Container, ion sensor system, and method for managing water quality of soil gap water

Abstract

To directly and continuously acquire the ionic concentration such as pH of soil gap water even if the soil to measure presents a poor water-holding property.SOLUTION: The present invention relates to a container attached to an ionic concentration measuring device having an ion sensor provided with a measurement sensor unit with an ISFET sensor and a reference electrode and arranged in a measurement target soil. The container includes: a container body with a water passing property; and a water holding material filled in the container body, in which the measurement sensor unit of the ion sensor and the reference electrode are inserted. The water holding material has a high water holding property than the measurement target soil.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a container used for measuring ion concentrations such as pH in soil pore water, an ion sensor system equipped with the container, and a method for managing the water quality of soil pore water using the container. [Background technology]

[0002] For example, the pH of soil pore water is generally measured indirectly, and in many cases, a pH measurement method using a glass electrode is adopted. In this method, the collected soil and water are mixed and stirred in a certain ratio, and then two electrodes, a glass electrode and a reference electrode, are inserted into the supernatant. The pH of the supernatant is obtained by measuring the potential difference between these two electrodes.

[0003] In this context, a pH measurement system capable of directly measuring the pH of soil pore water has been developed, as disclosed in Non-Patent Document 1. The pH measurement system in Non-Patent Document 1 includes a buried pH sensor and a reference electrode. The buried pH sensor has a sensor chip mounted on the tip of a PCB (Poly Chlorinated Biphenyl) substrate made from PCB, and an ISFET (Ion Sensitive Field Effect Transistor) sensor used for pH measurement is integrated on this sensor chip together with other sensors.

[0004] The tip of this buried pH sensor is inserted into the soil to place the sensor chip in the soil, and a reference electrode is inserted into the soil adjacent to it.The ion-sensitive membrane of the ISFET sensor then comes into contact with the soil moisture, capturing the hydrogen ion concentration in the moisture and outputting it as a voltage, allowing the pH to be measured continuously. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Futagawa et al., “Research on real-time pH measurement of soil with low water content using semiconductor pH sensor”, Institute of Electrical Engineers of Japan, Journal of the Institute of Electrical Engineers of Japan (Sensor and Micromachine Division), Vol. 138, No. 9, pp. 417-422, September 2018. Summary of the Invention [Problem to be solved by the invention]

[0006] According to Non-Patent Document 1, experiments have demonstrated that a pH measurement system can measure the pH even when the moisture content is low, so long as the measurement target has a particle size similar to that of decomposed granite.

[0007] However, if the soil to be measured is composed of coarse-grained soil such as excavated waste, there will be periods of time when the soil becomes dry, with the moisture content being less than 10%, depending on the weather. During this period, moisture will not come into contact with the ion-sensitive membrane of the ISFET sensor, or the circuit between the ISFET sensor and the reference electrode will be interrupted, making it impossible to obtain voltage, making it difficult to measure pH.

[0008] In addition, if a dry period continues, the pH sensor may cause problems in the pH measurement due to static electricity generated around the sensor. Furthermore, if the pH sensor is placed in direct contact with the excavation waste without any protection, the pH sensor is likely to break down.

[0009] The present invention has been made in consideration of such problems, and its main purpose is to directly and continuously obtain ion concentrations such as pH of soil pore water, even when the measurement target is soil with poor water retention. [Means for solving the problem]

[0010] In order to achieve this objective, the container of the present invention is a container that is attached to an ion concentration measuring device that has an ion sensor with a measurement sensor part equipped with an ISFET sensor and a reference electrode, and is placed in the soil to be measured, and is characterized in that it comprises a container body that has water permeability, and a water retention material that is filled into the container body and into which the measurement sensor part of the ion sensor and the reference electrode are inserted, and the water retention material has a higher water retention capacity than the soil to be measured.

[0011] The container of the present invention is characterized in that the ion sensor is a sensor for measuring pH.

