Permeability Testing Equipment

Abstract

To enable the measurement of hydraulic conductivity from low permeability ground to medium-high permeability ground with a single permeability test device.SOLUTION: Airtight water tanks for pouring test water in a permeability test device are composed of two sets of airtight water tanks, a first airtight water tank with a small volume located between an outer cylindrical body and an inner cylindrical body using inner and outer double cylinders with different diameters, and a second airtight water tank of large volume located within the inner cylinder. Openings for air inflow and water injection are provided in a lower part of the outer cylinder and a lower part of the inner cylinder, respectively. By connecting the second airtight water tank to the first airtight water tank through the openings for air inflow and water injection in the lower part of the inner cylindrical body, it is possible to measure hydraulic conductivity in low-permeability ground mainly composed of the first airtight water tank, and to measure hydraulic conductivity in medium-to-high-permeability ground in which the first and second airtight tanks are combined.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a configuration of a permeability test apparatus that can efficiently measure the permeability of various types of ground having different permeabilities. [Background technology]

[0002] One of the important functions of embankment structures (embankments) such as reservoir embankments and river embankments is to ensure safety against water level fluctuations and the infiltration of rainwater during rainfall. This hydraulic safety is governed by the permeability of the ground, and in order to properly manage and inspect this, a permeability test device that can measure the permeability of the ground easily and accurately is required.

[0003] Recently, such a permeability testing device has been provided, which comprises an airtight water tank consisting of a cylindrical body that forms the main body of the device, a sealable water inlet at the upper end of the airtight water tank, and a sealable opening at the lower end of the airtight water tank, the lower end of which is placed directly in a test hole in the ground that stores a predetermined amount of water, and the opening at the lower end of the airtight water tank functions as a Mariotte siphon-type constant water level maintaining tube and water injection tube, thereby reducing the water level in the airtight water tank according to the permeability of the ground in which the test hole is located, and the permeability is measured from the degree of reduction in the water level (see, for example, Patent Document 1).

[0004] With this type of device, when the water level in the test hole is filled above the upper end of the opening at the lower end of the airtight water tank, the opening is completely blocked by water, so no air flows into the airtight water tank and no water from the airtight water tank is poured into the test hole through the opening.

[0005] However, as water gradually seeps into the ground through the test hole from this state, the water level in the test hole drops accordingly, and the upper end of the opening is eventually opened to the outside air. Then, air flows into the airtight water tank in the form of bubbles through the upper end of the opening, and water in the airtight water tank flows out from the lower end of the opening according to the amount of air that flows in, and is poured into the test hole. Then, when the amount of poured water reaches a predetermined amount equal to or greater than the amount of infiltration, the water level in the test hole rises again, blocking the upper end of the opening, and a constant water level is maintained at this stage.

[0006] That is, in this device, the cylindrical device body forming the airtight water tank is installed directly in the test hole, and the opening at the lower end of the device (wall opening) functions as the constant water level holding pipe and water injection pipe of the conventional Mariotte siphon type in-situ permeability test device (see Patent Document 2). Therefore, there is no need for the long constant water level holding pipe and water injection pipe of the conventional Mariotte siphon type in-situ permeability test device. In addition, the structure of the airtight water tank itself can be simplified.

[0007] As a result, the permeability test device itself is basically composed of a single small-diameter cylinder, which greatly reduces costs. It is also easy to carry, and all that is required is to insert it into the test hole in the target ground and place it horizontally on the crushed stone filled in the test hole, making measurement work easy. The decrease in water level in the airtight water tank can also be easily read by making the cylinder that forms the main body of the device transparent and marking the scale on the cylinder.

[0008] However, in the case of this permeability test device, the main body of the device is a single cylindrical airtight water tank, and the water for measurement is always stored in the entire airtight water tank for the permeability test, regardless of the permeability of the target ground. Therefore, the cylindrical volume of the airtight water tank is usually set to a large volume corresponding to highly permeable ground such as gravel layers.

[0009] For this reason, when trying to use this device to measure the permeability of extremely low-permeability ground (low-permeability or impermeable ground), such as a clay layer, the water in the test hole seeps into the ground very slowly, so the amount of drop in the water level in the airtight water tank is extremely small, and the measurement takes an extremely long time (several hours to several days).

[0010] Therefore, when trying to achieve an appropriate measurement time depending on the differences in permeability of the target ground, including such impermeable ground, one method would be to prepare three airtight water tanks with different volumes (amount of water measured) - large, medium, and small - and use them to create three types of permeability test equipment with different measurement ranges for the permeability coefficient, one for low permeability ground, one for medium permeability ground, and one for high permeability ground.

[0011] However, if they did so, geological survey companies and the like would have to purchase each of the three types of permeability test equipment, which would be a huge expense. Also, when carrying out the measurement work, the permeability coefficient level of the ground to be measured is not known from the beginning, so it is not clear (cannot be selected) which type of permeability test equipment should be used for the measurement, and in the end, all types of permeability test equipment must be brought in for the measurement, which only complicates the measurement work and does not shorten the measurement time in any way. Furthermore, multiple permeability test equipment also places restrictions on storage space when not in use.

[0012] Therefore, the inventors of the present application have proposed a Mariotte siphon-type in-situ permeability testing device in which a semicircular arc-shaped partition wall is provided inside a single cylindrical airtight water tank, and two airtight water tanks, one large and one small, with different volumes are formed through the same arc-shaped partition wall, and openings that function as a constant water level maintaining pipe and a water injection pipe similar to those described above are provided in the outer wall of the lower end of each tank, making it possible to use the large-volume airtight water tank for medium- to high-permeability ground and the small-volume airtight water tank for low-permeability ground (see, for example, Patent Document 3).

[0013] According to this configuration, a single permeability test device can be used to appropriately measure the permeability of both low-permeability ground and medium-to-high-permeability ground, thus solving the problems associated with the need for multiple permeability test devices. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] JP 2012-127673 A [Patent Document 2] JP 2010-163801 A [Patent Document 3] JP 2015-45527 A Summary of the Invention [Problem to be solved by the invention]

[0015] However, in the case of the water permeability test device of the above-mentioned Patent Document 3, even though the two types of airtight water tanks with different volumes are structurally integrated, they are completely independent in terms of their measurement functions, and the airtight water tanks are not designed to be used in a form in which they are connected to each other. Therefore, when making a measurement, it is necessary to use two types of airtight water tanks, one large and one small, separately, and it is never possible to select only one of them for measurement. Of course, it is possible that when the measurement is first performed using a large-volume airtight water tank, the measurement target ground is fortunately medium-high permeability ground, or when the measurement is first performed using a small-volume airtight water tank, the measurement target ground is fortunately low permeability ground, but this is a matter of chance, and the reverse also occurs with the same probability.

[0016] Therefore, it is necessary to assume that measurements are basically taken twice individually, which results in the same complicated measurement work as in the case of using multiple permeability test devices as described above, and does not necessarily result in a reduction in measurement time.

[0017] In the case of the permeability test device of Patent Document 3, the volume of the airtight water tank for medium to high permeability ground must be large enough to handle the test by itself, and the volume of the airtight water tank for low permeability ground must be added to that, so the size of the entire airtight water tank (the diameter of the cylinder that forms the airtight water tank) becomes large by that amount. As a result, the device itself becomes large, leading to poor portability and operability during measurement.

[0018] Furthermore, in the case of the permeability test device of Patent Document 3, as in the case of the permeability test device of Patent Document 1, the constant water level state must be determined by the water level in the test hole. Moreover, this must be determined by whether or not the water level is at the upper end position of the opening for both air inflow and water injection at the lower end of the airtight water tank described above. However, the water level in the test hole is a certain distance (for example, about 5 cm) below the ground surface and cannot be seen horizontally. In addition, water is transparent. Therefore, it is not necessarily easy to determine whether the water level in the test hole is at the upper end position of the opening.

[0019] In addition, regarding the location of the openings, in the case of a large-volume airtight water tank, the openings for both air inflow and water injection are provided in multiple sets over a wide circumferential range excluding the corresponding portion of the small-volume airtight water tank, making them relatively easy to see, but in the case of a small-volume airtight water tank, there is only one such opening provided on a portion of the circumferential wall of the large-volume airtight water tank, making it completely invisible from the opposite side. Therefore, it is even more difficult to determine the constant water level state.

[0020] These difficulties in judging and seeing the constant water level state ultimately resulted in a deterioration in the accuracy of the permeability measurement data.

[0021] Furthermore, in the above-mentioned patent document, the installation of the main body of the device in the test hole is performed by laying a large amount of crushed stones in the test hole to form a flat installation surface for the main body of the device, and then using a level to set the main body vertically on the installation surface. However, it is not necessarily easy to lay a large amount of crushed stones in the test hole to form an installation surface for the main body of the device, and the crushed stones must be removed again after the measurement is completed. Setting the main body vertically on the installation surface using a level is also a tedious task.

[0022] The present invention has been made to solve such problems, and aims to provide a permeability test apparatus in which the airtight water tanks for injecting test water in a permeability test apparatus are configured as two sets of airtight water tanks, a first airtight water tank with a smaller volume located between the outer and inner cylinders, and a second airtight water tank with a larger volume located inside the inner cylinder, using a double cylinder with an inner and outer body of different diameters, and openings for air inflow and water injection are provided at the bottom of the outer cylinder and the bottom of the inner cylinder, respectively, and the second airtight water tank is connected to the first airtight water tank via the openings for air inflow and water injection at the bottom of the inner cylinder, making it possible to measure the permeability coefficient in low-permeability ground using the first airtight water tank as the center, and to measure the permeability coefficient in medium- to high-permeability ground by combining the first airtight water tank with the second airtight water tank. [Means for solving the problem]

[0023] To this end, the present invention is configured to include the following effective means for solving problems.

