JP6245499B2 - Groundwater level lowering system - Google Patents

Description

  The present invention relates to a groundwater level lowering system using a vacuum deep well, which is applied mainly for the purpose of lowering the groundwater level during excavation work.

  When constructing the foundations of civil engineering structures and underground structures such as subways, it is indispensable to take precautions to prevent groundwater from flowing out from the bottom and sides of the excavation or to prevent board swelling from occurring at the bottom of the excavation. As a countermeasure, a so-called groundwater level lowering method that lowers the groundwater level by draining groundwater from or near the bottom of the excavation has been widely used.

  The groundwater level lowering method is roughly divided into gravity drainage method and forced drainage method. The typical method is the deep well method (the deep well method) as the former method and the well point method as the latter method. It is done.

  Here, the deep well method is to pump groundwater flowing into the well with a submersible pump installed in the vicinity of the bottom of the well. Therefore, if the ground is highly permeable, the water level will drop by several tens of meters. Is possible.

  On the other hand, the well point method draws groundwater by the pressure difference from the atmospheric pressure generated by applying a vacuum with a vacuum pump. Therefore, although it is about half of that, it is forcibly drained by a pressure difference from the atmospheric pressure, so it can be applied to the ground with low water permeability.

  On the other hand, there is a construction method called a vacuum deep well that uses the above-mentioned two construction methods in combination, and by using the deep well construction method with a reduced pressure by a vacuum pump, the water level can be further lowered while taking advantage of both advantages.

  Moreover, in such a vacuum deep well method, if the groundwater level drops too much, the internal space of the well communicates with the voids between the soil particles in the ground and air enters the well, reducing the pressure reducing effect. However, an improved vacuum deep well method has been developed that can maintain the reduced pressure in the well even when the water level drops. Known (Patent Document 1).

JP 2011-256670 A Japanese Patent No. 4743355 Japanese Patent No. 4824435

  Here, according to the construction method described in Patent Document 1, the groundwater around the well pipe once flows between the well pipe and the inner pipe through the strainer formed in the well pipe, and then is an overflow section. Since the water flows into the inner pipe beyond the upper edge of the inner pipe and then is pumped by a submersible pump in the inner pipe, even if the water level in the inner pipe is lowered, it is not between the well pipe and the inner pipe. Thus, the water level is maintained with the overflow section as the lower limit, and thus it is possible to avoid the situation where air enters from the strainer.

  However, in such a construction method, it is necessary to install a submersible pump for pumping up groundwater not in a well pipe but in an inner pipe accommodated in the well pipe. Then, the inner pipe was accommodated in the well pipe, and then the submersible pump had to be re-installed in the inner pipe, resulting in a problem that time and labor were required.

  In addition, since the submersible pump must be installed in the well pipe through the inner pipe as described above, the well pipe has to be larger in diameter than that used for a general vacuum deep well. As a result, if it is a new pumping well, the cost of installation work will be expensive, and if it is an existing pumping well, the inner diameter of the well pipe is too small to accommodate the inner pipe. This has caused a problem that it is difficult to adopt the method.

  The present invention has been made in consideration of the above-described circumstances, and prevents the flow of air from flowing into the well pipe and maintaining the reduced pressure state in the well pipe when the groundwater level is lowered using the vacuum deep well. The aim is to provide a possible groundwater level lowering system.

In order to achieve the above object, a groundwater level lowering system according to the present invention comprises a well pipe embedded in the ground and a submerged water pipe installed near the bottom of the well pipe and connected to a pumping pipe. A pump and a vacuum pump connected to the internal space of the well pipe, and forming the well pipe by operating the submersible pump while depressurizing the internal space of the well pipe using the vacuum pump In the groundwater level lowering system configured to pump groundwater flowing into the well pipe through the groundwater inflow opening formed through the pumping pipe,
A water level evaluation means for evaluating the level of groundwater in the well pipe, and a flow rate control valve provided in the pumping pipe or a control means for controlling the submersible pump, and the submersible pump is disposed at the top of the groundwater inflow opening. The control means is positioned below the position, and the control means uses the evaluation value obtained by the water level evaluation means so that the groundwater level in the well pipe is higher than the groundwater inflow opening. The flow control valve or the submersible pump is controlled.

