum. Also, C _D is the drag coefficient is given by 0.5.

When the water flow cross-sectional area of the pipe is A, the maximum bubble radius ra _(max) can be expressed by the following equation (2).

r _{a (max)} = (A / π) ^0.5 (2)

When the flow rate of water flowing into the vertical pipe is Q, the flow velocity ν _w of the water flowing down the vertical pipe can be evaluated by the following equation (3).

ν _w = Q / A (3)

  The above equation (3) indicates that the flow velocity increases when the inner diameter of the vertical pipe is reduced and the cross-sectional area of water flow is reduced with respect to the flow rate flowing from the horizontal pipe.

Here, in the vertical pipe, by providing a vertical pipe structure such that the flow velocity of water flowing down the vertical pipe ν _w > the rising speed ν _a of the bubbles, the bubbles are entrained in the flow of water, and the gas-liquid mixed phase flow ( Since the gas-liquid two-phase flow) is formed, the siphon functions.

In order to satisfy the above condition of ν _w > ν _a , the following configuration can be considered.
(1) The inner diameter of the vertical pipe is reduced, the maximum diameter of bubbles that can be formed is reduced, and the rising speed of the bubbles is suppressed (Equations (1) and (2)).
(2) Decreasing the inner diameter of the vertical pipe to increase the water flow rate (Formula (3)).
(3) by devising the vertical pipe structure, bubbles micro, reduced by Miribaburu by the (smaller radius r _a of the bubble), suppress the rising speed of the bubbles (formula (1)).

  The suction force generator of the present embodiment has a vertical tube structure that has both the effects (1) to (3). According to the experiments and examinations by the present inventors, the siphon function is maintained even under a high air mixing rate by the vertical pipe structure having the gradually reducing connecting pipe 3 as shown in FIG. I got the knowledge that I can do it.

  As shown in FIG. 5, when a liquid is introduced from the circumferential direction of the circular tube and a gas is introduced at the same time, a gas-liquid two-phase flow flows like a vortex, and a large column of air is formed as the amount of air increases. . That is, as shown in FIGS. 3 and 4, when water and air flow down from the horizontal pipe toward the vertical pipe, if a certain amount of air is mixed in, a column of air is naturally formed in the vertical pipe. This phenomenon occurs similarly even if the diameter of the vertical pipe is reduced as a whole. Therefore, since the siphon is interrupted by the air column, it is necessary to change the air column to fine bubbles.

Therefore, in the present embodiment, the air is changed to micro and milli bubbles by hitting the water flow along the inner wall surface of the upper pipe 3a against the air column in the gradually reducing connection pipe 3 provided in the middle of the vertical pipe 1 as shown in FIG. is, to reduce the radius r _a of the bubble, so that uninterrupted siphon function.

  That is, as shown in FIG. 2, a frictional force (A below) acts on the interface between the flow of water and air, so that in the process that the water gathering at the center along the inner wall flows down to the thin pipe, It is made into micro and milli bubbles by flowing through and flows down together with water.

τ = ρ _a fu ² (A)
Where τ is the frictional force, ρ _a is the density of air, f is the coefficient of friction (a size of about 1 × 10 ⁻³ ), and u is the relative velocity of the air and water flow (Keiji Horikawa “Coastal Engineering” − (Introduction to marine engineering-see the University of Tokyo Press, page 317).

As described above, when water and air flow from the horizontal pipe 2 toward the vertical pipe 1, a column of air is formed at the substantially central portion in the upper pipe 3a and a water flow is formed along the inner wall surface. However, when the diameter of the connecting pipe 3 gradually decreases, the water flow becomes one, collides with an air column, and the air is sheared by a frictional force to form micro and millibubbles. _w > Satisfies the siphon function by satisfying the above condition of the bubble rising speed ν _a , and the micro- and milli-bubbled bubbles are mixed in water and stably flow as a gas-liquid two-phase flow. be able to.

