JP4255462B2 - Condensate well structure - Google Patents

Description

  The present invention relates to a condensate well structure, and more particularly, for example, to a condensate well structure used in a recharge method for returning groundwater pumped up to lower the groundwater level when excavating in the ground having a high groundwater level. .

  When excavating the ground to construct an underground structure, if the groundwater level is high, countermeasures such as a groundwater level lowering method or a chemical injection method are implemented. The groundwater level lowering method is a method for stabilizing the ground by pumping water from the ground and lowering the groundwater level at the necessary construction site. This groundwater level lowering construction method is a reliable groundwater countermeasure construction method against the waterstop construction method such as the chemical solution injection construction method, and is therefore excellent in safety especially in the construction under the railway.

  By the way, if the groundwater pumped up by the groundwater level lowering method is discharged into the sewers and rivers as it is, it will cause damage such as subsidence of the surrounding ground and lowering of the water level of the wells. For this reason, a method of returning the pumped groundwater to the ground, that is, a recharge method is widely implemented.

  However, in this recharge method, clogging occurs in the pore wall and filter of the condensate well due to suspended suspended solids, bacteria, and dissolved iron oxides contained in the groundwater. For this reason, the return efficiency is deteriorated, and in some cases, it may be forced to drain into a sewer or a river.

  That is, in the condensate well in the conventional recharge method, for example, as shown in FIG. 4, a casing pipe 52 equipped with a screen 51 made of a winding is installed inside a drilling hole 50 having a hole diameter of about 550 mm or larger. The water injection pipe 53 is installed inside the casing pipe 52, and the excavation hole 50 around the screen 51 is filled with a filter (filter gravel) 54 made of crushed stone.

  The groundwater pumped up is supplied to the casing pipe 52 through the water injection pipe 53 and returned to the ground through the screen 51 and the filter 54 at the lower end of the casing pipe 52. Here, the pressure of the groundwater supplied to the casing pipe 52 is about the natural head pressure, and the screen 51 and the filter 54 are clogged with the passage of time. For this reason, in the conventional condensate well, a cleaning drain pipe 57 having a cleaning pump 56 attached to the lower end is inserted, and the screen 51 and the filter 54 are reversely cleaned by pressurization, vacuum, or the like.

Patent Document 1 discloses a technique of pressurizing pumped ground water and returning it to the ground. However, in the technique disclosed in this document, the purpose of pressurization is to prevent oxidation of iron dissolved in the groundwater by blocking the groundwater from the atmosphere, and the structure of the condensate well is the conventional one shown in FIG. There is no difference. For this reason, when passing through a screen having a large opening area (referred to as a strainer tube in the same document), the flow velocity of the returned groundwater is greatly reduced, and the effect of preventing clogging due to pressurization cannot be expected.
JP 2002-256538 A

The present invention has been made based on the technical background as described above, and achieves the following object.
An object of the present invention is to provide a condensate well structure that prevents clogging due to suspended suspended solids, bacteria, oxides of dissolved iron, etc. in the condensate well, and can eliminate the need for backwashing operation. It is in.

The present invention employs the following means in order to achieve the above object.
That is, this invention is a condensate well structure for returning the groundwater pumped up to the ground under pressure,
A water injection pipe installed in the excavation hole, having an upper end connected to a return pipe on the ground having a pressure pump, a strainer part at the lower end , and a pipe diameter of φ30 to 50 mm ;
A filter material layer formed in an excavation hole around the strainer portion;
A water shielding layer formed in the excavation hole on the filter material layer, and
A sealing material layer formed in the excavation hole on the water shielding material layer,
The strainer part has a large number of water injection holes formed at intervals in the circumferential direction and the length direction over a length range of 500 to 2000 mm on the pipe wall of the water injection pipe itself ,
Returning groundwater returned to the ground while washing the filter material layer by pouring return groundwater pressurized to 200 to 1000 kPa by the pressure pump toward the filter material layer from the water injection hole. It is in the condensate well structure characterized by being composed .