[0012] The container of the present invention is characterized in that the container body and the water retention material are made of chemically inactive materials.

[0013] The container of the present invention is characterized in that the water retention material is made of granular material.

[0014] The container of the present invention is characterized in that the granular material is borosilicate glass beads.

[0015] In the container of the present invention, the measurement target soil contains coarse-grained soil, The particle size of the granular material is 0.1 mm or more and 1.0 mm or less.

[0016] The container of the present invention is characterized in that the particle size of the granular material is 0.1 mm or more and 1.0 mm or less.

[0017] The ion sensor system of the present invention is characterized by including the container of the present invention, an ion sensor provided with a measurement sensor portion equipped with an ISFET sensor, and an ion concentration measurement device having a reference electrode.

[0018] The water quality management method for soil pore water of the present invention is a method for managing the water quality of soil pore water in the soil to be measured by installing the container of the present invention in an ion concentration measuring device equipped with an ion sensor having a measurement sensor part equipped with an ISFET sensor and a reference electrode, and is characterized in that the measurement sensor part of the ion sensor and the reference electrode are inserted into the water retention material, and the container body is positioned at least at a depth where the water retention material is located in the soil to be measured.

[0019] The method for managing soil pore water quality of the present invention is characterized in that the soil to be measured is a banking material containing coarse-grained soil.

[0020] The method for managing soil pore water quality of the present invention is characterized in that a gate electrode is added in the form of stripes to the ion-sensitive membrane of the ISFET sensor.

[0021] According to the container of the present invention, even if the soil to be measured is poor in water retention, for example, composed of coarse-grained soil, the measurement sensor unit and the reference electrode of the ion concentration measuring device can be constantly kept wet by the moisture that has permeated the water-retentive material. This makes it possible to continuously and stably measure ion concentrations such as pH without data loss even if the soil to be measured intermittently dries out.

[0022] It is also possible to prevent the ISFET sensor installed in the measurement sensor unit from becoming damaged due to dryness and coming into contact with the soil being measured. Furthermore, if granular material is used as the water-retentive material, the water-retentive performance of the water-retentive material can be easily adjusted by changing the particle size, and the water that has permeated the water-retentive material can be easily exchanged.

[0023] Therefore, in embankments that use coarse-grained soil such as excavated waste as the embankment material, if the measurement sensor part and reference electrode of a buried pH sensor (ion sensor) are placed within the embankment material via a container, it will be possible to constantly monitor the pH of the embankment pore water and manage the water quality.

[0024] Furthermore, if a chemically inactive material, such as borosilicate glass beads, is used for the granules along with the container body, even if the soil to be measured is contaminated, it will not dissolve in acid or alkali and affect ion concentrations such as pH.

[0025] Therefore, for example, in an embankment in which coarse-grained soil containing pyrite that becomes acidic when exposed to the air is used as the embankment material and this is sealed with a water-impermeable covering soil, the measurement sensor part and reference electrode of a buried pH sensor (ion sensor) can be placed through a container in the embankment material. In this way, even if a problem occurs in the covering soil and the coarse-grained soil containing pyrite becomes acidic soil, and the pore water that comes into contact with the acidic soil becomes acidic, the phenomenon of the pH decreasing can be grasped at an early stage, and rational countermeasures can be considered and implemented before the acidified leachate spreads to the surrounding area.

[0026] In addition, by adding a gate electrode in a stripe pattern to the ion-sensitive membrane of the ISFET sensor in the measurement sensor section, stable pH measurement can be achieved over a long period of time. Therefore, combined with the water retention performance of the water-retentive material, it becomes possible to stably continue constant monitoring of the pore water in the embankment over a long period of time. Effect of the Invention

[0027] According to the present invention, the measurement sensor part and reference electrode of the ion sensor can be kept moistened using a water-retentive material that has a higher water retention capacity than the soil to be measured. Therefore, even if the soil to be measured has poor water retention capacity, it is possible to directly and continuously obtain ion concentrations such as the pH of the soil pore water. [Brief description of the drawings]