In the groundwater level lowering system according to the present invention, the water level evaluation means is installed in the groundwater in the well pipe and is configured to perform atmospheric pressure correction, and the atmospheric pressure and atmospheric pressure in the well pipe. A differential pressure gauge for measuring the differential pressure of the water column, and a calculation means, wherein the calculation means has a water level measured by the water level gauge as h ₁ and a water column height converted from the differential pressure measured by the differential pressure gauge. H ₂ , the water level h in the well pipe is given by
h = h ₁ + h ₂
It is comprised so that it may calculate using.

In the groundwater level lowering system according to the present invention, the water level evaluation means is installed in the groundwater in the well pipe and is configured not to perform atmospheric pressure correction, and measures the atmospheric pressure in the well pipe. When constituted by a barometer and a calculation means, the calculation means, when the water level measured by the water level meter is h ₃ , and the water column height converted from the pressure measured by the barometer is h ₄ , The water level h in the well pipe is expressed by the following formula:
h = h ₃ −h ₄
It is comprised so that it may calculate using.

  In the groundwater level lowering system according to the present invention, the pressure of the well pipe is reduced while reducing the internal space of the well pipe using a vacuum pump connected to the internal space of the well pipe in the same manner as a conventional vacuum deep well. By operating a submersible pump installed near the bottom, groundwater flowing into the well pipe through the groundwater inflow opening formed in the well pipe is pumped through the pumping pipe. It is equipped with a water level evaluation means for evaluating the level of groundwater and a control means for controlling a flow rate control valve or a submersible pump provided in the pumping pipe, and when pumping the groundwater flowing into the well pipe from the well pipe, The flow control valve or the submersible pump is controlled using the evaluation value obtained by the water level evaluation means so that the groundwater level in the well pipe is higher than the groundwater inflow opening.

  In this way, the groundwater level inside and outside the well pipe will always exceed the groundwater inflow opening, thus preventing air from entering through the groundwater inflow opening and maintaining the reduced pressure inside the well pipe. It becomes possible to do.

  The groundwater inflow opening can be configured as a strainer or part thereof.

  The flow rate control valve is an electromagnetic valve configured to make the flow rate variable, and includes a flow rate adjustment valve, a throttle valve, a stop valve, and the like.

  The water level evaluation means is arbitrary if it can measure the groundwater level in the well pipe, calculate the measured value as necessary, and then transmit the data to the control means as water level data. It can be constituted by a sensor, an electrode type liquid level displacement sensor, a non-contact type distance measuring device, a water detection sensor, a float type level meter, or the like. In addition, when adopting a water detection sensor, it may be arranged in a row along the vertical direction within the expected water level fluctuation range, and if it is a float type level meter, a wire A winding mechanism for automatically winding the wire may be attached to the inner surface of the well pipe and the tip of the wire may be connected to a float floating on the water surface.

Here, the water level evaluation means is a water level meter that is installed in the ground water in the well pipe and is configured to correct the atmospheric pressure, a differential pressure gauge that measures the pressure difference between the atmospheric pressure and the atmospheric pressure in the well pipe, and a computing means. When the water level measured by the water level gauge is h ₁ and the water column height converted from the differential pressure measured by the differential pressure gauge is h ₂ , the water level h in the well pipe is The following formula,
h = h ₁ + h ₂ (1)
The water level evaluation means is installed in the groundwater in the well pipe and is configured not to perform atmospheric pressure correction, and the barometer for measuring the atmospheric pressure in the well pipe, And calculating means, where the water level measured by the water level meter is h ₃ , and the water column height converted from the pressure measured by the barometer is h ₄ , the water level h in the well pipe is ,
h = h ₃ −h ₄ (2)
It can comprise so that it may calculate using.

  According to these structures, since a water level gauge, a differential pressure gauge, or a barometer is easy to obtain, a water level evaluation means can be comprised easily. Of the two configurations described above, in the latter configuration, it is not necessary to measure the atmospheric pressure, so that the labor of arranging the vent tube can be saved.