  The said condensate well structure can also take the aspect by which the net | network for preventing that the said filter material penetrate | invades into the said water injection hole is arrange | positioned on the outer periphery of the said strainer part.

  According to this invention, the strainer part has a structure in which a large number of water injection holes are provided in the pipe wall of the water injection pipe itself. For this reason, since the pressurized groundwater increases the flow velocity and is injected toward the filter material layer from the water injection hole, the strainer portion is not clogged. Further, the filter material layer is also in the same state as being constantly washed with high flow rate water injection, and the occurrence of clogging can be prevented. Therefore, the back washing operation is not necessary.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view showing an embodiment of the present invention. The groundwater level lowering method is a method of lowering the groundwater level of a construction site to be excavated by pumping up groundwater from a pumping well (not shown). In such a groundwater level lowering method, the recharge method is positioned as a method of returning the groundwater pumped up to the ground through a condensate well without discharging it into a river or the like.

  In the condensate well 1 according to the present invention, the water injection pipe 3 is directly installed in the excavation hole 2 formed by boring the ground without using a casing as in the conventional case. The water injection pipe 3 is connected to the return pipe 4 on the ground, and the groundwater pumped up in the pumping well is pressurized by the pressurizing pump 5 provided in the return pipe 4 and supplied to the water injection pipe 3.

  In order to return pressurized groundwater to the ground at a high flow rate, the water injection pipe 3 has a pipe diameter (outer diameter) of a small diameter of about φ30 to 50 mm. As this water injection pipe, a general carbon steel pipe for piping or a steel pipe for piping (gas pipe), for example, SGP32A (outer diameter 42.7 mm, inner diameter 35.7 mm) can be used. Thus, since the small diameter water injection pipe 3 is used, the excavation hole 2 is also as small as a drilling diameter of about φ116 mm.

  The water injection pipe 3 has a strainer section 6 at the lower end. Details of the strainer section 6 will be described later. In the excavation hole 2, a filter material layer 7 is formed around the strainer portion 6, a water shielding material layer 8 is formed on the filter material layer 7, and a sealing material layer is further formed on the water shielding material layer 8. 9 is formed.

  The filter material layer 7 is used to improve the water permeability of the return water to be injected. For example, the filter material layer 7 is formed by filling the excavation hole 2 with a granular material having a uniform particle size such as silica sand and having excellent water permeability. The The filter material may be used by mixing materials having different particle sizes depending on the formation. The water shielding material layer 8 blocks the sealing material from being mixed into the filter material layer 7 during the construction of the sealing material layer 9, and blocks the return water that has been injected from leaking to the sealing material layer 9 side. Is for. As the material of the water shielding material layer 8, bentonite (for example, pellets) which is a clay mineral-based water shielding material is used. The sealing material layer 9 is for preventing the groundwater from flowing backward due to the water pressure because the returned groundwater is poured from the strainer section 6 at a high pressure. The sealing material layer 9 is formed by injecting a cement-based solidifying material, for example, cement milk, into the excavation hole 2 above the water shielding material layer 8.

  FIG. 2 is an enlarged view of the strainer portion 6, (a) is an axial sectional view, and (b) is a sectional view taken along line AA in (a). In this embodiment, the strainer portion 6 is formed separately from the water injection pipe body 3a for the convenience of drilling and the like, and has a structure that is screw-connected to the water injection pipe body 3a (screws are not shown). It is a component of the water pipe 3. Therefore, the strainer part 6 may be integrated without being separable from the water injection pipe body 3a. The strainer section 6 is provided with a large number of water injection holes 10 in the tube wall over a predetermined length range.