[0028] [Figure 1] FIG. 1 is a schematic diagram showing a container and a pH measurement device according to an embodiment of the present invention. [Diagram 2] FIG. 1 is a diagram showing an outline of a stripe-gate type semiconductor pH sensor in which gate electrodes are added in a stripe pattern to an ion-sensitive membrane of an ISFET sensor in an embodiment of the present invention. [Diagram 3]FIG. 2 is a diagram showing how the quality of pore water in embankment material is managed using a pH measuring device using a container in an embodiment of the present invention. [Figure 4] FIG. 4 is a diagram showing a moisture characteristic curve when granular material is used as the water retention material in an embodiment of the present invention. [Diagram 5] FIG. 2 is a diagram showing the results of a moisture movement analysis of a water retention material in an embodiment of the present invention. [Figure 6] FIG. 13 is a diagram showing the results of a water flow experiment on a water retention material in an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] The present invention makes it possible to directly and continuously stably measure ion concentrations such as pH of soil pore water without being affected by the water retention performance of the soil being measured by using an ion concentration measuring device equipped with an ISFET sensor in combination with a container having a water retention function. The container and water quality management method of the present invention will be described in detail below with reference to Figures 1 to 6, taking as an example a case in which a pH measuring device equipped with a buried pH sensor is used as the ion concentration measuring device to measure pH.

[0030] <<Ion sensor system>> 1(a) and 1(b), an ion sensor system 100 is placed in soil G, the pH of which is to be measured. The ion sensor system 100 includes a pH measuring device 20 and a container 10, and a reference electrode 21 and a buried pH sensor 24, which constitute the pH measuring device 20, are inserted into the soil G, the container 10 being attached to the pH measuring device 20.

[0031] <<pH measuring device>> As shown in FIG. 1(b), the pH measurement device 20 includes a reference electrode 21, an embedded pH sensor 24, and a power supply device 25.

[0032] The buried pH sensor 24 has a measuring sensor unit 23 equipped with a sensor chip mounted on a thin plate-shaped substrate 22. The thin plate-shaped substrate 22 is shaped like a long, thin plate that can be easily pierced when the soil G to be measured is composed of homogeneous sandy soil such as decomposed grain soil. PCB (Poly Chlorinated Biphenyl) is used as the material.

[0033] The thin plate-shaped substrate 22 is not limited to the above-mentioned material and shape, and may be made of any material and be formed into any shape as long as it is a chemically inactive material and can be pierced into soil with a grain size similar to that of sandy soil. The above-mentioned measurement sensor unit 23 is provided on the tip side of this thin plate-shaped substrate 22.

[0034] The measurement sensor unit 23 includes a multimodal sensor chip that integrates an ISFET (Ion Sensitive Field Effect Transistor) sensor 231 used for pH measurement, together with a temperature sensor and an EC sensor (not shown). This sensor chip is connected to the power supply unit 25 from the base end side of the thin plate-like substrate 22 by wiring.

[0035] The ISFET sensor 231 used for pH measurement employs a stripe-gate type semiconductor pH sensor in which gate electrodes 27 are added in a stripe pattern to an ion-sensitive membrane 26 that responds to hydrogen ions, as shown in Figures 2(a) and 2(b), in order to enable stable pH measurement over a long period of time.

[0036] If the gate electrode 27 is not provided, the electric field direction is from the ISFET sensor 231 toward the solution L, and anions in the solution L permeate the ion-sensitive membrane 26. This causes the output voltage of the ISFET sensor 231 to decrease over time, resulting in a phenomenon called drift. When this drift occurs, the reliability of the pH measurement result decreases significantly, and it becomes necessary to periodically calibrate the pH measurement result using a pH standard solution.