It is a figure of the groundwater level fall system 1 concerning a 1st embodiment, (a) is a peripheral arrangement figure, and (b) is a block diagram. The flowchart which showed the operation | movement procedure of the groundwater level fall system 1 which concerns on 1st Embodiment. Explanatory drawing which showed the effect | action of the groundwater level fall system 1 which concerns on 1st Embodiment. The block diagram of the groundwater level fall system 41 which concerns on 2nd Embodiment. The flowchart which showed the operation | movement procedure of the groundwater level fall system 41 which concerns on 2nd Embodiment.

  Hereinafter, an embodiment of a groundwater level lowering system according to the present invention will be described with reference to the accompanying drawings.

[First Embodiment]
FIG. 1 is a diagram showing a groundwater level lowering system according to the present embodiment. As shown in the figure, the groundwater level lowering system 1 according to the present embodiment forms the excavation space 9 by digging up the ground area surrounded by the retaining wall while supporting the ground 8 with the retaining wall 10. In the same manner as in the conventional vacuum deep well method, the well pipe is decompressed using the vacuum pump 4 connected to the inner space 3 of the well pipe 2 while being decompressed. By operating the submersible pump 5 installed in the vicinity of the bottom of 2, the groundwater flowing into the well pipe is pumped through the pumping pipe 7 through the strainer 6 as the groundwater inflow opening formed in the well pipe 2. It is like that.

  Although the well pipe 2 is shown as an example embedded in the back side of the retaining wall 10 in the same figure, the number and positions of the well pipes 2 may cause groundwater to erupt from the bottom of the excavation space 9 or to generate board blisters. It is set appropriately so that it does not occur, and the groundwater level can be lowered sufficiently.

  Here, the groundwater level lowering system 1 according to the present embodiment is disposed at a position above the water surface in the water level gauge 11 disposed near the bottom of the well pipe 2 and the internal space 3 of the well pipe 2. The differential pressure gauge 12 and a sequencer (PLC) 13 as a control means and a calculation means are provided, and the water level gauge 11, the differential pressure gauge 12 and the sequencer 13 function as a water level evaluation means for evaluating the groundwater level in the well pipe 2. At the same time, the sequencer 13 controls the flow rate control valve 14 using the evaluation value obtained by the water level evaluation means described above so that the groundwater level in the well pipe 2 is higher than that of the strainer 6. Yes.

  The water level gauge 11 is configured to output the result of atmospheric pressure correction, and a vent tube (not shown) whose tip communicates with the atmosphere is connected to the water level gauge.

  The differential pressure gauge 12 is configured to measure the differential pressure between the atmospheric pressure in the well pipe 2 and the atmospheric pressure, and, like the water level gauge 11, a vent tube (not shown) whose tip is connected to the atmosphere is provided. Connect to the differential pressure gauge.

  The water level gauge 11 and the differential pressure gauge 12 can be appropriately selected from commercially available products.

  In order to lower the groundwater level by using the groundwater level lowering system 1 according to the present embodiment, the well is formed by using the vacuum pump 4 connected to the inner space 3 of the well pipe 2 in the same manner as in the conventional vacuum deep well method. By operating a submersible pump 5 installed near the bottom of the well pipe 2 while depressurizing the internal space 3 of the pipe, the groundwater flowing into the well pipe 2 via the strainer 6 is grounded via the pumping pipe 7. In this embodiment, as shown in the flowchart of FIG. 2, the water level meter 11 measures the level of groundwater in the well pipe 2, and is the internal space 3 of the well pipe 2 above the water surface. The pressure at the position is measured by the differential pressure gauge 12 as a differential pressure from the atmospheric pressure (step 101).

  Here, the water level measured by the water level gauge 11 is a water level corrected on the assumption that atmospheric pressure is acting on the water surface, and in the well pipe 2 under reduced pressure, a deviation from the actual water level occurs.

Therefore, when the water level measured by the water level gauge 11 is h ₁ and the water column height converted from the differential pressure measured by the differential pressure gauge 12 is h ₂ ,
h = h ₁ + h ₂ (1)
Is calculated by the sequencer 13 to calculate the water level h in the well pipe 2 (step 102).

The above equation (1) can be derived as follows. That is, if the pressure in the well pipe 2 is P ₁ (converted to a water column), the pressure due to only groundwater is P _w (converted to a water column), and the atmospheric pressure is P ₀ (converted to a water column), the water level h ₁ output from the water level gauge 11 is ,
h ₁ = P _w + P ₁ −P ₀
It becomes.

