JP2012021289A - Vacuum consolidation system and vacuum consolidation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vacuum consolidation system and a vacuum consolidation method capable of suppressing the loss of suction energy even when there is a height difference between a draining route and a water level of water desired to be sucked/drained or when the ground surface of soil is inclined or uneven.SOLUTION: The vacuum consolidation system includes: a water collecting pipe 12 for collecting water passing through a plurality of drains 11 placed in the soil, a header pipe 13 to which the water collecting pipe is connected; a negative pressure operation chamber 16 connected with the header pipe through the draining route and provided with a vacuum pump 16a; and an airtight container 18 connected with the header pipe and housing a draining pump 19. By keeping the header pipe horizontal and driving the vacuum pump and driving the draining pump inside the airtight container under the condition that there is the height difference in the draining route, a negative pressure is added inside the airtight container and the soil is improved by vacuum consolidation.

Description

  The present invention relates to a vacuum consolidation system and a vacuum consolidation method capable of suppressing loss of suction force.

  In the conventional technology for improving the consolidated ground using a vacuum pump, for example, after placing a vertical drain in soft ground, the negative pressure is applied using a negative pressure device using a vacuum pump to reduce the inside of the ground. Is used to promote consolidation of the ground (see, for example, Patent Documents 1 to 3).

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

  However, when suctioning and draining with a vacuum pump, if the position of the top of the installed drainage channel is higher than the level of the water to be suctioned or drained, the difference in height must be pumped, resulting in a loss of suction energy. There is a problem. This problem will be described with reference to FIG.

  As shown in FIG. 7, a plurality of vertical drains D are placed on the soft ground G to be improved, and the vertical drains D are connected to the water collecting pipe U through the air-impermeable portion F. Is connected to the header pipe L connecting the two. The connecting pipe I is connected to the header pipe L, and the connecting pipe I is extended and connected to the negative pressure working chamber P. By reducing the inside of the negative pressure working chamber P to a negative pressure with a vacuum pump, the pore water in the ground G is sucked and drained from the vertical drain D, and the soft ground G is improved by vacuum consolidation. At this time, when there is an obstacle T such as a bank or a dike between the header pipe L and the negative pressure working chamber P, the connection pipe I gets over the obstacle T. Therefore, the uppermost part of the connection pipe I and the soft ground G There is a considerable difference in height from the water level H. For this reason, since the negative pressure working chamber P has to pump up the difference in elevation, a loss of suction energy occurs.

  Furthermore, when the ground surface of the ground where the header pipe L is arranged has an inclination or unevenness, a loss of suction force due to energy loss or non-uniform suction force with respect to the drain may occur.

  In view of the problems of the prior art as described above, the present invention provides suction even when there is a difference in level between the drainage route and the water level to be sucked / drained, or when the ground surface of the ground is inclined or uneven. An object of the present invention is to provide a vacuum consolidation system and a vacuum consolidation method capable of suppressing energy loss.

  In order to achieve the above object, a vacuum consolidation system includes a water collecting pipe that collects water passing through a plurality of drains placed in the ground, a header pipe connected to the water collecting pipe, the header pipe, and a drainage path. A negative pressure chamber having a vacuum pump connected thereto, and an airtight container connected to the header pipe and containing a drainage pump, and keeping the header pipe horizontal and having a height difference in the drainage path. The vacuum pump is driven below, and the drainage pump in the airtight container is driven to apply a negative pressure to the airtight container to improve the ground by vacuum consolidation.

  According to this vacuum compaction system, a drainage pump in an airtight container connected to a header pipe is driven to lose suction energy even when there is a height difference between the drainage path and the water level to be sucked / drained. Further, by keeping the header pipe horizontal, it is possible to prevent loss of suction force due to energy loss, and it is possible to keep suction force acting on the drain uniform.

  In the vacuum compaction system, it is preferable to keep the header pipe horizontal by flooding the ground or the vicinity thereof so that the header pipe is floated on water.

  In this case, it is preferable that the ground or the vicinity thereof is submerged by guiding drainage from the airtight container to the ground or the vicinity thereof.