[0037] Therefore, a gate electrode 27 is added in a stripe shape to the ion-sensitive membrane 26, and a gate voltage lower than the potential of the solution L is applied to the gate electrode 27. Then, as shown in Fig. 2(b), the direction of the electric field can be controlled to be a direction from the solution L toward the ISFET sensor 231, and the anions can be kept in the solution L and the penetration of the anions into the ion-sensitive membrane 26 can be suppressed. This realizes stable pH measurement without drift over a long period of time.

[0038] 1(b), the reference electrode 21 is inserted into the soil G to be measured in the vicinity of the buried pH sensor 24, and is connected by wiring to a power supply unit 25. The power supply unit 25 is capable of controlling the voltage of hydrogen ions, applying a current, and measuring the voltage.

[0039] When measuring the pH of pore water in the soil G to be measured, the pH measuring device 20 having the above configuration is inserted into the soil G to be measured with the buried pH sensor 24 and the reference electrode 21 inserted into the container 10.

[0040] ≪≪Container≫≫ As shown in FIG. 1(b), the container 10 includes a water-retaining material 12, a filling material 13, and a container body 11 that houses these.

[0041] <Container body> The container body 11 is in the shape of a bag with an opening at the top, and is formed to a size having a height that allows the embedded pH sensor 24 and the reference electrode 21 to be housed therein, and a width that allows the two to be arranged with a space between them. Any material can be used for the container body 11 as long as it is chemically inactive and water permeable, and examples of such materials include polyethylene mesh material and nonwoven fabric.

[0042] <Water retention material> The water-retaining material 12 is a chemically inactive material like the container body 11, and can be of any material and shape as long as it is a material through which soil pore water can easily permeate when placed in the measurement target soil G and can retain the permeated soil pore water for a long period of time, as shown in Figure 1(a). Figure 1(b) shows an example in which a granular material is used as the water-retaining material 12.

[0043] Examples of chemically inactive granular materials that can be used include borosilicate glass (BG) beads, quartz glass beads, etc. In particular, borosilicate glass is a material that is superior in toughness, abrasion resistance, and chemical stability compared to general glass that is widely distributed on the market, and the glass components do not dissolve in acid or alkaline solutions.

[0044] When granular materials such as BG beads are used as the water-retentive material 12, the particle size is adjusted to ensure that the water-retentive material has a higher water-retentiveness than the measurement target soil G. At the same time, the water-retentive material 12 is also ensured to have mobility so that the water that permeates the material 12 can be easily exchanged. The water-retentive materials 12 are covered by the filling material 13 inside the container body 11.

[0045] <Filling material> As shown in Figure 1 (b), the filling material 13 is arranged in a layered manner on top of the water retention material 12 inside the container body 11, and is used as a lid for the water retention material 12, as a guide for inserting the buried pH sensor 24 and the reference electrode 21, and as a material for maintaining the posture after insertion.

[0046] The material may be any, for example a chemically resistant sponge, so long as it is made of a chemically inactive material like the container body 11. This chemically resistant sponge has two through holes with diameters substantially smaller than the cross sections of the embedded pH sensor 24 and the reference electrode 21, and the embedded pH sensor 24 and the reference electrode 21 are inserted through the through holes, respectively, to maintain the upright position.

[0047] Any shape and structure may be adopted as long as it can prevent the water retention material 12 from flowing away and can hold the embedded pH sensor 24 and the reference electrode 21 in the same position as when they were housed in the container body 11. Also, the filling material 13 does not necessarily have to be provided.

[0048] 1(b), the container 10 and pH measuring device 20 having the above configuration are configured such that the embedded pH sensor 24 and reference electrode 21 are inserted into the container body 11, and the measuring sensor part 23 provided on the tip side of the embedded pH sensor 24 is disposed in the water retention material 12. The tip side of the reference electrode 21 is inserted into the water retention material 12 with a gap therebetween.

[0049] In this state, the container 10 is placed so that at least the water retention material 12 is located within the measurement target soil G. Then, hydrogen ions in the interstitial water that have permeated from the measurement target soil G through the container body 11 into the water retention material 12 come into contact with the ion-sensitive membrane 26 of the ISFET sensor 231 mounted on the measurement sensor unit 23 of the buried pH sensor 24.