  According to the suction power generation device of the present embodiment, when water containing air is drawn from the horizontal pipe 2 to the vertical pipe 1 by the siphon function, a gas-liquid two-phase flow of water and air can be efficiently generated. The suction force can be generated stably by making the siphon function. When a siphon is used as a suction force, the siphon function is easily degraded when the amount of air mixed in with water is large. However, according to the present embodiment, the siphon function can be achieved even when the amount of mixed air is about 40% at the maximum. You can be uninterrupted.

  The air bubbles are easily coupled to each other, re-floating in the vertical pipe 1 and trying to flow backward, so that an air backflow prevention device that prevents the air bubbles from flowing back to the vertical pipe 1 (see FIGS. 6 and 7A). ) Is preferably provided.

  Further, in the suction power generation device of FIG. 1, the region where the gas-liquid two-phase flow is formed is in the vertical pipe 1 having a small inner diameter after passing through the gradually reducing connecting pipe 3. For this reason, in order to exert the siphon suction force more strongly in a limited vertical space, the length m of the gradually reducing connecting pipe 3 is 1 / of the length n of the vertical pipe 1 as shown in FIG. It is desirable to set it to about 3 or less (about 1/4 or less of the total length (m + n) of the vertical pipe 1 and the taper connecting pipe 3).

  In addition, the suction force generator of FIG. 1A is preferably used in combination with a vacuum pump power unit in consideration of a case where the siphon is restarted after the siphon function is temporarily stopped.

Next, the reason why the gradually reducing connecting pipe 3 is configured as the gradually reducing type will be described with reference to FIGS. The negative pressure generated by the siphon function in the vertical pipe can be evaluated using Bernoulli's theorem (energy equation). That is, the negative pressure head h _suction at the upper end _relative to the lower end in the vertical pipe can be expressed by the following equation (4).

h _suction = (p ₁ -p ₂ ) / (ρg)
= − (V ₁ ² −v ₂ ² ) / (2 g) − (z ₁ −z ₂ ) + h _loss (4)

Where ρ is density, g is gravitational acceleration, p is water pressure, v is flow velocity, z is vertical coordinates (upward is positive), h _loss is energy loss head, and subscripts 1 and 2 are upper end position and lower end position, respectively. Indicates.

In the above equation (4), it can be seen that (z ₁ −z ₂ ) increases as the distance between the upper end and the lower end increases, and the negative pressure increases. Further, it can be seen that when the energy loss when flowing vertically downward is large (when h _loss is large), the generated negative pressure becomes small. That is, in order to effectively generate the negative pressure, it is important to guide the flow smoothly and reduce energy loss as much as possible.

Here, in the case of a rapidly contracting tube in which the diameter of the tube is suddenly reduced, energy loss occurs because streamline separation occurs as shown in FIG. The energy loss head at this time can be expressed by the following equation (5).
h _loss = f _sc × v ₂ ² / (2 g) (5)

However, v ₂ is a flow velocity flowing through the reduced tube, f _sc is a loss coefficient, and takes values as shown in FIG. 17 according to the area ratio A1 / A2 (FIG. 16) before and after the rapid expansion.

On the other hand, in the case of a gradually contracting tube in which the diameter of the tube gradually decreases as shown in FIG. According to past research results, the loss factor f _sc of the gradually contracted tube is obtained as shown in FIG. 18, and it can be seen that the gradually reduced loss factor is considerably smaller than that of the rapidly contracted tube of FIG.

  As described above, in order to effectively generate a negative pressure while suppressing energy loss, it is desirable that the connecting pipe 3 in FIGS. 1A and 1B be a gradually contracting type (gradually contracting connecting pipe). In addition, according to the experiments by the present inventors, it is desirable that the taper angle θ is 45 ° or less, the flow energy loss is small, the flow becomes smooth, and the negative pressure is effectively generated. it can.

<Second Embodiment>
FIG. 6 is a diagram schematically showing the configuration of a vacuum consolidation ground improvement system that performs the vacuum consolidation ground improvement method according to the second embodiment. FIG. 7 is a diagram (a) showing a main part for explaining the function and effect of the air backflow prevention device provided at the lower end of the vertical water pipe shown in FIG. 6 and a diagram for explaining a problem occurring at the lower end of the vertical water pipe ( b).

