JP6432863B2 - Groundwater observation method and observation tube used therefor - Google Patents

Description

  The present invention mainly relates to a groundwater observation method for confirming water shielding performance and the like in a waste disposal site, and an observation tube used for the groundwater observation method.

  In the final disposal site for general waste and industrial waste, in order to prevent the contaminated water caused by the waste thrown into the upper ground part from diffusing into the lower ground part, An impermeable layer such as a viscous soil layer is provided between the two.

  In such a waste disposal site, after the landfill work is completed, the site may be highly used as a transportation site or an industrial site. In that case, a structure is built on the site to suit each application. Therefore, the foundation pile as the foundation may be driven so as to penetrate the impermeable layer and reach the support ground.

  As a method of placing foundation piles at the site of the waste disposal site, it is possible to suppress the entry of contaminants, such as waste, into the impermeable layer (viscous soil layer) due to the foundation pile placement, Adoption of the method using the Nakabori method is expected in the future because the amount of water permeation through the boundary with the impermeable layer is extremely small.

On the other hand, in the final disposal site for general waste and industrial waste, the technical standards stipulated by related laws and regulations, specifically, the water permeability is 1 × 10 ⁻⁷ m / s or less, and the layer thickness is 5 m or more. It is necessary to satisfy the water shielding performance equivalent to or better than that of the impermeable layer portion.

  In particular, when foundation piles are laid on the site of a waste disposal site, contaminants such as waste accompanying the placement of foundation piles are brought into the impermeable layer, and the boundary between the foundation pile and the impermeable layer It is necessary to observe the state of groundwater in order to confirm these effects because there is a concern that contaminated water will permeate through to the lower layer of the ground.

  Therefore, conventionally, as shown in FIG. 10, an observation well 3 is installed on the ground 2 on which the foundation pile 1 is placed so that the lower end reaches the ground lower layer (aquifer layer) 2c below the impermeable layer 2b. A method of observing whether or not contaminated water has diffused into the groundwater by collecting groundwater from the ground lower layer 2c through the strainer 3a at the lower end of the observation well and analyzing the groundwater is conceivable (for example, Patent Document 1). See).

JP 2001-280052 A

  However, in the conventional technology as described above, when the foundation pile is laid by the method using the Nakabori method, the contaminated water permeates to the ground lower layer through the boundary between the foundation pile and the impermeable layer (viscous soil layer). However, the contaminated water that permeated through the impermeable layer with a small amount of permeated water is diluted with groundwater, so even if the water collected from the lower ground using conventional observation wells is analyzed, There was a problem that it was difficult to evaluate the permeation of contaminated water through the boundary between the pile and the impermeable layer.

  Therefore, in view of such a conventional problem, the present invention is a groundwater that can evaluate the permeation through the boundary between the foundation pile and the impermeable layer when the foundation pile is placed on the site of the waste final disposal site. It was made for the purpose of providing an observation method and an observation tube used therefor.

The feature of the invention according to claim 1 for solving the conventional problems as described above is that an observation well is installed on the ground with an impermeable layer made of viscous soil between the upper and lower layers of the ground. In the groundwater observation method for analyzing the groundwater taken from the observation well and observing the state of the groundwater, the depth of the impermeable layer portion is investigated in advance, and a water intake hole communicating inside and outside the pipe is formed. The observation tube having a perforated portion provided at a desired position in the tube axis direction and excavating earth and sand in the observation tube until the lower end reaches the impermeable layer portion. after penetrating the body to the ground, the said perforated portion of the observation tube body is penetrated to further the ground until located in the impermeable layer section, thereafter, the chromatic of the observation tube body the below hole is closed by the shield and observation well the observation tube body, the survey said perforated portion In the groundwater observation method, water permeating the impermeable layer portion in a state matched to the depth of the impermeable layer portion is taken into the observation pipe through the intake hole .