[0050] This generates an interfacial potential according to the activity of the ions, and the electrical conductivity of the channel below the ion-sensitive membrane 26 changes depending on the magnitude of the interfacial potential, making it possible to convert the activity of a specific ion in the interstitial water into an electrical signal. By calibrating the electrical signal in advance with a standard solution of known pH, the pH can be measured from the electrical signal obtained from the interstitial water.

[0051] And because the water retention material 12 has a higher water retention capacity than the measurement target soil G, the measurement sensor unit 23 and the reference electrode 21 are constantly kept wet by the moisture that has permeated the water retention material 12. Therefore, even if the measurement target soil G has poor water retention capacity and is intermittently in a dry state, it is possible to continuously and stably measure pH without data loss.

[0052] It is also possible to avoid a situation in which the ISFET sensor 231 malfunctions due to drying and comes into contact with the measurement target soil G, resulting in damage to the ISFET sensor 231.

[0053] Furthermore, since the container body 11, water retention material 12, and filling material 13 that make up the container 10 are made of chemically inactive materials, even if the soil G to be measured is contaminated soil that becomes acidic, it is possible to avoid a situation in which the container 10 dissolves during measurement and affects the pH.

[0054] <<<How to manage soil pore water quality>>> The above-mentioned container 10 is attached to a pH measuring device 20 to constitute an ion sensor system 100, which is then buried in the embankment material 31 of an embankment 30 as shown in Fig. 3. In this way, the pH of the embankment pore water can be constantly monitored, and the water quality can be controlled.

[0055] The water quality control method will be described in detail below, taking as an example the case where pyrite-containing soil is used as the embankment material 31. Note that pyrite-containing soil is acidic soil generated during excavation work for mountain tunnels and large-scale shafts. It is neutral immediately after excavation, but it is known that when exposed to the atmosphere and reacts with oxygen, it becomes acidic with sulfuric acid, and the pH drops to 2 to 3.

[0056] When the above-mentioned soil containing pyrite is used as the embankment material 31, a so-called containment process is carried out, in which the embankment material 31 is enclosed with covering soil 32. For the covering soil 32, a water-impermeable material composed of a material containing a large amount of sandy soil or clayey soil is adopted to suppress the intrusion of moisture such as rain into the embankment material 31 and to block the supply of air (oxygen). The embankment 30 thus constructed is constructed, for example, as a road earthwork structure with pavement 40 provided on the top.

[0057] Although the above-mentioned embankment 30 has the embankment material 31 sealed in by the covering soil 32, the long-term use of the road constructed on the top of the embankment may cause cracks and damage to the road shoulder, pavement 40, and covering soil 32. When this happens, there is a risk that moisture will seep into the embankment material 31 through these cracks and damaged areas during rainfall. In this case, the location where the moisture content is expected to be highest is the foot of the slope.

[0058] Therefore, the container 10 is attached to the pH measuring device 20 in the manner described with reference to Fig. 1(b) and is placed near the foot of the slope at a depth that reaches the embankment material 31. At this time, water is permeated into the water-retentive material 12 in advance to make it wet.

[0059] As mentioned above, soil containing pyrite is generated from excavation work for mountain tunnels and large-scale shafts, and is therefore classified as coarse-grained soil (soil containing more than 50% sand and gravel). Therefore, when BG beads are used as the water-retaining material 12 of the container 10, the particle size should be set smaller than that of the sand and gravel, at about 0.1 mm to 1.0 mm, and preferably at about 0.5 mm to 0.8 mm.

[0060] As a result, for example, when rain falls, moisture penetrates into the embankment material 31, and the resulting pore water flows down and into the container body 11 of the container 10 near the toe of the slope. This pore water is then replaced with water that has previously permeated the water-retentive material 12, and the pH measuring device 20 measures the pH of this replaced pore water.