[0024] (1) Means for solving the problem according to the invention of claim 1 The means for solving the problems of this invention comprises an airtight water tank for injecting water in which water to be measured is stored, and openings for air inflow and water injection provided at the bottom of the airtight water tank. The bottom of the airtight water tank equipped with the openings for air inflow and water injection is submerged in a test hole on the ground side in which a predetermined amount of test water is stored, and the openings for air inflow and water injection function as a constant water level holding pipe and water injection pipe of a Mariott siphon type, and the permeability of the target ground is measured from the decrease in the water level in the airtight water tank. The apparatus for testing water permeability comprises an airtight water tank having two sets of tanks, a first airtight water tank having a smaller volume and located between an outer cylinder and an inner cylinder, and a second airtight water tank having a larger volume and located within the inner cylinder, using a double cylinder with an inner and an inner cylinder having different diameters, and openings for air inflow and water injection are provided at the lower part of the outer cylinder and the lower part of the inner cylinder, respectively, and the second airtight water tank is connected to the first airtight water tank via the openings for air inflow and water injection of the inner cylinder, A capillary space is provided between the outer periphery of the lower part of the outer cylinder and the lower periphery of the outer cylinder, where the surface tension is small and the water level rise is large. This makes it possible to measure the permeability coefficient of low-permeability ground using the first airtight water tank as the center, and to measure the permeability coefficient of medium to high-permeability ground using the first airtight water tank in combination with the second airtight water tank.

[0025] In the means for solving the problems of this invention, first, an airtight water tank for pouring water, in which water for measurement is stored, is configured as two sets of airtight water tanks, an inner and outer set of a first airtight water tank with a small volume located between the outer cylinder and the inner cylinder, and a second airtight water tank with a large volume located inside the inner cylinder, by a double inner and outer cylinder with different diameters. Air inlet and water inlet openings are provided at the bottom of the outer cylinder and the bottom of the inner cylinder, respectively, and the first and second sets of airtight water tanks are mutually connected via the air inlet and water inlet openings at the bottom of the inner cylinder.

[0026] Therefore, when the permeability test device is installed in a test hole in a given test ground whose permeability coefficient is unknown, the test water starts to infiltrate into the test ground through the test hole. Then, when the amount of infiltration reaches a predetermined amount or more, the water level of the test water in the test hole drops below the position of the air inlet opening at the bottom of the outer cylinder. Then, the air inlet opening at the bottom of the outer cylinder is opened to the atmosphere, and air flows into the first airtight water tank with a small volume from the air inlet opening and rises as air bubbles. In response to this, the negative pressure at the top of the first airtight water tank drops, and an amount of test water corresponding to the amount of the drop flows out from the water injection opening at the bottom of the outer cylinder and is injected into the test hole. This causes the water level of the test water in the test hole to rise again, and eventually the air inlet opening at the bottom of the outer cylinder is blocked by the test water in the test hole, and the inflow of air and the resulting rise of air bubbles cease, and the injection of water into the test hole is also stopped. As a result, the water level of the test water in the test hole returns to the original constant water level, while the water level of the measurement water in the first airtight water tank drops by the amount of water poured into the test hole. From the degree of drop (the amount of measurement water that has decreased over the measurement time) the permeability coefficient of the measurement ground is measured.

[0027] The drop in the water level in the first airtight water tank is read, for example, by providing a water level scale on the outer circumference of the outer cylinder, but in the case of the means for solving the problems of this invention, the volume (cross-sectional area) of the first airtight water tank itself is formed to be sufficiently small, and the tank portion is located between the outer cylinder and the inner cylinder and formed into a thin-walled ring structure, so the change in water level is large, and the amount of measurement water poured into the test hole (amount of decrease) is indicated by a relatively large drop span. Therefore, even if the measurement ground in which the test hole is formed is low-permeability ground with a small permeability coefficient and a low permeability amount per unit time, the scale corresponding to the drop in the water level becomes easy to read, and the measurement time is also shortened.

[0028] In the case of the problem solving means of the present invention, as described above, first, the permeability coefficient suitable for low-permeability ground is measured using the first airtight water tank with a small volume (cross-sectional area) on the outer periphery side of the cylindrical body. Then, if the measured ground is actually low-permeability ground with a small permeability coefficient and appropriate measurement data corresponding to it can be obtained, the measurement ends there. In other words, basically, the volume of the first airtight water tank is set to be sufficient to measure the permeability coefficient of low-permeability ground before the water level of the measurement water in the first airtight water tank drops to the position of the air inflow opening at the bottom of the inner cylindrical body.

[0029] However, even if the ground has a low permeability coefficient, there are cases where it is not possible to obtain appropriate measurement data, and the boundary between low permeability and medium permeability is not always clearly defined. In such cases, the amount of measurement water in the first airtight water tank, which has a small volume, is not enough. Therefore, in the means for solving the problems of this invention, in addition to the measurement using the measurement water in the first airtight water tank, it is possible to perform continuous measurement using the measurement water in the second airtight water tank for a predetermined period of time.

[0030] That is, in the case of the problem-solving means of this invention, the airtight water tank for pouring water is composed of two sets of airtight water tanks: a first airtight water tank of smaller volume located between the outer cylindrical body and the inner cylindrical body, and a second airtight water tank of larger volume located inside the inner cylindrical body, and the first and second sets of inner and outer airtight water tanks are connected to each other via openings for air inflow and water pouring at the bottom of the inner cylindrical body.

[0031] Therefore, when the water level in the first airtight water tank falls below the position of the air inlet opening at the bottom of the inner cylinder, air flows into the second airtight water tank through the air inlet opening, and the test water in the second airtight water tank is supplied to the first airtight water tank through the water injection opening at the bottom of the inner cylinder, so that even if the water level in the first airtight water tank falls below the position of the air inlet opening at the bottom of the inner cylinder, the measurement can be continued using the test water in the second airtight water tank. In other words, basically, the measurement of the permeability coefficient corresponding to the low-permeability ground is performed using only the first airtight water tank, but the second airtight water tank is also used when necessary. The expression "measurement of the permeability coefficient in the low-permeability ground mainly using the first airtight water tank" includes such cases.

[0032] On the other hand, if the measurement ground in which the test hole was formed is actually medium to high permeability ground with a large permeability coefficient, unlike the case of low permeability ground, the test water in the test hole will continue to seep into the ground, so a larger amount of measurement water will be required than in the case of low permeability ground.

[0033] In such a case, therefore, continuous measurements of the hydraulic conductivity are carried out by combining the first airtight water tank with a second airtight water tank.

[0034] That is, in this measurement, first, measurement of the permeability coefficient is started using the first airtight water tank and the openings for air inflow and water injection at the bottom of the outer cylinder, as in the case of the measurement of the permeability coefficient of the low permeability ground. However, in the case of medium to high permeability ground with a large permeability coefficient, the amount of measurement water up to the position of the opening for air inflow at the bottom of the inner cylinder in the first airtight water tank is not enough to inject water into the test hole, and the water level in the first airtight water tank will quickly drop below the position of the opening for air inflow at the bottom of the inner cylinder.

[0035] When the water level in the first airtight water tank falls below the position of the air inlet opening at the bottom of the inner cylinder, air flows into the second airtight water tank with a larger volume from the air inlet opening, and correspondingly, a sufficient amount of test water in the second airtight water tank with the same volume flows out from the water inlet opening at the bottom of the inner cylinder into the first airtight water tank, and further, water is injected into the test hole from the water inlet opening at the bottom of the outer cylinder through the first airtight water tank until a constant water level is reached. When the water level of the test water in the test hole reaches a constant water level and the air inlet opening at the bottom of the outer cylinder is blocked, water injection from the water inlet opening at the bottom of the outer cylinder stops, and the water level in the first airtight water tank rises accordingly. When the water level in the first airtight water tank rises to the position of the air inflow opening at the bottom of the inner cylinder, water injection into the first airtight water tank from the water injection opening at the bottom of the inner cylinder also stops, and the water level in the first airtight water tank becomes constant, while the water level in the second airtight water tank stabilizes at a predetermined lowered position.Then, the permeability coefficient of the medium-high permeability ground is appropriately measured from the degree of decrease (the passage of measurement time and the amount of decrease in the measured water during that time).

[0036] That is, in the configuration of the problem solving means of the present invention, when measuring the permeability of medium-high permeability ground, the test water in the first airtight water tank can be continuously used in addition to the test water in the second airtight water tank, and the total amount of the test water in the second airtight water tank and the test water in the first airtight water tank can be effectively used as the amount of water for measuring the permeability of medium-high permeability ground. Therefore, compared to the case where the small-volume first airtight water tank is used for low permeability ground and the large-volume second airtight water tank is used for medium-high permeability ground as completely separate dedicated airtight water tanks, the total volume (diameter of the device body with a cylindrical structure) can be reduced by the small-volume first airtight water tank. Therefore, handling during measurement is also easy. In addition, the constant water level state occurs in the first airtight water tank part of the device body, making it very easy to see.

[0037] In addition, in the problem-solving means of the present invention, in the above configuration, a capillary space is provided located near the air inlet on the lower outer periphery of the outer cylinder, and between the lower outer periphery of the outer cylinder, where the surface tension is low and the degree of water level rise is large.

[0038] With this configuration, the surface tension of the water at the air inflow opening of the outer cylinder forming the first airtight water tank is reduced, causing a small amount of water to permeate the opening, making it easier for air bubbles to be sucked into the first airtight water tank from the air inlet. As a result, a large amount of measurement data (relatively continuous measurement data) can be obtained in a short period of time even on low-permeability ground with a small permeability coefficient. This makes it possible to obtain more accurate measurement data than the conventional intermittent measurement data obtained by repeatedly achieving a constant water level. Measurement time is also reduced.

[0039] It is sufficient for the capillary space to be provided in correspondence with the air inflow opening at the bottom of the outer cylinder forming the first airtight water tank, and it is not necessary to provide it around the entire circumference of the bottom of the outer cylinder forming the first airtight water tank. If it is provided around the entire circumference of the bottom of the outer cylinder, the water level will rise too much, and the suction force of the air bubbles will decrease. Effect of the Invention

[0040] As a result, the permeability test device of the present invention allows continuous measurements with a single test device for low permeability ground, which requires a small amount of water to be measured, and medium to high permeability ground, which requires a medium or large amount of water to be measured. Moreover, it is possible to shorten the measurement time as much as possible in low permeability ground, and it is easy to install in the test hole. Therefore, the overall measurement efficiency is greatly improved, and the workability is excellent.

