Method for backfilling borehole and filler-containing swelling-retardant granular material for backfilling borehole

Abstract

To provide a method for backfilling a borehole, which enables the borehole to be backfilled with high accuracy, and to provide a filler-containing swelling-retardant granular material for backfilling a borehole.SOLUTION: A method for backfilling a borehole involves transporting a container filled with a swellable filler, a plurality of filler-containing swelling-retardant granular materials having a swelling-retardant layer that coats a surface of the swellable filler and delays the onset of swelling of the swellable filler, and water to a predetermined position within the borehole, and then releasing the plurality of filler-containing swelling-retardant granular materials and the water from the inside to the outside of the container, causing the water to penetrate the swellable filler in the plurality of filler-containing swelling-retardant granular materials, thereby causing the swellable filler to collapse the swelling-retardant layer and swell, thereby backfilling the borehole.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for backfilling a borehole and to a swelling retardant granular filler-containing material for backfilling a borehole. [Background technology]

[0002] When selecting a disposal site for radioactive waste, drilling surveys are conducted to confirm the geological structure, etc. Once the disposal site for radioactive waste is operational, the boreholes may become a pathway for radiation to migrate, so they must be backfilled.

[0003] The use of bentonite as a filler for backfilling excavated holes containing groundwater, such as boreholes, has been studied. As described in Patent Document 1, bentonite is also used as a measure to prevent lost circulation during drilling work.

[0004] Bentonite has the property of swelling instantly when it comes into contact with water. Therefore, it is conceivable to backfill the borehole by allowing the bentonite to swell with the water in the borehole. However, because the borehole is very deep, it is very difficult to reliably backfill the borehole by allowing the bentonite to fall freely from the hole mouth on the ground. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6071229 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a method for backfilling a borehole and a filler-containing, swelling-retardant granular material for backfilling a borehole, which can backfill the borehole with high accuracy. [Means for solving the problem]

[0007] [1] A method of backfilling a borehole, comprising the steps of: transporting a container filled with a swellable filler, a plurality of filler-containing, swelling-delayed granules having a swelling-delay layer that covers the surface of the swellable filler and delays the onset of swelling of the swellable filler, and water to a predetermined position within the borehole; then releasing the plurality of filler-containing, swelling-delayed granules and the water from the inside to the outside of the container; allowing the water to penetrate the swellable filler in the plurality of filler-containing, swelling-delayed granules; causing the swellable filler to swell while collapsing the swelling-delay layer, thereby backfilling the borehole. [2] The method for backfilling a borehole according to [1] above, wherein the swelling filler is a bentonite-based material. [3] The method for backfilling a borehole according to [1] or [2] above, wherein the swelling-retardant layer is non-hydrophilic. [4] The method for backfilling a borehole according to [3] above, wherein the swelling retardant layer is shellac. [5] The method for backfilling a borehole according to [1] or [2] above, wherein the swelling-retardant layer is hydrophilic. [6] The method for backfilling a borehole according to [5] above, wherein the swelling retardation layer is polyvinyl alcohol. [7] A method for backfilling a borehole described in any one of [1] to [6] above, in which the length of time for which the swelling start time of the swellable filler is delayed is controlled by changing the thickness of the swelling delay layer. [8] A filler-containing swelling-delaying granule for backfilling a borehole, comprising a swelling filler and a swelling-delaying layer that covers the surface of the swelling filler and delays the onset of swelling of the swelling filler. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a method for backfilling a borehole and a filler-containing, swelling-retardant granular material for backfilling a borehole, which can backfill the borehole with high accuracy. [Brief explanation of the drawings]