[0061] Even if the weather improves thereafter and the embankment material 31 becomes dry such that the moisture content falls below 10%, some of the pore water that has permeated into the water-retentive material 12 is retained in the container 10. Therefore, while the embankment material 31 is in a dry state, the pH measuring device 20 constantly measures the pH of the pore water that has permeated into the water-retentive material 12.

[0062] Then, at the time of the next rainfall, the pore water that has infiltrated into the embankment material 31 is replaced with the pore water retained in the water-retentive material 12. The pH measuring device 20 then measures the pH of this replaced pore water. In this way, the pH measuring device 20 continuously measures the pore water that flows from the embankment material 31 through the container body 11 and permeates into the water-retentive material 12, and constantly monitors the change in the pH of the pore water.

[0063] 2, the ISFET sensor 231 mounted on the measurement sensor unit 23 of the buried pH sensor 24 employs a stripe gate type semiconductor pH sensor capable of suppressing drift. Therefore, it becomes possible to stably continue the above-mentioned constant monitoring of the embankment pore water for a long period of time.

[0064] As a result, when the embankment material 31 is exposed due to deterioration over time of the covering soil 32 or non-uniformity in construction, it becomes possible to detect the phenomenon of a decrease in the pH of the embankment pore water at an early stage and to consider and implement rational countermeasures before the acidified leachate spreads around the embankment 30. In this way, it becomes possible to simplify management and significantly reduce the amount of work required, compared to the case where a collection pond is provided downstream of the embankment 30 to temporarily store the leachate and neutralize the pH.

[0065] <<Experiment>> The following experiment was carried out on the water retention of the water retention material 12 and the mobility of the infiltrated water when the measurement target soil G was coarse-grained soil and BG beads were used as the water retention material 12.

[0066] <Experiment on the water retention of water-retentive material 12> In the experiment, No. 7 crushed stone was prepared as a material equivalent to the coarse-grained soil. The No. 7 crushed stone was crushed stone adjusted to a particle size of 2 to 9.5 mm. In addition, BG beads adjusted to a particle size of 0.5 mm to 0.71 mm were prepared as the water-retaining material 12.

[0067] Water retention tests were conducted on the No. 7 crushed stone and BG beads, and the moisture characteristic curves were calculated using the van Genuchten model (van Genuchten: 1980), as shown in Figure 4. The moisture characteristic curve shows the relationship between the volumetric water content θ and the pressure head h, and is widely used as information that indicates the water retention characteristics of soil. Figure 4 shows that the BG beads have higher water retention than the No. 7 crushed stone.

[0068] Next, moisture characteristic curves were obtained from literature for glass beads with an average particle size of 0.1 mm and glass beads with an average particle size of 1.0 mm, and these were compared with the moisture characteristic curve for BG beads obtained based on the water retention test described above. The literature from which the moisture characteristic curve for glass beads was obtained is "Nishigaki et al., 'Research on the mechanism of unsaturated regions in rock masses (Joint research report on advanced fundamental engineering research)'", Okayama University Nuclear Cycle Development Institute, February 2002."

[0069] Figure 4 shows that the moisture characteristic curve of BG beads with particle size adjusted to 0.5mm to 0.71mm generally coincides with the tendency of literature values ​​for glass beads. Therefore, we considered glass beads to be equivalent to BG beads, and analyzed the change in the amount of moisture remaining in glass beads buried in No. 7 crushed stone using HYDRUS-2D (a general-purpose program for predicting moisture and salt movement in two-dimensional soils).

[0070] The analysis conditions were as shown in Figure 5(a), where an area filled with glass beads with an average particle size of 0.1 mm and an area filled with glass beads with an average particle size of 1.0 mm were set above the area filled with No. 7 crushed stone. Both areas were placed with sufficient space between them, and were set in the shape of a column with the same height L1 and width L2. In addition, a screen was installed at the bottom to allow only water to drain and prevent the No. 7 crushed stone from flowing away, forming a free drainage surface.