  The header pipe may be kept horizontal by arranging the header pipe on a flat ground.

  Further, the header pipe may be suspended by using an obstacle that causes a difference in height in the drainage path, and may be kept horizontal.

  Moreover, it is preferable that the header pipe is composed of a lightweight pipe composed of a material having a specific gravity of 1.0 or less. Since the header pipe is lightweight, it is advantageous when the header pipe is floated or suspended.

  When the header pipe is floated on water, floating means for the header pipe may be arranged. Thereby, a header pipe can be floated by the floating body means with which buoyancy, such as a buoy, acts instead of using a lightweight pipe with light specific gravity.

  In order to achieve the above object, a vacuum consolidation method includes a water collecting pipe that collects water passing through a plurality of drains placed in the ground, a header pipe to which the water collecting pipe is connected, the header pipe, and a drainage path. A negative pressure chamber having a vacuum pump connected thereto, and an airtight container connected to the header pipe and containing a drainage pump, to keep the header pipe horizontal and to have a height difference in the drainage path The vacuum pump is driven under conditions, and the drainage pump in the airtight container is driven to apply a negative pressure to the airtight container to improve the ground by vacuum consolidation.

  According to this vacuum compaction method, even if there is a height difference between the drainage path and the level of the water to be sucked / drained by driving the drainage pump in the airtight container connected to the header pipe, the suction energy is lost. Further, by keeping the header pipe horizontal, it is possible to prevent loss of suction force due to energy loss, and it is possible to keep suction force acting on the drain uniform.

  In the vacuum consolidation method, it is preferable to keep the header pipe horizontal by flooding the ground or the vicinity thereof so that the header pipe is floated on water.

  Further, a flat ground having no unevenness or inclination may be formed on or near the ground, and the header pipe may be installed on the flat ground. Thus, you may make it keep horizontal by installing a header pipe in a flat ground.

  Further, the header pipe may be suspended by using an obstacle that causes a difference in height in the drainage path, and may be kept horizontal.

  The vacuum compaction system is a vacuum collecting system that collects water passing through a plurality of drains placed in the ground, a header pipe to which the water collection pipe is connected, and a header pipe connected to the header pipe via a drainage path. A negative pressure working chamber having a pump, and configured to perform ground improvement by vacuum consolidation by keeping the header pipe horizontal and driving the vacuum pump to make the negative pressure working chamber negative pressure. May be. According to this vacuum consolidation system, by keeping the header pipe horizontal, it is possible to prevent a loss of suction force due to energy loss, and it is possible to keep the suction force acting on the drain uniform.

  According to the vacuum consolidation system and the vacuum consolidation method of the present invention, it is possible to suppress the loss of suction energy even when there is a height difference between the drainage path and the water level to be sucked / drained, and By maintaining the level, it is possible to prevent the loss of the suction force due to the energy loss, and it is possible to keep the suction force acting on each drain uniform.

It is a figure showing roughly the vacuum consolidation system by this embodiment. FIG. 2 is a schematic side view of the vacuum consolidation system of FIG. 1. It is the schematic for demonstrating the problem which generate | occur | produces when a header pipe is installed in the ground surface with an inclination and unevenness in a vacuum compaction system. It is a figure for demonstrating the solution means by this embodiment with respect to the problem of FIG. It is the schematic which shows the experimental apparatus produced in order to verify the effect of this invention as an Example. It is a graph which shows the experimental result by the experimental apparatus of FIG. It is the schematic of the conventional vacuum compaction system. It is a schematic side view of the vacuum compaction system for demonstrating another means and method for keeping the header pipe of FIG. 1, FIG. 2 horizontal.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a diagram schematically illustrating a vacuum consolidation system according to the present embodiment. FIG. 2 is a schematic side view of the vacuum compaction system of FIG. 2, illustration of the airtight container 18 and the like in FIG. 1 is omitted.

  As shown in FIGS. 1 and 2, the vacuum consolidation system 10 of the present embodiment includes a ground in which a number of vertical drains 11 are placed for ground improvement, and a negative pressure working chamber 16 installed for vacuum consolidation. This is preferable when there is an obstacle T having a height such as a bank or a bank between them.