[0009] [Figure 1]FIG. 1 is a schematic view showing an example of a method for backfilling a borehole according to an embodiment when a container of a dump bailer is on the ground. [Figure 2] FIG. 2 is a schematic view showing an example of the method for backfilling a borehole according to the embodiment, in which a water pressure pressurizing unit is installed at the upper end of a tubular member. [Figure 3] FIG. 3 is a schematic view showing an example of the state in which the container of the dump bailer is lowered to the launch position in the method for backfilling a borehole according to the embodiment. [Figure 4] FIG. 4 is an enlarged schematic view showing an example of a mechanism by which a container of a dump bailer emits filler-containing swelling-retardant granules and water in the method for backfilling a borehole according to an embodiment. [Figure 5] FIG. 5 is a schematic diagram illustrating an example of a method for backfilling a borehole according to an embodiment, in which the container of a dump bailer releases a filler-containing swelling-retardant granular material and water. [Figure 6] FIG. 6 is a graph showing the relationship between the thickness of the swelling-delay layer and the degree of swelling after 5 hours. [Figure 7] FIG. 7 is a graph showing the relationship between the thickness of the swelling-delay layer and the time required for swelling to begin. [Figure 8] FIG. 8 is a graph showing the relationship between the volume of the swelling-delay layer and the degree of swelling after 5 hours. [Figure 9] FIG. 9 is a graph showing the relationship between the volume of the swelling-delay layer and the time required for swelling to begin. [Figure 10] FIG. 10 shows an image taken with a digital camera of a filler-containing, swelling-retardant granule having a swelling-retardant layer of polyvinyl alcohol with a thickness of 0.55 mm at the start of immersion in ion-exchanged water. [Figure 11] FIG. 11 shows a digital image of a filler-containing, swelling-retardant granule having a 0.55 mm thick swelling-retardant layer of polyvinyl alcohol, taken 5 hours after the start of immersion in ion-exchanged water. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, a detailed description will be given based on an embodiment.

[0011] The present inventors have conducted extensive research into the following.

[0012] The use of bentonite pellets, which are granular bentonite, was considered for backfilling the borehole. Furthermore, the boreholes to be backfilled using this method are expected to reach depths of several hundred to several thousand meters underground. Therefore, rather than dumping bentonite pellets from the borehole's opening on the ground and allowing them to fall freely into the borehole, the researchers considered using a dump bailer to transport the bentonite pellets deep underground, and then releasing them from the dump bailer's container at the designated construction site.

[0013] When transporting bentonite pellets using a dump bailer, first, multiple bentonite pellets are loaded into the dump bailer's container on the ground. Next, the container, which is mounted on a tubular member installed in the borehole, is lowered to a predetermined position deep underground. Next, downward water pressure is applied via the tubular member to a piston installed at the top of the container. As the piston moves downward, it pushes the multiple bentonite pellets inside the container downward. When a predetermined pressure is reached, the lid at the bottom of the container opens, and the multiple bentonite pellets are ejected from the container.

[0014] As a result of trying to produce such bentonite pellets, the following problems became clear.

[0015] First, as the piston moved downward, several bentonite pellets were compressed inside the container, losing their original shape, before the lid at the bottom of the container was opened. As a result, a bentonite mass much larger than the bentonite pellets was formed directly below the piston. The bentonite mass grew so large that it came into close contact with the entire inner periphery of the container. As a result, this bentonite mass increased friction inside the container and prevented the piston from moving downward.

[0016] Even if the lid at the bottom of the container was then opened, water flowed into the container while the bentonite lump prevented the piston from moving downward, causing the bentonite pellets located below the bentonite lump in the container to instantly swell, making it impossible to eject the swollen bentonite pellets and bentonite lump from the container.

[0017] Furthermore, when this type of construction is carried out deep underground in a borehole, the water pressure inside the borehole is much higher than the pressure inside the container (atmospheric pressure), making it impossible to eject the bentonite pellets from the container.

[0018] The inventors discovered that the above problem was caused by the gaps between the bentonite pellets in the container being filled with gas such as air, and therefore came up with the idea of ​​filling the container with water to fill the gaps between the bentonite pellets with water.