Therefore, when this is transformed,
P _w = h ₁ + P ₀ −P ₁
However, (P ₀ −P ₁ ) is nothing but the differential pressure between the atmospheric pressure in the well pipe 2 and the atmospheric pressure.
P _w = h ₁ + h ₂
It becomes.

  If the water level measuring means consisting of the water level gauge 11, the differential pressure gauge 12 and the sequencer 13 evaluates the groundwater level in the well pipe 2 as the water level h, it is then compared with the monitoring lower limit water level H (step). 103).

  FIG. 3 shows the relationship between the water level h, the monitoring lower limit water level H, and the absolute lower limit water level H ′. The absolute lower limit water level H ′ is a water level corresponding to the uppermost position of the strainer 6 and is below the water level. For example, since air is mixed from the strainer 6, it is defined as a water level that should not be lowered, and the monitoring lower limit water level H is defined as a water level obtained by adding a margin height ΔH to the absolute lower limit water level H ′.

  ΔH is appropriately set from the water permeability of the ground 8, the discharge capacity of the water column pump 5, the degree of vacuum, and the like. The margin height ΔH can be set to 0, and in this case, the monitoring lower limit water level H matches the absolute lower limit water level H ′.

  Here, if the water level h is equal to or higher than the monitoring lower limit water level H (step 103, YES), the flow control valve 14 is opened via the sequencer 13 or is kept open as shown in FIG. (Step 104).

  If it does in this way, the groundwater which flowed in into the well pipe 2 will be pumped up again, or pumping will continue.

  On the other hand, if the water level h is below the monitoring lower limit water level H (step 103, NO) as shown in FIG. 5B, the flow control valve 14 is throttled or closed via the sequencer 13 or maintained. (Step 105).

  If it does in this way, since the pumping amount of the groundwater which flowed in into the well pipe 2 will decrease or the pumping itself will stop or those states will be continued, the groundwater in this well pipe by the inflow of groundwater to the well pipe 2 The water level rises and eventually exceeds the monitoring lower limit water level H.

  Hereinafter, by repeating Step 101 to Step 105 at every predetermined time, the groundwater level inside and outside the well pipe 2 is always maintained at a level above the strainer 6.

  As described above, according to the groundwater level lowering system 1 according to the present embodiment, when the groundwater flowing into the well pipe 2 is pumped from the well pipe, the water level evaluation including the water level gauge 11, the differential pressure gauge 12, and the sequencer 13 is performed. The flow rate control valve 14 is controlled via the sequencer 13 so that the groundwater level h in the well pipe 2 is evaluated by means, and the groundwater level in the well pipe 2 is higher than that of the strainer 6 using the evaluation value. As a result, the groundwater level inside and outside the well pipe 2 always exceeds the strainer 6, thus preventing air from being mixed from the strainer 6, thereby preventing the reduced pressure state in the well pipe 2 from being maintained. It is possible to secure high pumping capacity by the synergistic action of forced drainage and gravity drainage, as well as being able to stabilize the decompression state in the well pipe 2 It is possible to continuously demonstrate the advantages of the accumulation deep well become.

  In addition, according to the groundwater level lowering system 1 according to the present embodiment, since it is not necessary to adopt a double pipe structure as in the prior art, if the inner pipe is φ300 mm to 350 mm, it is φ350 mm to 400 mm. When a well pipe was necessary, it became possible to use a well pipe 2 having a diameter of 300 mm or less, and when newly installing a pumping well, the installation cost could be reduced, and for an existing pumping well, Since there is not enough space to accommodate the inner tube, there is no situation where the application itself becomes difficult.

  Further, according to the groundwater level lowering system 1 according to the present embodiment, it is only necessary to install the water level gauge 11 and the differential pressure gauge 12 in constructing the system. It is possible to introduce a system at a lower cost than in the prior art in which it is necessary to take complicated procedures such as housing the pipe and re-installing the submersible pump in the inner pipe.

  Further, according to the groundwater level lowering system 1 according to the present embodiment, the pressure inside the well pipe 2 can be measured by the differential pressure gauge 12 in the form of a differential pressure from the atmospheric pressure. The state can be monitored.

  In the present embodiment, the flow rate control valve 14 is controlled so that the groundwater level in the well pipe 2 is higher than that of the strainer 6, but instead, the submersible pump 5 may be controlled. Absent.