  That is, the vacuum consolidation system 10 includes a water collecting pipe 12 that collects water passing through a plurality of vertical drains 11 placed on soft ground, and a header pipe 13 that connects the water collecting pipe 12 so as to be connected by a head 12a. A negative pressure chamber 16 connected to the header pipe 13 via the connection pipes 14 and 15 and provided with a vacuum pump 16a; an airtight container 18 connected to the header pipe 13 via the connection pipe 17 and containing the pumping pump 19; Is provided. Each vertical drain 11 is connected to a water collecting pipe 12 through an air-impermeable portion 11a.

  The header pipe 13 is connected to a plurality of water collecting pipes 12 and is formed of a cylindrical pipe. The header pipe 13 is preferably made of a lightweight material such as resin having a specific gravity of less than 1.0. Thereby, as shown in FIG. 2, it is possible to easily float on the flooded portion 20 (water level H1) formed by flooding the ground to be improved.

  In addition, a floating means such as a buoy may be disposed around the header pipe 13 so that the header pipe 13 can be reliably lifted even when the header pipe 13 is not made of a lightweight material.

  Further, the water collecting pipe 12 and the connecting pipe 14 connected to the header pipe 13 may be connected via a known flexible joint, and the water collecting pipe 12 and the connecting pipe 14 are flexible. You may comprise from a pipe | tube.

  The vacuum consolidation system 10 of FIGS. 1 and 2 will be further described. A drainage facility composed of a pumping pump 16b and a drain pipe 16c is disposed in a negative pressure working chamber 16 that is depressurized by a vacuum pump 16a to generate a negative pressure, and the inside of the negative pressure working chamber 16 is sealed.

  A connecting pipe 15 and a header pipe 13 for guiding drainage to the negative pressure working chamber 16 are connected by a connecting pipe 14. The connecting pipe 14 constitutes a drainage path together with the connecting pipe 15. However, since the connecting pipe 14 is arranged along the obstacle T having a height such as a bank or a bank, the uppermost part of the connecting pipe 14 (drainage path) and the soft ground G A difference in height from the water level H occurs.

  A vertical drain 11 placed in the soft ground G for sucking pore water is connected to the water collecting pipe 12, and a header pipe 13 connected to an airtight container 18 having a pumping pump 19 and a plurality of water collecting pipes 12. Are connected at a low position in the drainage channel with a difference in elevation.

  Since the pumping pump 19 has the property of operating only in the water immersion state, the installation position of the airtight container 18 including the pumping pump 19 is set to be equal to or below the header pipe 13. Water is discharged from the pump 19 through the discharge pipe 19a. The airtight container 18 constitutes a negative pressure loss elimination device together with a pumping pump 19 accommodated therein. The shape of the airtight container 18 may be any shape such as a cube, a rectangular parallelepiped, or a cylinder, and any volume that can accommodate the pumping pump 19 is sufficient.

  By operating the vacuum pump 16a, the pressure in the negative pressure working chamber 16 is reduced to a negative pressure, and after confirming the passage of water from the soft ground G into the drain pipe 16c, the pumping pump 19 in the airtight container 18 is operated. To do.

  A separate drain pipe (not shown) is connected to the drain pipe 19a (or the drain pipe 19a is extended) to guide the drainage from the pump 19 in the airtight container 18 to the ground improvement area. In addition to returning to the flooded portion 20, the ground is flooded while supplying water separately as necessary.

  The vacuum consolidation system 10 of FIGS. 1 and 2 generates a negative pressure (suction force) by a vacuum pump 16a in the negative pressure working chamber 16, thereby allowing pore water passing through the vertical drain 11 from the soft ground G to be generated as shown in FIG. The soft ground G is improved by vacuum compaction by sucking and discharging through the water collecting pipe 12, the header pipe 13, the connecting pipes 14 and 15 in the arrow direction j.