[0041] In addition, the first airtight water tank used to measure the permeability of low-permeability ground has a small volume (cross-sectional area) and is ring-shaped, located between the outer cylinder and the inner cylinder. Therefore, even if the water level change in the test hole is small, the water level change in the first airtight water tank is shown as a large change. Therefore, even when measuring the permeability of low-permeability ground, the water level change is easy to read, making measurement easier. Measurement time is also shortened. [Brief description of the drawings]

[0042] [Figure 1] FIG. 1 is a front view showing the configuration of a test device main body of a water permeability test device according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a plan view of the main body of the testing device. [Diagram 3] 3 is a cross-sectional view of the portion cut along line AA in FIG. 2, showing the configuration of the main body of the test device. [Figure 4] 3 is a cross-sectional view of the portion cut along line BB in FIG. 2, showing the configuration of the main body of the test device. [Diagram 5] FIG. 2 is a perspective view showing a configuration of a main body of the test device. [Figure 6] This is an oblique view showing the configurations of the tripod, the test device main body, and the ground-side test hole when the test device main body of Figures 1 to 5 described above is suspended and installed over a test hole in the surface ground above the groundwater to be measured using a tripod, which is a support member, and the permeability coefficient of the surface ground is being measured. [Figure 7]7 is an explanatory cross-sectional view showing the relationship between the water level of the test water in the test hole and the positions of the first air inlet and first water inlet on the device body side in the measurement state of FIG. 6. [Figure 8] This is an enlarged explanatory cross-sectional view showing the relationship between the first and second air inlet positions on the device body and the first and second water inlet positions when the water level of the test water in the test hole is at a constant water level in the measurement state of Figure 6. [Figure 9] This is an explanatory enlarged cross-sectional view showing the state in which, in the measurement state of Figure 6, the water level of the test water in the test hole drops below the position of the first air inlet on the device main body due to infiltration into the ground, air flows into the first airtight water tank from the first air inlet, and in response, the test water in the first airtight water tank is injected into the test hole through the first water inlet on the device main body. [Figure 10] This is an explanatory enlarged cross-sectional view showing the air inflow state in which air flows into the first airtight water tank through the first air inlet when the water level of the test water in the test hole drops below the position of the first air inlet on the device main body side due to infiltration into the ground in the measurement state of Figure 6, and the transitional state in which the inflowing air is drawn into the first airtight water tank and turns into air bubbles. [Figure 11] This is an explanatory diagram showing the configuration of the shallow to deep ground, tripod, test equipment main body, and test hole in the shallow to deep ground when the test equipment main body of Figures 1 to 5 described above is installed over the test hole in the shallow to deep ground above the groundwater to be measured using a tripod, which is a hanging support member similar to that of Figure 6, and the permeability coefficient of the shallow to deep ground above the groundwater is being measured. [Figure 12] FIG. 2 is a front view similar to FIG. 1 showing the configuration of the main body of a permeability test device according to a second embodiment of the present invention in which a capillary space is provided at the first air inlet portion on the lower side of the main body of the test device to improve the measurement efficiency of low-permeability ground. [Figure 13] FIG. 4 is a cross-sectional view similar to FIG. 3, showing the configuration of the main body of the water permeability test apparatus. [Figure 14] FIG. 2 is a perspective view showing the configuration of a capillary space forming member provided in the main body of the water permeability test apparatus. [Figure 15] FIG. 2 is a development view showing the configuration of a capillary space forming member provided in the main body of the water permeability test apparatus. [Figure 16] FIG. 14 is an enlarged cross-sectional view (partially enlarged view of FIG. 13) showing the configuration of the lower part of the water permeability test apparatus main body provided with a capillary space forming member. [Figure 17] FIG. 13 is an explanatory enlarged cross-sectional view showing the effect of improving the measurement efficiency of low-permeability ground by a permeability test device in which a capillary space is formed by a capillary space forming member. [Figure 18] FIG. 1 is an explanatory diagram showing the configuration when a permeability test of shallow to deep layers of ground above groundwater is performed using a constant water level tank, a water supply pipe, a water stop packer, and a water injection pipe by a conventional permeability test device (Patent Document 1). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0043] First embodiment of the present invention 1 to 11 show the configuration of a ground permeability test device according to a first embodiment of the present invention and the state in which an on-site permeability test is carried out using the test device.

[0044] <Configuration of the main body of the permeability test device> First, Figs. 1 to 8 show the main body of the water permeability test device and the configuration of each part of the main body.

[0045] The permeability test apparatus 10 of this embodiment, as shown in Figures 1 to 4, is formed by coaxially inserting a second cylinder 12, which has a diameter smaller than that of the first cylinder 11 by a predetermined dimension and is approximately the same length as the first cylinder 11, into the first cylinder 11 of a predetermined diameter and length, to form a double-cylinder structure with two inner and outer cylinders, and highly sealing cover members 11a, 11b, 12a, 12b are fitted into the openings at the upper and lower ends of the first and second cylinders 11, 12, respectively, to integrate them with each other.

[0046] In this case, the upper end cover members 11a, 12a of the first and second cylinders 11, 12 are integrally joined and fixed to the upper end openings of the first and second cylinders 11, 12, while the lower end cover members 11b, 12b are detachably fitted to the lower end openings of the first and second cylinders 11, 12. This makes it possible to inject the test water into the first and second cylinders 11, 12 with the device main body turned upside down, as described later. In addition, a hanging ring 22 for hanging the device main body is fixed to the center of the upper end cover member 11a of the first cylinder 11.

[0047] A first airtight water tank 13 having a small volume and a ring-like (cylindrical) shape is formed between the first cylinder 11 having a large outer diameter and the second cylinder 12 having a small inner diameter, and a second airtight water tank 14 having a sufficiently large volume and a cylindrical shape compared to the first airtight water tank 13 is formed inside the first cylinder 11 having a small inner diameter. Injection of the test water into the first and second cylinders 11 and 12 specifically means injection into these first and second airtight water tanks 13 and 14.

[0048] The first and second airtight water tanks 13, 14 have different volumes, with the first airtight water tank 13 having a smaller volume being used primarily for measuring the permeability coefficient of low-permeability ground, and both the first airtight water tank 13 having a smaller volume and the second airtight water tank 14 having a larger volume being used primarily for measuring the permeability coefficient of medium to high-permeability ground, and the diameter and length of the first cylinder 11 and the diameter and length of the second cylinder 12 are set to values ​​that will realize a volume that enables an appropriate amount of water to be poured into the test hole 20 on the ground side (see Figures 6 and 7) in accordance with the differences in the permeability coefficients.

[0049] The first and second cylinders 11, 12 are formed of, for example, a highly transparent synthetic resin material (vinyl chloride resin, acrylic resin, etc.), and when filled with water for measurement, the generation of air bubbles (air inflow state) in the first and second airtight water tanks 13, 14 inside each cylinder and the corresponding drop in the water level (reduction in water volume) can be easily confirmed from the outside. For this purpose, a water volume scale (for example, in 1 mm units) 19 is provided on the front of the first cylinder 11.

[0050] At a predetermined height H1 from the lower end opening of the outer first cylinder 11, first air inlets 15, 15 are provided, which communicate from the outside (test hole 20) to the inside of the first airtight water tank 13, and at a predetermined height H2 from the lower end opening of the outer first cylinder 11, first water inlets 16, 16 are provided, which communicate from the inside of the first airtight water tank 13 to the outside (test hole 20). The first air inlets 15, 15 are located above the first water inlets 16, 16, and are provided at a predetermined height higher than the first water inlets 16, 16. These two pairs of upper and lower first air inlets 15, first water inlets 16 and first air inlets 15, first water inlets 16 are provided at positions facing each other at 180 degrees circumferentially (on both the left and right sides when viewed from the front view of FIG. 1).

[0051] Next, a second air inlet 17 communicating from the outer first airtight water tank 13 to the inner second airtight water tank 14 is provided at a predetermined height H3 from the lower end opening of the inner second cylinder 12, and a second water inlet 18 communicating from the inner second airtight water tank 14 to the outer first airtight water tank 13 is provided at a predetermined height H4 from the lower end opening of the second cylinder 12. The second air inlet 17 is located above the second water inlet 18 and is provided at a predetermined height higher than the second water inlet 18.

[0052] The second water inlet 18 is provided at a position slightly higher than the first water inlet 16,16 on the side of the first cylinder 11 (approximately halfway between the first water inlet 16,16 and the second air inlet 15,15), while the second air inlet 17 is provided at a position sufficiently higher than the first air inlet 15,15 on the side of the first cylinder 11. Moreover, the second air inlet 17 and the second water inlet 18 are provided at positions 180 degrees different from each other in the circumferential direction, and at positions 90 degrees different from the first air inlets 15,15 and the first water inlet 16,16 in the circumferential direction.

[0053] The first water inlet 16, 16 of the first cylinder 11 and the second water inlet 18 of the second cylinder 12 are each formed with a relatively large diameter (e.g., 10 mm) and are formed so that the central axis of the opening passage extends horizontally from the inner side to the outer side in the radial direction.

[0054] On the other hand, the first air inlet 15, 15 of the first cylinder 11 and the second air inlet 17 of the second cylinder 12 are formed to have a slightly smaller diameter (e.g., 8 mm) than the diameters of the first water inlet 15, 15 of the first cylinder 11 and the second water inlet 18 of the second cylinder 12, respectively, and each is formed so that the central axis of its opening extends obliquely from the outer side to the upper inside in the radial direction at a predetermined upward inclination angle.