[0019] With this configuration, the piston pressure does not contribute to increasing the contact force between the bentonite pellets, but acts on the lid at the bottom of the container as pore water pressure, allowing the bentonite pellets to be smoothly discharged from inside the container. However, with this configuration, the bentonite pellets swell inside the container due to the water filled in the container, so even if they are discharged, they become a paste rather than pellet-like. The inner wall of a borehole can be uneven, and in order to accurately fill such uneven parts of the borehole with bentonite, the bentonite needs to be discharged from the container in an unswollen state.

[0020] Based on the above findings, the inventors conducted further research and found that, in contrast to the conventional technology in which water is not charged into the container to prevent the bentonite from expanding, in order to smoothly release the granular bentonite outside the container and into the water in the borehole without causing it to expand, by actively charging water into the container and using a filler-containing, swelling-delayed granular material that does not expand (react) instantly to water but expands with a delay as a filler for backfilling the borehole, it is possible to backfill the borehole with precision, and based on these findings, the present invention was completed.

[0021] The method for backfilling a borehole of the present invention is a method for backfilling a borehole, which involves transporting a container filled with a swellable filler, a plurality of filler-containing, swelling-delayed granules having a swelling-delay layer that covers the surface of the swellable filler and delays the onset of swelling of the swellable filler, and water to a predetermined position within the borehole, and then releasing the plurality of filler-containing, swelling-delayed granules and water from the inside to the outside of the container, causing the water to penetrate the swellable filler in the plurality of filler-containing, swelling-delayed granules, which causes the swellable filler to swell while collapsing the swelling-delay layer, thereby backfilling the borehole.

[0022] Fig. 1 is a schematic diagram showing an example of a method for backfilling a borehole according to an embodiment, in which the container of a dump bailer is on the ground. Fig. 2 is a schematic diagram showing an example of a method for backfilling a borehole, in which a water pressure applying unit is installed at the upper end of a tubular member. Fig. 3 is a schematic diagram showing an example of a method for backfilling a borehole, in which the container of a dump bailer has been lowered to a release position. Fig. 4 is an enlarged schematic diagram showing an example of a mechanism by which the container of a dump bailer releases filler-containing, swelling-retardant granules and water in the method for backfilling a borehole. Fig. 5 is a schematic diagram showing an example of a method for backfilling a borehole, in which the container of a dump bailer has released filler-containing, swelling-retardant granules and water.

[0023] 1 to 5, the method for backfilling a borehole according to the embodiment is a method for backfilling a borehole H that is filled with water W, such as groundwater. The diameter of the borehole H to be backfilled is, for example, about 160 mm. The depth of the borehole H underground is, for example, about 300 m to 1000 m.

[0024] The container 2 of the dump bailer 1 is provided inside a tubular member 3 that constitutes the lifting device, and is movable up and down inside the tubular member 3. For example, the container 2 is cylindrical in shape. The tubular member 3 of the lifting device extends from the surface to deep underground in the borehole H. The entire inside of the tubular member 3, including the part of the tubular member 3 that protrudes above surface level, is filled with water.

[0025] 1 to 4, a plurality of filler-containing, swelling-retardant granules 10 and water 20 are loaded into a container 2 mounted inside a tubular member 3. The water 20 loaded into the container 2 fills the gaps between the plurality of filler-containing, swelling-retardant granules 10. The type of water 20 is not particularly limited, and may be, for example, tap water or water W from a borehole H.

[0026] Alternatively, a plurality of filler-containing, swelling-delayed granules 10 and water 20 may be loaded into container 2, and then container 2 may be mounted inside tubular member 3, or a plurality of filler-containing, swelling-delayed granules 10 and water 20 may be loaded into container 2 that is mounted inside tubular member 3. Filler-containing, swelling-delayed granules 10 are a filler used to backfill borehole H, and have expansion-delay properties such that they do not expand instantly in response to water but swell slowly.

[0027] When the container 2 is loaded with water 20 in addition to the plurality of filler-containing, swelling-retardant granules 10, piston pressure from the piston 6 acts on the lid 4, as will be described below.