  At this time, since the negative pressure working chamber 16 has to pump up the difference in height in the drainage path of the connecting pipe 14, the suction force by the negative pressure working chamber 16 is partially lost. The pumping pump 19 is driven to drain separately from the header pipe 13 into the airtight container 18 in the arrow direction k, and the water is discharged from the drain pipe 19a to drive the pumping pump 19 in the airtight container 18. The resulting negative pressure is applied, and this negative pressure is applied to the header pipe 13 through the connecting pipe 17.

  As described above, the header pipe is driven by the pumping pump 19 in the hermetic vessel 18 even if energy loss related to pumping occurs in the drainage path having a difference in height with respect to the suction force by the vacuum pump 16a in the negative pressure working chamber 16. In FIG. 13, the negative pressure is compensated and the loss of the suction force can be suppressed as a whole. As described above, the negative pressure loss elimination device using the airtight container 18 and the pumping pump 19 can eliminate the loss of the suction force even if the drainage path has a height difference as shown in FIGS.

  As described above, according to the vacuum consolidation system 10 of the present embodiment, the suction of the negative pressure working chamber 16 is performed by driving the pumping pump 19 in the airtight container 18 even if energy loss occurs due to the difference in height in the drainage path. Since power loss can be suppressed and eliminated, efficient suction and drainage can be carried out.

  Therefore, when performing vacuum consolidation improvement by draining pore water in soft ground, even if there is a height difference in the drainage path, it is possible to exert a high suction force, so the ground required for the soft ground to reach a predetermined strength The improvement period can be shortened.

  Next, in the vacuum consolidation improvement of soft ground, there are cases where the ground surface is inclined or uneven due to ground subsidence. A problem that occurs in such a case and a solution to the problem will be described with reference to FIGS.

  FIG. 3 is a schematic diagram for explaining a problem that occurs when the header pipe 13 is installed on a ground surface that is inclined or uneven. FIG. 4 is a diagram for explaining the solving means according to the present embodiment for the problem of FIG.

  Since the dissolved air in the drainage is vaporized under the condition that the high negative pressure is applied, if the header pipe 13 connected to the plurality of water collecting pipes 12 is simply installed on the ground surface of the ground, the ground surface has an inclination, that is, When the header pipe 13 is inclined so as to be lowered in the arrow direction Y as shown in FIG. 3, the dissolved air evaporated in the header ground 13 at the location M where the ground height is high is collected, while the water from the vertical drain 11 is collected by each collecting pipe 12. In the direction of the arrow a, and the drainage flows in the direction of the arrow b and concentrates at the low location N.

  Here, as shown in FIG. 3, the drainage flow rate Q from the header pipe 13 to the negative pressure working chamber 16 (FIGS. 1 and 2) through the connecting pipes 14a and 14b is given by the following formula (1).

  Here, v is an in-tube flow velocity of each connecting pipe, and A is a passing cross-sectional area thereof. i is the number of the connecting pipe through which water flows, and N is the total number of connecting pipes through which water flows.

Further, the energy loss head h _L due to friction of water flowing in the pipe is given by the Darcy-Weissbach equation of the following equation (2).

  Here, L is the tube length, D is the tube diameter, f is the friction coefficient, and g is the gravitational acceleration.

  In the condition where the horizontality of the header pipe 13 connected to the airtight container 18 in FIG. 1 is not maintained, air gathers at the upper part of the header pipe 13 and water gathers at the lower part as described above. The total number of connecting pipes that flow through decreases. In FIG. 3, air flows in the arrow direction c in the connecting pipe 14a, while water concentrates in the connecting pipe 14b and flows in the arrow direction d. For this reason, in order to secure the drainage flow rate, the flow velocity in the pipe must increase, but if the flow velocity in the pipe increases, the energy loss increases by the square of the flow velocity according to equation (2), so the energy loss becomes very large and suction is performed. It leads to the loss of power.

  Further, under the condition that the horizontality of the header pipe 13 is not maintained, a water head difference is generated between the upper part and the lower part due to water collecting at the location M where the ground height is low. Due to this water head difference, the suction force acting on the vertical drain 11 connected at the lower part of the header pipe 13 decreases, and a difference occurs in the suction force connected at the upper part of the header pipe 13. Such non-uniformity of the suction force is a big problem in ensuring the quality of ground improvement.