[0071] Under the above conditions, the initial moisture content was set to 30% for all areas of the No. 7 crushed stone, the glass beads with an average particle size of 0.1 mm, and the glass beads with an average particle size of 1.0 mm, and left to stand for 100 days. The moisture content of all areas after 100 days is shown in Figure 5(b).

[0072] Figure 5(b) shows that the moisture content in the area filled with No. 7 crushed stone has dropped from 30% to around 3%. On the other hand, the area filled with glass beads with an average particle size of 0.1 mm appears to maintain a moisture content well above 20%. The area filled with glass beads with an average particle size of 1.0 mm also maintains a moisture content of around 20%.

[0073] From the above results, it can be seen that if BG beads with a particle size of 0.1 mm or more and 1.0 mm or less are used as the water retention material 12, the moisture that has penetrated into the water retention material 12 can be maintained at a moisture content of around 20% for at least about 100 days. Therefore, if BG beads with a particle size of 0.1 mm or more and 1.0 mm or less are used as the water retention material 12 of the container 10, the pH measuring device 20 can continue to measure the pH of the moisture that has penetrated into the water retention material 12 even if a period of about 100 days occurs in which the coarse-grained soil becomes dry and the moisture content falls below 10%.

[0074] However, if the water retention material 12 has a high water retention capacity and the retained water is not easily exchanged, it is not possible to accurately capture the pH change of the pore water in the measurement target soil G. Therefore, an experiment was conducted on the mobility of water that has penetrated into the water retention material 12.

[0075] <Experiment on the mobility of water that has penetrated into the water-retentive material 12> In the experiment, as shown in Figure 6(a), No. 5 silica sand was used as the model soil S, and compaction was performed to make the soil particle density uniform. The container was a processed PVC cap with a diameter of 16.5 mm and a height of 75 mm. No. 5 silica sand was soil adjusted to a particle size of 0.3 mm to 0.8 mm.

[0076] Thereafter, a pH measuring device 20 was inserted and placed in this model soil S via a container 10. As described with reference to Fig. 1(b), the container 10 contains a measuring sensor part 23 of an embedded pH sensor 24 and a reference electrode 21 inserted in a water retention material 12. As the water retention material 12, BG beads with particle sizes adjusted to 0.5 mm to 0.71 mm were prepared.

[0077] Next, pure water was supplied as a water passage solution W1 to the model soil S at a flow rate of 7 to 8 mL / min to saturate the model soil S. After this, pH measurement of the pore water in the model soil S was started using the pH measuring device 20. In addition, the pore water W2 was sampled from the pore water sampler 50 at appropriate times, and the pH of this pore water W2 was measured by a pH measuring method using a glass electrode.

[0078] After a certain time had passed, a sulfuric acid solution adjusted to pH 2 was supplied as the water passage W1 in place of the pure water, and the model soil S was allowed to pass through it. After a certain time had passed, pure water was supplied as the water passage W1 in place of the sulfuric acid solution adjusted to pH 2, and the model soil S was allowed to pass through it.

[0079] During this period, the pH was continuously measured by the pH measuring device 20, and the pH of the interstitial water W2 collected by the pore water sampler 50 was repeatedly measured at appropriate times. Figure 6(b) shows the results of continuous pH measurement by the pH measuring device 20 and the pH measurement results of the interstitial water W2 collected by the pore water sampler 50.

[0080] As shown in FIG. 6(b), the pH of the pore water W2 fluctuates between pH 6 and 7 after the start of measurement when pure water is passed through, and then when a sulfuric acid solution is supplied instead of the pure water as the passing water W1, the pH drops to about pH 2. Furthermore, when pure water is supplied again instead of the sulfuric acid solution and passed through, the pH gradually rises to about pH 4. On the other hand, when the results of continuous pH measurements by the pH measuring device 20 are seen, it is found that there is a good correlation with the pH measurement results of the pore water W2 collected by the pore water sampler 50. Therefore, it can be evaluated that the embedded pH sensor 24 of the pH measuring device 20 is appropriately measuring the pH of the pore water W2 even when it is protected by the container 10.