[0055] By making the diameter of the first air inlet 15, 15 of the first cylinder 11 and the diameter of the second air inlet 17 of the second cylinder 12 relatively small in this way, the surface tension of the water on the airtight water tank side in each part can be reduced, and the diameter of air bubbles generated when the water is poured into the test water in the first and second airtight water tanks 13, 14 can be reduced. In this case, if the central axis of the opening of each of the air inlets 15, 15, 17 extends obliquely from the outer side in the radial direction to the inner upper side with a predetermined upward inclination angle, the air from each of the air inlets efficiently flows upward into the test water in the first and second airtight water tanks 13, 14, and a large number of continuous air bubbles are smoothly generated. As a result, the measurement water is poured out smoothly from the first water inlet 16, 16 of the first cylinder 11 and the second water inlet 18 of the second cylinder 12, and can responsively follow the drop in the water level in the test hole 20.

[0056] Therefore, with this configuration, the tracking and responsiveness to a drop in water level on the test hole 20 side is effectively improved, and even if the diameter of the first water inlet 16, 16 of the first cylinder 11 is narrowed to a certain extent to accommodate low-permeability ground, the water inlet 16, 16 can be sufficiently tracked to the water level fluctuations on the test hole 20 side.

[0057] Although not shown, the first air inlets 15, 15 and the first water inlets 16, 16 of the first cylinder 11 are provided with predetermined stopcocks that can be inserted and removed as accessories. These stopcocks are provided to prevent the injected test water from flowing out when the first cylinder 11 forming the first airtight water tank 13 and the second cylinder 12 forming the second airtight water tank 14 are filled with test water during measurement of the hydraulic conductivity described below, and each stopcock is removed underwater to prevent air from entering when the lower part of the body of the permeability test apparatus 10 is immersed in the test hole 20.

[0058] The injection of the test water into the first cylinder 11 forming the first airtight water tank 13 and the second cylinder 12 forming the second airtight water tank 14 is performed by inserting the stopcocks into the first air inlet 15, 15 and the first water inlet 16, 16 of the first cylinder 11, and then turning the device body upside down. At this time, the second air inlet 17 and the second water inlet 18 of the second cylinder 12 do not require stopcocks because the test water will not flow out to the outside as long as the test water is injected into the first and second cylinders 11, 12.

[0059] Then, when the injection of the test water into the first cylinder 11 forming the first airtight water tank 13 and the second cylinder 12 forming the second airtight water tank 14 is completed in this manner, the lid members 11b, 12b are fitted and sealed to the lower end openings of the first cylinder 11 and the second cylinder 12, respectively, and the vertical position of the device body is then returned to its original position, and the lower side is submerged until the first air inlet 15, 15 and the first water inlet 16, 16 are located in the test water W of the test hole 20, and the stopcock is removed in this state. This makes it possible to measure the hydraulic conductivity (see the state in FIG. 7). An example of the stopcock is shown in FIG. 7 and FIG. 8 of JP 2019-199766 A.

[0060] A water level scale 19 is provided on the front of the first cylinder 11 with a large outer diameter, for reading the change in water level in the first and second airtight water tanks 13, 14 in increments of, for example, 1 mm, as described above, and the change (decrease) in the water level in the first and second airtight water tanks 13, 14 can be confirmed using the water level scale 19.

[0061] <Installation structure of the permeability test device in the test hole on the measurement ground side> The permeability test apparatus 10 constructed as described above is configured to be used by hanging it in an accurate vertical position directly above the center of the test hole 20 via a tripod 5 equipped with a height adjustment means, as shown in Figure 6, for example.

[0062] The test hole 20 shown in Figure 6 is a constant water level hole with a bottomed cylindrical structure of 0.3 m in diameter and 0.3 m deep based on the standards of the Geotechnical Society, with the premise that the permeability coefficient of the surface ground will be measured, for example. This test hole 20 is simply shaped into a bottomed cylindrical structure after being dug with a shovel or the like, and crushed stone is not filled at the bottom (2 / 3 height from the bottom) as in the past, thereby forming a surface for installing a permeability test device. Therefore, even when the measurement ground has low permeability, the test water infiltrates relatively smoothly, and the crushed stone filling does not cause any obstructions.

[0063] The tripod 5 has three pairs of shoulders 51, 51, 51 at 120 degree intervals on the central tripod body 9, and three legs 52, 52, 52 are attached to the three pairs of shoulders 51, 51, 51 so that the legs can be opened in both directions. Each leg 52, 52, 52 has a three-section (three-stage) connection structure in which the diameter gradually decreases from the connection with the upper shoulders 51, 51, 51 to the lower ferrules 52a, 52a, 52a, and the standing height of the entire leg can be adjusted as desired by expanding and contracting between each connection. Each connection is provided with a locking mechanism.

[0064] A liftable elevator rack 7 is provided in the center of the tripod body 9 between the shoulders 51, 51, 51, penetrating from top to bottom. The outer periphery of the rack body of this elevator rack 7 is engaged with a specified worm (not shown) inside the tripod body 9, and the elevator rack 7 can be raised and lowered as desired by rotating the worm in both forward and reverse directions. Reference numeral 53 denotes a height adjustment handle for rotating the worm in both forward and reverse directions.

[0065] The elevator rack 7 is provided with a flange portion 6 at its upper end and a hook 7b at its lower end 7a for suspending the permeability test device 10. The suspending ring 11b at the upper end of the permeability test device 10 is engaged with the hook 7b, and the permeability test device 10 is suspended vertically as shown in the figure. The suspension of the permeability test device 10 is performed as follows.

[0066] That is, first, the first and second cylinders 11, 12 of the permeability test device 10 in Figures 1 to 5 are turned upside down, the lid members 11b, 12b fitted to the lower end openings of each are removed, and the test water is poured into the first and second cylinders 11, 12 until they are full. This fills the first and second airtight water tanks 13, 14 with the test water. In this state, the above-mentioned stopcocks have been inserted into the air inflow openings 15, 15 and the water injection openings 16, 16 at the bottom of the first cylinder 11 in advance, and they are securely sealed.

[0067] Next, a predetermined amount of test water is poured into the test hole 20 using a bucket or the like, and the water is stored at a predetermined water level. The water is stored in the test hole 20 in advance to measure the water level, and the water is checked to see if air bubbles are generated in the first airtight water tank 13 and if the water level is lowered. This is done after judging that the water has infiltrated from the test hole 20 into the ground and reached a predetermined level of saturation.

[0068] Thereafter, the three legs 52, 52, 52 of the tripod 5 are extended to a predetermined length taking into consideration the suspension height, and then opened at equal intervals on three sides, and the lower end protrusions 52a, 52a, 52a are erected so as to be positioned at the vertices of an equilateral triangle surrounding the test hole 20 containing the test water. As a result, the elevator rack 7 is positioned at the center of the circular test hole 20 and extends vertically.

[0069] Next, the water permeability test device 10 into which the injection of the test water has been completed is suspended from the lower end 7a of the elevator rack 7.

[0070] As a result, the water permeability test device 10 is positioned in the center (central part) of the test hole 20 in which the test water is stored, as shown in FIG. 10, and is suspended accurately vertically directly above it.

[0071] Next, the height of the elevator rack 7 is adjusted by operating the height adjustment handle 53, and the lower part of the permeability test device 10, which has the first air inlets 15,15 and the first water inlets 16,16 at the lower part of the first cylinder 11 and the second air inlet 17 and the second water inlet 18 at the lower part of the second cylinder 12, is inserted into the test hole 20 containing the test water W, for example, as shown in Figure 7. The insertion position into the test hole 20 containing the test water W is set at a position such that the water level of the test water W in the test hole 20 after insertion is slightly higher than the first air inlets 15,15 at the lower part of the first cylinder 11, as shown in the figure.

[0072] This state is shown in detail in an enlarged view in Fig. 8. In this state, the first air inlet 15, 15 at the bottom of the first cylinder 11 is entirely blocked from its top to bottom by the test water W in the test hole 20, so there is no inflow of air (drawn in by the negative pressure in the first airtight water tank 13), and no water is injected from the first water injection ports 16, 16 into the test hole 20. However, the test water W has started to permeate from the test hole 20 into the ground.

[0073] On the other hand, when the infiltration of the test water W into the ground through the test hole 20 from the state shown in FIG. 8 progresses, as shown in, for example, FIG. 9 and FIG. 10, the constant water level of the test water W in the test hole 20 gradually drops (see H0 in FIG. 10), the first air inlet 15, 15 at the bottom of the first cylinder 11 gradually opens, and air flows into the first airtight water tank 13 from the opening. The air that flows into the first airtight water tank 13 turns into air bubbles and rises upward in the tank 13. This inflow of air and the rise of the air bubbles are caused by the atmospheric pressure acting on the first air inlet 15, 15 at the bottom of the first cylinder 11 and the negative pressure in the first airtight water tank 13.

[0074] That is, when the constant water level described above drops due to the infiltration of the test water W into the ground, the first air inlets 15, 15 at the bottom of the first cylinder 11 gradually open from the upper side, and the water interface that was in equilibrium with the atmospheric pressure at the openings 15, 15 is pushed into the first airtight water tank 13 by the atmospheric pressure and is drawn into the first airtight water tank 13 by the negative pressure in the first airtight water tank 13. As a result, the water interface at the openings 15, 15 gradually becomes a concave interface that extends deeper into the first airtight water tank 13, as shown in an enlarged view in Fig. 10, for example, and when it enters the first airtight water tank 13, it is pulled upward by the negative pressure in the upper part of the first airtight water tank 13 and rises in the water as air bubbles (the so-called piping phenomenon). The air bubbles reaching the upper part of the first airtight water tank 13 reduce the negative pressure in the upper part of the airtight water tank 13, increasing the water pressure, and water is poured in response to this through the first water pouring ports 16,16.

[0075] As a result, the water level of the test water W in the test hole 20 returns to the constant water level state shown in Fig. 8. When the water level of the test water W in the test hole 20 returns to the constant water level state, the first air inlet 15, 15 is blocked by the test water W, and water injection from the first water injection port 16, 16 to the test hole 20 also stops. The hydraulic conductivity is measured from the degree of decrease in the water level in the first airtight water tank 13 during this period.