  On the other hand, the header pipe 13 is kept horizontal by making the header pipe 13 float in the flooded portion 20 of the water level H1 formed by spreading water on the ground as shown in FIGS. Can do. As a result, as shown in FIG. 4, water flowing from the vertical drain 11 through each water collecting pipe 12 in the arrow direction a enters the header pipe 13, flows uniformly through each connecting pipe 14 a, 14 b, and concentrates on one connecting pipe. Since this is not the case, it is possible to prevent the loss of the attractive force due to the energy loss as described above.

  Further, when the horizontality of the header pipe 13 is not maintained, there is a head difference between the upper part and the lower part. However, since the horizontality of the header pipe 13 is maintained, the head pipe 13 does not cause a head difference. The suction force acting on each vertical drain 11 can be kept uniform. For this reason, the quality of ground improvement can be ensured reliably.

  As shown in FIG. 1, even when a single connecting pipe 14 extends from the header pipe 13, if the header pipe 13 is not kept horizontal, only air may pass through the connecting pipe 14 or the header depending on conditions. The above-described water head difference may occur in the pipe 13, and the same problems as described above may occur. However, such a problem can be solved by floating the header pipe 13 in the flooded portion 20.

  In addition, when vacuum consolidation of soft ground is performed using a vacuum pump, the water on the ground surface dehydrates and evaporates due to consolidation consolidation and the influence of the sun, and cracks are likely to occur. However, as in this embodiment, water is applied on the ground to make the submerged portion 20 to keep the ground surface moist and maintain airtightness. The effect can also be obtained. Regardless of whether or not the header pipe is floated on the water, it is preferable to submerge the ground surface of the improved area by drainage from the airtight container 18.

  Next, another means and method for keeping the header pipe horizontal in this embodiment will be described with reference to FIG. FIG. 8 is a schematic side view of a vacuum compaction system for explaining another means and method for keeping the header pipe of FIGS. 1 and 2 horizontal.

  In the example of FIG. 8, the header pipe is suspended by using an obstacle T such as a bank or a bank, so that the header pipe is kept horizontal. That is, as shown in FIG. 8, a wire fixing portion 21 is provided above the obstacle T such as a bank or a bank, and the header pipe 13 is suspended by the wire 22 extending from the fixing portion 21. Thereby, it can install, keeping the header pipe 13 horizontal. In this case, it is preferable to suspend the header pipe 13 horizontally by arranging a plurality of wires 22 at predetermined intervals in the length direction of the header pipe 13.

  As another means and method for keeping the header pipe horizontal, a pedestal or block may be installed on the ground surface S, and the header pipe 13 may be placed on the pedestal or block to keep it horizontal. Good. Furthermore, a flat ground without unevenness or inclination may be formed on the ground or in the vicinity thereof, and the header pipe 13 may be installed horizontally on the flat ground.

Experimental example

  As an experimental example, in order to verify the effect of the negative pressure assist function exhibited by the airtight container containing the pump, a test apparatus as shown in FIG.

Outline of experiment The experiment was performed according to the following procedure.

  Step 1: A drainage path having a height difference is taken using a vertical pipe having a length of 2 m in a drainage path toward a negative pressure working chamber where pressure is reduced by a vacuum pump. An airtight container containing a pump is connected to the lower end of a 2 m long vertical pipe.

  Step 2: Fill the water from the upper end of the vertical pipe to the inside of the airtight container to set the initial conditions for the experiment.

Step 3: The vacuum pump is started while the pump in the airtight container is stopped, and the negative pressure in the negative pressure working chamber is kept constant at about −50 kN / m ² . Further, negative pressure is measured at each height position of St. 1 in the negative pressure chamber and St. 2 at the lower end of the vertical pipe.

  Step 4: Start up the pump in the airtight container after a certain period of time. The experiment is terminated when the water level in the vertical pipe with the difference in height is lowered from the initial 2.0 m height to 1.0 m height along with the drainage by the pump.