  These water injection holes 10 are provided at intervals in the circumferential direction (an angular interval of 180 degrees in this embodiment) and at intervals in the length direction. The water injection holes 10 adjacent in the vertical direction are arranged so as to have a phase difference of 90 degrees. The size of the water injection holes 10 is a small hole of about φ10 mm, and the interval (pitch) of the water injection holes 10 on the same bus is about 100 mm. Therefore, as can be understood from FIG. 2, the length range in which the water injection hole 10 is provided varies depending on the thickness of the formation, but is a short range of 500 to 2000 mm that is pinpoint injection (in this embodiment, 600 mm). Degree). The number, arrangement, and the like of the water injection holes 10 are determined according to the properties of the geological water to be injected and the amount of water injection. The shape of the water injection hole 10 is circular in the illustrated embodiment, but may be various shapes such as a polygon and a slit.

  A net 11 is attached to the outer periphery of the strainer portion 6 so as to surround the water injection hole 10. This net 11 is for preventing the material such as silica sand of the filter material layer 7 from entering the water injection hole 10 and is simple. If a filter material having a particle size larger than that of the water injection hole 10 is selected, the net 11 can be made unnecessary.

  According to the condensate well structure as described above, as shown in FIG. 3, the return groundwater pressurized to 200 to 1000 kPa by the pressurizing pump 5 passes through the water injection pipe 3 and from the water injection hole 10 of the strainer section 6. Water is poured toward the filter material layer 7. At that time, the flow rate in the water injection hole 10 is larger than the flow rate in the pipe, and water is injected at a high flow rate. For this reason, the strainer portion 6 is not clogged. Moreover, the filter material layer 7 is also in the same state as being constantly washed with high flow rate water injection, and can prevent clogging. Furthermore, the length range in which the water injection hole 10 is formed is short, and pinpoint injection according to the formation can be performed.

  The water injection pipe structure and the condensate well structure according to the present invention can be applied not only to the recharge method but also to other uses such as a groundwater heat utilization system.

  That is, the groundwater thermal energy possessed by the groundwater is a stable heat source that can be found everywhere, and the use of this heat source is an effective method from the viewpoint of reducing the environmental burden. In fact, in cold and snowy areas, it is used for melting snow on ramps such as approach sections such as three-dimensional intersections, melting snow on sidewalks and parking lots where snow is piled up, and for road cooling that also suppresses heat islands in urban areas. Is also being applied.

  As one such groundwater heat utilization system, there is an underground reduction system in which groundwater pumped from a pumping well is circulated through a heat exchange pipe, and groundwater from which only thermal energy is extracted is returned to the ground through a condensate well. . The water injection pipe structure and the condensate well structure according to the present invention can also be applied to the groundwater heat utilization system of the underground reduction method. As a result, problems such as land subsidence can be minimized.

It is sectional drawing which shows embodiment of this invention. The strainer part is shown enlarged, (a) is an axial sectional view, and (b) is a sectional view taken along line AA in (a). It is sectional drawing which shows a water injection state. It is sectional drawing which shows the conventional condensate well structure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Condensate well 2 Drilling hole 3 Water injection pipe 4 Return pipe 5 Pressure pump 6 Strainer part 7 Filter material layer 8 Water shielding material layer 9 Sealing material layer 10 Water injection hole 11 Net

Claims (2)

A condensate well structure for pumping up groundwater and returning it to the ground.
A water injection pipe installed in the excavation hole, having an upper end connected to a return pipe on the ground having a pressure pump, a strainer part at the lower end , and a pipe diameter of φ30 to 50 mm ;
A filter material layer formed in an excavation hole around the strainer portion;
A water shielding layer formed in the excavation hole on the filter material layer, and
A sealing material layer formed in the excavation hole on the water shielding material layer,
The strainer part has a large number of water injection holes formed at intervals in the circumferential direction and the length direction over a length range of 500 to 2000 mm on the pipe wall of the water injection pipe itself ,
Returning groundwater returned to the ground while washing the filter material layer by pouring return groundwater pressurized to 200 to 1000 kPa by the pressure pump toward the filter material layer from the water injection hole. Condensate well structure characterized by being constructed.   The condensate well structure according to claim 1, wherein a net for preventing the filter material from entering the water injection hole is disposed on an outer periphery of the strainer portion.

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