  According to a second aspect of the present invention, in addition to the configuration of the first aspect, the observation tube is formed in substantially the same shape as a foundation pile for a structure, and is formed on the ground by a method similar to that for the foundation pile. It is to be installed.

  According to a third aspect of the present invention, in addition to the structure of the first or second aspect, the observation tube is penetrated until the lower end thereof reaches the support base. It is to be used as a foundation pile.

  In addition to the structure of any one of claims 1 to 3, a feature of the invention described in claim 4 is provided with a support convex portion for supporting a shielding plate on the side surface of the observation tubular body under the perforated portion, The shielding body is formed by filling a shielding filler with or on the shielding plate supported by the support convex portion.

  According to a fifth aspect of the present invention, in addition to the configuration of any one of the first to fourth aspects, a plurality of the perforated portions are formed in the observation tube body at intervals in the tube axis direction. The observation tube is inserted into the ground so that at least any one of the plurality of perforated portions is located in the impermeable layer portion, and each intake hole of the perforated portion located above the impermeable layer portion is provided. While closing, it exists in closing the lower part of the lowermost said hole part located in the said impermeable layer part with the said shielding part.

  A feature of the invention described in claim 6 is an observation tube used in the groundwater observation method according to any one of claims 1 to 5, wherein a water intake hole communicating inside and outside the tube is formed. And an observation tube arranged so that the perforated portion is positioned in the impermeable layer portion when installed on the ground.

  The feature of the invention described in claim 7 is that, in addition to the configuration of claim 6, the perforated portion is formed to have a larger thickness in the tube diameter direction than the other portions.

  A feature of the invention described in claim 8 is that, in addition to the structure of claim 6 or 7, a support convex portion for supporting a shielding plate for closing the inside of the tube is provided on the inner surface below the perforated portion. .

In the groundwater observation method according to the present invention, as described above, an observation well is installed on the ground with an impermeable layer made of viscous soil between the upper and lower layers of the ground, and water is taken from the observation well. In the groundwater observation method for analyzing the groundwater and observing the state of the groundwater, the depth of the impermeable layer portion is investigated in advance, and a perforated portion in which a water intake hole communicating inside and outside the pipe is formed is piped. Using an observation tube provided in a desired position in the axial direction, excavating the earth and sand in the observation tube, and penetrating the observation tube into the ground until the lower end reaches the impermeable layer. was followed, wherein the perforated portion of the observation tube body is penetrated to further the ground until located in the impermeable layer section, thereafter, the shield downward from the perforated portion of the observation tube body in closed as an observation well the observation tube body, based on the perforated portion to the investigation said impermeable By intake of water penetrated into the impermeable layer section in a state to match the depth of the layer portion to the observation tube body through the intake hole, contaminated water through the boundary portion between the foundation pile and the impermeable layer section The presence or absence of transmission and the transmission status can be confirmed.

  Further, in the present invention, the observation tube is formed in substantially the same shape as the foundation pile for the structure, and flows into the observation tube by being installed on the ground by the same construction method as the foundation pile. By analyzing the water, it is possible to evaluate the state of contamination water permeation when a foundation pile penetrating the impermeable layer is installed.

  Furthermore, in the present invention, the observation pipe is penetrated until its lower end reaches the support base, and the observation pipe is used as a foundation pile of a structure after observation, whereby the observation pipe is used as a foundation pile. Can be used effectively.

  Furthermore, in the present invention, a support convex part for supporting a shielding plate is provided on the side surface of the observation tube below the perforated part, and the shield plate supported by the support convex part is on or on the shielding plate. By forming the shielding body by filling the shielding filler, the shielding body can be suitably provided below the perforated portion in the observation tube.

  In the present invention, a plurality of the perforated portions are formed at intervals in the tube axis direction on the observation tube body, and at least one of the plurality of perforated portions is located in the impermeable layer portion. The observation tubular body is penetrated into the ground to close each intake hole of the perforated part located above the impermeable layer part, and the lowest perforated part located in the impermeable layer part By closing the lower part with the shielding part, the position of the perforated part can be adjusted to the impermeable layer part even if the depth of the supporting ground part or the penetration depth of the observation tube is unknown.