[0028] On the other hand, when water 20 is not loaded into container 2, container 2 is loaded with a plurality of filler-containing, swelling-delayed granules 10, and the gaps between the plurality of filler-containing, swelling-delayed granules 10 are filled with a gas such as air. In this case, the piston pressure from piston 6 contributes to increasing the contact force between the plurality of filler-containing, swelling-delayed granules 10. As a result, when container 2 is moved into water W in borehole H, opening lid 4 while water pressure is applied from above makes it impossible to effectively release the plurality of filler-containing, swelling-delayed granules 10 out of container 2.

[0029] 4, the container 2 is provided with a lid 4 at its bottom. A hinge 4a is provided on a portion of the lid 4, and the lid 4 is provided so as to be able to open and close the bottom end of the container 2 around the hinge 4a. A piston 6 is provided above the plurality of filler-containing, swelling-retardant granules 10 placed inside the container 2.

[0030] A shear pin 5 is provided opposite hinge 4a. By connecting lid 4 to container 2, shear pin 5 restricts the movement of lid 4 that would open the bottom of container 2, maintaining the lid 4 in a closed position at the bottom of container 2. In this way, shear pin 5 maintains the closure of lid 4 against container 2, thereby preventing filler-containing swelling-retardant granules 10 and water 20 from leaking out from the bottom of the container. However, as described below, when a downward force greater than a predetermined level is applied to lid 4 from piston 6, shear pin 5 disengages, and lid 4 rotates around hinge 4a (clockwise in the drawing) and opens, thereby opening the bottom of container 2.

[0031] The filler-containing swelling-retarding granules 10 loaded inside the container 2 have a swelling filler 11 and a swelling-retarding layer 12 covering the surface of the swelling filler 11 .

[0032] The swellable filler 11 has swelling properties in water. That is, the swellable filler 11 starts to swell quickly when it comes into contact with water. From the viewpoint of good swelling in water, the swellable filler 11 is preferably made of a bentonite-based substance.

[0033] The bentonite-based material may be composed solely of bentonite, or may be composed of bentonite and a material other than bentonite.

[0034] The bentonite-based substance being composed only of bentonite means that the swelling filler 11 is composed only of bentonite. The bentonite-based substance being composed of bentonite and a substance other than bentonite means that the swelling filler 11 is composed of bentonite and a substance other than bentonite. In this case, the type of substance other than bentonite contained in the swelling filler 11 is not particularly limited, as long as the borehole H can be backfilled accurately.

[0035] Swelling-delay layer 12, which constitutes filler-containing swelling-delaying granules 10, is formed on the surface of swellable filler 11. By covering the surface of swellable filler 11 with swelling-delay layer 12, swelling-delay layer 12 inhibits contact between swellable filler 11 and water, delaying the onset of swelling of swellable filler 11. However, swelling-delay layer 12 does not prevent swelling of swellable filler 11 for a long period of time (for example, one month or more), but rather delays the onset of swelling of swellable filler 11 for a predetermined period of time.

[0036] If the filler-containing swelling-retardant granules 10 remain in the water W in the borehole H for a predetermined time or longer without swelling, the swelling-retardant layer 12 will be damaged or peeled off from the swelling filler 11 due to water pressure or deterioration over time, resulting in a defect in the swelling-retardant layer 12. When water W penetrates into the swelling filler 11 through the defective part of the swelling-retardant layer 12, the swelling filler 11 comes into contact with the water W and begins to swell.

[0037] In this way, the swelling-delay layer 12 can delay the time from when the filler-containing, swelling-delaying granules 10 come into contact with water until the swellable filler 11 comes into contact with water, and therefore the swelling-delay layer 12 can delay the time when the swellable filler 11 starts to swell. In this way, the swelling-delaying filler 10 starts to swell in water.

[0038] Furthermore, even if water 20 is filled inside container 2, filler-containing, swelling-delaying granules 10 (swellable filler 11) do not swell when filled inside container 2 due to the swelling-delaying layer 12. Therefore, as will be described later, multiple filler-containing, swelling-delaying granules 10 can be released to the outside of container 2 in granular form.