  Even in such a case, it is the same as the case of the flow rate control valve 14 in that the amount of pumped water is adjusted, and the same effect as described above can be obtained.

[Second Embodiment]
Next, a second embodiment will be described. Note that components that are substantially the same as those of the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  As shown in FIG. 4, the groundwater level lowering system 41 according to the present embodiment includes a water level meter 51 disposed in the vicinity of the bottom of the well pipe 2 and a position that is the internal space 3 of the well pipe and is above the water surface. And a sequencer (PLC) 53 as a control unit and a calculation unit, and the water level meter 51, the barometer 52 and the sequencer 53 evaluate the water level of the groundwater in the well pipe 2. In addition to functioning as a means, the sequencer 53 controls the flow rate control valve 14 using the evaluation value obtained by the above-described water level evaluation means so that the groundwater level in the well pipe 2 is higher than that of the strainer 6. It has become.

  The water level gauge 51 is a so-called absolute water level gauge configured to output without correcting the atmospheric pressure. Unlike the water level gauge 11, no vent tube is required.

  The barometer 52 is configured to measure the atmospheric pressure in the well pipe 2 and, like the water level gauge 51, the arrangement of the vent tube is not necessary.

  The water level gauge 51 and the barometer 52 can be appropriately selected from commercially available products.

  In order to lower the groundwater level by using the groundwater level lowering system 41 according to the present embodiment, the well is formed by using the vacuum pump 4 connected to the internal space 3 of the well pipe 2 in the same manner as in the conventional vacuum deep well method. By operating a submersible pump 5 installed near the bottom of the well pipe 2 while depressurizing the internal space 3 of the pipe, the groundwater flowing into the well pipe 2 via the strainer 6 is grounded via the pumping pipe 7. In this embodiment, as shown in the flowchart of FIG. 5, the water level meter 51 measures the level of groundwater in the well pipe 2, and the internal space 3 of the well pipe 2 is above the water surface. The barometric pressure at the position is measured by the barometer 52 (step 111).

  Here, the water level measured by the water level gauge 51 is a water level that is output assuming that all the pressure values are caused by the water pressure, and a deviation from the actual water level occurs in the well pipe 2 where the atmospheric pressure exists.

Therefore, when the water level measured by the water level gauge 51 is h ₃ and the water column height converted from the atmospheric pressure measured by the barometer 52 is h ₄ ,
h = h ₃ −h ₄ (2)
Is calculated by the sequencer 53 to calculate the water level h in the well pipe 2 (step 112).

The above equation (2) can be derived as follows. That is, if the pressure due to only groundwater is P _w (water column equivalent), the water level h ₃ output from the water level gauge 51 is
h ₃ = P _w + P ₄
It becomes.

Therefore, when this is transformed,
P _w = h ₃ −P ₄
It becomes.

  If the water level measuring means comprising the water level gauge 51, the barometer 52 and the sequencer 53 thus evaluates the groundwater level in the well pipe 2 as the water level h, then this is compared with the monitoring lower limit water level H (step) 113).

  Here, if the water level h is equal to or higher than the monitoring lower limit water level H (step 113, YES), the flow control valve 14 is opened or maintained through the sequencer 13 (step 114).

  If it does in this way, the groundwater which flowed in into the well pipe 2 will be pumped up again, or pumping will continue.

  On the other hand, if the water level h is below the monitoring lower limit water level H (step 113, NO), the flow control valve 14 is throttled or closed via the sequencer 13 or maintained in the state (step 115).

  If it does in this way, since the pumping amount of the groundwater which flowed in into the well pipe 2 will decrease or the pumping itself will stop or those states will be continued, the groundwater in this well pipe by the inflow of groundwater to the well pipe 2 The water level rises and eventually exceeds the monitoring lower limit water level H.

  Hereinafter, the ground water level inside and outside the well pipe 2 is always maintained at a level higher than the strainer 6 by repeating Steps 111 to 115 at predetermined times.