  The observation tube according to the present invention is an observation tube used in the groundwater observation method according to any one of claims 1 to 5, and has a perforated portion in which a water intake hole communicating inside and outside the tube is formed. And the perforated part is positioned so as to be located in the impermeable layer part when installed on the ground, so that the presence / absence of water permeation from the upper part of the ground and the permeation state thereof can be confirmed. Can be used for wells.

  Further, in the present invention, the perforated portion is formed thicker in the radial direction than the other portions, thereby reinforcing the cross-sectional defect due to the provision of the water intake hole, and the strength of the observation tube. Can be secured.

  Furthermore, in the present invention, the support convex portion for supporting the shielding plate that closes the inside of the pipe is projected on the inner surface below the perforated portion, so that the shield can be easily provided at an appropriate location.

It is a longitudinal section showing an example of an embodiment of a groundwater observation method concerning the present invention. (A)-(c) is a front view which shows the perforated part part of the perforated pipe material used for the tubular body for observation in FIG. 1, respectively. (A)-(h) is a longitudinal cross-sectional view which shows the installation process of the pipe for observation in the observation method of groundwater. It is a longitudinal cross-sectional view which shows the state of the perforated part part in FIG. It is a longitudinal cross-sectional view which shows another example of the embodiment of the observation method of the groundwater which concerns on this invention. (A)-(f) is a longitudinal cross-sectional view which shows the other Example of the installation process of the observation tube in the observation method of groundwater. It is a longitudinal cross-sectional view which shows another example of the embodiment of the observation method of the groundwater which concerns on this invention. (A) is the longitudinal cross-sectional view which shows the perforated part part of the observation pipe body in FIG. 7, (b) is the AA sectional view, (c) BB sectional drawing. It is a longitudinal cross-sectional view which shows another example of a porous tube material. It is a longitudinal cross-sectional view which shows the aspect of the conventional observation method of groundwater.

  Next, an embodiment of the groundwater observation method according to the present invention and the observation pipe used in the method will be described based on the examples shown in the drawings.

  In the embodiment shown in FIG. 1, the observation of groundwater at the site of a waste final disposal site that is highly utilized as a traffic site or an industrial site will be described as an example. explain.

  The ground 2 at the site of the waste disposal site includes an impermeable layer 2b made of viscous soil or the like below the upper layer 2a of the waste, and the impermeable layer 2b and the impermeable layer 2b are impermeable to water. The ground lower layer part 2c under the layer part 2b is insulated.

  In addition, when the waste final disposal site is used as a transportation site or an industrial site, the foundation pile 1 that forms the foundation of the structure penetrates the impermeable layer 2b and the lower end reaches the supporting ground 2d. It is designed to penetrate.

  The foundation pile 1 is formed by sequentially connecting pile pipe materials 1a, 1a ... such as steel pipes, and discharging the earth and sand inside by the Nakabori method, while the lower end reaches the impermeable layer portion 2b. It is installed by penetrating from the position until the lower end reaches the supporting ground 2d by hammering or the like.

  In such a waste final disposal site, the method of the present invention has an observation in which a perforated portion 11 formed with intake holes 10, 10... The observation tube 12 is used as an observation well by installing the observation tube 12 on the ground 2 so that the perforated portion 11 is located in the impermeable layer portion 2b. The groundwater that has flowed into the observation pipe 12 through 10, 10... Is taken, and the state of the groundwater is observed by analyzing the groundwater.

  The observation tube 12 is formed in substantially the same shape as the foundation pile 1 and has a perforated portion 11 formed with intake holes 10, 10... Communicating in and out of the tube at a desired position in the tube axis direction. The perforated part 11 is positioned in the impermeable layer part 2b when installed on the ground 2.