  The vacuum consolidation ground improvement system S1 of FIG. 6 includes a suction force generator having a vertical water pipe 21 and a horizontal water pipe 22, and a vacuum decompression device 20 indicated by a broken line in the figure, for improving the vacuum consolidation ground. A vertical drain 31 placed in the soft ground G is connected to the horizontal water pipe 22 through the air-impermeable portion 32 and the connection portion 33, and the horizontal water pipe 22 includes the vertical water pipe 21 and the vertical water pipe. 21 is connected at the upper end.

  The vertical water pipe 21 extends in the vertical direction and reaches the vicinity of the bottom surface 26a of the sealed chamber 26 installed in the basement. A bent pipe 28 is attached to the lower end of the vertical water pipe 21, and the distal end of the bent pipe 28 is the sealed chamber. 26 is below the water level H1 at the bottom. Moreover, the vertical water pipe 21 and the horizontal water pipe 22 are each formed of a cylindrical pipe, and the inner diameter of the vertical water pipe 21 is smaller than the inner diameter of the horizontal water pipe 22.

  The vacuum decompression device 20 includes a vacuum pump 23, a pumping pump 24 and a drain pipe 25 which are drainage facilities, and a sealed chamber 26 installed in the underground. The sealed chamber 26 accommodates the vertical water pipe 21, the pumping pump 24, and the drain pipe 25, and is decompressed by the vacuum pump 23 so that the vacuum decompression device 20 functions as a decompression generation source.

  The vertical drain material 31 is placed in the soft ground G to suck pore water in the soft ground G, and the air-impermeable portion 32 connected to the upper end of the vertical drain material 31 is located on the groundwater level surface H0. . Note that a plurality of vertical drain members 31 are placed in the soft ground G as necessary, and the configurations disclosed in Patent Documents 1 to 3, for example, together with the air-impermeable portion 32 and the connection portion 33. it can.

  As shown in FIG. 6, the vacuum consolidation ground improvement system S <b> 1 has an air backflow prevention device including a bent pipe 28 configured to bend about 90 ° from the vertical direction at the lower end of the vertical water pipe 21. As shown in FIG. 7A, the gas-liquid two-phase flow flowing in the vertical direction b ′ from the vertical water flow pipe 21 flows in the bending pipe 28 in the horizontal direction b ″ in the drawing and is discharged from the bending pipe 28, and the bubble e Rises to the water surface of the sealed chamber 26.

  Without the air backflow prevention device, as shown in FIG. 7B, when the gas-liquid two-phase flow is discharged from the lower end of the vertical water pipe 21 in the vertical direction b ′, it hits the bottom surface 26 a of the sealed chamber 26 and is reversed. In contrast to bb, the momentum disappears, the bubble e tries to re-float, and there is a possibility that it will combine with the bubble e flowing from the vertical direction b ′ and flow backward in the vertical water pipe 21. ) To change the flow direction of the gas-liquid two-phase flow to the lateral direction b ″ and to reliably discharge the bubbles e into the sealed chamber 26, as shown in FIG. The gas-liquid two-phase flow flows stably and can contribute to the stable maintenance of the siphon function.

  The vacuum consolidation ground improvement method by the vacuum consolidation ground improvement system S1 of FIG. 6 will be described. In addition to the suction force generated by reducing the pressure in the sealed chamber 26 by the vacuum pump 23 of the vacuum decompression device 20, the groundwater level surface H0 and the sealed chamber. The suction force by the siphon function due to the water level difference ΔH (= H0−H1) with the water level surface H1 in 26 is generated, and the soft ground G is sucked by sucking the pore water in the soft ground G by these suction forces. Consolidate. 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.

  According to the conventional vacuum consolidation ground improvement method, when the suction force is insufficient with only the vacuum pump, loading by embankment was used together, but by using the suction force by siphon function as in this embodiment Because loading due to embankment can be reduced or omitted, 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.