[0039] On the other hand, if the filler-containing, swelling-delayed granules 10 do not have a swelling-delay layer 12, the surface of the swellable filler 11 is not covered with the swelling-delay layer 12, and therefore the time from when the filler-containing, swelling-delayed granules 10 come into contact with water to when the swellable filler 11 comes into contact with water cannot be delayed, and therefore the swelling start time of the filler-containing, swelling-delayed granules in water cannot be delayed.

[0040] Additionally, the swelling delay layer 12 is preferably non-hydrophilic or hydrophilic.

[0041] When the swelling-delay layer 12 is non-hydrophilic, it is preferable that the swelling-delay layer 12 is made of shellac. In this case, if the thickness of the swelling-delay layer 12 is, for example, 0.15 mm or more and 0.30 mm or less when the major axis of the ellipsoidal swellable filler 11 is about 20 mm, the swelling start of the swellable filler 11 can be sufficiently delayed and excessive delay in the swelling start of the swellable filler 11 can be suppressed. In addition, the volume of the swelling-delay layer 12 in this case is, for example, 100 cm when the major axis of the ellipsoidal swellable filler 11 is about 20 mm. 3 More than 200cm 3 If the amount is equal to or less than this, the start of swelling of the swellable filler 11 can be sufficiently delayed, and excessive delay in the start of swelling of the swellable filler 11 can be suppressed.

[0042] When the swelling-delay layer 12 is hydrophilic, it is preferable that the swelling-delay layer 12 be made of polyvinyl alcohol. In this case, if the thickness of the swelling-delay layer 12 is, for example, 0.58 mm or more and 1.00 mm or less when the major axis of the ellipsoidal swellable filler 11 is about 20 mm, the swelling start of the swellable filler 11 can be sufficiently delayed and excessive delay in the swelling start of the swellable filler 11 can be suppressed. Furthermore, in this case, the volume of the swelling-delay layer 12 is, for example, 435 cm when the major axis of the ellipsoidal swellable filler 11 is about 20 mm. 3 More than 780cm 3 If the amount is equal to or less than this, the start of swelling of the swellable filler 11 can be sufficiently delayed, and excessive delay in the start of swelling of the swellable filler 11 can be suppressed.

[0043] The swelling-delay layer 12 may be a single layer or multiple layers. When the swelling-delay layer 12 is multiple layers, the multiple layers may be one type of layer or two or more types of layers.

[0044] A connecting part 2a is provided on the outside of the container 2, for example, on the outside of the upper part of the container 2 as shown in Figure 4, to connect with a connecting part 3a provided on the inside of the tubular member 3. The connecting part 3a is provided inside the tubular member 3 so as to be movable in the up and down direction.

[0045] As shown in Fig. 1, connecting portion 2a of container 2, which contains a plurality of filler-containing, swelling-retardant granules 10 and water 20, is connected to connecting portion 3a of tubular member 3 near the ground. Then, as shown in Fig. 2, container 2 is moved downward so that the upper end of tubular member 3 is closed by water pressure applying portion 7, and water pressure applying portion 7 is installed at the upper end of tubular member 3. Next, downward pressure is applied to the water W inside tubular member 3 by water pressure applying device 8 via water pressure applying portion 7. The downward pressure from water pressure applying device 8 moves container 2 downward inside borehole H. In this way, container 2 is transported to a predetermined position within borehole H, as shown in Fig. 3.

[0046] After the container 2 is transported to a predetermined position in the borehole H, a water pressure greater than the water pressure when the container 2 moved downward in the borehole H is applied, thereby discharging the plurality of filler-containing swelling-retardant granules 10 and water 20 from the inside to the outside of the container 2. The details of the discharging mechanism at this time are as follows.