  This observation pipe body 12 is appropriately welded with the penetration of the pile pipe materials 1a, 1a ... made of the same steel pipe as the foundation pile 1 and the perforated pipe material 13 having the perforated portion 11 into the ground 2. It is formed by connecting with the base pile 1 and is installed on the ground 2 by a construction method using the Nakabori construction method similarly to the foundation pile 1.

  The pile pipe materials 1a, 1a ... are formed in a cylindrical shape having both ends in the pipe axis direction opened by a steel pipe or the like used for the foundation pile 1, and the inside and outside of the pipe are shielded in the pipe diameter direction.

  The perforated pipe material 13 is formed in a cylindrical shape having both ends in the pipe axis direction opened by a steel pipe or the like similar to the pile pipe material 1a, and has a plurality of water intake holes 10, 10. A perforated portion 11 is provided.

  Although the aspect of the perforated part 11 is not particularly limited, for example, in FIG. 2A in which slit-like water intake holes 10, 10... Facing in the pipe axis direction are formed at intervals in the pipe circumferential direction. 2 (b) provided with a plurality of horizontally elongated slit-shaped intake holes 10, 10... Formed at intervals in the pipe circumferential direction. A round hole mold shown in FIG. 2 (c) composed of a mold, a large number of round hole-shaped water intake holes 10, 10...

  In the horizontally long type shown in FIG. 2B, the pipe circumferential direction positions of the plurality of water intake holes 10, 10... Formed at intervals in the pipe circumferential direction are shifted for each column, that is, The water intake holes 10, 10... Are arranged in a staggered manner for each row, and the water intake holes 10, 10. The water can be taken from the entire circumference of the observation tube 12.

  In addition, the perforated portion 11 is closed with a water-permeable shielding material having a water permeability made of a punching metal, a filter material, or the like, for example, when the earth and sand of the impermeable layer portion 2b is fragile. Further, it is possible to prevent the earth and sand of the impermeable layer portion 2b from being pushed into the observation pipe body 12 while allowing water intake from the water intake hole 10.

  Next, a specific method for installing the observation tube 12 on the ground 2 and observing groundwater will be described with reference to FIGS. 3 (a) to 3 (g).

  First, as a preliminary preparation, based on a plan map, a design drawing, etc., or if necessary, a grounding survey is performed on the ground 2 to be observed, and the ground upper layer 2a, impermeable layer 2b, ground lower layer 2c. The depth of each layer, the depth of the supporting ground 2d, and its state are confirmed.

  Then, as shown in FIG. 3 (a), the pile pipe 1a is removed until the lower end reaches the impermeable layer portion 2b while excavating the earth and sand in the pile pipe 1a using a drilling means such as a hammer grab or an auger (not shown) It penetrates into the ground upper layer part 2a.

  At that time, the upper end of the pile pipe material 1a is projected from the surface of the ground 2, and the inside and outside of the pipe are shielded by the ground upper layer portion 2a.

  Next, as shown in FIG. 3 (b), the perforated pipe material 13 is connected to the upper end of the penetrated pile pipe material 1a by welding or the like, and from this state, as shown in FIG. The observation tube 12 is penetrated to a desired position on the ground 2 by hitting with a machine or the like.

  Thereafter, as shown in FIG. 3 (d), the pile pipe material 1a is connected to the upper end of the observation tube 12 by welding or the like, and as shown in FIG. The observation tube 12 is inserted into the ground 2 until the perforated portion 11 is positioned in the impermeable layer portion 2b and the lower end reaches the supporting ground 2d.

  In addition, it is desirable that the position of the perforated part 11 is located below the intermediate part of the impermeable layer part 2b. In the case of an open-ended pile having a diameter D, the depth D is determined when the impermeable layer part 2b is normally consolidated. When the impervious layer portion 2b is overconsolidated, it has been confirmed through experiments and the like that the upper end position of the perforated portion 11 is incomplete. It is preferable to penetrate from the upper end of the water permeable layer portion 2b so as to be at a depth D to 3D.