[0076] <Basic configuration and operation of the permeability test device according to the first embodiment> As described above, the permeability test apparatus 10 according to the first embodiment comprises an airtight water tank for pouring water in which water to be measured is stored, and an air inlet and a water inlet provided at the bottom of the airtight water tank. The bottom of the airtight water tank equipped with the air inlet and the water inlet is submerged in a test hole on the ground side in which a predetermined amount of test water is stored, and the air inlet and the water inlet function as a Mariotte siphon type constant water level holding tube and a water inlet tube, and the permeability of the target ground is measured from the decrease in the water level in the airtight water tank. The airtight water tank is divided into a first airtight water tank 13 having a small volume and located between an outer first cylinder 11 and an inner second cylinder 12 using inner and outer double cylinders with different diameters, and an inner The first airtight water tank 13 is configured as a set of two airtight water tanks, with a second airtight water tank 14 of a larger volume located inside the second cylinder 12. A first air flow inlet 15,15 and a first water inlet 16,16 are provided at the bottom of the outer first cylinder 11, and a second air flow inlet 17 and a second water inlet 18 are provided at the bottom of the inner second cylinder 12. The second airtight water tank 14 is connected to the first airtight water tank 13 via the second air flow inlet 17 and second water inlet 18 of the inner second cylinder 12, making it possible to measure the permeability coefficient in low-permeability ground mainly using the first airtight water tank 13, and to measure the permeability coefficient in medium- to high-permeability ground by combining the first airtight water tank 13 with the second airtight water tank 14.

[0077] That is, in the permeability test device 10 according to the first embodiment, first, an airtight water tank for pouring water to be measured is constituted of two sets of airtight water tanks, an inner and outer one, consisting of a first airtight water tank 13 with a small volume located between the first outer cylinder 11 and the inner cylinder 12, and a second airtight water tank 14 with a large volume located inside the second inner cylinder 12, by a double inner and outer cylinder with different diameters. A first air inlet 15, 15 and a first water inlet 16, 16 are provided at the bottom of the first outer cylinder 11, and a second air inlet 17 and a second water inlet 18 are provided at the bottom of the second inner cylinder 12, respectively, and the first and second inner and outer sets of airtight water tanks 13, 14 are mutually communicated via the second air inlet 17 and the second water inlet 18 at the bottom of the second inner cylinder 12.

[0078] Therefore, when the permeability test device 10 is installed in the test hole 20 of a predetermined measurement ground whose permeability coefficient is unknown, the test water W starts to permeate into the measurement ground through the test hole 20. Then, when the amount of permeation reaches a predetermined amount or more, the water level of the test water W in the test hole 20 drops below the position of the first air inlet 15, 15 at the bottom of the first outer cylinder 11. Then, the first air inlet 15, 15 at the bottom of the first outer cylinder 11 is opened to the atmosphere, and air flows from the first air inlet 15, 15 into the first airtight water tank 13, which has a small volume, and rises as air bubbles. In response to this, the negative pressure in the upper part of the first airtight water tank 13 drops, and the amount of test water corresponding to the amount of the drop flows out from the first water inlet 16, 16 at the bottom of the first outer cylinder 11 and is poured into the test hole 20. This causes the level of the test water in the test hole 20 to rise again, and eventually the first air inlets 15, 15 at the bottom of the first outer cylinder 11 are blocked by the test water in the test hole 20, the inflow of air and the resulting rise of air bubbles cease, and water injection into the test hole 20 is stopped. This causes the level of the test water W in the test hole 20 to return to its original constant water level, while the level of the test water in the first airtight water tank 13 drops by the amount of water injected into the test hole 20. The permeability coefficient of the measurement ground is then measured from the degree of this drop (the passage of measurement time and the amount of measurement water reduced during that time).

[0079] The drop in the water level in the first airtight water tank 13 is read, for example, by the water level scale 19 provided on the outer periphery of the first outer cylinder 11, but in the case of the configuration of this first embodiment, the volume (cross-sectional area) of the first airtight water tank 13 itself is formed to be sufficiently small, and the tank portion is located between the first outer cylinder 11 and the second inner cylinder 12 and formed into a thin-walled ring (cylinder) structure, so that the change in water level is large, and the amount (reduction) of the measurement water injected into the test hole 20 is indicated by a relatively large drop span. Therefore, even if the measurement ground in which the test hole 20 is formed is a low-permeability ground with a small permeability coefficient and a small permeability amount per unit time, the scale corresponding to the drop in the water level becomes easy to read, and the measurement time is also shortened.

[0080] In the first embodiment, as described above, the permeability coefficient suitable for low-permeability ground is measured using the first airtight water tank 13 with a small volume (cross-sectional area) on the outer periphery of the cylindrical body. Then, if the measured ground is actually a low-permeability ground with a small permeability coefficient and appropriate measurement data corresponding to the low-permeability ground can be obtained, the measurement ends there. In other words, the volume of the first airtight water tank 13 is basically set to be sufficient to measure the permeability coefficient of the low-permeability ground before the water level of the measurement water in the first airtight water tank 13 drops to the position of the second air inlet opening 17 at the bottom of the second inner cylindrical body 12.

[0081] However, even if the ground has a low permeability coefficient, there are cases where appropriate measurement data cannot be obtained, and the boundary between low permeability and medium permeability is not always clearly defined. In such cases, the amount of sample water in the first airtight water tank 13, which has a small volume, is not enough. Therefore, in this embodiment, in addition to the measurement using the sample water in the first airtight water tank 13, it is possible to perform continuous measurement using the sample water in the second airtight water tank 14 for a predetermined period of time.

[0082] That is, in this embodiment, the airtight water tank for pouring water is composed of two sets of airtight water tanks: a first airtight water tank 13 of small volume located between the first outer cylinder 11 and the second inner cylinder 12, and a second airtight water tank 14 of large volume located within the second inner cylinder 12, and the first and second inner and outer sets of airtight water tanks 13, 14 are connected to each other via the second air inlet 17 and the second water pouring port 18 at the bottom of the second inner cylinder 12.

[0083] Therefore, when the water level in the first airtight water tank 13 falls below the second air inlet 17 at the bottom of the second inner cylinder 12, air flows into the second airtight water tank 14 from the second air inlet 17, and the test water in the second airtight water tank 14 is supplied to the first airtight water tank 13 through the second water inlet 18 at the bottom of the second inner cylinder 12, so that even if the water level of the test water in the first airtight water tank 13 falls below the second air inlet 17 at the bottom of the second inner cylinder 12, the measurement can be continued using the test water in the second airtight water tank 14. In other words, basically, the measurement of the permeability coefficient corresponding to the low permeability ground is performed using only the first airtight water tank 13, but the second airtight water tank 14 is also used when necessary. The expression "measurement of the permeability coefficient in low-permeability ground mainly using the first airtight water tank 13" includes such cases.

[0084] On the other hand, if the measurement ground in which the test hole 20 is formed is actually a medium to high permeability ground with a large permeability coefficient, unlike the case of low permeability ground, the test water in the test hole 20 will continue to seep into the ground, so a larger amount of measurement water will be required than in the case of low permeability ground.

[0085] In such a case, therefore, the first airtight water tank 13 is combined with the second airtight water tank 14 to continuously measure the hydraulic conductivity.

[0086] That is, in this measurement, first, measurement of the permeability coefficient is started using the first airtight water tank 13 and the first air inlets 15, 15 and the first water inlets 16, 16 at the bottom of the first outer cylinder 11, as in the case of the measurement of the permeability coefficient of the low permeability ground. However, in the case of medium to high permeability ground with a large permeability coefficient, the amount of measurement water up to the position of the second air inlet 17 at the bottom of the second inner cylinder 12 in the first airtight water tank 13 is insufficient for the amount of water injected into the test hole 20, and the water level in the first airtight water tank 13 will quickly drop below the position of the second air inlet 17 at the bottom of the second inner cylinder 12.

[0087] Then, when the water level in the first airtight water tank 13 drops below the position of the second air inlet 17 at the bottom of the second inner cylinder 12, air flows into the second airtight water tank 14 having a larger volume from the second air inlet 17, and correspondingly, a sufficient amount of test water in the second airtight water tank 14 having the same large volume flows out into the first airtight water tank 13 from the second water inlet 18 at the bottom of the second inner cylinder 12, and then water is injected into the test hole 20 from the first water inlet 16, 16 at the bottom of the first outer cylinder 11 via the first airtight water tank 13 until a constant water level is reached. As a result, the water level of the test water in the test hole 20 becomes constant, and when the first air inlets 15, 15 at the bottom of the first outer cylinder 11 are blocked, water injection from the first water inlets 16, 16 at the bottom of the first outer cylinder 11 stops, and the water level in the first airtight water tank 13 rises accordingly. When the water level in the first airtight water tank 13 rises to the position of the second air inlet 17 at the bottom of the second inner cylinder 12, water injection from the second water inlet 18 at the bottom of the second inner cylinder 12 into the first airtight water tank 13 also stops, and the water level in the first airtight water tank 13 becomes constant, while the water level in the second airtight water tank 14 stabilizes at a predetermined lowered position. From the degree of decrease (the passage of measurement time and the amount of decrease in the measured water during that time), the permeability coefficient of the medium-high permeability ground is appropriately measured.

[0088] That is, in the configuration of the first embodiment, when measuring the permeability of medium-high permeability ground, the test water in the first airtight water tank 13 can be used continuously in addition to the test water in the second airtight water tank 14, and the total amount of the test water in the second airtight water tank 14 and the test water in the first airtight water tank 13 can be effectively used as the amount of water for measuring the permeability of medium-high permeability ground. Therefore, compared to the case where the small-volume first airtight water tank 13 is used for low permeability ground and the large-volume second airtight water tank 14 is used for medium-high permeability ground as completely separate dedicated airtight water tanks, the total volume (diameter of the device body with a cylindrical structure) can be reduced by the small-volume first airtight water tank 13. Therefore, handling during measurement is also easy. In addition, the constant water level state occurs in the first airtight water tank part of the device body, making it very easy to see.