  As described above, according to the groundwater level lowering system 41 according to the present embodiment, when the groundwater flowing into the well pipe 2 is pumped from the well pipe, the water level evaluation including the water level gauge 51, the barometer 52 and the sequencer 53 is performed. The flow rate control valve 14 is controlled via the sequencer 53 so that the groundwater level h in the well pipe 2 is evaluated by means, and the groundwater level in the well pipe 2 is higher than that of the strainer 6 using the evaluation value. As a result, the groundwater level inside and outside the well pipe 2 always exceeds the strainer 6, thus preventing air from being mixed from the strainer 6, thereby preventing the reduced pressure state in the well pipe 2 from being maintained. It is possible to secure high pumping capacity by the synergistic action of forced drainage and gravity drainage by stabilizing the reduced pressure state in the well pipe 2 It is possible to continuously exert the advantages of the vacuum deep well.

  In addition, according to the groundwater level lowering system 41 according to the present embodiment, as in the case of the groundwater level lowering system 1, it is not necessary to adopt a double pipe structure as in the prior art, and therefore, for example, a well pipe 2 having a diameter of 300 mm or less is used. It is possible to reduce the installation cost when newly installing a pumping well, and it is difficult to apply the existing pumping well because there is not enough space to accommodate the inner pipe. Such a situation does not occur.

  Moreover, according to the groundwater level lowering system 41 according to the present embodiment, the system can be introduced at a low cost as in the case of the groundwater level lowering system 1.

  In addition, according to the groundwater level lowering system 41 according to the present embodiment, since it is not necessary to measure atmospheric pressure, it is possible to save the trouble of arranging the vent tube.

  Further, according to the groundwater level lowering system 41 according to the present embodiment, since the atmospheric pressure in the well pipe 2 can be measured by the barometer 52, the reduced pressure state in the well pipe 2 can be monitored.

  In the present embodiment, the flow rate control valve 14 is controlled so that the groundwater level in the well pipe 2 is higher than that of the strainer 6, but instead, the submersible pump 5 may be controlled. Absent.

  Even in such a case, it is the same as the case of the flow rate control valve 14 in that the amount of pumped water is adjusted, and the same effect as described above can be obtained.

1,41 Groundwater level lowering system 2 Well pipe 3 Internal space of well pipe 2 4 Vacuum pump 5 Submersible pump 6 Strainer (groundwater inflow opening)
7 Pumping pipe 8 Ground 11, 51 Water level gauge 12 Differential pressure gauge 13, 53 Sequencer (control means, calculation means)
14 Flow control valve 52 Barometer

Claims (3)

A well pipe buried in the ground, a submersible pump installed near the bottom of the well pipe and connected to a pumping pipe, and a vacuum pump connected to the internal space of the well pipe, using the vacuum pump By operating the submersible pump while decompressing the internal space of the well pipe, the ground water flowing into the well pipe is pumped through the pump pipe through the ground water inflow opening formed in the well pipe. In the groundwater level lowering system,
A water level evaluation means for evaluating the level of groundwater in the well pipe, and a flow rate control valve provided in the pumping pipe or a control means for controlling the submersible pump, and the submersible pump is disposed at the top of the groundwater inflow opening. The control means is positioned below the position, and the control means uses the evaluation value obtained by the water level evaluation means so that the groundwater level in the well pipe is higher than the groundwater inflow opening. A groundwater level lowering system characterized by controlling a flow rate control valve or the submersible pump. The water level evaluation means is a water level meter that is installed in the ground water in the well pipe and configured to correct atmospheric pressure, a differential pressure gauge that measures the pressure difference between the atmospheric pressure and the atmospheric pressure in the well pipe, and a calculation means And when the water level measured by the water level gauge is h ₁ and the water column height converted from the differential pressure measured by the differential pressure gauge is h ₂ , the water level in the well pipe h is the following formula:
h = h ₁ + h ₂
The groundwater level lowering system according to claim 1, wherein the groundwater level lowering system is configured to calculate using The water level evaluation means comprises a water level meter installed in ground water in the well pipe and configured not to perform atmospheric pressure correction, a barometer for measuring the pressure in the well pipe, and a calculation means, When the calculation means has a water level measured by the water level meter as h ₃ and a water column height converted from the atmospheric pressure measured by the barometer as h ₄ , the water level h in the well pipe is expressed by the following equation:
h = h ₃ −h ₄
The groundwater level lowering system according to claim 1, wherein the groundwater level lowering system is configured to calculate using

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