  Then, as shown in FIG. 3 (f), the sediment in the observation tube 12 is excavated to a desired depth, and the sediment up to the lower portion of the perforated portion 11 of the observation tube 12 is removed. ), The lower part of the observation tube 12 below the perforated part 11 is closed with a shield 14 and the upper part of the observation tube 12 above the shield 14 is taken as an observation well.

  The shield 14 is formed, for example, by placing concrete, the lower side of the observation tube 12 is closed from the perforated portion 11, and the water from the ground lower layer 2 c does not flow into the portion constituting the observation well. It is like that.

  In the observation tube 12 installed in this way, it is possible to suppress the entry of contaminants and the like into the impermeable layer 2b due to the penetration of the observation tube 12, and the observation tube 12 and the impermeable layer The amount of water permeation through the boundary with 2b can be extremely reduced.

  In order to observe groundwater using the observation well comprising the observation tube 12, first, a pumping means 15 for pumping up the water in the observation well is installed. In addition, as shown in FIG. 4, the pumping means 15 illustrated the case where the pumping pump was installed in the observation well, However, The aspect is not specifically limited, For example, a pumping pump is provided in the surface part by the water level in the monitoring well. It may be installed and pumped up.

  And this pumping means 15 is operated, the water stored in the observation well is excluded, the water level in the observation well is made lower than the position of the perforated part 11, and as shown in FIG. The water head difference h from the water level (groundwater level) is set to be large.

  Since the water head difference h inside and outside the pipe is thus large, as shown in FIG. 4, when the water w permeates the boundary portion between the observation tube 12 and the impermeable layer portion 2b, the water w is not Without passing through the water permeable layer portion 2b toward the lower ground lower layer portion 2c, the water permeable layer portion 2b flows into the observation tube 12 through the water intake holes 10, 10.

  Therefore, after confirming the water level, the water flowing into the observation pipe 12 through the intake holes 10, 10... Is pumped to the ground by the pumping means 15, and the water is analyzed to analyze the ground. The presence / absence of contaminated water permeation from the upper layer portion 2a and the permeation state thereof can be confirmed.

  That is, the water staying in the ground upper layer 2a of the site of the waste disposal site is in a highly alkaline, high salinity and reducing state, so that the water collected from the observation tube 12 has a pH and salinity concentration. , Electrical conductivity, oxidation-reduction potential, COD (chemical oxygen demand), BOD (biochemical oxygen demand), etc. are measured, and water staying in the upper layer 2a of the waste disposal site By comparing with the surrounding groundwater, it is possible to confirm whether or not contaminated water permeates from the ground upper layer portion 2a through the boundary between the observation tube 12 and the impermeable layer portion 2b and the permeation status thereof. .

  In addition, the observation tube 12 has the same shape as the foundation pile 1 used for the advanced use of the site of the waste disposal site, and is installed on the ground 2 by the same construction method as the foundation pile 1. Contaminated water through the boundary between the pile of the foundation pile 1 to be used and the impermeable layer 2b by confirming whether or not the polluted water permeated from the ground upper layer 2a using the observation tube 12 and its permeation state The presence or absence of transmission and the transmission status can be evaluated.

  Furthermore, since the observation tube 12 is configured in the same manner as the foundation pile 1 used in the advanced use of the site of the waste disposal site, the observation tube 12 is replaced with the foundation pile of the structure after the observation is completed. 1 can be used.

  In that case, as shown in FIG. 3 (h), concrete 16 or the like is filled in the observation tube 12 constituting the observation well, and at least the perforated portion 11 portion is reinforced to form the foundation pile 1. To improve the stability and safety of

  In addition, although the above-mentioned Example demonstrated the case where the one hole part 11 was provided in the desired position of the observation pipe 12, the depth to the support ground 2d and the foundation pile 1 (observation pipe 12) When the placement depth is unclear, as shown in FIG. 5, a plurality of perforated portions 11, 11... Are formed in the observation tube 12 at intervals in the tube axis direction. The observation tube 12 may be penetrated into the ground 2 so that at least one of the plurality of perforated portions 11 is located in the impermeable layer portion 2b.