Experimental results Fig. 6 shows the measurement results of the negative pressure. The vacuum pump was driven while the pump was stopped until 150 seconds passed. FIG. 6 shows that the negative pressure acting at the lower end of the vertical pipe is about 20 kN / m ² smaller than the negative pressure in the negative pressure working chamber because there is a water level difference of 2 m in the initial state at the lower end of the vertical pipe. I understand. That is, a negative pressure loss occurs at the lower end of the vertical pipe.

  On the other hand, when the pump is started after 150 seconds, a negative pressure is newly generated by the pump, so that the negative pressure increases in both the negative pressure chamber and the lower end of the vertical pipe. In particular, at the end of the experiment, a negative pressure higher than the negative pressure generated in the negative pressure chamber before the pumping pump is activated at the lower end of the vertical pipe, even though the water level in the vertical pipe is about 1 m. It was possible to verify that the negative pressure application effect by the pump in the airtight container was high.

  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 header pipe 13 and the negative pressure operating device are connected by a single connecting pipe 14, but the present invention is not limited to this, and is connected by two connecting pipes 14 a and 14 b as shown in FIG. 4. Alternatively, two or more may be connected.

  According to the vacuum consolidation system and method of the present invention, when performing ground improvement by vacuum consolidation of soft ground, even if there is a height difference in the drainage path, a high suction force can be exhibited, so that the soft ground has a predetermined strength. The ground improvement period required to reach it can be shortened.

DESCRIPTION OF SYMBOLS 10 Vacuum compaction system 11 Vertical drain 12 Water collecting pipe 13 Header pipe 14, 15 Connecting pipe 14a, 14b Connecting pipe 16 Negative pressure action chamber 16a Vacuum pump 16b Pumping pump 17 Connecting pipe 18 Airtight container 19 Pumping pump 20 Submerged part H1 Submerged part 20 Water level T Obstacle

Claims (10)

A water collecting pipe for collecting water passing through a plurality of drains placed in the ground;
A header pipe to which the water collecting pipe is connected;
A negative pressure working chamber having a vacuum pump connected to the header pipe through a drainage path;
An airtight container connected to the header pipe and containing a drain pump,
Keep the header pipe horizontal,
Driving the vacuum pump under conditions with a difference in elevation in the drainage path and driving the drainage pump in the hermetic container to apply a negative pressure in the hermetic container to improve the ground by vacuum consolidation Vacuum compaction system characterized by   The vacuum consolidation system according to claim 1, wherein the header pipe is kept horizontal by flooding the ground or the vicinity thereof to make the header pipe float in water.   The vacuum consolidation system according to claim 2, wherein the ground or the vicinity thereof is submerged by guiding drainage from the airtight container to the ground or the vicinity thereof.   The vacuum consolidation system according to claim 1, wherein the header pipe is kept horizontal by arranging the header pipe on a flat ground.   The vacuum consolidation system according to claim 1, wherein the header pipe is kept horizontal by suspending the header pipe using an obstacle that causes a height difference in the drainage path.   The vacuum consolidation system according to any one of claims 1 to 5, wherein the header pipe is composed of a lightweight pipe composed of a material having a specific gravity of 1.0 or less. A water collecting pipe for collecting water passing through a plurality of drains placed in the ground;
A header pipe to which the water collecting pipe is connected;
A negative pressure working chamber having a vacuum pump connected to the header pipe through a drainage path;
An airtight container connected to the header pipe and containing a drainage pump; and
Keep the header pipe horizontal,
The vacuum pump is driven under the condition that there is a difference in height in the drainage passage, and the drainage pump in the airtight container is driven to apply a negative pressure to the airtight container to improve the ground by vacuum consolidation. A vacuum consolidation method characterized by that.   The vacuum consolidation method according to claim 7, wherein the header pipe is kept horizontal by flooding the ground or the vicinity thereof to make the header pipe float in water. Form a flat ground without unevenness or inclination on the ground or the vicinity thereof,
The vacuum consolidation method according to claim 7, wherein the header pipe is installed on the flat ground.   The vacuum consolidation method according to claim 7, wherein the header pipe is kept horizontal by suspending the header pipe by using an obstacle that causes a height difference in the drainage path.

Images