  The suction power generation device according to the present embodiment includes a vertical water pipe 21 and a horizontal water pipe 22 that is connected to the vertical water pipe 21 at an upper portion and extends in the horizontal direction. Due to the water level difference from the front end side of the water pipe 22, a suction force acts by a siphon function from the front end of the horizontal water pipe 22 toward the lower end of the vertical water pipe 21, and the water flow cross-sectional area of the vertical water pipe 21 is horizontal. It is configured to be smaller than the cross-sectional area of the water pipe 22, and the air that is separated from the water in the horizontal water pipe 22 becomes bubbles in the vertical water pipe 21 and flows down as a gas-liquid two-phase flow. The suction force is generated by the siphon function. In the present embodiment, a gas-liquid two-phase flow in which water and gas are mixed in the vertical water pipe 21 is formed in order to make the siphon function even under conditions where the horizontal water pipe 22 includes air. Importantly, preferably, the inner diameter of the vertical water pipe 21 is 50% or less of the inner diameter of the horizontal water pipe 22 (when the inner diameter of the horizontal water pipe 22 exceeds 0.1 m) or 70% or less (the inner diameter of the horizontal water pipe 22). Is 0.1 m or less). Moreover, it is preferable to provide an air backflow prevention device as shown in FIG.

  The lift pump 24 is preferably a high head type with a head difference of 10 m or more, the sealed chamber 26 is installed deep in the ground, and the water level surface H1 in the sealed chamber 26 with respect to the ground water level surface H0 is secured to ensure the water level difference ΔH. Even if it is made lower, the stored water in the sealed chamber 26 can be drained.

<Third Embodiment>
FIG. 8 is a diagram schematically showing the configuration of a vacuum consolidation ground improvement system that performs the vacuum consolidation ground improvement method according to the third embodiment.

  The vacuum consolidation ground improvement system S2 of FIG. 8 has basically the same configuration as that of FIG. 6 except that the suction force generator is configured as shown in FIG. That is, a gradually reducing connection pipe 3 similar to that shown in FIG. 1 is disposed between the horizontal water pipe 22 and the vertical water pipe 21 having an inner diameter smaller than that of the horizontal water pipe 22, and the upper pipe 3 a of the gradually reduced connection pipe 3 is connected horizontally. It is connected to the water pipe 22. An air backflow prevention device comprising a bent pipe 28 similar to that shown in FIGS. 6 and 7A is provided at the lower end of the vertical water pipe 21 so that the bubbles e can be reliably discharged to the outside from the bent pipe 28. In addition, a gas-liquid two-phase flow of water and air can stably flow in the vertical water pipe 21 and contribute to the stable maintenance of the siphon function.

  8, in addition to the suction force by the vacuum pump 23, the water level difference ΔH (= H0−H1) between the ground water level surface H0 and the water level surface H1 in the sealed chamber 26, as in FIG. Although the vacuum consolidation ground improvement method can be executed by using the suction force generated by the siphon function caused by the above, the suction force generation device of FIG. Since the taper connection pipe 3 is provided in the vertical water pipe 21, the gas-liquid two-phase flow of water and air can be efficiently generated, and the suction force can be stably generated without interrupting the siphon function. Suction force can be efficiently applied to soft ground. For this reason, the vacuum consolidation ground improvement method can be stably executed, and the ground improvement period required until the soft ground reaches a predetermined strength can be shortened.

  EXAMPLES Next, although an Example demonstrates this invention concretely, this invention is not limited to a present Example.

Outline of the experiment An experiment was conducted to verify the effect of the taper connecting pipe provided in the vertical water pipe on the sustainability of the siphon function. The experimental apparatus is shown in FIG. The pipe diameter of the horizontal water pipe was 50 mm, and the pipe diameter of the vertical water pipe was 35 mm (reduced to 70% of the horizontal water pipe). The length of the gradually reducing connection pipe is 0.5 m corresponding to about ３ of the length of the vertical water pipe to be connected (about ¼ of the total length of the vertical water pipe and the gradually reducing pipe). And the reduction angle θ in FIG. 1B was set to 45 °. The water pressure gauges A to E are arranged as shown in FIG. A to St. E.