[0081] The container, ion sensor system, and soil pore water quality management method of the present invention are not limited to the above-described embodiments, and it goes without saying that various modifications are possible without departing from the spirit of the present invention.

[0082] For example, in the present embodiment, the pH measuring device 20 is attached to the container 10 and placed in the embankment material 31, and the pH of the embankment pore water is constantly monitored to control the water quality. However, the soil G to be measured is not limited to the embankment material 31. For example, the device can be placed in backfill soil to monitor the pH of the pore water in the backfill ground, and can be used in the water quality control of any earth structure.

[0083] In the present embodiment, the container 10 is attached to the pH measuring device 20, but the present invention is not limited to this. + , potassium ion K + , ammonium ion NH4 + , Lithium-ion Li + , calcium ion Ca 2+ , chloride ion Cl - , nitrate ion NO3 - , Carbonate ion CO3 2- It is also possible to employ an ion concentration measuring device provided with an ion-sensitive membrane 2 that responds to various ions such as those mentioned above, and to measure the ion concentration by mounting the container 10 thereon. [Explanation of symbols]

[0084] 100 Ion Sensor System 10 containers 11 Container body 12 Water-retaining materials 13 Filling material 20 pH measuring device (ion concentration measuring device) 21 Reference electrode 22 Thin plate-shaped substrate 23 Measurement sensor section 231 ISFET Sensor 24 Buried pH sensor (ion sensor) 25 Power supply 26 Ion-sensitive membrane 27 Gate electrode 30 Embankment 31 Embankment materials 32 Soil cover 40 Pavement 50 Pore water sampler S model soil W1 Water-flowing solution W2 Pore water

Claims

1. A container that is attached to an ion concentration measuring device having an ion sensor having a measurement sensor unit having an ISFET sensor and a reference electrode, and is placed in soil to be measured, A container body having water permeability; a water retention material filled in the container body and into which the measurement sensor portion of the ion sensor and the reference electrode are inserted; A container, wherein the water-retentive material has a higher water-retentiveness than the soil to be measured.

2. 2. The container according to claim 1, The container, wherein the ion sensor is a sensor for measuring pH.

3. 2. The container according to claim 1, A container characterized in that the container body and the water retention material are made of chemically inactive materials.

4. 2. The container according to claim 1, A container characterized in that the water-retaining material is composed of granules.

5. 5. The container according to claim 4, A container characterized in that the granular material is borosilicate glass beads.

6. 5. The container according to claim 4, The measurement target soil includes coarse-grained soil, A container characterized in that the particle size of the granular material is 0.1 mm or more and 1.0 mm or less.

7. 2. The container according to claim 1, A container characterized in that a filling material is provided in the container body to cover the water retention material.

8. A container according to any one of claims 1 to 7; An ion concentration measuring device having an ion sensor provided with a measurement sensor unit having an ISFET sensor and a reference electrode; An ion sensor system comprising:

9. A method for managing the quality of soil pore water, comprising installing the container according to any one of claims 1 to 7 in an ion concentration measuring device having an ion sensor provided with a measurement sensor unit having an ISFET sensor and a reference electrode, and managing the quality of pore water in soil to be measured, The measurement sensor portion of the ion sensor and the reference electrode are inserted into the water retention material, A method for managing soil pore water quality, comprising disposing the container body at a depth within the soil to be measured at which the water-retentive material is located.

10. The method for managing soil pore water quality according to claim 9, A method for managing soil pore water quality, wherein the soil to be measured is embankment material containing coarse-grained soil.

11. The method for managing soil pore water quality according to claim 9, A method for managing soil pore water quality, characterized in that a gate electrode is added in the form of stripes to the ion-sensitive film of the ISFET sensor.

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