[0047] First, when a water pressure greater than the water pressure when vessel 2 moved downward through borehole H is applied to vessel 2, increased downward pressure is exerted on piston 6, which is located above the plurality of filler-containing, swelling-delayed granules 10 loaded inside vessel 2, as shown in FIG. 4. At this time, water 20 is loaded inside vessel 2 in addition to the plurality of filler-containing, swelling-delayed granules 10, and the water 20 fills the spaces between the plurality of filler-containing, swelling-delayed granules 10. Therefore, piston 6 pushes downward not only the plurality of filler-containing, swelling-delayed granules 10 but also the water 20, and a downward force is exerted on lid 4 not only by the plurality of filler-containing, swelling-delayed granules 10 but also by the water 20. In other words, piston 6 pushes downward evenly the entire load in vessel 2 (filler-containing, swelling-delayed granules 10 and water 20), and the entire load in vessel 2 pushes lid 4 downward. In this way, piston pressure from piston 6 acts on lid 4.

[0048] When piston 6 pushes the contents of container 2 downward with a force greater than a predetermined value, the contents of container 2 apply a downward force greater than a predetermined value to lid 4, disengaging shear pin 5 that supports lid 4 while it is closing the bottom end of container 2, and lid 4 rotates clockwise around hinge 4a and opens. Thus, the bottom end of container 2, which was previously closed by lid 4, is opened, and multiple filler-containing, swelling-delayed granules 10 and water 20 are expelled from inside container 2 to the outside, as shown in Figure 5. The multiple filler-containing, swelling-delayed granules 10 expelled to the outside of container 2 are not swollen and are in a granular state, not a paste.

[0049] Because the piston pressure acts on the lid 4, even if upward water pressure is applied to the lid 4 from the water W in the borehole H, the load in the container 2, i.e., the multiple filler-containing swelling-retardant granules 10 and water 20, can be efficiently released outside the container 2.

[0050] The plurality of filler-containing, swelling-delayed granules 10 released outside the container 2 do not swell in the water W outside the container 2, i.e., in the borehole H, until a predetermined time has passed. In other words, the swellable filler 11 that constitutes the filler-containing, swelling-delayed granules 10 is covered with the swelling-delay layer 12, and therefore does not swell in the water W in the borehole H until a predetermined time has passed. The water W in the borehole H is, for example, groundwater in the borehole H, and may include the water 20 that was loaded inside the container 2.

[0051] Then, after a predetermined time has elapsed in the water W in the borehole H, the swellable filler 11 swells. Specifically, if the filler-containing, swelling-delayed granules 10 remain in the water W in the borehole H for a predetermined time or longer, water pressure, deterioration over time, or the like will cause part or all of the swelling-delay layer 12 to break or peel off from the swelling filler 11, resulting in a loss of the swelling-delay layer 12. When the swelling-delay layer 12 is lost, water W penetrates the swellable filler 11 of the filler-containing, swelling-delayed granules 10 through the lost portion of the swelling-delay layer 12, causing the swelling filler 11 to begin swelling while collapsing the swelling-delay layer 12. For example, the swellable filler 11 swells two or more hours after the filler-containing, swelling-delayed granules 10 are released outside the container 2. In such a filler-containing swelling-delaying granule 10, the length of time for which the swelling of the swellable filler 11 is delayed can be controlled by changing the thickness or volume of the swelling-delaying layer 12.

[0052] After the plurality of filler-containing, swelling-delayed granules 10 and water 20 have been released, the container 2 is moved from deep underground to the surface of the borehole H. After that, the plurality of filler-containing, swelling-delayed granules 10 and water 20 are loaded into the container 2 as described above, and the container 2 is then moved back to deep underground in the borehole H, where the plurality of filler-containing, swelling-delayed granules 10 and water 20 are released from the container 2 to the outside. By repeating this process, after a predetermined time has passed, the plurality of swelling fillers 11 begin to swell outside the container 2 and within the borehole H, allowing the borehole H to be accurately backfilled.

[0053] Next, an example of a method for producing the filler-containing swelling-delaying granules 10 will be described.