[0089] In the permeability testing apparatus of this first embodiment, the first air inlet 15, 15 and first water inlet 16, 16 provided at the bottom of the first outer cylinder 11 in the above configuration, and the second air inlet 17 and second water inlet 18 provided at the bottom of the second inner cylinder are separated into an opening dedicated to air inflow and an opening dedicated to water inflow, respectively, and the first air inlet 15, 15 and second air inlet 17 dedicated to air inflow are provided at a position a predetermined height higher than the first water inlet 16, 16 and second water inlet 18 dedicated to water inflow.

[0090] According to this configuration, when the water level in the first airtight water tank 13 having a smaller volume becomes lower than the position of the second air inlet 17 provided at the lower part of the second inner cylinder 12, the water level in the first airtight water tank 13 having a smaller volume becomes lower than the position of the second air inlet 17 provided at the lower part of the second inner cylinder 12, regardless of whether the water level in the first airtight water tank 13 having a smaller volume is lower than the position of the second air inlet 17 provided at the lower part of the second inner cylinder 12, or whether the water level in the first airtight water tank 13 having a smaller volume is lower than the position of the second air inlet 17 provided at the lower part of the second inner cylinder 12, the water level in the first airtight water tank 13 having a smaller volume becomes lower than the position of the second air inlet 17 provided at the lower part of the second inner cylinder 12, regardless of whether the water level in the first airtight water tank 13 having a smaller volume is lower than the position of the second air inlet 17 provided at the lower part of the second inner cylinder 12, regardless of whether the water level in the first airtight water tank 13 has a smaller volume ... The second air inlet 17 provided in the first cylinder 12 is opened, and air from the second air inlet 17 flows into the second airtight water tank 14 having a larger volume, while water in the second airtight water tank 14 is poured into the first airtight water tank 13 through the second water inlet 18 provided at the bottom of the inner second cylinder 12, and then water is poured into the test hole 20 via the first airtight water tank 13 and the first water inlets 16, 16 provided at the bottom of the outer first cylinder 11.

[0091] Then, when the water level in the test hole 20 reaches a constant level, the first air inlet 15, 15 at the bottom of the first outer cylinder 11 is blocked by the test water in the test hole 20, the flow of air into the first airtight water tank 13 stops, and the injection of water from the first water inlet 16, 16 at the bottom of the first outer cylinder 11 also stops.

[0092] As a result, the water level in the first airtight water tank 13 rises due to water being poured in from the second water inlet 18 provided at the bottom of the second inner cylinder 12, the second air inlet 17 at the bottom of the second inner cylinder 12 becomes blocked by the water in the first airtight water tank 13, the water pouring in from the second water inlet 18 provided at the bottom of the second inner cylinder 12 stops, and the water level in the first airtight water tank 13 is maintained at a constant water level based on the position of the second air inlet 17 at the bottom of the second inner cylinder 12.

[0093] That is, in this first embodiment, a constant water level is also realized in the first airtight water tank 13 on the test device side in conjunction with the constant water level in the test hole 20 on the measurement ground side. Moreover, the constant water level position in the first airtight water tank 13 on the test device side is formed at a position higher than the second water injection port 18 by a predetermined height.

[0094] Therefore, the constant water level position in the first airtight water tank 13 on the testing device main body side is at a position higher than the surface of the ground 21 by a predetermined dimension or more, and can be easily confirmed from the horizontal direction. Moreover, the constant water level in the first airtight water tank 13 is formed over the entire circumferential direction. Therefore, it can be easily confirmed from any position in the circumferential direction, and the measurement operator can easily and accurately determine that the water level in the test hole 20 has reached a constant water level without looking at the condition inside the test hole 20. As a result, the measurement work becomes significantly easier, and the measurement efficiency and measurement accuracy are also improved.

[0095] In this case, the second air inlet 17 provided at the bottom of the second inner cylinder 12 is provided at a position (sufficiently high position) that is a predetermined height higher than the first air inlets 15, 15 provided at the bottom of the first outer cylinder 11. Therefore, the constant water level position formed in the first airtight water tank 13 becomes sufficiently higher than the surface of the ground 21, and the timing of injection of the test water from the second airtight water tank 14 into the first airtight water tank 13 becomes earlier. Also, the water injection efficiency is improved.

[0096] In addition, in this first embodiment, the first air inlet 15, 15 and the first water inlet 16, 16 provided at the bottom of the first outer cylinder 11 and the second air inlet 17 and the second water inlet 18 provided at the bottom of the second inner cylinder 12 are provided at circumferential positions that differ from each other by, for example, 90 degrees.

[0097] If the first air inlet 15, 15 and the first water inlet 16, 16 provided at the bottom of the first outer cylinder 11 and the second air inlet 17 and the second water inlet 18 provided at the bottom of the second inner cylinder 12 are provided at the same circumferential position, they will face each other, and because the volume of the first airtight water tank 13 is small, the facing distance is extremely small, and there is a risk that the air flowing in from the first air inlet 15, 15 at the bottom of the first outer cylinder 11 will be mistakenly sucked into the second air inlet 17 at the bottom of the second inner cylinder 12 by negative pressure. In this case, it is not possible to obtain an accurate water level change according to the permeability level of the measurement ground using the second airtight water tank.

[0098] However, by arranging them at different circumferential positions as described above, the risk that air bubbles flowing in from the first air inlet 15, 15 at the bottom of the first outer cylindrical body 11 and rising quickly will be mistakenly sucked into the second air inlet 17 at the bottom of the second inner cylindrical body 12 is eliminated.

[0099] In addition, in the configuration of this first embodiment, as described above, the permeability test device 10, which is formed into an overall cylindrical structure, is suspended above the test hole 20 via a height-adjustable tripod (a specified hanging support means) 5 (see Figures 6 and 12).

[0100] With this configuration, during measurement, the cylindrical permeability test device 10 is reliably suspended vertically above the test hole 20 filled with test water, and the lower first air inflow openings 15,15 and the first water injection openings 16,16 can be easily and accurately set in an appropriate measurement start state with the lower first air inflow openings 15,15 and the lower first water injection openings 16,16 submerged. This eliminates the need to lay a large amount of crushed stone in the test hole 20 to form an installation surface for the permeability test device, as was done in the past, and the measurement work becomes significantly easier. Furthermore, since the vertical state is more reliably achieved, the measurement accuracy is improved.

[0101] As a result, the permeability test device 10 of the first embodiment described above allows continuous measurements with a single test device for low permeability ground, which requires a small amount of water to be measured, and medium to high permeability ground, which requires a medium or large amount of water to be measured. Moreover, it is possible to shorten the measurement time as much as possible in low permeability ground, and it is easy to install in the test hole 20. Therefore, the overall measurement efficiency is greatly improved, and the workability is excellent.

[0102] In addition, the first airtight water tank 13 for measuring the permeability of low-permeability ground has a small volume (cross-sectional area) and is ring-shaped (cylindrical) located between the outer first cylinder 11 and the inner second cylinder 12. Therefore, even if the water level change in the test hole 20 is small, the water level change in the first airtight water tank 13 is shown as a large change. Therefore, even when measuring the permeability of low-permeability ground, the water level change is easy to read, making measurement easier. Measurement time is also shortened.

[0103] In addition, the first air inlet 15, 15 and the first water inlet 16, 16 provided at the bottom of the outer first cylinder 11, and the second air inlet 17 and the second water inlet 18 provided at the bottom of the inner second cylinder 12 are provided separately and independently at the top and bottom of the openings dedicated to air inflow and water inflow, respectively, and the openings 15, 15 and 17 dedicated to air inflow are provided at a predetermined height higher than the openings 16, 16 and 18 dedicated to water inflow. Therefore, the openings for air inflow allow air to flow in and bubbles to be generated smoothly, and the inflow efficiency is high. In addition, the openings for water inflow allow water to flow smoothly, and the water inflow efficiency is high.

[0104] A constant water level corresponding to the constant water level of the test water in the test hole 20 is formed in the first airtight water tank 13 by the second air inlet 17 dedicated to air inflow at the bottom of the second inner cylinder 12. The constant water level position in the first airtight water tank 13 is at a predetermined height higher than the ground surface where the test hole 20 is located, because the second air inlet 17 dedicated to air inflow at the bottom of the second inner cylinder 12 is provided at a predetermined height higher than the second water inlet 18 dedicated to water injection. The constant water level is formed over the entire circumferential direction in the first airtight water tank 13. Therefore, it is extremely easy to check the constant water level compared to the conventional check in the test hole 20. This also makes the measurement work significantly easier and improves the measurement accuracy.

[0105] <Calculation of permeability coefficient from shallow to deep layers> In the explanation of Figures 6 to 10 above, a method has been described in which a shallow test hole 20 (diameter 30 cm, depth 30 cm) in accordance with the Geotechnical Society standard is formed in the surface layer of the ground, and a permeability test device 10 having the configuration shown in Figures 1 to 5 is installed in the test hole 20 to calculate the permeability coefficient.

[0106] However, the permeability test device 10 of the first embodiment described above is not limited to the case of shallow test holes 20 in the surface layer of the ground, but is capable of conducting permeability tests in deep test holes of 1 m or more in depth, and also at a wide range of depths, from shallow ground layers to deep ground layers as shown in Figure 11.

[0107] In the case of a deep test hole of 1 m or more, for example, the depth of the test hole 20 is divided into the first layer and the second layer, and measurements are taken sequentially in the same manner as in the case of the 30 cm deep test hole 20 described above.

[0108] In the case of shallow or deep ground as shown in FIG. 11, a boring machine is used to form the test hole 20A to be used, and the test hole 20A having a diameter into which the permeability test device 10 shown in FIG. 1 to FIG. 5 can be effectively inserted is excavated stepwise to the target depths L1 to L4. Then, permeability tests are performed at each depth, from the upper first layer No. 1, the second layer No. 2, the third layer No. 3, and the fourth layer No. 4, which are defined by the excavation depths L1 to L4, by excavating from the top to the bottom, and the permeability coefficient is calculated stepwise. The method of calculating the permeability coefficient at each depth is the same as in the case of the test hole 20 with a depth of 30 cm already described. The permeability coefficient obtained by the permeability test is the average value of the cumulative permeability coefficients K1 to K4 at each depth L1 to L4. As a result, useful permeability test values ​​from the surface layer to the deep layer (the first layer No. 1 to the fourth layer No. 4) that are truly required in the actual field can be obtained, rather than the permeability coefficient of the surface layer at a depth of about 30 cm.