Experiments were performed in the following procedure using the experimental apparatus of FIG.
Step 1: Plug the vertical water pipe, saturate the horizontal water pipe and the vertical water pipe with water, and tighten the water amount adjustment valve.
Step 2: Remove the plug of the vertical water pipe and open the water volume adjustment valve.
Step 3: A predetermined flow rate is set based on the numerical value of the water flow meter.
Step 4: Open the air adjustment valve and mix a predetermined amount of air. At this time, since the flow rate of water changes, it is adjusted again.
Step 5: Measure when the water flow rate is stable.

  As shown in Table 1, in addition to Examples, Comparative Examples 1 to 3 were similarly tested. That is, in the case where the upper side (large diameter) of the vertical water pipe in FIG. 9 is the vertical water pipe P1, and the lower side (small diameter) is the vertical water pipe P2, Comparative Example 1 has both the vertical water pipes P1, P2 having an inner diameter of 50 mm. Comparative Example 2 is the same as Comparative Example 1, except that an impervious rod having an inner diameter of 30 mm is inserted into the entire vertical water pipes P1 and P2 and the water flow cross section of the entire vertical water pipes P1 and P2. In Comparative Example 3, both the vertical water pipes P1 and P2 have an inner diameter of 35 mm, and are reduced to 70% of the vertical water pipe P1 having an inner diameter of 50 mm in the example. In addition, the bent pipe like FIG. 7A was attached to the lower end of the vertical water pipe as shown in FIG.

  Experiments were performed on the above Examples and Comparative Examples 1 to 3 by changing the air mixing rate and the flow rate. The flow rate in the vertical water pipe was changed by adjusting the water amount adjusting valve, and the air amount was changed by the air amount adjusting valve while being measured by the air amount meter.

Experimental results FIG. 10 shows the measurement result of the negative pressure in the pipe when the air mixing rate is 0% in Comparative Example 1, and the St. D and St. In E, St. Compared with A, it was confirmed that a negative pressure of about 18 kPa corresponding to the water head difference acts.

  Regarding the negative pressure measurement results in the tubes after the start of the experiments of Examples and Comparative Examples 2 and 3, St. An example of the change by the elapsed time of the pressure deviation in each position on the basis of the pressure of A is shown in FIGS. Further, in the examples and comparative examples 1 to 3, the relationship between the air mixing rate and the pressure deviation when the flow velocity is 0.4 m / second is shown in FIG. 14, and the air when the flow velocity is 0.7 m / second is shown. FIG. 15 shows the relationship between the mixing rate and the pressure deviation.

  14 and 15, it can be seen that the siphon does not function when air is mixed in Comparative Example 1 of the basic case in which the water flow cross-sectional area of the vertical water pipe is not changed. On the other hand, in Comparative Examples 2 and 3 in which the water flow cross-sectional area of the vertical water pipe is reduced, (1) the effect that the maximum diameter of bubbles that can be formed is reduced and the rising speed of the bubbles is suppressed, and (2) It can be seen that the siphon functions due to the effect of increasing the flow speed, but the allowable air mixing rate is about 5%.

  In this embodiment, the vertical tube structure combined with the reduced-diameter connecting pipe has the effect of significantly reducing the bubble rising speed by making the bubbles into micro and milli bubbles, as shown in FIGS. 14 and 15. In addition, it was confirmed that the air mixing rate can be significantly tolerated as compared with Comparative Examples 2 and 3, and an air mixing rate of about 40% at the maximum can be allowed. However, it can be seen that the siphon function is more easily maintained when the flow velocity is higher.

  As described above, as compared with the case where the cross-sectional area of the vertical water pipe is reduced as a whole as in Comparative Examples 2 and 3, the area of the vertical water pipe is reduced by providing a gradually reducing connection portion in the middle as in this embodiment. It has been confirmed that the siphon function can be effectively maintained.