  In that case, the water intake holes 10, 10... Of the perforated part 11 located above the impermeable layer part 2 b are closed, and the inflow of water from the ground upper layer part 2 a into the observation tube 12 is prevented. While preventing, the lower part of the lowermost hole part 11 located in the impermeable layer part 2b is closed with the shield 14, and the inflow of the water from the ground lower layer part 2c into the observation pipe 12 is prevented.

  The perforated portion 11 located above the impermeable layer portion 2b, that is, in the ground upper layer portion 2a is, for example, a casing 17 whose lower end is rooted to the impermeable layer portion 2b on the upper outer side of the observation tube 12. , And the upper portion of the observation tube 12 has a double tube structure so that the water intake holes 10, 10... Are closed.

  In that case, after excavating the earth and sand in the casing 17 constituting the observation pipe 12, the casing 17 is penetrated into the ground upper layer portion 2 a until the lower end reaches the impermeable layer portion 2 b, and then passed through the casing 17. The main body of the observation tube 12 may be penetrated into the ground.

  Moreover, the installation mode of the observation tube 12 is not limited to the above-described embodiment, and for example, the observation tube 12 may be configured as shown in FIGS. 6 (a) to 6 (f). In addition, the same code | symbol is attached | subjected and demonstrated to the structure similar to the above-mentioned Example.

  In this case, first, similarly to the case shown in FIGS. 3 (a) to 3 (b), the pile pipes 1a, 1a,... While excavating the earth and sand, the pile pipe 1a is penetrated until the lower end reaches the impermeable layer 2b and penetrated into the upper ground layer 2a, and the pile pipe 1a, 1a ... projecting from the ground surface has a perforated pipe. 13 are connected by welding or the like (FIGS. 6A to 6B).

  And as shown in FIG.6 (c)-FIG.6 (e) from that state, the perforated part 11 is located in the impermeable layer part 2b, and the observation pipe 12 is hit by a pile driver or the like, And it is made to penetrate into the ground 2 until the lower end reaches the supporting ground 2d.

  At that time, as shown in FIG. 6 (c), the lower end opening of the observation tube 12 is closed by the earth and sand 2ba constituting the impermeable layer portion 2b, and the observation tube 12 is driven in that state, thereby the bottom of the tube Is lowered as the observation tube 12 is driven, the inner bottom of the tube is located considerably below the position of the perforated portion 11, and a cavity 17 having a certain depth is formed below the perforated portion 11. The

  Accordingly, as shown in FIG. 6 (f), concrete is filled in the cavity 17 to form a shield 14 to form an observation well, and groundwater is observed by analyzing the water collected from this observation well.

  In the case where the inner bottom of the pipe is located considerably below the position of the perforated part 11 and a cavity of a certain depth is formed below the perforated part 11, as shown in FIGS. Are provided with support convex portions 21, 21... Supporting the shielding plate 20 on the inner surface of the observation tube 12 below the perforated portion 11, and supported by the support convex portions 21, 21. The shielding body 14 may be formed by filling the shielding plate 20 with a shielding filler 22 such as concrete.

  The supporting convex portions 21, 21,... Are formed in a rib shape projecting at an interval in the tube circumferential direction on the inner surface of the perforated tube material 13 constituting the observation tube 12, and a shielding plate on the upper surface thereof 20 is supported.

  The shielding plate 20 is made of a concrete plate, an iron plate, or the like, and is formed in a shape matched to the cross-sectional shape of the hollow portion of the observation tube 12, here circular, and supported by the support convex portions 21, 21. Thus, the inside of the observation tube 12 is closed.