[0054] For example, filler-containing, swelling-delayed granules 10 can be produced by immersing granular swellable filler 11 in a solution in which the material constituting swelling-delayed layer 12 is dissolved or dispersed, and then removing and drying the swellable filler 11. By repeating the immersion in and removal from the solution multiple times or by changing the concentration of the solution, the thickness of swelling-delayed layer 12 can be easily increased and controlled.

[0055] As another example, filler-containing swelling-retardant granules 10 can be produced by spraying a solution in which the materials constituting the swelling-retardant layer 12 are dissolved or dispersed onto granular swelling filler 11. By changing the number of sprays and the amount of solution sprayed, or by changing the concentration of the solution, the thickness of the swelling-retardant layer 12 can be easily increased and controlled.

[0056] Next, the swelling retardant granules containing a filler for backfilling a borehole according to the present invention will be described.

[0057] The filler-containing, swelling-delaying granules for backfilling boreholes of the present invention comprise a swellable filler 11 and a swelling-delaying layer 12 that coats the surface of the swellable filler 11 and delays the onset of swelling of the swellable filler 11. Preferably, the filler-containing, swelling-delaying granules for backfilling boreholes of the present invention are the filler-containing, swelling-delaying granules 10 used in the above-described method for backfilling boreholes of the present invention. Therefore, it is preferred that the configuration of the filler-containing, swelling-delaying granules for backfilling boreholes be the same as that of the filler-containing, swelling-delaying granules 10.

[0058] According to the embodiment described above, in order to smoothly release the filler-containing, swelling-delayed granules outside the container and into the water in the borehole without expanding them, filler-containing, swelling-delayed granules that do not expand instantly in water and have expansion-delay properties are used, and water is loaded into the container together with the filler-containing, swelling-delayed granules, thereby enabling the borehole to be backfilled accurately.

[0059] Although the embodiments have been described above, the present invention is not limited to the above embodiments, but includes all aspects encompassed by the concept and scope of the claims of the present disclosure, and can be modified in various ways within the scope of the present disclosure. [Example]

[0060] Next, examples and comparative examples will be described, but the present disclosure is not limited to these examples.

[0061] Example 1 Filler-containing swelling-retardant granules having a swelling-retardant layer of polyvinyl alcohol were prepared as follows.

[0062] Granular swellable filler (ellipsoids) consisting solely of bentonite was immersed in a 5.5% polyvinyl alcohol solution, immediately removed from the solution, and dried in a drying oven controlled at 80°C. This resulted in filler-containing, swelling-delayed granules, in which the surface of the granular swellable filler was coated with a swelling-delaying layer. The process from immersion in the solution to drying was repeated multiple times to obtain filler-containing, swelling-delayed granules with swelling-delaying layers of different thicknesses.

[0063] The volumes of the resulting filler-containing, swelling-delayed granules with different swelling-delay layer thicknesses, and granular swellable fillers (whose surfaces were not covered with a swelling-delay layer), were measured using a 3D scanner-type three-dimensional measuring device, and the thickness of the swelling-delayed layer was calculated by treating the filler-containing, swelling-delayed granules as ellipsoids.

[0064] In addition, filler-containing swelling-retardant granules and granular swelling fillers with different thicknesses of swelling-retardant layers were immersed in ion-exchanged water in a beaker, and fixed-point photographs were taken from the side at predetermined intervals using a digital camera. The degree of swelling was then observed after 5 hours of immersion in the ion-exchanged water in the beaker. Specifically, the height of the sample at the start of immersion was H o The height of the sample after 5 hours from the start of immersion is H5, and H o The normalized value (H5 / H o) was calculated, and the influence of the presence or absence of a swelling-retardant layer and the thickness and volume of the swelling-retardant layer on the degree of swelling of the filler-containing swelling-retardant granules was evaluated.