  According to the above experiment, in order to ensure that the suction force of the siphon acts even under conditions where there is vaporization of dissolved oxygen or the like and the presence of gas flowing in from the airtight leak portion of the water pipe, It was confirmed that it is important to stably form a gas-liquid two-phase flow by arranging a gradually reducing connection pipe and connecting it to a vertical water pipe having a small diameter.

  As described above, the embodiments and examples of 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, the suction force generator according to the present invention is applied to the vacuum consolidation ground improvement system, but is not limited to this, and may be applied as appropriate to other devices, systems, and other construction methods, and similar effects can be obtained. . Further, the vertical pipe (vertical water pipe) and the horizontal pipe (horizontal water pipe) may be other than the cylindrical pipe, for example, a rectangular tube.

  Further, the bent pipe 28 of the air backflow prevention device of FIGS. 6 to 8 can be configured to attach a pipe bent at about 90 ° to the lower end of the vertical water pipe 21, but is not limited thereto, and the vertical water pipe is not limited thereto. The lower end itself of 21 may be bent.

  According to the suction force generator according to the present invention, even when water contains gas, the suction force based on the principle of the siphon can be stably generated, so that the natural energy of the siphon can be used as much as possible without relying on a vacuum pump. Thus, the cost of electric power and the like can be reduced.

  According to the vacuum consolidation ground improvement method according to the present invention, it is possible to reduce or omit loading by embankment by using the suction force by the siphon function, and it is possible to reduce the use materials and equipment and shorten the work period. Since the suction force increases as compared with the conventional construction method, the ground improvement period required until the soft ground reaches a predetermined strength can be shortened.

1 Vertical pipe (first pipe)
2 Horizontal pipe (second pipe)
3 Taper connection pipe 20 Vacuum decompression device 21 Vertical water pipe 22 Horizontal water pipe 23 Vacuum pump 26 Sealed chamber 28 Bent pipe 31 Vertical drain material b Vertical direction e Bubble G Soft ground H0 Ground water level surface H1 Water level surface ΔH Water level in the sealed chamber Difference S1, S2 Vacuum consolidation ground improvement system θ Decrease angle

Claims (5)

A first pipe extending from the upper part toward the lower part; a second pipe connected to the first pipe at the upper part and extending in the horizontal direction; and a lower end side of the first pipe; For improving the ground by vacuum consolidation by applying a suction force by a siphon function from the tip of the second tube toward the lower end of the first tube due to a difference in water level between the tip of the two tubes A suction force generator,
The diameter of the first tube is smaller than the diameter of the second tube;
Connecting the second pipe and the first pipe via a gradually reducing connecting pipe whose diameter is gradually reduced;
Air that is present separately from water in the second pipe becomes bubbles in the gradually contracting connection pipe and flows down as a gas-liquid two-phase flow in the first pipe to generate a suction force by a siphon function ,
A sealed chamber that houses a lower end of the first tube;
A vacuum pump for depressurizing the sealed chamber;
A drainage facility for draining the stored water in the sealed chamber to the outside,
While applying a suction force by the siphon function to a suction force by the vacuum pump by reducing the pressure in the sealed chamber by the vacuum pump, draining the stored water in the sealed chamber by the drainage facility,
The suction force generator according to claim 1, wherein a lower end of the first pipe is located below a surface of the stored water in the sealed chamber .   2. The suction force generation according to claim 1, further comprising an air backflow prevention device for preventing a gas-liquid two-phase flow bubble flowing out from a lower end of the first pipe from re-floating into the first pipe and flowing back. apparatus.   3. The gradually reducing connection pipe according to claim 1 or 2, wherein the gradually reducing connecting pipe is linearly inclined to gradually decrease its inner diameter, and a gradually reducing angle θ is 45 ° or less when an extension line extending downward from the inclined line intersects. Suction force generator. 4. The suction force generation device according to claim 1 , wherein the gradually reducing connection pipe has an upper pipe having an inner diameter substantially the same as that of the second pipe on an upper side thereof . 5.   A vacuum consolidation ground improvement method characterized by performing ground improvement by vacuum consolidation in soft ground using the suction force generator according to any one of claims 1 to 4.