  Further, a cushioning material 23 made of sponge, rubber, urethane or the like is interposed between the outer edge of the shielding plate 20 and the inner side surface of the observation tube 13.

  Furthermore, the observation tube 12 is not limited to the embodiment described above, and as shown in FIG. 9, the thickness t2 of the perforated portion 11 in the tube diameter direction is thicker than the thickness t1 of other portions. Alternatively, the thickness of the entire observation tube 12 may be increased in the tube diameter direction to reinforce the cross-sectional defect due to the water intake holes 10, 10. In FIG. 9, the example in which the perforated portion 11 has a shape in which the thickness is increased inward toward the other portion (the portion having the thickness t1) has been described. It is good also as a shape which increased thickness toward.

  In the above-described embodiment, the observation of groundwater at the site of the final disposal site has been described as an example. However, the scope of application of the present invention is not limited to this. For example, contaminated soil exists on the impermeable layer. It can be applied to soil contaminated areas.

DESCRIPTION OF SYMBOLS 1 Foundation pile 1a Pile pipe body 2 Ground 2a Ground upper layer part 2b Impermeable layer part 2c Ground lower layer part 2d Support ground 10 Intake hole 11 Perforated part 12 Observation pipe 13 Perforated pipe material 14 Shield 15 Pumping means 16 Concrete 20 Shielding plate 21 Supporting convex portion 22 Shielding filler 23 Buffer material

Claims (8)

An observation well is installed on the ground where an impermeable layer made of viscous soil is interposed between the upper and lower layers of the ground, the groundwater taken from the observation well is analyzed, and the state of the groundwater is observed In the observation method,
Investigate the depth of the impermeable layer in advance,
Using an observation tube that has a perforated portion in which a water intake hole communicating inside and outside the tube is formed at a desired position in the tube axis direction,
While excavating the earth and sand in the observation tube, the observation tube is penetrated into the ground until the lower end reaches the impermeable layer portion, and then the observation tube is inserted into the impervious portion. Further penetrate the ground until it is located in the layer,
Thereafter, the downward from the perforated portion of the observation tube body is closed with the shield and observation well the observation tube body, the depth of the impermeable layer section based the perforated portion in the investigation A method for observing groundwater , wherein water permeating the impermeable layer portion in a state matched to the thickness is taken into the observation pipe through the water intake hole .   The observation pipe according to claim 1, wherein the observation pipe is formed in substantially the same shape as a foundation pile for a structure, and is installed on the ground by a method similar to that for the foundation pile.   The observation method for groundwater according to claim 1 or 2, wherein the observation tube is penetrated until a lower end thereof reaches a support base, and the observation tube is used as a foundation pile of a structure after observation.   A supporting convex part for supporting a shielding plate is provided on the side surface of the observation tube under the perforated part, and a shielding filler is filled with or on the shielding plate supported by the supporting convex part. The groundwater observation method according to claim 1, wherein the shield is formed.   A plurality of the perforated portions are formed at intervals in the tube axis direction on the observation tube body, and the observation tube is positioned so that at least one of the plurality of perforated portions is located in the impermeable layer portion. The body penetrates into the ground, closes each intake hole of the perforated part located above the impermeable layer part, and closes the shielding part below the lowest perforated part located in the impermeable layer part The method for observing groundwater according to any one of claims 1 to 4, wherein the groundwater is closed. An observation tube used in the groundwater observation method according to any one of claims 1 to 5,
It is provided with a perforated part in which a water intake hole communicating inside and outside the pipe is formed, and the perforated part is arranged so as to be positioned in the impermeable layer part when installed on the ground. Observation tube.   The observation tube according to claim 6, wherein the perforated portion is formed to have a thickness in a tube diameter direction larger than that of other portions.   The observation tube according to claim 6 or 7, wherein a support convex portion for supporting a shielding plate for closing the inside of the tube is provided on an inner surface below the perforated portion.

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