[0109] In this way, in the permeability test device of the first embodiment, the first layer No1 to the fourth layer No4, which are at different depths L1 to L4, are subjected to stepwise permeability tests similar to those described above, making it possible to perform permeability tests in a wide area from the shallow ground above the groundwater table to the deep ground (the permeability coefficient of any layer can be calculated). Furthermore, the aspect ratio h / r condition, which is expressed as the ratio of the wet head h to the radius r of the test hole 20A, and which satisfies h / r>10-50, can be easily satisfied.

[0110] Of course, it is possible to perform a permeability test in a shallow layer of ground using the conventional permeability test device mentioned above (Patent Document 1 / JP Patent Publication No. 2012-127673). The configuration in this case is shown in FIG.

[0111] In FIG. 18, the symbol 30 indicates a conventional single-tube type permeability test device, 31 indicates a cylinder forming an airtight water tank, 32 indicates an upper end cap of the extendable cylinder 31, 33 indicates a lower end cap of the extendable cylinder 31, 31a indicates a water volume scale, and 34, 34... indicate a number of openings which function as constant water level maintaining tubes and water injection tubes.

[0112] Reference numeral 40 denotes a constant water level tank having the same dimensions and shape as the test hole 20 in Fig. 7 of the above-mentioned first embodiment. On the inner wall surface of this constant water level tank 40, locking plates 41, 41... for installing the permeability test device 30 are provided with a specified gap between them and the bottom surface. The cylindrical permeability test device 30 is installed on the locking plates 41, 41....

[0113] On the other hand, reference numeral 20B denotes a small-diameter test hole dug to a predetermined depth L1 to L4, for example, by a hand auger. This test hole 20B is dug from depth L1 to L2, L3, and L4 in sequence, and permeability tests are conducted at each depth in sequence. It is not easy to form the test hole 20B by a hand auger, and it is not possible to properly dig a large-diameter hole, and it is not possible to form a test hole with a constant water level structure such as the test hole 20 in FIG. 7 described above. Therefore, it is impossible to insert the cylindrical permeability test device 30 into the test hole 20B dug by the hand auger.

[0114] Therefore, as described above, a constant water level tank 40 similar to the above-mentioned test hole 20 is installed on the top of the ground, a thin-diameter water supply pipe 42 is extended from the opening at the bottom, and a water injection pipe 44 is provided in the measurement area on the bottom side of the test hole 20B. An air-filled water stop packer 43 is provided at the bottom of the water supply pipe 42 to prevent the measurement water from the measurement area from leaking to the upper layer. The required air is supplied to the air-filled water stop packer 43 from an air pump on the ground via an air hose.

[0115] In this case, the permeability test using the permeability test apparatus 30 is basically the same as described above, and permeability tests are conducted sequentially from depth L1 to L2, L3, and L4, and the permeability coefficients K1 to K4 of each layer No1 to No4 corresponding to each depth are determined.

[0116] However, in this configuration, the permeability test device 30 cannot be inserted into the test hole 20B, so a separate constant water level tank 40 must be provided. Also, in addition to the water supply pipe 42 and water injection pipe 44, a water stop packer 43 and associated air hoses and air pumps are required. The installation and expansion work of the water stop packer 43 is very troublesome. Also, if the air pressure of the water stop packer 43 is low, measurement errors will occur due to water leakage. Depending on the soil type, the wall surface is prone to collapse.

[0117] In contrast, in the permeability test using the permeability test apparatus 10 of the first embodiment described above, as shown in FIG. 11, a boring machine is used to form a test hole 20A with a diameter sufficient to insert the permeability test apparatus 10, so that the permeability test apparatus 10 can be easily inserted, and the test hole 20A can be suspended and supported by a tripod 5 equipped with height adjustment means and an elevator rack 7 with an effective length according to the depth of the test hole 20A, so that the permeability test apparatus 10 can be easily and accurately positioned at a predetermined depth L1 to L4. If necessary, a hanging chain or hanging rope of a desired length may be interposed between the hook portion 7b on the elevator rack 7 side and the hanging ring 11b on the device main body side. Unlike excavation by a hand auger, excavation by a boring machine is not limited by depth or soil type, and free excavation to the groundwater level is possible.

[0118] Therefore, the above-mentioned problems of the conventional water permeability test apparatus 30 are certainly solved. Of course, as the test length increases as shown in Fig. 11, the amount of test water permeating into the ground also increases. Therefore, it goes without saying that the diameters of the above-mentioned first and second cylinders 11, 12 are increased and the volumes of the first and second airtight water tanks 13, 14 are increased according to the size of the test length.

[0119] Second embodiment of the present invention Next, Figs. 12 to 17 show the configuration and operation of a water permeability test device according to a second embodiment of the present invention.

[0120] <Configuration of the main body of the permeability test device> The configuration of the permeability test apparatus 10 according to the second embodiment, as shown in Figures 12, 13 and 16, for example, is characterized in that in the configuration of the permeability test apparatus 10 according to the first embodiment shown in Figures 1 to 10 above, a capillary space 4 is formed between the lower outer peripheral surface of the first outer cylinder 11 and the first air inflow openings 15, 15, which have a small surface tension and a large degree of water level rise, and by observing the water level change in this capillary space 4, the measurement efficiency of the permeability test in low-permeability ground is improved.

[0121] The first air inlets 15, 15 on the outer periphery of the lower part of the first cylinder 11 are provided at both the left and right sides of the outer periphery of the lower part of the first cylinder 11, and below them, first water inlets 16, 16 are provided in a pair at a predetermined interval. The capillary space 4 is formed by detachably fitting a capillary space forming member 1 shown in Figure 14 (perspective view) and Figure 15 (developed view) to the outer periphery of the lower part of the first cylinder 11 having the first air inlets 15, 15 and the first water inlets 16, 16.

[0122] As shown in Fig. 14 (perspective view), for example, the capillary space forming member 1 is composed of an elastic cylinder with a C-shaped cross section (an elastic cylinder with a C-shaped cross section that is a predetermined dimension larger than the semicircular dimension) that is fitted flush with the outer periphery of the lower part of the first cylinder 11 with a predetermined elastic pressure. The height of the cylinder part 2 is formed to be sufficiently high so that, in the fitted state, it exceeds the upper end of the first air inlet 15, 15 from the upper end of the edge part of the lower end cover member 11b of the first cylinder 11. A capillary space forming groove 3 of a predetermined depth (shallow) is provided on the inside of the left and right side walls 2a, 2a on the opening side in a manner surrounding the periphery of the first air inlet 15, 15 and the first water inlet 16, 16, so that the left and right side walls 2a, 2a on the opening side are partially made thin.

[0123] 14 and 15 (developed views), the capillary space forming groove 3 has an overall mountain shape (isosceles triangle shape) in the portions corresponding to the first air inlets 15, 15 and the first water inlets 16, 16, with the upper portion of the mountain shape surrounding the first air inlets 15, 15. The upper end portion of the mountain shape extends straight upward with a width slightly narrower than the diameter of the first air inlets 15, 15, and is open to the outside from the upper ends of both the left and right side walls 2a, 2a. A highly sealing rubber member (rubber sheet) 2c is affixed to the inner peripheral surface of the cylindrical wall excluding the capillary space forming groove 3, and when the cylindrical portion 2 is fitted to the outer periphery of the lower part of the first cylinder 11 as shown in Figures 12 and 13, the rubber member 2c provides a uniform and sufficient pressure to fit the inner peripheral surface except for the capillary space forming groove 3, and the fitting elasticity of the cylindrical portion 2 allows the cylindrical portion 2 to be fitted flush with good sealing properties. The fitting elasticity of the cylindrical portion 2 is at a level that allows the cylindrical portion 2 to be easily removed by pulling it in the opposite direction to when it was fitted.

[0124] In addition, a third water inlet 2b is provided in the lower part of the mountain-shaped capillary space forming groove 3, which corresponds to the first water inlet 16, 16, and has an inverted U-shaped third water inlet 2b whose upper end side arcuate part has the same diameter and is coaxially connected to each other. The shape of this third water inlet 2b may be the same as that of the first water inlet 16, 16. However, if it is inverted U-shaped and opens downward, the cylindrical part 2 of the capillary space forming member 1 does not interfere with the water inlet from the first water inlet 16, 16, and the water inlet distance into the test hole 20 can be shortened as much as possible, so that the water inlet efficiency can be improved. In addition, there is an advantage that capillary water can easily enter the first air inlet 15, 15 part.

[0125] As a result, in a state where the capillary space forming member 1 is fitted to the outer periphery of the lower part of the first cylinder 11, as shown in Fig. 16, for example, the capillary space forming groove 3 forms a narrow gap-like mountain-shaped capillary space 4 between the first air inlet 15, 15 and the first water inlet 16, 16 and the lower outer periphery of the first cylinder 11, and the upper part of the mountain-shaped capillary space 4 is opened to the outside (atmosphere) from the upper side through a narrow straight capillary space. This realizes a capillary space 4 with a flat gap structure similar to that of a capillary with a small tube diameter. In this case, the groove surface of the capillary space forming groove 3 and the outer periphery of the first cylinder 11 are naturally sufficiently wettable (a material with a small contact angle is selected).

[0126] In this case, the capillary space forming member 1 (its cylindrical portion 2) is molded from a transparent synthetic resin material with a certain rigidity and capable of elastic deformation when fitted to the outer periphery of the first cylinder 1. For the inner rubber member (rubber sheet) 2c, a soft transparent synthetic resin material with high sealing properties, such as silicone rubber, is used.