[0065] Figure 6 shows the relationship between the thickness of the swelling retardation layer and the degree of swelling after 5 hours (H5 / H o ) is a graph showing the relationship between the thickness of the swelling-delay layer and the time required for swelling to begin. FIG. 8 is a graph showing the relationship between the volume of the swelling-delay layer and the degree of swelling after 5 hours (H5 / H o 9 is a graph showing the relationship between the volume of the swelling-delay layer and the time required for swelling to begin. 3 The plot shows the results for the particulate swellable filler.

[0066] Figure 10 shows digital images of filler-containing, swelling-retardant granules with a 0.55 mm thick polyvinyl alcohol swelling-retardant layer taken at the start of immersion in ion-exchanged water. Figure 11 shows digital images of filler-containing, swelling-retardant granules with a 0.55 mm thick polyvinyl alcohol swelling-retardant layer taken 5 hours after immersion in ion-exchanged water.

[0067] Example 2 Filler-containing, swelling-retardant granules having a swelling-retardant layer made of shellac were produced in the same manner as in Example 1, except that the polyvinyl alcohol solution was replaced with a shellac solution.

[0068] As shown in Figures 6-11, the swelling rate of the filler-containing swelling-delayed granules decreased as the thickness and volume of the swelling-delayed layer increased. Furthermore, compared with polyvinyl alcohol, the shellac swelling-delayed layer suppressed the swelling rate of the filler-containing swelling-delayed granules. The transport time of the filler-containing swelling-delayed granules from the surface to the deep underground of the borehole varies depending on factors such as the depth of the borehole backfill. Therefore, by adjusting the thickness and volume of the swelling-delayed layer and selecting the type of swelling-delayed layer according to the required swelling delay time, it was suggested that the delay in the swelling start time of the swelling filler could be controlled, enabling accurate backfilling of the borehole.

[0069] In addition, filler-containing, swelling-retardant granules and granular swelling fillers, each with a swelling-retardant layer made of polyvinyl alcohol and a thickness of 0.55 mm, were immersed in ion-exchange water in a beaker and photographed at regular intervals from directly above using a digital camera.The results showed that the swelling rate of the filler-containing, swelling-retardant granules could be suppressed to about one-third of that of the granular swelling filler. [Explanation of symbols]

[0070] 1 Dump Bailer 2 containers 2a Connecting part 3 Tubular members 3a Connecting part 4 Lid 4a Hinge 5 Sharpin 6 pistons 7 Water pressure pressurizing section 8. Water pressure application device 10. Filler-containing swelling retardant granules 11 Swellable filler 12 Swelling retardation layer 20 water H borehole W Water (groundwater)

Claims

1. 1. A method for backfilling a borehole, comprising: A method for backfilling a borehole, comprising transporting a container filled with a swellable filler, a plurality of filler-containing, swelling-delayed granules having a swelling-delay layer that covers the surface of the swellable filler and delays the onset of swelling of the swellable filler, and water to a predetermined position within the borehole, and then releasing the plurality of filler-containing, swelling-delayed granules and the water from the inside to the outside of the container, causing the water to penetrate the swellable filler in the plurality of filler-containing, swelling-delayed granules, causing the swellable filler to swell while collapsing the swelling-delay layer, thereby backfilling the borehole.

2. 2. The method of claim 1, wherein the swelling filler material is a bentonite-based material.

3. 10. The method of claim 1, wherein the swelling retardation layer is non-hydrophilic.

4. 4. The method of claim 3, wherein the swelling retarding layer is shellac.

5. 10. The method of claim 1, wherein the swelling retardation layer is hydrophilic.

6. 6. The method of claim 5, wherein the swelling retardation layer is polyvinyl alcohol.

7. The method for backfilling a borehole according to any one of claims 1 to 6, wherein the thickness of the swelling delay layer is changed to control the length of time for which the swelling start time of the swellable filler is delayed.

8. a swellable filler; a swelling delay layer that covers the surface of the swellable filler and delays the start of swelling of the swellable filler; A filler-containing swelling retardant granule for backfilling a borehole, comprising:

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