[0127] In the case of such a configuration, when the water permeability test device 10 is installed in the test hole 20, the lower part spreads in a mountain shape at the first air inlet 15, 15 part at the bottom of the first outer cylinder 11 and is immersed in the test water in the test hole 20, and the upper part extends straight upward with a width slightly wider than the diameter of the first air inlet 15, 15 and is open to the atmosphere, forming a capillary space (a gap of a capillary structure) 4, and the test water W in the test hole 20 rises in a mountain shape to the first air inlet 15, 15 part by capillary action due to the capillary space 4 in a flat water film state. As a result, the water level of the test water W in the capillary space 4 becomes several centimeters higher than the surface water level of the test water W in the test hole 20. Then, the surface tension of the water decreases at the first air inlet 15, 15 part, making it easier for air to be sucked into the first airtight water tank 13. In this case, it is possible to form the capillary space 4 around the entire circumference of the lower part of the first cylinder 11, but doing so would increase the amount of rise of the test water W too much, which would actually reduce the suction force of the air (air bubbles). Therefore, in this second embodiment, the first air inlets 15, 15 are configured to correspond to the upper part of the mountain-shaped capillary space, thereby realizing an optimal rising state of the test water W (optimal negative pressure state / described later).

[0128] With this configuration, even if the ground has low permeability, only a small amount of water infiltrates into the ground, and the surface water level does not drop even after observing the state of the test water in the test hole 20 for a long time, the water level of the test water W in the test hole 20 drops due to a partial rise in the water level in the capillary space 4, and the inflow of air at the first air inlet 15, 15 is promoted, so that continuous air bubbles are generated relatively smoothly in the first airtight water tank 13. As a result, even in ground with a low permeability coefficient, a lot of measurement data can be obtained in a relatively short time, and the acquisition of intermittent measurement data as in the past can be improved to a relatively continuous acquisition of measurement data. In addition, since the capillary space forming member 1 is formed as a transparent body like the first and second cylinders 11, 12 on the main body side, the rise in the water level due to the capillary phenomenon can be clearly confirmed in real time, and measurement can be started as early as possible. This also makes it possible to shorten the measurement time and improve efficiency.

[0129] Moreover, the capillary space forming member 1 can be attached (fitted) to and detached from the first cylinder 11 on the main body side as desired, and can be used as necessary. For example, as described below, it is used for the purpose of shortening the measurement time and improving efficiency when a preliminary test after the formation of the test hole 20 confirms that the ground is low permeable. Therefore, the capillary space forming member 1 can also be added as an optional part to the permeability test device 10 of the first embodiment.

[0130] Here, the results of observing the moment when air bubbles are generated in the first airtight water tank 13 when the above-mentioned capillary space 4 is provided will be described in detail with reference to FIG.

[0131] That is, when the capillary space 4 is present, at the start of the measurement, the test water W has already risen to the first air inlet 15, 15 area in a water film state, while the surface water level (constant water level) in the test hole 20 corresponding to the first air inlet 15, 15 is partially lowered by several centimeters ΔH0 compared to the case where there is no capillary space 4 in Figure 10 above (see Figure 17).

[0132] When the test water W permeates into the ground from this state, no drop in the surface water level in the test hole 20 is observed (although it is too small to be determined), but a clear change appears in the upper part of the rising water in a mountain-shaped water film state in the capillary space 4. In other words, the permeation (reduction) of several milliliters of water into the ground, which cannot be confirmed as a change in the surface water level in the test hole 20, appears prominently in the upper part of the rising water (capillary water) in the capillary space 4, which is one of the water surfaces in the test hole 20 and has the smallest surface tension.

[0133] As the test water continues to infiltrate into the ground, the rising water in the capillary space 4 is drawn into the first airtight water tank 13 by the negative pressure in the first airtight water tank 13 at the first air inlet 15, 15 portion where the surface tension is small. That is, a piping phenomenon occurs due to the difference between the negative pressure in the capillary space 4 and the negative pressure in the first airtight water tank 13. As a result, air bubbles are generated in the first airtight water tank 13 and rise to the upper part of the first airtight water tank 13. Each of these air bubbles is very small and forms continuous bubbles with short intervals between generation. The drop in the scale of the water volume 19 to the 1 mm level cannot be read until several air bubbles have been generated. In the case of the permeability test device of the first embodiment without the capillary space 4, one air bubble is generated with the size of a 1 yen coin, and several of them are generated and grow larger while rising in the first airtight water tank 13. However, if the capillary space 4 is present, the size of the air bubbles hardly changes. This is believed to be due to the pressure of the air bubbles decreasing by the amount of rise caused by capillary action. The negative pressure in the first airtight water tank 13 then decreases by the pressure of the rising air bubbles, and a corresponding amount of test water flows out of the first water inlet 16, 16 and is poured into the test hole 20. As a result, the water level of the test water W in the test hole 20 returns to a constant water level state, the water level in the capillary space 4 also returns to its original constant water level state, the first air inlet 15, 15 is blocked, the inflow of air and the generation of air bubbles as described above cease, and water does not flow into the test hole 20 from the first water inlet 16, 16.

[0134] That is, in the case of the permeability test device of the first embodiment without the capillary space 4, the penetration of the test water into the ground directly affects the surface water level in the test hole 20, whereas in the case of the permeability test device of the second embodiment with the capillary space 4, the penetration of the test water into the ground affects the rising water in the capillary space 4, which has become negative pressure due to capillary action. In this respect, the mechanisms of bubble formation of the two are clearly different, and the permeability test device of the second embodiment with the capillary space 4 is effective when the permeability of the ground to be measured is low.

[0135] As described above, the mechanism of generating air bubbles is different between the water permeability test apparatus of the first embodiment without the capillary space 4 and the water permeability test apparatus of the second embodiment with the capillary space 4. When there is no capillary space 4, the piping action of air bubble formation occurs due to the difference between the atmospheric pressure acting on the first air inlet 15, 15 and the negative pressure in the first airtight water tank 13, whereas when there is a capillary space 4, the piping action of air bubble formation occurs due to the difference between the negative pressure of the rising water (capillary water) due to the capillary space 4 and the negative pressure in the first airtight water tank 13. In other words, air bubbles are more likely to be generated because the pressure of the rising water (capillary water) due to the capillary space 4 is lower than the atmospheric pressure.

[0136] The capillary space forming member 1 (cylindrical part 2) is used when the permeability of the ground to be measured is low, only a small amount of water infiltrates into the ground, and the surface water level does not drop even if the state of the test water W in the test hole 20 is observed for a long time. Therefore, it is not necessary to use it in the case of ground to be measured with medium to high permeability. Therefore, the setting (fitting into the first cylinder 11) is performed when it is confirmed that the ground to be measured is low permeability ground, for example, based on the results of a preliminary test before the main test in which a test hole 20 is formed and a predetermined amount of water is poured in to confirm the degree of water infiltration into the ground.

[0137] As for the actual fitting operation based on this premise, at the start of the test, the lower part of the permeability test apparatus 10 can be immersed in the test hole 20 containing the required test water W, and while in this immersed state, the water stop valves for the first air inlet 15,15 and the first water inlet 16,16 can be removed before fitting, or the apparatus can be initially fitted above the first air inlet 15,15 and first water inlet 16,16 of the first cylinder 11, and after the water stop valves are removed as described above, it can be slid down to a position corresponding to the first air inlet 15,15 and first water inlet 16,16 and set.

[0138] In the above description, the upper end portion of the mountain shape of the capillary forming groove 3 in the capillary space forming member 1 is described as extending straight upward with a width slightly narrower than the diameter of the first air inlet 15, 15, but this may be the same diameter as the diameter of the first air inlet 15, 15, or may be slightly wider. In this case, it is sufficient that the upper end portion of the mountain shape of the capillary forming groove 3 extending straight above the first air inlet 15, 15 extends at least a predetermined distance above the first air inlet 15, 15, and it is not necessary to form it higher than necessary. Therefore, the height of the cylindrical portion 2 of the capillary space forming member 1 does not need to be higher than necessary.

[0139] Other embodiments The configurations of the various parts of the first and second embodiments described above can be modified in various ways depending on the purpose, and are in no way limited to the above explanations and examples shown in the drawings. [Explanation of symbols]

[0140] Reference numeral 1 is a capillary space forming member, 2 is a cylindrical portion of the capillary space forming member 1, 3 is a capillary space forming groove, 4 is a capillary space, 5 is a tripod, 7 is an elevator rack, 9 is a tripod body, 10 is a water permeability test apparatus, 11 is a first cylinder, 12 is a second cylinder, 13 is a first airtight water tank, 14 is a second airtight water tank, 15 is a first air inlet, 16 is a first water inlet, 17 is a second air inlet, 18 is a second water inlet, 19 is a water level scale, 20 is a test hole, and 20A is a test hole.

Claims

[Claim 1] The device is a permeability tester that comprises an airtight water tank for injecting water in which water to be measured is stored, and openings for air inflow and water injection provided at the bottom of the airtight water tank, the bottom of the airtight water tank equipped with the openings for air inflow and water injection is submerged in a test hole on the ground side in which a predetermined amount of test water is stored, and the openings for air inflow and water injection function as a constant water level holding tube and water injection tube of a Mariotte siphon type, and the permeability of the target ground is measured from the decrease in the water level in the airtight water tank. The airtight water tank is made of a double cylinder with an inner and outer cylinder of different diameters, and is divided into a first airtight water tank with a small volume located between the outer cylinder and the inner cylinder, and a second airtight water tank with a large volume located inside the inner cylinder. This permeability testing device is characterized in that it is configured as two airtight water tanks, one with an airtight water tank and the other with openings for air inflow and water injection provided at the bottom of the outer cylinder and the bottom of the inner cylinder, respectively, the second airtight water tank is connected to the first airtight water tank via the openings for air inflow and water injection of the inner cylinder, and a capillary space is provided between the lower outer peripheral surface of the outer cylinder and the lower airtight water tank near the air inlet on the lower outer circumference of the outer cylinder, where the surface tension is low and the degree of water level rise is large, thereby making it possible to measure the permeability coefficient of low-permeability ground mainly using the first airtight water tank, and to measure the permeability coefficient of medium- to high-permeability ground by combining the first and second airtight water tanks.

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